Add new Rule: arrow-parens (#1384)

* Add new Rule: arrow-parens

* Add test

* modify some documentations

README.md

@@ -251,6 +251,7 @@ Core rules are included in the `tslint` package.
   * `"parameters"` checks alignment of function parameters.
   * `"arguments"` checks alignment of function call arguments.
   * `"statements"` checks alignment of statements.
+* `arrow-parens` requires parentheses around the parameters of arrow function definitions.
 * `ban` bans the use of specific functions. Options are ["object", "function"] pairs that ban the use of object.function().
 * `class-name` enforces PascalCased class and interface names.
 * `comment-format` enforces rules for single-line comments. Rule options:

src/rules/arrowParensRule.ts

@@ -0,0 +1,59 @@
+/**
+ * @license
+ * Copyright 2016 Palantir Technologies, Inc.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import * as ts from "typescript";
+
+import * as Lint from "../lint";
+
+export class Rule extends Lint.Rules.AbstractRule {
+    /* tslint:disable:object-literal-sort-keys */
+    public static metadata: Lint.IRuleMetadata = {
+        ruleName: "arrow-parens",
+        description: "Requires parentheses around the parameters of arrow function definitions.",
+        rationale: "Maintains stylistic consistency with other arrow function definitions.",
+        optionsDescription: "Not configurable.",
+        options: null,
+        optionExamples: ["true"],
+        type: "style",
+    };
+    /* tslint:enable:object-literal-sort-keys */
+
+    public static FAILURE_STRING = "Parentheses are required around the parameters of an arrow function definition";
+
+    public apply(sourceFile: ts.SourceFile): Lint.RuleFailure[] {
+        const newParensWalker = new ArrowParensWalker(sourceFile, this.getOptions());
+        return this.applyWithWalker(newParensWalker);
+    }
+}
+
+class ArrowParensWalker extends Lint.RuleWalker {
+    public visitArrowFunction(node: ts.FunctionLikeDeclaration) {
+        if (node.parameters.length === 1) {
+            const parameter = node.parameters[0];
+            const text = parameter.getText();
+            const firstToken = node.getFirstToken();
+            const lastToken = node.getChildAt(2);
+            const width = text.length;
+            const position = parameter.getStart();
+
+            if (firstToken.kind !== ts.SyntaxKind.OpenParenToken || lastToken.kind !== ts.SyntaxKind.CloseParenToken) {
+                this.addFailure(this.createFailure(position, width, Rule.FAILURE_STRING));
+            }
+        }
+        super.visitArrowFunction(node);
+    }
+}

src/tsconfig.json

@@ -69,6 +69,7 @@
         "language/walker/skippableTokenAwareRuleWalker.ts",
         "language/walker/syntaxWalker.ts",
         "rules/alignRule.ts",
+        "rules/arrowParensRule.ts",
         "rules/banRule.ts",
         "rules/classNameRule.ts",
         "rules/commentFormatRule.ts",

test/rules/arrow-parens/test.ts.lint

@@ -0,0 +1,15 @@
+// valid case
+var a = (a) => {};
+var b = (a: number) => {};
+var c = (a, b) => {};
+var f = (...rest) => {};
+var f = a: number => {}; // TSLint don't warn. But syntax is wrong.
+class Foo {
+    a: (a) =>{}
+}
+
+// invalid case
+var e = (a => {})(1);
+         ~            [Parentheses are required around the parameters of an arrow function definition]
+var f = a => {};
+        ~             [Parentheses are required around the parameters of an arrow function definition]

test/rules/arrow-parens/tslint.json

@@ -0,0 +1,5 @@
+{
+  "rules": {
+    "arrow-parens": true
+  }
+}

test/tsconfig.json

@@ -65,6 +65,7 @@
         "../src/ruleLoader.ts",
         "../src/rules.ts",
         "../src/rules/alignRule.ts",
+        "../src/rules/arrowParensRule.ts",
         "../src/rules/banRule.ts",
         "../src/rules/classNameRule.ts",
         "../src/rules/commentFormatRule.ts",
@@ -162,4 +163,4 @@
         "rule-tester/testData.ts",
         "rule-tester/utilsTests.ts"
     ]
-}
+}