fix: dispatch ALT+SPACE keydown to renderer on Windows

Chromium's DesktopWindowTreeHostWin::HandleKeyEvent() intentionally drops ALT+SPACE keydown events so that the subsequent WM_SYSCHAR message can open the system menu. This means that when an Electron app listens for 'system-context-menu' and calls preventDefault(), the ALT+SPACE keydown never reaches the renderer and 'before-input-event' never fires. Override HandleKeyEvent() to intercept ALT+SPACE keydown and dispatch it via SendEventToSink() so it flows through the normal input pipeline to the renderer. The subsequent WM_SYSCHAR is still handled by HandleIMEMessage() to emit 'system-context-menu', preserving existing behavior for apps that don't prevent default.
2026-03-19 03:02:02 -04:00 · 2026-03-04 16:09:36 +01:00
4 changed files with 60 additions and 0 deletions
--- a/shell/browser/ui/win/electron_desktop_window_tree_host_win.cc
+++ b/shell/browser/ui/win/electron_desktop_window_tree_host_win.cc
@@ -175,6 +175,24 @@ bool ElectronDesktopWindowTreeHostWin::HandleIMEMessage(UINT message,
                                                           l_param, result);
 }

+void ElectronDesktopWindowTreeHostWin::HandleKeyEvent(ui::KeyEvent* event) {
+  // views::DesktopWindowTreeHostWin::HandleKeyEvent() discards ALT+SPACE
+  // keydown events so WM_SYSCHAR can show the system menu. In Electron,
+  // we want ALT+SPACE to be dispatched to the renderer so it fires keydown
+  // events, particularly when the 'system-context-menu' event is
+  // default-prevented. The subsequent WM_SYSCHAR is still handled by
+  // HandleIMEMessage() to emit 'system-context-menu'.
+  if ((event->type() == ui::EventType::kKeyPressed) &&
+      (event->key_code() == ui::VKEY_SPACE) &&
+      (event->flags() & ui::EF_ALT_DOWN) &&
+      !(event->flags() & ui::EF_CONTROL_DOWN)) {
+    SendEventToSink(event);
+    return;
+  }
+
+  views::DesktopWindowTreeHostWin::HandleKeyEvent(event);
+}
+
 void ElectronDesktopWindowTreeHostWin::HandleVisibilityChanged(bool visible) {
  if (native_window_view_->widget())
    native_window_view_->widget()->OnNativeWidgetVisibilityChanged(visible);
--- a/shell/browser/ui/win/electron_desktop_window_tree_host_win.h
+++ b/shell/browser/ui/win/electron_desktop_window_tree_host_win.h
@@ -48,6 +48,7 @@ class ElectronDesktopWindowTreeHostWin : public views::DesktopWindowTreeHostWin,
                        WPARAM w_param,
                        LPARAM l_param,
                        LRESULT* result) override;
+  void HandleKeyEvent(ui::KeyEvent* event) override;
  void HandleVisibilityChanged(bool visible) override;
  void SetAllowScreenshots(bool allow) override;
  void Restore() override;
--- a/spec/api-browser-window-spec.ts
+++ b/spec/api-browser-window-spec.ts
@@ -2568,6 +2568,32 @@ describe('BrowserWindow module', () => {
    });
  });

+  ifdescribe(process.platform === 'win32')('BrowserWindow system-context-menu', () => {
+    it('dispatches the keyboard event to the renderer if prevented', async () => {
+      const w = new BrowserWindow({
+        show: false,
+        webPreferences: {
+          nodeIntegration: true,
+          contextIsolation: false
+        }
+      });
+
+      w.once('system-context-menu', (evt) => {
+        evt.preventDefault();
+      });
+
+      await w.loadFile(path.join(fixtures, 'pages', 'keydown-alt-space.html'));
+
+      const altSpace = once(ipcMain, 'alt-space-renderer');
+
+      // Simulate Alt+Space to create system-context-menu event.
+      w.webContents.sendInputEvent({ type: 'keyDown', keyCode: 'Space', modifiers: ['alt'] });
+      w.webContents.sendInputEvent({ type: 'keyUp', keyCode: 'Space', modifiers: ['alt'] });
+
+      await altSpace;
+    });
+  });
+
  ifdescribe(process.platform === 'win32')('BrowserWindow.{get|set}AccentColor', () => {
    afterEach(closeAllWindows);

--- a/spec/fixtures/pages/keydown-alt-space.html
+++ b/spec/fixtures/pages/keydown-alt-space.html
@@ -0,0 +1,15 @@
+<html>
+
+<body>
+  <script type="text/javascript" charset="utf-8">
+    const { ipcRenderer } = require('electron');
+
+    document.addEventListener("keydown", (e) => {
+      if (e.key === " " && e.altKey) {
+        ipcRenderer.send('alt-space-renderer');
+      }
+    });
+  </script>
+</body>
+
+</html>