Implementing traits local traits on 3rd party structs

[omarhogni]

I am trying to partially mirror a struct from a 3rd party crate and then implement other methods inside of a custom trait
to inject missing functionality.

Here is the code example

// Mirror the crates functionality
[frb(external)]
impl opcua::types::UAString {
    // Non supported signature due to reference
    #[frb(ignore)]
    pub fn value(&self) -> &Option<String> {}
    #[frb(sync)]
    pub fn set_value(&mut self, _value: Option<String>) {}
    #[frb(sync)]
    pub fn is_empty(&self) -> bool {}
    #[frb(sync)]
    pub fn len(&self) -> isize {}
    #[frb(sync)]
    pub fn null() -> opcua::types::UAString {}
    #[frb(sync)]
    pub fn is_null(&self) -> bool {}
    // Non supported signature due to void in return type
    #[frb(ignore)]
    pub fn substring(&self, _min: usize, _max: usize) -> Result<UAString, ()> {}
}

// Add functionality where the built in methods cannot be used.
pub trait CustomUAStringFunctions {
    #[frb(sync)]
    fn value_copy(&self) -> Option<String>;
    #[frb(sync)]
    fn substring_nonvoid(&self, min: usize, max: usize) -> Option<opcua::types::UAString>;
}

impl CustomUAStringFunctions for opcua::types::UAString {
    #[frb(sync)]
    fn value_copy(&self) -> Option<String> {
        self.value().clone()
    }
    #[frb(sync)]
    fn substring_nonvoid(&self, min: usize, max: usize) -> Option<opcua::types::UAString> {
        match self.substring(min, max) {
            Ok(val) => Some(val),
            Err(_) => None,
        }
    }
}

Mirroring works as expected but once I add the trait implementation flutter rust bridge references the type as it is owned by my project instead of the crate it originates from.

cargo build --release (pwd: /home/dl/sources/opcua-ffi/rust, env: {})
   Compiling opcua_ffi v0.0.1 (/home/dl/sources/opcua-ffi/rust)
error[E0433]: failed to resolve: could not find `UAString` in the crate root
  --> src/frb_generated.rs:99:60
   |
99 |                 let output_ok = Result::<_, ()>::Ok(crate::UAString::is_empty(&*api_that_guard))?;
   |                                                            ^^^^^^^^ could not find `UAString` in the crate root
   |
help: consider importing one of these structs
   |
28 + use crate::api::types::write_value::UAString;
   |
28 + use opcua::types::UAString;
   |
help: if you import `UAString`, refer to it directly
   |
99 -                 let output_ok = Result::<_, ()>::Ok(crate::UAString::is_empty(&*api_that_guard))?;
99 +                 let output_ok = Result::<_, ()>::Ok(UAString::is_empty(&*api_that_guard))?;

any help in resolving this would be appriciated.

[fzyzcjy]

Hmm I guess it is a bug. Feel free to PR to fix it, alternative I may work on it later. As a workaround, maybe try to pub use path::to::USString on your root level mod.rs, then the crate::UAString can really find it

[omarhogni]

This works but the functions defined in CustomUAStringFunctions do not appear in dart code for the UAString type. Only the abstract interface is translated

[fzyzcjy]

I see. Then could you please make a minimal reproducible sample? Then it would be easier to debug. Would be great to fork flutter_rust_bridge and modify minimally in the frb_example/dart_minimal folder.