[KmoM88]

I have updated unit test and verified the end-to-end PEP 621 pipeline:

1. Async Test Runner:
   Adapted test_task_python_project_build.py to use from .run_until_complete import run_until_complete instead of @pytest.mark.asyncio, aligning it with colcon-core's internal test conventions without requiring external plugins.
2. End-to-End Integration Tests (test/test_integration_pep621.py):
   Added integration tests exercising modern build backends:
   • Pure PEP 621 package build & runtime import with flit_core.
   • Entry point script generation and execution with hatchling ([project.scripts] $\rightarrow$ bin/ wrapper).
   • Rebuilds and removal of deleted files via remove_distributions.
   • Editable installs with --symlink-install via build_editable and PEP 610 recording.
3. Test Suite Status:
   All related tests pass cleanly:

   pytest test/test_package_identification_pep621.py \
          test/test_package_augmentation_pep621.py \
          test/test_task_python_project_build.py \
          test/test_install_wheel.py \
          test/test_remove_wheel.py \
          test/test_integration_pep621.py

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
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Additional details and impacted files

@@                Coverage Diff                @@
##             cottsay/pep621     #750   +/-   ##
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  Coverage                  ?   86.71%           
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  Files                     ?       79           
  Lines                     ?     4884           
  Branches                  ?      851           
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  Hits                      ?     4235           
  Misses                    ?      513           
  Partials                  ?      136           

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[KmoM88]

Following up on the PEP 517/518/621 discussion in #736 and the groundwork in cottsay/pep621:

This PR completes the core PEP 621 pipeline and brings it into full alignment with repository test standards:

1. Test Runner Alignment: Adapted async tests to from .run_until_complete import run_until_complete, matching colcon-core internal conventions without external pytest plugin dependencies.
2. Multi-Backend Integration Tests (test_integration_pep621.py): Added automated end-to-end fixtures validating real packaging workflows with flit_core and hatchling (pure PEP 621 packages, entry-point CLI script wrappers in bin/ with 0o755 permissions, clean rebuild removals, and editable builds).
3. Linters & CI Conformance: Fully compliant with flake8 and scspell3k.

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Staged Roadmap Proposal

To keep review manageable and prevent regressions, the broader modernization plan (covering subsequent stages such as PEP 660 non-Python data files symlinking and ROS 2 ament_python support in colcon-ros) is documented in this staged architectural proposal:

👉 https://gist.github.com/KmoM88/0357abff37b5a32ab801cac7d399d4ed

Stage	Component	Branch / Deliverable	Status
Stage 1 (Current)	colcon-core	PR #750 (feature/pep621-upstream-pr $\rightarrow$ cottsay/pep621)	In Review
Stage 2	colcon-core	feature/pep660-editable-data-files (Symlinking share/ assets for --symlink-install)	Ready & Tested
Stage 3	colcon-ros	feature/ros-ament-python-project (ament_python with pure pyproject.toml)	Ready & Tested
Stage 4	colcon-python-project	Deprecate standalone prototype repository	Planned