dropping support for the MINGW64 environment on Windows

[bhaller]

The GitHub Actions CI for SLiM has started failing, consistently, for the mingw64 Windows build. Here's an example:

https://github.com/MesserLab/SLiM/actions/runs/35225245006

The log for the failed build says:

 C:\Windows\system32\cmd.exe /D /S /C D:\a\_temp\setup-msys2\msys2.cmd -c "'pacman' '--noconfirm' '-S' '--needed' '--overwrite' '*' 'mingw-w64-x86_64-slim-simulator'"
  error: target not found: mingw-w64-x86_64-slim-simulator
  Error: Error: The process 'C:\Windows\system32\cmd.exe' failed with exit code 1

Poking around, here's the page for SLiM on MSYS2:

https://packages.msys2.org/base/mingw-w64-slim-simulator

And in the "Changes" tab of that, I do notice that there was a commit yesterday, 16 September – when this started happening – to msys2/MINGW-packages on GitHub that removes mingw64 from mingw_arch in mingw-w64-slim-simulator/PKGBUILD‎:

msys2/MINGW-packages#31635

No explanation is given on that commit regarding why this was done. I tried a little googling and didn't see anything relevant in terms of news about platforms being dropped, etc. I'll put a comment on that commit and see if I get an answer.

@rdinnager tagging you since you're the manager of the pacman stuff for SLiM.

[bhaller]

OK, I got a reply over on the msys2 issue:

@bhaller: Support for the MINGW64 environment has been deprecated. And some packages are being removed.
See: https://www.msys2.org/news/#2026-03-15-deprecating-the-mingw64-environment

I see you are already also building in the UCRT64 environment of MSYS2. Going forward, it might be best if you removed the tests in the MINGW64 environment from your CI and continued only with the UCRT64 environment from MSYS2.

So I'll do that now. As a result of this, SLiM is dropping support for the MINGW64 environment; if we don't have pacman for it any more, then it is clear which way the wind is blowing. I'll attempt to revise the manual regarding this, too; we'll see how that goes. Changing the title of this issue to reflect this decision.

[bhaller]

OK, I have dropped the MINGW64 environment from the GitHub Actions CI.

I think I need a Windows user to revise the manual's install and build instructions. @rdinnager or @chris-a-talbot, are either of you available to do this?

In the pacman install instructions, I think basically things like:

pacman -S mingw-w64-x86_64-slim-simulator

need to shift over to installing the UCRT64 version, the screenshot of the install process needs to be updated, maybe the discussion of the directories where things can be found needs changes, etc.

In section 2.3.2, "Building SLiM from sources on Windows", I think changes are also needed. It looks like those instructions are based on "MSYS2 MinGW 64-bit" which I guess is the thing that has been deprecated; so it should shift over to UCRT64. Maybe the prerequisites that need to be installed change (?). The actual Windows build stuff in SLiM's CMakeLists.txt might need to change too, I'm not sure.