Allow for duplicate docstrings in `@docs` and `@autodocs`, issue #1079

[manuelbb-upb]

This is a proposal on how to fix https://github.com/JuliaDocs/Documenter.jl/issues/1079. By default, the standard behavior is maintained, that is, duplicate docstrings are not printed. However, @docs and @autodocs now allow for passing an id, i.e.

 ```@docs id1
some_function
```

The id will be Base64-encoded and used to compare objects and to define URLs; the default id is the empty string. Docstrings from blocks with differing ids will be printed and have differing anchors.

Additionally, @index blocks will refer only to docstrings from blocks with the empty id string by default. This behavior can be changed by providing the keyword include_ids:

```@index
include_ids = ["", "id1"]
```

I have not yet adapted the documentation for the proposed syntax.

[fingolfin]

So, does it seem like this has a chance to be merged? In this case, I guess the main TODO is to adjust the documentation? Or is there any other major blocker?

[fredrikekre]

Yea, I am just not a big fan of the API here. If a @docs block is marked with an identifier, does that mean that all docstrings in that block are duplicates? I am guessing that the most common use case is when you would like to splice in a single docstring in a "manual page" that also should exist on a "reference page"? So in those cases there would probably be quite few docstrings, like

Some text describing `foo`:

```@docs duplicates
foo
```

etc...

[manuelbb-upb]

Yes, that's the main use case (for me personally, but also from what I gather at #1079).

From how it looks in this line indeed every single docstring in a single @docs block is marked with the id. But for the main use case that's fine as there will usually only be a single docstring per block.

As an alternative to the current syntax, maybe a new block type (e.g. @docstring) could be used? Instead of user assigned identifiers, we could generate a random uuid4() in the background and mention in the docs, that @docstring content will not be referenced in an @index.

[fredrikekre]

Yea, I have definitely wanted that myself too at some point.

I did not try this out, but one idea would be to only actually put the id if there are duplicates detected in the block.

[manuelbb-upb]

I did not try this out, but one idea would be to only actually put the id if there are duplicates detected in the block.

The problem I see with this approach (i.e., taking the user out of the loop) again is the behavior of @index. Suppose you had a manual page

Some text describing `foo`:

```@docs
foo
```

etc...

and a reference page

Module API Page

```@autodocs
…
```

Without further hints from the user, @index would then have duplicates and list both foo two times. If we disallow duplicates in @index, we would somehow have to decide, which docstring to point to.

[fredrikekre]

If we disallow duplicates in @index, we would somehow have to decide, which docstring to point to.

Yea, my idea then would be that the one without an id would be the canonical one where all links would point to, and the duplicated one. Is it useful to be able to link to both of them individually?

[mortenpi]

@manuelbb-upb: are you still interested on working on this?

I agree with @fredrikekre's feedback, but I would go further and say that I am not sure that the whole unique id thing is actually necessary. I would propose the following design as an alternative:

• Allow an at-docs block to be marked "duplicate" (e.g. with just @docs duplicate). Docstrings from such a block are spliced in, but at-ref links can not point to these. There should probably be a warning or an error if a particular docstring is included only as a duplicate.
• By default, duplicate docstrings are not included in the index, but there could be an option to include them as well (e.g. if you're doing per-page indices). I am not sure we really need any more fine-grained control over this.
• Each duplicate docstring would still need an internal HTML id=... (e.g. when linked to by an at-index), but we can generate this automatically.

Things such as more fine grained filtering and marking individual docstrings as duplicate (as opposed to whole blocks) are things could be implemented later if the demand arises.

[manuelbb-upb]

@mortenpi As it is not that urgent a feature request, I should be able to find some time in the next few weeks to adapt the proposed code changes to your suggestions. If I remember correctly, I actually first tried automatic UUIDs and then I might have overdone it a bit :grin: