Rollup merge of #129329 - eduardosm:rc-from-mut-slice, r=dtolnay

Implement `From<&mut {slice}>` for `Box/Rc/Arc<{slice}>`

ACP: https://github.com/rust-lang/libs-team/issues/424

New API:

```rust
impl<T: Clone> From<&mut [T]> for Box<[T]>
impl From<&mut str> for Box<str>
impl From<&mut CStr> for Box<CStr>
impl From<&mut OsStr> for Box<OsStr>
impl From<&mut Path> for Box<Path>

impl<T: Clone> From<&mut [T]> for Rc<[T]>
impl From<&mut str> for Rc<str>
impl From<&mut CStr> for Rc<CStr>
impl From<&mut OsStr> for Rc<OsStr>
impl From<&mut Path> for Rc<Path>

impl<T: Clone> From<&mut [T]> for Arc<[T]>
impl From<&mut str> for Arc<str>
impl From<&mut CStr> for Arc<CStr>
impl From<&mut OsStr> for Arc<OsStr>
impl From<&mut Path> for Arc<Path>
```

Since they are trait implementations, I think these are insta-stable.

As mentioned in https://github.com/rust-lang/libs-team/issues/424#issuecomment-2299415749, a crater run might be needed.

2 files changed, 55 insertions, 0 deletions

diff --git a/library/std/src/ffi/os_str.rs b/library/std/src/ffi/os_str.rs
index 2243f100643..b19d482feaa 100644
--- a/library/std/src/ffi/os_str.rs
+++ b/library/std/src/ffi/os_str.rs
@@ -1225,6 +1225,15 @@ impl From<&OsStr> for Box<OsStr> {
     }
 }
 
+#[stable(feature = "box_from_mut_slice", since = "CURRENT_RUSTC_VERSION")]
+impl From<&mut OsStr> for Box<OsStr> {
+    /// Copies the string into a newly allocated <code>[Box]&lt;[OsStr]&gt;</code>.
+    #[inline]
+    fn from(s: &mut OsStr) -> Box<OsStr> {
+        Self::from(&*s)
+    }
+}
+
 #[stable(feature = "box_from_cow", since = "1.45.0")]
 impl From<Cow<'_, OsStr>> for Box<OsStr> {
     /// Converts a `Cow<'a, OsStr>` into a <code>[Box]&lt;[OsStr]&gt;</code>,
@@ -1296,6 +1305,15 @@ impl From<&OsStr> for Arc<OsStr> {
     }
 }
 
+#[stable(feature = "shared_from_mut_slice", since = "CURRENT_RUSTC_VERSION")]
+impl From<&mut OsStr> for Arc<OsStr> {
+    /// Copies the string into a newly allocated <code>[Arc]&lt;[OsStr]&gt;</code>.
+    #[inline]
+    fn from(s: &mut OsStr) -> Arc<OsStr> {
+        Arc::from(&*s)
+    }
+}
+
 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
 impl From<OsString> for Rc<OsStr> {
     /// Converts an [`OsString`] into an <code>[Rc]<[OsStr]></code> by moving the [`OsString`]
@@ -1317,6 +1335,15 @@ impl From<&OsStr> for Rc<OsStr> {
     }
 }
 
+#[stable(feature = "shared_from_mut_slice", since = "CURRENT_RUSTC_VERSION")]
+impl From<&mut OsStr> for Rc<OsStr> {
+    /// Copies the string into a newly allocated <code>[Rc]&lt;[OsStr]&gt;</code>.
+    #[inline]
+    fn from(s: &mut OsStr) -> Rc<OsStr> {
+        Rc::from(&*s)
+    }
+}
+
 #[stable(feature = "cow_from_osstr", since = "1.28.0")]
 impl<'a> From<OsString> for Cow<'a, OsStr> {
     /// Moves the string into a [`Cow::Owned`].
diff --git a/library/std/src/path.rs b/library/std/src/path.rs
index 62125f885b2..5662a44d832 100644
--- a/library/std/src/path.rs
+++ b/library/std/src/path.rs
@@ -1762,6 +1762,16 @@ impl From<&Path> for Box<Path> {
     }
 }
 
+#[stable(feature = "box_from_mut_slice", since = "CURRENT_RUSTC_VERSION")]
+impl From<&mut Path> for Box<Path> {
+    /// Creates a boxed [`Path`] from a reference.
+    ///
+    /// This will allocate and clone `path` to it.
+    fn from(path: &mut Path) -> Box<Path> {
+        Self::from(&*path)
+    }
+}
+
 #[stable(feature = "box_from_cow", since = "1.45.0")]
 impl From<Cow<'_, Path>> for Box<Path> {
     /// Creates a boxed [`Path`] from a clone-on-write pointer.
@@ -1990,6 +2000,15 @@ impl From<&Path> for Arc<Path> {
     }
 }
 
+#[stable(feature = "shared_from_mut_slice", since = "CURRENT_RUSTC_VERSION")]
+impl From<&mut Path> for Arc<Path> {
+    /// Converts a [`Path`] into an [`Arc`] by copying the [`Path`] data into a new [`Arc`] buffer.
+    #[inline]
+    fn from(s: &mut Path) -> Arc<Path> {
+        Arc::from(&*s)
+    }
+}
+
 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
 impl From<PathBuf> for Rc<Path> {
     /// Converts a [`PathBuf`] into an <code>[Rc]<[Path]></code> by moving the [`PathBuf`] data into
@@ -2011,6 +2030,15 @@ impl From<&Path> for Rc<Path> {
     }
 }
 
+#[stable(feature = "shared_from_mut_slice", since = "CURRENT_RUSTC_VERSION")]
+impl From<&mut Path> for Rc<Path> {
+    /// Converts a [`Path`] into an [`Rc`] by copying the [`Path`] data into a new [`Rc`] buffer.
+    #[inline]
+    fn from(s: &mut Path) -> Rc<Path> {
+        Rc::from(&*s)
+    }
+}
+
 #[stable(feature = "rust1", since = "1.0.0")]
 impl ToOwned for Path {
     type Owned = PathBuf;