native functions returning void appear to be unable to return results

[davidhewitt]

I wrote this code (minimised):

duchess::java_package!
    package com.example;
    class MyService {
        public static native void initialise(java.lang.String);
    }
}

#[duchess::java_function(com.example.MyService::initialise)]
fn initialise(path: &java::lang::String) -> duchess::GlobalResult<()> { Ok(()) }

But I get the following compile error:

error[E0308]: mismatched types
   --> client-lib\src\service.rs:413:72
    |
413 |           #[duchess::java_function(com.example.NotebookService::initialise)]
    |                                                                 ^---------
    |                                                                 |
    |  _______________________________________________________________expected `()` because of return type
    | |
414 | |         fn initialise(path: &java::lang::String) -> duchess::GlobalResult<()> {
    | |                     ^- help: consider using a semicolon here: `;`
    | |_____________________|
    |                       expected `()`, found `Result<(), Error<Global<...>>>`
    |
    = note: expected unit type `()`
                    found enum `std::result::Result<(), duchess::Error<duchess::Global<Throwable>>>`

The compile error goes away if I replace void/GlobalResult<()> with java.lang.String/GlobalResult<String>.

[nikomatsakis]

Thanks for this! I'll take a look. Curious.

[davidhewitt]

Duplicate of #126