Shut down correctly while being asked a question.

doc/BUGS

@@ -9,8 +9,6 @@ Downloads
 - Download focus rectangle on windows
 - download-page on qute:htmllog is broken
 - Prevent invalid filenames (e.g. com1) when downloading on Windows
-- When quitting while being asked for a download filename: segfault / memory
-  corruption
 
 Webview
 -------

qutebrowser/app.py

@@ -704,6 +704,23 @@ class Application(QApplication):
             return
         self._shutting_down = True
         log.destroy.debug("Shutting down with status {}...".format(status))
+        if self.mainwindow.status.prompt.prompter.shutdown():
+            # If shutdown was called while we were asking a question, we're in
+            # a still sub-eventloop (which gets quitted now) and not in the
+            # main one.
+            # This means we need to defer the real shutdown to when we're back
+            # in the real main event loop, or we'll get a segfault.
+            log.destroy.debug("Deferring real shutdown because question was "
+                              "active.")
+            QTimer.singleShot(0, partial(self._shutdown, status))
+        else:
+            # If we have no questions to shut down, we are already in the real
+            # event loop, so we can shut down immediately.
+            self._shutdown(status)
+
+    def _shutdown(self, status):
+        """Second stage of shutdown."""
+        log.destroy.debug("Stage 2 of shutting down...")
         # Remove eventfilter
         if self.modeman is not None:
             log.destroy.debug("Removing eventfilter...")

qutebrowser/widgets/statusbar/prompter.py

@@ -157,6 +157,23 @@ class Prompter:
         self._busy = True
         return mode
 
+    def shutdown(self):
+        """Cancel all blocking questions.
+
+        Quits and removes all running eventloops.
+
+        Return:
+            True if loops needed to be aborted,
+            False otherwise.
+        """
+        if self._loops:
+            for loop in self._loops:
+                loop.quit()
+                loop.deleteLater()
+            return True
+        else:
+            return False
+
     @pyqtSlot(KeyMode)
     def on_mode_left(self, mode):
         """Clear and reset input when the mode was left."""