Fail loudly if BUCK file goes missing after running buckify_rocksdb.p…

…y script

buckifier/check_buck_targets.sh

@@ -1,7 +1,5 @@
 #!/usr/bin/env bash
 # Copyright (c) Facebook, Inc. and its affiliates. All Rights Reserved.
-# If clang_format_diff.py command is not specfied, we assume we are able to
-# access directly without any path.
 
 TGT_DIFF=`git diff BUCK | head -n 1`
 
@@ -17,6 +15,13 @@ cp BUCK BUCK.bkp
 
 ${PYTHON:-python3} buckifier/buckify_rocksdb.py
 
+if [[ ! -f "BUCK" ]]
+then
+  echo "buckifier/buckify_rocksdb.py was expected to (re)generate BUCK file."
+  echo "BUCK file is missing!"
+  exit 1
+fi
+
 TGT_DIFF=`git diff BUCK | head -n 1`
 
 if [ -z "$TGT_DIFF" ]