Regen completion if args change.

Allow completion functions to react dynamically to args as the user
inputs them. This allows config-cycle to filter out values that were
already provided.

Args provided after the maxsplit do not cause the completion to regen.
For example, successive words typed after `:open` just set the filter
pattern and do not spuriously regenerate the completion model.

qutebrowser/completion/completer.py

@@ -49,7 +49,7 @@ class Completer(QObject):
         _last_cursor_pos: The old cursor position so we avoid double completion
                           updates.
         _last_text: The old command text so we avoid double completion updates.
-        _last_completion_func: The completion function used for the last text.
+        _last_before_cursor: The prior value of before_cursor.
     """
 
     def __init__(self, *, cmd, win_id, parent=None):
@@ -62,7 +62,7 @@ class Completer(QObject):
         self._timer.timeout.connect(self._update_completion)
         self._last_cursor_pos = -1
         self._last_text = None
-        self._last_completion_func = None
+        self._last_before_cursor = None
         self._cmd.update_completion.connect(self.schedule_completion_update)
 
     def __repr__(self):
@@ -228,7 +228,7 @@ class Completer(QObject):
             # FIXME complete searches
             # https://github.com/qutebrowser/qutebrowser/issues/32
             completion.set_model(None)
-            self._last_completion_func = None
+            self._last_before_cursor = None
             return
 
         before_cursor, pattern, after_cursor = self._partition()
@@ -242,11 +242,11 @@ class Completer(QObject):
         if func is None:
             log.completion.debug('Clearing completion')
             completion.set_model(None)
-            self._last_completion_func = None
+            self._last_before_cursor = None
             return
 
-        if func != self._last_completion_func:
-            self._last_completion_func = func
+        if before_cursor != self._last_before_cursor:
+            self._last_before_cursor = before_cursor
             args = (x for x in before_cursor[1:] if not x.startswith('-'))
             with debug.log_time(log.completion, 'Starting {} completion'
                                 .format(func.__name__)):

qutebrowser/completion/models/configmodel.py

@@ -47,12 +47,12 @@ def customized_option(*, info):
     return model
 
 
-def value(optname, *_values, info):
+def value(optname, *values, info):
     """A CompletionModel filled with setting values.
 
     Args:
         optname: The name of the config option this model shows.
-        _values: The values already provided on the command line.
+        values: The values already provided on the command line.
         info: A CompletionInfo instance.
     """
     model = completionmodel.CompletionModel(column_widths=(30, 70, 0))
@@ -64,13 +64,18 @@ def value(optname, *_values, info):
 
     opt = info.config.get_opt(optname)
     default = opt.typ.to_str(opt.default)
-    cur_cat = listcategory.ListCategory(
-        "Current/Default",
-        [(current, "Current value"), (default, "Default value")])
-    model.add_category(cur_cat)
+    cur_def = []
+    if current not in values:
+        cur_def.append((current, "Current value"))
+    if default not in values:
+        cur_def.append((default, "Default value"))
+    if cur_def:
+        cur_cat = listcategory.ListCategory("Current/Default", cur_def)
+        model.add_category(cur_cat)
 
-    vals = opt.typ.complete()
-    if vals is not None:
+    vals = opt.typ.complete() or []
+    vals = [x for x in vals if x[0] not in values]
+    if vals:
         model.add_category(listcategory.ListCategory("Completions", vals))
     return model
 

tests/unit/completion/test_completer.py

@@ -223,6 +223,32 @@ def test_update_completion(txt, kind, pattern, pos_args, status_command_stub,
         completion_widget_stub.set_pattern.assert_called_once_with(pattern)
 
 
+@pytest.mark.parametrize('txt1, txt2, regen', [
+    (':config-cycle |', ':config-cycle a|', False),
+    (':config-cycle abc|', ':config-cycle abc |', True),
+    (':config-cycle abc |', ':config-cycle abc d|', False),
+    (':config-cycle abc def|', ':config-cycle abc def |', True),
+    # open has maxsplit=0, so all args just set the pattern, not the model
+    (':open |', ':open a|', False),
+    (':open abc|', ':open abc |', False),
+    (':open abc |', ':open abc d|', False),
+    (':open abc def|', ':open abc def |', False),
+])
+def test_regen_completion(txt1, txt2, regen, status_command_stub,
+                          completer_obj, completion_widget_stub, config_stub,
+                          key_config_stub):
+    """Test that the completion function is only called as needed."""
+    # set the initial state
+    _set_cmd_prompt(status_command_stub, txt1)
+    completer_obj.schedule_completion_update()
+    completion_widget_stub.set_model.reset_mock()
+
+    # "move" the cursor and check if the completion function was called
+    _set_cmd_prompt(status_command_stub, txt2)
+    completer_obj.schedule_completion_update()
+    assert completion_widget_stub.set_model.called == regen
+
+
 @pytest.mark.parametrize('before, newtxt, after', [
     (':|', 'set', ':set|'),
     (':| ', 'set', ':set|'),