From 79b6529991f75c2d58fd2d75ffc19613364ba007 Mon Sep 17 00:00:00 2001
From: Pasukhin Dmitry <dpasukhi@opencascade.com>
Date: Sun, 14 Jun 2026 10:45:03 +0100
Subject: [PATCH] Modeling Algorithms - Guard null curve in
 BRepExtrema_DistanceSS (#1307)

BRep_Tool::Curve() may return a null handle for edges without a 3D
curve (e.g. edges defined only by pcurves on a surface). The two call
sites in BRepExtrema_DistanceSS dereferenced the returned handle
without a null check, causing a crash when such edges were encountered
in edge-edge (PERFORM_C0) or edge-face distance computations.

Add null checks before dereferencing pCurv and return early if the
handle is null. Add GTests covering both code paths.
---
 .../BRepExtrema/BRepExtrema_DistanceSS.cxx    | 11 ++++
 .../BRepExtrema_DistShapeShape_Test.cxx       | 51 +++++++++++++++++++
 2 files changed, 62 insertions(+)

diff --git a/src/ModelingAlgorithms/TKTopAlgo/BRepExtrema/BRepExtrema_DistanceSS.cxx b/src/ModelingAlgorithms/TKTopAlgo/BRepExtrema/BRepExtrema_DistanceSS.cxx
index a285be0673..f6cedf30a4 100644
--- a/src/ModelingAlgorithms/TKTopAlgo/BRepExtrema/BRepExtrema_DistanceSS.cxx
+++ b/src/ModelingAlgorithms/TKTopAlgo/BRepExtrema/BRepExtrema_DistanceSS.cxx
@@ -517,6 +517,11 @@ static void PERFORM_C0(const TopoDS_Edge&                              S1,
     double                  aFOther, aLOther;
     occ::handle<Geom_Curve> pCurvOther = BRep_Tool::Curve(Eother, aFOther, aLOther);
 
+    if (pCurv.IsNull())
+    {
+      return;
+    }
+
     if (pCurv->Continuity() == GeomAbs_C0)
     {
       constexpr double epsP = Precision::PConfusion();
@@ -1096,6 +1101,12 @@ void BRepExtrema_DistanceSS::Perform(
 
   double                  aFirst, aLast;
   occ::handle<Geom_Curve> pCurv = BRep_Tool::Curve(theS1, aFirst, aLast);
+
+  if (pCurv.IsNull())
+  {
+    return;
+  }
+
   if (pCurv->Continuity() == GeomAbs_C0)
   {
     NCollection_Sequence<BRepExtrema_SolutionElem> SeqSolution1;
diff --git a/src/ModelingAlgorithms/TKTopAlgo/GTests/BRepExtrema_DistShapeShape_Test.cxx b/src/ModelingAlgorithms/TKTopAlgo/GTests/BRepExtrema_DistShapeShape_Test.cxx
index 297c8715bb..6f8d1ec28c 100644
--- a/src/ModelingAlgorithms/TKTopAlgo/GTests/BRepExtrema_DistShapeShape_Test.cxx
+++ b/src/ModelingAlgorithms/TKTopAlgo/GTests/BRepExtrema_DistShapeShape_Test.cxx
@@ -13,11 +13,21 @@
 
 #include <gtest/gtest.h>
 
+#include <BRep_Builder.hxx>
 #include <BRepBuilderAPI_MakeEdge.hxx>
+#include <BRepBuilderAPI_MakeFace.hxx>
 #include <BRepBuilderAPI_MakeVertex.hxx>
 #include <BRepExtrema_DistShapeShape.hxx>
+#include <Geom_Circle.hxx>
+#include <Geom_Line.hxx>
+#include <gp_Ax2.hxx>
+#include <gp_Circ.hxx>
+#include <gp_Dir.hxx>
+#include <gp_Lin.hxx>
+#include <gp_Pln.hxx>
 #include <gp_Pnt.hxx>
 #include <TopoDS_Edge.hxx>
+#include <TopoDS_Face.hxx>
 #include <TopoDS_Vertex.hxx>
 
 //=================================================================================================
@@ -41,3 +51,44 @@ TEST(BRepExtrema_DistShapeShapeTest, BUC60870_EdgeToVertexMinimumDistance)
   EXPECT_NEAR(aDist.Value(), aTheorDist, aTheorDist * aPercentMax)
     << "Minimum distance deviates from expected value 1.0";
 }
+
+//=================================================================================================
+
+// Verify that BRepExtrema_DistShapeShape does not crash when computing the distance
+// between two edges and one of them has no 3D curve (null Geom_Curve from BRep_Tool::Curve).
+// This exercises the null-check in the PERFORM_C0 helper.
+TEST(BRepExtrema_DistShapeShapeTest, EdgeEdge_Null3DCurve_NoCrash)
+{
+  const TopoDS_Edge aEdge1 = BRepBuilderAPI_MakeEdge(gp_Pnt(0, 0, 0), gp_Pnt(1, 0, 0)).Edge();
+
+  const occ::handle<Geom_Circle> aCircle =
+    new Geom_Circle(gp_Ax2(gp_Pnt(5, 0, 0), gp_Dir(0, 0, 1)), 1.0);
+  TopoDS_Edge aEdge2 = BRepBuilderAPI_MakeEdge(aCircle).Edge();
+
+  BRep_Builder aBuilder;
+  aBuilder.UpdateEdge(aEdge2, occ::handle<Geom_Curve>(), 1e-7);
+
+  BRepExtrema_DistShapeShape aDist(aEdge1, aEdge2, 10.0);
+  (void)aDist;
+}
+
+//=================================================================================================
+
+// Verify that BRepExtrema_DistShapeShape does not crash when computing the distance
+// between an edge with no 3D curve and a face.
+// This exercises the null-check in Perform(Edge, Face).
+TEST(BRepExtrema_DistShapeShapeTest, EdgeFace_Null3DCurve_NoCrash)
+{
+  const occ::handle<Geom_Circle> aCircle =
+    new Geom_Circle(gp_Ax2(gp_Pnt(5, 0, 0), gp_Dir(0, 0, 1)), 1.0);
+  TopoDS_Edge aEdge = BRepBuilderAPI_MakeEdge(aCircle).Edge();
+
+  BRep_Builder aBuilder;
+  aBuilder.UpdateEdge(aEdge, occ::handle<Geom_Curve>(), 1e-7);
+
+  const TopoDS_Face aFace =
+    BRepBuilderAPI_MakeFace(gp_Pln(gp_Pnt(0, 0, 5), gp_Dir(0, 0, 1)), -10, 10, -10, 10);
+
+  BRepExtrema_DistShapeShape aDist(aEdge, aFace, 10.0);
+  (void)aDist;
+}