Add no-multiple-var rule (#1191)

README.md

@@ -242,6 +242,8 @@ A sample configuration file with all options is available [here](https://github.
 * `no-internal-module` disallows internal `module` (use `namespace` instead).
 * `no-invalid-this` disallows using the `this` keyword outside of classes.
     * `no-this-in-function-in-method` disallows using the `this` keyword in functions within class methods.
+* `no-multiple-var` disallows multiple variable definitions in the same statement.
+* `no-use-before-declare` disallows usage of variables before their declaration.
 * `no-namespace` disallows both internal `module`s and `namespace`, but allows ES6-style external modules.
     * `allow-declarations` allows `declare namespace ... {}` to describe external APIs.
 * `no-null-keyword` disallows use of the `null` keyword literal.

docs/sample.tslint.json

@@ -71,6 +71,7 @@
       true,
       "no-this-in-function-in-method"
       ],
+    "no-multiple-var": true,
     "no-null-keyword": true,
     "no-reference": true,
     "no-require-imports": true,

src/rules/noMultipleVarRule.ts

@@ -0,0 +1,50 @@
+/**
+ * @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 {
+    public static FAILURE_STRING = "Forbidden multiple variable definitions in the same statement";
+
+    public apply(sourceFile: ts.SourceFile): Lint.RuleFailure[] {
+        const noMultipleVarWalker = new NoMultipleVarWalker(sourceFile, this.getOptions());
+        return this.applyWithWalker(noMultipleVarWalker);
+    }
+}
+
+class NoMultipleVarWalker extends Lint.RuleWalker {
+    public visitVariableStatement(node: ts.VariableStatement) {
+        const declarationList = node.declarationList;
+
+        if (declarationList.declarations.length > 1) {
+            this.addFailure(this.createFailure(node.getStart(), node.getWidth(), Rule.FAILURE_STRING));
+        }
+
+        super.visitVariableStatement(node);
+    }
+
+    public visitForStatement(node: ts.ForStatement) {
+        let initializer = node.initializer;
+        if (initializer && initializer.kind === ts.SyntaxKind.VariableDeclarationList &&
+                (<ts.VariableDeclarationList>initializer).declarations.length > 1) {
+            const declarationList = <ts.VariableDeclarationList>initializer;
+            this.addFailure(this.createFailure(declarationList.getStart(), declarationList.getWidth(), Rule.FAILURE_STRING));
+        }
+        super.visitForStatement(node);
+    }
+}

src/tsconfig.json

@@ -93,6 +93,7 @@
         "rules/noInferrableTypesRule.ts",
         "rules/noInternalModuleRule.ts",
         "rules/noInvalidThisRule.ts",
+        "rules/noMultipleVarRule.ts",
         "rules/noNamespaceRule.ts",
         "rules/noNullKeywordRule.ts",
         "rules/noReferenceRule.ts",

test/rules/no-multiple-var/test.ts.lint

@@ -0,0 +1,44 @@
+// valid cases
+var foo1;
+var foo2: number;
+var foo3 = 1;
+
+let foo4;
+let foo5: number;
+let foo6 = 1;
+
+const foo7: number = 1;
+const foo8 = 1;
+
+for (var i = 0; i > 1; i++) {}
+for (let i = 0; i > 1; i++) {}
+for (const i = 0; i > 1;) {}
+
+// invalid cases
+var foo9, foo10;
+~~~~~~~~~~~~~~~~ [0]
+var foo11: number, foo12: number;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ [0]
+var foo13 = 1, foo14 = 1;
+~~~~~~~~~~~~~~~~~~~~~~~~~ [0]
+
+let foo15, foo16;
+~~~~~~~~~~~~~~~~~ [0]
+let foo17: number, foo18: number;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ [0]
+let foo19 = 1, foo20 = 1;
+~~~~~~~~~~~~~~~~~~~~~~~~~ [0]
+
+const foo21: number = 1, foo22: number = 1;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ [0]
+const foo23 = 1, foo24 = 1;
+~~~~~~~~~~~~~~~~~~~~~~~~~~~ [0]
+
+for (var i = 0, j = 0; i > 1; i++) {}
+     ~~~~~~~~~~~~~~~~ [0]
+for (let i = 0, j = 0; i > 1; i++) {}
+     ~~~~~~~~~~~~~~~~ [0]
+for (const i = 0, j = 0; i > 1;) {}
+     ~~~~~~~~~~~~~~~~~~ [0]
+
+[0]: Forbidden multiple variable definitions in the same statement

test/rules/no-multiple-var/tslint.json

@@ -0,0 +1,5 @@
+{
+  "rules": {
+    "no-multiple-var": true
+  }
+}

test/tsconfig.json

@@ -90,6 +90,7 @@
         "../src/rules/noInferrableTypesRule.ts",
         "../src/rules/noInternalModuleRule.ts",
         "../src/rules/noInvalidThisRule.ts",
+        "../src/rules/noMultipleVarRule.ts",
         "../src/rules/noNamespaceRule.ts",
         "../src/rules/noNullKeywordRule.ts",
         "../src/rules/noReferenceRule.ts",