Add experimental_web_platform_features setting

Closes #7639

5 files changed, 63 insertions, 1 deletions

diff --git a/doc/changelog.asciidoc b/doc/changelog.asciidoc
index d512e0dd4..ef5123d29 100644
--- a/doc/changelog.asciidoc
+++ b/doc/changelog.asciidoc
@@ -50,6 +50,9 @@ Added
     * `qutedmenu` gained new `window` and `private` options.
     * `qute-keepassxc` now supports unlock-on-demand, multiple account
       selection via rofi, and inserting TOTP-codes (experimental).
+- New `qt.chromium.experimental_web_platform_features` setting, which is enabled
+  on Qt 5 by default, to maximize compatibility with websites despite an aging
+  Chromium backend.
 - New `colors.webpage.darkmode.increase_text_contrast` setting for Qt 6.3+
 - New `fonts.tooltip`, `colors.tooltip.bg` and `colors.tooltip.fg` settings.
 - New `log-qt-events` debug flag for `-D`
diff --git a/doc/help/settings.asciidoc b/doc/help/settings.asciidoc
index 34262b945..4a3a3c0e7 100644
--- a/doc/help/settings.asciidoc
+++ b/doc/help/settings.asciidoc
@@ -294,6 +294,7 @@
 |<<prompt.filebrowser,prompt.filebrowser>>|Show a filebrowser in download prompts.
 |<<prompt.radius,prompt.radius>>|Rounding radius (in pixels) for the edges of prompts.
 |<<qt.args,qt.args>>|Additional arguments to pass to Qt, without leading `--`.
+|<<qt.chromium.experimental_web_platform_features,qt.chromium.experimental_web_platform_features>>|Enables Web Platform features that are in development.
 |<<qt.chromium.low_end_device_mode,qt.chromium.low_end_device_mode>>|When to use Chromium's low-end device mode.
 |<<qt.chromium.process_model,qt.chromium.process_model>>|Which Chromium process model to use.
 |<<qt.chromium.sandboxing,qt.chromium.sandboxing>>|What sandboxing mechanisms in Chromium to use.
@@ -3851,6 +3852,25 @@ Type: <<types,List of String>>
 
 Default: empty
 
+[[qt.chromium.experimental_web_platform_features]]
+=== qt.chromium.experimental_web_platform_features
+Enables Web Platform features that are in development.
+This passes the `--enable-experimental-web-platform-features` flag to Chromium. By default, this is enabled with Qt 5 to maximize compatibility despite an aging Chromium base.
+
+This setting requires a restart.
+
+This setting is only available with the QtWebEngine backend.
+
+Type: <<types,String>>
+
+Valid values:
+
+ * +always+: Enable experimental web platform features.
+ * +auto+: Enable experimental web platform features when using Qt 5.
+ * +never+: Disable experimental web platform features.
+
+Default: +pass:[auto]+
+
 [[qt.chromium.low_end_device_mode]]
 === qt.chromium.low_end_device_mode
 When to use Chromium's low-end device mode.
diff --git a/qutebrowser/config/configdata.yml b/qutebrowser/config/configdata.yml
index bedcc2ade..8fbb67cb7 100644
--- a/qutebrowser/config/configdata.yml
+++ b/qutebrowser/config/configdata.yml
@@ -327,6 +327,23 @@ qt.chromium.sandboxing:
     - https://chromium.googlesource.com/chromium/src/\+/HEAD/docs/design/sandbox_faq.md[FAQ (Windows-centric)]
   # yamllint enable rule:line-length
 
+qt.chromium.experimental_web_platform_features:
+  type:
+    name: String
+    valid_values:
+      - always: Enable experimental web platform features.
+      - auto: Enable experimental web platform features when using Qt 5.
+      - never: Disable experimental web platform features.
+  default: auto
+  backend: QtWebEngine
+  restart: true
+  desc: >-
+    Enables Web Platform features that are in development.
+
+    This passes the `--enable-experimental-web-platform-features` flag to
+    Chromium. By default, this is enabled with Qt 5 to maximize compatibility
+    despite an aging Chromium base.
+
 qt.highdpi:
   type: Bool
   default: false
diff --git a/qutebrowser/config/qtargs.py b/qutebrowser/config/qtargs.py
index 8b7a85b64..1dd60c2c2 100644
--- a/qutebrowser/config/qtargs.py
+++ b/qutebrowser/config/qtargs.py
@@ -25,6 +25,7 @@ import argparse
 import pathlib
 from typing import Any, Dict, Iterator, List, Optional, Sequence, Tuple
 
+from qutebrowser.qt import machinery
 from qutebrowser.qt.core import QLocale
 
 from qutebrowser.config import config
@@ -331,7 +332,13 @@ _WEBENGINE_SETTINGS: Dict[str, Dict[Any, Optional[str]]] = {
         'enable-all': None,
         'disable-seccomp-bpf': '--disable-seccomp-filter-sandbox',
         'disable-all': '--no-sandbox',
-    }
+    },
+    'qt.chromium.experimental_web_platform_features': {
+        'always': '--enable-experimental-web-platform-features',
+        'never': None,
+        'auto':
+            '--enable-experimental-web-platform-features' if machinery.IS_QT5 else None,
+    },
 }
 
 
diff --git a/tests/unit/config/test_qtargs.py b/tests/unit/config/test_qtargs.py
index a65847929..91462338e 100644
--- a/tests/unit/config/test_qtargs.py
+++ b/tests/unit/config/test_qtargs.py
@@ -22,6 +22,7 @@ import logging
 
 import pytest
 
+from qutebrowser.qt import machinery
 from qutebrowser import qutebrowser
 from qutebrowser.config import qtargs, configdata
 from qutebrowser.utils import usertypes, version
@@ -488,6 +489,20 @@ class TestWebEngineArgs:
         args = qtargs.qt_args(parsed)
         assert '--lang=de' in args
 
+    @pytest.mark.parametrize('value, has_arg', [
+        ('always', True),
+        ('auto', machinery.IS_QT5),
+        ('never', False),
+    ])
+    def test_experimental_web_platform_features(
+        self, value, has_arg, parser, config_stub,
+    ):
+        config_stub.val.qt.chromium.experimental_web_platform_features = value
+
+        parsed = parser.parse_args([])
+        args = qtargs.qt_args(parsed)
+        assert ('--enable-experimental-web-platform-features' in args) == has_arg
+
     @pytest.mark.parametrize("version, expected", [
         ('5.15.2', False),
         ('5.15.9', False),