Bring the window forward on Windows without pressing Alt

desktop/src-tauri/src/main.rs

@@ -752,8 +752,13 @@ fn report_running_line<R: tauri::Runtime>(
 /// behind. So the deprecated call, through `set_focus`, is the one used. `AppHandle::show` first
 /// unhides an app hidden with Command-H, which `set_focus` does not.
 ///
-/// On Windows `set_focus` gets past the foreground lock (tao's `force_window_active`).
-/// `set_focus` does nothing to a hidden or minimised window, hence `show` and `unminimize` first.
+/// On Windows it is `SetForegroundWindow`, and when Windows refuses it (another app holds the
+/// foreground, as the browser does during sign-in) the taskbar button flashes instead. Never tao's
+/// `set_focus` there: past a refusal it presses and releases Alt to get by the foreground lock
+/// (`force_window_active`), and a lone Alt can put a WebView2 window into menu mode, which only a
+/// click, Alt+Tab or Esc ends. On Windows F setup froze for minutes right after "[front] the engine
+/// machine is prepared" with the browser in front. `set_focus` does nothing to a hidden or
+/// minimised window, hence `show` and `unminimize` first.
 fn bring_to_front<R: tauri::Runtime>(app: &tauri::AppHandle<R>, why: &str) {
     log::info!("[front] {why}");
     #[cfg(target_os = "macos")]
@@ -763,9 +768,60 @@ fn bring_to_front<R: tauri::Runtime>(app: &tauri::AppHandle<R>, why: &str) {
     };
     let _ = window.show();
     let _ = window.unminimize();
+    #[cfg(windows)]
+    {
+        let hwnd = window.hwnd().ok().map(|hwnd| hwnd.0 as isize);
+        let why = why.to_owned();
+        // On the window's own thread, as `notice::bring_to_front` is.
+        let _ = app.run_on_main_thread(move || {
+            let front = come_forward(
+                || {
+                    hwnd.is_some_and(|hwnd| {
+                        use windows::Win32::Foundation::HWND;
+                        use windows::Win32::UI::WindowsAndMessaging::SetForegroundWindow;
+                        // SAFETY: `hwnd` is this window's live handle, read just now.
+                        unsafe { SetForegroundWindow(HWND(hwnd as *mut core::ffi::c_void)) }
+                            .as_bool()
+                    })
+                },
+                || {
+                    let _ = window
+                        .request_user_attention(Some(tauri::UserAttentionType::Informational));
+                },
+            );
+            if front == Front::Flashed {
+                log::info!(
+                    "[front] {why}: Windows kept another window in front; flashed the taskbar"
+                );
+            }
+        });
+    }
+    #[cfg(not(windows))]
     let _ = window.set_focus();
 }
 
+/// How OpenBot's window came forward on Windows (`bring_to_front`).
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+#[cfg_attr(not(windows), allow(dead_code))]
+enum Front {
+    /// `SetForegroundWindow` put it in front.
+    Came,
+    /// Windows refused, and the taskbar button flashes for the person to come to it.
+    Flashed,
+}
+
+/// Bring the window forward with `set_foreground`, and if Windows refuses, `flash` its taskbar
+/// button. Nothing else: no key pressed or released on the person's behalf.
+#[cfg_attr(not(windows), allow(dead_code))]
+fn come_forward(set_foreground: impl FnOnce() -> bool, flash: impl FnOnce()) -> Front {
+    if set_foreground() {
+        Front::Came
+    } else {
+        flash();
+        Front::Flashed
+    }
+}
+
 /// The setup window asks to come to the front: its installation finished or failed, and the next
 /// step is the person's. See `bring_to_front`.
 #[tauri::command]
@@ -13112,6 +13168,49 @@ mod tests {
         assert_eq!(onto_a_screen(rect(-5000.0, 0.0, 1016.0, 839.0), &[]), None);
     }
 
+    /// Another app holds the foreground (the browser, signing in): Windows refuses
+    /// `SetForegroundWindow`, and the taskbar button flashes. Nothing else happens: no key is
+    /// pressed or released on the person's behalf. tao's `set_focus` pressed Alt there, and a lone
+    /// Alt can leave a WebView2 window in menu mode; on Windows F setup froze for minutes after
+    /// "[front] the engine machine is prepared" with the browser in front.
+    #[test]
+    fn coming_forward_with_another_window_in_front_flashes_and_sends_no_input() {
+        let done = std::cell::RefCell::new(Vec::new());
+        let front = come_forward(
+            || {
+                done.borrow_mut().push("set foreground");
+                false
+            },
+            || done.borrow_mut().push("flash the taskbar"),
+        );
+        assert_eq!(front, Front::Flashed);
+        assert_eq!(*done.borrow(), ["set foreground", "flash the taskbar"]);
+        // Allowed in front: nothing flashes.
+        let done = std::cell::RefCell::new(Vec::new());
+        let front = come_forward(
+            || {
+                done.borrow_mut().push("set foreground");
+                true
+            },
+            || done.borrow_mut().push("flash the taskbar"),
+        );
+        assert_eq!(front, Front::Came);
+        assert_eq!(*done.borrow(), ["set foreground"]);
+        // On Windows, `bring_to_front` never reaches tao's `set_focus` (its Alt press), and
+        // nothing in this file sends key input of its own.
+        let main = include_str!("main.rs");
+        let body = &main[main.find("fn bring_to_front<").unwrap()..];
+        let body = &body[..body.find("\n}\n").unwrap()];
+        let windows = &body[body.find("#[cfg(windows)]").unwrap()..];
+        let windows = &windows[..windows.find("#[cfg(not(windows))]").unwrap()];
+        assert!(!windows.contains("set_focus"), "{windows}");
+        assert!(body.contains("#[cfg(not(windows))]\n    let _ = window.set_focus();"));
+        let tests = main.find("#[cfg(test)]\nmod tests").unwrap_or(main.len());
+        for input in ["SendInput", "keybd_event", "VK_MENU"] {
+            assert!(!main[..tests].contains(input), "{input}");
+        }
+    }
+
     /// Windows cascades a window with no position of its own down and right on every launch. On
     /// a 1080p screen with a 48 px taskbar the third launch put a 1016 by 839 window's top at 234,
     /// its bottom at 1073, past the work area's 1032, and the account row behind the taskbar.