`bisect_ppx` doesn't see the instrumentation clause in my library

[hirrolot]

I have the following project structure:

.
├── bin
│   ├── dune
│   └── main.ml
├── dune-project
├── lib
│   ├── dune
│   └── pld.ml
├── pld.opam
└── test
    ├── dune
    └── test.ml

Inside lib/dune:

(library
 (public_name pld)
 (preprocess
  (pps ppx_deriving.show ppx_deriving.eq))
 (instrumentation
  (backend bisect_ppx)))

Inside test/dune:

(test
 (name test)
 (libraries pld ounit2))

I expect bisect_ppx to do test coverage of my lib. However, when I execute the following commands:

$ find . -name '*.coverage' | xargs rm -f
$ dune test --instrument-with bisect_ppx --force
$ bisect-ppx-report html

I obtain Error: no *.coverage files found.

What am I doing wrong? I think that bisect_ppx just doesn't see the instrumentation clause inside lib/dune. If I add the same clause in test/dune, it will generate test coverage (but rather uselessly -- for the tests themselves).

[hirrolot]

Well, it turns out that when I actually use functions from lib/ inside the tests, everything works perfectly. It's still, however, very confusing, and I don't know whether it's intended or not. With empty tests, I'd rather expect to see 0% test coverage.

[alopezz]

I think this is due to what's described in #136, #391 (I just encountered a similar issue and was looking for answers, too).

[aantron]

Perhaps the Error: no *.coverage files found message can include some hints as to what the cause can be, and the files not being linked into the project will be one of the hints.

[aantron]

It's difficult for Bisect to, in a general way, know that you might have files that have not been linked into the build of the test suite (what I meant by project above), but Bisect can make an effort to warn users about that in various places.