Dependency tracking between modules in dune

Romain Beauxis

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Mar 17, 2021, 10:47:16 AM3/17/21

to ocaml...@googlegroups.com, Samuel Mimram

Hi!

How are dependencies computed between modules in dune?

I am trying to convert a large codebase to dune (liquidsoap) and dune is reporting a dependency cycle that I cannot see in the code.

I'm wondering if that could be a bug with dune but I'm not sure how to go about debugging it.

Thanks for your help!

Romain

Yaron Minsky

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Mar 17, 2021, 10:30:29 PM3/17/21

to ocaml...@googlegroups.com, Samuel Mimram

This list is pretty much dead. I think you'll have better luck with
this question on discuss.ocaml.org.

y

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Romain Beauxis

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Mar 17, 2021, 10:40:16 PM3/17/21

to ocaml...@googlegroups.com, Samuel Mimram

Thanks for the answer. The issue was with us so we're unblocked now :-)

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Jeremie Dimino

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Mar 18, 2021, 7:16:14 AM3/18/21

to ocaml...@googlegroups.com, Samuel Mimram

FTR, there is a known issue with such cycles reporting in Dune: Dune observes the cycle in the graph where each module has its transitive list of dependencies listed as dependencies, rather than just its first step ones as reported by ocamldep. As a result, Dune report cycle that might not be obvious in the code. Such as A->B->A where in fact A depends on C and C depends on B but A doesn't mention B.

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Jeremie

Romain Beauxis

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Mar 18, 2021, 9:28:08 AM3/18/21

to ocaml...@googlegroups.com, Samuel Mimram

That is exactly what happened in our case.

As a side note, we were able to build using a plain Makefile with pre-filled file order so there's also the possibility that some reported cycles are not necessarily preventing a proper compilation?

Romain

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Jeremie Dimino

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Mar 18, 2021, 10:20:57 AM3/18/21

to ocaml...@googlegroups.com, Samuel Mimram

Yes, it can happen. A possible reason is ocamldep reporting a dependency that is not a real one.

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