Implementation work for Lite runtime and generator

src/ProtoGen/Helpers.cs

@@ -38,11 +38,5 @@ namespace Google.ProtocolBuffers.ProtoGen {
   /// Helpers to resolve class names etc.
   /// </summary>
   internal static class Helpers {
-    internal static void WriteNamespaces(TextGenerator writer) {
-      writer.WriteLine("using pb = global::Google.ProtocolBuffers;");
-      writer.WriteLine("using pbc = global::Google.ProtocolBuffers.Collections;");
-      writer.WriteLine("using pbd = global::Google.ProtocolBuffers.Descriptors;");
-      writer.WriteLine("using scg = global::System.Collections.Generic;");
-    }
   }
 }

src/ProtoGen/MessageGenerator.cs

@@ -69,12 +69,13 @@ namespace Google.ProtocolBuffers.ProtoGen {
 
       string identifier = GetUniqueFileScopeIdentifier(Descriptor);
 
-      // The descriptor for this type.
-      string access = Descriptor.File.CSharpOptions.NestClasses ? "private" : "internal";
-      writer.WriteLine("{0} static pbd::MessageDescriptor internal__{1}__Descriptor;", access, identifier);
-      writer.WriteLine("{0} static pb::FieldAccess.FieldAccessorTable<{1}, {1}.Builder> internal__{2}__FieldAccessorTable;",
-          access, FullClassName, identifier);
-
+      if (!UseLiteRuntime) {
+        // The descriptor for this type.
+        string access = Descriptor.File.CSharpOptions.NestClasses ? "private" : "internal";
+        writer.WriteLine("{0} static pbd::MessageDescriptor internal__{1}__Descriptor;", access, identifier);
+        writer.WriteLine("{0} static pb::FieldAccess.FieldAccessorTable<{1}, {1}.Builder> internal__{2}__FieldAccessorTable;",
+                         access, FullClassName, identifier);
+      }
       // Generate static members for all nested types.
       foreach (MessageDescriptor nestedMessage in Descriptor.NestedTypes) {
         new MessageGenerator(nestedMessage).GenerateStaticVariables(writer);
@@ -84,21 +85,23 @@ namespace Google.ProtocolBuffers.ProtoGen {
     internal void GenerateStaticVariableInitializers(TextGenerator writer) {
       string identifier = GetUniqueFileScopeIdentifier(Descriptor);
 
-      writer.Write("internal__{0}__Descriptor = ", identifier);
-      if (Descriptor.ContainingType == null) {
-        writer.WriteLine("Descriptor.MessageTypes[{0}];", Descriptor.Index);
-      } else {
-        writer.WriteLine("internal__{0}__Descriptor.NestedTypes[{1}];", GetUniqueFileScopeIdentifier(Descriptor.ContainingType), Descriptor.Index);
-      }
+      if (!UseLiteRuntime) {
+        writer.Write("internal__{0}__Descriptor = ", identifier);
+        if (Descriptor.ContainingType == null) {
+          writer.WriteLine("Descriptor.MessageTypes[{0}];", Descriptor.Index);
+        } else {
+          writer.WriteLine("internal__{0}__Descriptor.NestedTypes[{1}];", GetUniqueFileScopeIdentifier(Descriptor.ContainingType), Descriptor.Index);
+        }
 
-      writer.WriteLine("internal__{0}__FieldAccessorTable = ", identifier);
-      writer.WriteLine("    new pb::FieldAccess.FieldAccessorTable<{1}, {1}.Builder>(internal__{0}__Descriptor,",
-          identifier, FullClassName);
-      writer.Print("        new string[] { ");
-      foreach (FieldDescriptor field in Descriptor.Fields) {
-        writer.Write("\"{0}\", ", field.CSharpOptions.PropertyName);
+        writer.WriteLine("internal__{0}__FieldAccessorTable = ", identifier);
+        writer.WriteLine("    new pb::FieldAccess.FieldAccessorTable<{1}, {1}.Builder>(internal__{0}__Descriptor,",
+                         identifier, FullClassName);
+        writer.Print("        new string[] { ");
+        foreach (FieldDescriptor field in Descriptor.Fields) {
+          writer.Write("\"{0}\", ", field.CSharpOptions.PropertyName);
+        }
+        writer.WriteLine("});");
       }
-      writer.WriteLine("});");
 
       // Generate static member initializers for all nested types.
       foreach (MessageDescriptor nestedMessage in Descriptor.NestedTypes) {
@@ -111,8 +114,10 @@ namespace Google.ProtocolBuffers.ProtoGen {
     }
 
     public void Generate(TextGenerator writer) {
-      writer.WriteLine("{0} sealed partial class {1} : pb::{2}Message<{1}, {1}.Builder> {{",
-          ClassAccessLevel, ClassName, Descriptor.Proto.ExtensionRangeCount > 0 ? "Extendable" : "Generated");
+      writer.WriteLine("{0} sealed partial class {1} : pb::{2}Message{3}<{1}, {1}.Builder> {{",
+          ClassAccessLevel, ClassName, 
+          Descriptor.Proto.ExtensionRangeCount > 0 ? "Extendable" : "Generated",
+          UseLiteRuntime ? "Lite" : "");
       writer.Indent();
       // Must call BuildPartial() to make sure all lists are made read-only
       writer.WriteLine("private static readonly {0} defaultInstance = new Builder().BuildPartial();", ClassName);
@@ -128,16 +133,18 @@ namespace Google.ProtocolBuffers.ProtoGen {
       writer.WriteLine("  get { return this; }");
       writer.WriteLine("}");
       writer.WriteLine();
-      writer.WriteLine("public static pbd::MessageDescriptor Descriptor {");
-      writer.WriteLine("  get {{ return {0}.internal__{1}__Descriptor; }}", DescriptorUtil.GetFullUmbrellaClassName(Descriptor),
-          GetUniqueFileScopeIdentifier(Descriptor));
-      writer.WriteLine("}");
-      writer.WriteLine();
-      writer.WriteLine("protected override pb::FieldAccess.FieldAccessorTable<{0}, {0}.Builder> InternalFieldAccessors {{", ClassName);
-      writer.WriteLine("  get {{ return {0}.internal__{1}__FieldAccessorTable; }}", DescriptorUtil.GetFullUmbrellaClassName(Descriptor),
-          GetUniqueFileScopeIdentifier(Descriptor));
-      writer.WriteLine("}");
-      writer.WriteLine();
+      if (!UseLiteRuntime) {
+        writer.WriteLine("public static pbd::MessageDescriptor Descriptor {");
+        writer.WriteLine("  get {{ return {0}.internal__{1}__Descriptor; }}", DescriptorUtil.GetFullUmbrellaClassName(Descriptor),
+                         GetUniqueFileScopeIdentifier(Descriptor));
+        writer.WriteLine("}");
+        writer.WriteLine();
+        writer.WriteLine("protected override pb::FieldAccess.FieldAccessorTable<{0}, {0}.Builder> InternalFieldAccessors {{", ClassName);
+        writer.WriteLine("  get {{ return {0}.internal__{1}__FieldAccessorTable; }}", DescriptorUtil.GetFullUmbrellaClassName(Descriptor),
+                         GetUniqueFileScopeIdentifier(Descriptor));
+        writer.WriteLine("}");
+        writer.WriteLine();
+      }
 
       // Extensions don't need to go in an extra nested type 
       WriteChildren(writer, null, Descriptor.Extensions);

src/ProtoGen/SourceGeneratorBase.cs

@@ -40,8 +40,16 @@ namespace Google.ProtocolBuffers.ProtoGen {
 
     private readonly T descriptor;
 
+    protected readonly bool OptimizeSpeed;
+    protected readonly bool OptimizeSize;
+    protected readonly bool UseLiteRuntime;
+
     protected SourceGeneratorBase(T descriptor) {
       this.descriptor = descriptor;
+
+      OptimizeSize = descriptor.File.Options.OptimizeFor == Google.ProtocolBuffers.DescriptorProtos.FileOptions.Types.OptimizeMode.CODE_SIZE;
+      OptimizeSpeed = descriptor.File.Options.OptimizeFor == Google.ProtocolBuffers.DescriptorProtos.FileOptions.Types.OptimizeMode.SPEED;
+      UseLiteRuntime = descriptor.File.Options.OptimizeFor == Google.ProtocolBuffers.DescriptorProtos.FileOptions.Types.OptimizeMode.LITE_RUNTIME;
     }
 
     protected T Descriptor {

src/ProtoGen/UmbrellaClassGenerator.cs

@@ -83,7 +83,11 @@ namespace Google.ProtocolBuffers.ProtoGen {
         new MessageGenerator(message).GenerateStaticVariables(writer);
       }
       writer.WriteLine("#endregion");
-      WriteDescriptor(writer);
+      if (!UseLiteRuntime) {
+        WriteDescriptor(writer);
+      } else {
+        WriteLiteExtensions(writer);
+      }
       // The class declaration either gets closed before or after the children are written.
       if (!Descriptor.CSharpOptions.NestClasses) {
         writer.Outdent();
@@ -111,7 +115,12 @@ namespace Google.ProtocolBuffers.ProtoGen {
     private void WriteIntroduction(TextGenerator writer) {
       writer.WriteLine("// Generated by the protocol buffer compiler.  DO NOT EDIT!");
       writer.WriteLine();
-      Helpers.WriteNamespaces(writer);
+      writer.WriteLine("using pb = global::Google.ProtocolBuffers;");
+      if (!UseLiteRuntime) {
+        writer.WriteLine("using pbc = global::Google.ProtocolBuffers.Collections;");
+        writer.WriteLine("using pbd = global::Google.ProtocolBuffers.Descriptors;");
+      }
+      writer.WriteLine("using scg = global::System.Collections.Generic;");
 
       if (Descriptor.CSharpOptions.Namespace != "") {
         writer.WriteLine("namespace {0} {{", Descriptor.CSharpOptions.Namespace);
@@ -211,5 +220,23 @@ namespace Google.ProtocolBuffers.ProtoGen {
       writer.WriteLine("#endregion");
       writer.WriteLine();
     }
+
+    private void WriteLiteExtensions(TextGenerator writer) {
+      writer.WriteLine("#region Extensions");
+
+      writer.WriteLine("static {0}() {{", Descriptor.CSharpOptions.UmbrellaClassname);
+      writer.Indent();
+
+      foreach (MessageDescriptor message in Descriptor.MessageTypes) {
+        new MessageGenerator(message).GenerateStaticVariableInitializers(writer);
+      }
+      foreach (FieldDescriptor extension in Descriptor.Extensions) {
+        new ExtensionGenerator(extension).GenerateStaticVariableInitializers(writer);
+      }
+      writer.Outdent();
+      writer.WriteLine("}");
+      writer.WriteLine("#endregion");
+      writer.WriteLine();
+    }
   }
 }

src/ProtocolBuffers/CodedInputStream.cs

@@ -36,9 +36,7 @@ using System;
 using System.Collections.Generic;
 using System.IO;
 using System.Text;
-#if !LITE
 using Google.ProtocolBuffers.Descriptors;
-#endif
 
 namespace Google.ProtocolBuffers {
 
@@ -363,7 +361,7 @@ namespace Google.ProtocolBuffers {
     public long ReadSInt64() {
       return DecodeZigZag64(ReadRawVarint64());
     }
-#if !LITE
+
     /// <summary>
     /// Reads a field of any primitive type. Enums, groups and embedded
     /// messages are not handled by this method.
@@ -397,7 +395,6 @@ namespace Google.ProtocolBuffers {
           throw new ArgumentOutOfRangeException("Invalid field type " + fieldType);
       }
     }
-#endif
     #endregion
 
     #region Underlying reading primitives

src/ProtocolBuffers/CodedOutputStream.cs

@@ -35,9 +35,8 @@
 using System;
 using System.IO;
 using System.Text;
-#if !LITE
 using Google.ProtocolBuffers.Descriptors;
-#endif
+
 namespace Google.ProtocolBuffers {
 
   /// <summary>
@@ -279,7 +278,6 @@ namespace Google.ProtocolBuffers {
       WriteTag(WireFormat.MessageSetField.Item, WireFormat.WireType.EndGroup);
     }
 
-#if !LITE
     public void WriteField(FieldType fieldType, int fieldNumber, object value) {
       switch (fieldType) {
         case FieldType.Double: WriteDouble(fieldNumber, (double)value); break;
@@ -291,15 +289,15 @@ namespace Google.ProtocolBuffers {
         case FieldType.Fixed32: WriteFixed32(fieldNumber, (uint)value); break;
         case FieldType.Bool: WriteBool(fieldNumber, (bool)value); break;
         case FieldType.String: WriteString(fieldNumber, (string)value); break;
-        case FieldType.Group: WriteGroup(fieldNumber, (IMessage)value); break;
-        case FieldType.Message: WriteMessage(fieldNumber, (IMessage)value); break;
+        case FieldType.Group: WriteGroup(fieldNumber, (IMessageLite)value); break;
+        case FieldType.Message: WriteMessage(fieldNumber, (IMessageLite)value); break;
         case FieldType.Bytes: WriteBytes(fieldNumber, (ByteString)value); break;
         case FieldType.UInt32: WriteUInt32(fieldNumber, (uint)value); break;
         case FieldType.SFixed32: WriteSFixed32(fieldNumber, (int)value); break;
         case FieldType.SFixed64: WriteSFixed64(fieldNumber, (long)value); break;
         case FieldType.SInt32: WriteSInt32(fieldNumber, (int)value); break;
         case FieldType.SInt64: WriteSInt64(fieldNumber, (long)value); break;
-        case FieldType.Enum: WriteEnum(fieldNumber, ((EnumValueDescriptor)value).Number);
+        case FieldType.Enum: WriteEnum(fieldNumber, ((IEnumLite)value).Number);
           break;
       }
     }
@@ -315,19 +313,18 @@ namespace Google.ProtocolBuffers {
         case FieldType.Fixed32: WriteFixed32NoTag((uint)value); break;
         case FieldType.Bool: WriteBoolNoTag((bool)value); break;
         case FieldType.String: WriteStringNoTag((string)value); break;
-        case FieldType.Group: WriteGroupNoTag((IMessage)value); break;
-        case FieldType.Message: WriteMessageNoTag((IMessage)value); break;
+        case FieldType.Group: WriteGroupNoTag((IMessageLite)value); break;
+        case FieldType.Message: WriteMessageNoTag((IMessageLite)value); break;
         case FieldType.Bytes: WriteBytesNoTag((ByteString)value); break;
         case FieldType.UInt32: WriteUInt32NoTag((uint)value); break;
         case FieldType.SFixed32: WriteSFixed32NoTag((int)value); break;
         case FieldType.SFixed64: WriteSFixed64NoTag((long)value); break;
         case FieldType.SInt32: WriteSInt32NoTag((int)value); break;
         case FieldType.SInt64: WriteSInt64NoTag((long)value); break;
-        case FieldType.Enum: WriteEnumNoTag(((EnumValueDescriptor)value).Number);
+        case FieldType.Enum: WriteEnumNoTag(((IEnumLite)value).Number);
           break;
       }
     }
-#endif
     #endregion
 
     #region Writing of values without tags
@@ -995,7 +992,6 @@ namespace Google.ProtocolBuffers {
       return 10;
     }
 
-#if !LITE
     /// <summary>
     /// Compute the number of bytes that would be needed to encode a
     /// field of arbitrary type, including the tag, to the stream.
@@ -1011,15 +1007,15 @@ namespace Google.ProtocolBuffers {
         case FieldType.Fixed32: return ComputeFixed32Size(fieldNumber, (uint)value);
         case FieldType.Bool: return ComputeBoolSize(fieldNumber, (bool)value);
         case FieldType.String: return ComputeStringSize(fieldNumber, (string)value);
-        case FieldType.Group: return ComputeGroupSize(fieldNumber, (IMessage)value);
-        case FieldType.Message: return ComputeMessageSize(fieldNumber, (IMessage)value);
+        case FieldType.Group: return ComputeGroupSize(fieldNumber, (IMessageLite)value);
+        case FieldType.Message: return ComputeMessageSize(fieldNumber, (IMessageLite)value);
         case FieldType.Bytes: return ComputeBytesSize(fieldNumber, (ByteString)value);
         case FieldType.UInt32: return ComputeUInt32Size(fieldNumber, (uint)value);
         case FieldType.SFixed32: return ComputeSFixed32Size(fieldNumber, (int)value);
         case FieldType.SFixed64: return ComputeSFixed64Size(fieldNumber, (long)value);
         case FieldType.SInt32: return ComputeSInt32Size(fieldNumber, (int)value);
         case FieldType.SInt64: return ComputeSInt64Size(fieldNumber, (long)value);
-        case FieldType.Enum: return ComputeEnumSize(fieldNumber, ((EnumValueDescriptor)value).Number);
+        case FieldType.Enum: return ComputeEnumSize(fieldNumber, ((IEnumLite)value).Number);
         default:
           throw new ArgumentOutOfRangeException("Invalid field type " + fieldType);
       }
@@ -1040,20 +1036,19 @@ namespace Google.ProtocolBuffers {
         case FieldType.Fixed32: return ComputeFixed32SizeNoTag((uint)value);
         case FieldType.Bool: return ComputeBoolSizeNoTag((bool)value);
         case FieldType.String: return ComputeStringSizeNoTag((string)value);
-        case FieldType.Group: return ComputeGroupSizeNoTag((IMessage)value);
-        case FieldType.Message: return ComputeMessageSizeNoTag((IMessage)value);
+        case FieldType.Group: return ComputeGroupSizeNoTag((IMessageLite)value);
+        case FieldType.Message: return ComputeMessageSizeNoTag((IMessageLite)value);
         case FieldType.Bytes: return ComputeBytesSizeNoTag((ByteString)value);
         case FieldType.UInt32: return ComputeUInt32SizeNoTag((uint)value);
         case FieldType.SFixed32: return ComputeSFixed32SizeNoTag((int)value);
         case FieldType.SFixed64: return ComputeSFixed64SizeNoTag((long)value);
         case FieldType.SInt32: return ComputeSInt32SizeNoTag((int)value);
         case FieldType.SInt64: return ComputeSInt64SizeNoTag((long)value);
-        case FieldType.Enum: return ComputeEnumSizeNoTag(((EnumValueDescriptor)value).Number);
+        case FieldType.Enum: return ComputeEnumSizeNoTag(((IEnumLite)value).Number);
         default:
           throw new ArgumentOutOfRangeException("Invalid field type " + fieldType);
       }
     }
-#endif
 
     /// <summary>
     /// Compute the number of bytes that would be needed to encode a tag.

src/ProtocolBuffers/Descriptors/EnumDescriptor.cs

@@ -37,7 +37,7 @@ namespace Google.ProtocolBuffers.Descriptors {
   /// <summary>
   /// Descriptor for an enum type in a .proto file.
   /// </summary>
-  public sealed class EnumDescriptor : IndexedDescriptorBase<EnumDescriptorProto, EnumOptions> {
+  public sealed class EnumDescriptor : IndexedDescriptorBase<EnumDescriptorProto, EnumOptions>, IEnumLiteMap<EnumValueDescriptor> {
 
     private readonly MessageDescriptor containingType;
     private readonly IList<EnumValueDescriptor> values;
@@ -72,11 +72,18 @@ namespace Google.ProtocolBuffers.Descriptors {
       get { return values; }
     }
 
+    /// <summary>
+    /// Logic moved from FieldSet to continue current behavior
+    /// </summary>
+    public bool IsValidValue(IEnumLite value) {
+      return value is EnumValueDescriptor && ((EnumValueDescriptor)value).EnumDescriptor == this;
+    }
+
     /// <summary>
     /// Finds an enum value by number. If multiple enum values have the
     /// same number, this returns the first defined value with that number.
     /// </summary>
-    internal EnumValueDescriptor FindValueByNumber(int number) {
+    public EnumValueDescriptor FindValueByNumber(int number) {
       return File.DescriptorPool.FindEnumValueByNumber(this, number);
     }
 

src/ProtocolBuffers/Descriptors/EnumValueDescriptor.cs

@@ -36,7 +36,7 @@ namespace Google.ProtocolBuffers.Descriptors {
   /// <summary>
   /// Descriptor for a single enum value within an enum in a .proto file.
   /// </summary>
-  public sealed class EnumValueDescriptor : IndexedDescriptorBase<EnumValueDescriptorProto, EnumValueOptions> {
+  public sealed class EnumValueDescriptor : IndexedDescriptorBase<EnumValueDescriptorProto, EnumValueOptions>, IEnumLite {
 
     private readonly EnumDescriptor enumDescriptor;
 

src/ProtocolBuffers/Descriptors/FieldDescriptor.cs

@@ -40,7 +40,7 @@ namespace Google.ProtocolBuffers.Descriptors {
   /// <summary>
   /// Descriptor for a field or extension within a message in a .proto file.
   /// </summary>
-  public sealed class FieldDescriptor : IndexedDescriptorBase<FieldDescriptorProto, FieldOptions>, IComparable<FieldDescriptor> {
+  public sealed class FieldDescriptor : IndexedDescriptorBase<FieldDescriptorProto, FieldOptions>, IComparable<FieldDescriptor>, IFieldDescriptorLite {
 
     private readonly MessageDescriptor extensionScope;
     private EnumDescriptor enumType;
@@ -299,9 +299,26 @@ namespace Google.ProtocolBuffers.Descriptors {
       }
       return FieldNumber - other.FieldNumber;
     }
-    
 
     /// <summary>
+    /// Compares this descriptor with another one, ordering in "canonical" order
+    /// which simply means ascending order by field number. <paramref name="other"/>
+    /// must be a field of the same type, i.e. the <see cref="ContainingType"/> of
+    /// both fields must be the same.
+    /// </summary>
+    public int CompareTo(IFieldDescriptorLite other) {
+      return FieldNumber - other.FieldNumber;
+    }
+
+    IEnumLiteMap IFieldDescriptorLite.EnumType {
+      get { return EnumType; }
+    }
+
+    bool IFieldDescriptorLite.MessageSetWireFormat {
+      get { return ContainingType.Options.MessageSetWireFormat; }
+    }
+
+      /// <summary>
     /// For enum fields, returns the field's type.
     /// </summary>
     public EnumDescriptor EnumType {

src/ProtocolBuffers/DynamicMessage.cs

@@ -180,7 +180,7 @@ namespace Google.ProtocolBuffers {
     }
 
     public override IDictionary<FieldDescriptor, object> AllFields {
-      get { return fields.AllFields; }
+      get { return fields.AllFieldDescriptors; }
     }
 
     public override bool HasField(FieldDescriptor field) {
@@ -216,7 +216,7 @@ namespace Google.ProtocolBuffers {
     }
 
     public bool Initialized {
-      get { return fields.IsInitializedWithRespectTo(type); }
+      get { return fields.IsInitializedWithRespectTo(type.Fields); }
     }
 
     public override void WriteTo(CodedOutputStream output) {
@@ -335,7 +335,7 @@ namespace Google.ProtocolBuffers {
       }
 
       public override bool IsInitialized {
-          get { return fields.IsInitializedWithRespectTo(type); }
+          get { return fields.IsInitializedWithRespectTo(type.Fields); }
       }
 
       public override Builder MergeFrom(CodedInputStream input, ExtensionRegistry extensionRegistry) {
@@ -354,7 +354,7 @@ namespace Google.ProtocolBuffers {
       }
 
       public override IDictionary<FieldDescriptor, object> AllFields {
-        get { return fields.AllFields; }
+        get { return fields.AllFieldDescriptors; }
       }
 
       public override IBuilder CreateBuilderForField(FieldDescriptor field) {

src/ProtocolBuffers/EnumLite.cs

+using System;
+using System.Collections.Generic;
+using System.Text;
+
+namespace Google.ProtocolBuffers {
+
+  ///<summary>
+  ///Interface for an enum value or value descriptor, to be used in FieldSet.
+  ///The lite library stores enum values directly in FieldSets but the full
+  ///library stores EnumValueDescriptors in order to better support reflection.
+  ///</summary>
+  public interface IEnumLite {
+    int Number { get; }
+  }
+
+  ///<summary>
+  ///Interface for an object which maps integers to {@link EnumLite}s.
+  ///{@link Descriptors.EnumDescriptor} implements this interface by mapping
+  ///numbers to {@link Descriptors.EnumValueDescriptor}s.  Additionally,
+  ///every generated enum type has a static method internalGetValueMap() which
+  ///returns an implementation of this type that maps numbers to enum values.
+  ///</summary>
+  public interface IEnumLiteMap<T> : IEnumLiteMap
+    where T : IEnumLite {
+    T FindValueByNumber(int number);
+  }
+
+  public interface IEnumLiteMap {
+    bool IsValidValue(IEnumLite value);
+  }
+}

src/ProtocolBuffers/ExtendableMessage.cs

@@ -102,8 +102,8 @@ namespace Google.ProtocolBuffers {
     public override IDictionary<FieldDescriptor, object> AllFields {
       get {
         IDictionary<FieldDescriptor, object> result = GetMutableFieldMap();
-        foreach(KeyValuePair<FieldDescriptor, object> entry in extensions.AllFields) {
-          result[entry.Key] = entry.Value;
+        foreach(KeyValuePair<IFieldDescriptorLite, object> entry in extensions.AllFields) {
+          result[(FieldDescriptor)entry.Key] = entry.Value;
         }
         return Dictionaries.AsReadOnly(result);
       }
@@ -173,9 +173,9 @@ namespace Google.ProtocolBuffers {
     /// TODO(jonskeet): See if we can improve this in terms of readability.
     /// </summary>
     protected class ExtensionWriter {
-      readonly IEnumerator<KeyValuePair<FieldDescriptor, object>> iterator;
+      readonly IEnumerator<KeyValuePair<IFieldDescriptorLite, object>> iterator;
       readonly FieldSet extensions;
-      KeyValuePair<FieldDescriptor, object>? next = null;
+      KeyValuePair<IFieldDescriptorLite, object>? next = null;
 
       internal ExtensionWriter(ExtendableMessage<TMessage, TBuilder> message) {
         extensions = message.extensions;

src/ProtocolBuffers/GeneratedExtensionLite.cs

 using System;
+using Google.ProtocolBuffers.Descriptors;
 
 namespace Google.ProtocolBuffers {
 
@@ -7,4 +8,111 @@ namespace Google.ProtocolBuffers {
     object ContainingType { get; }
     IMessageLite MessageDefaultInstance { get; }
   }
+
+  public class ExtensionDescriptorLite {
+    private readonly EnumLiteMap enumTypeMap;
+    private readonly int number;
+    private readonly FieldType type;
+    private readonly bool isRepeated;
+    private readonly bool isPacked;
+
+    public ExtensionDescriptorLite(EnumLiteMap enumTypeMap, int number, FieldType type, bool isRepeated, bool isPacked) {
+      this.enumTypeMap = enumTypeMap;
+      this.number = number;
+      this.type = type;
+      this.isRepeated = isRepeated;
+      this.isPacked = isPacked;
+    }
+
+    public int Number {
+      get { return number; }
+    }
+  }
+  
+  public class EnumLiteMap { }
+
+  public class GeneratedExtensionLite<TContainingType, TExtensionType> : IGeneratedExtensionLite
+    where TContainingType : IMessageLite {
+
+    private readonly TContainingType containingTypeDefaultInstance;
+    private readonly TExtensionType defaultValue;
+    private readonly IMessageLite messageDefaultInstance;
+    private readonly ExtensionDescriptorLite descriptor;
+
+    // We can't always initialize a GeneratedExtension when we first construct
+    // it due to initialization order difficulties (namely, the default
+    // instances may not have been constructed yet).  So, we construct an
+    // uninitialized GeneratedExtension once, then call internalInit() on it
+    // later.  Generated code will always call internalInit() on all extensions
+    // as part of the static initialization code, and internalInit() throws an
+    // exception if called more than once, so this method is useless to users.
+    protected GeneratedExtensionLite(
+        TContainingType containingTypeDefaultInstance,
+        TExtensionType defaultValue,
+        IMessageLite messageDefaultInstance,
+        ExtensionDescriptorLite descriptor) {
+      this.containingTypeDefaultInstance = containingTypeDefaultInstance;
+      this.messageDefaultInstance = messageDefaultInstance;
+      this.defaultValue = defaultValue;
+      this.descriptor = descriptor;
+    }
+
+    /** For use by generated code only. */
+    public GeneratedExtensionLite(
+        TContainingType containingTypeDefaultInstance,
+        TExtensionType defaultValue,
+        IMessageLite messageDefaultInstance,
+      EnumLiteMap enumTypeMap,
+        int number,
+        FieldType type)
+      : this(containingTypeDefaultInstance, defaultValue, messageDefaultInstance,
+          new ExtensionDescriptorLite(enumTypeMap, number, type,
+            false /* isRepeated */, false /* isPacked */)) {
+    }
+
+    /** For use by generated code only. */
+    public GeneratedExtensionLite(
+      TContainingType containingTypeDefaultInstance,
+      TExtensionType defaultValue,
+      IMessageLite messageDefaultInstance,
+      EnumLiteMap enumTypeMap,
+      int number,
+      FieldType type,
+      bool isPacked)
+      : this(containingTypeDefaultInstance, defaultValue, messageDefaultInstance,
+          new ExtensionDescriptorLite(enumTypeMap, number, type,
+            true /* isRepeated */, isPacked)) {
+    }
+
+    /// <summary>
+    /// used for the extension registry
+    /// </summary>
+    object IGeneratedExtensionLite.ContainingType {
+      get { return ContainingTypeDefaultInstance; }
+    }
+      /**
+     * Default instance of the type being extended, used to identify that type.
+     */
+    public TContainingType ContainingTypeDefaultInstance {
+      get {
+        return containingTypeDefaultInstance;
+      }
+    }
+
+    /** Get the field number. */
+    public int Number {
+      get {
+        return descriptor.Number;
+      }
+    }
+    /**
+     * If the extension is an embedded message, this is the default instance of
+     * that type.
+     */
+    public IMessageLite MessageDefaultInstance {
+      get {
+        return messageDefaultInstance;
+      }
+    }
+  }
 }
\ No newline at end of file

src/ProtocolBuffers/ProtocolBuffers.csproj

@@ -90,6 +90,7 @@
     <Compile Include="Descriptors\PackageDescriptor.cs" />
     <Compile Include="Descriptors\ServiceDescriptor.cs" />
     <Compile Include="DynamicMessage.cs" />
+    <Compile Include="EnumLite.cs" />
     <Compile Include="ExtendableBuilder.cs" />
     <Compile Include="ExtendableMessage.cs" />
     <Compile Include="ExtensionInfo.cs">

src/ProtocolBuffers/ProtocolBuffersLite.csproj

@@ -46,6 +46,8 @@
   <ItemGroup>
     <Reference Include="mscorlib" />
     <Reference Include="System" />
+    <Reference Include="System.Data" />
+    <Reference Include="System.Xml" />
   </ItemGroup>
   <ItemGroup>
   </ItemGroup>
@@ -55,7 +57,17 @@
   <ItemGroup>
     <Compile Include="AbstractBuilderLite.cs" />
     <Compile Include="AbstractMessageLite.cs" />
+    <Compile Include="Collections\Dictionaries.cs" />
+    <Compile Include="Collections\Lists.cs" />
+    <Compile Include="Descriptors\FieldMappingAttribute.cs" />
+    <Compile Include="Descriptors\FieldType.cs" />
+    <Compile Include="Descriptors\MappedType.cs" />
+    <Compile Include="EnumLite.cs" />
+    <Compile Include="ExtendableMessageLite.cs" />
+    <Compile Include="FieldSet.cs" />
+    <Compile Include="GeneratedBuilderLite.cs" />
     <Compile Include="GeneratedExtensionLite.cs" />
+    <Compile Include="GeneratedMessageLite.cs" />
     <Compile Include="Properties\AssemblyInfo.cs" />
     <Compile Include="ByteString.cs" />
     <Compile Include="CodedInputStream.cs" />
@@ -66,6 +78,7 @@
       <SubType>Code</SubType>
     </Compile>
     <Compile Include="InvalidProtocolBufferException.cs" />
+    <Compile Include="ThrowHelper.cs" />
     <Compile Include="UninitializedMessageException.cs" />
     <Compile Include="WireFormat.cs" />
   </ItemGroup>

src/ProtocolBuffersLite.Test/ProtocolBuffersLite.Test.csproj

@@ -54,9 +54,13 @@
     <Reference Include="System.Xml" />
   </ItemGroup>
   <ItemGroup>
+    <Compile Include="..\..\tmp\UnitTestLiteProtoFile.cs">
+      <Link>UnitTestLiteProtoFile.cs</Link>
+    </Compile>
     <Compile Include="..\ProtocolBuffers.Test\Properties\AssemblyInfo.cs">
       <Link>Properties\AssemblyInfo.cs</Link>
     </Compile>
+    <Compile Include="Todo.cs" />
     <None Include="TestProtos\UnittestLite.cs" />
     <None Include="TestProtos\UnittestLiteImportsNonlite.cs" />
   </ItemGroup>