From 563d9ca2f3f20be169caad403cc9fcc3f2134150 Mon Sep 17 00:00:00 2001
From: Kovid Goyal <kovid@kovidgoyal.net>
Date: Sun, 21 Nov 2021 20:46:08 +0530
Subject: [PATCH] Restore QModelIndex::child

---
 src/calibre/gui2/pyqt6_compat.py         | 6 +++++-
 src/calibre/gui2/tweak_book/file_list.py | 5 +++--
 2 files changed, 8 insertions(+), 3 deletions(-)

diff --git a/src/calibre/gui2/pyqt6_compat.py b/src/calibre/gui2/pyqt6_compat.py
index a9d5615753..3fc293c602 100644
--- a/src/calibre/gui2/pyqt6_compat.py
+++ b/src/calibre/gui2/pyqt6_compat.py
@@ -8,7 +8,7 @@
 
 from qt.core import (
     QAction, QDialog, QDrag, QEventLoop, QMenu, QMessageBox, QSinglePointEvent,
-    QThread
+    QThread, QModelIndex
 )
 
 from calibre_extensions import progress_indicator
@@ -36,3 +36,7 @@ QMessageBox.exec_ = QMessageBox.exec
 # Restore ability to associate a menu with an action
 QAction.setMenu = lambda self, menu: progress_indicator.set_menu_on_action(self, menu)
 QAction.menu = lambda self, menu: progress_indicator.menu_for_action(self)
+
+
+# Restore QModelIndex child
+QModelIndex.child = lambda self, row, column: self.model().index(row, column, self)
diff --git a/src/calibre/gui2/tweak_book/file_list.py b/src/calibre/gui2/tweak_book/file_list.py
index b2da9aef81..3a2ebb5baa 100644
--- a/src/calibre/gui2/tweak_book/file_list.py
+++ b/src/calibre/gui2/tweak_book/file_list.py
@@ -173,8 +173,9 @@ class ItemDelegate(QStyledItemDelegate):  # {{{
 
         if hover:
             if top_level:
-                count = index.model().rowCount(index)
-                total_size = human_readable(sum(safe_size(index.child(r, 0)) for r in range(count)))
+                m = index.model()
+                count = m.rowCount(index)
+                total_size = human_readable(sum(safe_size(m.index(r, 0, index)) for r in range(count)))
                 suffix = f'{NBSP}{count}@{total_size}'
             else:
                 suffix = NBSP + human_readable(safe_size(index))