v3 errors with "error Only Win32 target is supported!"

[JasonGross]

  C:\hostedtoolcache\windows\opam\2.2.0\x86_64\opam.exe switch --no-install --packages=ocaml-base-compiler.4.11.1 create .
  
  <><> Installing new switch packages <><><><><><><><><><><><><><><><><><><><><><>
  Switch invariant: ["ocaml-base-compiler" {= "4.11.1"}]
  
  <><> Processing actions <><><><><><><><><><><><><><><><><><><><><><><><><><><><>
  -> installed base-bigarray.base
  -> installed base-threads.base
  -> installed base-unix.base
  -> retrieved ocaml-config.3  (2 extra sources)
  -> retrieved ocaml-config.3  (2 extra sources)
  -> retrieved ocaml-base-compiler.4.11.1  (https://github.com/ocaml/ocaml/archive/4.11.1.tar.gz)
  [ERROR] The compilation of ocaml-base-compiler.4.11.1 failed at "make -j3 world".
  
  #=== ERROR while compiling ocaml-base-compiler.4.11.1 =========================#
  # context     2.2.0 | win32/x86_64 |  | git+https://github.com/ocaml/opam-repository.git
  # path        D:\a\fiat-crypto\fiat-crypto\_opam\.opam-switch\build\ocaml-base-compiler.4.11.1
  # command     D:\cygwin\bin\make.exe -j3 world
  # exit-code   2
  # env-file    D:\.opam\log\ocaml-base-compiler-2360-cbf09e.env
  # output-file D:\.opam\log\ocaml-base-compiler-2360-cbf09e.out
  ### output ###
  # /usr/bin/make -C runtime  all
  # make[1]: Entering directory '/cygdrive/d/a/fiat-crypto/fiat-crypto/_opam/.opam-switch/build/ocaml-base-compiler.4.11.1/runtime'
  # echo "D:\a\fiat-crypto\fiat-crypto\_opam/lib/ocaml/stublibs" > ld.conf
  # tr -d '\r' < caml/instruct.h | \
  # sed -n -e '/^  /s/ \([A-Z]\)/ \&\&lbl_\1/gp' \
  #        -e '/^}/q' > caml/jumptbl.h
  # echo "D:\a\fiat-crypto\fiat-crypto\_opam/lib/ocaml" >> ld.conf
  # ../tools/make-version-header.sh ../VERSION > caml/version.h
  # gcc -c -O2 -fno-strict-aliasing -fwrapv -Wall -Wdeclaration-after-statement -fno-common -fexcess-precision=standard -fno-tree-vrp -g -D_FILE_OFFSET_BITS=64 -U_WIN32 -D_REENTRANT -DCAML_NAME_SPACE   -o stacks_b.o stacks.c
  # gcc -c -O2 -fno-strict-aliasing -fwrapv -Wall -Wdeclaration-after-statement -fno-common -fexcess-precision=standard -fno-tree-vrp -g -D_FILE_OFFSET_BITS=64 -U_WIN32 -D_REENTRANT -DCAML_NAME_SPACE   -o fix_code_b.o fix_code.c
  # In file included from C:/mingw64/x86_64-w64-mingw32/include/corecrt.h:10,
  #                  from C:/mingw64/x86_64-w64-mingw32/include/crtdefs.h:10,
  #                  from C:/mingw64/x86_64-w64-mingw32/include/string.h:9,
  #                  from stacks.c:20:
  # C:/mingw64/x86_64-w64-mingw32/include/_mingw.h:271:2: error: #error Only Win32 target is supported!
  #   271 | #error Only Win32 target is supported!
  #       |  ^~~~~
  # In file included from C:/mingw64/x86_64-w64-mingw32/include/stdarg.h:140,
  #                  from C:/mingw64/lib/gcc/x86_64-w64-mingw32/12.2.0/include/stdarg.h:1,
  #                  from caml/misc.h:30,
  #                  from caml/fail.h:26,
  #                  from stacks.c:22:
  # C:/mingw64/x86_64-w64-mingw32/include/_mingw_stdarg.h:11:2: error: #error Only Win32 target is supported!

mit-plv/fiat-crypto#1925
https://github.com/mit-plv/fiat-crypto/actions/runs/9754963239/job/26922701015?pr=1925

[smorimoto]

The PR adding windows support only back-ported the necessary fixes on OCaml 4.13 and up.

[JasonGross]

Why did ocaml-setup v2 work fine here, but v3 does not?

[smorimoto]

@JasonGross Because the version of opam has been updated to use the native opam repository instead of the slightly outdated repository for Windows. It should be possible to add support for older versions by backporting some commits to the OCaml compiler side.