Ignore non-proto3 files

[cdevienne]

In some case a proto3 file includes a proto2 file but will not use the message types in it
directly. Ignoring proto2 files instead of failing allows these cases to run smoothly.

[tiziano88]

Many thanks for this @cdevienne ! I am not too sure about this, since it would mean that if the binary is run against a purely proto2 directory, no output and no error will be emitted, which will definitely be confusing for users. So I would prefer not to merge this, but I am happy to discuss further, if you or anyone else has any strong opinion.

[cdevienne]

Hello @tiziano88
I had the case with the protobuf file "descriptor.proto", which I think we can add to the ignored file list.
Would it be more acceptable ?

[tiziano88]

Currently the ignored list exists because for those types the proto compiler will emit "native" structs in the target language rather than proto objects. For descriptor.proto I don't think this would be the case? If a proto3 file is including descriptor.proto (which is proto2), I think the correct thing to do is to error out? Otherwise the resulting generated will probably not make sense anyways, right?

[cdevienne]

Not exactly.
The descriptor file contains only things used by some extensions (like nrpc or gogo) to annotate the file, messages, fields, services and methods.
So while we need the file to load the sources, it defines nothing that will end up directly in the generated files. And as there are no proto3 version of this file (it uses proto2-only stuffs), in the elm-protobuf case the only valid behavior is to ignore it.

[tiziano88]

Well, I think what you describe is a possibility, but nothing stops a proto file from having a field of a type contained in descriptor.proto, in which case the result will be that elm-protobuf will succeed, but the resulting generated files will not compile. Anyway, I am interested to see an example of what you describe, I think in practice you are correct that in most cases it will be used for annotations only, and we can safely ignore those.

[cdevienne]

Unlike what I though at first, https://github.com/protocolbuffers/protobuf/blob/master/src/google/protobuf/descriptor.proto indeed containts messages and not only extensible things for annotations.

As long as elm-protobuf does compile non-proto3 files, and since there are valid cases were a proto3 files includes the descriptor file, I think we can safely ignore it.

One possibility would be to add an option to explicitly ignore files from the command line, something like:

--elm_out="ignore=google/protobuf/descriptor.proto:."

[cdevienne]

Here is an example of using descriptor.proto to define annotations:

https://github.com/nats-rpc/nrpc/blob/master/nrpc.proto

[cdevienne]

#21 provides a better way to address the original problem.