Auto merge of #133223 - zachs18:uniquerc-impls, r=Noratrieb

`UniqueRc` trait impls

UniqueRc tracking Issue: #112566

Stable traits: (i.e. impls behind only the `unique_rc_arc` feature gate)

* Support the same formatting as `Rc`:
  * `fmt::Debug` and `fmt::Display` delegate to the pointee.
  * `fmt::Pointer` prints the address of the pointee.
* Add explicit `!Send` and `!Sync` impls, to mirror `Rc`.
* Borrowing traits: `Borrow`, `BorrowMut`, `AsRef`, `AsMut`
  * `Rc` does not implement `BorrowMut` and `AsMut`, but `UniqueRc` can.
* Unconditional `Unpin`, like other heap-allocated types.
* Comparison traits `(Partial)Ord` and `(Partial)Eq` delegate to the pointees.
  * `PartialEq for UniqueRc` does not do `Rc`'s specialization shortcut for pointer equality when `T: Eq`, since by definition two `UniqueRc`s cannot share an allocation.
* `Hash` delegates to the pointee.
* `AsRawFd`, `AsFd`, `AsHandle`, `AsSocket` delegate to the pointee like `Rc`.
  * Sidenote: The bounds on `T` for the existing `Pointer<T>` impls for specifically `AsRawFd` and `AsSocket` do not allow `T: ?Sized`. For the added `UniqueRc` impls I allowed `T: ?Sized` for all four traits, but I did not change the existing (stable) impls.

Unstable traits:
* `DispatchFromDyn`, allows using `UniqueRc<Self>` as a method receiver under `feature(arbitrary_self_types)`.
* Existing `PinCoerceUnsized for UniqueRc` is generalized to allow non-`Global` allocators, like `Rc`.
* `DerefPure`, allows using `UniqueRc` in deref-patterns under `feature(deref_patterns)`, like `Rc`.

For documentation, `Rc` only has documentation on the comparison traits' methods, so I copied/adapted the documentation for those, and left the rest without impl-specific docs.

~~Edit: Marked as draft while I figure out `UnwindSafe`.~~
Edit: Ignoring `UnwindSafe` for this PR

5 files changed, 33 insertions, 0 deletions

diff --git a/library/std/src/lib.rs b/library/std/src/lib.rs
index 1cbf51463ea..2b97f73f79a 100644
--- a/library/std/src/lib.rs
+++ b/library/std/src/lib.rs
@@ -373,6 +373,7 @@
 #![feature(thin_box)]
 #![feature(try_reserve_kind)]
 #![feature(try_with_capacity)]
+#![feature(unique_rc_arc)]
 #![feature(vec_into_raw_parts)]
 // tidy-alphabetical-end
 //
diff --git a/library/std/src/os/fd/owned.rs b/library/std/src/os/fd/owned.rs
index 388b8a88a1a..abb13b75f50 100644
--- a/library/std/src/os/fd/owned.rs
+++ b/library/std/src/os/fd/owned.rs
@@ -428,6 +428,14 @@ impl<T: AsFd + ?Sized> AsFd for crate::rc::Rc<T> {
     }
 }
 
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: AsFd + ?Sized> AsFd for crate::rc::UniqueRc<T> {
+    #[inline]
+    fn as_fd(&self) -> BorrowedFd<'_> {
+        (**self).as_fd()
+    }
+}
+
 #[stable(feature = "asfd_ptrs", since = "1.64.0")]
 impl<T: AsFd + ?Sized> AsFd for Box<T> {
     #[inline]
diff --git a/library/std/src/os/fd/raw.rs b/library/std/src/os/fd/raw.rs
index 0d99d5492a2..22f5528248a 100644
--- a/library/std/src/os/fd/raw.rs
+++ b/library/std/src/os/fd/raw.rs
@@ -266,6 +266,14 @@ impl<T: AsRawFd> AsRawFd for crate::rc::Rc<T> {
     }
 }
 
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: AsRawFd + ?Sized> AsRawFd for crate::rc::UniqueRc<T> {
+    #[inline]
+    fn as_raw_fd(&self) -> RawFd {
+        (**self).as_raw_fd()
+    }
+}
+
 #[stable(feature = "asrawfd_ptrs", since = "1.63.0")]
 impl<T: AsRawFd> AsRawFd for Box<T> {
     #[inline]
diff --git a/library/std/src/os/windows/io/handle.rs b/library/std/src/os/windows/io/handle.rs
index a4fa94e2b96..76f5f549dd2 100644
--- a/library/std/src/os/windows/io/handle.rs
+++ b/library/std/src/os/windows/io/handle.rs
@@ -485,6 +485,14 @@ impl<T: AsHandle + ?Sized> AsHandle for crate::rc::Rc<T> {
     }
 }
 
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: AsHandle + ?Sized> AsHandle for crate::rc::UniqueRc<T> {
+    #[inline]
+    fn as_handle(&self) -> BorrowedHandle<'_> {
+        (**self).as_handle()
+    }
+}
+
 #[stable(feature = "as_windows_ptrs", since = "1.71.0")]
 impl<T: AsHandle + ?Sized> AsHandle for Box<T> {
     #[inline]
diff --git a/library/std/src/os/windows/io/socket.rs b/library/std/src/os/windows/io/socket.rs
index 272641ea6c7..c6d7bad9440 100644
--- a/library/std/src/os/windows/io/socket.rs
+++ b/library/std/src/os/windows/io/socket.rs
@@ -279,6 +279,14 @@ impl<T: AsSocket> AsSocket for crate::rc::Rc<T> {
     }
 }
 
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: AsSocket + ?Sized> AsSocket for crate::rc::UniqueRc<T> {
+    #[inline]
+    fn as_socket(&self) -> BorrowedSocket<'_> {
+        (**self).as_socket()
+    }
+}
+
 #[stable(feature = "as_windows_ptrs", since = "1.71.0")]
 impl<T: AsSocket> AsSocket for Box<T> {
     #[inline]