swift

f0d59d5d - RequirementMachine: Handle equivalence classes that both have a concrete type and protocol requirements

RequirementMachine: Handle equivalence classes that both have a concrete type and protocol requirements If a type parameter has a protocol conformance and a concrete type, we want to map associated types of the conformance to their concrete type witnesses. This is implemented as a post-processing pass in the completion procedure that runs after the equivalence class map has been built. If we have an equivalence class T => { conforms_to: [ P ], concrete: Foo }, then for each associated type A of P, we generate a new rule: T.[P:A].[concrete: Foo.A] => T.[P:A] (if Foo.A is concrete) T.[P:A] => T.(Foo.A) (if Foo.A is abstract) If this process introduced any new rules, we check for any new overlaps by re-running Knuth-Bendix completion; this may in turn introduce new concrete associated type overlaps, and so on. The overall completion procedure now alternates between Knuth-Bendix and rebuilding the equivalence class map; the rewrite system is complete when neither step is able to introduce any new rules.