STYLE: Replace UI with IT as index type for LevelSetNode VectorContainer

[N-Dekker]

itk.IT ("IdentifierType") is the most commonly supported index type for VectorContainer. (VectorContainer is wrapped for IT and UC, but not for UI, as index type.)

• Follow-up to pull request STYLE: Replace UL with IT as index type in itkPyVectorContainerTest.py #6800

[N-Dekker]

Still under construction. I see now: in C++, NodeContainerType also has unsigned int as index type. Probably related.

ITK/Modules/Segmentation/LevelSets/include/itkShapePriorMAPCostFunctionBase.h

Line 84 in 1a6558f

using NodeContainerType = VectorContainer<unsigned int, NodeType>;

[dzenanz]

Looks good on a glance.

[N-Dekker]

This force-pushed amend aims to address CI failures at https://open.cdash.org/tests/2723817696 saying:

  File "/Users/runner/work/1/s-build/Wrapping/Generators/Python/itk/support/template_class.py", line 527, in __getitem__
    this_item = self.__template__[key]
                ~~~~~~~~~~~~~~~~~^^^^^
KeyError: (<itkCType unsigned long>, <class 'itk.itkLevelSetNodePython.itkLevelSetNodeF2'>)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/Users/runner/work/1/s/Modules/Filtering/FastMarching/wrapping/test/FastMarchingImageFilterTest.py", line 131, in <module>
    NodeContainer = itk.VectorContainer[itk.IT, NodeType]
                    ~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^^
  File "/Users/runner/work/1/s-build/Wrapping/Generators/Python/itk/support/template_class.py", line 531, in __getitem__
    raise itk.TemplateTypeError(self, key)
itk.support.extras.TemplateTypeError: itk.VectorContainer is not wrapped for input type `itk.UL, itk.LevelSetNode[itk.F,2]`.

[N-Dekker]

This is a potentially breaking change, although in practice, VectorContainer<unsigned int, NodeType> and VectorContainer<NodeType> behave exactly the same.

[greptile-apps]

Greptile Summary

This change aligns LevelSetNode VectorContainer indices across the FastMarching and ShapePrior native APIs, Python wrapper declarations, and affected Python tests. The C++ aliases now use ITK’s default IdentifierType index, while the wrapper and tests use the corresponding itk.IT specialization.

No defect was identified in the reviewed changes. The focused declarations and Python wrapper registration consistently use the same container index type.

T-Rex validation blocked

Runtime verification of Python container acceptance could not run because the wrapped itk Python package is missing, and the repository’s documented build route requires the missing pixi package manager. The native syntax fallback also cannot run because the generated itkConfigure.h header is unavailable without a configured build tree.

Confidence Score: 5/5

The changed native aliases, wrapper specialization, and Python test call sites consistently use IdentifierType and itk.IT for LevelSetNode containers.

No review findings were emitted. Source inspection found the FastMarching and ShapePrior API container types aligned with the registered Python wrapper specialization and updated test usage.

Files Needing Attention: A configured ITK Python-wrapping build should run the focused FastMarching and ShapePrior Python tests for final runtime coverage; the relevant files are Modules/Filtering/FastMarching/wrapping/ITKFastMarchingBase.wrap and the affected Python test files.

T-Rex Logs

What T-Rex did

• Attempted the Python IT LevelSetNode integration probe and encountered a ModuleNotFoundError for itk, preventing container construction.
• Tried the wrapped-build configuration via Pixi, but Pixi was not found and the command exited with code 127.
• Ran a focused C++ syntax check for the LevelSet alias; it failed because itkConfigure.h was not generated due to a missing configured ITK build tree.
• Validated Python probe syntax and bytecode, but the missing wrapper runtime and build tooling prevented observing container acceptance behavior.
• Cross-proof validation confirms the same failure modes across proofs: missing itk module, missing Pixi wrapper/build tools, and missing ITK configuration, with no container acceptance observations at this checkout.

_{Ran code and verified through T-Rex}

_{Reviews (1): Last reviewed commit: "STYLE: Replace UI with IT as index type ..." | Re-trigger Greptile}

[thewtex]

OK, but not terribly excited about this change -- I think unsigned int was probably intended, and there is a breaking type change.

[N-Dekker]

OK, but not terribly excited about this change -- I think unsigned int was probably intended, and there is a breaking type change.

Thanks for your comment, @thewtex Looking at the code, I don't see why it was using unsigned int as index type, rather than itk.IT. The underlying std::vector<NodeType> is the same for both VectorContainer specializations, so technically I don't think it matters.

For end-users I think it would be clearer if we just stick with one index type, for VectorContainer. Eventually I think it would also allow us to remove some VectorContainer wrappings, for index types UC and US, but that's beyond the scope of this PR.