fix(py): propagate rules_python type stubs

[mkanat]

This is the most conservative change possible to make protobuf pyi files (which use rules_python underneath) propagate correctly (see my comment in #558). I could have made all the rules_py rules support putting pyi files in srcs, or made a new pyi_srcs, but I didn't want to propose a new API right now, so this seemed safer.

I did not just slop this PR out, I did review everything and have done multiple refinements to it on top of Codex's output. However, I'm not deeply familiar with all of the rules_py codebase so it's possible some of this isn't structured ideally.

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⚙️ Run configuration

Configuration used: Organization UI

Review profile: CHILL

Plan: Advanced

Run ID: 8764910e-3607-4d20-8502-a3da5c328fb6

📥 Commits

Reviewing files that changed from the base of the PR and between 3609650 and d612b53.

📒 Files selected for processing (14)

• docs/api/py.md
• py/private/py_info.bzl
• py/private/py_info_interop.bzl
• py/private/py_library.bzl
• py/private/py_unpacked_wheel.bzl
• py/private/py_venv/py_venv.bzl
• py/private/py_venv/py_venv_exec.bzl
• py/private/py_venv/types.bzl
• py/tests/py-info-interop/BUILD.bazel
• py/tests/py-info-interop/library.pyi
• py/tests/py-info-interop/pyi_propagation_test.bzl
• py/tests/py_venv_conflict/collision_order_test.bzl
• py/tests/py_venv_conflict/site_merge_order_test.bzl
• uv/private/whl_install/rule.bzl

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📝 Walkthrough

Walkthrough

Changes

Transitive Python type stub propagation

Layer / File(s)	Summary
Provider contracts and interoperability py/private/py_info.bzl, py/private/py_info_interop.bzl, docs/api/py.md	Providers and documentation define transitive_pyi_files. Interoperability reads the field from either provider or returns an empty depset.
py_library propagation and validation py/private/py_library.bzl, py/tests/py-info-interop/*	py_library collects .pyi files from dependencies and resolved virtual dependencies. Analysis tests verify cross-provider propagation.
Virtualenv and provider integration py/private/py_venv/*, py/private/py_unpacked_wheel.bzl, py/tests/py_venv_conflict/*, uv/private/whl_install/rule.bzl	Virtualenv providers carry .pyi files. Wheel and conflict fixtures initialize the field explicitly.

Priority: ⬇️ Low

Estimated code review effort: 3 (Moderate) | ~20 minutes

Merge Risk: ⚪ Minimal · up to d612b

This change propagates Python type-stub metadata through providers and virtualenv integration without identified merge-blocking risk.

Sequence Diagram(s)

sequenceDiagram
  participant rules_python_library
  participant py_library
  participant PyInfo
  participant pyi_propagation_test
  rules_python_library->>py_library: Provide library.pyi through rules_python PyInfo
  py_library->>PyInfo: Publish transitive_pyi_files
  PyInfo->>pyi_propagation_test: Expose propagated library.pyi
  pyi_propagation_test-->>py_library: Assert .pyi propagation and empty sources

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Suggested reviewers: jbedard

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 13.64% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 22 functions across 13 files. (1 skipped:…	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and concisely states the main change: propagation of rules_python type stubs.
Description check	✅ Passed	The description directly explains the purpose of the changes and the conservative implementation approach for propagating protobuf .pyi files.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

Full details: Docstring Coverage

Explanation

Docstring coverage is 13.64% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 22 functions across 13 files. (1 skipped: 1 unsupported.)

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[jbedard]

@codex

[chatgpt-codex-connector]

Codex Review Summary

This comment shows the latest Codex review activity on this pull request.

Review	Status	Commit	Review trigger
📝 Code Review	✅ Completed 2026-09-08T21:17:25.709281Z	d612b53	Manual request

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[jbedard]

@mkanat how can we test this? Checkout the existing typecheck CI job, but maybe you have other ideas?

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Reviewed commit: d612b530a3

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[xangcastle]

Thanks @mkanat. I picked up your commit as-is (authorship kept) in #1538 and built the rest on top: .pyi files in srcs are partitioned into transitive_pyi_files, venvs and launchers carry stubs into runfiles, and there is analysis + e2e coverage (rules_python pyi_srcs, protobuf _pb2.pyi, the compat flag). #1538 supersedes this one; I'll close it once that lands.

[mkanat]

Okay, thanks! Sorry I wasn't able to respond in time here, just been really busy.