Auto merge of #126877 - GrigorenkoPV:clone_to_uninit, r=dtolnay

CloneToUninit impls

As per #126799.

Also implements it for `Wtf8` and both versions of `os_str::Slice`.

Maybe it is worth to slap `#[inline]` on some of those impls.

r? `@dtolnay`

library/std/src/sys/os_str/bytes.rs

@@ -1,6 +1,9 @@
 //! The underlying OsString/OsStr implementation on Unix and many other
 //! systems: just a `Vec<u8>`/`[u8]`.
 
+use core::clone::CloneToUninit;
+use core::ptr::addr_of_mut;
+
 use crate::borrow::Cow;
 use crate::collections::TryReserveError;
 use crate::fmt::Write;
@@ -345,3 +348,13 @@ impl Slice {
         self.inner.eq_ignore_ascii_case(&other.inner)
     }
 }
+
+#[unstable(feature = "clone_to_uninit", issue = "126799")]
+unsafe impl CloneToUninit for Slice {
+    #[inline]
+    #[cfg_attr(debug_assertions, track_caller)]
+    unsafe fn clone_to_uninit(&self, dst: *mut Self) {
+        // SAFETY: we're just a wrapper around [u8]
+        unsafe { self.inner.clone_to_uninit(addr_of_mut!((*dst).inner)) }
+    }
+}

library/std/src/sys/os_str/wtf8.rs

@@ -1,5 +1,8 @@
 //! The underlying OsString/OsStr implementation on Windows is a
 //! wrapper around the "WTF-8" encoding; see the `wtf8` module for more.
+use core::clone::CloneToUninit;
+use core::ptr::addr_of_mut;
+
 use crate::borrow::Cow;
 use crate::collections::TryReserveError;
 use crate::rc::Rc;
@@ -268,3 +271,13 @@ impl Slice {
         self.inner.eq_ignore_ascii_case(&other.inner)
     }
 }
+
+#[unstable(feature = "clone_to_uninit", issue = "126799")]
+unsafe impl CloneToUninit for Slice {
+    #[inline]
+    #[cfg_attr(debug_assertions, track_caller)]
+    unsafe fn clone_to_uninit(&self, dst: *mut Self) {
+        // SAFETY: we're just a wrapper around Wtf8
+        unsafe { self.inner.clone_to_uninit(addr_of_mut!((*dst).inner)) }
+    }
+}