Add :config-diff command

doc/changelog.asciidoc

@@ -35,6 +35,7 @@ Added
 - New `:debug-keytester` command, which shows a "key tester" widget.
   Previously, that was only available as a separate application via `python3 -m
   scripts.keytester`.
+- New `:config-diff` command which opens the `qute://configdiff` page.
 
 Fixed
 ~~~~~

doc/help/commands.asciidoc

@@ -44,6 +44,7 @@ possible to run or bind multiple commands by separating them with `;;`.
 |<<config-cycle,config-cycle>>|Cycle an option between multiple values.
 |<<config-dict-add,config-dict-add>>|Add a key/value pair to a dictionary option.
 |<<config-dict-remove,config-dict-remove>>|Remove a key from a dict.
+|<<config-diff,config-diff>>|Show all customized options.
 |<<config-edit,config-edit>>|Open the config.py file in the editor.
 |<<config-list-add,config-list-add>>|Append a value to a config option that is a list.
 |<<config-list-remove,config-list-remove>>|Remove a value from a list.
@@ -328,6 +329,16 @@ Remove a key from a dict.
 ==== optional arguments
 * +*-t*+, +*--temp*+: Remove value temporarily until qutebrowser is closed.
 
+[[config-diff]]
+=== config-diff
+Syntax: +:config-diff [*--old*]+
+
+Show all customized options.
+
+==== optional arguments
+* +*-o*+, +*--old*+: Show difference for the pre-v1.0 files (qutebrowser.conf/keys.conf).
+
+
 [[config-edit]]
 === config-edit
 Syntax: +:config-edit [*--no-source*]+

qutebrowser/config/configcommands.py

@@ -261,6 +261,23 @@ class ConfigCommands:
         with self._handle_config_error():
             self._config.unset(option, save_yaml=not temp)
 
+    @cmdutils.register(instance='config-commands')
+    @cmdutils.argument('win_id', value=cmdutils.Value.win_id)
+    def config_diff(self, win_id: int, old: bool = False) -> None:
+        """Show all customized options.
+
+        Args:
+            old: Show difference for the pre-v1.0 files
+                 (qutebrowser.conf/keys.conf).
+        """
+        url = QUrl('qute://configdiff')
+        if old:
+            url.setPath('/old')
+
+        tabbed_browser = objreg.get('tabbed-browser',
+                                    scope='window', window=win_id)
+        tabbed_browser.load_url(url, newtab=False)
+
     @cmdutils.register(instance='config-commands')
     @cmdutils.argument('option', completion=configmodel.list_option)
     def config_list_add(self, option: str, value: str,

tests/unit/config/test_configcommands.py

@@ -212,6 +212,16 @@ class TestSet:
             commands.set(win_id=0, option='foo?')
 
 
+@pytest.mark.parametrize('old', [True, False])
+def test_diff(commands, tabbed_browser_stubs, old):
+    """Run ':config-diff'.
+
+    Should open qute://configdiff."""
+    commands.config_diff(win_id=0, old=old)
+    url = QUrl('qute://configdiff/old') if old else QUrl('qute://configdiff')
+    assert tabbed_browser_stubs[0].loaded_url == url
+
+
 class TestCycle:
 
     """Test :config-cycle."""