diff --git a/core/src/clone.rs b/core/src/clone.rs index 76a89eaaff86e..409fd2746f588 100644 --- a/core/src/clone.rs +++ b/core/src/clone.rs @@ -346,6 +346,27 @@ unsafe impl CloneToUninit for [T] { } } +#[unstable(feature = "clone_to_uninit", issue = "126799")] +unsafe impl CloneToUninit for str { + #[cfg_attr(debug_assertions, track_caller)] + unsafe fn clone_to_uninit(&self, dst: *mut Self) { + // SAFETY: str is just a [u8] with UTF-8 invariant + unsafe { self.as_bytes().clone_to_uninit(dst as *mut [u8]) } + } +} + +#[unstable(feature = "clone_to_uninit", issue = "126799")] +unsafe impl CloneToUninit for crate::ffi::CStr { + #[cfg_attr(debug_assertions, track_caller)] + unsafe fn clone_to_uninit(&self, dst: *mut Self) { + // SAFETY: For now, CStr is just a #[repr(trasnsparent)] [c_char] with some invariants. + // And we can cast [c_char] to [u8] on all supported platforms (see: to_bytes_with_nul). + // The pointer metadata properly preserves the length (NUL included). + // See: `cstr_metadata_is_length_with_nul` in tests. + unsafe { self.to_bytes_with_nul().clone_to_uninit(dst as *mut [u8]) } + } +} + /// Ownership of a collection of values stored in a non-owned `[MaybeUninit]`, some of which /// are not yet initialized. This is sort of like a `Vec` that doesn't own its allocation. /// Its responsibility is to provide cleanup on unwind by dropping the values that *are* diff --git a/core/tests/clone.rs b/core/tests/clone.rs index b7130f16f8795..71a328733b7c4 100644 --- a/core/tests/clone.rs +++ b/core/tests/clone.rs @@ -1,5 +1,7 @@ use core::clone::CloneToUninit; +use core::ffi::CStr; use core::mem::MaybeUninit; +use core::ptr; #[test] #[allow(suspicious_double_ref_op)] @@ -81,3 +83,41 @@ fn test_clone_to_uninit_slice_drops_on_panic() { drop(a); assert_eq!(COUNTER.load(Relaxed), 0); } + +#[test] +fn test_clone_to_uninit_str() { + let a = "hello"; + + let mut storage: MaybeUninit<[u8; 5]> = MaybeUninit::uninit(); + unsafe { a.clone_to_uninit(storage.as_mut_ptr() as *mut [u8] as *mut str) }; + assert_eq!(a.as_bytes(), unsafe { storage.assume_init() }.as_slice()); + + let mut b: Box = "world".into(); + assert_eq!(a.len(), b.len()); + assert_ne!(a, &*b); + unsafe { a.clone_to_uninit(ptr::from_mut::(&mut b)) }; + assert_eq!(a, &*b); +} + +#[test] +fn test_clone_to_uninit_cstr() { + let a = c"hello"; + + let mut storage: MaybeUninit<[u8; 6]> = MaybeUninit::uninit(); + unsafe { a.clone_to_uninit(storage.as_mut_ptr() as *mut [u8] as *mut CStr) }; + assert_eq!(a.to_bytes_with_nul(), unsafe { storage.assume_init() }.as_slice()); + + let mut b: Box = c"world".into(); + assert_eq!(a.count_bytes(), b.count_bytes()); + assert_ne!(a, &*b); + unsafe { a.clone_to_uninit(ptr::from_mut::(&mut b)) }; + assert_eq!(a, &*b); +} + +#[test] +fn cstr_metadata_is_length_with_nul() { + let s: &CStr = c"abcdef"; + let p: *const CStr = ptr::from_ref(s); + let bytes: *const [u8] = p as *const [u8]; + assert_eq!(s.to_bytes_with_nul().len(), bytes.len()); +}