Crate compilation error when using mirrored third party Enum in StreamSink

[SilverMira]

Describe the bug

Encountered a rust compilation error when I had both a function to return a third-party Enum to Dart land and a function that writes said Enum to a StreamSink.

cargo check errors

error[E0277]: the trait bound `allo_isolate::ffi::DartCObject: From<MyEnum>` is not satisfied
   --> src\frb_generated.rs:100:47
    |
100 | ...                   .stream_sink::<_, crate::api::simple::MyEnum>(),
    |                        -----------      ^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `From<MyEnum>` is not implemented for `allo_isolate::ffi::DartCObject`, which is required by `MyEnum: IntoDart`
    |                        |
    |                        required by a bound introduced by this call
    |
    = help: the following other types implement trait `From<T>`:
              <allo_isolate::ffi::DartCObject as From<DartOpaque>>
              <allo_isolate::ffi::DartCObject as From<RustOpaqueBase<T, A>>>
    = note: required for `MyEnum` to implement `Into<allo_isolate::ffi::DartCObject>`
    = note: required for `MyEnum` to implement `IntoDart`
note: required by a bound in `flutter_rust_bridge::rust2dart::context::TaskRust2DartContext::<Rust2DartCodec>::stream_sink`
   --> C:\Users\Mira\.cargo\registry\src\index.crates.io-6f17d22bba15001f\flutter_rust_bridge-2.0.0-dev.28\src\rust2dart\context.rs:33:12
    |
30  |     pub fn stream_sink<T, D>(&self) -> StreamSinkBase<T, Rust2DartCodec>
    |            ----------- required by a bound in this associated function
...
33  |         D: IntoDart,
    |            ^^^^^^^^ required by this bound in `TaskRust2DartContext::<Rust2DartCodec>::stream_sink`

error[E0277]: the trait bound `MyEnum: IntoIntoDart<MyEnum>` is not satisfied
   --> src\frb_generated.rs:100:44
    |
100 | ...                   .stream_sink::<_, crate::api::simple::MyEnum>(),
    |                        -----------   ^ the trait `IntoIntoDart<MyEnum>` is not implemented for `MyEnum`
    |                        |
    |                        required by a bound introduced by this call
    |
    = help: the trait `IntoIntoDart<mirror_MyEnum>` is implemented for `MyEnum`
    = help: for that trait implementation, expected `mirror_MyEnum`, found `MyEnum`
note: required by a bound in `flutter_rust_bridge::rust2dart::context::TaskRust2DartContext::<Rust2DartCodec>::stream_sink`
   --> C:\Users\Mira\.cargo\registry\src\index.crates.io-6f17d22bba15001f\flutter_rust_bridge-2.0.0-dev.28\src\rust2dart\context.rs:32:12
    |
30  |     pub fn stream_sink<T, D>(&self) -> StreamSinkBase<T, Rust2DartCodec>
    |            ----------- required by a bound in this associated function
31  |     where
32  |         T: IntoIntoDart<D>,
    |            ^^^^^^^^^^^^^^^ required by this bound in `TaskRust2DartContext::<Rust2DartCodec>::stream_sink`

For more information about this error, try `rustc --explain E0277`.
error: could not compile `rust_lib_repro_frb` (lib) due to 2 previous errors

Also, while preparing this repro, I noticed that apparently the mirrored 3rd party type must also implement Clone due to a derive(Clone) in frb_generated.rs, is this intended?

#[derive(Clone)]
pub struct mirror_MyEnum(crate::api::simple::MyEnum);

Steps to reproduce

1. flutter_rust_bridge_codegen create repro_frb
2. cd repro_frb
3. cargo new --lib rust-3rdparty
4. Modify and add Enum in rust-3rdparty/src/lib.rs

   #[derive(Clone)]
   pub enum MyEnum {
       Foo,
       Bar,
       Baz,
   }

5. Modify rust/Cargo.toml to have dependency on rust-3rdparty

   [dependencies]
   rust-3rdparty = { path = "../rust-3rdparty" }

6. Modify rust/src/api/simple.rs

   pub use rust_3rdparty::MyEnum;
   
   use crate::frb_generated::StreamSink;
   
   #[flutter_rust_bridge::frb(mirror(MyEnum))]
   pub enum _MyEnum {
       Foo,
       Bar,
       Baz,
   }
   
   pub fn get_enum() -> MyEnum {
       MyEnum::Foo
   }
   
   pub fn stream_enum(_sink: StreamSink<MyEnum>) {}

7. flutter_rust_bridge_codegen generate

Logs

N/A

Expected behavior

Rust bridge can compile

Generated binding code

No response

OS

Windows

Version of flutter_rust_bridge_codegen

2.0.0-dev.28

Flutter info

No response

Version of clang++

No response

Additional context

No response

[fzyzcjy]

Hmm, do you mean it is OK if we do either be return value or be in stream sink, but error if we do both; Or can the minimal reproducible sample be further reduced to halves?

I noticed that apparently the mirrored 3rd party type must also implement Clone due to a derive(Clone) in frb_generated.rs, is this intended?

If your enum does not support clone (or have other special properties), maybe just make it opaque instead of mirroring it.

[SilverMira]

The error happens as long as there is a mirrored Enum used in a StreamSink, even if the mirrored Enum is never used as a return value. Cargo check shows that the compilation error is within the generated code when instantiating the actual StreamSink during the .stream_sink call

StreamSink::new(
    context
        .rust2dart_context()
        .stream_sink::<_, MyEnum>(),
)

If MyEnum is not mirrored, then FRB generates it as opaque, which does compile, but makes it harder to use on the Dart land

[SilverMira]

While messing around with the generated code, it looks like the crate can compile if I manually changed the following.

StreamSink::new(
    context
        .rust2dart_context()
        .stream_sink::<_, mirror_MyEnum>(), // codegen had MyEnum as the generic type originally
)

Additionally, not sure if I encountered the same issue but in another way, I'm getting the same compilation error if there is a StreamSink<Option<TestStruct>> where TestStruct is opaque.

#[flutter_rust_bridge::frb(opaque)]
pub struct TestStruct {}
pub fn stream_struct(_sink: StreamSink<TestStruct>) {}
pub fn stream_struct_option(_sink: StreamSink<Option<TestStruct>>) {}

I looked at the StreamSink instantiation for stream_struct and stream_struct_option and noticed there was a difference. The ordinary StreamSink<TestStruct> which is compiling fine uses Local_Auto_Owned_RustOpaque_flutter_rust_bridgefor_generatedrust_asyncRwLockTestStruct as the generic type while the problematic StreamSink<Option<TestStruct>> was just using Option<TestStruct> as the generic type. Manually replacing the Option<TestStruct> generic type within frb_generated.rs with Option<Local_Auto_Owned_RustOpaque_flutter_rust_bridgefor_generatedrust_asyncRwLockTestStruct> in fact fixed the compilation issue and Dart land is even receiving the objects correctly.

frb_generated.rs

fn wire_stream_struct_impl(
    port_: flutter_rust_bridge::for_generated::MessagePort,
    ptr_: flutter_rust_bridge::for_generated::PlatformGeneralizedUint8ListPtr,
    rust_vec_len_: i32,
    data_len_: i32,
) {
    FLUTTER_RUST_BRIDGE_HANDLER.wrap_normal::<flutter_rust_bridge::for_generated::SseCodec,_,_>(flutter_rust_bridge::for_generated::TaskInfo{ debug_name: "stream_struct", port: Some(port_), mode: flutter_rust_bridge::for_generated::FfiCallMode::Stream }, move || { 
            let message = unsafe { flutter_rust_bridge::for_generated::Dart2RustMessageSse::from_wire(ptr_, rust_vec_len_, data_len_) };
            let mut deserializer = flutter_rust_bridge::for_generated::SseDeserializer::new(message);
            deserializer.end(); move |context|  {
                    transform_result_sse((move ||  {
                         Result::<_,()>::Ok(crate::api::simple::stream_struct(StreamSink::new(context.rust2dart_context().stream_sink::<_,Local_Auto_Owned_RustOpaque_flutter_rust_bridgefor_generatedrust_asyncRwLockTestStruct>())))
                    })())
                } })
}
fn wire_stream_struct_option_impl(
    port_: flutter_rust_bridge::for_generated::MessagePort,
    ptr_: flutter_rust_bridge::for_generated::PlatformGeneralizedUint8ListPtr,
    rust_vec_len_: i32,
    data_len_: i32,
) {
    FLUTTER_RUST_BRIDGE_HANDLER.wrap_normal::<flutter_rust_bridge::for_generated::SseCodec, _, _>(
        flutter_rust_bridge::for_generated::TaskInfo {
            debug_name: "stream_struct_option",
            port: Some(port_),
            mode: flutter_rust_bridge::for_generated::FfiCallMode::Stream,
        },
        move || {
            let message = unsafe {
                flutter_rust_bridge::for_generated::Dart2RustMessageSse::from_wire(
                    ptr_,
                    rust_vec_len_,
                    data_len_,
                )
            };
            let mut deserializer =
                flutter_rust_bridge::for_generated::SseDeserializer::new(message);
            deserializer.end();
            move |context| {
                transform_result_sse((move || {
                    Result::<_, ()>::Ok(crate::api::simple::stream_struct_option(StreamSink::new(
                        context
                            .rust2dart_context()
                            .stream_sink::<_, Option<TestStruct>>(), // <---- Problematic?
                    )))
                })())
            }
        },
    )
}

[fzyzcjy]

it looks like the crate can compile if I manually changed the following

Briefly check it and it looks like it should be mirror_Something. For example, from pure_dart example we can see some working code looks like:

Feel free to PR to fix it! Alternatively I will work on it in the next batch (hopefully within several days)

Manually replacing the Option generic type within frb_generated.rs with

Good observation! Then looks like it is missing generating this.

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