Resolve crash when editor tab is closed.

If an editor is open on a form in a tab and that tab is closed, rewire
the callback to print a warning. Previously, the callback would access a
deleted C++ object and cause a crash.
Resolves #2758.

qutebrowser/browser/commands.py

@@ -1621,6 +1621,9 @@ class CommandDispatcher:
         ed = editor.ExternalEditor(self._tabbed_browser)
         ed.editing_finished.connect(functools.partial(
             self.on_editing_finished, elem))
+        tab = self._current_widget()
+        tab.shutting_down.connect(functools.partial(
+            self.on_editor_orphaned, ed))
         ed.edit(text, caret_position)
 
     @cmdutils.register(instance='command-dispatcher', scope='window')
@@ -1647,6 +1650,11 @@ class CommandDispatcher:
         except webelem.Error as e:
             raise cmdexc.CommandError(str(e))
 
+    def on_editor_orphaned(self, ed):
+        ed.editing_finished.disconnect()
+        ed.editing_finished.connect(
+            lambda: message.warning('Edited element was closed'))
+
     @cmdutils.register(instance='command-dispatcher', maxsplit=0,
                        scope='window')
     def insert_text(self, text):

tests/end2end/features/editor.feature

@@ -115,6 +115,16 @@ Feature: Opening external editors
         And I run :click-element id qute-button
         Then the javascript message "text: foobar" should be logged
 
+    Scenario: Spawning an editor and closing the tab
+        When I set up a fake editor returning "foo" after 1s
+        And I open data/editor.html
+        And I run :click-element id qute-textarea
+        And I wait for "Entering mode KeyMode.insert (reason: clicking input)" in the log
+        And I run :open-editor
+        And I set tabs.last_close to blank
+        And I run :tab-close
+        Then the warning "Edited element was closed" should be shown
+
     @qtwebengine_todo: Caret mode is not implemented yet
     Scenario: Spawning an editor in caret mode
         When I set up a fake editor returning "foobar"

tests/end2end/features/test_editor_bdd.py

@@ -64,3 +64,21 @@ def set_up_editor(quteproc, server, tmpdir, text):
 def set_up_editor_empty(quteproc, server, tmpdir):
     """Set up editor.command to a small python script inserting empty text."""
     set_up_editor(quteproc, server, tmpdir, "")
+
+
+@bdd.when(bdd.parsers.parse(
+    'I set up a fake editor returning "{text}" after {t}s'))
+def set_up_editor_delay(quteproc, server, tmpdir, text, t):
+    """Set up editor.command to a small python script inserting a text."""
+    script = tmpdir / 'script.py'
+    script.write(textwrap.dedent("""
+        import sys
+        import time
+
+        time.sleep({t})
+
+        with open(sys.argv[1], 'w', encoding='utf-8') as f:
+            f.write({text!r})
+    """.format(text=text, t=t)))
+    editor = json.dumps([sys.executable, str(script), '{}'])
+    quteproc.set_setting('editor.command', editor)