Proposal: RDoc extension system

[okuramasafumi]

Abstract

I'd like to propose an extension system for RDoc.

YARD has been popular for years and new comment usages such as rbs-inline has been introduced. We need to organize efforts around comment space so that we don't have to duplicate our effort.

The important thing is that RDoc is currently the only library bundled with Ruby that handles comments. RDoc is used to parse CRuby's C comment so it's not realistic to remove it in near future. Therefore, I think RDoc is a good place for collecting efforts around comments and documentation.

Then an extension system comes in. Because we have different needs. When each extension is implemented as a gem, it's possible for other gems to bundle their extension to extend RDoc behavior. For example, language servers can extend RDoc so that it can be used with editors.

Details

RDoc has three main components: parsers, store and generators. It would be beneficial to be able to extend all of them.

Parsers https://github.com/ruby/rdoc/tree/master/lib/rdoc/parser

One of my concerns is that RDoc format is not used anymore. As far as I know, most gems use YARD format. Currently, if a language server wants to implement documentation feature, it needs to adopt both RDoc format and YARD format.

So I'd like to add YARD parser to RDoc. While this could be implemented directly, it's possible to have other new formats with extensions.

This might be trivial with something like below:

class MyParser
end

RDoc::Parser.add MyParser, :my_parser
RDoc::Parser.find :my_parser

Store https://github.com/ruby/rdoc/blob/master/lib/rdoc/store.rb

It's extremely hard to implement perfect data store. Language servers are an example. We didn't expect them, but now they play an important role. It was difficult to design data store for language servers before they come.

It would be great to have a way to extend store. It's not clear to me how to achieve this, though.

Generators https://github.com/ruby/rdoc/tree/master/lib/rdoc/generator

There are some use cases for new generators. For example, some might want to use a sophisticated template. More importantly, we can generate cache for documentation for other tools with a new generator.

Current RDoc features

Current RDoc features could be implemented as extensions. ri could be a good example.

Summary

The purpose of my proposal is to maintain RDoc as a place for collecting all the efforts around documentation and comment space. RDoc extension system makes it possible to keep the core of RDoc small as a bundled gem and let developers customize it.