Allow generating C# classes as records like public sealed record MyRequestMessage : IBufferMessage

[ganesh-tn]

Feature request

When using protobuf to generate C# code from .proto files, all messages are generated as mutable classes. Modern C# development favors immutable records for better testability, safety, and cleaner code.

Currently, if I want to use records with protobuf, I must abandon .proto files for a code-first approach.

Describe the solution you'd like

Add an option to generate C# records instead of classes.

Proposed MSBuild property:

<PropertyGroup>
  <GrpcMessagesAsRecords>true</GrpcMessagesAsRecords>
</PropertyGroup>

Or via metadata:

<Protobuf Include="myfile.proto" GrpcOutputOptions="messages_as_records" />

[Theory]
[InlineData("Alice", 25)]
[InlineData("Bob", 30)]
public void ProcessPerson_ShouldValidateAge(string name, int age)
{
    // NOTE: ValidRequests.NewPerson is a a readonly message record
    // Create variation with records using 'with'
    var result = fixture.Client.CreateNewPerson(
        ValidRequests.NewPerson with { Name = name, Age = age }
    );
    Assert.True(result.IsValid);
}

Describe alternatives you've considered

Post-build code transformation - Brittle and breaks on updates

Additional context

C# records were introduced in C# 9.0 (.NET 5.0) and are now widely adopted in the ecosystem.