Windows: opam fails to install `conf-libcurl`.

[yosefAlsuhaibani]

related: ocaml/opam-repository#26894.

Using setup-ocaml@v3 on a windows GHA run: trying to install conf-libcurl fails with the error /usr/bin/sh: line 1: curl-config: command not found. SSH-ing into the runner (w/https://github.com/mxschmitt/action-tmate
) I was able to find curl-config under /d/cygwin/usr/x86_64-w64-mingw32/sys-root/mingw/bin, which makes me believe that setup-ocaml isn't configuring the PATH correctly.

I've reproduced this here: yosefAlsuhaibani/test-ocaml-setup-windows#4, where in the latest commit this run fails (https://github.com/yosefAlsuhaibani/test-ocaml-setup-windows/actions/runs/11978037743/job/33397219358) which is done by this workflow (https://github.com/yosefAlsuhaibani/test-ocaml-setup-windows/actions/runs/11978037743/workflow).

[tobil4sk]

It looks like /usr/x86_64-w64-mingw32/sys-root/mingw/bin should be added to PATH by the mingw-w64-shims package: https://github.com/dra27/mingw-w64-shims/blob/3c4a82700d9b03443ad6f2927449f7a8f25a77cf/mingw-w64-shims.opam#L8, perhaps @dra27 might have some advice on what could be missing here?

[punchagan]

It looks like the problem here occurs when mingw-w64-shims package is recompiled (when conf-pkg-config, it's optional dependency is being added). mingw-w64-shims package is first being removed, which undoes the PATH changes done by that package, and conf-libcurl build step fails to find the curl-config tool in PATH.

A work around for this is to install run opam install conf-pkg-config before running opam install .

NOTE: You already seem to be running opam install --depext-only conf-pkg-config before opam install ., but this (--depext-only) doesn't trigger the recompile of the mingw-w64-shims package.

[smorimoto]

This looks like an issue that needs to be fixed further upstream.
@dra27 You may have some ideas to fix this.