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explain rigid aliases

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lcnr 2024-03-22 10:40:58 +01:00 committed by Boxy
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src/solve/normalization.md
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@ -12,7 +12,9 @@ One-step normalization is implemented via `NormalizesTo` goals. Unlike other goa
in the trait solver, `NormalizesTo` always expects the term to be an unconstrained
inference variable[^opaques]. Think of it as a function, taking an alias as input
and returning its underlying value. If the alias is rigid, `NormalizesTo` fails and
returns `NoSolution`.
returns `NoSolution`. This is the case for `<T as Trait>::Assoc` if there's a `T: Trait`
where-bound and for opaque types with `Reveal::UserFacing` unless they are in the
defining scope. We must not treat any aliases as rigid in coherence.
The underlying value may itself be an unnormalized alias, e.g.
`NormalizesTo(<<() as Id>::This as Id>::This)` only returns `<() as Id>::This`,