Render documentation of lints

[killercup]

Each of the Clippy lints is documented and the clippy docs are index (this one for the current version) that allows people to easily discover these lints. We should make the rustc built-in lints discoverable in this way as well.

• Provide tooling to render documentation similar to the Clippy one for the rustc build-in lints
  • generate docs that live next to the error index?
• We should add documentation to each of the built-in lints
  • might be inspired by Clippy's style
  • provide reasoning and example

[GuillaumeGomez]

We should definitely have such a thing. (maybe even extended to other things like compiler options?)

I suggest to generate a markdown file which will then be converted into HTML by rustdoc. Taking a look at how clippy's generated its own file (if that's how it's done) would be a good idea too.

[markmmm]

@GuillaumeGomez Is this done now that lints are documented in the Rustc book?

[GuillaumeGomez]

cc @steveklabnik

[steveklabnik]

Yes, this is done. New lints should get new docs; if any are missing, feel free to open one issue per lint.

[killercup]

This book? Where's the section on lints?

[steveklabnik]

It hits stable in the next release: https://doc.rust-lang.org/beta/rustc/lints/index.html

(This is distinct from that book; that's the contribution guide, this is the user guide)