Bug 1768031 - Reject top-level await in modules via an ESLint rule. r=Gijs

Differential Revision: https://phabricator.services.mozilla.com/D145892

docs/code-quality/lint/linters/eslint-plugin-mozilla.rst

@@ -54,6 +54,7 @@ The plugin implements the following rules:
    eslint-plugin-mozilla/reject-requires-await
    eslint-plugin-mozilla/reject-scriptableunicodeconverter
    eslint-plugin-mozilla/reject-some-requires
+   eslint-plugin-mozilla/reject-top-level-await
    eslint-plugin-mozilla/use-cc-etc
    eslint-plugin-mozilla/use-chromeutils-generateqi
    eslint-plugin-mozilla/use-chromeutils-import

docs/code-quality/lint/linters/eslint-plugin-mozilla/reject-top-level-await.rst

@@ -0,0 +1,26 @@
+reject-top-level-await
+======================
+
+Rejects ``await`` at the top-level of code in modules. Top-level ``await`` is
+not currently support in Gecko's component modules, so this is rejected.
+
+Examples of incorrect code for this rule:
+-----------------------------------------
+
+.. code-block:: js
+
+    await foo;
+
+    if (expr) {
+      await foo;
+    }
+
+    for await (let x of [1, 2, 3]) { }
+
+Examples of correct code for this rule:
+---------------------------------------
+
+.. code-block:: js
+
+    async function() { await foo; }
+    async function() { for await (let x of [1, 2, 3]) { } }

tools/lint/eslint/eslint-plugin-mozilla/lib/configs/recommended.js

@@ -49,6 +49,7 @@ module.exports = {
       },
       files: ["**/*.mjs", "**/*.jsm", "**/*.jsm.js"],
       rules: {
+        "mozilla/reject-top-level-await": "error",
         // Bug 1703953: We don't have a good way to check a file runs in a
         // privilieged context. Apply this for jsm files as we know those are
         // privilieged, and then include more directories elsewhere.

tools/lint/eslint/eslint-plugin-mozilla/lib/index.js

@@ -59,6 +59,7 @@ module.exports = {
     "reject-scriptableunicodeconverter": require("../lib/rules/reject-scriptableunicodeconverter"),
     "reject-relative-requires": require("../lib/rules/reject-relative-requires"),
     "reject-some-requires": require("../lib/rules/reject-some-requires"),
+    "reject-top-level-await": require("../lib/rules/reject-top-level-await"),
     "rejects-requires-await": require("../lib/rules/rejects-requires-await"),
     "use-cc-etc": require("../lib/rules/use-cc-etc"),
     "use-chromeutils-generateqi": require("../lib/rules/use-chromeutils-generateqi"),

tools/lint/eslint/eslint-plugin-mozilla/lib/rules/reject-top-level-await.js

@@ -0,0 +1,42 @@
+/**
+ * @fileoverview Don't allow only() in tests
+ *
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/.
+ */
+
+"use strict";
+
+var helpers = require("../helpers");
+
+module.exports = {
+  meta: {
+    docs: {
+      url:
+        "https://firefox-source-docs.mozilla.org/code-quality/lint/linters/eslint-plugin-mozilla/reject-top-level-await.html",
+    },
+    messages: {
+      rejectTopLevelAwait:
+        "Top-level await is not currently supported in component files.",
+    },
+    type: "problem",
+  },
+
+  create(context) {
+    return {
+      AwaitExpression(node) {
+        if (!helpers.getIsGlobalScope(context.getAncestors())) {
+          return;
+        }
+        context.report({ node, messageId: "rejectTopLevelAwait" });
+      },
+      ForOfStatement(node) {
+        if (!node.await || !helpers.getIsGlobalScope(context.getAncestors())) {
+          return;
+        }
+        context.report({ node, messageId: "rejectTopLevelAwait" });
+      },
+    };
+  },
+};

tools/lint/eslint/eslint-plugin-mozilla/package-lock.json

@@ -1,6 +1,6 @@
 {
   "name": "eslint-plugin-mozilla",
-  "version": "2.12.2",
+  "version": "2.12.3",
   "lockfileVersion": 1,
   "requires": true,
   "dependencies": {

tools/lint/eslint/eslint-plugin-mozilla/package.json

@@ -1,6 +1,6 @@
 {
   "name": "eslint-plugin-mozilla",
-  "version": "2.12.2",
+  "version": "2.12.3",
   "description": "A collection of rules that help enforce JavaScript coding standard in the Mozilla project.",
   "keywords": [
     "eslint",

tools/lint/eslint/eslint-plugin-mozilla/tests/reject-top-level-await.js

@@ -0,0 +1,36 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// ------------------------------------------------------------------------------
+// Requirements
+// ------------------------------------------------------------------------------
+
+var rule = require("../lib/rules/reject-top-level-await");
+var RuleTester = require("eslint").RuleTester;
+
+const ruleTester = new RuleTester({
+  parserOptions: { ecmaVersion: 13, sourceType: "module" },
+});
+
+// ------------------------------------------------------------------------------
+// Tests
+// ------------------------------------------------------------------------------
+
+function invalidCode(code, messageId) {
+  return { code, errors: [{ messageId: "rejectTopLevelAwait" }] };
+}
+
+ruleTester.run("reject-top-level-await", rule, {
+  valid: [
+    "async() => { await bar() }",
+    "async() => { for await (let x of []) {} }",
+  ],
+  invalid: [
+    invalidCode("await foo"),
+    invalidCode("{ await foo }"),
+    invalidCode("(await foo)"),
+    invalidCode("for await (let x of []) {}"),
+  ],
+});