`local_runtime_repo` writes absolute path of Xcode on macOS

[erikkerber]

🐞 bug report

(Sorry for all the annoying macOS specific bugs!)

Affected Rule

The issue is caused by the rule: `local_runtime_repo`

Is this a regression?

Yes(?)

Description

Starting with this change: https://github.com/bazel-contrib/rules_python/pull/2760/files#diff-33a51eb016b4b2a4b53d940f07c5388bd572ef61689051bc6f266ea7e5533c72R99

If running on macOS, /usr/bin/python3 is a system shim that will run a Python runtime located within Xcode. The path of Xcode will then show up in base_executable:

❯ /usr/bin/python3 python/private/get_local_runtime_info.py
{"major": 3, "minor": 9, "micro": 6, "include": "/Library/Python/3.9/include", "implementation_name": "cpython", "base_executable": "/Applications/Xcode-26.0.0-Beta.app/Contents/Developer/usr/bin/python3", "LDLIBRARY": "Python3.framework/Versions/3.9/Python3", "LIBDIR": "/Applications/Xcode.app/Contents/Developer/Library/Frameworks/Python3.framework/Versions/3.9/lib", "INSTSONAME": "Python3.framework/Versions/3.9/Python3", "PY3LIBRARY": "", "SHLIB_SUFFIX": ".so"}

This path then ends up in the run script for i.e. py_binary:

76:  PYTHON_BINARY = '/Applications/Xcode-26.0.0-Beta.app/Contents/Developer/usr/bin/python3'

🔬 Minimal Reproduction

1. macOS
2. local_runtime_repo setup with interpreter_path = "/usr/bin/python3"
3. build a py_binary target and observe the resulting run script
4. Change/move your Xcode version or path and rebuild. The py_binary path will be unchanged.

[aignas]

No need to be sorry, thanks for reporting this - it helps others who search for a similar issue.

What is the expected behaviour here?

[pennig]

Expected behavior is either:

• PYTHON_BINARY remains as /usr/bin/python3 and isn't resolved to the honest binary inside of Xcode.
• rules_python becomes sensitive to DEVELOPER_DIR and/or XCODE_VERSION (common env vars associated with the selected Xcode installation), so if those change it invalidates the bootstrap script's cache and it gets regenerated.

[aignas]

In my view the DEVELOPER_DIR and XCODE_VERSION awarness on osx would be preferred, because otherwise if the Python version is changed underthehood, the cache within bazel cannot be invalidated. Am I getting it right here?

If so, PRs on DEVELOPER_DIR and XCODE_VERSION awarness would be welcome! I don't use a Mac these days, so I cannot fully test or develop this.