## User-facing changes
- Intra-doc links to primitives that currently go to rust-lang.org/nightly/std/primitive.x.html will start going to channel that rustdoc was built with. Nightly will continue going to /nightly; Beta will link to /beta; stable compilers will link to /1.52.1 (or whatever version they were built as).
- Cross-crate links from std to core currently go to /nightly unconditionally. They will start going to /1.52.0 on stable channels (but remain the same on nightly channels).
- Intra-crate links from std to std (or core to core) currently go to the same URL they are hosted at; they will continue to do so. Notably, this is different from everything else because it can preserve the distinction between /stable and /1.52.0 by using relative links.
Note that "links" includes both intra-doc links and rustdoc's own
automatically generated hyperlinks.
## Implementation changes
- Update the testsuite to allow linking to /beta and /1.52.1 in docs
- Use an html_root_url for the standard library that's dependent on the channel
This avoids linking to nightly docs on stable.
- Update rustdoc to use channel-dependent links for primitives from an
unknown crate
- Set DOC_RUST_LANG_ORG_CHANNEL from bootstrap to ensure it's in sync
- Include doc.rust-lang.org in the channel
- Remove the difference between `parent_item` and `current_item`; these
should never have been different.
- Remove `current_item` from `resolve` and `variant_field` so that
`Self` is only substituted in one place at the very start.
- Resolve the current item as a `DefId`, not a `HirId`. This is what
actually fixed the bug.
Hacks:
- `clean` uses `TypedefItem` when it _really_ should be
`AssociatedTypeItem`. I tried fixing this without success and hacked
around it instead (see comments)
- This stringifies DefIds, then resolves them a second time. This is
really silly and rustdoc should just use DefIds throughout. Fixing
this is a larger task than I want to take on right now.
