Simply unused_parens check and add tests

src/test/ui/lint/issue-54538-unused-parens-lint.rs

@@ -0,0 +1,42 @@
+// Copyright 2018 The Rust Project Developers. See the COPYRIGHT
+// file at the top-level directory of this distribution and at
+// http://rust-lang.org/COPYRIGHT.
+//
+// Licensed under the Apache License, Version 2.0 <LICENSE-APACHE or
+// http://www.apache.org/licenses/LICENSE-2.0> or the MIT license
+// <LICENSE-MIT or http://opensource.org/licenses/MIT>, at your
+// option. This file may not be copied, modified, or distributed
+// except according to those terms.
+
+// compile-pass
+
+#![allow(unreachable_patterns)]
+#![allow(unused_variables)]
+#![warn(unused_parens)]
+
+struct A {
+    field: Option<String>,
+}
+
+fn main() {
+    let x = 3;
+    match x {
+        (_) => {}     //~ WARNING: unnecessary parentheses around pattern
+        (y) => {}     //~ WARNING: unnecessary parentheses around pattern
+        (ref r) => {} //~ WARNING: unnecessary parentheses around pattern
+        e @ 1...2 | (e @ (3...4)) => {}
+        //~^ WARNING: unnecessary parentheses around pattern (3 ... 4)
+        //~^ WARNING: unnecessary parentheses around pattern (e @ _)
+    }
+
+    let field = "foo".to_string();
+    let x: Option<A> = Some(A { field: Some(field) });
+    match x {
+        Some(A {
+            field: (ref a @ Some(_)),
+            //~^ WARNING: unnecessary parentheses around pattern
+            ..
+        }) => {}
+        _ => {}
+    }
+}

src/test/ui/lint/issue-54538-unused-parens-lint.stderr

@@ -0,0 +1,42 @@
+warning: unnecessary parentheses around pattern
+  --> $DIR/issue-54538-unused-parens-lint.rs:24:9
+   |
+LL |         (_) => {}     //~ WARNING: unnecessary parentheses around pattern
+   |         ^^^ help: remove these parentheses
+   |
+note: lint level defined here
+  --> $DIR/issue-54538-unused-parens-lint.rs:15:9
+   |
+LL | #![warn(unused_parens)]
+   |         ^^^^^^^^^^^^^
+
+warning: unnecessary parentheses around pattern
+  --> $DIR/issue-54538-unused-parens-lint.rs:25:9
+   |
+LL |         (y) => {}     //~ WARNING: unnecessary parentheses around pattern
+   |         ^^^ help: remove these parentheses
+
+warning: unnecessary parentheses around pattern
+  --> $DIR/issue-54538-unused-parens-lint.rs:26:9
+   |
+LL |         (ref r) => {} //~ WARNING: unnecessary parentheses around pattern
+   |         ^^^^^^^ help: remove these parentheses
+
+warning: unnecessary parentheses around pattern
+  --> $DIR/issue-54538-unused-parens-lint.rs:27:21
+   |
+LL |         e @ 1...2 | (e @ (3...4)) => {}
+   |                     ^^^^^^^^^^^^^ help: remove these parentheses
+
+warning: unnecessary parentheses around pattern
+  --> $DIR/issue-54538-unused-parens-lint.rs:27:26
+   |
+LL |         e @ 1...2 | (e @ (3...4)) => {}
+   |                          ^^^^^^^ help: remove these parentheses
+
+warning: unnecessary parentheses around pattern
+  --> $DIR/issue-54538-unused-parens-lint.rs:36:20
+   |
+LL |             field: (ref a @ Some(_)),
+   |                    ^^^^^^^^^^^^^^^^^ help: remove these parentheses
+