[Proto] Support polymorphic serialization for derived classes

[kengwang]

Motivation

Since the PbElem field of CommonElem(53) contains actual data, the ServiceType field is used to distinguish the type of data contained therein.

The TLVs also have this design model style.

It is hoped that the data structure can reflect this model design, making it easier to convert during serialization and deserialization.

Current

(Not Implemented CommonElem in V2)
In Lagrange.Core, directly read to a byte array and re-serialize.

Reference

Reference STJ's JsonDerivedTypeAttribute and JsonPolymorphicAttribute structures to achieve polymorphism.

Example

See Lagrange.Proto.Test/ProtoPolymorphismTest.cs

[ProtoPolymorphic(FieldNumber = 1)]
[ProtoDerivedType(typeof(DerivedClassA), 2)]
[ProtoDerivedType(typeof(DerivedClassB), 3)]
public class BaseClass
{
    public BaseClass() : this(-1) { }

    public BaseClass(int identifier)
    {
        IdentifierProperty = identifier;
    }

    [ProtoMember(1)] public int IdentifierProperty { get; set; }
}

public class DerivedClassA() : BaseClass(2)
{
    [ProtoMember(2)] public string NameProperty { get; set; }
}

public class DerivedClassB() : BaseClass(3)
{
    [ProtoMember(2)] public float ValueProperty { get; set; }
}

BaseClass original = new DerivedClassA { NameProperty = "TestName" };
byte[] bytes = ProtoSerializer.Serialize(original);
BaseClass deserialized = ProtoSerializer.Deserialize<BaseClass>(bytes);

To-do

• Implement in Lagrange.Proto.Generator
• Support multi-level inheritance
• Optimize code performance

Just a crazy idea

[kengwang]

Currently, it doesn't support multi-level inheritance. still improving.

Try to go to the root type first and then (un)wrap the protobuf type discriminator step by step, going down to the current type.

[Copilot]

Pull Request Overview

This PR implements polymorphic serialization support for protobuf-style serialization in the Lagrange.Proto library. The implementation allows base classes to define derived type mappings using attributes, enabling automatic serialization/deserialization of the correct derived type based on a discriminator field.

• Added polymorphic attribute system (ProtoPolymorphicAttribute and ProtoDerivedTypeAttribute) for defining type hierarchies
• Implemented runtime polymorphic type resolution during serialization and deserialization
• Extended the source generator to emit polymorphic-aware serialization code

Reviewed Changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
ThrowHelper.cs	Added error handling methods for polymorphic serialization scenarios
ProtoSerializer.Serialize.cs	Enhanced serialization logic to handle polymorphic types with discriminator fields
ProtoSerializer.Helpers.cs	Added helper methods for dynamic converter creation and reflection-based type info
ProtoSerializer.Deserialize.cs	Extended deserialization to support polymorphic type reconstruction
ProtoTypeResolver.Dynamic.cs	Added polymorphic metadata population and multi-level inheritance support
ProtoPolymorphicInfo.cs	New metadata classes for managing polymorphic type information
ProtoObjectInfo.cs	Added polymorphic info property to object metadata
ProtoPolymorphicAttribute.cs	New attribute for configuring polymorphic behavior
ProtoDerivedTypeAttribute.cs	New attribute for registering derived types with discriminators
ProtoPolymorphismTest.cs	Comprehensive test suite covering various polymorphic scenarios
Program.cs	Added example classes demonstrating polymorphic usage
ProtoSourceGenerator.Parser.cs	Enhanced parser to handle polymorphic attributes and inheritance
ProtoSourceGenerator.Emitter.TypeInfo.cs	Extended code generation for polymorphic type descriptors
ProtoSourceGenerator.Emitter.Serialize.cs	Added polymorphic-aware serialization code generation
PolymorphicTypeInfo.cs	New entity classes for representing polymorphic metadata

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[Copilot]

[nitpick] Missing space around the lambda arrow operator. Should be t => t.Value.Field == index for consistency with coding standards.

Suggested change

	var fieldInfo = fields.FirstOrDefault(t=>t.Value.Field == index);
	var fieldInfo = fields.FirstOrDefault(t => t.Value.Field == index);

[Copilot]

[nitpick] Missing space after the comma in BindingFlags parameter. Should be BindingFlags.NonPublic | BindingFlags.Instance with proper spacing.

Suggested change

	.GetField("ObjectInfo",BindingFlags.NonPublic | BindingFlags.Instance)!.GetValue(polyConverter)!;
	.GetField("ObjectInfo", BindingFlags.NonPublic | BindingFlags.Instance)!.GetValue(polyConverter)!;

[Copilot]

[nitpick] Missing space after comma in parameter list. Should be SourceWriter source, Dictionary<int, ProtoFieldInfo> fields.

Suggested change

	private void EmitFieldsInfo(SourceWriter source,Dictionary<int, ProtoFieldInfo> fields )
	private void EmitFieldsInfo(SourceWriter source, Dictionary<int, ProtoFieldInfo> fields )

[Copilot]

[nitpick] Extra space before comma in parameter list. Should be string identifier = \"\", CancellationToken token = default).

Suggested change

	private void PopulateFieldInfo(INamedTypeSymbol classSymbol, Dictionary<int, ProtoFieldInfo> fields, string identifier = "" ,CancellationToken token = default)
	private void PopulateFieldInfo(INamedTypeSymbol classSymbol, Dictionary<int, ProtoFieldInfo> fields, string identifier = "", CancellationToken token = default)