Define no-null-keyword rule

README.md

@@ -187,6 +187,7 @@ A sample configuration file with all options is available [here](https://github.
 * `no-eval` disallows `eval` function invocations.
 * `no-inferrable-types` disallows explicit type declarations for variables or parameters initialized to a number, string, or boolean.
 * `no-internal-module` disallows internal `module` (use `namespace` instead).
+* `no-null-keyword` disallows use of the `null` keyword literal
 * `no-require-imports` disallows invocation of `require()` (use ES6-style imports instead).
 * `no-shadowed-variable` disallows shadowed variable declarations.
 * `no-string-literal` disallows object access via string literals.

docs/sample.tslint.json

@@ -57,6 +57,7 @@
     "no-eval": true,
     "no-inferrable-types": false,
     "no-internal-module": true,
+    "no-null-keyword": true,
     "no-require-imports": true,
     "no-shadowed-variable": true,
     "no-string-literal": true,

src/rules/noNullKeywordRule.ts

@@ -0,0 +1,37 @@
+/*
+ * Copyright 2013 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.
+ */
+
+// with due reference to https://github.com/Microsoft/TypeScript/blob/7813121c4d77e50aad0eed3152ef1f1156c7b574/scripts/tslint/noNullRule.ts
+
+import * as Lint from "../lint";
+import * as ts from "typescript";
+
+export class Rule extends Lint.Rules.AbstractRule {
+    public static FAILURE_STRING = "Use 'undefined' instead of 'null'";
+
+    public apply(sourceFile: ts.SourceFile): Lint.RuleFailure[] {
+        return this.applyWithWalker(new NullWalker(sourceFile, this.getOptions()));
+    }
+}
+
+class NullWalker extends Lint.RuleWalker {
+    public visitNode(node: ts.Node) {
+        super.visitNode(node);
+        if (node.kind === ts.SyntaxKind.NullKeyword) {
+            this.addFailure(this.createFailure(node.getStart(), node.getWidth(), Rule.FAILURE_STRING));
+        }
+    }
+}

src/tsconfig.json

@@ -76,6 +76,7 @@
         "rules/noEvalRule.ts",
         "rules/noInferrableTypesRule.ts",
         "rules/noInternalModuleRule.ts",
+        "rules/noNullKeywordRule.ts",
         "rules/noRequireImportsRule.ts",
         "rules/noShadowedVariableRule.ts",
         "rules/noStringLiteralRule.ts",

test/files/rules/nonullkeyword.test.ts

@@ -0,0 +1,2 @@
+var x = null; // error
+console.log(null, x); // error

test/rules/noNullKeywordRuleTests.ts

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2013 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 Lint from "../lint";
+
+describe("<no-null-keyword>", () => {
+    const fileName = "rules/nonullkeyword.test.ts";
+    const NoNullKeywordRule = Lint.Test.getRule("no-null-keyword");
+    const actualFailures = Lint.Test.applyRuleOnFile(fileName, NoNullKeywordRule);
+
+    const createFailure = Lint.Test.createFailuresOnFile(fileName, NoNullKeywordRule.FAILURE_STRING);
+
+    it("disallows assignment 'null'", () => {
+        assert.equal(actualFailures.length, 2);
+
+        const expectedFailures = [
+            createFailure([1, 9], [1, 13]),
+            createFailure([2, 13], [2, 17])
+        ];
+
+        for (let failure of expectedFailures) {
+            Lint.Test.assertContainsFailure(actualFailures, failure);
+        }
+    });
+});

test/tsconfig.json

@@ -76,6 +76,7 @@
         "../src/rules/noEvalRule.ts",
         "../src/rules/noInferrableTypesRule.ts",
         "../src/rules/noInternalModuleRule.ts",
+        "../src/rules/noNullKeywordRule.ts",
         "../src/rules/noRequireImportsRule.ts",
         "../src/rules/noShadowedVariableRule.ts",
         "../src/rules/noStringLiteralRule.ts",
@@ -139,6 +140,7 @@
         "rules/noEvalRuleTests.ts",
         "rules/noInferrableTypesRuleTests.ts",
         "rules/noInternalModuleRuleTests.ts",
+        "rules/noNullKeywordRuleTests.ts",
         "rules/noRequireImportsRuleTests.ts",
         "rules/noShadowedVariableRuleTests.ts",
         "rules/noStringLiteralRuleTests.ts",
@@ -169,4 +171,4 @@
         "formatters/proseFormatterTests.ts",
         "formatters/verboseFormatterTests.ts"
     ]
-}
+}