Add colors.webpage.force_dark_color_scheme

See #4840, #4616

doc/changelog.asciidoc

@@ -15,6 +15,16 @@ breaking changes (such as renamed commands) can happen in minor releases.
 // `Fixed` for any bug fixes.
 // `Security` to invite users to upgrade in case of vulnerabilities.
 
+v1.10.0 (unreleased)
+--------------------
+
+Added
+~~~~~
+
+- New `colors.webpage.force_dark_color_scheme` setting which allows forcing
+  `prefer-color-scheme: dark` colors for websites (QtWebEngine with Qt 5.14 or
+  newer).
+
 v1.9.0 (2020-01-08)
 -------------------
 

doc/help/settings.asciidoc

@@ -109,6 +109,7 @@
 |<<colors.tabs.selected.odd.bg,colors.tabs.selected.odd.bg>>|Background color of selected odd tabs.
 |<<colors.tabs.selected.odd.fg,colors.tabs.selected.odd.fg>>|Foreground color of selected odd tabs.
 |<<colors.webpage.bg,colors.webpage.bg>>|Background color for webpages if unset (or empty to use the theme's color).
+|<<colors.webpage.force_dark_color_scheme,colors.webpage.force_dark_color_scheme>>|Force `prefer-color-scheme: dark` colors for websites.
 |<<completion.cmd_history_max_items,completion.cmd_history_max_items>>|Number of commands to save in the command history.
 |<<completion.delay,completion.delay>>|Delay (in milliseconds) before updating completions after typing a character.
 |<<completion.height,completion.height>>|Height (in pixels or as percentage of the window) of the completion.
@@ -1504,6 +1505,18 @@ Type: <<types,QtColor>>
 
 Default: +pass:[white]+
 
+[[colors.webpage.force_dark_color_scheme]]
+=== colors.webpage.force_dark_color_scheme
+Force `prefer-color-scheme: dark` colors for websites.
+
+Type: <<types,Bool>>
+
+Default: +pass:[false]+
+
+On QtWebEngine, this setting requires Qt 5.14 or newer.
+
+On QtWebKit, this setting is unavailable.
+
 [[completion.cmd_history_max_items]]
 === completion.cmd_history_max_items
 Number of commands to save in the command history.

qutebrowser/config/configdata.yml

@@ -2499,6 +2499,14 @@ colors.webpage.bg:
   desc: "Background color for webpages if unset (or empty to use the theme's
     color)."
 
+colors.webpage.force_dark_color_scheme:
+  default: false
+  type: Bool
+  desc: "Force `prefer-color-scheme: dark` colors for websites."
+  backend:
+    QtWebEngine: Qt 5.14
+    QtWebKit: false
+
 ## fonts
 
 fonts.monospace:

qutebrowser/config/configinit.py

@@ -267,6 +267,12 @@ def _qtwebengine_args(namespace: argparse.Namespace) -> typing.Iterator[str]:
             False: '--autoplay-policy=user-gesture-required',
         }
 
+    if qtutils.version_check('5.14'):
+        settings['colors.webpage.force_dark_color_scheme'] = {
+            True: '--force-dark-mode',
+            False: None,
+        }
+
     for setting, args in sorted(settings.items()):
         arg = args[config.instance.get(setting)]
         if arg is not None:

tests/unit/config/test_configinit.py

@@ -636,6 +636,27 @@ class TestQtArgs:
         else:
             assert arg in args
 
+    @pytest.mark.parametrize('force, new_qt, added', [
+        (True, True, True),
+        (True, False, False),
+        (False, True, False),
+        (False, False, False),
+    ])
+    def test_force_dark_color_scheme(self, config_stub, monkeypatch, parser,
+                                     force, new_qt, added):
+        monkeypatch.setattr(configinit.qtutils, 'version_check',
+                            lambda version, exact=False, compiled=True:
+                            new_qt)
+
+        monkeypatch.setattr(configinit.objects, 'backend',
+                            usertypes.Backend.QtWebEngine)
+
+        config_stub.val.colors.webpage.force_dark_color_scheme = force
+        parsed = parser.parse_args([])
+        args = configinit.qt_args(parsed)
+
+        assert ('--force-dark-mode' in args) == added
+
 
 @pytest.mark.parametrize('arg, confval, used', [
     # overridden by commandline arg