Adding upstream version 115.7.0esr.upstream/115.7.0esr

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

10 files changed, 2464 insertions, 0 deletions

diff --git a/third_party/rust/prost-derive/.cargo-checksum.json b/third_party/rust/prost-derive/.cargo-checksum.json
new file mode 100644
index 0000000000..e64d4cd29b
--- /dev/null
+++ b/third_party/rust/prost-derive/.cargo-checksum.json
@@ -0,0 +1 @@
+{"files":{"Cargo.toml":"4af10c29150183b223cd13b9eb0375fdbef6daba35e43a654c55c0491ca78ba2","README.md":"6c67fa1e48f14adfaf834f520f798ddfb79f90804f46cc215ee391a7d57913a4","src/field/group.rs":"dfd31b34008741abc857dc11362c11a06afd8eddceb62924443bf2bea117460a","src/field/map.rs":"69e1fa14cfeb4d4407b9c343a2a72b4ba68c3ecb7af912965a63b50e91dd61fb","src/field/message.rs":"fb910a563eba0b0c68a7a3855f7877535931faef4d788b05a3402f0cdd037e3e","src/field/mod.rs":"ca917a3f673623f0946e9e37ebad2916f3c1f8d163a1844143ef7d21d245394c","src/field/oneof.rs":"4fc488445b05e464070fadd8799cafb806db5c23d1494c4300cb293394863012","src/field/scalar.rs":"03d69f74daa2037a0210a086bd873ae9beca6b615e2973c96c43a6d0d30aa525","src/lib.rs":"8cfa6f1fc707e8931df82f9df67fa07e1b822b7581e4c9733e3ce24febabf708"},"package":"600d2f334aa05acb02a755e217ef1ab6dea4d51b58b7846588b747edec04efba"}
\ No newline at end of file
diff --git a/third_party/rust/prost-derive/Cargo.toml b/third_party/rust/prost-derive/Cargo.toml
new file mode 100644
index 0000000000..d6c2d3e74c
--- /dev/null
+++ b/third_party/rust/prost-derive/Cargo.toml
@@ -0,0 +1,40 @@
+# 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 believe there's an error in this file please file an
+# issue against the rust-lang/cargo repository. If you're
+# editing this file be aware that the upstream Cargo.toml
+# will likely look very different (and much more reasonable)
+
+[package]
+edition = "2018"
+name = "prost-derive"
+version = "0.8.0"
+authors = ["Dan Burkert <dan@danburkert.com>", "Tokio Contributors <team@tokio.rs>"]
+description = "A Protocol Buffers implementation for the Rust Language."
+documentation = "https://docs.rs/prost-derive"
+readme = "README.md"
+license = "Apache-2.0"
+repository = "https://github.com/tokio-rs/prost"
+
+[lib]
+proc_macro = true
+[dependencies.anyhow]
+version = "1"
+
+[dependencies.itertools]
+version = "0.10"
+
+[dependencies.proc-macro2]
+version = "1"
+
+[dependencies.quote]
+version = "1"
+
+[dependencies.syn]
+version = "1"
+features = ["extra-traits"]
diff --git a/third_party/rust/prost-derive/README.md b/third_party/rust/prost-derive/README.md
new file mode 100644
index 0000000000..a51050e7e6
--- /dev/null
+++ b/third_party/rust/prost-derive/README.md
@@ -0,0 +1,16 @@
+[![Documentation](https://docs.rs/prost-derive/badge.svg)](https://docs.rs/prost-derive/)
+[![Crate](https://img.shields.io/crates/v/prost-derive.svg)](https://crates.io/crates/prost-derive)
+
+# prost-derive
+
+`prost-derive` handles generating encoding and decoding implementations for Rust
+types annotated with `prost` annotation. For the most part, users of `prost`
+shouldn't need to interact with `prost-derive` directly.
+
+## License
+
+`prost-derive` is distributed under the terms of the Apache License (Version 2.0).
+
+See [LICENSE](../LICENSE) for details.
+
+Copyright 2017 Dan Burkert
diff --git a/third_party/rust/prost-derive/src/field/group.rs b/third_party/rust/prost-derive/src/field/group.rs
new file mode 100644
index 0000000000..6396128802
--- /dev/null
+++ b/third_party/rust/prost-derive/src/field/group.rs
@@ -0,0 +1,134 @@
+use anyhow::{bail, Error};
+use proc_macro2::TokenStream;
+use quote::{quote, ToTokens};
+use syn::Meta;
+
+use crate::field::{set_bool, set_option, tag_attr, word_attr, Label};
+
+#[derive(Clone)]
+pub struct Field {
+    pub label: Label,
+    pub tag: u32,
+}
+
+impl Field {
+    pub fn new(attrs: &[Meta], inferred_tag: Option<u32>) -> Result<Option<Field>, Error> {
+        let mut group = false;
+        let mut label = None;
+        let mut tag = None;
+        let mut boxed = false;
+
+        let mut unknown_attrs = Vec::new();
+
+        for attr in attrs {
+            if word_attr("group", attr) {
+                set_bool(&mut group, "duplicate group attributes")?;
+            } else if word_attr("boxed", attr) {
+                set_bool(&mut boxed, "duplicate boxed attributes")?;
+            } else if let Some(t) = tag_attr(attr)? {
+                set_option(&mut tag, t, "duplicate tag attributes")?;
+            } else if let Some(l) = Label::from_attr(attr) {
+                set_option(&mut label, l, "duplicate label attributes")?;
+            } else {
+                unknown_attrs.push(attr);
+            }
+        }
+
+        if !group {
+            return Ok(None);
+        }
+
+        match unknown_attrs.len() {
+            0 => (),
+            1 => bail!("unknown attribute for group field: {:?}", unknown_attrs[0]),
+            _ => bail!("unknown attributes for group field: {:?}", unknown_attrs),
+        }
+
+        let tag = match tag.or(inferred_tag) {
+            Some(tag) => tag,
+            None => bail!("group field is missing a tag attribute"),
+        };
+
+        Ok(Some(Field {
+            label: label.unwrap_or(Label::Optional),
+            tag,
+        }))
+    }
+
+    pub fn new_oneof(attrs: &[Meta]) -> Result<Option<Field>, Error> {
+        if let Some(mut field) = Field::new(attrs, None)? {
+            if let Some(attr) = attrs.iter().find(|attr| Label::from_attr(attr).is_some()) {
+                bail!(
+                    "invalid attribute for oneof field: {}",
+                    attr.path().into_token_stream()
+                );
+            }
+            field.label = Label::Required;
+            Ok(Some(field))
+        } else {
+            Ok(None)
+        }
+    }
+
+    pub fn encode(&self, ident: TokenStream) -> TokenStream {
+        let tag = self.tag;
+        match self.label {
+            Label::Optional => quote! {
+                if let Some(ref msg) = #ident {
+                    ::prost::encoding::group::encode(#tag, msg, buf);
+                }
+            },
+            Label::Required => quote! {
+                ::prost::encoding::group::encode(#tag, &#ident, buf);
+            },
+            Label::Repeated => quote! {
+                for msg in &#ident {
+                    ::prost::encoding::group::encode(#tag, msg, buf);
+                }
+            },
+        }
+    }
+
+    pub fn merge(&self, ident: TokenStream) -> TokenStream {
+        match self.label {
+            Label::Optional => quote! {
+                ::prost::encoding::group::merge(
+                    tag,
+                    wire_type,
+                    #ident.get_or_insert_with(Default::default),
+                    buf,
+                    ctx,
+                )
+            },
+            Label::Required => quote! {
+                ::prost::encoding::group::merge(tag, wire_type, #ident, buf, ctx)
+            },
+            Label::Repeated => quote! {
+                ::prost::encoding::group::merge_repeated(tag, wire_type, #ident, buf, ctx)
+            },
+        }
+    }
+
+    pub fn encoded_len(&self, ident: TokenStream) -> TokenStream {
+        let tag = self.tag;
+        match self.label {
+            Label::Optional => quote! {
+                #ident.as_ref().map_or(0, |msg| ::prost::encoding::group::encoded_len(#tag, msg))
+            },
+            Label::Required => quote! {
+                ::prost::encoding::group::encoded_len(#tag, &#ident)
+            },
+            Label::Repeated => quote! {
+                ::prost::encoding::group::encoded_len_repeated(#tag, &#ident)
+            },
+        }
+    }
+
+    pub fn clear(&self, ident: TokenStream) -> TokenStream {
+        match self.label {
+            Label::Optional => quote!(#ident = ::core::option::Option::None),
+            Label::Required => quote!(#ident.clear()),
+            Label::Repeated => quote!(#ident.clear()),
+        }
+    }
+}
diff --git a/third_party/rust/prost-derive/src/field/map.rs b/third_party/rust/prost-derive/src/field/map.rs
new file mode 100644
index 0000000000..1228a6fae2
--- /dev/null
+++ b/third_party/rust/prost-derive/src/field/map.rs
@@ -0,0 +1,394 @@
+use anyhow::{bail, Error};
+use proc_macro2::{Span, TokenStream};
+use quote::quote;
+use syn::{Ident, Lit, Meta, MetaNameValue, NestedMeta};
+
+use crate::field::{scalar, set_option, tag_attr};
+
+#[derive(Clone, Debug)]
+pub enum MapTy {
+    HashMap,
+    BTreeMap,
+}
+
+impl MapTy {
+    fn from_str(s: &str) -> Option<MapTy> {
+        match s {
+            "map" | "hash_map" => Some(MapTy::HashMap),
+            "btree_map" => Some(MapTy::BTreeMap),
+            _ => None,
+        }
+    }
+
+    fn module(&self) -> Ident {
+        match *self {
+            MapTy::HashMap => Ident::new("hash_map", Span::call_site()),
+            MapTy::BTreeMap => Ident::new("btree_map", Span::call_site()),
+        }
+    }
+
+    fn lib(&self) -> TokenStream {
+        match self {
+            MapTy::HashMap => quote! { std },
+            MapTy::BTreeMap => quote! { prost::alloc },
+        }
+    }
+}
+
+fn fake_scalar(ty: scalar::Ty) -> scalar::Field {
+    let kind = scalar::Kind::Plain(scalar::DefaultValue::new(&ty));
+    scalar::Field {
+        ty,
+        kind,
+        tag: 0, // Not used here
+    }
+}
+
+#[derive(Clone)]
+pub struct Field {
+    pub map_ty: MapTy,
+    pub key_ty: scalar::Ty,
+    pub value_ty: ValueTy,
+    pub tag: u32,
+}
+
+impl Field {
+    pub fn new(attrs: &[Meta], inferred_tag: Option<u32>) -> Result<Option<Field>, Error> {
+        let mut types = None;
+        let mut tag = None;
+
+        for attr in attrs {
+            if let Some(t) = tag_attr(attr)? {
+                set_option(&mut tag, t, "duplicate tag attributes")?;
+            } else if let Some(map_ty) = attr
+                .path()
+                .get_ident()
+                .and_then(|i| MapTy::from_str(&i.to_string()))
+            {
+                let (k, v): (String, String) = match &*attr {
+                    Meta::NameValue(MetaNameValue {
+                        lit: Lit::Str(lit), ..
+                    }) => {
+                        let items = lit.value();
+                        let mut items = items.split(',').map(ToString::to_string);
+                        let k = items.next().unwrap();
+                        let v = match items.next() {
+                            Some(k) => k,
+                            None => bail!("invalid map attribute: must have key and value types"),
+                        };
+                        if items.next().is_some() {
+                            bail!("invalid map attribute: {:?}", attr);
+                        }
+                        (k, v)
+                    }
+                    Meta::List(meta_list) => {
+                        // TODO(rustlang/rust#23121): slice pattern matching would make this much nicer.
+                        if meta_list.nested.len() != 2 {
+                            bail!("invalid map attribute: must contain key and value types");
+                        }
+                        let k = match &meta_list.nested[0] {
+                            NestedMeta::Meta(Meta::Path(k)) if k.get_ident().is_some() => {
+                                k.get_ident().unwrap().to_string()
+                            }
+                            _ => bail!("invalid map attribute: key must be an identifier"),
+                        };
+                        let v = match &meta_list.nested[1] {
+                            NestedMeta::Meta(Meta::Path(v)) if v.get_ident().is_some() => {
+                                v.get_ident().unwrap().to_string()
+                            }
+                            _ => bail!("invalid map attribute: value must be an identifier"),
+                        };
+                        (k, v)
+                    }
+                    _ => return Ok(None),
+                };
+                set_option(
+                    &mut types,
+                    (map_ty, key_ty_from_str(&k)?, ValueTy::from_str(&v)?),
+                    "duplicate map type attribute",
+                )?;
+            } else {
+                return Ok(None);
+            }
+        }
+
+        Ok(match (types, tag.or(inferred_tag)) {
+            (Some((map_ty, key_ty, value_ty)), Some(tag)) => Some(Field {
+                map_ty,
+                key_ty,
+                value_ty,
+                tag,
+            }),
+            _ => None,
+        })
+    }
+
+    pub fn new_oneof(attrs: &[Meta]) -> Result<Option<Field>, Error> {
+        Field::new(attrs, None)
+    }
+
+    /// Returns a statement which encodes the map field.
+    pub fn encode(&self, ident: TokenStream) -> TokenStream {
+        let tag = self.tag;
+        let key_mod = self.key_ty.module();
+        let ke = quote!(::prost::encoding::#key_mod::encode);
+        let kl = quote!(::prost::encoding::#key_mod::encoded_len);
+        let module = self.map_ty.module();
+        match &self.value_ty {
+            ValueTy::Scalar(scalar::Ty::Enumeration(ty)) => {
+                let default = quote!(#ty::default() as i32);
+                quote! {
+                    ::prost::encoding::#module::encode_with_default(
+                        #ke,
+                        #kl,
+                        ::prost::encoding::int32::encode,
+                        ::prost::encoding::int32::encoded_len,
+                        &(#default),
+                        #tag,
+                        &#ident,
+                        buf,
+                    );
+                }
+            }
+            ValueTy::Scalar(value_ty) => {
+                let val_mod = value_ty.module();
+                let ve = quote!(::prost::encoding::#val_mod::encode);
+                let vl = quote!(::prost::encoding::#val_mod::encoded_len);
+                quote! {
+                    ::prost::encoding::#module::encode(
+                        #ke,
+                        #kl,
+                        #ve,
+                        #vl,
+                        #tag,
+                        &#ident,
+                        buf,
+                    );
+                }
+            }
+            ValueTy::Message => quote! {
+                ::prost::encoding::#module::encode(
+                    #ke,
+                    #kl,
+                    ::prost::encoding::message::encode,
+                    ::prost::encoding::message::encoded_len,
+                    #tag,
+                    &#ident,
+                    buf,
+                );
+            },
+        }
+    }
+
+    /// Returns an expression which evaluates to the result of merging a decoded key value pair
+    /// into the map.
+    pub fn merge(&self, ident: TokenStream) -> TokenStream {
+        let key_mod = self.key_ty.module();
+        let km = quote!(::prost::encoding::#key_mod::merge);
+        let module = self.map_ty.module();
+        match &self.value_ty {
+            ValueTy::Scalar(scalar::Ty::Enumeration(ty)) => {
+                let default = quote!(#ty::default() as i32);
+                quote! {
+                    ::prost::encoding::#module::merge_with_default(
+                        #km,
+                        ::prost::encoding::int32::merge,
+                        #default,
+                        &mut #ident,
+                        buf,
+                        ctx,
+                    )
+                }
+            }
+            ValueTy::Scalar(value_ty) => {
+                let val_mod = value_ty.module();
+                let vm = quote!(::prost::encoding::#val_mod::merge);
+                quote!(::prost::encoding::#module::merge(#km, #vm, &mut #ident, buf, ctx))
+            }
+            ValueTy::Message => quote! {
+                ::prost::encoding::#module::merge(
+                    #km,
+                    ::prost::encoding::message::merge,
+                    &mut #ident,
+                    buf,
+                    ctx,
+                )
+            },
+        }
+    }
+
+    /// Returns an expression which evaluates to the encoded length of the map.
+    pub fn encoded_len(&self, ident: TokenStream) -> TokenStream {
+        let tag = self.tag;
+        let key_mod = self.key_ty.module();
+        let kl = quote!(::prost::encoding::#key_mod::encoded_len);
+        let module = self.map_ty.module();
+        match &self.value_ty {
+            ValueTy::Scalar(scalar::Ty::Enumeration(ty)) => {
+                let default = quote!(#ty::default() as i32);
+                quote! {
+                    ::prost::encoding::#module::encoded_len_with_default(
+                        #kl,
+                        ::prost::encoding::int32::encoded_len,
+                        &(#default),
+                        #tag,
+                        &#ident,
+                    )
+                }
+            }
+            ValueTy::Scalar(value_ty) => {
+                let val_mod = value_ty.module();
+                let vl = quote!(::prost::encoding::#val_mod::encoded_len);
+                quote!(::prost::encoding::#module::encoded_len(#kl, #vl, #tag, &#ident))
+            }
+            ValueTy::Message => quote! {
+                ::prost::encoding::#module::encoded_len(
+                    #kl,
+                    ::prost::encoding::message::encoded_len,
+                    #tag,
+                    &#ident,
+                )
+            },
+        }
+    }
+
+    pub fn clear(&self, ident: TokenStream) -> TokenStream {
+        quote!(#ident.clear())
+    }
+
+    /// Returns methods to embed in the message.
+    pub fn methods(&self, ident: &Ident) -> Option<TokenStream> {
+        if let ValueTy::Scalar(scalar::Ty::Enumeration(ty)) = &self.value_ty {
+            let key_ty = self.key_ty.rust_type();
+            let key_ref_ty = self.key_ty.rust_ref_type();
+
+            let get = Ident::new(&format!("get_{}", ident), Span::call_site());
+            let insert = Ident::new(&format!("insert_{}", ident), Span::call_site());
+            let take_ref = if self.key_ty.is_numeric() {
+                quote!(&)
+            } else {
+                quote!()
+            };
+
+            let get_doc = format!(
+                "Returns the enum value for the corresponding key in `{}`, \
+                 or `None` if the entry does not exist or it is not a valid enum value.",
+                ident,
+            );
+            let insert_doc = format!("Inserts a key value pair into `{}`.", ident);
+            Some(quote! {
+                #[doc=#get_doc]
+                pub fn #get(&self, key: #key_ref_ty) -> ::core::option::Option<#ty> {
+                    self.#ident.get(#take_ref key).cloned().and_then(#ty::from_i32)
+                }
+                #[doc=#insert_doc]
+                pub fn #insert(&mut self, key: #key_ty, value: #ty) -> ::core::option::Option<#ty> {
+                    self.#ident.insert(key, value as i32).and_then(#ty::from_i32)
+                }
+            })
+        } else {
+            None
+        }
+    }
+
+    /// Returns a newtype wrapper around the map, implementing nicer Debug
+    ///
+    /// The Debug tries to convert any enumerations met into the variants if possible, instead of
+    /// outputting the raw numbers.
+    pub fn debug(&self, wrapper_name: TokenStream) -> TokenStream {
+        let type_name = match self.map_ty {
+            MapTy::HashMap => Ident::new("HashMap", Span::call_site()),
+            MapTy::BTreeMap => Ident::new("BTreeMap", Span::call_site()),
+        };
+
+        // A fake field for generating the debug wrapper
+        let key_wrapper = fake_scalar(self.key_ty.clone()).debug(quote!(KeyWrapper));
+        let key = self.key_ty.rust_type();
+        let value_wrapper = self.value_ty.debug();
+        let libname = self.map_ty.lib();
+        let fmt = quote! {
+            fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
+                #key_wrapper
+                #value_wrapper
+                let mut builder = f.debug_map();
+                for (k, v) in self.0 {
+                    builder.entry(&KeyWrapper(k), &ValueWrapper(v));
+                }
+                builder.finish()
+            }
+        };
+        match &self.value_ty {
+            ValueTy::Scalar(ty) => {
+                let value = ty.rust_type();
+                quote! {
+                    struct #wrapper_name<'a>(&'a ::#libname::collections::#type_name<#key, #value>);
+                    impl<'a> ::core::fmt::Debug for #wrapper_name<'a> {
+                        #fmt
+                    }
+                }
+            }
+            ValueTy::Message => quote! {
+                struct #wrapper_name<'a, V: 'a>(&'a ::#libname::collections::#type_name<#key, V>);
+                impl<'a, V> ::core::fmt::Debug for #wrapper_name<'a, V>
+                where
+                    V: ::core::fmt::Debug + 'a,
+                {
+                    #fmt
+                }
+            },
+        }
+    }
+}
+
+fn key_ty_from_str(s: &str) -> Result<scalar::Ty, Error> {
+    let ty = scalar::Ty::from_str(s)?;
+    match ty {
+        scalar::Ty::Int32
+        | scalar::Ty::Int64
+        | scalar::Ty::Uint32
+        | scalar::Ty::Uint64
+        | scalar::Ty::Sint32
+        | scalar::Ty::Sint64
+        | scalar::Ty::Fixed32
+        | scalar::Ty::Fixed64
+        | scalar::Ty::Sfixed32
+        | scalar::Ty::Sfixed64
+        | scalar::Ty::Bool
+        | scalar::Ty::String => Ok(ty),
+        _ => bail!("invalid map key type: {}", s),
+    }
+}
+
+/// A map value type.
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum ValueTy {
+    Scalar(scalar::Ty),
+    Message,
+}
+
+impl ValueTy {
+    fn from_str(s: &str) -> Result<ValueTy, Error> {
+        if let Ok(ty) = scalar::Ty::from_str(s) {
+            Ok(ValueTy::Scalar(ty))
+        } else if s.trim() == "message" {
+            Ok(ValueTy::Message)
+        } else {
+            bail!("invalid map value type: {}", s);
+        }
+    }
+
+    /// Returns a newtype wrapper around the ValueTy for nicer debug.
+    ///
+    /// If the contained value is enumeration, it tries to convert it to the variant. If not, it
+    /// just forwards the implementation.
+    fn debug(&self) -> TokenStream {
+        match self {
+            ValueTy::Scalar(ty) => fake_scalar(ty.clone()).debug(quote!(ValueWrapper)),
+            ValueTy::Message => quote!(
+                fn ValueWrapper<T>(v: T) -> T {
+                    v
+                }
+            ),
+        }
+    }
+}
diff --git a/third_party/rust/prost-derive/src/field/message.rs b/third_party/rust/prost-derive/src/field/message.rs
new file mode 100644
index 0000000000..1ff7c37983
--- /dev/null
+++ b/third_party/rust/prost-derive/src/field/message.rs
@@ -0,0 +1,134 @@
+use anyhow::{bail, Error};
+use proc_macro2::TokenStream;
+use quote::{quote, ToTokens};
+use syn::Meta;
+
+use crate::field::{set_bool, set_option, tag_attr, word_attr, Label};
+
+#[derive(Clone)]
+pub struct Field {
+    pub label: Label,
+    pub tag: u32,
+}
+
+impl Field {
+    pub fn new(attrs: &[Meta], inferred_tag: Option<u32>) -> Result<Option<Field>, Error> {
+        let mut message = false;
+        let mut label = None;
+        let mut tag = None;
+        let mut boxed = false;
+
+        let mut unknown_attrs = Vec::new();
+
+        for attr in attrs {
+            if word_attr("message", attr) {
+                set_bool(&mut message, "duplicate message attribute")?;
+            } else if word_attr("boxed", attr) {
+                set_bool(&mut boxed, "duplicate boxed attribute")?;
+            } else if let Some(t) = tag_attr(attr)? {
+                set_option(&mut tag, t, "duplicate tag attributes")?;
+            } else if let Some(l) = Label::from_attr(attr) {
+                set_option(&mut label, l, "duplicate label attributes")?;
+            } else {
+                unknown_attrs.push(attr);
+            }
+        }
+
+        if !message {
+            return Ok(None);
+        }
+
+        match unknown_attrs.len() {
+            0 => (),
+            1 => bail!(
+                "unknown attribute for message field: {:?}",
+                unknown_attrs[0]
+            ),
+            _ => bail!("unknown attributes for message field: {:?}", unknown_attrs),
+        }
+
+        let tag = match tag.or(inferred_tag) {
+            Some(tag) => tag,
+            None => bail!("message field is missing a tag attribute"),
+        };
+
+        Ok(Some(Field {
+            label: label.unwrap_or(Label::Optional),
+            tag,
+        }))
+    }
+
+    pub fn new_oneof(attrs: &[Meta]) -> Result<Option<Field>, Error> {
+        if let Some(mut field) = Field::new(attrs, None)? {
+            if let Some(attr) = attrs.iter().find(|attr| Label::from_attr(attr).is_some()) {
+                bail!(
+                    "invalid attribute for oneof field: {}",
+                    attr.path().into_token_stream()
+                );
+            }
+            field.label = Label::Required;
+            Ok(Some(field))
+        } else {
+            Ok(None)
+        }
+    }
+
+    pub fn encode(&self, ident: TokenStream) -> TokenStream {
+        let tag = self.tag;
+        match self.label {
+            Label::Optional => quote! {
+                if let Some(ref msg) = #ident {
+                    ::prost::encoding::message::encode(#tag, msg, buf);
+                }
+            },
+            Label::Required => quote! {
+                ::prost::encoding::message::encode(#tag, &#ident, buf);
+            },
+            Label::Repeated => quote! {
+                for msg in &#ident {
+                    ::prost::encoding::message::encode(#tag, msg, buf);
+                }
+            },
+        }
+    }
+
+    pub fn merge(&self, ident: TokenStream) -> TokenStream {
+        match self.label {
+            Label::Optional => quote! {
+                ::prost::encoding::message::merge(wire_type,
+                                                 #ident.get_or_insert_with(Default::default),
+                                                 buf,
+                                                 ctx)
+            },
+            Label::Required => quote! {
+                ::prost::encoding::message::merge(wire_type, #ident, buf, ctx)
+            },
+            Label::Repeated => quote! {
+                ::prost::encoding::message::merge_repeated(wire_type, #ident, buf, ctx)
+            },
+        }
+    }
+
+    pub fn encoded_len(&self, ident: TokenStream) -> TokenStream {
+        let tag = self.tag;
+        match self.label {
+            Label::Optional => quote! {
+                #ident.as_ref().map_or(0, |msg| ::prost::encoding::message::encoded_len(#tag, msg))
+            },
+            Label::Required => quote! {
+                ::prost::encoding::message::encoded_len(#tag, &#ident)
+            },
+            Label::Repeated => quote! {
+                ::prost::encoding::message::encoded_len_repeated(#tag, &#ident)
+            },
+        }
+    }
+
+    pub fn clear(&self, ident: TokenStream) -> TokenStream {
+        match self.label {
+            Label::Optional => quote!(#ident = ::core::option::Option::None),
+            Label::Required => quote!(#ident.clear()),
+            Label::Repeated => quote!(#ident.clear()),
+        }
+    }
+}
diff --git a/third_party/rust/prost-derive/src/field/mod.rs b/third_party/rust/prost-derive/src/field/mod.rs
new file mode 100644
index 0000000000..09fef830ef
--- /dev/null
+++ b/third_party/rust/prost-derive/src/field/mod.rs
@@ -0,0 +1,366 @@
+mod group;
+mod map;
+mod message;
+mod oneof;
+mod scalar;
+
+use std::fmt;
+use std::slice;
+
+use anyhow::{bail, Error};
+use proc_macro2::TokenStream;
+use quote::quote;
+use syn::{Attribute, Ident, Lit, LitBool, Meta, MetaList, MetaNameValue, NestedMeta};
+
+#[derive(Clone)]
+pub enum Field {
+    /// A scalar field.
+    Scalar(scalar::Field),
+    /// A message field.
+    Message(message::Field),
+    /// A map field.
+    Map(map::Field),
+    /// A oneof field.
+    Oneof(oneof::Field),
+    /// A group field.
+    Group(group::Field),
+}
+
+impl Field {
+    /// Creates a new `Field` from an iterator of field attributes.
+    ///
+    /// If the meta items are invalid, an error will be returned.
+    /// If the field should be ignored, `None` is returned.
+    pub fn new(attrs: Vec<Attribute>, inferred_tag: Option<u32>) -> Result<Option<Field>, Error> {
+        let attrs = prost_attrs(attrs);
+
+        // TODO: check for ignore attribute.
+
+        let field = if let Some(field) = scalar::Field::new(&attrs, inferred_tag)? {
+            Field::Scalar(field)
+        } else if let Some(field) = message::Field::new(&attrs, inferred_tag)? {
+            Field::Message(field)
+        } else if let Some(field) = map::Field::new(&attrs, inferred_tag)? {
+            Field::Map(field)
+        } else if let Some(field) = oneof::Field::new(&attrs)? {
+            Field::Oneof(field)
+        } else if let Some(field) = group::Field::new(&attrs, inferred_tag)? {
+            Field::Group(field)
+        } else {
+            bail!("no type attribute");
+        };
+
+        Ok(Some(field))
+    }
+
+    /// Creates a new oneof `Field` from an iterator of field attributes.
+    ///
+    /// If the meta items are invalid, an error will be returned.
+    /// If the field should be ignored, `None` is returned.
+    pub fn new_oneof(attrs: Vec<Attribute>) -> Result<Option<Field>, Error> {
+        let attrs = prost_attrs(attrs);
+
+        // TODO: check for ignore attribute.
+
+        let field = if let Some(field) = scalar::Field::new_oneof(&attrs)? {
+            Field::Scalar(field)
+        } else if let Some(field) = message::Field::new_oneof(&attrs)? {
+            Field::Message(field)
+        } else if let Some(field) = map::Field::new_oneof(&attrs)? {
+            Field::Map(field)
+        } else if let Some(field) = group::Field::new_oneof(&attrs)? {
+            Field::Group(field)
+        } else {
+            bail!("no type attribute for oneof field");
+        };
+
+        Ok(Some(field))
+    }
+
+    pub fn tags(&self) -> Vec<u32> {
+        match *self {
+            Field::Scalar(ref scalar) => vec![scalar.tag],
+            Field::Message(ref message) => vec![message.tag],
+            Field::Map(ref map) => vec![map.tag],
+            Field::Oneof(ref oneof) => oneof.tags.clone(),
+            Field::Group(ref group) => vec![group.tag],
+        }
+    }
+
+    /// Returns a statement which encodes the field.
+    pub fn encode(&self, ident: TokenStream) -> TokenStream {
+        match *self {
+            Field::Scalar(ref scalar) => scalar.encode(ident),
+            Field::Message(ref message) => message.encode(ident),
+            Field::Map(ref map) => map.encode(ident),
+            Field::Oneof(ref oneof) => oneof.encode(ident),
+            Field::Group(ref group) => group.encode(ident),
+        }
+    }
+
+    /// Returns an expression which evaluates to the result of merging a decoded
+    /// value into the field.
+    pub fn merge(&self, ident: TokenStream) -> TokenStream {
+        match *self {
+            Field::Scalar(ref scalar) => scalar.merge(ident),
+            Field::Message(ref message) => message.merge(ident),
+            Field::Map(ref map) => map.merge(ident),
+            Field::Oneof(ref oneof) => oneof.merge(ident),
+            Field::Group(ref group) => group.merge(ident),
+        }
+    }
+
+    /// Returns an expression which evaluates to the encoded length of the field.
+    pub fn encoded_len(&self, ident: TokenStream) -> TokenStream {
+        match *self {
+            Field::Scalar(ref scalar) => scalar.encoded_len(ident),
+            Field::Map(ref map) => map.encoded_len(ident),
+            Field::Message(ref msg) => msg.encoded_len(ident),
+            Field::Oneof(ref oneof) => oneof.encoded_len(ident),
+            Field::Group(ref group) => group.encoded_len(ident),
+        }
+    }
+
+    /// Returns a statement which clears the field.
+    pub fn clear(&self, ident: TokenStream) -> TokenStream {
+        match *self {
+            Field::Scalar(ref scalar) => scalar.clear(ident),
+            Field::Message(ref message) => message.clear(ident),
+            Field::Map(ref map) => map.clear(ident),
+            Field::Oneof(ref oneof) => oneof.clear(ident),
+            Field::Group(ref group) => group.clear(ident),
+        }
+    }
+
+    pub fn default(&self) -> TokenStream {
+        match *self {
+            Field::Scalar(ref scalar) => scalar.default(),
+            _ => quote!(::core::default::Default::default()),
+        }
+    }
+
+    /// Produces the fragment implementing debug for the given field.
+    pub fn debug(&self, ident: TokenStream) -> TokenStream {
+        match *self {
+            Field::Scalar(ref scalar) => {
+                let wrapper = scalar.debug(quote!(ScalarWrapper));
+                quote! {
+                    {
+                        #wrapper
+                        ScalarWrapper(&#ident)
+                    }
+                }
+            }
+            Field::Map(ref map) => {
+                let wrapper = map.debug(quote!(MapWrapper));
+                quote! {
+                    {
+                        #wrapper
+                        MapWrapper(&#ident)
+                    }
+                }
+            }
+            _ => quote!(&#ident),
+        }
+    }
+
+    pub fn methods(&self, ident: &Ident) -> Option<TokenStream> {
+        match *self {
+            Field::Scalar(ref scalar) => scalar.methods(ident),
+            Field::Map(ref map) => map.methods(ident),
+            _ => None,
+        }
+    }
+}
+
+#[derive(Clone, Copy, PartialEq, Eq)]
+pub enum Label {
+    /// An optional field.
+    Optional,
+    /// A required field.
+    Required,
+    /// A repeated field.
+    Repeated,
+}
+
+impl Label {
+    fn as_str(self) -> &'static str {
+        match self {
+            Label::Optional => "optional",
+            Label::Required => "required",
+            Label::Repeated => "repeated",
+        }
+    }
+
+    fn variants() -> slice::Iter<'static, Label> {
+        const VARIANTS: &[Label] = &[Label::Optional, Label::Required, Label::Repeated];
+        VARIANTS.iter()
+    }
+
+    /// Parses a string into a field label.
+    /// If the string doesn't match a field label, `None` is returned.
+    fn from_attr(attr: &Meta) -> Option<Label> {
+        if let Meta::Path(ref path) = *attr {
+            for &label in Label::variants() {
+                if path.is_ident(label.as_str()) {
+                    return Some(label);
+                }
+            }
+        }
+        None
+    }
+}
+
+impl fmt::Debug for Label {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(self.as_str())
+    }
+}
+
+impl fmt::Display for Label {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(self.as_str())
+    }
+}
+
+/// Get the items belonging to the 'prost' list attribute, e.g. `#[prost(foo, bar="baz")]`.
+fn prost_attrs(attrs: Vec<Attribute>) -> Vec<Meta> {
+    attrs
+        .iter()
+        .flat_map(Attribute::parse_meta)
+        .flat_map(|meta| match meta {
+            Meta::List(MetaList { path, nested, .. }) => {
+                if path.is_ident("prost") {
+                    nested.into_iter().collect()
+                } else {
+                    Vec::new()
+                }
+            }
+            _ => Vec::new(),
+        })
+        .flat_map(|attr| -> Result<_, _> {
+            match attr {
+                NestedMeta::Meta(attr) => Ok(attr),
+                NestedMeta::Lit(lit) => bail!("invalid prost attribute: {:?}", lit),
+            }
+        })
+        .collect()
+}
+
+pub fn set_option<T>(option: &mut Option<T>, value: T, message: &str) -> Result<(), Error>
+where
+    T: fmt::Debug,
+{
+    if let Some(ref existing) = *option {
+        bail!("{}: {:?} and {:?}", message, existing, value);
+    }
+    *option = Some(value);
+    Ok(())
+}
+
+pub fn set_bool(b: &mut bool, message: &str) -> Result<(), Error> {
+    if *b {
+        bail!("{}", message);
+    } else {
+        *b = true;
+        Ok(())
+    }
+}
+
+/// Unpacks an attribute into a (key, boolean) pair, returning the boolean value.
+/// If the key doesn't match the attribute, `None` is returned.
+fn bool_attr(key: &str, attr: &Meta) -> Result<Option<bool>, Error> {
+    if !attr.path().is_ident(key) {
+        return Ok(None);
+    }
+    match *attr {
+        Meta::Path(..) => Ok(Some(true)),
+        Meta::List(ref meta_list) => {
+            // TODO(rustlang/rust#23121): slice pattern matching would make this much nicer.
+            if meta_list.nested.len() == 1 {
+                if let NestedMeta::Lit(Lit::Bool(LitBool { value, .. })) = meta_list.nested[0] {
+                    return Ok(Some(value));
+                }
+            }
+            bail!("invalid {} attribute", key);
+        }
+        Meta::NameValue(MetaNameValue {
+            lit: Lit::Str(ref lit),
+            ..
+        }) => lit
+            .value()
+            .parse::<bool>()
+            .map_err(Error::from)
+            .map(Option::Some),
+        Meta::NameValue(MetaNameValue {
+            lit: Lit::Bool(LitBool { value, .. }),
+            ..
+        }) => Ok(Some(value)),
+        _ => bail!("invalid {} attribute", key),
+    }
+}
+
+/// Checks if an attribute matches a word.
+fn word_attr(key: &str, attr: &Meta) -> bool {
+    if let Meta::Path(ref path) = *attr {
+        path.is_ident(key)
+    } else {
+        false
+    }
+}
+
+pub(super) fn tag_attr(attr: &Meta) -> Result<Option<u32>, Error> {
+    if !attr.path().is_ident("tag") {
+        return Ok(None);
+    }
+    match *attr {
+        Meta::List(ref meta_list) => {
+            // TODO(rustlang/rust#23121): slice pattern matching would make this much nicer.
+            if meta_list.nested.len() == 1 {
+                if let NestedMeta::Lit(Lit::Int(ref lit)) = meta_list.nested[0] {
+                    return Ok(Some(lit.base10_parse()?));
+                }
+            }
+            bail!("invalid tag attribute: {:?}", attr);
+        }
+        Meta::NameValue(ref meta_name_value) => match meta_name_value.lit {
+            Lit::Str(ref lit) => lit
+                .value()
+                .parse::<u32>()
+                .map_err(Error::from)
+                .map(Option::Some),
+            Lit::Int(ref lit) => Ok(Some(lit.base10_parse()?)),
+            _ => bail!("invalid tag attribute: {:?}", attr),
+        },
+        _ => bail!("invalid tag attribute: {:?}", attr),
+    }
+}
+
+fn tags_attr(attr: &Meta) -> Result<Option<Vec<u32>>, Error> {
+    if !attr.path().is_ident("tags") {
+        return Ok(None);
+    }
+    match *attr {
+        Meta::List(ref meta_list) => {
+            let mut tags = Vec::with_capacity(meta_list.nested.len());
+            for item in &meta_list.nested {
+                if let NestedMeta::Lit(Lit::Int(ref lit)) = *item {
+                    tags.push(lit.base10_parse()?);
+                } else {
+                    bail!("invalid tag attribute: {:?}", attr);
+                }
+            }
+            Ok(Some(tags))
+        }
+        Meta::NameValue(MetaNameValue {
+            lit: Lit::Str(ref lit),
+            ..
+        }) => lit
+            .value()
+            .split(',')
+            .map(|s| s.trim().parse::<u32>().map_err(Error::from))
+            .collect::<Result<Vec<u32>, _>>()
+            .map(Some),
+        _ => bail!("invalid tag attribute: {:?}", attr),
+    }
+}
diff --git a/third_party/rust/prost-derive/src/field/oneof.rs b/third_party/rust/prost-derive/src/field/oneof.rs
new file mode 100644
index 0000000000..7e7f08671c
--- /dev/null
+++ b/third_party/rust/prost-derive/src/field/oneof.rs
@@ -0,0 +1,99 @@
+use anyhow::{bail, Error};
+use proc_macro2::TokenStream;
+use quote::quote;
+use syn::{parse_str, Lit, Meta, MetaNameValue, NestedMeta, Path};
+
+use crate::field::{set_option, tags_attr};
+
+#[derive(Clone)]
+pub struct Field {
+    pub ty: Path,
+    pub tags: Vec<u32>,
+}
+
+impl Field {
+    pub fn new(attrs: &[Meta]) -> Result<Option<Field>, Error> {
+        let mut ty = None;
+        let mut tags = None;
+        let mut unknown_attrs = Vec::new();
+
+        for attr in attrs {
+            if attr.path().is_ident("oneof") {
+                let t = match *attr {
+                    Meta::NameValue(MetaNameValue {
+                        lit: Lit::Str(ref lit),
+                        ..
+                    }) => parse_str::<Path>(&lit.value())?,
+                    Meta::List(ref list) if list.nested.len() == 1 => {
+                        // TODO(rustlang/rust#23121): slice pattern matching would make this much nicer.
+                        if let NestedMeta::Meta(Meta::Path(ref path)) = list.nested[0] {
+                            if let Some(ident) = path.get_ident() {
+                                Path::from(ident.clone())
+                            } else {
+                                bail!("invalid oneof attribute: item must be an identifier");
+                            }
+                        } else {
+                            bail!("invalid oneof attribute: item must be an identifier");
+                        }
+                    }
+                    _ => bail!("invalid oneof attribute: {:?}", attr),
+                };
+                set_option(&mut ty, t, "duplicate oneof attribute")?;
+            } else if let Some(t) = tags_attr(attr)? {
+                set_option(&mut tags, t, "duplicate tags attributes")?;
+            } else {
+                unknown_attrs.push(attr);
+            }
+        }
+
+        let ty = match ty {
+            Some(ty) => ty,
+            None => return Ok(None),
+        };
+
+        match unknown_attrs.len() {
+            0 => (),
+            1 => bail!(
+                "unknown attribute for message field: {:?}",
+                unknown_attrs[0]
+            ),
+            _ => bail!("unknown attributes for message field: {:?}", unknown_attrs),
+        }
+
+        let tags = match tags {
+            Some(tags) => tags,
+            None => bail!("oneof field is missing a tags attribute"),
+        };
+
+        Ok(Some(Field { ty, tags }))
+    }
+
+    /// Returns a statement which encodes the oneof field.
+    pub fn encode(&self, ident: TokenStream) -> TokenStream {
+        quote! {
+            if let Some(ref oneof) = #ident {
+                oneof.encode(buf)
+            }
+        }
+    }
+
+    /// Returns an expression which evaluates to the result of decoding the oneof field.
+    pub fn merge(&self, ident: TokenStream) -> TokenStream {
+        let ty = &self.ty;
+        quote! {
+            #ty::merge(#ident, tag, wire_type, buf, ctx)
+        }
+    }
+
+    /// Returns an expression which evaluates to the encoded length of the oneof field.
+    pub fn encoded_len(&self, ident: TokenStream) -> TokenStream {
+        let ty = &self.ty;
+        quote! {
+            #ident.as_ref().map_or(0, #ty::encoded_len)
+        }
+    }
+
+    pub fn clear(&self, ident: TokenStream) -> TokenStream {
+        quote!(#ident = ::core::option::Option::None)
+    }
+}
diff --git a/third_party/rust/prost-derive/src/field/scalar.rs b/third_party/rust/prost-derive/src/field/scalar.rs
new file mode 100644
index 0000000000..75a4fe3a86
--- /dev/null
+++ b/third_party/rust/prost-derive/src/field/scalar.rs
@@ -0,0 +1,810 @@
+use std::convert::TryFrom;
+use std::fmt;
+
+use anyhow::{anyhow, bail, Error};
+use proc_macro2::{Span, TokenStream};
+use quote::{quote, ToTokens, TokenStreamExt};
+use syn::{parse_str, Ident, Lit, LitByteStr, Meta, MetaList, MetaNameValue, NestedMeta, Path};
+
+use crate::field::{bool_attr, set_option, tag_attr, Label};
+
+/// A scalar protobuf field.
+#[derive(Clone)]
+pub struct Field {
+    pub ty: Ty,
+    pub kind: Kind,
+    pub tag: u32,
+}
+
+impl Field {
+    pub fn new(attrs: &[Meta], inferred_tag: Option<u32>) -> Result<Option<Field>, Error> {
+        let mut ty = None;
+        let mut label = None;
+        let mut packed = None;
+        let mut default = None;
+        let mut tag = None;
+
+        let mut unknown_attrs = Vec::new();
+
+        for attr in attrs {
+            if let Some(t) = Ty::from_attr(attr)? {
+                set_option(&mut ty, t, "duplicate type attributes")?;
+            } else if let Some(p) = bool_attr("packed", attr)? {
+                set_option(&mut packed, p, "duplicate packed attributes")?;
+            } else if let Some(t) = tag_attr(attr)? {
+                set_option(&mut tag, t, "duplicate tag attributes")?;
+            } else if let Some(l) = Label::from_attr(attr) {
+                set_option(&mut label, l, "duplicate label attributes")?;
+            } else if let Some(d) = DefaultValue::from_attr(attr)? {
+                set_option(&mut default, d, "duplicate default attributes")?;
+            } else {
+                unknown_attrs.push(attr);
+            }
+        }
+
+        let ty = match ty {
+            Some(ty) => ty,
+            None => return Ok(None),
+        };
+
+        match unknown_attrs.len() {
+            0 => (),
+            1 => bail!("unknown attribute: {:?}", unknown_attrs[0]),
+            _ => bail!("unknown attributes: {:?}", unknown_attrs),
+        }
+
+        let tag = match tag.or(inferred_tag) {
+            Some(tag) => tag,
+            None => bail!("missing tag attribute"),
+        };
+
+        let has_default = default.is_some();
+        let default = default.map_or_else(
+            || Ok(DefaultValue::new(&ty)),
+            |lit| DefaultValue::from_lit(&ty, lit),
+        )?;
+
+        let kind = match (label, packed, has_default) {
+            (None, Some(true), _)
+            | (Some(Label::Optional), Some(true), _)
+            | (Some(Label::Required), Some(true), _) => {
+                bail!("packed attribute may only be applied to repeated fields");
+            }
+            (Some(Label::Repeated), Some(true), _) if !ty.is_numeric() => {
+                bail!("packed attribute may only be applied to numeric types");
+            }
+            (Some(Label::Repeated), _, true) => {
+                bail!("repeated fields may not have a default value");
+            }
+
+            (None, _, _) => Kind::Plain(default),
+            (Some(Label::Optional), _, _) => Kind::Optional(default),
+            (Some(Label::Required), _, _) => Kind::Required(default),
+            (Some(Label::Repeated), packed, false) if packed.unwrap_or_else(|| ty.is_numeric()) => {
+                Kind::Packed
+            }
+            (Some(Label::Repeated), _, false) => Kind::Repeated,
+        };
+
+        Ok(Some(Field { ty, kind, tag }))
+    }
+
+    pub fn new_oneof(attrs: &[Meta]) -> Result<Option<Field>, Error> {
+        if let Some(mut field) = Field::new(attrs, None)? {
+            match field.kind {
+                Kind::Plain(default) => {
+                    field.kind = Kind::Required(default);
+                    Ok(Some(field))
+                }
+                Kind::Optional(..) => bail!("invalid optional attribute on oneof field"),
+                Kind::Required(..) => bail!("invalid required attribute on oneof field"),
+                Kind::Packed | Kind::Repeated => bail!("invalid repeated attribute on oneof field"),
+            }
+        } else {
+            Ok(None)
+        }
+    }
+
+    pub fn encode(&self, ident: TokenStream) -> TokenStream {
+        let module = self.ty.module();
+        let encode_fn = match self.kind {
+            Kind::Plain(..) | Kind::Optional(..) | Kind::Required(..) => quote!(encode),
+            Kind::Repeated => quote!(encode_repeated),
+            Kind::Packed => quote!(encode_packed),
+        };
+        let encode_fn = quote!(::prost::encoding::#module::#encode_fn);
+        let tag = self.tag;
+
+        match self.kind {
+            Kind::Plain(ref default) => {
+                let default = default.typed();
+                quote! {
+                    if #ident != #default {
+                        #encode_fn(#tag, &#ident, buf);
+                    }
+                }
+            }
+            Kind::Optional(..) => quote! {
+                if let ::core::option::Option::Some(ref value) = #ident {
+                    #encode_fn(#tag, value, buf);
+                }
+            },
+            Kind::Required(..) | Kind::Repeated | Kind::Packed => quote! {
+                #encode_fn(#tag, &#ident, buf);
+            },
+        }
+    }
+
+    /// Returns an expression which evaluates to the result of merging a decoded
+    /// scalar value into the field.
+    pub fn merge(&self, ident: TokenStream) -> TokenStream {
+        let module = self.ty.module();
+        let merge_fn = match self.kind {
+            Kind::Plain(..) | Kind::Optional(..) | Kind::Required(..) => quote!(merge),
+            Kind::Repeated | Kind::Packed => quote!(merge_repeated),
+        };
+        let merge_fn = quote!(::prost::encoding::#module::#merge_fn);
+
+        match self.kind {
+            Kind::Plain(..) | Kind::Required(..) | Kind::Repeated | Kind::Packed => quote! {
+                #merge_fn(wire_type, #ident, buf, ctx)
+            },
+            Kind::Optional(..) => quote! {
+                #merge_fn(wire_type,
+                          #ident.get_or_insert_with(Default::default),
+                          buf,
+                          ctx)
+            },
+        }
+    }
+
+    /// Returns an expression which evaluates to the encoded length of the field.
+    pub fn encoded_len(&self, ident: TokenStream) -> TokenStream {
+        let module = self.ty.module();
+        let encoded_len_fn = match self.kind {
+            Kind::Plain(..) | Kind::Optional(..) | Kind::Required(..) => quote!(encoded_len),
+            Kind::Repeated => quote!(encoded_len_repeated),
+            Kind::Packed => quote!(encoded_len_packed),
+        };
+        let encoded_len_fn = quote!(::prost::encoding::#module::#encoded_len_fn);
+        let tag = self.tag;
+
+        match self.kind {
+            Kind::Plain(ref default) => {
+                let default = default.typed();
+                quote! {
+                    if #ident != #default {
+                        #encoded_len_fn(#tag, &#ident)
+                    } else {
+                        0
+                    }
+                }
+            }
+            Kind::Optional(..) => quote! {
+                #ident.as_ref().map_or(0, |value| #encoded_len_fn(#tag, value))
+            },
+            Kind::Required(..) | Kind::Repeated | Kind::Packed => quote! {
+                #encoded_len_fn(#tag, &#ident)
+            },
+        }
+    }
+
+    pub fn clear(&self, ident: TokenStream) -> TokenStream {
+        match self.kind {
+            Kind::Plain(ref default) | Kind::Required(ref default) => {
+                let default = default.typed();
+                match self.ty {
+                    Ty::String | Ty::Bytes(..) => quote!(#ident.clear()),
+                    _ => quote!(#ident = #default),
+                }
+            }
+            Kind::Optional(_) => quote!(#ident = ::core::option::Option::None),
+            Kind::Repeated | Kind::Packed => quote!(#ident.clear()),
+        }
+    }
+
+    /// Returns an expression which evaluates to the default value of the field.
+    pub fn default(&self) -> TokenStream {
+        match self.kind {
+            Kind::Plain(ref value) | Kind::Required(ref value) => value.owned(),
+            Kind::Optional(_) => quote!(::core::option::Option::None),
+            Kind::Repeated | Kind::Packed => quote!(::prost::alloc::vec::Vec::new()),
+        }
+    }
+
+    /// An inner debug wrapper, around the base type.
+    fn debug_inner(&self, wrap_name: TokenStream) -> TokenStream {
+        if let Ty::Enumeration(ref ty) = self.ty {
+            quote! {
+                struct #wrap_name<'a>(&'a i32);
+                impl<'a> ::core::fmt::Debug for #wrap_name<'a> {
+                    fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
+                        match #ty::from_i32(*self.0) {
+                            None => ::core::fmt::Debug::fmt(&self.0, f),
+                            Some(en) => ::core::fmt::Debug::fmt(&en, f),
+                        }
+                    }
+                }
+            }
+        } else {
+            quote! {
+                fn #wrap_name<T>(v: T) -> T { v }
+            }
+        }
+    }
+
+    /// Returns a fragment for formatting the field `ident` in `Debug`.
+    pub fn debug(&self, wrapper_name: TokenStream) -> TokenStream {
+        let wrapper = self.debug_inner(quote!(Inner));
+        let inner_ty = self.ty.rust_type();
+        match self.kind {
+            Kind::Plain(_) | Kind::Required(_) => self.debug_inner(wrapper_name),
+            Kind::Optional(_) => quote! {
+                struct #wrapper_name<'a>(&'a ::core::option::Option<#inner_ty>);
+                impl<'a> ::core::fmt::Debug for #wrapper_name<'a> {
+                    fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
+                        #wrapper
+                        ::core::fmt::Debug::fmt(&self.0.as_ref().map(Inner), f)
+                    }
+                }
+            },
+            Kind::Repeated | Kind::Packed => {
+                quote! {
+                    struct #wrapper_name<'a>(&'a ::prost::alloc::vec::Vec<#inner_ty>);
+                    impl<'a> ::core::fmt::Debug for #wrapper_name<'a> {
+                        fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
+                            let mut vec_builder = f.debug_list();
+                            for v in self.0 {
+                                #wrapper
+                                vec_builder.entry(&Inner(v));
+                            }
+                            vec_builder.finish()
+                        }
+                    }
+                }
+            }
+        }
+    }
+
+    /// Returns methods to embed in the message.
+    pub fn methods(&self, ident: &Ident) -> Option<TokenStream> {
+        let mut ident_str = ident.to_string();
+        if ident_str.starts_with("r#") {
+            ident_str = ident_str[2..].to_owned();
+        }
+
+        if let Ty::Enumeration(ref ty) = self.ty {
+            let set = Ident::new(&format!("set_{}", ident_str), Span::call_site());
+            let set_doc = format!("Sets `{}` to the provided enum value.", ident_str);
+            Some(match self.kind {
+                Kind::Plain(ref default) | Kind::Required(ref default) => {
+                    let get_doc = format!(
+                        "Returns the enum value of `{}`, \
+                         or the default if the field is set to an invalid enum value.",
+                        ident_str,
+                    );
+                    quote! {
+                        #[doc=#get_doc]
+                        pub fn #ident(&self) -> #ty {
+                            #ty::from_i32(self.#ident).unwrap_or(#default)
+                        }
+
+                        #[doc=#set_doc]
+                        pub fn #set(&mut self, value: #ty) {
+                            self.#ident = value as i32;
+                        }
+                    }
+                }
+                Kind::Optional(ref default) => {
+                    let get_doc = format!(
+                        "Returns the enum value of `{}`, \
+                         or the default if the field is unset or set to an invalid enum value.",
+                        ident_str,
+                    );
+                    quote! {
+                        #[doc=#get_doc]
+                        pub fn #ident(&self) -> #ty {
+                            self.#ident.and_then(#ty::from_i32).unwrap_or(#default)
+                        }
+
+                        #[doc=#set_doc]
+                        pub fn #set(&mut self, value: #ty) {
+                            self.#ident = ::core::option::Option::Some(value as i32);
+                        }
+                    }
+                }
+                Kind::Repeated | Kind::Packed => {
+                    let iter_doc = format!(
+                        "Returns an iterator which yields the valid enum values contained in `{}`.",
+                        ident_str,
+                    );
+                    let push = Ident::new(&format!("push_{}", ident_str), Span::call_site());
+                    let push_doc = format!("Appends the provided enum value to `{}`.", ident_str);
+                    quote! {
+                        #[doc=#iter_doc]
+                        pub fn #ident(&self) -> ::core::iter::FilterMap<
+                            ::core::iter::Cloned<::core::slice::Iter<i32>>,
+                            fn(i32) -> ::core::option::Option<#ty>,
+                        > {
+                            self.#ident.iter().cloned().filter_map(#ty::from_i32)
+                        }
+                        #[doc=#push_doc]
+                        pub fn #push(&mut self, value: #ty) {
+                            self.#ident.push(value as i32);
+                        }
+                    }
+                }
+            })
+        } else if let Kind::Optional(ref default) = self.kind {
+            let ty = self.ty.rust_ref_type();
+
+            let match_some = if self.ty.is_numeric() {
+                quote!(::core::option::Option::Some(val) => val,)
+            } else {
+                quote!(::core::option::Option::Some(ref val) => &val[..],)
+            };
+
+            let get_doc = format!(
+                "Returns the value of `{0}`, or the default value if `{0}` is unset.",
+                ident_str,
+            );
+
+            Some(quote! {
+                #[doc=#get_doc]
+                pub fn #ident(&self) -> #ty {
+                    match self.#ident {
+                        #match_some
+                        ::core::option::Option::None => #default,
+                    }
+                }
+            })
+        } else {
+            None
+        }
+    }
+}
+
+/// A scalar protobuf field type.
+#[derive(Clone, PartialEq, Eq)]
+pub enum Ty {
+    Double,
+    Float,
+    Int32,
+    Int64,
+    Uint32,
+    Uint64,
+    Sint32,
+    Sint64,
+    Fixed32,
+    Fixed64,
+    Sfixed32,
+    Sfixed64,
+    Bool,
+    String,
+    Bytes(BytesTy),
+    Enumeration(Path),
+}
+
+#[derive(Clone, Debug, PartialEq, Eq)]
+pub enum BytesTy {
+    Vec,
+    Bytes,
+}
+
+impl BytesTy {
+    fn try_from_str(s: &str) -> Result<Self, Error> {
+        match s {
+            "vec" => Ok(BytesTy::Vec),
+            "bytes" => Ok(BytesTy::Bytes),
+            _ => bail!("Invalid bytes type: {}", s),
+        }
+    }
+
+    fn rust_type(&self) -> TokenStream {
+        match self {
+            BytesTy::Vec => quote! { ::prost::alloc::vec::Vec<u8> },
+            BytesTy::Bytes => quote! { ::prost::bytes::Bytes },
+        }
+    }
+}
+
+impl Ty {
+    pub fn from_attr(attr: &Meta) -> Result<Option<Ty>, Error> {
+        let ty = match *attr {
+            Meta::Path(ref name) if name.is_ident("float") => Ty::Float,
+            Meta::Path(ref name) if name.is_ident("double") => Ty::Double,
+            Meta::Path(ref name) if name.is_ident("int32") => Ty::Int32,
+            Meta::Path(ref name) if name.is_ident("int64") => Ty::Int64,
+            Meta::Path(ref name) if name.is_ident("uint32") => Ty::Uint32,
+            Meta::Path(ref name) if name.is_ident("uint64") => Ty::Uint64,
+            Meta::Path(ref name) if name.is_ident("sint32") => Ty::Sint32,
+            Meta::Path(ref name) if name.is_ident("sint64") => Ty::Sint64,
+            Meta::Path(ref name) if name.is_ident("fixed32") => Ty::Fixed32,
+            Meta::Path(ref name) if name.is_ident("fixed64") => Ty::Fixed64,
+            Meta::Path(ref name) if name.is_ident("sfixed32") => Ty::Sfixed32,
+            Meta::Path(ref name) if name.is_ident("sfixed64") => Ty::Sfixed64,
+            Meta::Path(ref name) if name.is_ident("bool") => Ty::Bool,
+            Meta::Path(ref name) if name.is_ident("string") => Ty::String,
+            Meta::Path(ref name) if name.is_ident("bytes") => Ty::Bytes(BytesTy::Vec),
+            Meta::NameValue(MetaNameValue {
+                ref path,
+                lit: Lit::Str(ref l),
+                ..
+            }) if path.is_ident("bytes") => Ty::Bytes(BytesTy::try_from_str(&l.value())?),
+            Meta::NameValue(MetaNameValue {
+                ref path,
+                lit: Lit::Str(ref l),
+                ..
+            }) if path.is_ident("enumeration") => Ty::Enumeration(parse_str::<Path>(&l.value())?),
+            Meta::List(MetaList {
+                ref path,
+                ref nested,
+                ..
+            }) if path.is_ident("enumeration") => {
+                // TODO(rustlang/rust#23121): slice pattern matching would make this much nicer.
+                if nested.len() == 1 {
+                    if let NestedMeta::Meta(Meta::Path(ref path)) = nested[0] {
+                        Ty::Enumeration(path.clone())
+                    } else {
+                        bail!("invalid enumeration attribute: item must be an identifier");
+                    }
+                } else {
+                    bail!("invalid enumeration attribute: only a single identifier is supported");
+                }
+            }
+            _ => return Ok(None),
+        };
+        Ok(Some(ty))
+    }
+
+    pub fn from_str(s: &str) -> Result<Ty, Error> {
+        let enumeration_len = "enumeration".len();
+        let error = Err(anyhow!("invalid type: {}", s));
+        let ty = match s.trim() {
+            "float" => Ty::Float,
+            "double" => Ty::Double,
+            "int32" => Ty::Int32,
+            "int64" => Ty::Int64,
+            "uint32" => Ty::Uint32,
+            "uint64" => Ty::Uint64,
+            "sint32" => Ty::Sint32,
+            "sint64" => Ty::Sint64,
+            "fixed32" => Ty::Fixed32,
+            "fixed64" => Ty::Fixed64,
+            "sfixed32" => Ty::Sfixed32,
+            "sfixed64" => Ty::Sfixed64,
+            "bool" => Ty::Bool,
+            "string" => Ty::String,
+            "bytes" => Ty::Bytes(BytesTy::Vec),
+            s if s.len() > enumeration_len && &s[..enumeration_len] == "enumeration" => {
+                let s = &s[enumeration_len..].trim();
+                match s.chars().next() {
+                    Some('<') | Some('(') => (),
+                    _ => return error,
+                }
+                match s.chars().next_back() {
+                    Some('>') | Some(')') => (),
+                    _ => return error,
+                }
+
+                Ty::Enumeration(parse_str::<Path>(s[1..s.len() - 1].trim())?)
+            }
+            _ => return error,
+        };
+        Ok(ty)
+    }
+
+    /// Returns the type as it appears in protobuf field declarations.
+    pub fn as_str(&self) -> &'static str {
+        match *self {
+            Ty::Double => "double",
+            Ty::Float => "float",
+            Ty::Int32 => "int32",
+            Ty::Int64 => "int64",
+            Ty::Uint32 => "uint32",
+            Ty::Uint64 => "uint64",
+            Ty::Sint32 => "sint32",
+            Ty::Sint64 => "sint64",
+            Ty::Fixed32 => "fixed32",
+            Ty::Fixed64 => "fixed64",
+            Ty::Sfixed32 => "sfixed32",
+            Ty::Sfixed64 => "sfixed64",
+            Ty::Bool => "bool",
+            Ty::String => "string",
+            Ty::Bytes(..) => "bytes",
+            Ty::Enumeration(..) => "enum",
+        }
+    }
+
+    // TODO: rename to 'owned_type'.
+    pub fn rust_type(&self) -> TokenStream {
+        match self {
+            Ty::String => quote!(::prost::alloc::string::String),
+            Ty::Bytes(ty) => ty.rust_type(),
+            _ => self.rust_ref_type(),
+        }
+    }
+
+    // TODO: rename to 'ref_type'
+    pub fn rust_ref_type(&self) -> TokenStream {
+        match *self {
+            Ty::Double => quote!(f64),
+            Ty::Float => quote!(f32),
+            Ty::Int32 => quote!(i32),
+            Ty::Int64 => quote!(i64),
+            Ty::Uint32 => quote!(u32),
+            Ty::Uint64 => quote!(u64),
+            Ty::Sint32 => quote!(i32),
+            Ty::Sint64 => quote!(i64),
+            Ty::Fixed32 => quote!(u32),
+            Ty::Fixed64 => quote!(u64),
+            Ty::Sfixed32 => quote!(i32),
+            Ty::Sfixed64 => quote!(i64),
+            Ty::Bool => quote!(bool),
+            Ty::String => quote!(&str),
+            Ty::Bytes(..) => quote!(&[u8]),
+            Ty::Enumeration(..) => quote!(i32),
+        }
+    }
+
+    pub fn module(&self) -> Ident {
+        match *self {
+            Ty::Enumeration(..) => Ident::new("int32", Span::call_site()),
+            _ => Ident::new(self.as_str(), Span::call_site()),
+        }
+    }
+
+    /// Returns false if the scalar type is length delimited (i.e., `string` or `bytes`).
+    pub fn is_numeric(&self) -> bool {
+        !matches!(self, Ty::String | Ty::Bytes(..))
+    }
+}
+
+impl fmt::Debug for Ty {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(self.as_str())
+    }
+}
+
+impl fmt::Display for Ty {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str(self.as_str())
+    }
+}
+
+/// Scalar Protobuf field types.
+#[derive(Clone)]
+pub enum Kind {
+    /// A plain proto3 scalar field.
+    Plain(DefaultValue),
+    /// An optional scalar field.
+    Optional(DefaultValue),
+    /// A required proto2 scalar field.
+    Required(DefaultValue),
+    /// A repeated scalar field.
+    Repeated,
+    /// A packed repeated scalar field.
+    Packed,
+}
+
+/// Scalar Protobuf field default value.
+#[derive(Clone, Debug)]
+pub enum DefaultValue {
+    F64(f64),
+    F32(f32),
+    I32(i32),
+    I64(i64),
+    U32(u32),
+    U64(u64),
+    Bool(bool),
+    String(String),
+    Bytes(Vec<u8>),
+    Enumeration(TokenStream),
+    Path(Path),
+}
+
+impl DefaultValue {
+    pub fn from_attr(attr: &Meta) -> Result<Option<Lit>, Error> {
+        if !attr.path().is_ident("default") {
+            Ok(None)
+        } else if let Meta::NameValue(ref name_value) = *attr {
+            Ok(Some(name_value.lit.clone()))
+        } else {
+            bail!("invalid default value attribute: {:?}", attr)
+        }
+    }
+
+    pub fn from_lit(ty: &Ty, lit: Lit) -> Result<DefaultValue, Error> {
+        let is_i32 = *ty == Ty::Int32 || *ty == Ty::Sint32 || *ty == Ty::Sfixed32;
+        let is_i64 = *ty == Ty::Int64 || *ty == Ty::Sint64 || *ty == Ty::Sfixed64;
+
+        let is_u32 = *ty == Ty::Uint32 || *ty == Ty::Fixed32;
+        let is_u64 = *ty == Ty::Uint64 || *ty == Ty::Fixed64;
+
+        let empty_or_is = |expected, actual: &str| expected == actual || actual.is_empty();
+
+        let default = match lit {
+            Lit::Int(ref lit) if is_i32 && empty_or_is("i32", lit.suffix()) => {
+                DefaultValue::I32(lit.base10_parse()?)
+            }
+            Lit::Int(ref lit) if is_i64 && empty_or_is("i64", lit.suffix()) => {
+                DefaultValue::I64(lit.base10_parse()?)
+            }
+            Lit::Int(ref lit) if is_u32 && empty_or_is("u32", lit.suffix()) => {
+                DefaultValue::U32(lit.base10_parse()?)
+            }
+            Lit::Int(ref lit) if is_u64 && empty_or_is("u64", lit.suffix()) => {
+                DefaultValue::U64(lit.base10_parse()?)
+            }
+
+            Lit::Float(ref lit) if *ty == Ty::Float && empty_or_is("f32", lit.suffix()) => {
+                DefaultValue::F32(lit.base10_parse()?)
+            }
+            Lit::Int(ref lit) if *ty == Ty::Float => DefaultValue::F32(lit.base10_parse()?),
+
+            Lit::Float(ref lit) if *ty == Ty::Double && empty_or_is("f64", lit.suffix()) => {
+                DefaultValue::F64(lit.base10_parse()?)
+            }
+            Lit::Int(ref lit) if *ty == Ty::Double => DefaultValue::F64(lit.base10_parse()?),
+
+            Lit::Bool(ref lit) if *ty == Ty::Bool => DefaultValue::Bool(lit.value),
+            Lit::Str(ref lit) if *ty == Ty::String => DefaultValue::String(lit.value()),
+            Lit::ByteStr(ref lit)
+                if *ty == Ty::Bytes(BytesTy::Bytes) || *ty == Ty::Bytes(BytesTy::Vec) =>
+            {
+                DefaultValue::Bytes(lit.value())
+            }
+
+            Lit::Str(ref lit) => {
+                let value = lit.value();
+                let value = value.trim();
+
+                if let Ty::Enumeration(ref path) = *ty {
+                    let variant = Ident::new(value, Span::call_site());
+                    return Ok(DefaultValue::Enumeration(quote!(#path::#variant)));
+                }
+
+                // Parse special floating point values.
+                if *ty == Ty::Float {
+                    match value {
+                        "inf" => {
+                            return Ok(DefaultValue::Path(parse_str::<Path>(
+                                "::core::f32::INFINITY",
+                            )?));
+                        }
+                        "-inf" => {
+                            return Ok(DefaultValue::Path(parse_str::<Path>(
+                                "::core::f32::NEG_INFINITY",
+                            )?));
+                        }
+                        "nan" => {
+                            return Ok(DefaultValue::Path(parse_str::<Path>("::core::f32::NAN")?));
+                        }
+                        _ => (),
+                    }
+                }
+                if *ty == Ty::Double {
+                    match value {
+                        "inf" => {
+                            return Ok(DefaultValue::Path(parse_str::<Path>(
+                                "::core::f64::INFINITY",
+                            )?));
+                        }
+                        "-inf" => {
+                            return Ok(DefaultValue::Path(parse_str::<Path>(
+                                "::core::f64::NEG_INFINITY",
+                            )?));
+                        }
+                        "nan" => {
+                            return Ok(DefaultValue::Path(parse_str::<Path>("::core::f64::NAN")?));
+                        }
+                        _ => (),
+                    }
+                }
+
+                // Rust doesn't have a negative literals, so they have to be parsed specially.
+                if let Some(Ok(lit)) = value.strip_prefix('-').map(syn::parse_str::<Lit>) {
+                    match lit {
+                        Lit::Int(ref lit) if is_i32 && empty_or_is("i32", lit.suffix()) => {
+                            // Initially parse into an i64, so that i32::MIN does not overflow.
+                            let value: i64 = -lit.base10_parse()?;
+                            return Ok(i32::try_from(value).map(DefaultValue::I32)?);
+                        }
+                        Lit::Int(ref lit) if is_i64 && empty_or_is("i64", lit.suffix()) => {
+                            // Initially parse into an i128, so that i64::MIN does not overflow.
+                            let value: i128 = -lit.base10_parse()?;
+                            return Ok(i64::try_from(value).map(DefaultValue::I64)?);
+                        }
+                        Lit::Float(ref lit)
+                            if *ty == Ty::Float && empty_or_is("f32", lit.suffix()) =>
+                        {
+                            return Ok(DefaultValue::F32(-lit.base10_parse()?));
+                        }
+                        Lit::Float(ref lit)
+                            if *ty == Ty::Double && empty_or_is("f64", lit.suffix()) =>
+                        {
+                            return Ok(DefaultValue::F64(-lit.base10_parse()?));
+                        }
+                        Lit::Int(ref lit) if *ty == Ty::Float && lit.suffix().is_empty() => {
+                            return Ok(DefaultValue::F32(-lit.base10_parse()?));
+                        }
+                        Lit::Int(ref lit) if *ty == Ty::Double && lit.suffix().is_empty() => {
+                            return Ok(DefaultValue::F64(-lit.base10_parse()?));
+                        }
+                        _ => (),
+                    }
+                }
+                match syn::parse_str::<Lit>(&value) {
+                    Ok(Lit::Str(_)) => (),
+                    Ok(lit) => return DefaultValue::from_lit(ty, lit),
+                    _ => (),
+                }
+                bail!("invalid default value: {}", quote!(#value));
+            }
+            _ => bail!("invalid default value: {}", quote!(#lit)),
+        };
+
+        Ok(default)
+    }
+
+    pub fn new(ty: &Ty) -> DefaultValue {
+        match *ty {
+            Ty::Float => DefaultValue::F32(0.0),
+            Ty::Double => DefaultValue::F64(0.0),
+            Ty::Int32 | Ty::Sint32 | Ty::Sfixed32 => DefaultValue::I32(0),
+            Ty::Int64 | Ty::Sint64 | Ty::Sfixed64 => DefaultValue::I64(0),
+            Ty::Uint32 | Ty::Fixed32 => DefaultValue::U32(0),
+            Ty::Uint64 | Ty::Fixed64 => DefaultValue::U64(0),
+
+            Ty::Bool => DefaultValue::Bool(false),
+            Ty::String => DefaultValue::String(String::new()),
+            Ty::Bytes(..) => DefaultValue::Bytes(Vec::new()),
+            Ty::Enumeration(ref path) => DefaultValue::Enumeration(quote!(#path::default())),
+        }
+    }
+
+    pub fn owned(&self) -> TokenStream {
+        match *self {
+            DefaultValue::String(ref value) if value.is_empty() => {
+                quote!(::prost::alloc::string::String::new())
+            }
+            DefaultValue::String(ref value) => quote!(#value.into()),
+            DefaultValue::Bytes(ref value) if value.is_empty() => quote!(Default::default()),
+            DefaultValue::Bytes(ref value) => {
+                let lit = LitByteStr::new(value, Span::call_site());
+                quote!(#lit.as_ref().into())
+            }
+
+            ref other => other.typed(),
+        }
+    }
+
+    pub fn typed(&self) -> TokenStream {
+        if let DefaultValue::Enumeration(_) = *self {
+            quote!(#self as i32)
+        } else {
+            quote!(#self)
+        }
+    }
+}
+
+impl ToTokens for DefaultValue {
+    fn to_tokens(&self, tokens: &mut TokenStream) {
+        match *self {
+            DefaultValue::F64(value) => value.to_tokens(tokens),
+            DefaultValue::F32(value) => value.to_tokens(tokens),
+            DefaultValue::I32(value) => value.to_tokens(tokens),
+            DefaultValue::I64(value) => value.to_tokens(tokens),
+            DefaultValue::U32(value) => value.to_tokens(tokens),
+            DefaultValue::U64(value) => value.to_tokens(tokens),
+            DefaultValue::Bool(value) => value.to_tokens(tokens),
+            DefaultValue::String(ref value) => value.to_tokens(tokens),
+            DefaultValue::Bytes(ref value) => {
+                let byte_str = LitByteStr::new(value, Span::call_site());
+                tokens.append_all(quote!(#byte_str as &[u8]));
+            }
+            DefaultValue::Enumeration(ref value) => value.to_tokens(tokens),
+            DefaultValue::Path(ref value) => value.to_tokens(tokens),
+        }
+    }
+}
diff --git a/third_party/rust/prost-derive/src/lib.rs b/third_party/rust/prost-derive/src/lib.rs
new file mode 100644
index 0000000000..a517c41e80
--- /dev/null
+++ b/third_party/rust/prost-derive/src/lib.rs
@@ -0,0 +1,470 @@
+#![doc(html_root_url = "https://docs.rs/prost-derive/0.8.0")]
+// The `quote!` macro requires deep recursion.
+#![recursion_limit = "4096"]
+
+extern crate alloc;
+extern crate proc_macro;
+
+use anyhow::{bail, Error};
+use itertools::Itertools;
+use proc_macro::TokenStream;
+use proc_macro2::Span;
+use quote::quote;
+use syn::{
+    punctuated::Punctuated, Data, DataEnum, DataStruct, DeriveInput, Expr, Fields, FieldsNamed,
+    FieldsUnnamed, Ident, Variant,
+};
+
+mod field;
+use crate::field::Field;
+
+fn try_message(input: TokenStream) -> Result<TokenStream, Error> {
+    let input: DeriveInput = syn::parse(input)?;
+
+    let ident = input.ident;
+
+    let variant_data = match input.data {
+        Data::Struct(variant_data) => variant_data,
+        Data::Enum(..) => bail!("Message can not be derived for an enum"),
+        Data::Union(..) => bail!("Message can not be derived for a union"),
+    };
+
+    let generics = &input.generics;
+    let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
+
+    let fields = match variant_data {
+        DataStruct {
+            fields: Fields::Named(FieldsNamed { named: fields, .. }),
+            ..
+        }
+        | DataStruct {
+            fields:
+                Fields::Unnamed(FieldsUnnamed {
+                    unnamed: fields, ..
+                }),
+            ..
+        } => fields.into_iter().collect(),
+        DataStruct {
+            fields: Fields::Unit,
+            ..
+        } => Vec::new(),
+    };
+
+    let mut next_tag: u32 = 1;
+    let mut fields = fields
+        .into_iter()
+        .enumerate()
+        .flat_map(|(idx, field)| {
+            let field_ident = field
+                .ident
+                .unwrap_or_else(|| Ident::new(&idx.to_string(), Span::call_site()));
+            match Field::new(field.attrs, Some(next_tag)) {
+                Ok(Some(field)) => {
+                    next_tag = field.tags().iter().max().map(|t| t + 1).unwrap_or(next_tag);
+                    Some(Ok((field_ident, field)))
+                }
+                Ok(None) => None,
+                Err(err) => Some(Err(
+                    err.context(format!("invalid message field {}.{}", ident, field_ident))
+                )),
+            }
+        })
+        .collect::<Result<Vec<_>, _>>()?;
+
+    // We want Debug to be in declaration order
+    let unsorted_fields = fields.clone();
+
+    // Sort the fields by tag number so that fields will be encoded in tag order.
+    // TODO: This encodes oneof fields in the position of their lowest tag,
+    // regardless of the currently occupied variant, is that consequential?
+    // See: https://developers.google.com/protocol-buffers/docs/encoding#order
+    fields.sort_by_key(|&(_, ref field)| field.tags().into_iter().min().unwrap());
+    let fields = fields;
+
+    let mut tags = fields
+        .iter()
+        .flat_map(|&(_, ref field)| field.tags())
+        .collect::<Vec<_>>();
+    let num_tags = tags.len();
+    tags.sort_unstable();
+    tags.dedup();
+    if tags.len() != num_tags {
+        bail!("message {} has fields with duplicate tags", ident);
+    }
+
+    let encoded_len = fields
+        .iter()
+        .map(|&(ref field_ident, ref field)| field.encoded_len(quote!(self.#field_ident)));
+
+    let encode = fields
+        .iter()
+        .map(|&(ref field_ident, ref field)| field.encode(quote!(self.#field_ident)));
+
+    let merge = fields.iter().map(|&(ref field_ident, ref field)| {
+        let merge = field.merge(quote!(value));
+        let tags = field.tags().into_iter().map(|tag| quote!(#tag));
+        let tags = Itertools::intersperse(tags, quote!(|));
+
+        quote! {
+            #(#tags)* => {
+                let mut value = &mut self.#field_ident;
+                #merge.map_err(|mut error| {
+                    error.push(STRUCT_NAME, stringify!(#field_ident));
+                    error
+                })
+            },
+        }
+    });
+
+    let struct_name = if fields.is_empty() {
+        quote!()
+    } else {
+        quote!(
+            const STRUCT_NAME: &'static str = stringify!(#ident);
+        )
+    };
+
+    // TODO
+    let is_struct = true;
+
+    let clear = fields
+        .iter()
+        .map(|&(ref field_ident, ref field)| field.clear(quote!(self.#field_ident)));
+
+    let default = fields.iter().map(|&(ref field_ident, ref field)| {
+        let value = field.default();
+        quote!(#field_ident: #value,)
+    });
+
+    let methods = fields
+        .iter()
+        .flat_map(|&(ref field_ident, ref field)| field.methods(field_ident))
+        .collect::<Vec<_>>();
+    let methods = if methods.is_empty() {
+        quote!()
+    } else {
+        quote! {
+            #[allow(dead_code)]
+            impl #impl_generics #ident #ty_generics #where_clause {
+                #(#methods)*
+            }
+        }
+    };
+
+    let debugs = unsorted_fields.iter().map(|&(ref field_ident, ref field)| {
+        let wrapper = field.debug(quote!(self.#field_ident));
+        let call = if is_struct {
+            quote!(builder.field(stringify!(#field_ident), &wrapper))
+        } else {
+            quote!(builder.field(&wrapper))
+        };
+        quote! {
+             let builder = {
+                 let wrapper = #wrapper;
+                 #call
+             };
+        }
+    });
+    let debug_builder = if is_struct {
+        quote!(f.debug_struct(stringify!(#ident)))
+    } else {
+        quote!(f.debug_tuple(stringify!(#ident)))
+    };
+
+    let expanded = quote! {
+        impl #impl_generics ::prost::Message for #ident #ty_generics #where_clause {
+            #[allow(unused_variables)]
+            fn encode_raw<B>(&self, buf: &mut B) where B: ::prost::bytes::BufMut {
+                #(#encode)*
+            }
+
+            #[allow(unused_variables)]
+            fn merge_field<B>(
+                &mut self,
+                tag: u32,
+                wire_type: ::prost::encoding::WireType,
+                buf: &mut B,
+                ctx: ::prost::encoding::DecodeContext,
+            ) -> ::core::result::Result<(), ::prost::DecodeError>
+            where B: ::prost::bytes::Buf {
+                #struct_name
+                match tag {
+                    #(#merge)*
+                    _ => ::prost::encoding::skip_field(wire_type, tag, buf, ctx),
+                }
+            }
+
+            #[inline]
+            fn encoded_len(&self) -> usize {
+                0 #(+ #encoded_len)*
+            }
+
+            fn clear(&mut self) {
+                #(#clear;)*
+            }
+        }
+
+        impl #impl_generics Default for #ident #ty_generics #where_clause {
+            fn default() -> Self {
+                #ident {
+                    #(#default)*
+                }
+            }
+        }
+
+        impl #impl_generics ::core::fmt::Debug for #ident #ty_generics #where_clause {
+            fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
+                let mut builder = #debug_builder;
+                #(#debugs;)*
+                builder.finish()
+            }
+        }
+
+        #methods
+    };
+
+    Ok(expanded.into())
+}
+
+#[proc_macro_derive(Message, attributes(prost))]
+pub fn message(input: TokenStream) -> TokenStream {
+    try_message(input).unwrap()
+}
+
+fn try_enumeration(input: TokenStream) -> Result<TokenStream, Error> {
+    let input: DeriveInput = syn::parse(input)?;
+    let ident = input.ident;
+
+    let generics = &input.generics;
+    let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
+
+    let punctuated_variants = match input.data {
+        Data::Enum(DataEnum { variants, .. }) => variants,
+        Data::Struct(_) => bail!("Enumeration can not be derived for a struct"),
+        Data::Union(..) => bail!("Enumeration can not be derived for a union"),
+    };
+
+    // Map the variants into 'fields'.
+    let mut variants: Vec<(Ident, Expr)> = Vec::new();
+    for Variant {
+        ident,
+        fields,
+        discriminant,
+        ..
+    } in punctuated_variants
+    {
+        match fields {
+            Fields::Unit => (),
+            Fields::Named(_) | Fields::Unnamed(_) => {
+                bail!("Enumeration variants may not have fields")
+            }
+        }
+
+        match discriminant {
+            Some((_, expr)) => variants.push((ident, expr)),
+            None => bail!("Enumeration variants must have a disriminant"),
+        }
+    }
+
+    if variants.is_empty() {
+        panic!("Enumeration must have at least one variant");
+    }
+
+    let default = variants[0].0.clone();
+
+    let is_valid = variants
+        .iter()
+        .map(|&(_, ref value)| quote!(#value => true));
+    let from = variants.iter().map(
+        |&(ref variant, ref value)| quote!(#value => ::core::option::Option::Some(#ident::#variant)),
+    );
+
+    let is_valid_doc = format!("Returns `true` if `value` is a variant of `{}`.", ident);
+    let from_i32_doc = format!(
+        "Converts an `i32` to a `{}`, or `None` if `value` is not a valid variant.",
+        ident
+    );
+
+    let expanded = quote! {
+        impl #impl_generics #ident #ty_generics #where_clause {
+            #[doc=#is_valid_doc]
+            pub fn is_valid(value: i32) -> bool {
+                match value {
+                    #(#is_valid,)*
+                    _ => false,
+                }
+            }
+
+            #[doc=#from_i32_doc]
+            pub fn from_i32(value: i32) -> ::core::option::Option<#ident> {
+                match value {
+                    #(#from,)*
+                    _ => ::core::option::Option::None,
+                }
+            }
+        }
+
+        impl #impl_generics ::core::default::Default for #ident #ty_generics #where_clause {
+            fn default() -> #ident {
+                #ident::#default
+            }
+        }
+
+        impl #impl_generics ::core::convert::From::<#ident> for i32 #ty_generics #where_clause {
+            fn from(value: #ident) -> i32 {
+                value as i32
+            }
+        }
+    };
+
+    Ok(expanded.into())
+}
+
+#[proc_macro_derive(Enumeration, attributes(prost))]
+pub fn enumeration(input: TokenStream) -> TokenStream {
+    try_enumeration(input).unwrap()
+}
+
+fn try_oneof(input: TokenStream) -> Result<TokenStream, Error> {
+    let input: DeriveInput = syn::parse(input)?;
+
+    let ident = input.ident;
+
+    let variants = match input.data {
+        Data::Enum(DataEnum { variants, .. }) => variants,
+        Data::Struct(..) => bail!("Oneof can not be derived for a struct"),
+        Data::Union(..) => bail!("Oneof can not be derived for a union"),
+    };
+
+    let generics = &input.generics;
+    let (impl_generics, ty_generics, where_clause) = generics.split_for_impl();
+
+    // Map the variants into 'fields'.
+    let mut fields: Vec<(Ident, Field)> = Vec::new();
+    for Variant {
+        attrs,
+        ident: variant_ident,
+        fields: variant_fields,
+        ..
+    } in variants
+    {
+        let variant_fields = match variant_fields {
+            Fields::Unit => Punctuated::new(),
+            Fields::Named(FieldsNamed { named: fields, .. })
+            | Fields::Unnamed(FieldsUnnamed {
+                unnamed: fields, ..
+            }) => fields,
+        };
+        if variant_fields.len() != 1 {
+            bail!("Oneof enum variants must have a single field");
+        }
+        match Field::new_oneof(attrs)? {
+            Some(field) => fields.push((variant_ident, field)),
+            None => bail!("invalid oneof variant: oneof variants may not be ignored"),
+        }
+    }
+
+    let mut tags = fields
+        .iter()
+        .flat_map(|&(ref variant_ident, ref field)| -> Result<u32, Error> {
+            if field.tags().len() > 1 {
+                bail!(
+                    "invalid oneof variant {}::{}: oneof variants may only have a single tag",
+                    ident,
+                    variant_ident
+                );
+            }
+            Ok(field.tags()[0])
+        })
+        .collect::<Vec<_>>();
+    tags.sort_unstable();
+    tags.dedup();
+    if tags.len() != fields.len() {
+        panic!("invalid oneof {}: variants have duplicate tags", ident);
+    }
+
+    let encode = fields.iter().map(|&(ref variant_ident, ref field)| {
+        let encode = field.encode(quote!(*value));
+        quote!(#ident::#variant_ident(ref value) => { #encode })
+    });
+
+    let merge = fields.iter().map(|&(ref variant_ident, ref field)| {
+        let tag = field.tags()[0];
+        let merge = field.merge(quote!(value));
+        quote! {
+            #tag => {
+                match field {
+                    ::core::option::Option::Some(#ident::#variant_ident(ref mut value)) => {
+                        #merge
+                    },
+                    _ => {
+                        let mut owned_value = ::core::default::Default::default();
+                        let value = &mut owned_value;
+                        #merge.map(|_| *field = ::core::option::Option::Some(#ident::#variant_ident(owned_value)))
+                    },
+                }
+            }
+        }
+    });
+
+    let encoded_len = fields.iter().map(|&(ref variant_ident, ref field)| {
+        let encoded_len = field.encoded_len(quote!(*value));
+        quote!(#ident::#variant_ident(ref value) => #encoded_len)
+    });
+
+    let debug = fields.iter().map(|&(ref variant_ident, ref field)| {
+        let wrapper = field.debug(quote!(*value));
+        quote!(#ident::#variant_ident(ref value) => {
+            let wrapper = #wrapper;
+            f.debug_tuple(stringify!(#variant_ident))
+                .field(&wrapper)
+                .finish()
+        })
+    });
+
+    let expanded = quote! {
+        impl #impl_generics #ident #ty_generics #where_clause {
+            pub fn encode<B>(&self, buf: &mut B) where B: ::prost::bytes::BufMut {
+                match *self {
+                    #(#encode,)*
+                }
+            }
+
+            pub fn merge<B>(
+                field: &mut ::core::option::Option<#ident #ty_generics>,
+                tag: u32,
+                wire_type: ::prost::encoding::WireType,
+                buf: &mut B,
+                ctx: ::prost::encoding::DecodeContext,
+            ) -> ::core::result::Result<(), ::prost::DecodeError>
+            where B: ::prost::bytes::Buf {
+                match tag {
+                    #(#merge,)*
+                    _ => unreachable!(concat!("invalid ", stringify!(#ident), " tag: {}"), tag),
+                }
+            }
+
+            #[inline]
+            pub fn encoded_len(&self) -> usize {
+                match *self {
+                    #(#encoded_len,)*
+                }
+            }
+        }
+
+        impl #impl_generics ::core::fmt::Debug for #ident #ty_generics #where_clause {
+            fn fmt(&self, f: &mut ::core::fmt::Formatter) -> ::core::fmt::Result {
+                match *self {
+                    #(#debug,)*
+                }
+            }
+        }
+    };
+
+    Ok(expanded.into())
+}
+
+#[proc_macro_derive(Oneof, attributes(prost))]
+pub fn oneof(input: TokenStream) -> TokenStream {
+    try_oneof(input).unwrap()
+}