Implementing Synchronous Optional Callback Function

[vincent-herlemont]

I'm trying to implement a synchronous optional callback function using napi. I'm facing issues where I'm unable to find the type F in my current scope and my callback function is not being recognized as a function. Here's the code in question:

#[napi]
pub fn test_function<F>(&self, env: Env, callback: Option<F>) -> napi::Result<()>
where
  F: Fn(Option<napi::Error>, JsObject) -> napi::Result<()>,
{
  let mut js_object = env.create_object()?;
  js_object.set_named_property("test", env.create_string("test")?)?;
  let error = Some(napi::Error::from_reason("test error"));
  callback(error, js_object)?;
  Ok(())
}

Error

error[E0412]: cannot find type `F` in this scope
   --> crates/embedb-node/src/lib.rs:149:61
    |
149 |   pub fn test_function<F>(&self, env: Env, callback: Option<F>) -> napi::Result<()>
    |                                                             ^
    |
   ::: /home/vincentherlemont/.rustup/toolchains/1.69.0-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/ops/function.rs:76:1
    |
76  | pub trait Fn<Args: Tuple>: FnMut<Args> {
    | -------------------------------------- similarly named trait `Fn` defined here
    |
help: there is an enum variant `napi::bindgen_prelude::Either10::F` and 21 others; try using the variant's enum
    |
149 |   pub fn test_function<F>(&self, env: Env, callback: Option<napi::bindgen_prelude::Either10>) -> napi::Result<()>
    |                                                             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
149 |   pub fn test_function<F>(&self, env: Env, callback: Option<napi::bindgen_prelude::Either11>) -> napi::Result<()>
    |                                                             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
149 |   pub fn test_function<F>(&self, env: Env, callback: Option<napi::bindgen_prelude::Either12>) -> napi::Result<()>
    |                                                             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
149 |   pub fn test_function<F>(&self, env: Env, callback: Option<napi::bindgen_prelude::Either13>) -> napi::Result<()>
    |                                                             ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
      and 17 other candidates
help: a trait with a similar name exists
    |
149 |   pub fn test_function<F>(&self, env: Env, callback: Option<Fn>) -> napi::Result<()>
    |                                                             ~~

error[E0618]: expected function, found `Option<F>`
   --> crates/embedb-node/src/lib.rs:156:5
    |
149 |   pub fn test_function<F>(&self, env: Env, callback: Option<F>) -> napi::Result<()>
    |                                            -------- `callback` has type `Option<F>`
...
156 |     callback(error, js_object)?;
    |     ^^^^^^^^------------------
    |     |
    |     call expression requires function

From the error messages, it seems that F is not recognized as a type and the callback function is not recognized as a function.

My intention is to make the callback function optional and synchronous, as I do not wish to utilize ThreadsafeFunction if there's no way to make it synchronous. However, I'm not sure how to approach this issue.

Any guidance or help would be greatly appreciated.

[vincent-herlemont]

I don't know if this way to do let js_func = ctx.get::<JsFunction>(0)?; can solve my issue, but if there is a way with a static declaration with arguments I will prefer that.