Add stop-gap measure for sessions with Qt 5.15

See #5359

doc/changelog.asciidoc

@@ -40,6 +40,8 @@ Added
 Changed
 ~~~~~~~
 
+- First adaptions to Qt 5.15, including a stop-gap measure for session loading
+  not working properly with it.
 - Searching now wraps around the page by default with QtWebKit (where it didn't
   before). Set `search.wrap` to `false` to restore the old behavior.
 - The `{}` placeholder for search engines (the `url.searchengines` setting) now
@@ -58,7 +60,6 @@ Changed
     data.
 - The `dictcli.py` script now shows better error messages.
 - Various improvements to the `mkvenv.py` script (mainly useful for development).
-- First adoptions to Qt 5.15.
 - Minor performance improvements.
 
 Deprecated

qutebrowser/app.py

@@ -336,6 +336,10 @@ def _open_special_pages(args):
         ('old-qt-warning-shown',
          not qtutils.version_check('5.11'),
          'qute://warning/old-qt'),
+
+        ('session-warning-shown',
+         qtutils.version_check('5.15', compiled=False),
+         'qute://warning/sessions'),
     ]
 
     for state, condition, url in pages:

qutebrowser/browser/qutescheme.py

@@ -47,7 +47,7 @@
 from qutebrowser.browser import pdfjs, downloads, history
 from qutebrowser.config import config, configdata, configexc, configdiff
 from qutebrowser.utils import (version, utils, jinja, log, message, docutils,
-                               objreg, urlutils)
+                               objreg, urlutils, standarddir)
 from qutebrowser.qt import sip
 
 
@@ -576,6 +576,11 @@ def qute_warning(url):
     elif path == '/webkit':
         src = jinja.render('warning-webkit.html',
                            title='QtWebKit backend warning')
+    elif path == '/sessions':
+        src = jinja.render('warning-sessions.html',
+                           title='Qt 5.15 sessions warning',
+                           datadir=standarddir.data(),
+                           sep=os.sep)
     else:
         raise NotFoundError("Invalid warning page {}".format(path))
     return 'text/html', src

qutebrowser/browser/webengine/webenginetab.py

@@ -645,6 +645,12 @@ def deserialize(self, data):
         qtutils.deserialize(data, self._history)
 
     def load_items(self, items):
+        if qtutils.version_check('5.15', compiled=False):
+            # WORKAROUND for https://github.com/qutebrowser/qutebrowser/issues/5359
+            if items:
+                self._tab.load_url(items[-1].url)
+            return
+
         if items:
             self._tab.before_load_started.emit(items[-1].url)
 

qutebrowser/html/warning-sessions.html

@@ -0,0 +1,21 @@
+{% extends "styled.html" %}
+
+{% block content %}
+<h1>{{ title }}</h1>
+<span class="note">Note this warning will only appear once. Use <span class="mono">:open
+qute://warning/sessions</span> to show it again at a later time.</span>
+
+<p>You're using qutebrowser with Qt 5.15.</p>
+
+<p>Since Qt doesn't provide an API to load the history of a tab, qutebrowser relies on a reverse-engineered binary serialization format to load tab history from session files. With Qt 5.15, unfortunately that format changed (due to the underlying Chromium upgrade), in a way which makes it impossible for qutebrowser to load tab history from existing session data.</p>
+
+<p>At the time of writing (April 2020), a new session format which stores part of the needed binary data in saved sessions is <a href="https://github.com/qutebrowser/qutebrowser/issues/5359">in development</a> and will be released with qutebrowser v1.12.0.</p>
+
+<p>As a stop-gap measure:</p>
+
+<ul>
+    <li>Loading a session with this release will <b>only load the most recently opened page</b> for every tab. As a result, the back/forward-history of every tab <b>will be lost</b> as soon as the session is saved again.</li>
+    <li>A one-time backup of the session folder has been created at <span class="mono">{{ datadir }}{{ sep }}sessions{{ sep }}before-qt-515</span>.</li>
+</ul>
+
+{% endblock %}

qutebrowser/misc/sessions.py

@@ -24,6 +24,8 @@
 import itertools
 import urllib
 import typing
+import glob
+import shutil
 
 from PyQt5.QtCore import QUrl, QObject, QPoint, QTimer, pyqtSlot
 from PyQt5.QtWidgets import QApplication
@@ -59,6 +61,16 @@ def init(parent=None):
         parent: The parent to use for the SessionManager.
     """
     base_path = os.path.join(standarddir.data(), 'sessions')
+
+    # WORKAROUND for https://github.com/qutebrowser/qutebrowser/issues/5359
+    backup_path = os.path.join(base_path, 'before-qt-515')
+    if (os.path.exists(base_path) and
+            not os.path.exists(backup_path) and
+            qtutils.version_check('5.15', compiled=False)):
+        os.mkdir(backup_path)
+        for filename in glob.glob(os.path.join(base_path, '*.yml')):
+           shutil.copy(filename, backup_path)
+
     try:
         os.mkdir(base_path)
     except FileExistsError: