ci: add script to detect need of container image rebuild

Signed-off-by: Niels de Vos <ndevos@redhat.com>

scripts/container-needs-rebuild.sh

@@ -0,0 +1,47 @@
+#!/bin/sh
+#
+# Check for changes needed by the container image. Two flavours of images are
+# supported, namely 'test' and 'devel'.
+#
+# Usage: scripts/container-needs-rebuild.sh {test|devel} [git-since]
+#
+#   - flavour is either 'test' or 'devel'
+#   - the optional 'git-since' points to a git reference, 'origin/master' if
+#     not set
+#
+# Returns 0 in case changes do not affect the container image.
+# Returns 10 in case the changes need a rebuild of the container image.
+#
+
+FLAVOUR="${1}"
+
+if [ "${FLAVOUR}" != 'test' ] && [ "${FLAVOUR}" != 'devel' ]
+then
+	echo 'ERROR: flavour must be "test" or "devel"'
+	exit 1
+fi
+
+GIT_SINCE="${2}"
+if [ -z "${GIT_SINCE}" ]; then
+	GIT_SINCE='origin/master'
+fi
+
+MODIFIED_FILES=$(git diff --name-only "${GIT_SINCE}")
+
+# files used for container image input
+# :test container
+CONTAINER_FILES="build.env scripts/Dockerfile.${FLAVOUR}"
+
+for MF in ${MODIFIED_FILES}
+do
+	for CF in ${CONTAINER_FILES}
+	do
+		if [ "${MF}" = "${CF}" ]
+		then
+			echo "container needs rebuild, ${CF} was modified"
+			exit 10
+		fi
+	done
+done
+
+exit 0