Auto merge of #56549 - pietroalbini:rollup, r=pietroalbini

Rollup of 15 pull requests

Successful merges:

 - #51753 (Document `From` implementations)
 - #55563 (Improve no result found sentence in doc search)
 - #55987 (Add Weak.ptr_eq)
 - #56119 (Utilize `?` instead of `return None`.)
 - #56372 (Refer to the second borrow as the "second borrow" in E0501.rs)
 - #56388 (More MIR borrow check cleanup)
 - #56424 (Mention raw-ident syntax)
 - #56452 (Remove redundant clones)
 - #56456 (Handle existential types in dead code analysis)
 - #56466 (data_structures: remove tuple_slice)
 - #56476 (Fix invalid line number match)
 - #56497 (cleanup: remove static lifetimes from consts in libstd)
 - #56498 (Fix line numbers display)
 - #56523 (Added a bare-bones eslint config (removing jslint))
 - #56538 (Use inner iterator may_have_side_effect for Cloned)

Failed merges:

r? @ghost

2 files changed, 95 insertions, 1 deletions

diff --git a/src/liballoc/rc.rs b/src/liballoc/rc.rs
index 3ca6de191de..c0a947e7011 100644
--- a/src/liballoc/rc.rs
+++ b/src/liballoc/rc.rs
@@ -1187,8 +1187,9 @@ impl<T: ?Sized + Unsize<U>, U: ?Sized> DispatchFromDyn<Weak<U>> for Weak<T> {}
 
 impl<T> Weak<T> {
     /// Constructs a new `Weak<T>`, without allocating any memory.
-    /// Calling [`upgrade`][Weak::upgrade] on the return value always gives [`None`].
+    /// Calling [`upgrade`] on the return value always gives [`None`].
     ///
+    /// [`upgrade`]: #method.upgrade
     /// [`None`]: ../../std/option/enum.Option.html
     ///
     /// # Examples
@@ -1260,6 +1261,52 @@ impl<T: ?Sized> Weak<T> {
             Some(unsafe { self.ptr.as_ref() })
         }
     }
+
+    /// Returns true if the two `Weak`s point to the same value (not just values
+    /// that compare as equal).
+    ///
+    /// # Notes
+    ///
+    /// Since this compares pointers it means that `Weak::new()` will equal each
+    /// other, even though they don't point to any value.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(weak_ptr_eq)]
+    /// use std::rc::{Rc, Weak};
+    ///
+    /// let first_rc = Rc::new(5);
+    /// let first = Rc::downgrade(&first_rc);
+    /// let second = Rc::downgrade(&first_rc);
+    ///
+    /// assert!(Weak::ptr_eq(&first, &second));
+    ///
+    /// let third_rc = Rc::new(5);
+    /// let third = Rc::downgrade(&third_rc);
+    ///
+    /// assert!(!Weak::ptr_eq(&first, &third));
+    /// ```
+    ///
+    /// Comparing `Weak::new`.
+    ///
+    /// ```
+    /// #![feature(weak_ptr_eq)]
+    /// use std::rc::{Rc, Weak};
+    ///
+    /// let first = Weak::new();
+    /// let second = Weak::new();
+    /// assert!(Weak::ptr_eq(&first, &second));
+    ///
+    /// let third_rc = Rc::new(());
+    /// let third = Rc::downgrade(&third_rc);
+    /// assert!(!Weak::ptr_eq(&first, &third));
+    /// ```
+    #[inline]
+    #[unstable(feature = "weak_ptr_eq", issue = "55981")]
+    pub fn ptr_eq(this: &Self, other: &Self) -> bool {
+        this.ptr.as_ptr() == other.ptr.as_ptr()
+    }
 }
 
 #[stable(feature = "rc_weak", since = "1.4.0")]
diff --git a/src/liballoc/sync.rs b/src/liballoc/sync.rs
index 4f4031e3c4e..0a397f79103 100644
--- a/src/liballoc/sync.rs
+++ b/src/liballoc/sync.rs
@@ -1130,6 +1130,53 @@ impl<T: ?Sized> Weak<T> {
             Some(unsafe { self.ptr.as_ref() })
         }
     }
+
+    /// Returns true if the two `Weak`s point to the same value (not just values
+    /// that compare as equal).
+    ///
+    /// # Notes
+    ///
+    /// Since this compares pointers it means that `Weak::new()` will equal each
+    /// other, even though they don't point to any value.
+    ///
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(weak_ptr_eq)]
+    /// use std::sync::{Arc, Weak};
+    ///
+    /// let first_rc = Arc::new(5);
+    /// let first = Arc::downgrade(&first_rc);
+    /// let second = Arc::downgrade(&first_rc);
+    ///
+    /// assert!(Weak::ptr_eq(&first, &second));
+    ///
+    /// let third_rc = Arc::new(5);
+    /// let third = Arc::downgrade(&third_rc);
+    ///
+    /// assert!(!Weak::ptr_eq(&first, &third));
+    /// ```
+    ///
+    /// Comparing `Weak::new`.
+    ///
+    /// ```
+    /// #![feature(weak_ptr_eq)]
+    /// use std::sync::{Arc, Weak};
+    ///
+    /// let first = Weak::new();
+    /// let second = Weak::new();
+    /// assert!(Weak::ptr_eq(&first, &second));
+    ///
+    /// let third_rc = Arc::new(());
+    /// let third = Arc::downgrade(&third_rc);
+    /// assert!(!Weak::ptr_eq(&first, &third));
+    /// ```
+    #[inline]
+    #[unstable(feature = "weak_ptr_eq", issue = "55981")]
+    pub fn ptr_eq(this: &Self, other: &Self) -> bool {
+        this.ptr.as_ptr() == other.ptr.as_ptr()
+    }
 }
 
 #[stable(feature = "arc_weak", since = "1.4.0")]