[Sema] Improved error message for static functions on existential metatypes #2127
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…atypes Type level lookups can fail because the lookup is on an existential metatype, like `MyProtocol.staticMethod(_:)` is invalid; however the error message is unclear: “static member 'staticMethod(_:)' cannot be used on instance of type ‘MyProtocol.Protocol’”. This fix checks the base of member lookups that failed with the reason UR_TypeMemberOnInstance for being existential metatypes. It produces the clearer message “static member ‘staticMethod(_:)’ cannot be used on protocol metatype ‘MyProtocol.Protocol’”. This change makes it clear that the use of a static member on the *existential* metatype is the problem.
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What's in this pull request?
This improves the error message produced when static members are looked up on existential metatypes.
Now the compiler emits the warning
error: static member 'staticMethod(a:)' cannot be used on protocol metatype 'P.Protocol'. This better reflects why this is forbidden—the protocol cannot provide the static member.This addresses some FIXMEs in test/expr/unary/selector/selector.swift.
The compiler still emits the correct error messages for lookups on the
P.TypeandP.Protocolcases and no new cases are diagnosed as errors.Before merging this pull request to apple/swift repository:
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