Add winsymlinks:native to the CYGWIN environment variable when running a Cygwin executable on Windows

[kit-ty-kate]

Fixes #5782

Actually no, at least not yet. Upon creating the PR I realized another point in the code also modifies CYGWIN (in a destructive manner)

@dra27 I’m reading the comments for OpamProcess.cygwin_create_process_env and the use of win_create_process (which i’m also realizing does not exist in OCaml >= 5.0, which means opam can’t be compiled on Windows if you’re using ocaml 5) and I’m not sure if it’s just a relic of the past that can now be replaced by Unix.create_process_env or not? Was the issue encountered with Unix.create_process_env ever got fixed or was it only an issue in opam and thus not something that could actually be fixed upstream?

If it is a relic of the past I’ll go ahead and remove it and together with the current code, it should work.

[dra27]

In somewhat haste, nothing's been fixed in OCaml (nor is ever likely to be), so I believe the code is still needed. The stubs are still there, they are called caml_unix_create_process and caml_unix_create_process_native in OCaml 5.0+

[dra27]

Thanks for looking at this! The part in OpamProcess is completely orthogonal - that's all to do with getting the escaping of arguments correct. It doesn't destructively change CYGWIN though - it's editing it (in what's looking to me 9 years later to be a possibly over-pedantic fashion, but perhaps the rules for specifying options in the CYGWIN variable used to be more strict).

Regardless, it's definitely not interfering because my local workaround has been to set CYGWIN=winsymlinks:strict in my shell prior to invoking opam and it's not overriding it 🙂

[kit-ty-kate]

@dra27 done

[dra27]

A thought which didn't occur to me before - does this also apply when we're running commands from within opam (e.g. quite critically, tar)?

[kit-ty-kate]

ah i think you're right. That code should be in OpamProcess.cygwin_create_process_env instead

[rjbou]

lgtm, thanks!