backport-of: none

This expands the API to be more flexible, allowing for more visitation patterns
on graphs. This will be useful to avoid extra datasets (and allocations) in
cases where the expanded DFS API is sufficient.

This also fixes a bug with the previous DFS constructor, which left the start
node not marked as visited (even though it was immediately returned).

They can be obtained by accessing the `TyCtxt` where they are needed.

Local variables can never be exported.

The order of the `where` bounds on auto trait impls changed because
rustdoc currently sorts auto trait `where` bounds based on the `Debug`
output for the bound. Now that the bounds have an actual `Res`, they are
being unintentionally sorted by their `DefId` rather than their path.
So, I had to update a test for the change in ordering of the rendered
bounds.

If the path is for a trait, it is always true that `trait_did ==
Some(did)`, so instead, `external_path()` now takes an `is_trait`
boolean.

It was only used for sugaring `Fn` trait bounds, and rustdoc already
checks that the `did` is for a `Fn` (or `FnMut`, `FnOnce`) lang item,
so it's not necessary to also check that the `did` belongs to a trait.

…estebank

 Detect stricter constraints on gats where clauses in impls vs trait

I might try to see if I can do a bit more to improve these diagnostics, but any initial feedback is appreciated. I can also do any additional work in a followup PR.

r? `@estebank`

rustc: Remove local variable IDs from `Export`s

Local variables can never be exported.

…, r=pietroalbini

Remove extra unshallow from cherry-pick checker

This is already done by https://github.com/rust-lang/rust/blob/13db8440bbbe42870bc828d4ec3e965b38670277/src/ci/init_repo.sh#L32-L36 on the beta channel, and git throws an error if you attempt to unshallow an already non-shallow repository.

r? ```@pietroalbini```

generic_const_exprs: use thir for abstract consts instead of mir

Changes `AbstractConst` building to use `thir` instead of `mir` so that there's less chance of consts unifying when they shouldn't because lowering to mir dropped information (see `abstract-consts-as-cast-5.rs` test)

r? `@lcnr`

…h726

Rework DepthFirstSearch API

This expands the API to be more flexible, allowing for more visitation patterns
on graphs. This will be useful to avoid extra datasets (and allocations) in
cases where the expanded DFS API is sufficient.

This also fixes a bug with the previous DFS constructor, which left the start
node not marked as visited (even though it was immediately returned).

Commit written by ```@nikomatsakis``` originally, cherry picked from several commits in work on never type stabilization, but stands alone.

rustdoc: Cleanup `clean` part 1

Split out from rust-lang#88379.

These commits are completely independent of each other, and each is a fairly
small change (the last few are new commits; they are not from rust-lang#88379):

- Remove unnecessary `Cache.*_did` fields
- rustdoc: Get symbol for `TyParam` directly
- Create a valid `Res` in `external_path()`
- Remove unused `hir_id` parameter from `resolve_type`
- Fix redundant arguments in `external_path()`
- Remove unnecessary `is_trait` argument
- rustdoc: Cleanup a pattern match in `external_generic_args()`

r? ``@jyn514``

explicitly link to external `ena` docs

we currently do not link to the docs of `ena`: https://doc.rust-lang.org/nightly/nightly-rustc/rustc_infer/infer/struct.InferCtxtInner.html#method.const_unification_table