Show command completions for :bind.

All commands will be offered as completions for the <command> argument
of :bind.

Due to the way completers parse the command line, the following

bind --mode caret j

will throw off completions as 'caret' is treated as a positional arg in
terms of the argument count for completions.
In the above example, completion will be triggered for 'j' and no
completions will be given for the actual command.

bind --mode=caret j will complete correctly, though completions are not
filtered by the given mode.
I attempted an approach to filter the commands based on the mode but it
ended up being messy and flaky.

qutebrowser/completion/models/instances.py

@@ -29,7 +29,8 @@ import functools
 
 from PyQt5.QtCore import pyqtSlot
 
-from qutebrowser.completion.models import miscmodels, urlmodel, configmodel
+from qutebrowser.completion.models import (miscmodels, urlmodel, configmodel,
+                                           base)
 from qutebrowser.utils import objreg, usertypes, log, debug
 from qutebrowser.config import configdata
 
@@ -119,6 +120,13 @@ def init_session_completion():
     _instances[usertypes.Completion.sessions] = model
 
 
+def _init_empty_completion():
+    """Initialize empty completion model."""
+    log.completion.debug("Initializing empty completion.")
+    if usertypes.Completion.empty not in _instances:
+        _instances[usertypes.Completion.empty] = base.BaseCompletionModel()
+
+
 INITIALIZERS = {
     usertypes.Completion.command: _init_command_completion,
     usertypes.Completion.helptopic: _init_helptopic_completion,
@@ -130,6 +138,7 @@ INITIALIZERS = {
     usertypes.Completion.quickmark_by_name: init_quickmark_completions,
     usertypes.Completion.bookmark_by_url: init_bookmark_completions,
     usertypes.Completion.sessions: init_session_completion,
+    usertypes.Completion.empty: _init_empty_completion,
 }
 
 

qutebrowser/config/parsers/keyconf.py

@@ -27,7 +27,7 @@ from PyQt5.QtCore import pyqtSignal, QObject
 
 from qutebrowser.config import configdata, textwrapper
 from qutebrowser.commands import cmdutils, cmdexc
-from qutebrowser.utils import log, utils, qtutils, message
+from qutebrowser.utils import log, utils, qtutils, message, usertypes
 
 
 class KeyConfigError(Exception):
@@ -151,7 +151,9 @@ class KeyConfigParser(QObject):
             f.write(data)
 
     @cmdutils.register(instance='key-config', maxsplit=1, no_cmd_split=True,
-                       win_id='win_id')
+                       win_id='win_id',
+                       completion=[usertypes.Completion.empty,
+                                   usertypes.Completion.command])
     def bind(self, key, win_id, command=None, *, mode=None, force=False):
         """Bind a key to a command.
 

qutebrowser/utils/usertypes.py

@@ -238,7 +238,8 @@ KeyMode = enum('KeyMode', ['normal', 'hint', 'command', 'yesno', 'prompt',
 # Available command completions
 Completion = enum('Completion', ['command', 'section', 'option', 'value',
                                  'helptopic', 'quickmark_by_name',
-                                 'bookmark_by_url', 'url', 'tab', 'sessions'])
+                                 'bookmark_by_url', 'url', 'tab', 'sessions',
+                                 'empty'])
 
 
 # Exit statuses for errors. Needs to be an int for sys.exit.