RequirementMachine: Concrete contraction needs to substitute the parent type of a subject type sometimes #59310
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…ral mode We resolve protocol typealiases to DependentMemberTypes because the Requirement Machine treats them as rewrite rules. However, it doesn't do this for typealiases in protocol extensions. Fixes rdar://problem/94150249.
…ects an invariant violation
…nt type of a subject type sometimes If you have generic parameters <T, U> and requirements of the form: - T : P - T == ConcreteType<U> - T.[P]U : SomeClass - T.[P]U : SomeProto And furthermore SomeClass does not conform to SomeProto, we can't leave `T.[P]U : SomeClass` unsubstituted; we still have to replace `T` with `ConcreteType<U>` to transform the latter two requirements into: - U : SomeClass - U : SomeProto "Concrete contraction" is easily the hackiest part of the Requirement Machine; I need to come up with a more principled solution for the problem that it solves sooner or later. Fixes rdar://problem/94150249.
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If you have generic parameters
<T, U>and requirements of the form:T : PT == ConcreteType<U>T.[P]U : SomeClassT.[P]U : SomeProtoAnd furthermore SomeClass does not conform to SomeProto, we can't leave
T.[P]U : SomeClassunsubstituted; we still have to replaceTwithConcreteType<U>to transform the latter two requirements into:U : SomeClassU : SomeProto"Concrete contraction" is easily the hackiest part of the Requirement Machine; I need to come up with a more principled solution for the problem that it solves sooner or later.
Fixes rdar://problem/94150249.