Wayland: Implement glfwFocusWindow

This implements window focus requests via the xdg-activation-v1
protocol.  These requests will likely only work when another window of
the same application already has input focus, but that isn't unlike the
behavior of other platforms.

The GLFW_FEATURE_UNAVAILABLE error has been removed from this function
for now.

Related to #2284
Related to #2306
Related to #2439

README.md

@@ -178,6 +178,7 @@ information on what to include when reporting a bug.
  - [Cocoa] Bugfix: Touching event queue from secondary thread before main thread
    would abort (#1649)
  - [Wayland] Added support for `glfwRequestWindowAttention` (#2287)
+   [Wayland] Added support for `glfwFocusWindow`
  - [Wayland] Added dynamic loading of all Wayland libraries
  - [Wayland] Bugfix: `CLOCK_MONOTONIC` was not correctly enabled
  - [X11] Bugfix: Termination would segfault if the IM had been destroyed

docs/compat.dox

@@ -142,9 +142,8 @@ protocols either, no decorations will be drawn around windows.
 
 GLFW uses the [xdg-activation
 protocol](https://wayland.app/protocols/xdg-activation-v1)
-to enable attention requests.  This protocol is part of
+to implement window focus and attention requests.  If the running compositor
-wayland-protocols staging, and mandatory at build time.  If the running compositor
+does not support this protocol, window focus and attention requests do nothing.
-does not support this protocol, the attention requests do nothing.
 
 
 @section compat_glx GLX extensions

include/GLFW/glfw3.h

@@ -3856,11 +3856,11 @@ GLFWAPI void glfwHideWindow(GLFWwindow* window);
  *
  *  @param[in] window The window to give input focus.
  *
- *  @errors Possible errors include @ref GLFW_NOT_INITIALIZED, @ref
+ *  @errors Possible errors include @ref GLFW_NOT_INITIALIZED and @ref
- *  GLFW_PLATFORM_ERROR and @ref GLFW_FEATURE_UNAVAILABLE (see remarks).
+ *  GLFW_PLATFORM_ERROR.
  *
- *  @remark @wayland It is not possible for an application to set the input
+ *  @remark @wayland The compositor will likely ignore focus requests unless
- *  focus.  This function will emit @ref GLFW_FEATURE_UNAVAILABLE.
+ *  another window created by the same application already has input focus.
  *
  *  @thread_safety This function must only be called from the main thread.
  *

src/wl_window.c

@@ -2378,8 +2378,36 @@ void _glfwRequestWindowAttentionWayland(_GLFWwindow* window)
 
 void _glfwFocusWindowWayland(_GLFWwindow* window)
 {
-    _glfwInputError(GLFW_FEATURE_UNAVAILABLE,
+    if (!_glfw.wl.activationManager)
-                    "Wayland: The platform does not support setting the input focus");
+        return;
+
+    if (window->wl.activationToken)
+        xdg_activation_token_v1_destroy(window->wl.activationToken);
+
+    window->wl.activationToken =
+        xdg_activation_v1_get_activation_token(_glfw.wl.activationManager);
+    xdg_activation_token_v1_add_listener(window->wl.activationToken,
+                                         &xdgActivationListener,
+                                         window);
+
+    xdg_activation_token_v1_set_serial(window->wl.activationToken,
+                                       _glfw.wl.serial,
+                                       _glfw.wl.seat);
+
+    _GLFWwindow* requester = _glfw.wl.keyboardFocus;
+    if (requester)
+    {
+        xdg_activation_token_v1_set_surface(window->wl.activationToken,
+                                            requester->wl.surface);
+
+        if (requester->wl.appId)
+        {
+            xdg_activation_token_v1_set_app_id(window->wl.activationToken,
+                                               requester->wl.appId);
+        }
+    }
+
+    xdg_activation_token_v1_commit(window->wl.activationToken);
 }
 
 void _glfwSetWindowMonitorWayland(_GLFWwindow* window,