Auto merge of #59226 - kennytm:rollup, r=kennytm

Rollup of 37 pull requests

Successful merges:

 - #58854 (appveyor: Use VS2017 for all our images)
 - #58855 (std: Spin for a global malloc lock on wasm32)
 - #58873 (Fix "Auto-hide item methods documentation" setting)
 - #58901 (Change `std::fs::copy` to use `copyfile` on MacOS and iOS)
 - #58933 (Move alloc::prelude::* to alloc::prelude::v1, make alloc a subset of std)
 - #58938 (core: ensure VaList passes improper_ctypes lint)
 - #58941 (MIPS: add r6 support)
 - #58949 (SGX target: Expose thread id function in os module)
 - #58959 (Add release notes for PR #56243)
 - #58976 (Default to integrated `rust-lld` linker for UEFI targets)
 - #59009 (Fix SGX implementations of read/write_vectored.)
 - #59025 (Fix generic argument lookup for Self)
 - #59036 (Fix ICE in MIR pretty printing)
 - #59037 (Avoid some common false positives in intra doc link checking)
 - #59072 (we can now skip should_panic tests with the libtest harness)
 - #59079 (add suggestions to invalid macro item error)
 - #59082 (A few improvements to comments in user-facing crates)
 - #59102 (Consistent naming for duration_float methods and additional f32 methods)
 - #59118 (rustc: fix ICE when trait alias has bare Self)
 - #59139 (Unregress using scalar unions in constants.)
 - #59146 (Suggest return lifetime when there's only one named lifetime)
 - #59147 (Make std time tests more robust for platform differences)
 - #59152 (Stabilize Range*::contains.)
 - #59156 ([wg-async-await] Add regression test for #55809.)
 - #59158 (Revert "Don't generate minification variable if minification disabled")
 - #59169 (Add `-Z allow_features=...` flag)
 - #59173 (bootstrap: Default to a sensible llvm-suffix.)
 - #59175 (Don't run test launching `echo` since that doesn't exist on Windows)
 - #59180 (Use try blocks in rustc_codegen_ssa)
 - #59185 (No old chestnuts in iter::repeat docs)
 - #59201 (Remove restriction on isize/usize in repr(simd))
 - #59204 (Output diagnostic information for rustdoc)
 - #59206 (Improved test output)
 - #59208 (Reduce a Code Repetition Related to Bit Operation)
 - #59212 (Add x86_64 musl host to the manifest)
 - #59221 (Option and Result: Add references to documentation of as_ref and as_mut)
 - #59231 (Stabilize Option::copied)

1 files changed, 23 insertions, 2 deletions

diff --git a/src/libstd/fs.rs b/src/libstd/fs.rs
index 25f2dd73504..8c3d0da0a7e 100644
--- a/src/libstd/fs.rs
+++ b/src/libstd/fs.rs
@@ -211,7 +211,7 @@ pub struct DirBuilder {
     recursive: bool,
 }
 
-/// How large a buffer to pre-allocate before reading the entire file.
+/// Indicates how large a buffer to pre-allocate before reading the entire file.
 fn initial_buffer_size(file: &File) -> usize {
     // Allocate one extra byte so the buffer doesn't need to grow before the
     // final `read` call at the end of the file.  Don't worry about `usize`
@@ -1581,7 +1581,8 @@ pub fn rename<P: AsRef<Path>, Q: AsRef<Path>>(from: P, to: Q) -> io::Result<()>
 /// `O_CLOEXEC` is set for returned file descriptors.
 /// On Windows, this function currently corresponds to `CopyFileEx`. Alternate
 /// NTFS streams are copied but only the size of the main stream is returned by
-/// this function.
+/// this function. On MacOS, this function corresponds to `copyfile` with
+/// `COPYFILE_ALL`.
 /// Note that, this [may change in the future][changes].
 ///
 /// [changes]: ../io/index.html#platform-specific-behavior
@@ -2837,6 +2838,26 @@ mod tests {
     }
 
     #[test]
+    fn copy_file_follows_dst_symlink() {
+        let tmp = tmpdir();
+        if !got_symlink_permission(&tmp) { return };
+
+        let in_path = tmp.join("in.txt");
+        let out_path = tmp.join("out.txt");
+        let out_path_symlink = tmp.join("out_symlink.txt");
+
+        check!(fs::write(&in_path, "foo"));
+        check!(fs::write(&out_path, "bar"));
+        check!(symlink_file(&out_path, &out_path_symlink));
+
+        check!(fs::copy(&in_path, &out_path_symlink));
+
+        assert!(check!(out_path_symlink.symlink_metadata()).file_type().is_symlink());
+        assert_eq!(check!(fs::read(&out_path_symlink)), b"foo".to_vec());
+        assert_eq!(check!(fs::read(&out_path)), b"foo".to_vec());
+    }
+
+    #[test]
     fn symlinks_work() {
         let tmpdir = tmpdir();
         if !got_symlink_permission(&tmpdir) { return };