Auto merge of #65733 - Centril:rollup-0zth66f, r=Centril

Rollup of 12 pull requests

Successful merges:

 - #64178 (More Clippy fixes for alloc, core and std)
 - #65144 (Add Cow::is_borrowed and Cow::is_owned)
 - #65193 (Lockless LintStore)
 - #65479 (Add the `matches!( $expr, $pat ) -> bool` macro)
 - #65518 (Avoid ICE when checking `Destination` of `break` inside a closure)
 - #65583 (rustc_metadata: use a table for super_predicates, fn_sig, impl_trait_ref.)
 - #65641 (Derive `Rustc{En,De}codable` for `TokenStream`.)
 - #65648 (Eliminate `intersect_opt`.)
 - #65657 (Remove `InternedString`)
 - #65691 (Update E0659 error code long explanation to 2018 edition)
 - #65696 (Fix an issue with const inference variables sticking around under Chalk + NLL)
 - #65704 (relax ExactSizeIterator bound on write_bytes)

Failed merges:

r? @ghost

5 files changed, 45 insertions, 3 deletions

diff --git a/src/liballoc/borrow.rs b/src/liballoc/borrow.rs
index a9c5bce4c25..d2bdda83fa9 100644
--- a/src/liballoc/borrow.rs
+++ b/src/liballoc/borrow.rs
@@ -207,6 +207,47 @@ impl<B: ?Sized + ToOwned> Clone for Cow<'_, B> {
 }
 
 impl<B: ?Sized + ToOwned> Cow<'_, B> {
+    /// Returns true if the data is borrowed, i.e. if `to_mut` would require additional work.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(cow_is_borrowed)]
+    /// use std::borrow::Cow;
+    ///
+    /// let cow = Cow::Borrowed("moo");
+    /// assert!(cow.is_borrowed());
+    ///
+    /// let bull: Cow<'_, str> = Cow::Owned("...moo?".to_string());
+    /// assert!(!bull.is_borrowed());
+    /// ```
+    #[unstable(feature = "cow_is_borrowed", issue = "65143")]
+    pub fn is_borrowed(&self) -> bool {
+        match *self {
+            Borrowed(_) => true,
+            Owned(_) => false,
+        }
+    }
+
+    /// Returns true if the data is owned, i.e. if `to_mut` would be a no-op.
+    ///
+    /// # Examples
+    ///
+    /// ```
+    /// #![feature(cow_is_borrowed)]
+    /// use std::borrow::Cow;
+    ///
+    /// let cow: Cow<'_, str> = Cow::Owned("moo".to_string());
+    /// assert!(cow.is_owned());
+    ///
+    /// let bull = Cow::Borrowed("...moo?");
+    /// assert!(!bull.is_owned());
+    /// ```
+    #[unstable(feature = "cow_is_borrowed", issue = "65143")]
+    pub fn is_owned(&self) -> bool {
+        !self.is_borrowed()
+    }
+
     /// Acquires a mutable reference to the owned form of the data.
     ///
     /// Clones the data if it is not already owned.
diff --git a/src/liballoc/collections/vec_deque.rs b/src/liballoc/collections/vec_deque.rs
index 0bf573f5e25..8f3dfabd888 100644
--- a/src/liballoc/collections/vec_deque.rs
+++ b/src/liballoc/collections/vec_deque.rs
@@ -1817,7 +1817,7 @@ impl<T> VecDeque<T> {
             }
         }
 
-        return elem;
+        elem
     }
 
     /// Splits the `VecDeque` into two at the given index.
diff --git a/src/liballoc/lib.rs b/src/liballoc/lib.rs
index 3684162d8b1..94379afc2bd 100644
--- a/src/liballoc/lib.rs
+++ b/src/liballoc/lib.rs
@@ -85,6 +85,7 @@
 #![feature(const_generic_impls_guard)]
 #![feature(const_generics)]
 #![feature(const_in_array_repeat_expressions)]
+#![feature(cow_is_borrowed)]
 #![feature(dispatch_from_dyn)]
 #![feature(core_intrinsics)]
 #![feature(container_error_extra)]
diff --git a/src/liballoc/str.rs b/src/liballoc/str.rs
index 9231c2d3f1d..83816d8b954 100644
--- a/src/liballoc/str.rs
+++ b/src/liballoc/str.rs
@@ -456,7 +456,7 @@ impl str {
                 }
             }
         }
-        return s;
+        s
     }
 
     /// Converts a [`Box<str>`] into a [`String`] without copying or allocating.
diff --git a/src/liballoc/sync.rs b/src/liballoc/sync.rs
index 69f8f71197c..80d6c6e0d43 100644
--- a/src/liballoc/sync.rs
+++ b/src/liballoc/sync.rs
@@ -1638,7 +1638,7 @@ impl<T: ?Sized> Clone for Weak<T> {
             }
         }
 
-        return Weak { ptr: self.ptr };
+        Weak { ptr: self.ptr }
     }
 }