Returning an array in 0.21

[ndarilek]

Hey folks,

I'm upgrading a library from 0.19 to 0.21 and am having issues with a function returning an array of strings:

#[no_mangle]
#[allow(non_snake_case)]
pub unsafe extern "C" fn Java_app_waynav_engine_Perspective_nativeGetLayers(
    env: &mut JNIEnv,
    _class: JClass,
    ptr: jlong,
    key: JString,
) -> jobjectArray {
    let perspective = &mut *(ptr as *mut Perspective);
    let key: String = env.get_string(&key).unwrap().into();
    let layers = perspective.layers(key).unwrap();
    let array = env
        .new_object_array(
            layers.len() as i32,
            "java/lang/String",
            env.new_string("").unwrap(),
        )
        .unwrap();
    for (i, layer) in layers.iter().enumerate() {
        let layer = env.new_string(layer).unwrap();
        env.set_object_array_element(array, i as i32, layer)
            .unwrap();
    }
    array
}

The specific error:

error[E0308]: mismatched types
   --> src/jni.rs:122:5
    |
106 | ) -> jobjectArray {
    |      ------------ expected `*mut _jobject` because of return type
...
122 |     array
    |     ^^^^^ expected `*mut _jobject`, found `JObjectArray<'_>`
    |
    = note: expected raw pointer `*mut _jobject`
                    found struct `JObjectArray<'_>`
help: consider dereferencing the type
    |
122 |     **array
    |     ++
For more information about this error, try `rustc --explain E0308`.
error: could not compile `waynav` (lib) due to previous error

Following the suggestion doesn't get me anywhere:

error[E0382]: borrow of moved value: `array`
   --> src/jni.rs:122:6
    |
110 |     let array = env
    |         ----- move occurs because `array` has type `JObjectArray<'_>`, which does not implement the `Copy` trait
...
117 |     for (i, layer) in layers.iter().enumerate() {
    |     ------------------------------------------- inside of this loop
118 |         let layer = env.new_string(layer).unwrap();
119 |         env.set_object_array_element(array, i as i32, layer)
    |                                      ----- value moved here, in previous iteration of loop
...
122 |     **array
    |      ^^^^^^ value borrowed here after move
    |
    = note: borrow occurs due to deref coercion to `JObject<'_>`
note: deref defined here
   --> /usr/local/cargo/registry/src/index.crates.io-6f17d22bba15001f/jni-0.21.1/src/wrapper/objects/jobject_array.rs:26:5
    |
26  |     type Target = JObject<'local>;
    |     ^^^^^^^^^^^

These appear to be the last holdouts for my upgrade and I'm not sure what to do about them. I checked the migration docs but nothing seems to cover the case of creating and returning a Java array.

Thanks a bunch for any help.

[fpoli]

Have you tried using env.set_object_array_element(&array, ...) in the loop? I think a shared reference should be sufficient there, because the type of that method argument is AsRef.

[ndarilek]

Perfect, worked. Thanks!