Revamp to reflection.

Changes in brief:
1. Descriptor is now the entry point for all reflection.
2. IReflectedMessage has gone; there's now a Descriptor property in IMessage, which is explicitly implemented (due to the static property).
3. FieldAccessorTable has gone away
4. IFieldAccessor and OneofFieldAccessor still exist; we *could* put the functionality straight into FieldDescriptor and OneofDescriptor... I'm unsure about that.
5. There's a temporary property MessageDescriptor.FieldAccessorsByFieldNumber to make the test changes small - we probably want this to go away
6. Discovery for delegates is now via attributes applied to properties and the Clear method of a oneof

I'm happy with 1-3.
4 I'm unsure about - feedback welcome.
5 will go away
6 I'm unsure about, both in design and implementation. Should we have a ProtobufMessageAttribute too? Should we find all the relevant attributes in MessageDescriptor and pass them down, to avoid an O(N^2) scenario?

Generated code changes coming in the next commit.

1 files changed, 31 insertions, 3 deletions

diff --git a/csharp/src/Google.Protobuf/Reflection/MessageDescriptor.cs b/csharp/src/Google.Protobuf/Reflection/MessageDescriptor.cs
index 1c22c460..9413cf61 100644
--- a/csharp/src/Google.Protobuf/Reflection/MessageDescriptor.cs
+++ b/csharp/src/Google.Protobuf/Reflection/MessageDescriptor.cs
@@ -30,8 +30,10 @@
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 #endregion
 
+using Google.Protobuf.Collections;
 using System;
 using System.Collections.Generic;
+using System.Linq;
 
 namespace Google.Protobuf.Reflection
 {
@@ -60,11 +62,15 @@ namespace Google.Protobuf.Reflection
         private readonly IList<EnumDescriptor> enumTypes;
         private readonly IList<FieldDescriptor> fields;
         private readonly IList<OneofDescriptor> oneofs;
+        // CLR representation of the type described by this descriptor, if any.
+        private readonly Type generatedType;
+        private IDictionary<int, IFieldAccessor> fieldAccessorsByFieldNumber;
         
-        internal MessageDescriptor(DescriptorProto proto, FileDescriptor file, MessageDescriptor parent, int typeIndex)
+        internal MessageDescriptor(DescriptorProto proto, FileDescriptor file, MessageDescriptor parent, int typeIndex, IEnumerator<Type> generatedTypeIterator)
             : base(file, file.ComputeFullName(parent, proto.Name), typeIndex)
         {
             this.proto = proto;
+            generatedType = ReflectionUtil.GetNextType(generatedTypeIterator);
             containingType = parent;
 
             oneofs = DescriptorUtil.ConvertAndMakeReadOnly(proto.OneofDecl,
@@ -73,11 +79,11 @@ namespace Google.Protobuf.Reflection
 
             nestedTypes = DescriptorUtil.ConvertAndMakeReadOnly(proto.NestedType,
                                                                 (type, index) =>
-                                                                new MessageDescriptor(type, file, this, index));
+                                                                new MessageDescriptor(type, file, this, index, generatedTypeIterator));
 
             enumTypes = DescriptorUtil.ConvertAndMakeReadOnly(proto.EnumType,
                                                               (type, index) =>
-                                                              new EnumDescriptor(type, file, this, index));
+                                                              new EnumDescriptor(type, file, this, index, ReflectionUtil.GetNextType(generatedTypeIterator)));
 
             // TODO(jonskeet): Sort fields first?
             fields = DescriptorUtil.ConvertAndMakeReadOnly(proto.Field,
@@ -85,6 +91,14 @@ namespace Google.Protobuf.Reflection
                                                            new FieldDescriptor(field, file, this, index));
             file.DescriptorPool.AddSymbol(this);
         }
+                
+        /// <summary>
+        /// Returns the total number of nested types and enums, recursively.
+        /// </summary>
+        private int CountTotalGeneratedTypes()
+        {
+            return nestedTypes.Sum(nested => nested.CountTotalGeneratedTypes()) + enumTypes.Count;
+        }
 
         /// <summary>
         /// The brief name of the descriptor's target.
@@ -94,6 +108,11 @@ namespace Google.Protobuf.Reflection
         internal DescriptorProto Proto { get { return proto; } }
 
         /// <summary>
+        /// The generated type for this message, or <c>null</c> if the descriptor does not represent a generated type.
+        /// </summary>
+        public Type GeneratedType { get { return generatedType; } }
+
+        /// <summary>
         /// Returns whether this message is one of the "well known types" which may have runtime/protoc support.
         /// </summary>
         internal bool IsWellKnownType
@@ -142,6 +161,13 @@ namespace Google.Protobuf.Reflection
         }
 
         /// <summary>
+        /// Returns a map from field number to accessor.
+        /// TODO: Revisit this. It's mostly in place to make the transition from FieldAccessorTable
+        /// to descriptor-based reflection simple in terms of tests. Work out what we really want.
+        /// </summary>
+        public IDictionary<int, IFieldAccessor> FieldAccessorsByFieldNumber { get { return fieldAccessorsByFieldNumber; } }
+
+        /// <summary>
         /// Finds a field by field name.
         /// </summary>
         /// <param name="name">The unqualified name of the field (e.g. "foo").</param>
@@ -192,6 +218,8 @@ namespace Google.Protobuf.Reflection
             {
                 oneof.CrossLink();
             }
+
+            fieldAccessorsByFieldNumber = new ReadOnlyDictionary<int, IFieldAccessor>(fields.ToDictionary(field => field.FieldNumber, field => field.Accessor));
         }        
     }
 }
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