New: prefer-rest-params rule (fixes eslint#4108)

conf/eslint.json

@@ -163,8 +163,9 @@
         "padded-blocks": 0,
         "prefer-arrow-callback": 0,
         "prefer-const": 0,
-        "prefer-spread": 0,
         "prefer-reflect": 0,
+        "prefer-rest-params": 0,
+        "prefer-spread": 0,
         "prefer-template": 0,
         "quote-props": 0,
         "quotes": [0, "double"],

docs/rules/README.md

@@ -224,6 +224,7 @@ These rules are only relevant to ES6 environments.
 * [prefer-arrow-callback](prefer-arrow-callback.md) - suggest using arrow functions as callbacks
 * [prefer-const](prefer-const.md) - suggest using `const` declaration for variables that are never modified after declared
 * [prefer-reflect](prefer-reflect.md) - suggest using Reflect methods where applicable
+* [prefer-rest-params](prefer-rest-params.md) - suggest using the rest parameters instead of `arguments`
 * [prefer-spread](prefer-spread.md) - suggest using the spread operator instead of `.apply()`.
 * [prefer-template](prefer-template.md) - suggest using template literals instead of strings concatenation
 * [require-yield](require-yield.md) - disallow generator functions that do not have `yield`

docs/rules/prefer-rest-params.md

@@ -0,0 +1,54 @@
+# Suggest using the rest parameters instead of `arguments` (prefer-rest-params)
+
+There is rest parameters in ES2015.
+We can use that feature for variadic functions instead of `arguments` variable.
+
+`arguments` does not have methods of `Array.prototype`, so it's inconvenience a bit.
+
+## Rule Details
+
+This rule is aimed to flag usage of `arguments` variables.
+
+The following patterns are considered problems:
+
+```js
+function foo() {
+    console.log(arguments);                 /*error Use the rest parameters instead of "arguments". */
+}
+
+function foo(action) {
+    var args = [].slice.call(arguments, 1); /*error Use the rest parameters instead of "arguments". */
+    action.apply(null, args);
+}
+```
+
+The following patterns are considered not problems:
+
+```js
+function foo(...args) {
+    console.log(args);
+}
+
+function foo(action, ...args) {
+    action.apply(null, args); // or `action(...args)`, related with the `prefer-spread` rule.
+}
+
+// Note: the implicit arguments can be overwritten.
+function foo(arguments) {
+    console.log(arguments); // This is the first argument.
+}
+function foo() {
+    var arguments = 0;
+    console.log(arguments); // This is a local variable.
+}
+```
+
+## When Not To Use It
+
+This rule should not be used in ES3/5 environments.
+
+In ES2015 (ES6) or later, if you don't want to be notified about `arguments` variables, then it's safe to disable this rule.
+
+## Related rules
+
+* [prefer-spread](prefer-spread.md)

lib/rules/prefer-rest-params.js

@@ -0,0 +1,71 @@
+/**
+ * @fileoverview Rule to
+ * @author Toru Nagashima
+ * @copyright 2015 Toru Nagashima. All rights reserved.
+ * See LICENSE file in root directory for full license.
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Helpers
+//------------------------------------------------------------------------------
+
+/**
+ * Gets the variable object of `arguments` which is defined implicitly.
+ * @param {escope.Scope} scope - A scope to get.
+ * @returns {escope.Variable} The found variable object.
+ */
+function getVariableOfArguments(scope) {
+    var variables = scope.variables;
+    for (var i = 0; i < variables.length; ++i) {
+        var variable = variables[i];
+        if (variable.name === "arguments") {
+            // If there was a parameter which is named "arguments", the implicit "arguments" is not defined.
+            // So does fast return with null.
+            return (variable.identifiers.length === 0) ? variable : null;
+        }
+    }
+
+    /* istanbul ignore next : unreachable */
+    return null;
+}
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = function(context) {
+
+    /**
+     * Reports a given reference.
+     *
+     * @param {escope.Reference} reference - A reference to report.
+     * @returns {void}
+     */
+    function report(reference) {
+        context.report({
+            node: reference.identifier,
+            message: "Use the rest parameters instead of \"arguments\"."
+        });
+    }
+
+    /**
+     * Reports references of the implicit `arguments` variable if exist.
+     *
+     * @returns {void}
+     */
+    function checkForArguments() {
+        var argumentsVar = getVariableOfArguments(context.getScope());
+        if (argumentsVar) {
+            argumentsVar.references.forEach(report);
+        }
+    }
+
+    return {
+        FunctionDeclaration: checkForArguments,
+        FunctionExpression: checkForArguments
+    };
+};
+
+module.exports.schema = [];

tests/lib/rules/prefer-rest-params.js

@@ -0,0 +1,29 @@
+/**
+ * @fileoverview Tests for prefer-rest-params rule.
+ * @author Toru Nagashima
+ * @copyright 2015 Toru Nagashima. All rights reserved.
+ * See LICENSE file in root directory for full license.
+ */
+
+"use strict";
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+var rule = require("../../../lib/rules/prefer-rest-params"),
+    RuleTester = require("../../../lib/testers/rule-tester");
+
+var ruleTester = new RuleTester();
+ruleTester.run("prefer-rest-params", rule, {
+    valid: [
+        "arguments;",
+        "function foo(arguments) { arguments; }",
+        "function foo() { var arguments; arguments; }",
+        {code: "var foo = () => arguments;", ecmaFeatures: {arrowFunctions: true}}, // Arrows don't have "arguments".,
+        {code: "function foo(...args) { args; }", ecmaFeatures: {restParams: true}}
+    ],
+    invalid: [
+        {code: "function foo() { arguments; }", errors: [{type: "Identifier", message: "Use the rest parameters instead of \"arguments\"."}]}
+    ]
+});