(optional) not respected in (executable) and (library) stanza

[fangyi-zhou]

Expected Behavior

1. Run $ dune build
2. main.exe is compiled, main_lwt.exe is not compiled because it's optional and lwt is not installed.

Actual Behavior

Failed with missing lwt

Reproduction

https://github.com/fangyi-zhou/dune-optional-repro

Specifications

• Version of dune (output of dune --version): 2.7.1
• Version of ocaml (output of ocamlc --version) 4.11.0
• Operating system (distribution and version): macos 10.15.7
• Link to gist with verbose output (run dune with the --verbose flag):
  https://gist.github.com/fangyi-zhou/b41bfe07f77abd3219e1fdd09d408198

[nojb]

Hello, unless I missed something, there doesn't seem to be any (optional) annotation in your reproduction sample.

[fangyi-zhou]

Sorry, something was lost in creating the repro, but the behaviour is the same
https://github.com/fangyi-zhou/dune-optional-repro/blob/master/bin/dune#L12

[fangyi-zhou]

https://github.com/ocaml/dune/blob/master/test/blackbox-tests/test-cases/optional-executable.t/run.t
https://github.com/ocaml/dune/blob/master/test/blackbox-tests/test-cases/optional.t/run.t
It seems that the behaviour of (optional) is correct, but dune build decides to build all stanza regardless of optional. Am I doing it wrong?

[nojb]

I was able to reproduce. Indeed it is puzzling. I am investigating.

[nojb]

... and actually I think this is the expected behaviour. Indeed, this feature is meant to avoid adding hard-dependencies to OPAM packages, so you will get the desired behaviour only if you build the @install target. Other targets will still try to build the (optional) stanzas.

It would be great if you can confirm that you see the same behaviour.

[fangyi-zhou]

Thanks for the reply. I noticed that building @install omits the optional target.

I guess I can close this issue now.