Windows Docker Images

Windows Docker Images

Mark Elvers
1 min read

Categories

  • ocaml

Tags

  • tunbury.org

In my previous post on the base image builder, I included a footnote that we now had Windows 2025 workers, but I didn’t mention that the base images weren’t building.

Docker on Windows is very slow, so I have had a background task nudging these builds forward a little bit each day, and I’m pleased to now report that over the weekend, the images all built, and the entire dashboard is green!

The most significant change was moving away from fdopen’s opam to native opam. This has unlocked OCaml 5 builds for the first time but has removed images for OCaml < 4.13. MSVC 5.0-5.2 are not available as the MSVC port was broken until OCaml 5.3 ocaml/ocaml#12954. Each version is built on Windows Server LTSC 2019, LTSC 2022, and LTSC 2025.

OCaml Version MinGW MSVC
4.13.1 ✓ ✓
4.14.2 ✓ ✓
5.0.0 ✓ ✗
5.1.1 ✓ ✗
5.2.1 ✓ ✗
5.3.0 ✓ ✓
5.4.0 ✓ ✓

Below are the detailed changes.

PR 257 ocaml-dockerfile

src-opam/distro.ml:

  • Changed opam_repository to use standard ocaml/opam-repository.git for Windows instead of ocaml-opam/opam-repository-mingw.git#sunset
  • Added version filter: Windows builds now require OCaml >= 4.13 (native opam 2.2+ requires official packages)
  • MSVC filter: OCaml 5.0-5.2 excluded (MSVC support restored in 5.3)

src-opam/windows.ml:

  • ocaml_for_windows_package_exn now returns Ocaml_version.Opam.V2.package directly, using official package names (ocaml-base-compiler/ocaml-variants+options) instead of fdopen’s +mingw64/+msvc64 naming

src-opam/opam.ml:

  • Reduce parallelism on Windows to avoid OOM on unbound make -j
  • Update Visual Studio to Windows 11 SDK
  • create_switch adds system-mingw/system-msvc for all Windows versions (not just 5.x)
  • setup_default_opam_windows_msvc persists MSVC environment (PATH, INCLUDE, LIB, LIBPATH) with correct PATH ordering: MSVC → Cygwin → Windows

PR 339 docker-base-images

src/pipeline.ml:

  • Port package (system-mingw/system-msvc) added for all Windows versions
  • Removed fdopen overlay addition (maybe_add_overlay no longer called for Windows)
  • Removed opam repo remove ocurrent-overlay step
  • Changed depext to Option type - returns None for Windows (opam 2.2+ has depext built-in)
  • Uses opam_repository_master for Windows instead of opam_repository_mingw_sunset

src/git_repositories.ml (implied by pipeline changes):

  • Removed references to opam_repository_mingw_sunset and opam_overlays.
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