[Problem] Sketcher: endpoint-to-endpoint tangent with the same B-Spline does not work

[AjinkyaDahale]

Is there an existing issue for this?

• I have searched the existing issues

Problem description

To reproduce:

1. Create a B-spline long enough that the end points are close to each other.
2. Select both endpoints and apply tangent constraint.

The constraint behaves simply as if it were a coincidence constraint.

Full version info

OS: Manjaro Linux (GNOME/gnome)
Word size of FreeCAD: 64-bit
Version: 0.22.0dev.36176 +4 (Git)
Build type: Release
Branch: sketcher-join-curves-2
Hash: a292bb447bc532af8068624791087503ebdba89e
Python 3.11.7, Qt 5.15.12, Coin 4.0.1, Vtk 9.3.0, OCC 7.7.2
Locale: English/United States (en_US)
Installed mods: 
  * Curves 0.5.12
  * Curves.backup1662220878.4365516 0.4.4
  * ExtremeProDark 2.5.3
  * ProDarkThemePreferencePack 1.0.0
  * ProDarkThemePreferencePack.backup1662220881.5889003 1.0.0

Subproject(s) affected?

Sketcher

Anything else?

The problem is that the same normal is used in constraint solving, since the points are coincident. Further, there is also a "reduction" step in planegcs solver that replaces the variables associated with the points' coordinates with a single variable (since there is an equality constraint), so there is no way of knowing which normal to use even with pointers.

Code of Conduct

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