Add filename if QtOSError is used with QFileDevice

If we have a filename available, let's add it to the error message.

This also effectively reverts 00747be9d3790534e8b32464605d1b5b6c2d6627 since
that's not needed anymore (Qt 5.7 is the oldest supported release).

2 files changed, 13 insertions, 12 deletions

diff --git a/qutebrowser/utils/qtutils.py b/qutebrowser/utils/qtutils.py
index 3e8afae3f..109d2dfed 100644
--- a/qutebrowser/utils/qtutils.py
+++ b/qutebrowser/utils/qtutils.py
@@ -35,7 +35,7 @@ import typing
 
 import pkg_resources
 from PyQt5.QtCore import (qVersion, QEventLoop, QDataStream, QByteArray,
-                          QIODevice, QSaveFile, QT_VERSION_STR,
+                          QIODevice, QFileDevice, QSaveFile, QT_VERSION_STR,
                           PYQT_VERSION_STR, QObject, QUrl)
 from PyQt5.QtGui import QColor
 from PyQt5.QtWidgets import QApplication
@@ -44,9 +44,6 @@ try:
 except ImportError:  # pragma: no cover
     qWebKitVersion = None  # type: ignore[assignment]  # noqa: N816
 
-if typing.TYPE_CHECKING:
-    from PyQt5.QtCore import QFileDevice
-
 from qutebrowser.misc import objects
 from qutebrowser.utils import usertypes
 
@@ -74,13 +71,17 @@ class QtOSError(OSError):
         if msg is None:
             msg = dev.errorString()
 
+        self.qt_errno = None  # type: typing.Optional[QFileDevice.FileError]
+        if isinstance(dev, QFileDevice):
+            msg = self._init_filedev(dev, msg)
+
         super().__init__(msg)
 
-        self.qt_errno = None  # type: typing.Optional[QFileDevice.FileError]
-        try:
-            self.qt_errno = dev.error()
-        except AttributeError:
-            pass
+    def _init_filedev(self, dev: QFileDevice, msg: str) -> str:
+        self.qt_errno = dev.error()
+        filename = dev.fileName()
+        msg += ": {!r}".format(filename)
+        return msg
 
 
 def version_check(version: str,
diff --git a/tests/unit/utils/test_qtutils.py b/tests/unit/utils/test_qtutils.py
index 150a03f6e..81d198946 100644
--- a/tests/unit/utils/test_qtutils.py
+++ b/tests/unit/utils/test_qtutils.py
@@ -467,9 +467,9 @@ class TestSavefileOpen:
         with pytest.raises(OSError) as excinfo:
             with qtutils.savefile_open(str(filename)):
                 pass
-        errors = ["Filename refers to a directory",  # Qt >= 5.4
-                  "Commit failed!"]  # older Qt versions
-        assert str(excinfo.value) in errors
+
+        msg = "Filename refers to a directory: {!r}".format(str(filename))
+        assert str(excinfo.value) == msg
         assert tmpdir.listdir() == [filename]
 
     def test_failing_flush(self, tmpdir):