How can build backends avoid breaking users when they make backwards incompatible changes?

Packaging
59

Just as a brainstorm/out of curiosity, I did a little experiment to see what is necessary to forward the -W options to the subprocess:

# > docker run --rm -it python:3.10-bookworm /bin/bash

mkdir /tmp/test && cd /tmp/test

cat <<EOF > wrapper.py
import sys
import subprocess
from itertools import chain
from pprint import pprint

print("\n\n--- wrapper ---")
pprint(sys.warnoptions)


args = [
    sys.executable,
    *chain.from_iterable(("-W", opt) for opt in sys.warnoptions),
    *("-W", "default:not given by user"),
    "_subprocess.py"
]
print(subprocess.check_output(args, text=True))
EOF

cat <<EOF > _subprocess.py
import sys
from pprint import pprint

print("\n\n--- _subprocess ---")
pprint(sys.warnoptions)
EOF


PYTHONWARNINGS='once:via env var' python -W 'error:hello' -W 'always:world' wrapper.py

This is the output:

--- wrapper ---
['once:via env var', 'error:hello', 'always:world']


--- _subprocess ---
['once:via env var', 'error:hello', 'always:world', 'default:not given by user']

So it seems that doing the following may be enough:

subprocess.run([
    sys.executable,
    *chain.from_iterable(("-W", opt) for opt in sys.warnoptions),
    ...
])