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Require `#[repr(C)]` for `RelativePath` #2

lo48576 opened this Issue Dec 26, 2017 · 2 comments


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lo48576 commented Dec 26, 2017

I heard that the code such as below is unsound (lead to undefined behaviour):


Lines 271 to 280 in 49d76f3

/// A borrowed, immutable relative path.
pub struct RelativePath {
inner: str,
impl RelativePath {
/// Directly wraps a string slice as a `RelativePath` slice.
pub fn new<S: AsRef<str> + ?Sized>(s: &S) -> &RelativePath {
unsafe { mem::transmute(s.as_ref()) }

RelativePath type should have #[repr(C)] (stable) or #[repr(transparent)] (unstable) to be safe.

This is because Rust doesn't guarantee that str and RelativePath have the same internal representations (and it will be guaranteed by #[repr(C)]).

For detail:


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udoprog commented Dec 26, 2017

Also: rust-lang/rust#45910

Yeah, I'm keeping an eye on the stabilization for #[repr(transparent)] for this. I guess we could consider using #[repr(C)] until then.

@udoprog udoprog added the bug label Dec 26, 2017


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udoprog commented Aug 28, 2018

🎉 #[repr(transparent)] is now in stable (1.28)!

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