Installing Z3 via opam on Windows PowerShell with Cygwin requires cl

[LaifsV1]

Trying to install Z3 via opam for OCaml bindings in PowerShell with Cygwin does not use the Cygwin compilers, but uses cl instead. Is this intentional?

e.g.

The following actions will be performed:
=== install 1 package
  ∗ z3 4.15.2

<><> Processing actions <><><><><><><><><><><><><><><><><><><><><><><><><><>  🐫
⬇ retrieved z3.4.15.2  (cached)
[ERROR] The compilation of z3.4.15.2 failed at "make -C build -j 23".

#=== ERROR while compiling z3.4.15.2 ==========================================#
# context     2.5.0 | win32/x86_64 | ocaml.5.4.1 | https://opam.ocaml.org#40ee9f8d41e293fa1327d03c279f5e61e22157f8
# path        ~\AppData\Local\opam\default\.opam-switch\build\z3.4.15.2
# command     ~\AppData\Local\opam\.cygwin\root\bin\make.exe -C build -j 23
# exit-code   2
# env-file    ~\AppData\Local\opam\log\z3-25160-1d4b23.env
# output-file ~\AppData\Local\opam\log\z3-25160-1d4b23.out
### output ###
# make: Entering directory '/cygdrive/c/Users/<home>/AppData/Local/opam/default/.opam-switch/build/z3.4.15.2/build'
# make: cl: No such file or directory
# make: *** [Makefile:2753: smt\smt_statistics.obj] Error 127

edit: in this case, I can make some cl visible, but this would involve messing with the path when various projects could potentially be using different versions of it. but needing another environment for opam, when I'm already using Cygwin, feels unnecessary.

[wintersteiger]

IIRC that's due to a bug in the conf-python-3 package. Z3's build scripts decide what to use depending on the response to Python's os.name and opam/conf-python-3 decide that the native Windows Python is a good choice. Nowadays, Windows comes with a python.exe that will install Python via the Windows Store, so opam will find the wrong one on pretty much every Windows installation. The right thing to do is of course to chose the Cygwin python when Cygwin is used.