[Proto] Enhance Proto serialization to handle nullable types and improve ZigZag encoding

Author: Linwenxuan04

Lagrange.Proto.Generator/ProtoSourceGenerator.Emitter.Serialize.cs

@@ -118,10 +118,10 @@ private void EmitMember(SourceWriter source, int field, ProtoFieldInfo info, str
             {
                 string? special = info.WireType switch
                 {
-                    WireType.VarInt when info.TypeSymbol.IsIntegerType() && info.IsSigned => $"{WriterVarName}.{EncodeVarIntMethodName}({ProtoHelperTypeRef}.{ZigZagEncodeMethodName}({memberName}));",
+                    WireType.VarInt when info.TypeSymbol.IsIntegerType() && info.IsSigned => GetZigZagEncodeCall(info.TypeSymbol, memberName),
                     WireType.VarInt when info.TypeSymbol.IsIntegerType() => $"{WriterVarName}.{EncodeVarIntMethodName}({memberName});",
-                    WireType.Fixed32 when info.IsSigned => $"{WriterVarName}.{EncodeFixed32MethodName}({ProtoHelperTypeRef}.{ZigZagEncodeMethodName}({memberName}));",
-                    WireType.Fixed64 when info.IsSigned => $"{WriterVarName}.{EncodeFixed64MethodName}({ProtoHelperTypeRef}.{ZigZagEncodeMethodName}({memberName}));",
+                    WireType.Fixed32 when info.IsSigned => GetZigZagEncodeFixed32Call(info.TypeSymbol, memberName),
+                    WireType.Fixed64 when info.IsSigned => GetZigZagEncodeFixed64Call(info.TypeSymbol, memberName),
                     WireType.Fixed32 => $"{WriterVarName}.{EncodeFixed32MethodName}({memberName});",
                     WireType.Fixed64 => $"{WriterVarName}.{EncodeFixed64MethodName}({memberName});",
                     WireType.LengthDelimited when info.TypeSymbol.SpecialType == SpecialType.System_String => $"{WriterVarName}.{EncodeStringMethodName}({memberName});",
@@ -170,5 +170,39 @@ private void EmitIfShouldSerializeStatement(SourceWriter source, int tag, Action
             source.Indentation--;
             source.WriteLine("}");
         }
+        
+        private string GetZigZagEncodeCall(ITypeSymbol typeSymbol, string memberName)
+        {
+            // For signed byte types, we need to cast the ZigZag encoded result to unsigned
+            // to prevent sign extension when writing as varint
+            return typeSymbol.SpecialType switch
+            {
+                SpecialType.System_SByte => $"{WriterVarName}.{EncodeVarIntMethodName}((byte){ProtoHelperTypeRef}.{ZigZagEncodeMethodName}({memberName}));",
+                SpecialType.System_Int16 => $"{WriterVarName}.{EncodeVarIntMethodName}((ushort){ProtoHelperTypeRef}.{ZigZagEncodeMethodName}({memberName}));",
+                SpecialType.System_Int32 => $"{WriterVarName}.{EncodeVarIntMethodName}((uint){ProtoHelperTypeRef}.{ZigZagEncodeMethodName}({memberName}));",
+                SpecialType.System_Int64 => $"{WriterVarName}.{EncodeVarIntMethodName}((ulong){ProtoHelperTypeRef}.{ZigZagEncodeMethodName}({memberName}));",
+                _ => $"{WriterVarName}.{EncodeVarIntMethodName}({ProtoHelperTypeRef}.{ZigZagEncodeMethodName}({memberName}));"
+            };
+        }
+        
+        private string GetZigZagEncodeFixed32Call(ITypeSymbol typeSymbol, string memberName)
+        {
+            return typeSymbol.SpecialType switch
+            {
+                SpecialType.System_SByte => $"{WriterVarName}.{EncodeFixed32MethodName}((byte){ProtoHelperTypeRef}.{ZigZagEncodeMethodName}({memberName}));",
+                SpecialType.System_Int16 => $"{WriterVarName}.{EncodeFixed32MethodName}((ushort){ProtoHelperTypeRef}.{ZigZagEncodeMethodName}({memberName}));",
+                SpecialType.System_Int32 => $"{WriterVarName}.{EncodeFixed32MethodName}((uint){ProtoHelperTypeRef}.{ZigZagEncodeMethodName}({memberName}));",
+                _ => $"{WriterVarName}.{EncodeFixed32MethodName}({ProtoHelperTypeRef}.{ZigZagEncodeMethodName}({memberName}));"
+            };
+        }
+        
+        private string GetZigZagEncodeFixed64Call(ITypeSymbol typeSymbol, string memberName)
+        {
+            return typeSymbol.SpecialType switch
+            {
+                SpecialType.System_Int64 => $"{WriterVarName}.{EncodeFixed64MethodName}((ulong){ProtoHelperTypeRef}.{ZigZagEncodeMethodName}({memberName}));",
+                _ => $"{WriterVarName}.{EncodeFixed64MethodName}({ProtoHelperTypeRef}.{ZigZagEncodeMethodName}({memberName}));"
+            };
+        }
     }
 }

Lagrange.Proto.Generator/Utility/ProtoHelper.cs

@@ -24,6 +24,7 @@ public static byte[] EncodeVarInt(int value)
     public static WireType GetWireType(ITypeSymbol symbol)
     {
         if (SymbolResolver.IsRepeatedType(symbol, out var type)) symbol = type;
+        if (SymbolResolver.IsNullableType(symbol, out var elementType)) symbol = elementType;
 
         if (symbol.IsIntegerType() || symbol.TypeKind == TypeKind.Enum || symbol.SpecialType == SpecialType.System_Boolean) return WireType.VarInt;
         if (symbol.SpecialType == SpecialType.System_Single) return WireType.Fixed32;