AST: Fix wrong subject type in ProtocolConformanceRef::getAssociatedConformance()

Author: slavapestov

lib/AST/ProtocolConformanceRef.cpp

@@ -263,6 +263,15 @@ ProtocolConformanceRef::getAssociatedConformance(Type conformingType,
     return conformance->getAssociatedConformance(assocType, protocol);
   }
 
+  auto computeSubjectType = [&](Type conformingType) -> Type {
+    return assocType.transformRec(
+      [&](TypeBase *t) -> std::optional<Type> {
+        if (isa<GenericTypeParamType>(t))
+          return conformingType;
+        return std::nullopt;
+      });
+  };
+
   // An associated conformance of an archetype might be known to be
   // a concrete conformance, if the subject type is fixed to a concrete
   // type in the archetype's generic signature. We don't actually have
@@ -273,15 +282,8 @@ ProtocolConformanceRef::getAssociatedConformance(Type conformingType,
   // conformances where they store their subject types, we can also
   // cache the lookups inside the abstract conformance instance too.
   if (auto archetypeType = conformingType->getAs<ArchetypeType>()) {
-    conformingType = archetypeType->getInterfaceType();
     auto *genericEnv = archetypeType->getGenericEnvironment();
-
-    auto subjectType = assocType.transformRec(
-      [&](TypeBase *t) -> std::optional<Type> {
-        if (isa<GenericTypeParamType>(t))
-          return conformingType;
-        return std::nullopt;
-      });
+    auto subjectType = computeSubjectType(archetypeType->getInterfaceType());
 
     return lookupConformance(
         genericEnv->mapTypeIntoContext(subjectType),
@@ -293,12 +295,8 @@ ProtocolConformanceRef::getAssociatedConformance(Type conformingType,
   // signature of the substitution (or in the case of type variables,
   // we have no visibility into constraints). See the parallel hack
   // to handle this in SubstitutionMap::lookupConformance().
-  CONDITIONAL_ASSERT(conformingType->isTypeParameter() ||
-                     conformingType->isTypeVariableOrMember() ||
-                     conformingType->is<UnresolvedType>() ||
-                     conformingType->is<PlaceholderType>());
-
-  return ProtocolConformanceRef::forAbstract(conformingType, protocol);
+  auto subjectType = computeSubjectType(conformingType);
+  return ProtocolConformanceRef::forAbstract(subjectType, protocol);
 }
 
 /// Check of all types used by the conformance are canonical.