Rollup merge of #98202 - aticu:impl_tryfrom_osstr_for_str, r=Amanieu

Implement `TryFrom<&OsStr>` for `&str`

Recently when trying to work with `&OsStr` I was surprised to find this `impl` missing.

Since the `to_str` method already existed the actual implementation is fairly non-controversial, except for maybe the choice of the error type. I chose an opaque error here instead of something like `std::str::Utf8Error`, since that would already make a number of assumption about the underlying implementation of `OsStr`.

As this is a trait implementation, it is insta-stable, if I'm not mistaken?
Either way this will need an FCP.
I chose "1.64.0" as the version, since this is unlikely to land before the beta cut-off.

`@rustbot` modify labels: +T-libs-api

API Change Proposal: rust-lang/rust#99031 (accepted)

2 files changed, 5 insertions, 10 deletions

diff --git a/library/std/src/sys_common/wtf8.rs b/library/std/src/sys_common/wtf8.rs
index 31bb0ad25a6..c9d3e13cf0c 100644
--- a/library/std/src/sys_common/wtf8.rs
+++ b/library/std/src/sys_common/wtf8.rs
@@ -626,13 +626,8 @@ impl Wtf8 {
     ///
     /// This does not copy the data.
     #[inline]
-    pub fn as_str(&self) -> Option<&str> {
-        // Well-formed WTF-8 is also well-formed UTF-8
-        // if and only if it contains no surrogate.
-        match self.next_surrogate(0) {
-            None => Some(unsafe { str::from_utf8_unchecked(&self.bytes) }),
-            Some(_) => None,
-        }
+    pub fn as_str(&self) -> Result<&str, str::Utf8Error> {
+        str::from_utf8(&self.bytes)
     }
 
     /// Creates an owned `Wtf8Buf` from a borrowed `Wtf8`.
diff --git a/library/std/src/sys_common/wtf8/tests.rs b/library/std/src/sys_common/wtf8/tests.rs
index 1a302d64694..a07bbe6d7e4 100644
--- a/library/std/src/sys_common/wtf8/tests.rs
+++ b/library/std/src/sys_common/wtf8/tests.rs
@@ -521,11 +521,11 @@ fn wtf8_code_points() {
 
 #[test]
 fn wtf8_as_str() {
-    assert_eq!(Wtf8::from_str("").as_str(), Some(""));
-    assert_eq!(Wtf8::from_str("aé 💩").as_str(), Some("aé 💩"));
+    assert_eq!(Wtf8::from_str("").as_str(), Ok(""));
+    assert_eq!(Wtf8::from_str("aé 💩").as_str(), Ok("aé 💩"));
     let mut string = Wtf8Buf::new();
     string.push(CodePoint::from_u32(0xD800).unwrap());
-    assert_eq!(string.as_str(), None);
+    assert!(string.as_str().is_err());
 }
 
 #[test]