Adding upstream version 124.0.1.upstream/124.0.1

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

16 files changed, 3371 insertions, 0 deletions

diff --git a/third_party/rust/walkdir/.cargo-checksum.json b/third_party/rust/walkdir/.cargo-checksum.json
new file mode 100644
index 0000000000..1002a325a9
--- /dev/null
+++ b/third_party/rust/walkdir/.cargo-checksum.json
@@ -0,0 +1 @@
+{"files":{"COPYING":"01c266bced4a434da0051174d6bee16a4c82cf634e2679b6155d40d75012390f","Cargo.toml":"421e6948e2f34af6a8392512de0faaac8837b899b0e31df76ee45ca6f2246659","LICENSE-MIT":"0f96a83840e146e43c0ec96a22ec1f392e0680e6c1226e6f3ba87e0740af850f","README.md":"5fc28c8211fe74af2889a2eb859127f8d543e0f94be80659c307105ed831f84b","UNLICENSE":"7e12e5df4bae12cb21581ba157ced20e1986a0508dd10d0e8a4ab9a4cf94e85c","compare/nftw.c":"6b900b0ac78ce8ece1995f834b194fa14d87d744cabba8f475f0e10b21722c56","compare/walk.py":"d49e26d0b8b2b201d00f2f46bf1f9db46f873c27332da679c9a7adbbf54462d2","rustfmt.toml":"1ca600239a27401c4a43f363cf3f38183a212affc1f31bff3ae93234bbaec228","src/dent.rs":"99226b37127b0a18cf8541b0262fb43b1be52e61b5ae5c574499d316185c5f0d","src/error.rs":"f197c5c0a1006e622e053cc3c51aaafa8afd5a287fed30f18db59022876d47a0","src/lib.rs":"dca984890839db697b4182043678287370bd08ff766610e5b46091e70ce49591","src/tests/mod.rs":"bbce9174bfdbb4a81a9000f702be056b63b439cb8f1bcac64b8569368627d56d","src/tests/recursive.rs":"1afd9bb86cb04e8fead4d1e075efe00f6e16d7cf17bb3014f8c94e8adf869bea","src/tests/util.rs":"ca72ef96f82bb87d8c93d13d581ebb65efcd53fffa87097a84437acecbc30faa","src/util.rs":"14e0da711cad4825ead21446cd61a1444fd49bab853a8a239d8cb74b2caab351"},"package":"808cf2735cd4b6866113f648b791c6adc5714537bc222d9347bb203386ffda56"}
\ No newline at end of file
diff --git a/third_party/rust/walkdir/COPYING b/third_party/rust/walkdir/COPYING
new file mode 100644
index 0000000000..bb9c20a094
--- /dev/null
+++ b/third_party/rust/walkdir/COPYING
@@ -0,0 +1,3 @@
+This project is dual-licensed under the Unlicense and MIT licenses.
+
+You may use this code under the terms of either license.
diff --git a/third_party/rust/walkdir/Cargo.toml b/third_party/rust/walkdir/Cargo.toml
new file mode 100644
index 0000000000..49c666254d
--- /dev/null
+++ b/third_party/rust/walkdir/Cargo.toml
@@ -0,0 +1,41 @@
+# 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 = "walkdir"
+version = "2.3.2"
+authors = ["Andrew Gallant <jamslam@gmail.com>"]
+exclude = ["/ci/*", "/.travis.yml", "/appveyor.yml"]
+description = "Recursively walk a directory."
+homepage = "https://github.com/BurntSushi/walkdir"
+documentation = "https://docs.rs/walkdir/"
+readme = "README.md"
+keywords = ["directory", "recursive", "walk", "iterator"]
+categories = ["filesystem"]
+license = "Unlicense/MIT"
+repository = "https://github.com/BurntSushi/walkdir"
+[dependencies.same-file]
+version = "1.0.1"
+[dev-dependencies.doc-comment]
+version = "0.3"
+[target."cfg(windows)".dependencies.winapi]
+version = "0.3"
+features = ["std", "winnt"]
+
+[target."cfg(windows)".dependencies.winapi-util]
+version = "0.1.1"
+[badges.appveyor]
+repository = "BurntSushi/walkdir"
+
+[badges.travis-ci]
+repository = "BurntSushi/walkdir"
diff --git a/third_party/rust/walkdir/LICENSE-MIT b/third_party/rust/walkdir/LICENSE-MIT
new file mode 100644
index 0000000000..3b0a5dc09c
--- /dev/null
+++ b/third_party/rust/walkdir/LICENSE-MIT
@@ -0,0 +1,21 @@
+The MIT License (MIT)
+
+Copyright (c) 2015 Andrew Gallant
+
+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/walkdir/README.md b/third_party/rust/walkdir/README.md
new file mode 100644
index 0000000000..14bd4a9d26
--- /dev/null
+++ b/third_party/rust/walkdir/README.md
@@ -0,0 +1,139 @@
+walkdir
+=======
+A cross platform Rust library for efficiently walking a directory recursively.
+Comes with support for following symbolic links, controlling the number of
+open file descriptors and efficient mechanisms for pruning the entries in the
+directory tree.
+
+[![Build status](https://github.com/BurntSushi/walkdir/workflows/ci/badge.svg)](https://github.com/BurntSushi/walkdir/actions)
+[![](https://meritbadge.herokuapp.com/walkdir)](https://crates.io/crates/walkdir)
+
+Dual-licensed under MIT or the [UNLICENSE](https://unlicense.org/).
+
+### Documentation
+
+[docs.rs/walkdir](https://docs.rs/walkdir/)
+
+### Usage
+
+To use this crate, add `walkdir` as a dependency to your project's
+`Cargo.toml`:
+
+```toml
+[dependencies]
+walkdir = "2"
+```
+
+### Example
+
+The following code recursively iterates over the directory given and prints
+the path for each entry:
+
+```rust,no_run
+use walkdir::WalkDir;
+
+for entry in WalkDir::new("foo") {
+    let entry = entry.unwrap();
+    println!("{}", entry.path().display());
+}
+```
+
+Or, if you'd like to iterate over all entries and ignore any errors that may
+arise, use `filter_map`. (e.g., This code below will silently skip directories
+that the owner of the running process does not have permission to access.)
+
+```rust,no_run
+use walkdir::WalkDir;
+
+for entry in WalkDir::new("foo").into_iter().filter_map(|e| e.ok()) {
+    println!("{}", entry.path().display());
+}
+```
+
+### Example: follow symbolic links
+
+The same code as above, except `follow_links` is enabled:
+
+```rust,no_run
+use walkdir::WalkDir;
+
+for entry in WalkDir::new("foo").follow_links(true) {
+    let entry = entry.unwrap();
+    println!("{}", entry.path().display());
+}
+```
+
+### Example: skip hidden files and directories efficiently on unix
+
+This uses the `filter_entry` iterator adapter to avoid yielding hidden files
+and directories efficiently:
+
+```rust,no_run
+use walkdir::{DirEntry, WalkDir};
+
+fn is_hidden(entry: &DirEntry) -> bool {
+    entry.file_name()
+         .to_str()
+         .map(|s| s.starts_with("."))
+         .unwrap_or(false)
+}
+
+let walker = WalkDir::new("foo").into_iter();
+for entry in walker.filter_entry(|e| !is_hidden(e)) {
+    let entry = entry.unwrap();
+    println!("{}", entry.path().display());
+}
+```
+
+### Minimum Rust version policy
+
+This crate's minimum supported `rustc` version is `1.34.0`.
+
+The current policy is that the minimum Rust version required to use this crate
+can be increased in minor version updates. For example, if `crate 1.0` requires
+Rust 1.20.0, then `crate 1.0.z` for all values of `z` will also require Rust
+1.20.0 or newer. However, `crate 1.y` for `y > 0` may require a newer minimum
+version of Rust.
+
+In general, this crate will be conservative with respect to the minimum
+supported version of Rust.
+
+### Performance
+
+The short story is that performance is comparable with `find` and glibc's
+`nftw` on both a warm and cold file cache. In fact, I cannot observe any
+performance difference after running `find /`, `walkdir /` and `nftw /` on my
+local file system (SSD, ~3 million entries). More precisely, I am reasonably
+confident that this crate makes as few system calls and close to as few
+allocations as possible.
+
+I haven't recorded any benchmarks, but here are some things you can try with a
+local checkout of `walkdir`:
+
+```sh
+# The directory you want to recursively walk:
+DIR=$HOME
+
+# If you want to observe perf on a cold file cache, run this before *each*
+# command:
+sudo sh -c 'echo 3 > /proc/sys/vm/drop_caches'
+
+# To warm the caches
+find $DIR
+
+# Test speed of `find` on warm cache:
+time find $DIR
+
+# Compile and test speed of `walkdir` crate:
+cargo build --release --example walkdir
+time ./target/release/examples/walkdir $DIR
+
+# Compile and test speed of glibc's `nftw`:
+gcc -O3 -o nftw ./compare/nftw.c
+time ./nftw $DIR
+
+# For shits and giggles, test speed of Python's (2 or 3) os.walk:
+time python ./compare/walk.py $DIR
+```
+
+On my system, the performance of `walkdir`, `find` and `nftw` is comparable.
diff --git a/third_party/rust/walkdir/UNLICENSE b/third_party/rust/walkdir/UNLICENSE
new file mode 100644
index 0000000000..68a49daad8
--- /dev/null
+++ b/third_party/rust/walkdir/UNLICENSE
@@ -0,0 +1,24 @@
+This is free and unencumbered software released into the public domain.
+
+Anyone is free to copy, modify, publish, use, compile, sell, or
+distribute this software, either in source code form or as a compiled
+binary, for any purpose, commercial or non-commercial, and by any
+means.
+
+In jurisdictions that recognize copyright laws, the author or authors
+of this software dedicate any and all copyright interest in the
+software to the public domain. We make this dedication for the benefit
+of the public at large and to the detriment of our heirs and
+successors. We intend this dedication to be an overt act of
+relinquishment in perpetuity of all present and future rights to this
+software under copyright law.
+
+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 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.
+
+For more information, please refer to <http://unlicense.org/>
diff --git a/third_party/rust/walkdir/compare/nftw.c b/third_party/rust/walkdir/compare/nftw.c
new file mode 100644
index 0000000000..7d36e2fdf4
--- /dev/null
+++ b/third_party/rust/walkdir/compare/nftw.c
@@ -0,0 +1,25 @@
+#define _XOPEN_SOURCE 500
+#include <ftw.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+
+static int
+display_info(const char *fpath, const struct stat *sb,
+             int tflag, struct FTW *ftwbuf)
+{
+    printf("%s\n", fpath);
+    return 0;
+}
+
+int
+main(int argc, char *argv[])
+{
+    int flags = FTW_PHYS;
+    if (nftw((argc < 2) ? "." : argv[1], display_info, 20, flags) == -1) {
+        perror("nftw");
+        exit(EXIT_FAILURE);
+    }
+    exit(EXIT_SUCCESS);
+}
diff --git a/third_party/rust/walkdir/compare/walk.py b/third_party/rust/walkdir/compare/walk.py
new file mode 100644
index 0000000000..303d323e24
--- /dev/null
+++ b/third_party/rust/walkdir/compare/walk.py
@@ -0,0 +1,10 @@
+from __future__ import absolute_import, division, print_function
+
+import os
+import sys
+
+for dirpath, dirnames, filenames in os.walk(sys.argv[1]):
+    for n in dirnames:
+        print(os.path.join(dirpath, n))
+    for n in filenames:
+        print(os.path.join(dirpath, n))
diff --git a/third_party/rust/walkdir/rustfmt.toml b/third_party/rust/walkdir/rustfmt.toml
new file mode 100644
index 0000000000..aa37a218b9
--- /dev/null
+++ b/third_party/rust/walkdir/rustfmt.toml
@@ -0,0 +1,2 @@
+max_width = 79
+use_small_heuristics = "max"
diff --git a/third_party/rust/walkdir/src/dent.rs b/third_party/rust/walkdir/src/dent.rs
new file mode 100644
index 0000000000..a28ed3dea0
--- /dev/null
+++ b/third_party/rust/walkdir/src/dent.rs
@@ -0,0 +1,375 @@
+use std::ffi::OsStr;
+use std::fmt;
+use std::fs::{self, FileType};
+use std::path::{Path, PathBuf};
+
+use crate::error::Error;
+use crate::Result;
+
+/// A directory entry.
+///
+/// This is the type of value that is yielded from the iterators defined in
+/// this crate.
+///
+/// On Unix systems, this type implements the [`DirEntryExt`] trait, which
+/// provides efficient access to the inode number of the directory entry.
+///
+/// # Differences with `std::fs::DirEntry`
+///
+/// This type mostly mirrors the type by the same name in [`std::fs`]. There
+/// are some differences however:
+///
+/// * All recursive directory iterators must inspect the entry's type.
+/// Therefore, the value is stored and its access is guaranteed to be cheap and
+/// successful.
+/// * [`path`] and [`file_name`] return borrowed variants.
+/// * If [`follow_links`] was enabled on the originating iterator, then all
+/// operations except for [`path`] operate on the link target. Otherwise, all
+/// operations operate on the symbolic link.
+///
+/// [`std::fs`]: https://doc.rust-lang.org/stable/std/fs/index.html
+/// [`path`]: #method.path
+/// [`file_name`]: #method.file_name
+/// [`follow_links`]: struct.WalkDir.html#method.follow_links
+/// [`DirEntryExt`]: trait.DirEntryExt.html
+pub struct DirEntry {
+    /// The path as reported by the [`fs::ReadDir`] iterator (even if it's a
+    /// symbolic link).
+    ///
+    /// [`fs::ReadDir`]: https://doc.rust-lang.org/stable/std/fs/struct.ReadDir.html
+    path: PathBuf,
+    /// The file type. Necessary for recursive iteration, so store it.
+    ty: FileType,
+    /// Is set when this entry was created from a symbolic link and the user
+    /// expects the iterator to follow symbolic links.
+    follow_link: bool,
+    /// The depth at which this entry was generated relative to the root.
+    depth: usize,
+    /// The underlying inode number (Unix only).
+    #[cfg(unix)]
+    ino: u64,
+    /// The underlying metadata (Windows only). We store this on Windows
+    /// because this comes for free while reading a directory.
+    ///
+    /// We use this to determine whether an entry is a directory or not, which
+    /// works around a bug in Rust's standard library:
+    /// https://github.com/rust-lang/rust/issues/46484
+    #[cfg(windows)]
+    metadata: fs::Metadata,
+}
+
+impl DirEntry {
+    /// The full path that this entry represents.
+    ///
+    /// The full path is created by joining the parents of this entry up to the
+    /// root initially given to [`WalkDir::new`] with the file name of this
+    /// entry.
+    ///
+    /// Note that this *always* returns the path reported by the underlying
+    /// directory entry, even when symbolic links are followed. To get the
+    /// target path, use [`path_is_symlink`] to (cheaply) check if this entry
+    /// corresponds to a symbolic link, and [`std::fs::read_link`] to resolve
+    /// the target.
+    ///
+    /// [`WalkDir::new`]: struct.WalkDir.html#method.new
+    /// [`path_is_symlink`]: struct.DirEntry.html#method.path_is_symlink
+    /// [`std::fs::read_link`]: https://doc.rust-lang.org/stable/std/fs/fn.read_link.html
+    pub fn path(&self) -> &Path {
+        &self.path
+    }
+
+    /// The full path that this entry represents.
+    ///
+    /// Analogous to [`path`], but moves ownership of the path.
+    ///
+    /// [`path`]: struct.DirEntry.html#method.path
+    pub fn into_path(self) -> PathBuf {
+        self.path
+    }
+
+    /// Returns `true` if and only if this entry was created from a symbolic
+    /// link. This is unaffected by the [`follow_links`] setting.
+    ///
+    /// When `true`, the value returned by the [`path`] method is a
+    /// symbolic link name. To get the full target path, you must call
+    /// [`std::fs::read_link(entry.path())`].
+    ///
+    /// [`path`]: struct.DirEntry.html#method.path
+    /// [`follow_links`]: struct.WalkDir.html#method.follow_links
+    /// [`std::fs::read_link(entry.path())`]: https://doc.rust-lang.org/stable/std/fs/fn.read_link.html
+    pub fn path_is_symlink(&self) -> bool {
+        self.ty.is_symlink() || self.follow_link
+    }
+
+    /// Return the metadata for the file that this entry points to.
+    ///
+    /// This will follow symbolic links if and only if the [`WalkDir`] value
+    /// has [`follow_links`] enabled.
+    ///
+    /// # Platform behavior
+    ///
+    /// This always calls [`std::fs::symlink_metadata`].
+    ///
+    /// If this entry is a symbolic link and [`follow_links`] is enabled, then
+    /// [`std::fs::metadata`] is called instead.
+    ///
+    /// # Errors
+    ///
+    /// Similar to [`std::fs::metadata`], returns errors for path values that
+    /// the program does not have permissions to access or if the path does not
+    /// exist.
+    ///
+    /// [`WalkDir`]: struct.WalkDir.html
+    /// [`follow_links`]: struct.WalkDir.html#method.follow_links
+    /// [`std::fs::metadata`]: https://doc.rust-lang.org/std/fs/fn.metadata.html
+    /// [`std::fs::symlink_metadata`]: https://doc.rust-lang.org/stable/std/fs/fn.symlink_metadata.html
+    pub fn metadata(&self) -> Result<fs::Metadata> {
+        self.metadata_internal()
+    }
+
+    #[cfg(windows)]
+    fn metadata_internal(&self) -> Result<fs::Metadata> {
+        if self.follow_link {
+            fs::metadata(&self.path)
+        } else {
+            Ok(self.metadata.clone())
+        }
+        .map_err(|err| Error::from_entry(self, err))
+    }
+
+    #[cfg(not(windows))]
+    fn metadata_internal(&self) -> Result<fs::Metadata> {
+        if self.follow_link {
+            fs::metadata(&self.path)
+        } else {
+            fs::symlink_metadata(&self.path)
+        }
+        .map_err(|err| Error::from_entry(self, err))
+    }
+
+    /// Return the file type for the file that this entry points to.
+    ///
+    /// If this is a symbolic link and [`follow_links`] is `true`, then this
+    /// returns the type of the target.
+    ///
+    /// This never makes any system calls.
+    ///
+    /// [`follow_links`]: struct.WalkDir.html#method.follow_links
+    pub fn file_type(&self) -> fs::FileType {
+        self.ty
+    }
+
+    /// Return the file name of this entry.
+    ///
+    /// If this entry has no file name (e.g., `/`), then the full path is
+    /// returned.
+    pub fn file_name(&self) -> &OsStr {
+        self.path.file_name().unwrap_or_else(|| self.path.as_os_str())
+    }
+
+    /// Returns the depth at which this entry was created relative to the root.
+    ///
+    /// The smallest depth is `0` and always corresponds to the path given
+    /// to the `new` function on `WalkDir`. Its direct descendents have depth
+    /// `1`, and their descendents have depth `2`, and so on.
+    pub fn depth(&self) -> usize {
+        self.depth
+    }
+
+    /// Returns true if and only if this entry points to a directory.
+    ///
+    /// This works around a bug in Rust's standard library:
+    /// https://github.com/rust-lang/rust/issues/46484
+    #[cfg(windows)]
+    pub(crate) fn is_dir(&self) -> bool {
+        use std::os::windows::fs::MetadataExt;
+        use winapi::um::winnt::FILE_ATTRIBUTE_DIRECTORY;
+        self.metadata.file_attributes() & FILE_ATTRIBUTE_DIRECTORY != 0
+    }
+
+    /// Returns true if and only if this entry points to a directory.
+    #[cfg(not(windows))]
+    pub(crate) fn is_dir(&self) -> bool {
+        self.ty.is_dir()
+    }
+
+    #[cfg(windows)]
+    pub(crate) fn from_entry(
+        depth: usize,
+        ent: &fs::DirEntry,
+    ) -> Result<DirEntry> {
+        let path = ent.path();
+        let ty = ent
+            .file_type()
+            .map_err(|err| Error::from_path(depth, path.clone(), err))?;
+        let md = ent
+            .metadata()
+            .map_err(|err| Error::from_path(depth, path.clone(), err))?;
+        Ok(DirEntry {
+            path: path,
+            ty: ty,
+            follow_link: false,
+            depth: depth,
+            metadata: md,
+        })
+    }
+
+    #[cfg(unix)]
+    pub(crate) fn from_entry(
+        depth: usize,
+        ent: &fs::DirEntry,
+    ) -> Result<DirEntry> {
+        use std::os::unix::fs::DirEntryExt;
+
+        let ty = ent
+            .file_type()
+            .map_err(|err| Error::from_path(depth, ent.path(), err))?;
+        Ok(DirEntry {
+            path: ent.path(),
+            ty: ty,
+            follow_link: false,
+            depth: depth,
+            ino: ent.ino(),
+        })
+    }
+
+    #[cfg(not(any(unix, windows)))]
+    pub(crate) fn from_entry(
+        depth: usize,
+        ent: &fs::DirEntry,
+    ) -> Result<DirEntry> {
+        let ty = ent
+            .file_type()
+            .map_err(|err| Error::from_path(depth, ent.path(), err))?;
+        Ok(DirEntry {
+            path: ent.path(),
+            ty: ty,
+            follow_link: false,
+            depth: depth,
+        })
+    }
+
+    #[cfg(windows)]
+    pub(crate) fn from_path(
+        depth: usize,
+        pb: PathBuf,
+        follow: bool,
+    ) -> Result<DirEntry> {
+        let md = if follow {
+            fs::metadata(&pb)
+                .map_err(|err| Error::from_path(depth, pb.clone(), err))?
+        } else {
+            fs::symlink_metadata(&pb)
+                .map_err(|err| Error::from_path(depth, pb.clone(), err))?
+        };
+        Ok(DirEntry {
+            path: pb,
+            ty: md.file_type(),
+            follow_link: follow,
+            depth: depth,
+            metadata: md,
+        })
+    }
+
+    #[cfg(unix)]
+    pub(crate) fn from_path(
+        depth: usize,
+        pb: PathBuf,
+        follow: bool,
+    ) -> Result<DirEntry> {
+        use std::os::unix::fs::MetadataExt;
+
+        let md = if follow {
+            fs::metadata(&pb)
+                .map_err(|err| Error::from_path(depth, pb.clone(), err))?
+        } else {
+            fs::symlink_metadata(&pb)
+                .map_err(|err| Error::from_path(depth, pb.clone(), err))?
+        };
+        Ok(DirEntry {
+            path: pb,
+            ty: md.file_type(),
+            follow_link: follow,
+            depth: depth,
+            ino: md.ino(),
+        })
+    }
+
+    #[cfg(not(any(unix, windows)))]
+    pub(crate) fn from_path(
+        depth: usize,
+        pb: PathBuf,
+        follow: bool,
+    ) -> Result<DirEntry> {
+        let md = if follow {
+            fs::metadata(&pb)
+                .map_err(|err| Error::from_path(depth, pb.clone(), err))?
+        } else {
+            fs::symlink_metadata(&pb)
+                .map_err(|err| Error::from_path(depth, pb.clone(), err))?
+        };
+        Ok(DirEntry {
+            path: pb,
+            ty: md.file_type(),
+            follow_link: follow,
+            depth: depth,
+        })
+    }
+}
+
+impl Clone for DirEntry {
+    #[cfg(windows)]
+    fn clone(&self) -> DirEntry {
+        DirEntry {
+            path: self.path.clone(),
+            ty: self.ty,
+            follow_link: self.follow_link,
+            depth: self.depth,
+            metadata: self.metadata.clone(),
+        }
+    }
+
+    #[cfg(unix)]
+    fn clone(&self) -> DirEntry {
+        DirEntry {
+            path: self.path.clone(),
+            ty: self.ty,
+            follow_link: self.follow_link,
+            depth: self.depth,
+            ino: self.ino,
+        }
+    }
+
+    #[cfg(not(any(unix, windows)))]
+    fn clone(&self) -> DirEntry {
+        DirEntry {
+            path: self.path.clone(),
+            ty: self.ty,
+            follow_link: self.follow_link,
+            depth: self.depth,
+        }
+    }
+}
+
+impl fmt::Debug for DirEntry {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "DirEntry({:?})", self.path)
+    }
+}
+
+/// Unix-specific extension methods for `walkdir::DirEntry`
+#[cfg(unix)]
+pub trait DirEntryExt {
+    /// Returns the underlying `d_ino` field in the contained `dirent`
+    /// structure.
+    fn ino(&self) -> u64;
+}
+
+#[cfg(unix)]
+impl DirEntryExt for DirEntry {
+    /// Returns the underlying `d_ino` field in the contained `dirent`
+    /// structure.
+    fn ino(&self) -> u64 {
+        self.ino
+    }
+}
diff --git a/third_party/rust/walkdir/src/error.rs b/third_party/rust/walkdir/src/error.rs
new file mode 100644
index 0000000000..9e25a075ec
--- /dev/null
+++ b/third_party/rust/walkdir/src/error.rs
@@ -0,0 +1,265 @@
+use std::error;
+use std::fmt;
+use std::io;
+use std::path::{Path, PathBuf};
+
+use crate::DirEntry;
+
+/// An error produced by recursively walking a directory.
+///
+/// This error type is a light wrapper around [`std::io::Error`]. In
+/// particular, it adds the following information:
+///
+/// * The depth at which the error occurred in the file tree, relative to the
+/// root.
+/// * The path, if any, associated with the IO error.
+/// * An indication that a loop occurred when following symbolic links. In this
+/// case, there is no underlying IO error.
+///
+/// To maintain good ergonomics, this type has a
+/// [`impl From<Error> for std::io::Error`][impl] defined which preserves the original context.
+/// This allows you to use an [`io::Result`] with methods in this crate if you don't care about
+/// accessing the underlying error data in a structured form.
+///
+/// [`std::io::Error`]: https://doc.rust-lang.org/stable/std/io/struct.Error.html
+/// [`io::Result`]: https://doc.rust-lang.org/stable/std/io/type.Result.html
+/// [impl]: struct.Error.html#impl-From%3CError%3E
+#[derive(Debug)]
+pub struct Error {
+    depth: usize,
+    inner: ErrorInner,
+}
+
+#[derive(Debug)]
+enum ErrorInner {
+    Io { path: Option<PathBuf>, err: io::Error },
+    Loop { ancestor: PathBuf, child: PathBuf },
+}
+
+impl Error {
+    /// Returns the path associated with this error if one exists.
+    ///
+    /// For example, if an error occurred while opening a directory handle,
+    /// the error will include the path passed to [`std::fs::read_dir`].
+    ///
+    /// [`std::fs::read_dir`]: https://doc.rust-lang.org/stable/std/fs/fn.read_dir.html
+    pub fn path(&self) -> Option<&Path> {
+        match self.inner {
+            ErrorInner::Io { path: None, .. } => None,
+            ErrorInner::Io { path: Some(ref path), .. } => Some(path),
+            ErrorInner::Loop { ref child, .. } => Some(child),
+        }
+    }
+
+    /// Returns the path at which a cycle was detected.
+    ///
+    /// If no cycle was detected, [`None`] is returned.
+    ///
+    /// A cycle is detected when a directory entry is equivalent to one of
+    /// its ancestors.
+    ///
+    /// To get the path to the child directory entry in the cycle, use the
+    /// [`path`] method.
+    ///
+    /// [`None`]: https://doc.rust-lang.org/stable/std/option/enum.Option.html#variant.None
+    /// [`path`]: struct.Error.html#path
+    pub fn loop_ancestor(&self) -> Option<&Path> {
+        match self.inner {
+            ErrorInner::Loop { ref ancestor, .. } => Some(ancestor),
+            _ => None,
+        }
+    }
+
+    /// Returns the depth at which this error occurred relative to the root.
+    ///
+    /// The smallest depth is `0` and always corresponds to the path given to
+    /// the [`new`] function on [`WalkDir`]. Its direct descendents have depth
+    /// `1`, and their descendents have depth `2`, and so on.
+    ///
+    /// [`new`]: struct.WalkDir.html#method.new
+    /// [`WalkDir`]: struct.WalkDir.html
+    pub fn depth(&self) -> usize {
+        self.depth
+    }
+
+    /// Inspect the original [`io::Error`] if there is one.
+    ///
+    /// [`None`] is returned if the [`Error`] doesn't correspond to an
+    /// [`io::Error`]. This might happen, for example, when the error was
+    /// produced because a cycle was found in the directory tree while
+    /// following symbolic links.
+    ///
+    /// This method returns a borrowed value that is bound to the lifetime of the [`Error`]. To
+    /// obtain an owned value, the [`into_io_error`] can be used instead.
+    ///
+    /// > This is the original [`io::Error`] and is _not_ the same as
+    /// > [`impl From<Error> for std::io::Error`][impl] which contains additional context about the
+    /// error.
+    ///
+    /// # Example
+    ///
+    /// ```rust,no_run
+    /// use std::io;
+    /// use std::path::Path;
+    ///
+    /// use walkdir::WalkDir;
+    ///
+    /// for entry in WalkDir::new("foo") {
+    ///     match entry {
+    ///         Ok(entry) => println!("{}", entry.path().display()),
+    ///         Err(err) => {
+    ///             let path = err.path().unwrap_or(Path::new("")).display();
+    ///             println!("failed to access entry {}", path);
+    ///             if let Some(inner) = err.io_error() {
+    ///                 match inner.kind() {
+    ///                     io::ErrorKind::InvalidData => {
+    ///                         println!(
+    ///                             "entry contains invalid data: {}",
+    ///                             inner)
+    ///                     }
+    ///                     io::ErrorKind::PermissionDenied => {
+    ///                         println!(
+    ///                             "Missing permission to read entry: {}",
+    ///                             inner)
+    ///                     }
+    ///                     _ => {
+    ///                         println!(
+    ///                             "Unexpected error occurred: {}",
+    ///                             inner)
+    ///                     }
+    ///                 }
+    ///             }
+    ///         }
+    ///     }
+    /// }
+    /// ```
+    ///
+    /// [`None`]: https://doc.rust-lang.org/stable/std/option/enum.Option.html#variant.None
+    /// [`io::Error`]: https://doc.rust-lang.org/stable/std/io/struct.Error.html
+    /// [`From`]: https://doc.rust-lang.org/stable/std/convert/trait.From.html
+    /// [`Error`]: struct.Error.html
+    /// [`into_io_error`]: struct.Error.html#method.into_io_error
+    /// [impl]: struct.Error.html#impl-From%3CError%3E
+    pub fn io_error(&self) -> Option<&io::Error> {
+        match self.inner {
+            ErrorInner::Io { ref err, .. } => Some(err),
+            ErrorInner::Loop { .. } => None,
+        }
+    }
+
+    /// Similar to [`io_error`] except consumes self to convert to the original
+    /// [`io::Error`] if one exists.
+    ///
+    /// [`io_error`]: struct.Error.html#method.io_error
+    /// [`io::Error`]: https://doc.rust-lang.org/stable/std/io/struct.Error.html
+    pub fn into_io_error(self) -> Option<io::Error> {
+        match self.inner {
+            ErrorInner::Io { err, .. } => Some(err),
+            ErrorInner::Loop { .. } => None,
+        }
+    }
+
+    pub(crate) fn from_path(
+        depth: usize,
+        pb: PathBuf,
+        err: io::Error,
+    ) -> Self {
+        Error {
+            depth: depth,
+            inner: ErrorInner::Io { path: Some(pb), err: err },
+        }
+    }
+
+    pub(crate) fn from_entry(dent: &DirEntry, err: io::Error) -> Self {
+        Error {
+            depth: dent.depth(),
+            inner: ErrorInner::Io {
+                path: Some(dent.path().to_path_buf()),
+                err: err,
+            },
+        }
+    }
+
+    pub(crate) fn from_io(depth: usize, err: io::Error) -> Self {
+        Error { depth: depth, inner: ErrorInner::Io { path: None, err: err } }
+    }
+
+    pub(crate) fn from_loop(
+        depth: usize,
+        ancestor: &Path,
+        child: &Path,
+    ) -> Self {
+        Error {
+            depth: depth,
+            inner: ErrorInner::Loop {
+                ancestor: ancestor.to_path_buf(),
+                child: child.to_path_buf(),
+            },
+        }
+    }
+}
+
+impl error::Error for Error {
+    #[allow(deprecated)]
+    fn description(&self) -> &str {
+        match self.inner {
+            ErrorInner::Io { ref err, .. } => err.description(),
+            ErrorInner::Loop { .. } => "file system loop found",
+        }
+    }
+
+    fn cause(&self) -> Option<&dyn error::Error> {
+        self.source()
+    }
+
+    fn source(&self) -> Option<&(dyn error::Error + 'static)> {
+        match self.inner {
+            ErrorInner::Io { ref err, .. } => Some(err),
+            ErrorInner::Loop { .. } => None,
+        }
+    }
+}
+
+impl fmt::Display for Error {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        match self.inner {
+            ErrorInner::Io { path: None, ref err } => err.fmt(f),
+            ErrorInner::Io { path: Some(ref path), ref err } => write!(
+                f,
+                "IO error for operation on {}: {}",
+                path.display(),
+                err
+            ),
+            ErrorInner::Loop { ref ancestor, ref child } => write!(
+                f,
+                "File system loop found: \
+                 {} points to an ancestor {}",
+                child.display(),
+                ancestor.display()
+            ),
+        }
+    }
+}
+
+impl From<Error> for io::Error {
+    /// Convert the [`Error`] to an [`io::Error`], preserving the original
+    /// [`Error`] as the ["inner error"]. Note that this also makes the display
+    /// of the error include the context.
+    ///
+    /// This is different from [`into_io_error`] which returns the original
+    /// [`io::Error`].
+    ///
+    /// [`Error`]: struct.Error.html
+    /// [`io::Error`]: https://doc.rust-lang.org/stable/std/io/struct.Error.html
+    /// ["inner error"]: https://doc.rust-lang.org/std/io/struct.Error.html#method.into_inner
+    /// [`into_io_error`]: struct.WalkDir.html#method.into_io_error
+    fn from(walk_err: Error) -> io::Error {
+        let kind = match walk_err {
+            Error { inner: ErrorInner::Io { ref err, .. }, .. } => err.kind(),
+            Error { inner: ErrorInner::Loop { .. }, .. } => {
+                io::ErrorKind::Other
+            }
+        };
+        io::Error::new(kind, walk_err)
+    }
+}
diff --git a/third_party/rust/walkdir/src/lib.rs b/third_party/rust/walkdir/src/lib.rs
new file mode 100644
index 0000000000..929c5655e4
--- /dev/null
+++ b/third_party/rust/walkdir/src/lib.rs
@@ -0,0 +1,1161 @@
+/*!
+Crate `walkdir` provides an efficient and cross platform implementation
+of recursive directory traversal. Several options are exposed to control
+iteration, such as whether to follow symbolic links (default off), limit the
+maximum number of simultaneous open file descriptors and the ability to
+efficiently skip descending into directories.
+
+To use this crate, add `walkdir` as a dependency to your project's
+`Cargo.toml`:
+
+```toml
+[dependencies]
+walkdir = "2"
+```
+
+# From the top
+
+The [`WalkDir`] type builds iterators. The [`DirEntry`] type describes values
+yielded by the iterator. Finally, the [`Error`] type is a small wrapper around
+[`std::io::Error`] with additional information, such as if a loop was detected
+while following symbolic links (not enabled by default).
+
+[`WalkDir`]: struct.WalkDir.html
+[`DirEntry`]: struct.DirEntry.html
+[`Error`]: struct.Error.html
+[`std::io::Error`]: https://doc.rust-lang.org/stable/std/io/struct.Error.html
+
+# Example
+
+The following code recursively iterates over the directory given and prints
+the path for each entry:
+
+```no_run
+use walkdir::WalkDir;
+# use walkdir::Error;
+
+# fn try_main() -> Result<(), Error> {
+for entry in WalkDir::new("foo") {
+    println!("{}", entry?.path().display());
+}
+# Ok(())
+# }
+```
+
+Or, if you'd like to iterate over all entries and ignore any errors that
+may arise, use [`filter_map`]. (e.g., This code below will silently skip
+directories that the owner of the running process does not have permission to
+access.)
+
+```no_run
+use walkdir::WalkDir;
+
+for entry in WalkDir::new("foo").into_iter().filter_map(|e| e.ok()) {
+    println!("{}", entry.path().display());
+}
+```
+
+[`filter_map`]: https://doc.rust-lang.org/stable/std/iter/trait.Iterator.html#method.filter_map
+
+# Example: follow symbolic links
+
+The same code as above, except [`follow_links`] is enabled:
+
+```no_run
+use walkdir::WalkDir;
+# use walkdir::Error;
+
+# fn try_main() -> Result<(), Error> {
+for entry in WalkDir::new("foo").follow_links(true) {
+    println!("{}", entry?.path().display());
+}
+# Ok(())
+# }
+```
+
+[`follow_links`]: struct.WalkDir.html#method.follow_links
+
+# Example: skip hidden files and directories on unix
+
+This uses the [`filter_entry`] iterator adapter to avoid yielding hidden files
+and directories efficiently (i.e. without recursing into hidden directories):
+
+```no_run
+use walkdir::{DirEntry, WalkDir};
+# use walkdir::Error;
+
+fn is_hidden(entry: &DirEntry) -> bool {
+    entry.file_name()
+         .to_str()
+         .map(|s| s.starts_with("."))
+         .unwrap_or(false)
+}
+
+# fn try_main() -> Result<(), Error> {
+let walker = WalkDir::new("foo").into_iter();
+for entry in walker.filter_entry(|e| !is_hidden(e)) {
+    println!("{}", entry?.path().display());
+}
+# Ok(())
+# }
+```
+
+[`filter_entry`]: struct.IntoIter.html#method.filter_entry
+*/
+
+#![deny(missing_docs)]
+#![allow(unknown_lints)]
+
+#[cfg(doctest)]
+doc_comment::doctest!("../README.md");
+
+use std::cmp::{min, Ordering};
+use std::fmt;
+use std::fs::{self, ReadDir};
+use std::io;
+use std::path::{Path, PathBuf};
+use std::result;
+use std::vec;
+
+use same_file::Handle;
+
+pub use crate::dent::DirEntry;
+#[cfg(unix)]
+pub use crate::dent::DirEntryExt;
+pub use crate::error::Error;
+
+mod dent;
+mod error;
+#[cfg(test)]
+mod tests;
+mod util;
+
+/// Like try, but for iterators that return [`Option<Result<_, _>>`].
+///
+/// [`Option<Result<_, _>>`]: https://doc.rust-lang.org/stable/std/option/enum.Option.html
+macro_rules! itry {
+    ($e:expr) => {
+        match $e {
+            Ok(v) => v,
+            Err(err) => return Some(Err(From::from(err))),
+        }
+    };
+}
+
+/// A result type for walkdir operations.
+///
+/// Note that this result type embeds the error type in this crate. This
+/// is only useful if you care about the additional information provided by
+/// the error (such as the path associated with the error or whether a loop
+/// was dectected). If you want things to Just Work, then you can use
+/// [`io::Result`] instead since the error type in this package will
+/// automatically convert to an [`io::Result`] when using the [`try!`] macro.
+///
+/// [`io::Result`]: https://doc.rust-lang.org/stable/std/io/type.Result.html
+/// [`try!`]: https://doc.rust-lang.org/stable/std/macro.try.html
+pub type Result<T> = ::std::result::Result<T, Error>;
+
+/// A builder to create an iterator for recursively walking a directory.
+///
+/// Results are returned in depth first fashion, with directories yielded
+/// before their contents. If [`contents_first`] is true, contents are yielded
+/// before their directories. The order is unspecified but if [`sort_by`] is
+/// given, directory entries are sorted according to this function. Directory
+/// entries `.` and `..` are always omitted.
+///
+/// If an error occurs at any point during iteration, then it is returned in
+/// place of its corresponding directory entry and iteration continues as
+/// normal. If an error occurs while opening a directory for reading, then it
+/// is not descended into (but the error is still yielded by the iterator).
+/// Iteration may be stopped at any time. When the iterator is destroyed, all
+/// resources associated with it are freed.
+///
+/// [`contents_first`]: struct.WalkDir.html#method.contents_first
+/// [`sort_by`]: struct.WalkDir.html#method.sort_by
+///
+/// # Usage
+///
+/// This type implements [`IntoIterator`] so that it may be used as the subject
+/// of a `for` loop. You may need to call [`into_iter`] explicitly if you want
+/// to use iterator adapters such as [`filter_entry`].
+///
+/// Idiomatic use of this type should use method chaining to set desired
+/// options. For example, this only shows entries with a depth of `1`, `2` or
+/// `3` (relative to `foo`):
+///
+/// ```no_run
+/// use walkdir::WalkDir;
+/// # use walkdir::Error;
+///
+/// # fn try_main() -> Result<(), Error> {
+/// for entry in WalkDir::new("foo").min_depth(1).max_depth(3) {
+///     println!("{}", entry?.path().display());
+/// }
+/// # Ok(())
+/// # }
+/// ```
+///
+/// [`IntoIterator`]: https://doc.rust-lang.org/stable/std/iter/trait.IntoIterator.html
+/// [`into_iter`]: https://doc.rust-lang.org/nightly/core/iter/trait.IntoIterator.html#tymethod.into_iter
+/// [`filter_entry`]: struct.IntoIter.html#method.filter_entry
+///
+/// Note that the iterator by default includes the top-most directory. Since
+/// this is the only directory yielded with depth `0`, it is easy to ignore it
+/// with the [`min_depth`] setting:
+///
+/// ```no_run
+/// use walkdir::WalkDir;
+/// # use walkdir::Error;
+///
+/// # fn try_main() -> Result<(), Error> {
+/// for entry in WalkDir::new("foo").min_depth(1) {
+///     println!("{}", entry?.path().display());
+/// }
+/// # Ok(())
+/// # }
+/// ```
+///
+/// [`min_depth`]: struct.WalkDir.html#method.min_depth
+///
+/// This will only return descendents of the `foo` directory and not `foo`
+/// itself.
+///
+/// # Loops
+///
+/// This iterator (like most/all recursive directory iterators) assumes that
+/// no loops can be made with *hard* links on your file system. In particular,
+/// this would require creating a hard link to a directory such that it creates
+/// a loop. On most platforms, this operation is illegal.
+///
+/// Note that when following symbolic/soft links, loops are detected and an
+/// error is reported.
+#[derive(Debug)]
+pub struct WalkDir {
+    opts: WalkDirOptions,
+    root: PathBuf,
+}
+
+struct WalkDirOptions {
+    follow_links: bool,
+    max_open: usize,
+    min_depth: usize,
+    max_depth: usize,
+    sorter: Option<
+        Box<
+            dyn FnMut(&DirEntry, &DirEntry) -> Ordering
+                + Send
+                + Sync
+                + 'static,
+        >,
+    >,
+    contents_first: bool,
+    same_file_system: bool,
+}
+
+impl fmt::Debug for WalkDirOptions {
+    fn fmt(
+        &self,
+        f: &mut fmt::Formatter<'_>,
+    ) -> result::Result<(), fmt::Error> {
+        let sorter_str = if self.sorter.is_some() {
+            // FnMut isn't `Debug`
+            "Some(...)"
+        } else {
+            "None"
+        };
+        f.debug_struct("WalkDirOptions")
+            .field("follow_links", &self.follow_links)
+            .field("max_open", &self.max_open)
+            .field("min_depth", &self.min_depth)
+            .field("max_depth", &self.max_depth)
+            .field("sorter", &sorter_str)
+            .field("contents_first", &self.contents_first)
+            .field("same_file_system", &self.same_file_system)
+            .finish()
+    }
+}
+
+impl WalkDir {
+    /// Create a builder for a recursive directory iterator starting at the
+    /// file path `root`. If `root` is a directory, then it is the first item
+    /// yielded by the iterator. If `root` is a file, then it is the first
+    /// and only item yielded by the iterator. If `root` is a symlink, then it
+    /// is always followed for the purposes of directory traversal. (A root
+    /// `DirEntry` still obeys its documentation with respect to symlinks and
+    /// the `follow_links` setting.)
+    pub fn new<P: AsRef<Path>>(root: P) -> Self {
+        WalkDir {
+            opts: WalkDirOptions {
+                follow_links: false,
+                max_open: 10,
+                min_depth: 0,
+                max_depth: ::std::usize::MAX,
+                sorter: None,
+                contents_first: false,
+                same_file_system: false,
+            },
+            root: root.as_ref().to_path_buf(),
+        }
+    }
+
+    /// Set the minimum depth of entries yielded by the iterator.
+    ///
+    /// The smallest depth is `0` and always corresponds to the path given
+    /// to the `new` function on this type. Its direct descendents have depth
+    /// `1`, and their descendents have depth `2`, and so on.
+    pub fn min_depth(mut self, depth: usize) -> Self {
+        self.opts.min_depth = depth;
+        if self.opts.min_depth > self.opts.max_depth {
+            self.opts.min_depth = self.opts.max_depth;
+        }
+        self
+    }
+
+    /// Set the maximum depth of entries yield by the iterator.
+    ///
+    /// The smallest depth is `0` and always corresponds to the path given
+    /// to the `new` function on this type. Its direct descendents have depth
+    /// `1`, and their descendents have depth `2`, and so on.
+    ///
+    /// Note that this will not simply filter the entries of the iterator, but
+    /// it will actually avoid descending into directories when the depth is
+    /// exceeded.
+    pub fn max_depth(mut self, depth: usize) -> Self {
+        self.opts.max_depth = depth;
+        if self.opts.max_depth < self.opts.min_depth {
+            self.opts.max_depth = self.opts.min_depth;
+        }
+        self
+    }
+
+    /// Follow symbolic links. By default, this is disabled.
+    ///
+    /// When `yes` is `true`, symbolic links are followed as if they were
+    /// normal directories and files. If a symbolic link is broken or is
+    /// involved in a loop, an error is yielded.
+    ///
+    /// When enabled, the yielded [`DirEntry`] values represent the target of
+    /// the link while the path corresponds to the link. See the [`DirEntry`]
+    /// type for more details.
+    ///
+    /// [`DirEntry`]: struct.DirEntry.html
+    pub fn follow_links(mut self, yes: bool) -> Self {
+        self.opts.follow_links = yes;
+        self
+    }
+
+    /// Set the maximum number of simultaneously open file descriptors used
+    /// by the iterator.
+    ///
+    /// `n` must be greater than or equal to `1`. If `n` is `0`, then it is set
+    /// to `1` automatically. If this is not set, then it defaults to some
+    /// reasonably low number.
+    ///
+    /// This setting has no impact on the results yielded by the iterator
+    /// (even when `n` is `1`). Instead, this setting represents a trade off
+    /// between scarce resources (file descriptors) and memory. Namely, when
+    /// the maximum number of file descriptors is reached and a new directory
+    /// needs to be opened to continue iteration, then a previous directory
+    /// handle is closed and has its unyielded entries stored in memory. In
+    /// practice, this is a satisfying trade off because it scales with respect
+    /// to the *depth* of your file tree. Therefore, low values (even `1`) are
+    /// acceptable.
+    ///
+    /// Note that this value does not impact the number of system calls made by
+    /// an exhausted iterator.
+    ///
+    /// # Platform behavior
+    ///
+    /// On Windows, if `follow_links` is enabled, then this limit is not
+    /// respected. In particular, the maximum number of file descriptors opened
+    /// is proportional to the depth of the directory tree traversed.
+    pub fn max_open(mut self, mut n: usize) -> Self {
+        if n == 0 {
+            n = 1;
+        }
+        self.opts.max_open = n;
+        self
+    }
+
+    /// Set a function for sorting directory entries with a comparator
+    /// function.
+    ///
+    /// If a compare function is set, the resulting iterator will return all
+    /// paths in sorted order. The compare function will be called to compare
+    /// entries from the same directory.
+    ///
+    /// ```rust,no_run
+    /// use std::cmp;
+    /// use std::ffi::OsString;
+    /// use walkdir::WalkDir;
+    ///
+    /// WalkDir::new("foo").sort_by(|a,b| a.file_name().cmp(b.file_name()));
+    /// ```
+    pub fn sort_by<F>(mut self, cmp: F) -> Self
+    where
+        F: FnMut(&DirEntry, &DirEntry) -> Ordering + Send + Sync + 'static,
+    {
+        self.opts.sorter = Some(Box::new(cmp));
+        self
+    }
+
+    /// Set a function for sorting directory entries with a key extraction
+    /// function.
+    ///
+    /// If a compare function is set, the resulting iterator will return all
+    /// paths in sorted order. The compare function will be called to compare
+    /// entries from the same directory.
+    ///
+    /// ```rust,no_run
+    /// use std::cmp;
+    /// use std::ffi::OsString;
+    /// use walkdir::WalkDir;
+    ///
+    /// WalkDir::new("foo").sort_by_key(|a| a.file_name().to_owned());
+    /// ```
+    pub fn sort_by_key<K, F>(self, mut cmp: F) -> Self
+    where
+        F: FnMut(&DirEntry) -> K + Send + Sync + 'static,
+        K: Ord,
+    {
+        self.sort_by(move |a, b| cmp(a).cmp(&cmp(b)))
+    }
+
+    /// Sort directory entries by file name, to ensure a deterministic order.
+    ///
+    /// This is a convenience function for calling `Self::sort_by()`.
+    ///
+    /// ```rust,no_run
+    /// use walkdir::WalkDir;
+    ///
+    /// WalkDir::new("foo").sort_by_file_name();
+    /// ```
+    pub fn sort_by_file_name(self) -> Self {
+        self.sort_by(|a, b| a.file_name().cmp(b.file_name()))
+    }
+
+    /// Yield a directory's contents before the directory itself. By default,
+    /// this is disabled.
+    ///
+    /// When `yes` is `false` (as is the default), the directory is yielded
+    /// before its contents are read. This is useful when, e.g. you want to
+    /// skip processing of some directories.
+    ///
+    /// When `yes` is `true`, the iterator yields the contents of a directory
+    /// before yielding the directory itself. This is useful when, e.g. you
+    /// want to recursively delete a directory.
+    ///
+    /// # Example
+    ///
+    /// Assume the following directory tree:
+    ///
+    /// ```text
+    /// foo/
+    ///   abc/
+    ///     qrs
+    ///     tuv
+    ///   def/
+    /// ```
+    ///
+    /// With contents_first disabled (the default), the following code visits
+    /// the directory tree in depth-first order:
+    ///
+    /// ```no_run
+    /// use walkdir::WalkDir;
+    ///
+    /// for entry in WalkDir::new("foo") {
+    ///     let entry = entry.unwrap();
+    ///     println!("{}", entry.path().display());
+    /// }
+    ///
+    /// // foo
+    /// // foo/abc
+    /// // foo/abc/qrs
+    /// // foo/abc/tuv
+    /// // foo/def
+    /// ```
+    ///
+    /// With contents_first enabled:
+    ///
+    /// ```no_run
+    /// use walkdir::WalkDir;
+    ///
+    /// for entry in WalkDir::new("foo").contents_first(true) {
+    ///     let entry = entry.unwrap();
+    ///     println!("{}", entry.path().display());
+    /// }
+    ///
+    /// // foo/abc/qrs
+    /// // foo/abc/tuv
+    /// // foo/abc
+    /// // foo/def
+    /// // foo
+    /// ```
+    pub fn contents_first(mut self, yes: bool) -> Self {
+        self.opts.contents_first = yes;
+        self
+    }
+
+    /// Do not cross file system boundaries.
+    ///
+    /// When this option is enabled, directory traversal will not descend into
+    /// directories that are on a different file system from the root path.
+    ///
+    /// Currently, this option is only supported on Unix and Windows. If this
+    /// option is used on an unsupported platform, then directory traversal
+    /// will immediately return an error and will not yield any entries.
+    pub fn same_file_system(mut self, yes: bool) -> Self {
+        self.opts.same_file_system = yes;
+        self
+    }
+}
+
+impl IntoIterator for WalkDir {
+    type Item = Result<DirEntry>;
+    type IntoIter = IntoIter;
+
+    fn into_iter(self) -> IntoIter {
+        IntoIter {
+            opts: self.opts,
+            start: Some(self.root),
+            stack_list: vec![],
+            stack_path: vec![],
+            oldest_opened: 0,
+            depth: 0,
+            deferred_dirs: vec![],
+            root_device: None,
+        }
+    }
+}
+
+/// An iterator for recursively descending into a directory.
+///
+/// A value with this type must be constructed with the [`WalkDir`] type, which
+/// uses a builder pattern to set options such as min/max depth, max open file
+/// descriptors and whether the iterator should follow symbolic links. After
+/// constructing a `WalkDir`, call [`.into_iter()`] at the end of the chain.
+///
+/// The order of elements yielded by this iterator is unspecified.
+///
+/// [`WalkDir`]: struct.WalkDir.html
+/// [`.into_iter()`]: struct.WalkDir.html#into_iter.v
+#[derive(Debug)]
+pub struct IntoIter {
+    /// Options specified in the builder. Depths, max fds, etc.
+    opts: WalkDirOptions,
+    /// The start path.
+    ///
+    /// This is only `Some(...)` at the beginning. After the first iteration,
+    /// this is always `None`.
+    start: Option<PathBuf>,
+    /// A stack of open (up to max fd) or closed handles to directories.
+    /// An open handle is a plain [`fs::ReadDir`] while a closed handle is
+    /// a `Vec<fs::DirEntry>` corresponding to the as-of-yet consumed entries.
+    ///
+    /// [`fs::ReadDir`]: https://doc.rust-lang.org/stable/std/fs/struct.ReadDir.html
+    stack_list: Vec<DirList>,
+    /// A stack of file paths.
+    ///
+    /// This is *only* used when [`follow_links`] is enabled. In all other
+    /// cases this stack is empty.
+    ///
+    /// [`follow_links`]: struct.WalkDir.html#method.follow_links
+    stack_path: Vec<Ancestor>,
+    /// An index into `stack_list` that points to the oldest open directory
+    /// handle. If the maximum fd limit is reached and a new directory needs to
+    /// be read, the handle at this index is closed before the new directory is
+    /// opened.
+    oldest_opened: usize,
+    /// The current depth of iteration (the length of the stack at the
+    /// beginning of each iteration).
+    depth: usize,
+    /// A list of DirEntries corresponding to directories, that are
+    /// yielded after their contents has been fully yielded. This is only
+    /// used when `contents_first` is enabled.
+    deferred_dirs: Vec<DirEntry>,
+    /// The device of the root file path when the first call to `next` was
+    /// made.
+    ///
+    /// If the `same_file_system` option isn't enabled, then this is always
+    /// `None`. Conversely, if it is enabled, this is always `Some(...)` after
+    /// handling the root path.
+    root_device: Option<u64>,
+}
+
+/// An ancestor is an item in the directory tree traversed by walkdir, and is
+/// used to check for loops in the tree when traversing symlinks.
+#[derive(Debug)]
+struct Ancestor {
+    /// The path of this ancestor.
+    path: PathBuf,
+    /// An open file to this ancesor. This is only used on Windows where
+    /// opening a file handle appears to be quite expensive, so we choose to
+    /// cache it. This comes at the cost of not respecting the file descriptor
+    /// limit set by the user.
+    #[cfg(windows)]
+    handle: Handle,
+}
+
+impl Ancestor {
+    /// Create a new ancestor from the given directory path.
+    #[cfg(windows)]
+    fn new(dent: &DirEntry) -> io::Result<Ancestor> {
+        let handle = Handle::from_path(dent.path())?;
+        Ok(Ancestor { path: dent.path().to_path_buf(), handle: handle })
+    }
+
+    /// Create a new ancestor from the given directory path.
+    #[cfg(not(windows))]
+    fn new(dent: &DirEntry) -> io::Result<Ancestor> {
+        Ok(Ancestor { path: dent.path().to_path_buf() })
+    }
+
+    /// Returns true if and only if the given open file handle corresponds to
+    /// the same directory as this ancestor.
+    #[cfg(windows)]
+    fn is_same(&self, child: &Handle) -> io::Result<bool> {
+        Ok(child == &self.handle)
+    }
+
+    /// Returns true if and only if the given open file handle corresponds to
+    /// the same directory as this ancestor.
+    #[cfg(not(windows))]
+    fn is_same(&self, child: &Handle) -> io::Result<bool> {
+        Ok(child == &Handle::from_path(&self.path)?)
+    }
+}
+
+/// A sequence of unconsumed directory entries.
+///
+/// This represents the opened or closed state of a directory handle. When
+/// open, future entries are read by iterating over the raw `fs::ReadDir`.
+/// When closed, all future entries are read into memory. Iteration then
+/// proceeds over a [`Vec<fs::DirEntry>`].
+///
+/// [`fs::ReadDir`]: https://doc.rust-lang.org/stable/std/fs/struct.ReadDir.html
+/// [`Vec<fs::DirEntry>`]: https://doc.rust-lang.org/stable/std/vec/struct.Vec.html
+#[derive(Debug)]
+enum DirList {
+    /// An opened handle.
+    ///
+    /// This includes the depth of the handle itself.
+    ///
+    /// If there was an error with the initial [`fs::read_dir`] call, then it
+    /// is stored here. (We use an [`Option<...>`] to make yielding the error
+    /// exactly once simpler.)
+    ///
+    /// [`fs::read_dir`]: https://doc.rust-lang.org/stable/std/fs/fn.read_dir.html
+    /// [`Option<...>`]: https://doc.rust-lang.org/stable/std/option/enum.Option.html
+    Opened { depth: usize, it: result::Result<ReadDir, Option<Error>> },
+    /// A closed handle.
+    ///
+    /// All remaining directory entries are read into memory.
+    Closed(vec::IntoIter<Result<DirEntry>>),
+}
+
+impl Iterator for IntoIter {
+    type Item = Result<DirEntry>;
+    /// Advances the iterator and returns the next value.
+    ///
+    /// # Errors
+    ///
+    /// If the iterator fails to retrieve the next value, this method returns
+    /// an error value. The error will be wrapped in an Option::Some.
+    fn next(&mut self) -> Option<Result<DirEntry>> {
+        if let Some(start) = self.start.take() {
+            if self.opts.same_file_system {
+                let result = util::device_num(&start)
+                    .map_err(|e| Error::from_path(0, start.clone(), e));
+                self.root_device = Some(itry!(result));
+            }
+            let dent = itry!(DirEntry::from_path(0, start, false));
+            if let Some(result) = self.handle_entry(dent) {
+                return Some(result);
+            }
+        }
+        while !self.stack_list.is_empty() {
+            self.depth = self.stack_list.len();
+            if let Some(dentry) = self.get_deferred_dir() {
+                return Some(Ok(dentry));
+            }
+            if self.depth > self.opts.max_depth {
+                // If we've exceeded the max depth, pop the current dir
+                // so that we don't descend.
+                self.pop();
+                continue;
+            }
+            // Unwrap is safe here because we've verified above that
+            // `self.stack_list` is not empty
+            let next = self
+                .stack_list
+                .last_mut()
+                .expect("BUG: stack should be non-empty")
+                .next();
+            match next {
+                None => self.pop(),
+                Some(Err(err)) => return Some(Err(err)),
+                Some(Ok(dent)) => {
+                    if let Some(result) = self.handle_entry(dent) {
+                        return Some(result);
+                    }
+                }
+            }
+        }
+        if self.opts.contents_first {
+            self.depth = self.stack_list.len();
+            if let Some(dentry) = self.get_deferred_dir() {
+                return Some(Ok(dentry));
+            }
+        }
+        None
+    }
+}
+
+impl IntoIter {
+    /// Skips the current directory.
+    ///
+    /// This causes the iterator to stop traversing the contents of the least
+    /// recently yielded directory. This means any remaining entries in that
+    /// directory will be skipped (including sub-directories).
+    ///
+    /// Note that the ergonomics of this method are questionable since it
+    /// borrows the iterator mutably. Namely, you must write out the looping
+    /// condition manually. For example, to skip hidden entries efficiently on
+    /// unix systems:
+    ///
+    /// ```no_run
+    /// use walkdir::{DirEntry, WalkDir};
+    ///
+    /// fn is_hidden(entry: &DirEntry) -> bool {
+    ///     entry.file_name()
+    ///          .to_str()
+    ///          .map(|s| s.starts_with("."))
+    ///          .unwrap_or(false)
+    /// }
+    ///
+    /// let mut it = WalkDir::new("foo").into_iter();
+    /// loop {
+    ///     let entry = match it.next() {
+    ///         None => break,
+    ///         Some(Err(err)) => panic!("ERROR: {}", err),
+    ///         Some(Ok(entry)) => entry,
+    ///     };
+    ///     if is_hidden(&entry) {
+    ///         if entry.file_type().is_dir() {
+    ///             it.skip_current_dir();
+    ///         }
+    ///         continue;
+    ///     }
+    ///     println!("{}", entry.path().display());
+    /// }
+    /// ```
+    ///
+    /// You may find it more convenient to use the [`filter_entry`] iterator
+    /// adapter. (See its documentation for the same example functionality as
+    /// above.)
+    ///
+    /// [`filter_entry`]: #method.filter_entry
+    pub fn skip_current_dir(&mut self) {
+        if !self.stack_list.is_empty() {
+            self.pop();
+        }
+    }
+
+    /// Yields only entries which satisfy the given predicate and skips
+    /// descending into directories that do not satisfy the given predicate.
+    ///
+    /// The predicate is applied to all entries. If the predicate is
+    /// true, iteration carries on as normal. If the predicate is false, the
+    /// entry is ignored and if it is a directory, it is not descended into.
+    ///
+    /// This is often more convenient to use than [`skip_current_dir`]. For
+    /// example, to skip hidden files and directories efficiently on unix
+    /// systems:
+    ///
+    /// ```no_run
+    /// use walkdir::{DirEntry, WalkDir};
+    /// # use walkdir::Error;
+    ///
+    /// fn is_hidden(entry: &DirEntry) -> bool {
+    ///     entry.file_name()
+    ///          .to_str()
+    ///          .map(|s| s.starts_with("."))
+    ///          .unwrap_or(false)
+    /// }
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// for entry in WalkDir::new("foo")
+    ///                      .into_iter()
+    ///                      .filter_entry(|e| !is_hidden(e)) {
+    ///     println!("{}", entry?.path().display());
+    /// }
+    /// # Ok(())
+    /// # }
+    /// ```
+    ///
+    /// Note that the iterator will still yield errors for reading entries that
+    /// may not satisfy the predicate.
+    ///
+    /// Note that entries skipped with [`min_depth`] and [`max_depth`] are not
+    /// passed to this predicate.
+    ///
+    /// Note that if the iterator has `contents_first` enabled, then this
+    /// method is no different than calling the standard `Iterator::filter`
+    /// method (because directory entries are yielded after they've been
+    /// descended into).
+    ///
+    /// [`skip_current_dir`]: #method.skip_current_dir
+    /// [`min_depth`]: struct.WalkDir.html#method.min_depth
+    /// [`max_depth`]: struct.WalkDir.html#method.max_depth
+    pub fn filter_entry<P>(self, predicate: P) -> FilterEntry<Self, P>
+    where
+        P: FnMut(&DirEntry) -> bool,
+    {
+        FilterEntry { it: self, predicate: predicate }
+    }
+
+    fn handle_entry(
+        &mut self,
+        mut dent: DirEntry,
+    ) -> Option<Result<DirEntry>> {
+        if self.opts.follow_links && dent.file_type().is_symlink() {
+            dent = itry!(self.follow(dent));
+        }
+        let is_normal_dir = !dent.file_type().is_symlink() && dent.is_dir();
+        if is_normal_dir {
+            if self.opts.same_file_system && dent.depth() > 0 {
+                if itry!(self.is_same_file_system(&dent)) {
+                    itry!(self.push(&dent));
+                }
+            } else {
+                itry!(self.push(&dent));
+            }
+        } else if dent.depth() == 0 && dent.file_type().is_symlink() {
+            // As a special case, if we are processing a root entry, then we
+            // always follow it even if it's a symlink and follow_links is
+            // false. We are careful to not let this change the semantics of
+            // the DirEntry however. Namely, the DirEntry should still respect
+            // the follow_links setting. When it's disabled, it should report
+            // itself as a symlink. When it's enabled, it should always report
+            // itself as the target.
+            let md = itry!(fs::metadata(dent.path()).map_err(|err| {
+                Error::from_path(dent.depth(), dent.path().to_path_buf(), err)
+            }));
+            if md.file_type().is_dir() {
+                itry!(self.push(&dent));
+            }
+        }
+        if is_normal_dir && self.opts.contents_first {
+            self.deferred_dirs.push(dent);
+            None
+        } else if self.skippable() {
+            None
+        } else {
+            Some(Ok(dent))
+        }
+    }
+
+    fn get_deferred_dir(&mut self) -> Option<DirEntry> {
+        if self.opts.contents_first {
+            if self.depth < self.deferred_dirs.len() {
+                // Unwrap is safe here because we've guaranteed that
+                // `self.deferred_dirs.len()` can never be less than 1
+                let deferred: DirEntry = self
+                    .deferred_dirs
+                    .pop()
+                    .expect("BUG: deferred_dirs should be non-empty");
+                if !self.skippable() {
+                    return Some(deferred);
+                }
+            }
+        }
+        None
+    }
+
+    fn push(&mut self, dent: &DirEntry) -> Result<()> {
+        // Make room for another open file descriptor if we've hit the max.
+        let free =
+            self.stack_list.len().checked_sub(self.oldest_opened).unwrap();
+        if free == self.opts.max_open {
+            self.stack_list[self.oldest_opened].close();
+        }
+        // Open a handle to reading the directory's entries.
+        let rd = fs::read_dir(dent.path()).map_err(|err| {
+            Some(Error::from_path(self.depth, dent.path().to_path_buf(), err))
+        });
+        let mut list = DirList::Opened { depth: self.depth, it: rd };
+        if let Some(ref mut cmp) = self.opts.sorter {
+            let mut entries: Vec<_> = list.collect();
+            entries.sort_by(|a, b| match (a, b) {
+                (&Ok(ref a), &Ok(ref b)) => cmp(a, b),
+                (&Err(_), &Err(_)) => Ordering::Equal,
+                (&Ok(_), &Err(_)) => Ordering::Greater,
+                (&Err(_), &Ok(_)) => Ordering::Less,
+            });
+            list = DirList::Closed(entries.into_iter());
+        }
+        if self.opts.follow_links {
+            let ancestor = Ancestor::new(&dent)
+                .map_err(|err| Error::from_io(self.depth, err))?;
+            self.stack_path.push(ancestor);
+        }
+        // We push this after stack_path since creating the Ancestor can fail.
+        // If it fails, then we return the error and won't descend.
+        self.stack_list.push(list);
+        // If we had to close out a previous directory stream, then we need to
+        // increment our index the oldest still-open stream. We do this only
+        // after adding to our stack, in order to ensure that the oldest_opened
+        // index remains valid. The worst that can happen is that an already
+        // closed stream will be closed again, which is a no-op.
+        //
+        // We could move the close of the stream above into this if-body, but
+        // then we would have more than the maximum number of file descriptors
+        // open at a particular point in time.
+        if free == self.opts.max_open {
+            // Unwrap is safe here because self.oldest_opened is guaranteed to
+            // never be greater than `self.stack_list.len()`, which implies
+            // that the subtraction won't underflow and that adding 1 will
+            // never overflow.
+            self.oldest_opened = self.oldest_opened.checked_add(1).unwrap();
+        }
+        Ok(())
+    }
+
+    fn pop(&mut self) {
+        self.stack_list.pop().expect("BUG: cannot pop from empty stack");
+        if self.opts.follow_links {
+            self.stack_path.pop().expect("BUG: list/path stacks out of sync");
+        }
+        // If everything in the stack is already closed, then there is
+        // room for at least one more open descriptor and it will
+        // always be at the top of the stack.
+        self.oldest_opened = min(self.oldest_opened, self.stack_list.len());
+    }
+
+    fn follow(&self, mut dent: DirEntry) -> Result<DirEntry> {
+        dent =
+            DirEntry::from_path(self.depth, dent.path().to_path_buf(), true)?;
+        // The only way a symlink can cause a loop is if it points
+        // to a directory. Otherwise, it always points to a leaf
+        // and we can omit any loop checks.
+        if dent.is_dir() {
+            self.check_loop(dent.path())?;
+        }
+        Ok(dent)
+    }
+
+    fn check_loop<P: AsRef<Path>>(&self, child: P) -> Result<()> {
+        let hchild = Handle::from_path(&child)
+            .map_err(|err| Error::from_io(self.depth, err))?;
+        for ancestor in self.stack_path.iter().rev() {
+            let is_same = ancestor
+                .is_same(&hchild)
+                .map_err(|err| Error::from_io(self.depth, err))?;
+            if is_same {
+                return Err(Error::from_loop(
+                    self.depth,
+                    &ancestor.path,
+                    child.as_ref(),
+                ));
+            }
+        }
+        Ok(())
+    }
+
+    fn is_same_file_system(&mut self, dent: &DirEntry) -> Result<bool> {
+        let dent_device = util::device_num(dent.path())
+            .map_err(|err| Error::from_entry(dent, err))?;
+        Ok(self
+            .root_device
+            .map(|d| d == dent_device)
+            .expect("BUG: called is_same_file_system without root device"))
+    }
+
+    fn skippable(&self) -> bool {
+        self.depth < self.opts.min_depth || self.depth > self.opts.max_depth
+    }
+}
+
+impl DirList {
+    fn close(&mut self) {
+        if let DirList::Opened { .. } = *self {
+            *self = DirList::Closed(self.collect::<Vec<_>>().into_iter());
+        }
+    }
+}
+
+impl Iterator for DirList {
+    type Item = Result<DirEntry>;
+
+    #[inline(always)]
+    fn next(&mut self) -> Option<Result<DirEntry>> {
+        match *self {
+            DirList::Closed(ref mut it) => it.next(),
+            DirList::Opened { depth, ref mut it } => match *it {
+                Err(ref mut err) => err.take().map(Err),
+                Ok(ref mut rd) => rd.next().map(|r| match r {
+                    Ok(r) => DirEntry::from_entry(depth + 1, &r),
+                    Err(err) => Err(Error::from_io(depth + 1, err)),
+                }),
+            },
+        }
+    }
+}
+
+/// A recursive directory iterator that skips entries.
+///
+/// Values of this type are created by calling [`.filter_entry()`] on an
+/// `IntoIter`, which is formed by calling [`.into_iter()`] on a `WalkDir`.
+///
+/// Directories that fail the predicate `P` are skipped. Namely, they are
+/// never yielded and never descended into.
+///
+/// Entries that are skipped with the [`min_depth`] and [`max_depth`] options
+/// are not passed through this filter.
+///
+/// If opening a handle to a directory resulted in an error, then it is yielded
+/// and no corresponding call to the predicate is made.
+///
+/// Type parameter `I` refers to the underlying iterator and `P` refers to the
+/// predicate, which is usually `FnMut(&DirEntry) -> bool`.
+///
+/// [`.filter_entry()`]: struct.IntoIter.html#method.filter_entry
+/// [`.into_iter()`]: struct.WalkDir.html#into_iter.v
+/// [`min_depth`]: struct.WalkDir.html#method.min_depth
+/// [`max_depth`]: struct.WalkDir.html#method.max_depth
+#[derive(Debug)]
+pub struct FilterEntry<I, P> {
+    it: I,
+    predicate: P,
+}
+
+impl<P> Iterator for FilterEntry<IntoIter, P>
+where
+    P: FnMut(&DirEntry) -> bool,
+{
+    type Item = Result<DirEntry>;
+
+    /// Advances the iterator and returns the next value.
+    ///
+    /// # Errors
+    ///
+    /// If the iterator fails to retrieve the next value, this method returns
+    /// an error value. The error will be wrapped in an `Option::Some`.
+    fn next(&mut self) -> Option<Result<DirEntry>> {
+        loop {
+            let dent = match self.it.next() {
+                None => return None,
+                Some(result) => itry!(result),
+            };
+            if !(self.predicate)(&dent) {
+                if dent.is_dir() {
+                    self.it.skip_current_dir();
+                }
+                continue;
+            }
+            return Some(Ok(dent));
+        }
+    }
+}
+
+impl<P> FilterEntry<IntoIter, P>
+where
+    P: FnMut(&DirEntry) -> bool,
+{
+    /// Yields only entries which satisfy the given predicate and skips
+    /// descending into directories that do not satisfy the given predicate.
+    ///
+    /// The predicate is applied to all entries. If the predicate is
+    /// true, iteration carries on as normal. If the predicate is false, the
+    /// entry is ignored and if it is a directory, it is not descended into.
+    ///
+    /// This is often more convenient to use than [`skip_current_dir`]. For
+    /// example, to skip hidden files and directories efficiently on unix
+    /// systems:
+    ///
+    /// ```no_run
+    /// use walkdir::{DirEntry, WalkDir};
+    /// # use walkdir::Error;
+    ///
+    /// fn is_hidden(entry: &DirEntry) -> bool {
+    ///     entry.file_name()
+    ///          .to_str()
+    ///          .map(|s| s.starts_with("."))
+    ///          .unwrap_or(false)
+    /// }
+    ///
+    /// # fn try_main() -> Result<(), Error> {
+    /// for entry in WalkDir::new("foo")
+    ///                      .into_iter()
+    ///                      .filter_entry(|e| !is_hidden(e)) {
+    ///     println!("{}", entry?.path().display());
+    /// }
+    /// # Ok(())
+    /// # }
+    /// ```
+    ///
+    /// Note that the iterator will still yield errors for reading entries that
+    /// may not satisfy the predicate.
+    ///
+    /// Note that entries skipped with [`min_depth`] and [`max_depth`] are not
+    /// passed to this predicate.
+    ///
+    /// Note that if the iterator has `contents_first` enabled, then this
+    /// method is no different than calling the standard `Iterator::filter`
+    /// method (because directory entries are yielded after they've been
+    /// descended into).
+    ///
+    /// [`skip_current_dir`]: #method.skip_current_dir
+    /// [`min_depth`]: struct.WalkDir.html#method.min_depth
+    /// [`max_depth`]: struct.WalkDir.html#method.max_depth
+    pub fn filter_entry(self, predicate: P) -> FilterEntry<Self, P> {
+        FilterEntry { it: self, predicate: predicate }
+    }
+
+    /// Skips the current directory.
+    ///
+    /// This causes the iterator to stop traversing the contents of the least
+    /// recently yielded directory. This means any remaining entries in that
+    /// directory will be skipped (including sub-directories).
+    ///
+    /// Note that the ergonomics of this method are questionable since it
+    /// borrows the iterator mutably. Namely, you must write out the looping
+    /// condition manually. For example, to skip hidden entries efficiently on
+    /// unix systems:
+    ///
+    /// ```no_run
+    /// use walkdir::{DirEntry, WalkDir};
+    ///
+    /// fn is_hidden(entry: &DirEntry) -> bool {
+    ///     entry.file_name()
+    ///          .to_str()
+    ///          .map(|s| s.starts_with("."))
+    ///          .unwrap_or(false)
+    /// }
+    ///
+    /// let mut it = WalkDir::new("foo").into_iter();
+    /// loop {
+    ///     let entry = match it.next() {
+    ///         None => break,
+    ///         Some(Err(err)) => panic!("ERROR: {}", err),
+    ///         Some(Ok(entry)) => entry,
+    ///     };
+    ///     if is_hidden(&entry) {
+    ///         if entry.file_type().is_dir() {
+    ///             it.skip_current_dir();
+    ///         }
+    ///         continue;
+    ///     }
+    ///     println!("{}", entry.path().display());
+    /// }
+    /// ```
+    ///
+    /// You may find it more convenient to use the [`filter_entry`] iterator
+    /// adapter. (See its documentation for the same example functionality as
+    /// above.)
+    ///
+    /// [`filter_entry`]: #method.filter_entry
+    pub fn skip_current_dir(&mut self) {
+        self.it.skip_current_dir();
+    }
+}
diff --git a/third_party/rust/walkdir/src/tests/mod.rs b/third_party/rust/walkdir/src/tests/mod.rs
new file mode 100644
index 0000000000..ebf952dfc5
--- /dev/null
+++ b/third_party/rust/walkdir/src/tests/mod.rs
@@ -0,0 +1,4 @@
+#[macro_use]
+mod util;
+
+mod recursive;
diff --git a/third_party/rust/walkdir/src/tests/recursive.rs b/third_party/rust/walkdir/src/tests/recursive.rs
new file mode 100644
index 0000000000..4119f461d3
--- /dev/null
+++ b/third_party/rust/walkdir/src/tests/recursive.rs
@@ -0,0 +1,1023 @@
+use std::fs;
+use std::path::PathBuf;
+
+use crate::tests::util::Dir;
+use crate::WalkDir;
+
+#[test]
+fn send_sync_traits() {
+    use crate::{FilterEntry, IntoIter};
+
+    fn assert_send<T: Send>() {}
+    fn assert_sync<T: Sync>() {}
+
+    assert_send::<WalkDir>();
+    assert_sync::<WalkDir>();
+    assert_send::<IntoIter>();
+    assert_sync::<IntoIter>();
+    assert_send::<FilterEntry<IntoIter, u8>>();
+    assert_sync::<FilterEntry<IntoIter, u8>>();
+}
+
+#[test]
+fn empty() {
+    let dir = Dir::tmp();
+    let wd = WalkDir::new(dir.path());
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    assert_eq!(1, r.ents().len());
+    let ent = &r.ents()[0];
+    assert!(ent.file_type().is_dir());
+    assert!(!ent.path_is_symlink());
+    assert_eq!(0, ent.depth());
+    assert_eq!(dir.path(), ent.path());
+    assert_eq!(dir.path().file_name().unwrap(), ent.file_name());
+}
+
+#[test]
+fn empty_follow() {
+    let dir = Dir::tmp();
+    let wd = WalkDir::new(dir.path()).follow_links(true);
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    assert_eq!(1, r.ents().len());
+    let ent = &r.ents()[0];
+    assert!(ent.file_type().is_dir());
+    assert!(!ent.path_is_symlink());
+    assert_eq!(0, ent.depth());
+    assert_eq!(dir.path(), ent.path());
+    assert_eq!(dir.path().file_name().unwrap(), ent.file_name());
+}
+
+#[test]
+fn empty_file() {
+    let dir = Dir::tmp();
+    dir.touch("a");
+
+    let wd = WalkDir::new(dir.path().join("a"));
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    assert_eq!(1, r.ents().len());
+    let ent = &r.ents()[0];
+    assert!(ent.file_type().is_file());
+    assert!(!ent.path_is_symlink());
+    assert_eq!(0, ent.depth());
+    assert_eq!(dir.join("a"), ent.path());
+    assert_eq!("a", ent.file_name());
+}
+
+#[test]
+fn empty_file_follow() {
+    let dir = Dir::tmp();
+    dir.touch("a");
+
+    let wd = WalkDir::new(dir.path().join("a")).follow_links(true);
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    assert_eq!(1, r.ents().len());
+    let ent = &r.ents()[0];
+    assert!(ent.file_type().is_file());
+    assert!(!ent.path_is_symlink());
+    assert_eq!(0, ent.depth());
+    assert_eq!(dir.join("a"), ent.path());
+    assert_eq!("a", ent.file_name());
+}
+
+#[test]
+fn one_dir() {
+    let dir = Dir::tmp();
+    dir.mkdirp("a");
+
+    let wd = WalkDir::new(dir.path());
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let ents = r.ents();
+    assert_eq!(2, ents.len());
+    let ent = &ents[1];
+    assert_eq!(dir.join("a"), ent.path());
+    assert_eq!(1, ent.depth());
+    assert_eq!("a", ent.file_name());
+    assert!(ent.file_type().is_dir());
+}
+
+#[test]
+fn one_file() {
+    let dir = Dir::tmp();
+    dir.touch("a");
+
+    let wd = WalkDir::new(dir.path());
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let ents = r.ents();
+    assert_eq!(2, ents.len());
+    let ent = &ents[1];
+    assert_eq!(dir.join("a"), ent.path());
+    assert_eq!(1, ent.depth());
+    assert_eq!("a", ent.file_name());
+    assert!(ent.file_type().is_file());
+}
+
+#[test]
+fn one_dir_one_file() {
+    let dir = Dir::tmp();
+    dir.mkdirp("foo");
+    dir.touch("foo/a");
+
+    let wd = WalkDir::new(dir.path());
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let expected = vec![
+        dir.path().to_path_buf(),
+        dir.join("foo"),
+        dir.join("foo").join("a"),
+    ];
+    assert_eq!(expected, r.sorted_paths());
+}
+
+#[test]
+fn many_files() {
+    let dir = Dir::tmp();
+    dir.mkdirp("foo");
+    dir.touch_all(&["foo/a", "foo/b", "foo/c"]);
+
+    let wd = WalkDir::new(dir.path());
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let expected = vec![
+        dir.path().to_path_buf(),
+        dir.join("foo"),
+        dir.join("foo").join("a"),
+        dir.join("foo").join("b"),
+        dir.join("foo").join("c"),
+    ];
+    assert_eq!(expected, r.sorted_paths());
+}
+
+#[test]
+fn many_dirs() {
+    let dir = Dir::tmp();
+    dir.mkdirp("foo/a");
+    dir.mkdirp("foo/b");
+    dir.mkdirp("foo/c");
+
+    let wd = WalkDir::new(dir.path());
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let expected = vec![
+        dir.path().to_path_buf(),
+        dir.join("foo"),
+        dir.join("foo").join("a"),
+        dir.join("foo").join("b"),
+        dir.join("foo").join("c"),
+    ];
+    assert_eq!(expected, r.sorted_paths());
+}
+
+#[test]
+fn many_mixed() {
+    let dir = Dir::tmp();
+    dir.mkdirp("foo/a");
+    dir.mkdirp("foo/c");
+    dir.mkdirp("foo/e");
+    dir.touch_all(&["foo/b", "foo/d", "foo/f"]);
+
+    let wd = WalkDir::new(dir.path());
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let expected = vec![
+        dir.path().to_path_buf(),
+        dir.join("foo"),
+        dir.join("foo").join("a"),
+        dir.join("foo").join("b"),
+        dir.join("foo").join("c"),
+        dir.join("foo").join("d"),
+        dir.join("foo").join("e"),
+        dir.join("foo").join("f"),
+    ];
+    assert_eq!(expected, r.sorted_paths());
+}
+
+#[test]
+fn nested() {
+    let nested =
+        PathBuf::from("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p/q/r/s/t/u/v/w/x/y/z");
+    let dir = Dir::tmp();
+    dir.mkdirp(&nested);
+    dir.touch(nested.join("A"));
+
+    let wd = WalkDir::new(dir.path());
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let expected = vec![
+        dir.path().to_path_buf(),
+        dir.join("a"),
+        dir.join("a/b"),
+        dir.join("a/b/c"),
+        dir.join("a/b/c/d"),
+        dir.join("a/b/c/d/e"),
+        dir.join("a/b/c/d/e/f"),
+        dir.join("a/b/c/d/e/f/g"),
+        dir.join("a/b/c/d/e/f/g/h"),
+        dir.join("a/b/c/d/e/f/g/h/i"),
+        dir.join("a/b/c/d/e/f/g/h/i/j"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p/q"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p/q/r"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p/q/r/s"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p/q/r/s/t"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p/q/r/s/t/u"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p/q/r/s/t/u/v"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p/q/r/s/t/u/v/w"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p/q/r/s/t/u/v/w/x"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p/q/r/s/t/u/v/w/x/y"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p/q/r/s/t/u/v/w/x/y/z"),
+        dir.join(&nested).join("A"),
+    ];
+    assert_eq!(expected, r.sorted_paths());
+}
+
+#[test]
+fn nested_small_max_open() {
+    let nested =
+        PathBuf::from("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p/q/r/s/t/u/v/w/x/y/z");
+    let dir = Dir::tmp();
+    dir.mkdirp(&nested);
+    dir.touch(nested.join("A"));
+
+    let wd = WalkDir::new(dir.path()).max_open(1);
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let expected = vec![
+        dir.path().to_path_buf(),
+        dir.join("a"),
+        dir.join("a/b"),
+        dir.join("a/b/c"),
+        dir.join("a/b/c/d"),
+        dir.join("a/b/c/d/e"),
+        dir.join("a/b/c/d/e/f"),
+        dir.join("a/b/c/d/e/f/g"),
+        dir.join("a/b/c/d/e/f/g/h"),
+        dir.join("a/b/c/d/e/f/g/h/i"),
+        dir.join("a/b/c/d/e/f/g/h/i/j"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p/q"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p/q/r"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p/q/r/s"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p/q/r/s/t"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p/q/r/s/t/u"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p/q/r/s/t/u/v"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p/q/r/s/t/u/v/w"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p/q/r/s/t/u/v/w/x"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p/q/r/s/t/u/v/w/x/y"),
+        dir.join("a/b/c/d/e/f/g/h/i/j/k/l/m/n/o/p/q/r/s/t/u/v/w/x/y/z"),
+        dir.join(&nested).join("A"),
+    ];
+    assert_eq!(expected, r.sorted_paths());
+}
+
+#[test]
+fn siblings() {
+    let dir = Dir::tmp();
+    dir.mkdirp("foo");
+    dir.mkdirp("bar");
+    dir.touch_all(&["foo/a", "foo/b"]);
+    dir.touch_all(&["bar/a", "bar/b"]);
+
+    let wd = WalkDir::new(dir.path());
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let expected = vec![
+        dir.path().to_path_buf(),
+        dir.join("bar"),
+        dir.join("bar").join("a"),
+        dir.join("bar").join("b"),
+        dir.join("foo"),
+        dir.join("foo").join("a"),
+        dir.join("foo").join("b"),
+    ];
+    assert_eq!(expected, r.sorted_paths());
+}
+
+#[test]
+fn sym_root_file_nofollow() {
+    let dir = Dir::tmp();
+    dir.touch("a");
+    dir.symlink_file("a", "a-link");
+
+    let wd = WalkDir::new(dir.join("a-link"));
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let ents = r.sorted_ents();
+    assert_eq!(1, ents.len());
+    let link = &ents[0];
+
+    assert_eq!(dir.join("a-link"), link.path());
+
+    assert!(link.path_is_symlink());
+
+    assert_eq!(dir.join("a"), fs::read_link(link.path()).unwrap());
+
+    assert_eq!(0, link.depth());
+
+    assert!(link.file_type().is_symlink());
+    assert!(!link.file_type().is_file());
+    assert!(!link.file_type().is_dir());
+
+    assert!(link.metadata().unwrap().file_type().is_symlink());
+    assert!(!link.metadata().unwrap().is_file());
+    assert!(!link.metadata().unwrap().is_dir());
+}
+
+#[test]
+fn sym_root_file_follow() {
+    let dir = Dir::tmp();
+    dir.touch("a");
+    dir.symlink_file("a", "a-link");
+
+    let wd = WalkDir::new(dir.join("a-link")).follow_links(true);
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let ents = r.sorted_ents();
+    let link = &ents[0];
+
+    assert_eq!(dir.join("a-link"), link.path());
+
+    assert!(link.path_is_symlink());
+
+    assert_eq!(dir.join("a"), fs::read_link(link.path()).unwrap());
+
+    assert_eq!(0, link.depth());
+
+    assert!(!link.file_type().is_symlink());
+    assert!(link.file_type().is_file());
+    assert!(!link.file_type().is_dir());
+
+    assert!(!link.metadata().unwrap().file_type().is_symlink());
+    assert!(link.metadata().unwrap().is_file());
+    assert!(!link.metadata().unwrap().is_dir());
+}
+
+#[test]
+fn sym_root_dir_nofollow() {
+    let dir = Dir::tmp();
+    dir.mkdirp("a");
+    dir.symlink_dir("a", "a-link");
+    dir.touch("a/zzz");
+
+    let wd = WalkDir::new(dir.join("a-link"));
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let ents = r.sorted_ents();
+    assert_eq!(2, ents.len());
+    let link = &ents[0];
+
+    assert_eq!(dir.join("a-link"), link.path());
+
+    assert!(link.path_is_symlink());
+
+    assert_eq!(dir.join("a"), fs::read_link(link.path()).unwrap());
+
+    assert_eq!(0, link.depth());
+
+    assert!(link.file_type().is_symlink());
+    assert!(!link.file_type().is_file());
+    assert!(!link.file_type().is_dir());
+
+    assert!(link.metadata().unwrap().file_type().is_symlink());
+    assert!(!link.metadata().unwrap().is_file());
+    assert!(!link.metadata().unwrap().is_dir());
+
+    let link_zzz = &ents[1];
+    assert_eq!(dir.join("a-link").join("zzz"), link_zzz.path());
+    assert!(!link_zzz.path_is_symlink());
+}
+
+#[test]
+fn sym_root_dir_follow() {
+    let dir = Dir::tmp();
+    dir.mkdirp("a");
+    dir.symlink_dir("a", "a-link");
+    dir.touch("a/zzz");
+
+    let wd = WalkDir::new(dir.join("a-link")).follow_links(true);
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let ents = r.sorted_ents();
+    assert_eq!(2, ents.len());
+    let link = &ents[0];
+
+    assert_eq!(dir.join("a-link"), link.path());
+
+    assert!(link.path_is_symlink());
+
+    assert_eq!(dir.join("a"), fs::read_link(link.path()).unwrap());
+
+    assert_eq!(0, link.depth());
+
+    assert!(!link.file_type().is_symlink());
+    assert!(!link.file_type().is_file());
+    assert!(link.file_type().is_dir());
+
+    assert!(!link.metadata().unwrap().file_type().is_symlink());
+    assert!(!link.metadata().unwrap().is_file());
+    assert!(link.metadata().unwrap().is_dir());
+
+    let link_zzz = &ents[1];
+    assert_eq!(dir.join("a-link").join("zzz"), link_zzz.path());
+    assert!(!link_zzz.path_is_symlink());
+}
+
+#[test]
+fn sym_file_nofollow() {
+    let dir = Dir::tmp();
+    dir.touch("a");
+    dir.symlink_file("a", "a-link");
+
+    let wd = WalkDir::new(dir.path());
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let ents = r.sorted_ents();
+    assert_eq!(3, ents.len());
+    let (src, link) = (&ents[1], &ents[2]);
+
+    assert_eq!(dir.join("a"), src.path());
+    assert_eq!(dir.join("a-link"), link.path());
+
+    assert!(!src.path_is_symlink());
+    assert!(link.path_is_symlink());
+
+    assert_eq!(dir.join("a"), fs::read_link(link.path()).unwrap());
+
+    assert_eq!(1, src.depth());
+    assert_eq!(1, link.depth());
+
+    assert!(src.file_type().is_file());
+    assert!(link.file_type().is_symlink());
+    assert!(!link.file_type().is_file());
+    assert!(!link.file_type().is_dir());
+
+    assert!(src.metadata().unwrap().is_file());
+    assert!(link.metadata().unwrap().file_type().is_symlink());
+    assert!(!link.metadata().unwrap().is_file());
+    assert!(!link.metadata().unwrap().is_dir());
+}
+
+#[test]
+fn sym_file_follow() {
+    let dir = Dir::tmp();
+    dir.touch("a");
+    dir.symlink_file("a", "a-link");
+
+    let wd = WalkDir::new(dir.path()).follow_links(true);
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let ents = r.sorted_ents();
+    assert_eq!(3, ents.len());
+    let (src, link) = (&ents[1], &ents[2]);
+
+    assert_eq!(dir.join("a"), src.path());
+    assert_eq!(dir.join("a-link"), link.path());
+
+    assert!(!src.path_is_symlink());
+    assert!(link.path_is_symlink());
+
+    assert_eq!(dir.join("a"), fs::read_link(link.path()).unwrap());
+
+    assert_eq!(1, src.depth());
+    assert_eq!(1, link.depth());
+
+    assert!(src.file_type().is_file());
+    assert!(!link.file_type().is_symlink());
+    assert!(link.file_type().is_file());
+    assert!(!link.file_type().is_dir());
+
+    assert!(src.metadata().unwrap().is_file());
+    assert!(!link.metadata().unwrap().file_type().is_symlink());
+    assert!(link.metadata().unwrap().is_file());
+    assert!(!link.metadata().unwrap().is_dir());
+}
+
+#[test]
+fn sym_dir_nofollow() {
+    let dir = Dir::tmp();
+    dir.mkdirp("a");
+    dir.symlink_dir("a", "a-link");
+    dir.touch("a/zzz");
+
+    let wd = WalkDir::new(dir.path());
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let ents = r.sorted_ents();
+    assert_eq!(4, ents.len());
+    let (src, link) = (&ents[1], &ents[3]);
+
+    assert_eq!(dir.join("a"), src.path());
+    assert_eq!(dir.join("a-link"), link.path());
+
+    assert!(!src.path_is_symlink());
+    assert!(link.path_is_symlink());
+
+    assert_eq!(dir.join("a"), fs::read_link(link.path()).unwrap());
+
+    assert_eq!(1, src.depth());
+    assert_eq!(1, link.depth());
+
+    assert!(src.file_type().is_dir());
+    assert!(link.file_type().is_symlink());
+    assert!(!link.file_type().is_file());
+    assert!(!link.file_type().is_dir());
+
+    assert!(src.metadata().unwrap().is_dir());
+    assert!(link.metadata().unwrap().file_type().is_symlink());
+    assert!(!link.metadata().unwrap().is_file());
+    assert!(!link.metadata().unwrap().is_dir());
+}
+
+#[test]
+fn sym_dir_follow() {
+    let dir = Dir::tmp();
+    dir.mkdirp("a");
+    dir.symlink_dir("a", "a-link");
+    dir.touch("a/zzz");
+
+    let wd = WalkDir::new(dir.path()).follow_links(true);
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let ents = r.sorted_ents();
+    assert_eq!(5, ents.len());
+    let (src, link) = (&ents[1], &ents[3]);
+
+    assert_eq!(dir.join("a"), src.path());
+    assert_eq!(dir.join("a-link"), link.path());
+
+    assert!(!src.path_is_symlink());
+    assert!(link.path_is_symlink());
+
+    assert_eq!(dir.join("a"), fs::read_link(link.path()).unwrap());
+
+    assert_eq!(1, src.depth());
+    assert_eq!(1, link.depth());
+
+    assert!(src.file_type().is_dir());
+    assert!(!link.file_type().is_symlink());
+    assert!(!link.file_type().is_file());
+    assert!(link.file_type().is_dir());
+
+    assert!(src.metadata().unwrap().is_dir());
+    assert!(!link.metadata().unwrap().file_type().is_symlink());
+    assert!(!link.metadata().unwrap().is_file());
+    assert!(link.metadata().unwrap().is_dir());
+
+    let (src_zzz, link_zzz) = (&ents[2], &ents[4]);
+    assert_eq!(dir.join("a").join("zzz"), src_zzz.path());
+    assert_eq!(dir.join("a-link").join("zzz"), link_zzz.path());
+    assert!(!src_zzz.path_is_symlink());
+    assert!(!link_zzz.path_is_symlink());
+}
+
+#[test]
+fn sym_noloop() {
+    let dir = Dir::tmp();
+    dir.mkdirp("a/b/c");
+    dir.symlink_dir("a", "a/b/c/a-link");
+
+    let wd = WalkDir::new(dir.path());
+    let r = dir.run_recursive(wd);
+    // There's no loop if we aren't following symlinks.
+    r.assert_no_errors();
+
+    assert_eq!(5, r.ents().len());
+}
+
+#[test]
+fn sym_loop_detect() {
+    let dir = Dir::tmp();
+    dir.mkdirp("a/b/c");
+    dir.symlink_dir("a", "a/b/c/a-link");
+
+    let wd = WalkDir::new(dir.path()).follow_links(true);
+    let r = dir.run_recursive(wd);
+
+    let (ents, errs) = (r.sorted_ents(), r.errs());
+    assert_eq!(4, ents.len());
+    assert_eq!(1, errs.len());
+
+    let err = &errs[0];
+
+    let expected = dir.join("a/b/c/a-link");
+    assert_eq!(Some(&*expected), err.path());
+
+    let expected = dir.join("a");
+    assert_eq!(Some(&*expected), err.loop_ancestor());
+
+    assert_eq!(4, err.depth());
+    assert!(err.io_error().is_none());
+}
+
+#[test]
+fn sym_self_loop_no_error() {
+    let dir = Dir::tmp();
+    dir.symlink_file("a", "a");
+
+    let wd = WalkDir::new(dir.path());
+    let r = dir.run_recursive(wd);
+    // No errors occur because even though the symlink points to nowhere, it
+    // is never followed, and thus no error occurs.
+    r.assert_no_errors();
+    assert_eq!(2, r.ents().len());
+
+    let ent = &r.ents()[1];
+    assert_eq!(dir.join("a"), ent.path());
+    assert!(ent.path_is_symlink());
+
+    assert!(ent.file_type().is_symlink());
+    assert!(!ent.file_type().is_file());
+    assert!(!ent.file_type().is_dir());
+
+    assert!(ent.metadata().unwrap().file_type().is_symlink());
+    assert!(!ent.metadata().unwrap().file_type().is_file());
+    assert!(!ent.metadata().unwrap().file_type().is_dir());
+}
+
+#[test]
+fn sym_file_self_loop_io_error() {
+    let dir = Dir::tmp();
+    dir.symlink_file("a", "a");
+
+    let wd = WalkDir::new(dir.path()).follow_links(true);
+    let r = dir.run_recursive(wd);
+
+    let (ents, errs) = (r.sorted_ents(), r.errs());
+    assert_eq!(1, ents.len());
+    assert_eq!(1, errs.len());
+
+    let err = &errs[0];
+
+    let expected = dir.join("a");
+    assert_eq!(Some(&*expected), err.path());
+    assert_eq!(1, err.depth());
+    assert!(err.loop_ancestor().is_none());
+    assert!(err.io_error().is_some());
+}
+
+#[test]
+fn sym_dir_self_loop_io_error() {
+    let dir = Dir::tmp();
+    dir.symlink_dir("a", "a");
+
+    let wd = WalkDir::new(dir.path()).follow_links(true);
+    let r = dir.run_recursive(wd);
+
+    let (ents, errs) = (r.sorted_ents(), r.errs());
+    assert_eq!(1, ents.len());
+    assert_eq!(1, errs.len());
+
+    let err = &errs[0];
+
+    let expected = dir.join("a");
+    assert_eq!(Some(&*expected), err.path());
+    assert_eq!(1, err.depth());
+    assert!(err.loop_ancestor().is_none());
+    assert!(err.io_error().is_some());
+}
+
+#[test]
+fn min_depth_1() {
+    let dir = Dir::tmp();
+    dir.mkdirp("a/b");
+
+    let wd = WalkDir::new(dir.path()).min_depth(1);
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let expected = vec![dir.join("a"), dir.join("a").join("b")];
+    assert_eq!(expected, r.sorted_paths());
+}
+
+#[test]
+fn min_depth_2() {
+    let dir = Dir::tmp();
+    dir.mkdirp("a/b");
+
+    let wd = WalkDir::new(dir.path()).min_depth(2);
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let expected = vec![dir.join("a").join("b")];
+    assert_eq!(expected, r.sorted_paths());
+}
+
+#[test]
+fn max_depth_0() {
+    let dir = Dir::tmp();
+    dir.mkdirp("a/b");
+
+    let wd = WalkDir::new(dir.path()).max_depth(0);
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let expected = vec![dir.path().to_path_buf()];
+    assert_eq!(expected, r.sorted_paths());
+}
+
+#[test]
+fn max_depth_1() {
+    let dir = Dir::tmp();
+    dir.mkdirp("a/b");
+
+    let wd = WalkDir::new(dir.path()).max_depth(1);
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let expected = vec![dir.path().to_path_buf(), dir.join("a")];
+    assert_eq!(expected, r.sorted_paths());
+}
+
+#[test]
+fn max_depth_2() {
+    let dir = Dir::tmp();
+    dir.mkdirp("a/b");
+
+    let wd = WalkDir::new(dir.path()).max_depth(2);
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let expected =
+        vec![dir.path().to_path_buf(), dir.join("a"), dir.join("a").join("b")];
+    assert_eq!(expected, r.sorted_paths());
+}
+
+// FIXME: This test seems wrong. It should return nothing!
+#[test]
+fn min_max_depth_diff_nada() {
+    let dir = Dir::tmp();
+    dir.mkdirp("a/b/c");
+
+    let wd = WalkDir::new(dir.path()).min_depth(3).max_depth(2);
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let expected = vec![dir.join("a").join("b").join("c")];
+    assert_eq!(expected, r.sorted_paths());
+}
+
+#[test]
+fn min_max_depth_diff_0() {
+    let dir = Dir::tmp();
+    dir.mkdirp("a/b/c");
+
+    let wd = WalkDir::new(dir.path()).min_depth(2).max_depth(2);
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let expected = vec![dir.join("a").join("b")];
+    assert_eq!(expected, r.sorted_paths());
+}
+
+#[test]
+fn min_max_depth_diff_1() {
+    let dir = Dir::tmp();
+    dir.mkdirp("a/b/c");
+
+    let wd = WalkDir::new(dir.path()).min_depth(1).max_depth(2);
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let expected = vec![dir.join("a"), dir.join("a").join("b")];
+    assert_eq!(expected, r.sorted_paths());
+}
+
+#[test]
+fn contents_first() {
+    let dir = Dir::tmp();
+    dir.touch("a");
+
+    let wd = WalkDir::new(dir.path()).contents_first(true);
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let expected = vec![dir.join("a"), dir.path().to_path_buf()];
+    assert_eq!(expected, r.paths());
+}
+
+#[test]
+fn skip_current_dir() {
+    let dir = Dir::tmp();
+    dir.mkdirp("foo/bar/baz");
+    dir.mkdirp("quux");
+
+    let mut paths = vec![];
+    let mut it = WalkDir::new(dir.path()).into_iter();
+    while let Some(result) = it.next() {
+        let ent = result.unwrap();
+        paths.push(ent.path().to_path_buf());
+        if ent.file_name() == "bar" {
+            it.skip_current_dir();
+        }
+    }
+    paths.sort();
+
+    let expected = vec![
+        dir.path().to_path_buf(),
+        dir.join("foo"),
+        dir.join("foo").join("bar"),
+        dir.join("quux"),
+    ];
+    assert_eq!(expected, paths);
+}
+
+#[test]
+fn filter_entry() {
+    let dir = Dir::tmp();
+    dir.mkdirp("foo/bar/baz/abc");
+    dir.mkdirp("quux");
+
+    let wd = WalkDir::new(dir.path())
+        .into_iter()
+        .filter_entry(|ent| ent.file_name() != "baz");
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let expected = vec![
+        dir.path().to_path_buf(),
+        dir.join("foo"),
+        dir.join("foo").join("bar"),
+        dir.join("quux"),
+    ];
+    assert_eq!(expected, r.sorted_paths());
+}
+
+#[test]
+fn sort_by() {
+    let dir = Dir::tmp();
+    dir.mkdirp("foo/bar/baz/abc");
+    dir.mkdirp("quux");
+
+    let wd = WalkDir::new(dir.path())
+        .sort_by(|a, b| a.file_name().cmp(b.file_name()).reverse());
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let expected = vec![
+        dir.path().to_path_buf(),
+        dir.join("quux"),
+        dir.join("foo"),
+        dir.join("foo").join("bar"),
+        dir.join("foo").join("bar").join("baz"),
+        dir.join("foo").join("bar").join("baz").join("abc"),
+    ];
+    assert_eq!(expected, r.paths());
+}
+
+#[test]
+fn sort_by_key() {
+    let dir = Dir::tmp();
+    dir.mkdirp("foo/bar/baz/abc");
+    dir.mkdirp("quux");
+
+    let wd =
+        WalkDir::new(dir.path()).sort_by_key(|a| a.file_name().to_owned());
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let expected = vec![
+        dir.path().to_path_buf(),
+        dir.join("foo"),
+        dir.join("foo").join("bar"),
+        dir.join("foo").join("bar").join("baz"),
+        dir.join("foo").join("bar").join("baz").join("abc"),
+        dir.join("quux"),
+    ];
+    assert_eq!(expected, r.paths());
+}
+
+#[test]
+fn sort_by_file_name() {
+    let dir = Dir::tmp();
+    dir.mkdirp("foo/bar/baz/abc");
+    dir.mkdirp("quux");
+
+    let wd = WalkDir::new(dir.path()).sort_by_file_name();
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let expected = vec![
+        dir.path().to_path_buf(),
+        dir.join("foo"),
+        dir.join("foo").join("bar"),
+        dir.join("foo").join("bar").join("baz"),
+        dir.join("foo").join("bar").join("baz").join("abc"),
+        dir.join("quux"),
+    ];
+    assert_eq!(expected, r.paths());
+}
+
+#[test]
+fn sort_max_open() {
+    let dir = Dir::tmp();
+    dir.mkdirp("foo/bar/baz/abc");
+    dir.mkdirp("quux");
+
+    let wd = WalkDir::new(dir.path())
+        .max_open(1)
+        .sort_by(|a, b| a.file_name().cmp(b.file_name()).reverse());
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let expected = vec![
+        dir.path().to_path_buf(),
+        dir.join("quux"),
+        dir.join("foo"),
+        dir.join("foo").join("bar"),
+        dir.join("foo").join("bar").join("baz"),
+        dir.join("foo").join("bar").join("baz").join("abc"),
+    ];
+    assert_eq!(expected, r.paths());
+}
+
+#[cfg(target_os = "linux")]
+#[test]
+fn same_file_system() {
+    use std::path::Path;
+
+    // This test is a little weird since it's not clear whether it's a good
+    // idea to setup a distinct mounted volume in these tests. Instead, we
+    // probe for an existing one.
+    if !Path::new("/sys").is_dir() {
+        return;
+    }
+
+    let dir = Dir::tmp();
+    dir.touch("a");
+    dir.symlink_dir("/sys", "sys-link");
+
+    // First, do a sanity check that things work without following symlinks.
+    let wd = WalkDir::new(dir.path());
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let expected =
+        vec![dir.path().to_path_buf(), dir.join("a"), dir.join("sys-link")];
+    assert_eq!(expected, r.sorted_paths());
+
+    // ... now follow symlinks and ensure we don't descend into /sys.
+    let wd =
+        WalkDir::new(dir.path()).same_file_system(true).follow_links(true);
+    let r = dir.run_recursive(wd);
+    r.assert_no_errors();
+
+    let expected =
+        vec![dir.path().to_path_buf(), dir.join("a"), dir.join("sys-link")];
+    assert_eq!(expected, r.sorted_paths());
+}
+
+// Tests that skip_current_dir doesn't destroy internal invariants.
+//
+// See: https://github.com/BurntSushi/walkdir/issues/118
+#[test]
+fn regression_skip_current_dir() {
+    let dir = Dir::tmp();
+    dir.mkdirp("foo/a/b");
+    dir.mkdirp("foo/1/2");
+
+    let mut wd = WalkDir::new(dir.path()).max_open(1).into_iter();
+    wd.next();
+    wd.next();
+    wd.next();
+    wd.next();
+
+    wd.skip_current_dir();
+    wd.skip_current_dir();
+    wd.next();
+}
diff --git a/third_party/rust/walkdir/src/tests/util.rs b/third_party/rust/walkdir/src/tests/util.rs
new file mode 100644
index 0000000000..fdf06f555e
--- /dev/null
+++ b/third_party/rust/walkdir/src/tests/util.rs
@@ -0,0 +1,252 @@
+use std::env;
+use std::error;
+use std::fs::{self, File};
+use std::io;
+use std::path::{Path, PathBuf};
+use std::result;
+
+use crate::{DirEntry, Error};
+
+/// Create an error from a format!-like syntax.
+#[macro_export]
+macro_rules! err {
+    ($($tt:tt)*) => {
+        Box::<dyn error::Error + Send + Sync>::from(format!($($tt)*))
+    }
+}
+
+/// A convenient result type alias.
+pub type Result<T> = result::Result<T, Box<dyn error::Error + Send + Sync>>;
+
+/// The result of running a recursive directory iterator on a single directory.
+#[derive(Debug)]
+pub struct RecursiveResults {
+    ents: Vec<DirEntry>,
+    errs: Vec<Error>,
+}
+
+impl RecursiveResults {
+    /// Return all of the errors encountered during traversal.
+    pub fn errs(&self) -> &[Error] {
+        &self.errs
+    }
+
+    /// Assert that no errors have occurred.
+    pub fn assert_no_errors(&self) {
+        assert!(
+            self.errs.is_empty(),
+            "expected to find no errors, but found: {:?}",
+            self.errs
+        );
+    }
+
+    /// Return all the successfully retrieved directory entries in the order
+    /// in which they were retrieved.
+    pub fn ents(&self) -> &[DirEntry] {
+        &self.ents
+    }
+
+    /// Return all paths from all successfully retrieved directory entries.
+    ///
+    /// This does not include paths that correspond to an error.
+    pub fn paths(&self) -> Vec<PathBuf> {
+        self.ents.iter().map(|d| d.path().to_path_buf()).collect()
+    }
+
+    /// Return all the successfully retrieved directory entries, sorted
+    /// lexicographically by their full file path.
+    pub fn sorted_ents(&self) -> Vec<DirEntry> {
+        let mut ents = self.ents.clone();
+        ents.sort_by(|e1, e2| e1.path().cmp(e2.path()));
+        ents
+    }
+
+    /// Return all paths from all successfully retrieved directory entries,
+    /// sorted lexicographically.
+    ///
+    /// This does not include paths that correspond to an error.
+    pub fn sorted_paths(&self) -> Vec<PathBuf> {
+        self.sorted_ents().into_iter().map(|d| d.into_path()).collect()
+    }
+}
+
+/// A helper for managing a directory in which to run tests.
+///
+/// When manipulating paths within this directory, paths are interpreted
+/// relative to this directory.
+#[derive(Debug)]
+pub struct Dir {
+    dir: TempDir,
+}
+
+impl Dir {
+    /// Create a new empty temporary directory.
+    pub fn tmp() -> Dir {
+        let dir = TempDir::new().unwrap();
+        Dir { dir }
+    }
+
+    /// Return the path to this directory.
+    pub fn path(&self) -> &Path {
+        self.dir.path()
+    }
+
+    /// Return a path joined to the path to this directory.
+    pub fn join<P: AsRef<Path>>(&self, path: P) -> PathBuf {
+        self.path().join(path)
+    }
+
+    /// Run the given iterator and return the result as a distinct collection
+    /// of directory entries and errors.
+    pub fn run_recursive<I>(&self, it: I) -> RecursiveResults
+    where
+        I: IntoIterator<Item = result::Result<DirEntry, Error>>,
+    {
+        let mut results = RecursiveResults { ents: vec![], errs: vec![] };
+        for result in it {
+            match result {
+                Ok(ent) => results.ents.push(ent),
+                Err(err) => results.errs.push(err),
+            }
+        }
+        results
+    }
+
+    /// Create a directory at the given path, while creating all intermediate
+    /// directories as needed.
+    pub fn mkdirp<P: AsRef<Path>>(&self, path: P) {
+        let full = self.join(path);
+        fs::create_dir_all(&full)
+            .map_err(|e| {
+                err!("failed to create directory {}: {}", full.display(), e)
+            })
+            .unwrap();
+    }
+
+    /// Create an empty file at the given path. All ancestor directories must
+    /// already exists.
+    pub fn touch<P: AsRef<Path>>(&self, path: P) {
+        let full = self.join(path);
+        File::create(&full)
+            .map_err(|e| {
+                err!("failed to create file {}: {}", full.display(), e)
+            })
+            .unwrap();
+    }
+
+    /// Create empty files at the given paths. All ancestor directories must
+    /// already exists.
+    pub fn touch_all<P: AsRef<Path>>(&self, paths: &[P]) {
+        for p in paths {
+            self.touch(p);
+        }
+    }
+
+    /// Create a file symlink to the given src with the given link name.
+    pub fn symlink_file<P1: AsRef<Path>, P2: AsRef<Path>>(
+        &self,
+        src: P1,
+        link_name: P2,
+    ) {
+        #[cfg(windows)]
+        fn imp(src: &Path, link_name: &Path) -> io::Result<()> {
+            use std::os::windows::fs::symlink_file;
+            symlink_file(src, link_name)
+        }
+
+        #[cfg(unix)]
+        fn imp(src: &Path, link_name: &Path) -> io::Result<()> {
+            use std::os::unix::fs::symlink;
+            symlink(src, link_name)
+        }
+
+        let (src, link_name) = (self.join(src), self.join(link_name));
+        imp(&src, &link_name)
+            .map_err(|e| {
+                err!(
+                    "failed to symlink file {} with target {}: {}",
+                    src.display(),
+                    link_name.display(),
+                    e
+                )
+            })
+            .unwrap()
+    }
+
+    /// Create a directory symlink to the given src with the given link name.
+    pub fn symlink_dir<P1: AsRef<Path>, P2: AsRef<Path>>(
+        &self,
+        src: P1,
+        link_name: P2,
+    ) {
+        #[cfg(windows)]
+        fn imp(src: &Path, link_name: &Path) -> io::Result<()> {
+            use std::os::windows::fs::symlink_dir;
+            symlink_dir(src, link_name)
+        }
+
+        #[cfg(unix)]
+        fn imp(src: &Path, link_name: &Path) -> io::Result<()> {
+            use std::os::unix::fs::symlink;
+            symlink(src, link_name)
+        }
+
+        let (src, link_name) = (self.join(src), self.join(link_name));
+        imp(&src, &link_name)
+            .map_err(|e| {
+                err!(
+                    "failed to symlink directory {} with target {}: {}",
+                    src.display(),
+                    link_name.display(),
+                    e
+                )
+            })
+            .unwrap()
+    }
+}
+
+/// A simple wrapper for creating a temporary directory that is automatically
+/// deleted when it's dropped.
+///
+/// We use this in lieu of tempfile because tempfile brings in too many
+/// dependencies.
+#[derive(Debug)]
+pub struct TempDir(PathBuf);
+
+impl Drop for TempDir {
+    fn drop(&mut self) {
+        fs::remove_dir_all(&self.0).unwrap();
+    }
+}
+
+impl TempDir {
+    /// Create a new empty temporary directory under the system's configured
+    /// temporary directory.
+    pub fn new() -> Result<TempDir> {
+        #[allow(deprecated)]
+        use std::sync::atomic::{AtomicUsize, Ordering, ATOMIC_USIZE_INIT};
+
+        static TRIES: usize = 100;
+        #[allow(deprecated)]
+        static COUNTER: AtomicUsize = ATOMIC_USIZE_INIT;
+
+        let tmpdir = env::temp_dir();
+        for _ in 0..TRIES {
+            let count = COUNTER.fetch_add(1, Ordering::SeqCst);
+            let path = tmpdir.join("rust-walkdir").join(count.to_string());
+            if path.is_dir() {
+                continue;
+            }
+            fs::create_dir_all(&path).map_err(|e| {
+                err!("failed to create {}: {}", path.display(), e)
+            })?;
+            return Ok(TempDir(path));
+        }
+        Err(err!("failed to create temp dir after {} tries", TRIES))
+    }
+
+    /// Return the underlying path to this temporary directory.
+    pub fn path(&self) -> &Path {
+        &self.0
+    }
+}
diff --git a/third_party/rust/walkdir/src/util.rs b/third_party/rust/walkdir/src/util.rs
new file mode 100644
index 0000000000..b9fcad8bf2
--- /dev/null
+++ b/third_party/rust/walkdir/src/util.rs
@@ -0,0 +1,25 @@
+use std::io;
+use std::path::Path;
+
+#[cfg(unix)]
+pub fn device_num<P: AsRef<Path>>(path: P) -> io::Result<u64> {
+    use std::os::unix::fs::MetadataExt;
+
+    path.as_ref().metadata().map(|md| md.dev())
+}
+
+#[cfg(windows)]
+pub fn device_num<P: AsRef<Path>>(path: P) -> io::Result<u64> {
+    use winapi_util::{file, Handle};
+
+    let h = Handle::from_path_any(path)?;
+    file::information(h).map(|info| info.volume_serial_number())
+}
+
+#[cfg(not(any(unix, windows)))]
+pub fn device_num<P: AsRef<Path>>(_: P) -> io::Result<u64> {
+    Err(io::Error::new(
+        io::ErrorKind::Other,
+        "walkdir: same_file_system option not supported on this platform",
+    ))
+}