[Property wrappers] Improve enclosing-self subscript handling.

Extend handling of enclosing-self subscripts by differentiating
between the original wrapped property (which now goes through
`subscript(_enclosingInstance:wrapped:storage:)`) and the projected
property (which goes through
`subscript(_enclosingInstance:projected:storage:)`). The new middle
argument provides a key path to the property that was accessed,
allowing one to distinguish the property being updated.

include/swift/AST/DiagnosticsSema.def

@@ -4452,6 +4452,9 @@ ERROR(property_wrapper_type_requirement_not_accessible,none,
       "more restrictive access than its enclosing property wrapper type %3 "
       "(which is %select{private|fileprivate|internal|public|open}4)",
       (AccessLevel, DescriptiveDeclKind, DeclName, Type, AccessLevel))
+ERROR(property_wrapper_ambiguous_enclosing_self_subscript, none,
+      "property wrapper type %0 has multiple enclosing-self subscripts %1",
+      (Type, DeclName))
 
 ERROR(property_wrapper_attribute_not_on_property, none,
       "property wrapper attribute %0 can only be applied to a property",

include/swift/AST/KnownIdentifiers.def

@@ -56,6 +56,7 @@ IDENTIFIER(delegateValue)
 IDENTIFIER(dynamicallyCall)
 IDENTIFIER(dynamicMember)
 IDENTIFIER(Element)
+IDENTIFIER_(enclosingInstance)
 IDENTIFIER(Encodable)
 IDENTIFIER(encode)
 IDENTIFIER(encodeIfPresent)
@@ -95,6 +96,7 @@ IDENTIFIER_(ObjectiveCType)
 IDENTIFIER(Optional)
 IDENTIFIER_(OptionalNilComparisonType)
 IDENTIFIER(parameter)
+IDENTIFIER(projected)
 IDENTIFIER(projectedValue)
 IDENTIFIER(Protocol)
 IDENTIFIER(rawValue)
@@ -122,6 +124,7 @@ IDENTIFIER(WinSDK)
 IDENTIFIER(with)
 IDENTIFIER(withArguments)
 IDENTIFIER(withKeywordArguments)
+IDENTIFIER(wrapped)
 IDENTIFIER(wrappedValue)
 IDENTIFIER(wrapperValue)
 

include/swift/AST/PropertyWrappers.h

@@ -52,6 +52,17 @@ struct PropertyWrapperTypeInfo {
   /// will be created that redirects to this property.
   VarDecl *projectedValueVar = nullptr;
 
+  /// The static subscript through which the access of instance properties
+  /// of classes can be directed (instead of wrappedValue), providing the
+  /// ability to reason about the enclosing "self".
+  SubscriptDecl *enclosingInstanceWrappedSubscript = nullptr;
+
+  /// The static subscript through which the access of instance properties
+  /// of classes can be directed (instead of projectedValue), providing the
+  /// ability to reason about the enclosing "self".
+  SubscriptDecl *enclosingInstanceProjectedSubscript = nullptr;
+
+  ///
   /// Whether this is a valid property wrapper.
   bool isValid() const {
     return valueVar != nullptr;

lib/Sema/CodeSynthesis.cpp

@@ -369,6 +369,9 @@ static void maybeMarkTransparent(AccessorDecl *accessor, ASTContext &ctx) {
             return;
 
           break;
+        } else if (var->getOriginalWrappedProperty(
+                     PropertyWrapperSynthesizedPropertyKind::StorageWrapper)) {
+          break;
         }
       }
 
@@ -614,49 +617,20 @@ namespace {
 } // end anonymous namespace
 
 namespace  {
-  /// Describes the information needed to perform property wrapper access via the enclosing self.
+  /// Describes the information needed to perform property wrapper access via
+  /// the enclosing self.
   struct EnclosingSelfPropertyWrapperAccess {
     /// The (genreric) subscript that will be used to perform the access.
     SubscriptDecl *subscript;
 
     /// The property being accessed.
     VarDecl *accessedProperty;
-
-    /// The backing storage property.
-    VarDecl *backingProperty;
   };
 }
 
-/// Find the static subscript(_enclosingInstance:wrapped:storage:) that can be
-/// used to provide access to the wrapped value of a property wrapper.
-static SubscriptDecl *findEnclosingSelfSubscript(NominalTypeDecl *nominal) {
-  ASTContext &ctx = nominal->getASTContext();
-
-  // FIXME: Make these known identifiers.
-  Identifier argNames[] = {
-    ctx.getIdentifier("_enclosingInstance"),
-    ctx.getIdentifier("storage")
-  };
-  DeclName subscriptName(ctx, DeclBaseName::createSubscript(), argNames);
-
-  for (auto member : nominal->lookupDirect(subscriptName)) {
-    auto subscript = dyn_cast<SubscriptDecl>(member);
-    if (!subscript)
-      continue;
-
-    if (subscript->isInstanceMember())
-      continue;
-
-    // FIXME: Check access, types, etc, etc.
-    return subscript;
-  }
-
-  return nullptr;
-}
-
 /// Determine whether the given property should be accessed via the enclosing-self access pattern.
 static Optional<EnclosingSelfPropertyWrapperAccess>
-getEnclosingSelfPropertyWrapperAccess(VarDecl *property) {
+getEnclosingSelfPropertyWrapperAccess(VarDecl *property, bool forProjected) {
   // The enclosing-self pattern only applies to instance properties of
   // classes.
   if (!property->isInstanceMember())
@@ -674,12 +648,22 @@ getEnclosingSelfPropertyWrapperAccess(VarDecl *property) {
     return None;
 
   // Look for a generic subscript that fits the general form we need.
-  auto subscript = findEnclosingSelfSubscript(wrapperTypeDecl);
+  auto wrapperInfo = wrapperTypeDecl->getPropertyWrapperTypeInfo();
+  auto subscript =
+      forProjected ? wrapperInfo.enclosingInstanceProjectedSubscript
+                   : wrapperInfo.enclosingInstanceWrappedSubscript;
   if (!subscript)
     return None;
 
-  EnclosingSelfPropertyWrapperAccess result{
-      subscript, property, property->getPropertyWrapperBackingProperty()};
+  EnclosingSelfPropertyWrapperAccess result;
+  result.subscript = subscript;
+
+  if (forProjected) {
+    result.accessedProperty =
+        property->getPropertyWrapperBackingPropertyInfo().storageWrapperVar;
+  } else {
+    result.accessedProperty = property;
+  }
   return result;
 }
 
@@ -775,14 +759,15 @@ static Expr *buildStorageReference(AccessorDecl *accessor,
     // record that.
     unsigned lastWrapperIdx = var->getAttachedPropertyWrappers().size();
     unsigned firstWrapperIdx = 0;
-    enclosingSelfAccess = getEnclosingSelfPropertyWrapperAccess(var);
+    enclosingSelfAccess =
+        getEnclosingSelfPropertyWrapperAccess(var, /*forProjected=*/false);
     if (enclosingSelfAccess)
       firstWrapperIdx = 1;
 
     // Perform accesses to the wrappedValues along the composition chain.
     for (unsigned i : range(firstWrapperIdx, lastWrapperIdx)) {
-      underlyingVars.push_back(
-          var->getAttachedPropertyWrapperTypeInfo(i).valueVar);
+      auto wrapperInfo = var->getAttachedPropertyWrapperTypeInfo(i);
+      underlyingVars.push_back(wrapperInfo.valueVar);
     }
     semantics = AccessSemantics::DirectToStorage;
     selfAccessKind = SelfAccessorKind::Peer;
@@ -793,7 +778,12 @@ static Expr *buildStorageReference(AccessorDecl *accessor,
     auto var =
         cast<VarDecl>(accessor->getStorage())->getOriginalWrappedProperty();
     storage = var->getPropertyWrapperBackingProperty();
-    underlyingVars.push_back( var->getAttachedPropertyWrapperTypeInfo(0).projectedValueVar);
+    enclosingSelfAccess =
+        getEnclosingSelfPropertyWrapperAccess(var, /*forProjected=*/true);
+    if (!enclosingSelfAccess) {
+      underlyingVars.push_back(
+        var->getAttachedPropertyWrapperTypeInfo(0).projectedValueVar);
+    }
     semantics = AccessSemantics::DirectToStorage;
     selfAccessKind = SelfAccessorKind::Peer;
     break;
@@ -845,23 +835,38 @@ static Expr *buildStorageReference(AccessorDecl *accessor,
   if (isMemberLValue)
     type = LValueType::get(type);
 
+  // When we are performing access via a property wrapper's static subscript
+  // that accepts the enclosing self along with key paths, form that subscript
+  // operation now.
   if (enclosingSelfAccess) {
-    SubscriptDecl *subscriptDecl = enclosingSelfAccess->subscript;
-
     Type storageType = storage->getValueInterfaceType()
         .subst(subs, SubstFlags::UseErrorType);
+    // Metatype instance for the wrapper type itself.
     TypeExpr *wrapperMetatype = TypeExpr::createImplicit(storageType, ctx);
+
+    // Key path referring to the property being accessed.
+    Expr *propertyKeyPath = new (ctx) KeyPathDotExpr(SourceLoc());
+    propertyKeyPath = new (ctx) UnresolvedDotExpr(
+        propertyKeyPath, SourceLoc(),
+        enclosingSelfAccess->accessedProperty->getFullName(), DeclNameLoc(),
+        /*Implicit=*/true);
+    propertyKeyPath = new (ctx) KeyPathExpr(
+        SourceLoc(), nullptr, propertyKeyPath);
+
+    // Key path referring to the backing storage property.
     Expr *storageKeyPath = new (ctx) KeyPathDotExpr(SourceLoc());
     storageKeyPath = new (ctx) UnresolvedDotExpr(
         storageKeyPath, SourceLoc(), storage->getFullName(), DeclNameLoc(),
         /*Implicit=*/true);
     storageKeyPath = new (ctx) KeyPathExpr(
         SourceLoc(), nullptr, storageKeyPath);
-    Expr *args[2] = {
+    Expr *args[3] = {
       selfDRE,
+      propertyKeyPath,
       storageKeyPath
     };
 
+    SubscriptDecl *subscriptDecl = enclosingSelfAccess->subscript;
     auto &tc = static_cast<TypeChecker&>(*ctx.getLazyResolver());
     lookupExpr = SubscriptExpr::create(
         ctx, wrapperMetatype, SourceLoc(), args,

lib/Sema/TypeCheckPropertyWrapper.cpp

@@ -229,6 +229,67 @@ static ConstructorDecl *findDefaultInit(ASTContext &ctx,
   return init;
 }
 
+/// Determine whether we have a suitable static subscript to which we
+/// can pass along the enclosing self + key-paths.
+static SubscriptDecl *findEnclosingSelfSubscript(ASTContext &ctx,
+                                                 NominalTypeDecl *nominal,
+                                                 Identifier propertyName) {
+  Identifier argNames[] = {
+    ctx.Id_enclosingInstance,
+    propertyName,
+    ctx.Id_storage
+  };
+  DeclName subscriptName(ctx, DeclBaseName::createSubscript(), argNames);
+
+  SmallVector<SubscriptDecl *, 2> subscripts;
+  for (auto member : nominal->lookupDirect(subscriptName)) {
+    auto subscript = dyn_cast<SubscriptDecl>(member);
+    if (!subscript)
+      continue;
+
+    if (subscript->isInstanceMember())
+      continue;
+
+    if (subscript->getDeclContext() != nominal)
+      continue;
+
+    subscripts.push_back(subscript);
+  }
+
+  switch (subscripts.size()) {
+  case 0:
+    return nullptr;
+
+  case 1:
+    break;
+
+  default:
+    // Diagnose ambiguous init() initializers.
+    nominal->diagnose(diag::property_wrapper_ambiguous_enclosing_self_subscript,
+                      nominal->getDeclaredType(), subscriptName);
+    for (auto subscript : subscripts) {
+      subscript->diagnose(diag::kind_declname_declared_here,
+                          subscript->getDescriptiveKind(),
+                          subscript->getFullName());
+    }
+    return nullptr;
+
+  }
+
+  auto subscript = subscripts.front();
+  // the subscript must be as accessible as the nominal type.
+  if (subscript->getFormalAccess() < nominal->getFormalAccess()) {
+    subscript->diagnose(diag::property_wrapper_type_requirement_not_accessible,
+                        subscript->getFormalAccess(),
+                        subscript->getDescriptiveKind(),
+                        subscript->getFullName(), nominal->getDeclaredType(),
+                        nominal->getFormalAccess());
+    return nullptr;
+  }
+
+  return subscript;
+}
+
 llvm::Expected<PropertyWrapperTypeInfo>
 PropertyWrapperTypeInfoRequest::evaluate(
     Evaluator &eval, NominalTypeDecl *nominal) const {
@@ -275,6 +336,10 @@ PropertyWrapperTypeInfoRequest::evaluate(
   result.projectedValueVar =
     findValueProperty(ctx, nominal, ctx.Id_projectedValue,
                       /*allowMissing=*/true);
+  result.enclosingInstanceWrappedSubscript =
+    findEnclosingSelfSubscript(ctx, nominal, ctx.Id_wrapped);
+  result.enclosingInstanceProjectedSubscript =
+    findEnclosingSelfSubscript(ctx, nominal, ctx.Id_projected);
 
   // If there was no projectedValue property, but there is a delegateValue
   // or wrapperValue, property, use that and warn.

test/Interpreter/property_wrappers.swift

@@ -5,6 +5,14 @@ protocol Observed: AnyObject {
   func broadcastValueWillChange<T>(newValue: T)
 }
 
+struct Other<Value: Equatable> {
+  var value: Value
+
+  func hello() -> String {
+    return "Hello from \(value)"
+  }
+}
+
 @propertyWrapper
 struct Observable<Value: Equatable> {
   private var stored: Value
@@ -19,8 +27,14 @@ struct Observable<Value: Equatable> {
     set { fatalError("called wrappedValue setter") }
   }
 
-  static subscript<EnclosingSelf: Observed>(
+  var projectedValue: Other<Value> {
+    get { fatalError("called projectedValue getter") }
+    set { fatalError("called projectedValue setter") }
+  }
+  
+  static subscript<EnclosingSelf: Observed, FinalValue>(
       _enclosingInstance observed: EnclosingSelf,
+      wrapped wrappedKeyPath: ReferenceWritableKeyPath<EnclosingSelf, FinalValue>,
       storage storageKeyPath: ReferenceWritableKeyPath<EnclosingSelf, Self>
     ) -> Value {
     get {
@@ -34,6 +48,18 @@ struct Observable<Value: Equatable> {
       observed[keyPath: storageKeyPath].stored = newValue
     }
   }
+
+  static subscript<EnclosingSelf: Observed>(
+      _enclosingInstance observed: EnclosingSelf,
+      projected wrappedKeyPath: ReferenceWritableKeyPath<EnclosingSelf, Other<Value>>,
+      storage storageKeyPath: ReferenceWritableKeyPath<EnclosingSelf, Self>
+    ) -> Other<Value> {
+    get {
+      Other(value: observed[keyPath: storageKeyPath].stored)
+    }
+    set {
+    }
+  }
 }
 
 class MyType<T: Equatable>: Observed {
@@ -45,14 +71,17 @@ class MyType<T: Equatable>: Observed {
   
   func broadcastValueWillChange<T>(newValue: T) {
     print("Value of 'x' is changing from \(x) to \(newValue)")
+    print($x.hello())
   }
 }
 
 func testMyType(_ myType: MyType<Int>) {
   // CHECK: Value of 'x' is changing from 17 to 42
+  // CHECK-NEXT: Hello from 17
   myType.x = 42
 
   // CHECK-NEXT: Value of 'x' is changing from 42 to 25
+  // CHECK-NEXT: Hello from 42
   myType.x = 42
   myType.x = 25
 }

test/decl/var/property_wrappers_synthesis.swift

@@ -69,6 +69,7 @@ struct Observable<Value> {
   
   static subscript<EnclosingSelf>(
       _enclosingInstance observed: EnclosingSelf,
+      wrapped wrappedKeyPath: ReferenceWritableKeyPath<EnclosingSelf, Value>,
       storage storageKeyPath: ReferenceWritableKeyPath<EnclosingSelf, Self>
     ) -> Value {
     get {
@@ -85,9 +86,9 @@ class MyObservedType {
   @Observable var observedProperty = 17
 
   // CHECK: accessor_decl{{.*}}get_for=observedProperty
-  // CHECK:   subscript_expr implicit type='@lvalue Int' decl={{.*}}.Observable.subscript(_enclosingInstance:storage:)
+  // CHECK:   subscript_expr implicit type='@lvalue Int' decl={{.*}}.Observable.subscript(_enclosingInstance:wrapped:storage:)
 
   // CHECK: accessor_decl{{.*}}set_for=observedProperty
-  // CHECK:   subscript_expr implicit type='@lvalue Int' decl={{.*}}.Observable.subscript(_enclosingInstance:storage:)
+  // CHECK:   subscript_expr implicit type='@lvalue Int' decl={{.*}}.Observable.subscript(_enclosingInstance:wrapped:storage:)
 }