New Rule: no-non-null-assertion

src/language/walker/syntaxWalker.ts

@@ -234,6 +234,10 @@ export class SyntaxWalker {
         this.walkChildren(node);
     }
 
+    protected visitNonNullExpression(node: ts.NonNullExpression) {
+        this.walkChildren(node);
+    }
+
     protected visitNumericLiteral(node: ts.NumericLiteral) {
         this.walkChildren(node);
     }
@@ -560,6 +564,10 @@ export class SyntaxWalker {
                 this.visitNewExpression(node as ts.NewExpression);
                 break;
 
+            case ts.SyntaxKind.NonNullExpression:
+                this.visitNonNullExpression(node as ts.NonNullExpression);
+                break;
+
             case ts.SyntaxKind.NumericLiteral:
                 this.visitNumericLiteral(node as ts.NumericLiteral);
                 break;

src/rules/noNonNullAssertionRule.ts

@@ -0,0 +1,48 @@
+/**
+ * @license
+ * Copyright 2017 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 "../index";
+
+export class Rule extends Lint.Rules.AbstractRule {
+    /* tslint:disable:object-literal-sort-keys */
+    public static metadata: Lint.IRuleMetadata = {
+        ruleName: "no-non-null-assertion",
+        description: "Disallows non-null assertions.",
+        rationale: "Using non-null assertion cancels the benefits of the strict null checking mode.",
+        optionsDescription: "Not configurable.",
+        options: null,
+        optionExamples: ["true"],
+        type: "typescript",
+        typescriptOnly: true,
+    };
+    /* tslint:enable:object-literal-sort-keys */
+
+    public static FAILURE_STRING = "Forbidden non null assertion";
+
+    public apply(sourceFile: ts.SourceFile): Lint.RuleFailure[] {
+        return this.applyWithWalker(new NoNonNullAssertionWalker(sourceFile, this.getOptions()));
+    }
+}
+
+class NoNonNullAssertionWalker extends Lint.RuleWalker {
+    public visitNonNullExpression(node: ts.NonNullExpression) {
+        this.addFailureAtNode(node, Rule.FAILURE_STRING);
+        super.visitNonNullExpression(node);
+    }
+}

test/rules/no-non-null-assertion/test.ts.lint

@@ -0,0 +1,4 @@
+var x = null
+
+x!.y = null
+~~          [Forbidden non null assertion]

test/rules/no-non-null-assertion/tslint.json

@@ -0,0 +1,5 @@
+{
+  "rules": {
+    "no-non-null-assertion": true
+  }
+}