Sketcher: Fix loss of expression on trim (FreeCAD#27505)

Author: PaddleStroke

src/Mod/Sketcher/App/SketchObject.cpp

@@ -3361,7 +3361,8 @@ void createNewConstraintsForTrim(
     const std::vector<const Part::Geometry*> newGeos,
     std::vector<int>& idsOfOldConstraints,
     std::vector<Constraint*>& newConstraints,
-    std::set<int, std::greater<>>& geoIdsToBeDeleted
+    std::set<int, std::greater<>>& geoIdsToBeDeleted,
+    std::map<Constraint*, int>& newToOldConstraintMap
 )
 {
     const auto& allConstraints = obj->Constraints.getValues();
@@ -3386,6 +3387,7 @@ void createNewConstraintsForTrim(
                 PointPos::end
             )) {
             newConstraints.push_back(newConstr.release());
+            newToOldConstraintMap[newConstraints.back()] = oldConstrId;  // Map new to old
             isPoint1ConstrainedOnGeoId1 = true;
             continue;
         }
@@ -3399,6 +3401,7 @@ void createNewConstraintsForTrim(
                 PointPos::start
             )) {
             newConstraints.push_back(newConstr.release());
+            newToOldConstraintMap[newConstraints.back()] = oldConstrId;  // Map new to old
             isPoint2ConstrainedOnGeoId2 = true;
             continue;
         }
@@ -3408,7 +3411,12 @@ void createNewConstraintsForTrim(
             continue;
         }
         // constraint has not yet been changed
+        size_t sizeBefore = newConstraints.size();
         obj->deriveConstraintsForPieces(GeoId, newIds, newGeos, con, newConstraints);
+        // Map all newly added derived constraints to the old ID
+        for (size_t i = sizeBefore; i < newConstraints.size(); ++i) {
+            newToOldConstraintMap[newConstraints[i]] = oldConstrId;
+        }
     }
 
     // Add point-on-object/coincidence constraints with the newly exposed points.
@@ -3518,6 +3526,7 @@ int SketchObject::trim(int GeoId, const Base::Vector3d& point)
     std::vector<int> newIds;
     std::vector<Part::Geometry*> newGeos;
     std::vector<const Part::Geometry*> newGeosAsConsts;
+    std::map<Constraint*, int> newToOldConstraintMap;
 
     switch (paramsOfNewGeos.size()) {
         case 0: {
@@ -3580,7 +3589,8 @@ int SketchObject::trim(int GeoId, const Base::Vector3d& point)
         newGeosAsConsts,
         idsOfOldConstraints,
         newConstraints,
-        geoIdsToBeDeleted
+        geoIdsToBeDeleted,
+        newToOldConstraintMap
     );
 
     //******************* Step D => Replacing geometries and constraints
@@ -3599,6 +3609,16 @@ int SketchObject::trim(int GeoId, const Base::Vector3d& point)
         addConstraint(std::move(newConstr));
     };
 
+    std::map<Constraint*, std::shared_ptr<App::Expression>> exprBackup;
+    for (auto const& [newConstr, oldId] : newToOldConstraintMap) {
+        if (oldId >= 0 && oldId < (int)allConstraints.size()) {
+            auto exprInfo = getExpression(Constraints.createPath(oldId));
+            if (exprInfo.expression) {
+                exprBackup[newConstr] = std::shared_ptr<App::Expression>(exprInfo.expression->copy());
+            }
+        }
+    }
+
     delConstraints(std::move(idsOfOldConstraints), DeleteOption::NoFlag);
 
     if (!isOriginalCurvePeriodic) {
@@ -3652,7 +3672,17 @@ int SketchObject::trim(int GeoId, const Base::Vector3d& point)
         return constr->Type == ConstraintType::None;
     });
     delGeometries(geoIdsToBeDeleted.begin(), geoIdsToBeDeleted.end());
-    addConstraints(newConstraints);
+
+    int lastAddedIndex = addConstraints(newConstraints);
+    int firstAddedIndex = lastAddedIndex - (int)newConstraints.size() + 1;
+
+    // Restore expressions
+    for (int i = 0; i < (int)newConstraints.size(); ++firstAddedIndex, ++i) {
+        auto it = exprBackup.find(newConstraints[i]);
+        if (it != exprBackup.end()) {
+            setExpression(Constraints.createPath(firstAddedIndex), it->second);
+        }
+    }
 
     if (noRecomputes) {
         solve();