Actually, I think it's that ocamlbuild should be told to link libdai_stubs.a, and not try and build it. But also, I wanted to reference an existing work that links with C libraries, and I found ocamlbuild's example, with-c. I tried to build it, and I found that it isn't built by the harness default. Also, if you just try and build within just that raw directory in isolation, that it fails with a similar error I had been getting earlier. I looked around and found these:

https://stackoverflow.com/questions/19644451/how-to-make-ocamlbuild-compile-and-link-a-c-file-into-an-ocaml-project
https://l-lang.blogspot.com/2012/08/incorporating-c-code-in-ocaml-project.html

https://ocaml.org/learn/tutorials/ocamlbuild/Using_an_external_library.html

And I'm trying to follow, but they each give unique directions, each seem to not work for me.

On Sat, Aug 26, 2017 at 9:12 PM, Kenneth Adam Miller <kennethadammiller@gmail.com> wrote:

Hello,

I'm building a pair of companion oasis build spec and opam package setup for a C library. libdai I figured out how to get swig and oasis to build most things I need, but I'm having trouble getting oasis to not generate _stubs targets that aren't found. There is a static C/++ libdai.a file that is the product of the project I'm trying to wrap. I can't convince oasis to use that instead. Here's my _oasis target:

Library "dai"

  Path:                 ./

  Install:              false

  Modules:              Swig, Dai

  CompiledObject:       best

  CSources:             dai_wrap.cxx.c

  CCOpt:                -g -xc++ "-I../../include"

With a fresh clone of libdai, I get dai_wrap.cxx.c by doing the following in ./swig after building libdai:

$(SWIG) -ocaml -c++  dai.i

mv dai_wrap.cxx dai_wrap.cxx.c

sed -i -e 's/caml_array_length/caml_array_len/g' dai_wrap.cxx.c

I got my swig and dai ml files by doing the following:

swig2.0 -ocaml -co dai.ml

swig2.0 -ocaml -co swig.ml

swig2.0 -ocaml -co swig.mli

I build by doing the following:

ocaml setup.ml -configure

ocaml setup.ml -build


I get the following error:

Solver failed:

  Ocamlbuild knows of no rules that apply to a target named ./libdai_stubs.a. This can happen if you ask Ocamlbuild to build a target with the wrong extension (e.g. .opt instead of .native) or if the source files live in directories that have not been specified as include directories.

Compilation unsuccessful after building 8 targets (8 cached) in 00:00:00.

E: Failure("Command ''/usr/bin/ocamlbuild' ./libdai_stubs.a ./dlldai_stubs.so ./dai.cma ./dai.cmxa ./dai.a ./dai.cmxs -j 5 -tag debug' terminated with error code 6")

I want to make sure that the actual target shared library that was produced by the libdai build file itself is linked against. But oasis is assuming I have a _stubs target. I read in the documentation here that: "The usual idiom is to append _stubs to the name." 

https://ocaml.org/learn/tutorials/setting_up_with_oasis.html#Interfacing-with-C-code

And I think that that is the source of the error, but it isn't well explained. The ultimate things I originally wanted was to be able to use libdai with both the utop or the bytecode interpreter and with fully compiled targets. I was going to make libdai a library and then publicize it.

If anybody needs to replicate my issue, I have a docker container with this already.