Reference runtime-only ObjC classes with bare strings.

As part of this, rename TypeMetadataRecordKind to TypeReferenceKind
and consistently give it three bits of storage.

The better modelling of these type references appears to have been
sufficient to make dynamic conformance checks succeed, which is good
but unexpected.

Author: rjmccall

include/swift/ABI/Metadata.h

@@ -2062,32 +2062,37 @@ struct TargetTypeMetadataRecord {
   union {
     /// A direct reference to a nominal type descriptor.
     RelativeDirectPointerIntPair<TargetTypeContextDescriptor<Runtime>,
-                                 TypeMetadataRecordKind>
+                                 TypeReferenceKind>
       DirectNominalTypeDescriptor;
 
     /// An indirect reference to a nominal type descriptor.
     RelativeDirectPointerIntPair<TargetTypeContextDescriptor<Runtime> * const,
-                                 TypeMetadataRecordKind>
+                                 TypeReferenceKind>
       IndirectNominalTypeDescriptor;
+
+    // We only allow a subset of the TypeReferenceKinds here.
+    // Should we just acknowledge that this is a different enum?
   };
 
 public:
-  TypeMetadataRecordKind getTypeKind() const {
+  TypeReferenceKind getTypeKind() const {
     return DirectNominalTypeDescriptor.getInt();
   }
 
   const TargetTypeContextDescriptor<Runtime> *
   getTypeContextDescriptor() const {
     switch (getTypeKind()) {
-    case TypeMetadataRecordKind::DirectNominalTypeDescriptor:
+    case TypeReferenceKind::DirectNominalTypeDescriptor:
       return DirectNominalTypeDescriptor.getPointer();
 
-    case TypeMetadataRecordKind::Reserved:
-    case TypeMetadataRecordKind::IndirectObjCClass:
-      return nullptr;
-
-    case TypeMetadataRecordKind::IndirectNominalTypeDescriptor:
+    case TypeReferenceKind::IndirectNominalTypeDescriptor:
       return *IndirectNominalTypeDescriptor.getPointer();
+
+    // These types (and any others we might add to TypeReferenceKind
+    // in the future) are just never used in these lists.
+    case TypeReferenceKind::DirectObjCClassName:
+    case TypeReferenceKind::IndirectObjCClass:
+      return nullptr;
     }
 
     return nullptr;
@@ -2117,6 +2122,67 @@ using ProtocolRecord = TargetProtocolRecord<InProcess>;
 
 template<typename Runtime> class TargetGenericRequirementDescriptor;
 
+
+/// A referenc to a type.
+template <typename Runtime>
+struct TargetTypeReference {
+  union {
+    /// A direct reference to a nominal type descriptor.
+    RelativeDirectPointer<TargetTypeContextDescriptor<Runtime>>
+      DirectNominalTypeDescriptor;
+
+    /// An indirect reference to a nominal type descriptor.
+    RelativeDirectPointer<
+        ConstTargetMetadataPointer<Runtime, TargetTypeContextDescriptor>>
+      IndirectNominalTypeDescriptor;
+
+    /// An indirect reference to an Objective-C class.
+    RelativeDirectPointer<
+        ConstTargetMetadataPointer<Runtime, TargetClassMetadata>>
+      IndirectObjCClass;
+
+    /// A direct reference to an Objective-C class name.
+    RelativeDirectPointer<const char>
+      DirectObjCClassName;
+  };
+
+  const TargetTypeContextDescriptor<Runtime> *
+  getTypeContextDescriptor(TypeReferenceKind kind) const {
+    switch (kind) {
+    case TypeReferenceKind::DirectNominalTypeDescriptor:
+      return DirectNominalTypeDescriptor;
+
+    case TypeReferenceKind::IndirectNominalTypeDescriptor:
+      return *IndirectNominalTypeDescriptor;
+
+    case TypeReferenceKind::DirectObjCClassName:
+    case TypeReferenceKind::IndirectObjCClass:
+      return nullptr;
+    }
+
+    return nullptr;
+  }
+
+#if SWIFT_OBJC_INTEROP
+  /// If this type reference is one of the kinds that supports ObjC
+  /// references,
+  const TargetClassMetadata<Runtime> *
+  getObjCClass(TypeReferenceKind kind) const;
+#endif
+
+  const TargetClassMetadata<Runtime> * const *
+  getIndirectObjCClass(TypeReferenceKind kind) const {
+    assert(kind == TypeReferenceKind::IndirectObjCClass);
+    return IndirectObjCClass.get();
+  }
+
+  const char *getDirectObjCClassName(TypeReferenceKind kind) const {
+    assert(kind == TypeReferenceKind::DirectObjCClassName);
+    return DirectObjCClassName.get();
+  }
+};
+using TypeReference = TargetTypeReference<InProcess>;
+
 /// The structure of a protocol conformance.
 ///
 /// This contains enough static information to recover the witness table for a
@@ -2153,21 +2219,7 @@ struct TargetProtocolConformanceDescriptor final
   RelativeIndirectablePointer<ProtocolDescriptor> Protocol;
 
   // Some description of the type that conforms to the protocol.
-  union {
-    /// A direct reference to a nominal type descriptor.
-    RelativeDirectPointer<TargetTypeContextDescriptor<Runtime>>
-      DirectNominalTypeDescriptor;
-
-    /// An indirect reference to a nominal type descriptor.
-    RelativeDirectPointer<
-        ConstTargetMetadataPointer<Runtime, TargetTypeContextDescriptor>>
-      IndirectNominalTypeDescriptor;
-
-    /// An indirect reference to the metadata.
-    RelativeDirectPointer<
-        ConstTargetMetadataPointer<Runtime, TargetClassMetadata>>
-      IndirectObjCClass;
-  };
+  TargetTypeReference<Runtime> TypeRef;
 
   // The conformance, or a generator function for the conformance.
   union {
@@ -2187,45 +2239,24 @@ struct TargetProtocolConformanceDescriptor final
     return Protocol;
   }
 
-  TypeMetadataRecordKind getTypeKind() const {
+  TypeReferenceKind getTypeKind() const {
     return Flags.getTypeReferenceKind();
   }
 
   typename ConformanceFlags::ConformanceKind getConformanceKind() const {
     return Flags.getConformanceKind();
   }
-  
-  const TargetClassMetadata<Runtime> * const *getIndirectObjCClass() const {
-    switch (getTypeKind()) {
-    case TypeMetadataRecordKind::IndirectObjCClass:
-      break;
 
-    case TypeMetadataRecordKind::Reserved:
-      return nullptr;
+  const char *getDirectObjCClassName() const {
+    return TypeRef.getDirectObjCClassName(getTypeKind());
+  }
 
-    case TypeMetadataRecordKind::DirectNominalTypeDescriptor:
-    case TypeMetadataRecordKind::IndirectNominalTypeDescriptor:
-      assert(false && "not indirect class object");
-    }
-    
-    return IndirectObjCClass.get();
+  const TargetClassMetadata<Runtime> * const *getIndirectObjCClass() const {
+    return TypeRef.getIndirectObjCClass(getTypeKind());
   }
 
-  const TargetTypeContextDescriptor<Runtime> *
-  getTypeContextDescriptor() const {
-    switch (getTypeKind()) {
-    case TypeMetadataRecordKind::DirectNominalTypeDescriptor:
-      return DirectNominalTypeDescriptor;
-
-    case TypeMetadataRecordKind::IndirectNominalTypeDescriptor:
-      return *IndirectNominalTypeDescriptor;
-
-    case TypeMetadataRecordKind::Reserved:
-    case TypeMetadataRecordKind::IndirectObjCClass:
-      return nullptr;
-    }
-    
-    return nullptr;
+  const TargetTypeContextDescriptor<Runtime> *getTypeContextDescriptor() const {
+    return TypeRef.getTypeContextDescriptor(getTypeKind());
   }
 
   /// Retrieve the context of a retroactive conformance.
@@ -2287,7 +2318,7 @@ struct TargetProtocolConformanceDescriptor final
   ///
   /// We currently check that the descriptor:
   ///
-  /// 1. Has a valid TypeMetadataRecordKind.
+  /// 1. Has a valid TypeReferenceKind.
   /// 2. Has a valid conformance kind.
   void verify() const LLVM_ATTRIBUTE_USED;
 #endif
@@ -3344,7 +3375,7 @@ class TargetClassDescriptor final
     return !Superclass.isNull();
   }
 
-  TypeMetadataRecordKind getSuperclassReferenceKind() const {
+  TypeReferenceKind getSuperclassReferenceKind() const {
     return getTypeContextDescriptorFlags().class_getSuperclassReferenceKind();
   }
 

include/swift/ABI/MetadataValues.h

@@ -350,7 +350,7 @@ enum : unsigned {
 };
 
 /// Kinds of type metadata/protocol conformance records.
-enum class TypeMetadataRecordKind : unsigned {
+enum class TypeReferenceKind : unsigned {
   /// The conformance is for a nominal type referenced directly;
   /// getNominalTypeDescriptor() points to the nominal type descriptor.
   DirectNominalTypeDescriptor = 0x00,
@@ -359,9 +359,10 @@ enum class TypeMetadataRecordKind : unsigned {
   /// getNominalTypeDescriptor() points to the nominal type descriptor.
   IndirectNominalTypeDescriptor = 0x01,
 
-  /// Reserved for future use.
-  Reserved = 0x02,
-  
+  /// The conformance is for an Objective-C class that should be looked up
+  /// by class name.
+  DirectObjCClassName = 0x02,
+
   /// The conformance is for an Objective-C class that has no nominal type
   /// descriptor.
   /// getIndirectObjCClass() points to a variable that contains the pointer to
@@ -371,6 +372,8 @@ enum class TypeMetadataRecordKind : unsigned {
   /// unused.
   IndirectObjCClass = 0x03,
 
+  // We only reserve three bits for this in the various places we store it.
+
   First_Kind = DirectNominalTypeDescriptor,
   Last_Kind = IndirectObjCClass,
 };
@@ -593,7 +596,7 @@ class ConformanceFlags {
     return ConformanceFlags((Value & ~ConformanceKindMask) | int_type(kind));
   }
 
-  ConformanceFlags withTypeReferenceKind(TypeMetadataRecordKind kind) const {
+  ConformanceFlags withTypeReferenceKind(TypeReferenceKind kind) const {
     return ConformanceFlags((Value & ~TypeMetadataKindMask)
                             | (int_type(kind) << TypeMetadataKindShift));
   }
@@ -621,8 +624,8 @@ class ConformanceFlags {
   }
 
   /// Retrieve the type reference kind kind.
-  TypeMetadataRecordKind getTypeReferenceKind() const {
-    return TypeMetadataRecordKind(
+  TypeReferenceKind getTypeReferenceKind() const {
+    return TypeReferenceKind(
                       (Value & TypeMetadataKindMask) >> TypeMetadataKindShift);
   }
 
@@ -1231,16 +1234,16 @@ class TypeContextDescriptorFlags : public FlagSet<uint16_t> {
     /// Only meaningful for class descriptors.
     Class_HasResilientSuperclass = 14,
 
+    /// Whether the immediate class members in this metadata are allocated
+    /// at negative offsets.  For now, we don't use this.
+    Class_AreImmediateMembersNegative = 13,
+
     /// The kind of reference that this class makes to its superclass
-    /// descriptor.  A TypeMetadataRecordKind.
+    /// descriptor.  A TypeReferenceKind.
     ///
     /// Only meaningful for class descriptors.
-    Class_SuperclassReferenceKind = 12,
-    Class_SuperclassReferenceKind_width = 2,
-
-    /// Whether the immediate class members in this metadata are allocated
-    /// at negative offsets.  For now, we don't use this.
-    Class_AreImmediateMembersNegative = 11,
+    Class_SuperclassReferenceKind = 10,
+    Class_SuperclassReferenceKind_width = 3,
   };
 
 public:
@@ -1327,7 +1330,7 @@ class TypeContextDescriptorFlags : public FlagSet<uint16_t> {
 
   FLAGSET_DEFINE_FIELD_ACCESSORS(Class_SuperclassReferenceKind,
                                  Class_SuperclassReferenceKind_width,
-                                 TypeMetadataRecordKind,
+                                 TypeReferenceKind,
                                  class_getSuperclassReferenceKind,
                                  class_setSuperclassReferenceKind)
 };

include/swift/Remote/MetadataReader.h

@@ -603,16 +603,23 @@ class MetadataReader {
           return llvm::None;
 
         return cls->getClassBoundsAsSwiftSuperclass();
+      },
+      [](StoredPointer objcClassName) -> llvm::Optional<ClassMetadataBounds> {
+        // We have no ability to look up an ObjC class by name.
+        // FIXME: add a query for this; clients may have a way to do it.
+        return llvm::None;
       });
   }
 
-  template <class Result, class DescriptorFn, class MetadataFn>
+  template <class Result, class DescriptorFn, class MetadataFn,
+            class ClassNameFn>
   llvm::Optional<Result>
-  forTypeReference(TypeMetadataRecordKind refKind, StoredPointer ref,
+  forTypeReference(TypeReferenceKind refKind, StoredPointer ref,
                    const DescriptorFn &descriptorFn,
-                   const MetadataFn &metadataFn) {
+                   const MetadataFn &metadataFn,
+                   const ClassNameFn &classNameFn) {
     switch (refKind) {
-    case TypeMetadataRecordKind::IndirectNominalTypeDescriptor: {
+    case TypeReferenceKind::IndirectNominalTypeDescriptor: {
       StoredPointer descriptorAddress = 0;
       if (!Reader->readInteger(RemoteAddress(ref), &descriptorAddress))
         return llvm::None;
@@ -621,15 +628,18 @@ class MetadataReader {
       LLVM_FALLTHROUGH;
     }
 
-    case TypeMetadataRecordKind::DirectNominalTypeDescriptor: {
+    case TypeReferenceKind::DirectNominalTypeDescriptor: {
       auto descriptor = readContextDescriptor(ref);
       if (!descriptor)
         return llvm::None;
 
       return descriptorFn(descriptor);
     }
 
-    case TypeMetadataRecordKind::IndirectObjCClass: {
+    case TypeReferenceKind::DirectObjCClassName:
+      return classNameFn(ref);
+
+    case TypeReferenceKind::IndirectObjCClass: {
       StoredPointer classRef = 0;
       if (!Reader->readInteger(RemoteAddress(ref), &classRef))
         return llvm::None;
@@ -640,10 +650,9 @@ class MetadataReader {
 
       return metadataFn(metadata);
     }
-
-    default:
-      return llvm::None;
     }
+
+    return llvm::None;
   }
 
   /// Read a single generic type argument from a bound generic type