Modeling - Fix segfault in ChFi3d_Builder::IntersectMoreCorner (#1163)

Add null guards for two crash sites in IntersectMoreCorner where
topology map lookups can fail on shapes from prior boolean/chamfer
operations due to stale TShape pointers:

- Move Arcprol null check before cherche_face call (was after it,
  causing misleading exception on null edge argument).
- Add Arcprolbis null check before use in BRep_Tool::Parameter,
  which dereferences null TShape pointer causing segfault.

Both exceptions are caught by ChFi3d_Builder::Compute() and result
in graceful IsDone() == false instead of crash.

Add regression GTests for chamfer after boolean fusion and
sequential chamfer operations.

src/ModelingAlgorithms/TKFillet/ChFi3d/ChFi3d_Builder_C1.cxx

@@ -2890,12 +2890,14 @@ void ChFi3d_Builder::PerformIntersectionAtEnd(const int Index)
     }
     TopOpeBRepDS_Curve tcurv3d(Cc, tolreached);
     indcurve[nb - 1] = DStr.AddCurve(tcurv3d);
-    Interfp1         = ChFi3d_FilPointInDS(TopAbs_FORWARD,
+
+    Interfp1 = ChFi3d_FilPointInDS(TopAbs_FORWARD,
                                    indcurve[nb - 1],
                                    indpoint1,
                                    Cc->FirstParameter(),
                                    Isvtx1);
-    Interfp2         = ChFi3d_FilPointInDS(TopAbs_REVERSED,
+
+    Interfp2 = ChFi3d_FilPointInDS(TopAbs_REVERSED,
                                    indcurve[nb - 1],
                                    indpoint2,
                                    Cc->LastParameter(),
@@ -4401,6 +4403,10 @@ void ChFi3d_Builder::IntersectMoreCorner(const int Index)
       }
     }
 
+    // Guard: Arcprol may be null if the loop above found no matching edge.
+    if (Arcprol.IsNull())
+      throw StdFail_NotDone("IntersectMoreCorner: edge to be extended is not found");
+
     // Fopbis is the face containing the trace of fillet CP.Arc() which of does not contain Vtx.
     // Normally Fobis is either the same as Fop (cylinder), or Fobis is G1 with Fop.
     Fopbis.Orientation(TopAbs_FORWARD);
@@ -4408,9 +4414,6 @@ void ChFi3d_Builder::IntersectMoreCorner(const int Index)
     // Fop calls the 4th face non-used for the vertex
     cherche_face(myVFMap(Vtx), Arcprol, Fad, Fv, Fv, Fopbis);
     Fop.Orientation(TopAbs_FORWARD);
-
-    if (Arcprol.IsNull())
-      throw StdFail_NotDone("OneCorner : edge to be extended is not found");
     for (ex.Init(Fopbis, TopAbs_EDGE); ex.More(); ex.Next())
     {
       if (Arcprol.IsSame(ex.Current()))
@@ -4770,6 +4773,15 @@ void ChFi3d_Builder::IntersectMoreCorner(const int Index)
     }
     // end of modif
 
+    // Guard: Arcprolbis may be null if myVEMap(Vtx) contained only
+    // Arcprol, Arcspine, and Arcpiv (e.g. when topology maps carry stale
+    // data from shared TShape pointers after prior operations).
+    if (Arcprolbis.IsNull())
+    {
+      throw Standard_ConstructionError(
+        "IntersectMoreCorner: continuation edge (Arcprolbis) is not found");
+    }
+
     // Now the missing curves are constructed.
     for (ex.Init(Arcprolbis.Oriented(TopAbs_FORWARD), TopAbs_VERTEX); ex.More(); ex.Next())
     {

src/ModelingAlgorithms/TKFillet/GTests/BRepFilletAPI_MakeChamfer_Test.cxx

@@ -11,11 +11,18 @@
 // Alternatively, this file may be used under the terms of Open CASCADE
 // commercial license or contractual agreement.
 
+#include <BRepAlgoAPI_Fuse.hxx>
 #include <BRepCheck_Analyzer.hxx>
 #include <BRepFilletAPI_MakeChamfer.hxx>
 #include <BRepPrimAPI_MakeBox.hxx>
+#include <BRepPrimAPI_MakeCylinder.hxx>
+#include <gp_Ax2.hxx>
 #include <NCollection_IndexedDataMap.hxx>
+#include <NCollection_IndexedMap.hxx>
 #include <NCollection_List.hxx>
+#include <Standard_ConstructionError.hxx>
+#include <Standard_Failure.hxx>
+#include <StdFail_NotDone.hxx>
 #include <TopAbs_ShapeEnum.hxx>
 #include <TopExp.hxx>
 #include <TopExp_Explorer.hxx>
@@ -92,3 +99,145 @@ TEST(BRepFilletAPI_MakeChamferTest, ChamferMoreFaces)
   }
   EXPECT_GT(aFaceCount, 6);
 }
+
+// Regression test for issue #1163: chamfer after boolean fusion must not crash
+// due to null shapes in IntersectMoreCorner when topology maps carry stale data.
+// Edges at vertices shared by 3+ faces are selected to exercise the complex
+// corner-processing paths (IntersectMoreCorner / PerformOneCorner).
+TEST(BRepFilletAPI_MakeChamferTest, ChamferAfterBooleanFusion)
+{
+  BRepPrimAPI_MakeBox aBoxMaker(10.0, 10.0, 10.0);
+  const TopoDS_Shape& aBox = aBoxMaker.Shape();
+  ASSERT_TRUE(aBoxMaker.IsDone());
+
+  gp_Ax2                   anAxis(gp_Pnt(5.0, 0.0, 5.0), gp_Dir(0.0, 1.0, 0.0));
+  BRepPrimAPI_MakeCylinder aCylMaker(anAxis, 3.0, 10.0);
+  const TopoDS_Shape&      aCyl = aCylMaker.Shape();
+  ASSERT_TRUE(aCylMaker.IsDone());
+
+  BRepAlgoAPI_Fuse aFuse(aBox, aCyl);
+  ASSERT_TRUE(aFuse.IsDone());
+  const TopoDS_Shape& aFused = aFuse.Shape();
+
+  // Build vertex-to-face count map to identify complex vertices (3+ faces).
+  NCollection_IndexedDataMap<TopoDS_Shape, NCollection_List<TopoDS_Shape>, TopTools_ShapeMapHasher>
+    aVtxFaceMap;
+  TopExp::MapShapesAndAncestors(aFused, TopAbs_VERTEX, TopAbs_FACE, aVtxFaceMap);
+
+  NCollection_IndexedDataMap<TopoDS_Shape, NCollection_List<TopoDS_Shape>, TopTools_ShapeMapHasher>
+    anEdgeFaceMap;
+  TopExp::MapShapesAndAncestors(aFused, TopAbs_EDGE, TopAbs_FACE, anEdgeFaceMap);
+
+  // Select edges at vertices with 3+ adjacent faces (complex topology).
+  // The box-cylinder fusion geometry above is deterministic and always produces
+  // such edges at the intersection seam, so the assertion below is reliable.
+  BRepFilletAPI_MakeChamfer aChamfer(aFused);
+  int                       anEdgeCount = 0;
+  for (TopExp_Explorer anEdgeExp(aFused, TopAbs_EDGE); anEdgeExp.More() && anEdgeCount < 4;
+       anEdgeExp.Next())
+  {
+    const TopoDS_Edge& anEdge = TopoDS::Edge(anEdgeExp.Current());
+    if (!anEdgeFaceMap.Contains(anEdge) || anEdgeFaceMap.FindFromKey(anEdge).IsEmpty())
+      continue;
+
+    // Check if any vertex of this edge has 3+ faces.
+    bool hasComplexVertex = false;
+    for (TopExp_Explorer aVtxExp(anEdge, TopAbs_VERTEX); aVtxExp.More(); aVtxExp.Next())
+    {
+      if (aVtxFaceMap.Contains(aVtxExp.Current())
+          && aVtxFaceMap.FindFromKey(aVtxExp.Current()).Size() >= 3)
+      {
+        hasComplexVertex = true;
+        break;
+      }
+    }
+    if (!hasComplexVertex)
+      continue;
+
+    const TopoDS_Face& aFace = TopoDS::Face(anEdgeFaceMap.FindFromKey(anEdge).First());
+    aChamfer.Add(0.5, 0.5, anEdge, aFace);
+    anEdgeCount++;
+  }
+  ASSERT_GT(anEdgeCount, 0);
+
+  // Must not crash; may succeed or fail gracefully with IsDone() == false.
+  try
+  {
+    aChamfer.Build();
+    if (aChamfer.IsDone())
+    {
+      BRepCheck_Analyzer anAnalyzer(aChamfer.Shape());
+      EXPECT_TRUE(anAnalyzer.IsValid());
+    }
+  }
+  catch (const Standard_Failure&)
+  {
+    // Exception instead of crash is acceptable.
+  }
+}
+
+// Regression test for issue #1163: sequential chamfers on the same shape
+// must not crash due to stale TShape pointers in internal topology maps.
+// Each iteration selects a different edge (by index) and verifies the shape
+// topology changes, ensuring that successive operations actually modify the
+// topology maps that trigger the bug.
+TEST(BRepFilletAPI_MakeChamferTest, SequentialChamferNoCrash)
+{
+  BRepPrimAPI_MakeBox aBoxMaker(20.0, 20.0, 20.0);
+  const TopoDS_Shape& aBox = aBoxMaker.Shape();
+  ASSERT_TRUE(aBoxMaker.IsDone());
+
+  TopoDS_Shape aShape        = aBox;
+  int          aPrevEdges    = 0;
+  int          aSuccessCount = 0;
+
+  for (int i = 0; i < 3; ++i)
+  {
+    // Count edges and pick a different one each iteration.
+    NCollection_IndexedMap<TopoDS_Shape, TopTools_ShapeMapHasher> anEdgeMap;
+    TopExp::MapShapes(aShape, TopAbs_EDGE, anEdgeMap);
+    if (anEdgeMap.IsEmpty())
+      break;
+
+    // Verify topology actually changed after each successful chamfer.
+    if (i > 0 && aPrevEdges > 0)
+    {
+      EXPECT_NE(anEdgeMap.Extent(), aPrevEdges);
+    }
+    aPrevEdges = anEdgeMap.Extent();
+
+    // Select edge at different position each iteration to avoid re-chamfering the same edge.
+    int                anIdx  = (i * 3 + 1) % anEdgeMap.Extent() + 1;
+    const TopoDS_Edge& anEdge = TopoDS::Edge(anEdgeMap(anIdx));
+
+    BRepFilletAPI_MakeChamfer aChamfer(aShape);
+    aChamfer.Add(1.0, anEdge);
+
+    try
+    {
+      aChamfer.Build();
+      if (aChamfer.IsDone())
+      {
+        aShape = aChamfer.Shape();
+        aSuccessCount++;
+      }
+      else
+      {
+        break;
+      }
+    }
+    catch (const Standard_ConstructionError&)
+    {
+      // Null-guard from Fix 4 (Arcprolbis) - acceptable graceful failure.
+      break;
+    }
+    catch (const StdFail_NotDone&)
+    {
+      // Null-guard from Fix 3 (Arcprol) or existing Fv check - acceptable.
+      break;
+    }
+  }
+  // Verify at least one chamfer iteration succeeded, ensuring the test
+  // meaningfully exercises topology changes rather than trivially passing.
+  EXPECT_GE(aSuccessCount, 1);
+}