Add clarifying pattern lint comment and revert test

Author: kleimkuhler

src/librustc_lint/unused.rs

@@ -377,6 +377,10 @@ impl EarlyLintPass for UnusedParens {
 
     fn check_pat(&mut self, cx: &EarlyContext, p: &ast::Pat) {
         use ast::PatKind::{Paren, Range};
+        // The lint visitor will visit each subpattern of `p`. We do not want to lint any range
+        // pattern no matter where it occurs in the pattern. For something like `&(a..=b)`, there
+        // is a recursive `check_pat` on `a` and `b`, but we will assume that if there are
+        // unnecessry parens they serve a purpose of readability.
         if let Paren(ref pat) = p.node {
             match pat.node {
                 Range(..) => {}

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

@@ -11,7 +11,8 @@
 // run-pass
 
 fn main() {
+    #[allow(unused_parens)]
     match 0 {
-        pat => assert_eq!(pat, 0)
+        (pat) => assert_eq!(pat, 0)
     }
 }