Bug report

Bug description:

This loop can run forever if there's a cycle in the Makefile variable definitions:

To reproduce:

make clean
echo 'foo=$(foo)' > ./Modules/Setup.local
./configure
make  # hangs forever

Or more minimally:

make clean
echo 'foo=$(foo)' > ./Modules/Setup.local
make Makefile
./python -m sysconfig --generate-posix-vars  # hangs forever

Longer cycles are also possible, e.g. v1=$(v2), v2=$(v3), ...., v999=$(v1).

Note that this is less of an issue if the recursive variable definition gets expanded in the Makefile before python -m sysconfig --generate-posix-vars gets invoked. In that case, Make will detect the cycle and exit before the infinite loop occurs.

@serhiy-storchaka you may be interested, this is very similar to #136073

CPython versions tested on:

CPython main branch

Operating systems tested on:

Linux

Linked PRs

• gh-136097: Fix sysconfig._parse_makefile() #136166