GH-8188: Workaround for application.confirmExit

From now on, the browser and electron frontends listen on different
events when it comes to saving the app state and releasing the resources.
The browser behavior is unchanged.
Made the `will-prevent-unload` handling sync.

Signed-off-by: Akos Kitta <kittaakos@typefox.io>

packages/core/src/browser/frontend-application.ts

@@ -24,6 +24,7 @@ import { ShellLayoutRestorer, ApplicationShellLayoutMigrationError } from './she
 import { FrontendApplicationStateService } from './frontend-application-state';
 import { preventNavigation, parseCssTime, animationFrame } from './browser';
 import { CorePreferences } from './core-preferences';
+import { WindowService } from './window/window-service';
 
 /**
  * Clients can implement to get a callback for contributing widgets to a shell on start.
@@ -96,6 +97,9 @@ export class FrontendApplication {
     @inject(CorePreferences)
     protected readonly corePreferences: CorePreferences;
 
+    @inject(WindowService)
+    protected readonly windowsService: WindowService;
+
     constructor(
         @inject(CommandRegistry) protected readonly commands: CommandRegistry,
         @inject(MenuModelRegistry) protected readonly menus: MenuModelRegistry,
@@ -182,8 +186,7 @@ export class FrontendApplication {
      */
     protected registerEventListeners(): void {
         this.registerCompositionEventListeners(); /* Hotfix. See above. */
-
-        window.addEventListener('beforeunload', () => {
+        this.windowsService.onUnload(() => {
             this.stateService.state = 'closing_window';
             this.layoutRestorer.storeLayout(this);
             this.stopContributions();

packages/core/src/browser/window/default-window-service.ts

@@ -15,6 +15,7 @@
  ********************************************************************************/
 
 import { inject, injectable, named } from 'inversify';
+import { Event, Emitter } from '../../common';
 import { CorePreferences } from '../core-preferences';
 import { ContributionProvider } from '../../common/contribution-provider';
 import { FrontendApplicationContribution, FrontendApplication } from '../frontend-application';
@@ -24,6 +25,7 @@ import { WindowService } from './window-service';
 export class DefaultWindowService implements WindowService, FrontendApplicationContribution {
 
     protected frontendApplication: FrontendApplication;
+    protected onUnloadEmitter = new Emitter<void>();
 
     @inject(CorePreferences)
     protected readonly corePreferences: CorePreferences;
@@ -39,6 +41,7 @@ export class DefaultWindowService implements WindowService, FrontendApplicationC
                 return this.preventUnload(event);
             }
         });
+        this.registerUnloadListener();
     }
 
     openNewWindow(url: string): undefined {
@@ -61,6 +64,14 @@ export class DefaultWindowService implements WindowService, FrontendApplicationC
         return confirmExit !== 'always';
     }
 
+    protected registerUnloadListener(): void {
+        window.addEventListener('unload', () => this.onUnloadEmitter.fire());
+    }
+
+    get onUnload(): Event<void> {
+        return this.onUnloadEmitter.event;
+    }
+
     /**
      * Ask the user to confirm if they want to unload the window. Prevent it if they do not.
      * @param event The beforeunload event

packages/core/src/browser/window/window-service.ts

@@ -14,6 +14,8 @@
  * SPDX-License-Identifier: EPL-2.0 OR GPL-2.0 WITH Classpath-exception-2.0
  ********************************************************************************/
 
+import { Event } from '../../common/event';
+
 export interface NewWindowOptions {
     readonly external?: boolean;
 }
@@ -38,4 +40,10 @@ export interface WindowService {
      */
     canUnload(): boolean;
 
+    /**
+     * Fires when the `window` unloads. On this event, the frontend application can save its state and release resource.
+     * Saving the state and releasing any resources must be synchronous.
+     */
+    readonly onUnload: Event<void>;
+
 }

packages/core/src/electron-browser/window/electron-window-service.ts

@@ -15,6 +15,8 @@
  ********************************************************************************/
 
 import { injectable, inject } from 'inversify';
+import { remote } from 'electron';
+import { Event } from '../../common/event';
 import { NewWindowOptions } from '../../browser/window/window-service';
 import { DefaultWindowService } from '../../browser/window/default-window-service';
 import { ElectronMainWindowService } from '../../electron-common/electron-main-window-service';
@@ -30,6 +32,18 @@ export class ElectronWindowService extends DefaultWindowService {
         return undefined;
     }
 
+    registerUnloadListener(): void {
+        remote.getCurrentWindow().on('closed', () => this.onUnloadEmitter.fire());
+    }
+
+    /**
+     * Unlike the default implementation, this even is fires when the `ElectronWindow`
+     * [closes](https://github.com/electron/electron/blob/master/docs/api/browser-window.md#event-close).
+     */
+    get onUnload(): Event<void> {
+        return this.onUnloadEmitter.event;
+    }
+
     protected preventUnload(event: BeforeUnloadEvent): string | void {
         // The user will be shown a confirmation dialog by the will-prevent-unload handler in the Electron main script
         event.returnValue = false;

packages/core/src/electron-main/electron-main-application.ts

@@ -344,8 +344,8 @@ export class ElectronMainApplication {
      */
     protected attachWillPreventUnload(electronWindow: BrowserWindow): void {
         // Fired when a beforeunload handler tries to prevent the page unloading
-        electronWindow.webContents.on('will-prevent-unload', async event => {
-            const { response } = await dialog.showMessageBox(electronWindow, {
+        electronWindow.webContents.on('will-prevent-unload', event => {
+            const response = dialog.showMessageBoxSync(electronWindow, {
                 type: 'question',
                 buttons: ['Yes', 'No'],
                 title: 'Confirm',