From c7c7abcc71b9fd5170488dbf017d8411ef1ff738 Mon Sep 17 00:00:00 2001
From: Andy Hanson <anhans@microsoft.com>
Date: Fri, 19 Jan 2018 13:00:42 -0800
Subject: [PATCH] Add 'no-const-enum' rule

---
 docs/no-const-enum.md           | 16 ++++++++++++++++
 dtslint.json                    |  1 +
 src/rules/noConstEnumRule.ts    | 32 ++++++++++++++++++++++++++++++++
 test/no-const-enum/test.ts.lint |  7 +++++++
 test/no-const-enum/tslint.json  |  6 ++++++
 5 files changed, 62 insertions(+)
 create mode 100644 docs/no-const-enum.md
 create mode 100644 src/rules/noConstEnumRule.ts
 create mode 100644 test/no-const-enum/test.ts.lint
 create mode 100644 test/no-const-enum/tslint.json

diff --git a/docs/no-const-enum.md b/docs/no-const-enum.md
new file mode 100644
index 00000000..3d75db52
--- /dev/null
+++ b/docs/no-const-enum.md
@@ -0,0 +1,16 @@
+# no-const-enum
+
+Avoid using `const enum`s. These can't be used by JavaScript users or by TypeScript users with [`--isolatedModules`](https://www.typescriptlang.org/docs/handbook/compiler-options.html) enabled.
+
+**Bad**:
+
+```ts
+const enum Bit { Off, On }
+export function f(b: Bit): void;
+```
+
+**Good**:
+
+```ts
+export function f(b: 0 | 1): void;
+```
diff --git a/dtslint.json b/dtslint.json
index 563f1858..34a6e0f7 100644
--- a/dtslint.json
+++ b/dtslint.json
@@ -6,6 +6,7 @@
 		"expect": true,
 		"export-just-namespace": true,
 		"no-bad-reference": true,
+		"no-const-enum": true,
 		"no-dead-reference": true,
 		"no-padding": true,
 		"no-redundant-undefined": true,
diff --git a/src/rules/noConstEnumRule.ts b/src/rules/noConstEnumRule.ts
new file mode 100644
index 00000000..83180b7c
--- /dev/null
+++ b/src/rules/noConstEnumRule.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-const-enum",
+		description: "Forbid `const enum`",
+		optionsDescription: "Not configurable.",
+		options: null,
+		type: "functionality",
+		typescriptOnly: true,
+	};
+
+	static FAILURE_STRING = failure(
+		Rule.metadata.ruleName,
+		"Use of `const enum`s is forbidden.");
+
+	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 (ts.isEnumDeclaration(node) && node.modifiers && node.modifiers.some(m => m.kind === ts.SyntaxKind.ConstKeyword)) {
+			ctx.addFailureAtNode(node.name, Rule.FAILURE_STRING);
+		}
+		node.forEachChild(recur);
+	});
+}
diff --git a/test/no-const-enum/test.ts.lint b/test/no-const-enum/test.ts.lint
new file mode 100644
index 00000000..0502fc78
--- /dev/null
+++ b/test/no-const-enum/test.ts.lint
@@ -0,0 +1,7 @@
+const enum E {
+           ~ [0]
+}
+
+enum F {}
+
+[0]: Use of `const enum`s is forbidden. See: https://github.com/Microsoft/dtslint/blob/master/docs/no-const-enum.md
diff --git a/test/no-const-enum/tslint.json b/test/no-const-enum/tslint.json
new file mode 100644
index 00000000..f301cb1e
--- /dev/null
+++ b/test/no-const-enum/tslint.json
@@ -0,0 +1,6 @@
+{
+  "rulesDirectory": ["../../bin/rules"],
+  "rules": {
+    "no-const-enum": true
+  }
+}