[Neira12]

Summary

Fixes #152: the runtime core fails to build with "_POSIX_C_SOURCE" redefined / "_XOPEN_SOURCE" redefined errors from pyconfig.h.

Two things combine:

• glibc's POSIX.1-2024 update (glibc commit a5cc3018f3, "Add feature test macros for POSIX.1-2024") makes features.h set _POSIX_C_SOURCE 202405L and, with _GNU_SOURCE, _XOPEN_SOURCE 800. pyconfig.h defines them unconditionally as 200809L and 700 (Python 3.10 and 3.13 alike), so any file that includes a libc header before Python.h redefines them with a different value.
• GCC hides warnings inside system headers, so this only shows when the Python headers are not under a system include path (pyenv, conda, a self-built Python) — which matches the reporter's setup. With -Werror the warning stops the build.

python_plugin_bridge.h reaches Python.h after libc headers in plc_boot.c, plc_retain.cpp, plc_state_manager.cpp and unix_socket.c. The fix #undefs the two macros right before #include <Python.h> there. libc has already consumed them in features.h (include-guarded), so nothing it declares changes. The existing #pragma GCC diagnostic ignored "-Wcpp" does not cover macro redefinition in GCC; it is left as is. plugin_driver.c and plc_main.c include Python.h first and are not affected.

Ticket

External contribution, no RTOP ticket. Closes #152.

How it was tested

• Reproduced on Ubuntu 24.04 (GCC 13.3, glibc 2.39) by putting the Python 3.13 headers outside /usr/include (via a python3-embed.pc on PKG_CONFIG_PATH) and shadowing features.h with the POSIX.1-2024 values (202405L / 800). Before the change, make fails in plc_boot.c, plc_retain.cpp, plc_state_manager.cpp and unix_socket.c with the errors from the issue; after it, plc_main builds.
• Normal build (system Python headers, real glibc 2.39) still builds, and the preprocessed output of those four files is byte-identical before and after the change.
• tests/host/run.sh: all passed.
• clang-format --style=file reports no changes for the edited header.
• Not tested with a real glibc that ships the new values or with Python 3.10 itself; Python 3.10.22's configure.ac defines the same 200809L / 700.

Checklist

• bash scripts/run-pytest.sh passes: not run; the change is a C header include-order fix with no Python-side effect.
• pre-commit run clean: clang-format clean for the edited .h.
• Docs updated if behavior changed (README, CLAUDE.md, docs/): no documented behaviour changes.
• Follows the shared review process (summary in .claude/review-guidelines.md): no IPC, scan-cycle or plugin ABI change.

Contributor License Agreement

• I have read and agree to the Contributor License Agreement, version 1.0

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