Pass string, not index from on_selection_changed.

Simplify the CompletionWidget/Completer interface by changing
on_selection_changed to pass the newly selected text rather than the
index of the newly selected item.
This moves the logic from Completer to CompletionWidget but simplifies
the interaction between the two and makes testing easier.

qutebrowser/completion/completer.py

@@ -173,35 +173,30 @@ class Completer(QObject):
                     "partitioned: {} '{}' {}".format(prefix, center, postfix))
                 return prefix, center, postfix
 
-    @pyqtSlot(QItemSelection)
+    @pyqtSlot(str)
-    def on_selection_changed(self, selected):
+    def on_selection_changed(self, text):
         """Change the completed part if a new item was selected.
 
         Called from the views selectionChanged method.
 
         Args:
-            selected: New selection.
+            text: Newly selected text.
-            _deselected: Previous selection.
         """
-        indexes = selected.indexes()
+        if text is None:
-        if not indexes:
-            return
-        model = self._model()
-        data = model.data(indexes[0])
-        if data is None:
             return
         before, center, after = self._partition()
-        log.completion.debug("Changing {} to '{}'".format(center, data))
+        log.completion.debug("Changing {} to '{}'".format(center, text))
         try:
             maxsplit = cmdutils.cmd_dict[before[0]].maxsplit
         except (KeyError, IndexError):
             maxsplit = None
         if maxsplit is None:
-            data = self._quote(data)
+            text = self._quote(text)
+        model = self._model()
         if model.count() == 1 and config.get('completion', 'quick-complete'):
             # If we only have one item, we want to apply it immediately
             # and go on to the next part.
-            self._change_completed_part(data, before, after, immediate=True)
+            self._change_completed_part(text, before, after, immediate=True)
             if maxsplit is not None and maxsplit < len(before):
                 # If we are quick-completing the part after maxsplit, don't
                 # keep offering completions (see issue #1519)
@@ -209,7 +204,7 @@ class Completer(QObject):
         else:
             log.completion.debug("Will ignore next completion update.")
             self._ignore_change = True
-            self._change_completed_part(data, before, after)
+            self._change_completed_part(text, before, after)
 
     @pyqtSlot()
     def schedule_completion_update(self):

qutebrowser/completion/completionwidget.py

@@ -104,7 +104,7 @@ class CompletionView(QTreeView):
     """
 
     resize_completion = pyqtSignal()
-    selection_changed = pyqtSignal(QItemSelection)
+    selection_changed = pyqtSignal(str)
 
     def __init__(self, win_id, parent=None):
         super().__init__(parent)
@@ -310,7 +310,11 @@ class CompletionView(QTreeView):
         if not self._active:
             return
         super().selectionChanged(selected, deselected)
-        self.selection_changed.emit(selected)
+        indexes = selected.indexes()
+        if not indexes:
+            return
+        data = self.model().data(indexes[0])
+        self.selection_changed.emit(data)
 
     def resizeEvent(self, e):
         """Extend resizeEvent to adjust column size."""

tests/unit/completion/test_completer.py

@@ -242,18 +242,13 @@ def test_on_selection_changed(before, newtxt, after, completer_obj,
     then we expect a space to be appended after the current word.
     """
     model = unittest.mock.Mock()
-    model.data = unittest.mock.Mock(return_value=newtxt)
-    indexes = [unittest.mock.Mock()]
-    selection = unittest.mock.Mock()
-    selection.indexes = unittest.mock.Mock(return_value=indexes)
     completion_widget_stub.model.return_value = model
 
     def check(quick_complete, count, expected_txt, expected_pos):
         config_stub.data['completion']['quick-complete'] = quick_complete
-        model.count = unittest.mock.Mock(return_value=count)
+        model.count = lambda: count
         _set_cmd_prompt(status_command_stub, before)
-        completer_obj.on_selection_changed(selection)
+        completer_obj.on_selection_changed(newtxt)
-        model.data.assert_called_with(indexes[0])
         assert status_command_stub.text() == expected_txt
         assert status_command_stub.cursorPosition() == expected_pos
 
@@ -283,16 +278,11 @@ def test_quickcomplete_flicker(status_command_stub, completer_obj,
     quick-complete an entry after maxsplit.
     """
     model = unittest.mock.Mock()
-    model.data = unittest.mock.Mock(return_value='http://example.com')
-    indexes = [unittest.mock.Mock()]
-    selection = unittest.mock.Mock()
-    selection.indexes = unittest.mock.Mock(return_value=indexes)
-    completion_widget_stub.model.return_value = model
-
-    config_stub.data['completion']['quick-complete'] = True
     model.count = unittest.mock.Mock(return_value=1)
-    _set_cmd_prompt(status_command_stub, ':open |')
+    completion_widget_stub.model.return_value = model
-    completer_obj.on_selection_changed(selection)
+    config_stub.data['completion']['quick-complete'] = True
 
+    _set_cmd_prompt(status_command_stub, ':open |')
+    completer_obj.on_selection_changed('http://example.com')
     completer_obj.schedule_completion_update()
     assert not completion_widget_stub.set_model.called