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Sema can infer type witnesses for a small set of known conformances, to RawRepresentable, CaseIterable, and Differentiable. Previously, we would try to compute the type witness in this order: 1) First, via name lookup, to find an explicit nested type with the same name as an associated type. 2) Second, we would attempt inference. 3) Third, we would attempt derivation. Instead, let's do 3) before 2). This avoids circularity errors in situations where the witness can be derived, but inference fails. This breaks source compatibility with enum declarations where the raw type in the inheritance clause is a lie, and the user defines their own witnesses with mismatched types. However, I suspect this does not come up in practice, because if you don't synthesize witnesses, there is no way to access the actual raw literal values of the enum cases.
14 lines
232 B
Swift
14 lines
232 B
Swift
// RUN: %target-typecheck-verify-swift
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// This used to fail with "reference to invalid associated type 'RawValue' of type 'E'"
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_ = E(rawValue: 123)
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enum E : Int {
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case a = 123
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init?(rawValue: RawValue) {
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self = .a
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}
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}
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