Turns out, this has some really bad perf implications in large types (issue #88862). While we technically can handle them fine, it doesn't change test output either way. For now, revert with an added benchmark. Future attempts to change this back will have to consider perf.
Previously, we would 'forget' that we had `'static` regions in some
place during trait evaluation. This lead to us producing
`EvaluatedToOkModuloRegions` when we could have produced
`EvaluatedToOk`, causing us to perform unnecessary work.
This PR preserves `'static` regions when we canonicalize a predicate for
`evaluate_obligation`, and when we 'freshen' a predicate during trait
evaluation. Thie ensures that evaluating a predicate containing
`'static` regions can produce `EvaluatedToOk` (assuming that we
don't end up introducing any region dependencies during evaluation).
Building off of this improved caching, we use
`predicate_must_hold_considering_regions` during fulfillment of
projection predicates to see if we can skip performing additional work.
We already do this for trait predicates, but doing this for projection
predicates lead to mixed performance results without the above caching
improvements.
type is too big -> values of the type are too big
strictly speaking, `[u8; usize::MAX]` or even `[[[u128; usize::MAX]; usize::MAX]; usize::MAX]` are absolutely fine types as long as you don't try to deal with any values of it.
This error message seems to cause some confusion imo, for example in https://github.com/rust-lang/rust/pull/79135#issuecomment-729361380 so I would prefer us to be more precise here.
See the added test case which uses one of these types without causing an error.
r? ``@oli-obk``
