Fix install paths

[christophfroehlich]

This was completely coded by GPT-5.3-Codex and needs proper review and testing.

Summary

Fix Python generated-parameter module installation/import behavior across all colcon layouts (standard, isolated, and merge-install), resolving intermittent prerelease import failures.

Problem

Tests could fail with:

• ModuleNotFoundError: No module named 'generate_parameter_module_example.admittance_parameters'
• ModuleNotFoundError: No module named 'generate_parameter_module_example.custom_validation'

Root causes were path/layout mismatches in generation output handling and empty package __init__.py files in install space.

Changes

• Updated src/generate_parameter_library/generate_parameter_library_py/generate_parameter_library_py/setup_helper.py:

  • Parse setuptools args robustly (--opt value and --opt=value)
  • Support additional install/build flags (--build-lib, --install-lib, --prefix, --root)
  • Correctly map build* roots to matching install* roots (including build_isolated -> install_isolated)
  • Auto-detect merge vs isolated layout from AMENT_PREFIX_PATH
  • Avoid generating into source-resolving symlink paths

• Updated src/generate_parameter_library/generate_parameter_library_py/generate_parameter_library_py/generate_python_module.py:

  • Populate generated package __init__.py with namespace path extension when missing or empty

• Added src/generate_parameter_library/example_python/generate_parameter_module_example/init.py:

  • Namespace path extension for split source/install package resolution

Validation

All scenarios pass for generate_parameter_module_example:

• Standard layout: 48 passed, 0 failed
• Isolated layout (--build-base/--install-base): 48 passed, 0 failed
• Merge-install layout (--merge-install): 48 passed, 0 failed

Generated module is now written to the correct install location in each layout.

[saikishor]

As far as I understood, LGTM

[tylerjw]

Looks like this needs to be rebased. What more do you want to do here before we land this?

[christophfroehlich]

There were several related issues and I hoped that any of the the reporters would review it ;)
@Benjamin-Tan @sea-bass @imcelroy @xguay @MarqRazz @emulate-jonathanmanning @Flova

[tylerjw]

It looks like this breaks Python packages. The new source-directory skip leaves the generated module outside the package's import path. The build succeeds but then the python import fails.

[MarqRazz]

Thanks for pulling these issues together @christophfroehlich! I tested this on Lyrical and can confirm @tylerjw's report: with --symlink-install, colcon puts build/<pkg> (a symlink to src) ahead of site-packages, so Python imports the source package, and this PR no longer writes the generated module there. The example only passes because it has no source __init__.py.

I took a different approach in #393 to generate from setuptools' build_py/develop commands instead of parsing sys.argv. It passes regular, symlink, merge-install, overlay, and custom --install-base builds plus pip install -e, and fixes #192, #255 and #257. Since it replaces the approach here rather than building on it, I opened it separately. Happy to adjust however you and @tylerjw prefer.