Use QApplication.postEvent again

We had some funny segfaults reported during scrolling (i.e. with
QApplication.sendEvent), and some code already had to use postpone=True
so there was no segfault...

So now we're back to postEvent again, and eliminated the main reason for
segfaults with it, which was re-using (and -posting) events which had
already been posted.

At least during tests this seems to run stable, let's hope it helps for
the people having crashes as well.

qutebrowser/browser/browsertab.py

@@ -595,18 +595,20 @@ class AbstractTab(QWidget):
         """Return the widget events should be sent to."""
         raise NotImplementedError
 
-    def send_event(self, evt, *, postpone=False):
+    def send_event(self, evt):
         """Send the given event to the underlying widget.
 
-        Args:
-            postpone: Postpone the event to be handled later instead of
-                      immediately. Using this might cause crashes in Qt.
+        The event will be sent via QApplication.postEvent.
+        Note that a posted event may not be re-used in any way!
         """
+        # This only gives us some mild protection against re-using events, but
+        # it's certainly better than a segfault.
+        if getattr(evt, 'posted', False):
+            raise AssertionError("Can't re-use an event which was already "
+                                 "posted!")
         recipient = self._event_target()
-        if postpone:
+        evt.posted = True
         QApplication.postEvent(recipient, evt)
-        else:
-            QApplication.sendEvent(recipient, evt)
 
     @pyqtSlot(QUrl)
     def _on_link_clicked(self, url):

qutebrowser/browser/commands.py

@@ -1974,8 +1974,8 @@ class CommandDispatcher:
                 window = QApplication.focusWindow()
                 if window is None:
                     raise cmdexc.CommandError("No focused window!")
-                QApplication.sendEvent(window, press_event)
-                QApplication.sendEvent(window, release_event)
+                QApplication.postEvent(window, press_event)
+                QApplication.postEvent(window, release_event)
             else:
                 try:
                     tab = objreg.get('tab', scope='tab', tab='current')

qutebrowser/browser/webelem.py

@@ -376,9 +376,7 @@ class AbstractWebElement(collections.abc.MutableMapping):
         ]
 
         for evt in events:
-            # For some reason, postpone=True is needed here to *not* cause
-            # segfaults in misc.feature because of :fake-key later...
-            self._tab.send_event(evt, postpone=True)
+            self._tab.send_event(evt)
 
         def after_click():
             """Move cursor to end and reset override_target after clicking."""

qutebrowser/browser/webengine/webenginetab.py

@@ -214,9 +214,9 @@ class WebEngineScroller(browsertab.AbstractScroller):
 
     def _key_press(self, key, count=1):
         # FIXME:qtwebengine Abort scrolling if the minimum/maximum was reached.
+        for _ in range(count):
             press_evt = QKeyEvent(QEvent.KeyPress, key, Qt.NoModifier, 0, 0, 0)
             release_evt = QKeyEvent(QEvent.KeyRelease, key, Qt.NoModifier, 0, 0, 0)
-        for _ in range(count):
             self._tab.send_event(press_evt)
             self._tab.send_event(release_evt)
 

qutebrowser/browser/webkit/webkittab.py

@@ -409,14 +409,15 @@ class WebKitScroller(browsertab.AbstractScroller):
 
     def _key_press(self, key, count=1, getter_name=None, direction=None):
         frame = self._widget.page().mainFrame()
-        press_evt = QKeyEvent(QEvent.KeyPress, key, Qt.NoModifier, 0, 0, 0)
-        release_evt = QKeyEvent(QEvent.KeyRelease, key, Qt.NoModifier, 0, 0, 0)
         getter = None if getter_name is None else getattr(frame, getter_name)
 
         # FIXME:qtwebengine needed?
         # self._widget.setFocus()
 
         for _ in range(count):
+            press_evt = QKeyEvent(QEvent.KeyPress, key, Qt.NoModifier, 0, 0, 0)
+            release_evt = QKeyEvent(QEvent.KeyRelease, key, Qt.NoModifier,
+                                    0, 0, 0)
             # Abort scrolling if the minimum/maximum was reached.
             if (getter is not None and
                     frame.scrollBarValue(direction) == getter(direction)):

tests/end2end/features/scroll.feature

@@ -84,7 +84,6 @@ Feature: Scrolling
         And I wait until the scroll position changed to 0/0
         Then the page should not be scrolled
 
-    # causes segfault with postEvent instead of sendEvent
     Scenario: Scrolling down with count 10
         When I run :scroll down with count 10
         Then no crash should happen