Bug 1771751 - Reject static import for system module from non-system …

…module. r=Standard8

Differential Revision: https://phabricator.services.mozilla.com/D149183

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

@@ -56,6 +56,7 @@ The plugin implements the following rules:
    eslint-plugin-mozilla/reject-scriptableunicodeconverter
    eslint-plugin-mozilla/reject-some-requires
    eslint-plugin-mozilla/reject-top-level-await
+   eslint-plugin-mozilla/reject-import-system-module-from-non-system
    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-import-system-module-from-non-system.rst

@@ -0,0 +1,36 @@
+reject-import-system-module-from-non-system
+===========================================
+
+Rejects static import declaration for system modules (``.sys.mjs``) from non-system
+modules.
+
+Using static import for a system module into a non-system module would create a separate instance of the imported object(s) that is not shared with the other system modules and would break the per-process singleton expectation.
+
+The reason for this is that inside system modules, a static import will load the module into the shared global. Inside non-system modules, the static import will load into a different global (e.g. window). This will cause the module to be loaded into different scopes, and hence create separate instances. The fix is to use ``ChromeUtils.importESM`` which will import the object via the system module shared global scope.
+
+
+Examples of incorrect code for this rule:
+-----------------------------------------
+
+Inside a non-system module:
+
+.. code-block:: js
+
+    import { Services } from "resource://gre/modules/Services.sys.mjs";
+
+Examples of correct code for this rule:
+---------------------------------------
+
+Inside a non-system module:
+
+.. code-block:: js
+
+    const { Services } = ChromeUtils.importESM(
+      "resource://gre/modules/Services.sys.mjs"
+    );
+
+Inside a system module:
+
+.. code-block:: js
+
+    import { Services } from "resource://gre/modules/Services.sys.mjs";

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

@@ -82,6 +82,13 @@ module.exports = {
         ],
       },
     },
+    {
+      excludedFiles: ["**/*.sys.mjs"],
+      files: ["**/*.mjs"],
+      rules: {
+        "mozilla/reject-import-system-module-from-non-system": "error",
+      },
+    },
     {
       files: ["**/*.jsm", "**/*.jsm.js"],
       rules: {

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

@@ -55,6 +55,7 @@ module.exports = {
     "reject-addtask-only": require("../lib/rules/reject-addtask-only"),
     "reject-chromeutils-import-params": require("../lib/rules/reject-chromeutils-import-params"),
     "reject-global-this": require("../lib/rules/reject-global-this"),
+    "reject-import-system-module-from-non-system": require("../lib/rules/reject-import-system-module-from-non-system"),
     "reject-importGlobalProperties": require("../lib/rules/reject-importGlobalProperties"),
     "reject-osfile": require("../lib/rules/reject-osfile"),
     "reject-scriptableunicodeconverter": require("../lib/rules/reject-scriptableunicodeconverter"),

tools/lint/eslint/eslint-plugin-mozilla/lib/rules/reject-import-system-module-from-non-system.js

@@ -0,0 +1,36 @@
+/**
+ * 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/reject-import-system-module-from-non-system.html",
+    },
+    messages: {
+      rejectStaticImportSystemModuleFromNonSystem:
+        "System modules (*.sys.mjs) can be imported with static import declaration only from system modules.",
+    },
+    type: "problem",
+  },
+
+  create(context) {
+    return {
+      ImportDeclaration(node) {
+        if (!node.source.value.endsWith(".sys.mjs")) {
+          return;
+        }
+
+        context.report({
+          node,
+          messageId: "rejectStaticImportSystemModuleFromNonSystem",
+        });
+      },
+    };
+  },
+};

tools/lint/eslint/eslint-plugin-mozilla/tests/reject-import-system-module-from-non-system.js

@@ -0,0 +1,33 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+"use strict";
+
+// ------------------------------------------------------------------------------
+// Requirements
+// ------------------------------------------------------------------------------
+
+var rule = require("../lib/rules/reject-import-system-module-from-non-system");
+var RuleTester = require("eslint").RuleTester;
+
+const ruleTester = new RuleTester({
+  parserOptions: { ecmaVersion: 13, sourceType: "module" },
+});
+
+// ------------------------------------------------------------------------------
+// Tests
+// ------------------------------------------------------------------------------
+
+ruleTester.run("reject-import-system-module-from-non-system", rule, {
+  valid: [
+    {
+      code: `const { Services } = ChromeUtils.importESM("resource://gre/modules/Services.sys.mjs");`,
+    },
+  ],
+  invalid: [
+    {
+      code: `import { Services } from "resource://gre/modules/Services.sys.mjs";`,
+      errors: [{ messageId: "rejectStaticImportSystemModuleFromNonSystem" }],
+    },
+  ],
+});