Qt 6.9: Force software rendering for tests

Not yet quite sure what exactly is the culprit, but this seems to help for all
tests (!) to pass with Xvfb locally.

For now only scoped to Qt 6.9.0. Will probably already need to reevaluate with
the RC, but definitely with the final release.

See #8444

pytest.ini

@@ -79,7 +79,7 @@ qt_log_ignore =
     QItemSelectionModel: Selecting when no model has been set will result in a no-op.
     ^QSaveFile::commit: File \(.*[/\\]test_failing_flush0[/\\]foo\) is not open$
     ^The following paths were searched for Qt WebEngine dictionaries:.*
-    # Qt 6.9 Beta 1 and 2 and 3 with Xvfb
+    # Qt 6.9 Beta 1-3 with Xvfb
     ^Backend texture is not a Vulkan texture\.$
     # With offscreen platform plugin
     ^This plugin does not support (raise|propagateSizeHints)\(\)$

tests/conftest.py

@@ -213,11 +213,13 @@ def pytest_ignore_collect(collection_path: pathlib.Path) -> bool:
 
 
 @pytest.fixture(scope='session')
-def qapp_args():
-    """Make QtWebEngine unit tests run on older Qt versions + newer kernels."""
+def qapp_args() -> list[str]:
+    """Work around various issues when running QtWebEngine tests."""
     args = [sys.argv[0], "--webEngineArgs"]
     if testutils.disable_seccomp_bpf_sandbox():
         args.append(testutils.DISABLE_SECCOMP_BPF_FLAG)
+    if testutils.use_software_rendering():
+        args.append(testutils.SOFTWARE_RENDERING_FLAG)
 
     # Disabling PaintHoldingCrossOrigin makes tests needing UI interaction with
     # QtWebEngine more reliable.

tests/end2end/fixtures/quteprocess.py

@@ -448,8 +448,11 @@ class QuteProc(testprocess.Process):
                 '--qt-flag', 'disable-features=PaintHoldingCrossOrigin',
                 '--qt-arg', 'geometry', '800x600+0+0']
 
-        if self.request.config.webengine and testutils.disable_seccomp_bpf_sandbox():
-            args += testutils.DISABLE_SECCOMP_BPF_ARGS
+        if self.request.config.webengine:
+            if testutils.disable_seccomp_bpf_sandbox():
+                args += testutils.DISABLE_SECCOMP_BPF_ARGS
+            if testutils.use_software_rendering():
+                args += testutils.SOFTWARE_RENDERING_ARGS
 
         args.append('about:blank')
         return args

tests/end2end/test_invocations.py

@@ -45,8 +45,11 @@ def _base_args(config):
     else:
         args += ['--backend', 'webkit']
 
-    if config.webengine and testutils.disable_seccomp_bpf_sandbox():
-        args += testutils.DISABLE_SECCOMP_BPF_ARGS
+    if config.webengine:
+        if testutils.disable_seccomp_bpf_sandbox():
+            args += testutils.DISABLE_SECCOMP_BPF_ARGS
+        if testutils.use_software_rendering():
+            args += testutils.SOFTWARE_RENDERING_ARGS
 
     args.append('about:blank')
     return args

tests/helpers/testutils.py

@@ -264,6 +264,15 @@ def easyprivacy_txt():
     return _decompress_gzip_datafile("easyprivacy.txt.gz")
 
 
+def _has_qtwebengine() -> bool:
+    """Check whether QtWebEngine is available."""
+    try:
+        from qutebrowser.qt import webenginecore   # pylint: disable=unused-import
+    except ImportError:
+        return False
+    return True
+
+
 DISABLE_SECCOMP_BPF_FLAG = "--disable-seccomp-filter-sandbox"
 DISABLE_SECCOMP_BPF_ARGS = ["-s", "qt.chromium.sandboxing", "disable-seccomp-bpf"]
 
@@ -294,18 +303,15 @@ def _needs_map_discard_workaround(webengine_version: utils.VersionNumber) -> boo
     return libc_version >= affected_glibc and kernel_version >= affected_kernel
 
 
-def disable_seccomp_bpf_sandbox():
+
+def disable_seccomp_bpf_sandbox() -> bool:
     """Check whether we need to disable the seccomp BPF sandbox.
 
     This is needed for some QtWebEngine setups, with older Qt versions but
     newer kernels.
     """
-    try:
-        from qutebrowser.qt import webenginecore   # pylint: disable=unused-import
-    except ImportError:
-        # no QtWebEngine available
+    if not _has_qtwebengine():
         return False
-
     versions = version.qtwebengine_versions(avoid_init=True)
     return (
         versions.webengine == utils.VersionNumber(5, 15, 2)
@@ -313,6 +319,23 @@ def disable_seccomp_bpf_sandbox():
     )
 
 
+SOFTWARE_RENDERING_FLAG = "--disable-gpu"
+SOFTWARE_RENDERING_ARGS = ["-s", "qt.force_software_rendering", "chromium"]
+
+
+def use_software_rendering() -> bool:
+    """Check whether to enforce software rendering for tests."""
+    if not _has_qtwebengine():
+        return False
+
+    versions = version.qtwebengine_versions(avoid_init=True)
+    return (
+        # https://github.com/qutebrowser/qutebrowser/issues/8444#issuecomment-2569554046
+        # not on CI, but unknown how to tell apart affected / unaffected systems
+        versions.webengine == utils.VersionNumber(6, 9)
+    )
+
+
 def import_userscript(name):
     """Import a userscript via importlib.