`dune test` and test-only dependencies

Ecosystem
1

Does anyone have a solution for this scenario:

I am building an OCaml library, nothing exciting.

I have some tests for the library, the tests use some test-only deps (e.g. Popper)

I want to be able to:

  • install just the base lib deps and run dune build to build just the base lib
  • install the test deps and run dune test

So far it seems like these goals are mutually exclusive.

I can add :with-test markers in dune-project to separate the deps into a group that has to be installed with --with-test flag. That covers the opam install separation, but dune build still tries to build the tests.

The generated mylib.opam file has an entry like:

build: [
  ["dune" "subst"] {dev}
  [
    "dune"
    "build"
    "-p"
    name
    "-j"
    jobs
    "@install"
    "@runtest" {with-test}
    "@doc" {with-doc}
  ]
]

ā€¦which makes clear why tests are included.

So I had a chat with an agentā€¦

It said I can do dune build -p mylib @install to build just the base lib without tests. Ok, but Iā€™d like to be able to just do dune build for the base case, and then add args to apply other cases.

Next it gave me profiles, so now dune-project has:

(test
 (name mylib)
 (build_if
  (= %{profile} test))
...

and this lets me do dune build without test deps installed.

But now I have to dune test ā€“profile test to run the tests. Feels redundant.

I realise this isnā€™t the end of the world, but I feel like I should be able to configure dune test to work without extra args.

The agent says it isnā€™t possible to have both properties that I want though.

Or any wizards out there have a solution for this?

2 Likes
2

dune build is dune build @@default which translates to ā€œbuild the ā€˜defaultā€™ alias non-recursively (ignoring subdirs) at the current directoryā€. When you havenā€™t manually overridden the @default alias it defaults to @all. @all will build all the executables and libraries in your project, this includes your test executables.

If you donā€™t want dune build to build your test executables, then you can override the meaning of default in your workspace-level directory. See here for more information:

Here is a similar question from another user recently:

3 
(alias
 (name default)
 (deps
  (alias_rec lib/all)))

is lib/all a thing itself that dune recognises, or itā€™s a placeholder that I should replace with the name(s) of libs that I want build by the default target?

can I put this in dune-project? that feels right but the docs for alias are under dune

if it has to be in a dune fileā€¦ I have this project structure:

lib/
  dune
  mylib.ml
  extra.ml
tests/
  dune
  test_mylib.ml

do I need to override default alias in both dune files?

ie in lib/dune to say ā€œbuild mylib" and in tests/dune to say ā€œdo nothingā€?

(is this a bad project structure?)

4

This would go in a dune file at the same level as lib/ and tests/ since you want to override the meaning of default in that directory.

lib/all is something that dune recognises. Itā€™s the all alias inside of lib/. So having

in a dune file at your project root would tell dune that the meaning of the default alias here is to build lib/all rather than the default value of lib/all test/all.

This would give the meaning that you want to dune build at the root of your project.

1 Like
5

Thank you!

With this pointer and a bit of thought on my side I have now been able to get my project building the way I wanted

I now have a root dune file like:

(dirs lib test)

(alias
 (name default)
 (deps
  (alias_rec lib/all)))

(alias
 (name runtest)
 (deps
  (alias_rec test/all)))

and I can dune build just the main lib with no test deps installed

or install test deps and dune test to build and run the tests

itā€™s simpler and cleaner than the mess that Copilot had cobbled together, and Iā€™ve learned a bit about dune

1 Like
6

hmm, one snag is that dune build no longer automatically rebuilds myproject.opam

but I now understand one way to fix thatā€¦

(alias
 (name default)
 (deps
  (alias_rec lib/all)
  (file "oktree.opam")))

is there another way?

is there anything like (alias_rec lib/all) that would mean ā€œall the sugars in my dune-projectā€ or something?