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.

4 files changed, 156 insertions, 0 deletions

diff --git a/library/alloc/src/boxed/convert.rs b/library/alloc/src/boxed/convert.rs
index 19a583ca546..4430fff6677 100644
--- a/library/alloc/src/boxed/convert.rs
+++ b/library/alloc/src/boxed/convert.rs
@@ -110,6 +110,29 @@ impl<T: Clone> From<&[T]> for Box<[T]> {
 }
 
 #[cfg(not(no_global_oom_handling))]
+#[stable(feature = "box_from_mut_slice", since = "CURRENT_RUSTC_VERSION")]
+impl<T: Clone> From<&mut [T]> for Box<[T]> {
+    /// Converts a `&mut [T]` into a `Box<[T]>`
+    ///
+    /// This conversion allocates on the heap
+    /// and performs a copy of `slice` and its contents.
+    ///
+    /// # Examples
+    /// ```rust
+    /// // create a &mut [u8] which will be used to create a Box<[u8]>
+    /// let mut array = [104, 101, 108, 108, 111];
+    /// let slice: &mut [u8] = &mut array;
+    /// let boxed_slice: Box<[u8]> = Box::from(slice);
+    ///
+    /// println!("{boxed_slice:?}");
+    /// ```
+    #[inline]
+    fn from(slice: &mut [T]) -> Box<[T]> {
+        Self::from(&*slice)
+    }
+}
+
+#[cfg(not(no_global_oom_handling))]
 #[stable(feature = "box_from_cow", since = "1.45.0")]
 impl<T: Clone> From<Cow<'_, [T]>> for Box<[T]> {
     /// Converts a `Cow<'_, [T]>` into a `Box<[T]>`
@@ -148,6 +171,28 @@ impl From<&str> for Box<str> {
 }
 
 #[cfg(not(no_global_oom_handling))]
+#[stable(feature = "box_from_mut_slice", since = "CURRENT_RUSTC_VERSION")]
+impl From<&mut str> for Box<str> {
+    /// Converts a `&mut str` into a `Box<str>`
+    ///
+    /// This conversion allocates on the heap
+    /// and performs a copy of `s`.
+    ///
+    /// # Examples
+    ///
+    /// ```rust
+    /// let mut original = String::from("hello");
+    /// let original: &mut str = &mut original;
+    /// let boxed: Box<str> = Box::from(original);
+    /// println!("{boxed}");
+    /// ```
+    #[inline]
+    fn from(s: &mut str) -> Box<str> {
+        Self::from(&*s)
+    }
+}
+
+#[cfg(not(no_global_oom_handling))]
 #[stable(feature = "box_from_cow", since = "1.45.0")]
 impl From<Cow<'_, str>> for Box<str> {
     /// Converts a `Cow<'_, str>` into a `Box<str>`
diff --git a/library/alloc/src/ffi/c_str.rs b/library/alloc/src/ffi/c_str.rs
index d7e99f4a1a6..d91682b796e 100644
--- a/library/alloc/src/ffi/c_str.rs
+++ b/library/alloc/src/ffi/c_str.rs
@@ -772,6 +772,16 @@ impl From<&CStr> for Box<CStr> {
     }
 }
 
+#[cfg(not(test))]
+#[stable(feature = "box_from_mut_slice", since = "CURRENT_RUSTC_VERSION")]
+impl From<&mut CStr> for Box<CStr> {
+    /// Converts a `&mut CStr` into a `Box<CStr>`,
+    /// by copying the contents into a newly allocated [`Box`].
+    fn from(s: &mut CStr) -> Box<CStr> {
+        Self::from(&*s)
+    }
+}
+
 #[stable(feature = "box_from_cow", since = "1.45.0")]
 impl From<Cow<'_, CStr>> for Box<CStr> {
     /// Converts a `Cow<'a, CStr>` into a `Box<CStr>`,
@@ -910,6 +920,17 @@ impl From<&CStr> for Arc<CStr> {
     }
 }
 
+#[cfg(target_has_atomic = "ptr")]
+#[stable(feature = "shared_from_mut_slice", since = "CURRENT_RUSTC_VERSION")]
+impl From<&mut CStr> for Arc<CStr> {
+    /// Converts a `&mut CStr` into a `Arc<CStr>`,
+    /// by copying the contents into a newly allocated [`Arc`].
+    #[inline]
+    fn from(s: &mut CStr) -> Arc<CStr> {
+        Arc::from(&*s)
+    }
+}
+
 #[stable(feature = "shared_from_slice2", since = "1.24.0")]
 impl From<CString> for Rc<CStr> {
     /// Converts a [`CString`] into an <code>[Rc]<[CStr]></code> by moving the [`CString`]
@@ -932,6 +953,16 @@ impl From<&CStr> for Rc<CStr> {
     }
 }
 
+#[stable(feature = "shared_from_mut_slice", since = "CURRENT_RUSTC_VERSION")]
+impl From<&mut CStr> for Rc<CStr> {
+    /// Converts a `&mut CStr` into a `Rc<CStr>`,
+    /// by copying the contents into a newly allocated [`Rc`].
+    #[inline]
+    fn from(s: &mut CStr) -> Rc<CStr> {
+        Rc::from(&*s)
+    }
+}
+
 #[cfg(not(no_global_oom_handling))]
 #[stable(feature = "more_rc_default_impls", since = "1.80.0")]
 impl Default for Rc<CStr> {
diff --git a/library/alloc/src/rc.rs b/library/alloc/src/rc.rs
index fc8646e96d9..64b0520e983 100644
--- a/library/alloc/src/rc.rs
+++ b/library/alloc/src/rc.rs
@@ -2658,6 +2658,26 @@ impl<T: Clone> From<&[T]> for Rc<[T]> {
 }
 
 #[cfg(not(no_global_oom_handling))]
+#[stable(feature = "shared_from_mut_slice", since = "CURRENT_RUSTC_VERSION")]
+impl<T: Clone> From<&mut [T]> for Rc<[T]> {
+    /// Allocates a reference-counted slice and fills it by cloning `v`'s items.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use std::rc::Rc;
+    /// let mut original = [1, 2, 3];
+    /// let original: &mut [i32] = &mut original;
+    /// let shared: Rc<[i32]> = Rc::from(original);
+    /// assert_eq!(&[1, 2, 3], &shared[..]);
+    /// ```
+    #[inline]
+    fn from(v: &mut [T]) -> Rc<[T]> {
+        Rc::from(&*v)
+    }
+}
+
+#[cfg(not(no_global_oom_handling))]
 #[stable(feature = "shared_from_slice", since = "1.21.0")]
 impl From<&str> for Rc<str> {
     /// Allocates a reference-counted string slice and copies `v` into it.
@@ -2677,6 +2697,26 @@ impl From<&str> for Rc<str> {
 }
 
 #[cfg(not(no_global_oom_handling))]
+#[stable(feature = "shared_from_mut_slice", since = "CURRENT_RUSTC_VERSION")]
+impl From<&mut str> for Rc<str> {
+    /// Allocates a reference-counted string slice and copies `v` into it.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use std::rc::Rc;
+    /// let mut original = String::from("statue");
+    /// let original: &mut str = &mut original;
+    /// let shared: Rc<str> = Rc::from(original);
+    /// assert_eq!("statue", &shared[..]);
+    /// ```
+    #[inline]
+    fn from(v: &mut str) -> Rc<str> {
+        Rc::from(&*v)
+    }
+}
+
+#[cfg(not(no_global_oom_handling))]
 #[stable(feature = "shared_from_slice", since = "1.21.0")]
 impl From<String> for Rc<str> {
     /// Allocates a reference-counted string slice and copies `v` into it.
diff --git a/library/alloc/src/sync.rs b/library/alloc/src/sync.rs
index 98a2fe24257..f348fba6220 100644
--- a/library/alloc/src/sync.rs
+++ b/library/alloc/src/sync.rs
@@ -3615,6 +3615,26 @@ impl<T: Clone> From<&[T]> for Arc<[T]> {
 }
 
 #[cfg(not(no_global_oom_handling))]
+#[stable(feature = "shared_from_mut_slice", since = "CURRENT_RUSTC_VERSION")]
+impl<T: Clone> From<&mut [T]> for Arc<[T]> {
+    /// Allocates a reference-counted slice and fills it by cloning `v`'s items.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use std::sync::Arc;
+    /// let mut original = [1, 2, 3];
+    /// let original: &mut [i32] = &mut original;
+    /// let shared: Arc<[i32]> = Arc::from(original);
+    /// assert_eq!(&[1, 2, 3], &shared[..]);
+    /// ```
+    #[inline]
+    fn from(v: &mut [T]) -> Arc<[T]> {
+        Arc::from(&*v)
+    }
+}
+
+#[cfg(not(no_global_oom_handling))]
 #[stable(feature = "shared_from_slice", since = "1.21.0")]
 impl From<&str> for Arc<str> {
     /// Allocates a reference-counted `str` and copies `v` into it.
@@ -3634,6 +3654,26 @@ impl From<&str> for Arc<str> {
 }
 
 #[cfg(not(no_global_oom_handling))]
+#[stable(feature = "shared_from_mut_slice", since = "CURRENT_RUSTC_VERSION")]
+impl From<&mut str> for Arc<str> {
+    /// Allocates a reference-counted `str` and copies `v` into it.
+    ///
+    /// # Example
+    ///
+    /// ```
+    /// # use std::sync::Arc;
+    /// let mut original = String::from("eggplant");
+    /// let original: &mut str = &mut original;
+    /// let shared: Arc<str> = Arc::from(original);
+    /// assert_eq!("eggplant", &shared[..]);
+    /// ```
+    #[inline]
+    fn from(v: &mut str) -> Arc<str> {
+        Arc::from(&*v)
+    }
+}
+
+#[cfg(not(no_global_oom_handling))]
 #[stable(feature = "shared_from_slice", since = "1.21.0")]
 impl From<String> for Arc<str> {
     /// Allocates a reference-counted `str` and copies `v` into it.