Bug 1698842 - [devtools] Avoid a few cases where targetFront is null during a client side target switching. r=nchevobbe

Differential Revision: https://phabricator.services.mozilla.com/D108680

devtools/client/fronts/descriptors/tab.js

@@ -195,19 +195,26 @@ class TabDescriptorFront extends DescriptorMixin(
     }
 
     this._targetFrontPromise = (async () => {
-      let targetFront = null;
+      let newTargetFront = null;
       try {
         const targetForm = await super.getTarget();
-        targetFront = this._createTabTarget(targetForm);
-        await targetFront.attach();
+        newTargetFront = this._createTabTarget(targetForm);
+        await newTargetFront.attach();
       } catch (e) {
         console.log(
           `Request to connect to TabDescriptor "${this.id}" failed: ${e}`
         );
       }
-      this._targetFront = targetFront;
+
+      // Completely ignore the previous target.
+      // We might nullify the _targetFront unexpectely due to previous target
+      // being destroyed after the new is created
+      if (this._targetFront) {
+        this._targetFront.off("target-destroyed", this._onTargetDestroyed);
+      }
+      this._targetFront = newTargetFront;
       this._targetFrontPromise = null;
-      return targetFront;
+      return newTargetFront;
     })();
     return this._targetFrontPromise;
   }

devtools/shared/commands/target/target-command.js

@@ -542,17 +542,21 @@ class TargetCommand extends EventEmitter {
    *        The BrowsingContextTargetFront instance that navigated to another process
    */
   async onLocalTabRemotenessChange(targetFront) {
-    // By default, we do close the DevToolsClient when the target is destroyed.
-    // This happens when we close the toolbox (Toolbox.destroy calls Target.destroy),
-    // or when the tab is closes, the server emits tabDetached and the target
-    // destroy itself.
-    // Here, in the context of the process switch, the current target will be destroyed
-    // due to a tabDetached event and a we will create a new one. But we want to reuse
-    // the same client.
-    targetFront.shouldCloseClient = false;
+    // TabDescriptor may emit the event with a null targetFront, interpret that as if the previous target
+    // has already been destroyed
+    if (targetFront) {
+      // By default, we do close the DevToolsClient when the target is destroyed.
+      // This happens when we close the toolbox (Toolbox.destroy calls Target.destroy),
+      // or when the tab is closes, the server emits tabDetached and the target
+      // destroy itself.
+      // Here, in the context of the process switch, the current target will be destroyed
+      // due to a tabDetached event and a we will create a new one. But we want to reuse
+      // the same client.
+      targetFront.shouldCloseClient = false;
 
-    // Wait for the target to be destroyed so that TabDescriptorFactory clears its memoized target for this tab
-    await targetFront.once("target-destroyed");
+      // Wait for the target to be destroyed so that TabDescriptorFactory clears its memoized target for this tab
+      await targetFront.once("target-destroyed");
+    }
 
     // Fetch the new target from the descriptor.
     const newTarget = await this.descriptorFront.getTarget();