CI/CD for an OCaml Project with GitHub Actions

Build, test, and format-check your dune-based OCaml project.

OCaml projects use OPAM for packages and dune as the build system. The setup-ocaml action handles the OPAM switch and caching. This recipe builds, tests, and checks formatting.

What the pipeline does

set up OCaml and OPAM with caching
install deps with opam install
build with dune build
run tests with dune test
check formatting with dune fmt

The workflow

ocaml/setup-ocaml provisions the compiler and caches the OPAM switch. dune runtest executes the test stanzas.

.github/workflows/ci.yml

name: CI
on:
  push:
    branches: [main]
  pull_request:
jobs:
  build:
    runs-on: ubuntu-latest
    steps:
      - uses: actions/checkout@v4
      - uses: ocaml/setup-ocaml@v3
        with:
          ocaml-compiler: '5.2'
      - run: opam install . --deps-only --with-test
      - run: opam exec -- dune build
      - run: opam exec -- dune runtest
      - run: opam exec -- dune build @fmt

Caching and speed

setup-ocaml caches the OPAM switch and downloaded packages, which is the biggest speedup since building an OPAM switch from scratch is slow. The native compile is CPU-bound; cheaper managed runners such as Latchkey keep builds fast and auto-retry transient OPAM repository fetches.

Deploying

dune build produces a native executable under _build/default. Ship it in a slim container or attach it to a GitHub Release. For library packages, publish to the opam repository by opening a release PR with dune-release.

Key takeaways

setup-ocaml caches the OPAM switch for big speedups.
dune build, runtest, and @fmt cover build, test, and format.
Use dune-release to publish library packages to opam.