Simply unused_parens check and add tests

src/librustc_lint/unused.rs

@@ -274,7 +274,7 @@ impl UnusedParens {
                             parser::contains_exterior_struct_lit(&inner);
             if !necessary {
                 let pattern = pprust::expr_to_string(value);
-                Self::remove_outer_parens(cx, value.span, &pattern, msg)
+                Self::remove_outer_parens(cx, value.span, &pattern, msg);
             }
         }
     }
@@ -282,13 +282,10 @@ impl UnusedParens {
     fn check_unused_parens_pat(&self,
                                 cx: &EarlyContext,
                                 value: &ast::Pat,
-                                msg: &str,
-                                struct_lit_needs_parens: bool) {
+                                msg: &str) {
         if let ast::PatKind::Paren(_) = value.node {
-            if !struct_lit_needs_parens {
-                let pattern = pprust::pat_to_string(value);
-                Self::remove_outer_parens(cx, value.span, &pattern, msg)
-            }
+            let pattern = pprust::pat_to_string(value);
+            Self::remove_outer_parens(cx, value.span, &pattern, msg);
         }
     }
 
@@ -355,7 +352,9 @@ impl EarlyLintPass for UnusedParens {
                     // first "argument" is self (which sometimes needs parens)
                     MethodCall(_, ref args) => (&args[1..], "method"),
                     // actual catch-all arm
-                    _ => { return; }
+                    _ => {
+                        return;
+                    }
                 };
                 // Don't lint if this is a nested macro expansion: otherwise, the lint could
                 // trigger in situations that macro authors shouldn't have to care about, e.g.,
@@ -377,15 +376,9 @@ impl EarlyLintPass for UnusedParens {
     }
 
     fn check_pat(&mut self, cx: &EarlyContext, p: &ast::Pat) {
-        use ast::PatKind::*;
-        let (value, msg, struct_lit_needs_parens) = match p.node {
-            Ident(.., Some(ref pat)) => (pat, "optional subpattern", false),
-            Ref(ref pat, _) => (pat, "reference pattern", false),
-            Slice(_, Some(ref pat), _) => (pat, "optional position pattern", false),
-            Paren(_) => (p, "pattern", false),
-            _ => return,
-        };
-        self.check_unused_parens_pat(cx, &value, msg, struct_lit_needs_parens);
+        if let ast::PatKind::Paren(_) = p.node {
+            self.check_unused_parens_pat(cx, &p, "pattern");
+        }
     }
 
     fn check_stmt(&mut self, cx: &EarlyContext, s: &ast::Stmt) {

src/test/run-pass/binding/pat-tuple-7.rs

@@ -12,6 +12,6 @@
 
 fn main() {
     match 0 {
-        (pat) => assert_eq!(pat, 0)
+        pat => assert_eq!(pat, 0)
     }
 }

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
+