Swift Opt-In Reflection metadata

include/swift/AST/ASTContext.h

@@ -589,6 +589,9 @@ class ASTContext final {
   /// Retrieve the type Swift.AnyObject as a constraint.
   CanType getAnyObjectConstraint() const;
 
+  /// Retrieve the type Swift.Reflectable as a constraint.
+  CanType getReflectableConstraint() const;
+
   /// Retrieve the type Swift.AnyObject as an existential type.
   CanType getAnyObjectType() const;
 

include/swift/AST/Decl.h

@@ -5143,6 +5143,8 @@ class ProtocolDecl final : public NominalTypeDecl {
   /// True if this protocol can only be conformed to by class types.
   bool requiresClass() const;
 
+  bool inheritsReflectable() const;
+
   /// Determine whether an existential conforming to this protocol can be
   /// matched with a generic type parameter constrained to this protocol.
   /// This is only permitted if there is nothing "non-trivial" that we

include/swift/AST/DiagnosticsSema.def

@@ -7708,5 +7708,13 @@ ERROR(referencebindings_binding_must_be_to_lvalue,none,
 ERROR(result_depends_on_no_result,none,
       "Incorrect use of %0 with no result", (StringRef))
 
+//------------------------------------------------------------------------------
+// MARK: Reflectable
+//------------------------------------------------------------------------------
+
+ERROR(type_does_not_conform_reflectable_decl_owner,none,
+      "%kind0 requires that %1 be a Reflectable type",
+      (const ValueDecl *, Type, Type))
+
 #define UNDEFINE_DIAGNOSTIC_MACROS
 #include "DefineDiagnosticMacros.h"

include/swift/AST/ExistentialLayout.h

@@ -31,6 +31,7 @@ struct ExistentialLayout {
 
   ExistentialLayout() {
     hasExplicitAnyObject = false;
+    hasExplicitReflectable = false;
     hasInverseCopyable = false;
     containsNonObjCProtocol = false;
     containsParameterized = false;
@@ -47,6 +48,9 @@ struct ExistentialLayout {
   /// Whether the existential contains an explicit '& AnyObject' constraint.
   bool hasExplicitAnyObject : 1;
 
+  /// Whether the existential contains an explicit '& Reflectable' constraint.
+  bool hasExplicitReflectable : 1;
+
   /// Whether the existential contains an explicit '& ~Copyable' constraint.
   bool hasInverseCopyable : 1;
 
@@ -71,6 +75,8 @@ struct ExistentialLayout {
 
   bool isAnyObject() const;
 
+  bool isReflectable() const;
+
   bool isObjC() const {
     // FIXME: Does the superclass have to be @objc?
     return ((explicitSuperclass ||

include/swift/AST/IRGenOptions.h

@@ -89,7 +89,7 @@ enum class SwiftAsyncFramePointerKind : unsigned {
 };
 
 enum class ReflectionMetadataMode : unsigned {
-  None,         ///< Don't emit reflection metadata at all.
+  OptIn,        ///< Reflection is emitted only for Reflectable nominal types.
   DebuggerOnly, ///< Emit reflection metadata for the debugger, don't link them
                 ///  into runtime metadata and don't force them to stay alive.
   Runtime,      ///< Make reflection metadata fully available.

include/swift/AST/KnownIdentifiers.def

@@ -177,6 +177,7 @@ IDENTIFIER_WITH_NAME(RefCountedObjectLayout, "_RefCountedObject")
 IDENTIFIER_WITH_NAME(NativeRefCountedObjectLayout, "_NativeRefCountedObject")
 IDENTIFIER_WITH_NAME(ClassLayout, "_Class")
 IDENTIFIER_WITH_NAME(NativeClassLayout, "_NativeClass")
+IDENTIFIER_WITH_NAME(Reflectable, "Reflectable")
 
 // Operators
 IDENTIFIER_WITH_NAME(MatchOperator, "~=")

include/swift/AST/LayoutConstraint.h

@@ -100,6 +100,10 @@ class LayoutConstraintInfo
     return isClass(Kind);
   }
 
+  bool isReflectable() const {
+    return isReflectable(Kind);
+  }
+
   bool isNativeClass() const {
     return isNativeClass(Kind);
   }
@@ -194,6 +198,8 @@ class LayoutConstraintInfo
 
   static bool isClass(LayoutConstraintKind Kind);
 
+  static bool isReflectable(LayoutConstraintKind Kind);
+
   static bool isNativeClass(LayoutConstraintKind Kind);
 
   static bool isRefCounted(LayoutConstraintKind Kind);
@@ -217,6 +223,7 @@ class LayoutConstraintInfo
   static LayoutConstraintInfo ClassConstraintInfo;
   static LayoutConstraintInfo NativeClassConstraintInfo;
   static LayoutConstraintInfo TrivialConstraintInfo;
+  static LayoutConstraintInfo ReflectableConstraintInfo;
 };
 
 /// A wrapper class containing a reference to the actual LayoutConstraintInfo

include/swift/AST/LayoutConstraintKind.h

@@ -39,7 +39,9 @@ enum class LayoutConstraintKind : uint8_t {
   RefCountedObject,
   // It is a layout constraint representing a native reference counted object.
   NativeRefCountedObject,
-  LastLayout = NativeRefCountedObject,
+  // It is a layout constraint representing type that has reflection metadata available at runtime.
+  Reflectable,
+  LastLayout = Reflectable,
 };
 
 #endif

include/swift/AST/NameLookup.h

@@ -599,7 +599,7 @@ struct InheritedNominalEntry : Located<NominalTypeDecl *> {
 void getDirectlyInheritedNominalTypeDecls(
     llvm::PointerUnion<const TypeDecl *, const ExtensionDecl *> decl,
     unsigned i, llvm::SmallVectorImpl<InheritedNominalEntry> &result,
-    bool &anyObject);
+    bool &anyObject, bool &reflectable);
 
 /// Retrieve the set of nominal type declarations that are directly
 /// "inherited" by the given declaration, looking through typealiases
@@ -608,7 +608,7 @@ void getDirectlyInheritedNominalTypeDecls(
 /// If we come across the AnyObject type, set \c anyObject true.
 SmallVector<InheritedNominalEntry, 4> getDirectlyInheritedNominalTypeDecls(
     llvm::PointerUnion<const TypeDecl *, const ExtensionDecl *> decl,
-    bool &anyObject);
+    bool &anyObject, bool &reflectable);
 
 /// Retrieve the set of nominal type declarations that appear as the
 /// constraint type of any "Self" constraints in the where clause of the

include/swift/AST/TypeCheckRequests.h

@@ -4644,6 +4644,24 @@ class UniqueUnderlyingTypeSubstitutionsRequest
   void cacheResult(llvm::Optional<SubstitutionMap>) const;
 };
 
+/// Determine if protocol inherits Reflectable.
+class InheritsReflectableProtocolRequest
+    : public SimpleRequest<InheritsReflectableProtocolRequest,
+                         bool(ProtocolDecl *),
+                         RequestFlags::Cached> {
+public:
+  using SimpleRequest::SimpleRequest;
+
+private:
+  friend SimpleRequest;
+
+  bool evaluate(Evaluator &evaluator, ProtocolDecl *decl) const;
+
+public:
+  // Separate caching.
+  bool isCached() const { return true; }
+};
+
 #define SWIFT_TYPEID_ZONE TypeChecker
 #define SWIFT_TYPEID_HEADER "swift/AST/TypeCheckerTypeIDZone.def"
 #include "swift/Basic/DefineTypeIDZone.h"

include/swift/AST/TypeCheckerTypeIDZone.def

@@ -530,3 +530,5 @@ SWIFT_REQUEST(TypeChecker, SemanticDeclAttrsRequest,
 SWIFT_REQUEST(TypeChecker, UniqueUnderlyingTypeSubstitutionsRequest,
               llvm::Optional<SubstitutionMap>(const Decl *),
               SeparatelyCached, NoLocationInfo)
+SWIFT_REQUEST(TypeChecker, InheritsReflectableProtocolRequest, bool(ProtocolDecl *),
+              Cached, NoLocationInfo)