[codex] Add copy-free matrix view hooks

[dellaert]

Summary

• Add a generated gtwrap::internal::PyArgPolicy<T> / py_arg<T>(name) hook for pybind argument declarations.
• Keep the default Python behavior equivalent to pybind11::arg(name) so existing wrappers continue to use normal pybind conversion.
• Route generated typed Python arguments, including defaulted arguments, through the hook so downstream preambles can specialize policies such as .noconvert().
• Restrict the recent reference_internal return policy to const reference method returns, avoiding it for mutable references.
• Add MATLAB wrapper support for ConstMatrixView-style matrix view arguments by accepting MATLAB double matrices and generating unwrapMatrixView<T>(...) locals backed by the mxArray buffer.

Why

Downstream projects need a wrap-level extension point for copy-free matrix-view arguments without making wrap depend on project-specific Python CLI configuration. This lets GTSAM specialize Python matrix-view arguments in a preamble and lets MATLAB pass compatible double matrices into const Eigen matrix views without the existing unwrap<Matrix> copy.

Impact

Ordinary Python and MATLAB arguments keep their existing behavior. ConstMatrixView arguments are treated as MATLAB double matrix inputs and are passed through generated wrappers as value-like view objects, not pointer/shared-pointer objects.

Validation

• conda run -n py312 python -m unittest discover tests
• git diff --check
• git diff --cached --check
• MATLAB R2025b smoke compile: /Applications/MATLAB_R2025b.app/bin/mex ... /tmp/gtwrap_matrix_view_mex.cpp -outdir /tmp
• MATLAB R2025b runtime smoke: matlab -batch "addpath(/tmp); y = gtwrap_matrix_view_mex([1 3 5; 2 4 6]); assert(y == 2323); disp(y);"

[Copilot]

Pull request overview

Adds an extension point for pybind11 argument declarations by generating typed arguments through a gtwrap::internal::PyArgPolicy<T> / py_arg<T>(name) hook (defaulting to pybind11::arg(name)), and tightens reference_internal return policy emission to only apply to const-reference method returns.

Changes:

• Generate gtwrap::internal::PyArgPolicy + py_arg<T>(name) support code into produced pybind C++ and route generated named arguments (including defaulted args) through py_arg<T>(...).
• Update expected generated pybind outputs to reflect py_arg<T>(...) usage in .def(...) declarations.
• Add/extend unit tests and fixtures for the new argument policy hook and for restricting reference_internal to const-reference method returns.

Reviewed changes

Copilot reviewed 13 out of 13 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
gtwrap/pybind_wrapper.py	Implements the argument-policy hook injection and switches named argument emission to py_arg<T>(...); restricts reference_internal to const-ref method returns.
tests/test_pybind_wrapper.py	Adds coverage for the new arg-policy hook and the refined const-ref return policy behavior; allows passing a custom module template for targeted assertions.
tests/fixtures/arg_policies.i	New fixture exercising typed args + defaulted args for policy hook generation.
tests/fixtures/return_policies.i	New fixture validating reference_internal is emitted only for const-ref method returns.
tests/expected/python/*_pybind.cpp	Updates golden expected pybind C++ outputs to use gtwrap::internal::py_arg<T>(...) and include the generated hook support block.

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[Copilot]

Pull request overview

Copilot reviewed 18 out of 18 changed files in this pull request and generated 1 comment.

[Copilot]

Pull request overview

Copilot reviewed 18 out of 18 changed files in this pull request and generated no new comments.

[dellaert]

I tested this on my copy of GTSAM and it works like a charm. I will merge and vendor in this new version of wrap and monitor the situation on the GTSAM CI.