Refactor double_parens:

* Merge control flow before emission
* Check the AST before the macro check

Author: Jarcho

clippy_lints/src/double_parens.rs

@@ -40,35 +40,29 @@ declare_lint_pass!(DoubleParens => [DOUBLE_PARENS]);
 
 impl EarlyLintPass for DoubleParens {
     fn check_expr(&mut self, cx: &EarlyContext<'_>, expr: &Expr) {
-        if expr.span.from_expansion() {
-            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, 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, msg);
-                    }
-                }
+        let span = match &expr.kind {
+            ExprKind::Paren(in_paren) if matches!(in_paren.kind, ExprKind::Paren(_) | ExprKind::Tup(_)) => expr.span,
+            ExprKind::Call(_, params)
+                if let [param] = &**params
+                    && let ExprKind::Paren(_) = param.kind =>
+            {
+                param.span
             },
-            ExprKind::MethodCall(ref call) => {
-                if let [ref arg] = call.args[..] {
-                    if let ExprKind::Paren(_) = arg.kind {
-                        span_lint(cx, DOUBLE_PARENS, arg.span, msg);
-                    }
-                }
+            ExprKind::MethodCall(call)
+                if let [arg] = &*call.args
+                    && let ExprKind::Paren(_) = arg.kind =>
+            {
+                arg.span
             },
-            _ => {},
+            _ => return,
+        };
+        if !expr.span.from_expansion() {
+            span_lint(
+                cx,
+                DOUBLE_PARENS,
+                span,
+                "consider removing unnecessary double parentheses",
+            );
         }
     }
 }