Rollup merge of #61969 - MikailBag:master, r=Centril

Add #[repr(transparent)] for several types

In some functions, types mentioned in this PR are transmuted into their inner value.
Example for `PathBuf`: https://github.com/rust-lang/rust/blob/master/src/libstd/path.rs#L1132.
This PR adds `#[repr(transparent)]` to those types, so their correct behavior doesn't depend on compiler details. (As far as I understand, currently that line, converting `PathBuf` to `Vec<u8>`, is UB).

1 files changed, 12 insertions, 0 deletions

diff --git a/src/libstd/path.rs b/src/libstd/path.rs
index 87c071b512a..fd6ff1032bb 100644
--- a/src/libstd/path.rs
+++ b/src/libstd/path.rs
@@ -1123,6 +1123,12 @@ impl FusedIterator for Ancestors<'_> {}
 /// Which method works best depends on what kind of situation you're in.
 #[derive(Clone)]
 #[stable(feature = "rust1", since = "1.0.0")]
+// FIXME:
+// `PathBuf::as_mut_vec` current implementation relies
+// on `PathBuf` being layout-compatible with `Vec<u8>`.
+// When attribute privacy is implemented, `PathBuf` should be annotated as `#[repr(transparent)]`.
+// Anyway, `PathBuf` representation and layout are considered implementation detail, are
+// not documented and must not be relied upon.
 pub struct PathBuf {
     inner: OsString,
 }
@@ -1745,6 +1751,12 @@ impl AsRef<OsStr> for PathBuf {
 /// assert_eq!(extension, Some(OsStr::new("txt")));
 /// ```
 #[stable(feature = "rust1", since = "1.0.0")]
+// FIXME:
+// `Path::new` current implementation relies
+// on `Path` being layout-compatible with `OsStr`.
+// When attribute privacy is implemented, `Path` should be annotated as `#[repr(transparent)]`.
+// Anyway, `Path` representation and layout are considered implementation detail, are
+// not documented and must not be relied upon.
 pub struct Path {
     inner: OsStr,
 }