From 59bad275457d2576a26249f1f209913a2988b2ab Mon Sep 17 00:00:00 2001
From: Steve Pieper <pieper@isomics.com>
Date: Mon, 10 Aug 2026 14:05:20 -0400
Subject: [PATCH] COMP: Link the full Python library for wrapped modules where
 required

c44ce00 ("COMP: Only search for Python3 Development.Module component") switched
the wrapping to find only Python3 Development.Module, dropped
VTK_WRAP_PYTHON_FIND_LIBS, and removed VTK_Python3_LIBRARIES from the wrapped
module link line. Development.Module leaves the Python C-API symbols undefined
for the host interpreter to provide, which is fine where the linker allows
undefined symbols (macOS links MODULE targets with -undefined dynamic_lookup),
but on Linux the wrapped modules are linked with -Wl,--no-undefined and must
resolve the Python symbols at link time. The result is a link failure of every
wrapped Python module, e.g.:

  vtkAddonMathUtilitiesPython.cxx: undefined reference to `PyTuple_Size'

Restore the behavior the removed code provided, gated on
VTK_UNDEFINED_SYMBOLS_ALLOWED: keep Development.Module where undefined symbols
are allowed, otherwise require the full Development component and link
Python3::Python. VTK_WRAP_PYTHON_FIND_LIBS is set again so the block runs, and
VTK_Python3_LIBRARIES is re-added to the wrapped module link line.

Reproduced and fixed on an Ubuntu 22.04 Slicer superbuild: without the change
the inner build fails linking the wrapped modules; with it the full application
builds, packages, and runs (the wrapped classes, including inherited base-class
methods, work).

Co-Authored-By: Claude Opus 4.8 <noreply@anthropic.com>
---
 CMake/vtkMacroKitPythonWrap.cmake |  3 +++
 CMake/vtkWrapPython.cmake         | 13 ++++++++++++-
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/CMake/vtkMacroKitPythonWrap.cmake b/CMake/vtkMacroKitPythonWrap.cmake
index 3d03454..6f48852 100644
--- a/CMake/vtkMacroKitPythonWrap.cmake
+++ b/CMake/vtkMacroKitPythonWrap.cmake
@@ -159,6 +159,7 @@ macro(vtkMacroKitPythonWrap)
   endif()
 
   if(VTK_WRAP_PYTHON AND BUILD_SHARED_LIBS)
+    set(VTK_WRAP_PYTHON_FIND_LIBS 1)
     include(vtkWrapPython)
 
     set(TMP_WRAP_FILES ${MY_KIT_SRCS} ${MY_KIT_WRAP_HEADERS})
@@ -280,6 +281,7 @@ macro(vtkMacroKitPythonWrap)
       ${MY_KIT_NAME}PythonD
       ${MY_KIT_NAME}
       ${VTK_PYTHON_CORE}
+      ${VTK_Python3_LIBRARIES}
       ${VTK_KIT_PYTHON_LIBRARIES}
       ${MY_KIT_PYTHON_LIBRARIES}
       )
@@ -340,6 +342,7 @@ macro(vtkMacroKitPythonWrap)
     target_link_libraries(${MY_KIT_NAME}Python
       PRIVATE
         ${MY_KIT_NAME}
+        ${VTK_Python3_LIBRARIES}
         VTK::WrappingPythonCore
         VTK::Python
         )
diff --git a/CMake/vtkWrapPython.cmake b/CMake/vtkWrapPython.cmake
index 76f48da..c1c8f0c 100644
--- a/CMake/vtkWrapPython.cmake
+++ b/CMake/vtkWrapPython.cmake
@@ -233,7 +233,18 @@ $<$<BOOL:$<TARGET_PROPERTY:${TARGET},INCLUDE_DIRECTORIES>>:
 endmacro()
 
 if(VTK_WRAP_PYTHON_FIND_LIBS)
-  find_package(Python3 COMPONENTS Development.Module REQUIRED)
+  # Development.Module leaves the Python C-API symbols undefined for the host
+  # interpreter to provide. That is fine where the linker allows undefined
+  # symbols (macOS -undefined dynamic_lookup), but on Linux the wrapped modules
+  # link with -Wl,--no-undefined and must resolve the Python symbols at link
+  # time, so the full library (Python3::Python) is required there.
+  if(VTK_UNDEFINED_SYMBOLS_ALLOWED)
+    find_package(Python3 COMPONENTS Development.Module REQUIRED)
+    set(VTK_Python3_LIBRARIES "")
+  else()
+    find_package(Python3 COMPONENTS Development REQUIRED)
+    set(VTK_Python3_LIBRARIES Python3::Python)
+  endif()
 endif()
 
 # Determine the location of the supplied header in the include_dirs supplied.