Cannot Pass Vec as a Parameter to Java Function

[ktseytlin]

Hi!

Creating this ticket to track using Vec <-> List / ArrayList for function parameters.

Expectation: I can pass in a list of arguments (of any type) to a Java function via Duchess

Current: I can pass in a Vec<T> to a Rust function if it is a parameter for a Java Record. I cannot pass Vec<T> directly as parameters.

See code below for reproduction.

See compiler output for what I'm seeing for the two cases: test_with_string_array and test_with_string_list.

---

Java side:

import java.util.List;

public class KerenDemo {

    public void test_with_string_array(String[] x) {
        System.out.println(x);
    }

    public void test_with_string_list(List<String> x) {
        System.out.println(x);
    }

    public void test_record_param_is_string_list(StringListRecord input) {
        System.out.println(input.records());
    }
}

import java.util.List;

public record StringListRecord(
    List<String> records
) { }

Rust Side:

duchess::java_package! {
    package demo;

    class KerenDemo { * }
    class StringListRecord { * }
}

#[derive(Clone, Debug, PartialEq, duchess::ToJava)]
#[java(demo.StringListRecord)]
pub struct StringListRecord {
    pub records: Vec<String>,
}

pub struct DemoClient {
    client: duchess::Global<demo::KerenDemo>,
}

impl RustKerenDemo {
  pub fn new() -> Arc<Self> {
    Arc::new(DemoClient { client: Self::build_client().unwrap() })
  }

    fn build_client() -> duchess::GlobalResult<Global<demo::KerenDemo>> {
        duchess::Jvm::builder().launch_or_use_existing().unwrap();
        metering::KerenDemo::new().global().execute()
    }

  pub fn does_not_work (self: Arc<Self>) {
         tokio::task::spawn_blocking(move || {
            duchess::Jvm::attach_thread_permanently().unwrap();
            self.client
                .test_with_string_list(vec!["Some signature".into()])
                .execute()
                .unwrap();
        });
  }

  pub fn does_not_work_2 (self: Arc<Self>) {
         tokio::task::spawn_blocking(move || {
            duchess::Jvm::attach_thread_permanently().unwrap();
            self.client
                .test_with_string_array(vec![String::from("Some signature")])
                .execute()
                .unwrap();
        });
  }

  pub fn this_works(self: Arc<Self>) {
        let record = StringListRecord {
            records: vec!["Some signature".into()],
        };
         tokio::task::spawn_blocking(move || {
            duchess::Jvm::attach_thread_permanently().unwrap();
            self.client
                .test_record_param_is_string_list(&record)
                .execute()
                .unwrap();
        });
  }
}

Compiler output for the two functions above where it does not work:

   --> src/lib.rs:125:41
    |
125 |                 .test_with_string_array(vec![String::from("Some signature")])
    |                  ---------------------- ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ the trait `duchess::JvmOp` is not implemented for `Vec<std::string::String>`
    |                  |
    |                  required by a bound introduced by this call
    |
    = help: the following other types implement trait `duchess::JvmOp`:
              bool
              char
              i8
              i16
              i32
              i64
              u16
              f32
            and 192 others
    = note: required for `Vec<std::string::String>` to implement `duchess::IntoJava<Array<duchess::java::lang::String>>`
note: required by a bound in `ViewAsKerenDemoObj::<J, N>::test_with_string_array`
   --> src/lib.rs:14:1
    |
14  | / duchess::java_package! {
15  | |     package demo;
16  | |
17  | |     class KerenDemo { * }
18  | |     class StringListRecord { * }
20  | | }
    | |_^ required by this bound in `ViewAsKerenDemoObj::<J, N>::test_with_string_array`
    = note: this error originates in the macro `duchess::java_package` (in Nightly builds, run with -Z macro-backtrace for more info)

[nikomatsakis]

So, the short version is that you ought to call .to_java for the arguments to convert them into Java:

 pub fn does_not_work (self: Arc<Self>) {
         tokio::task::spawn_blocking(move || {
            duchess::Jvm::attach_thread_permanently().unwrap();
            self.client
                .test_with_string_list(vec!["Some signature".into()].to_java()) // <-- 
                .execute()
                .unwrap();
        });
  }

Does that work?

[nikomatsakis]

It seems somewhat inconsistent that we don't require `.to_java` on the case where `#[derive(ToJava)]` exists. I have to look at why that is.

…

On Mon, Jul 15, 2024, at 5:57 PM, Niko Matsakis wrote: So, the short version is that you ought to call `.to_java` for the arguments to convert them into Java: pub fn does_not_work (self: Arc<Self>) { tokio::task::spawn_blocking(move || { duchess::Jvm::attach_thread_permanently().unwrap(); self.client .test_with_string_list(vec!["Some signature".into()].to_java()) // <-- .execute() .unwrap(); }); } Does that work? — Reply to this email directly, view it on GitHub <#122 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/AABF4ZVYDRKZMO7NKIP6C43ZMRAWPAVCNFSM6AAAAABK5LR5KGVHI2DSMVQWIX3LMV43OSLTON2WKQ3PNVWWK3TUHMZDEMRZGUYDQMJSGQ>. You are receiving this because you are subscribed to this thread.Message ID: ***@***.***>