python-utils-r1.eclass: Add a sanity check for PYTHONPATH

Add a sanity check that ensures that PYTHONPATH does not contain any
relative paths.  While at it, also explicitly warn about PYTHONPATH
being set, so we know about it in build logs.

Signed-off-by: Michał Górny <mgorny@gentoo.org>

1 files changed, 34 insertions, 0 deletions

diff --git a/eclass/python-utils-r1.eclass b/eclass/python-utils-r1.eclass
index c47565fa1db2..cc33a1c1bffd 100644
--- a/eclass/python-utils-r1.eclass
+++ b/eclass/python-utils-r1.eclass
@@ -1544,4 +1544,38 @@ python_has_version() {
 	return 0
 }
 
+# @FUNCTION: _python_sanity_checks
+# @INTERNAL
+# @DESCRIPTION:
+# Perform additional environment sanity checks.
+_python_sanity_checks() {
+	debug-print-function ${FUNCNAME} "${@}"
+
+	[[ ${_PYTHON_SANITY_CHECKED} ]] && return
+
+	if [[ -v PYTHONPATH ]]; then
+		local x paths=()
+		mapfile -d ':' -t paths <<<${PYTHONPATH}
+
+		for x in "${paths[@]}"; do
+			if [[ ${x} != /* ]]; then
+				eerror "Relative path found in PYTHONPATH:"
+				eerror
+				eerror "  PYTHONPATH=${PYTHONPATH@Q}"
+				eerror
+				eerror "This is guaranteed to cause random breakage.  Please make sure that"
+				eerror "your PYTHONPATH contains absolute paths only (and only if necessary)."
+				eerror "Note that empty values (including ':' at either end and an empty"
+				eerror "PYTHONPATH) count as the current directory.  If no PYTHONPATH"
+				eerror "is intended, it needs to be unset instead."
+				die "Relative paths in PYTHONPATH are forbidden: ${x@Q}"
+			fi
+		done
+
+		elog "PYTHONPATH=${PYTHONPATH@Q}"
+	fi
+
+	_PYTHON_SANITY_CHECKED=1
+}
+
 fi