From 42cf53ea823813ba4dc4d7667e5c81e3f88fd2b1 Mon Sep 17 00:00:00 2001
From: Julian Descottes <jdescottes@mozilla.com>
Date: Mon, 16 Sep 2024 09:13:30 +0000
Subject: [PATCH] Bug 1917003 - [eslint] Add linter rule to ban await await
 r=Standard8,frontend-codestyle-reviewers

Differential Revision: https://phabricator.services.mozilla.com/D221187
---
 .../rules/reject-multiple-await.rst           | 23 ++++++++++++
 .../lib/configs/recommended.js                |  1 +
 .../eslint/eslint-plugin-mozilla/lib/index.js |  1 +
 .../lib/rules/reject-multiple-await.js        | 35 ++++++++++++++++++
 .../tests/reject-multiple-await.js            | 37 +++++++++++++++++++
 5 files changed, 97 insertions(+)
 create mode 100644 docs/code-quality/lint/linters/eslint-plugin-mozilla/rules/reject-multiple-await.rst
 create mode 100644 tools/lint/eslint/eslint-plugin-mozilla/lib/rules/reject-multiple-await.js
 create mode 100644 tools/lint/eslint/eslint-plugin-mozilla/tests/reject-multiple-await.js

diff --git a/docs/code-quality/lint/linters/eslint-plugin-mozilla/rules/reject-multiple-await.rst b/docs/code-quality/lint/linters/eslint-plugin-mozilla/rules/reject-multiple-await.rst
new file mode 100644
index 000000000000..a9ee4c215c97
--- /dev/null
+++ b/docs/code-quality/lint/linters/eslint-plugin-mozilla/rules/reject-multiple-await.rst
@@ -0,0 +1,23 @@
+reject-multiple-await
+=====================
+
+Disallows using `await await somePromise`. While this is valid syntax, this
+usually unintentional and can have a slightly different behavior from using a
+single `await`. Using `await await` should ideally be explained with a comment.
+
+Examples of incorrect code for this rule:
+-----------------------------------------
+
+.. code-block:: js
+
+    await await somePromise;
+    await await await somePromise;
+    await (await somePromise);
+
+
+Examples of correct code for this rule:
+---------------------------------------
+
+.. code-block:: js
+
+    await somePromise;
diff --git a/tools/lint/eslint/eslint-plugin-mozilla/lib/configs/recommended.js b/tools/lint/eslint/eslint-plugin-mozilla/lib/configs/recommended.js
index 56f760b835bf..27aa3fb9013d 100644
--- a/tools/lint/eslint/eslint-plugin-mozilla/lib/configs/recommended.js
+++ b/tools/lint/eslint/eslint-plugin-mozilla/lib/configs/recommended.js
@@ -176,6 +176,7 @@ module.exports = {
     "mozilla/reject-chromeutils-import": "error",
     "mozilla/reject-chromeutils-import-params": "error",
     "mozilla/reject-importGlobalProperties": ["error", "allownonwebidl"],
+    "mozilla/reject-multiple-await": "error",
     "mozilla/reject-multiple-getters-calls": "error",
     "mozilla/reject-scriptableunicodeconverter": "warn",
     "mozilla/rejects-requires-await": "error",
diff --git a/tools/lint/eslint/eslint-plugin-mozilla/lib/index.js b/tools/lint/eslint/eslint-plugin-mozilla/lib/index.js
index 23da078fe978..0d50402f0bad 100644
--- a/tools/lint/eslint/eslint-plugin-mozilla/lib/index.js
+++ b/tools/lint/eslint/eslint-plugin-mozilla/lib/index.js
@@ -76,6 +76,7 @@ module.exports = {
     "reject-importGlobalProperties": require("../lib/rules/reject-importGlobalProperties"),
     "reject-lazy-imports-into-globals": require("../lib/rules/reject-lazy-imports-into-globals"),
     "reject-mixing-eager-and-lazy": require("../lib/rules/reject-mixing-eager-and-lazy"),
+    "reject-multiple-await": require("../lib/rules/reject-multiple-await.js"),
     "reject-multiple-getters-calls": require("../lib/rules/reject-multiple-getters-calls"),
     "reject-scriptableunicodeconverter": require("../lib/rules/reject-scriptableunicodeconverter"),
     "reject-relative-requires": require("../lib/rules/reject-relative-requires"),
diff --git a/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/reject-multiple-await.js b/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/reject-multiple-await.js
new file mode 100644
index 000000000000..06f32cfb6464
--- /dev/null
+++ b/tools/lint/eslint/eslint-plugin-mozilla/lib/rules/reject-multiple-await.js
@@ -0,0 +1,35 @@
+/**
+ * @fileoverview Reject multiple await operators.
+ *
+ * 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";
+
+module.exports = {
+  meta: {
+    docs: {
+      url: "https://firefox-source-docs.mozilla.org/code-quality/lint/linters/eslint-plugin-mozilla/rules/reject-multiple-await.html",
+    },
+    messages: {
+      rejectMultipleAwait: "Do not use multiple await operators.",
+    },
+    schema: [],
+    type: "problem",
+  },
+
+  create(context) {
+    return {
+      AwaitExpression(node) {
+        if (
+          node.parent.type === "AwaitExpression" &&
+          node.parent.parent.type !== "AwaitExpression"
+        ) {
+          context.report({ node, messageId: "rejectMultipleAwait" });
+        }
+      },
+    };
+  },
+};
diff --git a/tools/lint/eslint/eslint-plugin-mozilla/tests/reject-multiple-await.js b/tools/lint/eslint/eslint-plugin-mozilla/tests/reject-multiple-await.js
new file mode 100644
index 000000000000..c5051a447107
--- /dev/null
+++ b/tools/lint/eslint/eslint-plugin-mozilla/tests/reject-multiple-await.js
@@ -0,0 +1,37 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// ------------------------------------------------------------------------------
+// Requirements
+// ------------------------------------------------------------------------------
+
+var rule = require("../lib/rules/reject-multiple-await");
+var RuleTester = require("eslint").RuleTester;
+
+const ruleTester = new RuleTester({ parserOptions: { ecmaVersion: "latest" } });
+
+// ------------------------------------------------------------------------------
+// Tests
+// ------------------------------------------------------------------------------
+
+function invalidCode(code) {
+  return { code, errors: [{ messageId: "rejectMultipleAwait" }] };
+}
+
+ruleTester.run("reject-multiple-await", rule, {
+  valid: [
+    "async () => await new Promise(r => r());",
+    "async () => await awaitSomething;",
+  ],
+  invalid: [
+    invalidCode("async () => await await new Promise(r => r());"),
+    invalidCode(`async () => {
+        await
+        await new Promise(r => r());
+    }`),
+    invalidCode("async () => await (await new Promise(r => r()));"),
+    invalidCode("async () => await await await new Promise(r => r());"),
+  ],
+});