ci: add auto format

.github/workflows/lint.yml

@@ -5,7 +5,9 @@ on:
   - pull_request
 
 jobs:
-  lint-fmt:
+  # auto fix formatting, Thanks to robur.coop for the implementation
+  # https://discuss.ocaml.org/t/ocamlformat-and-github-actions/15464
+  lint-auto-fmt:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout code
@@ -18,8 +20,25 @@ jobs:
           dune-cache: true
           allow-prerelease-opam: true
 
-      - name: Lint fmt
-        uses: ocaml/setup-ocaml/lint-fmt@v3
+      - name: Install ocamlformat
+        run: grep version .ocamlformat | cut -d '=' -f 2 | xargs -I V opam install ocamlformat=V
+
+      - name: Format code
+        run: |
+          git ls-files '*.ml' '*.mli' | xargs opam exec -- ocamlformat --inplace
+
+      - name: Check for modified files
+        id: git-check
+        run: echo "modified=$(if git diff-index --quiet HEAD --; then echo "false"; else echo "true"; fi)" >> $GITHUB_OUTPUT
+
+      - name: Commit and push changes
+        if: ${{ steps.git-check.outputs.modified == 'true' }}
+        run: |
+          git config --global user.name "Automated ocamlformat GitHub action, developed by robur.coop"
+          git config --global user.email "[email protected]"
+          git add -A
+          git commit -m "formatted code"
+          git push
 
   lint-opam:
     runs-on: ubuntu-latest