Rollup merge of #114800 - RalfJung:transparent, r=cuviper

std: add some missing repr(transparent)

For some types we don't want to stably guarantee this, so hide the `repr` from rustdoc. This nice approach was suggested by `@thomcc.`

1 files changed, 8 insertions, 2 deletions

diff --git a/library/std/src/sys/wasi/fd.rs b/library/std/src/sys/wasi/fd.rs
index 1b50c2ea6dd..d7295a799da 100644
--- a/library/std/src/sys/wasi/fd.rs
+++ b/library/std/src/sys/wasi/fd.rs
@@ -16,14 +16,20 @@ pub struct WasiFd {
 fn iovec<'a>(a: &'a mut [IoSliceMut<'_>]) -> &'a [wasi::Iovec] {
     assert_eq!(mem::size_of::<IoSliceMut<'_>>(), mem::size_of::<wasi::Iovec>());
     assert_eq!(mem::align_of::<IoSliceMut<'_>>(), mem::align_of::<wasi::Iovec>());
-    // SAFETY: `IoSliceMut` and `IoVec` have exactly the same memory layout
+    // SAFETY: `IoSliceMut` and `IoVec` have exactly the same memory layout.
+    // We decorate our `IoSliceMut` with `repr(transparent)` (see `io.rs`), and
+    // `crate::io::IoSliceMut` is a `repr(transparent)` wrapper around our type, so this is
+    // guaranteed.
     unsafe { mem::transmute(a) }
 }
 
 fn ciovec<'a>(a: &'a [IoSlice<'_>]) -> &'a [wasi::Ciovec] {
     assert_eq!(mem::size_of::<IoSlice<'_>>(), mem::size_of::<wasi::Ciovec>());
     assert_eq!(mem::align_of::<IoSlice<'_>>(), mem::align_of::<wasi::Ciovec>());
-    // SAFETY: `IoSlice` and `CIoVec` have exactly the same memory layout
+    // SAFETY: `IoSlice` and `CIoVec` have exactly the same memory layout.
+    // We decorate our `IoSlice` with `repr(transparent)` (see `io.rs`), and
+    // `crate::io::IoSlice` is a `repr(transparent)` wrapper around our type, so this is
+    // guaranteed.
     unsafe { mem::transmute(a) }
 }