Fix retrying downloads with QtWebEngine

Fixes #2298

CHANGELOG.asciidoc

@@ -34,6 +34,7 @@ Fixed
 
 - Added a workaround for a black screen with QtWebEngine with some setups
   (requires PyOpenGL to be installed)
+- Fixed crash when trying to retry downloads with QtWebEngine
 
 v0.10.1
 -------

qutebrowser/browser/downloads.py

@@ -507,6 +507,14 @@ class AbstractDownloadItem(QObject):
         """Retry a failed download."""
         raise NotImplementedError
 
+    @pyqtSlot()
+    def try_retry(self):
+        """Try to retry a download and show an error if it's unsupported."""
+        try:
+            self.retry()
+        except UnsupportedOperationError as e:
+            message.error(str(e))
+
     def _get_open_filename(self):
         """Get the filename to open a download.
 
@@ -968,7 +976,7 @@ class DownloadModel(QAbstractListModel):
                 raise cmdexc.CommandError("No failed downloads!")
             else:
                 download = to_retry[0]
-        download.retry()
+        download.try_retry()
 
     def can_clear(self):
         """Check if there are finished downloads to clear."""

qutebrowser/browser/downloadview.py

@@ -134,7 +134,7 @@ class DownloadView(QListView):
             if item.successful:
                 actions.append(("Open", item.open_file))
             else:
-                actions.append(("Retry", item.retry))
+                actions.append(("Retry", item.try_retry))
             actions.append(("Remove", item.remove))
         else:
             actions.append(("Cancel", item.cancel))

qutebrowser/browser/webengine/webenginedownloads.py

@@ -95,7 +95,8 @@ class DownloadItem(downloads.AbstractDownloadItem):
 
     def retry(self):
         # https://bugreports.qt.io/browse/QTBUG-56840
-        raise downloads.UnsupportedOperationError
+        raise downloads.UnsupportedOperationError(
+            "Retrying downloads is unsupported with QtWebEngine")
 
     def _get_open_filename(self):
         return self._filename

tests/end2end/features/downloads.feature

@@ -137,6 +137,14 @@ Feature: Downloading things from a website.
             does-not-exist
             does-not-exist
 
+    @qtwebkit_skip
+    Scenario: Retrying a failed download with QtWebEngine
+        When I open data/downloads/issue2298.html
+        And I run :click-element id download
+        And I wait for "Download error: *" in the log
+        And I run :download-retry
+        Then the error "Retrying downloads is unsupported with QtWebEngine" should be shown
+
     Scenario: Retrying with count
         When I run :download http://localhost:(port)/data/downloads/download.bin
         And I run :download http://localhost:(port)/does-not-exist