Bug report

Bug description:

When doing cross-builds, thePEP-739build-details.json gets generated using inconsistent data, some of which based on the build python, and some from the target platform python.

See for example the following gist:
https://gist.github.com/itamaro/8f23ebec2e142fd7480241b76c16c4e0

The gist contains thebuild-details.json generated for a 3.15 GIL-disabled build, using a 3.15 GIL-enabled build as the build-python.

Concretely:

cd~/pybuild/python/main-default./configure --with-pydebugmake -jcd~/pybuild/python/main-nogil./configure --with-pydebug --disable-gilmake -j# now use the GIL-enabled python to regenerate build-details.json for the nogil build_PYTHON_PROJECT_BASE=. _PYTHON_SYSCONFIGDATA_NAME=_sysconfigdata_td_darwin_darwin _PYTHON_SYSCONFIGDATA_PATH=build/lib.macosx-14.5-arm64-3.15~/pybuild/python/main-default/python.exe -E Tools/build/generate-build-details.py /tmp/build-details.json

Some examples from the gist:

Incorrect -abi.flags is["d"] instead of["t", "d"]:

"abi": {"flags": ["d"    ]  },

Correct -libpython.static has the correct SOABI, includingt:

"libpython": {"static":"/usr/local/lib/libpython3.15td.a"  },

Incorrect -suffixes.extensions includes extensions for the GIL-enabled ABI:

"extensions": [".cpython-315d-darwin.so",".cpython-315-darwin.so",".abi3.so",".so"    ]

Notes

I used a "cross-build" on the same MacOS host here, with GIL enabled vs GIL disabled, because it was the easiest for a full end-to-end repro on a single machine.
The issue is more general though, as I originally observed it when generatingbuild-info.json files for a MacOS-target runtime (both GIL enabled and disabled) using a Linux-GIL-enabled build-python. That setup is more involved, but the mixing is also more apparent, with some fields using "darwin" and other fields using "linux-gnu-x86_64" as the multiarch string.

CPython versions tested on:

CPython main branch, 3.15, 3.14

Operating systems tested on:

macOS, Linux