[AST] Make it possible to access type wrapper property (storage)

This is important because we need to force existance of the
underlying storage at the right moment.

Author: xedin

include/swift/AST/Decl.h

@@ -3760,6 +3760,11 @@ class NominalTypeDecl : public GenericTypeDecl, public IterableDeclContext {
   /// Return a type wrapper (if any) associated with this type.
   NominalTypeDecl *getTypeWrapper() const;
 
+  /// If this declaration has a type wrapper return a property that
+  /// is used for all type wrapper related operations (mainly for
+  /// applicable property access routing).
+  VarDecl *getTypeWrapperProperty() const;
+
   /// Get an initializer that could be used to instantiate a
   /// type wrapped type.
   ConstructorDecl *getTypeWrapperInitializer() const;

lib/Sema/TypeCheckStorage.cpp

@@ -103,6 +103,11 @@ static bool hasStoredProperties(NominalTypeDecl *decl) {
 }
 
 static void computeLoweredStoredProperties(NominalTypeDecl *decl) {
+  // If declaration has a type wrapper, make sure that
+  // `$_storage` property is synthesized.
+  if (decl->hasTypeWrapper())
+    (void)decl->getTypeWrapperProperty();
+
   // Just walk over the members of the type, forcing backing storage
   // for lazy properties, property and type wrappers to be synthesized.
   for (auto *member : decl->getMembers()) {

lib/Sema/TypeCheckTypeWrapper.cpp

@@ -135,6 +135,12 @@ Type GetTypeWrapperType::evaluate(Evaluator &evaluator,
   return type;
 }
 
+VarDecl *NominalTypeDecl::getTypeWrapperProperty() const {
+  auto *mutableSelf = const_cast<NominalTypeDecl *>(this);
+  return evaluateOrDefault(getASTContext().evaluator,
+                           GetTypeWrapperProperty{mutableSelf}, nullptr);
+}
+
 ConstructorDecl *NominalTypeDecl::getTypeWrapperInitializer() const {
   auto *mutableSelf = const_cast<NominalTypeDecl *>(this);
   return evaluateOrDefault(getASTContext().evaluator,
@@ -222,8 +228,7 @@ static SubscriptExpr *subscriptTypeWrappedProperty(VarDecl *var,
   if (!(parent && parent->hasTypeWrapper()))
     return nullptr;
 
-  auto *typeWrapperVar =
-      evaluateOrDefault(ctx.evaluator, GetTypeWrapperProperty{parent}, nullptr);
+  auto *typeWrapperVar = parent->getTypeWrapperProperty();
   auto *storageVar = var->getUnderlyingTypeWrapperStorage();
 
   assert(typeWrapperVar);