Add a decorator to prevent Exceptions (to prevent segfaults).

qutebrowser/browser/webpage.py

@@ -30,7 +30,8 @@ from PyQt5.QtWebKitWidgets import QWebPage
 
 from qutebrowser.config import config
 from qutebrowser.network import networkmanager
-from qutebrowser.utils import message, usertypes, log, http, jinja, qtutils
+from qutebrowser.utils import (message, usertypes, log, http, jinja, qtutils,
+                               utils)
 
 
 class BrowserPage(QWebPage):
@@ -223,6 +224,9 @@ class BrowserPage(QWebPage):
         """
         return ext in self._extension_handlers
 
+    # WORKAROUND for:
+    # http://www.riverbankcomputing.com/pipermail/pyqt/2014-August/034722.html
+    @utils.prevent_exceptions(False, PYQT_VERSION < 0x50302)
     def extension(self, ext, opt, out):
         """Override QWebPage::extension to provide error pages.
 
@@ -235,28 +239,11 @@ class BrowserPage(QWebPage):
             Handler return value.
         """
         try:
-            try:
+            handler = self._extension_handlers[ext]
-                handler = self._extension_handlers[ext]
+        except KeyError:
-            except KeyError:
+            log.webview.warning("Extension {} not supported!".format(ext))
-                log.webview.warning("Extension {} not supported!".format(ext))
+            return super().extension(ext, opt, out)
-                return super().extension(ext, opt, out)
+        return handler(opt, out)
-            return handler(opt, out)
-        except:  # pylint: disable=bare-except
-            if PYQT_VERSION >= 0x50302:
-                raise
-            else:
-                # WORKAROUND:
-                #
-                # Due to a bug in PyQt, exceptions inside extension() get
-                # swallowed:
-                # http://www.riverbankcomputing.com/pipermail/pyqt/2014-August/034722.html
-                #
-                # We used to re-raise the exception with a single-shot QTimer
-                # here, but that lead to a strange proble with a KeyError with
-                # some random jinja template stuff as content. For now, we only
-                # log it, so it doesn't pass 100% silently.
-                log.webview.exception("Error inside WebPage::extension")
-                return False
 
     def javaScriptAlert(self, _frame, msg):
         """Override javaScriptAlert to use the statusbar."""

qutebrowser/utils/utils.py

@@ -35,7 +35,7 @@ from PyQt5.QtGui import QKeySequence, QColor
 import pkg_resources
 
 import qutebrowser
-from qutebrowser.utils import qtutils
+from qutebrowser.utils import qtutils, log
 
 
 def elide(text, length):
@@ -494,3 +494,59 @@ def disabled_excepthook():
     # unchanged. Otherwise, we reset it.
     if sys.excepthook is sys.__excepthook__:
         sys.excepthook = old_excepthook
+
+
+class prevent_exceptions:  # pylint: disable=invalid-name
+
+    """Decorator to ignore and log exceptions.
+
+    This needs to be used for some places where PyQt segfaults on exceptions or
+    silently ignores them.
+
+    We used to re-raise the exception with a single-shot QTimer in a similiar
+    case, but that lead to a strange proble with a KeyError with some random
+    jinja template stuff as content. For now, we only log it, so it doesn't
+    pass 100% silently.
+
+    This could also be a function, but as a class (with a "wrong" name) it's
+    much cleaner to implement.
+
+    Attributes:
+        retval: The value to return in case of an exception.
+        predicate: The condition which needs to be True to prevent exceptions
+    """
+
+    def __init__(self, retval, predicate=True):
+        """Save decorator arguments.
+
+        Gets called on parse-time with the decorator arguments.
+
+        Args:
+            See class attributes.
+        """
+        self.retval = retval
+        self.predicate = predicate
+
+    def __call__(self, func):
+        """Gets called when a function should be decorated.
+
+        Args:
+            func: The function to be decorated.
+
+        Return:
+            The decorated function.
+        """
+        if not self.predicate:
+            return func
+
+        retval = self.retval
+
+        @functools.wraps(func)
+        def wrapper(*args, **kwargs):
+            try:
+                return func(*args, **kwargs)
+            except BaseException:
+                log.misc.exception("Error in {}".format(func.__qualname__))
+                return retval
+
+        return wrapper