Nuke the cache when the Qt version changed

https://bugreports.qt.io/browse/QTBUG-72532

qutebrowser/config/configfiles.py

@@ -30,7 +30,7 @@ import contextlib
 import typing
 
 import yaml
-from PyQt5.QtCore import pyqtSignal, QObject, QSettings
+from PyQt5.QtCore import pyqtSignal, QObject, QSettings, qVersion
 
 import qutebrowser
 from qutebrowser.config import configexc, config, configdata, configutils
@@ -55,6 +55,17 @@ class StateConfig(configparser.ConfigParser):
         super().__init__()
         self._filename = os.path.join(standarddir.data(), 'state')
         self.read(self._filename, encoding='utf-8')
+
+        qt_version = qVersion()
+        # We handle this here, so we can avoid setting qt_version_changed if
+        # the config is brand new, but can still set it when qt_version wasn't
+        # there before...
+        if 'general' in self:
+            old_qt_version = self['general'].get('qt_version', None)
+            self.qt_version_changed = old_qt_version != qt_version
+        else:
+            self.qt_version_changed = False
+
         for sect in ['general', 'geometry']:
             try:
                 self.add_section(sect)
@@ -65,6 +76,9 @@ class StateConfig(configparser.ConfigParser):
         for key in deleted_keys:
             self['general'].pop(key, None)
 
+        self['general']['qt_version'] = qt_version
+        self['general']['version'] = qutebrowser.__version__
+
     def init_save_manager(self,
                           save_manager: 'savemanager.SaveManager') -> None:
         """Make sure the config gets saved properly.
@@ -638,7 +652,6 @@ def init() -> None:
     """Initialize config storage not related to the main config."""
     global state
     state = StateConfig()
-    state['general']['version'] = qutebrowser.__version__
 
     # Set the QSettings path to something like
     # ~/.config/qutebrowser/qsettings/qutebrowser/qutebrowser.conf so it

qutebrowser/misc/backendproblem.py

@@ -26,6 +26,7 @@ import html
 import ctypes
 import ctypes.util
 import enum
+import shutil
 
 import attr
 from PyQt5.QtCore import Qt
@@ -33,8 +34,9 @@ from PyQt5.QtWidgets import (QApplication, QDialog, QPushButton, QHBoxLayout,
                              QVBoxLayout, QLabel, QMessageBox)
 from PyQt5.QtNetwork import QSslSocket
 
-from qutebrowser.config import config
-from qutebrowser.utils import usertypes, objreg, version, qtutils, log, utils
+from qutebrowser.config import config, configfiles
+from qutebrowser.utils import (usertypes, objreg, version, qtutils, log, utils,
+                               standarddir)
 from qutebrowser.misc import objects, msgbox
 
 
@@ -397,6 +399,29 @@ def _check_backend_modules():
     raise utils.Unreachable
 
 
+def _handle_cache_nuking():
+    """Nuke the QtWebEngine cache if the Qt version changed.
+
+    WORKAROUND for https://bugreports.qt.io/browse/QTBUG-72532
+    """
+    if not configfiles.state.qt_version_changed:
+        return
+
+    # Only nuke the cache in cases where we know there are problems.
+    # It seems these issues started with Qt 5.12.
+    # They should be fixed with Qt 5.12.5:
+    # https://codereview.qt-project.org/c/qt/qtwebengine-chromium/+/265408
+    affected = (qtutils.version_check('5.12', compiled=False) and not
+                qtutils.version_check('5.12.5', compiled=False))
+    if not affected:
+        return
+
+    log.init.info("Qt version changed, nuking QtWebEngine cache")
+    cache_dir = os.path.join(standarddir.cache(), 'webengine')
+    if os.path.exists(cache_dir):
+        shutil.rmtree(cache_dir)
+
+
 def init():
     """Check for various issues related to QtWebKit/QtWebEngine."""
     _check_backend_modules()
@@ -405,6 +430,7 @@ def init():
         _handle_wayland()
         _nvidia_shader_workaround()
         _handle_nouveau_graphics()
+        _handle_cache_nuking()
     else:
         assert objects.backend == usertypes.Backend.QtWebKit, objects.backend
         _handle_ssl_support(fatal=True)

tests/unit/config/test_configfiles.py

@@ -76,14 +76,48 @@ def autoconfig(config_tmpdir):
 
 
 @pytest.mark.parametrize('old_data, insert, new_data', [
-    (None, False, '[general]\n\n[geometry]\n\n'),
-    ('[general]\nfooled = true', False, '[general]\n\n[geometry]\n\n'),
-    ('[general]\nfoobar = 42', False,
-     '[general]\nfoobar = 42\n\n[geometry]\n\n'),
-    (None, True, '[general]\nnewval = 23\n\n[geometry]\n\n'),
+    (None,
+     False,
+     '[general]\n'
+     'qt_version = 5.6.7\n'
+     'version = 1.2.3\n'
+     '\n'
+     '[geometry]\n'
+     '\n'),
+    ('[general]\n'
+     'fooled = true',
+     False,
+     '[general]\n'
+     'qt_version = 5.6.7\n'
+     'version = 1.2.3\n'
+     '\n'
+     '[geometry]\n'
+     '\n'),
+    ('[general]\n'
+     'foobar = 42',
+     False,
+     '[general]\n'
+     'foobar = 42\n'
+     'qt_version = 5.6.7\n'
+     'version = 1.2.3\n'
+     '\n'
+     '[geometry]\n'
+     '\n'),
+    (None,
+     True,
+     '[general]\n'
+     'qt_version = 5.6.7\n'
+     'version = 1.2.3\n'
+     'newval = 23\n'
+     '\n'
+     '[geometry]\n'
+     '\n'),
 ])
-def test_state_config(fake_save_manager, data_tmpdir,
+def test_state_config(fake_save_manager, data_tmpdir, monkeypatch,
                       old_data, insert, new_data):
+    monkeypatch.setattr(configfiles.qutebrowser, '__version__', '1.2.3')
+    monkeypatch.setattr(configfiles, 'qVersion', lambda: '5.6.7')
+
     statefile = data_tmpdir / 'state'
     if old_data is not None:
         statefile.write_text(old_data, 'utf-8')
@@ -102,6 +136,28 @@ def test_state_config(fake_save_manager, data_tmpdir,
     fake_save_manager.add_saveable('state-config', unittest.mock.ANY)
 
 
+@pytest.mark.parametrize('old_version, new_version, changed', [
+    (None, '5.12.1', False),
+    ('5.12.1', '5.12.1', False),
+    ('5.12.2', '5.12.1', True),
+    ('5.12.1', '5.12.2', True),
+    ('5.13.0', '5.12.2', True),
+    ('5.12.2', '5.13.0', True),
+])
+def test_qt_version_changed(data_tmpdir, monkeypatch,
+                            old_version, new_version, changed):
+    monkeypatch.setattr(configfiles, 'qVersion', lambda: new_version)
+
+    statefile = data_tmpdir / 'state'
+    if old_version is not None:
+        data = ('[general]\n'
+                'qt_version = {}'.format(old_version))
+        statefile.write_text(data, 'utf-8')
+
+    state = configfiles.StateConfig()
+    assert state.qt_version_changed == changed
+
+
 class TestYaml:
 
     pytestmark = pytest.mark.usefixtures('config_tmpdir')