Adding upstream version 115.7.0esr.upstream/115.7.0esrupstream

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

85 files changed, 22610 insertions, 0 deletions

diff --git a/third_party/rust/serde_json/.cargo-checksum.json b/third_party/rust/serde_json/.cargo-checksum.json
new file mode 100644
index 0000000000..369b6fe170
--- /dev/null
+++ b/third_party/rust/serde_json/.cargo-checksum.json
@@ -0,0 +1 @@
+{"files":{"CONTRIBUTING.md":"f5270cafba66223a7b51ffc0d286075a17bb7cd88762fc80d333d3102629f4d8","Cargo.toml":"547ec897b43d41db797423629543e838ee4e08c6a4196a0756b5be0ef178adc1","LICENSE-APACHE":"62c7a1e35f56406896d7aa7ca52d0cc0d272ac022b5d2796e7d6905db8a3636a","LICENSE-MIT":"23f18e03dc49df91622fe2a76176497404e46ced8a715d9d2b67a7446571cca3","README.md":"1e5a86e6b5e79f92f9e7226d9a8ba16d4ec70567d153c9cacebcb582770378a1","build.rs":"0dd97b63a07aa2d4bbb4c7d0e73b521da130769da9f49f28a7b63332781eb3de","src/de.rs":"5dba95fc6a564917289bf1e404d59c74f95772f22ec92cb91d55053b65e93032","src/error.rs":"abb92a9bf62cb7f47141a733a9fd66ec8c369615d7e6f633d3536fd2a5ac74a2","src/features_check/error.rs":"d7359f864afbfe105a38abea9f563dc423036ebc4c956a5695a4beef144dc7ec","src/features_check/mod.rs":"2209f8d5c46b50c8a3b8dc22338dcaf0135d192e8b05d2f456cbe6a73104e958","src/io/core.rs":"9a4146802391fd202a36bebbf3b14b715ae09d8828cbe8e06a01214c470ebf5c","src/io/mod.rs":"fd1ed5080495cab21117f6f7d3c2c9e3687cad0c69a0cd087b08a145a9e672da","src/iter.rs":"f832c469cd7999d26ba9b76baa69b257a212a7edb3dfdf9b1d1bb35e8da85fa9","src/lexical/algorithm.rs":"4fbeb1994049348d1fc388dd1a29e481f8abb8fe1e28bfebf50f3bbce5fa5fbe","src/lexical/bhcomp.rs":"b7c68d74c0055eb67ec2c1bcf27bbc28bef8f1bbc43db8eb94ba69892230add6","src/lexical/bignum.rs":"4230cde10dc8eae456a713cf90ec4e48dff4b1d0c542621ce7f00f39ade2645e","src/lexical/cached.rs":"0e127398691f8042c19cde209e7f4b0161f0f3150342430145929f711e6fdac8","src/lexical/cached_float80.rs":"0f8f74a22cb7d871322a9893bffd0255ca10bf9dffd13afb2462dd3d7f51805f","src/lexical/digit.rs":"a265b9072194a62a67dfc4df3c86d4213097cf3f82280d025e0012a5a262fd9d","src/lexical/errors.rs":"6bc993febceb7dd96ac1c8c5c53b5f5a30297016c0f813ed8ff8d7938d01534d","src/lexical/exponent.rs":"387e945b97dc7ba48a7091c50d228a0dde3a1c4145703d4ab9c31191a91693b0","src/lexical/float.rs":"fe356213c92a049f4bef2f58bc0e3a26866ca06b8c1d74d0f961c5b883852cad","src/lexical/large_powers.rs":"34537f5c701afce1ec2a1fd3c14950381b2e27c9ad74f002c91f3708e8da9ca5","src/lexical/large_powers32.rs":"d533037c6141e6671102aee490c9cdeaba81e667ddca781b2b99db2c455e4a1a","src/lexical/large_powers64.rs":"745dd7c0cbe499eec027ef586248881011d9df20c7efab7929c1807b59886ba1","src/lexical/math.rs":"27e22b724cdf990cdacd0ccfc3749e6e2eb7529d43ebf6e95b1999560b9e199a","src/lexical/mod.rs":"4b4c5228779c0f135a4cb018700e3bcd495da48b74421a86f6b8b304acdef924","src/lexical/num.rs":"cf705c62612e31d704f43d94a633ea1243c6befad7ef5792e2e881a7fd21e809","src/lexical/parse.rs":"c2bfac4c70a19938ced61e991f4ec606764887cf12bac1a0978b5b5318a56aac","src/lexical/rounding.rs":"697207248ba17b7f4965aedb11d276261ada5b06d9c6265d8fd6246664ff6e3c","src/lexical/shift.rs":"bc1ed053dd63d45ac9c35302f18de9f00d94027f28af4ab749c9248439de832a","src/lexical/small_powers.rs":"4608dd218b8002435db7e1ec79d2d0fef5f47ae257b93353326d52ecc80cccda","src/lib.rs":"f055ef570d978397cfae0d814ddbbf2372b8839ab4ffe8fc4c3308c9b2a332de","src/macros.rs":"c9f23156faec8d5216d72b6a97eebd768efb3f75870a6e2beed824308587b998","src/map.rs":"14fa16650b462ef138bebe1d18cb296b0e1ff404f12f2c212f72ed7c969b3a12","src/number.rs":"425f528c5ec2fcb4dd3c87a633d0b2cd505f7a305a40dffa1f022a643eda938b","src/raw.rs":"6d46836486b8d1c58f2aff563285400b1b0ec163eee34e7be78e0fa7a99aa0e8","src/read.rs":"49b4b1d067b6485cbded28fb961666ab5df82c36661af722dbae756efb6b2891","src/ser.rs":"566ae0b1860861ad70efd17fb0f6ae326e76d60453b6538c783a40d4ce616851","src/value/de.rs":"78f938d960e285f671f3b86ed173d598a815690a14512d6daa94dee43d3ce4cf","src/value/from.rs":"2dcfed837b040447a61eae50bd3938106b090f8a292206aea686022767006625","src/value/index.rs":"8a99d8d50f5674181ced22f6e81dc529eaecb01e543e30346e51fe42cb4b8a5f","src/value/mod.rs":"81c62fcb50e92b2f424e361328df5b02621756781bf80b8e26fd3d13473b57cd","src/value/partial_eq.rs":"95de799d57f7f4310b64a9488c0a7286dee76dba4329cb69a96298a887e58586","src/value/ser.rs":"5ea04bdf30c1c79baeab66b922908b47f1910b07d2f4ed0927a9a2c1ef3fbf60","tests/compiletest.rs":"022a8e400ef813d7ea1875b944549cee5125f6a995dc33e93b48cba3e1b57bd1","tests/debug.rs":"a8451217c1e127ad6e653ef11e0513525ee350e1e37dd575758a8ee9301b28fb","tests/lexical.rs":"383e06283e15e1db7c6b818da3c84a3afa0059f6e9fc994b069919d81346ab91","tests/lexical/algorithm.rs":"da378df9ee24bfa033968d5c94e91b58e52c39bf6c825dec51c3eb7250cc5874","tests/lexical/exponent.rs":"26ea92abc654a6a88a8281552bca2f76ea1fa4c17d66a1dd6defe14f7d89b666","tests/lexical/float.rs":"0440f2d85c993bcccd925096d7f4136bf624ffd66b3c7ee565d158390685eb11","tests/lexical/math.rs":"4874be2103be5fbe8b8015354414df271ffa00fd815546fc077f15fb4d7a5a37","tests/lexical/num.rs":"6e650c40de85ed72ac06b6bf1487ba161f3824e26d827df6cfdf2bbdb8d05a05","tests/lexical/parse.rs":"17c73e0a59d462716d974b8dd23a291eb6efdc3a933248874e5eab7e7209d67f","tests/lexical/rounding.rs":"6c56e39ba534616c1b2146e8efa6eb57aed322e683bf23183cd32a61fae6447e","tests/macros/mod.rs":"93aa1d54af20bc2c55b6ae8db73c1414cda2626eb9fa7bd57b9d613a3c6e6a19","tests/map.rs":"dcc5212242e4e93703c4335d54f5603b0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\ No newline at end of file
diff --git a/third_party/rust/serde_json/CONTRIBUTING.md b/third_party/rust/serde_json/CONTRIBUTING.md
new file mode 100644
index 0000000000..26e15783a1
--- /dev/null
+++ b/third_party/rust/serde_json/CONTRIBUTING.md
@@ -0,0 +1,46 @@
+# Contributing to Serde
+
+Serde welcomes contribution from everyone in the form of suggestions, bug
+reports, pull requests, and feedback. This document gives some guidance if you
+are thinking of helping us.
+
+## Submitting bug reports and feature requests
+
+Serde development is spread across lots of repositories. In general, prefer to
+open issues against the main [serde-rs/serde] repository unless the topic is
+clearly specific to JSON.
+
+[serde-rs/serde]: https://github.com/serde-rs/serde
+
+When reporting a bug or asking for help, please include enough details so that
+the people helping you can reproduce the behavior you are seeing. For some tips
+on how to approach this, read about how to produce a [Minimal, Complete, and
+Verifiable example].
+
+[Minimal, Complete, and Verifiable example]: https://stackoverflow.com/help/mcve
+
+When making a feature request, please make it clear what problem you intend to
+solve with the feature, any ideas for how Serde could support solving that
+problem, any possible alternatives, and any disadvantages.
+
+## Running the test suite
+
+We encourage you to check that the test suite passes locally before submitting a
+pull request with your changes. If anything does not pass, typically it will be
+easier to iterate and fix it locally than waiting for the CI servers to run
+tests for you.
+
+The test suite requires a nightly compiler.
+
+```sh
+# Run the full test suite, including doc test and compile-tests
+cargo test
+```
+
+## Conduct
+
+In all Serde-related forums, we follow the [Rust Code of Conduct]. For
+escalation or moderation issues please contact Erick (erick.tryzelaar@gmail.com)
+instead of the Rust moderation team.
+
+[Rust Code of Conduct]: https://www.rust-lang.org/policies/code-of-conduct
diff --git a/third_party/rust/serde_json/Cargo.toml b/third_party/rust/serde_json/Cargo.toml
new file mode 100644
index 0000000000..cff28cd7b2
--- /dev/null
+++ b/third_party/rust/serde_json/Cargo.toml
@@ -0,0 +1,109 @@
+# THIS FILE IS AUTOMATICALLY GENERATED BY CARGO
+#
+# When uploading crates to the registry Cargo will automatically
+# "normalize" Cargo.toml files for maximal compatibility
+# with all versions of Cargo and also rewrite `path` dependencies
+# to registry (e.g., crates.io) dependencies.
+#
+# If you are reading this file be aware that the original Cargo.toml
+# will likely look very different (and much more reasonable).
+# See Cargo.toml.orig for the original contents.
+
+[package]
+edition = "2018"
+rust-version = "1.36"
+name = "serde_json"
+version = "1.0.93"
+authors = [
+    "Erick Tryzelaar <erick.tryzelaar@gmail.com>",
+    "David Tolnay <dtolnay@gmail.com>",
+]
+description = "A JSON serialization file format"
+documentation = "https://docs.rs/serde_json"
+readme = "README.md"
+keywords = [
+    "json",
+    "serde",
+    "serialization",
+]
+categories = [
+    "encoding",
+    "parser-implementations",
+    "no-std",
+]
+license = "MIT OR Apache-2.0"
+repository = "https://github.com/serde-rs/json"
+
+[package.metadata.docs.rs]
+features = [
+    "raw_value",
+    "unbounded_depth",
+]
+targets = ["x86_64-unknown-linux-gnu"]
+rustdoc-args = [
+    "--cfg",
+    "docsrs",
+]
+
+[package.metadata.playground]
+features = ["raw_value"]
+
+[lib]
+doc-scrape-examples = false
+
+[dependencies.indexmap]
+version = "1.5.2"
+features = ["std"]
+optional = true
+
+[dependencies.itoa]
+version = "1.0"
+
+[dependencies.ryu]
+version = "1.0"
+
+[dependencies.serde]
+version = "1.0.100"
+default-features = false
+
+[dev-dependencies.automod]
+version = "1.0"
+
+[dev-dependencies.indoc]
+version = "2.0"
+
+[dev-dependencies.ref-cast]
+version = "1.0"
+
+[dev-dependencies.rustversion]
+version = "1.0"
+
+[dev-dependencies.serde]
+version = "1.0.100"
+features = ["derive"]
+
+[dev-dependencies.serde_bytes]
+version = "0.11"
+
+[dev-dependencies.serde_derive]
+version = "1.0"
+
+[dev-dependencies.serde_stacker]
+version = "0.1"
+
+[dev-dependencies.trybuild]
+version = "1.0.49"
+features = ["diff"]
+
+[features]
+alloc = ["serde/alloc"]
+arbitrary_precision = []
+default = ["std"]
+float_roundtrip = []
+preserve_order = [
+    "indexmap",
+    "std",
+]
+raw_value = []
+std = ["serde/std"]
+unbounded_depth = []
diff --git a/third_party/rust/serde_json/LICENSE-APACHE b/third_party/rust/serde_json/LICENSE-APACHE
new file mode 100644
index 0000000000..1b5ec8b78e
--- /dev/null
+++ b/third_party/rust/serde_json/LICENSE-APACHE
@@ -0,0 +1,176 @@
+                              Apache License
+                        Version 2.0, January 2004
+                     http://www.apache.org/licenses/
+
+TERMS AND CONDITIONS FOR USE, REPRODUCTION, AND DISTRIBUTION
+
+1. Definitions.
+
+   "License" shall mean the terms and conditions for use, reproduction,
+   and distribution as defined by Sections 1 through 9 of this document.
+
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+
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+
+   "You" (or "Your") shall mean an individual or Legal Entity
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+5. Submission of Contributions. Unless You explicitly state otherwise,
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+6. Trademarks. This License does not grant permission to use the trade
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+7. Disclaimer of Warranty. Unless required by applicable law or
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+   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or
+   implied, including, without limitation, any warranties or conditions
+   of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A
+   PARTICULAR PURPOSE. You are solely responsible for determining the
+   appropriateness of using or redistributing the Work and assume any
+   risks associated with Your exercise of permissions under this License.
+
+8. Limitation of Liability. In no event and under no legal theory,
+   whether in tort (including negligence), contract, or otherwise,
+   unless required by applicable law (such as deliberate and grossly
+   negligent acts) or agreed to in writing, shall any Contributor be
+   liable to You for damages, including any direct, indirect, special,
+   incidental, or consequential damages of any character arising as a
+   result of this License or out of the use or inability to use the
+   Work (including but not limited to damages for loss of goodwill,
+   work stoppage, computer failure or malfunction, or any and all
+   other commercial damages or losses), even if such Contributor
+   has been advised of the possibility of such damages.
+
+9. Accepting Warranty or Additional Liability. While redistributing
+   the Work or Derivative Works thereof, You may choose to offer,
+   and charge a fee for, acceptance of support, warranty, indemnity,
+   or other liability obligations and/or rights consistent with this
+   License. However, in accepting such obligations, You may act only
+   on Your own behalf and on Your sole responsibility, not on behalf
+   of any other Contributor, and only if You agree to indemnify,
+   defend, and hold each Contributor harmless for any liability
+   incurred by, or claims asserted against, such Contributor by reason
+   of your accepting any such warranty or additional liability.
+
+END OF TERMS AND CONDITIONS
diff --git a/third_party/rust/serde_json/LICENSE-MIT b/third_party/rust/serde_json/LICENSE-MIT
new file mode 100644
index 0000000000..31aa79387f
--- /dev/null
+++ b/third_party/rust/serde_json/LICENSE-MIT
@@ -0,0 +1,23 @@
+Permission is hereby granted, free of charge, to any
+person obtaining a copy of this software and associated
+documentation files (the "Software"), to deal in the
+Software without restriction, including without
+limitation the rights to use, copy, modify, merge,
+publish, distribute, sublicense, and/or sell copies of
+the Software, and to permit persons to whom the Software
+is furnished to do so, subject to the following
+conditions:
+
+The above copyright notice and this permission notice
+shall be included in all copies or substantial portions
+of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF
+ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED
+TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A
+PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT
+SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
+OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR
+IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER
+DEALINGS IN THE SOFTWARE.
diff --git a/third_party/rust/serde_json/README.md b/third_party/rust/serde_json/README.md
new file mode 100644
index 0000000000..d704979247
--- /dev/null
+++ b/third_party/rust/serde_json/README.md
@@ -0,0 +1,390 @@
+# Serde JSON &emsp; [![Build Status]][actions] [![Latest Version]][crates.io] [![Rustc Version 1.36+]][rustc]
+
+[Build Status]: https://img.shields.io/github/actions/workflow/status/serde-rs/json/ci.yml?branch=master
+[actions]: https://github.com/serde-rs/json/actions?query=branch%3Amaster
+[Latest Version]: https://img.shields.io/crates/v/serde_json.svg
+[crates.io]: https://crates.io/crates/serde\_json
+[Rustc Version 1.36+]: https://img.shields.io/badge/rustc-1.36+-lightgray.svg
+[rustc]: https://blog.rust-lang.org/2019/07/04/Rust-1.36.0.html
+
+**Serde is a framework for *ser*ializing and *de*serializing Rust data structures efficiently and generically.**
+
+---
+
+```toml
+[dependencies]
+serde_json = "1.0"
+```
+
+You may be looking for:
+
+- [JSON API documentation](https://docs.rs/serde_json)
+- [Serde API documentation](https://docs.rs/serde)
+- [Detailed documentation about Serde](https://serde.rs/)
+- [Setting up `#[derive(Serialize, Deserialize)]`](https://serde.rs/derive.html)
+- [Release notes](https://github.com/serde-rs/json/releases)
+
+JSON is a ubiquitous open-standard format that uses human-readable text to
+transmit data objects consisting of key-value pairs.
+
+```json
+{
+    "name": "John Doe",
+    "age": 43,
+    "address": {
+        "street": "10 Downing Street",
+        "city": "London"
+    },
+    "phones": [
+        "+44 1234567",
+        "+44 2345678"
+    ]
+}
+```
+
+There are three common ways that you might find yourself needing to work with
+JSON data in Rust.
+
+ - **As text data.** An unprocessed string of JSON data that you receive on an
+   HTTP endpoint, read from a file, or prepare to send to a remote server.
+ - **As an untyped or loosely typed representation.** Maybe you want to check
+   that some JSON data is valid before passing it on, but without knowing the
+   structure of what it contains. Or you want to do very basic manipulations
+   like insert a key in a particular spot.
+ - **As a strongly typed Rust data structure.** When you expect all or most of
+   your data to conform to a particular structure and want to get real work done
+   without JSON's loosey-goosey nature tripping you up.
+
+Serde JSON provides efficient, flexible, safe ways of converting data between
+each of these representations.
+
+## Operating on untyped JSON values
+
+Any valid JSON data can be manipulated in the following recursive enum
+representation. This data structure is [`serde_json::Value`][value].
+
+```rust
+enum Value {
+    Null,
+    Bool(bool),
+    Number(Number),
+    String(String),
+    Array(Vec<Value>),
+    Object(Map<String, Value>),
+}
+```
+
+A string of JSON data can be parsed into a `serde_json::Value` by the
+[`serde_json::from_str`][from_str] function. There is also
+[`from_slice`][from_slice] for parsing from a byte slice &[u8] and
+[`from_reader`][from_reader] for parsing from any `io::Read` like a File or a
+TCP stream.
+
+<div align="right">
+<a href="https://play.rust-lang.org/?edition=2018&gist=d69d8e3156d4bb81c4461b60b772ab72" target="_blank">
+<img align="center" width="85" src="https://raw.githubusercontent.com/serde-rs/serde-rs.github.io/master/img/runtab.png">
+</a>
+</div>
+
+```rust
+use serde_json::{Result, Value};
+
+fn untyped_example() -> Result<()> {
+    // Some JSON input data as a &str. Maybe this comes from the user.
+    let data = r#"
+        {
+            "name": "John Doe",
+            "age": 43,
+            "phones": [
+                "+44 1234567",
+                "+44 2345678"
+            ]
+        }"#;
+
+    // Parse the string of data into serde_json::Value.
+    let v: Value = serde_json::from_str(data)?;
+
+    // Access parts of the data by indexing with square brackets.
+    println!("Please call {} at the number {}", v["name"], v["phones"][0]);
+
+    Ok(())
+}
+```
+
+The result of square bracket indexing like `v["name"]` is a borrow of the data
+at that index, so the type is `&Value`. A JSON map can be indexed with string
+keys, while a JSON array can be indexed with integer keys. If the type of the
+data is not right for the type with which it is being indexed, or if a map does
+not contain the key being indexed, or if the index into a vector is out of
+bounds, the returned element is `Value::Null`.
+
+When a `Value` is printed, it is printed as a JSON string. So in the code above,
+the output looks like `Please call "John Doe" at the number "+44 1234567"`. The
+quotation marks appear because `v["name"]` is a `&Value` containing a JSON
+string and its JSON representation is `"John Doe"`. Printing as a plain string
+without quotation marks involves converting from a JSON string to a Rust string
+with [`as_str()`] or avoiding the use of `Value` as described in the following
+section.
+
+[`as_str()`]: https://docs.rs/serde_json/1/serde_json/enum.Value.html#method.as_str
+
+The `Value` representation is sufficient for very basic tasks but can be tedious
+to work with for anything more significant. Error handling is verbose to
+implement correctly, for example imagine trying to detect the presence of
+unrecognized fields in the input data. The compiler is powerless to help you
+when you make a mistake, for example imagine typoing `v["name"]` as `v["nmae"]`
+in one of the dozens of places it is used in your code.
+
+## Parsing JSON as strongly typed data structures
+
+Serde provides a powerful way of mapping JSON data into Rust data structures
+largely automatically.
+
+<div align="right">
+<a href="https://play.rust-lang.org/?edition=2018&gist=15cfab66d38ff8a15a9cf1d8d897ac68" target="_blank">
+<img align="center" width="85" src="https://raw.githubusercontent.com/serde-rs/serde-rs.github.io/master/img/runtab.png">
+</a>
+</div>
+
+```rust
+use serde::{Deserialize, Serialize};
+use serde_json::Result;
+
+#[derive(Serialize, Deserialize)]
+struct Person {
+    name: String,
+    age: u8,
+    phones: Vec<String>,
+}
+
+fn typed_example() -> Result<()> {
+    // Some JSON input data as a &str. Maybe this comes from the user.
+    let data = r#"
+        {
+            "name": "John Doe",
+            "age": 43,
+            "phones": [
+                "+44 1234567",
+                "+44 2345678"
+            ]
+        }"#;
+
+    // Parse the string of data into a Person object. This is exactly the
+    // same function as the one that produced serde_json::Value above, but
+    // now we are asking it for a Person as output.
+    let p: Person = serde_json::from_str(data)?;
+
+    // Do things just like with any other Rust data structure.
+    println!("Please call {} at the number {}", p.name, p.phones[0]);
+
+    Ok(())
+}
+```
+
+This is the same `serde_json::from_str` function as before, but this time we
+assign the return value to a variable of type `Person` so Serde will
+automatically interpret the input data as a `Person` and produce informative
+error messages if the layout does not conform to what a `Person` is expected to
+look like.
+
+Any type that implements Serde's `Deserialize` trait can be deserialized this
+way. This includes built-in Rust standard library types like `Vec<T>` and
+`HashMap<K, V>`, as well as any structs or enums annotated with
+`#[derive(Deserialize)]`.
+
+Once we have `p` of type `Person`, our IDE and the Rust compiler can help us use
+it correctly like they do for any other Rust code. The IDE can autocomplete
+field names to prevent typos, which was impossible in the `serde_json::Value`
+representation. And the Rust compiler can check that when we write
+`p.phones[0]`, then `p.phones` is guaranteed to be a `Vec<String>` so indexing
+into it makes sense and produces a `String`.
+
+The necessary setup for using Serde's derive macros is explained on the *[Using
+derive]* page of the Serde site.
+
+[Using derive]: https://serde.rs/derive.html
+
+## Constructing JSON values
+
+Serde JSON provides a [`json!` macro][macro] to build `serde_json::Value`
+objects with very natural JSON syntax.
+
+<div align="right">
+<a href="https://play.rust-lang.org/?edition=2018&gist=6ccafad431d72b62e77cc34c8e879b24" target="_blank">
+<img align="center" width="85" src="https://raw.githubusercontent.com/serde-rs/serde-rs.github.io/master/img/runtab.png">
+</a>
+</div>
+
+```rust
+use serde_json::json;
+
+fn main() {
+    // The type of `john` is `serde_json::Value`
+    let john = json!({
+        "name": "John Doe",
+        "age": 43,
+        "phones": [
+            "+44 1234567",
+            "+44 2345678"
+        ]
+    });
+
+    println!("first phone number: {}", john["phones"][0]);
+
+    // Convert to a string of JSON and print it out
+    println!("{}", john.to_string());
+}
+```
+
+The `Value::to_string()` function converts a `serde_json::Value` into a `String`
+of JSON text.
+
+One neat thing about the `json!` macro is that variables and expressions can be
+interpolated directly into the JSON value as you are building it. Serde will
+check at compile time that the value you are interpolating is able to be
+represented as JSON.
+
+<div align="right">
+<a href="https://play.rust-lang.org/?edition=2018&gist=f9101a6e61dfc9e02c6a67f315ed24f2" target="_blank">
+<img align="center" width="85" src="https://raw.githubusercontent.com/serde-rs/serde-rs.github.io/master/img/runtab.png">
+</a>
+</div>
+
+```rust
+let full_name = "John Doe";
+let age_last_year = 42;
+
+// The type of `john` is `serde_json::Value`
+let john = json!({
+    "name": full_name,
+    "age": age_last_year + 1,
+    "phones": [
+        format!("+44 {}", random_phone())
+    ]
+});
+```
+
+This is amazingly convenient, but we have the problem we had before with
+`Value`: the IDE and Rust compiler cannot help us if we get it wrong. Serde JSON
+provides a better way of serializing strongly-typed data structures into JSON
+text.
+
+## Creating JSON by serializing data structures
+
+A data structure can be converted to a JSON string by
+[`serde_json::to_string`][to_string]. There is also
+[`serde_json::to_vec`][to_vec] which serializes to a `Vec<u8>` and
+[`serde_json::to_writer`][to_writer] which serializes to any `io::Write`
+such as a File or a TCP stream.
+
+<div align="right">
+<a href="https://play.rust-lang.org/?edition=2018&gist=3472242a08ed2ff88a944f2a2283b0ee" target="_blank">
+<img align="center" width="85" src="https://raw.githubusercontent.com/serde-rs/serde-rs.github.io/master/img/runtab.png">
+</a>
+</div>
+
+```rust
+use serde::{Deserialize, Serialize};
+use serde_json::Result;
+
+#[derive(Serialize, Deserialize)]
+struct Address {
+    street: String,
+    city: String,
+}
+
+fn print_an_address() -> Result<()> {
+    // Some data structure.
+    let address = Address {
+        street: "10 Downing Street".to_owned(),
+        city: "London".to_owned(),
+    };
+
+    // Serialize it to a JSON string.
+    let j = serde_json::to_string(&address)?;
+
+    // Print, write to a file, or send to an HTTP server.
+    println!("{}", j);
+
+    Ok(())
+}
+```
+
+Any type that implements Serde's `Serialize` trait can be serialized this way.
+This includes built-in Rust standard library types like `Vec<T>` and `HashMap<K,
+V>`, as well as any structs or enums annotated with `#[derive(Serialize)]`.
+
+## Performance
+
+It is fast. You should expect in the ballpark of 500 to 1000 megabytes per
+second deserialization and 600 to 900 megabytes per second serialization,
+depending on the characteristics of your data. This is competitive with the
+fastest C and C++ JSON libraries or even 30% faster for many use cases.
+Benchmarks live in the [serde-rs/json-benchmark] repo.
+
+[serde-rs/json-benchmark]: https://github.com/serde-rs/json-benchmark
+
+## Getting help
+
+Serde is one of the most widely used Rust libraries, so any place that
+Rustaceans congregate will be able to help you out. For chat, consider trying
+the [#rust-questions] or [#rust-beginners] channels of the unofficial community
+Discord (invite: <https://discord.gg/rust-lang-community>), the [#rust-usage] or
+[#beginners] channels of the official Rust Project Discord (invite:
+<https://discord.gg/rust-lang>), or the [#general][zulip] stream in Zulip. For
+asynchronous, consider the [\[rust\] tag on StackOverflow][stackoverflow], the
+[/r/rust] subreddit which has a pinned weekly easy questions post, or the Rust
+[Discourse forum][discourse]. It's acceptable to file a support issue in this
+repo, but they tend not to get as many eyes as any of the above and may get
+closed without a response after some time.
+
+[#rust-questions]: https://discord.com/channels/273534239310479360/274215136414400513
+[#rust-beginners]: https://discord.com/channels/273534239310479360/273541522815713281
+[#rust-usage]: https://discord.com/channels/442252698964721669/443150878111694848
+[#beginners]: https://discord.com/channels/442252698964721669/448238009733742612
+[zulip]: https://rust-lang.zulipchat.com/#narrow/stream/122651-general
+[stackoverflow]: https://stackoverflow.com/questions/tagged/rust
+[/r/rust]: https://www.reddit.com/r/rust
+[discourse]: https://users.rust-lang.org
+
+## No-std support
+
+As long as there is a memory allocator, it is possible to use serde_json without
+the rest of the Rust standard library. Disable the default "std" feature and
+enable the "alloc" feature:
+
+```toml
+[dependencies]
+serde_json = { version = "1.0", default-features = false, features = ["alloc"] }
+```
+
+For JSON support in Serde without a memory allocator, please see the
+[`serde-json-core`] crate.
+
+[`serde-json-core`]: https://github.com/rust-embedded-community/serde-json-core
+
+[value]: https://docs.rs/serde_json/1/serde_json/value/enum.Value.html
+[from_str]: https://docs.rs/serde_json/1/serde_json/de/fn.from_str.html
+[from_slice]: https://docs.rs/serde_json/1/serde_json/de/fn.from_slice.html
+[from_reader]: https://docs.rs/serde_json/1/serde_json/de/fn.from_reader.html
+[to_string]: https://docs.rs/serde_json/1/serde_json/ser/fn.to_string.html
+[to_vec]: https://docs.rs/serde_json/1/serde_json/ser/fn.to_vec.html
+[to_writer]: https://docs.rs/serde_json/1/serde_json/ser/fn.to_writer.html
+[macro]: https://docs.rs/serde_json/1/serde_json/macro.json.html
+
+<br>
+
+#### License
+
+<sup>
+Licensed under either of <a href="LICENSE-APACHE">Apache License, Version
+2.0</a> or <a href="LICENSE-MIT">MIT license</a> at your option.
+</sup>
+
+<br>
+
+<sub>
+Unless you explicitly state otherwise, any contribution intentionally submitted
+for inclusion in this crate by you, as defined in the Apache-2.0 license, shall
+be dual licensed as above, without any additional terms or conditions.
+</sub>
diff --git a/third_party/rust/serde_json/build.rs b/third_party/rust/serde_json/build.rs
new file mode 100644
index 0000000000..0e12602e46
--- /dev/null
+++ b/third_party/rust/serde_json/build.rs
@@ -0,0 +1,54 @@
+use std::env;
+use std::process::Command;
+use std::str::{self, FromStr};
+
+fn main() {
+    println!("cargo:rerun-if-changed=build.rs");
+
+    // Decide ideal limb width for arithmetic in the float parser. Refer to
+    // src/lexical/math.rs for where this has an effect.
+    let target_arch = env::var("CARGO_CFG_TARGET_ARCH").unwrap();
+    match target_arch.as_str() {
+        "aarch64" | "mips64" | "powerpc64" | "x86_64" => {
+            println!("cargo:rustc-cfg=limb_width_64");
+        }
+        _ => {
+            println!("cargo:rustc-cfg=limb_width_32");
+        }
+    }
+
+    let minor = match rustc_minor_version() {
+        Some(minor) => minor,
+        None => return,
+    };
+
+    // BTreeMap::get_key_value
+    // https://blog.rust-lang.org/2019/12/19/Rust-1.40.0.html#additions-to-the-standard-library
+    if minor < 40 {
+        println!("cargo:rustc-cfg=no_btreemap_get_key_value");
+    }
+
+    // BTreeMap::remove_entry
+    // https://blog.rust-lang.org/2020/07/16/Rust-1.45.0.html#library-changes
+    if minor < 45 {
+        println!("cargo:rustc-cfg=no_btreemap_remove_entry");
+    }
+
+    // BTreeMap::retain
+    // https://blog.rust-lang.org/2021/06/17/Rust-1.53.0.html#stabilized-apis
+    if minor < 53 {
+        println!("cargo:rustc-cfg=no_btreemap_retain");
+    }
+}
+
+fn rustc_minor_version() -> Option<u32> {
+    let rustc = env::var_os("RUSTC")?;
+    let output = Command::new(rustc).arg("--version").output().ok()?;
+    let version = str::from_utf8(&output.stdout).ok()?;
+    let mut pieces = version.split('.');
+    if pieces.next() != Some("rustc 1") {
+        return None;
+    }
+    let next = pieces.next()?;
+    u32::from_str(next).ok()
+}
diff --git a/third_party/rust/serde_json/src/de.rs b/third_party/rust/serde_json/src/de.rs
new file mode 100644
index 0000000000..88d0f2624d
--- /dev/null
+++ b/third_party/rust/serde_json/src/de.rs
@@ -0,0 +1,2606 @@
+//! Deserialize JSON data to a Rust data structure.
+
+use crate::error::{Error, ErrorCode, Result};
+#[cfg(feature = "float_roundtrip")]
+use crate::lexical;
+use crate::number::Number;
+use crate::read::{self, Fused, Reference};
+use alloc::string::String;
+use alloc::vec::Vec;
+#[cfg(feature = "float_roundtrip")]
+use core::iter;
+use core::iter::FusedIterator;
+use core::marker::PhantomData;
+use core::result;
+use core::str::FromStr;
+use serde::de::{self, Expected, Unexpected};
+use serde::forward_to_deserialize_any;
+
+#[cfg(feature = "arbitrary_precision")]
+use crate::number::NumberDeserializer;
+
+pub use crate::read::{Read, SliceRead, StrRead};
+
+#[cfg(feature = "std")]
+pub use crate::read::IoRead;
+
+//////////////////////////////////////////////////////////////////////////////
+
+/// A structure that deserializes JSON into Rust values.
+pub struct Deserializer<R> {
+    read: R,
+    scratch: Vec<u8>,
+    remaining_depth: u8,
+    #[cfg(feature = "float_roundtrip")]
+    single_precision: bool,
+    #[cfg(feature = "unbounded_depth")]
+    disable_recursion_limit: bool,
+}
+
+impl<'de, R> Deserializer<R>
+where
+    R: read::Read<'de>,
+{
+    /// Create a JSON deserializer from one of the possible serde_json input
+    /// sources.
+    ///
+    /// Typically it is more convenient to use one of these methods instead:
+    ///
+    ///   - Deserializer::from_str
+    ///   - Deserializer::from_slice
+    ///   - Deserializer::from_reader
+    pub fn new(read: R) -> Self {
+        Deserializer {
+            read,
+            scratch: Vec::new(),
+            remaining_depth: 128,
+            #[cfg(feature = "float_roundtrip")]
+            single_precision: false,
+            #[cfg(feature = "unbounded_depth")]
+            disable_recursion_limit: false,
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl<R> Deserializer<read::IoRead<R>>
+where
+    R: crate::io::Read,
+{
+    /// Creates a JSON deserializer from an `io::Read`.
+    ///
+    /// Reader-based deserializers do not support deserializing borrowed types
+    /// like `&str`, since the `std::io::Read` trait has no non-copying methods
+    /// -- everything it does involves copying bytes out of the data source.
+    pub fn from_reader(reader: R) -> Self {
+        Deserializer::new(read::IoRead::new(reader))
+    }
+}
+
+impl<'a> Deserializer<read::SliceRead<'a>> {
+    /// Creates a JSON deserializer from a `&[u8]`.
+    pub fn from_slice(bytes: &'a [u8]) -> Self {
+        Deserializer::new(read::SliceRead::new(bytes))
+    }
+}
+
+impl<'a> Deserializer<read::StrRead<'a>> {
+    /// Creates a JSON deserializer from a `&str`.
+    pub fn from_str(s: &'a str) -> Self {
+        Deserializer::new(read::StrRead::new(s))
+    }
+}
+
+macro_rules! overflow {
+    ($a:ident * 10 + $b:ident, $c:expr) => {
+        match $c {
+            c => $a >= c / 10 && ($a > c / 10 || $b > c % 10),
+        }
+    };
+}
+
+pub(crate) enum ParserNumber {
+    F64(f64),
+    U64(u64),
+    I64(i64),
+    #[cfg(feature = "arbitrary_precision")]
+    String(String),
+}
+
+impl ParserNumber {
+    fn visit<'de, V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self {
+            ParserNumber::F64(x) => visitor.visit_f64(x),
+            ParserNumber::U64(x) => visitor.visit_u64(x),
+            ParserNumber::I64(x) => visitor.visit_i64(x),
+            #[cfg(feature = "arbitrary_precision")]
+            ParserNumber::String(x) => visitor.visit_map(NumberDeserializer { number: x.into() }),
+        }
+    }
+
+    fn invalid_type(self, exp: &dyn Expected) -> Error {
+        match self {
+            ParserNumber::F64(x) => de::Error::invalid_type(Unexpected::Float(x), exp),
+            ParserNumber::U64(x) => de::Error::invalid_type(Unexpected::Unsigned(x), exp),
+            ParserNumber::I64(x) => de::Error::invalid_type(Unexpected::Signed(x), exp),
+            #[cfg(feature = "arbitrary_precision")]
+            ParserNumber::String(_) => de::Error::invalid_type(Unexpected::Other("number"), exp),
+        }
+    }
+}
+
+impl<'de, R: Read<'de>> Deserializer<R> {
+    /// The `Deserializer::end` method should be called after a value has been fully deserialized.
+    /// This allows the `Deserializer` to validate that the input stream is at the end or that it
+    /// only has trailing whitespace.
+    pub fn end(&mut self) -> Result<()> {
+        match tri!(self.parse_whitespace()) {
+            Some(_) => Err(self.peek_error(ErrorCode::TrailingCharacters)),
+            None => Ok(()),
+        }
+    }
+
+    /// Turn a JSON deserializer into an iterator over values of type T.
+    pub fn into_iter<T>(self) -> StreamDeserializer<'de, R, T>
+    where
+        T: de::Deserialize<'de>,
+    {
+        // This cannot be an implementation of std::iter::IntoIterator because
+        // we need the caller to choose what T is.
+        let offset = self.read.byte_offset();
+        StreamDeserializer {
+            de: self,
+            offset,
+            failed: false,
+            output: PhantomData,
+            lifetime: PhantomData,
+        }
+    }
+
+    /// Parse arbitrarily deep JSON structures without any consideration for
+    /// overflowing the stack.
+    ///
+    /// You will want to provide some other way to protect against stack
+    /// overflows, such as by wrapping your Deserializer in the dynamically
+    /// growing stack adapter provided by the serde_stacker crate. Additionally
+    /// you will need to be careful around other recursive operations on the
+    /// parsed result which may overflow the stack after deserialization has
+    /// completed, including, but not limited to, Display and Debug and Drop
+    /// impls.
+    ///
+    /// *This method is only available if serde_json is built with the
+    /// `"unbounded_depth"` feature.*
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use serde::Deserialize;
+    /// use serde_json::Value;
+    ///
+    /// fn main() {
+    ///     let mut json = String::new();
+    ///     for _ in 0..10000 {
+    ///         json = format!("[{}]", json);
+    ///     }
+    ///
+    ///     let mut deserializer = serde_json::Deserializer::from_str(&json);
+    ///     deserializer.disable_recursion_limit();
+    ///     let deserializer = serde_stacker::Deserializer::new(&mut deserializer);
+    ///     let value = Value::deserialize(deserializer).unwrap();
+    ///
+    ///     carefully_drop_nested_arrays(value);
+    /// }
+    ///
+    /// fn carefully_drop_nested_arrays(value: Value) {
+    ///     let mut stack = vec![value];
+    ///     while let Some(value) = stack.pop() {
+    ///         if let Value::Array(array) = value {
+    ///             stack.extend(array);
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    #[cfg(feature = "unbounded_depth")]
+    #[cfg_attr(docsrs, doc(cfg(feature = "unbounded_depth")))]
+    pub fn disable_recursion_limit(&mut self) {
+        self.disable_recursion_limit = true;
+    }
+
+    fn peek(&mut self) -> Result<Option<u8>> {
+        self.read.peek()
+    }
+
+    fn peek_or_null(&mut self) -> Result<u8> {
+        Ok(tri!(self.peek()).unwrap_or(b'\x00'))
+    }
+
+    fn eat_char(&mut self) {
+        self.read.discard();
+    }
+
+    fn next_char(&mut self) -> Result<Option<u8>> {
+        self.read.next()
+    }
+
+    fn next_char_or_null(&mut self) -> Result<u8> {
+        Ok(tri!(self.next_char()).unwrap_or(b'\x00'))
+    }
+
+    /// Error caused by a byte from next_char().
+    #[cold]
+    fn error(&self, reason: ErrorCode) -> Error {
+        let position = self.read.position();
+        Error::syntax(reason, position.line, position.column)
+    }
+
+    /// Error caused by a byte from peek().
+    #[cold]
+    fn peek_error(&self, reason: ErrorCode) -> Error {
+        let position = self.read.peek_position();
+        Error::syntax(reason, position.line, position.column)
+    }
+
+    /// Returns the first non-whitespace byte without consuming it, or `None` if
+    /// EOF is encountered.
+    fn parse_whitespace(&mut self) -> Result<Option<u8>> {
+        loop {
+            match tri!(self.peek()) {
+                Some(b' ') | Some(b'\n') | Some(b'\t') | Some(b'\r') => {
+                    self.eat_char();
+                }
+                other => {
+                    return Ok(other);
+                }
+            }
+        }
+    }
+
+    #[cold]
+    fn peek_invalid_type(&mut self, exp: &dyn Expected) -> Error {
+        let err = match self.peek_or_null().unwrap_or(b'\x00') {
+            b'n' => {
+                self.eat_char();
+                if let Err(err) = self.parse_ident(b"ull") {
+                    return err;
+                }
+                de::Error::invalid_type(Unexpected::Unit, exp)
+            }
+            b't' => {
+                self.eat_char();
+                if let Err(err) = self.parse_ident(b"rue") {
+                    return err;
+                }
+                de::Error::invalid_type(Unexpected::Bool(true), exp)
+            }
+            b'f' => {
+                self.eat_char();
+                if let Err(err) = self.parse_ident(b"alse") {
+                    return err;
+                }
+                de::Error::invalid_type(Unexpected::Bool(false), exp)
+            }
+            b'-' => {
+                self.eat_char();
+                match self.parse_any_number(false) {
+                    Ok(n) => n.invalid_type(exp),
+                    Err(err) => return err,
+                }
+            }
+            b'0'..=b'9' => match self.parse_any_number(true) {
+                Ok(n) => n.invalid_type(exp),
+                Err(err) => return err,
+            },
+            b'"' => {
+                self.eat_char();
+                self.scratch.clear();
+                match self.read.parse_str(&mut self.scratch) {
+                    Ok(s) => de::Error::invalid_type(Unexpected::Str(&s), exp),
+                    Err(err) => return err,
+                }
+            }
+            b'[' => de::Error::invalid_type(Unexpected::Seq, exp),
+            b'{' => de::Error::invalid_type(Unexpected::Map, exp),
+            _ => self.peek_error(ErrorCode::ExpectedSomeValue),
+        };
+
+        self.fix_position(err)
+    }
+
+    fn deserialize_number<V>(&mut self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        let peek = match tri!(self.parse_whitespace()) {
+            Some(b) => b,
+            None => {
+                return Err(self.peek_error(ErrorCode::EofWhileParsingValue));
+            }
+        };
+
+        let value = match peek {
+            b'-' => {
+                self.eat_char();
+                tri!(self.parse_integer(false)).visit(visitor)
+            }
+            b'0'..=b'9' => tri!(self.parse_integer(true)).visit(visitor),
+            _ => Err(self.peek_invalid_type(&visitor)),
+        };
+
+        match value {
+            Ok(value) => Ok(value),
+            Err(err) => Err(self.fix_position(err)),
+        }
+    }
+
+    fn scan_integer128(&mut self, buf: &mut String) -> Result<()> {
+        match tri!(self.next_char_or_null()) {
+            b'0' => {
+                buf.push('0');
+                // There can be only one leading '0'.
+                match tri!(self.peek_or_null()) {
+                    b'0'..=b'9' => Err(self.peek_error(ErrorCode::InvalidNumber)),
+                    _ => Ok(()),
+                }
+            }
+            c @ b'1'..=b'9' => {
+                buf.push(c as char);
+                while let c @ b'0'..=b'9' = tri!(self.peek_or_null()) {
+                    self.eat_char();
+                    buf.push(c as char);
+                }
+                Ok(())
+            }
+            _ => Err(self.error(ErrorCode::InvalidNumber)),
+        }
+    }
+
+    #[cold]
+    fn fix_position(&self, err: Error) -> Error {
+        err.fix_position(move |code| self.error(code))
+    }
+
+    fn parse_ident(&mut self, ident: &[u8]) -> Result<()> {
+        for expected in ident {
+            match tri!(self.next_char()) {
+                None => {
+                    return Err(self.error(ErrorCode::EofWhileParsingValue));
+                }
+                Some(next) => {
+                    if next != *expected {
+                        return Err(self.error(ErrorCode::ExpectedSomeIdent));
+                    }
+                }
+            }
+        }
+
+        Ok(())
+    }
+
+    fn parse_integer(&mut self, positive: bool) -> Result<ParserNumber> {
+        let next = match tri!(self.next_char()) {
+            Some(b) => b,
+            None => {
+                return Err(self.error(ErrorCode::EofWhileParsingValue));
+            }
+        };
+
+        match next {
+            b'0' => {
+                // There can be only one leading '0'.
+                match tri!(self.peek_or_null()) {
+                    b'0'..=b'9' => Err(self.peek_error(ErrorCode::InvalidNumber)),
+                    _ => self.parse_number(positive, 0),
+                }
+            }
+            c @ b'1'..=b'9' => {
+                let mut significand = (c - b'0') as u64;
+
+                loop {
+                    match tri!(self.peek_or_null()) {
+                        c @ b'0'..=b'9' => {
+                            let digit = (c - b'0') as u64;
+
+                            // We need to be careful with overflow. If we can,
+                            // try to keep the number as a `u64` until we grow
+                            // too large. At that point, switch to parsing the
+                            // value as a `f64`.
+                            if overflow!(significand * 10 + digit, u64::max_value()) {
+                                return Ok(ParserNumber::F64(tri!(
+                                    self.parse_long_integer(positive, significand),
+                                )));
+                            }
+
+                            self.eat_char();
+                            significand = significand * 10 + digit;
+                        }
+                        _ => {
+                            return self.parse_number(positive, significand);
+                        }
+                    }
+                }
+            }
+            _ => Err(self.error(ErrorCode::InvalidNumber)),
+        }
+    }
+
+    fn parse_number(&mut self, positive: bool, significand: u64) -> Result<ParserNumber> {
+        Ok(match tri!(self.peek_or_null()) {
+            b'.' => ParserNumber::F64(tri!(self.parse_decimal(positive, significand, 0))),
+            b'e' | b'E' => ParserNumber::F64(tri!(self.parse_exponent(positive, significand, 0))),
+            _ => {
+                if positive {
+                    ParserNumber::U64(significand)
+                } else {
+                    let neg = (significand as i64).wrapping_neg();
+
+                    // Convert into a float if we underflow, or on `-0`.
+                    if neg >= 0 {
+                        ParserNumber::F64(-(significand as f64))
+                    } else {
+                        ParserNumber::I64(neg)
+                    }
+                }
+            }
+        })
+    }
+
+    fn parse_decimal(
+        &mut self,
+        positive: bool,
+        mut significand: u64,
+        exponent_before_decimal_point: i32,
+    ) -> Result<f64> {
+        self.eat_char();
+
+        let mut exponent_after_decimal_point = 0;
+        while let c @ b'0'..=b'9' = tri!(self.peek_or_null()) {
+            let digit = (c - b'0') as u64;
+
+            if overflow!(significand * 10 + digit, u64::max_value()) {
+                let exponent = exponent_before_decimal_point + exponent_after_decimal_point;
+                return self.parse_decimal_overflow(positive, significand, exponent);
+            }
+
+            self.eat_char();
+            significand = significand * 10 + digit;
+            exponent_after_decimal_point -= 1;
+        }
+
+        // Error if there is not at least one digit after the decimal point.
+        if exponent_after_decimal_point == 0 {
+            match tri!(self.peek()) {
+                Some(_) => return Err(self.peek_error(ErrorCode::InvalidNumber)),
+                None => return Err(self.peek_error(ErrorCode::EofWhileParsingValue)),
+            }
+        }
+
+        let exponent = exponent_before_decimal_point + exponent_after_decimal_point;
+        match tri!(self.peek_or_null()) {
+            b'e' | b'E' => self.parse_exponent(positive, significand, exponent),
+            _ => self.f64_from_parts(positive, significand, exponent),
+        }
+    }
+
+    fn parse_exponent(
+        &mut self,
+        positive: bool,
+        significand: u64,
+        starting_exp: i32,
+    ) -> Result<f64> {
+        self.eat_char();
+
+        let positive_exp = match tri!(self.peek_or_null()) {
+            b'+' => {
+                self.eat_char();
+                true
+            }
+            b'-' => {
+                self.eat_char();
+                false
+            }
+            _ => true,
+        };
+
+        let next = match tri!(self.next_char()) {
+            Some(b) => b,
+            None => {
+                return Err(self.error(ErrorCode::EofWhileParsingValue));
+            }
+        };
+
+        // Make sure a digit follows the exponent place.
+        let mut exp = match next {
+            c @ b'0'..=b'9' => (c - b'0') as i32,
+            _ => {
+                return Err(self.error(ErrorCode::InvalidNumber));
+            }
+        };
+
+        while let c @ b'0'..=b'9' = tri!(self.peek_or_null()) {
+            self.eat_char();
+            let digit = (c - b'0') as i32;
+
+            if overflow!(exp * 10 + digit, i32::max_value()) {
+                let zero_significand = significand == 0;
+                return self.parse_exponent_overflow(positive, zero_significand, positive_exp);
+            }
+
+            exp = exp * 10 + digit;
+        }
+
+        let final_exp = if positive_exp {
+            starting_exp.saturating_add(exp)
+        } else {
+            starting_exp.saturating_sub(exp)
+        };
+
+        self.f64_from_parts(positive, significand, final_exp)
+    }
+
+    #[cfg(feature = "float_roundtrip")]
+    fn f64_from_parts(&mut self, positive: bool, significand: u64, exponent: i32) -> Result<f64> {
+        let f = if self.single_precision {
+            lexical::parse_concise_float::<f32>(significand, exponent) as f64
+        } else {
+            lexical::parse_concise_float::<f64>(significand, exponent)
+        };
+
+        if f.is_infinite() {
+            Err(self.error(ErrorCode::NumberOutOfRange))
+        } else {
+            Ok(if positive { f } else { -f })
+        }
+    }
+
+    #[cfg(not(feature = "float_roundtrip"))]
+    fn f64_from_parts(
+        &mut self,
+        positive: bool,
+        significand: u64,
+        mut exponent: i32,
+    ) -> Result<f64> {
+        let mut f = significand as f64;
+        loop {
+            match POW10.get(exponent.wrapping_abs() as usize) {
+                Some(&pow) => {
+                    if exponent >= 0 {
+                        f *= pow;
+                        if f.is_infinite() {
+                            return Err(self.error(ErrorCode::NumberOutOfRange));
+                        }
+                    } else {
+                        f /= pow;
+                    }
+                    break;
+                }
+                None => {
+                    if f == 0.0 {
+                        break;
+                    }
+                    if exponent >= 0 {
+                        return Err(self.error(ErrorCode::NumberOutOfRange));
+                    }
+                    f /= 1e308;
+                    exponent += 308;
+                }
+            }
+        }
+        Ok(if positive { f } else { -f })
+    }
+
+    #[cfg(feature = "float_roundtrip")]
+    #[cold]
+    #[inline(never)]
+    fn parse_long_integer(&mut self, positive: bool, partial_significand: u64) -> Result<f64> {
+        // To deserialize floats we'll first push the integer and fraction
+        // parts, both as byte strings, into the scratch buffer and then feed
+        // both slices to lexical's parser. For example if the input is
+        // `12.34e5` we'll push b"1234" into scratch and then pass b"12" and
+        // b"34" to lexical. `integer_end` will be used to track where to split
+        // the scratch buffer.
+        //
+        // Note that lexical expects the integer part to contain *no* leading
+        // zeroes and the fraction part to contain *no* trailing zeroes. The
+        // first requirement is already handled by the integer parsing logic.
+        // The second requirement will be enforced just before passing the
+        // slices to lexical in f64_long_from_parts.
+        self.scratch.clear();
+        self.scratch
+            .extend_from_slice(itoa::Buffer::new().format(partial_significand).as_bytes());
+
+        loop {
+            match tri!(self.peek_or_null()) {
+                c @ b'0'..=b'9' => {
+                    self.scratch.push(c);
+                    self.eat_char();
+                }
+                b'.' => {
+                    self.eat_char();
+                    return self.parse_long_decimal(positive, self.scratch.len());
+                }
+                b'e' | b'E' => {
+                    return self.parse_long_exponent(positive, self.scratch.len());
+                }
+                _ => {
+                    return self.f64_long_from_parts(positive, self.scratch.len(), 0);
+                }
+            }
+        }
+    }
+
+    #[cfg(not(feature = "float_roundtrip"))]
+    #[cold]
+    #[inline(never)]
+    fn parse_long_integer(&mut self, positive: bool, significand: u64) -> Result<f64> {
+        let mut exponent = 0;
+        loop {
+            match tri!(self.peek_or_null()) {
+                b'0'..=b'9' => {
+                    self.eat_char();
+                    // This could overflow... if your integer is gigabytes long.
+                    // Ignore that possibility.
+                    exponent += 1;
+                }
+                b'.' => {
+                    return self.parse_decimal(positive, significand, exponent);
+                }
+                b'e' | b'E' => {
+                    return self.parse_exponent(positive, significand, exponent);
+                }
+                _ => {
+                    return self.f64_from_parts(positive, significand, exponent);
+                }
+            }
+        }
+    }
+
+    #[cfg(feature = "float_roundtrip")]
+    #[cold]
+    fn parse_long_decimal(&mut self, positive: bool, integer_end: usize) -> Result<f64> {
+        let mut at_least_one_digit = integer_end < self.scratch.len();
+        while let c @ b'0'..=b'9' = tri!(self.peek_or_null()) {
+            self.scratch.push(c);
+            self.eat_char();
+            at_least_one_digit = true;
+        }
+
+        if !at_least_one_digit {
+            match tri!(self.peek()) {
+                Some(_) => return Err(self.peek_error(ErrorCode::InvalidNumber)),
+                None => return Err(self.peek_error(ErrorCode::EofWhileParsingValue)),
+            }
+        }
+
+        match tri!(self.peek_or_null()) {
+            b'e' | b'E' => self.parse_long_exponent(positive, integer_end),
+            _ => self.f64_long_from_parts(positive, integer_end, 0),
+        }
+    }
+
+    #[cfg(feature = "float_roundtrip")]
+    fn parse_long_exponent(&mut self, positive: bool, integer_end: usize) -> Result<f64> {
+        self.eat_char();
+
+        let positive_exp = match tri!(self.peek_or_null()) {
+            b'+' => {
+                self.eat_char();
+                true
+            }
+            b'-' => {
+                self.eat_char();
+                false
+            }
+            _ => true,
+        };
+
+        let next = match tri!(self.next_char()) {
+            Some(b) => b,
+            None => {
+                return Err(self.error(ErrorCode::EofWhileParsingValue));
+            }
+        };
+
+        // Make sure a digit follows the exponent place.
+        let mut exp = match next {
+            c @ b'0'..=b'9' => (c - b'0') as i32,
+            _ => {
+                return Err(self.error(ErrorCode::InvalidNumber));
+            }
+        };
+
+        while let c @ b'0'..=b'9' = tri!(self.peek_or_null()) {
+            self.eat_char();
+            let digit = (c - b'0') as i32;
+
+            if overflow!(exp * 10 + digit, i32::max_value()) {
+                let zero_significand = self.scratch.iter().all(|&digit| digit == b'0');
+                return self.parse_exponent_overflow(positive, zero_significand, positive_exp);
+            }
+
+            exp = exp * 10 + digit;
+        }
+
+        let final_exp = if positive_exp { exp } else { -exp };
+
+        self.f64_long_from_parts(positive, integer_end, final_exp)
+    }
+
+    // This cold code should not be inlined into the middle of the hot
+    // decimal-parsing loop above.
+    #[cfg(feature = "float_roundtrip")]
+    #[cold]
+    #[inline(never)]
+    fn parse_decimal_overflow(
+        &mut self,
+        positive: bool,
+        significand: u64,
+        exponent: i32,
+    ) -> Result<f64> {
+        let mut buffer = itoa::Buffer::new();
+        let significand = buffer.format(significand);
+        let fraction_digits = -exponent as usize;
+        self.scratch.clear();
+        if let Some(zeros) = fraction_digits.checked_sub(significand.len() + 1) {
+            self.scratch.extend(iter::repeat(b'0').take(zeros + 1));
+        }
+        self.scratch.extend_from_slice(significand.as_bytes());
+        let integer_end = self.scratch.len() - fraction_digits;
+        self.parse_long_decimal(positive, integer_end)
+    }
+
+    #[cfg(not(feature = "float_roundtrip"))]
+    #[cold]
+    #[inline(never)]
+    fn parse_decimal_overflow(
+        &mut self,
+        positive: bool,
+        significand: u64,
+        exponent: i32,
+    ) -> Result<f64> {
+        // The next multiply/add would overflow, so just ignore all further
+        // digits.
+        while let b'0'..=b'9' = tri!(self.peek_or_null()) {
+            self.eat_char();
+        }
+
+        match tri!(self.peek_or_null()) {
+            b'e' | b'E' => self.parse_exponent(positive, significand, exponent),
+            _ => self.f64_from_parts(positive, significand, exponent),
+        }
+    }
+
+    // This cold code should not be inlined into the middle of the hot
+    // exponent-parsing loop above.
+    #[cold]
+    #[inline(never)]
+    fn parse_exponent_overflow(
+        &mut self,
+        positive: bool,
+        zero_significand: bool,
+        positive_exp: bool,
+    ) -> Result<f64> {
+        // Error instead of +/- infinity.
+        if !zero_significand && positive_exp {
+            return Err(self.error(ErrorCode::NumberOutOfRange));
+        }
+
+        while let b'0'..=b'9' = tri!(self.peek_or_null()) {
+            self.eat_char();
+        }
+        Ok(if positive { 0.0 } else { -0.0 })
+    }
+
+    #[cfg(feature = "float_roundtrip")]
+    fn f64_long_from_parts(
+        &mut self,
+        positive: bool,
+        integer_end: usize,
+        exponent: i32,
+    ) -> Result<f64> {
+        let integer = &self.scratch[..integer_end];
+        let fraction = &self.scratch[integer_end..];
+
+        let f = if self.single_precision {
+            lexical::parse_truncated_float::<f32>(integer, fraction, exponent) as f64
+        } else {
+            lexical::parse_truncated_float::<f64>(integer, fraction, exponent)
+        };
+
+        if f.is_infinite() {
+            Err(self.error(ErrorCode::NumberOutOfRange))
+        } else {
+            Ok(if positive { f } else { -f })
+        }
+    }
+
+    fn parse_any_signed_number(&mut self) -> Result<ParserNumber> {
+        let peek = match tri!(self.peek()) {
+            Some(b) => b,
+            None => {
+                return Err(self.peek_error(ErrorCode::EofWhileParsingValue));
+            }
+        };
+
+        let value = match peek {
+            b'-' => {
+                self.eat_char();
+                self.parse_any_number(false)
+            }
+            b'0'..=b'9' => self.parse_any_number(true),
+            _ => Err(self.peek_error(ErrorCode::InvalidNumber)),
+        };
+
+        let value = match tri!(self.peek()) {
+            Some(_) => Err(self.peek_error(ErrorCode::InvalidNumber)),
+            None => value,
+        };
+
+        match value {
+            Ok(value) => Ok(value),
+            // The de::Error impl creates errors with unknown line and column.
+            // Fill in the position here by looking at the current index in the
+            // input. There is no way to tell whether this should call `error`
+            // or `peek_error` so pick the one that seems correct more often.
+            // Worst case, the position is off by one character.
+            Err(err) => Err(self.fix_position(err)),
+        }
+    }
+
+    #[cfg(not(feature = "arbitrary_precision"))]
+    fn parse_any_number(&mut self, positive: bool) -> Result<ParserNumber> {
+        self.parse_integer(positive)
+    }
+
+    #[cfg(feature = "arbitrary_precision")]
+    fn parse_any_number(&mut self, positive: bool) -> Result<ParserNumber> {
+        let mut buf = String::with_capacity(16);
+        if !positive {
+            buf.push('-');
+        }
+        self.scan_integer(&mut buf)?;
+        if positive {
+            if let Ok(unsigned) = buf.parse() {
+                return Ok(ParserNumber::U64(unsigned));
+            }
+        } else {
+            if let Ok(signed) = buf.parse() {
+                return Ok(ParserNumber::I64(signed));
+            }
+        }
+        Ok(ParserNumber::String(buf))
+    }
+
+    #[cfg(feature = "arbitrary_precision")]
+    fn scan_or_eof(&mut self, buf: &mut String) -> Result<u8> {
+        match tri!(self.next_char()) {
+            Some(b) => {
+                buf.push(b as char);
+                Ok(b)
+            }
+            None => Err(self.error(ErrorCode::EofWhileParsingValue)),
+        }
+    }
+
+    #[cfg(feature = "arbitrary_precision")]
+    fn scan_integer(&mut self, buf: &mut String) -> Result<()> {
+        match tri!(self.scan_or_eof(buf)) {
+            b'0' => {
+                // There can be only one leading '0'.
+                match tri!(self.peek_or_null()) {
+                    b'0'..=b'9' => Err(self.peek_error(ErrorCode::InvalidNumber)),
+                    _ => self.scan_number(buf),
+                }
+            }
+            b'1'..=b'9' => loop {
+                match tri!(self.peek_or_null()) {
+                    c @ b'0'..=b'9' => {
+                        self.eat_char();
+                        buf.push(c as char);
+                    }
+                    _ => {
+                        return self.scan_number(buf);
+                    }
+                }
+            },
+            _ => Err(self.error(ErrorCode::InvalidNumber)),
+        }
+    }
+
+    #[cfg(feature = "arbitrary_precision")]
+    fn scan_number(&mut self, buf: &mut String) -> Result<()> {
+        match tri!(self.peek_or_null()) {
+            b'.' => self.scan_decimal(buf),
+            e @ b'e' | e @ b'E' => self.scan_exponent(e as char, buf),
+            _ => Ok(()),
+        }
+    }
+
+    #[cfg(feature = "arbitrary_precision")]
+    fn scan_decimal(&mut self, buf: &mut String) -> Result<()> {
+        self.eat_char();
+        buf.push('.');
+
+        let mut at_least_one_digit = false;
+        while let c @ b'0'..=b'9' = tri!(self.peek_or_null()) {
+            self.eat_char();
+            buf.push(c as char);
+            at_least_one_digit = true;
+        }
+
+        if !at_least_one_digit {
+            match tri!(self.peek()) {
+                Some(_) => return Err(self.peek_error(ErrorCode::InvalidNumber)),
+                None => return Err(self.peek_error(ErrorCode::EofWhileParsingValue)),
+            }
+        }
+
+        match tri!(self.peek_or_null()) {
+            e @ b'e' | e @ b'E' => self.scan_exponent(e as char, buf),
+            _ => Ok(()),
+        }
+    }
+
+    #[cfg(feature = "arbitrary_precision")]
+    fn scan_exponent(&mut self, e: char, buf: &mut String) -> Result<()> {
+        self.eat_char();
+        buf.push(e);
+
+        match tri!(self.peek_or_null()) {
+            b'+' => {
+                self.eat_char();
+                buf.push('+');
+            }
+            b'-' => {
+                self.eat_char();
+                buf.push('-');
+            }
+            _ => {}
+        }
+
+        // Make sure a digit follows the exponent place.
+        match tri!(self.scan_or_eof(buf)) {
+            b'0'..=b'9' => {}
+            _ => {
+                return Err(self.error(ErrorCode::InvalidNumber));
+            }
+        }
+
+        while let c @ b'0'..=b'9' = tri!(self.peek_or_null()) {
+            self.eat_char();
+            buf.push(c as char);
+        }
+
+        Ok(())
+    }
+
+    fn parse_object_colon(&mut self) -> Result<()> {
+        match tri!(self.parse_whitespace()) {
+            Some(b':') => {
+                self.eat_char();
+                Ok(())
+            }
+            Some(_) => Err(self.peek_error(ErrorCode::ExpectedColon)),
+            None => Err(self.peek_error(ErrorCode::EofWhileParsingObject)),
+        }
+    }
+
+    fn end_seq(&mut self) -> Result<()> {
+        match tri!(self.parse_whitespace()) {
+            Some(b']') => {
+                self.eat_char();
+                Ok(())
+            }
+            Some(b',') => {
+                self.eat_char();
+                match self.parse_whitespace() {
+                    Ok(Some(b']')) => Err(self.peek_error(ErrorCode::TrailingComma)),
+                    _ => Err(self.peek_error(ErrorCode::TrailingCharacters)),
+                }
+            }
+            Some(_) => Err(self.peek_error(ErrorCode::TrailingCharacters)),
+            None => Err(self.peek_error(ErrorCode::EofWhileParsingList)),
+        }
+    }
+
+    fn end_map(&mut self) -> Result<()> {
+        match tri!(self.parse_whitespace()) {
+            Some(b'}') => {
+                self.eat_char();
+                Ok(())
+            }
+            Some(b',') => Err(self.peek_error(ErrorCode::TrailingComma)),
+            Some(_) => Err(self.peek_error(ErrorCode::TrailingCharacters)),
+            None => Err(self.peek_error(ErrorCode::EofWhileParsingObject)),
+        }
+    }
+
+    fn ignore_value(&mut self) -> Result<()> {
+        self.scratch.clear();
+        let mut enclosing = None;
+
+        loop {
+            let peek = match tri!(self.parse_whitespace()) {
+                Some(b) => b,
+                None => {
+                    return Err(self.peek_error(ErrorCode::EofWhileParsingValue));
+                }
+            };
+
+            let frame = match peek {
+                b'n' => {
+                    self.eat_char();
+                    tri!(self.parse_ident(b"ull"));
+                    None
+                }
+                b't' => {
+                    self.eat_char();
+                    tri!(self.parse_ident(b"rue"));
+                    None
+                }
+                b'f' => {
+                    self.eat_char();
+                    tri!(self.parse_ident(b"alse"));
+                    None
+                }
+                b'-' => {
+                    self.eat_char();
+                    tri!(self.ignore_integer());
+                    None
+                }
+                b'0'..=b'9' => {
+                    tri!(self.ignore_integer());
+                    None
+                }
+                b'"' => {
+                    self.eat_char();
+                    tri!(self.read.ignore_str());
+                    None
+                }
+                frame @ b'[' | frame @ b'{' => {
+                    self.scratch.extend(enclosing.take());
+                    self.eat_char();
+                    Some(frame)
+                }
+                _ => return Err(self.peek_error(ErrorCode::ExpectedSomeValue)),
+            };
+
+            let (mut accept_comma, mut frame) = match frame {
+                Some(frame) => (false, frame),
+                None => match enclosing.take() {
+                    Some(frame) => (true, frame),
+                    None => match self.scratch.pop() {
+                        Some(frame) => (true, frame),
+                        None => return Ok(()),
+                    },
+                },
+            };
+
+            loop {
+                match tri!(self.parse_whitespace()) {
+                    Some(b',') if accept_comma => {
+                        self.eat_char();
+                        break;
+                    }
+                    Some(b']') if frame == b'[' => {}
+                    Some(b'}') if frame == b'{' => {}
+                    Some(_) => {
+                        if accept_comma {
+                            return Err(self.peek_error(match frame {
+                                b'[' => ErrorCode::ExpectedListCommaOrEnd,
+                                b'{' => ErrorCode::ExpectedObjectCommaOrEnd,
+                                _ => unreachable!(),
+                            }));
+                        } else {
+                            break;
+                        }
+                    }
+                    None => {
+                        return Err(self.peek_error(match frame {
+                            b'[' => ErrorCode::EofWhileParsingList,
+                            b'{' => ErrorCode::EofWhileParsingObject,
+                            _ => unreachable!(),
+                        }));
+                    }
+                }
+
+                self.eat_char();
+                frame = match self.scratch.pop() {
+                    Some(frame) => frame,
+                    None => return Ok(()),
+                };
+                accept_comma = true;
+            }
+
+            if frame == b'{' {
+                match tri!(self.parse_whitespace()) {
+                    Some(b'"') => self.eat_char(),
+                    Some(_) => return Err(self.peek_error(ErrorCode::KeyMustBeAString)),
+                    None => return Err(self.peek_error(ErrorCode::EofWhileParsingObject)),
+                }
+                tri!(self.read.ignore_str());
+                match tri!(self.parse_whitespace()) {
+                    Some(b':') => self.eat_char(),
+                    Some(_) => return Err(self.peek_error(ErrorCode::ExpectedColon)),
+                    None => return Err(self.peek_error(ErrorCode::EofWhileParsingObject)),
+                }
+            }
+
+            enclosing = Some(frame);
+        }
+    }
+
+    fn ignore_integer(&mut self) -> Result<()> {
+        match tri!(self.next_char_or_null()) {
+            b'0' => {
+                // There can be only one leading '0'.
+                if let b'0'..=b'9' = tri!(self.peek_or_null()) {
+                    return Err(self.peek_error(ErrorCode::InvalidNumber));
+                }
+            }
+            b'1'..=b'9' => {
+                while let b'0'..=b'9' = tri!(self.peek_or_null()) {
+                    self.eat_char();
+                }
+            }
+            _ => {
+                return Err(self.error(ErrorCode::InvalidNumber));
+            }
+        }
+
+        match tri!(self.peek_or_null()) {
+            b'.' => self.ignore_decimal(),
+            b'e' | b'E' => self.ignore_exponent(),
+            _ => Ok(()),
+        }
+    }
+
+    fn ignore_decimal(&mut self) -> Result<()> {
+        self.eat_char();
+
+        let mut at_least_one_digit = false;
+        while let b'0'..=b'9' = tri!(self.peek_or_null()) {
+            self.eat_char();
+            at_least_one_digit = true;
+        }
+
+        if !at_least_one_digit {
+            return Err(self.peek_error(ErrorCode::InvalidNumber));
+        }
+
+        match tri!(self.peek_or_null()) {
+            b'e' | b'E' => self.ignore_exponent(),
+            _ => Ok(()),
+        }
+    }
+
+    fn ignore_exponent(&mut self) -> Result<()> {
+        self.eat_char();
+
+        match tri!(self.peek_or_null()) {
+            b'+' | b'-' => self.eat_char(),
+            _ => {}
+        }
+
+        // Make sure a digit follows the exponent place.
+        match tri!(self.next_char_or_null()) {
+            b'0'..=b'9' => {}
+            _ => {
+                return Err(self.error(ErrorCode::InvalidNumber));
+            }
+        }
+
+        while let b'0'..=b'9' = tri!(self.peek_or_null()) {
+            self.eat_char();
+        }
+
+        Ok(())
+    }
+
+    #[cfg(feature = "raw_value")]
+    fn deserialize_raw_value<V>(&mut self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.parse_whitespace()?;
+        self.read.begin_raw_buffering();
+        self.ignore_value()?;
+        self.read.end_raw_buffering(visitor)
+    }
+}
+
+impl FromStr for Number {
+    type Err = Error;
+
+    fn from_str(s: &str) -> result::Result<Self, Self::Err> {
+        Deserializer::from_str(s)
+            .parse_any_signed_number()
+            .map(Into::into)
+    }
+}
+
+#[cfg(not(feature = "float_roundtrip"))]
+static POW10: [f64; 309] = [
+    1e000, 1e001, 1e002, 1e003, 1e004, 1e005, 1e006, 1e007, 1e008, 1e009, //
+    1e010, 1e011, 1e012, 1e013, 1e014, 1e015, 1e016, 1e017, 1e018, 1e019, //
+    1e020, 1e021, 1e022, 1e023, 1e024, 1e025, 1e026, 1e027, 1e028, 1e029, //
+    1e030, 1e031, 1e032, 1e033, 1e034, 1e035, 1e036, 1e037, 1e038, 1e039, //
+    1e040, 1e041, 1e042, 1e043, 1e044, 1e045, 1e046, 1e047, 1e048, 1e049, //
+    1e050, 1e051, 1e052, 1e053, 1e054, 1e055, 1e056, 1e057, 1e058, 1e059, //
+    1e060, 1e061, 1e062, 1e063, 1e064, 1e065, 1e066, 1e067, 1e068, 1e069, //
+    1e070, 1e071, 1e072, 1e073, 1e074, 1e075, 1e076, 1e077, 1e078, 1e079, //
+    1e080, 1e081, 1e082, 1e083, 1e084, 1e085, 1e086, 1e087, 1e088, 1e089, //
+    1e090, 1e091, 1e092, 1e093, 1e094, 1e095, 1e096, 1e097, 1e098, 1e099, //
+    1e100, 1e101, 1e102, 1e103, 1e104, 1e105, 1e106, 1e107, 1e108, 1e109, //
+    1e110, 1e111, 1e112, 1e113, 1e114, 1e115, 1e116, 1e117, 1e118, 1e119, //
+    1e120, 1e121, 1e122, 1e123, 1e124, 1e125, 1e126, 1e127, 1e128, 1e129, //
+    1e130, 1e131, 1e132, 1e133, 1e134, 1e135, 1e136, 1e137, 1e138, 1e139, //
+    1e140, 1e141, 1e142, 1e143, 1e144, 1e145, 1e146, 1e147, 1e148, 1e149, //
+    1e150, 1e151, 1e152, 1e153, 1e154, 1e155, 1e156, 1e157, 1e158, 1e159, //
+    1e160, 1e161, 1e162, 1e163, 1e164, 1e165, 1e166, 1e167, 1e168, 1e169, //
+    1e170, 1e171, 1e172, 1e173, 1e174, 1e175, 1e176, 1e177, 1e178, 1e179, //
+    1e180, 1e181, 1e182, 1e183, 1e184, 1e185, 1e186, 1e187, 1e188, 1e189, //
+    1e190, 1e191, 1e192, 1e193, 1e194, 1e195, 1e196, 1e197, 1e198, 1e199, //
+    1e200, 1e201, 1e202, 1e203, 1e204, 1e205, 1e206, 1e207, 1e208, 1e209, //
+    1e210, 1e211, 1e212, 1e213, 1e214, 1e215, 1e216, 1e217, 1e218, 1e219, //
+    1e220, 1e221, 1e222, 1e223, 1e224, 1e225, 1e226, 1e227, 1e228, 1e229, //
+    1e230, 1e231, 1e232, 1e233, 1e234, 1e235, 1e236, 1e237, 1e238, 1e239, //
+    1e240, 1e241, 1e242, 1e243, 1e244, 1e245, 1e246, 1e247, 1e248, 1e249, //
+    1e250, 1e251, 1e252, 1e253, 1e254, 1e255, 1e256, 1e257, 1e258, 1e259, //
+    1e260, 1e261, 1e262, 1e263, 1e264, 1e265, 1e266, 1e267, 1e268, 1e269, //
+    1e270, 1e271, 1e272, 1e273, 1e274, 1e275, 1e276, 1e277, 1e278, 1e279, //
+    1e280, 1e281, 1e282, 1e283, 1e284, 1e285, 1e286, 1e287, 1e288, 1e289, //
+    1e290, 1e291, 1e292, 1e293, 1e294, 1e295, 1e296, 1e297, 1e298, 1e299, //
+    1e300, 1e301, 1e302, 1e303, 1e304, 1e305, 1e306, 1e307, 1e308,
+];
+
+macro_rules! deserialize_number {
+    ($method:ident) => {
+        fn $method<V>(self, visitor: V) -> Result<V::Value>
+        where
+            V: de::Visitor<'de>,
+        {
+            self.deserialize_number(visitor)
+        }
+    };
+}
+
+#[cfg(not(feature = "unbounded_depth"))]
+macro_rules! if_checking_recursion_limit {
+    ($($body:tt)*) => {
+        $($body)*
+    };
+}
+
+#[cfg(feature = "unbounded_depth")]
+macro_rules! if_checking_recursion_limit {
+    ($this:ident $($body:tt)*) => {
+        if !$this.disable_recursion_limit {
+            $this $($body)*
+        }
+    };
+}
+
+macro_rules! check_recursion {
+    ($this:ident $($body:tt)*) => {
+        if_checking_recursion_limit! {
+            $this.remaining_depth -= 1;
+            if $this.remaining_depth == 0 {
+                return Err($this.peek_error(ErrorCode::RecursionLimitExceeded));
+            }
+        }
+
+        $this $($body)*
+
+        if_checking_recursion_limit! {
+            $this.remaining_depth += 1;
+        }
+    };
+}
+
+impl<'de, 'a, R: Read<'de>> de::Deserializer<'de> for &'a mut Deserializer<R> {
+    type Error = Error;
+
+    #[inline]
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        let peek = match tri!(self.parse_whitespace()) {
+            Some(b) => b,
+            None => {
+                return Err(self.peek_error(ErrorCode::EofWhileParsingValue));
+            }
+        };
+
+        let value = match peek {
+            b'n' => {
+                self.eat_char();
+                tri!(self.parse_ident(b"ull"));
+                visitor.visit_unit()
+            }
+            b't' => {
+                self.eat_char();
+                tri!(self.parse_ident(b"rue"));
+                visitor.visit_bool(true)
+            }
+            b'f' => {
+                self.eat_char();
+                tri!(self.parse_ident(b"alse"));
+                visitor.visit_bool(false)
+            }
+            b'-' => {
+                self.eat_char();
+                tri!(self.parse_any_number(false)).visit(visitor)
+            }
+            b'0'..=b'9' => tri!(self.parse_any_number(true)).visit(visitor),
+            b'"' => {
+                self.eat_char();
+                self.scratch.clear();
+                match tri!(self.read.parse_str(&mut self.scratch)) {
+                    Reference::Borrowed(s) => visitor.visit_borrowed_str(s),
+                    Reference::Copied(s) => visitor.visit_str(s),
+                }
+            }
+            b'[' => {
+                check_recursion! {
+                    self.eat_char();
+                    let ret = visitor.visit_seq(SeqAccess::new(self));
+                }
+
+                match (ret, self.end_seq()) {
+                    (Ok(ret), Ok(())) => Ok(ret),
+                    (Err(err), _) | (_, Err(err)) => Err(err),
+                }
+            }
+            b'{' => {
+                check_recursion! {
+                    self.eat_char();
+                    let ret = visitor.visit_map(MapAccess::new(self));
+                }
+
+                match (ret, self.end_map()) {
+                    (Ok(ret), Ok(())) => Ok(ret),
+                    (Err(err), _) | (_, Err(err)) => Err(err),
+                }
+            }
+            _ => Err(self.peek_error(ErrorCode::ExpectedSomeValue)),
+        };
+
+        match value {
+            Ok(value) => Ok(value),
+            // The de::Error impl creates errors with unknown line and column.
+            // Fill in the position here by looking at the current index in the
+            // input. There is no way to tell whether this should call `error`
+            // or `peek_error` so pick the one that seems correct more often.
+            // Worst case, the position is off by one character.
+            Err(err) => Err(self.fix_position(err)),
+        }
+    }
+
+    fn deserialize_bool<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        let peek = match tri!(self.parse_whitespace()) {
+            Some(b) => b,
+            None => {
+                return Err(self.peek_error(ErrorCode::EofWhileParsingValue));
+            }
+        };
+
+        let value = match peek {
+            b't' => {
+                self.eat_char();
+                tri!(self.parse_ident(b"rue"));
+                visitor.visit_bool(true)
+            }
+            b'f' => {
+                self.eat_char();
+                tri!(self.parse_ident(b"alse"));
+                visitor.visit_bool(false)
+            }
+            _ => Err(self.peek_invalid_type(&visitor)),
+        };
+
+        match value {
+            Ok(value) => Ok(value),
+            Err(err) => Err(self.fix_position(err)),
+        }
+    }
+
+    deserialize_number!(deserialize_i8);
+    deserialize_number!(deserialize_i16);
+    deserialize_number!(deserialize_i32);
+    deserialize_number!(deserialize_i64);
+    deserialize_number!(deserialize_u8);
+    deserialize_number!(deserialize_u16);
+    deserialize_number!(deserialize_u32);
+    deserialize_number!(deserialize_u64);
+    #[cfg(not(feature = "float_roundtrip"))]
+    deserialize_number!(deserialize_f32);
+    deserialize_number!(deserialize_f64);
+
+    #[cfg(feature = "float_roundtrip")]
+    fn deserialize_f32<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.single_precision = true;
+        let val = self.deserialize_number(visitor);
+        self.single_precision = false;
+        val
+    }
+
+    fn deserialize_i128<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        let mut buf = String::new();
+
+        match tri!(self.parse_whitespace()) {
+            Some(b'-') => {
+                self.eat_char();
+                buf.push('-');
+            }
+            Some(_) => {}
+            None => {
+                return Err(self.peek_error(ErrorCode::EofWhileParsingValue));
+            }
+        };
+
+        tri!(self.scan_integer128(&mut buf));
+
+        let value = match buf.parse() {
+            Ok(int) => visitor.visit_i128(int),
+            Err(_) => {
+                return Err(self.error(ErrorCode::NumberOutOfRange));
+            }
+        };
+
+        match value {
+            Ok(value) => Ok(value),
+            Err(err) => Err(self.fix_position(err)),
+        }
+    }
+
+    fn deserialize_u128<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        match tri!(self.parse_whitespace()) {
+            Some(b'-') => {
+                return Err(self.peek_error(ErrorCode::NumberOutOfRange));
+            }
+            Some(_) => {}
+            None => {
+                return Err(self.peek_error(ErrorCode::EofWhileParsingValue));
+            }
+        }
+
+        let mut buf = String::new();
+        tri!(self.scan_integer128(&mut buf));
+
+        let value = match buf.parse() {
+            Ok(int) => visitor.visit_u128(int),
+            Err(_) => {
+                return Err(self.error(ErrorCode::NumberOutOfRange));
+            }
+        };
+
+        match value {
+            Ok(value) => Ok(value),
+            Err(err) => Err(self.fix_position(err)),
+        }
+    }
+
+    fn deserialize_char<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.deserialize_str(visitor)
+    }
+
+    fn deserialize_str<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        let peek = match tri!(self.parse_whitespace()) {
+            Some(b) => b,
+            None => {
+                return Err(self.peek_error(ErrorCode::EofWhileParsingValue));
+            }
+        };
+
+        let value = match peek {
+            b'"' => {
+                self.eat_char();
+                self.scratch.clear();
+                match tri!(self.read.parse_str(&mut self.scratch)) {
+                    Reference::Borrowed(s) => visitor.visit_borrowed_str(s),
+                    Reference::Copied(s) => visitor.visit_str(s),
+                }
+            }
+            _ => Err(self.peek_invalid_type(&visitor)),
+        };
+
+        match value {
+            Ok(value) => Ok(value),
+            Err(err) => Err(self.fix_position(err)),
+        }
+    }
+
+    fn deserialize_string<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.deserialize_str(visitor)
+    }
+
+    /// Parses a JSON string as bytes. Note that this function does not check
+    /// whether the bytes represent a valid UTF-8 string.
+    ///
+    /// The relevant part of the JSON specification is Section 8.2 of [RFC
+    /// 7159]:
+    ///
+    /// > When all the strings represented in a JSON text are composed entirely
+    /// > of Unicode characters (however escaped), then that JSON text is
+    /// > interoperable in the sense that all software implementations that
+    /// > parse it will agree on the contents of names and of string values in
+    /// > objects and arrays.
+    /// >
+    /// > However, the ABNF in this specification allows member names and string
+    /// > values to contain bit sequences that cannot encode Unicode characters;
+    /// > for example, "\uDEAD" (a single unpaired UTF-16 surrogate). Instances
+    /// > of this have been observed, for example, when a library truncates a
+    /// > UTF-16 string without checking whether the truncation split a
+    /// > surrogate pair.  The behavior of software that receives JSON texts
+    /// > containing such values is unpredictable; for example, implementations
+    /// > might return different values for the length of a string value or even
+    /// > suffer fatal runtime exceptions.
+    ///
+    /// [RFC 7159]: https://tools.ietf.org/html/rfc7159
+    ///
+    /// The behavior of serde_json is specified to fail on non-UTF-8 strings
+    /// when deserializing into Rust UTF-8 string types such as String, and
+    /// succeed with non-UTF-8 bytes when deserializing using this method.
+    ///
+    /// Escape sequences are processed as usual, and for `\uXXXX` escapes it is
+    /// still checked if the hex number represents a valid Unicode code point.
+    ///
+    /// # Examples
+    ///
+    /// You can use this to parse JSON strings containing invalid UTF-8 bytes,
+    /// or unpaired surrogates.
+    ///
+    /// ```
+    /// use serde_bytes::ByteBuf;
+    ///
+    /// fn look_at_bytes() -> Result<(), serde_json::Error> {
+    ///     let json_data = b"\"some bytes: \xe5\x00\xe5\"";
+    ///     let bytes: ByteBuf = serde_json::from_slice(json_data)?;
+    ///
+    ///     assert_eq!(b'\xe5', bytes[12]);
+    ///     assert_eq!(b'\0', bytes[13]);
+    ///     assert_eq!(b'\xe5', bytes[14]);
+    ///
+    ///     Ok(())
+    /// }
+    /// #
+    /// # look_at_bytes().unwrap();
+    /// ```
+    ///
+    /// Backslash escape sequences like `\n` are still interpreted and required
+    /// to be valid. `\u` escape sequences are required to represent a valid
+    /// Unicode code point or lone surrogate.
+    ///
+    /// ```
+    /// use serde_bytes::ByteBuf;
+    ///
+    /// fn look_at_bytes() -> Result<(), serde_json::Error> {
+    ///     let json_data = b"\"lone surrogate: \\uD801\"";
+    ///     let bytes: ByteBuf = serde_json::from_slice(json_data)?;
+    ///     let expected = b"lone surrogate: \xED\xA0\x81";
+    ///     assert_eq!(expected, bytes.as_slice());
+    ///     Ok(())
+    /// }
+    /// #
+    /// # look_at_bytes();
+    /// ```
+    fn deserialize_bytes<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        let peek = match tri!(self.parse_whitespace()) {
+            Some(b) => b,
+            None => {
+                return Err(self.peek_error(ErrorCode::EofWhileParsingValue));
+            }
+        };
+
+        let value = match peek {
+            b'"' => {
+                self.eat_char();
+                self.scratch.clear();
+                match tri!(self.read.parse_str_raw(&mut self.scratch)) {
+                    Reference::Borrowed(b) => visitor.visit_borrowed_bytes(b),
+                    Reference::Copied(b) => visitor.visit_bytes(b),
+                }
+            }
+            b'[' => self.deserialize_seq(visitor),
+            _ => Err(self.peek_invalid_type(&visitor)),
+        };
+
+        match value {
+            Ok(value) => Ok(value),
+            Err(err) => Err(self.fix_position(err)),
+        }
+    }
+
+    #[inline]
+    fn deserialize_byte_buf<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.deserialize_bytes(visitor)
+    }
+
+    /// Parses a `null` as a None, and any other values as a `Some(...)`.
+    #[inline]
+    fn deserialize_option<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        match tri!(self.parse_whitespace()) {
+            Some(b'n') => {
+                self.eat_char();
+                tri!(self.parse_ident(b"ull"));
+                visitor.visit_none()
+            }
+            _ => visitor.visit_some(self),
+        }
+    }
+
+    fn deserialize_unit<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        let peek = match tri!(self.parse_whitespace()) {
+            Some(b) => b,
+            None => {
+                return Err(self.peek_error(ErrorCode::EofWhileParsingValue));
+            }
+        };
+
+        let value = match peek {
+            b'n' => {
+                self.eat_char();
+                tri!(self.parse_ident(b"ull"));
+                visitor.visit_unit()
+            }
+            _ => Err(self.peek_invalid_type(&visitor)),
+        };
+
+        match value {
+            Ok(value) => Ok(value),
+            Err(err) => Err(self.fix_position(err)),
+        }
+    }
+
+    fn deserialize_unit_struct<V>(self, _name: &'static str, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.deserialize_unit(visitor)
+    }
+
+    /// Parses a newtype struct as the underlying value.
+    #[inline]
+    fn deserialize_newtype_struct<V>(self, name: &str, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        #[cfg(feature = "raw_value")]
+        {
+            if name == crate::raw::TOKEN {
+                return self.deserialize_raw_value(visitor);
+            }
+        }
+
+        let _ = name;
+        visitor.visit_newtype_struct(self)
+    }
+
+    fn deserialize_seq<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        let peek = match tri!(self.parse_whitespace()) {
+            Some(b) => b,
+            None => {
+                return Err(self.peek_error(ErrorCode::EofWhileParsingValue));
+            }
+        };
+
+        let value = match peek {
+            b'[' => {
+                check_recursion! {
+                    self.eat_char();
+                    let ret = visitor.visit_seq(SeqAccess::new(self));
+                }
+
+                match (ret, self.end_seq()) {
+                    (Ok(ret), Ok(())) => Ok(ret),
+                    (Err(err), _) | (_, Err(err)) => Err(err),
+                }
+            }
+            _ => Err(self.peek_invalid_type(&visitor)),
+        };
+
+        match value {
+            Ok(value) => Ok(value),
+            Err(err) => Err(self.fix_position(err)),
+        }
+    }
+
+    fn deserialize_tuple<V>(self, _len: usize, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.deserialize_seq(visitor)
+    }
+
+    fn deserialize_tuple_struct<V>(
+        self,
+        _name: &'static str,
+        _len: usize,
+        visitor: V,
+    ) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.deserialize_seq(visitor)
+    }
+
+    fn deserialize_map<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        let peek = match tri!(self.parse_whitespace()) {
+            Some(b) => b,
+            None => {
+                return Err(self.peek_error(ErrorCode::EofWhileParsingValue));
+            }
+        };
+
+        let value = match peek {
+            b'{' => {
+                check_recursion! {
+                    self.eat_char();
+                    let ret = visitor.visit_map(MapAccess::new(self));
+                }
+
+                match (ret, self.end_map()) {
+                    (Ok(ret), Ok(())) => Ok(ret),
+                    (Err(err), _) | (_, Err(err)) => Err(err),
+                }
+            }
+            _ => Err(self.peek_invalid_type(&visitor)),
+        };
+
+        match value {
+            Ok(value) => Ok(value),
+            Err(err) => Err(self.fix_position(err)),
+        }
+    }
+
+    fn deserialize_struct<V>(
+        self,
+        _name: &'static str,
+        _fields: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        let peek = match tri!(self.parse_whitespace()) {
+            Some(b) => b,
+            None => {
+                return Err(self.peek_error(ErrorCode::EofWhileParsingValue));
+            }
+        };
+
+        let value = match peek {
+            b'[' => {
+                check_recursion! {
+                    self.eat_char();
+                    let ret = visitor.visit_seq(SeqAccess::new(self));
+                }
+
+                match (ret, self.end_seq()) {
+                    (Ok(ret), Ok(())) => Ok(ret),
+                    (Err(err), _) | (_, Err(err)) => Err(err),
+                }
+            }
+            b'{' => {
+                check_recursion! {
+                    self.eat_char();
+                    let ret = visitor.visit_map(MapAccess::new(self));
+                }
+
+                match (ret, self.end_map()) {
+                    (Ok(ret), Ok(())) => Ok(ret),
+                    (Err(err), _) | (_, Err(err)) => Err(err),
+                }
+            }
+            _ => Err(self.peek_invalid_type(&visitor)),
+        };
+
+        match value {
+            Ok(value) => Ok(value),
+            Err(err) => Err(self.fix_position(err)),
+        }
+    }
+
+    /// Parses an enum as an object like `{"$KEY":$VALUE}`, where $VALUE is either a straight
+    /// value, a `[..]`, or a `{..}`.
+    #[inline]
+    fn deserialize_enum<V>(
+        self,
+        _name: &str,
+        _variants: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        match tri!(self.parse_whitespace()) {
+            Some(b'{') => {
+                check_recursion! {
+                    self.eat_char();
+                    let value = tri!(visitor.visit_enum(VariantAccess::new(self)));
+                }
+
+                match tri!(self.parse_whitespace()) {
+                    Some(b'}') => {
+                        self.eat_char();
+                        Ok(value)
+                    }
+                    Some(_) => Err(self.error(ErrorCode::ExpectedSomeValue)),
+                    None => Err(self.error(ErrorCode::EofWhileParsingObject)),
+                }
+            }
+            Some(b'"') => visitor.visit_enum(UnitVariantAccess::new(self)),
+            Some(_) => Err(self.peek_error(ErrorCode::ExpectedSomeValue)),
+            None => Err(self.peek_error(ErrorCode::EofWhileParsingValue)),
+        }
+    }
+
+    fn deserialize_identifier<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.deserialize_str(visitor)
+    }
+
+    fn deserialize_ignored_any<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        tri!(self.ignore_value());
+        visitor.visit_unit()
+    }
+}
+
+struct SeqAccess<'a, R: 'a> {
+    de: &'a mut Deserializer<R>,
+    first: bool,
+}
+
+impl<'a, R: 'a> SeqAccess<'a, R> {
+    fn new(de: &'a mut Deserializer<R>) -> Self {
+        SeqAccess { de, first: true }
+    }
+}
+
+impl<'de, 'a, R: Read<'de> + 'a> de::SeqAccess<'de> for SeqAccess<'a, R> {
+    type Error = Error;
+
+    fn next_element_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        let peek = match tri!(self.de.parse_whitespace()) {
+            Some(b']') => {
+                return Ok(None);
+            }
+            Some(b',') if !self.first => {
+                self.de.eat_char();
+                tri!(self.de.parse_whitespace())
+            }
+            Some(b) => {
+                if self.first {
+                    self.first = false;
+                    Some(b)
+                } else {
+                    return Err(self.de.peek_error(ErrorCode::ExpectedListCommaOrEnd));
+                }
+            }
+            None => {
+                return Err(self.de.peek_error(ErrorCode::EofWhileParsingList));
+            }
+        };
+
+        match peek {
+            Some(b']') => Err(self.de.peek_error(ErrorCode::TrailingComma)),
+            Some(_) => Ok(Some(tri!(seed.deserialize(&mut *self.de)))),
+            None => Err(self.de.peek_error(ErrorCode::EofWhileParsingValue)),
+        }
+    }
+}
+
+struct MapAccess<'a, R: 'a> {
+    de: &'a mut Deserializer<R>,
+    first: bool,
+}
+
+impl<'a, R: 'a> MapAccess<'a, R> {
+    fn new(de: &'a mut Deserializer<R>) -> Self {
+        MapAccess { de, first: true }
+    }
+}
+
+impl<'de, 'a, R: Read<'de> + 'a> de::MapAccess<'de> for MapAccess<'a, R> {
+    type Error = Error;
+
+    fn next_key_seed<K>(&mut self, seed: K) -> Result<Option<K::Value>>
+    where
+        K: de::DeserializeSeed<'de>,
+    {
+        let peek = match tri!(self.de.parse_whitespace()) {
+            Some(b'}') => {
+                return Ok(None);
+            }
+            Some(b',') if !self.first => {
+                self.de.eat_char();
+                tri!(self.de.parse_whitespace())
+            }
+            Some(b) => {
+                if self.first {
+                    self.first = false;
+                    Some(b)
+                } else {
+                    return Err(self.de.peek_error(ErrorCode::ExpectedObjectCommaOrEnd));
+                }
+            }
+            None => {
+                return Err(self.de.peek_error(ErrorCode::EofWhileParsingObject));
+            }
+        };
+
+        match peek {
+            Some(b'"') => seed.deserialize(MapKey { de: &mut *self.de }).map(Some),
+            Some(b'}') => Err(self.de.peek_error(ErrorCode::TrailingComma)),
+            Some(_) => Err(self.de.peek_error(ErrorCode::KeyMustBeAString)),
+            None => Err(self.de.peek_error(ErrorCode::EofWhileParsingValue)),
+        }
+    }
+
+    fn next_value_seed<V>(&mut self, seed: V) -> Result<V::Value>
+    where
+        V: de::DeserializeSeed<'de>,
+    {
+        tri!(self.de.parse_object_colon());
+
+        seed.deserialize(&mut *self.de)
+    }
+}
+
+struct VariantAccess<'a, R: 'a> {
+    de: &'a mut Deserializer<R>,
+}
+
+impl<'a, R: 'a> VariantAccess<'a, R> {
+    fn new(de: &'a mut Deserializer<R>) -> Self {
+        VariantAccess { de }
+    }
+}
+
+impl<'de, 'a, R: Read<'de> + 'a> de::EnumAccess<'de> for VariantAccess<'a, R> {
+    type Error = Error;
+    type Variant = Self;
+
+    fn variant_seed<V>(self, seed: V) -> Result<(V::Value, Self)>
+    where
+        V: de::DeserializeSeed<'de>,
+    {
+        let val = tri!(seed.deserialize(&mut *self.de));
+        tri!(self.de.parse_object_colon());
+        Ok((val, self))
+    }
+}
+
+impl<'de, 'a, R: Read<'de> + 'a> de::VariantAccess<'de> for VariantAccess<'a, R> {
+    type Error = Error;
+
+    fn unit_variant(self) -> Result<()> {
+        de::Deserialize::deserialize(self.de)
+    }
+
+    fn newtype_variant_seed<T>(self, seed: T) -> Result<T::Value>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        seed.deserialize(self.de)
+    }
+
+    fn tuple_variant<V>(self, _len: usize, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        de::Deserializer::deserialize_seq(self.de, visitor)
+    }
+
+    fn struct_variant<V>(self, fields: &'static [&'static str], visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        de::Deserializer::deserialize_struct(self.de, "", fields, visitor)
+    }
+}
+
+struct UnitVariantAccess<'a, R: 'a> {
+    de: &'a mut Deserializer<R>,
+}
+
+impl<'a, R: 'a> UnitVariantAccess<'a, R> {
+    fn new(de: &'a mut Deserializer<R>) -> Self {
+        UnitVariantAccess { de }
+    }
+}
+
+impl<'de, 'a, R: Read<'de> + 'a> de::EnumAccess<'de> for UnitVariantAccess<'a, R> {
+    type Error = Error;
+    type Variant = Self;
+
+    fn variant_seed<V>(self, seed: V) -> Result<(V::Value, Self)>
+    where
+        V: de::DeserializeSeed<'de>,
+    {
+        let variant = tri!(seed.deserialize(&mut *self.de));
+        Ok((variant, self))
+    }
+}
+
+impl<'de, 'a, R: Read<'de> + 'a> de::VariantAccess<'de> for UnitVariantAccess<'a, R> {
+    type Error = Error;
+
+    fn unit_variant(self) -> Result<()> {
+        Ok(())
+    }
+
+    fn newtype_variant_seed<T>(self, _seed: T) -> Result<T::Value>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        Err(de::Error::invalid_type(
+            Unexpected::UnitVariant,
+            &"newtype variant",
+        ))
+    }
+
+    fn tuple_variant<V>(self, _len: usize, _visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        Err(de::Error::invalid_type(
+            Unexpected::UnitVariant,
+            &"tuple variant",
+        ))
+    }
+
+    fn struct_variant<V>(self, _fields: &'static [&'static str], _visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        Err(de::Error::invalid_type(
+            Unexpected::UnitVariant,
+            &"struct variant",
+        ))
+    }
+}
+
+/// Only deserialize from this after peeking a '"' byte! Otherwise it may
+/// deserialize invalid JSON successfully.
+struct MapKey<'a, R: 'a> {
+    de: &'a mut Deserializer<R>,
+}
+
+macro_rules! deserialize_integer_key {
+    ($method:ident => $visit:ident) => {
+        fn $method<V>(self, visitor: V) -> Result<V::Value>
+        where
+            V: de::Visitor<'de>,
+        {
+            self.de.eat_char();
+            self.de.scratch.clear();
+            let string = tri!(self.de.read.parse_str(&mut self.de.scratch));
+            match (string.parse(), string) {
+                (Ok(integer), _) => visitor.$visit(integer),
+                (Err(_), Reference::Borrowed(s)) => visitor.visit_borrowed_str(s),
+                (Err(_), Reference::Copied(s)) => visitor.visit_str(s),
+            }
+        }
+    };
+}
+
+impl<'de, 'a, R> de::Deserializer<'de> for MapKey<'a, R>
+where
+    R: Read<'de>,
+{
+    type Error = Error;
+
+    #[inline]
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.de.eat_char();
+        self.de.scratch.clear();
+        match tri!(self.de.read.parse_str(&mut self.de.scratch)) {
+            Reference::Borrowed(s) => visitor.visit_borrowed_str(s),
+            Reference::Copied(s) => visitor.visit_str(s),
+        }
+    }
+
+    deserialize_integer_key!(deserialize_i8 => visit_i8);
+    deserialize_integer_key!(deserialize_i16 => visit_i16);
+    deserialize_integer_key!(deserialize_i32 => visit_i32);
+    deserialize_integer_key!(deserialize_i64 => visit_i64);
+    deserialize_integer_key!(deserialize_i128 => visit_i128);
+    deserialize_integer_key!(deserialize_u8 => visit_u8);
+    deserialize_integer_key!(deserialize_u16 => visit_u16);
+    deserialize_integer_key!(deserialize_u32 => visit_u32);
+    deserialize_integer_key!(deserialize_u64 => visit_u64);
+    deserialize_integer_key!(deserialize_u128 => visit_u128);
+
+    #[inline]
+    fn deserialize_option<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        // Map keys cannot be null.
+        visitor.visit_some(self)
+    }
+
+    #[inline]
+    fn deserialize_newtype_struct<V>(self, name: &'static str, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        #[cfg(feature = "raw_value")]
+        {
+            if name == crate::raw::TOKEN {
+                return self.de.deserialize_raw_value(visitor);
+            }
+        }
+
+        let _ = name;
+        visitor.visit_newtype_struct(self)
+    }
+
+    #[inline]
+    fn deserialize_enum<V>(
+        self,
+        name: &'static str,
+        variants: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.de.deserialize_enum(name, variants, visitor)
+    }
+
+    #[inline]
+    fn deserialize_bytes<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.de.deserialize_bytes(visitor)
+    }
+
+    #[inline]
+    fn deserialize_byte_buf<V>(self, visitor: V) -> Result<V::Value>
+    where
+        V: de::Visitor<'de>,
+    {
+        self.de.deserialize_bytes(visitor)
+    }
+
+    forward_to_deserialize_any! {
+        bool f32 f64 char str string unit unit_struct seq tuple tuple_struct map
+        struct identifier ignored_any
+    }
+}
+
+//////////////////////////////////////////////////////////////////////////////
+
+/// Iterator that deserializes a stream into multiple JSON values.
+///
+/// A stream deserializer can be created from any JSON deserializer using the
+/// `Deserializer::into_iter` method.
+///
+/// The data can consist of any JSON value. Values need to be a self-delineating value e.g.
+/// arrays, objects, or strings, or be followed by whitespace or a self-delineating value.
+///
+/// ```
+/// use serde_json::{Deserializer, Value};
+///
+/// fn main() {
+///     let data = "{\"k\": 3}1\"cool\"\"stuff\" 3{}  [0, 1, 2]";
+///
+///     let stream = Deserializer::from_str(data).into_iter::<Value>();
+///
+///     for value in stream {
+///         println!("{}", value.unwrap());
+///     }
+/// }
+/// ```
+pub struct StreamDeserializer<'de, R, T> {
+    de: Deserializer<R>,
+    offset: usize,
+    failed: bool,
+    output: PhantomData<T>,
+    lifetime: PhantomData<&'de ()>,
+}
+
+impl<'de, R, T> StreamDeserializer<'de, R, T>
+where
+    R: read::Read<'de>,
+    T: de::Deserialize<'de>,
+{
+    /// Create a JSON stream deserializer from one of the possible serde_json
+    /// input sources.
+    ///
+    /// Typically it is more convenient to use one of these methods instead:
+    ///
+    ///   - Deserializer::from_str(...).into_iter()
+    ///   - Deserializer::from_slice(...).into_iter()
+    ///   - Deserializer::from_reader(...).into_iter()
+    pub fn new(read: R) -> Self {
+        let offset = read.byte_offset();
+        StreamDeserializer {
+            de: Deserializer::new(read),
+            offset,
+            failed: false,
+            output: PhantomData,
+            lifetime: PhantomData,
+        }
+    }
+
+    /// Returns the number of bytes so far deserialized into a successful `T`.
+    ///
+    /// If a stream deserializer returns an EOF error, new data can be joined to
+    /// `old_data[stream.byte_offset()..]` to try again.
+    ///
+    /// ```
+    /// let data = b"[0] [1] [";
+    ///
+    /// let de = serde_json::Deserializer::from_slice(data);
+    /// let mut stream = de.into_iter::<Vec<i32>>();
+    /// assert_eq!(0, stream.byte_offset());
+    ///
+    /// println!("{:?}", stream.next()); // [0]
+    /// assert_eq!(3, stream.byte_offset());
+    ///
+    /// println!("{:?}", stream.next()); // [1]
+    /// assert_eq!(7, stream.byte_offset());
+    ///
+    /// println!("{:?}", stream.next()); // error
+    /// assert_eq!(8, stream.byte_offset());
+    ///
+    /// // If err.is_eof(), can join the remaining data to new data and continue.
+    /// let remaining = &data[stream.byte_offset()..];
+    /// ```
+    ///
+    /// *Note:* In the future this method may be changed to return the number of
+    /// bytes so far deserialized into a successful T *or* syntactically valid
+    /// JSON skipped over due to a type error. See [serde-rs/json#70] for an
+    /// example illustrating this.
+    ///
+    /// [serde-rs/json#70]: https://github.com/serde-rs/json/issues/70
+    pub fn byte_offset(&self) -> usize {
+        self.offset
+    }
+
+    fn peek_end_of_value(&mut self) -> Result<()> {
+        match tri!(self.de.peek()) {
+            Some(b' ') | Some(b'\n') | Some(b'\t') | Some(b'\r') | Some(b'"') | Some(b'[')
+            | Some(b']') | Some(b'{') | Some(b'}') | Some(b',') | Some(b':') | None => Ok(()),
+            Some(_) => {
+                let position = self.de.read.peek_position();
+                Err(Error::syntax(
+                    ErrorCode::TrailingCharacters,
+                    position.line,
+                    position.column,
+                ))
+            }
+        }
+    }
+}
+
+impl<'de, R, T> Iterator for StreamDeserializer<'de, R, T>
+where
+    R: Read<'de>,
+    T: de::Deserialize<'de>,
+{
+    type Item = Result<T>;
+
+    fn next(&mut self) -> Option<Result<T>> {
+        if R::should_early_return_if_failed && self.failed {
+            return None;
+        }
+
+        // skip whitespaces, if any
+        // this helps with trailing whitespaces, since whitespaces between
+        // values are handled for us.
+        match self.de.parse_whitespace() {
+            Ok(None) => {
+                self.offset = self.de.read.byte_offset();
+                None
+            }
+            Ok(Some(b)) => {
+                // If the value does not have a clear way to show the end of the value
+                // (like numbers, null, true etc.) we have to look for whitespace or
+                // the beginning of a self-delineated value.
+                let self_delineated_value = match b {
+                    b'[' | b'"' | b'{' => true,
+                    _ => false,
+                };
+                self.offset = self.de.read.byte_offset();
+                let result = de::Deserialize::deserialize(&mut self.de);
+
+                Some(match result {
+                    Ok(value) => {
+                        self.offset = self.de.read.byte_offset();
+                        if self_delineated_value {
+                            Ok(value)
+                        } else {
+                            self.peek_end_of_value().map(|_| value)
+                        }
+                    }
+                    Err(e) => {
+                        self.de.read.set_failed(&mut self.failed);
+                        Err(e)
+                    }
+                })
+            }
+            Err(e) => {
+                self.de.read.set_failed(&mut self.failed);
+                Some(Err(e))
+            }
+        }
+    }
+}
+
+impl<'de, R, T> FusedIterator for StreamDeserializer<'de, R, T>
+where
+    R: Read<'de> + Fused,
+    T: de::Deserialize<'de>,
+{
+}
+
+//////////////////////////////////////////////////////////////////////////////
+
+fn from_trait<'de, R, T>(read: R) -> Result<T>
+where
+    R: Read<'de>,
+    T: de::Deserialize<'de>,
+{
+    let mut de = Deserializer::new(read);
+    let value = tri!(de::Deserialize::deserialize(&mut de));
+
+    // Make sure the whole stream has been consumed.
+    tri!(de.end());
+    Ok(value)
+}
+
+/// Deserialize an instance of type `T` from an IO stream of JSON.
+///
+/// The content of the IO stream is deserialized directly from the stream
+/// without being buffered in memory by serde_json.
+///
+/// When reading from a source against which short reads are not efficient, such
+/// as a [`File`], you will want to apply your own buffering because serde_json
+/// will not buffer the input. See [`std::io::BufReader`].
+///
+/// It is expected that the input stream ends after the deserialized object.
+/// If the stream does not end, such as in the case of a persistent socket connection,
+/// this function will not return. It is possible instead to deserialize from a prefix of an input
+/// stream without looking for EOF by managing your own [`Deserializer`].
+///
+/// Note that counter to intuition, this function is usually slower than
+/// reading a file completely into memory and then applying [`from_str`]
+/// or [`from_slice`] on it. See [issue #160].
+///
+/// [`File`]: https://doc.rust-lang.org/std/fs/struct.File.html
+/// [`std::io::BufReader`]: https://doc.rust-lang.org/std/io/struct.BufReader.html
+/// [`from_str`]: ./fn.from_str.html
+/// [`from_slice`]: ./fn.from_slice.html
+/// [issue #160]: https://github.com/serde-rs/json/issues/160
+///
+/// # Example
+///
+/// Reading the contents of a file.
+///
+/// ```
+/// use serde::Deserialize;
+///
+/// use std::error::Error;
+/// use std::fs::File;
+/// use std::io::BufReader;
+/// use std::path::Path;
+///
+/// #[derive(Deserialize, Debug)]
+/// struct User {
+///     fingerprint: String,
+///     location: String,
+/// }
+///
+/// fn read_user_from_file<P: AsRef<Path>>(path: P) -> Result<User, Box<dyn Error>> {
+///     // Open the file in read-only mode with buffer.
+///     let file = File::open(path)?;
+///     let reader = BufReader::new(file);
+///
+///     // Read the JSON contents of the file as an instance of `User`.
+///     let u = serde_json::from_reader(reader)?;
+///
+///     // Return the `User`.
+///     Ok(u)
+/// }
+///
+/// fn main() {
+/// # }
+/// # fn fake_main() {
+///     let u = read_user_from_file("test.json").unwrap();
+///     println!("{:#?}", u);
+/// }
+/// ```
+///
+/// Reading from a persistent socket connection.
+///
+/// ```
+/// use serde::Deserialize;
+///
+/// use std::error::Error;
+/// use std::net::{TcpListener, TcpStream};
+///
+/// #[derive(Deserialize, Debug)]
+/// struct User {
+///     fingerprint: String,
+///     location: String,
+/// }
+///
+/// fn read_user_from_stream(tcp_stream: TcpStream) -> Result<User, Box<dyn Error>> {
+///     let mut de = serde_json::Deserializer::from_reader(tcp_stream);
+///     let u = User::deserialize(&mut de)?;
+///
+///     Ok(u)
+/// }
+///
+/// fn main() {
+/// # }
+/// # fn fake_main() {
+///     let listener = TcpListener::bind("127.0.0.1:4000").unwrap();
+///
+///     for stream in listener.incoming() {
+///         println!("{:#?}", read_user_from_stream(stream.unwrap()));
+///     }
+/// }
+/// ```
+///
+/// # Errors
+///
+/// This conversion can fail if the structure of the input does not match the
+/// structure expected by `T`, for example if `T` is a struct type but the input
+/// contains something other than a JSON map. It can also fail if the structure
+/// is correct but `T`'s implementation of `Deserialize` decides that something
+/// is wrong with the data, for example required struct fields are missing from
+/// the JSON map or some number is too big to fit in the expected primitive
+/// type.
+#[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
+pub fn from_reader<R, T>(rdr: R) -> Result<T>
+where
+    R: crate::io::Read,
+    T: de::DeserializeOwned,
+{
+    from_trait(read::IoRead::new(rdr))
+}
+
+/// Deserialize an instance of type `T` from bytes of JSON text.
+///
+/// # Example
+///
+/// ```
+/// use serde::Deserialize;
+///
+/// #[derive(Deserialize, Debug)]
+/// struct User {
+///     fingerprint: String,
+///     location: String,
+/// }
+///
+/// fn main() {
+///     // The type of `j` is `&[u8]`
+///     let j = b"
+///         {
+///             \"fingerprint\": \"0xF9BA143B95FF6D82\",
+///             \"location\": \"Menlo Park, CA\"
+///         }";
+///
+///     let u: User = serde_json::from_slice(j).unwrap();
+///     println!("{:#?}", u);
+/// }
+/// ```
+///
+/// # Errors
+///
+/// This conversion can fail if the structure of the input does not match the
+/// structure expected by `T`, for example if `T` is a struct type but the input
+/// contains something other than a JSON map. It can also fail if the structure
+/// is correct but `T`'s implementation of `Deserialize` decides that something
+/// is wrong with the data, for example required struct fields are missing from
+/// the JSON map or some number is too big to fit in the expected primitive
+/// type.
+pub fn from_slice<'a, T>(v: &'a [u8]) -> Result<T>
+where
+    T: de::Deserialize<'a>,
+{
+    from_trait(read::SliceRead::new(v))
+}
+
+/// Deserialize an instance of type `T` from a string of JSON text.
+///
+/// # Example
+///
+/// ```
+/// use serde::Deserialize;
+///
+/// #[derive(Deserialize, Debug)]
+/// struct User {
+///     fingerprint: String,
+///     location: String,
+/// }
+///
+/// fn main() {
+///     // The type of `j` is `&str`
+///     let j = "
+///         {
+///             \"fingerprint\": \"0xF9BA143B95FF6D82\",
+///             \"location\": \"Menlo Park, CA\"
+///         }";
+///
+///     let u: User = serde_json::from_str(j).unwrap();
+///     println!("{:#?}", u);
+/// }
+/// ```
+///
+/// # Errors
+///
+/// This conversion can fail if the structure of the input does not match the
+/// structure expected by `T`, for example if `T` is a struct type but the input
+/// contains something other than a JSON map. It can also fail if the structure
+/// is correct but `T`'s implementation of `Deserialize` decides that something
+/// is wrong with the data, for example required struct fields are missing from
+/// the JSON map or some number is too big to fit in the expected primitive
+/// type.
+pub fn from_str<'a, T>(s: &'a str) -> Result<T>
+where
+    T: de::Deserialize<'a>,
+{
+    from_trait(read::StrRead::new(s))
+}
diff --git a/third_party/rust/serde_json/src/error.rs b/third_party/rust/serde_json/src/error.rs
new file mode 100644
index 0000000000..1875ef08b0
--- /dev/null
+++ b/third_party/rust/serde_json/src/error.rs
@@ -0,0 +1,445 @@
+//! When serializing or deserializing JSON goes wrong.
+
+use crate::io;
+use alloc::boxed::Box;
+use alloc::string::{String, ToString};
+use core::fmt::{self, Debug, Display};
+use core::result;
+use core::str::FromStr;
+use serde::{de, ser};
+#[cfg(feature = "std")]
+use std::error;
+
+/// This type represents all possible errors that can occur when serializing or
+/// deserializing JSON data.
+pub struct Error {
+    /// This `Box` allows us to keep the size of `Error` as small as possible. A
+    /// larger `Error` type was substantially slower due to all the functions
+    /// that pass around `Result<T, Error>`.
+    err: Box<ErrorImpl>,
+}
+
+/// Alias for a `Result` with the error type `serde_json::Error`.
+pub type Result<T> = result::Result<T, Error>;
+
+impl Error {
+    /// One-based line number at which the error was detected.
+    ///
+    /// Characters in the first line of the input (before the first newline
+    /// character) are in line 1.
+    pub fn line(&self) -> usize {
+        self.err.line
+    }
+
+    /// One-based column number at which the error was detected.
+    ///
+    /// The first character in the input and any characters immediately
+    /// following a newline character are in column 1.
+    ///
+    /// Note that errors may occur in column 0, for example if a read from an IO
+    /// stream fails immediately following a previously read newline character.
+    pub fn column(&self) -> usize {
+        self.err.column
+    }
+
+    /// Categorizes the cause of this error.
+    ///
+    /// - `Category::Io` - failure to read or write bytes on an IO stream
+    /// - `Category::Syntax` - input that is not syntactically valid JSON
+    /// - `Category::Data` - input data that is semantically incorrect
+    /// - `Category::Eof` - unexpected end of the input data
+    pub fn classify(&self) -> Category {
+        match self.err.code {
+            ErrorCode::Message(_) => Category::Data,
+            ErrorCode::Io(_) => Category::Io,
+            ErrorCode::EofWhileParsingList
+            | ErrorCode::EofWhileParsingObject
+            | ErrorCode::EofWhileParsingString
+            | ErrorCode::EofWhileParsingValue => Category::Eof,
+            ErrorCode::ExpectedColon
+            | ErrorCode::ExpectedListCommaOrEnd
+            | ErrorCode::ExpectedObjectCommaOrEnd
+            | ErrorCode::ExpectedSomeIdent
+            | ErrorCode::ExpectedSomeValue
+            | ErrorCode::InvalidEscape
+            | ErrorCode::InvalidNumber
+            | ErrorCode::NumberOutOfRange
+            | ErrorCode::InvalidUnicodeCodePoint
+            | ErrorCode::ControlCharacterWhileParsingString
+            | ErrorCode::KeyMustBeAString
+            | ErrorCode::LoneLeadingSurrogateInHexEscape
+            | ErrorCode::TrailingComma
+            | ErrorCode::TrailingCharacters
+            | ErrorCode::UnexpectedEndOfHexEscape
+            | ErrorCode::RecursionLimitExceeded => Category::Syntax,
+        }
+    }
+
+    /// Returns true if this error was caused by a failure to read or write
+    /// bytes on an IO stream.
+    pub fn is_io(&self) -> bool {
+        self.classify() == Category::Io
+    }
+
+    /// Returns true if this error was caused by input that was not
+    /// syntactically valid JSON.
+    pub fn is_syntax(&self) -> bool {
+        self.classify() == Category::Syntax
+    }
+
+    /// Returns true if this error was caused by input data that was
+    /// semantically incorrect.
+    ///
+    /// For example, JSON containing a number is semantically incorrect when the
+    /// type being deserialized into holds a String.
+    pub fn is_data(&self) -> bool {
+        self.classify() == Category::Data
+    }
+
+    /// Returns true if this error was caused by prematurely reaching the end of
+    /// the input data.
+    ///
+    /// Callers that process streaming input may be interested in retrying the
+    /// deserialization once more data is available.
+    pub fn is_eof(&self) -> bool {
+        self.classify() == Category::Eof
+    }
+}
+
+/// Categorizes the cause of a `serde_json::Error`.
+#[derive(Copy, Clone, PartialEq, Eq, Debug)]
+pub enum Category {
+    /// The error was caused by a failure to read or write bytes on an IO
+    /// stream.
+    Io,
+
+    /// The error was caused by input that was not syntactically valid JSON.
+    Syntax,
+
+    /// The error was caused by input data that was semantically incorrect.
+    ///
+    /// For example, JSON containing a number is semantically incorrect when the
+    /// type being deserialized into holds a String.
+    Data,
+
+    /// The error was caused by prematurely reaching the end of the input data.
+    ///
+    /// Callers that process streaming input may be interested in retrying the
+    /// deserialization once more data is available.
+    Eof,
+}
+
+#[cfg(feature = "std")]
+#[allow(clippy::fallible_impl_from)]
+impl From<Error> for io::Error {
+    /// Convert a `serde_json::Error` into an `io::Error`.
+    ///
+    /// JSON syntax and data errors are turned into `InvalidData` IO errors.
+    /// EOF errors are turned into `UnexpectedEof` IO errors.
+    ///
+    /// ```
+    /// use std::io;
+    ///
+    /// enum MyError {
+    ///     Io(io::Error),
+    ///     Json(serde_json::Error),
+    /// }
+    ///
+    /// impl From<serde_json::Error> for MyError {
+    ///     fn from(err: serde_json::Error) -> MyError {
+    ///         use serde_json::error::Category;
+    ///         match err.classify() {
+    ///             Category::Io => {
+    ///                 MyError::Io(err.into())
+    ///             }
+    ///             Category::Syntax | Category::Data | Category::Eof => {
+    ///                 MyError::Json(err)
+    ///             }
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    fn from(j: Error) -> Self {
+        if let ErrorCode::Io(err) = j.err.code {
+            err
+        } else {
+            match j.classify() {
+                Category::Io => unreachable!(),
+                Category::Syntax | Category::Data => io::Error::new(io::ErrorKind::InvalidData, j),
+                Category::Eof => io::Error::new(io::ErrorKind::UnexpectedEof, j),
+            }
+        }
+    }
+}
+
+struct ErrorImpl {
+    code: ErrorCode,
+    line: usize,
+    column: usize,
+}
+
+pub(crate) enum ErrorCode {
+    /// Catchall for syntax error messages
+    Message(Box<str>),
+
+    /// Some IO error occurred while serializing or deserializing.
+    Io(io::Error),
+
+    /// EOF while parsing a list.
+    EofWhileParsingList,
+
+    /// EOF while parsing an object.
+    EofWhileParsingObject,
+
+    /// EOF while parsing a string.
+    EofWhileParsingString,
+
+    /// EOF while parsing a JSON value.
+    EofWhileParsingValue,
+
+    /// Expected this character to be a `':'`.
+    ExpectedColon,
+
+    /// Expected this character to be either a `','` or a `']'`.
+    ExpectedListCommaOrEnd,
+
+    /// Expected this character to be either a `','` or a `'}'`.
+    ExpectedObjectCommaOrEnd,
+
+    /// Expected to parse either a `true`, `false`, or a `null`.
+    ExpectedSomeIdent,
+
+    /// Expected this character to start a JSON value.
+    ExpectedSomeValue,
+
+    /// Invalid hex escape code.
+    InvalidEscape,
+
+    /// Invalid number.
+    InvalidNumber,
+
+    /// Number is bigger than the maximum value of its type.
+    NumberOutOfRange,
+
+    /// Invalid unicode code point.
+    InvalidUnicodeCodePoint,
+
+    /// Control character found while parsing a string.
+    ControlCharacterWhileParsingString,
+
+    /// Object key is not a string.
+    KeyMustBeAString,
+
+    /// Lone leading surrogate in hex escape.
+    LoneLeadingSurrogateInHexEscape,
+
+    /// JSON has a comma after the last value in an array or map.
+    TrailingComma,
+
+    /// JSON has non-whitespace trailing characters after the value.
+    TrailingCharacters,
+
+    /// Unexpected end of hex escape.
+    UnexpectedEndOfHexEscape,
+
+    /// Encountered nesting of JSON maps and arrays more than 128 layers deep.
+    RecursionLimitExceeded,
+}
+
+impl Error {
+    #[cold]
+    pub(crate) fn syntax(code: ErrorCode, line: usize, column: usize) -> Self {
+        Error {
+            err: Box::new(ErrorImpl { code, line, column }),
+        }
+    }
+
+    // Not public API. Should be pub(crate).
+    //
+    // Update `eager_json` crate when this function changes.
+    #[doc(hidden)]
+    #[cold]
+    pub fn io(error: io::Error) -> Self {
+        Error {
+            err: Box::new(ErrorImpl {
+                code: ErrorCode::Io(error),
+                line: 0,
+                column: 0,
+            }),
+        }
+    }
+
+    #[cold]
+    pub(crate) fn fix_position<F>(self, f: F) -> Self
+    where
+        F: FnOnce(ErrorCode) -> Error,
+    {
+        if self.err.line == 0 {
+            f(self.err.code)
+        } else {
+            self
+        }
+    }
+}
+
+impl Display for ErrorCode {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            ErrorCode::Message(msg) => f.write_str(msg),
+            ErrorCode::Io(err) => Display::fmt(err, f),
+            ErrorCode::EofWhileParsingList => f.write_str("EOF while parsing a list"),
+            ErrorCode::EofWhileParsingObject => f.write_str("EOF while parsing an object"),
+            ErrorCode::EofWhileParsingString => f.write_str("EOF while parsing a string"),
+            ErrorCode::EofWhileParsingValue => f.write_str("EOF while parsing a value"),
+            ErrorCode::ExpectedColon => f.write_str("expected `:`"),
+            ErrorCode::ExpectedListCommaOrEnd => f.write_str("expected `,` or `]`"),
+            ErrorCode::ExpectedObjectCommaOrEnd => f.write_str("expected `,` or `}`"),
+            ErrorCode::ExpectedSomeIdent => f.write_str("expected ident"),
+            ErrorCode::ExpectedSomeValue => f.write_str("expected value"),
+            ErrorCode::InvalidEscape => f.write_str("invalid escape"),
+            ErrorCode::InvalidNumber => f.write_str("invalid number"),
+            ErrorCode::NumberOutOfRange => f.write_str("number out of range"),
+            ErrorCode::InvalidUnicodeCodePoint => f.write_str("invalid unicode code point"),
+            ErrorCode::ControlCharacterWhileParsingString => {
+                f.write_str("control character (\\u0000-\\u001F) found while parsing a string")
+            }
+            ErrorCode::KeyMustBeAString => f.write_str("key must be a string"),
+            ErrorCode::LoneLeadingSurrogateInHexEscape => {
+                f.write_str("lone leading surrogate in hex escape")
+            }
+            ErrorCode::TrailingComma => f.write_str("trailing comma"),
+            ErrorCode::TrailingCharacters => f.write_str("trailing characters"),
+            ErrorCode::UnexpectedEndOfHexEscape => f.write_str("unexpected end of hex escape"),
+            ErrorCode::RecursionLimitExceeded => f.write_str("recursion limit exceeded"),
+        }
+    }
+}
+
+impl serde::de::StdError for Error {
+    #[cfg(feature = "std")]
+    fn source(&self) -> Option<&(dyn error::Error + 'static)> {
+        match &self.err.code {
+            ErrorCode::Io(err) => Some(err),
+            _ => None,
+        }
+    }
+}
+
+impl Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        Display::fmt(&*self.err, f)
+    }
+}
+
+impl Display for ErrorImpl {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        if self.line == 0 {
+            Display::fmt(&self.code, f)
+        } else {
+            write!(
+                f,
+                "{} at line {} column {}",
+                self.code, self.line, self.column
+            )
+        }
+    }
+}
+
+// Remove two layers of verbosity from the debug representation. Humans often
+// end up seeing this representation because it is what unwrap() shows.
+impl Debug for Error {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        write!(
+            f,
+            "Error({:?}, line: {}, column: {})",
+            self.err.code.to_string(),
+            self.err.line,
+            self.err.column
+        )
+    }
+}
+
+impl de::Error for Error {
+    #[cold]
+    fn custom<T: Display>(msg: T) -> Error {
+        make_error(msg.to_string())
+    }
+
+    #[cold]
+    fn invalid_type(unexp: de::Unexpected, exp: &dyn de::Expected) -> Self {
+        if let de::Unexpected::Unit = unexp {
+            Error::custom(format_args!("invalid type: null, expected {}", exp))
+        } else {
+            Error::custom(format_args!("invalid type: {}, expected {}", unexp, exp))
+        }
+    }
+}
+
+impl ser::Error for Error {
+    #[cold]
+    fn custom<T: Display>(msg: T) -> Error {
+        make_error(msg.to_string())
+    }
+}
+
+// Parse our own error message that looks like "{} at line {} column {}" to work
+// around erased-serde round-tripping the error through de::Error::custom.
+fn make_error(mut msg: String) -> Error {
+    let (line, column) = parse_line_col(&mut msg).unwrap_or((0, 0));
+    Error {
+        err: Box::new(ErrorImpl {
+            code: ErrorCode::Message(msg.into_boxed_str()),
+            line,
+            column,
+        }),
+    }
+}
+
+fn parse_line_col(msg: &mut String) -> Option<(usize, usize)> {
+    let start_of_suffix = match msg.rfind(" at line ") {
+        Some(index) => index,
+        None => return None,
+    };
+
+    // Find start and end of line number.
+    let start_of_line = start_of_suffix + " at line ".len();
+    let mut end_of_line = start_of_line;
+    while starts_with_digit(&msg[end_of_line..]) {
+        end_of_line += 1;
+    }
+
+    if !msg[end_of_line..].starts_with(" column ") {
+        return None;
+    }
+
+    // Find start and end of column number.
+    let start_of_column = end_of_line + " column ".len();
+    let mut end_of_column = start_of_column;
+    while starts_with_digit(&msg[end_of_column..]) {
+        end_of_column += 1;
+    }
+
+    if end_of_column < msg.len() {
+        return None;
+    }
+
+    // Parse numbers.
+    let line = match usize::from_str(&msg[start_of_line..end_of_line]) {
+        Ok(line) => line,
+        Err(_) => return None,
+    };
+    let column = match usize::from_str(&msg[start_of_column..end_of_column]) {
+        Ok(column) => column,
+        Err(_) => return None,
+    };
+
+    msg.truncate(start_of_suffix);
+    Some((line, column))
+}
+
+fn starts_with_digit(slice: &str) -> bool {
+    match slice.as_bytes().first() {
+        None => false,
+        Some(&byte) => byte >= b'0' && byte <= b'9',
+    }
+}
diff --git a/third_party/rust/serde_json/src/features_check/error.rs b/third_party/rust/serde_json/src/features_check/error.rs
new file mode 100644
index 0000000000..22e58235c7
--- /dev/null
+++ b/third_party/rust/serde_json/src/features_check/error.rs
@@ -0,0 +1 @@
+"serde_json requires that either `std` (default) or `alloc` feature is enabled"
diff --git a/third_party/rust/serde_json/src/features_check/mod.rs b/third_party/rust/serde_json/src/features_check/mod.rs
new file mode 100644
index 0000000000..d12032cef8
--- /dev/null
+++ b/third_party/rust/serde_json/src/features_check/mod.rs
@@ -0,0 +1,13 @@
+//! Shows a user-friendly compiler error on incompatible selected features.
+
+#[allow(unused_macros)]
+macro_rules! hide_from_rustfmt {
+    ($mod:item) => {
+        $mod
+    };
+}
+
+#[cfg(not(any(feature = "std", feature = "alloc")))]
+hide_from_rustfmt! {
+    mod error;
+}
diff --git a/third_party/rust/serde_json/src/io/core.rs b/third_party/rust/serde_json/src/io/core.rs
new file mode 100644
index 0000000000..465ab8b249
--- /dev/null
+++ b/third_party/rust/serde_json/src/io/core.rs
@@ -0,0 +1,79 @@
+//! Reimplements core logic and types from `std::io` in an `alloc`-friendly
+//! fashion.
+
+use alloc::vec::Vec;
+use core::fmt::{self, Display};
+use core::result;
+
+pub enum ErrorKind {
+    Other,
+}
+
+// IO errors can never occur in no-std mode. All our no-std IO implementations
+// are infallible.
+pub struct Error;
+
+impl Display for Error {
+    fn fmt(&self, _formatter: &mut fmt::Formatter<'_>) -> fmt::Result {
+        unreachable!()
+    }
+}
+
+impl Error {
+    pub(crate) fn new(_kind: ErrorKind, _error: &'static str) -> Error {
+        Error
+    }
+}
+
+pub type Result<T> = result::Result<T, Error>;
+
+pub trait Write {
+    fn write(&mut self, buf: &[u8]) -> Result<usize>;
+
+    fn write_all(&mut self, buf: &[u8]) -> Result<()> {
+        // All our Write impls in no_std mode always write the whole buffer in
+        // one call infallibly.
+        let result = self.write(buf);
+        debug_assert!(result.is_ok());
+        debug_assert_eq!(result.unwrap_or(0), buf.len());
+        Ok(())
+    }
+
+    fn flush(&mut self) -> Result<()>;
+}
+
+impl<W: Write> Write for &mut W {
+    #[inline]
+    fn write(&mut self, buf: &[u8]) -> Result<usize> {
+        (*self).write(buf)
+    }
+
+    #[inline]
+    fn write_all(&mut self, buf: &[u8]) -> Result<()> {
+        (*self).write_all(buf)
+    }
+
+    #[inline]
+    fn flush(&mut self) -> Result<()> {
+        (*self).flush()
+    }
+}
+
+impl Write for Vec<u8> {
+    #[inline]
+    fn write(&mut self, buf: &[u8]) -> Result<usize> {
+        self.extend_from_slice(buf);
+        Ok(buf.len())
+    }
+
+    #[inline]
+    fn write_all(&mut self, buf: &[u8]) -> Result<()> {
+        self.extend_from_slice(buf);
+        Ok(())
+    }
+
+    #[inline]
+    fn flush(&mut self) -> Result<()> {
+        Ok(())
+    }
+}
diff --git a/third_party/rust/serde_json/src/io/mod.rs b/third_party/rust/serde_json/src/io/mod.rs
new file mode 100644
index 0000000000..9dee4a0685
--- /dev/null
+++ b/third_party/rust/serde_json/src/io/mod.rs
@@ -0,0 +1,20 @@
+//! A tiny, `no_std`-friendly facade around `std::io`.
+//! Reexports types from `std` when available; otherwise reimplements and
+//! provides some of the core logic.
+//!
+//! The main reason that `std::io` hasn't found itself reexported as part of
+//! the `core` crate is the `std::io::{Read, Write}` traits' reliance on
+//! `std::io::Error`, which may contain internally a heap-allocated `Box<Error>`
+//! and/or now relying on OS-specific `std::backtrace::Backtrace`.
+
+pub use self::imp::{Error, ErrorKind, Result, Write};
+
+#[cfg(not(feature = "std"))]
+#[path = "core.rs"]
+mod imp;
+
+#[cfg(feature = "std")]
+use std::io as imp;
+
+#[cfg(feature = "std")]
+pub use std::io::{Bytes, Read};
diff --git a/third_party/rust/serde_json/src/iter.rs b/third_party/rust/serde_json/src/iter.rs
new file mode 100644
index 0000000000..9792916dcc
--- /dev/null
+++ b/third_party/rust/serde_json/src/iter.rs
@@ -0,0 +1,70 @@
+use crate::io;
+
+pub struct LineColIterator<I> {
+    iter: I,
+
+    /// Index of the current line. Characters in the first line of the input
+    /// (before the first newline character) are in line 1.
+    line: usize,
+
+    /// Index of the current column. The first character in the input and any
+    /// characters immediately following a newline character are in column 1.
+    /// The column is 0 immediately after a newline character has been read.
+    col: usize,
+
+    /// Byte offset of the start of the current line. This is the sum of lengths
+    /// of all previous lines. Keeping track of things this way allows efficient
+    /// computation of the current line, column, and byte offset while only
+    /// updating one of the counters in `next()` in the common case.
+    start_of_line: usize,
+}
+
+impl<I> LineColIterator<I>
+where
+    I: Iterator<Item = io::Result<u8>>,
+{
+    pub fn new(iter: I) -> LineColIterator<I> {
+        LineColIterator {
+            iter,
+            line: 1,
+            col: 0,
+            start_of_line: 0,
+        }
+    }
+
+    pub fn line(&self) -> usize {
+        self.line
+    }
+
+    pub fn col(&self) -> usize {
+        self.col
+    }
+
+    pub fn byte_offset(&self) -> usize {
+        self.start_of_line + self.col
+    }
+}
+
+impl<I> Iterator for LineColIterator<I>
+where
+    I: Iterator<Item = io::Result<u8>>,
+{
+    type Item = io::Result<u8>;
+
+    fn next(&mut self) -> Option<io::Result<u8>> {
+        match self.iter.next() {
+            None => None,
+            Some(Ok(b'\n')) => {
+                self.start_of_line += self.col + 1;
+                self.line += 1;
+                self.col = 0;
+                Some(Ok(b'\n'))
+            }
+            Some(Ok(c)) => {
+                self.col += 1;
+                Some(Ok(c))
+            }
+            Some(Err(e)) => Some(Err(e)),
+        }
+    }
+}
diff --git a/third_party/rust/serde_json/src/lexical/algorithm.rs b/third_party/rust/serde_json/src/lexical/algorithm.rs
new file mode 100644
index 0000000000..a2cbf18aff
--- /dev/null
+++ b/third_party/rust/serde_json/src/lexical/algorithm.rs
@@ -0,0 +1,193 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+//! Algorithms to efficiently convert strings to floats.
+
+use super::bhcomp::*;
+use super::cached::*;
+use super::errors::*;
+use super::float::ExtendedFloat;
+use super::num::*;
+use super::small_powers::*;
+
+// FAST
+// ----
+
+/// Convert mantissa to exact value for a non-base2 power.
+///
+/// Returns the resulting float and if the value can be represented exactly.
+pub(crate) fn fast_path<F>(mantissa: u64, exponent: i32) -> Option<F>
+where
+    F: Float,
+{
+    // `mantissa >> (F::MANTISSA_SIZE+1) != 0` effectively checks if the
+    // value has a no bits above the hidden bit, which is what we want.
+    let (min_exp, max_exp) = F::exponent_limit();
+    let shift_exp = F::mantissa_limit();
+    let mantissa_size = F::MANTISSA_SIZE + 1;
+    if mantissa == 0 {
+        Some(F::ZERO)
+    } else if mantissa >> mantissa_size != 0 {
+        // Would require truncation of the mantissa.
+        None
+    } else if exponent == 0 {
+        // 0 exponent, same as value, exact representation.
+        let float = F::as_cast(mantissa);
+        Some(float)
+    } else if exponent >= min_exp && exponent <= max_exp {
+        // Value can be exactly represented, return the value.
+        // Do not use powi, since powi can incrementally introduce
+        // error.
+        let float = F::as_cast(mantissa);
+        Some(float.pow10(exponent))
+    } else if exponent >= 0 && exponent <= max_exp + shift_exp {
+        // Check to see if we have a disguised fast-path, where the
+        // number of digits in the mantissa is very small, but and
+        // so digits can be shifted from the exponent to the mantissa.
+        // https://www.exploringbinary.com/fast-path-decimal-to-floating-point-conversion/
+        let small_powers = POW10_64;
+        let shift = exponent - max_exp;
+        let power = small_powers[shift as usize];
+
+        // Compute the product of the power, if it overflows,
+        // prematurely return early, otherwise, if we didn't overshoot,
+        // we can get an exact value.
+        let value = mantissa.checked_mul(power)?;
+        if value >> mantissa_size != 0 {
+            None
+        } else {
+            // Use powi, since it's correct, and faster on
+            // the fast-path.
+            let float = F::as_cast(value);
+            Some(float.pow10(max_exp))
+        }
+    } else {
+        // Cannot be exactly represented, exponent too small or too big,
+        // would require truncation.
+        None
+    }
+}
+
+// MODERATE
+// --------
+
+/// Multiply the floating-point by the exponent.
+///
+/// Multiply by pre-calculated powers of the base, modify the extended-
+/// float, and return if new value and if the value can be represented
+/// accurately.
+fn multiply_exponent_extended<F>(fp: &mut ExtendedFloat, exponent: i32, truncated: bool) -> bool
+where
+    F: Float,
+{
+    let powers = ExtendedFloat::get_powers();
+    let exponent = exponent.saturating_add(powers.bias);
+    let small_index = exponent % powers.step;
+    let large_index = exponent / powers.step;
+    if exponent < 0 {
+        // Guaranteed underflow (assign 0).
+        fp.mant = 0;
+        true
+    } else if large_index as usize >= powers.large.len() {
+        // Overflow (assign infinity)
+        fp.mant = 1 << 63;
+        fp.exp = 0x7FF;
+        true
+    } else {
+        // Within the valid exponent range, multiply by the large and small
+        // exponents and return the resulting value.
+
+        // Track errors to as a factor of unit in last-precision.
+        let mut errors: u32 = 0;
+        if truncated {
+            errors += u64::error_halfscale();
+        }
+
+        // Multiply by the small power.
+        // Check if we can directly multiply by an integer, if not,
+        // use extended-precision multiplication.
+        match fp
+            .mant
+            .overflowing_mul(powers.get_small_int(small_index as usize))
+        {
+            // Overflow, multiplication unsuccessful, go slow path.
+            (_, true) => {
+                fp.normalize();
+                fp.imul(&powers.get_small(small_index as usize));
+                errors += u64::error_halfscale();
+            }
+            // No overflow, multiplication successful.
+            (mant, false) => {
+                fp.mant = mant;
+                fp.normalize();
+            }
+        }
+
+        // Multiply by the large power
+        fp.imul(&powers.get_large(large_index as usize));
+        if errors > 0 {
+            errors += 1;
+        }
+        errors += u64::error_halfscale();
+
+        // Normalize the floating point (and the errors).
+        let shift = fp.normalize();
+        errors <<= shift;
+
+        u64::error_is_accurate::<F>(errors, fp)
+    }
+}
+
+/// Create a precise native float using an intermediate extended-precision float.
+///
+/// Return the float approximation and if the value can be accurately
+/// represented with mantissa bits of precision.
+#[inline]
+pub(crate) fn moderate_path<F>(
+    mantissa: u64,
+    exponent: i32,
+    truncated: bool,
+) -> (ExtendedFloat, bool)
+where
+    F: Float,
+{
+    let mut fp = ExtendedFloat {
+        mant: mantissa,
+        exp: 0,
+    };
+    let valid = multiply_exponent_extended::<F>(&mut fp, exponent, truncated);
+    (fp, valid)
+}
+
+// FALLBACK
+// --------
+
+/// Fallback path when the fast path does not work.
+///
+/// Uses the moderate path, if applicable, otherwise, uses the slow path
+/// as required.
+pub(crate) fn fallback_path<F>(
+    integer: &[u8],
+    fraction: &[u8],
+    mantissa: u64,
+    exponent: i32,
+    mantissa_exponent: i32,
+    truncated: bool,
+) -> F
+where
+    F: Float,
+{
+    // Moderate path (use an extended 80-bit representation).
+    let (fp, valid) = moderate_path::<F>(mantissa, mantissa_exponent, truncated);
+    if valid {
+        return fp.into_float::<F>();
+    }
+
+    // Slow path, fast path didn't work.
+    let b = fp.into_downward_float::<F>();
+    if b.is_special() {
+        // We have a non-finite number, we get to leave early.
+        b
+    } else {
+        bhcomp(b, integer, fraction, exponent)
+    }
+}
diff --git a/third_party/rust/serde_json/src/lexical/bhcomp.rs b/third_party/rust/serde_json/src/lexical/bhcomp.rs
new file mode 100644
index 0000000000..1f2a7bbdee
--- /dev/null
+++ b/third_party/rust/serde_json/src/lexical/bhcomp.rs
@@ -0,0 +1,218 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+//! Compare the mantissa to the halfway representation of the float.
+//!
+//! Compares the actual significant digits of the mantissa to the
+//! theoretical digits from `b+h`, scaled into the proper range.
+
+use super::bignum::*;
+use super::digit::*;
+use super::exponent::*;
+use super::float::*;
+use super::math::*;
+use super::num::*;
+use super::rounding::*;
+use core::{cmp, mem};
+
+// MANTISSA
+
+/// Parse the full mantissa into a big integer.
+///
+/// Max digits is the maximum number of digits plus one.
+fn parse_mantissa<F>(integer: &[u8], fraction: &[u8]) -> Bigint
+where
+    F: Float,
+{
+    // Main loop
+    let small_powers = POW10_LIMB;
+    let step = small_powers.len() - 2;
+    let max_digits = F::MAX_DIGITS - 1;
+    let mut counter = 0;
+    let mut value: Limb = 0;
+    let mut i: usize = 0;
+    let mut result = Bigint::default();
+
+    // Iteratively process all the data in the mantissa.
+    for &digit in integer.iter().chain(fraction) {
+        // We've parsed the max digits using small values, add to bignum
+        if counter == step {
+            result.imul_small(small_powers[counter]);
+            result.iadd_small(value);
+            counter = 0;
+            value = 0;
+        }
+
+        value *= 10;
+        value += as_limb(to_digit(digit).unwrap());
+
+        i += 1;
+        counter += 1;
+        if i == max_digits {
+            break;
+        }
+    }
+
+    // We will always have a remainder, as long as we entered the loop
+    // once, or counter % step is 0.
+    if counter != 0 {
+        result.imul_small(small_powers[counter]);
+        result.iadd_small(value);
+    }
+
+    // If we have any remaining digits after the last value, we need
+    // to add a 1 after the rest of the array, it doesn't matter where,
+    // just move it up. This is good for the worst-possible float
+    // representation. We also need to return an index.
+    // Since we already trimmed trailing zeros, we know there has
+    // to be a non-zero digit if there are any left.
+    if i < integer.len() + fraction.len() {
+        result.imul_small(10);
+        result.iadd_small(1);
+    }
+
+    result
+}
+
+// FLOAT OPS
+
+/// Calculate `b` from a a representation of `b` as a float.
+#[inline]
+pub(super) fn b_extended<F: Float>(f: F) -> ExtendedFloat {
+    ExtendedFloat::from_float(f)
+}
+
+/// Calculate `b+h` from a a representation of `b` as a float.
+#[inline]
+pub(super) fn bh_extended<F: Float>(f: F) -> ExtendedFloat {
+    // None of these can overflow.
+    let b = b_extended(f);
+    ExtendedFloat {
+        mant: (b.mant << 1) + 1,
+        exp: b.exp - 1,
+    }
+}
+
+// ROUNDING
+
+/// Custom round-nearest, tie-event algorithm for bhcomp.
+#[inline]
+fn round_nearest_tie_even(fp: &mut ExtendedFloat, shift: i32, is_truncated: bool) {
+    let (mut is_above, mut is_halfway) = round_nearest(fp, shift);
+    if is_halfway && is_truncated {
+        is_above = true;
+        is_halfway = false;
+    }
+    tie_even(fp, is_above, is_halfway);
+}
+
+// BHCOMP
+
+/// Calculate the mantissa for a big integer with a positive exponent.
+fn large_atof<F>(mantissa: Bigint, exponent: i32) -> F
+where
+    F: Float,
+{
+    let bits = mem::size_of::<u64>() * 8;
+
+    // Simple, we just need to multiply by the power of the radix.
+    // Now, we can calculate the mantissa and the exponent from this.
+    // The binary exponent is the binary exponent for the mantissa
+    // shifted to the hidden bit.
+    let mut bigmant = mantissa;
+    bigmant.imul_pow10(exponent as u32);
+
+    // Get the exact representation of the float from the big integer.
+    let (mant, is_truncated) = bigmant.hi64();
+    let exp = bigmant.bit_length() as i32 - bits as i32;
+    let mut fp = ExtendedFloat { mant, exp };
+    fp.round_to_native::<F, _>(|fp, shift| round_nearest_tie_even(fp, shift, is_truncated));
+    into_float(fp)
+}
+
+/// Calculate the mantissa for a big integer with a negative exponent.
+///
+/// This invokes the comparison with `b+h`.
+fn small_atof<F>(mantissa: Bigint, exponent: i32, f: F) -> F
+where
+    F: Float,
+{
+    // Get the significant digits and radix exponent for the real digits.
+    let mut real_digits = mantissa;
+    let real_exp = exponent;
+    debug_assert!(real_exp < 0);
+
+    // Get the significant digits and the binary exponent for `b+h`.
+    let theor = bh_extended(f);
+    let mut theor_digits = Bigint::from_u64(theor.mant);
+    let theor_exp = theor.exp;
+
+    // We need to scale the real digits and `b+h` digits to be the same
+    // order. We currently have `real_exp`, in `radix`, that needs to be
+    // shifted to `theor_digits` (since it is negative), and `theor_exp`
+    // to either `theor_digits` or `real_digits` as a power of 2 (since it
+    // may be positive or negative). Try to remove as many powers of 2
+    // as possible. All values are relative to `theor_digits`, that is,
+    // reflect the power you need to multiply `theor_digits` by.
+
+    // Can remove a power-of-two, since the radix is 10.
+    // Both are on opposite-sides of equation, can factor out a
+    // power of two.
+    //
+    // Example: 10^-10, 2^-10   -> ( 0, 10, 0)
+    // Example: 10^-10, 2^-15   -> (-5, 10, 0)
+    // Example: 10^-10, 2^-5    -> ( 5, 10, 0)
+    // Example: 10^-10, 2^5 -> (15, 10, 0)
+    let binary_exp = theor_exp - real_exp;
+    let halfradix_exp = -real_exp;
+    let radix_exp = 0;
+
+    // Carry out our multiplication.
+    if halfradix_exp != 0 {
+        theor_digits.imul_pow5(halfradix_exp as u32);
+    }
+    if radix_exp != 0 {
+        theor_digits.imul_pow10(radix_exp as u32);
+    }
+    if binary_exp > 0 {
+        theor_digits.imul_pow2(binary_exp as u32);
+    } else if binary_exp < 0 {
+        real_digits.imul_pow2(-binary_exp as u32);
+    }
+
+    // Compare real digits to theoretical digits and round the float.
+    match real_digits.compare(&theor_digits) {
+        cmp::Ordering::Greater => f.next_positive(),
+        cmp::Ordering::Less => f,
+        cmp::Ordering::Equal => f.round_positive_even(),
+    }
+}
+
+/// Calculate the exact value of the float.
+///
+/// Note: fraction must not have trailing zeros.
+pub(crate) fn bhcomp<F>(b: F, integer: &[u8], mut fraction: &[u8], exponent: i32) -> F
+where
+    F: Float,
+{
+    // Calculate the number of integer digits and use that to determine
+    // where the significant digits start in the fraction.
+    let integer_digits = integer.len();
+    let fraction_digits = fraction.len();
+    let digits_start = if integer_digits == 0 {
+        let start = fraction.iter().take_while(|&x| *x == b'0').count();
+        fraction = &fraction[start..];
+        start
+    } else {
+        0
+    };
+    let sci_exp = scientific_exponent(exponent, integer_digits, digits_start);
+    let count = F::MAX_DIGITS.min(integer_digits + fraction_digits - digits_start);
+    let scaled_exponent = sci_exp + 1 - count as i32;
+
+    let mantissa = parse_mantissa::<F>(integer, fraction);
+    if scaled_exponent >= 0 {
+        large_atof(mantissa, scaled_exponent)
+    } else {
+        small_atof(mantissa, scaled_exponent, b)
+    }
+}
diff --git a/third_party/rust/serde_json/src/lexical/bignum.rs b/third_party/rust/serde_json/src/lexical/bignum.rs
new file mode 100644
index 0000000000..f9551f534f
--- /dev/null
+++ b/third_party/rust/serde_json/src/lexical/bignum.rs
@@ -0,0 +1,33 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+//! Big integer type definition.
+
+use super::math::*;
+use alloc::vec::Vec;
+
+/// Storage for a big integer type.
+#[derive(Clone, PartialEq, Eq)]
+pub(crate) struct Bigint {
+    /// Internal storage for the Bigint, in little-endian order.
+    pub(crate) data: Vec<Limb>,
+}
+
+impl Default for Bigint {
+    fn default() -> Self {
+        Bigint {
+            data: Vec::with_capacity(20),
+        }
+    }
+}
+
+impl Math for Bigint {
+    #[inline]
+    fn data(&self) -> &Vec<Limb> {
+        &self.data
+    }
+
+    #[inline]
+    fn data_mut(&mut self) -> &mut Vec<Limb> {
+        &mut self.data
+    }
+}
diff --git a/third_party/rust/serde_json/src/lexical/cached.rs b/third_party/rust/serde_json/src/lexical/cached.rs
new file mode 100644
index 0000000000..ef5a9fe54d
--- /dev/null
+++ b/third_party/rust/serde_json/src/lexical/cached.rs
@@ -0,0 +1,82 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+//! Cached powers trait for extended-precision floats.
+
+use super::cached_float80;
+use super::float::ExtendedFloat;
+
+// POWERS
+
+/// Precalculated powers that uses two-separate arrays for memory-efficiency.
+#[doc(hidden)]
+pub(crate) struct ExtendedFloatArray {
+    // Pre-calculated mantissa for the powers.
+    pub mant: &'static [u64],
+    // Pre-calculated binary exponents for the powers.
+    pub exp: &'static [i32],
+}
+
+/// Allow indexing of values without bounds checking
+impl ExtendedFloatArray {
+    #[inline]
+    pub fn get_extended_float(&self, index: usize) -> ExtendedFloat {
+        let mant = self.mant[index];
+        let exp = self.exp[index];
+        ExtendedFloat { mant, exp }
+    }
+
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.mant.len()
+    }
+}
+
+// MODERATE PATH POWERS
+
+/// Precalculated powers of base N for the moderate path.
+#[doc(hidden)]
+pub(crate) struct ModeratePathPowers {
+    // Pre-calculated small powers.
+    pub small: ExtendedFloatArray,
+    // Pre-calculated large powers.
+    pub large: ExtendedFloatArray,
+    /// Pre-calculated small powers as 64-bit integers
+    pub small_int: &'static [u64],
+    // Step between large powers and number of small powers.
+    pub step: i32,
+    // Exponent bias for the large powers.
+    pub bias: i32,
+}
+
+/// Allow indexing of values without bounds checking
+impl ModeratePathPowers {
+    #[inline]
+    pub fn get_small(&self, index: usize) -> ExtendedFloat {
+        self.small.get_extended_float(index)
+    }
+
+    #[inline]
+    pub fn get_large(&self, index: usize) -> ExtendedFloat {
+        self.large.get_extended_float(index)
+    }
+
+    #[inline]
+    pub fn get_small_int(&self, index: usize) -> u64 {
+        self.small_int[index]
+    }
+}
+
+// CACHED EXTENDED POWERS
+
+/// Cached powers as a trait for a floating-point type.
+pub(crate) trait ModeratePathCache {
+    /// Get cached powers.
+    fn get_powers() -> &'static ModeratePathPowers;
+}
+
+impl ModeratePathCache for ExtendedFloat {
+    #[inline]
+    fn get_powers() -> &'static ModeratePathPowers {
+        cached_float80::get_powers()
+    }
+}
diff --git a/third_party/rust/serde_json/src/lexical/cached_float80.rs b/third_party/rust/serde_json/src/lexical/cached_float80.rs
new file mode 100644
index 0000000000..9beda3ddb1
--- /dev/null
+++ b/third_party/rust/serde_json/src/lexical/cached_float80.rs
@@ -0,0 +1,206 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+//! Cached exponents for basen values with 80-bit extended floats.
+//!
+//! Exact versions of base**n as an extended-precision float, with both
+//! large and small powers. Use the large powers to minimize the amount
+//! of compounded error.
+//!
+//! These values were calculated using Python, using the arbitrary-precision
+//! integer to calculate exact extended-representation of each value.
+//! These values are all normalized.
+
+use super::cached::{ExtendedFloatArray, ModeratePathPowers};
+
+// LOW-LEVEL
+// ---------
+
+// BASE10
+
+const BASE10_SMALL_MANTISSA: [u64; 10] = [
+    9223372036854775808,  // 10^0
+    11529215046068469760, // 10^1
+    14411518807585587200, // 10^2
+    18014398509481984000, // 10^3
+    11258999068426240000, // 10^4
+    14073748835532800000, // 10^5
+    17592186044416000000, // 10^6
+    10995116277760000000, // 10^7
+    13743895347200000000, // 10^8
+    17179869184000000000, // 10^9
+];
+const BASE10_SMALL_EXPONENT: [i32; 10] = [
+    -63, // 10^0
+    -60, // 10^1
+    -57, // 10^2
+    -54, // 10^3
+    -50, // 10^4
+    -47, // 10^5
+    -44, // 10^6
+    -40, // 10^7
+    -37, // 10^8
+    -34, // 10^9
+];
+const BASE10_LARGE_MANTISSA: [u64; 66] = [
+    11555125961253852697, // 10^-350
+    13451937075301367670, // 10^-340
+    15660115838168849784, // 10^-330
+    18230774251475056848, // 10^-320
+    10611707258198326947, // 10^-310
+    12353653155963782858, // 10^-300
+    14381545078898527261, // 10^-290
+    16742321987285426889, // 10^-280
+    9745314011399999080,  // 10^-270
+    11345038669416679861, // 10^-260
+    13207363278391631158, // 10^-250
+    15375394465392026070, // 10^-240
+    17899314949046850752, // 10^-230
+    10418772551374772303, // 10^-220
+    12129047596099288555, // 10^-210
+    14120069793541087484, // 10^-200
+    16437924692338667210, // 10^-190
+    9568131466127621947,  // 10^-180
+    11138771039116687545, // 10^-170
+    12967236152753102995, // 10^-160
+    15095849699286165408, // 10^-150
+    17573882009934360870, // 10^-140
+    10229345649675443343, // 10^-130
+    11908525658859223294, // 10^-120
+    13863348470604074297, // 10^-110
+    16139061738043178685, // 10^-100
+    9394170331095332911,  // 10^-90
+    10936253623915059621, // 10^-80
+    12731474852090538039, // 10^-70
+    14821387422376473014, // 10^-60
+    17254365866976409468, // 10^-50
+    10043362776618689222, // 10^-40
+    11692013098647223345, // 10^-30
+    13611294676837538538, // 10^-20
+    15845632502852867518, // 10^-10
+    9223372036854775808,  // 10^0
+    10737418240000000000, // 10^10
+    12500000000000000000, // 10^20
+    14551915228366851806, // 10^30
+    16940658945086006781, // 10^40
+    9860761315262647567,  // 10^50
+    11479437019748901445, // 10^60
+    13363823550460978230, // 10^70
+    15557538194652854267, // 10^80
+    18111358157653424735, // 10^90
+    10542197943230523224, // 10^100
+    12272733663244316382, // 10^110
+    14287342391028437277, // 10^120
+    16632655625031838749, // 10^130
+    9681479787123295682,  // 10^140
+    11270725851789228247, // 10^150
+    13120851772591970218, // 10^160
+    15274681817498023410, // 10^170
+    17782069995880619867, // 10^180
+    10350527006597618960, // 10^190
+    12049599325514420588, // 10^200
+    14027579833653779454, // 10^210
+    16330252207878254650, // 10^220
+    9505457831475799117,  // 10^230
+    11065809325636130661, // 10^240
+    12882297539194266616, // 10^250
+    14996968138956309548, // 10^260
+    17458768723248864463, // 10^270
+    10162340898095201970, // 10^280
+    11830521861667747109, // 10^290
+    13772540099066387756, // 10^300
+];
+const BASE10_LARGE_EXPONENT: [i32; 66] = [
+    -1226, // 10^-350
+    -1193, // 10^-340
+    -1160, // 10^-330
+    -1127, // 10^-320
+    -1093, // 10^-310
+    -1060, // 10^-300
+    -1027, // 10^-290
+    -994,  // 10^-280
+    -960,  // 10^-270
+    -927,  // 10^-260
+    -894,  // 10^-250
+    -861,  // 10^-240
+    -828,  // 10^-230
+    -794,  // 10^-220
+    -761,  // 10^-210
+    -728,  // 10^-200
+    -695,  // 10^-190
+    -661,  // 10^-180
+    -628,  // 10^-170
+    -595,  // 10^-160
+    -562,  // 10^-150
+    -529,  // 10^-140
+    -495,  // 10^-130
+    -462,  // 10^-120
+    -429,  // 10^-110
+    -396,  // 10^-100
+    -362,  // 10^-90
+    -329,  // 10^-80
+    -296,  // 10^-70
+    -263,  // 10^-60
+    -230,  // 10^-50
+    -196,  // 10^-40
+    -163,  // 10^-30
+    -130,  // 10^-20
+    -97,   // 10^-10
+    -63,   // 10^0
+    -30,   // 10^10
+    3,     // 10^20
+    36,    // 10^30
+    69,    // 10^40
+    103,   // 10^50
+    136,   // 10^60
+    169,   // 10^70
+    202,   // 10^80
+    235,   // 10^90
+    269,   // 10^100
+    302,   // 10^110
+    335,   // 10^120
+    368,   // 10^130
+    402,   // 10^140
+    435,   // 10^150
+    468,   // 10^160
+    501,   // 10^170
+    534,   // 10^180
+    568,   // 10^190
+    601,   // 10^200
+    634,   // 10^210
+    667,   // 10^220
+    701,   // 10^230
+    734,   // 10^240
+    767,   // 10^250
+    800,   // 10^260
+    833,   // 10^270
+    867,   // 10^280
+    900,   // 10^290
+    933,   // 10^300
+];
+const BASE10_SMALL_INT_POWERS: [u64; 10] = [
+    1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000,
+];
+const BASE10_STEP: i32 = 10;
+const BASE10_BIAS: i32 = 350;
+
+// HIGH LEVEL
+// ----------
+
+const BASE10_POWERS: ModeratePathPowers = ModeratePathPowers {
+    small: ExtendedFloatArray {
+        mant: &BASE10_SMALL_MANTISSA,
+        exp: &BASE10_SMALL_EXPONENT,
+    },
+    large: ExtendedFloatArray {
+        mant: &BASE10_LARGE_MANTISSA,
+        exp: &BASE10_LARGE_EXPONENT,
+    },
+    small_int: &BASE10_SMALL_INT_POWERS,
+    step: BASE10_STEP,
+    bias: BASE10_BIAS,
+};
+
+/// Get powers from base.
+pub(crate) fn get_powers() -> &'static ModeratePathPowers {
+    &BASE10_POWERS
+}
diff --git a/third_party/rust/serde_json/src/lexical/digit.rs b/third_party/rust/serde_json/src/lexical/digit.rs
new file mode 100644
index 0000000000..882aa9eef2
--- /dev/null
+++ b/third_party/rust/serde_json/src/lexical/digit.rs
@@ -0,0 +1,15 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+//! Helpers to convert and add digits from characters.
+
+// Convert u8 to digit.
+#[inline]
+pub(crate) fn to_digit(c: u8) -> Option<u32> {
+    (c as char).to_digit(10)
+}
+
+// Add digit to mantissa.
+#[inline]
+pub(crate) fn add_digit(value: u64, digit: u32) -> Option<u64> {
+    value.checked_mul(10)?.checked_add(digit as u64)
+}
diff --git a/third_party/rust/serde_json/src/lexical/errors.rs b/third_party/rust/serde_json/src/lexical/errors.rs
new file mode 100644
index 0000000000..cad4bd3d58
--- /dev/null
+++ b/third_party/rust/serde_json/src/lexical/errors.rs
@@ -0,0 +1,133 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+//! Estimate the error in an 80-bit approximation of a float.
+//!
+//! This estimates the error in a floating-point representation.
+//!
+//! This implementation is loosely based off the Golang implementation,
+//! found here:
+//!     https://golang.org/src/strconv/atof.go
+
+use super::float::*;
+use super::num::*;
+use super::rounding::*;
+
+pub(crate) trait FloatErrors {
+    /// Get the full error scale.
+    fn error_scale() -> u32;
+    /// Get the half error scale.
+    fn error_halfscale() -> u32;
+    /// Determine if the number of errors is tolerable for float precision.
+    fn error_is_accurate<F: Float>(count: u32, fp: &ExtendedFloat) -> bool;
+}
+
+/// Check if the error is accurate with a round-nearest rounding scheme.
+#[inline]
+fn nearest_error_is_accurate(errors: u64, fp: &ExtendedFloat, extrabits: u64) -> bool {
+    // Round-to-nearest, need to use the halfway point.
+    if extrabits == 65 {
+        // Underflow, we have a shift larger than the mantissa.
+        // Representation is valid **only** if the value is close enough
+        // overflow to the next bit within errors. If it overflows,
+        // the representation is **not** valid.
+        !fp.mant.overflowing_add(errors).1
+    } else {
+        let mask: u64 = lower_n_mask(extrabits);
+        let extra: u64 = fp.mant & mask;
+
+        // Round-to-nearest, need to check if we're close to halfway.
+        // IE, b10100 | 100000, where `|` signifies the truncation point.
+        let halfway: u64 = lower_n_halfway(extrabits);
+        let cmp1 = halfway.wrapping_sub(errors) < extra;
+        let cmp2 = extra < halfway.wrapping_add(errors);
+
+        // If both comparisons are true, we have significant rounding error,
+        // and the value cannot be exactly represented. Otherwise, the
+        // representation is valid.
+        !(cmp1 && cmp2)
+    }
+}
+
+impl FloatErrors for u64 {
+    #[inline]
+    fn error_scale() -> u32 {
+        8
+    }
+
+    #[inline]
+    fn error_halfscale() -> u32 {
+        u64::error_scale() / 2
+    }
+
+    #[inline]
+    fn error_is_accurate<F: Float>(count: u32, fp: &ExtendedFloat) -> bool {
+        // Determine if extended-precision float is a good approximation.
+        // If the error has affected too many units, the float will be
+        // inaccurate, or if the representation is too close to halfway
+        // that any operations could affect this halfway representation.
+        // See the documentation for dtoa for more information.
+        let bias = -(F::EXPONENT_BIAS - F::MANTISSA_SIZE);
+        let denormal_exp = bias - 63;
+        // This is always a valid u32, since (denormal_exp - fp.exp)
+        // will always be positive and the significand size is {23, 52}.
+        let extrabits = if fp.exp <= denormal_exp {
+            64 - F::MANTISSA_SIZE + denormal_exp - fp.exp
+        } else {
+            63 - F::MANTISSA_SIZE
+        };
+
+        // Our logic is as follows: we want to determine if the actual
+        // mantissa and the errors during calculation differ significantly
+        // from the rounding point. The rounding point for round-nearest
+        // is the halfway point, IE, this when the truncated bits start
+        // with b1000..., while the rounding point for the round-toward
+        // is when the truncated bits are equal to 0.
+        // To do so, we can check whether the rounding point +/- the error
+        // are >/< the actual lower n bits.
+        //
+        // For whether we need to use signed or unsigned types for this
+        // analysis, see this example, using u8 rather than u64 to simplify
+        // things.
+        //
+        // # Comparisons
+        //      cmp1 = (halfway - errors) < extra
+        //      cmp1 = extra < (halfway + errors)
+        //
+        // # Large Extrabits, Low Errors
+        //
+        //      extrabits = 8
+        //      halfway          =  0b10000000
+        //      extra            =  0b10000010
+        //      errors           =  0b00000100
+        //      halfway - errors =  0b01111100
+        //      halfway + errors =  0b10000100
+        //
+        //      Unsigned:
+        //          halfway - errors = 124
+        //          halfway + errors = 132
+        //          extra            = 130
+        //          cmp1             = true
+        //          cmp2             = true
+        //      Signed:
+        //          halfway - errors = 124
+        //          halfway + errors = -124
+        //          extra            = -126
+        //          cmp1             = false
+        //          cmp2             = true
+        //
+        // # Conclusion
+        //
+        // Since errors will always be small, and since we want to detect
+        // if the representation is accurate, we need to use an **unsigned**
+        // type for comparisons.
+
+        let extrabits = extrabits as u64;
+        let errors = count as u64;
+        if extrabits > 65 {
+            // Underflow, we have a literal 0.
+            return true;
+        }
+
+        nearest_error_is_accurate(errors, fp, extrabits)
+    }
+}
diff --git a/third_party/rust/serde_json/src/lexical/exponent.rs b/third_party/rust/serde_json/src/lexical/exponent.rs
new file mode 100644
index 0000000000..6fc51977ed
--- /dev/null
+++ b/third_party/rust/serde_json/src/lexical/exponent.rs
@@ -0,0 +1,50 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+//! Utilities to calculate exponents.
+
+/// Convert usize into i32 without overflow.
+///
+/// This is needed to ensure when adjusting the exponent relative to
+/// the mantissa we do not overflow for comically-long exponents.
+#[inline]
+fn into_i32(value: usize) -> i32 {
+    if value > i32::max_value() as usize {
+        i32::max_value()
+    } else {
+        value as i32
+    }
+}
+
+// EXPONENT CALCULATION
+
+// Calculate the scientific notation exponent without overflow.
+//
+// For example, 0.1 would be -1, and 10 would be 1 in base 10.
+#[inline]
+pub(crate) fn scientific_exponent(
+    exponent: i32,
+    integer_digits: usize,
+    fraction_start: usize,
+) -> i32 {
+    if integer_digits == 0 {
+        let fraction_start = into_i32(fraction_start);
+        exponent.saturating_sub(fraction_start).saturating_sub(1)
+    } else {
+        let integer_shift = into_i32(integer_digits - 1);
+        exponent.saturating_add(integer_shift)
+    }
+}
+
+// Calculate the mantissa exponent without overflow.
+//
+// Remove the number of digits that contributed to the mantissa past
+// the dot, and add the number of truncated digits from the mantissa,
+// to calculate the scaling factor for the mantissa from a raw exponent.
+#[inline]
+pub(crate) fn mantissa_exponent(exponent: i32, fraction_digits: usize, truncated: usize) -> i32 {
+    if fraction_digits > truncated {
+        exponent.saturating_sub(into_i32(fraction_digits - truncated))
+    } else {
+        exponent.saturating_add(into_i32(truncated - fraction_digits))
+    }
+}
diff --git a/third_party/rust/serde_json/src/lexical/float.rs b/third_party/rust/serde_json/src/lexical/float.rs
new file mode 100644
index 0000000000..2d434a29cb
--- /dev/null
+++ b/third_party/rust/serde_json/src/lexical/float.rs
@@ -0,0 +1,183 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+// FLOAT TYPE
+
+use super::num::*;
+use super::rounding::*;
+use super::shift::*;
+
+/// Extended precision floating-point type.
+///
+/// Private implementation, exposed only for testing purposes.
+#[doc(hidden)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub(crate) struct ExtendedFloat {
+    /// Mantissa for the extended-precision float.
+    pub mant: u64,
+    /// Binary exponent for the extended-precision float.
+    pub exp: i32,
+}
+
+impl ExtendedFloat {
+    // PROPERTIES
+
+    // OPERATIONS
+
+    /// Multiply two normalized extended-precision floats, as if by `a*b`.
+    ///
+    /// The precision is maximal when the numbers are normalized, however,
+    /// decent precision will occur as long as both values have high bits
+    /// set. The result is not normalized.
+    ///
+    /// Algorithm:
+    ///     1. Non-signed multiplication of mantissas (requires 2x as many bits as input).
+    ///     2. Normalization of the result (not done here).
+    ///     3. Addition of exponents.
+    pub(crate) fn mul(&self, b: &ExtendedFloat) -> ExtendedFloat {
+        // Logic check, values must be decently normalized prior to multiplication.
+        debug_assert!((self.mant & u64::HIMASK != 0) && (b.mant & u64::HIMASK != 0));
+
+        // Extract high-and-low masks.
+        let ah = self.mant >> u64::HALF;
+        let al = self.mant & u64::LOMASK;
+        let bh = b.mant >> u64::HALF;
+        let bl = b.mant & u64::LOMASK;
+
+        // Get our products
+        let ah_bl = ah * bl;
+        let al_bh = al * bh;
+        let al_bl = al * bl;
+        let ah_bh = ah * bh;
+
+        let mut tmp = (ah_bl & u64::LOMASK) + (al_bh & u64::LOMASK) + (al_bl >> u64::HALF);
+        // round up
+        tmp += 1 << (u64::HALF - 1);
+
+        ExtendedFloat {
+            mant: ah_bh + (ah_bl >> u64::HALF) + (al_bh >> u64::HALF) + (tmp >> u64::HALF),
+            exp: self.exp + b.exp + u64::FULL,
+        }
+    }
+
+    /// Multiply in-place, as if by `a*b`.
+    ///
+    /// The result is not normalized.
+    #[inline]
+    pub(crate) fn imul(&mut self, b: &ExtendedFloat) {
+        *self = self.mul(b);
+    }
+
+    // NORMALIZE
+
+    /// Normalize float-point number.
+    ///
+    /// Shift the mantissa so the number of leading zeros is 0, or the value
+    /// itself is 0.
+    ///
+    /// Get the number of bytes shifted.
+    #[inline]
+    pub(crate) fn normalize(&mut self) -> u32 {
+        // Note:
+        // Using the cltz intrinsic via leading_zeros is way faster (~10x)
+        // than shifting 1-bit at a time, via while loop, and also way
+        // faster (~2x) than an unrolled loop that checks at 32, 16, 4,
+        // 2, and 1 bit.
+        //
+        // Using a modulus of pow2 (which will get optimized to a bitwise
+        // and with 0x3F or faster) is slightly slower than an if/then,
+        // however, removing the if/then will likely optimize more branched
+        // code as it removes conditional logic.
+
+        // Calculate the number of leading zeros, and then zero-out
+        // any overflowing bits, to avoid shl overflow when self.mant == 0.
+        let shift = if self.mant == 0 {
+            0
+        } else {
+            self.mant.leading_zeros()
+        };
+        shl(self, shift as i32);
+        shift
+    }
+
+    // ROUND
+
+    /// Lossy round float-point number to native mantissa boundaries.
+    #[inline]
+    pub(crate) fn round_to_native<F, Algorithm>(&mut self, algorithm: Algorithm)
+    where
+        F: Float,
+        Algorithm: FnOnce(&mut ExtendedFloat, i32),
+    {
+        round_to_native::<F, _>(self, algorithm);
+    }
+
+    // FROM
+
+    /// Create extended float from native float.
+    #[inline]
+    pub fn from_float<F: Float>(f: F) -> ExtendedFloat {
+        from_float(f)
+    }
+
+    // INTO
+
+    /// Convert into default-rounded, lower-precision native float.
+    #[inline]
+    pub(crate) fn into_float<F: Float>(mut self) -> F {
+        self.round_to_native::<F, _>(round_nearest_tie_even);
+        into_float(self)
+    }
+
+    /// Convert into downward-rounded, lower-precision native float.
+    #[inline]
+    pub(crate) fn into_downward_float<F: Float>(mut self) -> F {
+        self.round_to_native::<F, _>(round_downward);
+        into_float(self)
+    }
+}
+
+// FROM FLOAT
+
+// Import ExtendedFloat from native float.
+#[inline]
+pub(crate) fn from_float<F>(f: F) -> ExtendedFloat
+where
+    F: Float,
+{
+    ExtendedFloat {
+        mant: u64::as_cast(f.mantissa()),
+        exp: f.exponent(),
+    }
+}
+
+// INTO FLOAT
+
+// Export extended-precision float to native float.
+//
+// The extended-precision float must be in native float representation,
+// with overflow/underflow appropriately handled.
+#[inline]
+pub(crate) fn into_float<F>(fp: ExtendedFloat) -> F
+where
+    F: Float,
+{
+    // Export floating-point number.
+    if fp.mant == 0 || fp.exp < F::DENORMAL_EXPONENT {
+        // sub-denormal, underflow
+        F::ZERO
+    } else if fp.exp >= F::MAX_EXPONENT {
+        // overflow
+        F::from_bits(F::INFINITY_BITS)
+    } else {
+        // calculate the exp and fraction bits, and return a float from bits.
+        let exp: u64;
+        if (fp.exp == F::DENORMAL_EXPONENT) && (fp.mant & F::HIDDEN_BIT_MASK.as_u64()) == 0 {
+            exp = 0;
+        } else {
+            exp = (fp.exp + F::EXPONENT_BIAS) as u64;
+        }
+        let exp = exp << F::MANTISSA_SIZE;
+        let mant = fp.mant & F::MANTISSA_MASK.as_u64();
+        F::from_bits(F::Unsigned::as_cast(mant | exp))
+    }
+}
diff --git a/third_party/rust/serde_json/src/lexical/large_powers.rs b/third_party/rust/serde_json/src/lexical/large_powers.rs
new file mode 100644
index 0000000000..c63ce1cf21
--- /dev/null
+++ b/third_party/rust/serde_json/src/lexical/large_powers.rs
@@ -0,0 +1,9 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+//! Precalculated large powers for limbs.
+
+#[cfg(limb_width_32)]
+pub(crate) use super::large_powers32::*;
+
+#[cfg(limb_width_64)]
+pub(crate) use super::large_powers64::*;
diff --git a/third_party/rust/serde_json/src/lexical/large_powers32.rs b/third_party/rust/serde_json/src/lexical/large_powers32.rs
new file mode 100644
index 0000000000..7991197262
--- /dev/null
+++ b/third_party/rust/serde_json/src/lexical/large_powers32.rs
@@ -0,0 +1,183 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+//! Precalculated large powers for 32-bit limbs.
+
+/// Large powers (&[u32]) for base5 operations.
+const POW5_1: [u32; 1] = [5];
+const POW5_2: [u32; 1] = [25];
+const POW5_3: [u32; 1] = [625];
+const POW5_4: [u32; 1] = [390625];
+const POW5_5: [u32; 2] = [2264035265, 35];
+const POW5_6: [u32; 3] = [2242703233, 762134875, 1262];
+const POW5_7: [u32; 5] = [3211403009, 1849224548, 3668416493, 3913284084, 1593091];
+const POW5_8: [u32; 10] = [
+    781532673, 64985353, 253049085, 594863151, 3553621484, 3288652808, 3167596762, 2788392729,
+    3911132675, 590,
+];
+const POW5_9: [u32; 19] = [
+    2553183233, 3201533787, 3638140786, 303378311, 1809731782, 3477761648, 3583367183, 649228654,
+    2915460784, 487929380, 1011012442, 1677677582, 3428152256, 1710878487, 1438394610, 2161952759,
+    4100910556, 1608314830, 349175,
+];
+const POW5_10: [u32; 38] = [
+    4234999809, 2012377703, 2408924892, 1570150255, 3090844311, 3273530073, 1187251475, 2498123591,
+    3364452033, 1148564857, 687371067, 2854068671, 1883165473, 505794538, 2988060450, 3159489326,
+    2531348317, 3215191468, 849106862, 3892080979, 3288073877, 2242451748, 4183778142, 2995818208,
+    2477501924, 325481258, 2487842652, 1774082830, 1933815724, 2962865281, 1168579910, 2724829000,
+    2360374019, 2315984659, 2360052375, 3251779801, 1664357844, 28,
+];
+const POW5_11: [u32; 75] = [
+    689565697, 4116392818, 1853628763, 516071302, 2568769159, 365238920, 336250165, 1283268122,
+    3425490969, 248595470, 2305176814, 2111925499, 507770399, 2681111421, 589114268, 591287751,
+    1708941527, 4098957707, 475844916, 3378731398, 2452339615, 2817037361, 2678008327, 1656645978,
+    2383430340, 73103988, 448667107, 2329420453, 3124020241, 3625235717, 3208634035, 2412059158,
+    2981664444, 4117622508, 838560765, 3069470027, 270153238, 1802868219, 3692709886, 2161737865,
+    2159912357, 2585798786, 837488486, 4237238160, 2540319504, 3798629246, 3748148874, 1021550776,
+    2386715342, 1973637538, 1823520457, 1146713475, 833971519, 3277251466, 905620390, 26278816,
+    2680483154, 2294040859, 373297482, 5996609, 4109575006, 512575049, 917036550, 1942311753,
+    2816916778, 3248920332, 1192784020, 3537586671, 2456567643, 2925660628, 759380297, 888447942,
+    3559939476, 3654687237, 805,
+];
+const POW5_12: [u32; 149] = [
+    322166785, 3809044581, 2994556223, 1239584207, 3962455841, 4001882964, 3053876612, 915114683,
+    2783289745, 785739093, 4253185907, 3931164994, 1370983858, 2553556126, 3360742076, 2255410929,
+    422849554, 2457422215, 3539495362, 1720790602, 1908931983, 1470596141, 592794347, 4219465164,
+    4085652704, 941661409, 2534650953, 885063988, 2355909854, 2812815516, 767256131, 3821757683,
+    2155151105, 3817418473, 281116564, 2834395026, 2821201622, 2524625843, 1511330880, 2572352493,
+    330571332, 2951088579, 2730271766, 4044456479, 4212286644, 2444937588, 3603420843, 2387148597,
+    1142537539, 3299235429, 1751012624, 861228086, 2873722519, 230498814, 1023297821, 2553128038,
+    3421129895, 2651917435, 2042981258, 1606787143, 2228751918, 447345732, 1930371132, 1784132011,
+    3612538790, 2275925090, 2487567871, 1080427616, 2009179183, 3383506781, 3899054063, 1950782960,
+    2168622213, 2717674390, 3616636027, 2079341593, 1530129217, 1461057425, 2406264415, 3674671357,
+    2972036238, 2019354295, 1455849819, 1866918619, 1324269294, 424891864, 2722422332, 2641594816,
+    1400249021, 3482963993, 3734946379, 225889849, 1891545473, 777383150, 3589824633, 4117601611,
+    4220028667, 334453379, 1083130821, 1060342180, 4208163139, 1489826908, 4163762246, 1096580926,
+    689301528, 2336054516, 1782865703, 4175148410, 3398369392, 2329412588, 3001580596, 59740741,
+    3202189932, 3351895776, 246185302, 718535188, 3772647488, 4151666556, 4055698133, 2461934110,
+    2281316281, 3466396836, 3536023465, 1064267812, 2955456354, 2423805422, 3627960790, 1325057500,
+    3876919979, 2009959531, 175455101, 184092852, 2358785571, 3842977831, 2485266289, 487121622,
+    4159252710, 4075707558, 459389244, 300652075, 2521346588, 3458976673, 888631636, 2076098096,
+    3844514585, 2363697580, 3729421522, 3051115477, 649395,
+];
+const POW5_13: [u32; 298] = [
+    711442433, 3564261005, 2399042279, 4170849936, 4010295575, 1423987028, 330414929, 1349249065,
+    4213813618, 3852031822, 4040843590, 2154565331, 3094013374, 1159028371, 3227065538, 2115927092,
+    2085102554, 488590542, 2609619432, 3602898805, 3812736528, 3269439096, 23816114, 253984538,
+    1035905997, 2942969204, 3400787671, 338562688, 1637191975, 740509713, 2264962817, 3410753922,
+    4162231428, 2282041228, 1759373012, 3155367777, 4278913285, 1420532801, 1981002276, 438054990,
+    1006507643, 1142697287, 1332538012, 2029019521, 3949305784, 818392641, 2491288846, 2716584663,
+    3648886102, 556814413, 444795339, 4071412999, 1066321706, 4253169466, 2510832316, 672091442,
+    4083256000, 2165985028, 1841538484, 3549854235, 364431512, 3707648143, 1162785440, 2268641545,
+    281340310, 735693841, 848809228, 1700785200, 2919703985, 4094234344, 58530286, 965505005,
+    1000010347, 3381961808, 3040089923, 1973852082, 2890971585, 1019960210, 4292895237, 2821887841,
+    3756675650, 3951282907, 3885870583, 1008791145, 503998487, 1881258362, 1949332730, 392996726,
+    2012973814, 3970014187, 2461725150, 2942547730, 3728066699, 2766901132, 3778532841, 1085564064,
+    2278673896, 1116879805, 3448726271, 774279411, 157211670, 1506320155, 531168605, 1362654525,
+    956967721, 2148871960, 769186085, 4186232894, 2055679604, 3248365487, 3981268013, 3975787984,
+    2489510517, 3309046495, 212771124, 933418041, 3371839114, 562115198, 1853601831, 757336096,
+    1354633440, 1486083256, 2872126393, 522920738, 1141587749, 3210903262, 1926940553, 3054024853,
+    2021162538, 2262742000, 1877899947, 3147002868, 669840763, 4158174590, 4238502559, 1023731922,
+    3386840011, 829588074, 3449720188, 2835142880, 2999162007, 813056473, 482949569, 638108879,
+    3067201471, 1026714238, 4004452838, 2383667807, 3999477803, 771648919, 630660440, 3827121348,
+    176185980, 2878191002, 2666149832, 3909811063, 2429163983, 2665690412, 907266128, 4269332098,
+    2022665808, 1527122180, 3072053668, 1072477492, 3006022924, 549664855, 2800340954, 37352654,
+    1212772743, 2711280533, 3029527946, 2511120040, 1305308377, 3474662224, 4226330922, 442988428,
+    954940108, 3274548099, 4212288177, 2688499880, 3982226758, 3922609956, 1279948029, 1939943640,
+    3650489901, 2733364929, 2494263275, 1864579964, 1225941120, 2390465139, 1267503249, 3533240729,
+    904410805, 2842550015, 2517736241, 1796069820, 3335274381, 673539835, 1924694759, 3598098235,
+    2792633405, 16535707, 3703535497, 3592841791, 2929082877, 1317622811, 294990855, 1396706563,
+    2383271770, 3853857605, 277813677, 277580220, 1101318484, 3761974115, 1132150143, 2544692622,
+    3419825776, 743770306, 1695464553, 1548693232, 2421159615, 2575672031, 2678971806, 1591267897,
+    626546738, 3823443129, 267710932, 1455435162, 2353985540, 3248523795, 335348168, 3872552561,
+    2814522612, 2634118860, 3503767026, 1301019273, 1414467789, 722985138, 3070909565, 4253482569,
+    3744939841, 558142907, 2229819389, 13833173, 77003966, 2763671364, 3905603970, 2931990126,
+    2280419384, 1879090457, 2934846267, 4284933164, 2331863845, 62191163, 3178861020, 1522063815,
+    785672270, 1215568492, 2936443917, 802972489, 2956820173, 3916732783, 2893572089, 1391232801,
+    3168640330, 2396859648, 894950918, 1103583736, 961991865, 2807302642, 305977505, 3054505899,
+    1048256994, 781017659, 2459278754, 3164823415, 537658277, 905753687, 464963300, 4149131560,
+    1029507924, 2278300961, 1231291503, 414073408, 3630740085, 2345841814, 475358196, 3258243317,
+    4167625072, 4178911231, 2927355042, 655438830, 3138378018, 623200562, 2785714112, 273403236,
+    807993669, 98,
+];
+const POW5_14: [u32; 595] = [
+    1691320321, 2671006246, 1682531301, 2072858707, 1240508969, 3108358191, 1125119096, 2470144952,
+    1610099978, 1690632660, 1941696884, 2663506355, 1006364675, 3909158537, 4147711374, 1072663936,
+    4078768933, 745751659, 4123687570, 471458681, 655028926, 4113407388, 3945524552, 985625313,
+    1254424514, 2127508744, 570530434, 945388122, 3194649404, 2589065070, 2731705399, 202030749,
+    2090780394, 3348662271, 1481754777, 1130635472, 4025144705, 1924486271, 2578567861, 125491448,
+    1558036315, 994248173, 3817216711, 763950077, 1030439870, 959586474, 3845661701, 483795093,
+    1637944470, 2275463649, 3398804829, 1758016486, 2665513698, 2004912571, 1094885097, 4223064276,
+    3307819021, 651121777, 1757003305, 3603542336, 129917786, 2215974994, 3042386306, 2205352757,
+    3944939700, 3710987569, 97967515, 1217242524, 930630949, 3660328512, 1787663098, 1784141600,
+    2500542892, 4034561586, 3444961378, 785043562, 3869499367, 885623728, 2625011087, 3053789617,
+    1965731793, 3900511934, 2648823592, 3851062028, 3321968688, 799195417, 1011847510, 1369129160,
+    1348009103, 2876796955, 2915408967, 3305284948, 263399535, 1715990604, 2645821294, 1587844552,
+    2624912049, 3035631499, 2306636348, 3499275462, 675152704, 854794152, 4004972748, 1739996642,
+    1333476491, 4012621867, 3658792931, 3297985728, 2864481726, 3066357406, 785287846, 1671499798,
+    433044045, 1919608025, 264833858, 3999983367, 1116778570, 1301982149, 4213901070, 4081649357,
+    536169226, 1389008649, 188923873, 373495152, 2551132278, 1800758715, 3951840330, 2632334454,
+    3118778225, 1034046547, 1862428410, 3037609062, 1994608505, 29051798, 2571685694, 264151332,
+    2260643090, 2717535964, 3508441116, 3283713017, 1903365635, 923575694, 1219598101, 2288281570,
+    3676533911, 1014136356, 555142354, 2389170030, 4185108175, 884862419, 836141292, 2957159173,
+    1997444768, 4233903127, 2876184692, 3089125070, 1480848293, 1097600237, 299700527, 2507669891,
+    2982628312, 2114881043, 2529576251, 2812279824, 2987750993, 4241938954, 2204775591, 1037094060,
+    829315638, 1231047149, 52608178, 3735136637, 3455232602, 962039123, 488286513, 50685385,
+    3516451821, 843975207, 1572355722, 675489076, 2428445672, 1555117248, 3708476086, 10375249,
+    4172112346, 2117510871, 2227658327, 3187664554, 3050656558, 328034318, 3179601324, 1247769761,
+    3439263953, 1431538938, 2962525068, 1213366289, 3813013550, 2651093719, 1860661503, 3933716208,
+    264320617, 789980519, 2257856172, 102000748, 977269860, 1113845122, 3008928583, 1461738106,
+    557786285, 2926560363, 1038106190, 3643478847, 828004507, 457818698, 1933056971, 373408056,
+    2076808229, 3160935130, 2781854874, 2519636100, 177606000, 4237103862, 3977834316, 1621936232,
+    2599050516, 319893558, 3343370366, 765044144, 976657331, 7026264, 294277429, 3829376742,
+    3029627280, 2705178718, 3614653880, 230519152, 3288033233, 293525479, 3805751881, 3227511198,
+    2520308544, 3648103003, 1111086184, 437622105, 2232033852, 3239146386, 584244184, 1450926016,
+    2462430443, 3226534010, 298582169, 4214576928, 1762099469, 964985185, 1585788148, 1641127666,
+    787006566, 2315956284, 3258232694, 2275058964, 2541003317, 1508235863, 2613339827, 4080647514,
+    1152057965, 3149266279, 731345410, 914737650, 65395712, 1884566942, 1379520432, 2611027720,
+    4163073378, 2619704967, 2746552541, 1388822415, 3005141199, 843440249, 4288674003, 3136174279,
+    4051522914, 4144149433, 3427566947, 3419023197, 3758479825, 3893877676, 96899594, 1657725776,
+    253618880, 434129337, 1499045748, 2996992534, 4036042074, 2110713869, 906222950, 928326225,
+    2541827893, 1604330202, 226792470, 4022228930, 815850898, 1466012310, 3377712199, 292769859,
+    2822055597, 3225701344, 3052947004, 385831222, 705324593, 4030158636, 3540280538, 2982120874,
+    2136414455, 255762046, 3852783591, 3262064164, 2358991588, 3756586117, 4143612643, 3326743817,
+    2897365738, 807711264, 3719310016, 3721264861, 3627337076, 944539331, 3640975513, 3712525681,
+    1162911839, 2008243316, 2179489649, 2867584109, 261861553, 3570253908, 2062868357, 2220328623,
+    3857004679, 3744109002, 4138041873, 1451860932, 2364975637, 2802161722, 2680106834, 753401584,
+    1223182946, 1245401957, 4163377735, 3565815922, 2216942838, 4036140094, 71979081, 3924559643,
+    400477238, 551750683, 1174153235, 859969898, 1185921017, 1711399735, 812991545, 4051735761,
+    3549118738, 1631653329, 3631835958, 3648867800, 1206500363, 2155893137, 361030362, 3454286017,
+    2505909489, 1083595169, 453595313, 1510564703, 1706163902, 1632924345, 1381875722, 1661526119,
+    1082778324, 3571910052, 1140625929, 851544870, 1145546234, 2938573139, 907528924, 1304752338,
+    1764668294, 1788942063, 1700368828, 104979467, 1413911959, 3327497828, 1956384744, 1272712474,
+    2815637534, 3307809377, 1320574940, 1111968962, 4073107827, 434096622, 169451929, 3201183459,
+    3331028877, 2852366972, 3369830128, 2924794558, 3106537952, 3739481231, 1612955817, 4138608722,
+    2721281595, 2755775390, 843505117, 982234295, 1157276611, 814674632, 4246504726, 3532006708,
+    992340967, 1647538031, 204696133, 193866982, 3899126129, 300851698, 1379496684, 1759463683,
+    1354782756, 1374637239, 3410883240, 1073406229, 3038431791, 1053909855, 3607043270, 173719711,
+    3733903830, 171820911, 1573050589, 932781534, 4183534770, 2158849555, 372245998, 3573073830,
+    841339264, 2759200520, 1610547277, 2603293319, 3890906486, 1557138278, 3964109906, 677238797,
+    537994297, 1124184993, 4287078344, 4207654540, 2943022776, 2977947524, 3255359985, 4098397558,
+    2274666217, 2915862060, 243524940, 2467726756, 2869020032, 507521339, 3403121914, 522051455,
+    1803903108, 3471254194, 473535371, 1948602036, 3352095732, 3116527002, 1795743673, 775867940,
+    2551469548, 3757442064, 3162525227, 3765412747, 3040105484, 1927625810, 48214767, 2997207130,
+    1342349989, 2536583992, 1501320191, 3592287317, 887432730, 967585477, 3334212779, 948663609,
+    1064513472, 15386372, 2465931737, 3230242590, 3036652803, 2063155087, 1927500726, 2821790499,
+    2187774383, 501520074, 3688568496, 3606711121, 2576459247, 3176542345, 378322447, 156541411,
+    1400607301, 1406179107, 677848877, 2253753529, 193196070, 4207435024, 4166396241, 509467541,
+    2906024136, 1221753746, 3375413222, 431327897, 2749265123, 2848827671, 3412997614, 2051920238,
+    1283516885, 1300498239, 1957256104, 2634010560, 3531900395, 360276850, 1461184973, 2012063967,
+    2873572430, 2914608609, 4289554777, 1539331673, 1859532928, 4213441063, 538215691, 3512720863,
+    4258743698, 3040408445, 982396546, 343095663, 4138069496, 1021581857, 214185242, 1968079460,
+    2864275059, 3347192726, 4096783459, 3259169450, 3707808869, 142485006, 399610869, 230556456,
+    2219467721, 4191227798, 2242548189, 3136366572, 179755707, 3464881829, 452317775, 3887426070,
+    3446430233, 1473370015, 1576807208, 3964523248, 419325089, 2373067114, 1596072055, 1928415752,
+    3635452689, 1005598891, 3335462724, 3290848636, 3669078247, 1178176812, 2110774376, 3068593619,
+    1253036518, 908857731, 3631223047, 4138506423, 2903592318, 3596915748, 3289036113, 3721512676,
+    2704409359, 3386016968, 3676268074, 2185259502, 1096257611, 3360076717, 3548676554, 170167319,
+    3360064287, 3899940843, 9640,
+];
+
+pub(crate) const POW5: [&'static [u32]; 14] = [
+    &POW5_1, &POW5_2, &POW5_3, &POW5_4, &POW5_5, &POW5_6, &POW5_7, &POW5_8, &POW5_9, &POW5_10,
+    &POW5_11, &POW5_12, &POW5_13, &POW5_14,
+];
diff --git a/third_party/rust/serde_json/src/lexical/large_powers64.rs b/third_party/rust/serde_json/src/lexical/large_powers64.rs
new file mode 100644
index 0000000000..ee36561088
--- /dev/null
+++ b/third_party/rust/serde_json/src/lexical/large_powers64.rs
@@ -0,0 +1,625 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+//! Precalculated large powers for 64-bit limbs.
+
+/// Large powers (&[u64]) for base5 operations.
+const POW5_1: [u64; 1] = [5];
+const POW5_2: [u64; 1] = [25];
+const POW5_3: [u64; 1] = [625];
+const POW5_4: [u64; 1] = [390625];
+const POW5_5: [u64; 1] = [152587890625];
+const POW5_6: [u64; 2] = [3273344365508751233, 1262];
+const POW5_7: [u64; 3] = [7942358959831785217, 16807427164405733357, 1593091];
+const POW5_8: [u64; 5] = [
+    279109966635548161,
+    2554917779393558781,
+    14124656261812188652,
+    11976055582626787546,
+    2537941837315,
+];
+const POW5_9: [u64; 10] = [
+    13750482914757213185,
+    1302999927698857842,
+    14936872543252795590,
+    2788415840139466767,
+    2095640732773017264,
+    7205570348933370714,
+    7348167152523113408,
+    9285516396840364274,
+    6907659600622710236,
+    349175,
+];
+const POW5_10: [u64; 19] = [
+    8643096425819600897,
+    6743743997439985372,
+    14059704609098336919,
+    10729359125898331411,
+    4933048501514368705,
+    12258131603170554683,
+    2172371001088594721,
+    13569903330219142946,
+    13809142207969578845,
+    16716360519037769646,
+    9631256923806107285,
+    12866941232305103710,
+    1397931361048440292,
+    7619627737732970332,
+    12725409486282665900,
+    11703051443360963910,
+    9947078370803086083,
+    13966287901448440471,
+    121923442132,
+];
+const POW5_11: [u64; 38] = [
+    17679772531488845825,
+    2216509366347768155,
+    1568689219195129479,
+    5511594616325588277,
+    1067709417009240089,
+    9070650952098657518,
+    11515285870634858015,
+    2539561553659505564,
+    17604889300961091799,
+    14511540856854204724,
+    12099083339557485471,
+    7115240299237943815,
+    313979240050606788,
+    10004784664717172195,
+    15570268847930131473,
+    10359715202835930803,
+    17685054012115162812,
+    13183273382855797757,
+    7743260039872919062,
+    9284593436392572926,
+    11105921222066415013,
+    18198799323400703846,
+    16314988383739458320,
+    4387527177871570570,
+    8476708682254672590,
+    4925096874831034057,
+    14075687868072027455,
+    112866656203221926,
+    9852830467773230418,
+    25755239915196746,
+    2201493076310172510,
+    8342165458688466438,
+    13954006576066379050,
+    15193819059903295636,
+    12565616718911389531,
+    3815854855847885129,
+    15696762163583540628,
+    805,
+];
+const POW5_12: [u64; 75] = [
+    16359721904723189761,
+    5323973632697650495,
+    17187956456762001185,
+    3930387638628283780,
+    3374723710406992273,
+    16884225088663222131,
+    10967440051041439154,
+    9686916182456720060,
+    10554548046311730194,
+    7390739362393647554,
+    6316162333127736719,
+    18122464886584070891,
+    4044404959645932768,
+    3801320885861987401,
+    12080950653257274590,
+    16414324262488991299,
+    16395687498836410113,
+    12173633940896186260,
+    10843185433142632150,
+    11048169832730399808,
+    12674828934734683716,
+    17370808310130582550,
+    10500926985433408692,
+    10252725158410704555,
+    14170108270502067523,
+    3698946465517688080,
+    989984870770509463,
+    10965601426733943069,
+    11389898658438335655,
+    6901098232861256586,
+    1921335291173932590,
+    7662788640922083388,
+    9775023833308395430,
+    4640401278902814207,
+    14532050972198413359,
+    8378549018693130223,
+    11672322628395371653,
+    8930704142764178555,
+    6275193859483102017,
+    15782593304269205087,
+    8673060659034172558,
+    8018354414354334043,
+    1824896661540749038,
+    11345563346725559868,
+    14959216444480821949,
+    970189517688324683,
+    3338835207603007873,
+    17684964260791738489,
+    1436466329061721851,
+    4554134986752476101,
+    6398757850768963907,
+    4709779218751158342,
+    10033277748582410264,
+    17932125878679265063,
+    10004750887749091440,
+    256584531835386932,
+    14396282740722731628,
+    3086085133731396950,
+    17831272085689600064,
+    10573926491412564693,
+    14888061047859191737,
+    4570995450261499817,
+    10410165022312935266,
+    5691078631447480790,
+    8632710455805418155,
+    790672778942823293,
+    16505464105756800547,
+    2092171438149740401,
+    17505030673829275878,
+    1291290830058928444,
+    14856191690683232796,
+    8916773426496500052,
+    10152003807578858265,
+    13104441193763861714,
+    649395,
+];
+const POW5_13: [u64; 149] = [
+    15308384451594534913,
+    17913664074042735335,
+    6115977719198531863,
+    5794980608663993169,
+    16544350702855106930,
+    9253787637781258566,
+    4977988951675168190,
+    9087837664087448770,
+    2098480401110016986,
+    15474332540882100712,
+    14042133997396540944,
+    1090855284423485362,
+    12639956485351058381,
+    1454115676006639319,
+    3180465001342538023,
+    14649076551958697729,
+    9801292446545910916,
+    13552201410826594004,
+    6101141927469189381,
+    1881431857880609316,
+    4907847477899433595,
+    8714572486973123228,
+    3514969632331374520,
+    11667642286891470094,
+    2391499697425323350,
+    17486585679659076043,
+    18267223761882105642,
+    2886610765822313148,
+    9302834862968900288,
+    15246507846733637044,
+    15924227519624562840,
+    9743741243284697760,
+    3159780987244964246,
+    7304816812369628428,
+    17584602612559717809,
+    4146812420657846766,
+    14525415362681041515,
+    8477630142371600195,
+    4380695748062263745,
+    12119915994367943173,
+    16970630866565485122,
+    4332724980155264503,
+    8079943140620527639,
+    1687908087554405626,
+    17051081099834002166,
+    12638146269730763230,
+    11883749876933445771,
+    4662462156371383785,
+    4796962238316531176,
+    3325504751659868927,
+    6469595803187862550,
+    5852556621152583005,
+    9229334792448387881,
+    17979733373938620709,
+    13951623534175792756,
+    17075879371091039277,
+    14212246479457938037,
+    4008999959804158260,
+    2414266395366403722,
+    3252733766253918247,
+    6382678985007829216,
+    2245927470982310841,
+    13790724502051307301,
+    13116936866733148041,
+    9718402891306794538,
+    13516274400356104875,
+    17859223875778049403,
+    4396895129099725471,
+    3563053650368467915,
+    12176845952536972668,
+    3492050964335269015,
+    2740656767075170753,
+    4409704077614761919,
+    10237775279597492710,
+    3314206875098230827,
+    16437361028114095448,
+    12361736225407656572,
+    16792510651790145480,
+    11449053143229929935,
+    18336641737580333136,
+    6558939822118891088,
+    4606255756908155300,
+    2360792578991605004,
+    160428430149144538,
+    11644861220729221511,
+    10785178451159739786,
+    14923560618031934681,
+    1902620814992781610,
+    14064076995338910412,
+    11547019064112212657,
+    16847481479966225734,
+    8331994491163145469,
+    11739712981738851885,
+    8008309968651120619,
+    10266969595459035264,
+    15175153381217702033,
+    12208659352573720245,
+    7714061140750342961,
+    2892831567213510541,
+    15453714249045017319,
+    71020323573871677,
+    15431137995750602633,
+    5659146884637671933,
+    5998809010488554503,
+    16552192379299157850,
+    1192197967194298797,
+    16157555793424861524,
+    10929371590994640255,
+    3194469143425738352,
+    6651586784672005225,
+    11062427140788057791,
+    6834443579468668318,
+    16421563197797455922,
+    6251046422506172884,
+    13952303462156793860,
+    16632486601871393224,
+    11313454360291325172,
+    5587835232504462834,
+    3105197524618514637,
+    18268568531031972989,
+    2397205535804309313,
+    59413027864729597,
+    11869878125348715710,
+    12592801707270523266,
+    8070632061321113656,
+    18403647807860650811,
+    267109013517069093,
+    6537214311028855260,
+    5220826919973709902,
+    3448740582779163661,
+    16822239213112884941,
+    5975299384311048185,
+    10294433804430712138,
+    4739856055412448774,
+    12057273038326387897,
+    13119002941950056609,
+    3354445304051737058,
+    13592813067499314594,
+    3890182464434078629,
+    17820384357466425060,
+    9785228118969879380,
+    1778431746734556271,
+    10075313876350055029,
+    13994048489400919028,
+    17948287074199726448,
+    2815088342305858722,
+    2676626035777198370,
+    1174257960026283968,
+    421714788677,
+];
+const POW5_14: [u64; 298] = [
+    11471884475673051137,
+    8902860357476377573,
+    13350296775839230505,
+    10609191786344608888,
+    7261211985859587338,
+    11439672689354862964,
+    16789708072300570627,
+    4607056528866348430,
+    3202978990421512997,
+    2024899620433984146,
+    17666950207239811774,
+    4233228489390288200,
+    9137580478688460738,
+    4060411066587388546,
+    11119949806060600124,
+    867715462473090103,
+    14382394941384869610,
+    4856042377419278489,
+    8265605599571137921,
+    538981667666252469,
+    4270263388700786523,
+    3281140600308898503,
+    4121392524544394174,
+    2077884106245940229,
+    9773041957329767574,
+    7550623316597646685,
+    8611033926449791714,
+    18137922955420802793,
+    2796546741236224013,
+    15477096484628446761,
+    9517540128113714010,
+    9471917970500821378,
+    15938570248662483124,
+    5228016831978462619,
+    15720991252586974501,
+    7662829825220776698,
+    17328310068068434348,
+    3371736428170309730,
+    3803724952191098855,
+    13115926536504376719,
+    16752571196153442257,
+    16540185467776259880,
+    3432518182450051120,
+    5880364967211798870,
+    12355748840305392783,
+    14196090758536469575,
+    7370123524686686319,
+    6819740424617592686,
+    13037938013537368753,
+    15029273671291927100,
+    3671312928327205696,
+    7473228676544792780,
+    17234079691312938123,
+    14164740848093544419,
+    13169904779481875902,
+    7179036968465894054,
+    8244653688947194445,
+    17179797746073799490,
+    5591970751047577674,
+    17530550506268329742,
+    5965746721852312330,
+    1604149463243472865,
+    7734199791463116918,
+    11305790396015856714,
+    4441196105025505137,
+    13046431581185664762,
+    124776524294606713,
+    1134521334706523966,
+    11671728093344476434,
+    14103440020972933148,
+    3966727403013869059,
+    9828094508409132821,
+    4355682486381147287,
+    10261407143988481234,
+    3800455155249557199,
+    12700901937937547500,
+    18184475466894579360,
+    13267691151779895412,
+    4714157123477697445,
+    10770360171308585263,
+    9083344917597998040,
+    12078649873810212155,
+    18218989082046199377,
+    4454285072780637351,
+    5287307245618354742,
+    16042289702059031730,
+    4131926574212754010,
+    217692071448455473,
+    3624845916216282093,
+    2901203491797614218,
+    6679177724033967080,
+    44561358851332790,
+    9094639944041587162,
+    13690915012276084311,
+    1408896670826320686,
+    5359130319612337580,
+    6148412925099835601,
+    5211368532286409612,
+    11386360825549027374,
+    16895182466965795071,
+    3392940493846427241,
+    438089879085393580,
+    4783928372776399972,
+    6278117363595909959,
+    12569481049412674733,
+    15648622492570893902,
+    1966316336235305115,
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+    730863073501675978,
+    16750118380379734815,
+    9640,
+];
+
+pub(crate) const POW5: [&[u64]; 14] = [
+    &POW5_1, &POW5_2, &POW5_3, &POW5_4, &POW5_5, &POW5_6, &POW5_7, &POW5_8, &POW5_9, &POW5_10,
+    &POW5_11, &POW5_12, &POW5_13, &POW5_14,
+];
diff --git a/third_party/rust/serde_json/src/lexical/math.rs b/third_party/rust/serde_json/src/lexical/math.rs
new file mode 100644
index 0000000000..37cc1d24ad
--- /dev/null
+++ b/third_party/rust/serde_json/src/lexical/math.rs
@@ -0,0 +1,886 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+//! Building-blocks for arbitrary-precision math.
+//!
+//! These algorithms assume little-endian order for the large integer
+//! buffers, so for a `vec![0, 1, 2, 3]`, `3` is the most significant limb,
+//! and `0` is the least significant limb.
+
+use super::large_powers;
+use super::num::*;
+use super::small_powers::*;
+use alloc::vec::Vec;
+use core::{cmp, iter, mem};
+
+// ALIASES
+// -------
+
+//  Type for a single limb of the big integer.
+//
+//  A limb is analogous to a digit in base10, except, it stores 32-bit
+//  or 64-bit numbers instead.
+//
+//  This should be all-known 64-bit platforms supported by Rust.
+//      https://forge.rust-lang.org/platform-support.html
+//
+//  Platforms where native 128-bit multiplication is explicitly supported:
+//      - x86_64 (Supported via `MUL`).
+//      - mips64 (Supported via `DMULTU`, which `HI` and `LO` can be read-from).
+//
+//  Platforms where native 64-bit multiplication is supported and
+//  you can extract hi-lo for 64-bit multiplications.
+//      aarch64 (Requires `UMULH` and `MUL` to capture high and low bits).
+//      powerpc64 (Requires `MULHDU` and `MULLD` to capture high and low bits).
+//
+//  Platforms where native 128-bit multiplication is not supported,
+//  requiring software emulation.
+//      sparc64 (`UMUL` only supported double-word arguments).
+
+// 32-BIT LIMB
+#[cfg(limb_width_32)]
+pub type Limb = u32;
+
+#[cfg(limb_width_32)]
+pub const POW5_LIMB: &[Limb] = &POW5_32;
+
+#[cfg(limb_width_32)]
+pub const POW10_LIMB: &[Limb] = &POW10_32;
+
+#[cfg(limb_width_32)]
+type Wide = u64;
+
+// 64-BIT LIMB
+#[cfg(limb_width_64)]
+pub type Limb = u64;
+
+#[cfg(limb_width_64)]
+pub const POW5_LIMB: &[Limb] = &POW5_64;
+
+#[cfg(limb_width_64)]
+pub const POW10_LIMB: &[Limb] = &POW10_64;
+
+#[cfg(limb_width_64)]
+type Wide = u128;
+
+/// Cast to limb type.
+#[inline]
+pub(crate) fn as_limb<T: Integer>(t: T) -> Limb {
+    Limb::as_cast(t)
+}
+
+/// Cast to wide type.
+#[inline]
+fn as_wide<T: Integer>(t: T) -> Wide {
+    Wide::as_cast(t)
+}
+
+// SPLIT
+// -----
+
+/// Split u64 into limbs, in little-endian order.
+#[inline]
+#[cfg(limb_width_32)]
+fn split_u64(x: u64) -> [Limb; 2] {
+    [as_limb(x), as_limb(x >> 32)]
+}
+
+/// Split u64 into limbs, in little-endian order.
+#[inline]
+#[cfg(limb_width_64)]
+fn split_u64(x: u64) -> [Limb; 1] {
+    [as_limb(x)]
+}
+
+// HI64
+// ----
+
+// NONZERO
+
+/// Check if any of the remaining bits are non-zero.
+#[inline]
+pub fn nonzero<T: Integer>(x: &[T], rindex: usize) -> bool {
+    let len = x.len();
+    let slc = &x[..len - rindex];
+    slc.iter().rev().any(|&x| x != T::ZERO)
+}
+
+/// Shift 64-bit integer to high 64-bits.
+#[inline]
+fn u64_to_hi64_1(r0: u64) -> (u64, bool) {
+    debug_assert!(r0 != 0);
+    let ls = r0.leading_zeros();
+    (r0 << ls, false)
+}
+
+/// Shift 2 64-bit integers to high 64-bits.
+#[inline]
+fn u64_to_hi64_2(r0: u64, r1: u64) -> (u64, bool) {
+    debug_assert!(r0 != 0);
+    let ls = r0.leading_zeros();
+    let rs = 64 - ls;
+    let v = match ls {
+        0 => r0,
+        _ => (r0 << ls) | (r1 >> rs),
+    };
+    let n = r1 << ls != 0;
+    (v, n)
+}
+
+/// Trait to export the high 64-bits from a little-endian slice.
+trait Hi64<T>: AsRef<[T]> {
+    /// Get the hi64 bits from a 1-limb slice.
+    fn hi64_1(&self) -> (u64, bool);
+
+    /// Get the hi64 bits from a 2-limb slice.
+    fn hi64_2(&self) -> (u64, bool);
+
+    /// Get the hi64 bits from a 3-limb slice.
+    fn hi64_3(&self) -> (u64, bool);
+
+    /// High-level exporter to extract the high 64 bits from a little-endian slice.
+    #[inline]
+    fn hi64(&self) -> (u64, bool) {
+        match self.as_ref().len() {
+            0 => (0, false),
+            1 => self.hi64_1(),
+            2 => self.hi64_2(),
+            _ => self.hi64_3(),
+        }
+    }
+}
+
+impl Hi64<u32> for [u32] {
+    #[inline]
+    fn hi64_1(&self) -> (u64, bool) {
+        debug_assert!(self.len() == 1);
+        let r0 = self[0] as u64;
+        u64_to_hi64_1(r0)
+    }
+
+    #[inline]
+    fn hi64_2(&self) -> (u64, bool) {
+        debug_assert!(self.len() == 2);
+        let r0 = (self[1] as u64) << 32;
+        let r1 = self[0] as u64;
+        u64_to_hi64_1(r0 | r1)
+    }
+
+    #[inline]
+    fn hi64_3(&self) -> (u64, bool) {
+        debug_assert!(self.len() >= 3);
+        let r0 = self[self.len() - 1] as u64;
+        let r1 = (self[self.len() - 2] as u64) << 32;
+        let r2 = self[self.len() - 3] as u64;
+        let (v, n) = u64_to_hi64_2(r0, r1 | r2);
+        (v, n || nonzero(self, 3))
+    }
+}
+
+impl Hi64<u64> for [u64] {
+    #[inline]
+    fn hi64_1(&self) -> (u64, bool) {
+        debug_assert!(self.len() == 1);
+        let r0 = self[0];
+        u64_to_hi64_1(r0)
+    }
+
+    #[inline]
+    fn hi64_2(&self) -> (u64, bool) {
+        debug_assert!(self.len() >= 2);
+        let r0 = self[self.len() - 1];
+        let r1 = self[self.len() - 2];
+        let (v, n) = u64_to_hi64_2(r0, r1);
+        (v, n || nonzero(self, 2))
+    }
+
+    #[inline]
+    fn hi64_3(&self) -> (u64, bool) {
+        self.hi64_2()
+    }
+}
+
+// SCALAR
+// ------
+
+// Scalar-to-scalar operations, for building-blocks for arbitrary-precision
+// operations.
+
+mod scalar {
+    use super::*;
+
+    // ADDITION
+
+    /// Add two small integers and return the resulting value and if overflow happens.
+    #[inline]
+    pub fn add(x: Limb, y: Limb) -> (Limb, bool) {
+        x.overflowing_add(y)
+    }
+
+    /// AddAssign two small integers and return if overflow happens.
+    #[inline]
+    pub fn iadd(x: &mut Limb, y: Limb) -> bool {
+        let t = add(*x, y);
+        *x = t.0;
+        t.1
+    }
+
+    // SUBTRACTION
+
+    /// Subtract two small integers and return the resulting value and if overflow happens.
+    #[inline]
+    pub fn sub(x: Limb, y: Limb) -> (Limb, bool) {
+        x.overflowing_sub(y)
+    }
+
+    /// SubAssign two small integers and return if overflow happens.
+    #[inline]
+    pub fn isub(x: &mut Limb, y: Limb) -> bool {
+        let t = sub(*x, y);
+        *x = t.0;
+        t.1
+    }
+
+    // MULTIPLICATION
+
+    /// Multiply two small integers (with carry) (and return the overflow contribution).
+    ///
+    /// Returns the (low, high) components.
+    #[inline]
+    pub fn mul(x: Limb, y: Limb, carry: Limb) -> (Limb, Limb) {
+        // Cannot overflow, as long as wide is 2x as wide. This is because
+        // the following is always true:
+        // `Wide::max_value() - (Narrow::max_value() * Narrow::max_value()) >= Narrow::max_value()`
+        let z: Wide = as_wide(x) * as_wide(y) + as_wide(carry);
+        let bits = mem::size_of::<Limb>() * 8;
+        (as_limb(z), as_limb(z >> bits))
+    }
+
+    /// Multiply two small integers (with carry) (and return if overflow happens).
+    #[inline]
+    pub fn imul(x: &mut Limb, y: Limb, carry: Limb) -> Limb {
+        let t = mul(*x, y, carry);
+        *x = t.0;
+        t.1
+    }
+} // scalar
+
+// SMALL
+// -----
+
+// Large-to-small operations, to modify a big integer from a native scalar.
+
+mod small {
+    use super::*;
+
+    // MULTIPLICATIION
+
+    /// ADDITION
+
+    /// Implied AddAssign implementation for adding a small integer to bigint.
+    ///
+    /// Allows us to choose a start-index in x to store, to allow incrementing
+    /// from a non-zero start.
+    #[inline]
+    pub fn iadd_impl(x: &mut Vec<Limb>, y: Limb, xstart: usize) {
+        if x.len() <= xstart {
+            x.push(y);
+        } else {
+            // Initial add
+            let mut carry = scalar::iadd(&mut x[xstart], y);
+
+            // Increment until overflow stops occurring.
+            let mut size = xstart + 1;
+            while carry && size < x.len() {
+                carry = scalar::iadd(&mut x[size], 1);
+                size += 1;
+            }
+
+            // If we overflowed the buffer entirely, need to add 1 to the end
+            // of the buffer.
+            if carry {
+                x.push(1);
+            }
+        }
+    }
+
+    /// AddAssign small integer to bigint.
+    #[inline]
+    pub fn iadd(x: &mut Vec<Limb>, y: Limb) {
+        iadd_impl(x, y, 0);
+    }
+
+    // SUBTRACTION
+
+    /// SubAssign small integer to bigint.
+    /// Does not do overflowing subtraction.
+    #[inline]
+    pub fn isub_impl(x: &mut Vec<Limb>, y: Limb, xstart: usize) {
+        debug_assert!(x.len() > xstart && (x[xstart] >= y || x.len() > xstart + 1));
+
+        // Initial subtraction
+        let mut carry = scalar::isub(&mut x[xstart], y);
+
+        // Increment until overflow stops occurring.
+        let mut size = xstart + 1;
+        while carry && size < x.len() {
+            carry = scalar::isub(&mut x[size], 1);
+            size += 1;
+        }
+        normalize(x);
+    }
+
+    // MULTIPLICATION
+
+    /// MulAssign small integer to bigint.
+    #[inline]
+    pub fn imul(x: &mut Vec<Limb>, y: Limb) {
+        // Multiply iteratively over all elements, adding the carry each time.
+        let mut carry: Limb = 0;
+        for xi in x.iter_mut() {
+            carry = scalar::imul(xi, y, carry);
+        }
+
+        // Overflow of value, add to end.
+        if carry != 0 {
+            x.push(carry);
+        }
+    }
+
+    /// Mul small integer to bigint.
+    #[inline]
+    pub fn mul(x: &[Limb], y: Limb) -> Vec<Limb> {
+        let mut z = Vec::<Limb>::default();
+        z.extend_from_slice(x);
+        imul(&mut z, y);
+        z
+    }
+
+    /// MulAssign by a power.
+    ///
+    /// Theoretically...
+    ///
+    /// Use an exponentiation by squaring method, since it reduces the time
+    /// complexity of the multiplication to ~`O(log(n))` for the squaring,
+    /// and `O(n*m)` for the result. Since `m` is typically a lower-order
+    /// factor, this significantly reduces the number of multiplications
+    /// we need to do. Iteratively multiplying by small powers follows
+    /// the nth triangular number series, which scales as `O(p^2)`, but
+    /// where `p` is `n+m`. In short, it scales very poorly.
+    ///
+    /// Practically....
+    ///
+    /// Exponentiation by Squaring:
+    ///     running 2 tests
+    ///     test bigcomp_f32_lexical ... bench:       1,018 ns/iter (+/- 78)
+    ///     test bigcomp_f64_lexical ... bench:       3,639 ns/iter (+/- 1,007)
+    ///
+    /// Exponentiation by Iterative Small Powers:
+    ///     running 2 tests
+    ///     test bigcomp_f32_lexical ... bench:         518 ns/iter (+/- 31)
+    ///     test bigcomp_f64_lexical ... bench:         583 ns/iter (+/- 47)
+    ///
+    /// Exponentiation by Iterative Large Powers (of 2):
+    ///     running 2 tests
+    ///     test bigcomp_f32_lexical ... bench:         671 ns/iter (+/- 31)
+    ///     test bigcomp_f64_lexical ... bench:       1,394 ns/iter (+/- 47)
+    ///
+    /// Even using worst-case scenarios, exponentiation by squaring is
+    /// significantly slower for our workloads. Just multiply by small powers,
+    /// in simple cases, and use precalculated large powers in other cases.
+    pub fn imul_pow5(x: &mut Vec<Limb>, n: u32) {
+        use super::large::KARATSUBA_CUTOFF;
+
+        let small_powers = POW5_LIMB;
+        let large_powers = large_powers::POW5;
+
+        if n == 0 {
+            // No exponent, just return.
+            // The 0-index of the large powers is `2^0`, which is 1, so we want
+            // to make sure we don't take that path with a literal 0.
+            return;
+        }
+
+        // We want to use the asymptotically faster algorithm if we're going
+        // to be using Karabatsu multiplication sometime during the result,
+        // otherwise, just use exponentiation by squaring.
+        let bit_length = 32 - n.leading_zeros() as usize;
+        debug_assert!(bit_length != 0 && bit_length <= large_powers.len());
+        if x.len() + large_powers[bit_length - 1].len() < 2 * KARATSUBA_CUTOFF {
+            // We can use iterative small powers to make this faster for the
+            // easy cases.
+
+            // Multiply by the largest small power until n < step.
+            let step = small_powers.len() - 1;
+            let power = small_powers[step];
+            let mut n = n as usize;
+            while n >= step {
+                imul(x, power);
+                n -= step;
+            }
+
+            // Multiply by the remainder.
+            imul(x, small_powers[n]);
+        } else {
+            // In theory, this code should be asymptotically a lot faster,
+            // in practice, our small::imul seems to be the limiting step,
+            // and large imul is slow as well.
+
+            // Multiply by higher order powers.
+            let mut idx: usize = 0;
+            let mut bit: usize = 1;
+            let mut n = n as usize;
+            while n != 0 {
+                if n & bit != 0 {
+                    debug_assert!(idx < large_powers.len());
+                    large::imul(x, large_powers[idx]);
+                    n ^= bit;
+                }
+                idx += 1;
+                bit <<= 1;
+            }
+        }
+    }
+
+    // BIT LENGTH
+
+    /// Get number of leading zero bits in the storage.
+    #[inline]
+    pub fn leading_zeros(x: &[Limb]) -> usize {
+        x.last().map_or(0, |x| x.leading_zeros() as usize)
+    }
+
+    /// Calculate the bit-length of the big-integer.
+    #[inline]
+    pub fn bit_length(x: &[Limb]) -> usize {
+        let bits = mem::size_of::<Limb>() * 8;
+        // Avoid overflowing, calculate via total number of bits
+        // minus leading zero bits.
+        let nlz = leading_zeros(x);
+        bits.checked_mul(x.len())
+            .map_or_else(usize::max_value, |v| v - nlz)
+    }
+
+    // SHL
+
+    /// Shift-left bits inside a buffer.
+    ///
+    /// Assumes `n < Limb::BITS`, IE, internally shifting bits.
+    #[inline]
+    pub fn ishl_bits(x: &mut Vec<Limb>, n: usize) {
+        // Need to shift by the number of `bits % Limb::BITS)`.
+        let bits = mem::size_of::<Limb>() * 8;
+        debug_assert!(n < bits);
+        if n == 0 {
+            return;
+        }
+
+        // Internally, for each item, we shift left by n, and add the previous
+        // right shifted limb-bits.
+        // For example, we transform (for u8) shifted left 2, to:
+        //      b10100100 b01000010
+        //      b10 b10010001 b00001000
+        let rshift = bits - n;
+        let lshift = n;
+        let mut prev: Limb = 0;
+        for xi in x.iter_mut() {
+            let tmp = *xi;
+            *xi <<= lshift;
+            *xi |= prev >> rshift;
+            prev = tmp;
+        }
+
+        // Always push the carry, even if it creates a non-normal result.
+        let carry = prev >> rshift;
+        if carry != 0 {
+            x.push(carry);
+        }
+    }
+
+    /// Shift-left `n` digits inside a buffer.
+    ///
+    /// Assumes `n` is not 0.
+    #[inline]
+    pub fn ishl_limbs(x: &mut Vec<Limb>, n: usize) {
+        debug_assert!(n != 0);
+        if !x.is_empty() {
+            x.reserve(n);
+            x.splice(..0, iter::repeat(0).take(n));
+        }
+    }
+
+    /// Shift-left buffer by n bits.
+    #[inline]
+    pub fn ishl(x: &mut Vec<Limb>, n: usize) {
+        let bits = mem::size_of::<Limb>() * 8;
+        // Need to pad with zeros for the number of `bits / Limb::BITS`,
+        // and shift-left with carry for `bits % Limb::BITS`.
+        let rem = n % bits;
+        let div = n / bits;
+        ishl_bits(x, rem);
+        if div != 0 {
+            ishl_limbs(x, div);
+        }
+    }
+
+    // NORMALIZE
+
+    /// Normalize the container by popping any leading zeros.
+    #[inline]
+    pub fn normalize(x: &mut Vec<Limb>) {
+        // Remove leading zero if we cause underflow. Since we're dividing
+        // by a small power, we have at max 1 int removed.
+        while x.last() == Some(&0) {
+            x.pop();
+        }
+    }
+} // small
+
+// LARGE
+// -----
+
+// Large-to-large operations, to modify a big integer from a native scalar.
+
+mod large {
+    use super::*;
+
+    // RELATIVE OPERATORS
+
+    /// Compare `x` to `y`, in little-endian order.
+    #[inline]
+    pub fn compare(x: &[Limb], y: &[Limb]) -> cmp::Ordering {
+        if x.len() > y.len() {
+            cmp::Ordering::Greater
+        } else if x.len() < y.len() {
+            cmp::Ordering::Less
+        } else {
+            let iter = x.iter().rev().zip(y.iter().rev());
+            for (&xi, &yi) in iter {
+                if xi > yi {
+                    return cmp::Ordering::Greater;
+                } else if xi < yi {
+                    return cmp::Ordering::Less;
+                }
+            }
+            // Equal case.
+            cmp::Ordering::Equal
+        }
+    }
+
+    /// Check if x is less than y.
+    #[inline]
+    pub fn less(x: &[Limb], y: &[Limb]) -> bool {
+        compare(x, y) == cmp::Ordering::Less
+    }
+
+    /// Check if x is greater than or equal to y.
+    #[inline]
+    pub fn greater_equal(x: &[Limb], y: &[Limb]) -> bool {
+        !less(x, y)
+    }
+
+    // ADDITION
+
+    /// Implied AddAssign implementation for bigints.
+    ///
+    /// Allows us to choose a start-index in x to store, so we can avoid
+    /// padding the buffer with zeros when not needed, optimized for vectors.
+    pub fn iadd_impl(x: &mut Vec<Limb>, y: &[Limb], xstart: usize) {
+        // The effective x buffer is from `xstart..x.len()`, so we need to treat
+        // that as the current range. If the effective y buffer is longer, need
+        // to resize to that, + the start index.
+        if y.len() > x.len() - xstart {
+            x.resize(y.len() + xstart, 0);
+        }
+
+        // Iteratively add elements from y to x.
+        let mut carry = false;
+        for (xi, yi) in x[xstart..].iter_mut().zip(y.iter()) {
+            // Only one op of the two can overflow, since we added at max
+            // Limb::max_value() + Limb::max_value(). Add the previous carry,
+            // and store the current carry for the next.
+            let mut tmp = scalar::iadd(xi, *yi);
+            if carry {
+                tmp |= scalar::iadd(xi, 1);
+            }
+            carry = tmp;
+        }
+
+        // Overflow from the previous bit.
+        if carry {
+            small::iadd_impl(x, 1, y.len() + xstart);
+        }
+    }
+
+    /// AddAssign bigint to bigint.
+    #[inline]
+    pub fn iadd(x: &mut Vec<Limb>, y: &[Limb]) {
+        iadd_impl(x, y, 0);
+    }
+
+    /// Add bigint to bigint.
+    #[inline]
+    pub fn add(x: &[Limb], y: &[Limb]) -> Vec<Limb> {
+        let mut z = Vec::<Limb>::default();
+        z.extend_from_slice(x);
+        iadd(&mut z, y);
+        z
+    }
+
+    // SUBTRACTION
+
+    /// SubAssign bigint to bigint.
+    pub fn isub(x: &mut Vec<Limb>, y: &[Limb]) {
+        // Basic underflow checks.
+        debug_assert!(greater_equal(x, y));
+
+        // Iteratively add elements from y to x.
+        let mut carry = false;
+        for (xi, yi) in x.iter_mut().zip(y.iter()) {
+            // Only one op of the two can overflow, since we added at max
+            // Limb::max_value() + Limb::max_value(). Add the previous carry,
+            // and store the current carry for the next.
+            let mut tmp = scalar::isub(xi, *yi);
+            if carry {
+                tmp |= scalar::isub(xi, 1);
+            }
+            carry = tmp;
+        }
+
+        if carry {
+            small::isub_impl(x, 1, y.len());
+        } else {
+            small::normalize(x);
+        }
+    }
+
+    // MULTIPLICATION
+
+    /// Number of digits to bottom-out to asymptotically slow algorithms.
+    ///
+    /// Karatsuba tends to out-perform long-multiplication at ~320-640 bits,
+    /// so we go halfway, while Newton division tends to out-perform
+    /// Algorithm D at ~1024 bits. We can toggle this for optimal performance.
+    pub const KARATSUBA_CUTOFF: usize = 32;
+
+    /// Grade-school multiplication algorithm.
+    ///
+    /// Slow, naive algorithm, using limb-bit bases and just shifting left for
+    /// each iteration. This could be optimized with numerous other algorithms,
+    /// but it's extremely simple, and works in O(n*m) time, which is fine
+    /// by me. Each iteration, of which there are `m` iterations, requires
+    /// `n` multiplications, and `n` additions, or grade-school multiplication.
+    fn long_mul(x: &[Limb], y: &[Limb]) -> Vec<Limb> {
+        // Using the immutable value, multiply by all the scalars in y, using
+        // the algorithm defined above. Use a single buffer to avoid
+        // frequent reallocations. Handle the first case to avoid a redundant
+        // addition, since we know y.len() >= 1.
+        let mut z: Vec<Limb> = small::mul(x, y[0]);
+        z.resize(x.len() + y.len(), 0);
+
+        // Handle the iterative cases.
+        for (i, &yi) in y[1..].iter().enumerate() {
+            let zi: Vec<Limb> = small::mul(x, yi);
+            iadd_impl(&mut z, &zi, i + 1);
+        }
+
+        small::normalize(&mut z);
+
+        z
+    }
+
+    /// Split two buffers into halfway, into (lo, hi).
+    #[inline]
+    pub fn karatsuba_split(z: &[Limb], m: usize) -> (&[Limb], &[Limb]) {
+        (&z[..m], &z[m..])
+    }
+
+    /// Karatsuba multiplication algorithm with roughly equal input sizes.
+    ///
+    /// Assumes `y.len() >= x.len()`.
+    fn karatsuba_mul(x: &[Limb], y: &[Limb]) -> Vec<Limb> {
+        if y.len() <= KARATSUBA_CUTOFF {
+            // Bottom-out to long division for small cases.
+            long_mul(x, y)
+        } else if x.len() < y.len() / 2 {
+            karatsuba_uneven_mul(x, y)
+        } else {
+            // Do our 3 multiplications.
+            let m = y.len() / 2;
+            let (xl, xh) = karatsuba_split(x, m);
+            let (yl, yh) = karatsuba_split(y, m);
+            let sumx = add(xl, xh);
+            let sumy = add(yl, yh);
+            let z0 = karatsuba_mul(xl, yl);
+            let mut z1 = karatsuba_mul(&sumx, &sumy);
+            let z2 = karatsuba_mul(xh, yh);
+            // Properly scale z1, which is `z1 - z2 - zo`.
+            isub(&mut z1, &z2);
+            isub(&mut z1, &z0);
+
+            // Create our result, which is equal to, in little-endian order:
+            // [z0, z1 - z2 - z0, z2]
+            //  z1 must be shifted m digits (2^(32m)) over.
+            //  z2 must be shifted 2*m digits (2^(64m)) over.
+            let len = z0.len().max(m + z1.len()).max(2 * m + z2.len());
+            let mut result = z0;
+            result.reserve_exact(len - result.len());
+            iadd_impl(&mut result, &z1, m);
+            iadd_impl(&mut result, &z2, 2 * m);
+
+            result
+        }
+    }
+
+    /// Karatsuba multiplication algorithm where y is substantially larger than x.
+    ///
+    /// Assumes `y.len() >= x.len()`.
+    fn karatsuba_uneven_mul(x: &[Limb], mut y: &[Limb]) -> Vec<Limb> {
+        let mut result = Vec::<Limb>::default();
+        result.resize(x.len() + y.len(), 0);
+
+        // This effectively is like grade-school multiplication between
+        // two numbers, except we're using splits on `y`, and the intermediate
+        // step is a Karatsuba multiplication.
+        let mut start = 0;
+        while !y.is_empty() {
+            let m = x.len().min(y.len());
+            let (yl, yh) = karatsuba_split(y, m);
+            let prod = karatsuba_mul(x, yl);
+            iadd_impl(&mut result, &prod, start);
+            y = yh;
+            start += m;
+        }
+        small::normalize(&mut result);
+
+        result
+    }
+
+    /// Forwarder to the proper Karatsuba algorithm.
+    #[inline]
+    fn karatsuba_mul_fwd(x: &[Limb], y: &[Limb]) -> Vec<Limb> {
+        if x.len() < y.len() {
+            karatsuba_mul(x, y)
+        } else {
+            karatsuba_mul(y, x)
+        }
+    }
+
+    /// MulAssign bigint to bigint.
+    #[inline]
+    pub fn imul(x: &mut Vec<Limb>, y: &[Limb]) {
+        if y.len() == 1 {
+            small::imul(x, y[0]);
+        } else {
+            // We're not really in a condition where using Karatsuba
+            // multiplication makes sense, so we're just going to use long
+            // division. ~20% speedup compared to:
+            //      *x = karatsuba_mul_fwd(x, y);
+            *x = karatsuba_mul_fwd(x, y);
+        }
+    }
+} // large
+
+// TRAITS
+// ------
+
+/// Traits for shared operations for big integers.
+///
+/// None of these are implemented using normal traits, since these
+/// are very expensive operations, and we want to deliberately
+/// and explicitly use these functions.
+pub(crate) trait Math: Clone + Sized + Default {
+    // DATA
+
+    /// Get access to the underlying data
+    fn data(&self) -> &Vec<Limb>;
+
+    /// Get access to the underlying data
+    fn data_mut(&mut self) -> &mut Vec<Limb>;
+
+    // RELATIVE OPERATIONS
+
+    /// Compare self to y.
+    #[inline]
+    fn compare(&self, y: &Self) -> cmp::Ordering {
+        large::compare(self.data(), y.data())
+    }
+
+    // PROPERTIES
+
+    /// Get the high 64-bits from the bigint and if there are remaining bits.
+    #[inline]
+    fn hi64(&self) -> (u64, bool) {
+        self.data().as_slice().hi64()
+    }
+
+    /// Calculate the bit-length of the big-integer.
+    /// Returns usize::max_value() if the value overflows,
+    /// IE, if `self.data().len() > usize::max_value() / 8`.
+    #[inline]
+    fn bit_length(&self) -> usize {
+        small::bit_length(self.data())
+    }
+
+    // INTEGER CONVERSIONS
+
+    /// Create new big integer from u64.
+    #[inline]
+    fn from_u64(x: u64) -> Self {
+        let mut v = Self::default();
+        let slc = split_u64(x);
+        v.data_mut().extend_from_slice(&slc);
+        v.normalize();
+        v
+    }
+
+    // NORMALIZE
+
+    /// Normalize the integer, so any leading zero values are removed.
+    #[inline]
+    fn normalize(&mut self) {
+        small::normalize(self.data_mut());
+    }
+
+    // ADDITION
+
+    /// AddAssign small integer.
+    #[inline]
+    fn iadd_small(&mut self, y: Limb) {
+        small::iadd(self.data_mut(), y);
+    }
+
+    // MULTIPLICATION
+
+    /// MulAssign small integer.
+    #[inline]
+    fn imul_small(&mut self, y: Limb) {
+        small::imul(self.data_mut(), y);
+    }
+
+    /// Multiply by a power of 2.
+    #[inline]
+    fn imul_pow2(&mut self, n: u32) {
+        self.ishl(n as usize);
+    }
+
+    /// Multiply by a power of 5.
+    #[inline]
+    fn imul_pow5(&mut self, n: u32) {
+        small::imul_pow5(self.data_mut(), n);
+    }
+
+    /// MulAssign by a power of 10.
+    #[inline]
+    fn imul_pow10(&mut self, n: u32) {
+        self.imul_pow5(n);
+        self.imul_pow2(n);
+    }
+
+    // SHIFTS
+
+    /// Shift-left the entire buffer n bits.
+    #[inline]
+    fn ishl(&mut self, n: usize) {
+        small::ishl(self.data_mut(), n);
+    }
+}
diff --git a/third_party/rust/serde_json/src/lexical/mod.rs b/third_party/rust/serde_json/src/lexical/mod.rs
new file mode 100644
index 0000000000..b1a45e218d
--- /dev/null
+++ b/third_party/rust/serde_json/src/lexical/mod.rs
@@ -0,0 +1,38 @@
+// The code in this module is derived from the `lexical` crate by @Alexhuszagh
+// which the author condensed into this minimal subset for use in serde_json.
+// For the serde_json use case we care more about reliably round tripping all
+// possible floating point values than about parsing any arbitrarily long string
+// of digits with perfect accuracy, as the latter would take a high cost in
+// compile time and performance.
+//
+// Dual licensed as MIT and Apache 2.0 just like the rest of serde_json, but
+// copyright Alexander Huszagh.
+
+//! Fast, minimal float-parsing algorithm.
+
+// MODULES
+pub(crate) mod algorithm;
+mod bhcomp;
+mod bignum;
+mod cached;
+mod cached_float80;
+mod digit;
+mod errors;
+pub(crate) mod exponent;
+pub(crate) mod float;
+mod large_powers;
+pub(crate) mod math;
+pub(crate) mod num;
+pub(crate) mod parse;
+pub(crate) mod rounding;
+mod shift;
+mod small_powers;
+
+#[cfg(limb_width_32)]
+mod large_powers32;
+
+#[cfg(limb_width_64)]
+mod large_powers64;
+
+// API
+pub use self::parse::{parse_concise_float, parse_truncated_float};
diff --git a/third_party/rust/serde_json/src/lexical/num.rs b/third_party/rust/serde_json/src/lexical/num.rs
new file mode 100644
index 0000000000..e47e003419
--- /dev/null
+++ b/third_party/rust/serde_json/src/lexical/num.rs
@@ -0,0 +1,440 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+//! Utilities for Rust numbers.
+
+use core::ops;
+
+/// Precalculated values of radix**i for i in range [0, arr.len()-1].
+/// Each value can be **exactly** represented as that type.
+const F32_POW10: [f32; 11] = [
+    1.0,
+    10.0,
+    100.0,
+    1000.0,
+    10000.0,
+    100000.0,
+    1000000.0,
+    10000000.0,
+    100000000.0,
+    1000000000.0,
+    10000000000.0,
+];
+
+/// Precalculated values of radix**i for i in range [0, arr.len()-1].
+/// Each value can be **exactly** represented as that type.
+const F64_POW10: [f64; 23] = [
+    1.0,
+    10.0,
+    100.0,
+    1000.0,
+    10000.0,
+    100000.0,
+    1000000.0,
+    10000000.0,
+    100000000.0,
+    1000000000.0,
+    10000000000.0,
+    100000000000.0,
+    1000000000000.0,
+    10000000000000.0,
+    100000000000000.0,
+    1000000000000000.0,
+    10000000000000000.0,
+    100000000000000000.0,
+    1000000000000000000.0,
+    10000000000000000000.0,
+    100000000000000000000.0,
+    1000000000000000000000.0,
+    10000000000000000000000.0,
+];
+
+/// Type that can be converted to primitive with `as`.
+pub trait AsPrimitive: Sized + Copy + PartialOrd {
+    fn as_u32(self) -> u32;
+    fn as_u64(self) -> u64;
+    fn as_u128(self) -> u128;
+    fn as_usize(self) -> usize;
+    fn as_f32(self) -> f32;
+    fn as_f64(self) -> f64;
+}
+
+macro_rules! as_primitive_impl {
+    ($($ty:ident)*) => {
+        $(
+            impl AsPrimitive for $ty {
+                #[inline]
+                fn as_u32(self) -> u32 {
+                    self as u32
+                }
+
+                #[inline]
+                fn as_u64(self) -> u64 {
+                    self as u64
+                }
+
+                #[inline]
+                fn as_u128(self) -> u128 {
+                    self as u128
+                }
+
+                #[inline]
+                fn as_usize(self) -> usize {
+                    self as usize
+                }
+
+                #[inline]
+                fn as_f32(self) -> f32 {
+                    self as f32
+                }
+
+                #[inline]
+                fn as_f64(self) -> f64 {
+                    self as f64
+                }
+            }
+        )*
+    };
+}
+
+as_primitive_impl! { u32 u64 u128 usize f32 f64 }
+
+/// An interface for casting between machine scalars.
+pub trait AsCast: AsPrimitive {
+    /// Creates a number from another value that can be converted into
+    /// a primitive via the `AsPrimitive` trait.
+    fn as_cast<N: AsPrimitive>(n: N) -> Self;
+}
+
+macro_rules! as_cast_impl {
+    ($ty:ident, $method:ident) => {
+        impl AsCast for $ty {
+            #[inline]
+            fn as_cast<N: AsPrimitive>(n: N) -> Self {
+                n.$method()
+            }
+        }
+    };
+}
+
+as_cast_impl!(u32, as_u32);
+as_cast_impl!(u64, as_u64);
+as_cast_impl!(u128, as_u128);
+as_cast_impl!(usize, as_usize);
+as_cast_impl!(f32, as_f32);
+as_cast_impl!(f64, as_f64);
+
+/// Numerical type trait.
+pub trait Number: AsCast + ops::Add<Output = Self> {}
+
+macro_rules! number_impl {
+    ($($ty:ident)*) => {
+        $(
+            impl Number for $ty {}
+        )*
+    };
+}
+
+number_impl! { u32 u64 u128 usize f32 f64 }
+
+/// Defines a trait that supports integral operations.
+pub trait Integer: Number + ops::BitAnd<Output = Self> + ops::Shr<i32, Output = Self> {
+    const ZERO: Self;
+}
+
+macro_rules! integer_impl {
+    ($($ty:tt)*) => {
+        $(
+            impl Integer for $ty {
+                const ZERO: Self = 0;
+            }
+        )*
+    };
+}
+
+integer_impl! { u32 u64 u128 usize }
+
+/// Type trait for the mantissa type.
+pub trait Mantissa: Integer {
+    /// Mask to extract the high bits from the integer.
+    const HIMASK: Self;
+    /// Mask to extract the low bits from the integer.
+    const LOMASK: Self;
+    /// Full size of the integer, in bits.
+    const FULL: i32;
+    /// Half size of the integer, in bits.
+    const HALF: i32 = Self::FULL / 2;
+}
+
+impl Mantissa for u64 {
+    const HIMASK: u64 = 0xFFFFFFFF00000000;
+    const LOMASK: u64 = 0x00000000FFFFFFFF;
+    const FULL: i32 = 64;
+}
+
+/// Get exact exponent limit for radix.
+pub trait Float: Number {
+    /// Unsigned type of the same size.
+    type Unsigned: Integer;
+
+    /// Literal zero.
+    const ZERO: Self;
+    /// Maximum number of digits that can contribute in the mantissa.
+    ///
+    /// We can exactly represent a float in radix `b` from radix 2 if
+    /// `b` is divisible by 2. This function calculates the exact number of
+    /// digits required to exactly represent that float.
+    ///
+    /// According to the "Handbook of Floating Point Arithmetic",
+    /// for IEEE754, with emin being the min exponent, p2 being the
+    /// precision, and b being the radix, the number of digits follows as:
+    ///
+    /// `−emin + p2 + ⌊(emin + 1) log(2, b) − log(1 − 2^(−p2), b)⌋`
+    ///
+    /// For f32, this follows as:
+    ///     emin = -126
+    ///     p2 = 24
+    ///
+    /// For f64, this follows as:
+    ///     emin = -1022
+    ///     p2 = 53
+    ///
+    /// In Python:
+    ///     `-emin + p2 + math.floor((emin+1)*math.log(2, b) - math.log(1-2**(-p2), b))`
+    ///
+    /// This was used to calculate the maximum number of digits for [2, 36].
+    const MAX_DIGITS: usize;
+
+    // MASKS
+
+    /// Bitmask for the sign bit.
+    const SIGN_MASK: Self::Unsigned;
+    /// Bitmask for the exponent, including the hidden bit.
+    const EXPONENT_MASK: Self::Unsigned;
+    /// Bitmask for the hidden bit in exponent, which is an implicit 1 in the fraction.
+    const HIDDEN_BIT_MASK: Self::Unsigned;
+    /// Bitmask for the mantissa (fraction), excluding the hidden bit.
+    const MANTISSA_MASK: Self::Unsigned;
+
+    // PROPERTIES
+
+    /// Positive infinity as bits.
+    const INFINITY_BITS: Self::Unsigned;
+    /// Positive infinity as bits.
+    const NEGATIVE_INFINITY_BITS: Self::Unsigned;
+    /// Size of the significand (mantissa) without hidden bit.
+    const MANTISSA_SIZE: i32;
+    /// Bias of the exponet
+    const EXPONENT_BIAS: i32;
+    /// Exponent portion of a denormal float.
+    const DENORMAL_EXPONENT: i32;
+    /// Maximum exponent value in float.
+    const MAX_EXPONENT: i32;
+
+    // ROUNDING
+
+    /// Default number of bits to shift (or 64 - mantissa size - 1).
+    const DEFAULT_SHIFT: i32;
+    /// Mask to determine if a full-carry occurred (1 in bit above hidden bit).
+    const CARRY_MASK: u64;
+
+    /// Get min and max exponent limits (exact) from radix.
+    fn exponent_limit() -> (i32, i32);
+
+    /// Get the number of digits that can be shifted from exponent to mantissa.
+    fn mantissa_limit() -> i32;
+
+    // Re-exported methods from std.
+    fn pow10(self, n: i32) -> Self;
+    fn from_bits(u: Self::Unsigned) -> Self;
+    fn to_bits(self) -> Self::Unsigned;
+    fn is_sign_positive(self) -> bool;
+    fn is_sign_negative(self) -> bool;
+
+    /// Returns true if the float is a denormal.
+    #[inline]
+    fn is_denormal(self) -> bool {
+        self.to_bits() & Self::EXPONENT_MASK == Self::Unsigned::ZERO
+    }
+
+    /// Returns true if the float is a NaN or Infinite.
+    #[inline]
+    fn is_special(self) -> bool {
+        self.to_bits() & Self::EXPONENT_MASK == Self::EXPONENT_MASK
+    }
+
+    /// Returns true if the float is infinite.
+    #[inline]
+    fn is_inf(self) -> bool {
+        self.is_special() && (self.to_bits() & Self::MANTISSA_MASK) == Self::Unsigned::ZERO
+    }
+
+    /// Get exponent component from the float.
+    #[inline]
+    fn exponent(self) -> i32 {
+        if self.is_denormal() {
+            return Self::DENORMAL_EXPONENT;
+        }
+
+        let bits = self.to_bits();
+        let biased_e = ((bits & Self::EXPONENT_MASK) >> Self::MANTISSA_SIZE).as_u32();
+        biased_e as i32 - Self::EXPONENT_BIAS
+    }
+
+    /// Get mantissa (significand) component from float.
+    #[inline]
+    fn mantissa(self) -> Self::Unsigned {
+        let bits = self.to_bits();
+        let s = bits & Self::MANTISSA_MASK;
+        if !self.is_denormal() {
+            s + Self::HIDDEN_BIT_MASK
+        } else {
+            s
+        }
+    }
+
+    /// Get next greater float for a positive float.
+    /// Value must be >= 0.0 and < INFINITY.
+    #[inline]
+    fn next_positive(self) -> Self {
+        debug_assert!(self.is_sign_positive() && !self.is_inf());
+        Self::from_bits(self.to_bits() + Self::Unsigned::as_cast(1u32))
+    }
+
+    /// Round a positive number to even.
+    #[inline]
+    fn round_positive_even(self) -> Self {
+        if self.mantissa() & Self::Unsigned::as_cast(1u32) == Self::Unsigned::as_cast(1u32) {
+            self.next_positive()
+        } else {
+            self
+        }
+    }
+}
+
+impl Float for f32 {
+    type Unsigned = u32;
+
+    const ZERO: f32 = 0.0;
+    const MAX_DIGITS: usize = 114;
+    const SIGN_MASK: u32 = 0x80000000;
+    const EXPONENT_MASK: u32 = 0x7F800000;
+    const HIDDEN_BIT_MASK: u32 = 0x00800000;
+    const MANTISSA_MASK: u32 = 0x007FFFFF;
+    const INFINITY_BITS: u32 = 0x7F800000;
+    const NEGATIVE_INFINITY_BITS: u32 = Self::INFINITY_BITS | Self::SIGN_MASK;
+    const MANTISSA_SIZE: i32 = 23;
+    const EXPONENT_BIAS: i32 = 127 + Self::MANTISSA_SIZE;
+    const DENORMAL_EXPONENT: i32 = 1 - Self::EXPONENT_BIAS;
+    const MAX_EXPONENT: i32 = 0xFF - Self::EXPONENT_BIAS;
+    const DEFAULT_SHIFT: i32 = u64::FULL - f32::MANTISSA_SIZE - 1;
+    const CARRY_MASK: u64 = 0x1000000;
+
+    #[inline]
+    fn exponent_limit() -> (i32, i32) {
+        (-10, 10)
+    }
+
+    #[inline]
+    fn mantissa_limit() -> i32 {
+        7
+    }
+
+    #[inline]
+    fn pow10(self, n: i32) -> f32 {
+        // Check the exponent is within bounds in debug builds.
+        debug_assert!({
+            let (min, max) = Self::exponent_limit();
+            n >= min && n <= max
+        });
+
+        if n > 0 {
+            self * F32_POW10[n as usize]
+        } else {
+            self / F32_POW10[-n as usize]
+        }
+    }
+
+    #[inline]
+    fn from_bits(u: u32) -> f32 {
+        f32::from_bits(u)
+    }
+
+    #[inline]
+    fn to_bits(self) -> u32 {
+        f32::to_bits(self)
+    }
+
+    #[inline]
+    fn is_sign_positive(self) -> bool {
+        f32::is_sign_positive(self)
+    }
+
+    #[inline]
+    fn is_sign_negative(self) -> bool {
+        f32::is_sign_negative(self)
+    }
+}
+
+impl Float for f64 {
+    type Unsigned = u64;
+
+    const ZERO: f64 = 0.0;
+    const MAX_DIGITS: usize = 769;
+    const SIGN_MASK: u64 = 0x8000000000000000;
+    const EXPONENT_MASK: u64 = 0x7FF0000000000000;
+    const HIDDEN_BIT_MASK: u64 = 0x0010000000000000;
+    const MANTISSA_MASK: u64 = 0x000FFFFFFFFFFFFF;
+    const INFINITY_BITS: u64 = 0x7FF0000000000000;
+    const NEGATIVE_INFINITY_BITS: u64 = Self::INFINITY_BITS | Self::SIGN_MASK;
+    const MANTISSA_SIZE: i32 = 52;
+    const EXPONENT_BIAS: i32 = 1023 + Self::MANTISSA_SIZE;
+    const DENORMAL_EXPONENT: i32 = 1 - Self::EXPONENT_BIAS;
+    const MAX_EXPONENT: i32 = 0x7FF - Self::EXPONENT_BIAS;
+    const DEFAULT_SHIFT: i32 = u64::FULL - f64::MANTISSA_SIZE - 1;
+    const CARRY_MASK: u64 = 0x20000000000000;
+
+    #[inline]
+    fn exponent_limit() -> (i32, i32) {
+        (-22, 22)
+    }
+
+    #[inline]
+    fn mantissa_limit() -> i32 {
+        15
+    }
+
+    #[inline]
+    fn pow10(self, n: i32) -> f64 {
+        // Check the exponent is within bounds in debug builds.
+        debug_assert!({
+            let (min, max) = Self::exponent_limit();
+            n >= min && n <= max
+        });
+
+        if n > 0 {
+            self * F64_POW10[n as usize]
+        } else {
+            self / F64_POW10[-n as usize]
+        }
+    }
+
+    #[inline]
+    fn from_bits(u: u64) -> f64 {
+        f64::from_bits(u)
+    }
+
+    #[inline]
+    fn to_bits(self) -> u64 {
+        f64::to_bits(self)
+    }
+
+    #[inline]
+    fn is_sign_positive(self) -> bool {
+        f64::is_sign_positive(self)
+    }
+
+    #[inline]
+    fn is_sign_negative(self) -> bool {
+        f64::is_sign_negative(self)
+    }
+}
diff --git a/third_party/rust/serde_json/src/lexical/parse.rs b/third_party/rust/serde_json/src/lexical/parse.rs
new file mode 100644
index 0000000000..e3d7f1e871
--- /dev/null
+++ b/third_party/rust/serde_json/src/lexical/parse.rs
@@ -0,0 +1,83 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+use super::algorithm::*;
+use super::bhcomp::*;
+use super::digit::*;
+use super::exponent::*;
+use super::num::*;
+
+// PARSERS
+// -------
+
+/// Parse float for which the entire integer and fraction parts fit into a 64
+/// bit mantissa.
+pub fn parse_concise_float<F>(mantissa: u64, mant_exp: i32) -> F
+where
+    F: Float,
+{
+    if let Some(float) = fast_path(mantissa, mant_exp) {
+        return float;
+    }
+
+    // Moderate path (use an extended 80-bit representation).
+    let truncated = false;
+    let (fp, valid) = moderate_path::<F>(mantissa, mant_exp, truncated);
+    if valid {
+        return fp.into_float::<F>();
+    }
+
+    let b = fp.into_downward_float::<F>();
+    if b.is_special() {
+        // We have a non-finite number, we get to leave early.
+        return b;
+    }
+
+    // Slow path, fast path didn't work.
+    let mut buffer = itoa::Buffer::new();
+    let integer = buffer.format(mantissa).as_bytes();
+    let fraction = &[];
+    bhcomp(b, integer, fraction, mant_exp)
+}
+
+/// Parse float from extracted float components.
+///
+/// * `integer`     - Slice containing the integer digits.
+/// * `fraction`    - Slice containing the fraction digits.
+/// * `exponent`    - Parsed, 32-bit exponent.
+///
+/// Precondition: The integer must not have leading zeros.
+pub fn parse_truncated_float<F>(integer: &[u8], mut fraction: &[u8], exponent: i32) -> F
+where
+    F: Float,
+{
+    // Trim trailing zeroes from the fraction part.
+    while fraction.last() == Some(&b'0') {
+        fraction = &fraction[..fraction.len() - 1];
+    }
+
+    // Calculate the number of truncated digits.
+    let mut truncated = 0;
+    let mut mantissa: u64 = 0;
+    let mut iter = integer.iter().chain(fraction);
+    for &c in &mut iter {
+        mantissa = match add_digit(mantissa, to_digit(c).unwrap()) {
+            Some(v) => v,
+            None => {
+                truncated = 1 + iter.count();
+                break;
+            }
+        };
+    }
+
+    let mant_exp = mantissa_exponent(exponent, fraction.len(), truncated);
+    let is_truncated = true;
+
+    fallback_path(
+        integer,
+        fraction,
+        mantissa,
+        exponent,
+        mant_exp,
+        is_truncated,
+    )
+}
diff --git a/third_party/rust/serde_json/src/lexical/rounding.rs b/third_party/rust/serde_json/src/lexical/rounding.rs
new file mode 100644
index 0000000000..6ec1292aa5
--- /dev/null
+++ b/third_party/rust/serde_json/src/lexical/rounding.rs
@@ -0,0 +1,231 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+//! Defines rounding schemes for floating-point numbers.
+
+use super::float::ExtendedFloat;
+use super::num::*;
+use super::shift::*;
+use core::mem;
+
+// MASKS
+
+/// Calculate a scalar factor of 2 above the halfway point.
+#[inline]
+pub(crate) fn nth_bit(n: u64) -> u64 {
+    let bits: u64 = mem::size_of::<u64>() as u64 * 8;
+    debug_assert!(n < bits, "nth_bit() overflow in shl.");
+
+    1 << n
+}
+
+/// Generate a bitwise mask for the lower `n` bits.
+#[inline]
+pub(crate) fn lower_n_mask(n: u64) -> u64 {
+    let bits: u64 = mem::size_of::<u64>() as u64 * 8;
+    debug_assert!(n <= bits, "lower_n_mask() overflow in shl.");
+
+    if n == bits {
+        u64::max_value()
+    } else {
+        (1 << n) - 1
+    }
+}
+
+/// Calculate the halfway point for the lower `n` bits.
+#[inline]
+pub(crate) fn lower_n_halfway(n: u64) -> u64 {
+    let bits: u64 = mem::size_of::<u64>() as u64 * 8;
+    debug_assert!(n <= bits, "lower_n_halfway() overflow in shl.");
+
+    if n == 0 {
+        0
+    } else {
+        nth_bit(n - 1)
+    }
+}
+
+/// Calculate a bitwise mask with `n` 1 bits starting at the `bit` position.
+#[inline]
+pub(crate) fn internal_n_mask(bit: u64, n: u64) -> u64 {
+    let bits: u64 = mem::size_of::<u64>() as u64 * 8;
+    debug_assert!(bit <= bits, "internal_n_halfway() overflow in shl.");
+    debug_assert!(n <= bits, "internal_n_halfway() overflow in shl.");
+    debug_assert!(bit >= n, "internal_n_halfway() overflow in sub.");
+
+    lower_n_mask(bit) ^ lower_n_mask(bit - n)
+}
+
+// NEAREST ROUNDING
+
+// Shift right N-bytes and round to the nearest.
+//
+// Return if we are above halfway and if we are halfway.
+#[inline]
+pub(crate) fn round_nearest(fp: &mut ExtendedFloat, shift: i32) -> (bool, bool) {
+    // Extract the truncated bits using mask.
+    // Calculate if the value of the truncated bits are either above
+    // the mid-way point, or equal to it.
+    //
+    // For example, for 4 truncated bytes, the mask would be b1111
+    // and the midway point would be b1000.
+    let mask: u64 = lower_n_mask(shift as u64);
+    let halfway: u64 = lower_n_halfway(shift as u64);
+
+    let truncated_bits = fp.mant & mask;
+    let is_above = truncated_bits > halfway;
+    let is_halfway = truncated_bits == halfway;
+
+    // Bit shift so the leading bit is in the hidden bit.
+    overflowing_shr(fp, shift);
+
+    (is_above, is_halfway)
+}
+
+// Tie rounded floating point to event.
+#[inline]
+pub(crate) fn tie_even(fp: &mut ExtendedFloat, is_above: bool, is_halfway: bool) {
+    // Extract the last bit after shifting (and determine if it is odd).
+    let is_odd = fp.mant & 1 == 1;
+
+    // Calculate if we need to roundup.
+    // We need to roundup if we are above halfway, or if we are odd
+    // and at half-way (need to tie-to-even).
+    if is_above || (is_odd && is_halfway) {
+        fp.mant += 1;
+    }
+}
+
+// Shift right N-bytes and round nearest, tie-to-even.
+//
+// Floating-point arithmetic uses round to nearest, ties to even,
+// which rounds to the nearest value, if the value is halfway in between,
+// round to an even value.
+#[inline]
+pub(crate) fn round_nearest_tie_even(fp: &mut ExtendedFloat, shift: i32) {
+    let (is_above, is_halfway) = round_nearest(fp, shift);
+    tie_even(fp, is_above, is_halfway);
+}
+
+// DIRECTED ROUNDING
+
+// Shift right N-bytes and round towards a direction.
+//
+// Return if we have any truncated bytes.
+#[inline]
+fn round_toward(fp: &mut ExtendedFloat, shift: i32) -> bool {
+    let mask: u64 = lower_n_mask(shift as u64);
+    let truncated_bits = fp.mant & mask;
+
+    // Bit shift so the leading bit is in the hidden bit.
+    overflowing_shr(fp, shift);
+
+    truncated_bits != 0
+}
+
+// Round down.
+#[inline]
+fn downard(_: &mut ExtendedFloat, _: bool) {}
+
+// Shift right N-bytes and round toward zero.
+//
+// Floating-point arithmetic defines round toward zero, which rounds
+// towards positive zero.
+#[inline]
+pub(crate) fn round_downward(fp: &mut ExtendedFloat, shift: i32) {
+    // Bit shift so the leading bit is in the hidden bit.
+    // No rounding schemes, so we just ignore everything else.
+    let is_truncated = round_toward(fp, shift);
+    downard(fp, is_truncated);
+}
+
+// ROUND TO FLOAT
+
+// Shift the ExtendedFloat fraction to the fraction bits in a native float.
+//
+// Floating-point arithmetic uses round to nearest, ties to even,
+// which rounds to the nearest value, if the value is halfway in between,
+// round to an even value.
+#[inline]
+pub(crate) fn round_to_float<F, Algorithm>(fp: &mut ExtendedFloat, algorithm: Algorithm)
+where
+    F: Float,
+    Algorithm: FnOnce(&mut ExtendedFloat, i32),
+{
+    // Calculate the difference to allow a single calculation
+    // rather than a loop, to minimize the number of ops required.
+    // This does underflow detection.
+    let final_exp = fp.exp + F::DEFAULT_SHIFT;
+    if final_exp < F::DENORMAL_EXPONENT {
+        // We would end up with a denormal exponent, try to round to more
+        // digits. Only shift right if we can avoid zeroing out the value,
+        // which requires the exponent diff to be < M::BITS. The value
+        // is already normalized, so we shouldn't have any issue zeroing
+        // out the value.
+        let diff = F::DENORMAL_EXPONENT - fp.exp;
+        if diff <= u64::FULL {
+            // We can avoid underflow, can get a valid representation.
+            algorithm(fp, diff);
+        } else {
+            // Certain underflow, assign literal 0s.
+            fp.mant = 0;
+            fp.exp = 0;
+        }
+    } else {
+        algorithm(fp, F::DEFAULT_SHIFT);
+    }
+
+    if fp.mant & F::CARRY_MASK == F::CARRY_MASK {
+        // Roundup carried over to 1 past the hidden bit.
+        shr(fp, 1);
+    }
+}
+
+// AVOID OVERFLOW/UNDERFLOW
+
+// Avoid overflow for large values, shift left as needed.
+//
+// Shift until a 1-bit is in the hidden bit, if the mantissa is not 0.
+#[inline]
+pub(crate) fn avoid_overflow<F>(fp: &mut ExtendedFloat)
+where
+    F: Float,
+{
+    // Calculate the difference to allow a single calculation
+    // rather than a loop, minimizing the number of ops required.
+    if fp.exp >= F::MAX_EXPONENT {
+        let diff = fp.exp - F::MAX_EXPONENT;
+        if diff <= F::MANTISSA_SIZE {
+            // Our overflow mask needs to start at the hidden bit, or at
+            // `F::MANTISSA_SIZE+1`, and needs to have `diff+1` bits set,
+            // to see if our value overflows.
+            let bit = (F::MANTISSA_SIZE + 1) as u64;
+            let n = (diff + 1) as u64;
+            let mask = internal_n_mask(bit, n);
+            if (fp.mant & mask) == 0 {
+                // If we have no 1-bit in the hidden-bit position,
+                // which is index 0, we need to shift 1.
+                let shift = diff + 1;
+                shl(fp, shift);
+            }
+        }
+    }
+}
+
+// ROUND TO NATIVE
+
+// Round an extended-precision float to a native float representation.
+#[inline]
+pub(crate) fn round_to_native<F, Algorithm>(fp: &mut ExtendedFloat, algorithm: Algorithm)
+where
+    F: Float,
+    Algorithm: FnOnce(&mut ExtendedFloat, i32),
+{
+    // Shift all the way left, to ensure a consistent representation.
+    // The following right-shifts do not work for a non-normalized number.
+    fp.normalize();
+
+    // Round so the fraction is in a native mantissa representation,
+    // and avoid overflow/underflow.
+    round_to_float::<F, _>(fp, algorithm);
+    avoid_overflow::<F>(fp);
+}
diff --git a/third_party/rust/serde_json/src/lexical/shift.rs b/third_party/rust/serde_json/src/lexical/shift.rs
new file mode 100644
index 0000000000..a0bae01e0f
--- /dev/null
+++ b/third_party/rust/serde_json/src/lexical/shift.rs
@@ -0,0 +1,46 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+//! Bit-shift helpers.
+
+use super::float::ExtendedFloat;
+use core::mem;
+
+// Shift extended-precision float right `shift` bytes.
+#[inline]
+pub(crate) fn shr(fp: &mut ExtendedFloat, shift: i32) {
+    let bits: u64 = mem::size_of::<u64>() as u64 * 8;
+    debug_assert!((shift as u64) < bits, "shr() overflow in shift right.");
+
+    fp.mant >>= shift;
+    fp.exp += shift;
+}
+
+// Shift extended-precision float right `shift` bytes.
+//
+// Accepts when the shift is the same as the type size, and
+// sets the value to 0.
+#[inline]
+pub(crate) fn overflowing_shr(fp: &mut ExtendedFloat, shift: i32) {
+    let bits: u64 = mem::size_of::<u64>() as u64 * 8;
+    debug_assert!(
+        (shift as u64) <= bits,
+        "overflowing_shr() overflow in shift right."
+    );
+
+    fp.mant = if shift as u64 == bits {
+        0
+    } else {
+        fp.mant >> shift
+    };
+    fp.exp += shift;
+}
+
+// Shift extended-precision float left `shift` bytes.
+#[inline]
+pub(crate) fn shl(fp: &mut ExtendedFloat, shift: i32) {
+    let bits: u64 = mem::size_of::<u64>() as u64 * 8;
+    debug_assert!((shift as u64) < bits, "shl() overflow in shift left.");
+
+    fp.mant <<= shift;
+    fp.exp -= shift;
+}
diff --git a/third_party/rust/serde_json/src/lexical/small_powers.rs b/third_party/rust/serde_json/src/lexical/small_powers.rs
new file mode 100644
index 0000000000..219d826116
--- /dev/null
+++ b/third_party/rust/serde_json/src/lexical/small_powers.rs
@@ -0,0 +1,70 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+//! Pre-computed small powers.
+
+// 32 BIT
+#[cfg(limb_width_32)]
+pub(crate) const POW5_32: [u32; 14] = [
+    1, 5, 25, 125, 625, 3125, 15625, 78125, 390625, 1953125, 9765625, 48828125, 244140625,
+    1220703125,
+];
+
+#[cfg(limb_width_32)]
+pub(crate) const POW10_32: [u32; 10] = [
+    1, 10, 100, 1000, 10000, 100000, 1000000, 10000000, 100000000, 1000000000,
+];
+
+// 64 BIT
+#[cfg(limb_width_64)]
+pub(crate) const POW5_64: [u64; 28] = [
+    1,
+    5,
+    25,
+    125,
+    625,
+    3125,
+    15625,
+    78125,
+    390625,
+    1953125,
+    9765625,
+    48828125,
+    244140625,
+    1220703125,
+    6103515625,
+    30517578125,
+    152587890625,
+    762939453125,
+    3814697265625,
+    19073486328125,
+    95367431640625,
+    476837158203125,
+    2384185791015625,
+    11920928955078125,
+    59604644775390625,
+    298023223876953125,
+    1490116119384765625,
+    7450580596923828125,
+];
+pub(crate) const POW10_64: [u64; 20] = [
+    1,
+    10,
+    100,
+    1000,
+    10000,
+    100000,
+    1000000,
+    10000000,
+    100000000,
+    1000000000,
+    10000000000,
+    100000000000,
+    1000000000000,
+    10000000000000,
+    100000000000000,
+    1000000000000000,
+    10000000000000000,
+    100000000000000000,
+    1000000000000000000,
+    10000000000000000000,
+];
diff --git a/third_party/rust/serde_json/src/lib.rs b/third_party/rust/serde_json/src/lib.rs
new file mode 100644
index 0000000000..48d0fe2191
--- /dev/null
+++ b/third_party/rust/serde_json/src/lib.rs
@@ -0,0 +1,421 @@
+//! # Serde JSON
+//!
+//! JSON is a ubiquitous open-standard format that uses human-readable text to
+//! transmit data objects consisting of key-value pairs.
+//!
+//! ```json
+//! {
+//!     "name": "John Doe",
+//!     "age": 43,
+//!     "address": {
+//!         "street": "10 Downing Street",
+//!         "city": "London"
+//!     },
+//!     "phones": [
+//!         "+44 1234567",
+//!         "+44 2345678"
+//!     ]
+//! }
+//! ```
+//!
+//! There are three common ways that you might find yourself needing to work
+//! with JSON data in Rust.
+//!
+//!  - **As text data.** An unprocessed string of JSON data that you receive on
+//!    an HTTP endpoint, read from a file, or prepare to send to a remote
+//!    server.
+//!  - **As an untyped or loosely typed representation.** Maybe you want to
+//!    check that some JSON data is valid before passing it on, but without
+//!    knowing the structure of what it contains. Or you want to do very basic
+//!    manipulations like insert a key in a particular spot.
+//!  - **As a strongly typed Rust data structure.** When you expect all or most
+//!    of your data to conform to a particular structure and want to get real
+//!    work done without JSON's loosey-goosey nature tripping you up.
+//!
+//! Serde JSON provides efficient, flexible, safe ways of converting data
+//! between each of these representations.
+//!
+//! # Operating on untyped JSON values
+//!
+//! Any valid JSON data can be manipulated in the following recursive enum
+//! representation. This data structure is [`serde_json::Value`][value].
+//!
+//! ```
+//! # use serde_json::{Number, Map};
+//! #
+//! # #[allow(dead_code)]
+//! enum Value {
+//!     Null,
+//!     Bool(bool),
+//!     Number(Number),
+//!     String(String),
+//!     Array(Vec<Value>),
+//!     Object(Map<String, Value>),
+//! }
+//! ```
+//!
+//! A string of JSON data can be parsed into a `serde_json::Value` by the
+//! [`serde_json::from_str`][from_str] function. There is also
+//! [`from_slice`][from_slice] for parsing from a byte slice &[u8] and
+//! [`from_reader`][from_reader] for parsing from any `io::Read` like a File or
+//! a TCP stream.
+//!
+//! ```
+//! use serde_json::{Result, Value};
+//!
+//! fn untyped_example() -> Result<()> {
+//!     // Some JSON input data as a &str. Maybe this comes from the user.
+//!     let data = r#"
+//!         {
+//!             "name": "John Doe",
+//!             "age": 43,
+//!             "phones": [
+//!                 "+44 1234567",
+//!                 "+44 2345678"
+//!             ]
+//!         }"#;
+//!
+//!     // Parse the string of data into serde_json::Value.
+//!     let v: Value = serde_json::from_str(data)?;
+//!
+//!     // Access parts of the data by indexing with square brackets.
+//!     println!("Please call {} at the number {}", v["name"], v["phones"][0]);
+//!
+//!     Ok(())
+//! }
+//! #
+//! # fn main() {
+//! #     untyped_example().unwrap();
+//! # }
+//! ```
+//!
+//! The result of square bracket indexing like `v["name"]` is a borrow of the
+//! data at that index, so the type is `&Value`. A JSON map can be indexed with
+//! string keys, while a JSON array can be indexed with integer keys. If the
+//! type of the data is not right for the type with which it is being indexed,
+//! or if a map does not contain the key being indexed, or if the index into a
+//! vector is out of bounds, the returned element is `Value::Null`.
+//!
+//! When a `Value` is printed, it is printed as a JSON string. So in the code
+//! above, the output looks like `Please call "John Doe" at the number "+44
+//! 1234567"`. The quotation marks appear because `v["name"]` is a `&Value`
+//! containing a JSON string and its JSON representation is `"John Doe"`.
+//! Printing as a plain string without quotation marks involves converting from
+//! a JSON string to a Rust string with [`as_str()`] or avoiding the use of
+//! `Value` as described in the following section.
+//!
+//! [`as_str()`]: crate::Value::as_str
+//!
+//! The `Value` representation is sufficient for very basic tasks but can be
+//! tedious to work with for anything more significant. Error handling is
+//! verbose to implement correctly, for example imagine trying to detect the
+//! presence of unrecognized fields in the input data. The compiler is powerless
+//! to help you when you make a mistake, for example imagine typoing `v["name"]`
+//! as `v["nmae"]` in one of the dozens of places it is used in your code.
+//!
+//! # Parsing JSON as strongly typed data structures
+//!
+//! Serde provides a powerful way of mapping JSON data into Rust data structures
+//! largely automatically.
+//!
+//! ```
+//! use serde::{Deserialize, Serialize};
+//! use serde_json::Result;
+//!
+//! #[derive(Serialize, Deserialize)]
+//! struct Person {
+//!     name: String,
+//!     age: u8,
+//!     phones: Vec<String>,
+//! }
+//!
+//! fn typed_example() -> Result<()> {
+//!     // Some JSON input data as a &str. Maybe this comes from the user.
+//!     let data = r#"
+//!         {
+//!             "name": "John Doe",
+//!             "age": 43,
+//!             "phones": [
+//!                 "+44 1234567",
+//!                 "+44 2345678"
+//!             ]
+//!         }"#;
+//!
+//!     // Parse the string of data into a Person object. This is exactly the
+//!     // same function as the one that produced serde_json::Value above, but
+//!     // now we are asking it for a Person as output.
+//!     let p: Person = serde_json::from_str(data)?;
+//!
+//!     // Do things just like with any other Rust data structure.
+//!     println!("Please call {} at the number {}", p.name, p.phones[0]);
+//!
+//!     Ok(())
+//! }
+//! #
+//! # fn main() {
+//! #     typed_example().unwrap();
+//! # }
+//! ```
+//!
+//! This is the same `serde_json::from_str` function as before, but this time we
+//! assign the return value to a variable of type `Person` so Serde will
+//! automatically interpret the input data as a `Person` and produce informative
+//! error messages if the layout does not conform to what a `Person` is expected
+//! to look like.
+//!
+//! Any type that implements Serde's `Deserialize` trait can be deserialized
+//! this way. This includes built-in Rust standard library types like `Vec<T>`
+//! and `HashMap<K, V>`, as well as any structs or enums annotated with
+//! `#[derive(Deserialize)]`.
+//!
+//! Once we have `p` of type `Person`, our IDE and the Rust compiler can help us
+//! use it correctly like they do for any other Rust code. The IDE can
+//! autocomplete field names to prevent typos, which was impossible in the
+//! `serde_json::Value` representation. And the Rust compiler can check that
+//! when we write `p.phones[0]`, then `p.phones` is guaranteed to be a
+//! `Vec<String>` so indexing into it makes sense and produces a `String`.
+//!
+//! # Constructing JSON values
+//!
+//! Serde JSON provides a [`json!` macro][macro] to build `serde_json::Value`
+//! objects with very natural JSON syntax.
+//!
+//! ```
+//! use serde_json::json;
+//!
+//! fn main() {
+//!     // The type of `john` is `serde_json::Value`
+//!     let john = json!({
+//!         "name": "John Doe",
+//!         "age": 43,
+//!         "phones": [
+//!             "+44 1234567",
+//!             "+44 2345678"
+//!         ]
+//!     });
+//!
+//!     println!("first phone number: {}", john["phones"][0]);
+//!
+//!     // Convert to a string of JSON and print it out
+//!     println!("{}", john.to_string());
+//! }
+//! ```
+//!
+//! The `Value::to_string()` function converts a `serde_json::Value` into a
+//! `String` of JSON text.
+//!
+//! One neat thing about the `json!` macro is that variables and expressions can
+//! be interpolated directly into the JSON value as you are building it. Serde
+//! will check at compile time that the value you are interpolating is able to
+//! be represented as JSON.
+//!
+//! ```
+//! # use serde_json::json;
+//! #
+//! # fn random_phone() -> u16 { 0 }
+//! #
+//! let full_name = "John Doe";
+//! let age_last_year = 42;
+//!
+//! // The type of `john` is `serde_json::Value`
+//! let john = json!({
+//!     "name": full_name,
+//!     "age": age_last_year + 1,
+//!     "phones": [
+//!         format!("+44 {}", random_phone())
+//!     ]
+//! });
+//! ```
+//!
+//! This is amazingly convenient, but we have the problem we had before with
+//! `Value`: the IDE and Rust compiler cannot help us if we get it wrong. Serde
+//! JSON provides a better way of serializing strongly-typed data structures
+//! into JSON text.
+//!
+//! # Creating JSON by serializing data structures
+//!
+//! A data structure can be converted to a JSON string by
+//! [`serde_json::to_string`][to_string]. There is also
+//! [`serde_json::to_vec`][to_vec] which serializes to a `Vec<u8>` and
+//! [`serde_json::to_writer`][to_writer] which serializes to any `io::Write`
+//! such as a File or a TCP stream.
+//!
+//! ```
+//! use serde::{Deserialize, Serialize};
+//! use serde_json::Result;
+//!
+//! #[derive(Serialize, Deserialize)]
+//! struct Address {
+//!     street: String,
+//!     city: String,
+//! }
+//!
+//! fn print_an_address() -> Result<()> {
+//!     // Some data structure.
+//!     let address = Address {
+//!         street: "10 Downing Street".to_owned(),
+//!         city: "London".to_owned(),
+//!     };
+//!
+//!     // Serialize it to a JSON string.
+//!     let j = serde_json::to_string(&address)?;
+//!
+//!     // Print, write to a file, or send to an HTTP server.
+//!     println!("{}", j);
+//!
+//!     Ok(())
+//! }
+//! #
+//! # fn main() {
+//! #     print_an_address().unwrap();
+//! # }
+//! ```
+//!
+//! Any type that implements Serde's `Serialize` trait can be serialized this
+//! way. This includes built-in Rust standard library types like `Vec<T>` and
+//! `HashMap<K, V>`, as well as any structs or enums annotated with
+//! `#[derive(Serialize)]`.
+//!
+//! # No-std support
+//!
+//! As long as there is a memory allocator, it is possible to use serde_json
+//! without the rest of the Rust standard library. Disable the default "std"
+//! feature and enable the "alloc" feature:
+//!
+//! ```toml
+//! [dependencies]
+//! serde_json = { version = "1.0", default-features = false, features = ["alloc"] }
+//! ```
+//!
+//! For JSON support in Serde without a memory allocator, please see the
+//! [`serde-json-core`] crate.
+//!
+//! [value]: crate::value::Value
+//! [from_str]: crate::de::from_str
+//! [from_slice]: crate::de::from_slice
+//! [from_reader]: crate::de::from_reader
+//! [to_string]: crate::ser::to_string
+//! [to_vec]: crate::ser::to_vec
+//! [to_writer]: crate::ser::to_writer
+//! [macro]: crate::json
+//! [`serde-json-core`]: https://github.com/rust-embedded-community/serde-json-core
+
+#![doc(html_root_url = "https://docs.rs/serde_json/1.0.93")]
+// Ignored clippy lints
+#![allow(
+    clippy::collapsible_else_if,
+    clippy::comparison_chain,
+    clippy::deprecated_cfg_attr,
+    clippy::doc_markdown,
+    clippy::excessive_precision,
+    clippy::explicit_auto_deref,
+    clippy::float_cmp,
+    clippy::manual_range_contains,
+    clippy::match_like_matches_macro,
+    clippy::match_single_binding,
+    clippy::needless_doctest_main,
+    clippy::needless_late_init,
+    // clippy bug: https://github.com/rust-lang/rust-clippy/issues/8366
+    clippy::ptr_arg,
+    clippy::return_self_not_must_use,
+    clippy::transmute_ptr_to_ptr,
+    clippy::unnecessary_wraps,
+    // clippy bug: https://github.com/rust-lang/rust-clippy/issues/5704
+    clippy::unnested_or_patterns,
+)]
+// Ignored clippy_pedantic lints
+#![allow(
+    // buggy
+    clippy::iter_not_returning_iterator, // https://github.com/rust-lang/rust-clippy/issues/8285
+    // Deserializer::from_str, into_iter
+    clippy::should_implement_trait,
+    // integer and float ser/de requires these sorts of casts
+    clippy::cast_possible_truncation,
+    clippy::cast_possible_wrap,
+    clippy::cast_precision_loss,
+    clippy::cast_sign_loss,
+    // correctly used
+    clippy::enum_glob_use,
+    clippy::if_not_else,
+    clippy::integer_division,
+    clippy::map_err_ignore,
+    clippy::match_same_arms,
+    clippy::similar_names,
+    clippy::unused_self,
+    clippy::wildcard_imports,
+    // things are often more readable this way
+    clippy::cast_lossless,
+    clippy::module_name_repetitions,
+    clippy::redundant_else,
+    clippy::shadow_unrelated,
+    clippy::single_match_else,
+    clippy::too_many_lines,
+    clippy::unreadable_literal,
+    clippy::unseparated_literal_suffix,
+    clippy::use_self,
+    clippy::zero_prefixed_literal,
+    // we support older compilers
+    clippy::checked_conversions,
+    clippy::mem_replace_with_default,
+    // noisy
+    clippy::missing_errors_doc,
+    clippy::must_use_candidate,
+)]
+#![allow(non_upper_case_globals)]
+#![deny(missing_docs)]
+#![cfg_attr(not(feature = "std"), no_std)]
+#![cfg_attr(docsrs, feature(doc_cfg))]
+
+extern crate alloc;
+
+#[cfg(feature = "std")]
+#[doc(inline)]
+pub use crate::de::from_reader;
+#[doc(inline)]
+pub use crate::de::{from_slice, from_str, Deserializer, StreamDeserializer};
+#[doc(inline)]
+pub use crate::error::{Error, Result};
+#[doc(inline)]
+pub use crate::ser::{to_string, to_string_pretty, to_vec, to_vec_pretty};
+#[cfg(feature = "std")]
+#[doc(inline)]
+pub use crate::ser::{to_writer, to_writer_pretty, Serializer};
+#[doc(inline)]
+pub use crate::value::{from_value, to_value, Map, Number, Value};
+
+// We only use our own error type; no need for From conversions provided by the
+// standard library's try! macro. This reduces lines of LLVM IR by 4%.
+macro_rules! tri {
+    ($e:expr $(,)?) => {
+        match $e {
+            core::result::Result::Ok(val) => val,
+            core::result::Result::Err(err) => return core::result::Result::Err(err),
+        }
+    };
+}
+
+#[macro_use]
+mod macros;
+
+pub mod de;
+pub mod error;
+pub mod map;
+#[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
+pub mod ser;
+#[cfg(not(feature = "std"))]
+mod ser;
+pub mod value;
+
+mod features_check;
+
+mod io;
+#[cfg(feature = "std")]
+mod iter;
+#[cfg(feature = "float_roundtrip")]
+mod lexical;
+mod number;
+mod read;
+
+#[cfg(feature = "raw_value")]
+mod raw;
diff --git a/third_party/rust/serde_json/src/macros.rs b/third_party/rust/serde_json/src/macros.rs
new file mode 100644
index 0000000000..5287998b46
--- /dev/null
+++ b/third_party/rust/serde_json/src/macros.rs
@@ -0,0 +1,303 @@
+/// Construct a `serde_json::Value` from a JSON literal.
+///
+/// ```
+/// # use serde_json::json;
+/// #
+/// let value = json!({
+///     "code": 200,
+///     "success": true,
+///     "payload": {
+///         "features": [
+///             "serde",
+///             "json"
+///         ]
+///     }
+/// });
+/// ```
+///
+/// Variables or expressions can be interpolated into the JSON literal. Any type
+/// interpolated into an array element or object value must implement Serde's
+/// `Serialize` trait, while any type interpolated into a object key must
+/// implement `Into<String>`. If the `Serialize` implementation of the
+/// interpolated type decides to fail, or if the interpolated type contains a
+/// map with non-string keys, the `json!` macro will panic.
+///
+/// ```
+/// # use serde_json::json;
+/// #
+/// let code = 200;
+/// let features = vec!["serde", "json"];
+///
+/// let value = json!({
+///     "code": code,
+///     "success": code == 200,
+///     "payload": {
+///         features[0]: features[1]
+///     }
+/// });
+/// ```
+///
+/// Trailing commas are allowed inside both arrays and objects.
+///
+/// ```
+/// # use serde_json::json;
+/// #
+/// let value = json!([
+///     "notice",
+///     "the",
+///     "trailing",
+///     "comma -->",
+/// ]);
+/// ```
+#[macro_export(local_inner_macros)]
+macro_rules! json {
+    // Hide distracting implementation details from the generated rustdoc.
+    ($($json:tt)+) => {
+        json_internal!($($json)+)
+    };
+}
+
+// Rocket relies on this because they export their own `json!` with a different
+// doc comment than ours, and various Rust bugs prevent them from calling our
+// `json!` from their `json!` so they call `json_internal!` directly. Check with
+// @SergioBenitez before making breaking changes to this macro.
+//
+// Changes are fine as long as `json_internal!` does not call any new helper
+// macros and can still be invoked as `json_internal!($($json)+)`.
+#[macro_export(local_inner_macros)]
+#[doc(hidden)]
+macro_rules! json_internal {
+    //////////////////////////////////////////////////////////////////////////
+    // TT muncher for parsing the inside of an array [...]. Produces a vec![...]
+    // of the elements.
+    //
+    // Must be invoked as: json_internal!(@array [] $($tt)*)
+    //////////////////////////////////////////////////////////////////////////
+
+    // Done with trailing comma.
+    (@array [$($elems:expr,)*]) => {
+        json_internal_vec![$($elems,)*]
+    };
+
+    // Done without trailing comma.
+    (@array [$($elems:expr),*]) => {
+        json_internal_vec![$($elems),*]
+    };
+
+    // Next element is `null`.
+    (@array [$($elems:expr,)*] null $($rest:tt)*) => {
+        json_internal!(@array [$($elems,)* json_internal!(null)] $($rest)*)
+    };
+
+    // Next element is `true`.
+    (@array [$($elems:expr,)*] true $($rest:tt)*) => {
+        json_internal!(@array [$($elems,)* json_internal!(true)] $($rest)*)
+    };
+
+    // Next element is `false`.
+    (@array [$($elems:expr,)*] false $($rest:tt)*) => {
+        json_internal!(@array [$($elems,)* json_internal!(false)] $($rest)*)
+    };
+
+    // Next element is an array.
+    (@array [$($elems:expr,)*] [$($array:tt)*] $($rest:tt)*) => {
+        json_internal!(@array [$($elems,)* json_internal!([$($array)*])] $($rest)*)
+    };
+
+    // Next element is a map.
+    (@array [$($elems:expr,)*] {$($map:tt)*} $($rest:tt)*) => {
+        json_internal!(@array [$($elems,)* json_internal!({$($map)*})] $($rest)*)
+    };
+
+    // Next element is an expression followed by comma.
+    (@array [$($elems:expr,)*] $next:expr, $($rest:tt)*) => {
+        json_internal!(@array [$($elems,)* json_internal!($next),] $($rest)*)
+    };
+
+    // Last element is an expression with no trailing comma.
+    (@array [$($elems:expr,)*] $last:expr) => {
+        json_internal!(@array [$($elems,)* json_internal!($last)])
+    };
+
+    // Comma after the most recent element.
+    (@array [$($elems:expr),*] , $($rest:tt)*) => {
+        json_internal!(@array [$($elems,)*] $($rest)*)
+    };
+
+    // Unexpected token after most recent element.
+    (@array [$($elems:expr),*] $unexpected:tt $($rest:tt)*) => {
+        json_unexpected!($unexpected)
+    };
+
+    //////////////////////////////////////////////////////////////////////////
+    // TT muncher for parsing the inside of an object {...}. Each entry is
+    // inserted into the given map variable.
+    //
+    // Must be invoked as: json_internal!(@object $map () ($($tt)*) ($($tt)*))
+    //
+    // We require two copies of the input tokens so that we can match on one
+    // copy and trigger errors on the other copy.
+    //////////////////////////////////////////////////////////////////////////
+
+    // Done.
+    (@object $object:ident () () ()) => {};
+
+    // Insert the current entry followed by trailing comma.
+    (@object $object:ident [$($key:tt)+] ($value:expr) , $($rest:tt)*) => {
+        let _ = $object.insert(($($key)+).into(), $value);
+        json_internal!(@object $object () ($($rest)*) ($($rest)*));
+    };
+
+    // Current entry followed by unexpected token.
+    (@object $object:ident [$($key:tt)+] ($value:expr) $unexpected:tt $($rest:tt)*) => {
+        json_unexpected!($unexpected);
+    };
+
+    // Insert the last entry without trailing comma.
+    (@object $object:ident [$($key:tt)+] ($value:expr)) => {
+        let _ = $object.insert(($($key)+).into(), $value);
+    };
+
+    // Next value is `null`.
+    (@object $object:ident ($($key:tt)+) (: null $($rest:tt)*) $copy:tt) => {
+        json_internal!(@object $object [$($key)+] (json_internal!(null)) $($rest)*);
+    };
+
+    // Next value is `true`.
+    (@object $object:ident ($($key:tt)+) (: true $($rest:tt)*) $copy:tt) => {
+        json_internal!(@object $object [$($key)+] (json_internal!(true)) $($rest)*);
+    };
+
+    // Next value is `false`.
+    (@object $object:ident ($($key:tt)+) (: false $($rest:tt)*) $copy:tt) => {
+        json_internal!(@object $object [$($key)+] (json_internal!(false)) $($rest)*);
+    };
+
+    // Next value is an array.
+    (@object $object:ident ($($key:tt)+) (: [$($array:tt)*] $($rest:tt)*) $copy:tt) => {
+        json_internal!(@object $object [$($key)+] (json_internal!([$($array)*])) $($rest)*);
+    };
+
+    // Next value is a map.
+    (@object $object:ident ($($key:tt)+) (: {$($map:tt)*} $($rest:tt)*) $copy:tt) => {
+        json_internal!(@object $object [$($key)+] (json_internal!({$($map)*})) $($rest)*);
+    };
+
+    // Next value is an expression followed by comma.
+    (@object $object:ident ($($key:tt)+) (: $value:expr , $($rest:tt)*) $copy:tt) => {
+        json_internal!(@object $object [$($key)+] (json_internal!($value)) , $($rest)*);
+    };
+
+    // Last value is an expression with no trailing comma.
+    (@object $object:ident ($($key:tt)+) (: $value:expr) $copy:tt) => {
+        json_internal!(@object $object [$($key)+] (json_internal!($value)));
+    };
+
+    // Missing value for last entry. Trigger a reasonable error message.
+    (@object $object:ident ($($key:tt)+) (:) $copy:tt) => {
+        // "unexpected end of macro invocation"
+        json_internal!();
+    };
+
+    // Missing colon and value for last entry. Trigger a reasonable error
+    // message.
+    (@object $object:ident ($($key:tt)+) () $copy:tt) => {
+        // "unexpected end of macro invocation"
+        json_internal!();
+    };
+
+    // Misplaced colon. Trigger a reasonable error message.
+    (@object $object:ident () (: $($rest:tt)*) ($colon:tt $($copy:tt)*)) => {
+        // Takes no arguments so "no rules expected the token `:`".
+        json_unexpected!($colon);
+    };
+
+    // Found a comma inside a key. Trigger a reasonable error message.
+    (@object $object:ident ($($key:tt)*) (, $($rest:tt)*) ($comma:tt $($copy:tt)*)) => {
+        // Takes no arguments so "no rules expected the token `,`".
+        json_unexpected!($comma);
+    };
+
+    // Key is fully parenthesized. This avoids clippy double_parens false
+    // positives because the parenthesization may be necessary here.
+    (@object $object:ident () (($key:expr) : $($rest:tt)*) $copy:tt) => {
+        json_internal!(@object $object ($key) (: $($rest)*) (: $($rest)*));
+    };
+
+    // Refuse to absorb colon token into key expression.
+    (@object $object:ident ($($key:tt)*) (: $($unexpected:tt)+) $copy:tt) => {
+        json_expect_expr_comma!($($unexpected)+);
+    };
+
+    // Munch a token into the current key.
+    (@object $object:ident ($($key:tt)*) ($tt:tt $($rest:tt)*) $copy:tt) => {
+        json_internal!(@object $object ($($key)* $tt) ($($rest)*) ($($rest)*));
+    };
+
+    //////////////////////////////////////////////////////////////////////////
+    // The main implementation.
+    //
+    // Must be invoked as: json_internal!($($json)+)
+    //////////////////////////////////////////////////////////////////////////
+
+    (null) => {
+        $crate::Value::Null
+    };
+
+    (true) => {
+        $crate::Value::Bool(true)
+    };
+
+    (false) => {
+        $crate::Value::Bool(false)
+    };
+
+    ([]) => {
+        $crate::Value::Array(json_internal_vec![])
+    };
+
+    ([ $($tt:tt)+ ]) => {
+        $crate::Value::Array(json_internal!(@array [] $($tt)+))
+    };
+
+    ({}) => {
+        $crate::Value::Object($crate::Map::new())
+    };
+
+    ({ $($tt:tt)+ }) => {
+        $crate::Value::Object({
+            let mut object = $crate::Map::new();
+            json_internal!(@object object () ($($tt)+) ($($tt)+));
+            object
+        })
+    };
+
+    // Any Serialize type: numbers, strings, struct literals, variables etc.
+    // Must be below every other rule.
+    ($other:expr) => {
+        $crate::to_value(&$other).unwrap()
+    };
+}
+
+// The json_internal macro above cannot invoke vec directly because it uses
+// local_inner_macros. A vec invocation there would resolve to $crate::vec.
+// Instead invoke vec here outside of local_inner_macros.
+#[macro_export]
+#[doc(hidden)]
+macro_rules! json_internal_vec {
+    ($($content:tt)*) => {
+        vec![$($content)*]
+    };
+}
+
+#[macro_export]
+#[doc(hidden)]
+macro_rules! json_unexpected {
+    () => {};
+}
+
+#[macro_export]
+#[doc(hidden)]
+macro_rules! json_expect_expr_comma {
+    ($e:expr , $($tt:tt)*) => {};
+}
diff --git a/third_party/rust/serde_json/src/map.rs b/third_party/rust/serde_json/src/map.rs
new file mode 100644
index 0000000000..3e8a3814c9
--- /dev/null
+++ b/third_party/rust/serde_json/src/map.rs
@@ -0,0 +1,940 @@
+//! A map of String to serde_json::Value.
+//!
+//! By default the map is backed by a [`BTreeMap`]. Enable the `preserve_order`
+//! feature of serde_json to use [`IndexMap`] instead.
+//!
+//! [`BTreeMap`]: https://doc.rust-lang.org/std/collections/struct.BTreeMap.html
+//! [`IndexMap`]: https://docs.rs/indexmap/*/indexmap/map/struct.IndexMap.html
+
+use crate::value::Value;
+use alloc::string::String;
+use core::borrow::Borrow;
+use core::fmt::{self, Debug};
+use core::hash::Hash;
+use core::iter::{FromIterator, FusedIterator};
+#[cfg(feature = "preserve_order")]
+use core::mem;
+use core::ops;
+use serde::de;
+
+#[cfg(not(feature = "preserve_order"))]
+use alloc::collections::{btree_map, BTreeMap};
+#[cfg(feature = "preserve_order")]
+use indexmap::{self, IndexMap};
+
+/// Represents a JSON key/value type.
+pub struct Map<K, V> {
+    map: MapImpl<K, V>,
+}
+
+#[cfg(not(feature = "preserve_order"))]
+type MapImpl<K, V> = BTreeMap<K, V>;
+#[cfg(feature = "preserve_order")]
+type MapImpl<K, V> = IndexMap<K, V>;
+
+impl Map<String, Value> {
+    /// Makes a new empty Map.
+    #[inline]
+    pub fn new() -> Self {
+        Map {
+            map: MapImpl::new(),
+        }
+    }
+
+    /// Makes a new empty Map with the given initial capacity.
+    #[inline]
+    pub fn with_capacity(capacity: usize) -> Self {
+        Map {
+            #[cfg(not(feature = "preserve_order"))]
+            map: {
+                // does not support with_capacity
+                let _ = capacity;
+                BTreeMap::new()
+            },
+            #[cfg(feature = "preserve_order")]
+            map: IndexMap::with_capacity(capacity),
+        }
+    }
+
+    /// Clears the map, removing all values.
+    #[inline]
+    pub fn clear(&mut self) {
+        self.map.clear();
+    }
+
+    /// Returns a reference to the value corresponding to the key.
+    ///
+    /// The key may be any borrowed form of the map's key type, but the ordering
+    /// on the borrowed form *must* match the ordering on the key type.
+    #[inline]
+    pub fn get<Q>(&self, key: &Q) -> Option<&Value>
+    where
+        String: Borrow<Q>,
+        Q: ?Sized + Ord + Eq + Hash,
+    {
+        self.map.get(key)
+    }
+
+    /// Returns true if the map contains a value for the specified key.
+    ///
+    /// The key may be any borrowed form of the map's key type, but the ordering
+    /// on the borrowed form *must* match the ordering on the key type.
+    #[inline]
+    pub fn contains_key<Q>(&self, key: &Q) -> bool
+    where
+        String: Borrow<Q>,
+        Q: ?Sized + Ord + Eq + Hash,
+    {
+        self.map.contains_key(key)
+    }
+
+    /// Returns a mutable reference to the value corresponding to the key.
+    ///
+    /// The key may be any borrowed form of the map's key type, but the ordering
+    /// on the borrowed form *must* match the ordering on the key type.
+    #[inline]
+    pub fn get_mut<Q>(&mut self, key: &Q) -> Option<&mut Value>
+    where
+        String: Borrow<Q>,
+        Q: ?Sized + Ord + Eq + Hash,
+    {
+        self.map.get_mut(key)
+    }
+
+    /// Returns the key-value pair matching the given key.
+    ///
+    /// The key may be any borrowed form of the map's key type, but the ordering
+    /// on the borrowed form *must* match the ordering on the key type.
+    #[inline]
+    #[cfg(any(feature = "preserve_order", not(no_btreemap_get_key_value)))]
+    pub fn get_key_value<Q>(&self, key: &Q) -> Option<(&String, &Value)>
+    where
+        String: Borrow<Q>,
+        Q: ?Sized + Ord + Eq + Hash,
+    {
+        self.map.get_key_value(key)
+    }
+
+    /// Inserts a key-value pair into the map.
+    ///
+    /// If the map did not have this key present, `None` is returned.
+    ///
+    /// If the map did have this key present, the value is updated, and the old
+    /// value is returned.
+    #[inline]
+    pub fn insert(&mut self, k: String, v: Value) -> Option<Value> {
+        self.map.insert(k, v)
+    }
+
+    /// Removes a key from the map, returning the value at the key if the key
+    /// was previously in the map.
+    ///
+    /// The key may be any borrowed form of the map's key type, but the ordering
+    /// on the borrowed form *must* match the ordering on the key type.
+    #[inline]
+    pub fn remove<Q>(&mut self, key: &Q) -> Option<Value>
+    where
+        String: Borrow<Q>,
+        Q: ?Sized + Ord + Eq + Hash,
+    {
+        #[cfg(feature = "preserve_order")]
+        return self.map.swap_remove(key);
+        #[cfg(not(feature = "preserve_order"))]
+        return self.map.remove(key);
+    }
+
+    /// Removes a key from the map, returning the stored key and value if the
+    /// key was previously in the map.
+    ///
+    /// The key may be any borrowed form of the map's key type, but the ordering
+    /// on the borrowed form *must* match the ordering on the key type.
+    pub fn remove_entry<Q>(&mut self, key: &Q) -> Option<(String, Value)>
+    where
+        String: Borrow<Q>,
+        Q: ?Sized + Ord + Eq + Hash,
+    {
+        #[cfg(any(feature = "preserve_order", not(no_btreemap_remove_entry)))]
+        return self.map.remove_entry(key);
+        #[cfg(all(
+            not(feature = "preserve_order"),
+            no_btreemap_remove_entry,
+            not(no_btreemap_get_key_value),
+        ))]
+        {
+            let (key, _value) = self.map.get_key_value(key)?;
+            let key = key.clone();
+            let value = self.map.remove::<String>(&key)?;
+            Some((key, value))
+        }
+        #[cfg(all(
+            not(feature = "preserve_order"),
+            no_btreemap_remove_entry,
+            no_btreemap_get_key_value,
+        ))]
+        {
+            use core::ops::{Bound, RangeBounds};
+
+            struct Key<'a, Q: ?Sized>(&'a Q);
+
+            impl<'a, Q: ?Sized> RangeBounds<Q> for Key<'a, Q> {
+                fn start_bound(&self) -> Bound<&Q> {
+                    Bound::Included(self.0)
+                }
+                fn end_bound(&self) -> Bound<&Q> {
+                    Bound::Included(self.0)
+                }
+            }
+
+            let mut range = self.map.range(Key(key));
+            let (key, _value) = range.next()?;
+            let key = key.clone();
+            let value = self.map.remove::<String>(&key)?;
+            Some((key, value))
+        }
+    }
+
+    /// Moves all elements from other into self, leaving other empty.
+    #[inline]
+    pub fn append(&mut self, other: &mut Self) {
+        #[cfg(feature = "preserve_order")]
+        self.map
+            .extend(mem::replace(&mut other.map, MapImpl::default()));
+        #[cfg(not(feature = "preserve_order"))]
+        self.map.append(&mut other.map);
+    }
+
+    /// Gets the given key's corresponding entry in the map for in-place
+    /// manipulation.
+    pub fn entry<S>(&mut self, key: S) -> Entry
+    where
+        S: Into<String>,
+    {
+        #[cfg(not(feature = "preserve_order"))]
+        use alloc::collections::btree_map::Entry as EntryImpl;
+        #[cfg(feature = "preserve_order")]
+        use indexmap::map::Entry as EntryImpl;
+
+        match self.map.entry(key.into()) {
+            EntryImpl::Vacant(vacant) => Entry::Vacant(VacantEntry { vacant }),
+            EntryImpl::Occupied(occupied) => Entry::Occupied(OccupiedEntry { occupied }),
+        }
+    }
+
+    /// Returns the number of elements in the map.
+    #[inline]
+    pub fn len(&self) -> usize {
+        self.map.len()
+    }
+
+    /// Returns true if the map contains no elements.
+    #[inline]
+    pub fn is_empty(&self) -> bool {
+        self.map.is_empty()
+    }
+
+    /// Gets an iterator over the entries of the map.
+    #[inline]
+    pub fn iter(&self) -> Iter {
+        Iter {
+            iter: self.map.iter(),
+        }
+    }
+
+    /// Gets a mutable iterator over the entries of the map.
+    #[inline]
+    pub fn iter_mut(&mut self) -> IterMut {
+        IterMut {
+            iter: self.map.iter_mut(),
+        }
+    }
+
+    /// Gets an iterator over the keys of the map.
+    #[inline]
+    pub fn keys(&self) -> Keys {
+        Keys {
+            iter: self.map.keys(),
+        }
+    }
+
+    /// Gets an iterator over the values of the map.
+    #[inline]
+    pub fn values(&self) -> Values {
+        Values {
+            iter: self.map.values(),
+        }
+    }
+
+    /// Gets an iterator over mutable values of the map.
+    #[inline]
+    pub fn values_mut(&mut self) -> ValuesMut {
+        ValuesMut {
+            iter: self.map.values_mut(),
+        }
+    }
+
+    /// Retains only the elements specified by the predicate.
+    ///
+    /// In other words, remove all pairs `(k, v)` such that `f(&k, &mut v)`
+    /// returns `false`.
+    #[cfg(not(no_btreemap_retain))]
+    #[inline]
+    pub fn retain<F>(&mut self, f: F)
+    where
+        F: FnMut(&String, &mut Value) -> bool,
+    {
+        self.map.retain(f);
+    }
+}
+
+#[allow(clippy::derivable_impls)] // clippy bug: https://github.com/rust-lang/rust-clippy/issues/7655
+impl Default for Map<String, Value> {
+    #[inline]
+    fn default() -> Self {
+        Map {
+            map: MapImpl::new(),
+        }
+    }
+}
+
+impl Clone for Map<String, Value> {
+    #[inline]
+    fn clone(&self) -> Self {
+        Map {
+            map: self.map.clone(),
+        }
+    }
+
+    #[inline]
+    fn clone_from(&mut self, source: &Self) {
+        self.map.clone_from(&source.map);
+    }
+}
+
+impl PartialEq for Map<String, Value> {
+    #[inline]
+    fn eq(&self, other: &Self) -> bool {
+        self.map.eq(&other.map)
+    }
+}
+
+impl Eq for Map<String, Value> {}
+
+/// Access an element of this map. Panics if the given key is not present in the
+/// map.
+///
+/// ```
+/// # use serde_json::Value;
+/// #
+/// # let val = &Value::String("".to_owned());
+/// # let _ =
+/// match val {
+///     Value::String(s) => Some(s.as_str()),
+///     Value::Array(arr) => arr[0].as_str(),
+///     Value::Object(map) => map["type"].as_str(),
+///     _ => None,
+/// }
+/// # ;
+/// ```
+impl<'a, Q> ops::Index<&'a Q> for Map<String, Value>
+where
+    String: Borrow<Q>,
+    Q: ?Sized + Ord + Eq + Hash,
+{
+    type Output = Value;
+
+    fn index(&self, index: &Q) -> &Value {
+        self.map.index(index)
+    }
+}
+
+/// Mutably access an element of this map. Panics if the given key is not
+/// present in the map.
+///
+/// ```
+/// # use serde_json::json;
+/// #
+/// # let mut map = serde_json::Map::new();
+/// # map.insert("key".to_owned(), serde_json::Value::Null);
+/// #
+/// map["key"] = json!("value");
+/// ```
+impl<'a, Q> ops::IndexMut<&'a Q> for Map<String, Value>
+where
+    String: Borrow<Q>,
+    Q: ?Sized + Ord + Eq + Hash,
+{
+    fn index_mut(&mut self, index: &Q) -> &mut Value {
+        self.map.get_mut(index).expect("no entry found for key")
+    }
+}
+
+impl Debug for Map<String, Value> {
+    #[inline]
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> Result<(), fmt::Error> {
+        self.map.fmt(formatter)
+    }
+}
+
+#[cfg(any(feature = "std", feature = "alloc"))]
+impl serde::ser::Serialize for Map<String, Value> {
+    #[inline]
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: serde::ser::Serializer,
+    {
+        use serde::ser::SerializeMap;
+        let mut map = tri!(serializer.serialize_map(Some(self.len())));
+        for (k, v) in self {
+            tri!(map.serialize_entry(k, v));
+        }
+        map.end()
+    }
+}
+
+impl<'de> de::Deserialize<'de> for Map<String, Value> {
+    #[inline]
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: de::Deserializer<'de>,
+    {
+        struct Visitor;
+
+        impl<'de> de::Visitor<'de> for Visitor {
+            type Value = Map<String, Value>;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str("a map")
+            }
+
+            #[inline]
+            fn visit_unit<E>(self) -> Result<Self::Value, E>
+            where
+                E: de::Error,
+            {
+                Ok(Map::new())
+            }
+
+            #[cfg(any(feature = "std", feature = "alloc"))]
+            #[inline]
+            fn visit_map<V>(self, mut visitor: V) -> Result<Self::Value, V::Error>
+            where
+                V: de::MapAccess<'de>,
+            {
+                let mut values = Map::new();
+
+                while let Some((key, value)) = tri!(visitor.next_entry()) {
+                    values.insert(key, value);
+                }
+
+                Ok(values)
+            }
+        }
+
+        deserializer.deserialize_map(Visitor)
+    }
+}
+
+impl FromIterator<(String, Value)> for Map<String, Value> {
+    fn from_iter<T>(iter: T) -> Self
+    where
+        T: IntoIterator<Item = (String, Value)>,
+    {
+        Map {
+            map: FromIterator::from_iter(iter),
+        }
+    }
+}
+
+impl Extend<(String, Value)> for Map<String, Value> {
+    fn extend<T>(&mut self, iter: T)
+    where
+        T: IntoIterator<Item = (String, Value)>,
+    {
+        self.map.extend(iter);
+    }
+}
+
+macro_rules! delegate_iterator {
+    (($name:ident $($generics:tt)*) => $item:ty) => {
+        impl $($generics)* Iterator for $name $($generics)* {
+            type Item = $item;
+            #[inline]
+            fn next(&mut self) -> Option<Self::Item> {
+                self.iter.next()
+            }
+            #[inline]
+            fn size_hint(&self) -> (usize, Option<usize>) {
+                self.iter.size_hint()
+            }
+        }
+
+        impl $($generics)* DoubleEndedIterator for $name $($generics)* {
+            #[inline]
+            fn next_back(&mut self) -> Option<Self::Item> {
+                self.iter.next_back()
+            }
+        }
+
+        impl $($generics)* ExactSizeIterator for $name $($generics)* {
+            #[inline]
+            fn len(&self) -> usize {
+                self.iter.len()
+            }
+        }
+
+        impl $($generics)* FusedIterator for $name $($generics)* {}
+    }
+}
+
+//////////////////////////////////////////////////////////////////////////////
+
+/// A view into a single entry in a map, which may either be vacant or occupied.
+/// This enum is constructed from the [`entry`] method on [`Map`].
+///
+/// [`entry`]: struct.Map.html#method.entry
+/// [`Map`]: struct.Map.html
+pub enum Entry<'a> {
+    /// A vacant Entry.
+    Vacant(VacantEntry<'a>),
+    /// An occupied Entry.
+    Occupied(OccupiedEntry<'a>),
+}
+
+/// A vacant Entry. It is part of the [`Entry`] enum.
+///
+/// [`Entry`]: enum.Entry.html
+pub struct VacantEntry<'a> {
+    vacant: VacantEntryImpl<'a>,
+}
+
+/// An occupied Entry. It is part of the [`Entry`] enum.
+///
+/// [`Entry`]: enum.Entry.html
+pub struct OccupiedEntry<'a> {
+    occupied: OccupiedEntryImpl<'a>,
+}
+
+#[cfg(not(feature = "preserve_order"))]
+type VacantEntryImpl<'a> = btree_map::VacantEntry<'a, String, Value>;
+#[cfg(feature = "preserve_order")]
+type VacantEntryImpl<'a> = indexmap::map::VacantEntry<'a, String, Value>;
+
+#[cfg(not(feature = "preserve_order"))]
+type OccupiedEntryImpl<'a> = btree_map::OccupiedEntry<'a, String, Value>;
+#[cfg(feature = "preserve_order")]
+type OccupiedEntryImpl<'a> = indexmap::map::OccupiedEntry<'a, String, Value>;
+
+impl<'a> Entry<'a> {
+    /// Returns a reference to this entry's key.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// let mut map = serde_json::Map::new();
+    /// assert_eq!(map.entry("serde").key(), &"serde");
+    /// ```
+    pub fn key(&self) -> &String {
+        match self {
+            Entry::Vacant(e) => e.key(),
+            Entry::Occupied(e) => e.key(),
+        }
+    }
+
+    /// Ensures a value is in the entry by inserting the default if empty, and
+    /// returns a mutable reference to the value in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let mut map = serde_json::Map::new();
+    /// map.entry("serde").or_insert(json!(12));
+    ///
+    /// assert_eq!(map["serde"], 12);
+    /// ```
+    pub fn or_insert(self, default: Value) -> &'a mut Value {
+        match self {
+            Entry::Vacant(entry) => entry.insert(default),
+            Entry::Occupied(entry) => entry.into_mut(),
+        }
+    }
+
+    /// Ensures a value is in the entry by inserting the result of the default
+    /// function if empty, and returns a mutable reference to the value in the
+    /// entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let mut map = serde_json::Map::new();
+    /// map.entry("serde").or_insert_with(|| json!("hoho"));
+    ///
+    /// assert_eq!(map["serde"], "hoho".to_owned());
+    /// ```
+    pub fn or_insert_with<F>(self, default: F) -> &'a mut Value
+    where
+        F: FnOnce() -> Value,
+    {
+        match self {
+            Entry::Vacant(entry) => entry.insert(default()),
+            Entry::Occupied(entry) => entry.into_mut(),
+        }
+    }
+
+    /// Provides in-place mutable access to an occupied entry before any
+    /// potential inserts into the map.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let mut map = serde_json::Map::new();
+    /// map.entry("serde")
+    ///     .and_modify(|e| *e = json!("rust"))
+    ///     .or_insert(json!("cpp"));
+    ///
+    /// assert_eq!(map["serde"], "cpp");
+    ///
+    /// map.entry("serde")
+    ///     .and_modify(|e| *e = json!("rust"))
+    ///     .or_insert(json!("cpp"));
+    ///
+    /// assert_eq!(map["serde"], "rust");
+    /// ```
+    pub fn and_modify<F>(self, f: F) -> Self
+    where
+        F: FnOnce(&mut Value),
+    {
+        match self {
+            Entry::Occupied(mut entry) => {
+                f(entry.get_mut());
+                Entry::Occupied(entry)
+            }
+            Entry::Vacant(entry) => Entry::Vacant(entry),
+        }
+    }
+}
+
+impl<'a> VacantEntry<'a> {
+    /// Gets a reference to the key that would be used when inserting a value
+    /// through the VacantEntry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use serde_json::map::Entry;
+    ///
+    /// let mut map = serde_json::Map::new();
+    ///
+    /// match map.entry("serde") {
+    ///     Entry::Vacant(vacant) => {
+    ///         assert_eq!(vacant.key(), &"serde");
+    ///     }
+    ///     Entry::Occupied(_) => unimplemented!(),
+    /// }
+    /// ```
+    #[inline]
+    pub fn key(&self) -> &String {
+        self.vacant.key()
+    }
+
+    /// Sets the value of the entry with the VacantEntry's key, and returns a
+    /// mutable reference to it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// use serde_json::map::Entry;
+    ///
+    /// let mut map = serde_json::Map::new();
+    ///
+    /// match map.entry("serde") {
+    ///     Entry::Vacant(vacant) => {
+    ///         vacant.insert(json!("hoho"));
+    ///     }
+    ///     Entry::Occupied(_) => unimplemented!(),
+    /// }
+    /// ```
+    #[inline]
+    pub fn insert(self, value: Value) -> &'a mut Value {
+        self.vacant.insert(value)
+    }
+}
+
+impl<'a> OccupiedEntry<'a> {
+    /// Gets a reference to the key in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// use serde_json::map::Entry;
+    ///
+    /// let mut map = serde_json::Map::new();
+    /// map.insert("serde".to_owned(), json!(12));
+    ///
+    /// match map.entry("serde") {
+    ///     Entry::Occupied(occupied) => {
+    ///         assert_eq!(occupied.key(), &"serde");
+    ///     }
+    ///     Entry::Vacant(_) => unimplemented!(),
+    /// }
+    /// ```
+    #[inline]
+    pub fn key(&self) -> &String {
+        self.occupied.key()
+    }
+
+    /// Gets a reference to the value in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// use serde_json::map::Entry;
+    ///
+    /// let mut map = serde_json::Map::new();
+    /// map.insert("serde".to_owned(), json!(12));
+    ///
+    /// match map.entry("serde") {
+    ///     Entry::Occupied(occupied) => {
+    ///         assert_eq!(occupied.get(), 12);
+    ///     }
+    ///     Entry::Vacant(_) => unimplemented!(),
+    /// }
+    /// ```
+    #[inline]
+    pub fn get(&self) -> &Value {
+        self.occupied.get()
+    }
+
+    /// Gets a mutable reference to the value in the entry.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// use serde_json::map::Entry;
+    ///
+    /// let mut map = serde_json::Map::new();
+    /// map.insert("serde".to_owned(), json!([1, 2, 3]));
+    ///
+    /// match map.entry("serde") {
+    ///     Entry::Occupied(mut occupied) => {
+    ///         occupied.get_mut().as_array_mut().unwrap().push(json!(4));
+    ///     }
+    ///     Entry::Vacant(_) => unimplemented!(),
+    /// }
+    ///
+    /// assert_eq!(map["serde"].as_array().unwrap().len(), 4);
+    /// ```
+    #[inline]
+    pub fn get_mut(&mut self) -> &mut Value {
+        self.occupied.get_mut()
+    }
+
+    /// Converts the entry into a mutable reference to its value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// use serde_json::map::Entry;
+    ///
+    /// let mut map = serde_json::Map::new();
+    /// map.insert("serde".to_owned(), json!([1, 2, 3]));
+    ///
+    /// match map.entry("serde") {
+    ///     Entry::Occupied(mut occupied) => {
+    ///         occupied.into_mut().as_array_mut().unwrap().push(json!(4));
+    ///     }
+    ///     Entry::Vacant(_) => unimplemented!(),
+    /// }
+    ///
+    /// assert_eq!(map["serde"].as_array().unwrap().len(), 4);
+    /// ```
+    #[inline]
+    pub fn into_mut(self) -> &'a mut Value {
+        self.occupied.into_mut()
+    }
+
+    /// Sets the value of the entry with the `OccupiedEntry`'s key, and returns
+    /// the entry's old value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// use serde_json::map::Entry;
+    ///
+    /// let mut map = serde_json::Map::new();
+    /// map.insert("serde".to_owned(), json!(12));
+    ///
+    /// match map.entry("serde") {
+    ///     Entry::Occupied(mut occupied) => {
+    ///         assert_eq!(occupied.insert(json!(13)), 12);
+    ///         assert_eq!(occupied.get(), 13);
+    ///     }
+    ///     Entry::Vacant(_) => unimplemented!(),
+    /// }
+    /// ```
+    #[inline]
+    pub fn insert(&mut self, value: Value) -> Value {
+        self.occupied.insert(value)
+    }
+
+    /// Takes the value of the entry out of the map, and returns it.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// use serde_json::map::Entry;
+    ///
+    /// let mut map = serde_json::Map::new();
+    /// map.insert("serde".to_owned(), json!(12));
+    ///
+    /// match map.entry("serde") {
+    ///     Entry::Occupied(occupied) => {
+    ///         assert_eq!(occupied.remove(), 12);
+    ///     }
+    ///     Entry::Vacant(_) => unimplemented!(),
+    /// }
+    /// ```
+    #[inline]
+    pub fn remove(self) -> Value {
+        #[cfg(feature = "preserve_order")]
+        return self.occupied.swap_remove();
+        #[cfg(not(feature = "preserve_order"))]
+        return self.occupied.remove();
+    }
+}
+
+//////////////////////////////////////////////////////////////////////////////
+
+impl<'a> IntoIterator for &'a Map<String, Value> {
+    type Item = (&'a String, &'a Value);
+    type IntoIter = Iter<'a>;
+    #[inline]
+    fn into_iter(self) -> Self::IntoIter {
+        Iter {
+            iter: self.map.iter(),
+        }
+    }
+}
+
+/// An iterator over a serde_json::Map's entries.
+pub struct Iter<'a> {
+    iter: IterImpl<'a>,
+}
+
+#[cfg(not(feature = "preserve_order"))]
+type IterImpl<'a> = btree_map::Iter<'a, String, Value>;
+#[cfg(feature = "preserve_order")]
+type IterImpl<'a> = indexmap::map::Iter<'a, String, Value>;
+
+delegate_iterator!((Iter<'a>) => (&'a String, &'a Value));
+
+//////////////////////////////////////////////////////////////////////////////
+
+impl<'a> IntoIterator for &'a mut Map<String, Value> {
+    type Item = (&'a String, &'a mut Value);
+    type IntoIter = IterMut<'a>;
+    #[inline]
+    fn into_iter(self) -> Self::IntoIter {
+        IterMut {
+            iter: self.map.iter_mut(),
+        }
+    }
+}
+
+/// A mutable iterator over a serde_json::Map's entries.
+pub struct IterMut<'a> {
+    iter: IterMutImpl<'a>,
+}
+
+#[cfg(not(feature = "preserve_order"))]
+type IterMutImpl<'a> = btree_map::IterMut<'a, String, Value>;
+#[cfg(feature = "preserve_order")]
+type IterMutImpl<'a> = indexmap::map::IterMut<'a, String, Value>;
+
+delegate_iterator!((IterMut<'a>) => (&'a String, &'a mut Value));
+
+//////////////////////////////////////////////////////////////////////////////
+
+impl IntoIterator for Map<String, Value> {
+    type Item = (String, Value);
+    type IntoIter = IntoIter;
+    #[inline]
+    fn into_iter(self) -> Self::IntoIter {
+        IntoIter {
+            iter: self.map.into_iter(),
+        }
+    }
+}
+
+/// An owning iterator over a serde_json::Map's entries.
+pub struct IntoIter {
+    iter: IntoIterImpl,
+}
+
+#[cfg(not(feature = "preserve_order"))]
+type IntoIterImpl = btree_map::IntoIter<String, Value>;
+#[cfg(feature = "preserve_order")]
+type IntoIterImpl = indexmap::map::IntoIter<String, Value>;
+
+delegate_iterator!((IntoIter) => (String, Value));
+
+//////////////////////////////////////////////////////////////////////////////
+
+/// An iterator over a serde_json::Map's keys.
+pub struct Keys<'a> {
+    iter: KeysImpl<'a>,
+}
+
+#[cfg(not(feature = "preserve_order"))]
+type KeysImpl<'a> = btree_map::Keys<'a, String, Value>;
+#[cfg(feature = "preserve_order")]
+type KeysImpl<'a> = indexmap::map::Keys<'a, String, Value>;
+
+delegate_iterator!((Keys<'a>) => &'a String);
+
+//////////////////////////////////////////////////////////////////////////////
+
+/// An iterator over a serde_json::Map's values.
+pub struct Values<'a> {
+    iter: ValuesImpl<'a>,
+}
+
+#[cfg(not(feature = "preserve_order"))]
+type ValuesImpl<'a> = btree_map::Values<'a, String, Value>;
+#[cfg(feature = "preserve_order")]
+type ValuesImpl<'a> = indexmap::map::Values<'a, String, Value>;
+
+delegate_iterator!((Values<'a>) => &'a Value);
+
+//////////////////////////////////////////////////////////////////////////////
+
+/// A mutable iterator over a serde_json::Map's values.
+pub struct ValuesMut<'a> {
+    iter: ValuesMutImpl<'a>,
+}
+
+#[cfg(not(feature = "preserve_order"))]
+type ValuesMutImpl<'a> = btree_map::ValuesMut<'a, String, Value>;
+#[cfg(feature = "preserve_order")]
+type ValuesMutImpl<'a> = indexmap::map::ValuesMut<'a, String, Value>;
+
+delegate_iterator!((ValuesMut<'a>) => &'a mut Value);
diff --git a/third_party/rust/serde_json/src/number.rs b/third_party/rust/serde_json/src/number.rs
new file mode 100644
index 0000000000..21a76411cc
--- /dev/null
+++ b/third_party/rust/serde_json/src/number.rs
@@ -0,0 +1,745 @@
+use crate::de::ParserNumber;
+use crate::error::Error;
+#[cfg(feature = "arbitrary_precision")]
+use crate::error::ErrorCode;
+#[cfg(feature = "arbitrary_precision")]
+use alloc::borrow::ToOwned;
+#[cfg(feature = "arbitrary_precision")]
+use alloc::string::{String, ToString};
+use core::fmt::{self, Debug, Display};
+#[cfg(not(feature = "arbitrary_precision"))]
+use core::hash::{Hash, Hasher};
+use serde::de::{self, Unexpected, Visitor};
+#[cfg(feature = "arbitrary_precision")]
+use serde::de::{IntoDeserializer, MapAccess};
+use serde::{forward_to_deserialize_any, Deserialize, Deserializer, Serialize, Serializer};
+
+#[cfg(feature = "arbitrary_precision")]
+pub(crate) const TOKEN: &str = "$serde_json::private::Number";
+
+/// Represents a JSON number, whether integer or floating point.
+#[derive(Clone, PartialEq, Eq, Hash)]
+pub struct Number {
+    n: N,
+}
+
+#[cfg(not(feature = "arbitrary_precision"))]
+#[derive(Copy, Clone)]
+enum N {
+    PosInt(u64),
+    /// Always less than zero.
+    NegInt(i64),
+    /// Always finite.
+    Float(f64),
+}
+
+#[cfg(not(feature = "arbitrary_precision"))]
+impl PartialEq for N {
+    fn eq(&self, other: &Self) -> bool {
+        match (self, other) {
+            (N::PosInt(a), N::PosInt(b)) => a == b,
+            (N::NegInt(a), N::NegInt(b)) => a == b,
+            (N::Float(a), N::Float(b)) => a == b,
+            _ => false,
+        }
+    }
+}
+
+// Implementing Eq is fine since any float values are always finite.
+#[cfg(not(feature = "arbitrary_precision"))]
+impl Eq for N {}
+
+#[cfg(not(feature = "arbitrary_precision"))]
+impl Hash for N {
+    fn hash<H: Hasher>(&self, h: &mut H) {
+        match *self {
+            N::PosInt(i) => i.hash(h),
+            N::NegInt(i) => i.hash(h),
+            N::Float(f) => {
+                if f == 0.0f64 {
+                    // There are 2 zero representations, +0 and -0, which
+                    // compare equal but have different bits. We use the +0 hash
+                    // for both so that hash(+0) == hash(-0).
+                    0.0f64.to_bits().hash(h);
+                } else {
+                    f.to_bits().hash(h);
+                }
+            }
+        }
+    }
+}
+
+#[cfg(feature = "arbitrary_precision")]
+type N = String;
+
+impl Number {
+    /// Returns true if the `Number` is an integer between `i64::MIN` and
+    /// `i64::MAX`.
+    ///
+    /// For any Number on which `is_i64` returns true, `as_i64` is guaranteed to
+    /// return the integer value.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let big = i64::max_value() as u64 + 10;
+    /// let v = json!({ "a": 64, "b": big, "c": 256.0 });
+    ///
+    /// assert!(v["a"].is_i64());
+    ///
+    /// // Greater than i64::MAX.
+    /// assert!(!v["b"].is_i64());
+    ///
+    /// // Numbers with a decimal point are not considered integers.
+    /// assert!(!v["c"].is_i64());
+    /// ```
+    #[inline]
+    pub fn is_i64(&self) -> bool {
+        #[cfg(not(feature = "arbitrary_precision"))]
+        match self.n {
+            N::PosInt(v) => v <= i64::max_value() as u64,
+            N::NegInt(_) => true,
+            N::Float(_) => false,
+        }
+        #[cfg(feature = "arbitrary_precision")]
+        self.as_i64().is_some()
+    }
+
+    /// Returns true if the `Number` is an integer between zero and `u64::MAX`.
+    ///
+    /// For any Number on which `is_u64` returns true, `as_u64` is guaranteed to
+    /// return the integer value.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let v = json!({ "a": 64, "b": -64, "c": 256.0 });
+    ///
+    /// assert!(v["a"].is_u64());
+    ///
+    /// // Negative integer.
+    /// assert!(!v["b"].is_u64());
+    ///
+    /// // Numbers with a decimal point are not considered integers.
+    /// assert!(!v["c"].is_u64());
+    /// ```
+    #[inline]
+    pub fn is_u64(&self) -> bool {
+        #[cfg(not(feature = "arbitrary_precision"))]
+        match self.n {
+            N::PosInt(_) => true,
+            N::NegInt(_) | N::Float(_) => false,
+        }
+        #[cfg(feature = "arbitrary_precision")]
+        self.as_u64().is_some()
+    }
+
+    /// Returns true if the `Number` can be represented by f64.
+    ///
+    /// For any Number on which `is_f64` returns true, `as_f64` is guaranteed to
+    /// return the floating point value.
+    ///
+    /// Currently this function returns true if and only if both `is_i64` and
+    /// `is_u64` return false but this is not a guarantee in the future.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let v = json!({ "a": 256.0, "b": 64, "c": -64 });
+    ///
+    /// assert!(v["a"].is_f64());
+    ///
+    /// // Integers.
+    /// assert!(!v["b"].is_f64());
+    /// assert!(!v["c"].is_f64());
+    /// ```
+    #[inline]
+    pub fn is_f64(&self) -> bool {
+        #[cfg(not(feature = "arbitrary_precision"))]
+        match self.n {
+            N::Float(_) => true,
+            N::PosInt(_) | N::NegInt(_) => false,
+        }
+        #[cfg(feature = "arbitrary_precision")]
+        {
+            for c in self.n.chars() {
+                if c == '.' || c == 'e' || c == 'E' {
+                    return self.n.parse::<f64>().ok().map_or(false, f64::is_finite);
+                }
+            }
+            false
+        }
+    }
+
+    /// If the `Number` is an integer, represent it as i64 if possible. Returns
+    /// None otherwise.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let big = i64::max_value() as u64 + 10;
+    /// let v = json!({ "a": 64, "b": big, "c": 256.0 });
+    ///
+    /// assert_eq!(v["a"].as_i64(), Some(64));
+    /// assert_eq!(v["b"].as_i64(), None);
+    /// assert_eq!(v["c"].as_i64(), None);
+    /// ```
+    #[inline]
+    pub fn as_i64(&self) -> Option<i64> {
+        #[cfg(not(feature = "arbitrary_precision"))]
+        match self.n {
+            N::PosInt(n) => {
+                if n <= i64::max_value() as u64 {
+                    Some(n as i64)
+                } else {
+                    None
+                }
+            }
+            N::NegInt(n) => Some(n),
+            N::Float(_) => None,
+        }
+        #[cfg(feature = "arbitrary_precision")]
+        self.n.parse().ok()
+    }
+
+    /// If the `Number` is an integer, represent it as u64 if possible. Returns
+    /// None otherwise.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let v = json!({ "a": 64, "b": -64, "c": 256.0 });
+    ///
+    /// assert_eq!(v["a"].as_u64(), Some(64));
+    /// assert_eq!(v["b"].as_u64(), None);
+    /// assert_eq!(v["c"].as_u64(), None);
+    /// ```
+    #[inline]
+    pub fn as_u64(&self) -> Option<u64> {
+        #[cfg(not(feature = "arbitrary_precision"))]
+        match self.n {
+            N::PosInt(n) => Some(n),
+            N::NegInt(_) | N::Float(_) => None,
+        }
+        #[cfg(feature = "arbitrary_precision")]
+        self.n.parse().ok()
+    }
+
+    /// Represents the number as f64 if possible. Returns None otherwise.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let v = json!({ "a": 256.0, "b": 64, "c": -64 });
+    ///
+    /// assert_eq!(v["a"].as_f64(), Some(256.0));
+    /// assert_eq!(v["b"].as_f64(), Some(64.0));
+    /// assert_eq!(v["c"].as_f64(), Some(-64.0));
+    /// ```
+    #[inline]
+    pub fn as_f64(&self) -> Option<f64> {
+        #[cfg(not(feature = "arbitrary_precision"))]
+        match self.n {
+            N::PosInt(n) => Some(n as f64),
+            N::NegInt(n) => Some(n as f64),
+            N::Float(n) => Some(n),
+        }
+        #[cfg(feature = "arbitrary_precision")]
+        self.n.parse::<f64>().ok().filter(|float| float.is_finite())
+    }
+
+    /// Converts a finite `f64` to a `Number`. Infinite or NaN values are not JSON
+    /// numbers.
+    ///
+    /// ```
+    /// # use std::f64;
+    /// #
+    /// # use serde_json::Number;
+    /// #
+    /// assert!(Number::from_f64(256.0).is_some());
+    ///
+    /// assert!(Number::from_f64(f64::NAN).is_none());
+    /// ```
+    #[inline]
+    pub fn from_f64(f: f64) -> Option<Number> {
+        if f.is_finite() {
+            let n = {
+                #[cfg(not(feature = "arbitrary_precision"))]
+                {
+                    N::Float(f)
+                }
+                #[cfg(feature = "arbitrary_precision")]
+                {
+                    ryu::Buffer::new().format_finite(f).to_owned()
+                }
+            };
+            Some(Number { n })
+        } else {
+            None
+        }
+    }
+
+    #[cfg(feature = "arbitrary_precision")]
+    /// Not public API. Only tests use this.
+    #[doc(hidden)]
+    #[inline]
+    pub fn from_string_unchecked(n: String) -> Self {
+        Number { n }
+    }
+}
+
+impl Display for Number {
+    #[cfg(not(feature = "arbitrary_precision"))]
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        match self.n {
+            N::PosInt(u) => formatter.write_str(itoa::Buffer::new().format(u)),
+            N::NegInt(i) => formatter.write_str(itoa::Buffer::new().format(i)),
+            N::Float(f) => formatter.write_str(ryu::Buffer::new().format_finite(f)),
+        }
+    }
+
+    #[cfg(feature = "arbitrary_precision")]
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        Display::fmt(&self.n, formatter)
+    }
+}
+
+impl Debug for Number {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        write!(formatter, "Number({})", self)
+    }
+}
+
+impl Serialize for Number {
+    #[cfg(not(feature = "arbitrary_precision"))]
+    #[inline]
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        match self.n {
+            N::PosInt(u) => serializer.serialize_u64(u),
+            N::NegInt(i) => serializer.serialize_i64(i),
+            N::Float(f) => serializer.serialize_f64(f),
+        }
+    }
+
+    #[cfg(feature = "arbitrary_precision")]
+    #[inline]
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        use serde::ser::SerializeStruct;
+
+        let mut s = serializer.serialize_struct(TOKEN, 1)?;
+        s.serialize_field(TOKEN, &self.n)?;
+        s.end()
+    }
+}
+
+impl<'de> Deserialize<'de> for Number {
+    #[inline]
+    fn deserialize<D>(deserializer: D) -> Result<Number, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        struct NumberVisitor;
+
+        impl<'de> Visitor<'de> for NumberVisitor {
+            type Value = Number;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str("a JSON number")
+            }
+
+            #[inline]
+            fn visit_i64<E>(self, value: i64) -> Result<Number, E> {
+                Ok(value.into())
+            }
+
+            #[inline]
+            fn visit_u64<E>(self, value: u64) -> Result<Number, E> {
+                Ok(value.into())
+            }
+
+            #[inline]
+            fn visit_f64<E>(self, value: f64) -> Result<Number, E>
+            where
+                E: de::Error,
+            {
+                Number::from_f64(value).ok_or_else(|| de::Error::custom("not a JSON number"))
+            }
+
+            #[cfg(feature = "arbitrary_precision")]
+            #[inline]
+            fn visit_map<V>(self, mut visitor: V) -> Result<Number, V::Error>
+            where
+                V: de::MapAccess<'de>,
+            {
+                let value = visitor.next_key::<NumberKey>()?;
+                if value.is_none() {
+                    return Err(de::Error::invalid_type(Unexpected::Map, &self));
+                }
+                let v: NumberFromString = visitor.next_value()?;
+                Ok(v.value)
+            }
+        }
+
+        deserializer.deserialize_any(NumberVisitor)
+    }
+}
+
+#[cfg(feature = "arbitrary_precision")]
+struct NumberKey;
+
+#[cfg(feature = "arbitrary_precision")]
+impl<'de> de::Deserialize<'de> for NumberKey {
+    fn deserialize<D>(deserializer: D) -> Result<NumberKey, D::Error>
+    where
+        D: de::Deserializer<'de>,
+    {
+        struct FieldVisitor;
+
+        impl<'de> de::Visitor<'de> for FieldVisitor {
+            type Value = ();
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str("a valid number field")
+            }
+
+            fn visit_str<E>(self, s: &str) -> Result<(), E>
+            where
+                E: de::Error,
+            {
+                if s == TOKEN {
+                    Ok(())
+                } else {
+                    Err(de::Error::custom("expected field with custom name"))
+                }
+            }
+        }
+
+        deserializer.deserialize_identifier(FieldVisitor)?;
+        Ok(NumberKey)
+    }
+}
+
+#[cfg(feature = "arbitrary_precision")]
+pub struct NumberFromString {
+    pub value: Number,
+}
+
+#[cfg(feature = "arbitrary_precision")]
+impl<'de> de::Deserialize<'de> for NumberFromString {
+    fn deserialize<D>(deserializer: D) -> Result<NumberFromString, D::Error>
+    where
+        D: de::Deserializer<'de>,
+    {
+        struct Visitor;
+
+        impl<'de> de::Visitor<'de> for Visitor {
+            type Value = NumberFromString;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str("string containing a number")
+            }
+
+            fn visit_str<E>(self, s: &str) -> Result<NumberFromString, E>
+            where
+                E: de::Error,
+            {
+                let n = tri!(s.parse().map_err(de::Error::custom));
+                Ok(NumberFromString { value: n })
+            }
+        }
+
+        deserializer.deserialize_str(Visitor)
+    }
+}
+
+#[cfg(feature = "arbitrary_precision")]
+fn invalid_number() -> Error {
+    Error::syntax(ErrorCode::InvalidNumber, 0, 0)
+}
+
+macro_rules! deserialize_any {
+    (@expand [$($num_string:tt)*]) => {
+        #[cfg(not(feature = "arbitrary_precision"))]
+        #[inline]
+        fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Error>
+        where
+            V: Visitor<'de>,
+        {
+            match self.n {
+                N::PosInt(u) => visitor.visit_u64(u),
+                N::NegInt(i) => visitor.visit_i64(i),
+                N::Float(f) => visitor.visit_f64(f),
+            }
+        }
+
+        #[cfg(feature = "arbitrary_precision")]
+        #[inline]
+        fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Error>
+            where V: Visitor<'de>
+        {
+            if let Some(u) = self.as_u64() {
+                return visitor.visit_u64(u);
+            } else if let Some(i) = self.as_i64() {
+                return visitor.visit_i64(i);
+            } else if let Some(f) = self.as_f64() {
+                if ryu::Buffer::new().format_finite(f) == self.n || f.to_string() == self.n {
+                    return visitor.visit_f64(f);
+                }
+            }
+
+            visitor.visit_map(NumberDeserializer {
+                number: Some(self.$($num_string)*),
+            })
+        }
+    };
+
+    (owned) => {
+        deserialize_any!(@expand [n]);
+    };
+
+    (ref) => {
+        deserialize_any!(@expand [n.clone()]);
+    };
+}
+
+macro_rules! deserialize_number {
+    ($deserialize:ident => $visit:ident) => {
+        #[cfg(not(feature = "arbitrary_precision"))]
+        fn $deserialize<V>(self, visitor: V) -> Result<V::Value, Error>
+        where
+            V: Visitor<'de>,
+        {
+            self.deserialize_any(visitor)
+        }
+
+        #[cfg(feature = "arbitrary_precision")]
+        fn $deserialize<V>(self, visitor: V) -> Result<V::Value, Error>
+        where
+            V: de::Visitor<'de>,
+        {
+            visitor.$visit(self.n.parse().map_err(|_| invalid_number())?)
+        }
+    };
+}
+
+impl<'de> Deserializer<'de> for Number {
+    type Error = Error;
+
+    deserialize_any!(owned);
+
+    deserialize_number!(deserialize_i8 => visit_i8);
+    deserialize_number!(deserialize_i16 => visit_i16);
+    deserialize_number!(deserialize_i32 => visit_i32);
+    deserialize_number!(deserialize_i64 => visit_i64);
+    deserialize_number!(deserialize_i128 => visit_i128);
+    deserialize_number!(deserialize_u8 => visit_u8);
+    deserialize_number!(deserialize_u16 => visit_u16);
+    deserialize_number!(deserialize_u32 => visit_u32);
+    deserialize_number!(deserialize_u64 => visit_u64);
+    deserialize_number!(deserialize_u128 => visit_u128);
+    deserialize_number!(deserialize_f32 => visit_f32);
+    deserialize_number!(deserialize_f64 => visit_f64);
+
+    forward_to_deserialize_any! {
+        bool char str string bytes byte_buf option unit unit_struct
+        newtype_struct seq tuple tuple_struct map struct enum identifier
+        ignored_any
+    }
+}
+
+impl<'de, 'a> Deserializer<'de> for &'a Number {
+    type Error = Error;
+
+    deserialize_any!(ref);
+
+    deserialize_number!(deserialize_i8 => visit_i8);
+    deserialize_number!(deserialize_i16 => visit_i16);
+    deserialize_number!(deserialize_i32 => visit_i32);
+    deserialize_number!(deserialize_i64 => visit_i64);
+    deserialize_number!(deserialize_i128 => visit_i128);
+    deserialize_number!(deserialize_u8 => visit_u8);
+    deserialize_number!(deserialize_u16 => visit_u16);
+    deserialize_number!(deserialize_u32 => visit_u32);
+    deserialize_number!(deserialize_u64 => visit_u64);
+    deserialize_number!(deserialize_u128 => visit_u128);
+    deserialize_number!(deserialize_f32 => visit_f32);
+    deserialize_number!(deserialize_f64 => visit_f64);
+
+    forward_to_deserialize_any! {
+        bool char str string bytes byte_buf option unit unit_struct
+        newtype_struct seq tuple tuple_struct map struct enum identifier
+        ignored_any
+    }
+}
+
+#[cfg(feature = "arbitrary_precision")]
+pub(crate) struct NumberDeserializer {
+    pub number: Option<String>,
+}
+
+#[cfg(feature = "arbitrary_precision")]
+impl<'de> MapAccess<'de> for NumberDeserializer {
+    type Error = Error;
+
+    fn next_key_seed<K>(&mut self, seed: K) -> Result<Option<K::Value>, Error>
+    where
+        K: de::DeserializeSeed<'de>,
+    {
+        if self.number.is_none() {
+            return Ok(None);
+        }
+        seed.deserialize(NumberFieldDeserializer).map(Some)
+    }
+
+    fn next_value_seed<V>(&mut self, seed: V) -> Result<V::Value, Error>
+    where
+        V: de::DeserializeSeed<'de>,
+    {
+        seed.deserialize(self.number.take().unwrap().into_deserializer())
+    }
+}
+
+#[cfg(feature = "arbitrary_precision")]
+struct NumberFieldDeserializer;
+
+#[cfg(feature = "arbitrary_precision")]
+impl<'de> Deserializer<'de> for NumberFieldDeserializer {
+    type Error = Error;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_borrowed_str(TOKEN)
+    }
+
+    forward_to_deserialize_any! {
+        bool u8 u16 u32 u64 u128 i8 i16 i32 i64 i128 f32 f64 char str string seq
+        bytes byte_buf map struct option unit newtype_struct ignored_any
+        unit_struct tuple_struct tuple enum identifier
+    }
+}
+
+impl From<ParserNumber> for Number {
+    fn from(value: ParserNumber) -> Self {
+        let n = match value {
+            ParserNumber::F64(f) => {
+                #[cfg(not(feature = "arbitrary_precision"))]
+                {
+                    N::Float(f)
+                }
+                #[cfg(feature = "arbitrary_precision")]
+                {
+                    f.to_string()
+                }
+            }
+            ParserNumber::U64(u) => {
+                #[cfg(not(feature = "arbitrary_precision"))]
+                {
+                    N::PosInt(u)
+                }
+                #[cfg(feature = "arbitrary_precision")]
+                {
+                    u.to_string()
+                }
+            }
+            ParserNumber::I64(i) => {
+                #[cfg(not(feature = "arbitrary_precision"))]
+                {
+                    N::NegInt(i)
+                }
+                #[cfg(feature = "arbitrary_precision")]
+                {
+                    i.to_string()
+                }
+            }
+            #[cfg(feature = "arbitrary_precision")]
+            ParserNumber::String(s) => s,
+        };
+        Number { n }
+    }
+}
+
+macro_rules! impl_from_unsigned {
+    (
+        $($ty:ty),*
+    ) => {
+        $(
+            impl From<$ty> for Number {
+                #[inline]
+                fn from(u: $ty) -> Self {
+                    let n = {
+                        #[cfg(not(feature = "arbitrary_precision"))]
+                        { N::PosInt(u as u64) }
+                        #[cfg(feature = "arbitrary_precision")]
+                        {
+                            itoa::Buffer::new().format(u).to_owned()
+                        }
+                    };
+                    Number { n }
+                }
+            }
+        )*
+    };
+}
+
+macro_rules! impl_from_signed {
+    (
+        $($ty:ty),*
+    ) => {
+        $(
+            impl From<$ty> for Number {
+                #[inline]
+                fn from(i: $ty) -> Self {
+                    let n = {
+                        #[cfg(not(feature = "arbitrary_precision"))]
+                        {
+                            if i < 0 {
+                                N::NegInt(i as i64)
+                            } else {
+                                N::PosInt(i as u64)
+                            }
+                        }
+                        #[cfg(feature = "arbitrary_precision")]
+                        {
+                            itoa::Buffer::new().format(i).to_owned()
+                        }
+                    };
+                    Number { n }
+                }
+            }
+        )*
+    };
+}
+
+impl_from_unsigned!(u8, u16, u32, u64, usize);
+impl_from_signed!(i8, i16, i32, i64, isize);
+
+#[cfg(feature = "arbitrary_precision")]
+impl_from_unsigned!(u128);
+#[cfg(feature = "arbitrary_precision")]
+impl_from_signed!(i128);
+
+impl Number {
+    #[cfg(not(feature = "arbitrary_precision"))]
+    #[cold]
+    pub(crate) fn unexpected(&self) -> Unexpected {
+        match self.n {
+            N::PosInt(u) => Unexpected::Unsigned(u),
+            N::NegInt(i) => Unexpected::Signed(i),
+            N::Float(f) => Unexpected::Float(f),
+        }
+    }
+
+    #[cfg(feature = "arbitrary_precision")]
+    #[cold]
+    pub(crate) fn unexpected(&self) -> Unexpected {
+        Unexpected::Other("number")
+    }
+}
diff --git a/third_party/rust/serde_json/src/raw.rs b/third_party/rust/serde_json/src/raw.rs
new file mode 100644
index 0000000000..6aa4ffcb61
--- /dev/null
+++ b/third_party/rust/serde_json/src/raw.rs
@@ -0,0 +1,531 @@
+use crate::error::Error;
+use alloc::borrow::ToOwned;
+use alloc::boxed::Box;
+use alloc::string::String;
+use core::fmt::{self, Debug, Display};
+use core::mem;
+use serde::de::value::BorrowedStrDeserializer;
+use serde::de::{
+    self, Deserialize, DeserializeSeed, Deserializer, IntoDeserializer, MapAccess, Unexpected,
+    Visitor,
+};
+use serde::forward_to_deserialize_any;
+use serde::ser::{Serialize, SerializeStruct, Serializer};
+
+/// Reference to a range of bytes encompassing a single valid JSON value in the
+/// input data.
+///
+/// A `RawValue` can be used to defer parsing parts of a payload until later,
+/// or to avoid parsing it at all in the case that part of the payload just
+/// needs to be transferred verbatim into a different output object.
+///
+/// When serializing, a value of this type will retain its original formatting
+/// and will not be minified or pretty-printed.
+///
+/// # Note
+///
+/// `RawValue` is only available if serde\_json is built with the `"raw_value"`
+/// feature.
+///
+/// ```toml
+/// [dependencies]
+/// serde_json = { version = "1.0", features = ["raw_value"] }
+/// ```
+///
+/// # Example
+///
+/// ```
+/// use serde::{Deserialize, Serialize};
+/// use serde_json::{Result, value::RawValue};
+///
+/// #[derive(Deserialize)]
+/// struct Input<'a> {
+///     code: u32,
+///     #[serde(borrow)]
+///     payload: &'a RawValue,
+/// }
+///
+/// #[derive(Serialize)]
+/// struct Output<'a> {
+///     info: (u32, &'a RawValue),
+/// }
+///
+/// // Efficiently rearrange JSON input containing separate "code" and "payload"
+/// // keys into a single "info" key holding an array of code and payload.
+/// //
+/// // This could be done equivalently using serde_json::Value as the type for
+/// // payload, but &RawValue will perform better because it does not require
+/// // memory allocation. The correct range of bytes is borrowed from the input
+/// // data and pasted verbatim into the output.
+/// fn rearrange(input: &str) -> Result<String> {
+///     let input: Input = serde_json::from_str(input)?;
+///
+///     let output = Output {
+///         info: (input.code, input.payload),
+///     };
+///
+///     serde_json::to_string(&output)
+/// }
+///
+/// fn main() -> Result<()> {
+///     let out = rearrange(r#" {"code": 200, "payload": {}} "#)?;
+///
+///     assert_eq!(out, r#"{"info":[200,{}]}"#);
+///
+///     Ok(())
+/// }
+/// ```
+///
+/// # Ownership
+///
+/// The typical usage of `RawValue` will be in the borrowed form:
+///
+/// ```
+/// # use serde::Deserialize;
+/// # use serde_json::value::RawValue;
+/// #
+/// #[derive(Deserialize)]
+/// struct SomeStruct<'a> {
+///     #[serde(borrow)]
+///     raw_value: &'a RawValue,
+/// }
+/// ```
+///
+/// The borrowed form is suitable when deserializing through
+/// [`serde_json::from_str`] and [`serde_json::from_slice`] which support
+/// borrowing from the input data without memory allocation.
+///
+/// When deserializing through [`serde_json::from_reader`] you will need to use
+/// the boxed form of `RawValue` instead. This is almost as efficient but
+/// involves buffering the raw value from the I/O stream into memory.
+///
+/// [`serde_json::from_str`]: ../fn.from_str.html
+/// [`serde_json::from_slice`]: ../fn.from_slice.html
+/// [`serde_json::from_reader`]: ../fn.from_reader.html
+///
+/// ```
+/// # use serde::Deserialize;
+/// # use serde_json::value::RawValue;
+/// #
+/// #[derive(Deserialize)]
+/// struct SomeStruct {
+///     raw_value: Box<RawValue>,
+/// }
+/// ```
+#[cfg_attr(not(doc), repr(transparent))]
+#[cfg_attr(docsrs, doc(cfg(feature = "raw_value")))]
+pub struct RawValue {
+    json: str,
+}
+
+impl RawValue {
+    fn from_borrowed(json: &str) -> &Self {
+        unsafe { mem::transmute::<&str, &RawValue>(json) }
+    }
+
+    fn from_owned(json: Box<str>) -> Box<Self> {
+        unsafe { mem::transmute::<Box<str>, Box<RawValue>>(json) }
+    }
+
+    fn into_owned(raw_value: Box<Self>) -> Box<str> {
+        unsafe { mem::transmute::<Box<RawValue>, Box<str>>(raw_value) }
+    }
+}
+
+impl Clone for Box<RawValue> {
+    fn clone(&self) -> Self {
+        (**self).to_owned()
+    }
+}
+
+impl ToOwned for RawValue {
+    type Owned = Box<RawValue>;
+
+    fn to_owned(&self) -> Self::Owned {
+        RawValue::from_owned(self.json.to_owned().into_boxed_str())
+    }
+}
+
+impl Default for Box<RawValue> {
+    fn default() -> Self {
+        RawValue::from_borrowed("null").to_owned()
+    }
+}
+
+impl Debug for RawValue {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter
+            .debug_tuple("RawValue")
+            .field(&format_args!("{}", &self.json))
+            .finish()
+    }
+}
+
+impl Display for RawValue {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.write_str(&self.json)
+    }
+}
+
+impl RawValue {
+    /// Convert an owned `String` of JSON data to an owned `RawValue`.
+    ///
+    /// This function is equivalent to `serde_json::from_str::<Box<RawValue>>`
+    /// except that we avoid an allocation and memcpy if both of the following
+    /// are true:
+    ///
+    /// - the input has no leading or trailing whitespace, and
+    /// - the input has capacity equal to its length.
+    pub fn from_string(json: String) -> Result<Box<Self>, Error> {
+        {
+            let borrowed = crate::from_str::<&Self>(&json)?;
+            if borrowed.json.len() < json.len() {
+                return Ok(borrowed.to_owned());
+            }
+        }
+        Ok(Self::from_owned(json.into_boxed_str()))
+    }
+
+    /// Access the JSON text underlying a raw value.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// use serde::Deserialize;
+    /// use serde_json::{Result, value::RawValue};
+    ///
+    /// #[derive(Deserialize)]
+    /// struct Response<'a> {
+    ///     code: u32,
+    ///     #[serde(borrow)]
+    ///     payload: &'a RawValue,
+    /// }
+    ///
+    /// fn process(input: &str) -> Result<()> {
+    ///     let response: Response = serde_json::from_str(input)?;
+    ///
+    ///     let payload = response.payload.get();
+    ///     if payload.starts_with('{') {
+    ///         // handle a payload which is a JSON map
+    ///     } else {
+    ///         // handle any other type
+    ///     }
+    ///
+    ///     Ok(())
+    /// }
+    ///
+    /// fn main() -> Result<()> {
+    ///     process(r#" {"code": 200, "payload": {}} "#)?;
+    ///     Ok(())
+    /// }
+    /// ```
+    pub fn get(&self) -> &str {
+        &self.json
+    }
+}
+
+impl From<Box<RawValue>> for Box<str> {
+    fn from(raw_value: Box<RawValue>) -> Self {
+        RawValue::into_owned(raw_value)
+    }
+}
+
+/// Convert a `T` into a boxed `RawValue`.
+///
+/// # Example
+///
+/// ```
+/// // Upstream crate
+/// # #[derive(Serialize)]
+/// pub struct Thing {
+///     foo: String,
+///     bar: Option<String>,
+///     extra_data: Box<RawValue>,
+/// }
+///
+/// // Local crate
+/// use serde::Serialize;
+/// use serde_json::value::{to_raw_value, RawValue};
+///
+/// #[derive(Serialize)]
+/// struct MyExtraData {
+///     a: u32,
+///     b: u32,
+/// }
+///
+/// let my_thing = Thing {
+///     foo: "FooVal".into(),
+///     bar: None,
+///     extra_data: to_raw_value(&MyExtraData { a: 1, b: 2 }).unwrap(),
+/// };
+/// # assert_eq!(
+/// #     serde_json::to_value(my_thing).unwrap(),
+/// #     serde_json::json!({
+/// #         "foo": "FooVal",
+/// #         "bar": null,
+/// #         "extra_data": { "a": 1, "b": 2 }
+/// #     })
+/// # );
+/// ```
+///
+/// # Errors
+///
+/// This conversion can fail if `T`'s implementation of `Serialize` decides to
+/// fail, or if `T` contains a map with non-string keys.
+///
+/// ```
+/// use std::collections::BTreeMap;
+///
+/// // The keys in this map are vectors, not strings.
+/// let mut map = BTreeMap::new();
+/// map.insert(vec![32, 64], "x86");
+///
+/// println!("{}", serde_json::value::to_raw_value(&map).unwrap_err());
+/// ```
+#[cfg_attr(docsrs, doc(cfg(feature = "raw_value")))]
+pub fn to_raw_value<T>(value: &T) -> Result<Box<RawValue>, Error>
+where
+    T: ?Sized + Serialize,
+{
+    let json_string = crate::to_string(value)?;
+    Ok(RawValue::from_owned(json_string.into_boxed_str()))
+}
+
+pub const TOKEN: &str = "$serde_json::private::RawValue";
+
+impl Serialize for RawValue {
+    fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+    where
+        S: Serializer,
+    {
+        let mut s = serializer.serialize_struct(TOKEN, 1)?;
+        s.serialize_field(TOKEN, &self.json)?;
+        s.end()
+    }
+}
+
+impl<'de: 'a, 'a> Deserialize<'de> for &'a RawValue {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        struct ReferenceVisitor;
+
+        impl<'de> Visitor<'de> for ReferenceVisitor {
+            type Value = &'de RawValue;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                write!(formatter, "any valid JSON value")
+            }
+
+            fn visit_map<V>(self, mut visitor: V) -> Result<Self::Value, V::Error>
+            where
+                V: MapAccess<'de>,
+            {
+                let value = visitor.next_key::<RawKey>()?;
+                if value.is_none() {
+                    return Err(de::Error::invalid_type(Unexpected::Map, &self));
+                }
+                visitor.next_value_seed(ReferenceFromString)
+            }
+        }
+
+        deserializer.deserialize_newtype_struct(TOKEN, ReferenceVisitor)
+    }
+}
+
+impl<'de> Deserialize<'de> for Box<RawValue> {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        struct BoxedVisitor;
+
+        impl<'de> Visitor<'de> for BoxedVisitor {
+            type Value = Box<RawValue>;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                write!(formatter, "any valid JSON value")
+            }
+
+            fn visit_map<V>(self, mut visitor: V) -> Result<Self::Value, V::Error>
+            where
+                V: MapAccess<'de>,
+            {
+                let value = visitor.next_key::<RawKey>()?;
+                if value.is_none() {
+                    return Err(de::Error::invalid_type(Unexpected::Map, &self));
+                }
+                visitor.next_value_seed(BoxedFromString)
+            }
+        }
+
+        deserializer.deserialize_newtype_struct(TOKEN, BoxedVisitor)
+    }
+}
+
+struct RawKey;
+
+impl<'de> Deserialize<'de> for RawKey {
+    fn deserialize<D>(deserializer: D) -> Result<RawKey, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        struct FieldVisitor;
+
+        impl<'de> Visitor<'de> for FieldVisitor {
+            type Value = ();
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str("raw value")
+            }
+
+            fn visit_str<E>(self, s: &str) -> Result<(), E>
+            where
+                E: de::Error,
+            {
+                if s == TOKEN {
+                    Ok(())
+                } else {
+                    Err(de::Error::custom("unexpected raw value"))
+                }
+            }
+        }
+
+        deserializer.deserialize_identifier(FieldVisitor)?;
+        Ok(RawKey)
+    }
+}
+
+pub struct ReferenceFromString;
+
+impl<'de> DeserializeSeed<'de> for ReferenceFromString {
+    type Value = &'de RawValue;
+
+    fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        deserializer.deserialize_str(self)
+    }
+}
+
+impl<'de> Visitor<'de> for ReferenceFromString {
+    type Value = &'de RawValue;
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("raw value")
+    }
+
+    fn visit_borrowed_str<E>(self, s: &'de str) -> Result<Self::Value, E>
+    where
+        E: de::Error,
+    {
+        Ok(RawValue::from_borrowed(s))
+    }
+}
+
+pub struct BoxedFromString;
+
+impl<'de> DeserializeSeed<'de> for BoxedFromString {
+    type Value = Box<RawValue>;
+
+    fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        deserializer.deserialize_str(self)
+    }
+}
+
+impl<'de> Visitor<'de> for BoxedFromString {
+    type Value = Box<RawValue>;
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("raw value")
+    }
+
+    fn visit_str<E>(self, s: &str) -> Result<Self::Value, E>
+    where
+        E: de::Error,
+    {
+        Ok(RawValue::from_owned(s.to_owned().into_boxed_str()))
+    }
+
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    fn visit_string<E>(self, s: String) -> Result<Self::Value, E>
+    where
+        E: de::Error,
+    {
+        Ok(RawValue::from_owned(s.into_boxed_str()))
+    }
+}
+
+struct RawKeyDeserializer;
+
+impl<'de> Deserializer<'de> for RawKeyDeserializer {
+    type Error = Error;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_borrowed_str(TOKEN)
+    }
+
+    forward_to_deserialize_any! {
+        bool u8 u16 u32 u64 u128 i8 i16 i32 i64 i128 f32 f64 char str string seq
+        bytes byte_buf map struct option unit newtype_struct ignored_any
+        unit_struct tuple_struct tuple enum identifier
+    }
+}
+
+pub struct OwnedRawDeserializer {
+    pub raw_value: Option<String>,
+}
+
+impl<'de> MapAccess<'de> for OwnedRawDeserializer {
+    type Error = Error;
+
+    fn next_key_seed<K>(&mut self, seed: K) -> Result<Option<K::Value>, Error>
+    where
+        K: de::DeserializeSeed<'de>,
+    {
+        if self.raw_value.is_none() {
+            return Ok(None);
+        }
+        seed.deserialize(RawKeyDeserializer).map(Some)
+    }
+
+    fn next_value_seed<V>(&mut self, seed: V) -> Result<V::Value, Error>
+    where
+        V: de::DeserializeSeed<'de>,
+    {
+        seed.deserialize(self.raw_value.take().unwrap().into_deserializer())
+    }
+}
+
+pub struct BorrowedRawDeserializer<'de> {
+    pub raw_value: Option<&'de str>,
+}
+
+impl<'de> MapAccess<'de> for BorrowedRawDeserializer<'de> {
+    type Error = Error;
+
+    fn next_key_seed<K>(&mut self, seed: K) -> Result<Option<K::Value>, Error>
+    where
+        K: de::DeserializeSeed<'de>,
+    {
+        if self.raw_value.is_none() {
+            return Ok(None);
+        }
+        seed.deserialize(RawKeyDeserializer).map(Some)
+    }
+
+    fn next_value_seed<V>(&mut self, seed: V) -> Result<V::Value, Error>
+    where
+        V: de::DeserializeSeed<'de>,
+    {
+        seed.deserialize(BorrowedStrDeserializer::new(self.raw_value.take().unwrap()))
+    }
+}
diff --git a/third_party/rust/serde_json/src/read.rs b/third_party/rust/serde_json/src/read.rs
new file mode 100644
index 0000000000..fc3a3ca748
--- /dev/null
+++ b/third_party/rust/serde_json/src/read.rs
@@ -0,0 +1,1004 @@
+use crate::error::{Error, ErrorCode, Result};
+use alloc::vec::Vec;
+use core::char;
+use core::cmp;
+use core::ops::Deref;
+use core::str;
+
+#[cfg(feature = "std")]
+use crate::io;
+#[cfg(feature = "std")]
+use crate::iter::LineColIterator;
+
+#[cfg(feature = "raw_value")]
+use crate::raw::BorrowedRawDeserializer;
+#[cfg(all(feature = "raw_value", feature = "std"))]
+use crate::raw::OwnedRawDeserializer;
+#[cfg(feature = "raw_value")]
+use serde::de::Visitor;
+
+/// Trait used by the deserializer for iterating over input. This is manually
+/// "specialized" for iterating over &[u8]. Once feature(specialization) is
+/// stable we can use actual specialization.
+///
+/// This trait is sealed and cannot be implemented for types outside of
+/// `serde_json`.
+pub trait Read<'de>: private::Sealed {
+    #[doc(hidden)]
+    fn next(&mut self) -> Result<Option<u8>>;
+    #[doc(hidden)]
+    fn peek(&mut self) -> Result<Option<u8>>;
+
+    /// Only valid after a call to peek(). Discards the peeked byte.
+    #[doc(hidden)]
+    fn discard(&mut self);
+
+    /// Position of the most recent call to next().
+    ///
+    /// The most recent call was probably next() and not peek(), but this method
+    /// should try to return a sensible result if the most recent call was
+    /// actually peek() because we don't always know.
+    ///
+    /// Only called in case of an error, so performance is not important.
+    #[doc(hidden)]
+    fn position(&self) -> Position;
+
+    /// Position of the most recent call to peek().
+    ///
+    /// The most recent call was probably peek() and not next(), but this method
+    /// should try to return a sensible result if the most recent call was
+    /// actually next() because we don't always know.
+    ///
+    /// Only called in case of an error, so performance is not important.
+    #[doc(hidden)]
+    fn peek_position(&self) -> Position;
+
+    /// Offset from the beginning of the input to the next byte that would be
+    /// returned by next() or peek().
+    #[doc(hidden)]
+    fn byte_offset(&self) -> usize;
+
+    /// Assumes the previous byte was a quotation mark. Parses a JSON-escaped
+    /// string until the next quotation mark using the given scratch space if
+    /// necessary. The scratch space is initially empty.
+    #[doc(hidden)]
+    fn parse_str<'s>(&'s mut self, scratch: &'s mut Vec<u8>) -> Result<Reference<'de, 's, str>>;
+
+    /// Assumes the previous byte was a quotation mark. Parses a JSON-escaped
+    /// string until the next quotation mark using the given scratch space if
+    /// necessary. The scratch space is initially empty.
+    ///
+    /// This function returns the raw bytes in the string with escape sequences
+    /// expanded but without performing unicode validation.
+    #[doc(hidden)]
+    fn parse_str_raw<'s>(
+        &'s mut self,
+        scratch: &'s mut Vec<u8>,
+    ) -> Result<Reference<'de, 's, [u8]>>;
+
+    /// Assumes the previous byte was a quotation mark. Parses a JSON-escaped
+    /// string until the next quotation mark but discards the data.
+    #[doc(hidden)]
+    fn ignore_str(&mut self) -> Result<()>;
+
+    /// Assumes the previous byte was a hex escape sequnce ('\u') in a string.
+    /// Parses next hexadecimal sequence.
+    #[doc(hidden)]
+    fn decode_hex_escape(&mut self) -> Result<u16>;
+
+    /// Switch raw buffering mode on.
+    ///
+    /// This is used when deserializing `RawValue`.
+    #[cfg(feature = "raw_value")]
+    #[doc(hidden)]
+    fn begin_raw_buffering(&mut self);
+
+    /// Switch raw buffering mode off and provides the raw buffered data to the
+    /// given visitor.
+    #[cfg(feature = "raw_value")]
+    #[doc(hidden)]
+    fn end_raw_buffering<V>(&mut self, visitor: V) -> Result<V::Value>
+    where
+        V: Visitor<'de>;
+
+    /// Whether StreamDeserializer::next needs to check the failed flag. True
+    /// for IoRead, false for StrRead and SliceRead which can track failure by
+    /// truncating their input slice to avoid the extra check on every next
+    /// call.
+    #[doc(hidden)]
+    const should_early_return_if_failed: bool;
+
+    /// Mark a persistent failure of StreamDeserializer, either by setting the
+    /// flag or by truncating the input data.
+    #[doc(hidden)]
+    fn set_failed(&mut self, failed: &mut bool);
+}
+
+pub struct Position {
+    pub line: usize,
+    pub column: usize,
+}
+
+pub enum Reference<'b, 'c, T>
+where
+    T: ?Sized + 'static,
+{
+    Borrowed(&'b T),
+    Copied(&'c T),
+}
+
+impl<'b, 'c, T> Deref for Reference<'b, 'c, T>
+where
+    T: ?Sized + 'static,
+{
+    type Target = T;
+
+    fn deref(&self) -> &Self::Target {
+        match *self {
+            Reference::Borrowed(b) => b,
+            Reference::Copied(c) => c,
+        }
+    }
+}
+
+/// JSON input source that reads from a std::io input stream.
+#[cfg(feature = "std")]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
+pub struct IoRead<R>
+where
+    R: io::Read,
+{
+    iter: LineColIterator<io::Bytes<R>>,
+    /// Temporary storage of peeked byte.
+    ch: Option<u8>,
+    #[cfg(feature = "raw_value")]
+    raw_buffer: Option<Vec<u8>>,
+}
+
+/// JSON input source that reads from a slice of bytes.
+//
+// This is more efficient than other iterators because peek() can be read-only
+// and we can compute line/col position only if an error happens.
+pub struct SliceRead<'a> {
+    slice: &'a [u8],
+    /// Index of the *next* byte that will be returned by next() or peek().
+    index: usize,
+    #[cfg(feature = "raw_value")]
+    raw_buffering_start_index: usize,
+}
+
+/// JSON input source that reads from a UTF-8 string.
+//
+// Able to elide UTF-8 checks by assuming that the input is valid UTF-8.
+pub struct StrRead<'a> {
+    delegate: SliceRead<'a>,
+    #[cfg(feature = "raw_value")]
+    data: &'a str,
+}
+
+// Prevent users from implementing the Read trait.
+mod private {
+    pub trait Sealed {}
+}
+
+//////////////////////////////////////////////////////////////////////////////
+
+#[cfg(feature = "std")]
+impl<R> IoRead<R>
+where
+    R: io::Read,
+{
+    /// Create a JSON input source to read from a std::io input stream.
+    pub fn new(reader: R) -> Self {
+        IoRead {
+            iter: LineColIterator::new(reader.bytes()),
+            ch: None,
+            #[cfg(feature = "raw_value")]
+            raw_buffer: None,
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl<R> private::Sealed for IoRead<R> where R: io::Read {}
+
+#[cfg(feature = "std")]
+impl<R> IoRead<R>
+where
+    R: io::Read,
+{
+    fn parse_str_bytes<'s, T, F>(
+        &'s mut self,
+        scratch: &'s mut Vec<u8>,
+        validate: bool,
+        result: F,
+    ) -> Result<T>
+    where
+        T: 's,
+        F: FnOnce(&'s Self, &'s [u8]) -> Result<T>,
+    {
+        loop {
+            let ch = tri!(next_or_eof(self));
+            if !ESCAPE[ch as usize] {
+                scratch.push(ch);
+                continue;
+            }
+            match ch {
+                b'"' => {
+                    return result(self, scratch);
+                }
+                b'\\' => {
+                    tri!(parse_escape(self, validate, scratch));
+                }
+                _ => {
+                    if validate {
+                        return error(self, ErrorCode::ControlCharacterWhileParsingString);
+                    }
+                    scratch.push(ch);
+                }
+            }
+        }
+    }
+}
+
+#[cfg(feature = "std")]
+impl<'de, R> Read<'de> for IoRead<R>
+where
+    R: io::Read,
+{
+    #[inline]
+    fn next(&mut self) -> Result<Option<u8>> {
+        match self.ch.take() {
+            Some(ch) => {
+                #[cfg(feature = "raw_value")]
+                {
+                    if let Some(buf) = &mut self.raw_buffer {
+                        buf.push(ch);
+                    }
+                }
+                Ok(Some(ch))
+            }
+            None => match self.iter.next() {
+                Some(Err(err)) => Err(Error::io(err)),
+                Some(Ok(ch)) => {
+                    #[cfg(feature = "raw_value")]
+                    {
+                        if let Some(buf) = &mut self.raw_buffer {
+                            buf.push(ch);
+                        }
+                    }
+                    Ok(Some(ch))
+                }
+                None => Ok(None),
+            },
+        }
+    }
+
+    #[inline]
+    fn peek(&mut self) -> Result<Option<u8>> {
+        match self.ch {
+            Some(ch) => Ok(Some(ch)),
+            None => match self.iter.next() {
+                Some(Err(err)) => Err(Error::io(err)),
+                Some(Ok(ch)) => {
+                    self.ch = Some(ch);
+                    Ok(self.ch)
+                }
+                None => Ok(None),
+            },
+        }
+    }
+
+    #[cfg(not(feature = "raw_value"))]
+    #[inline]
+    fn discard(&mut self) {
+        self.ch = None;
+    }
+
+    #[cfg(feature = "raw_value")]
+    fn discard(&mut self) {
+        if let Some(ch) = self.ch.take() {
+            if let Some(buf) = &mut self.raw_buffer {
+                buf.push(ch);
+            }
+        }
+    }
+
+    fn position(&self) -> Position {
+        Position {
+            line: self.iter.line(),
+            column: self.iter.col(),
+        }
+    }
+
+    fn peek_position(&self) -> Position {
+        // The LineColIterator updates its position during peek() so it has the
+        // right one here.
+        self.position()
+    }
+
+    fn byte_offset(&self) -> usize {
+        match self.ch {
+            Some(_) => self.iter.byte_offset() - 1,
+            None => self.iter.byte_offset(),
+        }
+    }
+
+    fn parse_str<'s>(&'s mut self, scratch: &'s mut Vec<u8>) -> Result<Reference<'de, 's, str>> {
+        self.parse_str_bytes(scratch, true, as_str)
+            .map(Reference::Copied)
+    }
+
+    fn parse_str_raw<'s>(
+        &'s mut self,
+        scratch: &'s mut Vec<u8>,
+    ) -> Result<Reference<'de, 's, [u8]>> {
+        self.parse_str_bytes(scratch, false, |_, bytes| Ok(bytes))
+            .map(Reference::Copied)
+    }
+
+    fn ignore_str(&mut self) -> Result<()> {
+        loop {
+            let ch = tri!(next_or_eof(self));
+            if !ESCAPE[ch as usize] {
+                continue;
+            }
+            match ch {
+                b'"' => {
+                    return Ok(());
+                }
+                b'\\' => {
+                    tri!(ignore_escape(self));
+                }
+                _ => {
+                    return error(self, ErrorCode::ControlCharacterWhileParsingString);
+                }
+            }
+        }
+    }
+
+    fn decode_hex_escape(&mut self) -> Result<u16> {
+        let mut n = 0;
+        for _ in 0..4 {
+            match decode_hex_val(tri!(next_or_eof(self))) {
+                None => return error(self, ErrorCode::InvalidEscape),
+                Some(val) => {
+                    n = (n << 4) + val;
+                }
+            }
+        }
+        Ok(n)
+    }
+
+    #[cfg(feature = "raw_value")]
+    fn begin_raw_buffering(&mut self) {
+        self.raw_buffer = Some(Vec::new());
+    }
+
+    #[cfg(feature = "raw_value")]
+    fn end_raw_buffering<V>(&mut self, visitor: V) -> Result<V::Value>
+    where
+        V: Visitor<'de>,
+    {
+        let raw = self.raw_buffer.take().unwrap();
+        let raw = match String::from_utf8(raw) {
+            Ok(raw) => raw,
+            Err(_) => return error(self, ErrorCode::InvalidUnicodeCodePoint),
+        };
+        visitor.visit_map(OwnedRawDeserializer {
+            raw_value: Some(raw),
+        })
+    }
+
+    const should_early_return_if_failed: bool = true;
+
+    #[inline]
+    #[cold]
+    fn set_failed(&mut self, failed: &mut bool) {
+        *failed = true;
+    }
+}
+
+//////////////////////////////////////////////////////////////////////////////
+
+impl<'a> SliceRead<'a> {
+    /// Create a JSON input source to read from a slice of bytes.
+    pub fn new(slice: &'a [u8]) -> Self {
+        SliceRead {
+            slice,
+            index: 0,
+            #[cfg(feature = "raw_value")]
+            raw_buffering_start_index: 0,
+        }
+    }
+
+    fn position_of_index(&self, i: usize) -> Position {
+        let mut position = Position { line: 1, column: 0 };
+        for ch in &self.slice[..i] {
+            match *ch {
+                b'\n' => {
+                    position.line += 1;
+                    position.column = 0;
+                }
+                _ => {
+                    position.column += 1;
+                }
+            }
+        }
+        position
+    }
+
+    /// The big optimization here over IoRead is that if the string contains no
+    /// backslash escape sequences, the returned &str is a slice of the raw JSON
+    /// data so we avoid copying into the scratch space.
+    fn parse_str_bytes<'s, T, F>(
+        &'s mut self,
+        scratch: &'s mut Vec<u8>,
+        validate: bool,
+        result: F,
+    ) -> Result<Reference<'a, 's, T>>
+    where
+        T: ?Sized + 's,
+        F: for<'f> FnOnce(&'s Self, &'f [u8]) -> Result<&'f T>,
+    {
+        // Index of the first byte not yet copied into the scratch space.
+        let mut start = self.index;
+
+        loop {
+            while self.index < self.slice.len() && !ESCAPE[self.slice[self.index] as usize] {
+                self.index += 1;
+            }
+            if self.index == self.slice.len() {
+                return error(self, ErrorCode::EofWhileParsingString);
+            }
+            match self.slice[self.index] {
+                b'"' => {
+                    if scratch.is_empty() {
+                        // Fast path: return a slice of the raw JSON without any
+                        // copying.
+                        let borrowed = &self.slice[start..self.index];
+                        self.index += 1;
+                        return result(self, borrowed).map(Reference::Borrowed);
+                    } else {
+                        scratch.extend_from_slice(&self.slice[start..self.index]);
+                        self.index += 1;
+                        return result(self, scratch).map(Reference::Copied);
+                    }
+                }
+                b'\\' => {
+                    scratch.extend_from_slice(&self.slice[start..self.index]);
+                    self.index += 1;
+                    tri!(parse_escape(self, validate, scratch));
+                    start = self.index;
+                }
+                _ => {
+                    self.index += 1;
+                    if validate {
+                        return error(self, ErrorCode::ControlCharacterWhileParsingString);
+                    }
+                }
+            }
+        }
+    }
+}
+
+impl<'a> private::Sealed for SliceRead<'a> {}
+
+impl<'a> Read<'a> for SliceRead<'a> {
+    #[inline]
+    fn next(&mut self) -> Result<Option<u8>> {
+        // `Ok(self.slice.get(self.index).map(|ch| { self.index += 1; *ch }))`
+        // is about 10% slower.
+        Ok(if self.index < self.slice.len() {
+            let ch = self.slice[self.index];
+            self.index += 1;
+            Some(ch)
+        } else {
+            None
+        })
+    }
+
+    #[inline]
+    fn peek(&mut self) -> Result<Option<u8>> {
+        // `Ok(self.slice.get(self.index).map(|ch| *ch))` is about 10% slower
+        // for some reason.
+        Ok(if self.index < self.slice.len() {
+            Some(self.slice[self.index])
+        } else {
+            None
+        })
+    }
+
+    #[inline]
+    fn discard(&mut self) {
+        self.index += 1;
+    }
+
+    fn position(&self) -> Position {
+        self.position_of_index(self.index)
+    }
+
+    fn peek_position(&self) -> Position {
+        // Cap it at slice.len() just in case the most recent call was next()
+        // and it returned the last byte.
+        self.position_of_index(cmp::min(self.slice.len(), self.index + 1))
+    }
+
+    fn byte_offset(&self) -> usize {
+        self.index
+    }
+
+    fn parse_str<'s>(&'s mut self, scratch: &'s mut Vec<u8>) -> Result<Reference<'a, 's, str>> {
+        self.parse_str_bytes(scratch, true, as_str)
+    }
+
+    fn parse_str_raw<'s>(
+        &'s mut self,
+        scratch: &'s mut Vec<u8>,
+    ) -> Result<Reference<'a, 's, [u8]>> {
+        self.parse_str_bytes(scratch, false, |_, bytes| Ok(bytes))
+    }
+
+    fn ignore_str(&mut self) -> Result<()> {
+        loop {
+            while self.index < self.slice.len() && !ESCAPE[self.slice[self.index] as usize] {
+                self.index += 1;
+            }
+            if self.index == self.slice.len() {
+                return error(self, ErrorCode::EofWhileParsingString);
+            }
+            match self.slice[self.index] {
+                b'"' => {
+                    self.index += 1;
+                    return Ok(());
+                }
+                b'\\' => {
+                    self.index += 1;
+                    tri!(ignore_escape(self));
+                }
+                _ => {
+                    return error(self, ErrorCode::ControlCharacterWhileParsingString);
+                }
+            }
+        }
+    }
+
+    fn decode_hex_escape(&mut self) -> Result<u16> {
+        if self.index + 4 > self.slice.len() {
+            self.index = self.slice.len();
+            return error(self, ErrorCode::EofWhileParsingString);
+        }
+
+        let mut n = 0;
+        for _ in 0..4 {
+            let ch = decode_hex_val(self.slice[self.index]);
+            self.index += 1;
+            match ch {
+                None => return error(self, ErrorCode::InvalidEscape),
+                Some(val) => {
+                    n = (n << 4) + val;
+                }
+            }
+        }
+        Ok(n)
+    }
+
+    #[cfg(feature = "raw_value")]
+    fn begin_raw_buffering(&mut self) {
+        self.raw_buffering_start_index = self.index;
+    }
+
+    #[cfg(feature = "raw_value")]
+    fn end_raw_buffering<V>(&mut self, visitor: V) -> Result<V::Value>
+    where
+        V: Visitor<'a>,
+    {
+        let raw = &self.slice[self.raw_buffering_start_index..self.index];
+        let raw = match str::from_utf8(raw) {
+            Ok(raw) => raw,
+            Err(_) => return error(self, ErrorCode::InvalidUnicodeCodePoint),
+        };
+        visitor.visit_map(BorrowedRawDeserializer {
+            raw_value: Some(raw),
+        })
+    }
+
+    const should_early_return_if_failed: bool = false;
+
+    #[inline]
+    #[cold]
+    fn set_failed(&mut self, _failed: &mut bool) {
+        self.slice = &self.slice[..self.index];
+    }
+}
+
+//////////////////////////////////////////////////////////////////////////////
+
+impl<'a> StrRead<'a> {
+    /// Create a JSON input source to read from a UTF-8 string.
+    pub fn new(s: &'a str) -> Self {
+        StrRead {
+            delegate: SliceRead::new(s.as_bytes()),
+            #[cfg(feature = "raw_value")]
+            data: s,
+        }
+    }
+}
+
+impl<'a> private::Sealed for StrRead<'a> {}
+
+impl<'a> Read<'a> for StrRead<'a> {
+    #[inline]
+    fn next(&mut self) -> Result<Option<u8>> {
+        self.delegate.next()
+    }
+
+    #[inline]
+    fn peek(&mut self) -> Result<Option<u8>> {
+        self.delegate.peek()
+    }
+
+    #[inline]
+    fn discard(&mut self) {
+        self.delegate.discard();
+    }
+
+    fn position(&self) -> Position {
+        self.delegate.position()
+    }
+
+    fn peek_position(&self) -> Position {
+        self.delegate.peek_position()
+    }
+
+    fn byte_offset(&self) -> usize {
+        self.delegate.byte_offset()
+    }
+
+    fn parse_str<'s>(&'s mut self, scratch: &'s mut Vec<u8>) -> Result<Reference<'a, 's, str>> {
+        self.delegate.parse_str_bytes(scratch, true, |_, bytes| {
+            // The deserialization input came in as &str with a UTF-8 guarantee,
+            // and the \u-escapes are checked along the way, so don't need to
+            // check here.
+            Ok(unsafe { str::from_utf8_unchecked(bytes) })
+        })
+    }
+
+    fn parse_str_raw<'s>(
+        &'s mut self,
+        scratch: &'s mut Vec<u8>,
+    ) -> Result<Reference<'a, 's, [u8]>> {
+        self.delegate.parse_str_raw(scratch)
+    }
+
+    fn ignore_str(&mut self) -> Result<()> {
+        self.delegate.ignore_str()
+    }
+
+    fn decode_hex_escape(&mut self) -> Result<u16> {
+        self.delegate.decode_hex_escape()
+    }
+
+    #[cfg(feature = "raw_value")]
+    fn begin_raw_buffering(&mut self) {
+        self.delegate.begin_raw_buffering();
+    }
+
+    #[cfg(feature = "raw_value")]
+    fn end_raw_buffering<V>(&mut self, visitor: V) -> Result<V::Value>
+    where
+        V: Visitor<'a>,
+    {
+        let raw = &self.data[self.delegate.raw_buffering_start_index..self.delegate.index];
+        visitor.visit_map(BorrowedRawDeserializer {
+            raw_value: Some(raw),
+        })
+    }
+
+    const should_early_return_if_failed: bool = false;
+
+    #[inline]
+    #[cold]
+    fn set_failed(&mut self, failed: &mut bool) {
+        self.delegate.set_failed(failed);
+    }
+}
+
+//////////////////////////////////////////////////////////////////////////////
+
+impl<'a, 'de, R> private::Sealed for &'a mut R where R: Read<'de> {}
+
+impl<'a, 'de, R> Read<'de> for &'a mut R
+where
+    R: Read<'de>,
+{
+    fn next(&mut self) -> Result<Option<u8>> {
+        R::next(self)
+    }
+
+    fn peek(&mut self) -> Result<Option<u8>> {
+        R::peek(self)
+    }
+
+    fn discard(&mut self) {
+        R::discard(self);
+    }
+
+    fn position(&self) -> Position {
+        R::position(self)
+    }
+
+    fn peek_position(&self) -> Position {
+        R::peek_position(self)
+    }
+
+    fn byte_offset(&self) -> usize {
+        R::byte_offset(self)
+    }
+
+    fn parse_str<'s>(&'s mut self, scratch: &'s mut Vec<u8>) -> Result<Reference<'de, 's, str>> {
+        R::parse_str(self, scratch)
+    }
+
+    fn parse_str_raw<'s>(
+        &'s mut self,
+        scratch: &'s mut Vec<u8>,
+    ) -> Result<Reference<'de, 's, [u8]>> {
+        R::parse_str_raw(self, scratch)
+    }
+
+    fn ignore_str(&mut self) -> Result<()> {
+        R::ignore_str(self)
+    }
+
+    fn decode_hex_escape(&mut self) -> Result<u16> {
+        R::decode_hex_escape(self)
+    }
+
+    #[cfg(feature = "raw_value")]
+    fn begin_raw_buffering(&mut self) {
+        R::begin_raw_buffering(self);
+    }
+
+    #[cfg(feature = "raw_value")]
+    fn end_raw_buffering<V>(&mut self, visitor: V) -> Result<V::Value>
+    where
+        V: Visitor<'de>,
+    {
+        R::end_raw_buffering(self, visitor)
+    }
+
+    const should_early_return_if_failed: bool = R::should_early_return_if_failed;
+
+    fn set_failed(&mut self, failed: &mut bool) {
+        R::set_failed(self, failed);
+    }
+}
+
+//////////////////////////////////////////////////////////////////////////////
+
+/// Marker for whether StreamDeserializer can implement FusedIterator.
+pub trait Fused: private::Sealed {}
+impl<'a> Fused for SliceRead<'a> {}
+impl<'a> Fused for StrRead<'a> {}
+
+// Lookup table of bytes that must be escaped. A value of true at index i means
+// that byte i requires an escape sequence in the input.
+static ESCAPE: [bool; 256] = {
+    const CT: bool = true; // control character \x00..=\x1F
+    const QU: bool = true; // quote \x22
+    const BS: bool = true; // backslash \x5C
+    const __: bool = false; // allow unescaped
+    [
+        //   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F
+        CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, // 0
+        CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, CT, // 1
+        __, __, QU, __, __, __, __, __, __, __, __, __, __, __, __, __, // 2
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // 3
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // 4
+        __, __, __, __, __, __, __, __, __, __, __, __, BS, __, __, __, // 5
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // 6
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // 7
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // 8
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // 9
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // A
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // B
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // C
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // D
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // E
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // F
+    ]
+};
+
+fn next_or_eof<'de, R>(read: &mut R) -> Result<u8>
+where
+    R: ?Sized + Read<'de>,
+{
+    match tri!(read.next()) {
+        Some(b) => Ok(b),
+        None => error(read, ErrorCode::EofWhileParsingString),
+    }
+}
+
+fn peek_or_eof<'de, R>(read: &mut R) -> Result<u8>
+where
+    R: ?Sized + Read<'de>,
+{
+    match tri!(read.peek()) {
+        Some(b) => Ok(b),
+        None => error(read, ErrorCode::EofWhileParsingString),
+    }
+}
+
+fn error<'de, R, T>(read: &R, reason: ErrorCode) -> Result<T>
+where
+    R: ?Sized + Read<'de>,
+{
+    let position = read.position();
+    Err(Error::syntax(reason, position.line, position.column))
+}
+
+fn as_str<'de, 's, R: Read<'de>>(read: &R, slice: &'s [u8]) -> Result<&'s str> {
+    str::from_utf8(slice).or_else(|_| error(read, ErrorCode::InvalidUnicodeCodePoint))
+}
+
+/// Parses a JSON escape sequence and appends it into the scratch space. Assumes
+/// the previous byte read was a backslash.
+fn parse_escape<'de, R: Read<'de>>(
+    read: &mut R,
+    validate: bool,
+    scratch: &mut Vec<u8>,
+) -> Result<()> {
+    let ch = tri!(next_or_eof(read));
+
+    match ch {
+        b'"' => scratch.push(b'"'),
+        b'\\' => scratch.push(b'\\'),
+        b'/' => scratch.push(b'/'),
+        b'b' => scratch.push(b'\x08'),
+        b'f' => scratch.push(b'\x0c'),
+        b'n' => scratch.push(b'\n'),
+        b'r' => scratch.push(b'\r'),
+        b't' => scratch.push(b'\t'),
+        b'u' => {
+            fn encode_surrogate(scratch: &mut Vec<u8>, n: u16) {
+                scratch.extend_from_slice(&[
+                    (n >> 12 & 0b0000_1111) as u8 | 0b1110_0000,
+                    (n >> 6 & 0b0011_1111) as u8 | 0b1000_0000,
+                    (n & 0b0011_1111) as u8 | 0b1000_0000,
+                ]);
+            }
+
+            let c = match tri!(read.decode_hex_escape()) {
+                n @ 0xDC00..=0xDFFF => {
+                    return if validate {
+                        error(read, ErrorCode::LoneLeadingSurrogateInHexEscape)
+                    } else {
+                        encode_surrogate(scratch, n);
+                        Ok(())
+                    };
+                }
+
+                // Non-BMP characters are encoded as a sequence of two hex
+                // escapes, representing UTF-16 surrogates. If deserializing a
+                // utf-8 string the surrogates are required to be paired,
+                // whereas deserializing a byte string accepts lone surrogates.
+                n1 @ 0xD800..=0xDBFF => {
+                    if tri!(peek_or_eof(read)) == b'\\' {
+                        read.discard();
+                    } else {
+                        return if validate {
+                            read.discard();
+                            error(read, ErrorCode::UnexpectedEndOfHexEscape)
+                        } else {
+                            encode_surrogate(scratch, n1);
+                            Ok(())
+                        };
+                    }
+
+                    if tri!(peek_or_eof(read)) == b'u' {
+                        read.discard();
+                    } else {
+                        return if validate {
+                            read.discard();
+                            error(read, ErrorCode::UnexpectedEndOfHexEscape)
+                        } else {
+                            encode_surrogate(scratch, n1);
+                            // The \ prior to this byte started an escape sequence,
+                            // so we need to parse that now. This recursive call
+                            // does not blow the stack on malicious input because
+                            // the escape is not \u, so it will be handled by one
+                            // of the easy nonrecursive cases.
+                            parse_escape(read, validate, scratch)
+                        };
+                    }
+
+                    let n2 = tri!(read.decode_hex_escape());
+
+                    if n2 < 0xDC00 || n2 > 0xDFFF {
+                        return error(read, ErrorCode::LoneLeadingSurrogateInHexEscape);
+                    }
+
+                    let n = (((n1 - 0xD800) as u32) << 10 | (n2 - 0xDC00) as u32) + 0x1_0000;
+
+                    match char::from_u32(n) {
+                        Some(c) => c,
+                        None => {
+                            return error(read, ErrorCode::InvalidUnicodeCodePoint);
+                        }
+                    }
+                }
+
+                // Every u16 outside of the surrogate ranges above is guaranteed
+                // to be a legal char.
+                n => char::from_u32(n as u32).unwrap(),
+            };
+
+            scratch.extend_from_slice(c.encode_utf8(&mut [0_u8; 4]).as_bytes());
+        }
+        _ => {
+            return error(read, ErrorCode::InvalidEscape);
+        }
+    }
+
+    Ok(())
+}
+
+/// Parses a JSON escape sequence and discards the value. Assumes the previous
+/// byte read was a backslash.
+fn ignore_escape<'de, R>(read: &mut R) -> Result<()>
+where
+    R: ?Sized + Read<'de>,
+{
+    let ch = tri!(next_or_eof(read));
+
+    match ch {
+        b'"' | b'\\' | b'/' | b'b' | b'f' | b'n' | b'r' | b't' => {}
+        b'u' => {
+            // At this point we don't care if the codepoint is valid. We just
+            // want to consume it. We don't actually know what is valid or not
+            // at this point, because that depends on if this string will
+            // ultimately be parsed into a string or a byte buffer in the "real"
+            // parse.
+
+            tri!(read.decode_hex_escape());
+        }
+        _ => {
+            return error(read, ErrorCode::InvalidEscape);
+        }
+    }
+
+    Ok(())
+}
+
+static HEX: [u8; 256] = {
+    const __: u8 = 255; // not a hex digit
+    [
+        //   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // 0
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // 1
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // 2
+        00, 01, 02, 03, 04, 05, 06, 07, 08, 09, __, __, __, __, __, __, // 3
+        __, 10, 11, 12, 13, 14, 15, __, __, __, __, __, __, __, __, __, // 4
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // 5
+        __, 10, 11, 12, 13, 14, 15, __, __, __, __, __, __, __, __, __, // 6
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // 7
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // 8
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // 9
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // A
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // B
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // C
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // D
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // E
+        __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // F
+    ]
+};
+
+fn decode_hex_val(val: u8) -> Option<u16> {
+    let n = HEX[val as usize] as u16;
+    if n == 255 {
+        None
+    } else {
+        Some(n)
+    }
+}
diff --git a/third_party/rust/serde_json/src/ser.rs b/third_party/rust/serde_json/src/ser.rs
new file mode 100644
index 0000000000..80c2deb0c1
--- /dev/null
+++ b/third_party/rust/serde_json/src/ser.rs
@@ -0,0 +1,2179 @@
+//! Serialize a Rust data structure into JSON data.
+
+use crate::error::{Error, ErrorCode, Result};
+use crate::io;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::fmt::{self, Display};
+use core::num::FpCategory;
+use serde::ser::{self, Impossible, Serialize};
+
+/// A structure for serializing Rust values into JSON.
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
+pub struct Serializer<W, F = CompactFormatter> {
+    writer: W,
+    formatter: F,
+}
+
+impl<W> Serializer<W>
+where
+    W: io::Write,
+{
+    /// Creates a new JSON serializer.
+    #[inline]
+    pub fn new(writer: W) -> Self {
+        Serializer::with_formatter(writer, CompactFormatter)
+    }
+}
+
+impl<'a, W> Serializer<W, PrettyFormatter<'a>>
+where
+    W: io::Write,
+{
+    /// Creates a new JSON pretty print serializer.
+    #[inline]
+    pub fn pretty(writer: W) -> Self {
+        Serializer::with_formatter(writer, PrettyFormatter::new())
+    }
+}
+
+impl<W, F> Serializer<W, F>
+where
+    W: io::Write,
+    F: Formatter,
+{
+    /// Creates a new JSON visitor whose output will be written to the writer
+    /// specified.
+    #[inline]
+    pub fn with_formatter(writer: W, formatter: F) -> Self {
+        Serializer { writer, formatter }
+    }
+
+    /// Unwrap the `Writer` from the `Serializer`.
+    #[inline]
+    pub fn into_inner(self) -> W {
+        self.writer
+    }
+}
+
+impl<'a, W, F> ser::Serializer for &'a mut Serializer<W, F>
+where
+    W: io::Write,
+    F: Formatter,
+{
+    type Ok = ();
+    type Error = Error;
+
+    type SerializeSeq = Compound<'a, W, F>;
+    type SerializeTuple = Compound<'a, W, F>;
+    type SerializeTupleStruct = Compound<'a, W, F>;
+    type SerializeTupleVariant = Compound<'a, W, F>;
+    type SerializeMap = Compound<'a, W, F>;
+    type SerializeStruct = Compound<'a, W, F>;
+    type SerializeStructVariant = Compound<'a, W, F>;
+
+    #[inline]
+    fn serialize_bool(self, value: bool) -> Result<()> {
+        self.formatter
+            .write_bool(&mut self.writer, value)
+            .map_err(Error::io)
+    }
+
+    #[inline]
+    fn serialize_i8(self, value: i8) -> Result<()> {
+        self.formatter
+            .write_i8(&mut self.writer, value)
+            .map_err(Error::io)
+    }
+
+    #[inline]
+    fn serialize_i16(self, value: i16) -> Result<()> {
+        self.formatter
+            .write_i16(&mut self.writer, value)
+            .map_err(Error::io)
+    }
+
+    #[inline]
+    fn serialize_i32(self, value: i32) -> Result<()> {
+        self.formatter
+            .write_i32(&mut self.writer, value)
+            .map_err(Error::io)
+    }
+
+    #[inline]
+    fn serialize_i64(self, value: i64) -> Result<()> {
+        self.formatter
+            .write_i64(&mut self.writer, value)
+            .map_err(Error::io)
+    }
+
+    fn serialize_i128(self, value: i128) -> Result<()> {
+        self.formatter
+            .write_i128(&mut self.writer, value)
+            .map_err(Error::io)
+    }
+
+    #[inline]
+    fn serialize_u8(self, value: u8) -> Result<()> {
+        self.formatter
+            .write_u8(&mut self.writer, value)
+            .map_err(Error::io)
+    }
+
+    #[inline]
+    fn serialize_u16(self, value: u16) -> Result<()> {
+        self.formatter
+            .write_u16(&mut self.writer, value)
+            .map_err(Error::io)
+    }
+
+    #[inline]
+    fn serialize_u32(self, value: u32) -> Result<()> {
+        self.formatter
+            .write_u32(&mut self.writer, value)
+            .map_err(Error::io)
+    }
+
+    #[inline]
+    fn serialize_u64(self, value: u64) -> Result<()> {
+        self.formatter
+            .write_u64(&mut self.writer, value)
+            .map_err(Error::io)
+    }
+
+    fn serialize_u128(self, value: u128) -> Result<()> {
+        self.formatter
+            .write_u128(&mut self.writer, value)
+            .map_err(Error::io)
+    }
+
+    #[inline]
+    fn serialize_f32(self, value: f32) -> Result<()> {
+        match value.classify() {
+            FpCategory::Nan | FpCategory::Infinite => self
+                .formatter
+                .write_null(&mut self.writer)
+                .map_err(Error::io),
+            _ => self
+                .formatter
+                .write_f32(&mut self.writer, value)
+                .map_err(Error::io),
+        }
+    }
+
+    #[inline]
+    fn serialize_f64(self, value: f64) -> Result<()> {
+        match value.classify() {
+            FpCategory::Nan | FpCategory::Infinite => self
+                .formatter
+                .write_null(&mut self.writer)
+                .map_err(Error::io),
+            _ => self
+                .formatter
+                .write_f64(&mut self.writer, value)
+                .map_err(Error::io),
+        }
+    }
+
+    #[inline]
+    fn serialize_char(self, value: char) -> Result<()> {
+        // A char encoded as UTF-8 takes 4 bytes at most.
+        let mut buf = [0; 4];
+        self.serialize_str(value.encode_utf8(&mut buf))
+    }
+
+    #[inline]
+    fn serialize_str(self, value: &str) -> Result<()> {
+        format_escaped_str(&mut self.writer, &mut self.formatter, value).map_err(Error::io)
+    }
+
+    #[inline]
+    fn serialize_bytes(self, value: &[u8]) -> Result<()> {
+        use serde::ser::SerializeSeq;
+        let mut seq = tri!(self.serialize_seq(Some(value.len())));
+        for byte in value {
+            tri!(seq.serialize_element(byte));
+        }
+        seq.end()
+    }
+
+    #[inline]
+    fn serialize_unit(self) -> Result<()> {
+        self.formatter
+            .write_null(&mut self.writer)
+            .map_err(Error::io)
+    }
+
+    #[inline]
+    fn serialize_unit_struct(self, _name: &'static str) -> Result<()> {
+        self.serialize_unit()
+    }
+
+    #[inline]
+    fn serialize_unit_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+    ) -> Result<()> {
+        self.serialize_str(variant)
+    }
+
+    /// Serialize newtypes without an object wrapper.
+    #[inline]
+    fn serialize_newtype_struct<T>(self, _name: &'static str, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        value.serialize(self)
+    }
+
+    #[inline]
+    fn serialize_newtype_variant<T>(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+        value: &T,
+    ) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        tri!(self
+            .formatter
+            .begin_object(&mut self.writer)
+            .map_err(Error::io));
+        tri!(self
+            .formatter
+            .begin_object_key(&mut self.writer, true)
+            .map_err(Error::io));
+        tri!(self.serialize_str(variant));
+        tri!(self
+            .formatter
+            .end_object_key(&mut self.writer)
+            .map_err(Error::io));
+        tri!(self
+            .formatter
+            .begin_object_value(&mut self.writer)
+            .map_err(Error::io));
+        tri!(value.serialize(&mut *self));
+        tri!(self
+            .formatter
+            .end_object_value(&mut self.writer)
+            .map_err(Error::io));
+        self.formatter
+            .end_object(&mut self.writer)
+            .map_err(Error::io)
+    }
+
+    #[inline]
+    fn serialize_none(self) -> Result<()> {
+        self.serialize_unit()
+    }
+
+    #[inline]
+    fn serialize_some<T>(self, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        value.serialize(self)
+    }
+
+    #[inline]
+    fn serialize_seq(self, len: Option<usize>) -> Result<Self::SerializeSeq> {
+        tri!(self
+            .formatter
+            .begin_array(&mut self.writer)
+            .map_err(Error::io));
+        if len == Some(0) {
+            tri!(self
+                .formatter
+                .end_array(&mut self.writer)
+                .map_err(Error::io));
+            Ok(Compound::Map {
+                ser: self,
+                state: State::Empty,
+            })
+        } else {
+            Ok(Compound::Map {
+                ser: self,
+                state: State::First,
+            })
+        }
+    }
+
+    #[inline]
+    fn serialize_tuple(self, len: usize) -> Result<Self::SerializeTuple> {
+        self.serialize_seq(Some(len))
+    }
+
+    #[inline]
+    fn serialize_tuple_struct(
+        self,
+        _name: &'static str,
+        len: usize,
+    ) -> Result<Self::SerializeTupleStruct> {
+        self.serialize_seq(Some(len))
+    }
+
+    #[inline]
+    fn serialize_tuple_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+        len: usize,
+    ) -> Result<Self::SerializeTupleVariant> {
+        tri!(self
+            .formatter
+            .begin_object(&mut self.writer)
+            .map_err(Error::io));
+        tri!(self
+            .formatter
+            .begin_object_key(&mut self.writer, true)
+            .map_err(Error::io));
+        tri!(self.serialize_str(variant));
+        tri!(self
+            .formatter
+            .end_object_key(&mut self.writer)
+            .map_err(Error::io));
+        tri!(self
+            .formatter
+            .begin_object_value(&mut self.writer)
+            .map_err(Error::io));
+        self.serialize_seq(Some(len))
+    }
+
+    #[inline]
+    fn serialize_map(self, len: Option<usize>) -> Result<Self::SerializeMap> {
+        tri!(self
+            .formatter
+            .begin_object(&mut self.writer)
+            .map_err(Error::io));
+        if len == Some(0) {
+            tri!(self
+                .formatter
+                .end_object(&mut self.writer)
+                .map_err(Error::io));
+            Ok(Compound::Map {
+                ser: self,
+                state: State::Empty,
+            })
+        } else {
+            Ok(Compound::Map {
+                ser: self,
+                state: State::First,
+            })
+        }
+    }
+
+    #[inline]
+    fn serialize_struct(self, name: &'static str, len: usize) -> Result<Self::SerializeStruct> {
+        match name {
+            #[cfg(feature = "arbitrary_precision")]
+            crate::number::TOKEN => Ok(Compound::Number { ser: self }),
+            #[cfg(feature = "raw_value")]
+            crate::raw::TOKEN => Ok(Compound::RawValue { ser: self }),
+            _ => self.serialize_map(Some(len)),
+        }
+    }
+
+    #[inline]
+    fn serialize_struct_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+        len: usize,
+    ) -> Result<Self::SerializeStructVariant> {
+        tri!(self
+            .formatter
+            .begin_object(&mut self.writer)
+            .map_err(Error::io));
+        tri!(self
+            .formatter
+            .begin_object_key(&mut self.writer, true)
+            .map_err(Error::io));
+        tri!(self.serialize_str(variant));
+        tri!(self
+            .formatter
+            .end_object_key(&mut self.writer)
+            .map_err(Error::io));
+        tri!(self
+            .formatter
+            .begin_object_value(&mut self.writer)
+            .map_err(Error::io));
+        self.serialize_map(Some(len))
+    }
+
+    fn collect_str<T>(self, value: &T) -> Result<()>
+    where
+        T: ?Sized + Display,
+    {
+        use self::fmt::Write;
+
+        struct Adapter<'ser, W: 'ser, F: 'ser> {
+            writer: &'ser mut W,
+            formatter: &'ser mut F,
+            error: Option<io::Error>,
+        }
+
+        impl<'ser, W, F> Write for Adapter<'ser, W, F>
+        where
+            W: io::Write,
+            F: Formatter,
+        {
+            fn write_str(&mut self, s: &str) -> fmt::Result {
+                debug_assert!(self.error.is_none());
+                match format_escaped_str_contents(self.writer, self.formatter, s) {
+                    Ok(()) => Ok(()),
+                    Err(err) => {
+                        self.error = Some(err);
+                        Err(fmt::Error)
+                    }
+                }
+            }
+        }
+
+        tri!(self
+            .formatter
+            .begin_string(&mut self.writer)
+            .map_err(Error::io));
+        {
+            let mut adapter = Adapter {
+                writer: &mut self.writer,
+                formatter: &mut self.formatter,
+                error: None,
+            };
+            match write!(adapter, "{}", value) {
+                Ok(()) => debug_assert!(adapter.error.is_none()),
+                Err(fmt::Error) => {
+                    return Err(Error::io(adapter.error.expect("there should be an error")));
+                }
+            }
+        }
+        self.formatter
+            .end_string(&mut self.writer)
+            .map_err(Error::io)
+    }
+}
+
+// Not public API. Should be pub(crate).
+#[doc(hidden)]
+#[derive(Eq, PartialEq)]
+pub enum State {
+    Empty,
+    First,
+    Rest,
+}
+
+// Not public API. Should be pub(crate).
+#[doc(hidden)]
+pub enum Compound<'a, W: 'a, F: 'a> {
+    Map {
+        ser: &'a mut Serializer<W, F>,
+        state: State,
+    },
+    #[cfg(feature = "arbitrary_precision")]
+    Number { ser: &'a mut Serializer<W, F> },
+    #[cfg(feature = "raw_value")]
+    RawValue { ser: &'a mut Serializer<W, F> },
+}
+
+impl<'a, W, F> ser::SerializeSeq for Compound<'a, W, F>
+where
+    W: io::Write,
+    F: Formatter,
+{
+    type Ok = ();
+    type Error = Error;
+
+    #[inline]
+    fn serialize_element<T>(&mut self, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        match self {
+            Compound::Map { ser, state } => {
+                tri!(ser
+                    .formatter
+                    .begin_array_value(&mut ser.writer, *state == State::First)
+                    .map_err(Error::io));
+                *state = State::Rest;
+                tri!(value.serialize(&mut **ser));
+                ser.formatter
+                    .end_array_value(&mut ser.writer)
+                    .map_err(Error::io)
+            }
+            #[cfg(feature = "arbitrary_precision")]
+            Compound::Number { .. } => unreachable!(),
+            #[cfg(feature = "raw_value")]
+            Compound::RawValue { .. } => unreachable!(),
+        }
+    }
+
+    #[inline]
+    fn end(self) -> Result<()> {
+        match self {
+            Compound::Map { ser, state } => match state {
+                State::Empty => Ok(()),
+                _ => ser.formatter.end_array(&mut ser.writer).map_err(Error::io),
+            },
+            #[cfg(feature = "arbitrary_precision")]
+            Compound::Number { .. } => unreachable!(),
+            #[cfg(feature = "raw_value")]
+            Compound::RawValue { .. } => unreachable!(),
+        }
+    }
+}
+
+impl<'a, W, F> ser::SerializeTuple for Compound<'a, W, F>
+where
+    W: io::Write,
+    F: Formatter,
+{
+    type Ok = ();
+    type Error = Error;
+
+    #[inline]
+    fn serialize_element<T>(&mut self, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        ser::SerializeSeq::serialize_element(self, value)
+    }
+
+    #[inline]
+    fn end(self) -> Result<()> {
+        ser::SerializeSeq::end(self)
+    }
+}
+
+impl<'a, W, F> ser::SerializeTupleStruct for Compound<'a, W, F>
+where
+    W: io::Write,
+    F: Formatter,
+{
+    type Ok = ();
+    type Error = Error;
+
+    #[inline]
+    fn serialize_field<T>(&mut self, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        ser::SerializeSeq::serialize_element(self, value)
+    }
+
+    #[inline]
+    fn end(self) -> Result<()> {
+        ser::SerializeSeq::end(self)
+    }
+}
+
+impl<'a, W, F> ser::SerializeTupleVariant for Compound<'a, W, F>
+where
+    W: io::Write,
+    F: Formatter,
+{
+    type Ok = ();
+    type Error = Error;
+
+    #[inline]
+    fn serialize_field<T>(&mut self, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        ser::SerializeSeq::serialize_element(self, value)
+    }
+
+    #[inline]
+    fn end(self) -> Result<()> {
+        match self {
+            Compound::Map { ser, state } => {
+                match state {
+                    State::Empty => {}
+                    _ => tri!(ser.formatter.end_array(&mut ser.writer).map_err(Error::io)),
+                }
+                tri!(ser
+                    .formatter
+                    .end_object_value(&mut ser.writer)
+                    .map_err(Error::io));
+                ser.formatter.end_object(&mut ser.writer).map_err(Error::io)
+            }
+            #[cfg(feature = "arbitrary_precision")]
+            Compound::Number { .. } => unreachable!(),
+            #[cfg(feature = "raw_value")]
+            Compound::RawValue { .. } => unreachable!(),
+        }
+    }
+}
+
+impl<'a, W, F> ser::SerializeMap for Compound<'a, W, F>
+where
+    W: io::Write,
+    F: Formatter,
+{
+    type Ok = ();
+    type Error = Error;
+
+    #[inline]
+    fn serialize_key<T>(&mut self, key: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        match self {
+            Compound::Map { ser, state } => {
+                tri!(ser
+                    .formatter
+                    .begin_object_key(&mut ser.writer, *state == State::First)
+                    .map_err(Error::io));
+                *state = State::Rest;
+
+                tri!(key.serialize(MapKeySerializer { ser: *ser }));
+
+                ser.formatter
+                    .end_object_key(&mut ser.writer)
+                    .map_err(Error::io)
+            }
+            #[cfg(feature = "arbitrary_precision")]
+            Compound::Number { .. } => unreachable!(),
+            #[cfg(feature = "raw_value")]
+            Compound::RawValue { .. } => unreachable!(),
+        }
+    }
+
+    #[inline]
+    fn serialize_value<T>(&mut self, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        match self {
+            Compound::Map { ser, .. } => {
+                tri!(ser
+                    .formatter
+                    .begin_object_value(&mut ser.writer)
+                    .map_err(Error::io));
+                tri!(value.serialize(&mut **ser));
+                ser.formatter
+                    .end_object_value(&mut ser.writer)
+                    .map_err(Error::io)
+            }
+            #[cfg(feature = "arbitrary_precision")]
+            Compound::Number { .. } => unreachable!(),
+            #[cfg(feature = "raw_value")]
+            Compound::RawValue { .. } => unreachable!(),
+        }
+    }
+
+    #[inline]
+    fn end(self) -> Result<()> {
+        match self {
+            Compound::Map { ser, state } => match state {
+                State::Empty => Ok(()),
+                _ => ser.formatter.end_object(&mut ser.writer).map_err(Error::io),
+            },
+            #[cfg(feature = "arbitrary_precision")]
+            Compound::Number { .. } => unreachable!(),
+            #[cfg(feature = "raw_value")]
+            Compound::RawValue { .. } => unreachable!(),
+        }
+    }
+}
+
+impl<'a, W, F> ser::SerializeStruct for Compound<'a, W, F>
+where
+    W: io::Write,
+    F: Formatter,
+{
+    type Ok = ();
+    type Error = Error;
+
+    #[inline]
+    fn serialize_field<T>(&mut self, key: &'static str, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        match self {
+            Compound::Map { .. } => ser::SerializeMap::serialize_entry(self, key, value),
+            #[cfg(feature = "arbitrary_precision")]
+            Compound::Number { ser, .. } => {
+                if key == crate::number::TOKEN {
+                    value.serialize(NumberStrEmitter(ser))
+                } else {
+                    Err(invalid_number())
+                }
+            }
+            #[cfg(feature = "raw_value")]
+            Compound::RawValue { ser, .. } => {
+                if key == crate::raw::TOKEN {
+                    value.serialize(RawValueStrEmitter(ser))
+                } else {
+                    Err(invalid_raw_value())
+                }
+            }
+        }
+    }
+
+    #[inline]
+    fn end(self) -> Result<()> {
+        match self {
+            Compound::Map { .. } => ser::SerializeMap::end(self),
+            #[cfg(feature = "arbitrary_precision")]
+            Compound::Number { .. } => Ok(()),
+            #[cfg(feature = "raw_value")]
+            Compound::RawValue { .. } => Ok(()),
+        }
+    }
+}
+
+impl<'a, W, F> ser::SerializeStructVariant for Compound<'a, W, F>
+where
+    W: io::Write,
+    F: Formatter,
+{
+    type Ok = ();
+    type Error = Error;
+
+    #[inline]
+    fn serialize_field<T>(&mut self, key: &'static str, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        match *self {
+            Compound::Map { .. } => ser::SerializeStruct::serialize_field(self, key, value),
+            #[cfg(feature = "arbitrary_precision")]
+            Compound::Number { .. } => unreachable!(),
+            #[cfg(feature = "raw_value")]
+            Compound::RawValue { .. } => unreachable!(),
+        }
+    }
+
+    #[inline]
+    fn end(self) -> Result<()> {
+        match self {
+            Compound::Map { ser, state } => {
+                match state {
+                    State::Empty => {}
+                    _ => tri!(ser.formatter.end_object(&mut ser.writer).map_err(Error::io)),
+                }
+                tri!(ser
+                    .formatter
+                    .end_object_value(&mut ser.writer)
+                    .map_err(Error::io));
+                ser.formatter.end_object(&mut ser.writer).map_err(Error::io)
+            }
+            #[cfg(feature = "arbitrary_precision")]
+            Compound::Number { .. } => unreachable!(),
+            #[cfg(feature = "raw_value")]
+            Compound::RawValue { .. } => unreachable!(),
+        }
+    }
+}
+
+struct MapKeySerializer<'a, W: 'a, F: 'a> {
+    ser: &'a mut Serializer<W, F>,
+}
+
+#[cfg(feature = "arbitrary_precision")]
+fn invalid_number() -> Error {
+    Error::syntax(ErrorCode::InvalidNumber, 0, 0)
+}
+
+#[cfg(feature = "raw_value")]
+fn invalid_raw_value() -> Error {
+    Error::syntax(ErrorCode::ExpectedSomeValue, 0, 0)
+}
+
+fn key_must_be_a_string() -> Error {
+    Error::syntax(ErrorCode::KeyMustBeAString, 0, 0)
+}
+
+impl<'a, W, F> ser::Serializer for MapKeySerializer<'a, W, F>
+where
+    W: io::Write,
+    F: Formatter,
+{
+    type Ok = ();
+    type Error = Error;
+
+    #[inline]
+    fn serialize_str(self, value: &str) -> Result<()> {
+        self.ser.serialize_str(value)
+    }
+
+    #[inline]
+    fn serialize_unit_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+    ) -> Result<()> {
+        self.ser.serialize_str(variant)
+    }
+
+    #[inline]
+    fn serialize_newtype_struct<T>(self, _name: &'static str, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        value.serialize(self)
+    }
+
+    type SerializeSeq = Impossible<(), Error>;
+    type SerializeTuple = Impossible<(), Error>;
+    type SerializeTupleStruct = Impossible<(), Error>;
+    type SerializeTupleVariant = Impossible<(), Error>;
+    type SerializeMap = Impossible<(), Error>;
+    type SerializeStruct = Impossible<(), Error>;
+    type SerializeStructVariant = Impossible<(), Error>;
+
+    fn serialize_bool(self, _value: bool) -> Result<()> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_i8(self, value: i8) -> Result<()> {
+        tri!(self
+            .ser
+            .formatter
+            .begin_string(&mut self.ser.writer)
+            .map_err(Error::io));
+        tri!(self
+            .ser
+            .formatter
+            .write_i8(&mut self.ser.writer, value)
+            .map_err(Error::io));
+        self.ser
+            .formatter
+            .end_string(&mut self.ser.writer)
+            .map_err(Error::io)
+    }
+
+    fn serialize_i16(self, value: i16) -> Result<()> {
+        tri!(self
+            .ser
+            .formatter
+            .begin_string(&mut self.ser.writer)
+            .map_err(Error::io));
+        tri!(self
+            .ser
+            .formatter
+            .write_i16(&mut self.ser.writer, value)
+            .map_err(Error::io));
+        self.ser
+            .formatter
+            .end_string(&mut self.ser.writer)
+            .map_err(Error::io)
+    }
+
+    fn serialize_i32(self, value: i32) -> Result<()> {
+        tri!(self
+            .ser
+            .formatter
+            .begin_string(&mut self.ser.writer)
+            .map_err(Error::io));
+        tri!(self
+            .ser
+            .formatter
+            .write_i32(&mut self.ser.writer, value)
+            .map_err(Error::io));
+        self.ser
+            .formatter
+            .end_string(&mut self.ser.writer)
+            .map_err(Error::io)
+    }
+
+    fn serialize_i64(self, value: i64) -> Result<()> {
+        tri!(self
+            .ser
+            .formatter
+            .begin_string(&mut self.ser.writer)
+            .map_err(Error::io));
+        tri!(self
+            .ser
+            .formatter
+            .write_i64(&mut self.ser.writer, value)
+            .map_err(Error::io));
+        self.ser
+            .formatter
+            .end_string(&mut self.ser.writer)
+            .map_err(Error::io)
+    }
+
+    fn serialize_i128(self, value: i128) -> Result<()> {
+        tri!(self
+            .ser
+            .formatter
+            .begin_string(&mut self.ser.writer)
+            .map_err(Error::io));
+        tri!(self
+            .ser
+            .formatter
+            .write_i128(&mut self.ser.writer, value)
+            .map_err(Error::io));
+        self.ser
+            .formatter
+            .end_string(&mut self.ser.writer)
+            .map_err(Error::io)
+    }
+
+    fn serialize_u8(self, value: u8) -> Result<()> {
+        tri!(self
+            .ser
+            .formatter
+            .begin_string(&mut self.ser.writer)
+            .map_err(Error::io));
+        tri!(self
+            .ser
+            .formatter
+            .write_u8(&mut self.ser.writer, value)
+            .map_err(Error::io));
+        self.ser
+            .formatter
+            .end_string(&mut self.ser.writer)
+            .map_err(Error::io)
+    }
+
+    fn serialize_u16(self, value: u16) -> Result<()> {
+        tri!(self
+            .ser
+            .formatter
+            .begin_string(&mut self.ser.writer)
+            .map_err(Error::io));
+        tri!(self
+            .ser
+            .formatter
+            .write_u16(&mut self.ser.writer, value)
+            .map_err(Error::io));
+        self.ser
+            .formatter
+            .end_string(&mut self.ser.writer)
+            .map_err(Error::io)
+    }
+
+    fn serialize_u32(self, value: u32) -> Result<()> {
+        tri!(self
+            .ser
+            .formatter
+            .begin_string(&mut self.ser.writer)
+            .map_err(Error::io));
+        tri!(self
+            .ser
+            .formatter
+            .write_u32(&mut self.ser.writer, value)
+            .map_err(Error::io));
+        self.ser
+            .formatter
+            .end_string(&mut self.ser.writer)
+            .map_err(Error::io)
+    }
+
+    fn serialize_u64(self, value: u64) -> Result<()> {
+        tri!(self
+            .ser
+            .formatter
+            .begin_string(&mut self.ser.writer)
+            .map_err(Error::io));
+        tri!(self
+            .ser
+            .formatter
+            .write_u64(&mut self.ser.writer, value)
+            .map_err(Error::io));
+        self.ser
+            .formatter
+            .end_string(&mut self.ser.writer)
+            .map_err(Error::io)
+    }
+
+    fn serialize_u128(self, value: u128) -> Result<()> {
+        tri!(self
+            .ser
+            .formatter
+            .begin_string(&mut self.ser.writer)
+            .map_err(Error::io));
+        tri!(self
+            .ser
+            .formatter
+            .write_u128(&mut self.ser.writer, value)
+            .map_err(Error::io));
+        self.ser
+            .formatter
+            .end_string(&mut self.ser.writer)
+            .map_err(Error::io)
+    }
+
+    fn serialize_f32(self, _value: f32) -> Result<()> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_f64(self, _value: f64) -> Result<()> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_char(self, value: char) -> Result<()> {
+        self.ser.serialize_str(&value.to_string())
+    }
+
+    fn serialize_bytes(self, _value: &[u8]) -> Result<()> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_unit(self) -> Result<()> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_unit_struct(self, _name: &'static str) -> Result<()> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_newtype_variant<T>(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _value: &T,
+    ) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_none(self) -> Result<()> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_some<T>(self, _value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_seq(self, _len: Option<usize>) -> Result<Self::SerializeSeq> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_tuple(self, _len: usize) -> Result<Self::SerializeTuple> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_tuple_struct(
+        self,
+        _name: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleStruct> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_tuple_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleVariant> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_struct(self, _name: &'static str, _len: usize) -> Result<Self::SerializeStruct> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_struct_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeStructVariant> {
+        Err(key_must_be_a_string())
+    }
+
+    fn collect_str<T>(self, value: &T) -> Result<()>
+    where
+        T: ?Sized + Display,
+    {
+        self.ser.collect_str(value)
+    }
+}
+
+#[cfg(feature = "arbitrary_precision")]
+struct NumberStrEmitter<'a, W: 'a + io::Write, F: 'a + Formatter>(&'a mut Serializer<W, F>);
+
+#[cfg(feature = "arbitrary_precision")]
+impl<'a, W: io::Write, F: Formatter> ser::Serializer for NumberStrEmitter<'a, W, F> {
+    type Ok = ();
+    type Error = Error;
+
+    type SerializeSeq = Impossible<(), Error>;
+    type SerializeTuple = Impossible<(), Error>;
+    type SerializeTupleStruct = Impossible<(), Error>;
+    type SerializeTupleVariant = Impossible<(), Error>;
+    type SerializeMap = Impossible<(), Error>;
+    type SerializeStruct = Impossible<(), Error>;
+    type SerializeStructVariant = Impossible<(), Error>;
+
+    fn serialize_bool(self, _v: bool) -> Result<()> {
+        Err(invalid_number())
+    }
+
+    fn serialize_i8(self, _v: i8) -> Result<()> {
+        Err(invalid_number())
+    }
+
+    fn serialize_i16(self, _v: i16) -> Result<()> {
+        Err(invalid_number())
+    }
+
+    fn serialize_i32(self, _v: i32) -> Result<()> {
+        Err(invalid_number())
+    }
+
+    fn serialize_i64(self, _v: i64) -> Result<()> {
+        Err(invalid_number())
+    }
+
+    fn serialize_i128(self, _v: i128) -> Result<()> {
+        Err(invalid_number())
+    }
+
+    fn serialize_u8(self, _v: u8) -> Result<()> {
+        Err(invalid_number())
+    }
+
+    fn serialize_u16(self, _v: u16) -> Result<()> {
+        Err(invalid_number())
+    }
+
+    fn serialize_u32(self, _v: u32) -> Result<()> {
+        Err(invalid_number())
+    }
+
+    fn serialize_u64(self, _v: u64) -> Result<()> {
+        Err(invalid_number())
+    }
+
+    fn serialize_u128(self, _v: u128) -> Result<()> {
+        Err(invalid_number())
+    }
+
+    fn serialize_f32(self, _v: f32) -> Result<()> {
+        Err(invalid_number())
+    }
+
+    fn serialize_f64(self, _v: f64) -> Result<()> {
+        Err(invalid_number())
+    }
+
+    fn serialize_char(self, _v: char) -> Result<()> {
+        Err(invalid_number())
+    }
+
+    fn serialize_str(self, value: &str) -> Result<()> {
+        let NumberStrEmitter(serializer) = self;
+        serializer
+            .formatter
+            .write_number_str(&mut serializer.writer, value)
+            .map_err(Error::io)
+    }
+
+    fn serialize_bytes(self, _value: &[u8]) -> Result<()> {
+        Err(invalid_number())
+    }
+
+    fn serialize_none(self) -> Result<()> {
+        Err(invalid_number())
+    }
+
+    fn serialize_some<T>(self, _value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        Err(invalid_number())
+    }
+
+    fn serialize_unit(self) -> Result<()> {
+        Err(invalid_number())
+    }
+
+    fn serialize_unit_struct(self, _name: &'static str) -> Result<()> {
+        Err(invalid_number())
+    }
+
+    fn serialize_unit_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+    ) -> Result<()> {
+        Err(invalid_number())
+    }
+
+    fn serialize_newtype_struct<T>(self, _name: &'static str, _value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        Err(invalid_number())
+    }
+
+    fn serialize_newtype_variant<T>(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _value: &T,
+    ) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        Err(invalid_number())
+    }
+
+    fn serialize_seq(self, _len: Option<usize>) -> Result<Self::SerializeSeq> {
+        Err(invalid_number())
+    }
+
+    fn serialize_tuple(self, _len: usize) -> Result<Self::SerializeTuple> {
+        Err(invalid_number())
+    }
+
+    fn serialize_tuple_struct(
+        self,
+        _name: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleStruct> {
+        Err(invalid_number())
+    }
+
+    fn serialize_tuple_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleVariant> {
+        Err(invalid_number())
+    }
+
+    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap> {
+        Err(invalid_number())
+    }
+
+    fn serialize_struct(self, _name: &'static str, _len: usize) -> Result<Self::SerializeStruct> {
+        Err(invalid_number())
+    }
+
+    fn serialize_struct_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeStructVariant> {
+        Err(invalid_number())
+    }
+}
+
+#[cfg(feature = "raw_value")]
+struct RawValueStrEmitter<'a, W: 'a + io::Write, F: 'a + Formatter>(&'a mut Serializer<W, F>);
+
+#[cfg(feature = "raw_value")]
+impl<'a, W: io::Write, F: Formatter> ser::Serializer for RawValueStrEmitter<'a, W, F> {
+    type Ok = ();
+    type Error = Error;
+
+    type SerializeSeq = Impossible<(), Error>;
+    type SerializeTuple = Impossible<(), Error>;
+    type SerializeTupleStruct = Impossible<(), Error>;
+    type SerializeTupleVariant = Impossible<(), Error>;
+    type SerializeMap = Impossible<(), Error>;
+    type SerializeStruct = Impossible<(), Error>;
+    type SerializeStructVariant = Impossible<(), Error>;
+
+    fn serialize_bool(self, _v: bool) -> Result<()> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_i8(self, _v: i8) -> Result<()> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_i16(self, _v: i16) -> Result<()> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_i32(self, _v: i32) -> Result<()> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_i64(self, _v: i64) -> Result<()> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_i128(self, _v: i128) -> Result<()> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_u8(self, _v: u8) -> Result<()> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_u16(self, _v: u16) -> Result<()> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_u32(self, _v: u32) -> Result<()> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_u64(self, _v: u64) -> Result<()> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_u128(self, _v: u128) -> Result<()> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_f32(self, _v: f32) -> Result<()> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_f64(self, _v: f64) -> Result<()> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_char(self, _v: char) -> Result<()> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_str(self, value: &str) -> Result<()> {
+        let RawValueStrEmitter(serializer) = self;
+        serializer
+            .formatter
+            .write_raw_fragment(&mut serializer.writer, value)
+            .map_err(Error::io)
+    }
+
+    fn serialize_bytes(self, _value: &[u8]) -> Result<()> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_none(self) -> Result<()> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_some<T>(self, _value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_unit(self) -> Result<()> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_unit_struct(self, _name: &'static str) -> Result<()> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_unit_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+    ) -> Result<()> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_newtype_struct<T>(self, _name: &'static str, _value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_newtype_variant<T>(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _value: &T,
+    ) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_seq(self, _len: Option<usize>) -> Result<Self::SerializeSeq> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_tuple(self, _len: usize) -> Result<Self::SerializeTuple> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_tuple_struct(
+        self,
+        _name: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleStruct> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_tuple_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleVariant> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_struct(self, _name: &'static str, _len: usize) -> Result<Self::SerializeStruct> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn serialize_struct_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeStructVariant> {
+        Err(ser::Error::custom("expected RawValue"))
+    }
+
+    fn collect_str<T>(self, value: &T) -> Result<Self::Ok>
+    where
+        T: ?Sized + Display,
+    {
+        self.serialize_str(&value.to_string())
+    }
+}
+
+/// Represents a character escape code in a type-safe manner.
+pub enum CharEscape {
+    /// An escaped quote `"`
+    Quote,
+    /// An escaped reverse solidus `\`
+    ReverseSolidus,
+    /// An escaped solidus `/`
+    Solidus,
+    /// An escaped backspace character (usually escaped as `\b`)
+    Backspace,
+    /// An escaped form feed character (usually escaped as `\f`)
+    FormFeed,
+    /// An escaped line feed character (usually escaped as `\n`)
+    LineFeed,
+    /// An escaped carriage return character (usually escaped as `\r`)
+    CarriageReturn,
+    /// An escaped tab character (usually escaped as `\t`)
+    Tab,
+    /// An escaped ASCII plane control character (usually escaped as
+    /// `\u00XX` where `XX` are two hex characters)
+    AsciiControl(u8),
+}
+
+impl CharEscape {
+    #[inline]
+    fn from_escape_table(escape: u8, byte: u8) -> CharEscape {
+        match escape {
+            self::BB => CharEscape::Backspace,
+            self::TT => CharEscape::Tab,
+            self::NN => CharEscape::LineFeed,
+            self::FF => CharEscape::FormFeed,
+            self::RR => CharEscape::CarriageReturn,
+            self::QU => CharEscape::Quote,
+            self::BS => CharEscape::ReverseSolidus,
+            self::UU => CharEscape::AsciiControl(byte),
+            _ => unreachable!(),
+        }
+    }
+}
+
+/// This trait abstracts away serializing the JSON control characters, which allows the user to
+/// optionally pretty print the JSON output.
+pub trait Formatter {
+    /// Writes a `null` value to the specified writer.
+    #[inline]
+    fn write_null<W>(&mut self, writer: &mut W) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        writer.write_all(b"null")
+    }
+
+    /// Writes a `true` or `false` value to the specified writer.
+    #[inline]
+    fn write_bool<W>(&mut self, writer: &mut W, value: bool) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        let s = if value {
+            b"true" as &[u8]
+        } else {
+            b"false" as &[u8]
+        };
+        writer.write_all(s)
+    }
+
+    /// Writes an integer value like `-123` to the specified writer.
+    #[inline]
+    fn write_i8<W>(&mut self, writer: &mut W, value: i8) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        let mut buffer = itoa::Buffer::new();
+        let s = buffer.format(value);
+        writer.write_all(s.as_bytes())
+    }
+
+    /// Writes an integer value like `-123` to the specified writer.
+    #[inline]
+    fn write_i16<W>(&mut self, writer: &mut W, value: i16) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        let mut buffer = itoa::Buffer::new();
+        let s = buffer.format(value);
+        writer.write_all(s.as_bytes())
+    }
+
+    /// Writes an integer value like `-123` to the specified writer.
+    #[inline]
+    fn write_i32<W>(&mut self, writer: &mut W, value: i32) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        let mut buffer = itoa::Buffer::new();
+        let s = buffer.format(value);
+        writer.write_all(s.as_bytes())
+    }
+
+    /// Writes an integer value like `-123` to the specified writer.
+    #[inline]
+    fn write_i64<W>(&mut self, writer: &mut W, value: i64) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        let mut buffer = itoa::Buffer::new();
+        let s = buffer.format(value);
+        writer.write_all(s.as_bytes())
+    }
+
+    /// Writes an integer value like `-123` to the specified writer.
+    #[inline]
+    fn write_i128<W>(&mut self, writer: &mut W, value: i128) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        let mut buffer = itoa::Buffer::new();
+        let s = buffer.format(value);
+        writer.write_all(s.as_bytes())
+    }
+
+    /// Writes an integer value like `123` to the specified writer.
+    #[inline]
+    fn write_u8<W>(&mut self, writer: &mut W, value: u8) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        let mut buffer = itoa::Buffer::new();
+        let s = buffer.format(value);
+        writer.write_all(s.as_bytes())
+    }
+
+    /// Writes an integer value like `123` to the specified writer.
+    #[inline]
+    fn write_u16<W>(&mut self, writer: &mut W, value: u16) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        let mut buffer = itoa::Buffer::new();
+        let s = buffer.format(value);
+        writer.write_all(s.as_bytes())
+    }
+
+    /// Writes an integer value like `123` to the specified writer.
+    #[inline]
+    fn write_u32<W>(&mut self, writer: &mut W, value: u32) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        let mut buffer = itoa::Buffer::new();
+        let s = buffer.format(value);
+        writer.write_all(s.as_bytes())
+    }
+
+    /// Writes an integer value like `123` to the specified writer.
+    #[inline]
+    fn write_u64<W>(&mut self, writer: &mut W, value: u64) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        let mut buffer = itoa::Buffer::new();
+        let s = buffer.format(value);
+        writer.write_all(s.as_bytes())
+    }
+
+    /// Writes an integer value like `123` to the specified writer.
+    #[inline]
+    fn write_u128<W>(&mut self, writer: &mut W, value: u128) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        let mut buffer = itoa::Buffer::new();
+        let s = buffer.format(value);
+        writer.write_all(s.as_bytes())
+    }
+
+    /// Writes a floating point value like `-31.26e+12` to the specified writer.
+    #[inline]
+    fn write_f32<W>(&mut self, writer: &mut W, value: f32) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        let mut buffer = ryu::Buffer::new();
+        let s = buffer.format_finite(value);
+        writer.write_all(s.as_bytes())
+    }
+
+    /// Writes a floating point value like `-31.26e+12` to the specified writer.
+    #[inline]
+    fn write_f64<W>(&mut self, writer: &mut W, value: f64) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        let mut buffer = ryu::Buffer::new();
+        let s = buffer.format_finite(value);
+        writer.write_all(s.as_bytes())
+    }
+
+    /// Writes a number that has already been rendered to a string.
+    #[inline]
+    fn write_number_str<W>(&mut self, writer: &mut W, value: &str) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        writer.write_all(value.as_bytes())
+    }
+
+    /// Called before each series of `write_string_fragment` and
+    /// `write_char_escape`.  Writes a `"` to the specified writer.
+    #[inline]
+    fn begin_string<W>(&mut self, writer: &mut W) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        writer.write_all(b"\"")
+    }
+
+    /// Called after each series of `write_string_fragment` and
+    /// `write_char_escape`.  Writes a `"` to the specified writer.
+    #[inline]
+    fn end_string<W>(&mut self, writer: &mut W) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        writer.write_all(b"\"")
+    }
+
+    /// Writes a string fragment that doesn't need any escaping to the
+    /// specified writer.
+    #[inline]
+    fn write_string_fragment<W>(&mut self, writer: &mut W, fragment: &str) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        writer.write_all(fragment.as_bytes())
+    }
+
+    /// Writes a character escape code to the specified writer.
+    #[inline]
+    fn write_char_escape<W>(&mut self, writer: &mut W, char_escape: CharEscape) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        use self::CharEscape::*;
+
+        let s = match char_escape {
+            Quote => b"\\\"",
+            ReverseSolidus => b"\\\\",
+            Solidus => b"\\/",
+            Backspace => b"\\b",
+            FormFeed => b"\\f",
+            LineFeed => b"\\n",
+            CarriageReturn => b"\\r",
+            Tab => b"\\t",
+            AsciiControl(byte) => {
+                static HEX_DIGITS: [u8; 16] = *b"0123456789abcdef";
+                let bytes = &[
+                    b'\\',
+                    b'u',
+                    b'0',
+                    b'0',
+                    HEX_DIGITS[(byte >> 4) as usize],
+                    HEX_DIGITS[(byte & 0xF) as usize],
+                ];
+                return writer.write_all(bytes);
+            }
+        };
+
+        writer.write_all(s)
+    }
+
+    /// Called before every array.  Writes a `[` to the specified
+    /// writer.
+    #[inline]
+    fn begin_array<W>(&mut self, writer: &mut W) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        writer.write_all(b"[")
+    }
+
+    /// Called after every array.  Writes a `]` to the specified
+    /// writer.
+    #[inline]
+    fn end_array<W>(&mut self, writer: &mut W) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        writer.write_all(b"]")
+    }
+
+    /// Called before every array value.  Writes a `,` if needed to
+    /// the specified writer.
+    #[inline]
+    fn begin_array_value<W>(&mut self, writer: &mut W, first: bool) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        if first {
+            Ok(())
+        } else {
+            writer.write_all(b",")
+        }
+    }
+
+    /// Called after every array value.
+    #[inline]
+    fn end_array_value<W>(&mut self, _writer: &mut W) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        Ok(())
+    }
+
+    /// Called before every object.  Writes a `{` to the specified
+    /// writer.
+    #[inline]
+    fn begin_object<W>(&mut self, writer: &mut W) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        writer.write_all(b"{")
+    }
+
+    /// Called after every object.  Writes a `}` to the specified
+    /// writer.
+    #[inline]
+    fn end_object<W>(&mut self, writer: &mut W) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        writer.write_all(b"}")
+    }
+
+    /// Called before every object key.
+    #[inline]
+    fn begin_object_key<W>(&mut self, writer: &mut W, first: bool) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        if first {
+            Ok(())
+        } else {
+            writer.write_all(b",")
+        }
+    }
+
+    /// Called after every object key.  A `:` should be written to the
+    /// specified writer by either this method or
+    /// `begin_object_value`.
+    #[inline]
+    fn end_object_key<W>(&mut self, _writer: &mut W) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        Ok(())
+    }
+
+    /// Called before every object value.  A `:` should be written to
+    /// the specified writer by either this method or
+    /// `end_object_key`.
+    #[inline]
+    fn begin_object_value<W>(&mut self, writer: &mut W) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        writer.write_all(b":")
+    }
+
+    /// Called after every object value.
+    #[inline]
+    fn end_object_value<W>(&mut self, _writer: &mut W) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        Ok(())
+    }
+
+    /// Writes a raw JSON fragment that doesn't need any escaping to the
+    /// specified writer.
+    #[inline]
+    fn write_raw_fragment<W>(&mut self, writer: &mut W, fragment: &str) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        writer.write_all(fragment.as_bytes())
+    }
+}
+
+/// This structure compacts a JSON value with no extra whitespace.
+#[derive(Clone, Debug)]
+pub struct CompactFormatter;
+
+impl Formatter for CompactFormatter {}
+
+/// This structure pretty prints a JSON value to make it human readable.
+#[derive(Clone, Debug)]
+pub struct PrettyFormatter<'a> {
+    current_indent: usize,
+    has_value: bool,
+    indent: &'a [u8],
+}
+
+impl<'a> PrettyFormatter<'a> {
+    /// Construct a pretty printer formatter that defaults to using two spaces for indentation.
+    pub fn new() -> Self {
+        PrettyFormatter::with_indent(b"  ")
+    }
+
+    /// Construct a pretty printer formatter that uses the `indent` string for indentation.
+    pub fn with_indent(indent: &'a [u8]) -> Self {
+        PrettyFormatter {
+            current_indent: 0,
+            has_value: false,
+            indent,
+        }
+    }
+}
+
+impl<'a> Default for PrettyFormatter<'a> {
+    fn default() -> Self {
+        PrettyFormatter::new()
+    }
+}
+
+impl<'a> Formatter for PrettyFormatter<'a> {
+    #[inline]
+    fn begin_array<W>(&mut self, writer: &mut W) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        self.current_indent += 1;
+        self.has_value = false;
+        writer.write_all(b"[")
+    }
+
+    #[inline]
+    fn end_array<W>(&mut self, writer: &mut W) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        self.current_indent -= 1;
+
+        if self.has_value {
+            tri!(writer.write_all(b"\n"));
+            tri!(indent(writer, self.current_indent, self.indent));
+        }
+
+        writer.write_all(b"]")
+    }
+
+    #[inline]
+    fn begin_array_value<W>(&mut self, writer: &mut W, first: bool) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        tri!(writer.write_all(if first { b"\n" } else { b",\n" }));
+        indent(writer, self.current_indent, self.indent)
+    }
+
+    #[inline]
+    fn end_array_value<W>(&mut self, _writer: &mut W) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        self.has_value = true;
+        Ok(())
+    }
+
+    #[inline]
+    fn begin_object<W>(&mut self, writer: &mut W) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        self.current_indent += 1;
+        self.has_value = false;
+        writer.write_all(b"{")
+    }
+
+    #[inline]
+    fn end_object<W>(&mut self, writer: &mut W) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        self.current_indent -= 1;
+
+        if self.has_value {
+            tri!(writer.write_all(b"\n"));
+            tri!(indent(writer, self.current_indent, self.indent));
+        }
+
+        writer.write_all(b"}")
+    }
+
+    #[inline]
+    fn begin_object_key<W>(&mut self, writer: &mut W, first: bool) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        tri!(writer.write_all(if first { b"\n" } else { b",\n" }));
+        indent(writer, self.current_indent, self.indent)
+    }
+
+    #[inline]
+    fn begin_object_value<W>(&mut self, writer: &mut W) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        writer.write_all(b": ")
+    }
+
+    #[inline]
+    fn end_object_value<W>(&mut self, _writer: &mut W) -> io::Result<()>
+    where
+        W: ?Sized + io::Write,
+    {
+        self.has_value = true;
+        Ok(())
+    }
+}
+
+fn format_escaped_str<W, F>(writer: &mut W, formatter: &mut F, value: &str) -> io::Result<()>
+where
+    W: ?Sized + io::Write,
+    F: ?Sized + Formatter,
+{
+    tri!(formatter.begin_string(writer));
+    tri!(format_escaped_str_contents(writer, formatter, value));
+    formatter.end_string(writer)
+}
+
+fn format_escaped_str_contents<W, F>(
+    writer: &mut W,
+    formatter: &mut F,
+    value: &str,
+) -> io::Result<()>
+where
+    W: ?Sized + io::Write,
+    F: ?Sized + Formatter,
+{
+    let bytes = value.as_bytes();
+
+    let mut start = 0;
+
+    for (i, &byte) in bytes.iter().enumerate() {
+        let escape = ESCAPE[byte as usize];
+        if escape == 0 {
+            continue;
+        }
+
+        if start < i {
+            tri!(formatter.write_string_fragment(writer, &value[start..i]));
+        }
+
+        let char_escape = CharEscape::from_escape_table(escape, byte);
+        tri!(formatter.write_char_escape(writer, char_escape));
+
+        start = i + 1;
+    }
+
+    if start == bytes.len() {
+        return Ok(());
+    }
+
+    formatter.write_string_fragment(writer, &value[start..])
+}
+
+const BB: u8 = b'b'; // \x08
+const TT: u8 = b't'; // \x09
+const NN: u8 = b'n'; // \x0A
+const FF: u8 = b'f'; // \x0C
+const RR: u8 = b'r'; // \x0D
+const QU: u8 = b'"'; // \x22
+const BS: u8 = b'\\'; // \x5C
+const UU: u8 = b'u'; // \x00...\x1F except the ones above
+const __: u8 = 0;
+
+// Lookup table of escape sequences. A value of b'x' at index i means that byte
+// i is escaped as "\x" in JSON. A value of 0 means that byte i is not escaped.
+static ESCAPE: [u8; 256] = [
+    //   1   2   3   4   5   6   7   8   9   A   B   C   D   E   F
+    UU, UU, UU, UU, UU, UU, UU, UU, BB, TT, NN, UU, FF, RR, UU, UU, // 0
+    UU, UU, UU, UU, UU, UU, UU, UU, UU, UU, UU, UU, UU, UU, UU, UU, // 1
+    __, __, QU, __, __, __, __, __, __, __, __, __, __, __, __, __, // 2
+    __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // 3
+    __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // 4
+    __, __, __, __, __, __, __, __, __, __, __, __, BS, __, __, __, // 5
+    __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // 6
+    __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // 7
+    __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // 8
+    __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // 9
+    __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // A
+    __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // B
+    __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // C
+    __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // D
+    __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // E
+    __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, __, // F
+];
+
+/// Serialize the given data structure as JSON into the IO stream.
+///
+/// # Errors
+///
+/// Serialization can fail if `T`'s implementation of `Serialize` decides to
+/// fail, or if `T` contains a map with non-string keys.
+#[inline]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
+pub fn to_writer<W, T>(writer: W, value: &T) -> Result<()>
+where
+    W: io::Write,
+    T: ?Sized + Serialize,
+{
+    let mut ser = Serializer::new(writer);
+    value.serialize(&mut ser)
+}
+
+/// Serialize the given data structure as pretty-printed JSON into the IO
+/// stream.
+///
+/// # Errors
+///
+/// Serialization can fail if `T`'s implementation of `Serialize` decides to
+/// fail, or if `T` contains a map with non-string keys.
+#[inline]
+#[cfg_attr(docsrs, doc(cfg(feature = "std")))]
+pub fn to_writer_pretty<W, T>(writer: W, value: &T) -> Result<()>
+where
+    W: io::Write,
+    T: ?Sized + Serialize,
+{
+    let mut ser = Serializer::pretty(writer);
+    value.serialize(&mut ser)
+}
+
+/// Serialize the given data structure as a JSON byte vector.
+///
+/// # Errors
+///
+/// Serialization can fail if `T`'s implementation of `Serialize` decides to
+/// fail, or if `T` contains a map with non-string keys.
+#[inline]
+pub fn to_vec<T>(value: &T) -> Result<Vec<u8>>
+where
+    T: ?Sized + Serialize,
+{
+    let mut writer = Vec::with_capacity(128);
+    tri!(to_writer(&mut writer, value));
+    Ok(writer)
+}
+
+/// Serialize the given data structure as a pretty-printed JSON byte vector.
+///
+/// # Errors
+///
+/// Serialization can fail if `T`'s implementation of `Serialize` decides to
+/// fail, or if `T` contains a map with non-string keys.
+#[inline]
+pub fn to_vec_pretty<T>(value: &T) -> Result<Vec<u8>>
+where
+    T: ?Sized + Serialize,
+{
+    let mut writer = Vec::with_capacity(128);
+    tri!(to_writer_pretty(&mut writer, value));
+    Ok(writer)
+}
+
+/// Serialize the given data structure as a String of JSON.
+///
+/// # Errors
+///
+/// Serialization can fail if `T`'s implementation of `Serialize` decides to
+/// fail, or if `T` contains a map with non-string keys.
+#[inline]
+pub fn to_string<T>(value: &T) -> Result<String>
+where
+    T: ?Sized + Serialize,
+{
+    let vec = tri!(to_vec(value));
+    let string = unsafe {
+        // We do not emit invalid UTF-8.
+        String::from_utf8_unchecked(vec)
+    };
+    Ok(string)
+}
+
+/// Serialize the given data structure as a pretty-printed String of JSON.
+///
+/// # Errors
+///
+/// Serialization can fail if `T`'s implementation of `Serialize` decides to
+/// fail, or if `T` contains a map with non-string keys.
+#[inline]
+pub fn to_string_pretty<T>(value: &T) -> Result<String>
+where
+    T: ?Sized + Serialize,
+{
+    let vec = tri!(to_vec_pretty(value));
+    let string = unsafe {
+        // We do not emit invalid UTF-8.
+        String::from_utf8_unchecked(vec)
+    };
+    Ok(string)
+}
+
+fn indent<W>(wr: &mut W, n: usize, s: &[u8]) -> io::Result<()>
+where
+    W: ?Sized + io::Write,
+{
+    for _ in 0..n {
+        tri!(wr.write_all(s));
+    }
+
+    Ok(())
+}
diff --git a/third_party/rust/serde_json/src/value/de.rs b/third_party/rust/serde_json/src/value/de.rs
new file mode 100644
index 0000000000..9c266d08ae
--- /dev/null
+++ b/third_party/rust/serde_json/src/value/de.rs
@@ -0,0 +1,1377 @@
+use crate::error::Error;
+use crate::map::Map;
+use crate::number::Number;
+use crate::value::Value;
+use alloc::borrow::{Cow, ToOwned};
+use alloc::string::String;
+#[cfg(feature = "raw_value")]
+use alloc::string::ToString;
+use alloc::vec::{self, Vec};
+use core::fmt;
+use core::slice;
+use core::str::FromStr;
+use serde::de::{
+    self, Deserialize, DeserializeSeed, EnumAccess, Expected, IntoDeserializer, MapAccess,
+    SeqAccess, Unexpected, VariantAccess, Visitor,
+};
+use serde::forward_to_deserialize_any;
+
+#[cfg(feature = "arbitrary_precision")]
+use crate::number::NumberFromString;
+
+impl<'de> Deserialize<'de> for Value {
+    #[inline]
+    fn deserialize<D>(deserializer: D) -> Result<Value, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        struct ValueVisitor;
+
+        impl<'de> Visitor<'de> for ValueVisitor {
+            type Value = Value;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str("any valid JSON value")
+            }
+
+            #[inline]
+            fn visit_bool<E>(self, value: bool) -> Result<Value, E> {
+                Ok(Value::Bool(value))
+            }
+
+            #[inline]
+            fn visit_i64<E>(self, value: i64) -> Result<Value, E> {
+                Ok(Value::Number(value.into()))
+            }
+
+            #[inline]
+            fn visit_u64<E>(self, value: u64) -> Result<Value, E> {
+                Ok(Value::Number(value.into()))
+            }
+
+            #[inline]
+            fn visit_f64<E>(self, value: f64) -> Result<Value, E> {
+                Ok(Number::from_f64(value).map_or(Value::Null, Value::Number))
+            }
+
+            #[cfg(any(feature = "std", feature = "alloc"))]
+            #[inline]
+            fn visit_str<E>(self, value: &str) -> Result<Value, E>
+            where
+                E: serde::de::Error,
+            {
+                self.visit_string(String::from(value))
+            }
+
+            #[cfg(any(feature = "std", feature = "alloc"))]
+            #[inline]
+            fn visit_string<E>(self, value: String) -> Result<Value, E> {
+                Ok(Value::String(value))
+            }
+
+            #[inline]
+            fn visit_none<E>(self) -> Result<Value, E> {
+                Ok(Value::Null)
+            }
+
+            #[inline]
+            fn visit_some<D>(self, deserializer: D) -> Result<Value, D::Error>
+            where
+                D: serde::Deserializer<'de>,
+            {
+                Deserialize::deserialize(deserializer)
+            }
+
+            #[inline]
+            fn visit_unit<E>(self) -> Result<Value, E> {
+                Ok(Value::Null)
+            }
+
+            #[inline]
+            fn visit_seq<V>(self, mut visitor: V) -> Result<Value, V::Error>
+            where
+                V: SeqAccess<'de>,
+            {
+                let mut vec = Vec::new();
+
+                while let Some(elem) = tri!(visitor.next_element()) {
+                    vec.push(elem);
+                }
+
+                Ok(Value::Array(vec))
+            }
+
+            #[cfg(any(feature = "std", feature = "alloc"))]
+            fn visit_map<V>(self, mut visitor: V) -> Result<Value, V::Error>
+            where
+                V: MapAccess<'de>,
+            {
+                match visitor.next_key_seed(KeyClassifier)? {
+                    #[cfg(feature = "arbitrary_precision")]
+                    Some(KeyClass::Number) => {
+                        let number: NumberFromString = visitor.next_value()?;
+                        Ok(Value::Number(number.value))
+                    }
+                    #[cfg(feature = "raw_value")]
+                    Some(KeyClass::RawValue) => {
+                        let value = visitor.next_value_seed(crate::raw::BoxedFromString)?;
+                        crate::from_str(value.get()).map_err(de::Error::custom)
+                    }
+                    Some(KeyClass::Map(first_key)) => {
+                        let mut values = Map::new();
+
+                        values.insert(first_key, tri!(visitor.next_value()));
+                        while let Some((key, value)) = tri!(visitor.next_entry()) {
+                            values.insert(key, value);
+                        }
+
+                        Ok(Value::Object(values))
+                    }
+                    None => Ok(Value::Object(Map::new())),
+                }
+            }
+        }
+
+        deserializer.deserialize_any(ValueVisitor)
+    }
+}
+
+impl FromStr for Value {
+    type Err = Error;
+    fn from_str(s: &str) -> Result<Value, Error> {
+        super::super::de::from_str(s)
+    }
+}
+
+macro_rules! deserialize_number {
+    ($method:ident) => {
+        #[cfg(not(feature = "arbitrary_precision"))]
+        fn $method<V>(self, visitor: V) -> Result<V::Value, Error>
+        where
+            V: Visitor<'de>,
+        {
+            match self {
+                Value::Number(n) => n.deserialize_any(visitor),
+                _ => Err(self.invalid_type(&visitor)),
+            }
+        }
+
+        #[cfg(feature = "arbitrary_precision")]
+        fn $method<V>(self, visitor: V) -> Result<V::Value, Error>
+        where
+            V: Visitor<'de>,
+        {
+            match self {
+                Value::Number(n) => n.$method(visitor),
+                _ => self.deserialize_any(visitor),
+            }
+        }
+    };
+}
+
+fn visit_array<'de, V>(array: Vec<Value>, visitor: V) -> Result<V::Value, Error>
+where
+    V: Visitor<'de>,
+{
+    let len = array.len();
+    let mut deserializer = SeqDeserializer::new(array);
+    let seq = tri!(visitor.visit_seq(&mut deserializer));
+    let remaining = deserializer.iter.len();
+    if remaining == 0 {
+        Ok(seq)
+    } else {
+        Err(serde::de::Error::invalid_length(
+            len,
+            &"fewer elements in array",
+        ))
+    }
+}
+
+fn visit_object<'de, V>(object: Map<String, Value>, visitor: V) -> Result<V::Value, Error>
+where
+    V: Visitor<'de>,
+{
+    let len = object.len();
+    let mut deserializer = MapDeserializer::new(object);
+    let map = tri!(visitor.visit_map(&mut deserializer));
+    let remaining = deserializer.iter.len();
+    if remaining == 0 {
+        Ok(map)
+    } else {
+        Err(serde::de::Error::invalid_length(
+            len,
+            &"fewer elements in map",
+        ))
+    }
+}
+
+impl<'de> serde::Deserializer<'de> for Value {
+    type Error = Error;
+
+    #[inline]
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        match self {
+            Value::Null => visitor.visit_unit(),
+            Value::Bool(v) => visitor.visit_bool(v),
+            Value::Number(n) => n.deserialize_any(visitor),
+            #[cfg(any(feature = "std", feature = "alloc"))]
+            Value::String(v) => visitor.visit_string(v),
+            Value::Array(v) => visit_array(v, visitor),
+            Value::Object(v) => visit_object(v, visitor),
+        }
+    }
+
+    deserialize_number!(deserialize_i8);
+    deserialize_number!(deserialize_i16);
+    deserialize_number!(deserialize_i32);
+    deserialize_number!(deserialize_i64);
+    deserialize_number!(deserialize_i128);
+    deserialize_number!(deserialize_u8);
+    deserialize_number!(deserialize_u16);
+    deserialize_number!(deserialize_u32);
+    deserialize_number!(deserialize_u64);
+    deserialize_number!(deserialize_u128);
+    deserialize_number!(deserialize_f32);
+    deserialize_number!(deserialize_f64);
+
+    #[inline]
+    fn deserialize_option<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        match self {
+            Value::Null => visitor.visit_none(),
+            _ => visitor.visit_some(self),
+        }
+    }
+
+    #[inline]
+    fn deserialize_enum<V>(
+        self,
+        _name: &str,
+        _variants: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        let (variant, value) = match self {
+            Value::Object(value) => {
+                let mut iter = value.into_iter();
+                let (variant, value) = match iter.next() {
+                    Some(v) => v,
+                    None => {
+                        return Err(serde::de::Error::invalid_value(
+                            Unexpected::Map,
+                            &"map with a single key",
+                        ));
+                    }
+                };
+                // enums are encoded in json as maps with a single key:value pair
+                if iter.next().is_some() {
+                    return Err(serde::de::Error::invalid_value(
+                        Unexpected::Map,
+                        &"map with a single key",
+                    ));
+                }
+                (variant, Some(value))
+            }
+            Value::String(variant) => (variant, None),
+            other => {
+                return Err(serde::de::Error::invalid_type(
+                    other.unexpected(),
+                    &"string or map",
+                ));
+            }
+        };
+
+        visitor.visit_enum(EnumDeserializer { variant, value })
+    }
+
+    #[inline]
+    fn deserialize_newtype_struct<V>(
+        self,
+        name: &'static str,
+        visitor: V,
+    ) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        #[cfg(feature = "raw_value")]
+        {
+            if name == crate::raw::TOKEN {
+                return visitor.visit_map(crate::raw::OwnedRawDeserializer {
+                    raw_value: Some(self.to_string()),
+                });
+            }
+        }
+
+        let _ = name;
+        visitor.visit_newtype_struct(self)
+    }
+
+    fn deserialize_bool<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        match self {
+            Value::Bool(v) => visitor.visit_bool(v),
+            _ => Err(self.invalid_type(&visitor)),
+        }
+    }
+
+    fn deserialize_char<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        self.deserialize_string(visitor)
+    }
+
+    fn deserialize_str<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        self.deserialize_string(visitor)
+    }
+
+    fn deserialize_string<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        match self {
+            #[cfg(any(feature = "std", feature = "alloc"))]
+            Value::String(v) => visitor.visit_string(v),
+            _ => Err(self.invalid_type(&visitor)),
+        }
+    }
+
+    fn deserialize_bytes<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        self.deserialize_byte_buf(visitor)
+    }
+
+    fn deserialize_byte_buf<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        match self {
+            #[cfg(any(feature = "std", feature = "alloc"))]
+            Value::String(v) => visitor.visit_string(v),
+            Value::Array(v) => visit_array(v, visitor),
+            _ => Err(self.invalid_type(&visitor)),
+        }
+    }
+
+    fn deserialize_unit<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        match self {
+            Value::Null => visitor.visit_unit(),
+            _ => Err(self.invalid_type(&visitor)),
+        }
+    }
+
+    fn deserialize_unit_struct<V>(self, _name: &'static str, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        self.deserialize_unit(visitor)
+    }
+
+    fn deserialize_seq<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        match self {
+            Value::Array(v) => visit_array(v, visitor),
+            _ => Err(self.invalid_type(&visitor)),
+        }
+    }
+
+    fn deserialize_tuple<V>(self, _len: usize, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        self.deserialize_seq(visitor)
+    }
+
+    fn deserialize_tuple_struct<V>(
+        self,
+        _name: &'static str,
+        _len: usize,
+        visitor: V,
+    ) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        self.deserialize_seq(visitor)
+    }
+
+    fn deserialize_map<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        match self {
+            Value::Object(v) => visit_object(v, visitor),
+            _ => Err(self.invalid_type(&visitor)),
+        }
+    }
+
+    fn deserialize_struct<V>(
+        self,
+        _name: &'static str,
+        _fields: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        match self {
+            Value::Array(v) => visit_array(v, visitor),
+            Value::Object(v) => visit_object(v, visitor),
+            _ => Err(self.invalid_type(&visitor)),
+        }
+    }
+
+    fn deserialize_identifier<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        self.deserialize_string(visitor)
+    }
+
+    fn deserialize_ignored_any<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        drop(self);
+        visitor.visit_unit()
+    }
+}
+
+struct EnumDeserializer {
+    variant: String,
+    value: Option<Value>,
+}
+
+impl<'de> EnumAccess<'de> for EnumDeserializer {
+    type Error = Error;
+    type Variant = VariantDeserializer;
+
+    fn variant_seed<V>(self, seed: V) -> Result<(V::Value, VariantDeserializer), Error>
+    where
+        V: DeserializeSeed<'de>,
+    {
+        let variant = self.variant.into_deserializer();
+        let visitor = VariantDeserializer { value: self.value };
+        seed.deserialize(variant).map(|v| (v, visitor))
+    }
+}
+
+impl<'de> IntoDeserializer<'de, Error> for Value {
+    type Deserializer = Self;
+
+    fn into_deserializer(self) -> Self::Deserializer {
+        self
+    }
+}
+
+struct VariantDeserializer {
+    value: Option<Value>,
+}
+
+impl<'de> VariantAccess<'de> for VariantDeserializer {
+    type Error = Error;
+
+    fn unit_variant(self) -> Result<(), Error> {
+        match self.value {
+            Some(value) => Deserialize::deserialize(value),
+            None => Ok(()),
+        }
+    }
+
+    fn newtype_variant_seed<T>(self, seed: T) -> Result<T::Value, Error>
+    where
+        T: DeserializeSeed<'de>,
+    {
+        match self.value {
+            Some(value) => seed.deserialize(value),
+            None => Err(serde::de::Error::invalid_type(
+                Unexpected::UnitVariant,
+                &"newtype variant",
+            )),
+        }
+    }
+
+    fn tuple_variant<V>(self, _len: usize, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        match self.value {
+            Some(Value::Array(v)) => {
+                if v.is_empty() {
+                    visitor.visit_unit()
+                } else {
+                    visit_array(v, visitor)
+                }
+            }
+            Some(other) => Err(serde::de::Error::invalid_type(
+                other.unexpected(),
+                &"tuple variant",
+            )),
+            None => Err(serde::de::Error::invalid_type(
+                Unexpected::UnitVariant,
+                &"tuple variant",
+            )),
+        }
+    }
+
+    fn struct_variant<V>(
+        self,
+        _fields: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        match self.value {
+            Some(Value::Object(v)) => visit_object(v, visitor),
+            Some(other) => Err(serde::de::Error::invalid_type(
+                other.unexpected(),
+                &"struct variant",
+            )),
+            None => Err(serde::de::Error::invalid_type(
+                Unexpected::UnitVariant,
+                &"struct variant",
+            )),
+        }
+    }
+}
+
+struct SeqDeserializer {
+    iter: vec::IntoIter<Value>,
+}
+
+impl SeqDeserializer {
+    fn new(vec: Vec<Value>) -> Self {
+        SeqDeserializer {
+            iter: vec.into_iter(),
+        }
+    }
+}
+
+impl<'de> SeqAccess<'de> for SeqDeserializer {
+    type Error = Error;
+
+    fn next_element_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Error>
+    where
+        T: DeserializeSeed<'de>,
+    {
+        match self.iter.next() {
+            Some(value) => seed.deserialize(value).map(Some),
+            None => Ok(None),
+        }
+    }
+
+    fn size_hint(&self) -> Option<usize> {
+        match self.iter.size_hint() {
+            (lower, Some(upper)) if lower == upper => Some(upper),
+            _ => None,
+        }
+    }
+}
+
+struct MapDeserializer {
+    iter: <Map<String, Value> as IntoIterator>::IntoIter,
+    value: Option<Value>,
+}
+
+impl MapDeserializer {
+    fn new(map: Map<String, Value>) -> Self {
+        MapDeserializer {
+            iter: map.into_iter(),
+            value: None,
+        }
+    }
+}
+
+impl<'de> MapAccess<'de> for MapDeserializer {
+    type Error = Error;
+
+    fn next_key_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Error>
+    where
+        T: DeserializeSeed<'de>,
+    {
+        match self.iter.next() {
+            Some((key, value)) => {
+                self.value = Some(value);
+                let key_de = MapKeyDeserializer {
+                    key: Cow::Owned(key),
+                };
+                seed.deserialize(key_de).map(Some)
+            }
+            None => Ok(None),
+        }
+    }
+
+    fn next_value_seed<T>(&mut self, seed: T) -> Result<T::Value, Error>
+    where
+        T: DeserializeSeed<'de>,
+    {
+        match self.value.take() {
+            Some(value) => seed.deserialize(value),
+            None => Err(serde::de::Error::custom("value is missing")),
+        }
+    }
+
+    fn size_hint(&self) -> Option<usize> {
+        match self.iter.size_hint() {
+            (lower, Some(upper)) if lower == upper => Some(upper),
+            _ => None,
+        }
+    }
+}
+
+macro_rules! deserialize_value_ref_number {
+    ($method:ident) => {
+        #[cfg(not(feature = "arbitrary_precision"))]
+        fn $method<V>(self, visitor: V) -> Result<V::Value, Error>
+        where
+            V: Visitor<'de>,
+        {
+            match self {
+                Value::Number(n) => n.deserialize_any(visitor),
+                _ => Err(self.invalid_type(&visitor)),
+            }
+        }
+
+        #[cfg(feature = "arbitrary_precision")]
+        fn $method<V>(self, visitor: V) -> Result<V::Value, Error>
+        where
+            V: Visitor<'de>,
+        {
+            match self {
+                Value::Number(n) => n.$method(visitor),
+                _ => self.deserialize_any(visitor),
+            }
+        }
+    };
+}
+
+fn visit_array_ref<'de, V>(array: &'de [Value], visitor: V) -> Result<V::Value, Error>
+where
+    V: Visitor<'de>,
+{
+    let len = array.len();
+    let mut deserializer = SeqRefDeserializer::new(array);
+    let seq = tri!(visitor.visit_seq(&mut deserializer));
+    let remaining = deserializer.iter.len();
+    if remaining == 0 {
+        Ok(seq)
+    } else {
+        Err(serde::de::Error::invalid_length(
+            len,
+            &"fewer elements in array",
+        ))
+    }
+}
+
+fn visit_object_ref<'de, V>(object: &'de Map<String, Value>, visitor: V) -> Result<V::Value, Error>
+where
+    V: Visitor<'de>,
+{
+    let len = object.len();
+    let mut deserializer = MapRefDeserializer::new(object);
+    let map = tri!(visitor.visit_map(&mut deserializer));
+    let remaining = deserializer.iter.len();
+    if remaining == 0 {
+        Ok(map)
+    } else {
+        Err(serde::de::Error::invalid_length(
+            len,
+            &"fewer elements in map",
+        ))
+    }
+}
+
+impl<'de> serde::Deserializer<'de> for &'de Value {
+    type Error = Error;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        match self {
+            Value::Null => visitor.visit_unit(),
+            Value::Bool(v) => visitor.visit_bool(*v),
+            Value::Number(n) => n.deserialize_any(visitor),
+            Value::String(v) => visitor.visit_borrowed_str(v),
+            Value::Array(v) => visit_array_ref(v, visitor),
+            Value::Object(v) => visit_object_ref(v, visitor),
+        }
+    }
+
+    deserialize_value_ref_number!(deserialize_i8);
+    deserialize_value_ref_number!(deserialize_i16);
+    deserialize_value_ref_number!(deserialize_i32);
+    deserialize_value_ref_number!(deserialize_i64);
+    deserialize_number!(deserialize_i128);
+    deserialize_value_ref_number!(deserialize_u8);
+    deserialize_value_ref_number!(deserialize_u16);
+    deserialize_value_ref_number!(deserialize_u32);
+    deserialize_value_ref_number!(deserialize_u64);
+    deserialize_number!(deserialize_u128);
+    deserialize_value_ref_number!(deserialize_f32);
+    deserialize_value_ref_number!(deserialize_f64);
+
+    fn deserialize_option<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        match *self {
+            Value::Null => visitor.visit_none(),
+            _ => visitor.visit_some(self),
+        }
+    }
+
+    fn deserialize_enum<V>(
+        self,
+        _name: &str,
+        _variants: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        let (variant, value) = match self {
+            Value::Object(value) => {
+                let mut iter = value.into_iter();
+                let (variant, value) = match iter.next() {
+                    Some(v) => v,
+                    None => {
+                        return Err(serde::de::Error::invalid_value(
+                            Unexpected::Map,
+                            &"map with a single key",
+                        ));
+                    }
+                };
+                // enums are encoded in json as maps with a single key:value pair
+                if iter.next().is_some() {
+                    return Err(serde::de::Error::invalid_value(
+                        Unexpected::Map,
+                        &"map with a single key",
+                    ));
+                }
+                (variant, Some(value))
+            }
+            Value::String(variant) => (variant, None),
+            other => {
+                return Err(serde::de::Error::invalid_type(
+                    other.unexpected(),
+                    &"string or map",
+                ));
+            }
+        };
+
+        visitor.visit_enum(EnumRefDeserializer { variant, value })
+    }
+
+    #[inline]
+    fn deserialize_newtype_struct<V>(
+        self,
+        name: &'static str,
+        visitor: V,
+    ) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        #[cfg(feature = "raw_value")]
+        {
+            if name == crate::raw::TOKEN {
+                return visitor.visit_map(crate::raw::OwnedRawDeserializer {
+                    raw_value: Some(self.to_string()),
+                });
+            }
+        }
+
+        let _ = name;
+        visitor.visit_newtype_struct(self)
+    }
+
+    fn deserialize_bool<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        match *self {
+            Value::Bool(v) => visitor.visit_bool(v),
+            _ => Err(self.invalid_type(&visitor)),
+        }
+    }
+
+    fn deserialize_char<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        self.deserialize_str(visitor)
+    }
+
+    fn deserialize_str<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        match self {
+            Value::String(v) => visitor.visit_borrowed_str(v),
+            _ => Err(self.invalid_type(&visitor)),
+        }
+    }
+
+    fn deserialize_string<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        self.deserialize_str(visitor)
+    }
+
+    fn deserialize_bytes<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        match self {
+            Value::String(v) => visitor.visit_borrowed_str(v),
+            Value::Array(v) => visit_array_ref(v, visitor),
+            _ => Err(self.invalid_type(&visitor)),
+        }
+    }
+
+    fn deserialize_byte_buf<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        self.deserialize_bytes(visitor)
+    }
+
+    fn deserialize_unit<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        match *self {
+            Value::Null => visitor.visit_unit(),
+            _ => Err(self.invalid_type(&visitor)),
+        }
+    }
+
+    fn deserialize_unit_struct<V>(self, _name: &'static str, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        self.deserialize_unit(visitor)
+    }
+
+    fn deserialize_seq<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        match self {
+            Value::Array(v) => visit_array_ref(v, visitor),
+            _ => Err(self.invalid_type(&visitor)),
+        }
+    }
+
+    fn deserialize_tuple<V>(self, _len: usize, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        self.deserialize_seq(visitor)
+    }
+
+    fn deserialize_tuple_struct<V>(
+        self,
+        _name: &'static str,
+        _len: usize,
+        visitor: V,
+    ) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        self.deserialize_seq(visitor)
+    }
+
+    fn deserialize_map<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        match self {
+            Value::Object(v) => visit_object_ref(v, visitor),
+            _ => Err(self.invalid_type(&visitor)),
+        }
+    }
+
+    fn deserialize_struct<V>(
+        self,
+        _name: &'static str,
+        _fields: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        match self {
+            Value::Array(v) => visit_array_ref(v, visitor),
+            Value::Object(v) => visit_object_ref(v, visitor),
+            _ => Err(self.invalid_type(&visitor)),
+        }
+    }
+
+    fn deserialize_identifier<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        self.deserialize_str(visitor)
+    }
+
+    fn deserialize_ignored_any<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        visitor.visit_unit()
+    }
+}
+
+struct EnumRefDeserializer<'de> {
+    variant: &'de str,
+    value: Option<&'de Value>,
+}
+
+impl<'de> EnumAccess<'de> for EnumRefDeserializer<'de> {
+    type Error = Error;
+    type Variant = VariantRefDeserializer<'de>;
+
+    fn variant_seed<V>(self, seed: V) -> Result<(V::Value, Self::Variant), Error>
+    where
+        V: DeserializeSeed<'de>,
+    {
+        let variant = self.variant.into_deserializer();
+        let visitor = VariantRefDeserializer { value: self.value };
+        seed.deserialize(variant).map(|v| (v, visitor))
+    }
+}
+
+struct VariantRefDeserializer<'de> {
+    value: Option<&'de Value>,
+}
+
+impl<'de> VariantAccess<'de> for VariantRefDeserializer<'de> {
+    type Error = Error;
+
+    fn unit_variant(self) -> Result<(), Error> {
+        match self.value {
+            Some(value) => Deserialize::deserialize(value),
+            None => Ok(()),
+        }
+    }
+
+    fn newtype_variant_seed<T>(self, seed: T) -> Result<T::Value, Error>
+    where
+        T: DeserializeSeed<'de>,
+    {
+        match self.value {
+            Some(value) => seed.deserialize(value),
+            None => Err(serde::de::Error::invalid_type(
+                Unexpected::UnitVariant,
+                &"newtype variant",
+            )),
+        }
+    }
+
+    fn tuple_variant<V>(self, _len: usize, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        match self.value {
+            Some(Value::Array(v)) => {
+                if v.is_empty() {
+                    visitor.visit_unit()
+                } else {
+                    visit_array_ref(v, visitor)
+                }
+            }
+            Some(other) => Err(serde::de::Error::invalid_type(
+                other.unexpected(),
+                &"tuple variant",
+            )),
+            None => Err(serde::de::Error::invalid_type(
+                Unexpected::UnitVariant,
+                &"tuple variant",
+            )),
+        }
+    }
+
+    fn struct_variant<V>(
+        self,
+        _fields: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        match self.value {
+            Some(Value::Object(v)) => visit_object_ref(v, visitor),
+            Some(other) => Err(serde::de::Error::invalid_type(
+                other.unexpected(),
+                &"struct variant",
+            )),
+            None => Err(serde::de::Error::invalid_type(
+                Unexpected::UnitVariant,
+                &"struct variant",
+            )),
+        }
+    }
+}
+
+struct SeqRefDeserializer<'de> {
+    iter: slice::Iter<'de, Value>,
+}
+
+impl<'de> SeqRefDeserializer<'de> {
+    fn new(slice: &'de [Value]) -> Self {
+        SeqRefDeserializer { iter: slice.iter() }
+    }
+}
+
+impl<'de> SeqAccess<'de> for SeqRefDeserializer<'de> {
+    type Error = Error;
+
+    fn next_element_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Error>
+    where
+        T: DeserializeSeed<'de>,
+    {
+        match self.iter.next() {
+            Some(value) => seed.deserialize(value).map(Some),
+            None => Ok(None),
+        }
+    }
+
+    fn size_hint(&self) -> Option<usize> {
+        match self.iter.size_hint() {
+            (lower, Some(upper)) if lower == upper => Some(upper),
+            _ => None,
+        }
+    }
+}
+
+struct MapRefDeserializer<'de> {
+    iter: <&'de Map<String, Value> as IntoIterator>::IntoIter,
+    value: Option<&'de Value>,
+}
+
+impl<'de> MapRefDeserializer<'de> {
+    fn new(map: &'de Map<String, Value>) -> Self {
+        MapRefDeserializer {
+            iter: map.into_iter(),
+            value: None,
+        }
+    }
+}
+
+impl<'de> MapAccess<'de> for MapRefDeserializer<'de> {
+    type Error = Error;
+
+    fn next_key_seed<T>(&mut self, seed: T) -> Result<Option<T::Value>, Error>
+    where
+        T: DeserializeSeed<'de>,
+    {
+        match self.iter.next() {
+            Some((key, value)) => {
+                self.value = Some(value);
+                let key_de = MapKeyDeserializer {
+                    key: Cow::Borrowed(&**key),
+                };
+                seed.deserialize(key_de).map(Some)
+            }
+            None => Ok(None),
+        }
+    }
+
+    fn next_value_seed<T>(&mut self, seed: T) -> Result<T::Value, Error>
+    where
+        T: DeserializeSeed<'de>,
+    {
+        match self.value.take() {
+            Some(value) => seed.deserialize(value),
+            None => Err(serde::de::Error::custom("value is missing")),
+        }
+    }
+
+    fn size_hint(&self) -> Option<usize> {
+        match self.iter.size_hint() {
+            (lower, Some(upper)) if lower == upper => Some(upper),
+            _ => None,
+        }
+    }
+}
+
+struct MapKeyDeserializer<'de> {
+    key: Cow<'de, str>,
+}
+
+macro_rules! deserialize_integer_key {
+    ($method:ident => $visit:ident) => {
+        fn $method<V>(self, visitor: V) -> Result<V::Value, Error>
+        where
+            V: Visitor<'de>,
+        {
+            match (self.key.parse(), self.key) {
+                (Ok(integer), _) => visitor.$visit(integer),
+                (Err(_), Cow::Borrowed(s)) => visitor.visit_borrowed_str(s),
+                #[cfg(any(feature = "std", feature = "alloc"))]
+                (Err(_), Cow::Owned(s)) => visitor.visit_string(s),
+            }
+        }
+    };
+}
+
+impl<'de> serde::Deserializer<'de> for MapKeyDeserializer<'de> {
+    type Error = Error;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        BorrowedCowStrDeserializer::new(self.key).deserialize_any(visitor)
+    }
+
+    deserialize_integer_key!(deserialize_i8 => visit_i8);
+    deserialize_integer_key!(deserialize_i16 => visit_i16);
+    deserialize_integer_key!(deserialize_i32 => visit_i32);
+    deserialize_integer_key!(deserialize_i64 => visit_i64);
+    deserialize_integer_key!(deserialize_i128 => visit_i128);
+    deserialize_integer_key!(deserialize_u8 => visit_u8);
+    deserialize_integer_key!(deserialize_u16 => visit_u16);
+    deserialize_integer_key!(deserialize_u32 => visit_u32);
+    deserialize_integer_key!(deserialize_u64 => visit_u64);
+    deserialize_integer_key!(deserialize_u128 => visit_u128);
+
+    #[inline]
+    fn deserialize_option<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        // Map keys cannot be null.
+        visitor.visit_some(self)
+    }
+
+    #[inline]
+    fn deserialize_newtype_struct<V>(
+        self,
+        _name: &'static str,
+        visitor: V,
+    ) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        visitor.visit_newtype_struct(self)
+    }
+
+    fn deserialize_enum<V>(
+        self,
+        name: &'static str,
+        variants: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Error>
+    where
+        V: Visitor<'de>,
+    {
+        self.key
+            .into_deserializer()
+            .deserialize_enum(name, variants, visitor)
+    }
+
+    forward_to_deserialize_any! {
+        bool f32 f64 char str string bytes byte_buf unit unit_struct seq tuple
+        tuple_struct map struct identifier ignored_any
+    }
+}
+
+struct KeyClassifier;
+
+enum KeyClass {
+    Map(String),
+    #[cfg(feature = "arbitrary_precision")]
+    Number,
+    #[cfg(feature = "raw_value")]
+    RawValue,
+}
+
+impl<'de> DeserializeSeed<'de> for KeyClassifier {
+    type Value = KeyClass;
+
+    fn deserialize<D>(self, deserializer: D) -> Result<Self::Value, D::Error>
+    where
+        D: serde::Deserializer<'de>,
+    {
+        deserializer.deserialize_str(self)
+    }
+}
+
+impl<'de> Visitor<'de> for KeyClassifier {
+    type Value = KeyClass;
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("a string key")
+    }
+
+    fn visit_str<E>(self, s: &str) -> Result<Self::Value, E>
+    where
+        E: de::Error,
+    {
+        match s {
+            #[cfg(feature = "arbitrary_precision")]
+            crate::number::TOKEN => Ok(KeyClass::Number),
+            #[cfg(feature = "raw_value")]
+            crate::raw::TOKEN => Ok(KeyClass::RawValue),
+            _ => Ok(KeyClass::Map(s.to_owned())),
+        }
+    }
+
+    #[cfg(any(feature = "std", feature = "alloc"))]
+    fn visit_string<E>(self, s: String) -> Result<Self::Value, E>
+    where
+        E: de::Error,
+    {
+        match s.as_str() {
+            #[cfg(feature = "arbitrary_precision")]
+            crate::number::TOKEN => Ok(KeyClass::Number),
+            #[cfg(feature = "raw_value")]
+            crate::raw::TOKEN => Ok(KeyClass::RawValue),
+            _ => Ok(KeyClass::Map(s)),
+        }
+    }
+}
+
+impl Value {
+    #[cold]
+    fn invalid_type<E>(&self, exp: &dyn Expected) -> E
+    where
+        E: serde::de::Error,
+    {
+        serde::de::Error::invalid_type(self.unexpected(), exp)
+    }
+
+    #[cold]
+    fn unexpected(&self) -> Unexpected {
+        match self {
+            Value::Null => Unexpected::Unit,
+            Value::Bool(b) => Unexpected::Bool(*b),
+            Value::Number(n) => n.unexpected(),
+            Value::String(s) => Unexpected::Str(s),
+            Value::Array(_) => Unexpected::Seq,
+            Value::Object(_) => Unexpected::Map,
+        }
+    }
+}
+
+struct BorrowedCowStrDeserializer<'de> {
+    value: Cow<'de, str>,
+}
+
+impl<'de> BorrowedCowStrDeserializer<'de> {
+    fn new(value: Cow<'de, str>) -> Self {
+        BorrowedCowStrDeserializer { value }
+    }
+}
+
+impl<'de> de::Deserializer<'de> for BorrowedCowStrDeserializer<'de> {
+    type Error = Error;
+
+    fn deserialize_any<V>(self, visitor: V) -> Result<V::Value, Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        match self.value {
+            Cow::Borrowed(string) => visitor.visit_borrowed_str(string),
+            #[cfg(any(feature = "std", feature = "alloc"))]
+            Cow::Owned(string) => visitor.visit_string(string),
+        }
+    }
+
+    fn deserialize_enum<V>(
+        self,
+        _name: &str,
+        _variants: &'static [&'static str],
+        visitor: V,
+    ) -> Result<V::Value, Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        visitor.visit_enum(self)
+    }
+
+    forward_to_deserialize_any! {
+        bool i8 i16 i32 i64 i128 u8 u16 u32 u64 u128 f32 f64 char str string
+        bytes byte_buf option unit unit_struct newtype_struct seq tuple
+        tuple_struct map struct identifier ignored_any
+    }
+}
+
+impl<'de> de::EnumAccess<'de> for BorrowedCowStrDeserializer<'de> {
+    type Error = Error;
+    type Variant = UnitOnly;
+
+    fn variant_seed<T>(self, seed: T) -> Result<(T::Value, Self::Variant), Error>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        let value = seed.deserialize(self)?;
+        Ok((value, UnitOnly))
+    }
+}
+
+struct UnitOnly;
+
+impl<'de> de::VariantAccess<'de> for UnitOnly {
+    type Error = Error;
+
+    fn unit_variant(self) -> Result<(), Error> {
+        Ok(())
+    }
+
+    fn newtype_variant_seed<T>(self, _seed: T) -> Result<T::Value, Error>
+    where
+        T: de::DeserializeSeed<'de>,
+    {
+        Err(de::Error::invalid_type(
+            Unexpected::UnitVariant,
+            &"newtype variant",
+        ))
+    }
+
+    fn tuple_variant<V>(self, _len: usize, _visitor: V) -> Result<V::Value, Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        Err(de::Error::invalid_type(
+            Unexpected::UnitVariant,
+            &"tuple variant",
+        ))
+    }
+
+    fn struct_variant<V>(
+        self,
+        _fields: &'static [&'static str],
+        _visitor: V,
+    ) -> Result<V::Value, Error>
+    where
+        V: de::Visitor<'de>,
+    {
+        Err(de::Error::invalid_type(
+            Unexpected::UnitVariant,
+            &"struct variant",
+        ))
+    }
+}
diff --git a/third_party/rust/serde_json/src/value/from.rs b/third_party/rust/serde_json/src/value/from.rs
new file mode 100644
index 0000000000..c5a6a3960b
--- /dev/null
+++ b/third_party/rust/serde_json/src/value/from.rs
@@ -0,0 +1,277 @@
+use super::Value;
+use crate::map::Map;
+use crate::number::Number;
+use alloc::borrow::Cow;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+use core::iter::FromIterator;
+
+macro_rules! from_integer {
+    ($($ty:ident)*) => {
+        $(
+            impl From<$ty> for Value {
+                fn from(n: $ty) -> Self {
+                    Value::Number(n.into())
+                }
+            }
+        )*
+    };
+}
+
+from_integer! {
+    i8 i16 i32 i64 isize
+    u8 u16 u32 u64 usize
+}
+
+#[cfg(feature = "arbitrary_precision")]
+from_integer! {
+    i128 u128
+}
+
+impl From<f32> for Value {
+    /// Convert 32-bit floating point number to `Value`
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use serde_json::Value;
+    ///
+    /// let f: f32 = 13.37;
+    /// let x: Value = f.into();
+    /// ```
+    fn from(f: f32) -> Self {
+        From::from(f as f64)
+    }
+}
+
+impl From<f64> for Value {
+    /// Convert 64-bit floating point number to `Value`
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use serde_json::Value;
+    ///
+    /// let f: f64 = 13.37;
+    /// let x: Value = f.into();
+    /// ```
+    fn from(f: f64) -> Self {
+        Number::from_f64(f).map_or(Value::Null, Value::Number)
+    }
+}
+
+impl From<bool> for Value {
+    /// Convert boolean to `Value`
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use serde_json::Value;
+    ///
+    /// let b = false;
+    /// let x: Value = b.into();
+    /// ```
+    fn from(f: bool) -> Self {
+        Value::Bool(f)
+    }
+}
+
+impl From<String> for Value {
+    /// Convert `String` to `Value`
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use serde_json::Value;
+    ///
+    /// let s: String = "lorem".to_string();
+    /// let x: Value = s.into();
+    /// ```
+    fn from(f: String) -> Self {
+        Value::String(f)
+    }
+}
+
+impl<'a> From<&'a str> for Value {
+    /// Convert string slice to `Value`
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use serde_json::Value;
+    ///
+    /// let s: &str = "lorem";
+    /// let x: Value = s.into();
+    /// ```
+    fn from(f: &str) -> Self {
+        Value::String(f.to_string())
+    }
+}
+
+impl<'a> From<Cow<'a, str>> for Value {
+    /// Convert copy-on-write string to `Value`
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use serde_json::Value;
+    /// use std::borrow::Cow;
+    ///
+    /// let s: Cow<str> = Cow::Borrowed("lorem");
+    /// let x: Value = s.into();
+    /// ```
+    ///
+    /// ```
+    /// use serde_json::Value;
+    /// use std::borrow::Cow;
+    ///
+    /// let s: Cow<str> = Cow::Owned("lorem".to_string());
+    /// let x: Value = s.into();
+    /// ```
+    fn from(f: Cow<'a, str>) -> Self {
+        Value::String(f.into_owned())
+    }
+}
+
+impl From<Number> for Value {
+    /// Convert `Number` to `Value`
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use serde_json::{Number, Value};
+    ///
+    /// let n = Number::from(7);
+    /// let x: Value = n.into();
+    /// ```
+    fn from(f: Number) -> Self {
+        Value::Number(f)
+    }
+}
+
+impl From<Map<String, Value>> for Value {
+    /// Convert map (with string keys) to `Value`
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use serde_json::{Map, Value};
+    ///
+    /// let mut m = Map::new();
+    /// m.insert("Lorem".to_string(), "ipsum".into());
+    /// let x: Value = m.into();
+    /// ```
+    fn from(f: Map<String, Value>) -> Self {
+        Value::Object(f)
+    }
+}
+
+impl<T: Into<Value>> From<Vec<T>> for Value {
+    /// Convert a `Vec` to `Value`
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use serde_json::Value;
+    ///
+    /// let v = vec!["lorem", "ipsum", "dolor"];
+    /// let x: Value = v.into();
+    /// ```
+    fn from(f: Vec<T>) -> Self {
+        Value::Array(f.into_iter().map(Into::into).collect())
+    }
+}
+
+impl<'a, T: Clone + Into<Value>> From<&'a [T]> for Value {
+    /// Convert a slice to `Value`
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use serde_json::Value;
+    ///
+    /// let v: &[&str] = &["lorem", "ipsum", "dolor"];
+    /// let x: Value = v.into();
+    /// ```
+    fn from(f: &'a [T]) -> Self {
+        Value::Array(f.iter().cloned().map(Into::into).collect())
+    }
+}
+
+impl<T: Into<Value>> FromIterator<T> for Value {
+    /// Convert an iteratable type to a `Value`
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use serde_json::Value;
+    ///
+    /// let v = std::iter::repeat(42).take(5);
+    /// let x: Value = v.collect();
+    /// ```
+    ///
+    /// ```
+    /// use serde_json::Value;
+    ///
+    /// let v: Vec<_> = vec!["lorem", "ipsum", "dolor"];
+    /// let x: Value = v.into_iter().collect();
+    /// ```
+    ///
+    /// ```
+    /// use std::iter::FromIterator;
+    /// use serde_json::Value;
+    ///
+    /// let x: Value = Value::from_iter(vec!["lorem", "ipsum", "dolor"]);
+    /// ```
+    fn from_iter<I: IntoIterator<Item = T>>(iter: I) -> Self {
+        Value::Array(iter.into_iter().map(Into::into).collect())
+    }
+}
+
+impl<K: Into<String>, V: Into<Value>> FromIterator<(K, V)> for Value {
+    /// Convert an iteratable type to a `Value`
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use serde_json::Value;
+    ///
+    /// let v: Vec<_> = vec![("lorem", 40), ("ipsum", 2)];
+    /// let x: Value = v.into_iter().collect();
+    /// ```
+    fn from_iter<I: IntoIterator<Item = (K, V)>>(iter: I) -> Self {
+        Value::Object(
+            iter.into_iter()
+                .map(|(k, v)| (k.into(), v.into()))
+                .collect(),
+        )
+    }
+}
+
+impl From<()> for Value {
+    /// Convert `()` to `Value`
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// use serde_json::Value;
+    ///
+    /// let u = ();
+    /// let x: Value = u.into();
+    /// ```
+    fn from((): ()) -> Self {
+        Value::Null
+    }
+}
+
+impl<T> From<Option<T>> for Value
+where
+    T: Into<Value>,
+{
+    fn from(opt: Option<T>) -> Self {
+        match opt {
+            None => Value::Null,
+            Some(value) => Into::into(value),
+        }
+    }
+}
diff --git a/third_party/rust/serde_json/src/value/index.rs b/third_party/rust/serde_json/src/value/index.rs
new file mode 100644
index 0000000000..c74042b75a
--- /dev/null
+++ b/third_party/rust/serde_json/src/value/index.rs
@@ -0,0 +1,258 @@
+use super::Value;
+use crate::map::Map;
+use alloc::borrow::ToOwned;
+use alloc::string::String;
+use core::fmt::{self, Display};
+use core::ops;
+
+/// A type that can be used to index into a `serde_json::Value`.
+///
+/// The [`get`] and [`get_mut`] methods of `Value` accept any type that
+/// implements `Index`, as does the [square-bracket indexing operator]. This
+/// trait is implemented for strings which are used as the index into a JSON
+/// map, and for `usize` which is used as the index into a JSON array.
+///
+/// [`get`]: ../enum.Value.html#method.get
+/// [`get_mut`]: ../enum.Value.html#method.get_mut
+/// [square-bracket indexing operator]: ../enum.Value.html#impl-Index%3CI%3E
+///
+/// This trait is sealed and cannot be implemented for types outside of
+/// `serde_json`.
+///
+/// # Examples
+///
+/// ```
+/// # use serde_json::json;
+/// #
+/// let data = json!({ "inner": [1, 2, 3] });
+///
+/// // Data is a JSON map so it can be indexed with a string.
+/// let inner = &data["inner"];
+///
+/// // Inner is a JSON array so it can be indexed with an integer.
+/// let first = &inner[0];
+///
+/// assert_eq!(first, 1);
+/// ```
+pub trait Index: private::Sealed {
+    /// Return None if the key is not already in the array or object.
+    #[doc(hidden)]
+    fn index_into<'v>(&self, v: &'v Value) -> Option<&'v Value>;
+
+    /// Return None if the key is not already in the array or object.
+    #[doc(hidden)]
+    fn index_into_mut<'v>(&self, v: &'v mut Value) -> Option<&'v mut Value>;
+
+    /// Panic if array index out of bounds. If key is not already in the object,
+    /// insert it with a value of null. Panic if Value is a type that cannot be
+    /// indexed into, except if Value is null then it can be treated as an empty
+    /// object.
+    #[doc(hidden)]
+    fn index_or_insert<'v>(&self, v: &'v mut Value) -> &'v mut Value;
+}
+
+impl Index for usize {
+    fn index_into<'v>(&self, v: &'v Value) -> Option<&'v Value> {
+        match v {
+            Value::Array(vec) => vec.get(*self),
+            _ => None,
+        }
+    }
+    fn index_into_mut<'v>(&self, v: &'v mut Value) -> Option<&'v mut Value> {
+        match v {
+            Value::Array(vec) => vec.get_mut(*self),
+            _ => None,
+        }
+    }
+    fn index_or_insert<'v>(&self, v: &'v mut Value) -> &'v mut Value {
+        match v {
+            Value::Array(vec) => {
+                let len = vec.len();
+                vec.get_mut(*self).unwrap_or_else(|| {
+                    panic!(
+                        "cannot access index {} of JSON array of length {}",
+                        self, len
+                    )
+                })
+            }
+            _ => panic!("cannot access index {} of JSON {}", self, Type(v)),
+        }
+    }
+}
+
+impl Index for str {
+    fn index_into<'v>(&self, v: &'v Value) -> Option<&'v Value> {
+        match v {
+            Value::Object(map) => map.get(self),
+            _ => None,
+        }
+    }
+    fn index_into_mut<'v>(&self, v: &'v mut Value) -> Option<&'v mut Value> {
+        match v {
+            Value::Object(map) => map.get_mut(self),
+            _ => None,
+        }
+    }
+    fn index_or_insert<'v>(&self, v: &'v mut Value) -> &'v mut Value {
+        if let Value::Null = v {
+            *v = Value::Object(Map::new());
+        }
+        match v {
+            Value::Object(map) => map.entry(self.to_owned()).or_insert(Value::Null),
+            _ => panic!("cannot access key {:?} in JSON {}", self, Type(v)),
+        }
+    }
+}
+
+impl Index for String {
+    fn index_into<'v>(&self, v: &'v Value) -> Option<&'v Value> {
+        self[..].index_into(v)
+    }
+    fn index_into_mut<'v>(&self, v: &'v mut Value) -> Option<&'v mut Value> {
+        self[..].index_into_mut(v)
+    }
+    fn index_or_insert<'v>(&self, v: &'v mut Value) -> &'v mut Value {
+        self[..].index_or_insert(v)
+    }
+}
+
+impl<'a, T> Index for &'a T
+where
+    T: ?Sized + Index,
+{
+    fn index_into<'v>(&self, v: &'v Value) -> Option<&'v Value> {
+        (**self).index_into(v)
+    }
+    fn index_into_mut<'v>(&self, v: &'v mut Value) -> Option<&'v mut Value> {
+        (**self).index_into_mut(v)
+    }
+    fn index_or_insert<'v>(&self, v: &'v mut Value) -> &'v mut Value {
+        (**self).index_or_insert(v)
+    }
+}
+
+// Prevent users from implementing the Index trait.
+mod private {
+    pub trait Sealed {}
+    impl Sealed for usize {}
+    impl Sealed for str {}
+    impl Sealed for alloc::string::String {}
+    impl<'a, T> Sealed for &'a T where T: ?Sized + Sealed {}
+}
+
+/// Used in panic messages.
+struct Type<'a>(&'a Value);
+
+impl<'a> Display for Type<'a> {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        match *self.0 {
+            Value::Null => formatter.write_str("null"),
+            Value::Bool(_) => formatter.write_str("boolean"),
+            Value::Number(_) => formatter.write_str("number"),
+            Value::String(_) => formatter.write_str("string"),
+            Value::Array(_) => formatter.write_str("array"),
+            Value::Object(_) => formatter.write_str("object"),
+        }
+    }
+}
+
+// The usual semantics of Index is to panic on invalid indexing.
+//
+// That said, the usual semantics are for things like Vec and BTreeMap which
+// have different use cases than Value. If you are working with a Vec, you know
+// that you are working with a Vec and you can get the len of the Vec and make
+// sure your indices are within bounds. The Value use cases are more
+// loosey-goosey. You got some JSON from an endpoint and you want to pull values
+// out of it. Outside of this Index impl, you already have the option of using
+// value.as_array() and working with the Vec directly, or matching on
+// Value::Array and getting the Vec directly. The Index impl means you can skip
+// that and index directly into the thing using a concise syntax. You don't have
+// to check the type, you don't have to check the len, it is all about what you
+// expect the Value to look like.
+//
+// Basically the use cases that would be well served by panicking here are
+// better served by using one of the other approaches: get and get_mut,
+// as_array, or match. The value of this impl is that it adds a way of working
+// with Value that is not well served by the existing approaches: concise and
+// careless and sometimes that is exactly what you want.
+impl<I> ops::Index<I> for Value
+where
+    I: Index,
+{
+    type Output = Value;
+
+    /// Index into a `serde_json::Value` using the syntax `value[0]` or
+    /// `value["k"]`.
+    ///
+    /// Returns `Value::Null` if the type of `self` does not match the type of
+    /// the index, for example if the index is a string and `self` is an array
+    /// or a number. Also returns `Value::Null` if the given key does not exist
+    /// in the map or the given index is not within the bounds of the array.
+    ///
+    /// For retrieving deeply nested values, you should have a look at the
+    /// `Value::pointer` method.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let data = json!({
+    ///     "x": {
+    ///         "y": ["z", "zz"]
+    ///     }
+    /// });
+    ///
+    /// assert_eq!(data["x"]["y"], json!(["z", "zz"]));
+    /// assert_eq!(data["x"]["y"][0], json!("z"));
+    ///
+    /// assert_eq!(data["a"], json!(null)); // returns null for undefined values
+    /// assert_eq!(data["a"]["b"], json!(null)); // does not panic
+    /// ```
+    fn index(&self, index: I) -> &Value {
+        static NULL: Value = Value::Null;
+        index.index_into(self).unwrap_or(&NULL)
+    }
+}
+
+impl<I> ops::IndexMut<I> for Value
+where
+    I: Index,
+{
+    /// Write into a `serde_json::Value` using the syntax `value[0] = ...` or
+    /// `value["k"] = ...`.
+    ///
+    /// If the index is a number, the value must be an array of length bigger
+    /// than the index. Indexing into a value that is not an array or an array
+    /// that is too small will panic.
+    ///
+    /// If the index is a string, the value must be an object or null which is
+    /// treated like an empty object. If the key is not already present in the
+    /// object, it will be inserted with a value of null. Indexing into a value
+    /// that is neither an object nor null will panic.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let mut data = json!({ "x": 0 });
+    ///
+    /// // replace an existing key
+    /// data["x"] = json!(1);
+    ///
+    /// // insert a new key
+    /// data["y"] = json!([false, false, false]);
+    ///
+    /// // replace an array value
+    /// data["y"][0] = json!(true);
+    ///
+    /// // inserted a deeply nested key
+    /// data["a"]["b"]["c"]["d"] = json!(true);
+    ///
+    /// println!("{}", data);
+    /// ```
+    fn index_mut(&mut self, index: I) -> &mut Value {
+        index.index_or_insert(self)
+    }
+}
diff --git a/third_party/rust/serde_json/src/value/mod.rs b/third_party/rust/serde_json/src/value/mod.rs
new file mode 100644
index 0000000000..470b6b24da
--- /dev/null
+++ b/third_party/rust/serde_json/src/value/mod.rs
@@ -0,0 +1,987 @@
+//! The Value enum, a loosely typed way of representing any valid JSON value.
+//!
+//! # Constructing JSON
+//!
+//! Serde JSON provides a [`json!` macro][macro] to build `serde_json::Value`
+//! objects with very natural JSON syntax.
+//!
+//! ```
+//! use serde_json::json;
+//!
+//! fn main() {
+//!     // The type of `john` is `serde_json::Value`
+//!     let john = json!({
+//!         "name": "John Doe",
+//!         "age": 43,
+//!         "phones": [
+//!             "+44 1234567",
+//!             "+44 2345678"
+//!         ]
+//!     });
+//!
+//!     println!("first phone number: {}", john["phones"][0]);
+//!
+//!     // Convert to a string of JSON and print it out
+//!     println!("{}", john.to_string());
+//! }
+//! ```
+//!
+//! The `Value::to_string()` function converts a `serde_json::Value` into a
+//! `String` of JSON text.
+//!
+//! One neat thing about the `json!` macro is that variables and expressions can
+//! be interpolated directly into the JSON value as you are building it. Serde
+//! will check at compile time that the value you are interpolating is able to
+//! be represented as JSON.
+//!
+//! ```
+//! # use serde_json::json;
+//! #
+//! # fn random_phone() -> u16 { 0 }
+//! #
+//! let full_name = "John Doe";
+//! let age_last_year = 42;
+//!
+//! // The type of `john` is `serde_json::Value`
+//! let john = json!({
+//!     "name": full_name,
+//!     "age": age_last_year + 1,
+//!     "phones": [
+//!         format!("+44 {}", random_phone())
+//!     ]
+//! });
+//! ```
+//!
+//! A string of JSON data can be parsed into a `serde_json::Value` by the
+//! [`serde_json::from_str`][from_str] function. There is also
+//! [`from_slice`][from_slice] for parsing from a byte slice `&[u8]` and
+//! [`from_reader`][from_reader] for parsing from any `io::Read` like a File or
+//! a TCP stream.
+//!
+//! ```
+//! use serde_json::{json, Value, Error};
+//!
+//! fn untyped_example() -> Result<(), Error> {
+//!     // Some JSON input data as a &str. Maybe this comes from the user.
+//!     let data = r#"
+//!         {
+//!             "name": "John Doe",
+//!             "age": 43,
+//!             "phones": [
+//!                 "+44 1234567",
+//!                 "+44 2345678"
+//!             ]
+//!         }"#;
+//!
+//!     // Parse the string of data into serde_json::Value.
+//!     let v: Value = serde_json::from_str(data)?;
+//!
+//!     // Access parts of the data by indexing with square brackets.
+//!     println!("Please call {} at the number {}", v["name"], v["phones"][0]);
+//!
+//!     Ok(())
+//! }
+//! #
+//! # untyped_example().unwrap();
+//! ```
+//!
+//! [macro]: crate::json
+//! [from_str]: crate::de::from_str
+//! [from_slice]: crate::de::from_slice
+//! [from_reader]: crate::de::from_reader
+
+use crate::error::Error;
+use crate::io;
+use alloc::string::String;
+use alloc::vec::Vec;
+use core::fmt::{self, Debug, Display};
+use core::mem;
+use core::str;
+use serde::de::DeserializeOwned;
+use serde::ser::Serialize;
+
+pub use self::index::Index;
+pub use self::ser::Serializer;
+pub use crate::map::Map;
+pub use crate::number::Number;
+
+#[cfg(feature = "raw_value")]
+pub use crate::raw::{to_raw_value, RawValue};
+
+/// Represents any valid JSON value.
+///
+/// See the [`serde_json::value` module documentation](self) for usage examples.
+#[derive(Clone, Eq, PartialEq)]
+pub enum Value {
+    /// Represents a JSON null value.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let v = json!(null);
+    /// ```
+    Null,
+
+    /// Represents a JSON boolean.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let v = json!(true);
+    /// ```
+    Bool(bool),
+
+    /// Represents a JSON number, whether integer or floating point.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let v = json!(12.5);
+    /// ```
+    Number(Number),
+
+    /// Represents a JSON string.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let v = json!("a string");
+    /// ```
+    String(String),
+
+    /// Represents a JSON array.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let v = json!(["an", "array"]);
+    /// ```
+    Array(Vec<Value>),
+
+    /// Represents a JSON object.
+    ///
+    /// By default the map is backed by a BTreeMap. Enable the `preserve_order`
+    /// feature of serde_json to use IndexMap instead, which preserves
+    /// entries in the order they are inserted into the map. In particular, this
+    /// allows JSON data to be deserialized into a Value and serialized to a
+    /// string while retaining the order of map keys in the input.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let v = json!({ "an": "object" });
+    /// ```
+    Object(Map<String, Value>),
+}
+
+impl Debug for Value {
+    fn fmt(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        match self {
+            Value::Null => formatter.write_str("Null"),
+            Value::Bool(boolean) => write!(formatter, "Bool({})", boolean),
+            Value::Number(number) => Debug::fmt(number, formatter),
+            Value::String(string) => write!(formatter, "String({:?})", string),
+            Value::Array(vec) => {
+                formatter.write_str("Array ")?;
+                Debug::fmt(vec, formatter)
+            }
+            Value::Object(map) => {
+                formatter.write_str("Object ")?;
+                Debug::fmt(map, formatter)
+            }
+        }
+    }
+}
+
+impl Display for Value {
+    /// Display a JSON value as a string.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let json = json!({ "city": "London", "street": "10 Downing Street" });
+    ///
+    /// // Compact format:
+    /// //
+    /// // {"city":"London","street":"10 Downing Street"}
+    /// let compact = format!("{}", json);
+    /// assert_eq!(compact,
+    ///     "{\"city\":\"London\",\"street\":\"10 Downing Street\"}");
+    ///
+    /// // Pretty format:
+    /// //
+    /// // {
+    /// //   "city": "London",
+    /// //   "street": "10 Downing Street"
+    /// // }
+    /// let pretty = format!("{:#}", json);
+    /// assert_eq!(pretty,
+    ///     "{\n  \"city\": \"London\",\n  \"street\": \"10 Downing Street\"\n}");
+    /// ```
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        struct WriterFormatter<'a, 'b: 'a> {
+            inner: &'a mut fmt::Formatter<'b>,
+        }
+
+        impl<'a, 'b> io::Write for WriterFormatter<'a, 'b> {
+            fn write(&mut self, buf: &[u8]) -> io::Result<usize> {
+                // Safety: the serializer below only emits valid utf8 when using
+                // the default formatter.
+                let s = unsafe { str::from_utf8_unchecked(buf) };
+                tri!(self.inner.write_str(s).map_err(io_error));
+                Ok(buf.len())
+            }
+
+            fn flush(&mut self) -> io::Result<()> {
+                Ok(())
+            }
+        }
+
+        fn io_error(_: fmt::Error) -> io::Error {
+            // Error value does not matter because Display impl just maps it
+            // back to fmt::Error.
+            io::Error::new(io::ErrorKind::Other, "fmt error")
+        }
+
+        let alternate = f.alternate();
+        let mut wr = WriterFormatter { inner: f };
+        if alternate {
+            // {:#}
+            super::ser::to_writer_pretty(&mut wr, self).map_err(|_| fmt::Error)
+        } else {
+            // {}
+            super::ser::to_writer(&mut wr, self).map_err(|_| fmt::Error)
+        }
+    }
+}
+
+fn parse_index(s: &str) -> Option<usize> {
+    if s.starts_with('+') || (s.starts_with('0') && s.len() != 1) {
+        return None;
+    }
+    s.parse().ok()
+}
+
+impl Value {
+    /// Index into a JSON array or map. A string index can be used to access a
+    /// value in a map, and a usize index can be used to access an element of an
+    /// array.
+    ///
+    /// Returns `None` if the type of `self` does not match the type of the
+    /// index, for example if the index is a string and `self` is an array or a
+    /// number. Also returns `None` if the given key does not exist in the map
+    /// or the given index is not within the bounds of the array.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let object = json!({ "A": 65, "B": 66, "C": 67 });
+    /// assert_eq!(*object.get("A").unwrap(), json!(65));
+    ///
+    /// let array = json!([ "A", "B", "C" ]);
+    /// assert_eq!(*array.get(2).unwrap(), json!("C"));
+    ///
+    /// assert_eq!(array.get("A"), None);
+    /// ```
+    ///
+    /// Square brackets can also be used to index into a value in a more concise
+    /// way. This returns `Value::Null` in cases where `get` would have returned
+    /// `None`.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let object = json!({
+    ///     "A": ["a", "á", "à"],
+    ///     "B": ["b", "b́"],
+    ///     "C": ["c", "ć", "ć̣", "ḉ"],
+    /// });
+    /// assert_eq!(object["B"][0], json!("b"));
+    ///
+    /// assert_eq!(object["D"], json!(null));
+    /// assert_eq!(object[0]["x"]["y"]["z"], json!(null));
+    /// ```
+    pub fn get<I: Index>(&self, index: I) -> Option<&Value> {
+        index.index_into(self)
+    }
+
+    /// Mutably index into a JSON array or map. A string index can be used to
+    /// access a value in a map, and a usize index can be used to access an
+    /// element of an array.
+    ///
+    /// Returns `None` if the type of `self` does not match the type of the
+    /// index, for example if the index is a string and `self` is an array or a
+    /// number. Also returns `None` if the given key does not exist in the map
+    /// or the given index is not within the bounds of the array.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let mut object = json!({ "A": 65, "B": 66, "C": 67 });
+    /// *object.get_mut("A").unwrap() = json!(69);
+    ///
+    /// let mut array = json!([ "A", "B", "C" ]);
+    /// *array.get_mut(2).unwrap() = json!("D");
+    /// ```
+    pub fn get_mut<I: Index>(&mut self, index: I) -> Option<&mut Value> {
+        index.index_into_mut(self)
+    }
+
+    /// Returns true if the `Value` is an Object. Returns false otherwise.
+    ///
+    /// For any Value on which `is_object` returns true, `as_object` and
+    /// `as_object_mut` are guaranteed to return the map representation of the
+    /// object.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let obj = json!({ "a": { "nested": true }, "b": ["an", "array"] });
+    ///
+    /// assert!(obj.is_object());
+    /// assert!(obj["a"].is_object());
+    ///
+    /// // array, not an object
+    /// assert!(!obj["b"].is_object());
+    /// ```
+    pub fn is_object(&self) -> bool {
+        self.as_object().is_some()
+    }
+
+    /// If the `Value` is an Object, returns the associated Map. Returns None
+    /// otherwise.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let v = json!({ "a": { "nested": true }, "b": ["an", "array"] });
+    ///
+    /// // The length of `{"nested": true}` is 1 entry.
+    /// assert_eq!(v["a"].as_object().unwrap().len(), 1);
+    ///
+    /// // The array `["an", "array"]` is not an object.
+    /// assert_eq!(v["b"].as_object(), None);
+    /// ```
+    pub fn as_object(&self) -> Option<&Map<String, Value>> {
+        match self {
+            Value::Object(map) => Some(map),
+            _ => None,
+        }
+    }
+
+    /// If the `Value` is an Object, returns the associated mutable Map.
+    /// Returns None otherwise.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let mut v = json!({ "a": { "nested": true } });
+    ///
+    /// v["a"].as_object_mut().unwrap().clear();
+    /// assert_eq!(v, json!({ "a": {} }));
+    /// ```
+    pub fn as_object_mut(&mut self) -> Option<&mut Map<String, Value>> {
+        match self {
+            Value::Object(map) => Some(map),
+            _ => None,
+        }
+    }
+
+    /// Returns true if the `Value` is an Array. Returns false otherwise.
+    ///
+    /// For any Value on which `is_array` returns true, `as_array` and
+    /// `as_array_mut` are guaranteed to return the vector representing the
+    /// array.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let obj = json!({ "a": ["an", "array"], "b": { "an": "object" } });
+    ///
+    /// assert!(obj["a"].is_array());
+    ///
+    /// // an object, not an array
+    /// assert!(!obj["b"].is_array());
+    /// ```
+    pub fn is_array(&self) -> bool {
+        self.as_array().is_some()
+    }
+
+    /// If the `Value` is an Array, returns the associated vector. Returns None
+    /// otherwise.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let v = json!({ "a": ["an", "array"], "b": { "an": "object" } });
+    ///
+    /// // The length of `["an", "array"]` is 2 elements.
+    /// assert_eq!(v["a"].as_array().unwrap().len(), 2);
+    ///
+    /// // The object `{"an": "object"}` is not an array.
+    /// assert_eq!(v["b"].as_array(), None);
+    /// ```
+    pub fn as_array(&self) -> Option<&Vec<Value>> {
+        match self {
+            Value::Array(array) => Some(array),
+            _ => None,
+        }
+    }
+
+    /// If the `Value` is an Array, returns the associated mutable vector.
+    /// Returns None otherwise.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let mut v = json!({ "a": ["an", "array"] });
+    ///
+    /// v["a"].as_array_mut().unwrap().clear();
+    /// assert_eq!(v, json!({ "a": [] }));
+    /// ```
+    pub fn as_array_mut(&mut self) -> Option<&mut Vec<Value>> {
+        match self {
+            Value::Array(list) => Some(list),
+            _ => None,
+        }
+    }
+
+    /// Returns true if the `Value` is a String. Returns false otherwise.
+    ///
+    /// For any Value on which `is_string` returns true, `as_str` is guaranteed
+    /// to return the string slice.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let v = json!({ "a": "some string", "b": false });
+    ///
+    /// assert!(v["a"].is_string());
+    ///
+    /// // The boolean `false` is not a string.
+    /// assert!(!v["b"].is_string());
+    /// ```
+    pub fn is_string(&self) -> bool {
+        self.as_str().is_some()
+    }
+
+    /// If the `Value` is a String, returns the associated str. Returns None
+    /// otherwise.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let v = json!({ "a": "some string", "b": false });
+    ///
+    /// assert_eq!(v["a"].as_str(), Some("some string"));
+    ///
+    /// // The boolean `false` is not a string.
+    /// assert_eq!(v["b"].as_str(), None);
+    ///
+    /// // JSON values are printed in JSON representation, so strings are in quotes.
+    /// //
+    /// //    The value is: "some string"
+    /// println!("The value is: {}", v["a"]);
+    ///
+    /// // Rust strings are printed without quotes.
+    /// //
+    /// //    The value is: some string
+    /// println!("The value is: {}", v["a"].as_str().unwrap());
+    /// ```
+    pub fn as_str(&self) -> Option<&str> {
+        match self {
+            Value::String(s) => Some(s),
+            _ => None,
+        }
+    }
+
+    /// Returns true if the `Value` is a Number. Returns false otherwise.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let v = json!({ "a": 1, "b": "2" });
+    ///
+    /// assert!(v["a"].is_number());
+    ///
+    /// // The string `"2"` is a string, not a number.
+    /// assert!(!v["b"].is_number());
+    /// ```
+    pub fn is_number(&self) -> bool {
+        match *self {
+            Value::Number(_) => true,
+            _ => false,
+        }
+    }
+
+    /// Returns true if the `Value` is an integer between `i64::MIN` and
+    /// `i64::MAX`.
+    ///
+    /// For any Value on which `is_i64` returns true, `as_i64` is guaranteed to
+    /// return the integer value.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let big = i64::max_value() as u64 + 10;
+    /// let v = json!({ "a": 64, "b": big, "c": 256.0 });
+    ///
+    /// assert!(v["a"].is_i64());
+    ///
+    /// // Greater than i64::MAX.
+    /// assert!(!v["b"].is_i64());
+    ///
+    /// // Numbers with a decimal point are not considered integers.
+    /// assert!(!v["c"].is_i64());
+    /// ```
+    pub fn is_i64(&self) -> bool {
+        match self {
+            Value::Number(n) => n.is_i64(),
+            _ => false,
+        }
+    }
+
+    /// Returns true if the `Value` is an integer between zero and `u64::MAX`.
+    ///
+    /// For any Value on which `is_u64` returns true, `as_u64` is guaranteed to
+    /// return the integer value.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let v = json!({ "a": 64, "b": -64, "c": 256.0 });
+    ///
+    /// assert!(v["a"].is_u64());
+    ///
+    /// // Negative integer.
+    /// assert!(!v["b"].is_u64());
+    ///
+    /// // Numbers with a decimal point are not considered integers.
+    /// assert!(!v["c"].is_u64());
+    /// ```
+    pub fn is_u64(&self) -> bool {
+        match self {
+            Value::Number(n) => n.is_u64(),
+            _ => false,
+        }
+    }
+
+    /// Returns true if the `Value` is a number that can be represented by f64.
+    ///
+    /// For any Value on which `is_f64` returns true, `as_f64` is guaranteed to
+    /// return the floating point value.
+    ///
+    /// Currently this function returns true if and only if both `is_i64` and
+    /// `is_u64` return false but this is not a guarantee in the future.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let v = json!({ "a": 256.0, "b": 64, "c": -64 });
+    ///
+    /// assert!(v["a"].is_f64());
+    ///
+    /// // Integers.
+    /// assert!(!v["b"].is_f64());
+    /// assert!(!v["c"].is_f64());
+    /// ```
+    pub fn is_f64(&self) -> bool {
+        match self {
+            Value::Number(n) => n.is_f64(),
+            _ => false,
+        }
+    }
+
+    /// If the `Value` is an integer, represent it as i64 if possible. Returns
+    /// None otherwise.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let big = i64::max_value() as u64 + 10;
+    /// let v = json!({ "a": 64, "b": big, "c": 256.0 });
+    ///
+    /// assert_eq!(v["a"].as_i64(), Some(64));
+    /// assert_eq!(v["b"].as_i64(), None);
+    /// assert_eq!(v["c"].as_i64(), None);
+    /// ```
+    pub fn as_i64(&self) -> Option<i64> {
+        match self {
+            Value::Number(n) => n.as_i64(),
+            _ => None,
+        }
+    }
+
+    /// If the `Value` is an integer, represent it as u64 if possible. Returns
+    /// None otherwise.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let v = json!({ "a": 64, "b": -64, "c": 256.0 });
+    ///
+    /// assert_eq!(v["a"].as_u64(), Some(64));
+    /// assert_eq!(v["b"].as_u64(), None);
+    /// assert_eq!(v["c"].as_u64(), None);
+    /// ```
+    pub fn as_u64(&self) -> Option<u64> {
+        match self {
+            Value::Number(n) => n.as_u64(),
+            _ => None,
+        }
+    }
+
+    /// If the `Value` is a number, represent it as f64 if possible. Returns
+    /// None otherwise.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let v = json!({ "a": 256.0, "b": 64, "c": -64 });
+    ///
+    /// assert_eq!(v["a"].as_f64(), Some(256.0));
+    /// assert_eq!(v["b"].as_f64(), Some(64.0));
+    /// assert_eq!(v["c"].as_f64(), Some(-64.0));
+    /// ```
+    pub fn as_f64(&self) -> Option<f64> {
+        match self {
+            Value::Number(n) => n.as_f64(),
+            _ => None,
+        }
+    }
+
+    /// Returns true if the `Value` is a Boolean. Returns false otherwise.
+    ///
+    /// For any Value on which `is_boolean` returns true, `as_bool` is
+    /// guaranteed to return the boolean value.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let v = json!({ "a": false, "b": "false" });
+    ///
+    /// assert!(v["a"].is_boolean());
+    ///
+    /// // The string `"false"` is a string, not a boolean.
+    /// assert!(!v["b"].is_boolean());
+    /// ```
+    pub fn is_boolean(&self) -> bool {
+        self.as_bool().is_some()
+    }
+
+    /// If the `Value` is a Boolean, returns the associated bool. Returns None
+    /// otherwise.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let v = json!({ "a": false, "b": "false" });
+    ///
+    /// assert_eq!(v["a"].as_bool(), Some(false));
+    ///
+    /// // The string `"false"` is a string, not a boolean.
+    /// assert_eq!(v["b"].as_bool(), None);
+    /// ```
+    pub fn as_bool(&self) -> Option<bool> {
+        match *self {
+            Value::Bool(b) => Some(b),
+            _ => None,
+        }
+    }
+
+    /// Returns true if the `Value` is a Null. Returns false otherwise.
+    ///
+    /// For any Value on which `is_null` returns true, `as_null` is guaranteed
+    /// to return `Some(())`.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let v = json!({ "a": null, "b": false });
+    ///
+    /// assert!(v["a"].is_null());
+    ///
+    /// // The boolean `false` is not null.
+    /// assert!(!v["b"].is_null());
+    /// ```
+    pub fn is_null(&self) -> bool {
+        self.as_null().is_some()
+    }
+
+    /// If the `Value` is a Null, returns (). Returns None otherwise.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let v = json!({ "a": null, "b": false });
+    ///
+    /// assert_eq!(v["a"].as_null(), Some(()));
+    ///
+    /// // The boolean `false` is not null.
+    /// assert_eq!(v["b"].as_null(), None);
+    /// ```
+    pub fn as_null(&self) -> Option<()> {
+        match *self {
+            Value::Null => Some(()),
+            _ => None,
+        }
+    }
+
+    /// Looks up a value by a JSON Pointer.
+    ///
+    /// JSON Pointer defines a string syntax for identifying a specific value
+    /// within a JavaScript Object Notation (JSON) document.
+    ///
+    /// A Pointer is a Unicode string with the reference tokens separated by `/`.
+    /// Inside tokens `/` is replaced by `~1` and `~` is replaced by `~0`. The
+    /// addressed value is returned and if there is no such value `None` is
+    /// returned.
+    ///
+    /// For more information read [RFC6901](https://tools.ietf.org/html/rfc6901).
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let data = json!({
+    ///     "x": {
+    ///         "y": ["z", "zz"]
+    ///     }
+    /// });
+    ///
+    /// assert_eq!(data.pointer("/x/y/1").unwrap(), &json!("zz"));
+    /// assert_eq!(data.pointer("/a/b/c"), None);
+    /// ```
+    pub fn pointer(&self, pointer: &str) -> Option<&Value> {
+        if pointer.is_empty() {
+            return Some(self);
+        }
+        if !pointer.starts_with('/') {
+            return None;
+        }
+        pointer
+            .split('/')
+            .skip(1)
+            .map(|x| x.replace("~1", "/").replace("~0", "~"))
+            .try_fold(self, |target, token| match target {
+                Value::Object(map) => map.get(&token),
+                Value::Array(list) => parse_index(&token).and_then(|x| list.get(x)),
+                _ => None,
+            })
+    }
+
+    /// Looks up a value by a JSON Pointer and returns a mutable reference to
+    /// that value.
+    ///
+    /// JSON Pointer defines a string syntax for identifying a specific value
+    /// within a JavaScript Object Notation (JSON) document.
+    ///
+    /// A Pointer is a Unicode string with the reference tokens separated by `/`.
+    /// Inside tokens `/` is replaced by `~1` and `~` is replaced by `~0`. The
+    /// addressed value is returned and if there is no such value `None` is
+    /// returned.
+    ///
+    /// For more information read [RFC6901](https://tools.ietf.org/html/rfc6901).
+    ///
+    /// # Example of Use
+    ///
+    /// ```
+    /// use serde_json::Value;
+    ///
+    /// fn main() {
+    ///     let s = r#"{"x": 1.0, "y": 2.0}"#;
+    ///     let mut value: Value = serde_json::from_str(s).unwrap();
+    ///
+    ///     // Check value using read-only pointer
+    ///     assert_eq!(value.pointer("/x"), Some(&1.0.into()));
+    ///     // Change value with direct assignment
+    ///     *value.pointer_mut("/x").unwrap() = 1.5.into();
+    ///     // Check that new value was written
+    ///     assert_eq!(value.pointer("/x"), Some(&1.5.into()));
+    ///     // Or change the value only if it exists
+    ///     value.pointer_mut("/x").map(|v| *v = 1.5.into());
+    ///
+    ///     // "Steal" ownership of a value. Can replace with any valid Value.
+    ///     let old_x = value.pointer_mut("/x").map(Value::take).unwrap();
+    ///     assert_eq!(old_x, 1.5);
+    ///     assert_eq!(value.pointer("/x").unwrap(), &Value::Null);
+    /// }
+    /// ```
+    pub fn pointer_mut(&mut self, pointer: &str) -> Option<&mut Value> {
+        if pointer.is_empty() {
+            return Some(self);
+        }
+        if !pointer.starts_with('/') {
+            return None;
+        }
+        pointer
+            .split('/')
+            .skip(1)
+            .map(|x| x.replace("~1", "/").replace("~0", "~"))
+            .try_fold(self, |target, token| match target {
+                Value::Object(map) => map.get_mut(&token),
+                Value::Array(list) => parse_index(&token).and_then(move |x| list.get_mut(x)),
+                _ => None,
+            })
+    }
+
+    /// Takes the value out of the `Value`, leaving a `Null` in its place.
+    ///
+    /// ```
+    /// # use serde_json::json;
+    /// #
+    /// let mut v = json!({ "x": "y" });
+    /// assert_eq!(v["x"].take(), json!("y"));
+    /// assert_eq!(v, json!({ "x": null }));
+    /// ```
+    pub fn take(&mut self) -> Value {
+        mem::replace(self, Value::Null)
+    }
+}
+
+/// The default value is `Value::Null`.
+///
+/// This is useful for handling omitted `Value` fields when deserializing.
+///
+/// # Examples
+///
+/// ```
+/// # use serde::Deserialize;
+/// use serde_json::Value;
+///
+/// #[derive(Deserialize)]
+/// struct Settings {
+///     level: i32,
+///     #[serde(default)]
+///     extras: Value,
+/// }
+///
+/// # fn try_main() -> Result<(), serde_json::Error> {
+/// let data = r#" { "level": 42 } "#;
+/// let s: Settings = serde_json::from_str(data)?;
+///
+/// assert_eq!(s.level, 42);
+/// assert_eq!(s.extras, Value::Null);
+/// #
+/// #     Ok(())
+/// # }
+/// #
+/// # try_main().unwrap()
+/// ```
+impl Default for Value {
+    fn default() -> Value {
+        Value::Null
+    }
+}
+
+mod de;
+mod from;
+mod index;
+mod partial_eq;
+mod ser;
+
+/// Convert a `T` into `serde_json::Value` which is an enum that can represent
+/// any valid JSON data.
+///
+/// # Example
+///
+/// ```
+/// use serde::Serialize;
+/// use serde_json::json;
+///
+/// use std::error::Error;
+///
+/// #[derive(Serialize)]
+/// struct User {
+///     fingerprint: String,
+///     location: String,
+/// }
+///
+/// fn compare_json_values() -> Result<(), Box<Error>> {
+///     let u = User {
+///         fingerprint: "0xF9BA143B95FF6D82".to_owned(),
+///         location: "Menlo Park, CA".to_owned(),
+///     };
+///
+///     // The type of `expected` is `serde_json::Value`
+///     let expected = json!({
+///         "fingerprint": "0xF9BA143B95FF6D82",
+///         "location": "Menlo Park, CA",
+///     });
+///
+///     let v = serde_json::to_value(u).unwrap();
+///     assert_eq!(v, expected);
+///
+///     Ok(())
+/// }
+/// #
+/// # compare_json_values().unwrap();
+/// ```
+///
+/// # Errors
+///
+/// This conversion can fail if `T`'s implementation of `Serialize` decides to
+/// fail, or if `T` contains a map with non-string keys.
+///
+/// ```
+/// use std::collections::BTreeMap;
+///
+/// fn main() {
+///     // The keys in this map are vectors, not strings.
+///     let mut map = BTreeMap::new();
+///     map.insert(vec![32, 64], "x86");
+///
+///     println!("{}", serde_json::to_value(map).unwrap_err());
+/// }
+/// ```
+// Taking by value is more friendly to iterator adapters, option and result
+// consumers, etc. See https://github.com/serde-rs/json/pull/149.
+pub fn to_value<T>(value: T) -> Result<Value, Error>
+where
+    T: Serialize,
+{
+    value.serialize(Serializer)
+}
+
+/// Interpret a `serde_json::Value` as an instance of type `T`.
+///
+/// # Example
+///
+/// ```
+/// use serde::Deserialize;
+/// use serde_json::json;
+///
+/// #[derive(Deserialize, Debug)]
+/// struct User {
+///     fingerprint: String,
+///     location: String,
+/// }
+///
+/// fn main() {
+///     // The type of `j` is `serde_json::Value`
+///     let j = json!({
+///         "fingerprint": "0xF9BA143B95FF6D82",
+///         "location": "Menlo Park, CA"
+///     });
+///
+///     let u: User = serde_json::from_value(j).unwrap();
+///     println!("{:#?}", u);
+/// }
+/// ```
+///
+/// # Errors
+///
+/// This conversion can fail if the structure of the Value does not match the
+/// structure expected by `T`, for example if `T` is a struct type but the Value
+/// contains something other than a JSON map. It can also fail if the structure
+/// is correct but `T`'s implementation of `Deserialize` decides that something
+/// is wrong with the data, for example required struct fields are missing from
+/// the JSON map or some number is too big to fit in the expected primitive
+/// type.
+pub fn from_value<T>(value: Value) -> Result<T, Error>
+where
+    T: DeserializeOwned,
+{
+    T::deserialize(value)
+}
diff --git a/third_party/rust/serde_json/src/value/partial_eq.rs b/third_party/rust/serde_json/src/value/partial_eq.rs
new file mode 100644
index 0000000000..b4ef84c4f3
--- /dev/null
+++ b/third_party/rust/serde_json/src/value/partial_eq.rs
@@ -0,0 +1,95 @@
+use super::Value;
+use alloc::string::String;
+
+fn eq_i64(value: &Value, other: i64) -> bool {
+    value.as_i64().map_or(false, |i| i == other)
+}
+
+fn eq_u64(value: &Value, other: u64) -> bool {
+    value.as_u64().map_or(false, |i| i == other)
+}
+
+fn eq_f64(value: &Value, other: f64) -> bool {
+    value.as_f64().map_or(false, |i| i == other)
+}
+
+fn eq_bool(value: &Value, other: bool) -> bool {
+    value.as_bool().map_or(false, |i| i == other)
+}
+
+fn eq_str(value: &Value, other: &str) -> bool {
+    value.as_str().map_or(false, |i| i == other)
+}
+
+impl PartialEq<str> for Value {
+    fn eq(&self, other: &str) -> bool {
+        eq_str(self, other)
+    }
+}
+
+impl<'a> PartialEq<&'a str> for Value {
+    fn eq(&self, other: &&str) -> bool {
+        eq_str(self, *other)
+    }
+}
+
+impl PartialEq<Value> for str {
+    fn eq(&self, other: &Value) -> bool {
+        eq_str(other, self)
+    }
+}
+
+impl<'a> PartialEq<Value> for &'a str {
+    fn eq(&self, other: &Value) -> bool {
+        eq_str(other, *self)
+    }
+}
+
+impl PartialEq<String> for Value {
+    fn eq(&self, other: &String) -> bool {
+        eq_str(self, other.as_str())
+    }
+}
+
+impl PartialEq<Value> for String {
+    fn eq(&self, other: &Value) -> bool {
+        eq_str(other, self.as_str())
+    }
+}
+
+macro_rules! partialeq_numeric {
+    ($($eq:ident [$($ty:ty)*])*) => {
+        $($(
+            impl PartialEq<$ty> for Value {
+                fn eq(&self, other: &$ty) -> bool {
+                    $eq(self, *other as _)
+                }
+            }
+
+            impl PartialEq<Value> for $ty {
+                fn eq(&self, other: &Value) -> bool {
+                    $eq(other, *self as _)
+                }
+            }
+
+            impl<'a> PartialEq<$ty> for &'a Value {
+                fn eq(&self, other: &$ty) -> bool {
+                    $eq(*self, *other as _)
+                }
+            }
+
+            impl<'a> PartialEq<$ty> for &'a mut Value {
+                fn eq(&self, other: &$ty) -> bool {
+                    $eq(*self, *other as _)
+                }
+            }
+        )*)*
+    }
+}
+
+partialeq_numeric! {
+    eq_i64[i8 i16 i32 i64 isize]
+    eq_u64[u8 u16 u32 u64 usize]
+    eq_f64[f32 f64]
+    eq_bool[bool]
+}
diff --git a/third_party/rust/serde_json/src/value/ser.rs b/third_party/rust/serde_json/src/value/ser.rs
new file mode 100644
index 0000000000..a29814e92a
--- /dev/null
+++ b/third_party/rust/serde_json/src/value/ser.rs
@@ -0,0 +1,1044 @@
+use crate::error::{Error, ErrorCode, Result};
+use crate::map::Map;
+use crate::number::Number;
+use crate::value::{to_value, Value};
+use alloc::borrow::ToOwned;
+use alloc::string::{String, ToString};
+use alloc::vec::Vec;
+#[cfg(not(feature = "arbitrary_precision"))]
+use core::convert::TryFrom;
+use core::fmt::Display;
+use core::result;
+use serde::ser::{Impossible, Serialize};
+
+impl Serialize for Value {
+    #[inline]
+    fn serialize<S>(&self, serializer: S) -> result::Result<S::Ok, S::Error>
+    where
+        S: ::serde::Serializer,
+    {
+        match self {
+            Value::Null => serializer.serialize_unit(),
+            Value::Bool(b) => serializer.serialize_bool(*b),
+            Value::Number(n) => n.serialize(serializer),
+            Value::String(s) => serializer.serialize_str(s),
+            Value::Array(v) => v.serialize(serializer),
+            #[cfg(any(feature = "std", feature = "alloc"))]
+            Value::Object(m) => {
+                use serde::ser::SerializeMap;
+                let mut map = tri!(serializer.serialize_map(Some(m.len())));
+                for (k, v) in m {
+                    tri!(map.serialize_entry(k, v));
+                }
+                map.end()
+            }
+        }
+    }
+}
+
+/// Serializer whose output is a `Value`.
+///
+/// This is the serializer that backs [`serde_json::to_value`][crate::to_value].
+/// Unlike the main serde_json serializer which goes from some serializable
+/// value of type `T` to JSON text, this one goes from `T` to
+/// `serde_json::Value`.
+///
+/// The `to_value` function is implementable as:
+///
+/// ```
+/// use serde::Serialize;
+/// use serde_json::{Error, Value};
+///
+/// pub fn to_value<T>(input: T) -> Result<Value, Error>
+/// where
+///     T: Serialize,
+/// {
+///     input.serialize(serde_json::value::Serializer)
+/// }
+/// ```
+pub struct Serializer;
+
+impl serde::Serializer for Serializer {
+    type Ok = Value;
+    type Error = Error;
+
+    type SerializeSeq = SerializeVec;
+    type SerializeTuple = SerializeVec;
+    type SerializeTupleStruct = SerializeVec;
+    type SerializeTupleVariant = SerializeTupleVariant;
+    type SerializeMap = SerializeMap;
+    type SerializeStruct = SerializeMap;
+    type SerializeStructVariant = SerializeStructVariant;
+
+    #[inline]
+    fn serialize_bool(self, value: bool) -> Result<Value> {
+        Ok(Value::Bool(value))
+    }
+
+    #[inline]
+    fn serialize_i8(self, value: i8) -> Result<Value> {
+        self.serialize_i64(value as i64)
+    }
+
+    #[inline]
+    fn serialize_i16(self, value: i16) -> Result<Value> {
+        self.serialize_i64(value as i64)
+    }
+
+    #[inline]
+    fn serialize_i32(self, value: i32) -> Result<Value> {
+        self.serialize_i64(value as i64)
+    }
+
+    fn serialize_i64(self, value: i64) -> Result<Value> {
+        Ok(Value::Number(value.into()))
+    }
+
+    fn serialize_i128(self, value: i128) -> Result<Value> {
+        #[cfg(feature = "arbitrary_precision")]
+        {
+            Ok(Value::Number(value.into()))
+        }
+
+        #[cfg(not(feature = "arbitrary_precision"))]
+        {
+            if let Ok(value) = u64::try_from(value) {
+                Ok(Value::Number(value.into()))
+            } else if let Ok(value) = i64::try_from(value) {
+                Ok(Value::Number(value.into()))
+            } else {
+                Err(Error::syntax(ErrorCode::NumberOutOfRange, 0, 0))
+            }
+        }
+    }
+
+    #[inline]
+    fn serialize_u8(self, value: u8) -> Result<Value> {
+        self.serialize_u64(value as u64)
+    }
+
+    #[inline]
+    fn serialize_u16(self, value: u16) -> Result<Value> {
+        self.serialize_u64(value as u64)
+    }
+
+    #[inline]
+    fn serialize_u32(self, value: u32) -> Result<Value> {
+        self.serialize_u64(value as u64)
+    }
+
+    #[inline]
+    fn serialize_u64(self, value: u64) -> Result<Value> {
+        Ok(Value::Number(value.into()))
+    }
+
+    fn serialize_u128(self, value: u128) -> Result<Value> {
+        #[cfg(feature = "arbitrary_precision")]
+        {
+            Ok(Value::Number(value.into()))
+        }
+
+        #[cfg(not(feature = "arbitrary_precision"))]
+        {
+            if let Ok(value) = u64::try_from(value) {
+                Ok(Value::Number(value.into()))
+            } else {
+                Err(Error::syntax(ErrorCode::NumberOutOfRange, 0, 0))
+            }
+        }
+    }
+
+    #[inline]
+    fn serialize_f32(self, value: f32) -> Result<Value> {
+        self.serialize_f64(value as f64)
+    }
+
+    #[inline]
+    fn serialize_f64(self, value: f64) -> Result<Value> {
+        Ok(Number::from_f64(value).map_or(Value::Null, Value::Number))
+    }
+
+    #[inline]
+    fn serialize_char(self, value: char) -> Result<Value> {
+        let mut s = String::new();
+        s.push(value);
+        Ok(Value::String(s))
+    }
+
+    #[inline]
+    fn serialize_str(self, value: &str) -> Result<Value> {
+        Ok(Value::String(value.to_owned()))
+    }
+
+    fn serialize_bytes(self, value: &[u8]) -> Result<Value> {
+        let vec = value.iter().map(|&b| Value::Number(b.into())).collect();
+        Ok(Value::Array(vec))
+    }
+
+    #[inline]
+    fn serialize_unit(self) -> Result<Value> {
+        Ok(Value::Null)
+    }
+
+    #[inline]
+    fn serialize_unit_struct(self, _name: &'static str) -> Result<Value> {
+        self.serialize_unit()
+    }
+
+    #[inline]
+    fn serialize_unit_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+    ) -> Result<Value> {
+        self.serialize_str(variant)
+    }
+
+    #[inline]
+    fn serialize_newtype_struct<T>(self, _name: &'static str, value: &T) -> Result<Value>
+    where
+        T: ?Sized + Serialize,
+    {
+        value.serialize(self)
+    }
+
+    fn serialize_newtype_variant<T>(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+        value: &T,
+    ) -> Result<Value>
+    where
+        T: ?Sized + Serialize,
+    {
+        let mut values = Map::new();
+        values.insert(String::from(variant), tri!(to_value(value)));
+        Ok(Value::Object(values))
+    }
+
+    #[inline]
+    fn serialize_none(self) -> Result<Value> {
+        self.serialize_unit()
+    }
+
+    #[inline]
+    fn serialize_some<T>(self, value: &T) -> Result<Value>
+    where
+        T: ?Sized + Serialize,
+    {
+        value.serialize(self)
+    }
+
+    fn serialize_seq(self, len: Option<usize>) -> Result<Self::SerializeSeq> {
+        Ok(SerializeVec {
+            vec: Vec::with_capacity(len.unwrap_or(0)),
+        })
+    }
+
+    fn serialize_tuple(self, len: usize) -> Result<Self::SerializeTuple> {
+        self.serialize_seq(Some(len))
+    }
+
+    fn serialize_tuple_struct(
+        self,
+        _name: &'static str,
+        len: usize,
+    ) -> Result<Self::SerializeTupleStruct> {
+        self.serialize_seq(Some(len))
+    }
+
+    fn serialize_tuple_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+        len: usize,
+    ) -> Result<Self::SerializeTupleVariant> {
+        Ok(SerializeTupleVariant {
+            name: String::from(variant),
+            vec: Vec::with_capacity(len),
+        })
+    }
+
+    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap> {
+        Ok(SerializeMap::Map {
+            map: Map::new(),
+            next_key: None,
+        })
+    }
+
+    fn serialize_struct(self, name: &'static str, len: usize) -> Result<Self::SerializeStruct> {
+        match name {
+            #[cfg(feature = "arbitrary_precision")]
+            crate::number::TOKEN => Ok(SerializeMap::Number { out_value: None }),
+            #[cfg(feature = "raw_value")]
+            crate::raw::TOKEN => Ok(SerializeMap::RawValue { out_value: None }),
+            _ => self.serialize_map(Some(len)),
+        }
+    }
+
+    fn serialize_struct_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeStructVariant> {
+        Ok(SerializeStructVariant {
+            name: String::from(variant),
+            map: Map::new(),
+        })
+    }
+
+    fn collect_str<T>(self, value: &T) -> Result<Value>
+    where
+        T: ?Sized + Display,
+    {
+        Ok(Value::String(value.to_string()))
+    }
+}
+
+pub struct SerializeVec {
+    vec: Vec<Value>,
+}
+
+pub struct SerializeTupleVariant {
+    name: String,
+    vec: Vec<Value>,
+}
+
+pub enum SerializeMap {
+    Map {
+        map: Map<String, Value>,
+        next_key: Option<String>,
+    },
+    #[cfg(feature = "arbitrary_precision")]
+    Number { out_value: Option<Value> },
+    #[cfg(feature = "raw_value")]
+    RawValue { out_value: Option<Value> },
+}
+
+pub struct SerializeStructVariant {
+    name: String,
+    map: Map<String, Value>,
+}
+
+impl serde::ser::SerializeSeq for SerializeVec {
+    type Ok = Value;
+    type Error = Error;
+
+    fn serialize_element<T>(&mut self, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        self.vec.push(tri!(to_value(value)));
+        Ok(())
+    }
+
+    fn end(self) -> Result<Value> {
+        Ok(Value::Array(self.vec))
+    }
+}
+
+impl serde::ser::SerializeTuple for SerializeVec {
+    type Ok = Value;
+    type Error = Error;
+
+    fn serialize_element<T>(&mut self, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        serde::ser::SerializeSeq::serialize_element(self, value)
+    }
+
+    fn end(self) -> Result<Value> {
+        serde::ser::SerializeSeq::end(self)
+    }
+}
+
+impl serde::ser::SerializeTupleStruct for SerializeVec {
+    type Ok = Value;
+    type Error = Error;
+
+    fn serialize_field<T>(&mut self, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        serde::ser::SerializeSeq::serialize_element(self, value)
+    }
+
+    fn end(self) -> Result<Value> {
+        serde::ser::SerializeSeq::end(self)
+    }
+}
+
+impl serde::ser::SerializeTupleVariant for SerializeTupleVariant {
+    type Ok = Value;
+    type Error = Error;
+
+    fn serialize_field<T>(&mut self, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        self.vec.push(tri!(to_value(value)));
+        Ok(())
+    }
+
+    fn end(self) -> Result<Value> {
+        let mut object = Map::new();
+
+        object.insert(self.name, Value::Array(self.vec));
+
+        Ok(Value::Object(object))
+    }
+}
+
+impl serde::ser::SerializeMap for SerializeMap {
+    type Ok = Value;
+    type Error = Error;
+
+    fn serialize_key<T>(&mut self, key: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        match self {
+            SerializeMap::Map { next_key, .. } => {
+                *next_key = Some(tri!(key.serialize(MapKeySerializer)));
+                Ok(())
+            }
+            #[cfg(feature = "arbitrary_precision")]
+            SerializeMap::Number { .. } => unreachable!(),
+            #[cfg(feature = "raw_value")]
+            SerializeMap::RawValue { .. } => unreachable!(),
+        }
+    }
+
+    fn serialize_value<T>(&mut self, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        match self {
+            SerializeMap::Map { map, next_key } => {
+                let key = next_key.take();
+                // Panic because this indicates a bug in the program rather than an
+                // expected failure.
+                let key = key.expect("serialize_value called before serialize_key");
+                map.insert(key, tri!(to_value(value)));
+                Ok(())
+            }
+            #[cfg(feature = "arbitrary_precision")]
+            SerializeMap::Number { .. } => unreachable!(),
+            #[cfg(feature = "raw_value")]
+            SerializeMap::RawValue { .. } => unreachable!(),
+        }
+    }
+
+    fn end(self) -> Result<Value> {
+        match self {
+            SerializeMap::Map { map, .. } => Ok(Value::Object(map)),
+            #[cfg(feature = "arbitrary_precision")]
+            SerializeMap::Number { .. } => unreachable!(),
+            #[cfg(feature = "raw_value")]
+            SerializeMap::RawValue { .. } => unreachable!(),
+        }
+    }
+}
+
+struct MapKeySerializer;
+
+fn key_must_be_a_string() -> Error {
+    Error::syntax(ErrorCode::KeyMustBeAString, 0, 0)
+}
+
+impl serde::Serializer for MapKeySerializer {
+    type Ok = String;
+    type Error = Error;
+
+    type SerializeSeq = Impossible<String, Error>;
+    type SerializeTuple = Impossible<String, Error>;
+    type SerializeTupleStruct = Impossible<String, Error>;
+    type SerializeTupleVariant = Impossible<String, Error>;
+    type SerializeMap = Impossible<String, Error>;
+    type SerializeStruct = Impossible<String, Error>;
+    type SerializeStructVariant = Impossible<String, Error>;
+
+    #[inline]
+    fn serialize_unit_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        variant: &'static str,
+    ) -> Result<String> {
+        Ok(variant.to_owned())
+    }
+
+    #[inline]
+    fn serialize_newtype_struct<T>(self, _name: &'static str, value: &T) -> Result<String>
+    where
+        T: ?Sized + Serialize,
+    {
+        value.serialize(self)
+    }
+
+    fn serialize_bool(self, _value: bool) -> Result<String> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_i8(self, value: i8) -> Result<String> {
+        Ok(value.to_string())
+    }
+
+    fn serialize_i16(self, value: i16) -> Result<String> {
+        Ok(value.to_string())
+    }
+
+    fn serialize_i32(self, value: i32) -> Result<String> {
+        Ok(value.to_string())
+    }
+
+    fn serialize_i64(self, value: i64) -> Result<String> {
+        Ok(value.to_string())
+    }
+
+    fn serialize_u8(self, value: u8) -> Result<String> {
+        Ok(value.to_string())
+    }
+
+    fn serialize_u16(self, value: u16) -> Result<String> {
+        Ok(value.to_string())
+    }
+
+    fn serialize_u32(self, value: u32) -> Result<String> {
+        Ok(value.to_string())
+    }
+
+    fn serialize_u64(self, value: u64) -> Result<String> {
+        Ok(value.to_string())
+    }
+
+    fn serialize_f32(self, _value: f32) -> Result<String> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_f64(self, _value: f64) -> Result<String> {
+        Err(key_must_be_a_string())
+    }
+
+    #[inline]
+    fn serialize_char(self, value: char) -> Result<String> {
+        Ok({
+            let mut s = String::new();
+            s.push(value);
+            s
+        })
+    }
+
+    #[inline]
+    fn serialize_str(self, value: &str) -> Result<String> {
+        Ok(value.to_owned())
+    }
+
+    fn serialize_bytes(self, _value: &[u8]) -> Result<String> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_unit(self) -> Result<String> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_unit_struct(self, _name: &'static str) -> Result<String> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_newtype_variant<T>(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _value: &T,
+    ) -> Result<String>
+    where
+        T: ?Sized + Serialize,
+    {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_none(self) -> Result<String> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_some<T>(self, _value: &T) -> Result<String>
+    where
+        T: ?Sized + Serialize,
+    {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_seq(self, _len: Option<usize>) -> Result<Self::SerializeSeq> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_tuple(self, _len: usize) -> Result<Self::SerializeTuple> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_tuple_struct(
+        self,
+        _name: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleStruct> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_tuple_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleVariant> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_struct(self, _name: &'static str, _len: usize) -> Result<Self::SerializeStruct> {
+        Err(key_must_be_a_string())
+    }
+
+    fn serialize_struct_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeStructVariant> {
+        Err(key_must_be_a_string())
+    }
+
+    fn collect_str<T>(self, value: &T) -> Result<String>
+    where
+        T: ?Sized + Display,
+    {
+        Ok(value.to_string())
+    }
+}
+
+impl serde::ser::SerializeStruct for SerializeMap {
+    type Ok = Value;
+    type Error = Error;
+
+    fn serialize_field<T>(&mut self, key: &'static str, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        match self {
+            SerializeMap::Map { .. } => serde::ser::SerializeMap::serialize_entry(self, key, value),
+            #[cfg(feature = "arbitrary_precision")]
+            SerializeMap::Number { out_value } => {
+                if key == crate::number::TOKEN {
+                    *out_value = Some(value.serialize(NumberValueEmitter)?);
+                    Ok(())
+                } else {
+                    Err(invalid_number())
+                }
+            }
+            #[cfg(feature = "raw_value")]
+            SerializeMap::RawValue { out_value } => {
+                if key == crate::raw::TOKEN {
+                    *out_value = Some(value.serialize(RawValueEmitter)?);
+                    Ok(())
+                } else {
+                    Err(invalid_raw_value())
+                }
+            }
+        }
+    }
+
+    fn end(self) -> Result<Value> {
+        match self {
+            SerializeMap::Map { .. } => serde::ser::SerializeMap::end(self),
+            #[cfg(feature = "arbitrary_precision")]
+            SerializeMap::Number { out_value, .. } => {
+                Ok(out_value.expect("number value was not emitted"))
+            }
+            #[cfg(feature = "raw_value")]
+            SerializeMap::RawValue { out_value, .. } => {
+                Ok(out_value.expect("raw value was not emitted"))
+            }
+        }
+    }
+}
+
+impl serde::ser::SerializeStructVariant for SerializeStructVariant {
+    type Ok = Value;
+    type Error = Error;
+
+    fn serialize_field<T>(&mut self, key: &'static str, value: &T) -> Result<()>
+    where
+        T: ?Sized + Serialize,
+    {
+        self.map.insert(String::from(key), tri!(to_value(value)));
+        Ok(())
+    }
+
+    fn end(self) -> Result<Value> {
+        let mut object = Map::new();
+
+        object.insert(self.name, Value::Object(self.map));
+
+        Ok(Value::Object(object))
+    }
+}
+
+#[cfg(feature = "arbitrary_precision")]
+struct NumberValueEmitter;
+
+#[cfg(feature = "arbitrary_precision")]
+fn invalid_number() -> Error {
+    Error::syntax(ErrorCode::InvalidNumber, 0, 0)
+}
+
+#[cfg(feature = "arbitrary_precision")]
+impl serde::ser::Serializer for NumberValueEmitter {
+    type Ok = Value;
+    type Error = Error;
+
+    type SerializeSeq = Impossible<Value, Error>;
+    type SerializeTuple = Impossible<Value, Error>;
+    type SerializeTupleStruct = Impossible<Value, Error>;
+    type SerializeTupleVariant = Impossible<Value, Error>;
+    type SerializeMap = Impossible<Value, Error>;
+    type SerializeStruct = Impossible<Value, Error>;
+    type SerializeStructVariant = Impossible<Value, Error>;
+
+    fn serialize_bool(self, _v: bool) -> Result<Value> {
+        Err(invalid_number())
+    }
+
+    fn serialize_i8(self, _v: i8) -> Result<Value> {
+        Err(invalid_number())
+    }
+
+    fn serialize_i16(self, _v: i16) -> Result<Value> {
+        Err(invalid_number())
+    }
+
+    fn serialize_i32(self, _v: i32) -> Result<Value> {
+        Err(invalid_number())
+    }
+
+    fn serialize_i64(self, _v: i64) -> Result<Value> {
+        Err(invalid_number())
+    }
+
+    fn serialize_u8(self, _v: u8) -> Result<Value> {
+        Err(invalid_number())
+    }
+
+    fn serialize_u16(self, _v: u16) -> Result<Value> {
+        Err(invalid_number())
+    }
+
+    fn serialize_u32(self, _v: u32) -> Result<Value> {
+        Err(invalid_number())
+    }
+
+    fn serialize_u64(self, _v: u64) -> Result<Value> {
+        Err(invalid_number())
+    }
+
+    fn serialize_f32(self, _v: f32) -> Result<Value> {
+        Err(invalid_number())
+    }
+
+    fn serialize_f64(self, _v: f64) -> Result<Value> {
+        Err(invalid_number())
+    }
+
+    fn serialize_char(self, _v: char) -> Result<Value> {
+        Err(invalid_number())
+    }
+
+    fn serialize_str(self, value: &str) -> Result<Value> {
+        let n = tri!(value.to_owned().parse());
+        Ok(Value::Number(n))
+    }
+
+    fn serialize_bytes(self, _value: &[u8]) -> Result<Value> {
+        Err(invalid_number())
+    }
+
+    fn serialize_none(self) -> Result<Value> {
+        Err(invalid_number())
+    }
+
+    fn serialize_some<T>(self, _value: &T) -> Result<Value>
+    where
+        T: ?Sized + Serialize,
+    {
+        Err(invalid_number())
+    }
+
+    fn serialize_unit(self) -> Result<Value> {
+        Err(invalid_number())
+    }
+
+    fn serialize_unit_struct(self, _name: &'static str) -> Result<Value> {
+        Err(invalid_number())
+    }
+
+    fn serialize_unit_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+    ) -> Result<Value> {
+        Err(invalid_number())
+    }
+
+    fn serialize_newtype_struct<T>(self, _name: &'static str, _value: &T) -> Result<Value>
+    where
+        T: ?Sized + Serialize,
+    {
+        Err(invalid_number())
+    }
+
+    fn serialize_newtype_variant<T>(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _value: &T,
+    ) -> Result<Value>
+    where
+        T: ?Sized + Serialize,
+    {
+        Err(invalid_number())
+    }
+
+    fn serialize_seq(self, _len: Option<usize>) -> Result<Self::SerializeSeq> {
+        Err(invalid_number())
+    }
+
+    fn serialize_tuple(self, _len: usize) -> Result<Self::SerializeTuple> {
+        Err(invalid_number())
+    }
+
+    fn serialize_tuple_struct(
+        self,
+        _name: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleStruct> {
+        Err(invalid_number())
+    }
+
+    fn serialize_tuple_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleVariant> {
+        Err(invalid_number())
+    }
+
+    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap> {
+        Err(invalid_number())
+    }
+
+    fn serialize_struct(self, _name: &'static str, _len: usize) -> Result<Self::SerializeStruct> {
+        Err(invalid_number())
+    }
+
+    fn serialize_struct_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeStructVariant> {
+        Err(invalid_number())
+    }
+}
+
+#[cfg(feature = "raw_value")]
+struct RawValueEmitter;
+
+#[cfg(feature = "raw_value")]
+fn invalid_raw_value() -> Error {
+    Error::syntax(ErrorCode::ExpectedSomeValue, 0, 0)
+}
+
+#[cfg(feature = "raw_value")]
+impl serde::ser::Serializer for RawValueEmitter {
+    type Ok = Value;
+    type Error = Error;
+
+    type SerializeSeq = Impossible<Value, Error>;
+    type SerializeTuple = Impossible<Value, Error>;
+    type SerializeTupleStruct = Impossible<Value, Error>;
+    type SerializeTupleVariant = Impossible<Value, Error>;
+    type SerializeMap = Impossible<Value, Error>;
+    type SerializeStruct = Impossible<Value, Error>;
+    type SerializeStructVariant = Impossible<Value, Error>;
+
+    fn serialize_bool(self, _v: bool) -> Result<Value> {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_i8(self, _v: i8) -> Result<Value> {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_i16(self, _v: i16) -> Result<Value> {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_i32(self, _v: i32) -> Result<Value> {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_i64(self, _v: i64) -> Result<Value> {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_u8(self, _v: u8) -> Result<Value> {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_u16(self, _v: u16) -> Result<Value> {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_u32(self, _v: u32) -> Result<Value> {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_u64(self, _v: u64) -> Result<Value> {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_f32(self, _v: f32) -> Result<Value> {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_f64(self, _v: f64) -> Result<Value> {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_char(self, _v: char) -> Result<Value> {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_str(self, value: &str) -> Result<Value> {
+        crate::from_str(value)
+    }
+
+    fn serialize_bytes(self, _value: &[u8]) -> Result<Value> {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_none(self) -> Result<Value> {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_some<T>(self, _value: &T) -> Result<Value>
+    where
+        T: ?Sized + Serialize,
+    {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_unit(self) -> Result<Value> {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_unit_struct(self, _name: &'static str) -> Result<Value> {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_unit_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+    ) -> Result<Value> {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_newtype_struct<T>(self, _name: &'static str, _value: &T) -> Result<Value>
+    where
+        T: ?Sized + Serialize,
+    {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_newtype_variant<T>(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _value: &T,
+    ) -> Result<Value>
+    where
+        T: ?Sized + Serialize,
+    {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_seq(self, _len: Option<usize>) -> Result<Self::SerializeSeq> {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_tuple(self, _len: usize) -> Result<Self::SerializeTuple> {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_tuple_struct(
+        self,
+        _name: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleStruct> {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_tuple_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeTupleVariant> {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_map(self, _len: Option<usize>) -> Result<Self::SerializeMap> {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_struct(self, _name: &'static str, _len: usize) -> Result<Self::SerializeStruct> {
+        Err(invalid_raw_value())
+    }
+
+    fn serialize_struct_variant(
+        self,
+        _name: &'static str,
+        _variant_index: u32,
+        _variant: &'static str,
+        _len: usize,
+    ) -> Result<Self::SerializeStructVariant> {
+        Err(invalid_raw_value())
+    }
+
+    fn collect_str<T>(self, value: &T) -> Result<Self::Ok>
+    where
+        T: ?Sized + Display,
+    {
+        self.serialize_str(&value.to_string())
+    }
+}
diff --git a/third_party/rust/serde_json/tests/compiletest.rs b/third_party/rust/serde_json/tests/compiletest.rs
new file mode 100644
index 0000000000..7974a6249e
--- /dev/null
+++ b/third_party/rust/serde_json/tests/compiletest.rs
@@ -0,0 +1,7 @@
+#[rustversion::attr(not(nightly), ignore)]
+#[cfg_attr(miri, ignore)]
+#[test]
+fn ui() {
+    let t = trybuild::TestCases::new();
+    t.compile_fail("tests/ui/*.rs");
+}
diff --git a/third_party/rust/serde_json/tests/debug.rs b/third_party/rust/serde_json/tests/debug.rs
new file mode 100644
index 0000000000..8ddcf5a381
--- /dev/null
+++ b/third_party/rust/serde_json/tests/debug.rs
@@ -0,0 +1,81 @@
+use indoc::indoc;
+use serde_json::{json, Number, Value};
+
+#[test]
+fn number() {
+    assert_eq!(format!("{:?}", Number::from(1)), "Number(1)");
+    assert_eq!(format!("{:?}", Number::from(-1)), "Number(-1)");
+    assert_eq!(
+        format!("{:?}", Number::from_f64(1.0).unwrap()),
+        "Number(1.0)"
+    );
+}
+
+#[test]
+fn value_null() {
+    assert_eq!(format!("{:?}", json!(null)), "Null");
+}
+
+#[test]
+fn value_bool() {
+    assert_eq!(format!("{:?}", json!(true)), "Bool(true)");
+    assert_eq!(format!("{:?}", json!(false)), "Bool(false)");
+}
+
+#[test]
+fn value_number() {
+    assert_eq!(format!("{:?}", json!(1)), "Number(1)");
+    assert_eq!(format!("{:?}", json!(-1)), "Number(-1)");
+    assert_eq!(format!("{:?}", json!(1.0)), "Number(1.0)");
+    assert_eq!(Number::from_f64(1.0).unwrap().to_string(), "1.0"); // not just "1"
+    assert_eq!(Number::from_f64(12e40).unwrap().to_string(), "1.2e41");
+}
+
+#[test]
+fn value_string() {
+    assert_eq!(format!("{:?}", json!("s")), "String(\"s\")");
+}
+
+#[test]
+fn value_array() {
+    assert_eq!(format!("{:?}", json!([])), "Array []");
+}
+
+#[test]
+fn value_object() {
+    assert_eq!(format!("{:?}", json!({})), "Object {}");
+}
+
+#[test]
+fn error() {
+    let err = serde_json::from_str::<Value>("{0}").unwrap_err();
+    let expected = "Error(\"key must be a string\", line: 1, column: 2)";
+    assert_eq!(format!("{:?}", err), expected);
+}
+
+#[test]
+fn indented() {
+    let j = json!({
+        "Array": [true],
+        "Bool": true,
+        "EmptyArray": [],
+        "EmptyObject": {},
+        "Null": null,
+        "Number": 1,
+        "String": "...",
+    });
+    let expected = indoc! {r#"
+        Object {
+            "Array": Array [
+                Bool(true),
+            ],
+            "Bool": Bool(true),
+            "EmptyArray": Array [],
+            "EmptyObject": Object {},
+            "Null": Null,
+            "Number": Number(1),
+            "String": String("..."),
+        }"#
+    };
+    assert_eq!(format!("{:#?}", j), expected);
+}
diff --git a/third_party/rust/serde_json/tests/lexical.rs b/third_party/rust/serde_json/tests/lexical.rs
new file mode 100644
index 0000000000..6e0f07b8c3
--- /dev/null
+++ b/third_party/rust/serde_json/tests/lexical.rs
@@ -0,0 +1,52 @@
+#![allow(
+    clippy::cast_lossless,
+    clippy::cast_possible_truncation,
+    clippy::cast_possible_wrap,
+    clippy::cast_precision_loss,
+    clippy::cast_sign_loss,
+    clippy::comparison_chain,
+    clippy::doc_markdown,
+    clippy::excessive_precision,
+    clippy::float_cmp,
+    clippy::if_not_else,
+    clippy::module_name_repetitions,
+    clippy::needless_late_init,
+    clippy::shadow_unrelated,
+    clippy::similar_names,
+    clippy::single_match_else,
+    clippy::too_many_lines,
+    clippy::unreadable_literal,
+    clippy::unseparated_literal_suffix,
+    clippy::wildcard_imports
+)]
+
+extern crate alloc;
+
+#[path = "../src/lexical/mod.rs"]
+mod lexical;
+
+mod lib {
+    pub use std::vec::Vec;
+    pub use std::{cmp, iter, mem, ops};
+}
+
+#[path = "lexical/algorithm.rs"]
+mod algorithm;
+
+#[path = "lexical/exponent.rs"]
+mod exponent;
+
+#[path = "lexical/float.rs"]
+mod float;
+
+#[path = "lexical/math.rs"]
+mod math;
+
+#[path = "lexical/num.rs"]
+mod num;
+
+#[path = "lexical/parse.rs"]
+mod parse;
+
+#[path = "lexical/rounding.rs"]
+mod rounding;
diff --git a/third_party/rust/serde_json/tests/lexical/algorithm.rs b/third_party/rust/serde_json/tests/lexical/algorithm.rs
new file mode 100644
index 0000000000..7f3a2c6241
--- /dev/null
+++ b/third_party/rust/serde_json/tests/lexical/algorithm.rs
@@ -0,0 +1,110 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+use crate::lexical::algorithm::*;
+use crate::lexical::num::Float;
+
+#[test]
+fn float_fast_path_test() {
+    // valid
+    let mantissa = (1 << f32::MANTISSA_SIZE) - 1;
+    let (min_exp, max_exp) = f32::exponent_limit();
+    for exp in min_exp..=max_exp {
+        let f = fast_path::<f32>(mantissa, exp);
+        assert!(f.is_some(), "should be valid {:?}.", (mantissa, exp));
+    }
+
+    // Check slightly above valid exponents
+    let f = fast_path::<f32>(123, 15);
+    assert_eq!(f, Some(1.23e+17));
+
+    // Exponent is 1 too high, pushes over the mantissa.
+    let f = fast_path::<f32>(123, 16);
+    assert!(f.is_none());
+
+    // Mantissa is too large, checked_mul should overflow.
+    let f = fast_path::<f32>(mantissa, 11);
+    assert!(f.is_none());
+
+    // invalid exponents
+    let (min_exp, max_exp) = f32::exponent_limit();
+    let f = fast_path::<f32>(mantissa, min_exp - 1);
+    assert!(f.is_none(), "exponent under min_exp");
+
+    let f = fast_path::<f32>(mantissa, max_exp + 1);
+    assert!(f.is_none(), "exponent above max_exp");
+}
+
+#[test]
+fn double_fast_path_test() {
+    // valid
+    let mantissa = (1 << f64::MANTISSA_SIZE) - 1;
+    let (min_exp, max_exp) = f64::exponent_limit();
+    for exp in min_exp..=max_exp {
+        let f = fast_path::<f64>(mantissa, exp);
+        assert!(f.is_some(), "should be valid {:?}.", (mantissa, exp));
+    }
+
+    // invalid exponents
+    let (min_exp, max_exp) = f64::exponent_limit();
+    let f = fast_path::<f64>(mantissa, min_exp - 1);
+    assert!(f.is_none(), "exponent under min_exp");
+
+    let f = fast_path::<f64>(mantissa, max_exp + 1);
+    assert!(f.is_none(), "exponent above max_exp");
+
+    assert_eq!(
+        Some(0.04628372940652459),
+        fast_path::<f64>(4628372940652459, -17)
+    );
+    assert_eq!(None, fast_path::<f64>(26383446160308229, -272));
+}
+
+#[test]
+fn moderate_path_test() {
+    let (f, valid) = moderate_path::<f64>(1234567890, -1, false);
+    assert!(valid, "should be valid");
+    assert_eq!(f.into_float::<f64>(), 123456789.0);
+
+    let (f, valid) = moderate_path::<f64>(1234567891, -1, false);
+    assert!(valid, "should be valid");
+    assert_eq!(f.into_float::<f64>(), 123456789.1);
+
+    let (f, valid) = moderate_path::<f64>(12345678912, -2, false);
+    assert!(valid, "should be valid");
+    assert_eq!(f.into_float::<f64>(), 123456789.12);
+
+    let (f, valid) = moderate_path::<f64>(123456789123, -3, false);
+    assert!(valid, "should be valid");
+    assert_eq!(f.into_float::<f64>(), 123456789.123);
+
+    let (f, valid) = moderate_path::<f64>(1234567891234, -4, false);
+    assert!(valid, "should be valid");
+    assert_eq!(f.into_float::<f64>(), 123456789.1234);
+
+    let (f, valid) = moderate_path::<f64>(12345678912345, -5, false);
+    assert!(valid, "should be valid");
+    assert_eq!(f.into_float::<f64>(), 123456789.12345);
+
+    let (f, valid) = moderate_path::<f64>(123456789123456, -6, false);
+    assert!(valid, "should be valid");
+    assert_eq!(f.into_float::<f64>(), 123456789.123456);
+
+    let (f, valid) = moderate_path::<f64>(1234567891234567, -7, false);
+    assert!(valid, "should be valid");
+    assert_eq!(f.into_float::<f64>(), 123456789.1234567);
+
+    let (f, valid) = moderate_path::<f64>(12345678912345679, -8, false);
+    assert!(valid, "should be valid");
+    assert_eq!(f.into_float::<f64>(), 123456789.12345679);
+
+    let (f, valid) = moderate_path::<f64>(4628372940652459, -17, false);
+    assert!(valid, "should be valid");
+    assert_eq!(f.into_float::<f64>(), 0.04628372940652459);
+
+    let (f, valid) = moderate_path::<f64>(26383446160308229, -272, false);
+    assert!(valid, "should be valid");
+    assert_eq!(f.into_float::<f64>(), 2.6383446160308229e-256);
+
+    let (_, valid) = moderate_path::<f64>(26383446160308230, -272, false);
+    assert!(!valid, "should be invalid");
+}
diff --git a/third_party/rust/serde_json/tests/lexical/exponent.rs b/third_party/rust/serde_json/tests/lexical/exponent.rs
new file mode 100644
index 0000000000..f7a847be38
--- /dev/null
+++ b/third_party/rust/serde_json/tests/lexical/exponent.rs
@@ -0,0 +1,54 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+use crate::lexical::exponent::*;
+
+#[test]
+fn scientific_exponent_test() {
+    // 0 digits in the integer
+    assert_eq!(scientific_exponent(0, 0, 5), -6);
+    assert_eq!(scientific_exponent(10, 0, 5), 4);
+    assert_eq!(scientific_exponent(-10, 0, 5), -16);
+
+    // >0 digits in the integer
+    assert_eq!(scientific_exponent(0, 1, 5), 0);
+    assert_eq!(scientific_exponent(0, 2, 5), 1);
+    assert_eq!(scientific_exponent(0, 2, 20), 1);
+    assert_eq!(scientific_exponent(10, 2, 20), 11);
+    assert_eq!(scientific_exponent(-10, 2, 20), -9);
+
+    // Underflow
+    assert_eq!(
+        scientific_exponent(i32::min_value(), 0, 0),
+        i32::min_value()
+    );
+    assert_eq!(
+        scientific_exponent(i32::min_value(), 0, 5),
+        i32::min_value()
+    );
+
+    // Overflow
+    assert_eq!(
+        scientific_exponent(i32::max_value(), 0, 0),
+        i32::max_value() - 1
+    );
+    assert_eq!(
+        scientific_exponent(i32::max_value(), 5, 0),
+        i32::max_value()
+    );
+}
+
+#[test]
+fn mantissa_exponent_test() {
+    assert_eq!(mantissa_exponent(10, 5, 0), 5);
+    assert_eq!(mantissa_exponent(0, 5, 0), -5);
+    assert_eq!(
+        mantissa_exponent(i32::max_value(), 5, 0),
+        i32::max_value() - 5
+    );
+    assert_eq!(mantissa_exponent(i32::max_value(), 0, 5), i32::max_value());
+    assert_eq!(mantissa_exponent(i32::min_value(), 5, 0), i32::min_value());
+    assert_eq!(
+        mantissa_exponent(i32::min_value(), 0, 5),
+        i32::min_value() + 5
+    );
+}
diff --git a/third_party/rust/serde_json/tests/lexical/float.rs b/third_party/rust/serde_json/tests/lexical/float.rs
new file mode 100644
index 0000000000..c87e7e1ed9
--- /dev/null
+++ b/third_party/rust/serde_json/tests/lexical/float.rs
@@ -0,0 +1,581 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+use crate::lexical::float::ExtendedFloat;
+use crate::lexical::rounding::round_nearest_tie_even;
+use std::{f32, f64};
+
+// NORMALIZE
+
+fn check_normalize(mant: u64, exp: i32, shift: u32, r_mant: u64, r_exp: i32) {
+    let mut x = ExtendedFloat { mant, exp };
+    assert_eq!(x.normalize(), shift);
+    assert_eq!(
+        x,
+        ExtendedFloat {
+            mant: r_mant,
+            exp: r_exp
+        }
+    );
+}
+
+#[test]
+fn normalize_test() {
+    // F32
+    // 0
+    check_normalize(0, 0, 0, 0, 0);
+
+    // min value
+    check_normalize(1, -149, 63, 9223372036854775808, -212);
+
+    // 1.0e-40
+    check_normalize(71362, -149, 47, 10043308644012916736, -196);
+
+    // 1.0e-20
+    check_normalize(12379400, -90, 40, 13611294244890214400, -130);
+
+    // 1.0
+    check_normalize(8388608, -23, 40, 9223372036854775808, -63);
+
+    // 1e20
+    check_normalize(11368684, 43, 40, 12500000250510966784, 3);
+
+    // max value
+    check_normalize(16777213, 104, 40, 18446740775174668288, 64);
+
+    // F64
+
+    // min value
+    check_normalize(1, -1074, 63, 9223372036854775808, -1137);
+
+    // 1.0e-250
+    check_normalize(6448907850777164, -883, 11, 13207363278391631872, -894);
+
+    // 1.0e-150
+    check_normalize(7371020360979573, -551, 11, 15095849699286165504, -562);
+
+    // 1.0e-45
+    check_normalize(6427752177035961, -202, 11, 13164036458569648128, -213);
+
+    // 1.0e-40
+    check_normalize(4903985730770844, -185, 11, 10043362776618688512, -196);
+
+    // 1.0e-20
+    check_normalize(6646139978924579, -119, 11, 13611294676837537792, -130);
+
+    // 1.0
+    check_normalize(4503599627370496, -52, 11, 9223372036854775808, -63);
+
+    // 1e20
+    check_normalize(6103515625000000, 14, 11, 12500000000000000000, 3);
+
+    // 1e40
+    check_normalize(8271806125530277, 80, 11, 16940658945086007296, 69);
+
+    // 1e150
+    check_normalize(5503284107318959, 446, 11, 11270725851789228032, 435);
+
+    // 1e250
+    check_normalize(6290184345309700, 778, 11, 12882297539194265600, 767);
+
+    // max value
+    check_normalize(9007199254740991, 971, 11, 18446744073709549568, 960);
+}
+
+// ROUND
+
+fn check_round_to_f32(mant: u64, exp: i32, r_mant: u64, r_exp: i32) {
+    let mut x = ExtendedFloat { mant, exp };
+    x.round_to_native::<f32, _>(round_nearest_tie_even);
+    assert_eq!(
+        x,
+        ExtendedFloat {
+            mant: r_mant,
+            exp: r_exp
+        }
+    );
+}
+
+#[test]
+fn round_to_f32_test() {
+    // This is lossy, so some of these values are **slightly** rounded.
+
+    // underflow
+    check_round_to_f32(9223372036854775808, -213, 0, -149);
+
+    // min value
+    check_round_to_f32(9223372036854775808, -212, 1, -149);
+
+    // 1.0e-40
+    check_round_to_f32(10043308644012916736, -196, 71362, -149);
+
+    // 1.0e-20
+    check_round_to_f32(13611294244890214400, -130, 12379400, -90);
+
+    // 1.0
+    check_round_to_f32(9223372036854775808, -63, 8388608, -23);
+
+    // 1e20
+    check_round_to_f32(12500000250510966784, 3, 11368684, 43);
+
+    // max value
+    check_round_to_f32(18446740775174668288, 64, 16777213, 104);
+
+    // overflow
+    check_round_to_f32(18446740775174668288, 65, 16777213, 105);
+}
+
+fn check_round_to_f64(mant: u64, exp: i32, r_mant: u64, r_exp: i32) {
+    let mut x = ExtendedFloat { mant, exp };
+    x.round_to_native::<f64, _>(round_nearest_tie_even);
+    assert_eq!(
+        x,
+        ExtendedFloat {
+            mant: r_mant,
+            exp: r_exp
+        }
+    );
+}
+
+#[test]
+fn round_to_f64_test() {
+    // This is lossy, so some of these values are **slightly** rounded.
+
+    // underflow
+    check_round_to_f64(9223372036854775808, -1138, 0, -1074);
+
+    // min value
+    check_round_to_f64(9223372036854775808, -1137, 1, -1074);
+
+    // 1.0e-250
+    check_round_to_f64(15095849699286165504, -562, 7371020360979573, -551);
+
+    // 1.0e-150
+    check_round_to_f64(15095849699286165504, -562, 7371020360979573, -551);
+
+    // 1.0e-45
+    check_round_to_f64(13164036458569648128, -213, 6427752177035961, -202);
+
+    // 1.0e-40
+    check_round_to_f64(10043362776618688512, -196, 4903985730770844, -185);
+
+    // 1.0e-20
+    check_round_to_f64(13611294676837537792, -130, 6646139978924579, -119);
+
+    // 1.0
+    check_round_to_f64(9223372036854775808, -63, 4503599627370496, -52);
+
+    // 1e20
+    check_round_to_f64(12500000000000000000, 3, 6103515625000000, 14);
+
+    // 1e40
+    check_round_to_f64(16940658945086007296, 69, 8271806125530277, 80);
+
+    // 1e150
+    check_round_to_f64(11270725851789228032, 435, 5503284107318959, 446);
+
+    // 1e250
+    check_round_to_f64(12882297539194265600, 767, 6290184345309700, 778);
+
+    // max value
+    check_round_to_f64(18446744073709549568, 960, 9007199254740991, 971);
+
+    // Bug fixes
+    // 1.2345e-308
+    check_round_to_f64(10234494226754558294, -1086, 2498655817078750, -1074);
+}
+
+fn assert_normalized_eq(mut x: ExtendedFloat, mut y: ExtendedFloat) {
+    x.normalize();
+    y.normalize();
+    assert_eq!(x, y);
+}
+
+#[test]
+fn from_float() {
+    let values: [f32; 26] = [
+        1e-40, 2e-40, 1e-35, 2e-35, 1e-30, 2e-30, 1e-25, 2e-25, 1e-20, 2e-20, 1e-15, 2e-15, 1e-10,
+        2e-10, 1e-5, 2e-5, 1.0, 2.0, 1e5, 2e5, 1e10, 2e10, 1e15, 2e15, 1e20, 2e20,
+    ];
+    for value in &values {
+        assert_normalized_eq(
+            ExtendedFloat::from_float(*value),
+            ExtendedFloat::from_float(*value as f64),
+        );
+    }
+}
+
+// TO
+
+// Sample of interesting numbers to check during standard test builds.
+const INTEGERS: [u64; 32] = [
+    0,                    // 0x0
+    1,                    // 0x1
+    7,                    // 0x7
+    15,                   // 0xF
+    112,                  // 0x70
+    119,                  // 0x77
+    127,                  // 0x7F
+    240,                  // 0xF0
+    247,                  // 0xF7
+    255,                  // 0xFF
+    2032,                 // 0x7F0
+    2039,                 // 0x7F7
+    2047,                 // 0x7FF
+    4080,                 // 0xFF0
+    4087,                 // 0xFF7
+    4095,                 // 0xFFF
+    65520,                // 0xFFF0
+    65527,                // 0xFFF7
+    65535,                // 0xFFFF
+    1048560,              // 0xFFFF0
+    1048567,              // 0xFFFF7
+    1048575,              // 0xFFFFF
+    16777200,             // 0xFFFFF0
+    16777207,             // 0xFFFFF7
+    16777215,             // 0xFFFFFF
+    268435440,            // 0xFFFFFF0
+    268435447,            // 0xFFFFFF7
+    268435455,            // 0xFFFFFFF
+    4294967280,           // 0xFFFFFFF0
+    4294967287,           // 0xFFFFFFF7
+    4294967295,           // 0xFFFFFFFF
+    18446744073709551615, // 0xFFFFFFFFFFFFFFFF
+];
+
+#[test]
+fn to_f32_test() {
+    // underflow
+    let x = ExtendedFloat {
+        mant: 9223372036854775808,
+        exp: -213,
+    };
+    assert_eq!(x.into_float::<f32>(), 0.0);
+
+    // min value
+    let x = ExtendedFloat {
+        mant: 9223372036854775808,
+        exp: -212,
+    };
+    assert_eq!(x.into_float::<f32>(), 1e-45);
+
+    // 1.0e-40
+    let x = ExtendedFloat {
+        mant: 10043308644012916736,
+        exp: -196,
+    };
+    assert_eq!(x.into_float::<f32>(), 1e-40);
+
+    // 1.0e-20
+    let x = ExtendedFloat {
+        mant: 13611294244890214400,
+        exp: -130,
+    };
+    assert_eq!(x.into_float::<f32>(), 1e-20);
+
+    // 1.0
+    let x = ExtendedFloat {
+        mant: 9223372036854775808,
+        exp: -63,
+    };
+    assert_eq!(x.into_float::<f32>(), 1.0);
+
+    // 1e20
+    let x = ExtendedFloat {
+        mant: 12500000250510966784,
+        exp: 3,
+    };
+    assert_eq!(x.into_float::<f32>(), 1e20);
+
+    // max value
+    let x = ExtendedFloat {
+        mant: 18446740775174668288,
+        exp: 64,
+    };
+    assert_eq!(x.into_float::<f32>(), 3.402823e38);
+
+    // almost max, high exp
+    let x = ExtendedFloat {
+        mant: 1048575,
+        exp: 108,
+    };
+    assert_eq!(x.into_float::<f32>(), 3.4028204e38);
+
+    // max value + 1
+    let x = ExtendedFloat {
+        mant: 16777216,
+        exp: 104,
+    };
+    assert_eq!(x.into_float::<f32>(), f32::INFINITY);
+
+    // max value + 1
+    let x = ExtendedFloat {
+        mant: 1048576,
+        exp: 108,
+    };
+    assert_eq!(x.into_float::<f32>(), f32::INFINITY);
+
+    // 1e40
+    let x = ExtendedFloat {
+        mant: 16940658945086007296,
+        exp: 69,
+    };
+    assert_eq!(x.into_float::<f32>(), f32::INFINITY);
+
+    // Integers.
+    for int in &INTEGERS {
+        let fp = ExtendedFloat { mant: *int, exp: 0 };
+        assert_eq!(fp.into_float::<f32>(), *int as f32, "{:?} as f32", *int);
+    }
+}
+
+#[test]
+fn to_f64_test() {
+    // underflow
+    let x = ExtendedFloat {
+        mant: 9223372036854775808,
+        exp: -1138,
+    };
+    assert_eq!(x.into_float::<f64>(), 0.0);
+
+    // min value
+    let x = ExtendedFloat {
+        mant: 9223372036854775808,
+        exp: -1137,
+    };
+    assert_eq!(x.into_float::<f64>(), 5e-324);
+
+    // 1.0e-250
+    let x = ExtendedFloat {
+        mant: 13207363278391631872,
+        exp: -894,
+    };
+    assert_eq!(x.into_float::<f64>(), 1e-250);
+
+    // 1.0e-150
+    let x = ExtendedFloat {
+        mant: 15095849699286165504,
+        exp: -562,
+    };
+    assert_eq!(x.into_float::<f64>(), 1e-150);
+
+    // 1.0e-45
+    let x = ExtendedFloat {
+        mant: 13164036458569648128,
+        exp: -213,
+    };
+    assert_eq!(x.into_float::<f64>(), 1e-45);
+
+    // 1.0e-40
+    let x = ExtendedFloat {
+        mant: 10043362776618688512,
+        exp: -196,
+    };
+    assert_eq!(x.into_float::<f64>(), 1e-40);
+
+    // 1.0e-20
+    let x = ExtendedFloat {
+        mant: 13611294676837537792,
+        exp: -130,
+    };
+    assert_eq!(x.into_float::<f64>(), 1e-20);
+
+    // 1.0
+    let x = ExtendedFloat {
+        mant: 9223372036854775808,
+        exp: -63,
+    };
+    assert_eq!(x.into_float::<f64>(), 1.0);
+
+    // 1e20
+    let x = ExtendedFloat {
+        mant: 12500000000000000000,
+        exp: 3,
+    };
+    assert_eq!(x.into_float::<f64>(), 1e20);
+
+    // 1e40
+    let x = ExtendedFloat {
+        mant: 16940658945086007296,
+        exp: 69,
+    };
+    assert_eq!(x.into_float::<f64>(), 1e40);
+
+    // 1e150
+    let x = ExtendedFloat {
+        mant: 11270725851789228032,
+        exp: 435,
+    };
+    assert_eq!(x.into_float::<f64>(), 1e150);
+
+    // 1e250
+    let x = ExtendedFloat {
+        mant: 12882297539194265600,
+        exp: 767,
+    };
+    assert_eq!(x.into_float::<f64>(), 1e250);
+
+    // max value
+    let x = ExtendedFloat {
+        mant: 9007199254740991,
+        exp: 971,
+    };
+    assert_eq!(x.into_float::<f64>(), 1.7976931348623157e308);
+
+    // max value
+    let x = ExtendedFloat {
+        mant: 18446744073709549568,
+        exp: 960,
+    };
+    assert_eq!(x.into_float::<f64>(), 1.7976931348623157e308);
+
+    // overflow
+    let x = ExtendedFloat {
+        mant: 9007199254740992,
+        exp: 971,
+    };
+    assert_eq!(x.into_float::<f64>(), f64::INFINITY);
+
+    // overflow
+    let x = ExtendedFloat {
+        mant: 18446744073709549568,
+        exp: 961,
+    };
+    assert_eq!(x.into_float::<f64>(), f64::INFINITY);
+
+    // Underflow
+    // Adapted from failures in strtod.
+    let x = ExtendedFloat {
+        exp: -1139,
+        mant: 18446744073709550712,
+    };
+    assert_eq!(x.into_float::<f64>(), 0.0);
+
+    let x = ExtendedFloat {
+        exp: -1139,
+        mant: 18446744073709551460,
+    };
+    assert_eq!(x.into_float::<f64>(), 0.0);
+
+    let x = ExtendedFloat {
+        exp: -1138,
+        mant: 9223372036854776103,
+    };
+    assert_eq!(x.into_float::<f64>(), 5e-324);
+
+    // Integers.
+    for int in &INTEGERS {
+        let fp = ExtendedFloat { mant: *int, exp: 0 };
+        assert_eq!(fp.into_float::<f64>(), *int as f64, "{:?} as f64", *int);
+    }
+}
+
+// OPERATIONS
+
+fn check_mul(a: ExtendedFloat, b: ExtendedFloat, c: ExtendedFloat) {
+    let r = a.mul(&b);
+    assert_eq!(r, c);
+}
+
+#[test]
+fn mul_test() {
+    // Normalized (64-bit mantissa)
+    let a = ExtendedFloat {
+        mant: 13164036458569648128,
+        exp: -213,
+    };
+    let b = ExtendedFloat {
+        mant: 9223372036854775808,
+        exp: -62,
+    };
+    let c = ExtendedFloat {
+        mant: 6582018229284824064,
+        exp: -211,
+    };
+    check_mul(a, b, c);
+
+    // Check with integers
+    // 64-bit mantissa
+    let mut a = ExtendedFloat { mant: 10, exp: 0 };
+    let mut b = ExtendedFloat { mant: 10, exp: 0 };
+    a.normalize();
+    b.normalize();
+    assert_eq!(a.mul(&b).into_float::<f64>(), 100.0);
+
+    // Check both values need high bits set.
+    let a = ExtendedFloat {
+        mant: 1 << 32,
+        exp: -31,
+    };
+    let b = ExtendedFloat {
+        mant: 1 << 32,
+        exp: -31,
+    };
+    assert_eq!(a.mul(&b).into_float::<f64>(), 4.0);
+
+    // Check both values need high bits set.
+    let a = ExtendedFloat {
+        mant: 10 << 31,
+        exp: -31,
+    };
+    let b = ExtendedFloat {
+        mant: 10 << 31,
+        exp: -31,
+    };
+    assert_eq!(a.mul(&b).into_float::<f64>(), 100.0);
+}
+
+fn check_imul(mut a: ExtendedFloat, b: ExtendedFloat, c: ExtendedFloat) {
+    a.imul(&b);
+    assert_eq!(a, c);
+}
+
+#[test]
+fn imul_test() {
+    // Normalized (64-bit mantissa)
+    let a = ExtendedFloat {
+        mant: 13164036458569648128,
+        exp: -213,
+    };
+    let b = ExtendedFloat {
+        mant: 9223372036854775808,
+        exp: -62,
+    };
+    let c = ExtendedFloat {
+        mant: 6582018229284824064,
+        exp: -211,
+    };
+    check_imul(a, b, c);
+
+    // Check with integers
+    // 64-bit mantissa
+    let mut a = ExtendedFloat { mant: 10, exp: 0 };
+    let mut b = ExtendedFloat { mant: 10, exp: 0 };
+    a.normalize();
+    b.normalize();
+    a.imul(&b);
+    assert_eq!(a.into_float::<f64>(), 100.0);
+
+    // Check both values need high bits set.
+    let mut a = ExtendedFloat {
+        mant: 1 << 32,
+        exp: -31,
+    };
+    let b = ExtendedFloat {
+        mant: 1 << 32,
+        exp: -31,
+    };
+    a.imul(&b);
+    assert_eq!(a.into_float::<f64>(), 4.0);
+
+    // Check both values need high bits set.
+    let mut a = ExtendedFloat {
+        mant: 10 << 31,
+        exp: -31,
+    };
+    let b = ExtendedFloat {
+        mant: 10 << 31,
+        exp: -31,
+    };
+    a.imul(&b);
+    assert_eq!(a.into_float::<f64>(), 100.0);
+}
diff --git a/third_party/rust/serde_json/tests/lexical/math.rs b/third_party/rust/serde_json/tests/lexical/math.rs
new file mode 100644
index 0000000000..79d3ef3ee5
--- /dev/null
+++ b/third_party/rust/serde_json/tests/lexical/math.rs
@@ -0,0 +1,211 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+use crate::lexical::math::{Limb, Math};
+use std::cmp;
+
+#[derive(Clone, Default)]
+struct Bigint {
+    data: Vec<Limb>,
+}
+
+impl Math for Bigint {
+    fn data(&self) -> &Vec<Limb> {
+        &self.data
+    }
+
+    fn data_mut(&mut self) -> &mut Vec<Limb> {
+        &mut self.data
+    }
+}
+
+#[cfg(limb_width_32)]
+pub(crate) fn from_u32(x: &[u32]) -> Vec<Limb> {
+    x.iter().cloned().collect()
+}
+
+#[cfg(limb_width_64)]
+pub(crate) fn from_u32(x: &[u32]) -> Vec<Limb> {
+    let mut v = Vec::<Limb>::default();
+    for xi in x.chunks(2) {
+        match xi.len() {
+            1 => v.push(xi[0] as u64),
+            2 => v.push(((xi[1] as u64) << 32) | (xi[0] as u64)),
+            _ => unreachable!(),
+        }
+    }
+
+    v
+}
+
+#[test]
+fn compare_test() {
+    // Simple
+    let x = Bigint {
+        data: from_u32(&[1]),
+    };
+    let y = Bigint {
+        data: from_u32(&[2]),
+    };
+    assert_eq!(x.compare(&y), cmp::Ordering::Less);
+    assert_eq!(x.compare(&x), cmp::Ordering::Equal);
+    assert_eq!(y.compare(&x), cmp::Ordering::Greater);
+
+    // Check asymmetric
+    let x = Bigint {
+        data: from_u32(&[5, 1]),
+    };
+    let y = Bigint {
+        data: from_u32(&[2]),
+    };
+    assert_eq!(x.compare(&y), cmp::Ordering::Greater);
+    assert_eq!(x.compare(&x), cmp::Ordering::Equal);
+    assert_eq!(y.compare(&x), cmp::Ordering::Less);
+
+    // Check when we use reverse ordering properly.
+    let x = Bigint {
+        data: from_u32(&[5, 1, 9]),
+    };
+    let y = Bigint {
+        data: from_u32(&[6, 2, 8]),
+    };
+    assert_eq!(x.compare(&y), cmp::Ordering::Greater);
+    assert_eq!(x.compare(&x), cmp::Ordering::Equal);
+    assert_eq!(y.compare(&x), cmp::Ordering::Less);
+
+    // Complex scenario, check it properly uses reverse ordering.
+    let x = Bigint {
+        data: from_u32(&[0, 1, 9]),
+    };
+    let y = Bigint {
+        data: from_u32(&[4294967295, 0, 9]),
+    };
+    assert_eq!(x.compare(&y), cmp::Ordering::Greater);
+    assert_eq!(x.compare(&x), cmp::Ordering::Equal);
+    assert_eq!(y.compare(&x), cmp::Ordering::Less);
+}
+
+#[test]
+fn hi64_test() {
+    assert_eq!(Bigint::from_u64(0xA).hi64(), (0xA000000000000000, false));
+    assert_eq!(Bigint::from_u64(0xAB).hi64(), (0xAB00000000000000, false));
+    assert_eq!(
+        Bigint::from_u64(0xAB00000000).hi64(),
+        (0xAB00000000000000, false)
+    );
+    assert_eq!(
+        Bigint::from_u64(0xA23456789A).hi64(),
+        (0xA23456789A000000, false)
+    );
+}
+
+#[test]
+fn bit_length_test() {
+    let x = Bigint {
+        data: from_u32(&[0, 0, 0, 1]),
+    };
+    assert_eq!(x.bit_length(), 97);
+
+    let x = Bigint {
+        data: from_u32(&[0, 0, 0, 3]),
+    };
+    assert_eq!(x.bit_length(), 98);
+
+    let x = Bigint {
+        data: from_u32(&[1 << 31]),
+    };
+    assert_eq!(x.bit_length(), 32);
+}
+
+#[test]
+fn iadd_small_test() {
+    // Overflow check (single)
+    // This should set all the internal data values to 0, the top
+    // value to (1<<31), and the bottom value to (4>>1).
+    // This is because the max_value + 1 leads to all 0s, we set the
+    // topmost bit to 1.
+    let mut x = Bigint {
+        data: from_u32(&[4294967295]),
+    };
+    x.iadd_small(5);
+    assert_eq!(x.data, from_u32(&[4, 1]));
+
+    // No overflow, single value
+    let mut x = Bigint {
+        data: from_u32(&[5]),
+    };
+    x.iadd_small(7);
+    assert_eq!(x.data, from_u32(&[12]));
+
+    // Single carry, internal overflow
+    let mut x = Bigint::from_u64(0x80000000FFFFFFFF);
+    x.iadd_small(7);
+    assert_eq!(x.data, from_u32(&[6, 0x80000001]));
+
+    // Double carry, overflow
+    let mut x = Bigint::from_u64(0xFFFFFFFFFFFFFFFF);
+    x.iadd_small(7);
+    assert_eq!(x.data, from_u32(&[6, 0, 1]));
+}
+
+#[test]
+fn imul_small_test() {
+    // No overflow check, 1-int.
+    let mut x = Bigint {
+        data: from_u32(&[5]),
+    };
+    x.imul_small(7);
+    assert_eq!(x.data, from_u32(&[35]));
+
+    // No overflow check, 2-ints.
+    let mut x = Bigint::from_u64(0x4000000040000);
+    x.imul_small(5);
+    assert_eq!(x.data, from_u32(&[0x00140000, 0x140000]));
+
+    // Overflow, 1 carry.
+    let mut x = Bigint {
+        data: from_u32(&[0x33333334]),
+    };
+    x.imul_small(5);
+    assert_eq!(x.data, from_u32(&[4, 1]));
+
+    // Overflow, 1 carry, internal.
+    let mut x = Bigint::from_u64(0x133333334);
+    x.imul_small(5);
+    assert_eq!(x.data, from_u32(&[4, 6]));
+
+    // Overflow, 2 carries.
+    let mut x = Bigint::from_u64(0x3333333333333334);
+    x.imul_small(5);
+    assert_eq!(x.data, from_u32(&[4, 0, 1]));
+}
+
+#[test]
+fn shl_test() {
+    // Pattern generated via `''.join(["1" +"0"*i for i in range(20)])`
+    let mut big = Bigint {
+        data: from_u32(&[0xD2210408]),
+    };
+    big.ishl(5);
+    assert_eq!(big.data, from_u32(&[0x44208100, 0x1A]));
+    big.ishl(32);
+    assert_eq!(big.data, from_u32(&[0, 0x44208100, 0x1A]));
+    big.ishl(27);
+    assert_eq!(big.data, from_u32(&[0, 0, 0xD2210408]));
+
+    // 96-bits of previous pattern
+    let mut big = Bigint {
+        data: from_u32(&[0x20020010, 0x8040100, 0xD2210408]),
+    };
+    big.ishl(5);
+    assert_eq!(big.data, from_u32(&[0x400200, 0x802004, 0x44208101, 0x1A]));
+    big.ishl(32);
+    assert_eq!(
+        big.data,
+        from_u32(&[0, 0x400200, 0x802004, 0x44208101, 0x1A])
+    );
+    big.ishl(27);
+    assert_eq!(
+        big.data,
+        from_u32(&[0, 0, 0x20020010, 0x8040100, 0xD2210408])
+    );
+}
diff --git a/third_party/rust/serde_json/tests/lexical/num.rs b/third_party/rust/serde_json/tests/lexical/num.rs
new file mode 100644
index 0000000000..1a94be0130
--- /dev/null
+++ b/third_party/rust/serde_json/tests/lexical/num.rs
@@ -0,0 +1,76 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+use crate::lexical::num::{AsPrimitive, Float, Integer, Number};
+
+fn check_as_primitive<T: AsPrimitive>(t: T) {
+    let _: u32 = t.as_u32();
+    let _: u64 = t.as_u64();
+    let _: u128 = t.as_u128();
+    let _: usize = t.as_usize();
+    let _: f32 = t.as_f32();
+    let _: f64 = t.as_f64();
+}
+
+#[test]
+fn as_primitive_test() {
+    check_as_primitive(1u32);
+    check_as_primitive(1u64);
+    check_as_primitive(1u128);
+    check_as_primitive(1usize);
+    check_as_primitive(1f32);
+    check_as_primitive(1f64);
+}
+
+fn check_number<T: Number>(x: T, y: T) {
+    // Copy, partialeq, partialord
+    let _ = x;
+    assert!(x < y);
+    assert!(x != y);
+
+    // Operations
+    let _ = y + x;
+
+    // Conversions already tested.
+}
+
+#[test]
+fn number_test() {
+    check_number(1u32, 5);
+    check_number(1u64, 5);
+    check_number(1u128, 5);
+    check_number(1usize, 5);
+    check_number(1f32, 5.0);
+    check_number(1f64, 5.0);
+}
+
+fn check_integer<T: Integer>(x: T) {
+    // Bitwise operations
+    let _ = x & T::ZERO;
+}
+
+#[test]
+fn integer_test() {
+    check_integer(65u32);
+    check_integer(65u64);
+    check_integer(65u128);
+    check_integer(65usize);
+}
+
+fn check_float<T: Float>(x: T) {
+    // Check functions
+    let _ = x.pow10(5);
+    let _ = x.to_bits();
+    assert!(T::from_bits(x.to_bits()) == x);
+
+    // Check properties
+    let _ = x.to_bits() & T::SIGN_MASK;
+    let _ = x.to_bits() & T::EXPONENT_MASK;
+    let _ = x.to_bits() & T::HIDDEN_BIT_MASK;
+    let _ = x.to_bits() & T::MANTISSA_MASK;
+}
+
+#[test]
+fn float_test() {
+    check_float(123f32);
+    check_float(123f64);
+}
diff --git a/third_party/rust/serde_json/tests/lexical/parse.rs b/third_party/rust/serde_json/tests/lexical/parse.rs
new file mode 100644
index 0000000000..80ca25e772
--- /dev/null
+++ b/third_party/rust/serde_json/tests/lexical/parse.rs
@@ -0,0 +1,204 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+use crate::lexical::num::Float;
+use crate::lexical::parse::{parse_concise_float, parse_truncated_float};
+use core::f64;
+use core::fmt::Debug;
+
+fn check_concise_float<F>(mantissa: u64, exponent: i32, expected: F)
+where
+    F: Float + Debug,
+{
+    assert_eq!(parse_concise_float::<F>(mantissa, exponent), expected);
+}
+
+fn check_truncated_float<F>(integer: &str, fraction: &str, exponent: i32, expected: F)
+where
+    F: Float + Debug,
+{
+    let integer = integer.as_bytes();
+    let fraction = fraction.as_bytes();
+    assert_eq!(
+        parse_truncated_float::<F>(integer, fraction, exponent),
+        expected,
+    );
+}
+
+#[test]
+fn parse_f32_test() {
+    check_concise_float(0, 0, 0.0_f32);
+    check_concise_float(12345, -4, 1.2345_f32);
+    check_concise_float(12345, -3, 12.345_f32);
+    check_concise_float(123456789, -4, 12345.6789_f32);
+    check_concise_float(12345, 6, 1.2345e10_f32);
+    check_concise_float(12345, -42, 1.2345e-38_f32);
+
+    // Check expected rounding, using borderline cases.
+    // Round-down, halfway
+    check_concise_float(16777216, 0, 16777216.0_f32);
+    check_concise_float(16777217, 0, 16777216.0_f32);
+    check_concise_float(16777218, 0, 16777218.0_f32);
+    check_concise_float(33554432, 0, 33554432.0_f32);
+    check_concise_float(33554434, 0, 33554432.0_f32);
+    check_concise_float(33554436, 0, 33554436.0_f32);
+    check_concise_float(17179869184, 0, 17179869184.0_f32);
+    check_concise_float(17179870208, 0, 17179869184.0_f32);
+    check_concise_float(17179871232, 0, 17179871232.0_f32);
+
+    // Round-up, halfway
+    check_concise_float(16777218, 0, 16777218.0_f32);
+    check_concise_float(16777219, 0, 16777220.0_f32);
+    check_concise_float(16777220, 0, 16777220.0_f32);
+
+    check_concise_float(33554436, 0, 33554436.0_f32);
+    check_concise_float(33554438, 0, 33554440.0_f32);
+    check_concise_float(33554440, 0, 33554440.0_f32);
+
+    check_concise_float(17179871232, 0, 17179871232.0_f32);
+    check_concise_float(17179872256, 0, 17179873280.0_f32);
+    check_concise_float(17179873280, 0, 17179873280.0_f32);
+
+    // Round-up, above halfway
+    check_concise_float(33554435, 0, 33554436.0_f32);
+    check_concise_float(17179870209, 0, 17179871232.0_f32);
+
+    // Check exactly halfway, round-up at halfway
+    check_truncated_float("1", "00000017881393432617187499", 0, 1.0000001_f32);
+    check_truncated_float("1", "000000178813934326171875", 0, 1.0000002_f32);
+    check_truncated_float("1", "00000017881393432617187501", 0, 1.0000002_f32);
+}
+
+#[test]
+fn parse_f64_test() {
+    check_concise_float(0, 0, 0.0_f64);
+    check_concise_float(12345, -4, 1.2345_f64);
+    check_concise_float(12345, -3, 12.345_f64);
+    check_concise_float(123456789, -4, 12345.6789_f64);
+    check_concise_float(12345, 6, 1.2345e10_f64);
+    check_concise_float(12345, -312, 1.2345e-308_f64);
+
+    // Check expected rounding, using borderline cases.
+    // Round-down, halfway
+    check_concise_float(9007199254740992, 0, 9007199254740992.0_f64);
+    check_concise_float(9007199254740993, 0, 9007199254740992.0_f64);
+    check_concise_float(9007199254740994, 0, 9007199254740994.0_f64);
+
+    check_concise_float(18014398509481984, 0, 18014398509481984.0_f64);
+    check_concise_float(18014398509481986, 0, 18014398509481984.0_f64);
+    check_concise_float(18014398509481988, 0, 18014398509481988.0_f64);
+
+    check_concise_float(9223372036854775808, 0, 9223372036854775808.0_f64);
+    check_concise_float(9223372036854776832, 0, 9223372036854775808.0_f64);
+    check_concise_float(9223372036854777856, 0, 9223372036854777856.0_f64);
+
+    check_truncated_float(
+        "11417981541647679048466287755595961091061972992",
+        "",
+        0,
+        11417981541647679048466287755595961091061972992.0_f64,
+    );
+    check_truncated_float(
+        "11417981541647680316116887983825362587765178368",
+        "",
+        0,
+        11417981541647679048466287755595961091061972992.0_f64,
+    );
+    check_truncated_float(
+        "11417981541647681583767488212054764084468383744",
+        "",
+        0,
+        11417981541647681583767488212054764084468383744.0_f64,
+    );
+
+    // Round-up, halfway
+    check_concise_float(9007199254740994, 0, 9007199254740994.0_f64);
+    check_concise_float(9007199254740995, 0, 9007199254740996.0_f64);
+    check_concise_float(9007199254740996, 0, 9007199254740996.0_f64);
+
+    check_concise_float(18014398509481988, 0, 18014398509481988.0_f64);
+    check_concise_float(18014398509481990, 0, 18014398509481992.0_f64);
+    check_concise_float(18014398509481992, 0, 18014398509481992.0_f64);
+
+    check_concise_float(9223372036854777856, 0, 9223372036854777856.0_f64);
+    check_concise_float(9223372036854778880, 0, 9223372036854779904.0_f64);
+    check_concise_float(9223372036854779904, 0, 9223372036854779904.0_f64);
+
+    check_truncated_float(
+        "11417981541647681583767488212054764084468383744",
+        "",
+        0,
+        11417981541647681583767488212054764084468383744.0_f64,
+    );
+    check_truncated_float(
+        "11417981541647682851418088440284165581171589120",
+        "",
+        0,
+        11417981541647684119068688668513567077874794496.0_f64,
+    );
+    check_truncated_float(
+        "11417981541647684119068688668513567077874794496",
+        "",
+        0,
+        11417981541647684119068688668513567077874794496.0_f64,
+    );
+
+    // Round-up, above halfway
+    check_concise_float(9223372036854776833, 0, 9223372036854777856.0_f64);
+    check_truncated_float(
+        "11417981541647680316116887983825362587765178369",
+        "",
+        0,
+        11417981541647681583767488212054764084468383744.0_f64,
+    );
+
+    // Rounding error
+    // Adapted from failures in strtod.
+    check_concise_float(22250738585072014, -324, 2.2250738585072014e-308_f64);
+    check_truncated_float("2", "2250738585072011360574097967091319759348195463516456480234261097248222220210769455165295239081350879141491589130396211068700864386945946455276572074078206217433799881410632673292535522868813721490129811224514518898490572223072852551331557550159143974763979834118019993239625482890171070818506906306666559949382757725720157630626906633326475653000092458883164330377797918696120494973903778297049050510806099407302629371289589500035837999672072543043602840788957717961509455167482434710307026091446215722898802581825451803257070188608721131280795122334262883686223215037756666225039825343359745688844239002654981983854879482922068947216898310996983658468140228542433306603398508864458040010349339704275671864433837704860378616227717385456230658746790140867233276367187499", -308, 2.225073858507201e-308_f64);
+    check_truncated_float("2", "22507385850720113605740979670913197593481954635164564802342610972482222202107694551652952390813508791414915891303962110687008643869459464552765720740782062174337998814106326732925355228688137214901298112245145188984905722230728525513315575501591439747639798341180199932396254828901710708185069063066665599493827577257201576306269066333264756530000924588831643303777979186961204949739037782970490505108060994073026293712895895000358379996720725430436028407889577179615094551674824347103070260914462157228988025818254518032570701886087211312807951223342628836862232150377566662250398253433597456888442390026549819838548794829220689472168983109969836584681402285424333066033985088644580400103493397042756718644338377048603786162277173854562306587467901408672332763671875", -308, 2.2250738585072014e-308_f64);
+    check_truncated_float("2", "2250738585072011360574097967091319759348195463516456480234261097248222220210769455165295239081350879141491589130396211068700864386945946455276572074078206217433799881410632673292535522868813721490129811224514518898490572223072852551331557550159143974763979834118019993239625482890171070818506906306666559949382757725720157630626906633326475653000092458883164330377797918696120494973903778297049050510806099407302629371289589500035837999672072543043602840788957717961509455167482434710307026091446215722898802581825451803257070188608721131280795122334262883686223215037756666225039825343359745688844239002654981983854879482922068947216898310996983658468140228542433306603398508864458040010349339704275671864433837704860378616227717385456230658746790140867233276367187501", -308, 2.2250738585072014e-308_f64);
+    check_truncated_float("179769313486231580793728971405303415079934132710037826936173778980444968292764750946649017977587207096330286416692887910946555547851940402630657488671505820681908902000708383676273854845817711531764475730270069855571366959622842914819860834936475292719074168444365510704342711559699508093042880177904174497791", "9999999999999999999999999999999999999999999999999999999999999999999999", 0, 1.7976931348623157e+308_f64);
+    check_truncated_float("7", "4109846876186981626485318930233205854758970392148714663837852375101326090531312779794975454245398856969484704316857659638998506553390969459816219401617281718945106978546710679176872575177347315553307795408549809608457500958111373034747658096871009590975442271004757307809711118935784838675653998783503015228055934046593739791790738723868299395818481660169122019456499931289798411362062484498678713572180352209017023903285791732520220528974020802906854021606612375549983402671300035812486479041385743401875520901590172592547146296175134159774938718574737870961645638908718119841271673056017045493004705269590165763776884908267986972573366521765567941072508764337560846003984904972149117463085539556354188641513168478436313080237596295773983001708984374999", -324, 5.0e-324_f64);
+    check_truncated_float("7", "4109846876186981626485318930233205854758970392148714663837852375101326090531312779794975454245398856969484704316857659638998506553390969459816219401617281718945106978546710679176872575177347315553307795408549809608457500958111373034747658096871009590975442271004757307809711118935784838675653998783503015228055934046593739791790738723868299395818481660169122019456499931289798411362062484498678713572180352209017023903285791732520220528974020802906854021606612375549983402671300035812486479041385743401875520901590172592547146296175134159774938718574737870961645638908718119841271673056017045493004705269590165763776884908267986972573366521765567941072508764337560846003984904972149117463085539556354188641513168478436313080237596295773983001708984375", -324, 1.0e-323_f64);
+    check_truncated_float("7", "4109846876186981626485318930233205854758970392148714663837852375101326090531312779794975454245398856969484704316857659638998506553390969459816219401617281718945106978546710679176872575177347315553307795408549809608457500958111373034747658096871009590975442271004757307809711118935784838675653998783503015228055934046593739791790738723868299395818481660169122019456499931289798411362062484498678713572180352209017023903285791732520220528974020802906854021606612375549983402671300035812486479041385743401875520901590172592547146296175134159774938718574737870961645638908718119841271673056017045493004705269590165763776884908267986972573366521765567941072508764337560846003984904972149117463085539556354188641513168478436313080237596295773983001708984375001", -324, 1.0e-323_f64);
+    check_truncated_float("", "0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000024703282292062327208828439643411068618252990130716238221279284125033775363510437593264991818081799618989828234772285886546332835517796989819938739800539093906315035659515570226392290858392449105184435931802849936536152500319370457678249219365623669863658480757001585769269903706311928279558551332927834338409351978015531246597263579574622766465272827220056374006485499977096599470454020828166226237857393450736339007967761930577506740176324673600968951340535537458516661134223766678604162159680461914467291840300530057530849048765391711386591646239524912623653881879636239373280423891018672348497668235089863388587925628302755995657524455507255189313690836254779186948667994968324049705821028513185451396213837722826145437693412532098591327667236328125", 0, 0.0_f64);
+
+    // Rounding error
+    // Adapted from:
+    //  https://www.exploringbinary.com/how-glibc-strtod-works/
+    check_truncated_float("", "000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000022250738585072008890245868760858598876504231122409594654935248025624400092282356951787758888037591552642309780950434312085877387158357291821993020294379224223559819827501242041788969571311791082261043971979604000454897391938079198936081525613113376149842043271751033627391549782731594143828136275113838604094249464942286316695429105080201815926642134996606517803095075913058719846423906068637102005108723282784678843631944515866135041223479014792369585208321597621066375401613736583044193603714778355306682834535634005074073040135602968046375918583163124224521599262546494300836851861719422417646455137135420132217031370496583210154654068035397417906022589503023501937519773030945763173210852507299305089761582519159720757232455434770912461317493580281734466552734375", 0, 2.2250738585072011e-308_f64);
+
+    // Rounding error
+    // Adapted from test-parse-random failures.
+    check_concise_float(1009, -31, 1.009e-28_f64);
+    check_concise_float(18294, 304, f64::INFINITY);
+
+    // Rounding error
+    // Adapted from a @dangrabcad's issue #20.
+    check_concise_float(7689539722041643, 149, 7.689539722041643e164_f64);
+    check_truncated_float("768953972204164300000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000", "", 0, 7.689539722041643e164_f64);
+    check_truncated_float("768953972204164300000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000", "0", 0, 7.689539722041643e164_f64);
+
+    // Check other cases similar to @dangrabcad's issue #20.
+    check_truncated_float("9223372036854776833", "0", 0, 9223372036854777856.0_f64);
+    check_truncated_float(
+        "11417981541647680316116887983825362587765178369",
+        "0",
+        0,
+        11417981541647681583767488212054764084468383744.0_f64,
+    );
+    check_concise_float(90071992547409950, -1, 9007199254740996.0_f64);
+    check_concise_float(180143985094819900, -1, 18014398509481992.0_f64);
+    check_truncated_float("9223372036854778880", "0", 0, 9223372036854779904.0_f64);
+    check_truncated_float(
+        "11417981541647682851418088440284165581171589120",
+        "0",
+        0,
+        11417981541647684119068688668513567077874794496.0_f64,
+    );
+
+    // Check other cases ostensibly identified via proptest.
+    check_truncated_float("71610528364411830000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000", "0", 0, 71610528364411830000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000.0_f64);
+    check_truncated_float("126769393745745060000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000", "0", 0, 126769393745745060000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000.0_f64);
+    check_truncated_float("38652960461239320000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000", "0", 0, 38652960461239320000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000.0_f64);
+}
diff --git a/third_party/rust/serde_json/tests/lexical/rounding.rs b/third_party/rust/serde_json/tests/lexical/rounding.rs
new file mode 100644
index 0000000000..7ea17716c3
--- /dev/null
+++ b/third_party/rust/serde_json/tests/lexical/rounding.rs
@@ -0,0 +1,316 @@
+// Adapted from https://github.com/Alexhuszagh/rust-lexical.
+
+use crate::lexical::float::ExtendedFloat;
+use crate::lexical::num::Float;
+use crate::lexical::rounding::*;
+
+// MASKS
+
+#[test]
+fn lower_n_mask_test() {
+    assert_eq!(lower_n_mask(0u64), 0b0);
+    assert_eq!(lower_n_mask(1u64), 0b1);
+    assert_eq!(lower_n_mask(2u64), 0b11);
+    assert_eq!(lower_n_mask(10u64), 0b1111111111);
+    assert_eq!(lower_n_mask(32u64), 0b11111111111111111111111111111111);
+}
+
+#[test]
+fn lower_n_halfway_test() {
+    assert_eq!(lower_n_halfway(0u64), 0b0);
+    assert_eq!(lower_n_halfway(1u64), 0b1);
+    assert_eq!(lower_n_halfway(2u64), 0b10);
+    assert_eq!(lower_n_halfway(10u64), 0b1000000000);
+    assert_eq!(lower_n_halfway(32u64), 0b10000000000000000000000000000000);
+}
+
+#[test]
+fn nth_bit_test() {
+    assert_eq!(nth_bit(0u64), 0b1);
+    assert_eq!(nth_bit(1u64), 0b10);
+    assert_eq!(nth_bit(2u64), 0b100);
+    assert_eq!(nth_bit(10u64), 0b10000000000);
+    assert_eq!(nth_bit(31u64), 0b10000000000000000000000000000000);
+}
+
+#[test]
+fn internal_n_mask_test() {
+    assert_eq!(internal_n_mask(1u64, 0u64), 0b0);
+    assert_eq!(internal_n_mask(1u64, 1u64), 0b1);
+    assert_eq!(internal_n_mask(2u64, 1u64), 0b10);
+    assert_eq!(internal_n_mask(4u64, 2u64), 0b1100);
+    assert_eq!(internal_n_mask(10u64, 2u64), 0b1100000000);
+    assert_eq!(internal_n_mask(10u64, 4u64), 0b1111000000);
+    assert_eq!(
+        internal_n_mask(32u64, 4u64),
+        0b11110000000000000000000000000000
+    );
+}
+
+// NEAREST ROUNDING
+
+#[test]
+fn round_nearest_test() {
+    // Check exactly halfway (b'1100000')
+    let mut fp = ExtendedFloat { mant: 0x60, exp: 0 };
+    let (above, halfway) = round_nearest(&mut fp, 6);
+    assert!(!above);
+    assert!(halfway);
+    assert_eq!(fp.mant, 1);
+
+    // Check above halfway (b'1100001')
+    let mut fp = ExtendedFloat { mant: 0x61, exp: 0 };
+    let (above, halfway) = round_nearest(&mut fp, 6);
+    assert!(above);
+    assert!(!halfway);
+    assert_eq!(fp.mant, 1);
+
+    // Check below halfway (b'1011111')
+    let mut fp = ExtendedFloat { mant: 0x5F, exp: 0 };
+    let (above, halfway) = round_nearest(&mut fp, 6);
+    assert!(!above);
+    assert!(!halfway);
+    assert_eq!(fp.mant, 1);
+}
+
+// DIRECTED ROUNDING
+
+#[test]
+fn round_downward_test() {
+    // b0000000
+    let mut fp = ExtendedFloat { mant: 0x00, exp: 0 };
+    round_downward(&mut fp, 6);
+    assert_eq!(fp.mant, 0);
+
+    // b1000000
+    let mut fp = ExtendedFloat { mant: 0x40, exp: 0 };
+    round_downward(&mut fp, 6);
+    assert_eq!(fp.mant, 1);
+
+    // b1100000
+    let mut fp = ExtendedFloat { mant: 0x60, exp: 0 };
+    round_downward(&mut fp, 6);
+    assert_eq!(fp.mant, 1);
+
+    // b1110000
+    let mut fp = ExtendedFloat { mant: 0x70, exp: 0 };
+    round_downward(&mut fp, 6);
+    assert_eq!(fp.mant, 1);
+}
+
+#[test]
+fn round_nearest_tie_even_test() {
+    // Check round-up, halfway
+    let mut fp = ExtendedFloat { mant: 0x60, exp: 0 };
+    round_nearest_tie_even(&mut fp, 6);
+    assert_eq!(fp.mant, 2);
+
+    // Check round-down, halfway
+    let mut fp = ExtendedFloat { mant: 0x20, exp: 0 };
+    round_nearest_tie_even(&mut fp, 6);
+    assert_eq!(fp.mant, 0);
+
+    // Check round-up, above halfway
+    let mut fp = ExtendedFloat { mant: 0x61, exp: 0 };
+    round_nearest_tie_even(&mut fp, 6);
+    assert_eq!(fp.mant, 2);
+
+    let mut fp = ExtendedFloat { mant: 0x21, exp: 0 };
+    round_nearest_tie_even(&mut fp, 6);
+    assert_eq!(fp.mant, 1);
+
+    // Check round-down, below halfway
+    let mut fp = ExtendedFloat { mant: 0x5F, exp: 0 };
+    round_nearest_tie_even(&mut fp, 6);
+    assert_eq!(fp.mant, 1);
+
+    let mut fp = ExtendedFloat { mant: 0x1F, exp: 0 };
+    round_nearest_tie_even(&mut fp, 6);
+    assert_eq!(fp.mant, 0);
+}
+
+// HIGH-LEVEL
+
+#[test]
+fn round_to_float_test() {
+    // Denormal
+    let mut fp = ExtendedFloat {
+        mant: 1 << 63,
+        exp: f64::DENORMAL_EXPONENT - 15,
+    };
+    round_to_float::<f64, _>(&mut fp, round_nearest_tie_even);
+    assert_eq!(fp.mant, 1 << 48);
+    assert_eq!(fp.exp, f64::DENORMAL_EXPONENT);
+
+    // Halfway, round-down (b'1000000000000000000000000000000000000000000000000000010000000000')
+    let mut fp = ExtendedFloat {
+        mant: 0x8000000000000400,
+        exp: -63,
+    };
+    round_to_float::<f64, _>(&mut fp, round_nearest_tie_even);
+    assert_eq!(fp.mant, 1 << 52);
+    assert_eq!(fp.exp, -52);
+
+    // Halfway, round-up (b'1000000000000000000000000000000000000000000000000000110000000000')
+    let mut fp = ExtendedFloat {
+        mant: 0x8000000000000C00,
+        exp: -63,
+    };
+    round_to_float::<f64, _>(&mut fp, round_nearest_tie_even);
+    assert_eq!(fp.mant, (1 << 52) + 2);
+    assert_eq!(fp.exp, -52);
+
+    // Above halfway
+    let mut fp = ExtendedFloat {
+        mant: 0x8000000000000401,
+        exp: -63,
+    };
+    round_to_float::<f64, _>(&mut fp, round_nearest_tie_even);
+    assert_eq!(fp.mant, (1 << 52) + 1);
+    assert_eq!(fp.exp, -52);
+
+    let mut fp = ExtendedFloat {
+        mant: 0x8000000000000C01,
+        exp: -63,
+    };
+    round_to_float::<f64, _>(&mut fp, round_nearest_tie_even);
+    assert_eq!(fp.mant, (1 << 52) + 2);
+    assert_eq!(fp.exp, -52);
+
+    // Below halfway
+    let mut fp = ExtendedFloat {
+        mant: 0x80000000000003FF,
+        exp: -63,
+    };
+    round_to_float::<f64, _>(&mut fp, round_nearest_tie_even);
+    assert_eq!(fp.mant, 1 << 52);
+    assert_eq!(fp.exp, -52);
+
+    let mut fp = ExtendedFloat {
+        mant: 0x8000000000000BFF,
+        exp: -63,
+    };
+    round_to_float::<f64, _>(&mut fp, round_nearest_tie_even);
+    assert_eq!(fp.mant, (1 << 52) + 1);
+    assert_eq!(fp.exp, -52);
+}
+
+#[test]
+fn avoid_overflow_test() {
+    // Avoid overflow, fails by 1
+    let mut fp = ExtendedFloat {
+        mant: 0xFFFFFFFFFFFF,
+        exp: f64::MAX_EXPONENT + 5,
+    };
+    avoid_overflow::<f64>(&mut fp);
+    assert_eq!(fp.mant, 0xFFFFFFFFFFFF);
+    assert_eq!(fp.exp, f64::MAX_EXPONENT + 5);
+
+    // Avoid overflow, succeeds
+    let mut fp = ExtendedFloat {
+        mant: 0xFFFFFFFFFFFF,
+        exp: f64::MAX_EXPONENT + 4,
+    };
+    avoid_overflow::<f64>(&mut fp);
+    assert_eq!(fp.mant, 0x1FFFFFFFFFFFE0);
+    assert_eq!(fp.exp, f64::MAX_EXPONENT - 1);
+}
+
+#[test]
+fn round_to_native_test() {
+    // Overflow
+    let mut fp = ExtendedFloat {
+        mant: 0xFFFFFFFFFFFF,
+        exp: f64::MAX_EXPONENT + 4,
+    };
+    round_to_native::<f64, _>(&mut fp, round_nearest_tie_even);
+    assert_eq!(fp.mant, 0x1FFFFFFFFFFFE0);
+    assert_eq!(fp.exp, f64::MAX_EXPONENT - 1);
+
+    // Need denormal
+    let mut fp = ExtendedFloat {
+        mant: 1,
+        exp: f64::DENORMAL_EXPONENT + 48,
+    };
+    round_to_native::<f64, _>(&mut fp, round_nearest_tie_even);
+    assert_eq!(fp.mant, 1 << 48);
+    assert_eq!(fp.exp, f64::DENORMAL_EXPONENT);
+
+    // Halfway, round-down (b'10000000000000000000000000000000000000000000000000000100000')
+    let mut fp = ExtendedFloat {
+        mant: 0x400000000000020,
+        exp: -58,
+    };
+    round_to_native::<f64, _>(&mut fp, round_nearest_tie_even);
+    assert_eq!(fp.mant, 1 << 52);
+    assert_eq!(fp.exp, -52);
+
+    // Halfway, round-up (b'10000000000000000000000000000000000000000000000000001100000')
+    let mut fp = ExtendedFloat {
+        mant: 0x400000000000060,
+        exp: -58,
+    };
+    round_to_native::<f64, _>(&mut fp, round_nearest_tie_even);
+    assert_eq!(fp.mant, (1 << 52) + 2);
+    assert_eq!(fp.exp, -52);
+
+    // Above halfway
+    let mut fp = ExtendedFloat {
+        mant: 0x400000000000021,
+        exp: -58,
+    };
+    round_to_native::<f64, _>(&mut fp, round_nearest_tie_even);
+    assert_eq!(fp.mant, (1 << 52) + 1);
+    assert_eq!(fp.exp, -52);
+
+    let mut fp = ExtendedFloat {
+        mant: 0x400000000000061,
+        exp: -58,
+    };
+    round_to_native::<f64, _>(&mut fp, round_nearest_tie_even);
+    assert_eq!(fp.mant, (1 << 52) + 2);
+    assert_eq!(fp.exp, -52);
+
+    // Below halfway
+    let mut fp = ExtendedFloat {
+        mant: 0x40000000000001F,
+        exp: -58,
+    };
+    round_to_native::<f64, _>(&mut fp, round_nearest_tie_even);
+    assert_eq!(fp.mant, 1 << 52);
+    assert_eq!(fp.exp, -52);
+
+    let mut fp = ExtendedFloat {
+        mant: 0x40000000000005F,
+        exp: -58,
+    };
+    round_to_native::<f64, _>(&mut fp, round_nearest_tie_even);
+    assert_eq!(fp.mant, (1 << 52) + 1);
+    assert_eq!(fp.exp, -52);
+
+    // Underflow
+    // Adapted from failures in strtod.
+    let mut fp = ExtendedFloat {
+        exp: -1139,
+        mant: 18446744073709550712,
+    };
+    round_to_native::<f64, _>(&mut fp, round_nearest_tie_even);
+    assert_eq!(fp.mant, 0);
+    assert_eq!(fp.exp, 0);
+
+    let mut fp = ExtendedFloat {
+        exp: -1139,
+        mant: 18446744073709551460,
+    };
+    round_to_native::<f64, _>(&mut fp, round_nearest_tie_even);
+    assert_eq!(fp.mant, 0);
+    assert_eq!(fp.exp, 0);
+
+    let mut fp = ExtendedFloat {
+        exp: -1138,
+        mant: 9223372036854776103,
+    };
+    round_to_native::<f64, _>(&mut fp, round_nearest_tie_even);
+    assert_eq!(fp.mant, 1);
+    assert_eq!(fp.exp, -1074);
+}
diff --git a/third_party/rust/serde_json/tests/macros/mod.rs b/third_party/rust/serde_json/tests/macros/mod.rs
new file mode 100644
index 0000000000..aaf820f074
--- /dev/null
+++ b/third_party/rust/serde_json/tests/macros/mod.rs
@@ -0,0 +1,61 @@
+#![allow(unused_macro_rules)]
+
+macro_rules! json_str {
+    ([]) => {
+        "[]"
+    };
+    ([ $e0:tt $(, $e:tt)* $(,)? ]) => {
+        concat!("[",
+            json_str!($e0),
+            $(",", json_str!($e),)*
+        "]")
+    };
+    ({}) => {
+        "{}"
+    };
+    ({ $k0:tt : $v0:tt $(, $k:tt : $v:tt)* $(,)? }) => {
+        concat!("{",
+            stringify!($k0), ":", json_str!($v0),
+            $(",", stringify!($k), ":", json_str!($v),)*
+        "}")
+    };
+    (($other:tt)) => {
+        $other
+    };
+    ($other:tt) => {
+        stringify!($other)
+    };
+}
+
+macro_rules! pretty_str {
+    ($json:tt) => {
+        pretty_str_impl!("", $json)
+    };
+}
+
+macro_rules! pretty_str_impl {
+    ($indent:expr, []) => {
+        "[]"
+    };
+    ($indent:expr, [ $e0:tt $(, $e:tt)* $(,)? ]) => {
+        concat!("[\n  ",
+            $indent, pretty_str_impl!(concat!("  ", $indent), $e0),
+            $(",\n  ", $indent, pretty_str_impl!(concat!("  ", $indent), $e),)*
+        "\n", $indent, "]")
+    };
+    ($indent:expr, {}) => {
+        "{}"
+    };
+    ($indent:expr, { $k0:tt : $v0:tt $(, $k:tt : $v:tt)* $(,)? }) => {
+        concat!("{\n  ",
+            $indent, stringify!($k0), ": ", pretty_str_impl!(concat!("  ", $indent), $v0),
+            $(",\n  ", $indent, stringify!($k), ": ", pretty_str_impl!(concat!("  ", $indent), $v),)*
+        "\n", $indent, "}")
+    };
+    ($indent:expr, ($other:tt)) => {
+        $other
+    };
+    ($indent:expr, $other:tt) => {
+        stringify!($other)
+    };
+}
diff --git a/third_party/rust/serde_json/tests/map.rs b/third_party/rust/serde_json/tests/map.rs
new file mode 100644
index 0000000000..ae01969561
--- /dev/null
+++ b/third_party/rust/serde_json/tests/map.rs
@@ -0,0 +1,47 @@
+use serde_json::{from_str, Map, Value};
+
+#[test]
+fn test_preserve_order() {
+    // Sorted order
+    #[cfg(not(feature = "preserve_order"))]
+    const EXPECTED: &[&str] = &["a", "b", "c"];
+
+    // Insertion order
+    #[cfg(feature = "preserve_order")]
+    const EXPECTED: &[&str] = &["b", "a", "c"];
+
+    let v: Value = from_str(r#"{"b":null,"a":null,"c":null}"#).unwrap();
+    let keys: Vec<_> = v.as_object().unwrap().keys().collect();
+    assert_eq!(keys, EXPECTED);
+}
+
+#[test]
+fn test_append() {
+    // Sorted order
+    #[cfg(not(feature = "preserve_order"))]
+    const EXPECTED: &[&str] = &["a", "b", "c"];
+
+    // Insertion order
+    #[cfg(feature = "preserve_order")]
+    const EXPECTED: &[&str] = &["b", "a", "c"];
+
+    let mut v: Value = from_str(r#"{"b":null,"a":null,"c":null}"#).unwrap();
+    let val = v.as_object_mut().unwrap();
+    let mut m = Map::new();
+    m.append(val);
+    let keys: Vec<_> = m.keys().collect();
+
+    assert_eq!(keys, EXPECTED);
+    assert!(val.is_empty());
+}
+
+#[cfg(not(no_btreemap_retain))]
+#[test]
+fn test_retain() {
+    let mut v: Value = from_str(r#"{"b":null,"a":null,"c":null}"#).unwrap();
+    let val = v.as_object_mut().unwrap();
+    val.retain(|k, _| k.as_str() != "b");
+
+    let keys: Vec<_> = val.keys().collect();
+    assert_eq!(keys, &["a", "c"]);
+}
diff --git a/third_party/rust/serde_json/tests/regression.rs b/third_party/rust/serde_json/tests/regression.rs
new file mode 100644
index 0000000000..fb2b25c89b
--- /dev/null
+++ b/third_party/rust/serde_json/tests/regression.rs
@@ -0,0 +1,3 @@
+mod regression {
+    automod::dir!("tests/regression");
+}
diff --git a/third_party/rust/serde_json/tests/regression/issue520.rs b/third_party/rust/serde_json/tests/regression/issue520.rs
new file mode 100644
index 0000000000..9ed367731b
--- /dev/null
+++ b/third_party/rust/serde_json/tests/regression/issue520.rs
@@ -0,0 +1,20 @@
+#![allow(clippy::float_cmp)]
+
+use serde_derive::{Serialize, Deserialize};
+
+#[derive(Serialize, Deserialize, Debug)]
+#[serde(tag = "type", content = "data")]
+enum E {
+    Float(f32),
+}
+
+#[test]
+fn test() {
+    let e = E::Float(159.1);
+    let v = serde_json::to_value(e).unwrap();
+    let e = serde_json::from_value::<E>(v).unwrap();
+
+    match e {
+        E::Float(f) => assert_eq!(f, 159.1),
+    }
+}
diff --git a/third_party/rust/serde_json/tests/regression/issue795.rs b/third_party/rust/serde_json/tests/regression/issue795.rs
new file mode 100644
index 0000000000..bb82852c54
--- /dev/null
+++ b/third_party/rust/serde_json/tests/regression/issue795.rs
@@ -0,0 +1,59 @@
+#![allow(clippy::assertions_on_result_states)]
+
+use serde::de::{
+    Deserialize, Deserializer, EnumAccess, IgnoredAny, MapAccess, VariantAccess, Visitor,
+};
+use serde_json::json;
+use std::fmt;
+
+#[derive(Debug)]
+pub enum Enum {
+    Variant { x: u8 },
+}
+
+impl<'de> Deserialize<'de> for Enum {
+    fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+    where
+        D: Deserializer<'de>,
+    {
+        struct EnumVisitor;
+
+        impl<'de> Visitor<'de> for EnumVisitor {
+            type Value = Enum;
+
+            fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+                formatter.write_str("enum Enum")
+            }
+
+            fn visit_enum<A>(self, data: A) -> Result<Self::Value, A::Error>
+            where
+                A: EnumAccess<'de>,
+            {
+                let (IgnoredAny, variant) = data.variant()?;
+                variant.struct_variant(&["x"], self)
+            }
+
+            fn visit_map<A>(self, mut data: A) -> Result<Self::Value, A::Error>
+            where
+                A: MapAccess<'de>,
+            {
+                let mut x = 0;
+                if let Some((IgnoredAny, value)) = data.next_entry()? {
+                    x = value;
+                }
+                Ok(Enum::Variant { x })
+            }
+        }
+
+        deserializer.deserialize_enum("Enum", &["Variant"], EnumVisitor)
+    }
+}
+
+#[test]
+fn test() {
+    let s = r#" {"Variant":{"x":0,"y":0}} "#;
+    assert!(serde_json::from_str::<Enum>(s).is_err());
+
+    let j = json!({"Variant":{"x":0,"y":0}});
+    assert!(serde_json::from_value::<Enum>(j).is_err());
+}
diff --git a/third_party/rust/serde_json/tests/regression/issue845.rs b/third_party/rust/serde_json/tests/regression/issue845.rs
new file mode 100644
index 0000000000..56037ae669
--- /dev/null
+++ b/third_party/rust/serde_json/tests/regression/issue845.rs
@@ -0,0 +1,74 @@
+#![allow(clippy::trait_duplication_in_bounds)] // https://github.com/rust-lang/rust-clippy/issues/8757
+
+use serde::{Deserialize, Deserializer};
+use std::convert::TryFrom;
+use std::fmt::{self, Display};
+use std::marker::PhantomData;
+use std::str::FromStr;
+
+pub struct NumberVisitor<T> {
+    marker: PhantomData<T>,
+}
+
+impl<'de, T> serde::de::Visitor<'de> for NumberVisitor<T>
+where
+    T: TryFrom<u64> + TryFrom<i64> + FromStr,
+    <T as TryFrom<u64>>::Error: Display,
+    <T as TryFrom<i64>>::Error: Display,
+    <T as FromStr>::Err: Display,
+{
+    type Value = T;
+
+    fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+        formatter.write_str("an integer or string")
+    }
+
+    fn visit_u64<E>(self, v: u64) -> Result<Self::Value, E>
+    where
+        E: serde::de::Error,
+    {
+        T::try_from(v).map_err(serde::de::Error::custom)
+    }
+
+    fn visit_i64<E>(self, v: i64) -> Result<Self::Value, E>
+    where
+        E: serde::de::Error,
+    {
+        T::try_from(v).map_err(serde::de::Error::custom)
+    }
+
+    fn visit_str<E>(self, v: &str) -> Result<Self::Value, E>
+    where
+        E: serde::de::Error,
+    {
+        v.parse().map_err(serde::de::Error::custom)
+    }
+}
+
+fn deserialize_integer_or_string<'de, D, T>(deserializer: D) -> Result<T, D::Error>
+where
+    D: Deserializer<'de>,
+    T: TryFrom<u64> + TryFrom<i64> + FromStr,
+    <T as TryFrom<u64>>::Error: Display,
+    <T as TryFrom<i64>>::Error: Display,
+    <T as FromStr>::Err: Display,
+{
+    deserializer.deserialize_any(NumberVisitor {
+        marker: PhantomData,
+    })
+}
+
+#[derive(Deserialize, Debug)]
+pub struct Struct {
+    #[serde(deserialize_with = "deserialize_integer_or_string")]
+    pub i: i64,
+}
+
+#[test]
+fn test() {
+    let j = r#" {"i":100} "#;
+    println!("{:?}", serde_json::from_str::<Struct>(j).unwrap());
+
+    let j = r#" {"i":"100"} "#;
+    println!("{:?}", serde_json::from_str::<Struct>(j).unwrap());
+}
diff --git a/third_party/rust/serde_json/tests/regression/issue953.rs b/third_party/rust/serde_json/tests/regression/issue953.rs
new file mode 100644
index 0000000000..771aa5287c
--- /dev/null
+++ b/third_party/rust/serde_json/tests/regression/issue953.rs
@@ -0,0 +1,9 @@
+use serde_json::Value;
+
+#[test]
+fn test() {
+    let x1 = serde_json::from_str::<Value>("18446744073709551615.");
+    assert!(x1.is_err());
+    let x2 = serde_json::from_str::<Value>("18446744073709551616.");
+    assert!(x2.is_err());
+}
diff --git a/third_party/rust/serde_json/tests/stream.rs b/third_party/rust/serde_json/tests/stream.rs
new file mode 100644
index 0000000000..ec6b9e3d02
--- /dev/null
+++ b/third_party/rust/serde_json/tests/stream.rs
@@ -0,0 +1,183 @@
+#![cfg(not(feature = "preserve_order"))]
+#![allow(clippy::assertions_on_result_states)]
+
+use serde_json::{json, Deserializer, Value};
+
+// Rustfmt issue https://github.com/rust-lang-nursery/rustfmt/issues/2740
+#[rustfmt::skip]
+macro_rules! test_stream {
+    ($data:expr, $ty:ty, |$stream:ident| $test:block) => {
+        {
+            let de = Deserializer::from_str($data);
+            let mut $stream = de.into_iter::<$ty>();
+            assert_eq!($stream.byte_offset(), 0);
+            $test
+        }
+        {
+            let de = Deserializer::from_slice($data.as_bytes());
+            let mut $stream = de.into_iter::<$ty>();
+            assert_eq!($stream.byte_offset(), 0);
+            $test
+        }
+        {
+            let mut bytes = $data.as_bytes();
+            let de = Deserializer::from_reader(&mut bytes);
+            let mut $stream = de.into_iter::<$ty>();
+            assert_eq!($stream.byte_offset(), 0);
+            $test
+        }
+    };
+}
+
+#[test]
+fn test_json_stream_newlines() {
+    let data = "{\"x\":39} {\"x\":40}{\"x\":41}\n{\"x\":42}";
+
+    test_stream!(data, Value, |stream| {
+        assert_eq!(stream.next().unwrap().unwrap()["x"], 39);
+        assert_eq!(stream.byte_offset(), 8);
+
+        assert_eq!(stream.next().unwrap().unwrap()["x"], 40);
+        assert_eq!(stream.byte_offset(), 17);
+
+        assert_eq!(stream.next().unwrap().unwrap()["x"], 41);
+        assert_eq!(stream.byte_offset(), 25);
+
+        assert_eq!(stream.next().unwrap().unwrap()["x"], 42);
+        assert_eq!(stream.byte_offset(), 34);
+
+        assert!(stream.next().is_none());
+        assert_eq!(stream.byte_offset(), 34);
+    });
+}
+
+#[test]
+fn test_json_stream_trailing_whitespaces() {
+    let data = "{\"x\":42} \t\n";
+
+    test_stream!(data, Value, |stream| {
+        assert_eq!(stream.next().unwrap().unwrap()["x"], 42);
+        assert_eq!(stream.byte_offset(), 8);
+
+        assert!(stream.next().is_none());
+        assert_eq!(stream.byte_offset(), 11);
+    });
+}
+
+#[test]
+fn test_json_stream_truncated() {
+    let data = "{\"x\":40}\n{\"x\":";
+
+    test_stream!(data, Value, |stream| {
+        assert_eq!(stream.next().unwrap().unwrap()["x"], 40);
+        assert_eq!(stream.byte_offset(), 8);
+
+        assert!(stream.next().unwrap().unwrap_err().is_eof());
+        assert_eq!(stream.byte_offset(), 9);
+    });
+}
+
+#[test]
+fn test_json_stream_truncated_decimal() {
+    let data = "{\"x\":4.";
+
+    test_stream!(data, Value, |stream| {
+        assert!(stream.next().unwrap().unwrap_err().is_eof());
+        assert_eq!(stream.byte_offset(), 0);
+    });
+}
+
+#[test]
+fn test_json_stream_truncated_negative() {
+    let data = "{\"x\":-";
+
+    test_stream!(data, Value, |stream| {
+        assert!(stream.next().unwrap().unwrap_err().is_eof());
+        assert_eq!(stream.byte_offset(), 0);
+    });
+}
+
+#[test]
+fn test_json_stream_truncated_exponent() {
+    let data = "{\"x\":4e";
+
+    test_stream!(data, Value, |stream| {
+        assert!(stream.next().unwrap().unwrap_err().is_eof());
+        assert_eq!(stream.byte_offset(), 0);
+    });
+}
+
+#[test]
+fn test_json_stream_empty() {
+    let data = "";
+
+    test_stream!(data, Value, |stream| {
+        assert!(stream.next().is_none());
+        assert_eq!(stream.byte_offset(), 0);
+    });
+}
+
+#[test]
+fn test_json_stream_primitive() {
+    let data = "{} true{}1[]\nfalse\"hey\"2 ";
+
+    test_stream!(data, Value, |stream| {
+        assert_eq!(stream.next().unwrap().unwrap(), json!({}));
+        assert_eq!(stream.byte_offset(), 2);
+
+        assert_eq!(stream.next().unwrap().unwrap(), true);
+        assert_eq!(stream.byte_offset(), 7);
+
+        assert_eq!(stream.next().unwrap().unwrap(), json!({}));
+        assert_eq!(stream.byte_offset(), 9);
+
+        assert_eq!(stream.next().unwrap().unwrap(), 1);
+        assert_eq!(stream.byte_offset(), 10);
+
+        assert_eq!(stream.next().unwrap().unwrap(), json!([]));
+        assert_eq!(stream.byte_offset(), 12);
+
+        assert_eq!(stream.next().unwrap().unwrap(), false);
+        assert_eq!(stream.byte_offset(), 18);
+
+        assert_eq!(stream.next().unwrap().unwrap(), "hey");
+        assert_eq!(stream.byte_offset(), 23);
+
+        assert_eq!(stream.next().unwrap().unwrap(), 2);
+        assert_eq!(stream.byte_offset(), 24);
+
+        assert!(stream.next().is_none());
+        assert_eq!(stream.byte_offset(), 25);
+    });
+}
+
+#[test]
+fn test_json_stream_invalid_literal() {
+    let data = "truefalse";
+
+    test_stream!(data, Value, |stream| {
+        let second = stream.next().unwrap().unwrap_err();
+        assert_eq!(second.to_string(), "trailing characters at line 1 column 5");
+    });
+}
+
+#[test]
+fn test_json_stream_invalid_number() {
+    let data = "1true";
+
+    test_stream!(data, Value, |stream| {
+        let second = stream.next().unwrap().unwrap_err();
+        assert_eq!(second.to_string(), "trailing characters at line 1 column 2");
+    });
+}
+
+#[test]
+fn test_error() {
+    let data = "true wrong false";
+
+    test_stream!(data, Value, |stream| {
+        assert_eq!(stream.next().unwrap().unwrap(), true);
+        assert!(stream.next().unwrap().is_err());
+        assert!(stream.next().is_none());
+    });
+}
diff --git a/third_party/rust/serde_json/tests/test.rs b/third_party/rust/serde_json/tests/test.rs
new file mode 100644
index 0000000000..f62a545e7f
--- /dev/null
+++ b/third_party/rust/serde_json/tests/test.rs
@@ -0,0 +1,2408 @@
+#![cfg(not(feature = "preserve_order"))]
+#![allow(
+    clippy::assertions_on_result_states,
+    clippy::cast_precision_loss,
+    clippy::derive_partial_eq_without_eq,
+    clippy::excessive_precision,
+    clippy::float_cmp,
+    clippy::items_after_statements,
+    clippy::shadow_unrelated,
+    clippy::too_many_lines,
+    clippy::unreadable_literal,
+    clippy::unseparated_literal_suffix,
+    clippy::vec_init_then_push,
+    clippy::zero_sized_map_values
+)]
+#![cfg_attr(feature = "trace-macros", feature(trace_macros))]
+#[cfg(feature = "trace-macros")]
+trace_macros!(true);
+
+#[macro_use]
+mod macros;
+
+#[cfg(feature = "raw_value")]
+use ref_cast::RefCast;
+use serde::de::{self, IgnoredAny, IntoDeserializer};
+use serde::ser::{self, SerializeMap, SerializeSeq, Serializer};
+use serde::{Deserialize, Serialize};
+use serde_bytes::{ByteBuf, Bytes};
+#[cfg(feature = "raw_value")]
+use serde_json::value::RawValue;
+use serde_json::{
+    from_reader, from_slice, from_str, from_value, json, to_string, to_string_pretty, to_value,
+    to_vec, Deserializer, Number, Value,
+};
+use std::collections::hash_map::DefaultHasher;
+use std::collections::BTreeMap;
+#[cfg(feature = "raw_value")]
+use std::collections::HashMap;
+use std::fmt::{self, Debug};
+use std::hash::{Hash, Hasher};
+use std::io;
+use std::iter;
+use std::marker::PhantomData;
+use std::mem;
+use std::str::FromStr;
+use std::string::ToString;
+use std::{f32, f64};
+use std::{i16, i32, i64, i8};
+use std::{u16, u32, u64, u8};
+
+macro_rules! treemap {
+    () => {
+        BTreeMap::new()
+    };
+    ($($k:expr => $v:expr),+) => {
+        {
+            let mut m = BTreeMap::new();
+            $(
+                m.insert($k, $v);
+            )+
+            m
+        }
+    };
+}
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+#[serde(deny_unknown_fields)]
+enum Animal {
+    Dog,
+    Frog(String, Vec<isize>),
+    Cat { age: usize, name: String },
+    AntHive(Vec<String>),
+}
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+struct Inner {
+    a: (),
+    b: usize,
+    c: Vec<String>,
+}
+
+#[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+struct Outer {
+    inner: Vec<Inner>,
+}
+
+fn test_encode_ok<T>(errors: &[(T, &str)])
+where
+    T: PartialEq + Debug + ser::Serialize,
+{
+    for &(ref value, out) in errors {
+        let out = out.to_string();
+
+        let s = to_string(value).unwrap();
+        assert_eq!(s, out);
+
+        let v = to_value(value).unwrap();
+        let s = to_string(&v).unwrap();
+        assert_eq!(s, out);
+    }
+}
+
+fn test_pretty_encode_ok<T>(errors: &[(T, &str)])
+where
+    T: PartialEq + Debug + ser::Serialize,
+{
+    for &(ref value, out) in errors {
+        let out = out.to_string();
+
+        let s = to_string_pretty(value).unwrap();
+        assert_eq!(s, out);
+
+        let v = to_value(value).unwrap();
+        let s = to_string_pretty(&v).unwrap();
+        assert_eq!(s, out);
+    }
+}
+
+#[test]
+fn test_write_null() {
+    let tests = &[((), "null")];
+    test_encode_ok(tests);
+    test_pretty_encode_ok(tests);
+}
+
+#[test]
+fn test_write_u64() {
+    let tests = &[(3u64, "3"), (u64::MAX, &u64::MAX.to_string())];
+    test_encode_ok(tests);
+    test_pretty_encode_ok(tests);
+}
+
+#[test]
+fn test_write_i64() {
+    let tests = &[
+        (3i64, "3"),
+        (-2i64, "-2"),
+        (-1234i64, "-1234"),
+        (i64::MIN, &i64::MIN.to_string()),
+    ];
+    test_encode_ok(tests);
+    test_pretty_encode_ok(tests);
+}
+
+#[test]
+fn test_write_f64() {
+    let tests = &[
+        (3.0, "3.0"),
+        (3.1, "3.1"),
+        (-1.5, "-1.5"),
+        (0.5, "0.5"),
+        (f64::MIN, "-1.7976931348623157e308"),
+        (f64::MAX, "1.7976931348623157e308"),
+        (f64::EPSILON, "2.220446049250313e-16"),
+    ];
+    test_encode_ok(tests);
+    test_pretty_encode_ok(tests);
+}
+
+#[test]
+fn test_encode_nonfinite_float_yields_null() {
+    let v = to_value(::std::f64::NAN).unwrap();
+    assert!(v.is_null());
+
+    let v = to_value(::std::f64::INFINITY).unwrap();
+    assert!(v.is_null());
+
+    let v = to_value(::std::f32::NAN).unwrap();
+    assert!(v.is_null());
+
+    let v = to_value(::std::f32::INFINITY).unwrap();
+    assert!(v.is_null());
+}
+
+#[test]
+fn test_write_str() {
+    let tests = &[("", "\"\""), ("foo", "\"foo\"")];
+    test_encode_ok(tests);
+    test_pretty_encode_ok(tests);
+}
+
+#[test]
+fn test_write_bool() {
+    let tests = &[(true, "true"), (false, "false")];
+    test_encode_ok(tests);
+    test_pretty_encode_ok(tests);
+}
+
+#[test]
+fn test_write_char() {
+    let tests = &[
+        ('n', "\"n\""),
+        ('"', "\"\\\"\""),
+        ('\\', "\"\\\\\""),
+        ('/', "\"/\""),
+        ('\x08', "\"\\b\""),
+        ('\x0C', "\"\\f\""),
+        ('\n', "\"\\n\""),
+        ('\r', "\"\\r\""),
+        ('\t', "\"\\t\""),
+        ('\x0B', "\"\\u000b\""),
+        ('\u{3A3}', "\"\u{3A3}\""),
+    ];
+    test_encode_ok(tests);
+    test_pretty_encode_ok(tests);
+}
+
+#[test]
+fn test_write_list() {
+    test_encode_ok(&[
+        (vec![], "[]"),
+        (vec![true], "[true]"),
+        (vec![true, false], "[true,false]"),
+    ]);
+
+    test_encode_ok(&[
+        (vec![vec![], vec![], vec![]], "[[],[],[]]"),
+        (vec![vec![1, 2, 3], vec![], vec![]], "[[1,2,3],[],[]]"),
+        (vec![vec![], vec![1, 2, 3], vec![]], "[[],[1,2,3],[]]"),
+        (vec![vec![], vec![], vec![1, 2, 3]], "[[],[],[1,2,3]]"),
+    ]);
+
+    test_pretty_encode_ok(&[
+        (vec![vec![], vec![], vec![]], pretty_str!([[], [], []])),
+        (
+            vec![vec![1, 2, 3], vec![], vec![]],
+            pretty_str!([[1, 2, 3], [], []]),
+        ),
+        (
+            vec![vec![], vec![1, 2, 3], vec![]],
+            pretty_str!([[], [1, 2, 3], []]),
+        ),
+        (
+            vec![vec![], vec![], vec![1, 2, 3]],
+            pretty_str!([[], [], [1, 2, 3]]),
+        ),
+    ]);
+
+    test_pretty_encode_ok(&[
+        (vec![], "[]"),
+        (vec![true], pretty_str!([true])),
+        (vec![true, false], pretty_str!([true, false])),
+    ]);
+
+    let long_test_list = json!([false, null, ["foo\nbar", 3.5]]);
+
+    test_encode_ok(&[(
+        long_test_list.clone(),
+        json_str!([false, null, ["foo\nbar", 3.5]]),
+    )]);
+
+    test_pretty_encode_ok(&[(
+        long_test_list,
+        pretty_str!([false, null, ["foo\nbar", 3.5]]),
+    )]);
+}
+
+#[test]
+fn test_write_object() {
+    test_encode_ok(&[
+        (treemap!(), "{}"),
+        (treemap!("a".to_string() => true), "{\"a\":true}"),
+        (
+            treemap!(
+                "a".to_string() => true,
+                "b".to_string() => false
+            ),
+            "{\"a\":true,\"b\":false}",
+        ),
+    ]);
+
+    test_encode_ok(&[
+        (
+            treemap![
+                "a".to_string() => treemap![],
+                "b".to_string() => treemap![],
+                "c".to_string() => treemap![]
+            ],
+            "{\"a\":{},\"b\":{},\"c\":{}}",
+        ),
+        (
+            treemap![
+                "a".to_string() => treemap![
+                    "a".to_string() => treemap!["a" => vec![1,2,3]],
+                    "b".to_string() => treemap![],
+                    "c".to_string() => treemap![]
+                ],
+                "b".to_string() => treemap![],
+                "c".to_string() => treemap![]
+            ],
+            "{\"a\":{\"a\":{\"a\":[1,2,3]},\"b\":{},\"c\":{}},\"b\":{},\"c\":{}}",
+        ),
+        (
+            treemap![
+                "a".to_string() => treemap![],
+                "b".to_string() => treemap![
+                    "a".to_string() => treemap!["a" => vec![1,2,3]],
+                    "b".to_string() => treemap![],
+                    "c".to_string() => treemap![]
+                ],
+                "c".to_string() => treemap![]
+            ],
+            "{\"a\":{},\"b\":{\"a\":{\"a\":[1,2,3]},\"b\":{},\"c\":{}},\"c\":{}}",
+        ),
+        (
+            treemap![
+                "a".to_string() => treemap![],
+                "b".to_string() => treemap![],
+                "c".to_string() => treemap![
+                    "a".to_string() => treemap!["a" => vec![1,2,3]],
+                    "b".to_string() => treemap![],
+                    "c".to_string() => treemap![]
+                ]
+            ],
+            "{\"a\":{},\"b\":{},\"c\":{\"a\":{\"a\":[1,2,3]},\"b\":{},\"c\":{}}}",
+        ),
+    ]);
+
+    test_encode_ok(&[(treemap!['c' => ()], "{\"c\":null}")]);
+
+    test_pretty_encode_ok(&[
+        (
+            treemap![
+                "a".to_string() => treemap![],
+                "b".to_string() => treemap![],
+                "c".to_string() => treemap![]
+            ],
+            pretty_str!({
+                "a": {},
+                "b": {},
+                "c": {}
+            }),
+        ),
+        (
+            treemap![
+                "a".to_string() => treemap![
+                    "a".to_string() => treemap!["a" => vec![1,2,3]],
+                    "b".to_string() => treemap![],
+                    "c".to_string() => treemap![]
+                ],
+                "b".to_string() => treemap![],
+                "c".to_string() => treemap![]
+            ],
+            pretty_str!({
+                "a": {
+                    "a": {
+                        "a": [
+                            1,
+                            2,
+                            3
+                        ]
+                    },
+                    "b": {},
+                    "c": {}
+                },
+                "b": {},
+                "c": {}
+            }),
+        ),
+        (
+            treemap![
+                "a".to_string() => treemap![],
+                "b".to_string() => treemap![
+                    "a".to_string() => treemap!["a" => vec![1,2,3]],
+                    "b".to_string() => treemap![],
+                    "c".to_string() => treemap![]
+                ],
+                "c".to_string() => treemap![]
+            ],
+            pretty_str!({
+                "a": {},
+                "b": {
+                    "a": {
+                        "a": [
+                            1,
+                            2,
+                            3
+                        ]
+                    },
+                    "b": {},
+                    "c": {}
+                },
+                "c": {}
+            }),
+        ),
+        (
+            treemap![
+                "a".to_string() => treemap![],
+                "b".to_string() => treemap![],
+                "c".to_string() => treemap![
+                    "a".to_string() => treemap!["a" => vec![1,2,3]],
+                    "b".to_string() => treemap![],
+                    "c".to_string() => treemap![]
+                ]
+            ],
+            pretty_str!({
+                "a": {},
+                "b": {},
+                "c": {
+                    "a": {
+                        "a": [
+                            1,
+                            2,
+                            3
+                        ]
+                    },
+                    "b": {},
+                    "c": {}
+                }
+            }),
+        ),
+    ]);
+
+    test_pretty_encode_ok(&[
+        (treemap!(), "{}"),
+        (
+            treemap!("a".to_string() => true),
+            pretty_str!({
+                "a": true
+            }),
+        ),
+        (
+            treemap!(
+                "a".to_string() => true,
+                "b".to_string() => false
+            ),
+            pretty_str!( {
+                "a": true,
+                "b": false
+            }),
+        ),
+    ]);
+
+    let complex_obj = json!({
+        "b": [
+            {"c": "\x0c\x1f\r"},
+            {"d": ""}
+        ]
+    });
+
+    test_encode_ok(&[(
+        complex_obj.clone(),
+        json_str!({
+            "b": [
+                {
+                    "c": (r#""\f\u001f\r""#)
+                },
+                {
+                    "d": ""
+                }
+            ]
+        }),
+    )]);
+
+    test_pretty_encode_ok(&[(
+        complex_obj,
+        pretty_str!({
+            "b": [
+                {
+                    "c": (r#""\f\u001f\r""#)
+                },
+                {
+                    "d": ""
+                }
+            ]
+        }),
+    )]);
+}
+
+#[test]
+fn test_write_tuple() {
+    test_encode_ok(&[((5,), "[5]")]);
+
+    test_pretty_encode_ok(&[((5,), pretty_str!([5]))]);
+
+    test_encode_ok(&[((5, (6, "abc")), "[5,[6,\"abc\"]]")]);
+
+    test_pretty_encode_ok(&[((5, (6, "abc")), pretty_str!([5, [6, "abc"]]))]);
+}
+
+#[test]
+fn test_write_enum() {
+    test_encode_ok(&[
+        (Animal::Dog, "\"Dog\""),
+        (
+            Animal::Frog("Henry".to_string(), vec![]),
+            "{\"Frog\":[\"Henry\",[]]}",
+        ),
+        (
+            Animal::Frog("Henry".to_string(), vec![349]),
+            "{\"Frog\":[\"Henry\",[349]]}",
+        ),
+        (
+            Animal::Frog("Henry".to_string(), vec![349, 102]),
+            "{\"Frog\":[\"Henry\",[349,102]]}",
+        ),
+        (
+            Animal::Cat {
+                age: 5,
+                name: "Kate".to_string(),
+            },
+            "{\"Cat\":{\"age\":5,\"name\":\"Kate\"}}",
+        ),
+        (
+            Animal::AntHive(vec!["Bob".to_string(), "Stuart".to_string()]),
+            "{\"AntHive\":[\"Bob\",\"Stuart\"]}",
+        ),
+    ]);
+
+    test_pretty_encode_ok(&[
+        (Animal::Dog, "\"Dog\""),
+        (
+            Animal::Frog("Henry".to_string(), vec![]),
+            pretty_str!({
+                "Frog": [
+                    "Henry",
+                    []
+                ]
+            }),
+        ),
+        (
+            Animal::Frog("Henry".to_string(), vec![349]),
+            pretty_str!({
+                "Frog": [
+                    "Henry",
+                    [
+                        349
+                    ]
+                ]
+            }),
+        ),
+        (
+            Animal::Frog("Henry".to_string(), vec![349, 102]),
+            pretty_str!({
+                "Frog": [
+                    "Henry",
+                    [
+                      349,
+                      102
+                    ]
+                ]
+            }),
+        ),
+    ]);
+}
+
+#[test]
+fn test_write_option() {
+    test_encode_ok(&[(None, "null"), (Some("jodhpurs"), "\"jodhpurs\"")]);
+
+    test_encode_ok(&[
+        (None, "null"),
+        (Some(vec!["foo", "bar"]), "[\"foo\",\"bar\"]"),
+    ]);
+
+    test_pretty_encode_ok(&[(None, "null"), (Some("jodhpurs"), "\"jodhpurs\"")]);
+
+    test_pretty_encode_ok(&[
+        (None, "null"),
+        (Some(vec!["foo", "bar"]), pretty_str!(["foo", "bar"])),
+    ]);
+}
+
+#[test]
+fn test_write_newtype_struct() {
+    #[derive(Serialize, PartialEq, Debug)]
+    struct Newtype(BTreeMap<String, i32>);
+
+    let inner = Newtype(treemap!(String::from("inner") => 123));
+    let outer = treemap!(String::from("outer") => to_value(&inner).unwrap());
+
+    test_encode_ok(&[(inner, r#"{"inner":123}"#)]);
+
+    test_encode_ok(&[(outer, r#"{"outer":{"inner":123}}"#)]);
+}
+
+#[test]
+fn test_deserialize_number_to_untagged_enum() {
+    #[derive(Eq, PartialEq, Deserialize, Debug)]
+    #[serde(untagged)]
+    enum E {
+        N(i64),
+    }
+
+    assert_eq!(E::N(0), E::deserialize(Number::from(0)).unwrap());
+}
+
+fn test_parse_ok<T>(tests: Vec<(&str, T)>)
+where
+    T: Clone + Debug + PartialEq + ser::Serialize + de::DeserializeOwned,
+{
+    for (s, value) in tests {
+        let v: T = from_str(s).unwrap();
+        assert_eq!(v, value.clone());
+
+        let v: T = from_slice(s.as_bytes()).unwrap();
+        assert_eq!(v, value.clone());
+
+        // Make sure we can deserialize into a `Value`.
+        let json_value: Value = from_str(s).unwrap();
+        assert_eq!(json_value, to_value(&value).unwrap());
+
+        // Make sure we can deserialize from a `&Value`.
+        let v = T::deserialize(&json_value).unwrap();
+        assert_eq!(v, value);
+
+        // Make sure we can deserialize from a `Value`.
+        let v: T = from_value(json_value.clone()).unwrap();
+        assert_eq!(v, value);
+
+        // Make sure we can round trip back to `Value`.
+        let json_value2: Value = from_value(json_value.clone()).unwrap();
+        assert_eq!(json_value2, json_value);
+
+        // Make sure we can fully ignore.
+        let twoline = s.to_owned() + "\n3735928559";
+        let mut de = Deserializer::from_str(&twoline);
+        IgnoredAny::deserialize(&mut de).unwrap();
+        assert_eq!(0xDEAD_BEEF, u64::deserialize(&mut de).unwrap());
+
+        // Make sure every prefix is an EOF error, except that a prefix of a
+        // number may be a valid number.
+        if !json_value.is_number() {
+            for (i, _) in s.trim_end().char_indices() {
+                assert!(from_str::<Value>(&s[..i]).unwrap_err().is_eof());
+                assert!(from_str::<IgnoredAny>(&s[..i]).unwrap_err().is_eof());
+            }
+        }
+    }
+}
+
+// For testing representations that the deserializer accepts but the serializer
+// never generates. These do not survive a round-trip through Value.
+fn test_parse_unusual_ok<T>(tests: Vec<(&str, T)>)
+where
+    T: Clone + Debug + PartialEq + ser::Serialize + de::DeserializeOwned,
+{
+    for (s, value) in tests {
+        let v: T = from_str(s).unwrap();
+        assert_eq!(v, value.clone());
+
+        let v: T = from_slice(s.as_bytes()).unwrap();
+        assert_eq!(v, value.clone());
+    }
+}
+
+macro_rules! test_parse_err {
+    ($name:ident::<$($ty:ty),*>($arg:expr) => $expected:expr) => {
+        let actual = $name::<$($ty),*>($arg).unwrap_err().to_string();
+        assert_eq!(actual, $expected, "unexpected {} error", stringify!($name));
+    };
+}
+
+fn test_parse_err<T>(errors: &[(&str, &'static str)])
+where
+    T: Debug + PartialEq + de::DeserializeOwned,
+{
+    for &(s, err) in errors {
+        test_parse_err!(from_str::<T>(s) => err);
+        test_parse_err!(from_slice::<T>(s.as_bytes()) => err);
+    }
+}
+
+fn test_parse_slice_err<T>(errors: &[(&[u8], &'static str)])
+where
+    T: Debug + PartialEq + de::DeserializeOwned,
+{
+    for &(s, err) in errors {
+        test_parse_err!(from_slice::<T>(s) => err);
+    }
+}
+
+fn test_fromstr_parse_err<T>(errors: &[(&str, &'static str)])
+where
+    T: Debug + PartialEq + FromStr,
+    <T as FromStr>::Err: ToString,
+{
+    for &(s, err) in errors {
+        let actual = s.parse::<T>().unwrap_err().to_string();
+        assert_eq!(actual, err, "unexpected parsing error");
+    }
+}
+
+#[test]
+fn test_parse_null() {
+    test_parse_err::<()>(&[
+        ("n", "EOF while parsing a value at line 1 column 1"),
+        ("nul", "EOF while parsing a value at line 1 column 3"),
+        ("nulla", "trailing characters at line 1 column 5"),
+    ]);
+
+    test_parse_ok(vec![("null", ())]);
+}
+
+#[test]
+fn test_parse_bool() {
+    test_parse_err::<bool>(&[
+        ("t", "EOF while parsing a value at line 1 column 1"),
+        ("truz", "expected ident at line 1 column 4"),
+        ("f", "EOF while parsing a value at line 1 column 1"),
+        ("faz", "expected ident at line 1 column 3"),
+        ("truea", "trailing characters at line 1 column 5"),
+        ("falsea", "trailing characters at line 1 column 6"),
+    ]);
+
+    test_parse_ok(vec![
+        ("true", true),
+        (" true ", true),
+        ("false", false),
+        (" false ", false),
+    ]);
+}
+
+#[test]
+fn test_parse_char() {
+    test_parse_err::<char>(&[
+        (
+            "\"ab\"",
+            "invalid value: string \"ab\", expected a character at line 1 column 4",
+        ),
+        (
+            "10",
+            "invalid type: integer `10`, expected a character at line 1 column 2",
+        ),
+    ]);
+
+    test_parse_ok(vec![
+        ("\"n\"", 'n'),
+        ("\"\\\"\"", '"'),
+        ("\"\\\\\"", '\\'),
+        ("\"/\"", '/'),
+        ("\"\\b\"", '\x08'),
+        ("\"\\f\"", '\x0C'),
+        ("\"\\n\"", '\n'),
+        ("\"\\r\"", '\r'),
+        ("\"\\t\"", '\t'),
+        ("\"\\u000b\"", '\x0B'),
+        ("\"\\u000B\"", '\x0B'),
+        ("\"\u{3A3}\"", '\u{3A3}'),
+    ]);
+}
+
+#[test]
+fn test_parse_number_errors() {
+    test_parse_err::<f64>(&[
+        ("+", "expected value at line 1 column 1"),
+        (".", "expected value at line 1 column 1"),
+        ("-", "EOF while parsing a value at line 1 column 1"),
+        ("00", "invalid number at line 1 column 2"),
+        ("0x80", "trailing characters at line 1 column 2"),
+        ("\\0", "expected value at line 1 column 1"),
+        (".0", "expected value at line 1 column 1"),
+        ("0.", "EOF while parsing a value at line 1 column 2"),
+        ("1.", "EOF while parsing a value at line 1 column 2"),
+        ("1.a", "invalid number at line 1 column 3"),
+        ("1.e1", "invalid number at line 1 column 3"),
+        ("1e", "EOF while parsing a value at line 1 column 2"),
+        ("1e+", "EOF while parsing a value at line 1 column 3"),
+        ("1a", "trailing characters at line 1 column 2"),
+        (
+            "100e777777777777777777777777777",
+            "number out of range at line 1 column 14",
+        ),
+        (
+            "-100e777777777777777777777777777",
+            "number out of range at line 1 column 15",
+        ),
+        (
+            "1000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             000000000", // 1e309
+            "number out of range at line 1 column 310",
+        ),
+        (
+            "1000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             .0e9", // 1e309
+            "number out of range at line 1 column 305",
+        ),
+        (
+            "1000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             e9", // 1e309
+            "number out of range at line 1 column 303",
+        ),
+    ]);
+}
+
+#[test]
+fn test_parse_i64() {
+    test_parse_ok(vec![
+        ("-2", -2),
+        ("-1234", -1234),
+        (" -1234 ", -1234),
+        (&i64::MIN.to_string(), i64::MIN),
+        (&i64::MAX.to_string(), i64::MAX),
+    ]);
+}
+
+#[test]
+fn test_parse_u64() {
+    test_parse_ok(vec![
+        ("0", 0u64),
+        ("3", 3u64),
+        ("1234", 1234),
+        (&u64::MAX.to_string(), u64::MAX),
+    ]);
+}
+
+#[test]
+fn test_parse_negative_zero() {
+    for negative_zero in &[
+        "-0",
+        "-0.0",
+        "-0e2",
+        "-0.0e2",
+        "-1e-400",
+        "-1e-4000000000000000000000000000000000000000000000000",
+    ] {
+        assert!(
+            from_str::<f32>(negative_zero).unwrap().is_sign_negative(),
+            "should have been negative: {:?}",
+            negative_zero,
+        );
+        assert!(
+            from_str::<f64>(negative_zero).unwrap().is_sign_negative(),
+            "should have been negative: {:?}",
+            negative_zero,
+        );
+    }
+}
+
+#[test]
+fn test_parse_f64() {
+    test_parse_ok(vec![
+        ("0.0", 0.0f64),
+        ("3.0", 3.0f64),
+        ("3.1", 3.1),
+        ("-1.2", -1.2),
+        ("0.4", 0.4),
+        // Edge case from:
+        // https://github.com/serde-rs/json/issues/536#issuecomment-583714900
+        ("2.638344616030823e-256", 2.638344616030823e-256),
+    ]);
+
+    #[cfg(not(feature = "arbitrary_precision"))]
+    test_parse_ok(vec![
+        // With arbitrary-precision enabled, this parses as Number{"3.00"}
+        // but the float is Number{"3.0"}
+        ("3.00", 3.0f64),
+        ("0.4e5", 0.4e5),
+        ("0.4e+5", 0.4e5),
+        ("0.4e15", 0.4e15),
+        ("0.4e+15", 0.4e15),
+        ("0.4e-01", 0.4e-1),
+        (" 0.4e-01 ", 0.4e-1),
+        ("0.4e-001", 0.4e-1),
+        ("0.4e-0", 0.4e0),
+        ("0.00e00", 0.0),
+        ("0.00e+00", 0.0),
+        ("0.00e-00", 0.0),
+        ("3.5E-2147483647", 0.0),
+        ("0.0100000000000000000001", 0.01),
+        (
+            &format!("{}", (i64::MIN as f64) - 1.0),
+            (i64::MIN as f64) - 1.0,
+        ),
+        (
+            &format!("{}", (u64::MAX as f64) + 1.0),
+            (u64::MAX as f64) + 1.0,
+        ),
+        (&format!("{}", f64::EPSILON), f64::EPSILON),
+        (
+            "0.0000000000000000000000000000000000000000000000000123e50",
+            1.23,
+        ),
+        ("100e-777777777777777777777777777", 0.0),
+        (
+            "1010101010101010101010101010101010101010",
+            10101010101010101010e20,
+        ),
+        (
+            "0.1010101010101010101010101010101010101010",
+            0.1010101010101010101,
+        ),
+        ("0e1000000000000000000000000000000000000000000000", 0.0),
+        (
+            "1000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             00000000",
+            1e308,
+        ),
+        (
+            "1000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             .0e8",
+            1e308,
+        ),
+        (
+            "1000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             e8",
+            1e308,
+        ),
+        (
+            "1000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000000000000000000000000000000000000000000000\
+             000000000000000000e-10",
+            1e308,
+        ),
+    ]);
+}
+
+#[test]
+fn test_value_as_f64() {
+    let v = serde_json::from_str::<Value>("1e1000");
+
+    #[cfg(not(feature = "arbitrary_precision"))]
+    assert!(v.is_err());
+
+    #[cfg(feature = "arbitrary_precision")]
+    assert_eq!(v.unwrap().as_f64(), None);
+}
+
+// Test roundtrip with some values that were not perfectly roundtripped by the
+// old f64 deserializer.
+#[cfg(feature = "float_roundtrip")]
+#[test]
+fn test_roundtrip_f64() {
+    for &float in &[
+        // Samples from quickcheck-ing roundtrip with `input: f64`. Comments
+        // indicate the value returned by the old deserializer.
+        51.24817837550540_4,  // 51.2481783755054_1
+        -93.3113703768803_3,  // -93.3113703768803_2
+        -36.5739948427534_36, // -36.5739948427534_4
+        52.31400820410624_4,  // 52.31400820410624_
+        97.4536532003468_5,   // 97.4536532003468_4
+        // Samples from `rng.next_u64` + `f64::from_bits` + `is_finite` filter.
+        2.0030397744267762e-253,
+        7.101215824554616e260,
+        1.769268377902049e74,
+        -1.6727517818542075e58,
+        3.9287532173373315e299,
+    ] {
+        let json = serde_json::to_string(&float).unwrap();
+        let output: f64 = serde_json::from_str(&json).unwrap();
+        assert_eq!(float, output);
+    }
+}
+
+#[test]
+fn test_roundtrip_f32() {
+    // This number has 1 ULP error if parsed via f64 and converted to f32.
+    // https://github.com/serde-rs/json/pull/671#issuecomment-628534468
+    let float = 7.038531e-26;
+    let json = serde_json::to_string(&float).unwrap();
+    let output: f32 = serde_json::from_str(&json).unwrap();
+    assert_eq!(float, output);
+}
+
+#[test]
+fn test_serialize_char() {
+    let value = json!(
+        ({
+            let mut map = BTreeMap::new();
+            map.insert('c', ());
+            map
+        })
+    );
+    assert_eq!(&Value::Null, value.get("c").unwrap());
+}
+
+#[cfg(feature = "arbitrary_precision")]
+#[test]
+fn test_malicious_number() {
+    #[derive(Serialize)]
+    #[serde(rename = "$serde_json::private::Number")]
+    struct S {
+        #[serde(rename = "$serde_json::private::Number")]
+        f: &'static str,
+    }
+
+    let actual = serde_json::to_value(&S { f: "not a number" })
+        .unwrap_err()
+        .to_string();
+    assert_eq!(actual, "invalid number at line 1 column 1");
+}
+
+#[test]
+fn test_parse_number() {
+    test_parse_ok(vec![
+        ("0.0", Number::from_f64(0.0f64).unwrap()),
+        ("3.0", Number::from_f64(3.0f64).unwrap()),
+        ("3.1", Number::from_f64(3.1).unwrap()),
+        ("-1.2", Number::from_f64(-1.2).unwrap()),
+        ("0.4", Number::from_f64(0.4).unwrap()),
+    ]);
+
+    test_fromstr_parse_err::<Number>(&[
+        (" 1.0", "invalid number at line 1 column 1"),
+        ("1.0 ", "invalid number at line 1 column 4"),
+        ("\t1.0", "invalid number at line 1 column 1"),
+        ("1.0\t", "invalid number at line 1 column 4"),
+    ]);
+
+    #[cfg(feature = "arbitrary_precision")]
+    test_parse_ok(vec![
+        ("1e999", Number::from_string_unchecked("1e999".to_owned())),
+        ("1e+999", Number::from_string_unchecked("1e+999".to_owned())),
+        ("-1e999", Number::from_string_unchecked("-1e999".to_owned())),
+        ("1e-999", Number::from_string_unchecked("1e-999".to_owned())),
+        ("1E999", Number::from_string_unchecked("1E999".to_owned())),
+        ("1E+999", Number::from_string_unchecked("1E+999".to_owned())),
+        ("-1E999", Number::from_string_unchecked("-1E999".to_owned())),
+        ("1E-999", Number::from_string_unchecked("1E-999".to_owned())),
+        ("1E+000", Number::from_string_unchecked("1E+000".to_owned())),
+        (
+            "2.3e999",
+            Number::from_string_unchecked("2.3e999".to_owned()),
+        ),
+        (
+            "-2.3e999",
+            Number::from_string_unchecked("-2.3e999".to_owned()),
+        ),
+    ]);
+}
+
+#[test]
+fn test_parse_string() {
+    test_parse_err::<String>(&[
+        ("\"", "EOF while parsing a string at line 1 column 1"),
+        ("\"lol", "EOF while parsing a string at line 1 column 4"),
+        ("\"lol\"a", "trailing characters at line 1 column 6"),
+        (
+            "\"\\uD83C\\uFFFF\"",
+            "lone leading surrogate in hex escape at line 1 column 13",
+        ),
+        (
+            "\"\n\"",
+            "control character (\\u0000-\\u001F) found while parsing a string at line 2 column 0",
+        ),
+        (
+            "\"\x1F\"",
+            "control character (\\u0000-\\u001F) found while parsing a string at line 1 column 2",
+        ),
+    ]);
+
+    test_parse_slice_err::<String>(&[
+        (
+            &[b'"', 159, 146, 150, b'"'],
+            "invalid unicode code point at line 1 column 5",
+        ),
+        (
+            &[b'"', b'\\', b'n', 159, 146, 150, b'"'],
+            "invalid unicode code point at line 1 column 7",
+        ),
+        (
+            &[b'"', b'\\', b'u', 48, 48, 51],
+            "EOF while parsing a string at line 1 column 6",
+        ),
+        (
+            &[b'"', b'\\', b'u', 250, 48, 51, 48, b'"'],
+            "invalid escape at line 1 column 4",
+        ),
+        (
+            &[b'"', b'\\', b'u', 48, 250, 51, 48, b'"'],
+            "invalid escape at line 1 column 5",
+        ),
+        (
+            &[b'"', b'\\', b'u', 48, 48, 250, 48, b'"'],
+            "invalid escape at line 1 column 6",
+        ),
+        (
+            &[b'"', b'\\', b'u', 48, 48, 51, 250, b'"'],
+            "invalid escape at line 1 column 7",
+        ),
+        (
+            &[b'"', b'\n', b'"'],
+            "control character (\\u0000-\\u001F) found while parsing a string at line 2 column 0",
+        ),
+        (
+            &[b'"', b'\x1F', b'"'],
+            "control character (\\u0000-\\u001F) found while parsing a string at line 1 column 2",
+        ),
+    ]);
+
+    test_parse_ok(vec![
+        ("\"\"", String::new()),
+        ("\"foo\"", "foo".to_string()),
+        (" \"foo\" ", "foo".to_string()),
+        ("\"\\\"\"", "\"".to_string()),
+        ("\"\\b\"", "\x08".to_string()),
+        ("\"\\n\"", "\n".to_string()),
+        ("\"\\r\"", "\r".to_string()),
+        ("\"\\t\"", "\t".to_string()),
+        ("\"\\u12ab\"", "\u{12ab}".to_string()),
+        ("\"\\uAB12\"", "\u{AB12}".to_string()),
+        ("\"\\uD83C\\uDF95\"", "\u{1F395}".to_string()),
+    ]);
+}
+
+#[test]
+fn test_parse_list() {
+    test_parse_err::<Vec<f64>>(&[
+        ("[", "EOF while parsing a list at line 1 column 1"),
+        ("[ ", "EOF while parsing a list at line 1 column 2"),
+        ("[1", "EOF while parsing a list at line 1 column 2"),
+        ("[1,", "EOF while parsing a value at line 1 column 3"),
+        ("[1,]", "trailing comma at line 1 column 4"),
+        ("[1 2]", "expected `,` or `]` at line 1 column 4"),
+        ("[]a", "trailing characters at line 1 column 3"),
+    ]);
+
+    test_parse_ok(vec![
+        ("[]", vec![]),
+        ("[ ]", vec![]),
+        ("[null]", vec![()]),
+        (" [ null ] ", vec![()]),
+    ]);
+
+    test_parse_ok(vec![("[true]", vec![true])]);
+
+    test_parse_ok(vec![("[3,1]", vec![3u64, 1]), (" [ 3 , 1 ] ", vec![3, 1])]);
+
+    test_parse_ok(vec![("[[3], [1, 2]]", vec![vec![3u64], vec![1, 2]])]);
+
+    test_parse_ok(vec![("[1]", (1u64,))]);
+
+    test_parse_ok(vec![("[1, 2]", (1u64, 2u64))]);
+
+    test_parse_ok(vec![("[1, 2, 3]", (1u64, 2u64, 3u64))]);
+
+    test_parse_ok(vec![("[1, [2, 3]]", (1u64, (2u64, 3u64)))]);
+}
+
+#[test]
+fn test_parse_object() {
+    test_parse_err::<BTreeMap<String, u32>>(&[
+        ("{", "EOF while parsing an object at line 1 column 1"),
+        ("{ ", "EOF while parsing an object at line 1 column 2"),
+        ("{1", "key must be a string at line 1 column 2"),
+        ("{ \"a\"", "EOF while parsing an object at line 1 column 5"),
+        ("{\"a\"", "EOF while parsing an object at line 1 column 4"),
+        ("{\"a\" ", "EOF while parsing an object at line 1 column 5"),
+        ("{\"a\" 1", "expected `:` at line 1 column 6"),
+        ("{\"a\":", "EOF while parsing a value at line 1 column 5"),
+        ("{\"a\":1", "EOF while parsing an object at line 1 column 6"),
+        ("{\"a\":1 1", "expected `,` or `}` at line 1 column 8"),
+        ("{\"a\":1,", "EOF while parsing a value at line 1 column 7"),
+        ("{}a", "trailing characters at line 1 column 3"),
+    ]);
+
+    test_parse_ok(vec![
+        ("{}", treemap!()),
+        ("{ }", treemap!()),
+        ("{\"a\":3}", treemap!("a".to_string() => 3u64)),
+        ("{ \"a\" : 3 }", treemap!("a".to_string() => 3)),
+        (
+            "{\"a\":3,\"b\":4}",
+            treemap!("a".to_string() => 3, "b".to_string() => 4),
+        ),
+        (
+            " { \"a\" : 3 , \"b\" : 4 } ",
+            treemap!("a".to_string() => 3, "b".to_string() => 4),
+        ),
+    ]);
+
+    test_parse_ok(vec![(
+        "{\"a\": {\"b\": 3, \"c\": 4}}",
+        treemap!(
+            "a".to_string() => treemap!(
+                "b".to_string() => 3u64,
+                "c".to_string() => 4
+            )
+        ),
+    )]);
+
+    test_parse_ok(vec![("{\"c\":null}", treemap!('c' => ()))]);
+}
+
+#[test]
+fn test_parse_struct() {
+    test_parse_err::<Outer>(&[
+        (
+            "5",
+            "invalid type: integer `5`, expected struct Outer at line 1 column 1",
+        ),
+        (
+            "\"hello\"",
+            "invalid type: string \"hello\", expected struct Outer at line 1 column 7",
+        ),
+        (
+            "{\"inner\": true}",
+            "invalid type: boolean `true`, expected a sequence at line 1 column 14",
+        ),
+        ("{}", "missing field `inner` at line 1 column 2"),
+        (
+            r#"{"inner": [{"b": 42, "c": []}]}"#,
+            "missing field `a` at line 1 column 29",
+        ),
+    ]);
+
+    test_parse_ok(vec![
+        (
+            "{
+                \"inner\": []
+            }",
+            Outer { inner: vec![] },
+        ),
+        (
+            "{
+                \"inner\": [
+                    { \"a\": null, \"b\": 2, \"c\": [\"abc\", \"xyz\"] }
+                ]
+            }",
+            Outer {
+                inner: vec![Inner {
+                    a: (),
+                    b: 2,
+                    c: vec!["abc".to_string(), "xyz".to_string()],
+                }],
+            },
+        ),
+    ]);
+
+    let v: Outer = from_str(
+        "[
+            [
+                [ null, 2, [\"abc\", \"xyz\"] ]
+            ]
+        ]",
+    )
+    .unwrap();
+
+    assert_eq!(
+        v,
+        Outer {
+            inner: vec![Inner {
+                a: (),
+                b: 2,
+                c: vec!["abc".to_string(), "xyz".to_string()],
+            }],
+        }
+    );
+
+    let j = json!([null, 2, []]);
+    Inner::deserialize(&j).unwrap();
+    Inner::deserialize(j).unwrap();
+}
+
+#[test]
+fn test_parse_option() {
+    test_parse_ok(vec![
+        ("null", None::<String>),
+        ("\"jodhpurs\"", Some("jodhpurs".to_string())),
+    ]);
+
+    #[derive(Clone, Debug, PartialEq, Serialize, Deserialize)]
+    struct Foo {
+        x: Option<isize>,
+    }
+
+    let value: Foo = from_str("{}").unwrap();
+    assert_eq!(value, Foo { x: None });
+
+    test_parse_ok(vec![
+        ("{\"x\": null}", Foo { x: None }),
+        ("{\"x\": 5}", Foo { x: Some(5) }),
+    ]);
+}
+
+#[test]
+fn test_parse_enum_errors() {
+    test_parse_err::<Animal>(
+        &[
+            ("{}", "expected value at line 1 column 2"),
+            ("[]", "expected value at line 1 column 1"),
+            ("\"unknown\"",
+             "unknown variant `unknown`, expected one of `Dog`, `Frog`, `Cat`, `AntHive` at line 1 column 9"),
+            ("{\"unknown\":null}",
+             "unknown variant `unknown`, expected one of `Dog`, `Frog`, `Cat`, `AntHive` at line 1 column 10"),
+            ("{\"Dog\":", "EOF while parsing a value at line 1 column 7"),
+            ("{\"Dog\":}", "expected value at line 1 column 8"),
+            ("{\"Dog\":{}}", "invalid type: map, expected unit at line 1 column 7"),
+            ("\"Frog\"", "invalid type: unit variant, expected tuple variant"),
+            ("\"Frog\" 0 ", "invalid type: unit variant, expected tuple variant"),
+            ("{\"Frog\":{}}",
+             "invalid type: map, expected tuple variant Animal::Frog at line 1 column 8"),
+            ("{\"Cat\":[]}", "invalid length 0, expected struct variant Animal::Cat with 2 elements at line 1 column 9"),
+            ("{\"Cat\":[0]}", "invalid length 1, expected struct variant Animal::Cat with 2 elements at line 1 column 10"),
+            ("{\"Cat\":[0, \"\", 2]}", "trailing characters at line 1 column 16"),
+            ("{\"Cat\":{\"age\": 5, \"name\": \"Kate\", \"foo\":\"bar\"}",
+             "unknown field `foo`, expected `age` or `name` at line 1 column 39"),
+
+            // JSON does not allow trailing commas in data structures
+            ("{\"Cat\":[0, \"Kate\",]}", "trailing comma at line 1 column 19"),
+            ("{\"Cat\":{\"age\": 2, \"name\": \"Kate\",}}",
+             "trailing comma at line 1 column 34"),
+        ],
+    );
+}
+
+#[test]
+fn test_parse_enum() {
+    test_parse_ok(vec![
+        ("\"Dog\"", Animal::Dog),
+        (" \"Dog\" ", Animal::Dog),
+        (
+            "{\"Frog\":[\"Henry\",[]]}",
+            Animal::Frog("Henry".to_string(), vec![]),
+        ),
+        (
+            " { \"Frog\": [ \"Henry\" , [ 349, 102 ] ] } ",
+            Animal::Frog("Henry".to_string(), vec![349, 102]),
+        ),
+        (
+            "{\"Cat\": {\"age\": 5, \"name\": \"Kate\"}}",
+            Animal::Cat {
+                age: 5,
+                name: "Kate".to_string(),
+            },
+        ),
+        (
+            " { \"Cat\" : { \"age\" : 5 , \"name\" : \"Kate\" } } ",
+            Animal::Cat {
+                age: 5,
+                name: "Kate".to_string(),
+            },
+        ),
+        (
+            " { \"AntHive\" : [\"Bob\", \"Stuart\"] } ",
+            Animal::AntHive(vec!["Bob".to_string(), "Stuart".to_string()]),
+        ),
+    ]);
+
+    test_parse_unusual_ok(vec![
+        ("{\"Dog\":null}", Animal::Dog),
+        (" { \"Dog\" : null } ", Animal::Dog),
+    ]);
+
+    test_parse_ok(vec![(
+        concat!(
+            "{",
+            "  \"a\": \"Dog\",",
+            "  \"b\": {\"Frog\":[\"Henry\", []]}",
+            "}"
+        ),
+        treemap!(
+            "a".to_string() => Animal::Dog,
+            "b".to_string() => Animal::Frog("Henry".to_string(), vec![])
+        ),
+    )]);
+}
+
+#[test]
+fn test_parse_trailing_whitespace() {
+    test_parse_ok(vec![
+        ("[1, 2] ", vec![1u64, 2]),
+        ("[1, 2]\n", vec![1, 2]),
+        ("[1, 2]\t", vec![1, 2]),
+        ("[1, 2]\t \n", vec![1, 2]),
+    ]);
+}
+
+#[test]
+fn test_multiline_errors() {
+    test_parse_err::<BTreeMap<String, String>>(&[(
+        "{\n  \"foo\":\n \"bar\"",
+        "EOF while parsing an object at line 3 column 6",
+    )]);
+}
+
+#[test]
+fn test_missing_option_field() {
+    #[derive(Debug, PartialEq, Deserialize)]
+    struct Foo {
+        x: Option<u32>,
+    }
+
+    let value: Foo = from_str("{}").unwrap();
+    assert_eq!(value, Foo { x: None });
+
+    let value: Foo = from_str("{\"x\": 5}").unwrap();
+    assert_eq!(value, Foo { x: Some(5) });
+
+    let value: Foo = from_value(json!({})).unwrap();
+    assert_eq!(value, Foo { x: None });
+
+    let value: Foo = from_value(json!({"x": 5})).unwrap();
+    assert_eq!(value, Foo { x: Some(5) });
+}
+
+#[test]
+fn test_missing_nonoption_field() {
+    #[derive(Debug, PartialEq, Deserialize)]
+    struct Foo {
+        x: u32,
+    }
+
+    test_parse_err::<Foo>(&[("{}", "missing field `x` at line 1 column 2")]);
+}
+
+#[test]
+fn test_missing_renamed_field() {
+    #[derive(Debug, PartialEq, Deserialize)]
+    struct Foo {
+        #[serde(rename = "y")]
+        x: Option<u32>,
+    }
+
+    let value: Foo = from_str("{}").unwrap();
+    assert_eq!(value, Foo { x: None });
+
+    let value: Foo = from_str("{\"y\": 5}").unwrap();
+    assert_eq!(value, Foo { x: Some(5) });
+
+    let value: Foo = from_value(json!({})).unwrap();
+    assert_eq!(value, Foo { x: None });
+
+    let value: Foo = from_value(json!({"y": 5})).unwrap();
+    assert_eq!(value, Foo { x: Some(5) });
+}
+
+#[test]
+fn test_serialize_seq_with_no_len() {
+    #[derive(Clone, Debug, PartialEq)]
+    struct MyVec<T>(Vec<T>);
+
+    impl<T> ser::Serialize for MyVec<T>
+    where
+        T: ser::Serialize,
+    {
+        #[inline]
+        fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+        where
+            S: ser::Serializer,
+        {
+            let mut seq = serializer.serialize_seq(None)?;
+            for elem in &self.0 {
+                seq.serialize_element(elem)?;
+            }
+            seq.end()
+        }
+    }
+
+    struct Visitor<T> {
+        marker: PhantomData<MyVec<T>>,
+    }
+
+    impl<'de, T> de::Visitor<'de> for Visitor<T>
+    where
+        T: de::Deserialize<'de>,
+    {
+        type Value = MyVec<T>;
+
+        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+            formatter.write_str("array")
+        }
+
+        #[inline]
+        fn visit_unit<E>(self) -> Result<MyVec<T>, E>
+        where
+            E: de::Error,
+        {
+            Ok(MyVec(Vec::new()))
+        }
+
+        #[inline]
+        fn visit_seq<V>(self, mut visitor: V) -> Result<MyVec<T>, V::Error>
+        where
+            V: de::SeqAccess<'de>,
+        {
+            let mut values = Vec::new();
+
+            while let Some(value) = visitor.next_element()? {
+                values.push(value);
+            }
+
+            Ok(MyVec(values))
+        }
+    }
+
+    impl<'de, T> de::Deserialize<'de> for MyVec<T>
+    where
+        T: de::Deserialize<'de>,
+    {
+        fn deserialize<D>(deserializer: D) -> Result<MyVec<T>, D::Error>
+        where
+            D: de::Deserializer<'de>,
+        {
+            deserializer.deserialize_map(Visitor {
+                marker: PhantomData,
+            })
+        }
+    }
+
+    let mut vec = Vec::new();
+    vec.push(MyVec(Vec::new()));
+    vec.push(MyVec(Vec::new()));
+    let vec: MyVec<MyVec<u32>> = MyVec(vec);
+
+    test_encode_ok(&[(vec.clone(), "[[],[]]")]);
+
+    let s = to_string_pretty(&vec).unwrap();
+    let expected = pretty_str!([[], []]);
+    assert_eq!(s, expected);
+}
+
+#[test]
+fn test_serialize_map_with_no_len() {
+    #[derive(Clone, Debug, PartialEq)]
+    struct MyMap<K, V>(BTreeMap<K, V>);
+
+    impl<K, V> ser::Serialize for MyMap<K, V>
+    where
+        K: ser::Serialize + Ord,
+        V: ser::Serialize,
+    {
+        #[inline]
+        fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+        where
+            S: ser::Serializer,
+        {
+            let mut map = serializer.serialize_map(None)?;
+            for (k, v) in &self.0 {
+                map.serialize_entry(k, v)?;
+            }
+            map.end()
+        }
+    }
+
+    struct Visitor<K, V> {
+        marker: PhantomData<MyMap<K, V>>,
+    }
+
+    impl<'de, K, V> de::Visitor<'de> for Visitor<K, V>
+    where
+        K: de::Deserialize<'de> + Eq + Ord,
+        V: de::Deserialize<'de>,
+    {
+        type Value = MyMap<K, V>;
+
+        fn expecting(&self, formatter: &mut fmt::Formatter) -> fmt::Result {
+            formatter.write_str("map")
+        }
+
+        #[inline]
+        fn visit_unit<E>(self) -> Result<MyMap<K, V>, E>
+        where
+            E: de::Error,
+        {
+            Ok(MyMap(BTreeMap::new()))
+        }
+
+        #[inline]
+        fn visit_map<Visitor>(self, mut visitor: Visitor) -> Result<MyMap<K, V>, Visitor::Error>
+        where
+            Visitor: de::MapAccess<'de>,
+        {
+            let mut values = BTreeMap::new();
+
+            while let Some((key, value)) = visitor.next_entry()? {
+                values.insert(key, value);
+            }
+
+            Ok(MyMap(values))
+        }
+    }
+
+    impl<'de, K, V> de::Deserialize<'de> for MyMap<K, V>
+    where
+        K: de::Deserialize<'de> + Eq + Ord,
+        V: de::Deserialize<'de>,
+    {
+        fn deserialize<D>(deserializer: D) -> Result<MyMap<K, V>, D::Error>
+        where
+            D: de::Deserializer<'de>,
+        {
+            deserializer.deserialize_map(Visitor {
+                marker: PhantomData,
+            })
+        }
+    }
+
+    let mut map = BTreeMap::new();
+    map.insert("a", MyMap(BTreeMap::new()));
+    map.insert("b", MyMap(BTreeMap::new()));
+    let map: MyMap<_, MyMap<u32, u32>> = MyMap(map);
+
+    test_encode_ok(&[(map.clone(), "{\"a\":{},\"b\":{}}")]);
+
+    let s = to_string_pretty(&map).unwrap();
+    let expected = pretty_str!({
+        "a": {},
+        "b": {}
+    });
+    assert_eq!(s, expected);
+}
+
+#[cfg(not(miri))]
+#[test]
+fn test_deserialize_from_stream() {
+    use serde_json::to_writer;
+    use std::net::{TcpListener, TcpStream};
+    use std::thread;
+
+    #[derive(Debug, PartialEq, Serialize, Deserialize)]
+    struct Message {
+        message: String,
+    }
+
+    let l = TcpListener::bind("localhost:20000").unwrap();
+
+    thread::spawn(|| {
+        let l = l;
+        for stream in l.incoming() {
+            let mut stream = stream.unwrap();
+            let read_stream = stream.try_clone().unwrap();
+
+            let mut de = Deserializer::from_reader(read_stream);
+            let request = Message::deserialize(&mut de).unwrap();
+            let response = Message {
+                message: request.message,
+            };
+            to_writer(&mut stream, &response).unwrap();
+        }
+    });
+
+    let mut stream = TcpStream::connect("localhost:20000").unwrap();
+    let request = Message {
+        message: "hi there".to_string(),
+    };
+    to_writer(&mut stream, &request).unwrap();
+
+    let mut de = Deserializer::from_reader(stream);
+    let response = Message::deserialize(&mut de).unwrap();
+
+    assert_eq!(request, response);
+}
+
+#[test]
+fn test_serialize_rejects_bool_keys() {
+    let map = treemap!(
+        true => 2,
+        false => 4
+    );
+
+    let err = to_vec(&map).unwrap_err();
+    assert_eq!(err.to_string(), "key must be a string");
+}
+
+#[test]
+fn test_serialize_rejects_adt_keys() {
+    let map = treemap!(
+        Some("a") => 2,
+        Some("b") => 4,
+        None => 6
+    );
+
+    let err = to_vec(&map).unwrap_err();
+    assert_eq!(err.to_string(), "key must be a string");
+}
+
+#[test]
+fn test_bytes_ser() {
+    let buf = vec![];
+    let bytes = Bytes::new(&buf);
+    assert_eq!(to_string(&bytes).unwrap(), "[]".to_string());
+
+    let buf = vec![1, 2, 3];
+    let bytes = Bytes::new(&buf);
+    assert_eq!(to_string(&bytes).unwrap(), "[1,2,3]".to_string());
+}
+
+#[test]
+fn test_byte_buf_ser() {
+    let bytes = ByteBuf::new();
+    assert_eq!(to_string(&bytes).unwrap(), "[]".to_string());
+
+    let bytes = ByteBuf::from(vec![1, 2, 3]);
+    assert_eq!(to_string(&bytes).unwrap(), "[1,2,3]".to_string());
+}
+
+#[test]
+fn test_byte_buf_de() {
+    let bytes = ByteBuf::new();
+    let v: ByteBuf = from_str("[]").unwrap();
+    assert_eq!(v, bytes);
+
+    let bytes = ByteBuf::from(vec![1, 2, 3]);
+    let v: ByteBuf = from_str("[1, 2, 3]").unwrap();
+    assert_eq!(v, bytes);
+}
+
+#[test]
+fn test_byte_buf_de_lone_surrogate() {
+    let bytes = ByteBuf::from(vec![237, 160, 188]);
+    let v: ByteBuf = from_str(r#""\ud83c""#).unwrap();
+    assert_eq!(v, bytes);
+
+    let bytes = ByteBuf::from(vec![237, 160, 188, 10]);
+    let v: ByteBuf = from_str(r#""\ud83c\n""#).unwrap();
+    assert_eq!(v, bytes);
+
+    let bytes = ByteBuf::from(vec![237, 160, 188, 32]);
+    let v: ByteBuf = from_str(r#""\ud83c ""#).unwrap();
+    assert_eq!(v, bytes);
+
+    let bytes = ByteBuf::from(vec![237, 176, 129]);
+    let v: ByteBuf = from_str(r#""\udc01""#).unwrap();
+    assert_eq!(v, bytes);
+
+    let res = from_str::<ByteBuf>(r#""\ud83c\!""#);
+    assert!(res.is_err());
+
+    let res = from_str::<ByteBuf>(r#""\ud83c\u""#);
+    assert!(res.is_err());
+
+    let res = from_str::<ByteBuf>(r#""\ud83c\ud83c""#);
+    assert!(res.is_err());
+}
+
+#[cfg(feature = "raw_value")]
+#[test]
+fn test_raw_de_lone_surrogate() {
+    use serde_json::value::RawValue;
+
+    assert!(from_str::<Box<RawValue>>(r#""\ud83c""#).is_ok());
+    assert!(from_str::<Box<RawValue>>(r#""\ud83c\n""#).is_ok());
+    assert!(from_str::<Box<RawValue>>(r#""\ud83c ""#).is_ok());
+    assert!(from_str::<Box<RawValue>>(r#""\udc01 ""#).is_ok());
+    assert!(from_str::<Box<RawValue>>(r#""\udc01\!""#).is_err());
+    assert!(from_str::<Box<RawValue>>(r#""\udc01\u""#).is_err());
+    assert!(from_str::<Box<RawValue>>(r#""\ud83c\ud83c""#).is_ok());
+}
+
+#[test]
+fn test_byte_buf_de_multiple() {
+    let s: Vec<ByteBuf> = from_str(r#"["ab\nc", "cd\ne"]"#).unwrap();
+    let a = ByteBuf::from(b"ab\nc".to_vec());
+    let b = ByteBuf::from(b"cd\ne".to_vec());
+    assert_eq!(vec![a, b], s);
+}
+
+#[test]
+fn test_json_pointer() {
+    // Test case taken from https://tools.ietf.org/html/rfc6901#page-5
+    let data: Value = from_str(
+        r#"{
+        "foo": ["bar", "baz"],
+        "": 0,
+        "a/b": 1,
+        "c%d": 2,
+        "e^f": 3,
+        "g|h": 4,
+        "i\\j": 5,
+        "k\"l": 6,
+        " ": 7,
+        "m~n": 8
+    }"#,
+    )
+    .unwrap();
+    assert_eq!(data.pointer("").unwrap(), &data);
+    assert_eq!(data.pointer("/foo").unwrap(), &json!(["bar", "baz"]));
+    assert_eq!(data.pointer("/foo/0").unwrap(), &json!("bar"));
+    assert_eq!(data.pointer("/").unwrap(), &json!(0));
+    assert_eq!(data.pointer("/a~1b").unwrap(), &json!(1));
+    assert_eq!(data.pointer("/c%d").unwrap(), &json!(2));
+    assert_eq!(data.pointer("/e^f").unwrap(), &json!(3));
+    assert_eq!(data.pointer("/g|h").unwrap(), &json!(4));
+    assert_eq!(data.pointer("/i\\j").unwrap(), &json!(5));
+    assert_eq!(data.pointer("/k\"l").unwrap(), &json!(6));
+    assert_eq!(data.pointer("/ ").unwrap(), &json!(7));
+    assert_eq!(data.pointer("/m~0n").unwrap(), &json!(8));
+    // Invalid pointers
+    assert!(data.pointer("/unknown").is_none());
+    assert!(data.pointer("/e^f/ertz").is_none());
+    assert!(data.pointer("/foo/00").is_none());
+    assert!(data.pointer("/foo/01").is_none());
+}
+
+#[test]
+fn test_json_pointer_mut() {
+    // Test case taken from https://tools.ietf.org/html/rfc6901#page-5
+    let mut data: Value = from_str(
+        r#"{
+        "foo": ["bar", "baz"],
+        "": 0,
+        "a/b": 1,
+        "c%d": 2,
+        "e^f": 3,
+        "g|h": 4,
+        "i\\j": 5,
+        "k\"l": 6,
+        " ": 7,
+        "m~n": 8
+    }"#,
+    )
+    .unwrap();
+
+    // Basic pointer checks
+    assert_eq!(data.pointer_mut("/foo").unwrap(), &json!(["bar", "baz"]));
+    assert_eq!(data.pointer_mut("/foo/0").unwrap(), &json!("bar"));
+    assert_eq!(data.pointer_mut("/").unwrap(), 0);
+    assert_eq!(data.pointer_mut("/a~1b").unwrap(), 1);
+    assert_eq!(data.pointer_mut("/c%d").unwrap(), 2);
+    assert_eq!(data.pointer_mut("/e^f").unwrap(), 3);
+    assert_eq!(data.pointer_mut("/g|h").unwrap(), 4);
+    assert_eq!(data.pointer_mut("/i\\j").unwrap(), 5);
+    assert_eq!(data.pointer_mut("/k\"l").unwrap(), 6);
+    assert_eq!(data.pointer_mut("/ ").unwrap(), 7);
+    assert_eq!(data.pointer_mut("/m~0n").unwrap(), 8);
+
+    // Invalid pointers
+    assert!(data.pointer_mut("/unknown").is_none());
+    assert!(data.pointer_mut("/e^f/ertz").is_none());
+    assert!(data.pointer_mut("/foo/00").is_none());
+    assert!(data.pointer_mut("/foo/01").is_none());
+
+    // Mutable pointer checks
+    *data.pointer_mut("/").unwrap() = 100.into();
+    assert_eq!(data.pointer("/").unwrap(), 100);
+    *data.pointer_mut("/foo/0").unwrap() = json!("buzz");
+    assert_eq!(data.pointer("/foo/0").unwrap(), &json!("buzz"));
+
+    // Example of ownership stealing
+    assert_eq!(
+        data.pointer_mut("/a~1b")
+            .map(|m| mem::replace(m, json!(null)))
+            .unwrap(),
+        1
+    );
+    assert_eq!(data.pointer("/a~1b").unwrap(), &json!(null));
+
+    // Need to compare against a clone so we don't anger the borrow checker
+    // by taking out two references to a mutable value
+    let mut d2 = data.clone();
+    assert_eq!(data.pointer_mut("").unwrap(), &mut d2);
+}
+
+#[test]
+fn test_stack_overflow() {
+    let brackets: String = iter::repeat('[')
+        .take(127)
+        .chain(iter::repeat(']').take(127))
+        .collect();
+    let _: Value = from_str(&brackets).unwrap();
+
+    let brackets = "[".repeat(129);
+    test_parse_err::<Value>(&[(&brackets, "recursion limit exceeded at line 1 column 128")]);
+}
+
+#[test]
+#[cfg(feature = "unbounded_depth")]
+fn test_disable_recursion_limit() {
+    let brackets: String = iter::repeat('[')
+        .take(140)
+        .chain(iter::repeat(']').take(140))
+        .collect();
+
+    let mut deserializer = Deserializer::from_str(&brackets);
+    deserializer.disable_recursion_limit();
+    Value::deserialize(&mut deserializer).unwrap();
+}
+
+#[test]
+fn test_integer_key() {
+    // map with integer keys
+    let map = treemap!(
+        1 => 2,
+        -1 => 6
+    );
+    let j = r#"{"-1":6,"1":2}"#;
+    test_encode_ok(&[(&map, j)]);
+    test_parse_ok(vec![(j, map)]);
+
+    let j = r#"{"x":null}"#;
+    test_parse_err::<BTreeMap<i32, ()>>(&[(
+        j,
+        "invalid type: string \"x\", expected i32 at line 1 column 4",
+    )]);
+}
+
+#[test]
+fn test_integer128_key() {
+    let map = treemap! {
+        100000000000000000000000000000000000000u128 => ()
+    };
+    let j = r#"{"100000000000000000000000000000000000000":null}"#;
+    assert_eq!(to_string(&map).unwrap(), j);
+    assert_eq!(from_str::<BTreeMap<u128, ()>>(j).unwrap(), map);
+}
+
+#[test]
+fn test_deny_float_key() {
+    #[derive(Eq, PartialEq, Ord, PartialOrd)]
+    struct Float;
+    impl Serialize for Float {
+        fn serialize<S>(&self, serializer: S) -> Result<S::Ok, S::Error>
+        where
+            S: Serializer,
+        {
+            serializer.serialize_f32(1.0)
+        }
+    }
+
+    // map with float key
+    let map = treemap!(Float => "x");
+    assert!(serde_json::to_value(map).is_err());
+}
+
+#[test]
+fn test_borrowed_key() {
+    let map: BTreeMap<&str, ()> = from_str("{\"borrowed\":null}").unwrap();
+    let expected = treemap! { "borrowed" => () };
+    assert_eq!(map, expected);
+
+    #[derive(Deserialize, Debug, Ord, PartialOrd, Eq, PartialEq)]
+    struct NewtypeStr<'a>(&'a str);
+
+    let map: BTreeMap<NewtypeStr, ()> = from_str("{\"borrowed\":null}").unwrap();
+    let expected = treemap! { NewtypeStr("borrowed") => () };
+    assert_eq!(map, expected);
+}
+
+#[test]
+fn test_effectively_string_keys() {
+    #[derive(Eq, PartialEq, Ord, PartialOrd, Debug, Clone, Serialize, Deserialize)]
+    enum Enum {
+        One,
+        Two,
+    }
+    let map = treemap! {
+        Enum::One => 1,
+        Enum::Two => 2
+    };
+    let expected = r#"{"One":1,"Two":2}"#;
+    test_encode_ok(&[(&map, expected)]);
+    test_parse_ok(vec![(expected, map)]);
+
+    #[derive(Eq, PartialEq, Ord, PartialOrd, Debug, Clone, Serialize, Deserialize)]
+    struct Wrapper(String);
+    let map = treemap! {
+        Wrapper("zero".to_owned()) => 0,
+        Wrapper("one".to_owned()) => 1
+    };
+    let expected = r#"{"one":1,"zero":0}"#;
+    test_encode_ok(&[(&map, expected)]);
+    test_parse_ok(vec![(expected, map)]);
+}
+
+#[test]
+fn test_json_macro() {
+    // This is tricky because the <...> is not a single TT and the comma inside
+    // looks like an array element separator.
+    let _ = json!([
+        <Result<(), ()> as Clone>::clone(&Ok(())),
+        <Result<(), ()> as Clone>::clone(&Err(()))
+    ]);
+
+    // Same thing but in the map values.
+    let _ = json!({
+        "ok": <Result<(), ()> as Clone>::clone(&Ok(())),
+        "err": <Result<(), ()> as Clone>::clone(&Err(()))
+    });
+
+    // It works in map keys but only if they are parenthesized.
+    let _ = json!({
+        (<Result<&str, ()> as Clone>::clone(&Ok("")).unwrap()): "ok",
+        (<Result<(), &str> as Clone>::clone(&Err("")).unwrap_err()): "err"
+    });
+
+    #[deny(unused_results)]
+    let _ = json!({ "architecture": [true, null] });
+}
+
+#[test]
+fn issue_220() {
+    #[derive(Debug, PartialEq, Eq, Deserialize)]
+    enum E {
+        V(u8),
+    }
+
+    assert!(from_str::<E>(r#" "V"0 "#).is_err());
+
+    assert_eq!(from_str::<E>(r#"{"V": 0}"#).unwrap(), E::V(0));
+}
+
+macro_rules! number_partialeq_ok {
+    ($($n:expr)*) => {
+        $(
+            let value = to_value($n).unwrap();
+            let s = $n.to_string();
+            assert_eq!(value, $n);
+            assert_eq!($n, value);
+            assert_ne!(value, s);
+        )*
+    }
+}
+
+#[test]
+fn test_partialeq_number() {
+    number_partialeq_ok!(0 1 100
+        i8::MIN i8::MAX i16::MIN i16::MAX i32::MIN i32::MAX i64::MIN i64::MAX
+        u8::MIN u8::MAX u16::MIN u16::MAX u32::MIN u32::MAX u64::MIN u64::MAX
+        f32::MIN f32::MAX f32::MIN_EXP f32::MAX_EXP f32::MIN_POSITIVE
+        f64::MIN f64::MAX f64::MIN_EXP f64::MAX_EXP f64::MIN_POSITIVE
+        f32::consts::E f32::consts::PI f32::consts::LN_2 f32::consts::LOG2_E
+        f64::consts::E f64::consts::PI f64::consts::LN_2 f64::consts::LOG2_E
+    );
+}
+
+#[test]
+#[cfg(integer128)]
+#[cfg(feature = "arbitrary_precision")]
+fn test_partialeq_integer128() {
+    number_partialeq_ok!(i128::MIN i128::MAX u128::MIN u128::MAX)
+}
+
+#[test]
+fn test_partialeq_string() {
+    let v = to_value("42").unwrap();
+    assert_eq!(v, "42");
+    assert_eq!("42", v);
+    assert_ne!(v, 42);
+    assert_eq!(v, String::from("42"));
+    assert_eq!(String::from("42"), v);
+}
+
+#[test]
+fn test_partialeq_bool() {
+    let v = to_value(true).unwrap();
+    assert_eq!(v, true);
+    assert_eq!(true, v);
+    assert_ne!(v, false);
+    assert_ne!(v, "true");
+    assert_ne!(v, 1);
+    assert_ne!(v, 0);
+}
+
+struct FailReader(io::ErrorKind);
+
+impl io::Read for FailReader {
+    fn read(&mut self, _: &mut [u8]) -> io::Result<usize> {
+        Err(io::Error::new(self.0, "oh no!"))
+    }
+}
+
+#[test]
+fn test_category() {
+    assert!(from_str::<String>("123").unwrap_err().is_data());
+
+    assert!(from_str::<String>("]").unwrap_err().is_syntax());
+
+    assert!(from_str::<String>("").unwrap_err().is_eof());
+    assert!(from_str::<String>("\"").unwrap_err().is_eof());
+    assert!(from_str::<String>("\"\\").unwrap_err().is_eof());
+    assert!(from_str::<String>("\"\\u").unwrap_err().is_eof());
+    assert!(from_str::<String>("\"\\u0").unwrap_err().is_eof());
+    assert!(from_str::<String>("\"\\u00").unwrap_err().is_eof());
+    assert!(from_str::<String>("\"\\u000").unwrap_err().is_eof());
+
+    assert!(from_str::<Vec<usize>>("[").unwrap_err().is_eof());
+    assert!(from_str::<Vec<usize>>("[0").unwrap_err().is_eof());
+    assert!(from_str::<Vec<usize>>("[0,").unwrap_err().is_eof());
+
+    assert!(from_str::<BTreeMap<String, usize>>("{")
+        .unwrap_err()
+        .is_eof());
+    assert!(from_str::<BTreeMap<String, usize>>("{\"k\"")
+        .unwrap_err()
+        .is_eof());
+    assert!(from_str::<BTreeMap<String, usize>>("{\"k\":")
+        .unwrap_err()
+        .is_eof());
+    assert!(from_str::<BTreeMap<String, usize>>("{\"k\":0")
+        .unwrap_err()
+        .is_eof());
+    assert!(from_str::<BTreeMap<String, usize>>("{\"k\":0,")
+        .unwrap_err()
+        .is_eof());
+
+    let fail = FailReader(io::ErrorKind::NotConnected);
+    assert!(from_reader::<_, String>(fail).unwrap_err().is_io());
+}
+
+#[test]
+// Clippy false positive: https://github.com/Manishearth/rust-clippy/issues/292
+#[allow(clippy::needless_lifetimes)]
+fn test_into_io_error() {
+    fn io_error<'de, T: Deserialize<'de> + Debug>(j: &'static str) -> io::Error {
+        from_str::<T>(j).unwrap_err().into()
+    }
+
+    assert_eq!(
+        io_error::<String>("\"\\u").kind(),
+        io::ErrorKind::UnexpectedEof
+    );
+    assert_eq!(io_error::<String>("0").kind(), io::ErrorKind::InvalidData);
+    assert_eq!(io_error::<String>("]").kind(), io::ErrorKind::InvalidData);
+
+    let fail = FailReader(io::ErrorKind::NotConnected);
+    let io_err: io::Error = from_reader::<_, u8>(fail).unwrap_err().into();
+    assert_eq!(io_err.kind(), io::ErrorKind::NotConnected);
+}
+
+#[test]
+fn test_borrow() {
+    let s: &str = from_str("\"borrowed\"").unwrap();
+    assert_eq!("borrowed", s);
+
+    let s: &str = from_slice(b"\"borrowed\"").unwrap();
+    assert_eq!("borrowed", s);
+}
+
+#[test]
+fn null_invalid_type() {
+    let err = serde_json::from_str::<String>("null").unwrap_err();
+    assert_eq!(
+        format!("{}", err),
+        String::from("invalid type: null, expected a string at line 1 column 4")
+    );
+}
+
+#[test]
+fn test_integer128() {
+    let signed = &[i128::min_value(), -1, 0, 1, i128::max_value()];
+    let unsigned = &[0, 1, u128::max_value()];
+
+    for integer128 in signed {
+        let expected = integer128.to_string();
+        assert_eq!(to_string(integer128).unwrap(), expected);
+        assert_eq!(from_str::<i128>(&expected).unwrap(), *integer128);
+    }
+
+    for integer128 in unsigned {
+        let expected = integer128.to_string();
+        assert_eq!(to_string(integer128).unwrap(), expected);
+        assert_eq!(from_str::<u128>(&expected).unwrap(), *integer128);
+    }
+
+    test_parse_err::<i128>(&[
+        (
+            "-170141183460469231731687303715884105729",
+            "number out of range at line 1 column 40",
+        ),
+        (
+            "170141183460469231731687303715884105728",
+            "number out of range at line 1 column 39",
+        ),
+    ]);
+
+    test_parse_err::<u128>(&[
+        ("-1", "number out of range at line 1 column 1"),
+        (
+            "340282366920938463463374607431768211456",
+            "number out of range at line 1 column 39",
+        ),
+    ]);
+}
+
+#[test]
+fn test_integer128_to_value() {
+    let signed = &[i128::from(i64::min_value()), i128::from(u64::max_value())];
+    let unsigned = &[0, u128::from(u64::max_value())];
+
+    for integer128 in signed {
+        let expected = integer128.to_string();
+        assert_eq!(to_value(integer128).unwrap().to_string(), expected);
+    }
+
+    for integer128 in unsigned {
+        let expected = integer128.to_string();
+        assert_eq!(to_value(integer128).unwrap().to_string(), expected);
+    }
+
+    if !cfg!(feature = "arbitrary_precision") {
+        let err = to_value(u128::from(u64::max_value()) + 1).unwrap_err();
+        assert_eq!(err.to_string(), "number out of range");
+    }
+}
+
+#[cfg(feature = "raw_value")]
+#[test]
+fn test_borrowed_raw_value() {
+    #[derive(Serialize, Deserialize)]
+    struct Wrapper<'a> {
+        a: i8,
+        #[serde(borrow)]
+        b: &'a RawValue,
+        c: i8,
+    }
+
+    let wrapper_from_str: Wrapper =
+        serde_json::from_str(r#"{"a": 1, "b": {"foo": 2}, "c": 3}"#).unwrap();
+    assert_eq!(r#"{"foo": 2}"#, wrapper_from_str.b.get());
+
+    let wrapper_to_string = serde_json::to_string(&wrapper_from_str).unwrap();
+    assert_eq!(r#"{"a":1,"b":{"foo": 2},"c":3}"#, wrapper_to_string);
+
+    let wrapper_to_value = serde_json::to_value(&wrapper_from_str).unwrap();
+    assert_eq!(json!({"a": 1, "b": {"foo": 2}, "c": 3}), wrapper_to_value);
+
+    let array_from_str: Vec<&RawValue> =
+        serde_json::from_str(r#"["a", 42, {"foo": "bar"}, null]"#).unwrap();
+    assert_eq!(r#""a""#, array_from_str[0].get());
+    assert_eq!(r#"42"#, array_from_str[1].get());
+    assert_eq!(r#"{"foo": "bar"}"#, array_from_str[2].get());
+    assert_eq!(r#"null"#, array_from_str[3].get());
+
+    let array_to_string = serde_json::to_string(&array_from_str).unwrap();
+    assert_eq!(r#"["a",42,{"foo": "bar"},null]"#, array_to_string);
+}
+
+#[cfg(feature = "raw_value")]
+#[test]
+fn test_raw_value_in_map_key() {
+    #[derive(RefCast)]
+    #[repr(transparent)]
+    struct RawMapKey(RawValue);
+
+    impl<'de> Deserialize<'de> for &'de RawMapKey {
+        fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+        where
+            D: serde::Deserializer<'de>,
+        {
+            let raw_value = <&RawValue>::deserialize(deserializer)?;
+            Ok(RawMapKey::ref_cast(raw_value))
+        }
+    }
+
+    impl PartialEq for RawMapKey {
+        fn eq(&self, other: &Self) -> bool {
+            self.0.get() == other.0.get()
+        }
+    }
+
+    impl Eq for RawMapKey {}
+
+    impl Hash for RawMapKey {
+        fn hash<H: Hasher>(&self, hasher: &mut H) {
+            self.0.get().hash(hasher);
+        }
+    }
+
+    let map_from_str: HashMap<&RawMapKey, &RawValue> =
+        serde_json::from_str(r#" {"\\k":"\\v"} "#).unwrap();
+    let (map_k, map_v) = map_from_str.into_iter().next().unwrap();
+    assert_eq!("\"\\\\k\"", map_k.0.get());
+    assert_eq!("\"\\\\v\"", map_v.get());
+}
+
+#[cfg(feature = "raw_value")]
+#[test]
+fn test_boxed_raw_value() {
+    #[derive(Serialize, Deserialize)]
+    struct Wrapper {
+        a: i8,
+        b: Box<RawValue>,
+        c: i8,
+    }
+
+    let wrapper_from_str: Wrapper =
+        serde_json::from_str(r#"{"a": 1, "b": {"foo": 2}, "c": 3}"#).unwrap();
+    assert_eq!(r#"{"foo": 2}"#, wrapper_from_str.b.get());
+
+    let wrapper_from_reader: Wrapper =
+        serde_json::from_reader(br#"{"a": 1, "b": {"foo": 2}, "c": 3}"#.as_ref()).unwrap();
+    assert_eq!(r#"{"foo": 2}"#, wrapper_from_reader.b.get());
+
+    let wrapper_from_value: Wrapper =
+        serde_json::from_value(json!({"a": 1, "b": {"foo": 2}, "c": 3})).unwrap();
+    assert_eq!(r#"{"foo":2}"#, wrapper_from_value.b.get());
+
+    let wrapper_to_string = serde_json::to_string(&wrapper_from_str).unwrap();
+    assert_eq!(r#"{"a":1,"b":{"foo": 2},"c":3}"#, wrapper_to_string);
+
+    let wrapper_to_value = serde_json::to_value(&wrapper_from_str).unwrap();
+    assert_eq!(json!({"a": 1, "b": {"foo": 2}, "c": 3}), wrapper_to_value);
+
+    let array_from_str: Vec<Box<RawValue>> =
+        serde_json::from_str(r#"["a", 42, {"foo": "bar"}, null]"#).unwrap();
+    assert_eq!(r#""a""#, array_from_str[0].get());
+    assert_eq!(r#"42"#, array_from_str[1].get());
+    assert_eq!(r#"{"foo": "bar"}"#, array_from_str[2].get());
+    assert_eq!(r#"null"#, array_from_str[3].get());
+
+    let array_from_reader: Vec<Box<RawValue>> =
+        serde_json::from_reader(br#"["a", 42, {"foo": "bar"}, null]"#.as_ref()).unwrap();
+    assert_eq!(r#""a""#, array_from_reader[0].get());
+    assert_eq!(r#"42"#, array_from_reader[1].get());
+    assert_eq!(r#"{"foo": "bar"}"#, array_from_reader[2].get());
+    assert_eq!(r#"null"#, array_from_reader[3].get());
+
+    let array_to_string = serde_json::to_string(&array_from_str).unwrap();
+    assert_eq!(r#"["a",42,{"foo": "bar"},null]"#, array_to_string);
+}
+
+#[cfg(feature = "raw_value")]
+#[test]
+fn test_raw_invalid_utf8() {
+    let j = &[b'"', b'\xCE', b'\xF8', b'"'];
+    let value_err = serde_json::from_slice::<Value>(j).unwrap_err();
+    let raw_value_err = serde_json::from_slice::<Box<RawValue>>(j).unwrap_err();
+
+    assert_eq!(
+        value_err.to_string(),
+        "invalid unicode code point at line 1 column 4",
+    );
+    assert_eq!(
+        raw_value_err.to_string(),
+        "invalid unicode code point at line 1 column 4",
+    );
+}
+
+#[cfg(feature = "raw_value")]
+#[test]
+fn test_serialize_unsized_value_to_raw_value() {
+    assert_eq!(
+        serde_json::value::to_raw_value("foobar").unwrap().get(),
+        r#""foobar""#,
+    );
+}
+
+#[test]
+fn test_borrow_in_map_key() {
+    #[derive(Deserialize, Debug)]
+    struct Outer {
+        #[allow(dead_code)]
+        map: BTreeMap<MyMapKey, ()>,
+    }
+
+    #[derive(Ord, PartialOrd, Eq, PartialEq, Debug)]
+    struct MyMapKey(usize);
+
+    impl<'de> Deserialize<'de> for MyMapKey {
+        fn deserialize<D>(deserializer: D) -> Result<Self, D::Error>
+        where
+            D: de::Deserializer<'de>,
+        {
+            let s = <&str>::deserialize(deserializer)?;
+            let n = s.parse().map_err(de::Error::custom)?;
+            Ok(MyMapKey(n))
+        }
+    }
+
+    let value = json!({ "map": { "1": null } });
+    Outer::deserialize(&value).unwrap();
+}
+
+#[test]
+fn test_value_into_deserializer() {
+    #[derive(Deserialize)]
+    struct Outer {
+        inner: Inner,
+    }
+
+    #[derive(Deserialize)]
+    struct Inner {
+        string: String,
+    }
+
+    let mut map = BTreeMap::new();
+    map.insert("inner", json!({ "string": "Hello World" }));
+
+    let outer = Outer::deserialize(map.into_deserializer()).unwrap();
+    assert_eq!(outer.inner.string, "Hello World");
+}
+
+#[test]
+fn hash_positive_and_negative_zero() {
+    fn hash(obj: impl Hash) -> u64 {
+        let mut hasher = DefaultHasher::new();
+        obj.hash(&mut hasher);
+        hasher.finish()
+    }
+
+    let k1 = serde_json::from_str::<Number>("0.0").unwrap();
+    let k2 = serde_json::from_str::<Number>("-0.0").unwrap();
+    if cfg!(feature = "arbitrary_precision") {
+        assert_ne!(k1, k2);
+        assert_ne!(hash(k1), hash(k2));
+    } else {
+        assert_eq!(k1, k2);
+        assert_eq!(hash(k1), hash(k2));
+    }
+}
diff --git a/third_party/rust/serde_json/tests/ui/missing_colon.rs b/third_party/rust/serde_json/tests/ui/missing_colon.rs
new file mode 100644
index 0000000000..d93b7b907d
--- /dev/null
+++ b/third_party/rust/serde_json/tests/ui/missing_colon.rs
@@ -0,0 +1,5 @@
+use serde_json::json;
+
+fn main() {
+    json!({ "a" });
+}
diff --git a/third_party/rust/serde_json/tests/ui/missing_colon.stderr b/third_party/rust/serde_json/tests/ui/missing_colon.stderr
new file mode 100644
index 0000000000..1515211adf
--- /dev/null
+++ b/third_party/rust/serde_json/tests/ui/missing_colon.stderr
@@ -0,0 +1,12 @@
+error: unexpected end of macro invocation
+ --> tests/ui/missing_colon.rs:4:5
+  |
+4 |     json!({ "a" });
+  |     ^^^^^^^^^^^^^^ missing tokens in macro arguments
+  |
+note: while trying to match `@`
+ --> src/macros.rs
+  |
+  |     (@array [$($elems:expr,)*]) => {
+  |      ^
+  = note: this error originates in the macro `json_internal` which comes from the expansion of the macro `json` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/serde_json/tests/ui/missing_comma.rs b/third_party/rust/serde_json/tests/ui/missing_comma.rs
new file mode 100644
index 0000000000..8818c3e60c
--- /dev/null
+++ b/third_party/rust/serde_json/tests/ui/missing_comma.rs
@@ -0,0 +1,5 @@
+use serde_json::json;
+
+fn main() {
+    json!({ "1": "" "2": "" });
+}
diff --git a/third_party/rust/serde_json/tests/ui/missing_comma.stderr b/third_party/rust/serde_json/tests/ui/missing_comma.stderr
new file mode 100644
index 0000000000..bafa0f8915
--- /dev/null
+++ b/third_party/rust/serde_json/tests/ui/missing_comma.stderr
@@ -0,0 +1,13 @@
+error: no rules expected the token `"2"`
+ --> tests/ui/missing_comma.rs:4:21
+  |
+4 |     json!({ "1": "" "2": "" });
+  |                    -^^^ no rules expected this token in macro call
+  |                    |
+  |                    help: missing comma here
+  |
+note: while trying to match `,`
+ --> src/macros.rs
+  |
+  |     ($e:expr , $($tt:tt)*) => {};
+  |              ^
diff --git a/third_party/rust/serde_json/tests/ui/missing_value.rs b/third_party/rust/serde_json/tests/ui/missing_value.rs
new file mode 100644
index 0000000000..0ba14e22c2
--- /dev/null
+++ b/third_party/rust/serde_json/tests/ui/missing_value.rs
@@ -0,0 +1,5 @@
+use serde_json::json;
+
+fn main() {
+    json!({ "a" : });
+}
diff --git a/third_party/rust/serde_json/tests/ui/missing_value.stderr b/third_party/rust/serde_json/tests/ui/missing_value.stderr
new file mode 100644
index 0000000000..9c9de99ca9
--- /dev/null
+++ b/third_party/rust/serde_json/tests/ui/missing_value.stderr
@@ -0,0 +1,12 @@
+error: unexpected end of macro invocation
+ --> tests/ui/missing_value.rs:4:5
+  |
+4 |     json!({ "a" : });
+  |     ^^^^^^^^^^^^^^^^ missing tokens in macro arguments
+  |
+note: while trying to match `@`
+ --> src/macros.rs
+  |
+  |     (@array [$($elems:expr,)*]) => {
+  |      ^
+  = note: this error originates in the macro `json_internal` which comes from the expansion of the macro `json` (in Nightly builds, run with -Z macro-backtrace for more info)
diff --git a/third_party/rust/serde_json/tests/ui/not_found.rs b/third_party/rust/serde_json/tests/ui/not_found.rs
new file mode 100644
index 0000000000..2df6870dc3
--- /dev/null
+++ b/third_party/rust/serde_json/tests/ui/not_found.rs
@@ -0,0 +1,5 @@
+use serde_json::json;
+
+fn main() {
+    json!({ "a" : x });
+}
diff --git a/third_party/rust/serde_json/tests/ui/not_found.stderr b/third_party/rust/serde_json/tests/ui/not_found.stderr
new file mode 100644
index 0000000000..6fec180409
--- /dev/null
+++ b/third_party/rust/serde_json/tests/ui/not_found.stderr
@@ -0,0 +1,5 @@
+error[E0425]: cannot find value `x` in this scope
+ --> tests/ui/not_found.rs:4:19
+  |
+4 |     json!({ "a" : x });
+  |                   ^ not found in this scope
diff --git a/third_party/rust/serde_json/tests/ui/parse_expr.rs b/third_party/rust/serde_json/tests/ui/parse_expr.rs
new file mode 100644
index 0000000000..e7f1805b1e
--- /dev/null
+++ b/third_party/rust/serde_json/tests/ui/parse_expr.rs
@@ -0,0 +1,5 @@
+use serde_json::json;
+
+fn main() {
+    json!({ "a" : ~ });
+}
diff --git a/third_party/rust/serde_json/tests/ui/parse_expr.stderr b/third_party/rust/serde_json/tests/ui/parse_expr.stderr
new file mode 100644
index 0000000000..cd3e1c94d1
--- /dev/null
+++ b/third_party/rust/serde_json/tests/ui/parse_expr.stderr
@@ -0,0 +1,11 @@
+error: no rules expected the token `~`
+ --> tests/ui/parse_expr.rs:4:19
+  |
+4 |     json!({ "a" : ~ });
+  |                   ^ no rules expected this token in macro call
+  |
+note: while trying to match meta-variable `$e:expr`
+ --> src/macros.rs
+  |
+  |     ($e:expr , $($tt:tt)*) => {};
+  |      ^^^^^^^
diff --git a/third_party/rust/serde_json/tests/ui/parse_key.rs b/third_party/rust/serde_json/tests/ui/parse_key.rs
new file mode 100644
index 0000000000..858bd71692
--- /dev/null
+++ b/third_party/rust/serde_json/tests/ui/parse_key.rs
@@ -0,0 +1,5 @@
+use serde_json::json;
+
+fn main() {
+    json!({ "".s : true });
+}
diff --git a/third_party/rust/serde_json/tests/ui/parse_key.stderr b/third_party/rust/serde_json/tests/ui/parse_key.stderr
new file mode 100644
index 0000000000..f10c21800e
--- /dev/null
+++ b/third_party/rust/serde_json/tests/ui/parse_key.stderr
@@ -0,0 +1,5 @@
+error[E0609]: no field `s` on type `&'static str`
+ --> tests/ui/parse_key.rs:4:16
+  |
+4 |     json!({ "".s : true });
+  |                ^
diff --git a/third_party/rust/serde_json/tests/ui/unexpected_after_array_element.rs b/third_party/rust/serde_json/tests/ui/unexpected_after_array_element.rs
new file mode 100644
index 0000000000..226c58cf17
--- /dev/null
+++ b/third_party/rust/serde_json/tests/ui/unexpected_after_array_element.rs
@@ -0,0 +1,5 @@
+use serde_json::json;
+
+fn main() {
+    json!([ true => ]);
+}
diff --git a/third_party/rust/serde_json/tests/ui/unexpected_after_array_element.stderr b/third_party/rust/serde_json/tests/ui/unexpected_after_array_element.stderr
new file mode 100644
index 0000000000..ef449f764d
--- /dev/null
+++ b/third_party/rust/serde_json/tests/ui/unexpected_after_array_element.stderr
@@ -0,0 +1,7 @@
+error: no rules expected the token `=>`
+ --> tests/ui/unexpected_after_array_element.rs:4:18
+  |
+4 |     json!([ true => ]);
+  |                  ^^ no rules expected this token in macro call
+  |
+  = note: while trying to match end of macro
diff --git a/third_party/rust/serde_json/tests/ui/unexpected_after_map_entry.rs b/third_party/rust/serde_json/tests/ui/unexpected_after_map_entry.rs
new file mode 100644
index 0000000000..0dfb731559
--- /dev/null
+++ b/third_party/rust/serde_json/tests/ui/unexpected_after_map_entry.rs
@@ -0,0 +1,5 @@
+use serde_json::json;
+
+fn main() {
+    json!({ "k": true => });
+}
diff --git a/third_party/rust/serde_json/tests/ui/unexpected_after_map_entry.stderr b/third_party/rust/serde_json/tests/ui/unexpected_after_map_entry.stderr
new file mode 100644
index 0000000000..c62d90ba0d
--- /dev/null
+++ b/third_party/rust/serde_json/tests/ui/unexpected_after_map_entry.stderr
@@ -0,0 +1,7 @@
+error: no rules expected the token `=>`
+ --> tests/ui/unexpected_after_map_entry.rs:4:23
+  |
+4 |     json!({ "k": true => });
+  |                       ^^ no rules expected this token in macro call
+  |
+  = note: while trying to match end of macro
diff --git a/third_party/rust/serde_json/tests/ui/unexpected_colon.rs b/third_party/rust/serde_json/tests/ui/unexpected_colon.rs
new file mode 100644
index 0000000000..e767ea6f7d
--- /dev/null
+++ b/third_party/rust/serde_json/tests/ui/unexpected_colon.rs
@@ -0,0 +1,5 @@
+use serde_json::json;
+
+fn main() {
+    json!({ : true });
+}
diff --git a/third_party/rust/serde_json/tests/ui/unexpected_colon.stderr b/third_party/rust/serde_json/tests/ui/unexpected_colon.stderr
new file mode 100644
index 0000000000..7e47726bc6
--- /dev/null
+++ b/third_party/rust/serde_json/tests/ui/unexpected_colon.stderr
@@ -0,0 +1,7 @@
+error: no rules expected the token `:`
+ --> tests/ui/unexpected_colon.rs:4:13
+  |
+4 |     json!({ : true });
+  |             ^ no rules expected this token in macro call
+  |
+  = note: while trying to match end of macro
diff --git a/third_party/rust/serde_json/tests/ui/unexpected_comma.rs b/third_party/rust/serde_json/tests/ui/unexpected_comma.rs
new file mode 100644
index 0000000000..338874ed8f
--- /dev/null
+++ b/third_party/rust/serde_json/tests/ui/unexpected_comma.rs
@@ -0,0 +1,5 @@
+use serde_json::json;
+
+fn main() {
+    json!({ "a" , "b": true });
+}
diff --git a/third_party/rust/serde_json/tests/ui/unexpected_comma.stderr b/third_party/rust/serde_json/tests/ui/unexpected_comma.stderr
new file mode 100644
index 0000000000..552f399a50
--- /dev/null
+++ b/third_party/rust/serde_json/tests/ui/unexpected_comma.stderr
@@ -0,0 +1,7 @@
+error: no rules expected the token `,`
+ --> tests/ui/unexpected_comma.rs:4:17
+  |
+4 |     json!({ "a" , "b": true });
+  |                 ^ no rules expected this token in macro call
+  |
+  = note: while trying to match end of macro