Handle a parameter to property behaviors.

For prototyping purposes, we only support a single trailing closure parameter to begin with.

include/swift/AST/Decl.h

@@ -3609,17 +3609,16 @@ enum class AccessStrategy : unsigned char {
 struct BehaviorRecord {
   // The behavior name.
   TypeRepr *ProtocolName;
-  // The parameter function, if any.
-  FuncDecl *Param;
+  // The parameter expression, if any.
+  Expr *Param;
   
   Optional<NormalProtocolConformance *> Conformance = None;
   // The 'value' property from the behavior protocol that provides the property
   // implementation.
   VarDecl *ValueDecl = nullptr;
   
-  
   BehaviorRecord(TypeRepr *ProtocolName,
-                 FuncDecl *Param)
+                 Expr *Param)
     : ProtocolName(ProtocolName), Param(Param)
   {}
   
@@ -3919,7 +3918,7 @@ public:
   void setComputedSetter(FuncDecl *Set);
 
   /// \brief Add a behavior to a property.
-  void addBehavior(TypeRepr *Type, FuncDecl *Param);
+  void addBehavior(TypeRepr *Type, Expr *Param);
 
   /// \brief Set a materializeForSet accessor for this declaration.
   ///

include/swift/AST/DiagnosticsParse.def

@@ -256,6 +256,9 @@ ERROR(addressor_with_getter,none,
 ERROR(addressor_with_setter,none,
       "%select{variable|subscript}0 cannot provide both 'address' and "
       "a setter; use an ordinary getter instead", (unsigned))
+ERROR(behavior_multiple_vars,none,
+      "applying property behavior with parameter to multiple variables is "
+      "not supported", ())
 
 // Import
 ERROR(decl_expected_module_name,none,

include/swift/AST/DiagnosticsSema.def

@@ -1564,18 +1564,14 @@ ERROR(property_behavior_value_type_doesnt_match,none,
       (Identifier, Type, Identifier, Type))
 NOTE(property_behavior_value_decl_here,none,
      "'value' property declared here", ())
-ERROR(property_behavior_invalid_initialValue_reqt,none,
-      "property behavior %0 'initialValue' requirement must be static, "
-      "get-only, and of type 'Self.Value'", (Identifier))
-ERROR(property_behavior_requires_initialValue,none,
-      "property behavior %0 requires an initializer in the declaration of %1",
+ERROR(property_behavior_invalid_parameter_reqt,none,
+      "property behavior %0 has a 'parameter' requirement that is "
+      "static or generic", (Identifier))
+ERROR(property_behavior_requires_parameter,none,
+      "property behavior %0 requires a parameter in the declaration of %1",
       (Identifier, Identifier))
-ERROR(property_behavior_requires_unique_initialValue,none,
-      "property behavior %0 cannot destructure an initializer expression in a "
-      "compound pattern",
-      (Identifier))
-ERROR(property_behavior_invalid_initializer,none,
-      "initializer expression provided, but property behavior %0 does not "
+ERROR(property_behavior_invalid_parameter,none,
+      "parameter expression provided, but property behavior %0 does not "
       "use it",
       (Identifier))
 

include/swift/AST/KnownIdentifiers.def

@@ -41,7 +41,6 @@ IDENTIFIER(generate)
 IDENTIFIER(Generator)
 IDENTIFIER(hashValue)
 IDENTIFIER(init)
-IDENTIFIER(initialValue)
 IDENTIFIER(initStorage)
 IDENTIFIER(load)
 IDENTIFIER(next)
@@ -50,6 +49,7 @@ IDENTIFIER(objectAtIndexedSubscript)
 IDENTIFIER(objectForKeyedSubscript)
 IDENTIFIER(ObjectiveC)
 IDENTIFIER_(OptionalNilComparisonType)
+IDENTIFIER(parameter)
 IDENTIFIER(Protocol)
 IDENTIFIER(rawValue)
 IDENTIFIER(RawValue)

lib/AST/Decl.cpp

@@ -2872,7 +2872,7 @@ void AbstractStorageDecl::setComputedSetter(FuncDecl *Set) {
 }
 
 void AbstractStorageDecl::addBehavior(TypeRepr *Type,
-                                      FuncDecl *Param) {
+                                      Expr *Param) {
   assert(BehaviorInfo.getPointer() == nullptr && "already set behavior!");
   auto mem = getASTContext().Allocate(sizeof(BehaviorRecord),
                                       alignof(BehaviorRecord));

lib/Parse/ParseDecl.cpp

@@ -3956,14 +3956,64 @@ ParserStatus Parser::parseDeclVar(ParseDeclOptions Flags,
     if (consumeIf(tok::kw___behavior)) {
       auto type = parseType(diag::expected_behavior_name,
                             /*handle completion*/ true);
-      // TODO: recovery. could scan to next closing bracket
       if (type.isParseError())
         return makeParserError();
       if (type.hasCodeCompletion())
         return makeParserCodeCompletionStatus();
       
+      // Parse a following trailing closure argument.
+      // FIXME: Handle generalized parameters.
+      Expr *paramExpr = nullptr;
+      if (Tok.is(tok::l_brace)) {
+        // Record the variables that we're trying to set up.  This allows us
+        // to cleanly reject "var x = x" when "x" isn't bound to an enclosing
+        // decl (even though names aren't injected into scope when the parameter
+        // is parsed).
+        SmallVector<VarDecl *, 4> Vars;
+        Vars.append(DisabledVars.begin(), DisabledVars.end());
+        pattern->collectVariables(Vars);
+        
+        llvm::SaveAndRestore<decltype(DisabledVars)>
+        RestoreCurVars(DisabledVars, Vars);
+        
+        llvm::SaveAndRestore<decltype(DisabledVarReason)>
+        RestoreReason(DisabledVarReason, diag::var_init_self_referential);
+
+        // Set up a decl context for the closure.
+        // This will be recontextualized to a method we synthesize during
+        // type checking.
+        if (!CurDeclContext->isLocalContext() && !topLevelDecl && !initContext)
+          initContext = Context.createPatternBindingContext(CurDeclContext);
+        Optional<ParseFunctionBody> initParser;
+        Optional<ContextChange> topLevelParser;
+        if (topLevelDecl)
+          topLevelParser.emplace(*this, topLevelDecl,
+                                 &State->getTopLevelContext());
+        if (initContext)
+          initParser.emplace(*this, initContext);
+
+        auto closure = parseExprClosure();
+        usedInitContext = true;
+        if (closure.isParseError())
+          return makeParserError();
+        if (closure.hasCodeCompletion())
+          return makeParserCodeCompletionStatus();
+        paramExpr = closure.get();
+      }
+
+      unsigned numVars = 0;
       pattern->forEachVariable([&](VarDecl *VD) {
-        VD->addBehavior(type.get(), nullptr);
+        ++numVars;
+        // TODO: Support parameter closure with multiple vars. This is tricky
+        // since the behavior's parameter type may be dependent on the
+        // property type, so we'd need to clone the closure expr for each var
+        // to re-type-check it.
+        if (numVars > 1 && paramExpr) {
+          diagnose(paramExpr->getLoc(), diag::behavior_multiple_vars);
+          paramExpr = nullptr;
+        }
+        
+        VD->addBehavior(type.get(), paramExpr);
       });
     // If we syntactically match the second decl-var production, with a
     // var-get-set clause, parse the var-get-set clause.

lib/Sema/CodeSynthesis.cpp

@@ -1293,75 +1293,159 @@ void TypeChecker::completePropertyBehaviorStorage(VarDecl *VD,
                     ConcreteDeclRef(Context, Storage->getSetter(), MemberSubs));
 }
 
-void TypeChecker::completePropertyBehaviorInitialValue(VarDecl *VD,
-                               VarDecl *BehaviorInitialValue,
+void TypeChecker::completePropertyBehaviorParameter(VarDecl *VD,
+                               FuncDecl *BehaviorParameter,
                                NormalProtocolConformance *BehaviorConformance,
                                ArrayRef<Substitution> SelfInterfaceSubs,
                                ArrayRef<Substitution> SelfContextSubs) {
-  // Create a property to witness the requirement.
+  // Create a method to witness the requirement.
   auto DC = VD->getDeclContext();
   SmallString<64> NameBuf = VD->getName().str();
-  NameBuf += ".initialValue";
-  auto InitialValueName = Context.getIdentifier(NameBuf);
-  // TODO: non-static initialValue
-  assert(BehaviorInitialValue->isStatic());
-  auto *InitialValue = new (Context) VarDecl(/*static*/ true,
-                                             /*let*/ false,
-                                             VD->getLoc(),
-                                             InitialValueName,
-                                            SelfContextSubs[1].getReplacement(),
+  NameBuf += ".parameter";
+  auto ParameterBaseName = Context.getIdentifier(NameBuf);
+
+  // Substitute the requirement type into the conforming context.
+  auto sig = BehaviorConformance->getProtocol()->getGenericSignatureOfContext();
+  auto ParameterTy = BehaviorParameter->getInterfaceType()
+    ->castTo<AnyFunctionType>()
+    ->getResult();
+  
+  TypeSubstitutionMap interfaceMap = sig->getSubstitutionMap(SelfInterfaceSubs);
+  auto SubstInterfaceTy = ParameterTy.subst(VD->getModuleContext(),
+                                            interfaceMap, SubstOptions());
+  assert(SubstInterfaceTy && "storage type substitution failed?!");
+  
+  TypeSubstitutionMap contextMap = sig->getSubstitutionMap(SelfContextSubs);
+  auto SubstContextTy = ParameterTy.subst(VD->getModuleContext(),
+                                                 contextMap, SubstOptions());
+  assert(SubstContextTy && "storage type substitution failed?!");
+
+  auto SubstBodyResultTy = SubstContextTy->castTo<AnyFunctionType>()
+    ->getResult();
+  
+  // Add the Self type back to the interface and context types.
+  if (DC->isTypeContext()) {
+    if (DC->isGenericContext()) {
+      auto genericSig = DC->getGenericSignatureOfContext();
+      SubstInterfaceTy = GenericFunctionType::get(genericSig,
+                                                  DC->getSelfInterfaceType(),
+                                                  SubstInterfaceTy,
+                                                  AnyFunctionType::ExtInfo());
+      auto genericParams = DC->getGenericParamsOfContext();
+      SubstContextTy = PolymorphicFunctionType::get(DC->getSelfTypeInContext(),
+                                                    SubstContextTy,
+                                                    genericParams);
+    } else {
+      SubstInterfaceTy = FunctionType::get(DC->getSelfInterfaceType(),
+                                           SubstInterfaceTy);
+      SubstContextTy = FunctionType::get(DC->getSelfTypeInContext(),
+                                         SubstContextTy);
+    }
+  }
+  
+  // Borrow the parameters from the requirement declaration.
+  SmallVector<ParameterList *, 2> ParamLists;
+  if (DC->isTypeContext()) {
+    auto self = new (Context) ParamDecl(/*let*/ true, SourceLoc(), SourceLoc(),
+                                        Identifier(), SourceLoc(),
+                                        Context.Id_self,
+                                        DC->getSelfTypeInContext(), DC);
+    self->setInterfaceType(DC->getSelfInterfaceType());
+    self->setImplicit();
+    
+    ParamLists.push_back(ParameterList::create(Context, SourceLoc(),
+                                               self, SourceLoc()));
+    ParamLists.back()->get(0)->setImplicit();
+  }
+  
+  assert(BehaviorParameter->getParameterLists().size() == 2);
+  SmallVector<ParamDecl *, 4> Params;
+  SmallVector<Identifier, 4> NameComponents;
+  
+  auto *DeclaredParams = BehaviorParameter->getParameterList(1);
+  for (unsigned i : indices(*DeclaredParams)) {
+    auto declaredParam = DeclaredParams->get(i);
+    auto declaredParamTy = declaredParam->getInterfaceType();
+    auto interfaceTy = declaredParamTy.subst(DC->getParentModule(),
+                                             interfaceMap,
+                                             SubstOptions());
+    assert(interfaceTy);
+    auto contextTy = declaredParamTy.subst(DC->getParentModule(),
+                                           contextMap, SubstOptions());
+    assert(contextTy);
+
+    SmallString<64> ParamNameBuf;
+    {
+      llvm::raw_svector_ostream names(ParamNameBuf);
+      names << "%arg." << i;
+    }
+    auto param = new (Context) ParamDecl(/*let*/ true, SourceLoc(), SourceLoc(),
+                                         Identifier(),
+                                         SourceLoc(),
+                                         Context.getIdentifier(ParamNameBuf),
+                                         contextTy, DC);
+    param->setInterfaceType(interfaceTy);
+    param->setImplicit();
+    Params.push_back(param);
+    NameComponents.push_back(Identifier());
+  }
+  ParamLists.push_back(ParameterList::create(Context, Params));
+
+  auto *Parameter = FuncDecl::create(Context, SourceLoc(),
+                                     StaticSpellingKind::None,
+                                     SourceLoc(),
+                                     DeclName(Context, ParameterBaseName,
+                                              NameComponents),
+                                     SourceLoc(), SourceLoc(),
+                                     SourceLoc(), nullptr, SubstContextTy,
+                                     ParamLists,
+                                     TypeLoc::withoutLoc(SubstBodyResultTy),
                                      DC);
-  InitialValue->setInterfaceType(SelfInterfaceSubs[1].getReplacement());
-  InitialValue->setUserAccessible(false);
-  // Mark the vardecl to be final, implicit, and private.  In a class, this
+
+  Parameter->setInterfaceType(SubstInterfaceTy);
+  // Mark the method to be final, implicit, and private.  In a class, this
   // prevents it from being dynamically dispatched.
-  if (VD->getDeclContext()->getAsClassOrClassExtensionContext())
-    makeFinal(Context, InitialValue);
-  InitialValue->setImplicit();
-  InitialValue->setAccessibility(Accessibility::Private);
-  InitialValue->setIsBeingTypeChecked();
-
-  addMemberToContextIfNeeded(InitialValue, DC);
-  
-  Pattern *InitialPBDPattern = new (Context) NamedPattern(InitialValue,
-                                                          /*implicit*/true);
-  InitialPBDPattern = new (Context) TypedPattern(InitialPBDPattern,
-                      TypeLoc::withoutLoc(SelfContextSubs[1].getReplacement()),
-                      /*implicit*/ true);
-  auto *InitialPBD = PatternBindingDecl::create(Context,
-                                              /*staticloc*/SourceLoc(),
-                                              StaticSpellingKind::KeywordStatic,
-                                              VD->getLoc(),
-                                              InitialPBDPattern, nullptr,
-                                              VD->getDeclContext());
-  InitialPBD->setImplicit();
-  InitialPBD->setInitializerChecked(0);
-  addMemberToContextIfNeeded(InitialPBD, VD->getDeclContext(), VD);
-  
-  // Create a getter.
-  auto Get = createGetterPrototype(InitialValue, *this);
-  addMemberToContextIfNeeded(Get, DC);
-  
-  // Take the initializer from the PatternBindingDecl for VD.
-  auto *InitValue = VD->getParentInitializer();
-  auto PBD = VD->getParentPatternBinding();
-  unsigned entryIndex = PBD->getPatternEntryIndexForVarDecl(VD);
-  PBD->setInit(entryIndex, nullptr);
-  PBD->setInitializerChecked(entryIndex);
+  if (DC->getAsClassOrClassExtensionContext())
+    makeFinal(Context, Parameter);
+  Parameter->setImplicit();
+  Parameter->setAccessibility(Accessibility::Private);
+  Parameter->setIsBeingTypeChecked();
+  Parameter->setBodyResultType(SubstBodyResultTy);
 
   // Recontextualize any closure declcontexts nested in the initializer to
-  // realize that they are in the getter function.
-  InitValue->walk(RecontextualizeClosures(Get));
+  // realize that they are in the parameter function.
+  assert(VD->getBehavior()->Param);
+  VD->getBehavior()->Param->walk(RecontextualizeClosures(Parameter));
+  
+  // Apply and return the closure in the function context.
+  SmallVector<Expr *, 4> argRefs;
+  SmallVector<Identifier, 4> argNames;
+  for (unsigned i : indices(Params)) {
+    auto param = Params[i];
+    auto expr = new (Context) DeclRefExpr(param, DeclNameLoc(),
+                                          /*implicit*/ true);
+    argRefs.push_back(expr);
+    argNames.push_back(DeclaredParams->get(i)->getName());
+  }
+  auto argTuple = TupleExpr::create(Context, SourceLoc(), argRefs,
+                                    argNames,
+                                    {}, SourceLoc(),
+                                    /*trailing closure*/ false,
+                                    /*implicit*/ true);
+  auto apply = new (Context) CallExpr(VD->getBehavior()->Param, argTuple,
+                                      /*implicit*/ true);
   
   // Return the expression value.
-  auto Ret = new (Context) ReturnStmt(SourceLoc(), InitValue,
+  auto Ret = new (Context) ReturnStmt(SourceLoc(), apply,
                                       /*implicit*/ true);
   auto Body = BraceStmt::create(Context, SourceLoc(), ASTNode(Ret),
                                 SourceLoc(), /*implicit*/ true);
-  Get->setBody(Body);
+  Parameter->setBody(Body);
   
-  InitialValue->makeComputed(SourceLoc(), Get, nullptr, nullptr, SourceLoc());
-  InitialValue->setIsBeingTypeChecked(false);
+  Parameter->setIsBeingTypeChecked(false);
+  typeCheckDecl(Parameter, true);
+  typeCheckDecl(Parameter, false);
+  addMemberToContextIfNeeded(Parameter, DC);
 
   // Add the witnesses to the conformance.
   ArrayRef<Substitution> MemberSubs;
@@ -1370,10 +1454,8 @@ void TypeChecker::completePropertyBehaviorInitialValue(VarDecl *VD,
     ->getForwardingSubstitutions(Context);
   }
 
-  BehaviorConformance->setWitness(BehaviorInitialValue,
-                            ConcreteDeclRef(Context, InitialValue, MemberSubs));
-  BehaviorConformance->setWitness(BehaviorInitialValue->getGetter(),
-                            ConcreteDeclRef(Context, Get, MemberSubs));
+  BehaviorConformance->setWitness(BehaviorParameter,
+                               ConcreteDeclRef(Context, Parameter, MemberSubs));
 }
 
 void TypeChecker::completePropertyBehaviorAccessors(VarDecl *VD,

lib/Sema/TypeCheckDecl.cpp

@@ -2641,6 +2641,8 @@ static void checkVarBehavior(VarDecl *decl, TypeChecker &TC) {
   //
   // It'd probably be cleaner to model as `where Self: ...` constraints when
   // we have those.
+  //
+  // TODO: Handle non-protocol requirements ('class', base class, etc.)
   for (auto refinedProto : behaviorProto->getInheritedProtocols(&TC)) {
     ProtocolConformance *inherited = nullptr;
     
@@ -2772,7 +2774,7 @@ static void checkVarBehavior(VarDecl *decl, TypeChecker &TC) {
   // Now that type witnesses are done, satisfy property and method requirements.
   conformance->setState(ProtocolConformanceState::Checking);
 
-  bool requiresInitialValue = false;
+  bool requiresParameter = false;
   for (auto requirementDecl : behaviorProto->getMembers()) {
     auto requirement = dyn_cast<ValueDecl>(requirementDecl);
     if (!requirement)
@@ -2783,6 +2785,8 @@ static void checkVarBehavior(VarDecl *decl, TypeChecker &TC) {
     if (auto varReqt = dyn_cast<VarDecl>(requirement)) {
       // Match a storage requirement.
       if (varReqt->getName() == TC.Context.Id_storage) {
+        TC.validateDecl(varReqt);
+
         auto storageTy = varReqt->getInterfaceType();
         auto expectedInitStorageTy =
           FunctionType::get(TC.Context.TheEmptyTupleType, storageTy);
@@ -2814,6 +2818,7 @@ static void checkVarBehavior(VarDecl *decl, TypeChecker &TC) {
               TC.diagnose(foundFunc->getLoc(),
                           diag::property_behavior_protocol_reqt_here,
                           TC.Context.Id_initStorage);
+              conformance->setInvalid();
               break;
             }
             
@@ -2828,6 +2833,7 @@ static void checkVarBehavior(VarDecl *decl, TypeChecker &TC) {
           for (auto found : lookup)
             TC.diagnose(found.Decl->getLoc(),
                         diag::found_candidate);
+          conformance->setInvalid();
           continue;
         }
         
@@ -2849,67 +2855,56 @@ static void checkVarBehavior(VarDecl *decl, TypeChecker &TC) {
                                            interfaceSubs,
                                            contextSubs);
         continue;
-      // Handle an initialValue requirement.
-      } else if (varReqt->getName() == TC.Context.Id_initialValue) {
-        requiresInitialValue = true;
-        
-        // The requirement should be static, get-only, and have the type of the
-        // Value.
-        // TODO: A "deferred" initialization would be an instance requirement.
-        Type valueTy = GenericTypeParamType::get(0, 0, TC.Context);
-        assert(valueReqt && "no Value associated type?!");
-        valueTy = DependentMemberType::get(valueTy, valueReqt, TC.Context);
-  
-        if (!varReqt->isStatic()
-            || varReqt->isSettable(dc)
-            || !varReqt->getInterfaceType()->isEqual(valueTy)) {
-          TC.diagnose(behavior->getLoc(),
-                      diag::property_behavior_invalid_initialValue_reqt,
-                      behaviorProto->getName());
-          TC.diagnose(varReqt->getLoc(),
-                      diag::property_behavior_protocol_reqt_here,
-                      TC.Context.Id_initialValue);
-          continue;
-        }
-        
-        // The declaration must have an initializer expression.
-        // FIXME: It should have the initializer to itself too, no 'var (a,b)=x'
-        if (!decl->getParentInitializer()) {
-          TC.diagnose(behavior->getLoc(),
-                      diag::property_behavior_requires_initialValue,
-                      behaviorProto->getName(),
-                      decl->getName());
-          continue;
-        }
-        
-        if (!isa<NamedPattern>(
-                    decl->getParentPattern()->getSemanticsProvidingPattern())) {
-          TC.diagnose(decl->getParentInitializer()->getLoc(),
-                      diag::property_behavior_requires_unique_initialValue,
-                      behaviorProto->getName());
-          continue;
-        }
-        
-        // TODO: Support initialValue requirements in non-type contexts.
-        if (!dc->isTypeContext()) {
-          TC.diagnose(behavior->getLoc(),
-                      diag::property_behavior_with_feature_not_supported,
-                      behaviorProto->getName(), "initial value requirement");
-          conformance->setInvalid();
-          continue;
-        }
-        
-        // Wrap the initializer expression in a get-only property to
-        TC.completePropertyBehaviorInitialValue(decl, varReqt,
-                                                conformance,
-                                                interfaceSubs,
-                                                contextSubs);
-        continue;
       }
     } else if (auto func = dyn_cast<FuncDecl>(requirement)) {
       // Handle accessors as part of their property.
       if (func->isAccessor())
         continue;
+      
+      // Handle a parameter block requirement.
+      if (func->getName() == TC.Context.Id_parameter) {
+        requiresParameter = true;
+        
+        TC.validateDecl(func);
+        
+        // The requirement should be for a nongeneric instance method.
+        if (func->isStatic() || func->isGeneric()) {
+          TC.diagnose(behavior->getLoc(),
+                      diag::property_behavior_invalid_parameter_reqt,
+                      behaviorProto->getName());
+          TC.diagnose(varReqt->getLoc(),
+                      diag::property_behavior_protocol_reqt_here,
+                      TC.Context.Id_parameter);
+          conformance->setInvalid();
+          continue;
+        }
+        
+        // The declaration must have a parameter.
+        if (!decl->getBehavior()->Param) {
+          TC.diagnose(behavior->getLoc(),
+                      diag::property_behavior_requires_parameter,
+                      behaviorProto->getName(),
+                      decl->getName());
+          conformance->setInvalid();
+          continue;
+        }
+        
+        // TODO: Support parameter requirements in non-type contexts.
+        if (!dc->isTypeContext()) {
+          TC.diagnose(behavior->getLoc(),
+                      diag::property_behavior_with_feature_not_supported,
+                      behaviorProto->getName(), "parameter requirement");
+          conformance->setInvalid();
+          continue;
+        }
+        
+        // Wrap the initializer expression in a get-only property to
+        TC.completePropertyBehaviorParameter(decl, func,
+                                             conformance,
+                                             interfaceSubs,
+                                             contextSubs);
+        continue;
+      }
     }
 
     unknownRequirement(requirement);
@@ -2919,9 +2914,9 @@ static void checkVarBehavior(VarDecl *decl, TypeChecker &TC) {
   // use it, complain.
   // TODO: The initializer could eventually be consumed by DI-style
   // initialization.
-  if (!requiresInitialValue && decl->getParentInitializer()) {
-    TC.diagnose(decl->getParentInitializer()->getLoc(),
-                diag::property_behavior_invalid_initializer,
+  if (!requiresParameter && decl->getBehavior()->Param) {
+    TC.diagnose(decl->getBehavior()->Param->getLoc(),
+                diag::property_behavior_invalid_parameter,
                 behaviorProto->getName());
   }
   

lib/Sema/TypeChecker.h

@@ -1031,10 +1031,10 @@ public:
                                ArrayRef<Substitution> SelfInterfaceSubs,
                                ArrayRef<Substitution> SelfContextSubs);
   
-  /// Instantiate the initial value implementation for a behavior-backed
+  /// Instantiate the parameter implementation for a behavior-backed
   /// property.
-  void completePropertyBehaviorInitialValue(VarDecl *VD,
-                               VarDecl *BehaviorInitialValue,
+  void completePropertyBehaviorParameter(VarDecl *VD,
+                               FuncDecl *BehaviorParameter,
                                NormalProtocolConformance *BehaviorConformance,
                                ArrayRef<Substitution> SelfInterfaceSubs,
                                ArrayRef<Substitution> SelfContextSubs);

test/Interpreter/property_behavior.swift

@@ -38,7 +38,7 @@ extension delayedImmutable {
 protocol lazy {
   associatedtype Value
   var storage: Value? { get set }
-  static var initialValue: Value { get }
+  func parameter() -> Value
 }
 extension lazy {
   var value: Value {
@@ -46,7 +46,7 @@ extension lazy {
       if let existing = storage {
         return existing
       }
-      let value = Self.initialValue
+      let value = parameter()
       storage = value
       return value
     }
@@ -69,7 +69,7 @@ func evaluateLazy() -> Int {
 
 class Foo {
   var x: Int __behavior delayedImmutable
-  var y = evaluateLazy() __behavior lazy
+  var y: Int __behavior lazy { evaluateLazy() }
 }
 
 var DelayedImmutable = TestSuite("DelayedImmutable")

test/SILGen/property_behavior.swift

@@ -120,7 +120,7 @@ func exerciseStorage<T>(inout _ sx: S2<T>, inout _ sy: S2<Int>,
 protocol withInit {
   associatedtype Value
   var storage: Value? { get set }
-  static var initialValue: Value { get }
+  func parameter() -> Value
 }
 extension withInit {
   var value: Value {
@@ -131,14 +131,14 @@ extension withInit {
   static func initStorage() -> Value? { }
 }
 
-// TODO: initialValue behaviors in non-instance context
+// TODO: parameterized behaviors in non-instance context
 func any<T>() -> T { }
 
 struct S3<T> {
-  var instance: T = any() __behavior withInit
+  var instance: T __behavior withInit { any() }
 }
 class C3<T> {
-  var instance: T = any() __behavior withInit
+  var instance: T __behavior withInit { any() }
 }
 
 func exerciseStorage<T>(inout _ sx: S3<T>, inout _ sy: S3<Int>,

test/decl/var/behaviors.swift

@@ -184,44 +184,37 @@ struct S<T> {
   static var testGetset: T __behavior getset
 }
 
-protocol initialValue {
+protocol parameterized {
   associatedtype Value
-  static var initialValue: Value { get }
+  func parameter() -> Value
 }
-extension initialValue {
+extension parameterized {
   var value: Value {
     get { }
     set { }
   }
 }
 
-let compoundInitialValue = (0,0)
-
-struct TestInitialValues {
-  var hasInitialValue: Int = 0 __behavior initialValue
-  var (sharedInitialValue1, sharedInitialValue2): (Int,Int) 
-    = compoundInitialValue __behavior initialValue // expected-error * {{cannot destructure}}
-  var missingInitialValue: Int __behavior initialValue // expected-error{{requires an initializer}}
-  // TODO: "return expression" message is wrong
-  var invalidInitialValue: Int = 5.5 __behavior initialValue // expected-error{{cannot convert return expression of type 'Double' to return type 'Int'}}
+struct TestParameters {
+  var hasParameter: Int __behavior parameterized { 0 }
+  var (sharedParameter1, sharedParameter2): (Int,Int) 
+    __behavior parameterized { 0 }  // expected-error {{multiple variables is not supported}} expected-error{{sharedParameter2}}
+  var missingParameter: Int __behavior parameterized // expected-error{{requires a parameter}}
+  var invalidParameter: Int __behavior parameterized { 5.5 } // expected-error{{cannot convert return expression of type 'Double' to return type 'Int'}}
 }
 
 // TODO
-var globalInitialValue: Int = 0 __behavior initialValue // expected-error{{not supported}}
+var globalParameter: Int __behavior parameterized { 0 } // expected-error{{not supported}}
 
-protocol noInitialValue {
+protocol noParameter {
   associatedtype Value
 }
-extension noInitialValue {
+extension noParameter {
   var value: Value {
     get { }
     set { }
   }
 }
 
-var hasNoInitialValue: Int __behavior noInitialValue
-var hasUnwantedInitialValue: Int = 0 __behavior noInitialValue // expected-error{{initializer expression provided, but property behavior 'noInitialValue' does not use it}}
-var (hasUnwantedSharedInitialValue1,
-     hasUnwantedSharedInitialValue2): (Int, Int)
-  = compoundInitialValue // expected-error * {{initializer expression provided, but property behavior 'noInitialValue' does not use it}}
-  __behavior noInitialValue
+var hasNoParameter: Int __behavior noParameter
+var hasUnwantedParameter: Int __behavior noParameter { 0 } // expected-error{{parameter expression provided, but property behavior 'noParameter' does not use it}}