Cycles in normalization can cause evaluations to change from Unknown to
Err. This means that some selection that were applicable no longer are.
To avoid this:
* Selection candidates that are known to be applicable are prefered
over candidates that are not.
* We don't ICE if a candidate is no longer applicable.
Trait predicate ambiguities are not always in `Self`
When reporting ambiguities in trait predicates, the compiler incorrectly assumed the ambiguity was always in the type the trait should be implemented on, and never the generic parameters of the trait. This caused silly suggestions for predicates like `<KnownType as Trait<_>>`, such as giving explicit types to completely unrelated variables that happened to be of type `KnownType`.
This also reverts #73027, which worked around this issue in some cases and does not appear to be necessary any more.
fixes#77982fixes#78055
Try to make ObligationForest more efficient
This PR tries to decrease the number of allocations in ObligationForest, as well as moves some cold path code to an uninlined function.
normalize substs while inlining
fixes#68347 or more precisely, this fixes the same ICE in rust analyser as veloren is pinned to a specific nightly
and had an error with the current one.
I didn't look into creating an MVCE here as that seems fairly annoying, will spend a few minutes doing so rn. (failed)
r? `@eddyb` cc `@bjorn3`
Replace tuple of infer vars for upvar_tys with single infer var
This commit allows us to decide the number of captures required after
completing capture ananysis, which is required as part of implementing
RFC-2229.
closes https://github.com/rust-lang/project-rfc-2229/issues/4
r? `@nikomatsakis`
Use tracing spans in rustc_trait_selection
Spans are very helpful when debugging this code. It's also hot enough to make a good benchmark.
r? `@oli-obk`
Depending on if upvar_tys inferred or not, we were returning either an
inference variable which later resolves to a tuple or else the upvar tys
themselves
Co-authored-by: Roxane Fruytier <roxane.fruytier@hotmail.com>
This commit allows us to decide the number of captures required after
completing capture ananysis, which is required as part of implementing
RFC-2229.
Co-authored-by: Aman Arora <me@aman-arora.com>
Co-authored-by: Jenny Wills <wills.jenniferg@gmail.com>
Only check the own predicates of associated types when confirming
projection candidates.
Also consider implied bounds when comparing trait and impl methods.
Normalizing `<dyn Iterator<Item = ()> as Iterator>::Item` no longer
requires selecting `dyn Iterator<Item = ()>: Iterator`. This was
previously worked around by using a special type-folder to normalize
things.
Bounds of the form `type Future: Future<Result=Self::Result>` exist in
some ecosystem crates. To validate these bounds for trait objects we
need to normalize `Self::Result` in a way that doesn't cause a cycle.
