[SE-0335] Enable explicit existential types.

include/swift/AST/ASTContext.h

@@ -531,7 +531,7 @@ class ASTContext final {
 
   /// Retrieve the declaration of Swift.Error.
   ProtocolDecl *getErrorDecl() const;
-  CanType getExceptionType() const;
+  CanType getErrorExistentialType() const;
 
 #define KNOWN_STDLIB_TYPE_DECL(NAME, DECL_CLASS, NUM_GENERIC_PARAMS) \
   /** Retrieve the declaration of Swift.NAME. */ \

include/swift/AST/ASTDemangler.h

@@ -66,7 +66,7 @@ class ASTBuilder {
 
   Demangle::NodeFactory &getNodeFactory() { return Factory; }
 
-  Type decodeMangledType(NodePointer node);
+  Type decodeMangledType(NodePointer node, bool forRequirement = true);
   Type createBuiltinType(StringRef builtinName, StringRef mangledName);
 
   TypeDecl *createTypeDecl(NodePointer node);
@@ -109,7 +109,8 @@ class ASTBuilder {
 
   Type createProtocolCompositionType(ArrayRef<ProtocolDecl *> protocols,
                                      Type superclass,
-                                     bool isClassBound);
+                                     bool isClassBound,
+                                     bool forRequirement = true);
 
   Type createExistentialMetatypeType(Type instance,
                      Optional<Demangle::ImplMetatypeRepresentation> repr=None);

include/swift/AST/ASTSynthesis.h

@@ -56,7 +56,7 @@ inline Type synthesizeType(SynthesisContext &SC,
   switch (kind) {
   case _any: return SC.Context.TheAnyType;
   case _bridgeObject: return SC.Context.TheBridgeObjectType;
-  case _error: return SC.Context.getExceptionType();
+  case _error: return SC.Context.getErrorExistentialType();
   case _executor: return SC.Context.TheExecutorType;
   case _job: return SC.Context.TheJobType;
   case _nativeObject: return SC.Context.TheNativeObjectType;

include/swift/AST/Decl.h

@@ -4363,6 +4363,11 @@ class ProtocolDecl final : public NominalTypeDecl {
   /// not exist.
   AssociatedTypeDecl *getAssociatedType(Identifier name) const;
 
+  /// Returns the existential type for this protocol.
+  Type getExistentialType() const {
+    return ExistentialType::get(getDeclaredInterfaceType());
+  }
+
   /// Walk this protocol and all of the protocols inherited by this protocol,
   /// transitively, invoking the callback function for each protocol.
   ///

include/swift/AST/DiagnosticsSema.def

@@ -2441,8 +2441,8 @@ ERROR(protocol_composition_one_class,none,
       "contains class %1", (Type, Type))
 
 ERROR(requires_conformance_nonprotocol,none,
-      "type %0 constrained to non-protocol, non-class type %1",
-      (Type, Type))
+      "type %0 constrained to non-protocol, non-class type '%1'",
+      (Type, StringRef))
 NOTE(requires_conformance_nonprotocol_fixit,none,
      "use '%0 == %1' to require '%0' to be '%1'",
      (StringRef, StringRef))
@@ -4648,8 +4648,6 @@ ERROR(unchecked_not_inheritance_clause,none,
 ERROR(unchecked_not_existential,none,
       "'unchecked' attribute cannot apply to non-protocol type %0", (Type))
 
-WARNING(unnecessary_any,none,
-         "'any' is redundant on type %0", (Type))
 ERROR(any_not_existential,none,
        "'any' has no effect on %select{concrete type|type parameter}0 %1",
        (bool, Type))

include/swift/AST/PrintOptions.h

@@ -278,6 +278,10 @@ struct PrintOptions {
 
   bool PrintImplicitAttrs = true;
 
+  /// Whether to print the \c any keyword for existential
+  /// types.
+  bool PrintExplicitAny = false;
+
   /// Whether to skip keywords with a prefix of underscore such as __consuming.
   bool SkipUnderscoredKeywords = false;
 

include/swift/AST/ProtocolConformance.h

@@ -660,7 +660,7 @@ class SelfProtocolConformance : public RootProtocolConformance {
 public:
   /// Get the protocol being conformed to.
   ProtocolDecl *getProtocol() const {
-    return getType()->castTo<ProtocolType>()->getDecl();
+    return dyn_cast<ProtocolDecl>(getType()->getAnyNominal());
   }
 
   /// Get the declaration context in which this conformance was declared.

include/swift/AST/Type.h

@@ -385,6 +385,7 @@ class CanType : public Type {
 
   static bool isReferenceTypeImpl(CanType type, const GenericSignatureImpl *sig,
                                   bool functionsCount);
+  static bool isConstraintTypeImpl(CanType type);
   static bool isExistentialTypeImpl(CanType type);
   static bool isAnyExistentialTypeImpl(CanType type);
   static bool isObjCExistentialTypeImpl(CanType type);
@@ -457,6 +458,10 @@ class CanType : public Type {
                                /*functions count*/ false);
   }
 
+  bool isConstraintType() const {
+    return isConstraintTypeImpl(*this);
+  }
+
   /// Is this type existential?
   bool isExistentialType() const {
     return isExistentialTypeImpl(*this);

include/swift/AST/Types.h

@@ -727,6 +727,9 @@ class alignas(1 << TypeAlignInBits) TypeBase
     return getRecursiveProperties().hasDependentMember();
   }
 
+  /// Whether this type represents a generic constraint.
+  bool isConstraintType() const;
+
   /// isExistentialType - Determines whether this type is an existential type,
   /// whose real (runtime) type is unknown but which is known to conform to
   /// some set of protocols. Protocol and protocol-conformance types are
@@ -2731,6 +2734,8 @@ class ExistentialMetatypeType : public AnyMetatypeType {
   static bool classof(const TypeBase *T) {
     return T->getKind() == TypeKind::ExistentialMetatype;
   }
+
+  Type getExistentialInstanceType();
 
 private:
   ExistentialMetatypeType(Type T, const ASTContext *C,
@@ -5243,7 +5248,7 @@ class ExistentialType final : public TypeBase {
         ConstraintType(constraintType) {}
 
 public:
-  static ExistentialType *get(Type constraint);
+  static Type get(Type constraint);
 
   Type getConstraintType() const { return ConstraintType; }
 
@@ -6335,6 +6340,15 @@ inline GenericTypeParamType *TypeBase::getRootGenericParam() {
   return t->castTo<GenericTypeParamType>();
 }
 
+inline bool TypeBase::isConstraintType() const {
+  return getCanonicalType().isConstraintType();
+}
+
+inline bool CanType::isConstraintTypeImpl(CanType type) {
+  return (isa<ProtocolType>(type) ||
+          isa<ProtocolCompositionType>(type));
+}
+
 inline bool TypeBase::isExistentialType() {
   return getCanonicalType().isExistentialType();
 }
@@ -6441,6 +6455,8 @@ inline NominalTypeDecl *TypeBase::getNominalOrBoundGenericNominal() {
 inline NominalTypeDecl *CanType::getNominalOrBoundGenericNominal() const {
   if (auto Ty = dyn_cast<NominalOrBoundGenericNominalType>(*this))
     return Ty->getDecl();
+  if (auto Ty = dyn_cast<ExistentialType>(*this))
+    return Ty->getConstraintType()->getNominalOrBoundGenericNominal();
   return nullptr;
 }
 
@@ -6449,6 +6465,9 @@ inline NominalTypeDecl *TypeBase::getAnyNominal() {
 }
 
 inline Type TypeBase::getNominalParent() {
+  if (auto existential = getAs<ExistentialType>())
+    return existential->getConstraintType()->getNominalParent();
+
   return castTo<AnyGenericType>()->getParent();
 }
 

include/swift/Basic/LangOptions.h

@@ -315,7 +315,7 @@ namespace swift {
 
     /// Enable support for explicit existential types via the \c any
     /// keyword.
-    bool EnableExplicitExistentialTypes = false;
+    bool EnableExplicitExistentialTypes = true;
 
     /// Enable experimental flow-sensitive concurrent captures.
     bool EnableExperimentalFlowSensitiveConcurrentCaptures = false;

include/swift/Demangling/TypeDecoder.h

@@ -372,12 +372,16 @@ void decodeRequirement(NodePointer node,
 
     BuiltType constraintType;
     if (child->getKind() ==
-            Demangle::Node::Kind::DependentGenericConformanceRequirement ||
-        child->getKind() ==
-            Demangle::Node::Kind::DependentGenericSameTypeRequirement) {
+        Demangle::Node::Kind::DependentGenericConformanceRequirement) {
       constraintType = Builder.decodeMangledType(child->getChild(1));
       if (!constraintType)
         return;
+    } else if (child->getKind() ==
+               Demangle::Node::Kind::DependentGenericSameTypeRequirement) {
+      constraintType = Builder.decodeMangledType(
+          child->getChild(1), /*forRequirement=*/false);
+      if (!constraintType)
+        return;
     }
 
     switch (child->getKind()) {
@@ -468,15 +472,17 @@ class TypeDecoder {
   explicit TypeDecoder(BuilderType &Builder) : Builder(Builder) {}
 
   /// Given a demangle tree, attempt to turn it into a type.
-  TypeLookupErrorOr<BuiltType> decodeMangledType(NodePointer Node) {
-    return decodeMangledType(Node, 0);
+  TypeLookupErrorOr<BuiltType> decodeMangledType(NodePointer Node,
+                                                 bool forRequirement = true) {
+    return decodeMangledType(Node, 0, forRequirement);
   }
 
 protected:
   static const unsigned MaxDepth = 1024;
 
   TypeLookupErrorOr<BuiltType> decodeMangledType(NodePointer Node,
-                                                 unsigned depth) {
+                                                 unsigned depth,
+                                                 bool forRequirement = true) {
     if (depth > TypeDecoder::MaxDepth)
       return TypeLookupError("Mangled type is too complex");
 
@@ -499,7 +505,8 @@ class TypeDecoder {
       if (Node->getNumChildren() < 1)
         return MAKE_NODE_TYPE_ERROR0(Node, "no children.");
 
-      return decodeMangledType(Node->getChild(0), depth + 1);
+      return decodeMangledType(Node->getChild(0), depth + 1,
+                               forRequirement);
     case NodeKind::Class:
     {
 #if SWIFT_OBJC_INTEROP
@@ -543,7 +550,8 @@ class TypeDecoder {
         return MAKE_NODE_TYPE_ERROR0(genericArgs, "is not TypeList");
 
       for (auto genericArg : *genericArgs) {
-        auto paramType = decodeMangledType(genericArg, depth + 1);
+        auto paramType = decodeMangledType(genericArg, depth + 1,
+                                           /*forRequirement=*/false);
         if (paramType.isError())
           return paramType;
         args.push_back(paramType.getType());
@@ -698,14 +706,16 @@ class TypeDecoder {
       }
 
       return Builder.createProtocolCompositionType(Protocols, Superclass,
-                                                   IsClassBound);
+                                                   IsClassBound,
+                                                   forRequirement);
     }
 
     case NodeKind::Protocol:
     case NodeKind::ProtocolSymbolicReference: {
       if (auto Proto = decodeMangledProtocolType(Node, depth + 1)) {
         return Builder.createProtocolCompositionType(Proto, BuiltType(),
-                                                     /*IsClassBound=*/false);
+                                                     /*IsClassBound=*/false,
+                                                     forRequirement);
       }
 
       return MAKE_NODE_TYPE_ERROR0(Node, "failed to decode protocol type");
@@ -845,7 +855,8 @@ class TypeDecoder {
                           Node->getKind() == NodeKind::EscapingObjCBlock);
 
       auto result =
-          decodeMangledType(Node->getChild(firstChildIdx + 1), depth + 1);
+          decodeMangledType(Node->getChild(firstChildIdx + 1), depth + 1,
+                            /*forRequirement=*/false);
       if (result.isError())
         return result;
       return Builder.createFunctionType(
@@ -962,7 +973,8 @@ class TypeDecoder {
       if (Node->getNumChildren() < 1)
         return MAKE_NODE_TYPE_ERROR0(Node, "no children");
 
-      return decodeMangledType(Node->getChild(0), depth + 1);
+      return decodeMangledType(Node->getChild(0), depth + 1,
+                               /*forRequirement=*/false);
 
     case NodeKind::Tuple: {
       llvm::SmallVector<BuiltType, 8> elements;
@@ -994,7 +1006,8 @@ class TypeDecoder {
 
         // Decode the element type.
         auto elementType =
-            decodeMangledType(element->getChild(typeChildIndex), depth + 1);
+            decodeMangledType(element->getChild(typeChildIndex), depth + 1,
+                              /*forRequirement=*/false);
         if (elementType.isError())
           return elementType;
 
@@ -1012,9 +1025,11 @@ class TypeDecoder {
                                       "fewer children (%zu) than required (2)",
                                       Node->getNumChildren());
 
-        return decodeMangledType(Node->getChild(1), depth + 1);
+        return decodeMangledType(Node->getChild(1), depth + 1,
+                                 /*forRequirement=*/false);
       }
-      return decodeMangledType(Node->getChild(0), depth + 1);
+      return decodeMangledType(Node->getChild(0), depth + 1,
+                               /*forRequirement=*/false);
 
     case NodeKind::DependentGenericType: {
       if (Node->getNumChildren() < 2)
@@ -1161,7 +1176,8 @@ return {}; // Not Implemented!
                 "more substitutions than generic params");
           while (index >= genericParamsAtDepth[paramDepth])
             ++paramDepth, index = 0;
-          auto substTy = decodeMangledType(subst, depth + 1);
+          auto substTy = decodeMangledType(subst, depth + 1,
+                                           /*forRequirement=*/false);
           if (substTy.isError())
             return substTy;
           substitutions.emplace_back(
@@ -1243,7 +1259,8 @@ return {}; // Not Implemented!
         if (genericsNode->getKind() != NodeKind::TypeList)
           break;
         for (auto argNode : *genericsNode) {
-          auto arg = decodeMangledType(argNode, depth + 1);
+          auto arg = decodeMangledType(argNode, depth + 1,
+                                       /*forRequirement=*/false);
           if (arg.isError())
             return arg;
           genericArgsBuf.push_back(arg.getType());
@@ -1480,7 +1497,8 @@ return {}; // Not Implemented!
         }
       }
 
-      auto paramType = decodeMangledType(node, depth + 1);
+      auto paramType = decodeMangledType(node, depth + 1,
+                                         /*forRequirement=*/false);
       if (paramType.isError())
         return false;
 
@@ -1544,8 +1562,10 @@ return {}; // Not Implemented!
 
 template <typename BuilderType>
 inline TypeLookupErrorOr<typename BuilderType::BuiltType>
-decodeMangledType(BuilderType &Builder, NodePointer Node) {
-  return TypeDecoder<BuilderType>(Builder).decodeMangledType(Node);
+decodeMangledType(BuilderType &Builder, NodePointer Node,
+                  bool forRequirement = false) {
+  return TypeDecoder<BuilderType>(Builder)
+      .decodeMangledType(Node, forRequirement);
 }
 
 SWIFT_END_INLINE_NAMESPACE

include/swift/Reflection/TypeRefBuilder.h

@@ -289,7 +289,7 @@ class TypeRefBuilder {
 
   void clearNodeFactory() { Dem.clear(); }
 
-  BuiltType decodeMangledType(Node *node);
+  BuiltType decodeMangledType(Node *node, bool forRequirement = true);
 
   ///
   /// Factory methods for all TypeRef kinds
@@ -492,7 +492,8 @@ class TypeRefBuilder {
 
   const ProtocolCompositionTypeRef *
   createProtocolCompositionType(llvm::ArrayRef<BuiltProtocolDecl> protocols,
-                                BuiltType superclass, bool isClassBound) {
+                                BuiltType superclass, bool isClassBound,
+                                bool forRequirement = true) {
     std::vector<const TypeRef *> protocolRefs;
     for (const auto &protocol : protocols) {
       if (!protocol)

include/swift/SIL/SILCloner.h

@@ -2220,7 +2220,7 @@ visitOpenExistentialMetatypeInst(OpenExistentialMetatypeInst *Inst) {
   auto openedType = Inst->getType().getASTType();
   auto exType = Inst->getOperand()->getType().getASTType();
   while (auto exMetatype = dyn_cast<ExistentialMetatypeType>(exType)) {
-    exType = exMetatype.getInstanceType();
+    exType = exMetatype->getExistentialInstanceType()->getCanonicalType();
     openedType = cast<MetatypeType>(openedType).getInstanceType();
   }
   remapOpenedType(cast<OpenedArchetypeType>(openedType));

include/swift/SIL/SILInstruction.h

@@ -7072,7 +7072,7 @@ class InitExistentialMetatypeInst final
     auto exType = getType().getASTType();
     auto concreteType = getOperand()->getType().getASTType();
     while (auto exMetatype = dyn_cast<ExistentialMetatypeType>(exType)) {
-      exType = exMetatype.getInstanceType();
+      exType = exMetatype->getExistentialInstanceType()->getCanonicalType();
       concreteType = cast<MetatypeType>(concreteType).getInstanceType();
     }
     assert(exType.isExistentialType());

lib/APIDigester/ModuleAnalyzerNodes.cpp

@@ -1017,6 +1017,12 @@ static StringRef getTypeName(SDKContext &Ctx, Type Ty,
   if (auto *NAT = dyn_cast<TypeAliasType>(Ty.getPointer())) {
     return NAT->getDecl()->getNameStr();
   }
+
+  if (auto existential = Ty->getAs<ExistentialType>()) {
+    return getTypeName(Ctx, existential->getConstraintType(),
+                       IsImplicitlyUnwrappedOptional);
+  }
+
   if (Ty->getAnyNominal()) {
     if (IsImplicitlyUnwrappedOptional) {
       assert(Ty->getOptionalObjectType());