What should happen when exposing code from a private package?

[NatKarmios]

Suppose I'm writing a library, and I want to simplify the interface and documentation by making all but the toplevel module private using the package stanza, where the toplevel module re-exposes code from private packages.

When I try add this library as a dependency, and try use that private code via the re-exposed interface, compilation fails with missing .cmis.

I understand that this may be intended behaviour; if that is the case, should the compiler, when compiling the library, warn about exposed interfaces that can't be used?

A minimal reproduction can be found here: https://github.com/NatKarmios/dune-private-bug

[Alizter]

When you install private libraries in a package, their interface files will no longer appear to consumers. This is detailed in the (package) section of the library stanza doc: https://dune.readthedocs.io/en/stable/dune-files.html#library

The error message I get in Dune 3.7+ is:

 File "executable/MyExe/bin/myexe.ml", line 1, characters 5-32:
  1 | open Mylib.Utils.Syntaxes.Option
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  Error: The module Mylib.Utils is an alias for module Utils, which is missing
  [1]

Which I don't think can be any better.

Maybe we can add a note to the documentation about making module aliases of modules of a private library. Since I don't see any realistic way to allow for such a behaviour.

[rgrinberg]

I understand that this may be intended behaviour; if that is the case, should the compiler, when compiling the library, warn about exposed interfaces that can't be used?

You're allowed to do this, but I think you need to write the interface of your module explicitly.

Alternatively, you could try doing (libraries (re_export utils)) which should work. Although it might not, because I've never thought about this use case.