Outdated documentation for feature `lang_items`

[kadiwa4]

Location

src/doc/unstable-book/src/language-features/lang-items.md or https://doc.rust-lang.org/unstable-book/language-features/lang-items.html

Summary

The examples don't compile and the list of lang items is outdated.

Should the list at the bottom of the page still be updated? The amount of language items has grown and there's already a list here in the source code.

[kadiwa4]

@rustbot claim
@rustbot label: +A-lang-item

[jyn514]

I think linking to the source code is better than trying to keep the list up to date, yes. We might still want to document the language items that are required for a no_std binary, since those are "user facing" in a way the others aren't.

[jyn514]

Ideally we could find a way to run rustdoc on the examples (as doctests) so they don't get outdated.

[kadiwa4]

The no_std guidance could be added to the nomicon because there's already a page there.