[Sema] RuntimeMetadata: Allow declaring init(attachedTo:) overloads in extensions

Author: xedin

lib/Sema/TypeCheckAttr.cpp

@@ -7041,7 +7041,8 @@ void AttributeChecker::visitRuntimeMetadataAttr(RuntimeMetadataAttr *attr) {
 
   // Check whether type marked as runtime attribute capable has an initializer
   // with first parameter labeled as `attachedTo:`.
-  for (auto *member : nominal->getMembers()) {
+  for (auto *member :
+       nominal->lookupDirect(DeclBaseName::createConstructor())) {
     auto *init = dyn_cast<ConstructorDecl>(member);
     if (!init)
       continue;

test/type/runtime_discoverable_attrs.swift

@@ -157,3 +157,15 @@ class MembersWithAvailability {
 func test_local_types_with_conformances() {
   struct X : Flagged {}
 }
+
+@runtimeMetadata
+struct AttrWithInitsInExts {
+}
+
+extension AttrWithInitsInExts {
+  init(attachedTo: Any.Type) {}
+}
+
+@AttrWithInitsInExts
+struct TestAttrWithExts { // Ok
+}