BitsPython

# BitsPython — shared build-time Python helpers (bits-recipe-tools)
#
# Source after the base recipe include:
#   . $(bits-include BitsPython)
#
# Provides:
#   bits_pythonpath_from_deps   add every dependency's site-packages to PYTHONPATH
#   bits_enable_cython          put the bits-built Cython on PATH + PYTHONPATH
#
# Background: bits' build environment exports each dependency's $*_ROOT but, unlike
# the runtime modulefile, does NOT add its lib/pythonX.Y/site-packages to PYTHONPATH.
# Any build-time Python step that imports a dependency module (code generators,
# configure probes, Cython) therefore fails with ModuleNotFoundError unless the
# recipe puts those paths on PYTHONPATH itself.  These helpers factor out that
# boilerplate, which was previously copy-pasted across several recipes.

# Resolve the Python X.Y version of the stack's interpreter.  Prefers the
# dependency Python (PYTHON_ROOT / mixed-case Python_ROOT that bits' init.sh
# exports) over whatever python3 happens to be on PATH.  Echoes e.g. "3.13".
function _bits_py_xy() {
  "${PYTHON_ROOT:-${Python_ROOT:-/usr}}/bin/python3" \
    -c 'import sys; print("%d.%d" % sys.version_info[:2])' 2>/dev/null || echo 3
}

# bits_pythonpath_from_deps — add each dependency's site-packages to PYTHONPATH.
#
# Scans every *_ROOT in the environment (bits sets one per dependency; the regex
# accepts both the mixed-case names from init.sh and the uppercase names from
# new-style modulefiles) and prepends its lib/pythonX.Y/site-packages when that
# directory exists.  Safe to call from SetBuildEnv() or at recipe scope.
#
# IMPORTANT: this function ends with `return 0` on purpose.  The scan loop's last
# statement is `[ -d "$sp" ] && export ...`, whose status is non-zero whenever the
# final dependency scanned has no site-packages directory.  CMakeRecipe.Run()
# calls SetBuildEnv as a standalone command under `set -e`, so a non-zero return
# would abort the build SILENTLY before Configure.  Always return success.
function bits_pythonpath_from_deps() {
  # Under --initdotsh-from-modules (the default) each dependency's init.sh already
  # puts its lib/pythonX.Y/site-packages on PYTHONPATH, so this scan is redundant.
  [ -n "${BITS_INITDOTSH_FROM_MODULES}" ] && return 0
  local _pyver _r _sp
  _pyver=$(_bits_py_xy)
  for _r in $(env | grep -E '^[A-Za-z][A-Za-z0-9_]*_ROOT=' | cut -d= -f1 | sort -u); do
    _sp="${!_r}/lib/python${_pyver}/site-packages"
    [ -d "${_sp}" ] && export PYTHONPATH="${_sp}${PYTHONPATH:+:${PYTHONPATH}}"
  done
  return 0
}

# bits_enable_cython — make the bits-built Cython importable and runnable.
#
# Puts $CYTHON_ROOT/bin on PATH and its site-packages on PYTHONPATH so that an
# Autotools configure can detect "Cython >= X" and `make` can re-run the `cython`
# launcher to regenerate stale .pyx-derived C/C++ (the shipped *.cpp in many HEP
# tarballs were produced by an old Cython and use CPython internals removed in
# 3.12/3.13).  No-op when CYTHON_ROOT is unset.
#
# Call at RECIPE SCOPE when regeneration happens at `make` time and the recipe's
# Configure() runs its body in a subshell ( ... ) — a subshell-local export would
# not reach the separate Make step.  Calling it inside a non-subshell Configure()
# is also fine.  The recipe still removes its own stale generated files (the
# filenames are package-specific).
function bits_enable_cython() {
  # Under --initdotsh-from-modules (the default) the Cython dependency's init.sh
  # already exports its bin on PATH and its site-packages on PYTHONPATH.
  [ -n "${BITS_INITDOTSH_FROM_MODULES}" ] && return 0
  [ -n "${CYTHON_ROOT}" ] || return 0
  local _pyver
  _pyver=$(_bits_py_xy)
  export PATH="${CYTHON_ROOT}/bin:${PATH}"
  export PYTHONPATH="${CYTHON_ROOT}/lib/python${_pyver}/site-packages${PYTHONPATH:+:${PYTHONPATH}}"
  return 0
}