Sketcher: Only autoscale if the datum being edited is the scale defining datum (#22419)

src/Mod/Sketcher/App/SketchObject.cpp

@@ -7600,21 +7600,21 @@ int SketchObject::getGeoIdFromCompleteGeometryIndex(int completeGeometryIndex) c
     else
         return (completeGeometryIndex - completeGeometryCount);
 }
-bool SketchObject::hasSingleScaleDefiningConstraint() const
+int SketchObject::getSingleScaleDefiningConstraint() const
 {
     const std::vector<Constraint*>& vals = this->Constraints.getValues();
 
-    bool foundOne = false;
-    for (auto val : vals) {
+    int found = -1;
+    for (size_t i = 0; i < vals.size(); ++i) {
         // An angle does not define scale
-        if (val->isDimensional() && val->Type != Angle) {
-            if (foundOne) {
-                return false;
+        if (vals[i]->isDimensional() && vals[i]->Type != Angle) {
+            if (found != -1) { // More than one scale defining constraint
+                return -1;
             }
-            foundOne = true;
+            found = i;
         }
     }
-    return foundOne;
+    return found;
 }
 
 std::unique_ptr<const GeometryFacade> SketchObject::getGeometryFacade(int GeoId) const

src/Mod/Sketcher/App/SketchObject.h

@@ -272,7 +272,9 @@ public:
 
     int getGeoIdFromCompleteGeometryIndex(int completeGeometryIndex) const;
 
-    bool hasSingleScaleDefiningConstraint() const;
+    // Returns the index of the scale defining constraint if
+    // there is only one and -1 otherwise
+    int getSingleScaleDefiningConstraint() const;
 
     /// returns non zero if the sketch contains conflicting constraints
     int hasConflicts() const;

src/Mod/Sketcher/Gui/EditDatumDialog.cpp

@@ -409,8 +409,15 @@ void EditDatumDialog::performAutoScale(double newDatum)
          || (autoScaleMode
                  == static_cast<int>(SketcherGui::AutoScaleMode::WhenNoScaleFeatureIsVisible)
              && !hasVisualFeature(sketch, nullptr, Gui::Application::Instance->activeDocument())))
-        && sketch->getExternalGeometryCount() <= 2 && sketch->hasSingleScaleDefiningConstraint()) {
+        && sketch->getExternalGeometryCount() <= 2) {
         try {
+            // Handle the case where multiple datum constraints are present but only one is scale
+            // defining e.g. a bunch of angle constraints and a single length constraint
+            int scaleDefiningConstraint = sketch->getSingleScaleDefiningConstraint();
+            if (scaleDefiningConstraint != ConstrNbr) {
+                return;
+            }
+
             double oldDatum = sketch->getDatum(ConstrNbr);
             double scaleFactor = newDatum / oldDatum;
             float initLabelDistance = sketch->Constraints[ConstrNbr]->LabelDistance;