From 887c8d3bdf55e05d4ff8fed6e3b56321fd4cc6b9 Mon Sep 17 00:00:00 2001
From: tetektoza <tetektoza@gmail.com>
Date: Wed, 7 Jan 2026 20:59:02 +0100
Subject: [PATCH] Sketcher: Fix crash when applying constraints during
 selection batching

Currently, the selection batching optimization introduced in #26663
stores ElementItem/ConstraintItem pointers in a buffer to be processed
on the next event loop cycle via `QTimer::singleShot`.

When a constraint is applied,
`slotElementsChanged()/slotConstraintsChanged()`
rebuilds the list widget, destroying all items. However, the selection
buffer was not cleared, leaving dangling pointers. When
`processSelectionBuffer()`
executed, it attempted to call `QListWidget::row()` on deleted items,
causing a segmentation fault.

So, this patch fixes it by clearing `selectionBuffer` when the list is
rebuilt, since the buffered pointers are invalidated anyway.
---
 src/Mod/Sketcher/Gui/TaskSketcherConstraints.cpp | 1 +
 src/Mod/Sketcher/Gui/TaskSketcherElements.cpp    | 1 +
 2 files changed, 2 insertions(+)

diff --git a/src/Mod/Sketcher/Gui/TaskSketcherConstraints.cpp b/src/Mod/Sketcher/Gui/TaskSketcherConstraints.cpp
index caa6c178c6..2fa922bcfc 100644
--- a/src/Mod/Sketcher/Gui/TaskSketcherConstraints.cpp
+++ b/src/Mod/Sketcher/Gui/TaskSketcherConstraints.cpp
@@ -1708,6 +1708,7 @@ void TaskSketcherConstraints::slotConstraintsChanged()
     assert(sketchView);
 
     constraintMap.clear();
+    selectionBuffer.clear();
 
     // Build up ListView with the constraints
     const Sketcher::SketchObject* sketch = sketchView->getSketchObject();
diff --git a/src/Mod/Sketcher/Gui/TaskSketcherElements.cpp b/src/Mod/Sketcher/Gui/TaskSketcherElements.cpp
index 98d5cefe6d..095c67b632 100644
--- a/src/Mod/Sketcher/Gui/TaskSketcherElements.cpp
+++ b/src/Mod/Sketcher/Gui/TaskSketcherElements.cpp
@@ -1875,6 +1875,7 @@ void TaskSketcherElements::slotElementsChanged()
 
     ui->listWidgetElements->clear();
     elementMap.clear();
+    selectionBuffer.clear();
 
     using GeometryState = ElementItem::GeometryState;