COMP: Fix linker errors and disable broken Python wrapping

Two pre-existing issues exposed by working CI:

1. src/ executables fail to link against ITK shared libraries in
   external-module builds. The VariationalRegistration_LIBRARIES
   variable contains target names but the external-module CMake
   context doesn't fully resolve their link dependencies. Adding
   ITK_LIBRARIES (set by find_package(ITK)) provides the complete
   transitive link set:

     undefined reference to itk::DataObject::GetUpdateMTime()
     undefined reference to itk::DataObject::DataHasBeenGenerated()
     undefined reference to typeinfo for itk::ExceptionObject

2. Seven .wrap files pass the wrong number of template arguments:
   - Regularizer, DiffusionRegularizer, ElasticRegularizer,
     GaussianRegularizer, CurvatureRegularizer: all take 1 template
     param (TDisplacementField) but wrapping uses
     itk_wrap_image_filter with 2 image types
   - StopCriterion: takes (TRegistrationFilter, TMRFilter) — not
     image types at all
   - MultiResolutionFilter: takes 4 params, wrapping provides 2

   These wrapping files have never produced working Python bindings.
   Disabled in wrapping/CMakeLists.txt; the 9 correctly-wrapped
   3-parameter filters remain active.

   ITK v6 is NOT required — these are wrapping authoring bugs, not
   API incompatibilities.

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

Author: hjmjohnson

src/CMakeLists.txt

@@ -29,9 +29,9 @@ if(WIN32) # Check if we are on Windows
 endif()
 
 add_executable(VariationalRegistration ${VariationalRegistration_SRC})
-target_link_libraries(VariationalRegistration ${VariationalRegistration_LIBRARIES})
+target_link_libraries(VariationalRegistration ${VariationalRegistration_LIBRARIES} ${ITK_LIBRARIES})
 
 add_executable(VariationalRegistration2D ${VariationalRegistration_SRC})
-target_link_libraries(VariationalRegistration2D ${VariationalRegistration_LIBRARIES})
+target_link_libraries(VariationalRegistration2D ${VariationalRegistration_LIBRARIES} ${ITK_LIBRARIES})
 set_target_properties(VariationalRegistration2D PROPERTIES COMPILE_FLAGS -DUSE_2D_IMPL)
 

wrapping/CMakeLists.txt

@@ -1,22 +1,35 @@
 itk_wrap_module(VariationalRegistration)
 
 set(WRAPPER_SUBMODULE_ORDER
+   # 3-parameter filters (InputImage, OutputImage/MovingImage, DisplacementField)
+   # — wrapping uses itk_wrap_image_filter_combinations correctly.
    itkContinuousBorderWarpImageFilter
    itkVariationalDiffeomorphicRegistrationFilter
-   itkVariationalRegistrationCurvatureRegularizer
    itkVariationalRegistrationDemonsFunction
-   itkVariationalRegistrationDiffusionRegularizer
-   itkVariationalRegistrationElasticRegularizer
    itkVariationalRegistrationFastNCCFunction
    itkVariationalRegistrationFilter
    itkVariationalRegistrationFunction
-   itkVariationalRegistrationGaussianRegularizer
-   itkVariationalRegistrationMultiResolutionFilter
    itkVariationalRegistrationNCCFunction
-   itkVariationalRegistrationRegularizer
    itkVariationalRegistrationSSDFunction
-   itkVariationalRegistrationStopCriterion
-   itkVariationalSymmetricDiffeomorphicRegistrationFilter)
+   itkVariationalSymmetricDiffeomorphicRegistrationFilter
+   #
+   # The following are DISABLED because their .wrap files pass the wrong
+   # number of template arguments (they use itk_wrap_image_filter with 2
+   # image types but the classes take 1 non-image or N != 2 params):
+   #
+   # itkVariationalRegistrationRegularizer        — 1 param (TDisplacementField)
+   # itkVariationalRegistrationCurvatureRegularizer — 1 param + FFTW guard
+   # itkVariationalRegistrationDiffusionRegularizer — 1 param
+   # itkVariationalRegistrationElasticRegularizer  — 1 param
+   # itkVariationalRegistrationGaussianRegularizer — 1 param
+   # itkVariationalRegistrationStopCriterion       — 2 params (TRegistrationFilter, TMRFilter)
+   # itkVariationalRegistrationMultiResolutionFilter — 4 params
+   #
+   # These have never had working Python wrapping. Correct .wrap files
+   # for single-param displacement-field classes need direct
+   # itk_wrap_template calls. See ITK's itkDisplacementFieldTransform.wrap
+   # for the canonical pattern. Left as future work for the module maintainer.
+   )
 
 itk_auto_load_submodules()
 itk_end_wrap_module()