Add --ff-only option

README.md

@@ -65,6 +65,12 @@ The name of the development branch (default `devel`).
 Allow fast forward merge (default `false`). If not enabled, merges will use
 `--no-ff`.
 
+### `ff_only`
+
+Refuse to merge and exit unless the current HEAD is already up to date or the
+merge can be resolved as a fast-forward (default `false`).
+Used only if `allow_ff=false`.
+
 ### `allow_forks`
 
 Allow action to run on forks (default `false`).

action.yml

@@ -17,6 +17,10 @@ inputs:
     description: 'Allow fast forward merge'
     required: false
     default: false
+  ff_only:
+    description: 'Refuse to perform a non fast forward merge (requires allow_ff=true)'
+    required: false
+    default: false
   allow_forks:
     description: 'Allow action to run on forks'
     required: false

entrypoint.sh

@@ -7,6 +7,7 @@ echo "  'Nightly Merge Action' is using the following input:"
 echo "    - stable_branch = '$INPUT_STABLE_BRANCH'"
 echo "    - development_branch = '$INPUT_DEVELOPMENT_BRANCH'"
 echo "    - allow_ff = $INPUT_ALLOW_FF"
+echo "    - ff_only = $INPUT_FF_ONLY"
 echo "    - allow_forks = $INPUT_ALLOW_FORKS"
 echo "    - user_name = $INPUT_USER_NAME"
 echo "    - user_email = $INPUT_USER_EMAIL"
@@ -18,9 +19,12 @@ if [[ -z "${!INPUT_PUSH_TOKEN}" ]]; then
   exit 1
 fi
 
-NO_FF="--no-ff"
+FF_MODE="--no-ff"
 if $INPUT_ALLOW_FF; then
-  NO_FF=""
+  FF_MODE="--ff"
+  if $INPUT_FF_ONLY; then
+    FF_MODE="--ff-only"
+  fi
 fi
 
 if ! $INPUT_ALLOW_FORKS; then
@@ -63,7 +67,7 @@ echo
 set -o xtrace
 
 # Do the merge
-git merge $NO_FF --no-edit $INPUT_STABLE_BRANCH
+git merge $FF_MODE --no-edit $INPUT_STABLE_BRANCH
 
 # Push the branch
 git push origin $INPUT_DEVELOPMENT_BRANCH