AST: Members of @_weakLinked types are implicitly @_weakLinked

Author: slavapestov

include/swift/AST/Attr.def

@@ -362,7 +362,7 @@ DECL_ATTR(_clangImporterSynthesizedType, ClangImporterSynthesizedType,
   NotSerialized, 74)
 SIMPLE_DECL_ATTR(_weakLinked, WeakLinked,
   OnNominalType | OnAssociatedType | OnFunc | OnAccessor | OnVar |
-  OnSubscript | OnConstructor | OnEnumElement | UserInaccessible,
+  OnSubscript | OnConstructor | OnEnumElement | OnExtension | UserInaccessible,
   75)
 SIMPLE_DECL_ATTR(_frozen, Frozen,
   OnEnum |

lib/AST/Decl.cpp

@@ -557,6 +557,12 @@ bool Decl::isWeakImported(ModuleDecl *fromModule) const {
   if (auto *dtor = dyn_cast<DestructorDecl>(this))
     return cast<ClassDecl>(dtor->getDeclContext())->isWeakImported(fromModule);
 
+  auto *dc = getDeclContext();
+  if (auto *ext = dyn_cast<ExtensionDecl>(dc))
+    return ext->isWeakImported(fromModule);
+  if (auto *ntd = dyn_cast<NominalTypeDecl>(dc))
+    return ntd->isWeakImported(fromModule);
+
   // FIXME: Also check availability when containingModule is resilient.
   return false;
 }

test/IRGen/Inputs/weak_import_native_helper.swift

@@ -83,7 +83,10 @@ public protocol P {
 }
 
 @_weakLinked
-public struct WeakS {}
+public struct WeakS {
+  public init() {}
+  public func weakMember() {}
+}
 
 @_weakLinked
 public enum WeakE {}

test/IRGen/weak_import_native.swift

@@ -55,6 +55,10 @@ func testStruct() {
   let z = s[0]
   s[0] = z
   s[0] += 1
+
+  // CHECK-DAG: declare extern_weak {{.+}} @"$s25weak_import_native_helper5WeakSV0A6MemberyyF"
+  let w = WeakS()
+  w.weakMember()
 }
 
 func testEnum() {