Update: add fixer for no-extra-parens (fixes #6944) (#6950)

eslint · Aug 26, 2016 · c210510 · c210510
1 parent ca3d448
commit c210510
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diff --git a/docs/rules/no-extra-parens.md b/docs/rules/no-extra-parens.md
@@ -1,5 +1,7 @@
 # disallow unnecessary parentheses (no-extra-parens)
 
+(fixable) The `--fix` option on the [command line](../user-guide/command-line-interface#fix) automatically fixes problems reported by this rule.
+
 This rule restricts the use of parentheses to only where they are necessary.
 
 ## Rule Details

diff --git a/lib/rules/no-extra-parens.js b/lib/rules/no-extra-parens.js
@@ -9,6 +9,7 @@
 //------------------------------------------------------------------------------
 
 const astUtils = require("../ast-utils.js");
+const esUtils = require("esutils");
 
 module.exports = {
     meta: {
@@ -18,6 +19,8 @@ module.exports = {
             recommended: false
         },
 
+        fixable: "code",
+
         schema: {
             anyOf: [
                 {
@@ -256,16 +259,64 @@ module.exports = {
             throw new Error("unreachable");
         }
 
+        /**
+         * Determines whether a node should be preceded by an additional space when removing parens
+         * @param {ASTNode} node node to evaluate; must be surrounded by parentheses
+         * @returns {boolean} `true` if a space should be inserted before the node
+         * @private
+         */
+        function requiresLeadingSpace(node) {
+            const leftParenToken = sourceCode.getTokenBefore(node);
+            const tokenBeforeLeftParen = sourceCode.getTokenBefore(node, 1);
+            const firstToken = sourceCode.getFirstToken(node);
+
+            // If there is already whitespace before the previous token, don't add more.
+            if (!tokenBeforeLeftParen || tokenBeforeLeftParen.end !== leftParenToken.start) {
+                return false;
+            }
+
+            // If the parens are preceded by a keyword (e.g. `typeof(0)`), a space should be inserted (`typeof 0`)
+            const precededByKeyword = tokenBeforeLeftParen.type === "Keyword";
+
+            // However, a space should not be inserted unless the first character of the token is an identifier part
+            // e.g. `typeof([])` should be fixed to `typeof[]`
+            const startsWithIdentifierPart = esUtils.code.isIdentifierPartES6(firstToken.value.charCodeAt(0));
+
+            // If the parens are preceded by and start with a unary plus/minus (e.g. `+(+foo)`), a space should be inserted (`+ +foo`)
+            const precededByUnaryPlus = tokenBeforeLeftParen.type === "Punctuator" && tokenBeforeLeftParen.value === "+";
+            const precededByUnaryMinus = tokenBeforeLeftParen.type === "Punctuator" && tokenBeforeLeftParen.value === "-";
+
+            const startsWithUnaryPlus = firstToken.type === "Punctuator" && firstToken.value === "+";
+            const startsWithUnaryMinus = firstToken.type === "Punctuator" && firstToken.value === "-";
+
+            return (precededByKeyword && startsWithIdentifierPart) ||
+                (precededByUnaryPlus && startsWithUnaryPlus) ||
+                (precededByUnaryMinus && startsWithUnaryMinus);
+        }
+
         /**
          * Report the node
          * @param {ASTNode} node node to evaluate
          * @returns {void}
          * @private
          */
         function report(node) {
-            const previousToken = sourceCode.getTokenBefore(node);
-
-            context.report(node, previousToken.loc.start, "Gratuitous parentheses around expression.");
+            const leftParenToken = sourceCode.getTokenBefore(node);
+            const rightParenToken = sourceCode.getTokenAfter(node);
+
+            context.report({
+                node,
+                loc: leftParenToken.loc.start,
+                message: "Gratuitous parentheses around expression.",
+                fix(fixer) {
+                    const parenthesizedSource = sourceCode.text.slice(leftParenToken.range[1], rightParenToken.range[0]);
+
+                    return fixer.replaceTextRange([
+                        leftParenToken.range[0],
+                        rightParenToken.range[1]
+                    ], (requiresLeadingSpace(node) ? " " : "") + parenthesizedSource);
+                }
+            });
         }
 
         /**