Dune expects .so files generated even when shared libraries are not supported

[aantron]

See ocsigen/lwt#599. @rgrinberg, can you move the most relevant details into a comment on this issue?

[rgrinberg]

My idea consists of 2 parts:

• Add a mechanism for customizing compiler flags in a "global" way via workspace files: Customize workspace via environment variable #1053. This will make it possible to inject flags such as -static whenever such a need arises instead of relying on editing $ ocamlc - config

• Adding a flag to the env stanza to disable .so targets. Here, there's a bit of uncertainty on how to proceed. We could have a crude no_shared_objects flag, or we could have a field like (default_targets (:standard \ shared_objects)) if we want something more extensible.

Given both of these points, it will be possible to solve this problem for Lwt (and any other lib) by passing a workspace file that adds -static to :standard, and disables the generation of .so rules. We could have a high level, combined option to do both at once, since many users will not create about these details.

cc @avsm and @mghallin who are both users that I think are interested in an easy way of creating static binaries.

[aantron]

Also ccing @gruenewa and @lvicentesanchez from the original Lwt issue.

[ghost]

Is the issue that when the OCaml compiler is not configured to support shared library, then ocamlmklib won't produce a .so while dune expects that it will?

[rgrinberg]

@diml yeah, that's the gist of it.

[ghost]

Ok. We can determine whether the compiler support shared libraries by looking for SUPPORTS_SHARED_LIBRARIES in the Makefile.config file installed by ocaml in ocamlc -where.

Dune already supports a (no_dynlink) field for libraries, so I believe that all that needs to be done is mimic the behavior of (no_dynlink) systematically when SUPPORT_SHARED_LIBRARIES is set to false.