Bug 1380009 - Enable the ESLint no-return-await call to avoid unnecessary intermediate promise creation. r=mossop

MozReview-Commit-ID: EnhSBHMjurr

--HG--
extra : rebase_source : 74ba4c10e369067629af95bf705a9acd0df1089b

accessible/tests/browser/e10s/browser_treeupdate_list.js

@@ -10,7 +10,7 @@ loadScripts({ name: 'role.js', dir: MOCHITESTS_DIR });
 async function setDisplayAndWaitForReorder(browser, value) {
   let onReorder = waitForEvent(EVENT_REORDER, 'ul');
   await invokeSetStyle(browser, 'li', 'display', value);
-  return await onReorder;
+  return onReorder;
 }
 
 addAccessibleTask(`

browser/base/content/test/alerts/browser_notification_tab_switching.js

@@ -25,7 +25,7 @@ add_task(async function test_notificationPreventDefaultAndSwitchTabs() {
     // First, show a notification that will be have the tab-switching prevented.
     function promiseNotificationEvent(evt) {
       return ContentTask.spawn(aBrowser, evt, async function(contentEvt) {
-        return await new Promise(resolve => {
+        return new Promise(resolve => {
           let contentNotification = content.wrappedJSObject._notification;
           contentNotification.addEventListener(contentEvt, function(event) {
             resolve({ defaultPrevented: event.defaultPrevented });

browser/base/content/test/general/browser_aboutCertError.js

@@ -134,7 +134,7 @@ add_task(async function checkWrongSystemTimeWarning() {
     info("Loading and waiting for the cert error");
     await certErrorLoaded;
 
-    return await ContentTask.spawn(browser, null, async function() {
+    return ContentTask.spawn(browser, null, async function() {
       let doc = content.document;
       let div = doc.getElementById("wrongSystemTimePanel");
       let systemDateDiv = doc.getElementById("wrongSystemTime_systemDate");

browser/base/content/test/static/browser_misused_characters_in_strings.js

@@ -152,10 +152,10 @@ async function getAllTheFiles(extension) {
   let appDirGreD = Services.dirsvc.get("GreD", Ci.nsIFile);
   let appDirXCurProcD = Services.dirsvc.get("XCurProcD", Ci.nsIFile);
   if (appDirGreD.contains(appDirXCurProcD)) {
-    return await generateURIsFromDirTree(appDirGreD, [extension]);
+    return generateURIsFromDirTree(appDirGreD, [extension]);
   }
   if (appDirXCurProcD.contains(appDirGreD)) {
-    return await generateURIsFromDirTree(appDirXCurProcD, [extension]);
+    return generateURIsFromDirTree(appDirXCurProcD, [extension]);
   }
   let urisGreD = await generateURIsFromDirTree(appDirGreD, [extension]);
   let urisXCurProcD = await generateURIsFromDirTree(appDirXCurProcD, [extension]);

browser/components/extensions/test/browser/browser_ext_browserAction_popup_resize.js

@@ -2,10 +2,10 @@
 /* vim: set sts=2 sw=2 et tw=80: */
 "use strict";
 
-async function openPanel(extension, win = window, awaitLoad = false) {
+function openPanel(extension, win = window, awaitLoad = false) {
   clickBrowserAction(extension, win);
 
-  return await awaitExtensionPanel(extension, win, awaitLoad);
+  return awaitExtensionPanel(extension, win, awaitLoad);
 }
 
 add_task(async function testBrowserActionPopupResize() {

browser/components/extensions/test/browser/browser_ext_contextMenus_onclick.js

@@ -107,9 +107,9 @@ add_task(async function() {
     info(`onClicked from: ${await extension.awaitMessage("onClicked-fired")}`);
   }
 
-  async function getCounts(page) {
+  function getCounts(page) {
     extension.sendMessage(page, "get-click-counts");
-    return await extension.awaitMessage("click-counts");
+    return extension.awaitMessage("click-counts");
   }
   async function resetCounts() {
     extension.sendMessage("tab", "clear-click-counts");

browser/components/originattributes/test/browser/browser_blobURLIsolation.js

@@ -50,12 +50,12 @@ function page_deblobify(browser, blobURL) {
       return "xhr error";
     }
 
-    return await blobToString(blob);
+    return blobToString(blob);
   });
 }
 
 function workerIO(browser, scriptFile, message) {
-  return ContentTask.spawn(browser, {scriptFile, message}, async function(args) {
+  return ContentTask.spawn(browser, {scriptFile, message}, function(args) {
     let worker = new content.Worker(args.scriptFile);
     let promise = new content.Promise(function(resolve) {
       let listenFunction = function(event) {
@@ -66,7 +66,7 @@ function workerIO(browser, scriptFile, message) {
       worker.addEventListener("message", listenFunction);
     });
     worker.postMessage(args.message);
-    return await promise;
+    return promise;
   });
 }
 

browser/components/originattributes/test/browser/browser_cookieIsolation.js

@@ -10,8 +10,8 @@ const key = "key" + Math.random().toString();
 const re = new RegExp(key + "=([0-9\.]+)");
 
 // Define the testing function
-async function doTest(aBrowser) {
-  return await ContentTask.spawn(aBrowser, [key, re],
+function doTest(aBrowser) {
+  return ContentTask.spawn(aBrowser, [key, re],
                            function([contentKey, contentRe]) {
     let result = contentRe.exec(content.document.cookie);
     if (result) {

browser/components/originattributes/test/browser/browser_localStorageIsolation.js

@@ -9,8 +9,8 @@ const TEST_PAGE = "http://mochi.test:8888/browser/browser/components/" +
 const key = Math.random().toString();
 
 // Define the testing function
-async function doTest(aBrowser) {
-  return await ContentTask.spawn(aBrowser, key, function(contentKey) {
+function doTest(aBrowser) {
+  return ContentTask.spawn(aBrowser, key, function(contentKey) {
     let value = content.localStorage.getItem(contentKey);
     if (value === null) {
       // No value is found, so we create one.

browser/components/places/PlacesUIUtils.jsm

@@ -1544,7 +1544,7 @@ this.PlacesUIUtils = {
     let info = await PlacesUtils.bookmarks.fetch(aGuidOrInfo);
     if (!info)
       return null;
-    return (await this.promiseNodeLikeFromFetchInfo(info));
+    return this.promiseNodeLikeFromFetchInfo(info);
   }
 };
 

browser/components/preferences/in-content-new/applications.js

@@ -2087,12 +2087,12 @@ var gApplicationsPane = {
    *          the Downloads folder if aIndex == 1,
    *          the folder stored in browser.download.dir
    */
-  async _indexToFolder(aIndex) {
+  _indexToFolder(aIndex) {
     switch (aIndex) {
       case 0:
-        return await this._getDownloadsFolder("Desktop");
+        return this._getDownloadsFolder("Desktop");
       case 1:
-        return await this._getDownloadsFolder("Downloads");
+        return this._getDownloadsFolder("Downloads");
     }
     var currentDirPref = document.getElementById("browser.download.dir");
     return currentDirPref.value;

browser/components/preferences/in-content/main.js

@@ -653,12 +653,12 @@ var gMainPane = {
    *          the Downloads folder if aIndex == 1,
    *          the folder stored in browser.download.dir
    */
-  async _indexToFolder(aIndex) {
+  _indexToFolder(aIndex) {
     switch (aIndex) {
       case 0:
-        return await this._getDownloadsFolder("Desktop");
+        return this._getDownloadsFolder("Desktop");
       case 1:
-        return await this._getDownloadsFolder("Downloads");
+        return this._getDownloadsFolder("Downloads");
     }
     var currentDirPref = document.getElementById("browser.download.dir");
     return currentDirPref.value;

browser/experiments/Experiments.jsm

@@ -1761,11 +1761,11 @@ Experiments.ExperimentEntry.prototype = {
    *
    * @return Promise<> Resolved when the operation is complete.
    */
-  async start() {
+  start() {
     this._log.trace("start() for " + this.id);
 
     this._enabled = true;
-    return await this.reconcileAddonState();
+    return this.reconcileAddonState();
   },
 
   // Async install of the addon for this experiment, part of the start task above.
@@ -1775,7 +1775,7 @@ Experiments.ExperimentEntry.prototype = {
     let install = await addonInstallForURL(this._manifestData.xpiURL, hash);
     gActiveInstallURLs.add(install.sourceURI.spec);
 
-    return await new Promise((resolve, reject) => {
+    return new Promise((resolve, reject) => {
       let failureHandler = (failureInstall, handler) => {
         let message = "AddonInstall " + handler + " for " + this.id + ", state=" +
                      (failureInstall.state || "?") + ", error=" + failureInstall.error;

browser/extensions/shield-recipe-client/lib/ClientEnvironment.jsm

@@ -36,11 +36,11 @@ this.ClientEnvironment = {
    * The server request is made lazily and is cached for the entire browser
    * session.
    */
-  async getClientClassification() {
+  getClientClassification() {
     if (!_classifyRequest) {
       _classifyRequest = NormandyApi.classifyClient();
     }
-    return await _classifyRequest;
+    return _classifyRequest;
   },
 
   clearClassifyCache() {

browser/extensions/shield-recipe-client/lib/NormandyApi.jsm

@@ -138,13 +138,13 @@ this.NormandyApi = {
   async fetchActions() {
     const actionApiUrl = await this.getApiUrl("action-list");
     const res = await this.get(actionApiUrl);
-    return await res.json();
+    return res.json();
   },
 
   async fetchImplementation(action) {
     const response = await fetch(action.implementation_url);
     if (response.ok) {
-      return await response.text();
+      return response.text();
     }
 
     throw new Error(`Failed to fetch action implementation for ${action.name}: ${response.status}`);

browser/modules/ReaderParent.jsm

@@ -122,7 +122,7 @@ var ReaderParent = {
    * @resolves JS object representing the article, or null if no article is found.
    */
   async _getArticle(url, browser) {
-    return await ReaderMode.downloadAndParseDocument(url).catch(e => {
+    return ReaderMode.downloadAndParseDocument(url).catch(e => {
       if (e && e.newURL) {
         // Pass up the error so we can navigate the browser in question to the new URL:
         throw e;

dom/indexedDB/test/head.js

@@ -82,7 +82,7 @@ function setFinishedCallback(callback, win)
     win = window;
   }
   ContentTask.spawn(win.gBrowser.selectedBrowser, null, async function() {
-    return await new Promise(resolve => {
+    return new Promise(resolve => {
       content.wrappedJSObject.testFinishedCallback = (result, exception) => {
         info("got finished callback");
         resolve({result, exception});

dom/media/PeerConnection.js

@@ -528,11 +528,11 @@ class RTCPeerConnection {
       if (this._closed) {
         return null;
       }
-      return await func();
+      return func();
     })();
     // don't propagate errors in the operations chain (this is a fork of p).
     this._operationsChain = p.catch(() => {});
-    return await p;
+    return p;
   }
 
   // It's basically impossible to use async directly in JSImplemented code,
@@ -764,7 +764,7 @@ class RTCPeerConnection {
   async _createOffer(options) {
     this._checkClosed();
     let origin = Cu.getWebIDLCallerPrincipal().origin;
-    return await this._chain(async () => {
+    return this._chain(async () => {
       let haveAssertion;
       if (this._localIdp.enabled) {
         haveAssertion = this._getIdentityAssertion(origin);
@@ -795,7 +795,7 @@ class RTCPeerConnection {
   async _createAnswer(options) {
     this._checkClosed();
     let origin = Cu.getWebIDLCallerPrincipal().origin;
-    return await this._chain(async () => {
+    return this._chain(async () => {
       // We give up line-numbers in errors by doing this here, but do all
       // state-checks inside the chain, to support the legacy feature that
       // callers don't have to wait for setRemoteDescription to finish.
@@ -846,7 +846,7 @@ class RTCPeerConnection {
         });
       }
     }
-    return await this._havePermission;
+    return this._havePermission;
   }
 
   setLocalDescription(desc, onSucc, onErr) {
@@ -875,7 +875,7 @@ class RTCPeerConnection {
           "InvalidParameterError");
     }
 
-    return await this._chain(async () => {
+    return this._chain(async () => {
       await this._getPermission();
       await new Promise((resolve, reject) => {
         this._onSetLocalDescriptionSuccess = resolve;
@@ -958,7 +958,7 @@ class RTCPeerConnection {
     // Get caller's origin before hitting the promise chain
     let origin = Cu.getWebIDLCallerPrincipal().origin;
 
-    return await this._chain(async () => {
+    return this._chain(async () => {
       let haveSetRemote = (async () => {
         await this._getPermission();
         await new Promise((resolve, reject) => {
@@ -984,7 +984,7 @@ class RTCPeerConnection {
 
   async _getIdentityAssertion(origin) {
     await this._certificateReady;
-    return await this._localIdp.getIdentityAssertion(this._impl.fingerprint, origin);
+    return this._localIdp.getIdentityAssertion(this._impl.fingerprint, origin);
   }
 
   getIdentityAssertion() {
@@ -1039,7 +1039,7 @@ class RTCPeerConnection {
           "Invalid candidate (both sdpMid and sdpMLineIndex are null).",
           "TypeError");
     }
-    return await this._chain(() => {
+    return this._chain(() => {
       if (!this.remoteDescription) {
         throw new this._win.DOMException(
             "setRemoteDescription needs to called before addIceCandidate",
@@ -1095,7 +1095,7 @@ class RTCPeerConnection {
 
   async _replaceTrack(sender, withTrack) {
     this._checkClosed();
-    return await this._chain(() => new Promise((resolve, reject) => {
+    return this._chain(() => new Promise((resolve, reject) => {
       this._onReplaceTrackSender = sender;
       this._onReplaceTrackWithTrack = withTrack;
       this._onReplaceTrackSuccess = resolve;
@@ -1242,7 +1242,7 @@ class RTCPeerConnection {
 
   async _getStats(selector, isLegacy) {
     // getStats is allowed even in closed state.
-    return await this._chain(() => new Promise((resolve, reject) => {
+    return this._chain(() => new Promise((resolve, reject) => {
       this._onGetStatsIsLegacy = isLegacy;
       this._onGetStatsSuccess = resolve;
       this._onGetStatsFailure = reject;

services/common/kinto-storage-adapter.js

@@ -248,7 +248,7 @@ class FirefoxAdapter extends Kinto.adapters.BaseAdapter {
     const conn = await Sqlite.openConnection(opts).then(this._init);
     try {
       Sqlite.shutdown.addBlocker("Kinto storage adapter connection closing",
-                                 async () => await conn.close());
+                                 () => conn.close());
     } catch (e) {
       // It's too late to block shutdown, just close the connection.
       await conn.close();

services/sync/tests/unit/test_bookmark_duping.js

@@ -52,7 +52,7 @@ async function syncIdToId(syncId) {
 async function getFolderChildrenIDs(folderId) {
   let folderSyncId = PlacesSyncUtils.bookmarks.guidToSyncId(await PlacesUtils.promiseItemGuid(folderId));
   let syncIds = await PlacesSyncUtils.bookmarks.fetchChildSyncIds(folderSyncId);
-  return Promise.all(syncIds.map(async (syncId) => await syncIdToId(syncId)));
+  return Promise.all(syncIds.map((syncId) => syncIdToId(syncId)));
 }
 
 async function createFolder(parentId, title) {

toolkit/components/extensions/ExtensionPreferencesManager.jsm

@@ -310,6 +310,6 @@ this.ExtensionPreferencesManager = {
         return "not_controllable";
       }
     }
-    return await ExtensionSettingsStore.getLevelOfControl(extension, STORE_TYPE, name);
+    return ExtensionSettingsStore.getLevelOfControl(extension, STORE_TYPE, name);
   },
 };

toolkit/components/extensions/ExtensionSettingsStore.jsm

@@ -266,8 +266,8 @@ this.ExtensionSettingsStore = {
    *          corresponds to the current top precedent setting, or null if
    *          the current top precedent setting has not changed.
    */
-  async removeSetting(extension, type, key) {
-    return await alterSetting(extension, type, key, "remove");
+  removeSetting(extension, type, key) {
+    return alterSetting(extension, type, key, "remove");
   },
 
   /**
@@ -286,8 +286,8 @@ this.ExtensionSettingsStore = {
    *          corresponds to the current top precedent setting, or null if
    *          the current top precedent setting has not changed.
    */
-  async enable(extension, type, key) {
-    return await alterSetting(extension, type, key, "enable");
+  enable(extension, type, key) {
+    return alterSetting(extension, type, key, "enable");
   },
 
   /**
@@ -306,8 +306,8 @@ this.ExtensionSettingsStore = {
    *          corresponds to the current top precedent setting, or null if
    *          the current top precedent setting has not changed.
    */
-  async disable(extension, type, key) {
-    return await alterSetting(extension, type, key, "disable");
+  disable(extension, type, key) {
+    return alterSetting(extension, type, key, "disable");
   },
 
   /**
@@ -340,8 +340,8 @@ this.ExtensionSettingsStore = {
    *
    * @returns {object} An object with properties for key and value.
    */
-  async getSetting(type, key) {
-    return await getTopItem(type, key);
+  getSetting(type, key) {
+    return getTopItem(type, key);
   },
 
   /**

toolkit/components/extensions/ExtensionStorageSync.jsm

@@ -607,7 +607,7 @@ class CryptoCollection {
 
   async sync(extensionStorageSync) {
     const collection = await this.getCollection();
-    return await extensionStorageSync._syncCollection(collection, {
+    return extensionStorageSync._syncCollection(collection, {
       strategy: "server_wins",
     });
   }
@@ -830,9 +830,9 @@ class ExtensionStorageSync {
    *                 Additional options to be passed to sync().
    * @returns {Promise<SyncResultObject>}
    */
-  async _syncCollection(collection, options) {
+  _syncCollection(collection, options) {
     // FIXME: this should support syncing to self-hosted
-    return await this._requestWithToken(`Syncing ${collection.name}`, async function(token) {
+    return this._requestWithToken(`Syncing ${collection.name}`, function(token) {
       const allOptions = Object.assign({}, {
         remote: prefStorageSyncServerURL,
         headers: {
@@ -840,7 +840,7 @@ class ExtensionStorageSync {
         },
       }, options);
 
-      return await collection.sync(allOptions);
+      return collection.sync(allOptions);
     });
   }
 
@@ -861,7 +861,7 @@ class ExtensionStorageSync {
         const newToken = await this._fxaService.getOAuthToken(FXA_OAUTH_OPTIONS);
 
         // If this fails too, let it go.
-        return await f(newToken);
+        return f(newToken);
       }
       // Otherwise, we don't know how to handle this error, so just reraise.
       throw e;
@@ -873,15 +873,15 @@ class ExtensionStorageSync {
    *
    * @returns {Promise<void>}
    */
-  async _deleteBucket() {
+  _deleteBucket() {
     log.error("Deleting default bucket and everything in it");
-    return await this._requestWithToken("Clearing server", async function(token) {
+    return this._requestWithToken("Clearing server", function(token) {
       const headers = {Authorization: "Bearer " + token};
       const kintoHttp = new KintoHttpClient(prefStorageSyncServerURL, {
         headers: headers,
         timeout: KINTO_REQUEST_TIMEOUT,
       });
-      return await kintoHttp.deleteBucket("default");
+      return kintoHttp.deleteBucket("default");
     });
   }
 
@@ -955,7 +955,7 @@ class ExtensionStorageSync {
       // We had a conflict which was automatically resolved. We now
       // have a new keyring which might have keys for the
       // collections. Recurse.
-      return await this.ensureCanSync(extIds);
+      return this.ensureCanSync(extIds);
     }
 
     // No conflicts. We're good.
@@ -1098,7 +1098,7 @@ class ExtensionStorageSync {
           // Reupload our keyring, which is the only new keyring.
           // We don't want client_wins here because another device
           // could have uploaded another keyring in the meantime.
-          return await this.cryptoCollection.sync(this);
+          return this.cryptoCollection.sync(this);
         }
       }
       throw e;

toolkit/components/extensions/ext-privacy.js

@@ -28,14 +28,14 @@ const getPrivacyAPI = (extension, name, callback) => {
         value: await callback(),
       };
     },
-    async set(details) {
+    set(details) {
       checkScope(details.scope);
-      return await ExtensionPreferencesManager.setSetting(
+      return ExtensionPreferencesManager.setSetting(
         extension, name, details.value);
     },
-    async clear(details) {
+    clear(details) {
       checkScope(details.scope);
-      return await ExtensionPreferencesManager.removeSetting(
+      return ExtensionPreferencesManager.removeSetting(
         extension, name);
     },
   };

toolkit/components/extensions/test/xpcshell/test_ext_schemas_async.js

@@ -149,9 +149,9 @@ add_task(async function testParameterValidation() {
 
 add_task(async function testAsyncResults() {
   await Schemas.load("data:," + JSON.stringify(schemaJson));
-  async function runWithCallback(func) {
+  function runWithCallback(func) {
     do_print(`Calling testnamespace.${func.name}, expecting callback with result`);
-    return await new Promise(resolve => {
+    return new Promise(resolve => {
       let result = "uninitialized value";
       let returnValue = func(reply => {
         result = reply;
@@ -164,9 +164,9 @@ add_task(async function testAsyncResults() {
     });
   }
 
-  async function runFailCallback(func) {
+  function runFailCallback(func) {
     do_print(`Calling testnamespace.${func.name}, expecting callback with error`);
-    return await new Promise(resolve => {
+    return new Promise(resolve => {
       func(reply => {
         do_check_eq(reply, undefined);
         resolve(context.lastError.message); // eslint-disable-line no-undef

toolkit/components/places/Bookmarks.jsm

@@ -834,9 +834,7 @@ var Bookmarks = Object.freeze({
       throw new Error("numberOfItems argument must be greater than zero");
     }
 
-    return (async function() {
-      return await fetchRecentBookmarks(numberOfItems);
-    })();
+    return fetchRecentBookmarks(numberOfItems);
   },
 
   /**

toolkit/components/places/PlacesTransactions.jsm

@@ -1029,7 +1029,7 @@ async function createItemsFromBookmarksTree(tree, restoring = false,
 
     return guid;
   }
-  return await createItem(tree,
+  return createItem(tree,
                     tree.parentGuid,
                     tree.index);
 }

toolkit/components/places/tests/bookmarks/test_sync_fields.js

@@ -127,8 +127,8 @@ class TestCases {
   }
 
   async testSeparators() {
-    let insertSyncedBookmark = async uri => {
-      return await this.insertBookmark(PlacesUtils.bookmarks.unfiledGuid,
+    let insertSyncedBookmark = uri => {
+      return this.insertBookmark(PlacesUtils.bookmarks.unfiledGuid,
                                  NetUtil.newURI(uri),
                                  PlacesUtils.bookmarks.DEFAULT_INDEX,
                                  "A bookmark name");
@@ -253,19 +253,19 @@ class SyncTestCases extends TestCases {
   async createFolder(parentGuid, title, index) {
     let parentId = await PlacesUtils.promiseItemId(parentGuid);
     let id = PlacesUtils.bookmarks.createFolder(parentId, title, index);
-    return await PlacesUtils.promiseItemGuid(id);
+    return PlacesUtils.promiseItemGuid(id);
   }
 
   async insertBookmark(parentGuid, uri, index, title) {
     let parentId = await PlacesUtils.promiseItemId(parentGuid);
     let id = PlacesUtils.bookmarks.insertBookmark(parentId, uri, index, title);
-    return await PlacesUtils.promiseItemGuid(id);
+    return PlacesUtils.promiseItemGuid(id);
   }
 
   async insertSeparator(parentGuid, index) {
     let parentId = await PlacesUtils.promiseItemId(parentGuid);
     let id = PlacesUtils.bookmarks.insertSeparator(parentId, index);
-    return await PlacesUtils.promiseItemGuid(id);
+    return PlacesUtils.promiseItemGuid(id);
   }
 
   async moveItem(guid, newParentGuid, index) {

toolkit/components/places/tests/history/test_removeByFilter.js

@@ -146,13 +146,13 @@ add_task(async function test_removeByFilter() {
       // Case A 1: Dates
       await removeByFilterTester(sameHostVisits,
                                  { beginDate: new Date(2004, 1, 1), endDate: new Date(2006, 1, 1) },
-                                 async () => await assertInDB(remoteUriList[0]),
-                                 async () => await checkClosure(remoteUriList[0]),
+                                 () => assertInDB(remoteUriList[0]),
+                                 () => checkClosure(remoteUriList[0]),
                                  callbackUse, bookmarkedUri(remoteUriList));
       // Case A 2: Single Sub-host
       await removeByFilterTester(sameHostVisits, { host: "mozilla.org" },
-                                 async () => await assertInDB(remoteUriList[0]),
-                                 async () => await checkClosure(remoteUriList[0]),
+                                 () => assertInDB(remoteUriList[0]),
+                                 () => checkClosure(remoteUriList[0]),
                                  callbackUse, bookmarkedUri(remoteUriList));
       // Case A 3: Multiple subhost
       await removeByFilterTester(randomHostVisits, { host: "*.mozilla.org" },
@@ -176,13 +176,13 @@ add_task(async function test_removeByFilter() {
     // Case B 1: Date
     await removeByFilterTester(sameHostVisits,
                                { beginDate: new Date(2001, 1, 1), endDate: new Date(2002, 1, 1) },
-                               async () => await assertInDB(remoteUriList[0]),
-                               async () => await assertInDB(remoteUriList[0]),
+                               () => assertInDB(remoteUriList[0]),
+                               () => assertInDB(remoteUriList[0]),
                                callbackUse);
     // Case B 2 : Single subhost
     await removeByFilterTester(sameHostVisits, { host: "notthere.org" },
-                               async () => await assertInDB(remoteUriList[0]),
-                               async () => await assertInDB(remoteUriList[0]),
+                               () => assertInDB(remoteUriList[0]),
+                               () => assertInDB(remoteUriList[0]),
                                callbackUse);
     // Case B 3 : Multiple subhosts
     await removeByFilterTester(randomHostVisits, { host: "*.notthere.org" },
@@ -196,8 +196,8 @@ add_task(async function test_removeByFilter() {
                                { host: "mozilla.org",
                                  beginDate: new Date(2004, 1, 1),
                                  endDate: new Date(2006, 1, 1) },
-                               async () => await assertInDB(remoteUriList[0]),
-                               async () => await assertNotInDB(remoteUriList[0]),
+                               () => assertInDB(remoteUriList[0]),
+                               () => assertNotInDB(remoteUriList[0]),
                                callbackUse);
     // Case C 2: multiple subhost
     await removeByFilterTester(randomHostVisits,

toolkit/components/places/tests/migration/test_current_from_v34.js

@@ -51,7 +51,7 @@ function insertBookmark(db, info) {
         { url: url.href, guid: placeGuid,
           rev_host: PlacesUtils.getReversedHost(url) });
     }
-    return await insertItem(db, info);
+    return insertItem(db, info);
   });
 }
 

toolkit/components/places/tests/unifiedcomplete/head_autocomplete.js

@@ -437,14 +437,14 @@ function makeTestServer(port = -1) {
   return httpServer;
 }
 
-async function addTestEngine(basename, httpServer = undefined) {
+function addTestEngine(basename, httpServer = undefined) {
   httpServer = httpServer || makeTestServer();
   httpServer.registerDirectory("/", do_get_cwd());
   let dataUrl =
     "http://localhost:" + httpServer.identity.primaryPort + "/data/";
 
   do_print("Adding engine: " + basename);
-  return await new Promise(resolve => {
+  return new Promise(resolve => {
     Services.obs.addObserver(function obs(subject, topic, data) {
       let engine = subject.QueryInterface(Ci.nsISearchEngine);
       do_print("Observed " + data + " for " + engine.name);

toolkit/components/places/tests/unit/test_promiseBookmarksTree.js

@@ -156,10 +156,10 @@ async function new_bookmark(aInfo) {
   await PlacesTransactions.NewBookmark(aInfo).transact();
 }
 
-async function new_folder(aInfo) {
+function new_folder(aInfo) {
   if (!("title" in aInfo))
     aInfo.title = "Test Item (folder) " + itemsCount;
-  return await PlacesTransactions.NewFolder(aInfo).transact();
+  return PlacesTransactions.NewFolder(aInfo).transact();
 }
 
 // Walks a result nodes tree and test promiseBookmarksTree for each node.
@@ -190,7 +190,7 @@ async function test_promiseBookmarksTreeAgainstResult(aItemGuid = "",
   let itemId = aItemGuid ?
     await PlacesUtils.promiseItemId(aItemGuid) : PlacesUtils.placesRootId;
   let node = PlacesUtils.getFolderContents(itemId).root;
-  return await test_promiseBookmarksTreeForEachNode(node, aOptions, aExcludedGuids);
+  return test_promiseBookmarksTreeForEachNode(node, aOptions, aExcludedGuids);
 }
 
 add_task(async function() {

toolkit/components/reader/ReaderMode.jsm

@@ -224,13 +224,13 @@ this.ReaderMode = {
    * @return {Promise}
    * @resolves JS object representing the article, or null if no article is found.
    */
-  async parseDocument(doc) {
+  parseDocument(doc) {
     if (!this._shouldCheckUri(doc.documentURIObject) || !this._shouldCheckUri(doc.baseURIObject, true)) {
       this.log("Reader mode disabled for URI");
       return null;
     }
 
-    return await this._readerParse(doc);
+    return this._readerParse(doc);
   },
 
   /**
@@ -247,7 +247,7 @@ this.ReaderMode = {
       return null;
     }
 
-    return await this._readerParse(doc);
+    return this._readerParse(doc);
   },
 
   _downloadDocument(url) {

toolkit/components/viewsource/test/browser/head.js

@@ -76,7 +76,7 @@ function waitForViewSourceWindow() {
  * @param browser - the <xul:browser> to open view source for.
  * @returns the new tab or window which shows the source.
  */
-async function openViewSource(browser) {
+function openViewSource(browser) {
   let openPromise;
   if (Services.prefs.getBoolPref("view_source.tab")) {
     openPromise = BrowserTestUtils.waitForNewTab(gBrowser, null);
@@ -86,7 +86,7 @@ async function openViewSource(browser) {
 
   window.BrowserViewSource(browser);
 
-  return (await openPromise);
+  return openPromise;
 }
 
 /**
@@ -120,7 +120,7 @@ async function openViewPartialSource(aCSSSelector) {
   EventUtils.synthesizeMouseAtCenter(item, {});
   await popupHiddenPromise;
 
-  return (await openPromise);
+  return openPromise;
 }
 
 /**
@@ -153,7 +153,7 @@ async function openViewFrameSourceTab(aCSSSelector) {
   EventUtils.synthesizeMouseAtCenter(item, {});
   await popupHiddenPromise;
 
-  return (await newTabPromise);
+  return newTabPromise;
 }
 
 registerCleanupFunction(function() {

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

@@ -264,6 +264,9 @@ module.exports = {
     // Disallow multiple spaces in regular expressions
     "no-regex-spaces": "error",
 
+    // Disallows unnecessary `return await ...`.
+    "no-return-await": "error",
+
     // Disallow assignments where both sides are exactly the same
     "no-self-assign": "error",