From b3bd225a641fef1802f475c677603d5444bdf0f8 Mon Sep 17 00:00:00 2001
From: PaddleStroke <pierrelouis.boyer@gmail.com>
Date: Fri, 18 Jul 2025 16:53:35 +0200
Subject: [PATCH] Assembly: Fix crash 20614 (#22538)

---
 src/Mod/Assembly/App/AssemblyObject.cpp | 24 +++++++++++++++++++++++-
 src/Mod/Assembly/App/AssemblyObject.h   |  2 ++
 2 files changed, 25 insertions(+), 1 deletion(-)

diff --git a/src/Mod/Assembly/App/AssemblyObject.cpp b/src/Mod/Assembly/App/AssemblyObject.cpp
index b7318f0938..07fc236247 100644
--- a/src/Mod/Assembly/App/AssemblyObject.cpp
+++ b/src/Mod/Assembly/App/AssemblyObject.cpp
@@ -1334,7 +1334,7 @@ AssemblyObject::makeMbdJoint(App::DocumentObject* joint)
     JointType jointType = getJointType(joint);
 
     std::shared_ptr<ASMTJoint> mbdJoint = makeMbdJointOfType(joint, jointType);
-    if (!mbdJoint) {
+    if (!mbdJoint || !isMbDJointValid(joint)) {
         return {};
     }
 
@@ -1724,6 +1724,28 @@ int AssemblyObject::slidingPartIndex(App::DocumentObject* joint)
     return slidingFound;
 }
 
+bool AssemblyObject::isMbDJointValid(App::DocumentObject* joint)
+{
+    // When dragging a part, we are bundling fixed parts together.
+    // This may lead to a conflicting joint that is self referencing a MbD part.
+    // The solver crash when fed such a bad joint. So we make sure it does not happen.
+    App::DocumentObject* part1 = getMovingPartFromRef(this, joint, "Reference1");
+    App::DocumentObject* part2 = getMovingPartFromRef(this, joint, "Reference2");
+    if (!part1 || !part2) {
+        return false;
+    }
+
+    // If this joint is self-referential it must be ignored.
+    if (getMbDPart(part1) == getMbDPart(part2)) {
+        Base::Console().warning(
+            "Assembly: Ignoring joint (%s) because its parts are connected by a fixed "
+            "joint bundle. This joint is a conflicting or redundant constraint.\n",
+            joint->getFullLabel());
+        return false;
+    }
+    return true;
+}
+
 AssemblyObject::MbDPartData AssemblyObject::getMbDData(App::DocumentObject* part)
 {
     auto it = objectPartMap.find(part);
diff --git a/src/Mod/Assembly/App/AssemblyObject.h b/src/Mod/Assembly/App/AssemblyObject.h
index acf19f668b..af63b31e1c 100644
--- a/src/Mod/Assembly/App/AssemblyObject.h
+++ b/src/Mod/Assembly/App/AssemblyObject.h
@@ -188,6 +188,8 @@ public:
 
     std::vector<App::DocumentObject*> getMotionsFromSimulation(App::DocumentObject* sim);
 
+    bool isMbDJointValid(App::DocumentObject* joint);
+
 private:
     std::shared_ptr<MbD::ASMTAssembly> mbdAssembly;