Do not allow arrow functions as the "factory" function for registerSe…

…rviceDorDoc (#26776)

* don't allow registration of arrow function as factory

* apply lint fixes

* Do not allow arrow functions as the "factory" function

.eslintrc

@@ -80,6 +80,7 @@
     "local/is-experiment-on": 2,
     "local/json-configuration": 2,
     "local/no-array-destructuring": 2,
+    "local/no-arrow-on-register-functions": 2,
     "local/no-deep-destructuring": 2,
     "local/no-destructure-assignment-params": 2,
     "local/no-duplicate-import": 2,

build-system/eslint-rules/no-arrow-on-register-functions.js

@@ -0,0 +1,32 @@
+/**
+ * Copyright 2020 The AMP HTML Authors. All Rights Reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS-IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+'use strict';
+
+const expression = 'CallExpression[callee.property.name=registerServiceForDoc]';
+module.exports = function(context) {
+  return {
+    [expression]: function(node) {
+      if (node.arguments[1].type === 'ArrowFunctionExpression') {
+        // TODO(erwinm): add fixer method.
+        context.report({
+          node,
+          message:
+            'The 2nd argument of registerServiceForDoc should not be an arrow function.',
+        });
+      }
+    },
+  };
+};

extensions/amp-geo/0.1/amp-geo.js

@@ -425,5 +425,7 @@ let geoDeferred = null;
 AMP.extension('amp-geo', '0.1', AMP => {
   geoDeferred = new Deferred();
   AMP.registerElement(TAG, AmpGeo);
-  AMP.registerServiceForDoc(SERVICE_TAG, () => geoDeferred.promise);
+  AMP.registerServiceForDoc(SERVICE_TAG, function() {
+    return geoDeferred.promise;
+  });
 });

extensions/amp-next-page/0.1/amp-next-page.js

@@ -302,6 +302,8 @@ function extractAdSenseTextContent(el) {
 
 AMP.extension(TAG, '0.1', AMP => {
   const service = new NextPageService();
-  AMP.registerServiceForDoc(SERVICE_ID, () => service);
+  AMP.registerServiceForDoc(SERVICE_ID, function() {
+    return service;
+  });
   AMP.registerElement(TAG, AmpNextPage, CSS);
 });

extensions/amp-subscriptions-google/0.1/amp-subscriptions-google.js

@@ -622,7 +622,7 @@ AMP.extension(TAG, '0.1', function(AMP) {
      * @param {!../../../src/service/ampdoc-impl.AmpDoc} ampdoc
      * @return {*} TODO(#23582): Specify return type
      */
-    ampdoc => {
+    function(ampdoc) {
       const platformService = new GoogleSubscriptionsPlatformService(ampdoc);
       const element = ampdoc.getHeadNode();
       Services.subscriptionsServiceForDoc(element).then(service => {