Cleanup .modified pipeline files

Also update comments accordingly to make it clear what pipeline files
are used to check validity.

Signed-off-by: Chenxiong Qi <[email protected]>

hack/validate-migration.sh

@@ -101,6 +101,7 @@ list_preprocessed_pipelines() {
 # This function checks two aspects:
 # - whether the migration file exits successfully or not.
 # - whether the migration file modifies a pipeline. If nothing changed, it is treated a failure.
+# The modified pipeline is saved into a separate file with suffix '.modified'.
 check_apply_on_pipelines() {
     local -r migration_file=$1
     local -r run_log_file=$(mktemp --suffix=-migration-run-test)
@@ -300,8 +301,15 @@ check_apply_in_real_cluster() {
     else
         kubectl create namespace ${K8S_TEST_NS}
     fi
-    local -r apply_logfile=$(mktemp --suffix="-${FUNCNAME[0]}")
-    local -r modified_pipeline_files=$(find "${WORK_DIR}/pipelines" -type f -name "*.modified")
+    local apply_logfile
+    local modified_pipeline_files
+    apply_logfile=$(mktemp --suffix="-${FUNCNAME[0]}")
+    modified_pipeline_files=$(find "${WORK_DIR}/pipelines" -type f -name "*.modified")
+    if [ -z "$modified_pipeline_files" ]; then
+        echo "error: No modified pipeline file is found." >&2
+        echo "error: Please check if migrations work correctly to update pipelines." >&2
+        exit 1
+    fi
     while read -r pl_file; do
         if ! kubectl apply -f "$pl_file" -n ${K8S_TEST_NS} 2>"$apply_logfile" >/dev/null; then
             echo "${FUNCNAME[0]}: failed to apply pipeline to cluster: $pl_file" >&2
@@ -338,6 +346,8 @@ main() {
         check_pass_shellcheck "$migration_file"
         check_migrations_is_in_task_version_specific_dir "$migration_file"
         check_version_match "$migration_file"
+        # Cleanup any existing pipeline files modified previously.
+        find "${WORK_DIR}/pipelines" -type f -name "*.modified" -delete
         check_apply_on_pipelines "$migration_file"
         check_apply_in_real_cluster
     done