Honor *some* Enter/Leave events with detail==Inferior

Commit 19086d70fa made AwesomeWM ignore all Enter/Leave events with
detail==Inferior. However, when leaving a titlebar by moving the cursor
into the actual client window, the corresponding event actually has
detail==Inferior. The same is true for the opposite direction: Leaving a
client window by entering the titlebar.

Thus, this commit fixes the code to handle theses cases again.

This was tested with the following in rc.lua (and with a systray icon
and a client with titlebars).

screen[1].mywibox:connect_signal("mouse::enter", function() print("enter mywibox") end)
screen[1].mywibox:connect_signal("mouse::leave", function() print("leave mywibox") end)
client.connect_signal("mouse::enter", function() print("enter client") end)
client.connect_signal("mouse::leave", function() print("leave client") end)
client.connect_signal("manage", function(c)
    local d = c:titlebar_top()
    d:connect_signal("mouse::enter", function() print("enter titlebar") end)
    d:connect_signal("mouse::leave", function() print("leave titlebar") end)
end)

Fixes: https://github.com/awesomeWM/awesome/pull/2611#issuecomment-457892746
Signed-off-by: Uli Schlachter <psychon@znc.in>

event.c

@@ -586,24 +586,38 @@ event_handle_leavenotify(xcb_leave_notify_event_t *ev)
      * Ignore events with non-normal modes. Those are because a grab
      * activated/deactivated. Everything will be "back to normal" after the
      * grab.
-     *
-     * Also ignore events with detail "inferior". This means that the window was
-     * left for a child window, i.e. the pointer is basically still inside of
-     * our window.
      */
-    if(ev->mode != XCB_NOTIFY_MODE_NORMAL || ev->detail == XCB_NOTIFY_DETAIL_INFERIOR)
+    if(ev->mode != XCB_NOTIFY_MODE_NORMAL)
         return;
 
     if((c = client_getbyframewin(ev->event)))
     {
+        /* The window was left in some way, so definitely no titlebar has the
+         * mouse cursor.
+         */
+        lua_pushnil(L);
+        event_drawable_under_mouse(L, -1);
+        lua_pop(L, 1);
+
+        /* If detail is inferior, it means that the cursor is now in some child
+         * window of our window. Thus, the titlebar was left, but now the cursor
+         * is in the actual child window. Thus, ignore detail=Inferior for
+         * leaving client windows.
+         */
+        if(ev->detail != XCB_NOTIFY_DETAIL_INFERIOR) {
             luaA_object_push(L, c);
             luaA_object_emit_signal(L, -1, "mouse::leave", 0);
             lua_pop(L, 1);
         }
-
+    } else if(ev->detail != XCB_NOTIFY_DETAIL_INFERIOR) {
+        /* Some window was left. This must be a drawin. Ignore detail=Inferior,
+         * because this means that some child window now contains the mouse
+         * cursor, i.e. a systray window. Everything else is a real 'leave'.
+         */
         lua_pushnil(L);
         event_drawable_under_mouse(L, -1);
         lua_pop(L, 1);
+    }
 }
 
 /** The enter notify event handler.
@@ -622,15 +636,20 @@ event_handle_enternotify(xcb_enter_notify_event_t *ev)
      * Ignore events with non-normal modes. Those are because a grab
      * activated/deactivated. Everything will be "back to normal" after the
      * grab.
-     *
-     * Also ignore events with detail "inferior". This means that the cursor was
-     * previously inside of a child window and now left that child window. For
-     * our purposes, the cursor was already inside our window before.
      */
-    if(ev->mode != XCB_NOTIFY_MODE_NORMAL || ev->detail == XCB_NOTIFY_DETAIL_INFERIOR)
+    if(ev->mode != XCB_NOTIFY_MODE_NORMAL)
         return;
 
-    if((drawin = drawin_getbywin(ev->event)))
+    /*
+     * We ignore events with detail "inferior".  This detail means that the
+     * cursor was previously inside of a child window and now left that child
+     * window. For our purposes, the cursor was already inside our window
+     * before.
+     * One exception are titlebars: They are not their own window, but are
+     * "outside of the actual client window".
+     */
+
+    if(ev->detail != XCB_NOTIFY_DETAIL_INFERIOR && (drawin = drawin_getbywin(ev->event)))
     {
         luaA_object_push(L, drawin);
         luaA_object_push_item(L, -1, drawin->drawable);
@@ -641,18 +660,25 @@ event_handle_enternotify(xcb_enter_notify_event_t *ev)
     if((c = client_getbyframewin(ev->event)))
     {
         luaA_object_push(L, c);
+        /* Detail=Inferior means that a child of the frame window now contains
+         * the mouse cursor, i.e. the actual client now has the cursor. All
+         * other details mean that the client itself was really left.
+         */
+        if(ev->detail != XCB_NOTIFY_DETAIL_INFERIOR) {
             luaA_object_emit_signal(L, -1, "mouse::enter", 0);
+        }
 
         drawable_t *d = client_get_drawable(c, ev->event_x, ev->event_y);
         if (d)
         {
             luaA_object_push_item(L, -1, d);
+        } else {
+            lua_pushnil(L);
+        }
         event_drawable_under_mouse(L, -1);
-            lua_pop(L, 1);
+        lua_pop(L, 2);
     }
-        lua_pop(L, 1);
+    else if (ev->detail != XCB_NOTIFY_DETAIL_INFERIOR && ev->event == globalconf.screen->root) {
-    }
-    else if (ev->event == globalconf.screen->root) {
         /* When there are multiple X screens with awesome running separate
          * instances, reset focus.
          */