Bullet-proof tray icon against nonexistent icon file

app/SystemTrayService.ts

@@ -2,7 +2,14 @@
 // SPDX-License-Identifier: AGPL-3.0-only
 
 import { join } from 'path';
-import { BrowserWindow, app, Menu, Tray } from 'electron';
+import {
+  BrowserWindow,
+  Menu,
+  NativeImage,
+  Tray,
+  app,
+  nativeImage,
+} from 'electron';
 import * as log from '../ts/logging/log';
 import type { LocaleMessagesType } from '../ts/types/I18N';
 
@@ -105,7 +112,14 @@ export class SystemTrayService {
     this.tray = this.tray || this.createTray();
     const { browserWindow, tray } = this;
 
+    try {
       tray.setImage(getIcon(this.unreadCount));
+    } catch (err: unknown) {
+      log.warn(
+        'System tray service: failed to set preferred image. Falling back...'
+      );
+      tray.setImage(getDefaultIcon());
+    }
 
     // NOTE: we want to have the show/hide entry available in the tray icon
     // context menu, since the 'click' event may not work on all platforms.
@@ -169,7 +183,7 @@ export class SystemTrayService {
     log.info('System tray service: creating the tray');
 
     // This icon may be swiftly overwritten.
-    const result = new Tray(getIcon(this.unreadCount));
+    const result = new Tray(getDefaultIcon());
 
     // Note: "When app indicator is used on Linux, the click event is ignored." This
     //   doesn't mean that the click event is always ignored on Linux; it depends on how
@@ -223,6 +237,12 @@ function getIcon(unreadCount: number) {
   return join(__dirname, '..', 'images', `icon_${iconSize}.png`);
 }
 
+let defaultIcon: undefined | NativeImage;
+function getDefaultIcon(): NativeImage {
+  defaultIcon ??= nativeImage.createFromPath(getIcon(0));
+  return defaultIcon;
+}
+
 function forceOnTop(browserWindow: BrowserWindow) {
   // On some versions of GNOME the window may not be on top when restored.
   // This trick should fix it.

ts/test-node/app/SystemTrayService_test.ts

@@ -3,7 +3,7 @@
 
 import { assert } from 'chai';
 import * as sinon from 'sinon';
-import { BrowserWindow, MenuItem, Tray } from 'electron';
+import { BrowserWindow, MenuItem, Tray, nativeImage } from 'electron';
 import * as path from 'path';
 
 import { SystemTrayService } from '../../../app/SystemTrayService';
@@ -208,9 +208,9 @@ describe('SystemTrayService', () => {
     // Ideally, there'd be something like `tray.getImage`, but that doesn't exist. We also
     //   can't spy on `Tray.prototype.setImage` because it's not defined that way. So we
     //   spy on the specific instance, just to get the image.
-    const setContextMenuSpy = sandbox.spy(tray, 'setImage');
+    const setImageSpy = sandbox.spy(tray, 'setImage');
     const getImagePath = (): string => {
-      const result = setContextMenuSpy.lastCall?.firstArg;
+      const result = setImageSpy.lastCall?.firstArg;
       if (!result) {
         throw new Error('Expected tray.setImage to be called at least once');
       }
@@ -230,4 +230,27 @@ describe('SystemTrayService', () => {
     service.setUnreadCount(0);
     assert.match(path.parse(getImagePath()).base, /^icon_\d+\.png$/);
   });
+
+  it('uses a fallback image if the icon file cannot be found', () => {
+    const service = newService();
+    service.setEnabled(true);
+    service.setMainWindow(new BrowserWindow({ show: false }));
+
+    const tray = service._getTray();
+    if (!tray) {
+      throw new Error('Test setup failed: expected a tray');
+    }
+
+    const setImageStub = sandbox.stub(tray, 'setImage');
+    setImageStub.withArgs(sinon.match.string).throws('Failed to load');
+
+    service.setUnreadCount(4);
+
+    // Electron doesn't export this class, so we have to wrestle it out.
+    const NativeImage = nativeImage.createEmpty().constructor;
+
+    sinon.assert.calledTwice(setImageStub);
+    sinon.assert.calledWith(setImageStub, sinon.match.string);
+    sinon.assert.calledWith(setImageStub, sinon.match.instanceOf(NativeImage));
+  });
 });