Auto merge of #47046 - Manishearth:intra-doc-links, r=eddyb,GuillaumeGomez,QuietMisdreavus,Manishearth

Implement RFC 1946 - intra-rustdoc links

https://github.com/rust-lang/rfcs/pull/1946 https://github.com/rust-lang/rust/issues/43466

Note for reviewers: The plain line counts are a little inflated because of how the markdown link parsing was done. [Read the file diff with "whitespace only" changes removed](https://github.com/rust-lang/rust/pull/47046/files?w=1) to get a better view of what actually changed there.

This pulls the name/path resolution mechanisms out of the compiler and runs it on the markdown in a crate's docs, so that links can be made to `SomeStruct` directly rather than finding the folder path to `struct.SomeStruct.html`. Check the `src/test/rustdoc/intra-paths.rs` test in this PR for a demo. The change was... a little invasive, but unlocks a really powerful mechanism for writing documentation that doesn't care about where an item was written to on the hard disk.

Items included:

 - [x] Make work with the hoedown renderer
 - [x] Handle relative paths
 - [x] Parse out the "path ambiguities" qualifiers (`[crate foo]`, `[struct Foo]`, `[foo()]`, `[static FOO]`, `[foo!]`, etc)
 - [x] Resolve foreign macros
 - [x] Resolve local macros
 - [x] Handle the use of inner/outer attributes giving different resolution scopes (handling for non-modules pushed to different PR)

Items not included:

 - [ ] Make sure cross-crate inlining works (blocked on refactor described in https://github.com/rust-lang/rust/pull/47046#issuecomment-354824520)
 - [ ] Implied Shortcut Reference Links (where just doing `[::std::iter::Iterator][]` without a reference anchor will resolve using the reference name rather than the link target) (requires modifying the markdown parser - blocked on Hoedown/Pulldown switch and https://github.com/google/pulldown-cmark/issues/121)
 - [ ] Handle enum variants and UFCS methods (Enum variants link to the enum page, associated methods don't link at all)
 - [ ] Emit more warnings/errors when things fail to resolve (linking to a value-namespaced item without a qualifier will emit an error, otherwise the link is just treated as a url, not a rust path)
 - [ ] Give better spans for resolution errors (currently the span for the first doc comment is used)
 - [ ] Check for inner doc comments on things that aren't modules

I'm making the PR, but it should be noted that most of the work was done by Misdreavus :smile:

(Editor's note: This has become a lie, check that commit log, Manish did a ton of work after this PR was opened `>_>`)

0 files changed, 0 insertions, 0 deletions