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)

1 files changed, 19 insertions, 1 deletions

diff --git a/library/std/src/ffi/os_str.rs b/library/std/src/ffi/os_str.rs
index bb577acf769..fbdf7f5ecac 100644
--- a/library/std/src/ffi/os_str.rs
+++ b/library/std/src/ffi/os_str.rs
@@ -745,7 +745,7 @@ impl OsStr {
                   without modifying the original"]
     #[inline]
     pub fn to_str(&self) -> Option<&str> {
-        self.inner.to_str()
+        self.inner.to_str().ok()
     }
 
     /// Converts an `OsStr` to a <code>[Cow]<[str]></code>.
@@ -1165,6 +1165,24 @@ impl<'a> From<Cow<'a, OsStr>> for OsString {
     }
 }
 
+#[stable(feature = "str_tryfrom_osstr_impl", since = "CURRENT_RUSTC_VERSION")]
+impl<'a> TryFrom<&'a OsStr> for &'a str {
+    type Error = crate::str::Utf8Error;
+
+    /// Tries to convert an `&OsStr` to a `&str`.
+    ///
+    /// ```
+    /// use std::ffi::OsStr;
+    ///
+    /// let os_str = OsStr::new("foo");
+    /// let as_str = <&str>::try_from(os_str).unwrap();
+    /// assert_eq!(as_str, "foo");
+    /// ```
+    fn try_from(value: &'a OsStr) -> Result<Self, Self::Error> {
+        value.inner.to_str()
+    }
+}
+
 #[stable(feature = "box_default_extra", since = "1.17.0")]
 impl Default for Box<OsStr> {
     #[inline]