Revert to outputing a content-empty file when rendering a hidden module

[panglesd]

Hidden modules stopped creating an output file with "render source code", since calling html-generate on them was used to generate the associated source code.

However, this breaks dune rules in some cases (see issue #1013), as dune always expect an output to the execution of the command. See #1013 for a case where it happens.

With the separation of implementation and interface pipelines (see #1067), we will stop generating those content-empty files when rendering source code.

I think this fix should be included as a hotfix to the 2.3 and 2.4 branches, to maintain compatibility with dune rules (and ensure eio can build its doc).

@talex5 could you confirm that this patch fixes your issue?

[talex5]

It seems to be working - thanks!

$ opam pin odoc.dev https://github.com/panglesd/odoc.git#fix-1013
$ opam pin odoc-parser.dev https://github.com/panglesd/odoc.git#fix-1013
$ dune build @doc; echo $status
0

[Julow]

Looks good!

What do you think of deprecating this behavior so it can be removed again later ?

[jonludlam]

I'm not sure it's necessary. We'll certainly need a fix to dune for this issue - even with this PR merged dune will produce a completely empty file for modules with double underscores, which is of no use to anyone. Once that's fixed (and we've merged the PR changing how we do source rendering), nobody will ever be calling html-generate on hidden modules any more, so we might not need to revert this change. It doesn't seem a bad principle that calling html-generate will produce something - perhaps an html file saying "This module has been hidden". What do you think?

[panglesd]

I agree that having odoc html-generate always output something seems something we want, and that telling the reader why the documentation does not appear (as opposed to outputing an empty file) seems better. I'll add that to the PR.

[Julow]

I agree, it make sense to always generate something and the driver can easily skip generating these. The new paragraph is a nice touch !