Install MouseEventFilter on new WebEngine children

For some reason, when e.g. visiting duckduckgo and then heise.de,
QtWebEngine suddenly gets a new QOpenGLWidget as focusProxy.

We install an extra eventFilter observing the ChildAdded event and
re-adding the MouseEventFilter when that happens.

qutebrowser/browser/browsertab.py

@@ -485,9 +485,6 @@ def __init__(self, win_id, parent=None):
         self._mouse_event_filter = mouse.MouseEventFilter(self, parent=self)
         self.backend = None
 
-    def _event_filter_target(self):
-        raise NotImplementedError
-
     def _set_widget(self, widget):
         # pylint: disable=protected-access
         self._widget = widget
@@ -499,8 +496,10 @@ def _set_widget(self, widget):
         self.search._widget = widget
         self.printing._widget = widget
         widget.mouse_wheel_zoom.connect(self.zoom._on_mouse_wheel_zoom)
-        event_filter_target = self._event_filter_target()
-        event_filter_target.installEventFilter(self._mouse_event_filter)
+        self._install_event_filter()
+
+    def _install_event_filter(self):
+        raise NotImplementedError
 
     def _set_load_status(self, val):
         """Setter for load_status."""

qutebrowser/browser/mouse.py

@@ -21,12 +21,38 @@
 
 
 from qutebrowser.config import config
-from qutebrowser.utils import message
+from qutebrowser.utils import message, debug, log
 
 
 from PyQt5.QtCore import QObject, QEvent, Qt
 
 
+class ChildEventFilter(QObject):
+
+    """An event filter re-adding MouseEventFilter on ChildEvent.
+
+    This is needed because QtWebEngine likes to randomly change its
+    focusProxy...
+
+    FIXME:qtwebengine Add a test for this happening
+    """
+
+    def __init__(self, eventfilter, widget, parent=None):
+        super().__init__(parent)
+        self._filter = eventfilter
+        assert widget is not None
+        self._widget = widget
+
+    def eventFilter(self, obj, event):
+        if event.type() == QEvent.ChildAdded:
+            child = event.child()
+            log.mouse.debug("{} got new child {}, installing filter".format(
+                obj, child))
+            assert obj is self._widget
+            child.installEventFilter(self._filter)
+        return False
+
+
 class MouseEventFilter(QObject):
 
     """Handle mouse events on a tab."""
@@ -38,7 +64,7 @@ def __init__(self, tab, parent=None):
             QEvent.MouseButtonPress: self._handle_mouse_press,
         }
 
-    def _handle_mouse_press(self, e):
+    def _handle_mouse_press(self, _obj, e):
         """Handle pressing of a mouse button."""
         is_rocker_gesture = (config.get('input', 'rocker-gestures') and
                              e.buttons() == Qt.LeftButton | Qt.RightButton)
@@ -69,9 +95,9 @@ def _mousepress_backforward(self, e):
                 message.error(self._tab.win_id, "At end of history.",
                               immediately=True)
 
-    def eventFilter(self, _obj, event):
+    def eventFilter(self, obj, event):
         """Filter events going to a QWeb(Engine)View."""
         evtype = event.type()
         if evtype not in self._handlers:
             return False
-        return self._handlers[evtype](event)
+        return self._handlers[evtype](obj, event)

qutebrowser/browser/webengine/webenginetab.py

@@ -31,7 +31,7 @@
 from PyQt5.QtWebEngineWidgets import QWebEnginePage, QWebEngineScript
 # pylint: enable=no-name-in-module,import-error,useless-suppression
 
-from qutebrowser.browser import browsertab
+from qutebrowser.browser import browsertab, mouse
 from qutebrowser.browser.webengine import webview, webengineelem
 from qutebrowser.utils import usertypes, qtutils, log, javascript, utils
 
@@ -335,6 +335,7 @@ def __init__(self, win_id, mode_manager, parent=None):
         self.backend = usertypes.Backend.QtWebEngine
         # init js stuff
         self._init_js()
+        self._child_event_filter = None
 
     def _init_js(self):
         js_code = '\n'.join([
@@ -359,8 +360,12 @@ def _init_js(self):
         # FIXME:qtwebengine  what about runsOnSubFrames?
         page.scripts().insert(script)
 
-    def _event_filter_target(self):
-        return self._widget.focusProxy()
+    def _install_event_filter(self):
+        self._widget.focusProxy().installEventFilter(self._mouse_event_filter)
+        self._child_event_filter = mouse.ChildEventFilter(
+            eventfilter=self._mouse_event_filter, widget=self._widget,
+            parent=self)
+        self._widget.installEventFilter(self._child_event_filter)
 
     def openurl(self, url):
         self._openurl_prepare(url)

qutebrowser/browser/webkit/webkittab.py

@@ -510,8 +510,8 @@ def __init__(self, win_id, mode_manager, parent=None):
         self.zoom.set_default()
         self.backend = usertypes.Backend.QtWebKit
 
-    def _event_filter_target(self):
-        return self._widget
+    def _install_event_filter(self):
+        self._widget.installEventFilter(self._mouse_event_filter)
 
     def openurl(self, url):
         self._openurl_prepare(url)

tests/unit/browser/test_tab.py

@@ -107,9 +107,6 @@ def __init__(self, win_id, parent=None):
         self.search = browsertab.AbstractSearch(parent=self)
         self.printing = browsertab.AbstractPrinting()
 
-    def _event_filter_target(self):
-        return self._widget
-
 
 @pytest.mark.skipif(PYQT_VERSION < 0x050600,
                     reason='Causes segfaults, see #1638')