Use the last known timestamp when calling xcb_set_input_focus(). (#2332)

In most cases this won't make a difference, but consider the following
scenario:

* Some application acquires input focus on its own (which the window manager
  is not involved in, so it will "always" work).
* Before the FocusIn / FocusOut events are processed by i3, the
  workflow to push X changes is run, resulting in xcb_set_input_focus()
  being called.

Using XCB_CURRENT_TIME, this means i3 will "win" and override the focus,
even though it simply wasn't aware (yet) that focus had already been taken
over by someone else. When processing the FocusIn / FocusOut events, i3
assumes that the focus is already set which results in a broken focus
state as i3 assumes some container has the input focus when it doesn't.

With the new behavior, i3's attempt to set the input focus will fail if
the FocusIn / FocusOut events have not yet processed. Once they are processed,
the focus state will be automatically corrected.

fixes #2322

diff --git a/src/x.c b/src/x.c
index ca7d8ae44aea2aa26f9bb9d7d9a8f67244d4336a..6fd3297a918dd318308cfcb75c0a286561204fc1 100644 (file)
--- a/src/x.c
+++ b/src/x.c
@@ -1115,7 +1115,7 @@ void x_push_changes(Con *con) {
                     values[0] = CHILD_EVENT_MASK & ~(XCB_EVENT_MASK_FOCUS_CHANGE);
                     xcb_change_window_attributes(conn, focused->window->id, XCB_CW_EVENT_MASK, values);
                 }
-                xcb_set_input_focus(conn, XCB_INPUT_FOCUS_POINTER_ROOT, to_focus, XCB_CURRENT_TIME);
+                xcb_set_input_focus(conn, XCB_INPUT_FOCUS_POINTER_ROOT, to_focus, last_timestamp);
                 if (focused->window != NULL) {
                     values[0] = CHILD_EVENT_MASK;
                     xcb_change_window_attributes(conn, focused->window->id, XCB_CW_EVENT_MASK, values);
@@ -1135,7 +1135,7 @@ void x_push_changes(Con *con) {
         /* If we still have no window to focus, we focus the EWMH window instead. We use this rather than the
          * root window in order to avoid an X11 fallback mechanism causing a ghosting effect (see #1378). */
         DLOG("Still no window focused, better set focus to the EWMH support window (%d)\n", ewmh_window);
-        xcb_set_input_focus(conn, XCB_INPUT_FOCUS_POINTER_ROOT, ewmh_window, XCB_CURRENT_TIME);
+        xcb_set_input_focus(conn, XCB_INPUT_FOCUS_POINTER_ROOT, ewmh_window, last_timestamp);
         ewmh_update_active_window(XCB_WINDOW_NONE);
         focused_id = ewmh_window;
     }