Allow targets in subdirectories

[samoht]

When trying to wrap existing complex projects, it would be very convenient to write something like:

(rule
   (deps (source_tree src))
   (targets src/bin/foo)
   (action (run make -C src bin/foo)))

Unfortunately dune complains with:

Error: src/bin/foo does not denote a file in the current directory

[nojb]

I think this should be doable with #3268

[samoht]

I haven't found a way to make it work with subdirs, as my use-case needs to call make at the root of src and it will produces files sub-directories (.e.g in src/bin, src/includes/, etc).

[samoht]

(also if I try to copy the files at the root in the action, I have a problem similar to #3345 where dune complains that it doesn't know how to generate this files)

[lubegasimon]

We’re (at odoc) also blocked by this issue. Basically, the current scheme for generator tests in odoc is so irritating, thus a need for improvement.

For example we have these rules that're generated as a result of generated dune files concept by the help of include stanza.

(rule
    (targets html.gen/test/Bugs/index.html)
    (deps bugs.odocl)
    (action
        (run odoc html-generate --indent -o html.gen %{deps})))
(rule
    (alias runtest)
    (action
        (diff html/test/Bugs/index.html html.gen/test/Bugs/index.html)))

And what we want is for dune to be able to generate the html.gen/test/Bugs/index.html in the _build/default/... dir and html/test/Bugs/index.html in our source tree.

But dune complains with

Error: html.gen/test/Bugs/index.html does not denote a file in the current
directory

(There is a RFC on this topic though)

[sim642]

I hit the same issue trying to gradually port configure+Makefile to dune. Eventually I came up with the following hacky workaround.

In dune:

(rule
 (alias configure)
 (deps
  ; ...
  )
 (targets
  ; ...
  ; HACK: workaround for https://github.com/ocaml/dune/issues/3374
  src__machdep-ml.c
  src__cilversion.ml
  lib__perl5__App__Cilly__CilConfig.pm)
 (action (progn
  (run ./configure)
  ; HACK: workaround for https://github.com/ocaml/dune/issues/3374
  ; HACK: use "run cp" instead of "copy" to avoid implicit unsupported subdir deps
  (run cp src/machdep-ml.c src__machdep-ml.c)
  (run cp src/cilversion.ml src__cilversion.ml)
  (run cp lib/perl5/App/Cilly/CilConfig.pm lib__perl5__App__Cilly__CilConfig.pm))))

In src/dune:

; HACK: workaround for https://github.com/ocaml/dune/issues/3374
(rule (action (copy ../src__machdep-ml.c machdep-ml.c)))
(rule (action (copy ../src__cilversion.ml cilversion.ml)))

[rgrinberg]

There's now an experimental directory targets feature that you can try out. See test-cases/directory-targets/main.t for examples.