travisstaloch / protobuf-zig Goto Github PK

currently, running $ zig build fails. here is the output:

~/.../zig/protobuf-zig $ zig build
install
└─ install protoc-gen-zig
   └─ zig build-exe protoc-gen-zig Debug native failure
error: the following command terminated unexpectedly:
... <COMMAND HERE> ...

i tried running <COMMAND HERE> (minus the final --listen=- arg) and it segfaults so i'm not sure what the problem is.

trying to generate code for a simple recursive message type produces the following dependency loop error.

$ script/gen-all.sh -I examples examples/recursive.proto 
zig-out/bin/protoc-zig --zig_out=gen -I examples examples/recursive.proto
zig test gen/recursive.pb.zig --pkg-begin protobuf src/lib.zig --pkg-begin protobuf src/lib.zig --pkg-end -freference-trace
src/google/protobuf/compiler/protobuf-types.zig:144:13: error: dependency loop detected
        pub const descriptor = MessageDescriptor.init(Self);
        ~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
referenced by:
    init: src/google/protobuf/compiler/protobuf-types.zig:305:56
    descriptor: src/google/protobuf/compiler/protobuf-types.zig:144:49
    field_descriptors: gen/recursive.pb.zig:64:5

i'm tracking ziglang/zig#12325 hoping it will fix this. i'd rather wait for it than proceed with generating c code and using it cause the c route gets messy very fast. i don't to deal with 3 files per generated .proto nor want users to have to do so.

what is happening here? each generated .proto message type needs to have const descriptor and field_descriptors decls. this is because in deserialize() desc needs a reference to fields here. and later a desc.field needs a reference back to a MessageDescriptor here.

i have considered and played with these workarounds:

• using with -ofmt=c to generate compatible struct defs for types in protobuf-types.zig and here. but it seems -ofmt=c doesn't gen structs decls yet.
• generating c code myself. this is possible now by manually setting gen.zig#output_format = .c. however this means that i have to make sure my zig structs are exactly synced up with c structs. this is a pain to do manually. maybe it could be automated? its easier to just wait for now and see if the issue above fixes it.
  • the idea would be to keep {Field,Message,Enum}Descriptor in a .proto file and generate zig and c code from it.

The following file results in the error below it.

// examples/proto3_optional.proto
syntax = "proto3";

message Proto3MsgWithOptional {
  optional string hello = 1;
}

$ zig build run --  examples/proto3_optional.proto
# ... garbage protobuf output here
proto3_optional.proto: is a proto3 file that contains optional fields, but code generator protoc-gen-zig hasn't been updated to support optional fields in proto3. Please ask the owner of this code generator to support proto3 optional.

SystemProtocError
~/projects/zig/protobuf-zig/src/main.zig:93:9: 0x2301a4 in main (protoc-zig)
        return error.SystemProtocError;
        ^

i think protobuf-zig's main.zig is missing a step for integrating with protoc. it reads a protobuf encoded CodeGeneratorRequest but never sends a CodeGeneratorResponse back. Instead, it just writes directly to the file.

the resulting CodeGeneratorResponse needs to have the FEATURE_PROTO3_OPTIONAL set

RESOURCES:

• jeromegn/protobuf.cr#38
• https://github.com/protocolbuffers/protobuf/blob/main/docs/implementing_proto3_presence.md#signaling-that-your-code-generator-supports-proto3-optional
• https://github.com/protocolbuffers/protobuf-go/blob/master/cmd/protoc-gen-go/main.go