Support new flag: opam env --bare for use with GitHub actions

[shayne-fletcher]

Environment variables can be made available to steps in a GitHub workflow job by writing the variable definitions to the $GITHUB_ENV file.

• opam env prints an environment in terms of bash commands
• opam env --sexp prints an environment as an s-expression

If there existed a flag --bare (say) that printed an environment as exactlyVAR=VALUE lines e.g.

  OPAM_SWITCH_PREFIX=/home/foo-user/.opam/default
  CAML_LD_LIBRARY_PATH=/home/foo-user/.opam/default/lib/ocaml/stublibs:/home/foo-user/.opam/default/lib/ocaml
  ...

that is, equivalent to

  opam env | sed -e "s/ export .*//g" -e "s/'//g" -e "s/\;//g"

then, a github action to configure an OPAM environment could be very simply written as just

  - run: opam env --bare >> $GITHUB_ENV

[kit-ty-kate]

the feature request sound fine to me on its own, however for its use-case opam exec -- ... is most commonly used instead. How does that compare in terms of usability/complexity compared to using $GITHUB_ENV?

[shayne-fletcher]

significantly less convenient for us. using $GITHUB_ENV we can configure all subsequent job shells to implicitly be OPAM environments in the same way users are encouraged to add eval $(opam env) to their bash initialization file. set it and forget it.

[kit-ty-kate]

fair enough. We don’t have time to implement it until after the final release of opam 2.2.0 and even after larger works will most likely take priority but at least we’ll be more free to look at it.
If you want to have a stab at it (e.g. following the path of the --sexp option) you’re most than welcome to in the meantime