New: no-useless-rest-spread rule

docs/rules/no-useless-rest-spread.md

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+# Disallow unnecessary rest/spread operators (no-useless-rest-spread)
+
+## Rule Details
+
+Examples of **incorrect** code for this rule:
+
+```js
+/*eslint no-useless-rest-spread: "error"*/
+
+let list = [a, ...[b, c], d]
+foo(...[a, b, c])
+
+let [a, b, ...[c, d]] = list;
+function foo(a, b, ...[c, d]) {
+}
+```
+
+Examples of **correct** code for this rule:
+
+```js
+/*eslint no-useless-rest-spread: "error"*/
+
+let list = [a, b, c, d]
+foo(a, b, c)
+
+let [a, b, c, d] = list;
+function foo(a, b, c, d) {
+}
+```

lib/rules/no-useless-rest-spread.js

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+/**
+ * @fileoverview Rule to disallow unnecessary spread operators.
+ * @author Toru Nagashima
+ */
+
+"use strict"
+
+//------------------------------------------------------------------------------
+// Helpers
+//------------------------------------------------------------------------------
+
+//------------------------------------------------------------------------------
+// Rule Definition
+//------------------------------------------------------------------------------
+
+module.exports = {
+    meta: {
+        docs: {
+            description: "Disallow unnecessary spread operators.",
+            category: "Stylistic Issues",
+            recommended: false,
+        },
+        schema: [],
+    },
+
+    create: function(context) {
+        return {
+            SpreadElement: function(node) {
+                if (node.argument.type === "ArrayExpression") {
+                    context.report({
+                        node: node,
+                        message: "Unexpected a spread operator.",
+                    })
+                }
+            },
+
+            RestElement: function(node) {
+                if (node.argument.type === "ArrayPattern") {
+                    context.report({
+                        node: node,
+                        message: "Unexpected a rest operator.",
+                    })
+                }
+            },
+        }
+    },
+}

tests/lib/rules/no-useless-rest-spread.js

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+/**
+ * @fileoverview Tests for no-useless-rest-spread rule.
+ * @author Toru Nagashima
+ */
+"use strict"
+
+//------------------------------------------------------------------------------
+// Requirements
+//------------------------------------------------------------------------------
+
+var rule = require("../../../lib/rules/no-useless-rest-spread")
+var RuleTester = require("eslint").RuleTester
+
+//------------------------------------------------------------------------------
+// Tests
+//------------------------------------------------------------------------------
+
+var ruleTester = new RuleTester()
+
+ruleTester.run("no-useless-rest-spread", rule, {
+    valid: [
+        {code: "let list = [...a, ...b]", env: {es6: true}},
+        {code: "foo(...a, ...b)", env: {es6: true}},
+        {code: "let [a, b, c, ...d] = obj", env: {es6: true}},
+        {code: "function foo(a, b, c, ...d) {}", env: {es6: true}},
+    ],
+    invalid: [
+        {code: "let list = [...[x, y, x], ...b]", env: {es6: true}, errors: ["Unexpected a spread operator."]},
+        {code: "foo(...a, ...[x, y, x])", env: {es6: true}, errors: ["Unexpected a spread operator."]},
+        {code: "let [a, ...[b, c, ...d]] = obj", env: {es6: true}, errors: ["Unexpected a rest operator."]},
+
+        // Acorn cannot parse this
+        // {code: "function foo(a, ...[b, c, ...d]) {}", env: {es6: true}, errors: ["Unexpected a rest operator."]},
+    ],
+})