Implement dark mode for Qt 5.15.2

See #5752

3 files changed, 40 insertions, 19 deletions

diff --git a/doc/changelog.asciidoc b/doc/changelog.asciidoc
index 23182bcae..25206f286 100644
--- a/doc/changelog.asciidoc
+++ b/doc/changelog.asciidoc
@@ -66,6 +66,7 @@ Changed
   `--asciidoc-python path/to/python --asciidoc path/to/asciidoc.py`
   instead of the former
   `--asciidoc path/to/python path/to/asciidoc.py`.
+- Dark mode is now supported with Qt 5.15.2 (which is not released yet)
 - The `readability-js` userscript now adds some CSS to improve the reader mode
   styling in various scenarios:
   * Images are now shrinked to the page width, similarly to what Firefox' reader
diff --git a/qutebrowser/config/qtargs.py b/qutebrowser/config/qtargs.py
index b81194c22..a9d92e95d 100644
--- a/qutebrowser/config/qtargs.py
+++ b/qutebrowser/config/qtargs.py
@@ -61,6 +61,21 @@ def qt_args(namespace: argparse.Namespace) -> typing.List[str]:
     return argv
 
 
+def _darkmode_prefix() -> str:
+    """Return the prefix to use for darkmode settings."""
+    try:
+        from PyQt5.QtWebEngine import PYQT_WEBENGINE_VERSION
+    except ImportError:
+        # Added in PyQt 5.13
+        return 'darkMode'
+
+    if PYQT_WEBENGINE_VERSION >= 0x050f02:
+        # QtWebEngine 5.15.2 comes with Chromium 83
+        return 'forceDarkMode'
+    else:
+        return 'darkMode'
+
+
 def _darkmode_settings() -> typing.Iterator[typing.Tuple[str, str]]:
     """Get necessary blink settings to configure dark mode for QtWebEngine."""
     if not config.val.colors.webpage.darkmode.enabled:
@@ -139,10 +154,7 @@ def _darkmode_settings() -> typing.Iterator[typing.Tuple[str, str]]:
         if mapping is not None:
             value = mapping[value]
 
-        # FIXME: This is "forceDarkMode" starting with Chromium 83
-        prefix = 'darkMode'
-
-        yield prefix + key, str(value)
+        yield _darkmode_prefix() + key, str(value)
 
 
 def _qtwebengine_enabled_features(
diff --git a/tests/unit/config/test_qtargs.py b/tests/unit/config/test_qtargs.py
index 639975694..784978c72 100644
--- a/tests/unit/config/test_qtargs.py
+++ b/tests/unit/config/test_qtargs.py
@@ -400,7 +400,14 @@ class TestQtArgs:
         parsed = parser.parse_args([])
         args = qtargs.qt_args(parsed)
 
-        assert '--blink-settings=darkModeEnabled=true' in args
+        old_setting = '--blink-settings=darkModeEnabled=true'
+        new_setting = '--blink-settings=forceDarkModeEnabled=true'
+
+        assert old_setting in args or new_setting in args
+
+
+def add_prefix(name):
+    return qtargs._darkmode_prefix() + name
 
 
 class TestDarkMode:
@@ -421,25 +428,25 @@ class TestDarkMode:
         (
             {'enabled': True},
             True,
-            [('darkModeEnabled', 'true')]
+            [(add_prefix('Enabled'), 'true')]
         ),
         (
             {'enabled': True},
             False,
-            [('darkMode', '4')]
+            [(add_prefix(''), '4')]
         ),
 
         # Algorithm
         (
             {'enabled': True, 'algorithm': 'brightness-rgb'},
             True,
-            [('darkModeEnabled', 'true'),
-             ('darkModeInversionAlgorithm', '2')],
+            [(add_prefix('Enabled'), 'true'),
+             (add_prefix('InversionAlgorithm'), '2')],
         ),
         (
             {'enabled': True, 'algorithm': 'brightness-rgb'},
             False,
-            [('darkMode', '2')],
+            [(add_prefix(''), '2')],
         ),
 
     ])
@@ -455,19 +462,19 @@ class TestDarkMode:
 
     @pytest.mark.parametrize('setting, value, exp_key, exp_val', [
         ('contrast', -0.5,
-         'darkModeContrast', '-0.5'),
+         add_prefix('Contrast'), '-0.5'),
         ('policy.page', 'smart',
-         'darkModePagePolicy', '1'),
+         add_prefix('PagePolicy'), '1'),
         ('policy.images', 'smart',
-         'darkModeImagePolicy', '2'),
+         add_prefix('ImagePolicy'), '2'),
         ('threshold.text', 100,
-         'darkModeTextBrightnessThreshold', '100'),
+         add_prefix('TextBrightnessThreshold'), '100'),
         ('threshold.background', 100,
-         'darkModeBackgroundBrightnessThreshold', '100'),
+         add_prefix('BackgroundBrightnessThreshold'), '100'),
         ('grayscale.all', True,
-         'darkModeGrayscale', 'true'),
+         add_prefix('Grayscale'), 'true'),
         ('grayscale.images', 0.5,
-         'darkModeImageGrayscale', '0.5'),
+         add_prefix('ImageGrayscale'), '0.5'),
     ])
     def test_customization(self, config_stub, monkeypatch,
                            setting, value, exp_key, exp_val):
@@ -477,7 +484,7 @@ class TestDarkMode:
                             lambda version, exact=False, compiled=True:
                             True)
 
-        expected = [('darkModeEnabled', 'true'), (exp_key, exp_val)]
+        expected = [(add_prefix('Enabled'), 'true'), (exp_key, exp_val)]
         assert list(qtargs._darkmode_settings()) == expected
 
     def test_new_chromium(self):
@@ -493,7 +500,8 @@ class TestDarkMode:
         assert version._chromium_version() in [
             'unavailable',  # QtWebKit
             '77.0.3865.129',  # Qt 5.14
-            '80.0.3987.163',  # Qt 5.15
+            '80.0.3987.163',  # Qt 5.15.0
+            '83.0.4103.122',  # Qt 5.15.2
         ]
 
     def test_options(self, configdata_init):