Set up clang-format in CI

.gitlab-ci.yml

@@ -8,6 +8,7 @@
 # with this file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
 stages:
+  - checkformat
   - buildsmoketests
   - smoketests
   - build
@@ -18,6 +19,7 @@ variables:
   EIGEN_CI_CMAKE_GENEATOR: "Ninja"
 
 include:
+  - "/ci/checkformat.gitlab-ci.yml"
   - "/ci/smoketests.gitlab-ci.yml"
   - "/ci/build.gitlab-ci.yml"
   - "/ci/test.gitlab-ci.yml"

ci/checkformat.gitlab-ci.yml

@@ -0,0 +1,11 @@
+checkformat:clangformat:
+  stage: checkformat
+  image: ubuntu:23.10
+  only:
+    - merge_requests
+  allow_failure: true
+  before_script:
+    - apt-get update -y
+    - apt-get install -y --no-install-recommends git clang-format-17
+  script:
+    - git clang-format-17 --diff --commit ${CI_MERGE_REQUEST_DIFF_BASE_SHA}