Type error regression when using enum called Result

[thedjinn]

I am working on a project that uses Prost (via Tonic) to compile a protobuf file for use with gRPC. The file compiles fine with prost 0.11.9, but when switching to prost 0.12.0 the generated Rust file contains type errors.

The minimal protobuf file required to reproduce the problem is this one:

syntax = "proto3";

package fail;

enum Result {
  HELLO = 0;
}

message FailMessage {
  Result result = 1;
}

When attempting to compile the generated rust file the following errors are returned:

error[E0107]: enum takes 0 generic arguments but 2 generic arguments were supplied
 --> /private/tmp/tonicfail/target/debug/build/tonicfail-ca0c3cb604ffea00/out/fail.rs:2:28
  |
2 | #[derive(Clone, PartialEq, ::prost::Message)]
  |                            ^^^^^^^^^^^^^^^^- help: remove these generics
  |                            |
  |                            expected 0 generic arguments
  |
note: enum defined here, with 0 generic parameters
 --> /private/tmp/tonicfail/target/debug/build/tonicfail-ca0c3cb604ffea00/out/fail.rs:9:10
  |
9 | pub enum Result {
  |          ^^^^^^
  = note: this error originates in the derive macro `::prost::Message` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0308]: mismatched types
   --> /private/tmp/tonicfail/target/debug/build/tonicfail-ca0c3cb604ffea00/out/fail.rs:2:28
    |
2   | #[derive(Clone, PartialEq, ::prost::Message)]
    |                            ^^^^^^^^^^^^^^^^
    |                            |
    |                            expected `Result`, found `Result<_, _>`
    |                            expected due to this
    |
    = note: `std::result::Result<_, _>` and `proto::Result` have similar names, but are actually distinct types
note: `std::result::Result<_, _>` is defined in crate `core`
   --> /Users/djinn/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/result.rs:502:1
    |
502 | pub enum Result<T, E> {
    | ^^^^^^^^^^^^^^^^^^^^^
note: `proto::Result` is defined in the current crate
   --> /private/tmp/tonicfail/target/debug/build/tonicfail-ca0c3cb604ffea00/out/fail.rs:9:1
    |
9   | pub enum Result {
    | ^^^^^^^^^^^^^^^
    = note: this error originates in the derive macro `::prost::Message` (in Nightly builds, run with -Z macro-backtrace for more info)

error[E0308]: mismatched types
   --> /private/tmp/tonicfail/target/debug/build/tonicfail-ca0c3cb604ffea00/out/fail.rs:2:28
    |
2   | #[derive(Clone, PartialEq, ::prost::Message)]
    |                            ^^^^^^^^^^^^^^^^
    |                            |
    |                            expected `Result`, found `Result<_, _>`
    |                            this expression has type `proto::Result`
    |
    = note: `std::result::Result<_, _>` and `proto::Result` have similar names, but are actually distinct types
note: `std::result::Result<_, _>` is defined in crate `core`
   --> /Users/djinn/.rustup/toolchains/stable-x86_64-apple-darwin/lib/rustlib/src/rust/library/core/src/result.rs:502:1
    |
502 | pub enum Result<T, E> {
    | ^^^^^^^^^^^^^^^^^^^^^
note: `proto::Result` is defined in the current crate
   --> /private/tmp/tonicfail/target/debug/build/tonicfail-ca0c3cb604ffea00/out/fail.rs:9:1
    |
9   | pub enum Result {
    | ^^^^^^^^^^^^^^^
    = note: this error originates in the derive macro `::prost::Message` (in Nightly builds, run with -Z macro-backtrace for more info)

Some errors have detailed explanations: E0107, E0308.
For more information about an error, try `rustc --explain E0107`.
error: could not compile `tonicfail` (bin "tonicfail") due to 3 previous errors

If desired I can provide a minimal Rust project that demonstrates the failed compilation.

[tustvold]

We're also running into this in https://github.com/apache/arrow-rs/tree/master/arrow-flight

[anstylian]

I am facing the same one, with message Result and I am preparing a pull request
the issue introduced in this commit: ca73cbe

[LucioFranco]

@anstylian does your commit work? Happy to review a PR that fixes it.

[anstylian]

I have test it locally and works, but because you asked me that I have created a unit-test for it.
I have created a unit-test for this issue and it can be found here.
The above branch also contains a fix for the nix flakes of prost. cargo test was not working for me, running it from inside the tests folder. I need to add cmake and ninja in buildInputs.
My "test" basically makes compilation to fail if there is a collision between a users defined Result and Rust Result type.

After that I have created this where I have added the same unit-test for Option type.

@LucioFranco you can let me know which branch you want to merge and I can open you a new PR if its not the one already open.

[Victor-N-Suadicani]

Ran into this issue as well. Would really appreciate a swift bug fix release 🙏

[c0mm4nd]

Ran into this issue as well. Would really appreciate a swift bug fix release 🙏+1

[LucioFranco]

@anstylian yeah go ahead and make a PR with both. Should be easier to review.

[anstylian]

@LucioFranco
Currently I have 3 PR for this issue, you can choose to merge one, and close the others. Each PR contains its own description.

1. PR Fixes 905, fix: Use full path of Result type + unit test + Option unti test #917
2. PR Fixes 905, fix: Use full path of Result type + unit test #916
3. PR Fixes: #905, fix: Use full path of Result type #906

[thedjinn]

Thanks everyone for the work involved in getting this resolved.

[LucioFranco]

This has been released as v0.12.1