Make sure to account for the right item universal regions in borrowck
Fixes https://github.com/rust-lang/rust/issues/144608.
The ICE comes from a mismatch between the liberated late bound regions (i.e. "`ReLateParam`"s) that come from promoting closure outlives, and the regions we have in our region vid mapping from `UniversalRegions`.
When building `UniversalRegions`, we end up using the liberated regions from the binder of the closure's signature:
c8bb4e8a12/compiler/rustc_borrowck/src/universal_regions.rs (L521)
Notably, this signature may be anonymized if the closure signature being deduced comes from an external constraints:
c8bb4e8a12/compiler/rustc_hir_typeck/src/closure.rs (L759-L762)
This is true in the test file I committed, where the signature is influenced by the `impl FnMut(&mut ())` RPIT.
However, when promoting a type outlives constraint we end up creating a late bound lifetime mapping that disagrees with those liberated late bound regions we constructed in `UniversalRegions`:
c8bb4e8a12/compiler/rustc_borrowck/src/universal_regions.rs (L299)
Specifically, in `for_each_late_bound_region_in_item` (which is called by `for_each_late_bound_region_in_recursive_scope`), we were using `tcx.late_bound_vars` which uses the late bound regions *from the HIR*. This query both undercounts the late bound regions (e.g. those that end up being deduced from bounds), and also doesn't account for the fact that we anonymize them in the signature as mentioned above.
c8bb4e8a12/compiler/rustc_borrowck/src/universal_regions.rs (L977)
This PR fixes that function to use the *correct signature*, which properly considers the bound vars that come from deducing the signature of the closure, and which comes from the closure's args from the `type_of` query.
08e26fc678