Assembly: Prevent crash when toggling rigid of grounded sub assembly (#24761)

* Assembly: Prevent crash when toggling rigid of grounded sub assembly

* to squash

* to squash

* Update AssemblyLink.cpp

src/Mod/Assembly/App/AssemblyLink.cpp

@@ -101,6 +101,26 @@ void AssemblyLink::onChanged(const App::Property* prop)
     if (prop == &Rigid) {
         Base::Placement movePlc;
 
+        // A flexible sub-assembly cannot be grounded.
+        // If a rigid sub-assembly has an object that is grounded, we also remove it.
+        auto groundedJoints = getParentAssembly()->getGroundedJoints();
+        for (auto* joint : groundedJoints) {
+            auto* propObj =
+                dynamic_cast<App::PropertyLink*>(joint->getPropertyByName("ObjectToGround"));
+            if (!propObj) {
+                continue;
+            }
+            auto* groundedObj = propObj->getValue();
+            if (auto* linkElt = dynamic_cast<App::LinkElement*>(groundedObj)) {
+                // hasObject does not handle link groups so we must handle it manually.
+                groundedObj = linkElt->getLinkGroup();
+            }
+
+            if (Rigid.getValue() ? hasObject(groundedObj) : groundedObj == this) {
+                getDocument()->removeObject(joint->getNameInDocument());
+            }
+        }
+
         if (Rigid.getValue()) {
             // movePlc needs to be computed before updateContents.
             App::DocumentObject* firstLink = nullptr;

src/Mod/Assembly/App/AssemblyObject.cpp

@@ -781,6 +781,11 @@ std::unordered_set<App::DocumentObject*> AssemblyObject::getGroundedParts()
         if (propObj) {
             App::DocumentObject* objToGround = propObj->getValue();
             if (objToGround) {
+                if (auto* asmLink = dynamic_cast<AssemblyLink*>(objToGround)) {
+                    if (!asmLink->isRigid()) {
+                        continue;
+                    }
+                }
                 groundedSet.insert(objToGround);
             }
         }

src/Mod/Assembly/Gui/ViewProviderAssembly.cpp

@@ -628,6 +628,12 @@ bool ViewProviderAssembly::canDragObjectIn3d(App::DocumentObject* obj) const
         return false;
     }
 
+    if (auto* asmLink = dynamic_cast<Assembly::AssemblyLink*>(obj)) {
+        if (!asmLink->isRigid()) {
+            return false;
+        }
+    }
+
     auto* assemblyPart = getObject<AssemblyObject>();
 
     // Check if the selected object is a child of the assembly