Add a warning if QTWEBENGINE_CHROMIUM_FLAGS is set

See #6065

qutebrowser/config/qtargs.py

@@ -26,7 +26,7 @@ from typing import Any, Dict, Iterator, List, Optional, Sequence, Tuple
 
 from qutebrowser.config import config
 from qutebrowser.misc import objects
-from qutebrowser.utils import usertypes, qtutils, utils
+from qutebrowser.utils import usertypes, qtutils, utils, log
 
 
 _ENABLE_FEATURES = '--enable-features='
@@ -266,6 +266,15 @@ def init_envvars() -> None:
             os.environ['QT_QUICK_BACKEND'] = 'software'
         elif software_rendering == 'chromium':
             os.environ['QT_WEBENGINE_DISABLE_NOUVEAU_WORKAROUND'] = '1'
+
+        qtwe_flags_var = 'QTWEBENGINE_CHROMIUM_FLAGS'
+        qtwe_flags = os.environ.get(qtwe_flags_var)
+        if qtwe_flags is not None:
+            log.init.warning(
+                f"You have {qtwe_flags_var}={qtwe_flags!r} set in your environment. "
+                "This is currently unsupported and interferes with qutebrowser's own "
+                "flag handling (including workarounds for certain crashes). "
+                "Consider using the qt.args qutebrowser setting instead.")
     else:
         assert objects.backend == usertypes.Backend.QtWebKit, objects.backend
 

tests/unit/config/test_qtargs.py

@@ -18,6 +18,7 @@
 
 import sys
 import os
+import logging
 
 import pytest
 
@@ -552,3 +553,29 @@ class TestEnvVars:
         monkeypatch.setattr(qtargs.objects, 'backend',
                             usertypes.Backend.QtWebKit)
         qtargs.init_envvars()
+
+    @pytest.mark.parametrize('backend, value, expected', [
+        (usertypes.Backend.QtWebKit, None, None),
+        (usertypes.Backend.QtWebKit, '--test', None),
+
+        (usertypes.Backend.QtWebEngine, None, None),
+        (usertypes.Backend.QtWebEngine, '', "''"),
+        (usertypes.Backend.QtWebEngine, '--xyz', "'--xyz'"),
+    ])
+    def test_qtwe_flags_warning(self, monkeypatch, config_stub, caplog,
+                                backend, value, expected):
+        monkeypatch.setattr(qtargs.objects, 'backend', backend)
+        if value is None:
+            monkeypatch.delenv('QTWEBENGINE_CHROMIUM_FLAGS', raising=False)
+        else:
+            monkeypatch.setenv('QTWEBENGINE_CHROMIUM_FLAGS', value)
+
+        with caplog.at_level(logging.WARNING):
+            qtargs.init_envvars()
+
+        if expected is None:
+            assert not caplog.messages
+        else:
+            assert len(caplog.messages) == 1
+            msg = caplog.messages[0]
+            assert msg.startswith(f'You have QTWEBENGINE_CHROMIUM_FLAGS={expected} set')