Merge pull request swiftlang#79386 from ktoso/pick-wip-correct-metadata-lookup-result-type

[6.1][Distributed] Improve getting return type metadata for distributed invocations

Author: ktoso

stdlib/public/runtime/MetadataLookup.cpp

@@ -2942,8 +2942,12 @@ swift_func_getReturnTypeInfo(const char *typeNameStart, size_t typeNameLength,
 
   SubstGenericParametersFromMetadata substFn(genericEnv, genericArguments);
 
-  DecodedMetadataBuilder builder(
-      demangler,
+  auto request = MetadataRequest(MetadataState::Complete);
+
+  NodePointer nodePointer = resultType->getFirstChild();
+  auto typeInfoOrErr = swift_getTypeByMangledNode(
+      request, demangler, nodePointer,
+      /*arguments=*/genericArguments,
       /*substGenericParam=*/
       [&substFn](unsigned depth, unsigned index) {
         return substFn.getMetadata(depth, index).Ptr;
@@ -2953,9 +2957,12 @@ swift_func_getReturnTypeInfo(const char *typeNameStart, size_t typeNameLength,
         return substFn.getWitnessTable(type, index);
       });
 
-  TypeDecoder<DecodedMetadataBuilder> decoder(builder);
+  if (typeInfoOrErr.isError()) {
+    return nullptr;
+  }
 
-  return decodeType(decoder, resultType->getFirstChild());
+  auto typeInfo = typeInfoOrErr.getType();
+  return typeInfo.getMetadata();
 }
 
 SWIFT_CC(swift) SWIFT_RUNTIME_STDLIB_SPI

test/Distributed/Inputs/FakeDistributedActorSystems.swift

@@ -459,7 +459,7 @@ public final class FakeInvocationDecoder: DistributedTargetInvocationDecoder {
 
   var argumentIndex: Int = 0
 
-  fileprivate init(
+  public init(
     args: [Any],
     substitutions: [Any.Type] = [],
     returnType: Any.Type? = nil,