Skip invalid history items when saving a session

Opening a download in a new tab leaves a "dead" tab (see example of a "dead" tab below)
behind. When saving a session containing such a "dead" tab, we end up with entries in
the session like this one:
```yaml
  - active: true
    history:
    - active: true
      last_visited: '1970-01-01T02:00:00'
      pinned: false
      scroll-pos:
        x: 0
        y: 0
      title: ''
      url: ''
      zoom: 1.0
```

When loading a session containing such a "dead" tab, qutebrowser does not restore any
history of that session and logs the following error:
```
ERROR: Failed to load session default: PyQt6.QtCore.QUrl('') is not valid
```

As pointed out by @The-Compiler in this comment[1], the behavior of
`QWebEngineHistoryItem::isValid()`[2] changed somehow between Qt 6.4 and 6.5.
`QWebEngineHistoryItem::isValid()` now returns `True` for "dead" tabs, even though the
history item is not valid (i.e. `url().isValid()` returns `False`).

To fix this we simply add an additional check if the URL is valid before adding a tab to
the session to be saved.

[1] https://github.com/qutebrowser/qutebrowser/issues/7696#issuecomment-1672854592
[2] https://github.com/qt/qtwebengine/blob/v6.5.2/src/core/api/qwebenginehistory.cpp#L69-L75

2 files changed, 27 insertions, 0 deletions

diff --git a/qutebrowser/misc/sessions.py b/qutebrowser/misc/sessions.py
index da447c747..dd63904cd 100644
--- a/qutebrowser/misc/sessions.py
+++ b/qutebrowser/misc/sessions.py
@@ -239,6 +239,13 @@ class SessionManager(QObject):
         for idx, item in enumerate(history):
             qtutils.ensure_valid(item)
             item_data = self._save_tab_item(tab, idx, item)
+
+            if not item.url().isValid():
+                # WORKAROUND Qt 6.5 regression
+                # https://github.com/qutebrowser/qutebrowser/issues/7696
+                log.sessions.debug(f"Skipping invalid history item: {item}")
+                continue
+
             if item.url().scheme() == 'qute' and item.url().host() == 'back':
                 # don't add qute://back to the session file
                 if item_data.get('active', False) and data['history']:
diff --git a/tests/end2end/features/sessions.feature b/tests/end2end/features/sessions.feature
index a5533f014..9a61baf61 100644
--- a/tests/end2end/features/sessions.feature
+++ b/tests/end2end/features/sessions.feature
@@ -328,6 +328,26 @@ Feature: Saving and loading sessions
                 - active: true
                   url: http://localhost:*/data/numbers/5.txt
 
+  # https://github.com/qutebrowser/qutebrowser/issues/7696
+  @qtwebkit_skip
+  Scenario: Saving session with an empty download tab
+    When I open data/downloads/downloads.html
+    And I run :click-element --force-event -t tab id download
+    And I wait for "Asking question <qutebrowser.utils.usertypes.Question default='*' mode=<PromptMode.download: 5> *" in the log
+    And I run :mode-leave
+    And I run :session-save current
+    And I run :session-load --clear current
+    And I wait until data/downloads/downloads.html is loaded
+    Then the session should look like:
+      windows:
+        - tabs:
+          - history:
+            - active: true
+              title: Simple downloads
+              url: http://localhost:*/data/downloads/downloads.html
+          - active: true
+            history: []
+
   # :session-delete
 
   Scenario: Deleting a directory