AST: Change signature of LookupConformanceFn #81202
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slavapestov
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tshortli
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Instead of passing in the substituted type, we pass in the InFlightSubstitution. This allows the substituted type to be recovered if needed, but we can now skip computing it for the common case of LookUpConformanceInSubstitutionMap.
The abstract conformance hack is no longer necessary, so now all of the cases can all be handled by ProtocolConformanceRef::getAssociatedConformance(), without having to dispatch on the conformance kind.
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The primitive form of subst() takes a pair of callbacks, to substitute generic parameters and conformances, respectively. We then implement substitution of arbitrary types in terms of these callbacks.
The LookupConformanceFn callback used to take both the original type and the substituted type of the conformance, so to perform a substitution on a dependent member type
T.[P]A, we would first recursively substituteT, and then invoke LookupConformanceFn withT, the substituted type forT, andP. This returns a conformance, and we then project the type witness forAto get the final result.While
LookUpConformanceInModuleneeds the substitutedTfor example,LookUpConformanceInSubstitutionMapdoes not; it callsSubstitutionMap::lookupConformance(), which only needs the originalTand theP. To avoid this unnecessary bit of computation in the common case where we're calling subst() with a pair of callbacks that look into a substitution map, let's change the callback's signature to receive theInFlightSubstitution &instead of the substitutedT. The substituted type can then be recovered by callingsubst(IFS)on the original typeT.Also, remove an ancient hack in
SubstitutionMap::lookupConformance()that is no longer necessary, now that we track subject types in abstract conformances. Previously, if any of the steps in a conformance path were abstract, we would fall back to global conformance lookup here, because we didn't have enough information to proceed. We do now.