Add options for enabling ABI mangling namespace.

* CMake option VTK_ABI_NAMESPACE_NAME with default <DEFAULT>.
  * <DEFAULT> implies empty string or no namespace mangling.
* Configurable header vtkABINamespace.h.in added to Common::Core.
* Include vtkABINamespace.h in VTK modules.
* Link Common::Core to vtkTestOpenGLVersion which needs vtkABINamespace.h.
* VTK_NO_ABI_NAMESPACE can be used to disable namespace mangling for an
entire module (used in Wrapping/Tools).

CMake/vtkABINamespace.h.in

@@ -0,0 +1,14 @@
+#ifndef vtkABINamespace_h
+#define vtkABINamespace_h
+
+#ifndef VTK_NO_ABI_NAMESPACE
+#if defined(__cplusplus)
+#define VTK_ABI_NAMESPACE_BEGIN @VTK_ABI_NAMESPACE_BEGIN@
+#define VTK_ABI_NAMESPACE_END @VTK_ABI_NAMESPACE_END@
+#else
+#define VTK_ABI_NAMESPACE_BEGIN
+#define VTK_ABI_NAMESPACE_END
+#endif
+#endif // VTK_NO_ABI_NAMESPACE
+
+#endif // vtkABINamespace_h

CMake/vtkModule.cmake

@@ -3569,6 +3569,15 @@ function (vtk_module_add_module name)
       "The ${_vtk_build_module} module has no source files.")
   endif ()
 
+  set(_vtk_add_module_has_cxx FALSE)
+  foreach (source IN LISTS _vtk_add_module_SOURCES)
+    get_filename_component(source_ext "${source}" EXT)
+    if (source_ext MATCHES "cxx$")
+      set(_vtk_add_module_has_cxx TRUE)
+      break()
+    endif ()
+  endforeach ()
+
   get_property(_vtk_add_module_third_party GLOBAL
     PROPERTY  "_vtk_module_${_vtk_build_module}_third_party")
 
@@ -3944,6 +3953,16 @@ function (vtk_module_add_module name)
         "INTERFACE_vtk_module_implementable" 1)
   endif ()
 
+  # Include the ABI Namespace macros if this is a module with C++ sources
+  if (_vtk_add_module_has_cxx)
+    # Include the ABI Namespace macros
+    string(APPEND _vtk_add_module_module_content
+      "
+/* Include ABI Namespace */
+#include \"vtkABINamespace.h\"
+")
+  endif ()
+
   if (_vtk_add_module_implementable OR _vtk_add_module_implements)
     set_property(TARGET "${_vtk_add_module_real_target}"
       PROPERTY

Common/Core/CMakeLists.txt

@@ -3,6 +3,29 @@ cmake_dependent_option(VTK_USE_64BIT_TIMESTAMPS "Build VTK with 64 bit timestamp
   "NOT CMAKE_SIZEOF_VOID_P GREATER 4" ON)
 mark_as_advanced(VTK_USE_64BIT_TIMESTAMPS)
 
+# Mangle VTK symbols
+set(VTK_ABI_NAMESPACE_NAME
+  "<DEFAULT>"
+  CACHE STRING "Inline namespace name for mangling VTK symbols.")
+if (VTK_ABI_NAMESPACE_NAME STREQUAL "<DEFAULT>")
+  # The default is to not have an ABI namespace.
+  # This is consistent with the existing practice.
+  set(VTK_ABI_NAMESPACE_NAME "")
+endif ()
+mark_as_advanced(VTK_ABI_NAMESPACE_NAME)
+if (VTK_ABI_NAMESPACE_NAME)
+  message(STATUS "VTK ABI namespace: ${VTK_ABI_NAMESPACE_NAME}")
+  set(VTK_ABI_NAMESPACE_BEGIN "inline namespace ${VTK_ABI_NAMESPACE_NAME} {")
+  set(VTK_ABI_NAMESPACE_END "}")
+else ()
+  set(VTK_ABI_NAMESPACE_BEGIN "")
+  set(VTK_ABI_NAMESPACE_END "")
+endif ()
+configure_file(
+  "${vtk_cmake_dir}/vtkABINamespace.h.in"
+  "${CMAKE_CURRENT_BINARY_DIR}/vtkABINamespace.h"
+  @ONLY)
+
 if (CMAKE_SIZEOF_VOID_P GREATER 4)
  set(vtk_use_64bit_ids_default ON)
 else ()
@@ -321,6 +344,7 @@ set(headers
   vtkWindows.h
   vtkWrappingHints.h
   ${vtk_smp_headers}
+  "${CMAKE_CURRENT_BINARY_DIR}/vtkABINamespace.h"
   "${CMAKE_CURRENT_BINARY_DIR}/vtkArrayDispatchArrayList.h"
   "${CMAKE_CURRENT_BINARY_DIR}/vtkMathConfigure.h"
   "${CMAKE_CURRENT_BINARY_DIR}/vtkTypeListMacros.h"

Rendering/OpenGL2/CMakeLists.txt

@@ -110,7 +110,7 @@ if (WIN32 AND (NOT CMAKE_CROSSCOMPILING OR DEFINED CMAKE_CROSSCOMPILING_EMULATOR
   set_target_properties(vtkTestOpenGLVersion
     PROPERTIES
       WIN32_EXECUTABLE TRUE)
-  target_link_libraries(vtkTestOpenGLVersion PRIVATE opengl32)
+  target_link_libraries(vtkTestOpenGLVersion PRIVATE opengl32 VTK::CommonCore)
   list(APPEND headers vtkTestOpenGLVersion.h)
 endif ()
 

Wrapping/Tools/CMakeLists.txt

@@ -40,6 +40,8 @@ set_property(SOURCE vtkParseMain.c
   PROPERTY
     COMPILE_DEFINITIONS "VTK_PARSE_VERSION=\"${VTK_MAJOR_VERSION}.${VTK_MINOR_VERSION}\"")
 
+add_definitions(-DVTK_NO_ABI_NAMESPACE)
+
 vtk_module_add_module("${ns}::WrappingTools"
   SOURCES ${sources}
   HEADERS ${headers})