UniqueRc: Add more trait impls.

* Support the same formatting as Rc
* Add explicit !Send and !Sync impls, to mirror Rc
* DispatchFromDyn
* borrowing traits and Unpin

Author: zachs18

Diff for: library/alloc/src/rc.rs

@@ -3684,7 +3684,6 @@ fn data_offset_align(align: usize) -> usize {
 /// previous example, `UniqueRc` allows for more flexibility in the construction of cyclic data,
 /// including fallible or async constructors.
 #[unstable(feature = "unique_rc_arc", issue = "112566")]
-#[derive(Debug)]
 pub struct UniqueRc<
     T: ?Sized,
     #[unstable(feature = "allocator_api", issue = "32838")] A: Allocator = Global,
@@ -3694,12 +3693,80 @@ pub struct UniqueRc<
     alloc: A,
 }
 
+// Not necessary for correctness since `UniqueRc` contains `NonNull`,
+// but having an explicit negative impl is nice for documentation purposes
+// and results in nicer error messages.
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized, A: Allocator> !Send for UniqueRc<T, A> {}
+
+// Not necessary for correctness since `UniqueRc` contains `NonNull`,
+// but having an explicit negative impl is nice for documentation purposes
+// and results in nicer error messages.
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized, A: Allocator> !Sync for UniqueRc<T, A> {}
+
 #[unstable(feature = "unique_rc_arc", issue = "112566")]
 impl<T: ?Sized + Unsize<U>, U: ?Sized, A: Allocator> CoerceUnsized<UniqueRc<U, A>>
     for UniqueRc<T, A>
 {
 }
 
+//#[unstable(feature = "unique_rc_arc", issue = "112566")]
+#[unstable(feature = "dispatch_from_dyn", issue = "none")]
+impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<UniqueRc<U>> for UniqueRc<T> {}
+
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized + fmt::Display, A: Allocator> fmt::Display for UniqueRc<T, A> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Display::fmt(&**self, f)
+    }
+}
+
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized + fmt::Debug, A: Allocator> fmt::Debug for UniqueRc<T, A> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Debug::fmt(&**self, f)
+    }
+}
+
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized, A: Allocator> fmt::Pointer for UniqueRc<T, A> {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        fmt::Pointer::fmt(&(&raw const **self), f)
+    }
+}
+
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized, A: Allocator> borrow::Borrow<T> for UniqueRc<T, A> {
+    fn borrow(&self) -> &T {
+        &**self
+    }
+}
+
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized, A: Allocator> borrow::BorrowMut<T> for UniqueRc<T, A> {
+    fn borrow_mut(&mut self) -> &mut T {
+        &mut **self
+    }
+}
+
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized, A: Allocator> AsRef<T> for UniqueRc<T, A> {
+    fn as_ref(&self) -> &T {
+        &**self
+    }
+}
+
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized, A: Allocator> AsMut<T> for UniqueRc<T, A> {
+    fn as_mut(&mut self) -> &mut T {
+        &mut **self
+    }
+}
+
+#[unstable(feature = "unique_rc_arc", issue = "112566")]
+impl<T: ?Sized, A: Allocator> Unpin for UniqueRc<T, A> {}
+
 // Depends on A = Global
 impl<T> UniqueRc<T> {
     /// Creates a new `UniqueRc`.