Jakob Möllås Jakob Möllås - 10 months ago 65
C# Question

Preserving proto comments when generating C# with protobuf-net

We are using protobuf-net to handle our Protocol Buffer needs in a C# application. Since we share our .proto files with other, non-managed applications, we are generating our code from the .proto files (not using the code-first protobuf-net approach). In order to stay as DRY as possible, we keep a lot of interface documentation inside the .proto files themselves. We generate the C# code by means of protogen.exe, called by a project build target.

Now, is there any way to (automatically) transfer these comments into the compiled C# code?

Basically, given a .proto like this:

// This message is used to request a resource from the server
message GetResource
// The identifier of the requested resource
required string resourceId = 1;

...I would like something like this (IExtensible methods omitted for readability):

/// <summary>
/// This message is used to request a resource from the server
/// </summary>
public partial class GetResource : global::ProtoBuf.IExtensible
public GetResource() {}

private string _resourceId;

/// <summary>
/// The identifier of the requested resource
/// [Required] <-- Would be nice...
/// </summary>
[global::ProtoBuf.ProtoMember(1, IsRequired = true, Name=@"resourceId",
DataFormat = global::ProtoBuf.DataFormat.Default)]
public string ResourceId
get { return _resourceId; }
set { _resourceId = value; }

Answer Source

At the current time, I believe the answer is "no". To the best of my knowledge, "protoc" (Google's tool for parsing .proto files, which is used under the hood) silently discards the comments - so there is nothing available to read from. If a custom parser was written, then yes it would be possible, but there is also a language ambiguity about which comments apply to which lines, for example:

// this probably relates to resourceId
required string resourceId = 1;

required int foo = 2; // but... is this foo? or bar?
                      // and what about this?

       // what does this relate to? and why?

// and this? what are the rules?
required int bar = 3;

So for 2 different reasons: at the moment, no. All suggestions considered, though... especially if they come with a custom parser included :)

Note that AFAIK this information is missing from most (all?) implementations for this reason. I'm happy to be corrected, though.