Avoid listing workers if connected to Fennec v59 (#5761)

Author: juliandescottes

src/client/firefox/commands.js

@@ -31,6 +31,9 @@ import { makePendingLocationId } from "../../utils/breakpoint";
 
 import { createSource, createBreakpointLocation } from "./create";
 
+import { getDeviceFront } from "./fronts-device";
+import { Services } from "devtools-modules";
+
 let bpClients: BPClients;
 let threadClient: ThreadClient;
 let tabTarget: TabTarget;
@@ -317,14 +320,46 @@ async function fetchSources() {
   return sources.map(source => createSource(source, { supportsWasm }));
 }
 
+/**
+ * Temporary helper to check if the current server will support a call to
+ * listWorkers. On Fennec 60 or older, the call will silently crash and prevent
+ * the client from resuming.
+ * XXX: Remove when FF60 for Android is no longer used or available.
+ *
+ * See https://bugzilla.mozilla.org/show_bug.cgi?id=1443550 for more details.
+ */
+async function checkServerSupportsListWorkers() {
+  const root = await tabTarget.root;
+  const deviceFront = await getDeviceFront(debuggerClient, root);
+  const description = await deviceFront.getDescription();
+
+  const isFennec = description.apptype === "mobile/android";
+  if (!isFennec) {
+    // Explicitly return true early to avoid calling Services.vs.compare.
+    // This would force us to extent the Services shim provided by
+    // devtools-modules, used when this code runs in a tab.
+    return true;
+  }
+
+  // We are only interested in Fennec release versions here.
+  // We assume that the server fix for Bug 1443550 will land in FF61.
+  const version = description.platformversion;
+  return Services.vc.compare(version, "61.0") >= 0;
+}
+
 async function fetchWorkers(): Promise<{ workers: Worker[] }> {
+  // Temporary workaround for Bug 1443550
+  // XXX: Remove when FF60 for Android is no longer used or available.
+  const supportsListWorkers = await checkServerSupportsListWorkers();
+
   // NOTE: The Worker and Browser Content toolboxes do not have a parent
   // with a listWorkers function
   // TODO: there is a listWorkers property, but it is not a function on the
   // parent. Investigate what it is
   if (
     !threadClient._parent ||
-    typeof threadClient._parent.listWorkers != "function"
+    typeof threadClient._parent.listWorkers != "function" ||
+    !supportsListWorkers
   ) {
     return Promise.resolve({ workers: [] });
   }

src/client/firefox/fronts-device.js

@@ -0,0 +1,15 @@
+/* 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/>. */
+
+export function getDeviceFront() {
+  return {
+    getDescription: function() {
+      return {
+        // Return anything that will not match Fennec v59
+        apptype: "apptype",
+        version: "version"
+      };
+    }
+  };
+}

src/client/firefox/types.js

@@ -241,6 +241,7 @@ export type TabTarget = {
     ) => void
   },
   form: { consoleActor: any },
+  root: any,
   activeTab: {
     navigateTo: string => Promise<*>,
     reload: () => Promise<*>

webpack.config.js

@@ -58,6 +58,7 @@ function buildConfig(envConfig) {
     extra.excludeMap = {
       "./source-editor": "devtools/client/sourceeditor/editor",
       "./test-flag": "devtools/shared/flags",
+      "./fronts-device": "devtools/shared/fronts/device",
       react: "devtools/client/shared/vendor/react",
       redux: "devtools/client/shared/vendor/redux",
       "react-dom": "devtools/client/shared/vendor/react-dom",