node/tools/eslint/lib/rules/arrow-parens.js

/**
 * @fileoverview Rule to require parens in arrow function arguments.
 * @author Jxck
 * @copyright 2015 Jxck. All rights reserved.
 */
"use strict";

//------------------------------------------------------------------------------
// Rule Definition
//------------------------------------------------------------------------------

module.exports = function(context) {
    var message = "Expected parentheses around arrow function argument.";
    var asNeededMessage = "Unexpected parentheses around single function argument";
    var asNeeded = context.options[0] === "as-needed";

    /**
     * Determines whether a arrow function argument end with `)`
     * @param {ASTNode} node The arrow function node.
     * @returns {void}
     */
    function parens(node) {
        var token = context.getFirstToken(node);

        // as-needed: x => x
        if (asNeeded && node.params.length === 1 && node.params[0].type === "Identifier") {
            if (token.type === "Punctuator" && token.value === "(") {
                context.report(node, asNeededMessage);
            }
            return;
        }

        if (token.type === "Identifier") {
            var after = context.getTokenAfter(token);

            // (x) => x
            if (after.value !== ")") {
                context.report(node, message);
            }
        }
    }

    return {
        "ArrowFunctionExpression": parens
    };
};

module.exports.schema = [
    {
        "enum": ["always", "as-needed"]
    }
];