Bug 1761072 - Replace use of ExtensionParent in devtools' ExtensionsBackgroundScriptStatusWatcher r=rpl,jdescottes

ExtensionParent.jsm cannot be loaded without a profile, as explained at
https://bugzilla.mozilla.org/show_bug.cgi?id=1761072#c5.

But ExtensionsBackgroundScriptStatusWatcher would try to (lazily) load
the module before a profile was ready, in order to subscribe to future
changes. To avoid loading this whole ExtensionParent.jsm module, I have
replaced the event propagation mechanism with observers.

Differential Revision: https://phabricator.services.mozilla.com/D142065

devtools/server/actors/resources/extensions-backgroundscript-status.js

@@ -4,11 +4,7 @@
 
 "use strict";
 
-loader.lazyImporter(
-  this,
-  "ExtensionParent",
-  "resource://gre/modules/ExtensionParent.jsm"
-);
+const Services = require("Services");
 
 const {
   TYPES: { EXTENSIONS_BGSCRIPT_STATUS },
@@ -33,20 +29,25 @@ class ExtensionsBackgroundScriptStatusWatcher {
    *        Dictionary object with following attributes:
    *        - onAvailable: mandatory function
    *          This will be called for each resource.
-   *        - onUpdated: optional function
-   *          This would be called multiple times for each resource.
    */
-  async watch(rootActor, { onAvailable, onUpdated }) {
+  async watch(rootActor, { onAvailable }) {
     this.rootActor = rootActor;
     this.onAvailable = onAvailable;
-    this.onUpdated = onUpdated;
 
-    this.unwatchBackgroundStatusUpdates = ExtensionParent.DebugUtils.watchBackgroundScriptStatusUpdates(
-      this.onBackgroundScriptStatus
-    );
+    Services.obs.addObserver(this, "extension:background-script-status");
   }
 
-  onBackgroundScriptStatus = (addonId, isRunning) => {
+  observe(subject, topic, data) {
+    switch (topic) {
+      case "extension:background-script-status": {
+        const { addonId, isRunning } = subject.wrappedJSObject;
+        this.onBackgroundScriptStatus(addonId, isRunning);
+        break;
+      }
+    }
+  }
+
+  onBackgroundScriptStatus(addonId, isRunning) {
     this.onAvailable([
       {
         resourceType: EXTENSIONS_BGSCRIPT_STATUS,
@@ -56,10 +57,13 @@ class ExtensionsBackgroundScriptStatusWatcher {
         },
       },
     ]);
-  };
+  }
 
   destroy() {
-    this.unwatchBackgroundStatusUpdates?.();
+    if (this.onAvailable) {
+      this.onAvailable = null;
+      Services.obs.removeObserver(this, "extension:background-script-status");
+    }
   }
 }
 

toolkit/components/extensions/ExtensionParent.jsm

@@ -1503,17 +1503,6 @@ const DebugUtils = {
     throw Error(`Unable to terminate background script for ${addonId}`);
   },
 
-  watchBackgroundScriptStatusUpdates(callback) {
-    const listener = (_evtName, addonId, isRunning) => {
-      callback(addonId, isRunning);
-    };
-    apiManager.on(`devtools:background-script-status`, listener);
-
-    return () => {
-      apiManager.off(`devtools:background-script-status`, listener);
-    };
-  },
-
   /**
    * Retrieve a XUL browser element which has been configured to be able to connect
    * the devtools actor with the process where the extension is running.

toolkit/components/extensions/parent/ext-backgroundPage.js

@@ -40,6 +40,13 @@ XPCOMUtils.defineLazyPreferenceGetter(
   delay => Math.min(Math.max(delay, 100), 5 * 60 * 1000)
 );
 
+function notifyBackgroundScriptStatus(addonId, isRunning) {
+  // Notify devtools when the background scripts is started or stopped
+  // (used to show the current status in about:debugging).
+  const subject = { addonId, isRunning };
+  Services.obs.notifyObservers(subject, "extension:background-script-status");
+}
+
 // Responsible for the background_page section of the manifest.
 class BackgroundPage extends HiddenExtensionPage {
   constructor(extension, options) {
@@ -100,20 +107,10 @@ class BackgroundPage extends HiddenExtensionPage {
       await Promise.all(context.listenerPromises);
       context.listenerPromises = null;
 
-      // Notify devtools when the background scripts is started or stopped
-      // (used to show the current status in about:debugging).
-      extensions.emit(
-        `devtools:background-script-status`,
-        extension.id,
-        true /* isRunning */
-      );
+      notifyBackgroundScriptStatus(extension.id, true);
       context.callOnClose({
         close() {
-          extensions.emit(
-            `devtools:background-script-status`,
-            extension.id,
-            false /* isRunning */
-          );
+          notifyBackgroundScriptStatus(extension.id, false);
         },
       });
     }
@@ -211,20 +208,10 @@ class BackgroundWorker {
       await Promise.all(context.listenerPromises);
       context.listenerPromises = null;
 
-      // Notify devtools when the background scripts is started or stopped
-      // (used to show the current status in about:debugging).
-      extensions.emit(
-        `devtools:background-script-status`,
-        extension.id,
-        true /* isRunning */
-      );
+      notifyBackgroundScriptStatus(extension.id, true);
       context.callOnClose({
         close() {
-          extensions.emit(
-            `devtools:background-script-status`,
-            extension.id,
-            false /* isRunning */
-          );
+          notifyBackgroundScriptStatus(extension.id, false);
         },
       });
     }