Crazy idea: generating messages through function-style proc macro instead of build.rs

[vorner]

The build.rs approach to compiling proto files works, but is in some ways cumbersome.

I wonder if it would be possible to abuse the function-style procedural macros to generate the messages „inline“ somehow. From what I get, the input of the macro is only tokenized, but not checked in other ways, and .proto might be similar enough to pass through the rust tokenizer.

So I wonder if it would make sense to try to do something like that and see if/how that would work and how much effort that would take:

prost_derive::compile! {
    input!("../protos/my_message.proto");
}

[timthelion]

This would be nice except that this might interfering with learning/debugging. Currently, it's often easier to look directly in target/debug/../out/fooproto.rs and read the generated code to figure out how something works, than it is to try to figure out how the documentation relates to your exact protobuf file.

[danburkert]

I think this is a good idea, definitely worth exploring. Taking a step back, it seems that prosts inflexibility regarding codegen[1] is working well for the 80% case, but there's a long tail of applications which need something a bit more tailored. Perhaps it would be worth looking into an additional api in prost-build to make it more like a library. It may be as simple as exposing Config::generate publicaly, although more thought should probably be put into it. Two potential consumers are a proc-macro, and a protoc plugin for doing ahead-of-time code generation[2].

[1]: specifically, prost strongly encourages or requires codegen to be done in a build.rs with the help of prost-build.

[2]: prost used to provide this, but I removed it citing lack of interest; the project has grown significantly in user base since then, though.