Disable QtNetwork cache on Qt 5.8

See #2427

CHANGELOG.asciidoc

@@ -37,6 +37,8 @@ Changed
 - PAC on QtWebKit now supports SOCKS5 as type.
 - Comments in the config file are now before the individual
   options instead of being before sections.
+- The HTTP cache is disabled with QtWebKit on Qt 5.8 now as it leads to frequent
+  crashes due to a Qt bug.
 
 Fixed
 ~~~~~

qutebrowser/browser/webkit/cache.py

@@ -25,7 +25,7 @@ from PyQt5.QtCore import pyqtSlot
 from PyQt5.QtNetwork import QNetworkDiskCache, QNetworkCacheMetaData
 
 from qutebrowser.config import config
-from qutebrowser.utils import utils, objreg
+from qutebrowser.utils import utils, objreg, qtutils
 
 
 class DiskCache(QNetworkDiskCache):
@@ -53,6 +53,9 @@ class DiskCache(QNetworkDiskCache):
         size = config.get('storage', 'cache-size')
         if size is None:
             size = 1024 * 1024 * 50  # default from QNetworkDiskCachePrivate
+        # WORKAROUND for https://github.com/qutebrowser/qutebrowser/issues/2427
+        if qtutils.version_check('5.8', exact=True):
+            size = 0
         self.setMaximumCacheSize(size)
 
     def _maybe_activate(self):