IRGen: Derive the proper formal Self type for @convention(*method) methods on Optional. #5492
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…thods on Optional. Now that Optional's type parameter can be lowered, we can't make the assumption that a substituted nominal type in SIL is usable as-is as a formal type. At this moment, we can at least still rely on the fact that only nominals have methods, so we can at least go up to the original unsubstituted function type, extract the Self type from there, and do formal AST type substitution on it. This is still only a stopgap solution that wouldn't necessarily work once we start allowing conformances to be added to structural types, or even constrained extensions on Optional such as 'extension <T: class, U: class> Optional<(T) -> U>, but is good enough to fix SR-3021 for the language today. We would need something like the "substituted generic signature" concept to fully fix this.
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@swift-ci Please smoke test and merge |
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@rjmccall Mind reviewing this for 3.0 as well? |
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Ah, yes, that makes sense. I agree with both your short-term fix and the longer-term proposal to use a substituted function type. |
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To be clear, LGTM. :) |
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Now that Optional's type parameter can be lowered, we can't make the assumption that a substituted nominal type in SIL is usable as-is as a formal type. At this moment, we can at least still rely on the fact that only nominals have methods, so we can at least go up to the original unsubstituted function type, extract the nominal Self type from there, and do formal AST type substitution on it. This is still only a stopgap solution that wouldn't necessarily work once we start allowing conformances to be added to structural types, or even constrained extensions on Optional such as
extension <T: class, U: class> Optional<(T) -> U>, but is good enough to fix SR-3021 for the language today. We would need something like the "substituted generic signature" concept to fully fix this.