Rollup merge of #65112 - jack-t:type-parens-lint, r=varkor

Add lint and tests for unnecessary parens around types

This is my first contribution to the Rust project, so I apologize if I'm not doing things the right way.

The PR fixes #64169. It adds a lint and tests for unnecessary parentheses around types. I've run `tidy` and `rustfmt` — I'm not totally sure it worked right, though — and I've tried to follow the instructions linked in the readme.

I tried to think through all the variants of `ast::TyKind` to find exceptions to this lint, and I could only find the one mentioned in the original issue, which concerns types with `dyn`. I'm not a Rust expert, thought, so I may well be missing something.

There's also a problem with getting this to build. The new lint catches several things in the, e.g., `core`. Because `x.py` seems to build with an equivalent of `-Werror`, what would have been warnings cause the build to break. I got it to build and the tests to pass with `--warnings warn` on my `x.py build` and `x.py test` commands.

1 files changed, 3 insertions, 3 deletions

diff --git a/src/libstd/collections/hash/map.rs b/src/libstd/collections/hash/map.rs
index 6b0225a1b44..de2f12c9f33 100644
--- a/src/libstd/collections/hash/map.rs
+++ b/src/libstd/collections/hash/map.rs
@@ -1818,7 +1818,7 @@ impl<'a, K, V> Iterator for Keys<'a, K, V> {
     type Item = &'a K;
 
     #[inline]
-    fn next(&mut self) -> Option<(&'a K)> {
+    fn next(&mut self) -> Option<&'a K> {
         self.inner.next().map(|(k, _)| k)
     }
     #[inline]
@@ -1841,7 +1841,7 @@ impl<'a, K, V> Iterator for Values<'a, K, V> {
     type Item = &'a V;
 
     #[inline]
-    fn next(&mut self) -> Option<(&'a V)> {
+    fn next(&mut self) -> Option<&'a V> {
         self.inner.next().map(|(_, v)| v)
     }
     #[inline]
@@ -1864,7 +1864,7 @@ impl<'a, K, V> Iterator for ValuesMut<'a, K, V> {
     type Item = &'a mut V;
 
     #[inline]
-    fn next(&mut self) -> Option<(&'a mut V)> {
+    fn next(&mut self) -> Option<&'a mut V> {
         self.inner.next().map(|(_, v)| v)
     }
     #[inline]