double-parens: make lint adhere to lint message convention and do minor refactoring

Author: matthiaskrgr

clippy_lints/src/double_parens.rs

@@ -45,41 +45,28 @@ impl EarlyLintPass for DoubleParens {
             return;
         }
 
+        let msg: &str = "consider removing unnecessary double parentheses";
+
         match expr.kind {
             ExprKind::Paren(ref in_paren) => match in_paren.kind {
                 ExprKind::Paren(_) | ExprKind::Tup(_) => {
-                    span_lint(
-                        cx,
-                        DOUBLE_PARENS,
-                        expr.span,
-                        "Consider removing unnecessary double parentheses",
-                    );
+                    span_lint(cx, DOUBLE_PARENS, expr.span, &msg);
                 },
                 _ => {},
             },
             ExprKind::Call(_, ref params) => {
                 if params.len() == 1 {
                     let param = &params[0];
                     if let ExprKind::Paren(_) = param.kind {
-                        span_lint(
-                            cx,
-                            DOUBLE_PARENS,
-                            param.span,
-                            "Consider removing unnecessary double parentheses",
-                        );
+                        span_lint(cx, DOUBLE_PARENS, param.span, &msg);
                     }
                 }
             },
             ExprKind::MethodCall(_, ref params, _) => {
                 if params.len() == 2 {
                     let param = &params[1];
                     if let ExprKind::Paren(_) = param.kind {
-                        span_lint(
-                            cx,
-                            DOUBLE_PARENS,
-                            param.span,
-                            "Consider removing unnecessary double parentheses",
-                        );
+                        span_lint(cx, DOUBLE_PARENS, param.span, &msg);
                     }
                 }
             },

tests/ui/double_parens.stderr

@@ -1,36 +1,36 @@
-error: Consider removing unnecessary double parentheses
+error: consider removing unnecessary double parentheses
   --> $DIR/double_parens.rs:15:5
    |
 LL |     ((0))
    |     ^^^^^
    |
    = note: `-D clippy::double-parens` implied by `-D warnings`
 
-error: Consider removing unnecessary double parentheses
+error: consider removing unnecessary double parentheses
   --> $DIR/double_parens.rs:19:14
    |
 LL |     dummy_fn((0));
    |              ^^^
 
-error: Consider removing unnecessary double parentheses
+error: consider removing unnecessary double parentheses
   --> $DIR/double_parens.rs:23:20
    |
 LL |     x.dummy_method((0));
    |                    ^^^
 
-error: Consider removing unnecessary double parentheses
+error: consider removing unnecessary double parentheses
   --> $DIR/double_parens.rs:27:5
    |
 LL |     ((1, 2))
    |     ^^^^^^^^
 
-error: Consider removing unnecessary double parentheses
+error: consider removing unnecessary double parentheses
   --> $DIR/double_parens.rs:31:5
    |
 LL |     (())
    |     ^^^^
 
-error: Consider removing unnecessary double parentheses
+error: consider removing unnecessary double parentheses
   --> $DIR/double_parens.rs:53:16
    |
 LL |     assert_eq!(((1, 2)), (1, 2), "Error");