Crash when applying tangent constraint #26734
Description
Problem description
Unfortunately, I have always had a lot of problem with attaching tangent lines and arcs to construction circles.
Now, I have made a minimum working example that crashes 1.1rc2 and 1.2.0dev weekly on my computer each time.
Sketcher: Two circles touching each other, connected by two lines. The lines are drawn with the tangent auto-constraint on one circle. When trying to apply the tangent constraint on the other circle, FreeCAD crashes. Sometimes it works on the first line, but crashes on the second line.
Workbench affected?
Sketcher
Steps to reproduce
Open the file, open the sketch.
Choose tangent constraint, click one of the lines and then the lower circle.
Expected behavior
Both lines should be applied tangent constraint with endpoint tangency.
Actual behavior
In this example, it works on the left line and endpoint tangency is applied. When I do the same on the right line, you just see my desktop background because FreeCAD has crashed.
Development version About Info (in Safe Mode)
OS: Fedora Linux 42 (Xfce) (XFCE/xfce/xcb)
Architecture: x86_64
Version: 1.2.0dev.20260106 (Git shallow) AppImage
Build date: 2026/01/06 15:36:19
Build type: Release
Branch: (HEAD detached at 9b64da8)
Hash: 9b64da827a112d88a025be26316e3d023ff491dc
Python 3.11.14, Qt 6.8.3, Coin 4.0.3, Vtk 9.3.1, boost 1_86, Eigen3 3.4.0, PySide 6.8.3
shiboken 6.8.3, xerces-c 3.3.0, IfcOpenShell 0.8.2, OCC 7.8.1
Locale: German/Germany (de_DE)
Navigation Style/Orbit Style/Rotation Mode: CAD/Rounded Arcball/Window center
Stylesheet/Theme/QtStyle: FreeCAD.qss/FreeCAD Dark/
Logical DPI/Physical DPI/Pixel Ratio: 96/101.6/1