RFR: 8298405: Implement JEP 467: Markdown Documentation Comments [v69]

[Pavel Rappo]

On Wed, 15 May 2024 21:04:36 GMT, Jonathan Gibbons <jjg at openjdk.org> wrote:

>> Please review a patch to add support for Markdown syntax in documentation comments, as described in the associated JEP.
>> 
>> Notable features:
>> 
>> * support for `///` documentation comments in `JavaTokenizer`
>> * new module `jdk.internal.md` -- a private copy of the `commonmark-java` library
>> * updates to `DocCommentParser` to treat `///` comments as Markdown
>> * updates to the standard doclet to render Markdown comments in HTML
>
> Jonathan Gibbons has updated the pull request incrementally with one additional commit since the last revision:
> 
>   update tests for dangling doc comments, per review feedback

> > A meta question about the JEP: Why don't Javadoc features (like snippets and markdown comments) don't go through preview, while Compiler features mostly do? Is there any bar for previews?
> 
> Jon could probably reply more substantially, but my understanding is that [_JEP 12: Preview Features_](https://openjdk.org/jeps/12) is barely applicable here (emphasis mine):
> 
> > ## Summary
> > A _preview feature_ is a new feature of the Java language, Java Virtual Machine, or **Java SE API** that is fully specified, fully implemented, and yet impermanent. It is available in a JDK feature release to provoke developer feedback based on real world use; this may lead to it becoming permanent in a future Java SE Platform.
> 
> Technically, the only reason we could invoke JEP 12 here would be a tiny change to `Elements`, which is Java SE. But let's be honest, that change is not what _JEP 467: Markdown Documentation Comments_ is about.

Additionally, JavaDoc supports Preview APIs, but does not support previews (meta-previews?) of its own features. We simply don't have a mechanism to say: "Hey, that thing you are looking at is a new feature of JavaDoc. Click _here_ to learn more."

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PR Comment: https://git.openjdk.org/jdk/pull/16388#issuecomment-2115404225