ci: Run style checks on merge requests

.gitlab-ci.yml

@@ -5,8 +5,18 @@ include:
 stages:
  - build
  - test
+ - style-checks
  - package
 
+workflow:
+  rules:
+    - if: $CI_PIPELINE_SOURCE == 'merge_request_event'
+    # Don't trigger a branch pipeline if there is an open MR
+    - if: $CI_COMMIT_BRANCH && $CI_OPEN_MERGE_REQUESTS
+      when: never
+    - if: $CI_COMMIT_TAG
+    - if: $CI_COMMIT_BRANCH
+
 .before_script: &before_script
   before_script:
     - export DEBIAN_FRONTEND=noninteractive
@@ -65,6 +75,34 @@ test:native-debian-trixie:
     variables:
       - $PKG_ONLY == "1"
 
+format-check:
+  <<: *tags
+  <<: *image
+  before_script:
+    - export DEBIAN_FRONTEND=noninteractive
+    - apt-get -y update
+    - apt-get -y install uncrustify git python3
+  stage: style-checks
+  needs: []
+  script:
+    - |
+      if [ -n "$CI_MERGE_REQUEST_TARGET_BRANCH_NAME" ]; then
+        git remote add target $CI_MERGE_REQUEST_PROJECT_URL.git
+        echo "Fetching MR target branch $CI_MERGE_REQUEST_TARGET_BRANCH_NAME from $CI_MERGE_REQUEST_PROJECT_URL"
+        git fetch target "$CI_MERGE_REQUEST_TARGET_BRANCH_NAME"
+        git fetch --deepen=100 origin HEAD
+        merge_base=$(git merge-base "target/$CI_MERGE_REQUEST_TARGET_BRANCH_NAME" HEAD)
+        if [ -z "$merge_base" ]; then
+          echo "Could't determine merge base"
+          exit 1
+        fi
+        echo "Merge base: $merge_base"
+        ./.gitlab-ci/check-style.py --dry-run --sha $merge_base
+      else
+        echo "Not a merge request"
+      fi
+  allow_failure: true
+
 package:deb-debian-trixie:arm64:
   variables:
     L5_DOCKER_IMAGE: debian:trixie