git-cp: continue to merge when merge.ff is only (#1070)

Signed-off-by: spacewander <spacewanderlzx@gmail.com>

bin/git-cp

@@ -38,6 +38,12 @@ else
  exit 40
  fi
 
+ MERGE_OPT=
+ ff=$(git config --get merge.ff)
+ if [[ "$ff" == "only" ]]; then
+ MERGE_OPT="--ff"
+ fi
+
  echo "Copying $CURRENT_FILENAME into $DESTINATION_FILENAME"
 
  INTERMEDIATE_FILENAME="${CURRENT_FILENAME//\//__}-move-to-${DESTINATION_FILENAME//\//__}"
@@ -59,7 +65,8 @@ else
  git reset --hard HEAD^
 
  # We keep both files
- git merge "${DESTINATION_SAVED}" "${INTERMEDIATE_SAVED}" -m "Duplicate ${CURRENT_FILENAME} history."
+ # shellcheck disable=SC2086
+ git merge $MERGE_OPT "${DESTINATION_SAVED}" "${INTERMEDIATE_SAVED}" -m "Duplicate ${CURRENT_FILENAME} history."
 
  # We get back our original name
  git mv "${INTERMEDIATE_FILENAME}" "${CURRENT_FILENAME}"