[TypeChecker] Type wrappers (experimental feature)

include/swift/AST/Attr.def

@@ -763,6 +763,11 @@ DECL_ATTR(_expose, Expose,
   ABIStableToAdd | ABIStableToRemove | APIStableToAdd | APIStableToRemove,
   133)
 
+SIMPLE_DECL_ATTR(typeWrapper, TypeWrapper,
+  OnStruct | OnClass | OnEnum |
+  ABIStableToAdd | ABIStableToRemove | APIStableToAdd | APIStableToRemove,
+  134)
+
 // If you're adding a new underscored attribute here, please document it in
 // docs/ReferenceGuides/UnderscoredAttributes.md.
 

include/swift/AST/Decl.h

@@ -3754,6 +3754,21 @@ class NominalTypeDecl : public GenericTypeDecl, public IterableDeclContext {
     return getGlobalActorInstance() != nullptr;
   }
 
+  /// Returns true if this type has a type wrapper custom attribute.
+  bool hasTypeWrapper() const { return bool(getTypeWrapper()); }
+
+  /// 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;
+
   // Implement isa/cast/dyncast/etc.
   static bool classof(const Decl *D) {
     return D->getKind() >= DeclKind::First_NominalTypeDecl &&
@@ -5549,7 +5564,18 @@ class VarDecl : public AbstractStorageDecl {
   /// Return true if this property either has storage or has an attached property
   /// wrapper that has storage.
   bool hasStorageOrWrapsStorage() const;
-
+
+  /// Whether this property belongs to a type wrapped type and has
+  /// all access to it routed through a type wrapper.
+  bool isAccessedViaTypeWrapper() const;
+
+  /// For type wrapped properties (see \c isAccessedViaTypeWrapper)
+  /// all access is routed through a type wrapper.
+  ///
+  /// \returns an underlying type wrapper property which is a
+  /// storage endpoint for all access to this property.
+  VarDecl *getUnderlyingTypeWrapperStorage() const;
+
   /// Visit all auxiliary declarations to this VarDecl.
   ///
   /// An auxiliary declaration is a declaration synthesized by the compiler to support

include/swift/AST/DiagnosticsSema.def

@@ -6476,5 +6476,46 @@ ERROR(moveOnly_not_allowed_here,none,
 ERROR(move_expression_not_passed_lvalue,none,
       "'move' can only be applied to lvalues", ())
 
+//------------------------------------------------------------------------------
+// MARK: Type Wrappers
+//------------------------------------------------------------------------------
+
+ERROR(type_wrappers_are_experimental,none,
+      "type wrappers are an experimental feature", ())
+
+ERROR(type_wrapper_attribute_not_allowed_here,none,
+      "type wrapper attribute %0 can only be applied to a class, struct",
+      (Identifier))
+
+ERROR(type_wrapper_requires_a_single_generic_param,none,
+      "type wrapper has to declare a single generic parameter "
+      "for underlying storage type", ())
+
+ERROR(cannot_use_multiple_type_wrappers,none,
+      "type %0 cannot use more than one type wrapper", ())
+
+ERROR(type_wrapper_requires_memberwise_init,none,
+      "type wrapper type %0 does not contain a required initializer"
+      " - init(memberwise:)",
+      (DeclName))
+
+ERROR(type_wrapper_requires_subscript,none,
+      "type wrapper type %0 does not contain a required subscript"
+      " - subscript(storedKeyPath:)",
+      (DeclName))
+
+ERROR(type_wrapper_failable_init,none,
+      "type wrapper initializer %0 cannot be failable", (DeclName))
+
+ERROR(type_wrapper_invalid_subscript_param_type, none,
+      "type wrapper subscript expects a key path parameter type (got: %0)",
+      (Type))
+
+ERROR(type_wrapper_type_requirement_not_accessible,none,
+      "%select{private|fileprivate|internal|public|open}0 %1 %2 cannot have "
+      "more restrictive access than its enclosing type wrapper type %3 "
+      "(which is %select{private|fileprivate|internal|public|open}4)",
+      (AccessLevel, DescriptiveDeclKind, DeclName, Type, AccessLevel))
+
 #define UNDEFINE_DIAGNOSTIC_MACROS
 #include "DefineDiagnosticMacros.h"

include/swift/AST/KnownIdentifiers.def

@@ -307,6 +307,12 @@ IDENTIFIER(decodeNextArgument)
 IDENTIFIER(SerializationRequirement)
 IDENTIFIER_WITH_NAME(builderSelf, "$builderSelf")
 
+// Type wrappers
+IDENTIFIER_WITH_NAME(TypeWrapperStorage, "$Storage")
+IDENTIFIER_WITH_NAME(TypeWrapperProperty, "$_storage")
+IDENTIFIER(storageKeyPath)
+IDENTIFIER(memberwise)
+
 #undef IDENTIFIER
 #undef IDENTIFIER_
 #undef IDENTIFIER_WITH_NAME

include/swift/AST/TypeCheckRequests.h

@@ -3364,6 +3364,10 @@ enum class CustomAttrTypeKind {
   /// unbound generic types.
   PropertyWrapper,
 
+  /// Just like property wrappers, type wrappers are represented
+  /// as custom type attributes and allow unbound generic types.
+  TypeWrapper,
+
   /// Global actors are represented as custom type attributes. They don't
   /// have any particularly interesting semantics.
   GlobalActor,
@@ -3499,6 +3503,174 @@ class GetSourceFileAsyncNode
   bool isCached() const { return true; }
 };
 
+/// Return a type wrapper (if any) associated with the given declaration.
+class GetTypeWrapper
+    : public SimpleRequest<GetTypeWrapper, NominalTypeDecl *(NominalTypeDecl *),
+                           RequestFlags::Cached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+private:
+  friend SimpleRequest;
+
+  NominalTypeDecl *evaluate(Evaluator &evaluator, NominalTypeDecl *) const;
+
+public:
+  bool isCached() const { return true; }
+};
+
+/// Return a type of the type wrapper (if any) associated with the given
+/// declaration.
+class GetTypeWrapperType
+    : public SimpleRequest<GetTypeWrapperType, Type(NominalTypeDecl *),
+                           RequestFlags::Cached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+private:
+  friend SimpleRequest;
+
+  Type evaluate(Evaluator &evaluator, NominalTypeDecl *) const;
+
+public:
+  bool isCached() const { return true; }
+};
+
+/// Inject or get `$Storage` type which has all of the stored properties
+/// of the given type with a type wrapper.
+class GetTypeWrapperStorage
+    : public SimpleRequest<GetTypeWrapperStorage,
+                           NominalTypeDecl *(NominalTypeDecl *),
+                           RequestFlags::Cached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+private:
+  friend SimpleRequest;
+
+  NominalTypeDecl *evaluate(Evaluator &evaluator, NominalTypeDecl *) const;
+
+public:
+  bool isCached() const { return true; }
+};
+
+/// Inject or get `$_storage` property which is used to route accesses through
+/// to all stored properties of a type that has a type wrapper.
+class GetTypeWrapperProperty
+    : public SimpleRequest<GetTypeWrapperProperty, VarDecl *(NominalTypeDecl *),
+                           RequestFlags::Cached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+private:
+  friend SimpleRequest;
+
+  VarDecl *evaluate(Evaluator &evaluator, NominalTypeDecl *) const;
+
+public:
+  bool isCached() const { return true; }
+};
+
+/// Given a stored property associated with a type wrapped type,
+/// produce a property that mirrors it in the type wrapper context.
+class GetTypeWrapperStorageForProperty
+    : public SimpleRequest<GetTypeWrapperStorageForProperty,
+                           VarDecl *(VarDecl *), RequestFlags::Cached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+private:
+  friend SimpleRequest;
+
+  VarDecl *evaluate(Evaluator &evaluator, VarDecl *) const;
+
+public:
+  bool isCached() const { return true; }
+};
+
+/// Synthesize the body of a getter for a stored property that belongs to
+/// a type wrapped type.
+class SynthesizeTypeWrappedPropertyGetterBody
+    : public SimpleRequest<SynthesizeTypeWrappedPropertyGetterBody,
+                           BraceStmt *(AccessorDecl *), RequestFlags::Cached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+private:
+  friend SimpleRequest;
+
+  BraceStmt *evaluate(Evaluator &evaluator, AccessorDecl *) const;
+
+public:
+  bool isCached() const { return true; }
+};
+
+/// Synthesize the body of a setter for a stored property that belongs to
+/// a type wrapped type.
+class SynthesizeTypeWrappedPropertySetterBody
+    : public SimpleRequest<SynthesizeTypeWrappedPropertySetterBody,
+                           BraceStmt *(AccessorDecl *), RequestFlags::Cached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+private:
+  friend SimpleRequest;
+
+  BraceStmt *evaluate(Evaluator &evaluator, AccessorDecl *) const;
+
+public:
+  bool isCached() const { return true; }
+};
+
+/// Inject or get `$Storage` type which has all of the stored properties
+/// of the given type with a type wrapper.
+class IsPropertyAccessedViaTypeWrapper
+    : public SimpleRequest<IsPropertyAccessedViaTypeWrapper, bool(VarDecl *),
+                           RequestFlags::Cached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+private:
+  friend SimpleRequest;
+
+  bool evaluate(Evaluator &evaluator, VarDecl *) const;
+
+public:
+  bool isCached() const { return true; }
+};
+
+class SynthesizeTypeWrapperInitializer
+    : public SimpleRequest<SynthesizeTypeWrapperInitializer,
+                           ConstructorDecl *(NominalTypeDecl *),
+                           RequestFlags::Cached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+private:
+  friend SimpleRequest;
+
+  ConstructorDecl *evaluate(Evaluator &evaluator, NominalTypeDecl *) const;
+
+public:
+  bool isCached() const { return true; }
+};
+
+class SynthesizeTypeWrapperInitializerBody
+    : public SimpleRequest<SynthesizeTypeWrapperInitializerBody,
+                           BraceStmt *(ConstructorDecl *),
+                           RequestFlags::Cached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+private:
+  friend SimpleRequest;
+
+  BraceStmt *evaluate(Evaluator &evaluator, ConstructorDecl *) const;
+
+public:
+  bool isCached() const { return true; }
+};
+
 void simple_display(llvm::raw_ostream &out, ASTNode node);
 void simple_display(llvm::raw_ostream &out, Type value);
 void simple_display(llvm::raw_ostream &out, const TypeRepr *TyR);

include/swift/AST/TypeCheckerTypeIDZone.def

@@ -399,3 +399,33 @@ SWIFT_REQUEST(TypeChecker, ClosureEffectsRequest,
 SWIFT_REQUEST(TypeChecker, GetSourceFileAsyncNode,
               AwaitExpr *(const SourceFile *),
               Cached, NoLocationInfo)
+SWIFT_REQUEST(TypeChecker, GetTypeWrapper,
+              NominalTypeDecl *(NominalTypeDecl *),
+              Cached, NoLocationInfo)
+SWIFT_REQUEST(TypeChecker, GetTypeWrapperType,
+              Type(NominalTypeDecl *),
+              Cached, NoLocationInfo)
+SWIFT_REQUEST(TypeChecker, GetTypeWrapperStorage,
+              NominalTypeDecl *(NominalTypeDecl *),
+              Cached, NoLocationInfo)
+SWIFT_REQUEST(TypeChecker, GetTypeWrapperProperty,
+              VarDecl *(NominalTypeDecl *),
+              Cached, NoLocationInfo)
+SWIFT_REQUEST(TypeChecker, GetTypeWrapperStorageForProperty,
+              VarDecl *(VarDecl *),
+              Cached, NoLocationInfo)
+SWIFT_REQUEST(TypeChecker, SynthesizeTypeWrappedPropertyGetterBody,
+              BraceStmt *(AccessorDecl *),
+              Cached, NoLocationInfo)
+SWIFT_REQUEST(TypeChecker, SynthesizeTypeWrappedPropertySetterBody,
+              BraceStmt *(AccessorDecl *),
+              Cached, NoLocationInfo)
+SWIFT_REQUEST(TypeChecker, IsPropertyAccessedViaTypeWrapper,
+              bool(VarDecl *),
+              Cached, NoLocationInfo)
+SWIFT_REQUEST(TypeChecker, SynthesizeTypeWrapperInitializer,
+              ConstructorDecl *(NominalTypeDecl *),
+              Cached, NoLocationInfo)
+SWIFT_REQUEST(TypeChecker, SynthesizeTypeWrapperInitializerBody,
+              BraceStmt *(ConstructorDecl *),
+              Cached, NoLocationInfo)

include/swift/Basic/Features.def

@@ -122,6 +122,11 @@ EXPERIMENTAL_FEATURE(SendableCompletionHandlers)
 /// Enables opaque type erasure without also enabling implict dynamic
 EXPERIMENTAL_FEATURE(OpaqueTypeErasure)
 
+/// Whether to enable experimental @typeWrapper feature which allows to
+/// declare a type that controls access to all stored properties of the
+/// wrapped type.
+EXPERIMENTAL_FEATURE(TypeWrappers)
+
 #undef EXPERIMENTAL_FEATURE
 #undef UPCOMING_FEATURE
 #undef SUPPRESSIBLE_LANGUAGE_FEATURE

lib/AST/ASTPrinter.cpp

@@ -2935,6 +2935,10 @@ static bool usesFeatureSpecializeAttributeWithAvailability(Decl *decl) {
   return false;
 }
 
+static bool usesFeatureTypeWrappers(Decl *decl) {
+  return decl->getAttrs().hasAttribute<TypeWrapperAttr>();
+}
+
 static void suppressingFeatureSpecializeAttributeWithAvailability(
                                         PrintOptions &options,
                                         llvm::function_ref<void()> action) {

lib/AST/Decl.cpp

@@ -6733,7 +6733,8 @@ bool VarDecl::hasStorageOrWrapsStorage() const {
 }
 
 void VarDecl::visitAuxiliaryDecls(llvm::function_ref<void(VarDecl *)> visit) const {
-  if (getDeclContext()->isTypeContext() || isImplicit())
+  if (getDeclContext()->isTypeContext() ||
+      (isImplicit() && !isa<ParamDecl>(this)))
     return;
 
   if (getAttrs().hasAttribute<LazyAttr>()) {

lib/AST/TypeCheckRequests.cpp

@@ -1531,6 +1531,10 @@ void swift::simple_display(llvm::raw_ostream &out, CustomAttrTypeKind value) {
     out << "property-wrapper";
     return;
 
+  case CustomAttrTypeKind::TypeWrapper:
+    out << "type-wrapper";
+    return;
+
   case CustomAttrTypeKind::GlobalActor:
     out << "global-actor";
     return;

lib/Sema/CMakeLists.txt

@@ -61,6 +61,7 @@ add_swift_host_library(swiftSema STATIC
   TypeCheckNameLookup.cpp
   TypeCheckPattern.cpp
   TypeCheckPropertyWrapper.cpp
+  TypeCheckTypeWrapper.cpp
   TypeCheckProtocol.cpp
   TypeCheckProtocolInference.cpp
   TypeCheckRegex.cpp