Add :debug-log-filter none

This allows us to clear any filters. Useful for users, and needed for
the tests.

CHANGELOG.asciidoc

@@ -24,6 +24,8 @@ Added
 - New `ui -> keyhint-delay` setting to configure the delay until
   the keyhint overlay pops up.
 - New `-s` option for `:open` to force a HTTPS scheme.
+- `:debug-log-filter` now accepts `none` as an argument to clear any log
+  filters.
 
 Changed
 ~~~~~~~

qutebrowser/misc/utilcmds.py

@@ -293,16 +293,22 @@ def debug_log_filter(filters: str):
     """Change the log filter for console logging.
 
     Args:
-        filters: A comma separated list of logger names.
+        filters: A comma separated list of logger names. Can also be "none" to
+                 clear any existing filters.
     """
+    if log.console_filter is None:
+        raise cmdexc.CommandError("No log.console_filter. Not attached "
+                                  "to a console?")
+
+    if filters.strip().lower() == 'none':
+        log.console_filter.names = None
+        return
+
     if not set(filters.split(',')).issubset(log.LOGGER_NAMES):
         raise cmdexc.CommandError("filters: Invalid value {} - expected one "
                                   "of: {}".format(filters,
                                                   ', '.join(log.LOGGER_NAMES)))
 
-    if log.console_filter is None:
-        raise cmdexc.CommandError("No log.console_filter. Not attached "
-                                  "to a console?")
     log.console_filter.names = filters.split(',')
 
 

tests/end2end/features/utilcmds.feature

@@ -166,5 +166,8 @@ Feature: Miscellaneous utility commands exposed to the user.
         Then the error "filters: Invalid value blah - expected one of: statusbar, *" should be shown
 
     Scenario: Using debug-log-filter
-        When I run :debug-log-filter webview
-        Then no crash should happen
+        When I run :debug-log-filter commands,ipc,webview
+        And I run :enter-mode insert
+        And I run :debug-log-filter none
+        And I run :leave-mode
+        Then "Entering mode KeyMode.insert *" should not be logged