Proto message named `Option` shadows `core::option::Option`, causing type errors on oneof fields

[th0114nd]

Summary

When a proto message is named Option, buffa's codegen generates a Rust struct named Option that shadows core::option::Option. If that message also has a oneof field, the generated code emits pub value: Option<foo::Value> where Option is intended to be core::option::Option, but Rust resolves it to the proto-generated struct (which takes 0 generic arguments).

This is valid protobuf accepted by protoc. Both prost and the official Go/C++/Java codegen handle this pattern without issues.

Minimal reproducer

syntax = "proto3";
package test.option_shadow;

message Picker {
  repeated Option options = 1;

  message Option {
    string title = 1;
    oneof value {
      uint64 int_value = 2;
    }
  }
}

// build.rs
fn main() {
    buffa_build::Config::new()
        .files(&["option_shadow.proto"])
        .includes(&["."])
        .include_file("_include.rs")
        .compile()
        .unwrap();
}

Error

error[E0107]: struct takes 0 generic arguments but 1 generic argument was supplied
   --> .../option_shadow.rs:233:20
    |
233 |         pub value: Option<option::Value>,
    |                    ^^^^^^--------------- help: remove the unnecessary generics
    |                    |
    |                    expected 0 generic arguments
    |
note: struct defined here, with 0 generic parameters
   --> .../option_shadow.rs:230:16
    |
230 |     pub struct Option {
    |                ^^^^^^

Expected behavior

Code generation should produce compilable code. The codegen should fully qualify ::core::option::Option<T> wherever it uses the standard Option type, so that a proto message named Option does not shadow it.

More generally, any proto name that collides with a Rust prelude type (Option, Result, Box, String, Vec, etc.) should be handled to avoid shadowing. Option is the most commonly hit case.

Context

This pattern appears in real-world proto schemas. We currently work around it by post-processing the generated code to replace bare Option< with ::core::option::Option<.

Version

buffa 0.3.0 / buffa-build 0.3.0 (crates.io)

[jlucaso1]

Same problem here