Add `no-any-union` rule

docs/no-any-union.md

@@ -0,0 +1,27 @@
+# no-any-union
+
+Forbids to include `any` in a union. When `any` is used in a union type, the resulting type is still `any`.
+
+**Bad**:
+
+```ts
+function f(x: string | any): void;
+```
+
+**Good**:
+
+```ts
+function f(x: string): void;
+```
+
+Or:
+```ts
+function f(x: any): void;
+```
+
+Or:
+```ts
+function f(x: string | object): void;
+```
+
+While the `string` portion of this type annotation may _look_ useful, it in fact offers no additional typechecking over simply using `any`.

docs/no-dead-reference.md

@@ -1,3 +1,5 @@
+# no-dead-reference
+
 A `<reference>` comment should go at the top of a file -- otherwise it is just a normal comment.
 
 **Bad**:

dtslint.json

@@ -10,6 +10,7 @@
 		"no-padding": true,
 		"no-relative-import-in-test": true,
 		"strict-export-declare-modifiers": true,
+		"no-any-union": true,
 		"no-single-declare-module": true,
 		"no-useless-files": true,
 		"prefer-declare-function": true,

src/rules/noAnyUnionRule.ts

@@ -0,0 +1,32 @@
+import * as Lint from "tslint";
+import * as ts from "typescript";
+
+import { failure } from "../util";
+
+export class Rule extends Lint.Rules.AbstractRule {
+	static metadata: Lint.IRuleMetadata = {
+		ruleName: "no-any-union",
+		description: "Forbid a union to contain `any`",
+		optionsDescription: "Not configurable.",
+		options: null,
+		type: "functionality",
+		typescriptOnly: true,
+	};
+
+	static FAILURE_STRING = failure(
+		Rule.metadata.ruleName,
+		"Including `any` in a union will override all other members of the union.");
+
+	apply(sourceFile: ts.SourceFile): Lint.RuleFailure[] {
+		return this.applyWithFunction(sourceFile, walk);
+	}
+}
+
+function walk(ctx: Lint.WalkContext<void>): void {
+    ctx.sourceFile.forEachChild(function recur(node) {
+        if (node.kind === ts.SyntaxKind.AnyKeyword && ts.isUnionTypeNode(node.parent!)) {
+            ctx.addFailureAtNode(node, Rule.FAILURE_STRING);
+        }
+        node.forEachChild(recur);
+    });
+}

test/no-any-union/test.d.ts.lint

@@ -0,0 +1,4 @@
+export const x: any;
+
+export const y: string | any;
+                         ~~~  [Including `any` in a union will override all other members of the union. See: https://github.com/Microsoft/dtslint/blob/master/docs/no-any-union.md]

test/no-any-union/tslint.json

@@ -0,0 +1,6 @@
+{
+    "rulesDirectory": ["../../bin/rules"],
+    "rules": {
+      "no-any-union": true
+    }
+  }