0033895: fix null surface crash in fixshape

data/step/tessellated_tetrahedron_ap242.step

@@ -0,0 +1,83 @@
+ISO-10303-21;
+HEADER;
+/* Generated by OCCT for testing shape healing with tessellated geometry */
+FILE_DESCRIPTION(('Tessellated tetrahedron in AP242'),'2;1');
+FILE_NAME('tessellated_tetrahedron_ap242.step','2025-06-19T10:00:00',('OpenCASCADE'),('Organization'),'7.8.0','OpenCASCADE STEP Writer','');
+FILE_SCHEMA(('AP242_MANAGED_MODEL_BASED_3D_ENGINEERING_MIM_LF { 1 0 10303 442 1 1 4 }'));
+ENDSEC;
+DATA;
+/* Application context */
+#1 = APPLICATION_PROTOCOL_DEFINITION('international standard','ap242_managed_model_based_3d_engineering',2014,#2);
+#2 = APPLICATION_CONTEXT('managed model based 3d engineering');
+
+/* Product definition structure */
+#3 = SHAPE_DEFINITION_REPRESENTATION(#4,#10);
+#4 = PRODUCT_DEFINITION_SHAPE('tessellated shape','shape definition for tessellated tetrahedron',#5);
+#5 = PRODUCT_DEFINITION('design','',#6,#9);
+#6 = PRODUCT_DEFINITION_FORMATION('','',#7);
+#7 = PRODUCT('Tetrahedron','Tetrahedron','',(#8));
+#8 = PRODUCT_CONTEXT('',#2,'mechanical');
+#9 = PRODUCT_DEFINITION_CONTEXT('part definition',#2,'design');
+
+/* Shape representation with tessellated solid */
+#10 = TESSELLATED_SHAPE_REPRESENTATION('tessellated representation',(#11,#12),#16);
+#11 = AXIS2_PLACEMENT_3D('',#13,#14,#15);
+#12 = TESSELLATED_SOLID('tetrahedron solid',(#17,#18,#19,#20),.T.);
+
+/* Coordinate system */
+#13 = CARTESIAN_POINT('',(0.,0.,0.));
+#14 = DIRECTION('',(0.,0.,1.));
+#15 = DIRECTION('',(1.,0.,0.));
+
+/* Representation context with units */
+#16 = ( GEOMETRIC_REPRESENTATION_CONTEXT(3) 
+GLOBAL_UNCERTAINTY_ASSIGNED_CONTEXT((#21)) 
+GLOBAL_UNIT_ASSIGNED_CONTEXT((#22,#23,#24)) 
+REPRESENTATION_CONTEXT('Context','3D Context with UNIT and UNCERTAINTY') );
+
+/* Tetrahedron faces */
+/* Base triangle - vertices 1,2,3 */
+#17 = TRIANGULATED_FACE('Base',#25,3,(
+    (0.,0.,-1.),    /* Normal pointing down */
+    (0.,0.,-1.),
+    (0.,0.,-1.)
+),$,(1,3,2),((1,3,2)));
+
+/* Side face 1 - vertices 1,2,4 */
+#18 = TRIANGULATED_FACE('Side1',#25,3,(
+    (0.,-0.942809,0.333333),    /* Outward normals */
+    (0.,-0.942809,0.333333),
+    (0.,-0.942809,0.333333)
+),$,(1,2,4),((1,2,4)));
+
+/* Side face 2 - vertices 2,3,4 */
+#19 = TRIANGULATED_FACE('Side2',#25,3,(
+    (0.816497,0.471405,0.333333),
+    (0.816497,0.471405,0.333333),
+    (0.816497,0.471405,0.333333)
+),$,(2,3,4),((2,3,4)));
+
+/* Side face 3 - vertices 3,1,4 */
+#20 = TRIANGULATED_FACE('Side3',#25,3,(
+    (-0.816497,0.471405,0.333333),
+    (-0.816497,0.471405,0.333333),
+    (-0.816497,0.471405,0.333333)
+),$,(3,1,4),((3,1,4)));
+
+/* Units and uncertainty */
+#21 = UNCERTAINTY_MEASURE_WITH_UNIT(LENGTH_MEASURE(1.E-07),#22,
+  'distance_accuracy_value','confusion accuracy');
+#22 = ( LENGTH_UNIT() NAMED_UNIT(*) SI_UNIT(.MILLI.,.METRE.) );
+#23 = ( NAMED_UNIT(*) PLANE_ANGLE_UNIT() SI_UNIT($,.RADIAN.) );
+#24 = ( NAMED_UNIT(*) SI_UNIT($,.STERADIAN.) SOLID_ANGLE_UNIT() );
+
+/* Tetrahedron vertex coordinates */
+#25 = COORDINATES_LIST('vertices',4,(
+    (0.,0.,0.),         /* Base vertex 1 */
+    (100.,0.,0.),       /* Base vertex 2 */
+    (50.,86.602540378,0.),      /* Base vertex 3 */
+    (50.,28.867513459,81.649658093)     /* Apex */
+));
+
+ENDSEC;
+END-ISO-10303-21;

src/ModelingAlgorithms/TKShHealing/GTests/FILES.cmake

@@ -2,4 +2,5 @@
 set(OCCT_TKShHealing_GTests_FILES_LOCATION "${CMAKE_CURRENT_LIST_DIR}")
 
 set(OCCT_TKShHealing_GTests_FILES
-)
+  ShapeHealing_TessellatedTest.cxx
+)

src/ModelingAlgorithms/TKShHealing/GTests/ShapeHealing_TessellatedTest.cxx

@@ -0,0 +1,119 @@
+// Copyright (c) 2025 OPEN CASCADE SAS
+//
+// This file is part of Open CASCADE Technology software library.
+//
+// This library is free software; you can redistribute it and/or modify it under
+// the terms of the GNU Lesser General Public License version 2.1 as published
+// by the Free Software Foundation, with special exception defined in the file
+// OCCT_LGPL_EXCEPTION.txt. Consult the file LICENSE_LGPL_21.txt included in OCCT
+// distribution for complete text of the license and disclaimer of any warranty.
+//
+// Alternatively, this file may be used under the terms of Open CASCADE
+// commercial license or contractual agreement.
+
+// OCCT headers
+#include <BRepCheck_Analyzer.hxx>
+#include <BRepCheck_ListIteratorOfListOfStatus.hxx>
+#include <STEPControl_Reader.hxx>
+#include <ShapeFix_Shape.hxx>
+#include <Standard_NullObject.hxx>
+#include <TopoDS.hxx>
+#include <TopoDS_Shape.hxx>
+#include <TopExp_Explorer.hxx>
+
+// GoogleTest headers
+#include <gtest/gtest.h>
+
+// System headers
+#include <fstream>
+
+//! Test fixture for shape healing operations on tessellated geometry.
+//! This fixture loads a tessellated tetrahedron from a STEP file
+//! and provides it for testing shape healing algorithms.
+//! Related to bug 33895: fixshape crashes on tessellated geometry without surfaces.
+class ShapeHealing_TessellatedTest : public ::testing::Test
+{
+protected:
+  TopoDS_Shape myShape;
+
+  void SetUp() override
+  {
+    // Load the tessellated tetrahedron STEP file
+    STEPControl_Reader aReader;
+
+    // Use relative path from test execution directory
+    const char* aFileName = "data/step/tessellated_tetrahedron_ap242.step";
+
+    // Check if file exists
+    std::ifstream aFile(aFileName);
+    if (!aFile.good())
+    {
+      GTEST_SKIP() << "Test file not found: " << aFileName;
+      return;
+    }
+    aFile.close();
+
+    IFSelect_ReturnStatus aStatus = aReader.ReadFile(aFileName);
+    ASSERT_EQ(aStatus, IFSelect_RetDone) << "Failed to read STEP file";
+
+    Standard_Integer aNbRoots = aReader.NbRootsForTransfer();
+    ASSERT_GT(aNbRoots, 0) << "No roots found in STEP file";
+
+    aReader.TransferRoots();
+
+    // Get the shape
+    myShape = aReader.OneShape();
+    ASSERT_FALSE(myShape.IsNull()) << "Loaded shape is null";
+  }
+};
+
+//! Test that the shape loads successfully and has expected structure.
+//! Verifies that the tessellated tetrahedron has 4 faces, 1 shell, and 1 solid.
+//! Also checks that the shape is considered invalid due to missing surfaces.
+TEST_F(ShapeHealing_TessellatedTest, LoadAndValidateShape)
+{
+  // Count sub-shapes
+  Standard_Integer aNbFaces  = 0;
+  Standard_Integer aNbShells = 0;
+  Standard_Integer aNbSolids = 0;
+
+  for (TopExp_Explorer anExp(myShape, TopAbs_FACE); anExp.More(); anExp.Next())
+  {
+    aNbFaces++;
+  }
+
+  for (TopExp_Explorer anExp(myShape, TopAbs_SHELL); anExp.More(); anExp.Next())
+  {
+    aNbShells++;
+  }
+
+  for (TopExp_Explorer anExp(myShape, TopAbs_SOLID); anExp.More(); anExp.Next())
+  {
+    aNbSolids++;
+  }
+
+  // Expected: 4 faces (tetrahedron), 1 shell, 1 solid
+  // Note: This test verifies the specific tessellated tetrahedron structure
+  EXPECT_EQ(aNbFaces, 4) << "Tessellated tetrahedron should have 4 faces";
+  EXPECT_EQ(aNbShells, 1) << "Should have 1 shell";
+  EXPECT_EQ(aNbSolids, 1) << "Should have 1 solid";
+
+  // Check shape validity
+  BRepCheck_Analyzer aChecker(myShape);
+  EXPECT_FALSE(aChecker.IsValid()) << "Tessellated shape without surfaces should not be valid";
+}
+
+//! Test that ShapeFix_Shape throws exception on tessellated geometry.
+//! Verifies that attempting to heal a tessellated shape without surfaces
+//! throws a Standard_NullObject exception instead of crashing.
+//! This test reproduces bug 33895.
+TEST_F(ShapeHealing_TessellatedTest, ShapeFixThrowsException)
+{
+  Handle(ShapeFix_Shape) aFixer = new ShapeFix_Shape(myShape);
+  aFixer->SetPrecision(1.0e-6);
+  aFixer->SetMaxTolerance(1.0);
+
+  // This should throw Standard_NullObject exception instead of crashing
+  EXPECT_THROW({ aFixer->Perform(); }, Standard_NullObject)
+    << "ShapeFix_Shape should throw exception for tessellated geometry";
+}

src/ModelingAlgorithms/TKShHealing/ShapeAnalysis/ShapeAnalysis_Surface.cxx

@@ -33,6 +33,7 @@
 #include <Adaptor3d_IsoCurve.hxx>
 #include <BndLib_Add3dCurve.hxx>
 #include <ElSLib.hxx>
+#include <Standard_NullObject.hxx>
 #include <Geom_BezierSurface.hxx>
 #include <Geom_BoundedSurface.hxx>
 #include <Geom_ConicalSurface.hxx>
@@ -105,6 +106,8 @@ ShapeAnalysis_Surface::ShapeAnalysis_Surface(const Handle(Geom_Surface)& S)
       myUCloseVal(-1),
       myVCloseVal(-1)
 {
+  // Bug 33895: Prevent crash when surface is null
+  Standard_NullObject_Raise_if(mySurf.IsNull(), "ShapeAnalysis_Surface: Cannot create with null surface");
   mySurf->Bounds(myUF, myUL, myVF, myVL);
   myAdSur = new GeomAdaptor_Surface(mySurf);
 }
@@ -115,6 +118,8 @@ void ShapeAnalysis_Surface::Init(const Handle(Geom_Surface)& S)
 {
   if (mySurf == S)
     return;
+  // Bug 33895: Prevent crash when surface is null
+  Standard_NullObject_Raise_if(S.IsNull(), "ShapeAnalysis_Surface::Init: Cannot initialize with null surface");
   myExtOK     = Standard_False; //: 30
   mySurf      = S;
   myNbDeg     = -1;

tests/bugs/step/bug33895

@@ -0,0 +1,39 @@
+puts "========"
+puts "bug33895"
+puts "========"
+puts ""
+#################################################
+# Bug 33895: fixshape crashes on tessellated geometry without surfaces
+# Test fixshape on tessellated tetrahedron in AP242
+# Expect exception on tessellated geometry without surfaces
+#################################################
+
+pload XDE MODELING
+
+stepread [locate_data_file tessellated_tetrahedron_ap242.step] a *
+
+# Check what kind of shape we get
+checknbshapes a_1 -t
+
+# Validate shape - will show BRepCheck_NoSurface errors
+checkshape a_1
+
+# Test fixshape - expect exception
+set exception_thrown 0
+if {[catch {fixshape result a_1} err]} {
+  puts "EXPECTED: Exception caught during fixshape: $err"
+  if {[string match "*Standard_NullObject*" $err]} {
+    puts "SUCCESS: Correct exception type (Standard_NullObject)"
+    set exception_thrown 1
+  } else {
+    puts "ERROR: Wrong exception type"
+  }
+} else {
+  puts "ERROR: No exception thrown - fixshape should fail on tessellated geometry"
+}
+
+if {$exception_thrown == 0} {
+  puts "TEST FAILED: Expected Standard_NullObject exception"
+} else {
+  puts "TEST PASSED: Exception properly thrown for tessellated geometry"
+}