WIP: use build_if in test stanzas

[emillon]

This is making sure that ocaml/dune#7899 fits the build for eio. For now I'm checking that CI passes, I'll update this with questions later.

[emillon]

( actually if someone can enable the workflow so that I can see the CI results :) )

[emillon]

It seems to work: the disabled tests do not run. Other than what's currently in the diff, is there something else that's not satisfactory at the moment?

The current situation with (allow_empty) does not look great to me. Maybe this warning should only trigger when -p thispackage is passed, I think that this would solve most issues.

[talex5]

Thanks - this looks much better! Would be very happy to get rid of the allow_empty bits too, indeed.

[talex5]

Other than what's currently in the diff, is there something else that's not satisfactory at the moment?

One minor annoyance is that we can't attach a (package eio_main) to the benchmark executable. As a work-around we define it as a (test) instead, which does take a package, and then disable the test part using (action (progn)):

eio/bench/dune

Lines 1 to 8 in 264a7d0

	; This should be an executable, but dune won't let us associate non-installed executables
	; to packages, so we use this work-around.
	(test
	(name main)
	(package eio_main)
	(deps ./main.exe)
	(action (progn)) ; Don't run as a test
	(libraries eio_main yojson))

(reported at ocaml/dune#5621, though maybe it should be a separate issue)

[avsm]

@emillon just wanted to check on the status of this -- will this feature be in the dune 2.9.0 release, and have you had a chance to look at @talex5's comment above regarding the benchmark executable?

[emillon]

(build_if) is part of 3.9.0 which has been just submitted to opam-repository.

As for the benchmark executable, yes that seems valid as well. Maybe we can have a system to override which alias (test) adds the rule to; in which case dune runtest would do nothing but dune build @bench would run the benchmark. I believe that it would work?

[talex5]

Maybe we can have a system to override which alias (test) adds the rule to; in which case dune runtest would do nothing but dune build @bench would run the benchmark. I believe that it would work?

That sounds useful for this case. But it would be nice to fix the problem with executable too (for the reasons given in ocaml/dune#5621).

[talex5]

Fixed in #582 - thanks!