enabled_if not masking a library target

[avsm]

eio has the following dune file frag:

(test
 (name test)
 (package eio_linux)
 (enabled_if (= %{system} "linux"))
 (modules test)
 (libraries alcotest eio_linux))

doing a build on macos results in this error:

File "lib_eio_linux/tests/dune", line 30, characters 21-30:
30 |  (libraries alcotest eio_linux))
                          ^^^^^^^^^
Error: Library "eio_linux" in _build/default/lib_eio_linux is hidden
(unsatisfied 'enabled_if').
-> required by _build/default/lib_eio_linux/tests/test.bc
-> required by alias lib_eio_linux/tests/all
-> required by alias default

cc @talex5 @patricoferris

It would be good if the exists_if in the dune file stops the library target from being attempted to be resolved.

[emillon]

I had a look at this, this is only caused in the presence of stubs. Here's a repro case:

  $ cat > dune-project << EOF
  > (lang dune 2.0)
  > EOF

  $ cat > dune << EOF
  > (library
  >  (name l)
  >  (modules l)
  >  (foreign_stubs
  >   (language c)
  >   (names stubs))
  >  (enabled_if false))
  > 
  > (test
  >  (name t)
  >  (modules t)
  >  (libraries l)
  >  (enabled_if false))
  > EOF

  $ touch t.ml l.ml stubs.c

  $ dune build

I'll have a look at a possible fix.