Use byte as index for known type names

Uses a byte instead of an int to index known type names. We'll need to revisit this if the number of known types grows beyond 256.

To make serialization a bit easier, I've added methods for reading/writing bytes to `JsonDataReader` and `JsonDataWriter`.

Author: DustinCampbell

src/Compiler/Microsoft.CodeAnalysis.Razor.Compiler/src/Language/TypeNameObject.cs

@@ -13,15 +13,15 @@ namespace Microsoft.AspNetCore.Razor.Language;
 internal readonly struct TypeNameObject
 {
     private static readonly ImmutableArray<string> s_knownTypeNames;
-    private static readonly FrozenDictionary<string, int> s_typeNameToIndex;
+    private static readonly FrozenDictionary<string, byte> s_typeNameToIndex;
 
     private static readonly int s_booleanIndex;
     private static readonly int s_stringIndex;
 
     static TypeNameObject()
     {
         var knownTypeNames = ImmutableArray.CreateBuilder<string>();
-        var typeNameToIndex = new Dictionary<string, int>(StringComparer.Ordinal);
+        var typeNameToIndex = new Dictionary<string, byte>(StringComparer.Ordinal);
 
         Add<object>("object");
         s_booleanIndex = Add<bool>("bool");
@@ -50,7 +50,8 @@ static TypeNameObject()
         int Add<T>(string? alias = null)
         {
             var fullName = typeof(T).FullName!;
-            var index = knownTypeNames.Count;
+            Debug.Assert(knownTypeNames.Count < byte.MaxValue, "Too many known type names to fit in a byte index.");
+            var index = (byte)knownTypeNames.Count;
             knownTypeNames.Add(fullName);
             typeNameToIndex.Add(fullName, index);
 
@@ -63,10 +64,10 @@ int Add<T>(string? alias = null)
         }
     }
 
-    private readonly int? _index;
+    private readonly byte? _index;
     private readonly string? _stringValue;
 
-    public TypeNameObject(int index)
+    public TypeNameObject(byte index)
     {
         Debug.Assert(index >= 0 && index < s_knownTypeNames.Length);
 
@@ -84,7 +85,7 @@ public TypeNameObject(string? stringValue)
 
     public bool IsNull => _index is null && _stringValue is null;
 
-    public int? Index => _index;
+    public byte? Index => _index;
     public string? StringValue => _stringValue;
 
     public static TypeNameObject From(string? typeName)
@@ -104,7 +105,7 @@ public static TypeNameObject From(string? typeName)
 
     public readonly string? GetTypeName()
     {
-        if (_index is int index)
+        if (_index is byte index)
         {
             return s_knownTypeNames[index];
         }
@@ -114,7 +115,7 @@ public static TypeNameObject From(string? typeName)
 
     public void AppendToChecksum(in Checksum.Builder builder)
     {
-        if (_index is int index)
+        if (_index is byte index)
         {
             builder.AppendData(index);
         }

src/Razor/src/Microsoft.CodeAnalysis.Razor.Workspaces/Serialization/MessagePack/Formatters/TagHelpers/TypeNameObjectFormatter.cs

@@ -37,7 +37,7 @@ public override TypeNameObject Deserialize(ref MessagePackReader reader, Seriali
         switch (typeNameKind)
         {
             case TypeNameKind.Index:
-                var index = reader.ReadInt32();
+                var index = reader.ReadByte();
                 return new(index);
             case TypeNameKind.String:
                 var fullName = CachedStringFormatter.Instance.Deserialize(ref reader, options).AssumeNotNull();
@@ -58,7 +58,7 @@ public override void Serialize(ref MessagePackWriter writer, TypeNameObject valu
 
         writer.WriteArrayHeader(PropertyCount);
 
-        if (value.Index is int index)
+        if (value.Index is byte index)
         {
             writer.Write((byte)TypeNameKind.Index);
             writer.Write(index);

src/Shared/Microsoft.AspNetCore.Razor.Serialization.Json/JsonDataReader.cs

@@ -139,6 +139,41 @@ public bool TryReadBoolean(string propertyName, out bool value)
         return false;
     }
 
+    public byte ReadByte()
+    {
+        _reader.CheckToken(JsonToken.Integer);
+
+        var result = Convert.ToByte(_reader.Value);
+        _reader.Read();
+
+        return result;
+    }
+
+    public byte ReadByteOrDefault(string propertyName, byte defaultValue = default)
+        => TryReadPropertyName(propertyName) ? ReadByte() : defaultValue;
+
+    public byte ReadByteOrZero(string propertyName)
+        => TryReadPropertyName(propertyName) ? ReadByte() : (byte)0;
+
+    public bool TryReadByte(string propertyName, out byte value)
+    {
+        if (TryReadPropertyName(propertyName))
+        {
+            value = ReadByte();
+            return true;
+        }
+
+        value = default;
+        return false;
+    }
+
+    public byte ReadByte(string propertyName)
+    {
+        ReadPropertyName(propertyName);
+
+        return ReadByte();
+    }
+
     public int ReadInt32()
     {
         _reader.CheckToken(JsonToken.Integer);

src/Shared/Microsoft.AspNetCore.Razor.Serialization.Json/JsonDataWriter.cs

@@ -68,6 +68,30 @@ public void WriteIfNotFalse(string propertyName, bool value)
         }
     }
 
+    public void Write(byte value)
+    {
+        _writer.WriteValue(value);
+    }
+
+    public void Write(string propertyName, byte value)
+    {
+        _writer.WritePropertyName(propertyName);
+        _writer.WriteValue(value);
+    }
+
+    public void WriteIfNotZero(string propertyName, byte value)
+    {
+        WriteIfNotDefault(propertyName, value, defaultValue: (byte)0);
+    }
+
+    public void WriteIfNotDefault(string propertyName, byte value, byte defaultValue)
+    {
+        if (value != defaultValue)
+        {
+            Write(propertyName, value);
+        }
+    }
+
     public void Write(int value)
     {
         _writer.WriteValue(value);

src/Shared/Microsoft.AspNetCore.Razor.Serialization.Json/ObjectReaders_TagHelpers.cs

@@ -219,7 +219,7 @@ static TypeNameObject ReadTypeNameObject(JsonDataReader reader, string propertyN
 
             if (reader.IsInteger)
             {
-                var index = reader.ReadInt32();
+                var index = reader.ReadByte();
                 return new(index);
             }
 

src/Shared/Microsoft.AspNetCore.Razor.Serialization.Json/ObjectWriters_TagHelpers.cs

@@ -62,7 +62,7 @@ static void WriteDocumentationObject(JsonDataWriter writer, string propertyName,
 
         static void WriteTypeNameObject(JsonDataWriter writer, string propertyName, TypeNameObject typeNameObject)
         {
-            if (typeNameObject.Index is int index)
+            if (typeNameObject.Index is byte index)
             {
                 writer.Write(propertyName, index);
             }