feat(napi): provide reject method in Task trait

Do some cleanup logic if needed

napi/src/async_work.rs

@@ -93,10 +93,13 @@ unsafe extern "C" fn complete<T: Task>(
   let value_ptr = mem::replace(&mut work.value, Ok(mem::MaybeUninit::zeroed()));
   let deferred = mem::replace(&mut work.deferred, ptr::null_mut());
   let napi_async_work = mem::replace(&mut work.napi_async_work, ptr::null_mut());
-  let value = value_ptr.and_then(move |v| {
-    let output = v.assume_init();
-    work.inner_task.resolve(Env::from_raw(env), output)
-  });
+  let value = match value_ptr {
+    Ok(v) => {
+      let output = v.assume_init();
+      work.inner_task.resolve(Env::from_raw(env), output)
+    }
+    Err(e) => work.inner_task.reject(Env::from_raw(env), e),
+  };
   match check_status!(status).and_then(move |_| value) {
     Ok(v) => {
       let status = sys::napi_resolve_deferred(env, deferred, v.raw());

napi/src/task.rs

@@ -1,11 +1,17 @@
-use crate::js_values::NapiValue;
-use crate::{Env, Result};
+use crate::{js_values::NapiValue, Env, Error, Result};
 
-pub trait Task: Send {
+pub trait Task: Send + Sized {
   type Output: Send + Sized + 'static;
   type JsValue: NapiValue;
 
+  /// Compute logic in libuv thread
   fn compute(&mut self) -> Result<Self::Output>;
 
+  /// Into this method if `compute` return `Ok`
   fn resolve(self, env: Env, output: Self::Output) -> Result<Self::JsValue>;
+
+  /// Into this method if `compute` return `Err`
+  fn reject(self, _env: Env, err: Error) -> Result<Self::JsValue> {
+    Err(err)
+  }
 }

test_module/__test__/spawn.spec.ts

@@ -12,3 +12,14 @@ test('should be able to spawn thread with ref value', async (t) => {
   const result = await bindings.testSpawnThreadWithRef(Buffer.from(fixture))
   t.is(result, fixture.length)
 })
+
+test('should be able to spawn with error', async (t) => {
+  const fixture = Array.from({ length: 10 }).fill('0').join('')
+  const err = new Error('Unreachable')
+  try {
+    await bindings.testSpawnThreadWithRef(Buffer.from(fixture))
+    throw err
+  } catch (e) {
+    t.not(e, err)
+  }
+})

test_module/src/task.rs

@@ -1,6 +1,8 @@
 use std::convert::TryInto;
 
-use napi::{CallContext, Env, JsBuffer, JsBufferValue, JsNumber, JsObject, Ref, Result, Task};
+use napi::{
+  CallContext, Env, Error, JsBuffer, JsBufferValue, JsNumber, JsObject, Ref, Result, Task,
+};
 
 struct ComputeFib {
   n: u32,
@@ -56,6 +58,9 @@ impl Task for CountBufferLength {
   type JsValue = JsNumber;
 
   fn compute(&mut self) -> Result<Self::Output> {
+    if self.data.len() == 10 {
+      return Err(Error::from_reason("len can't be 5".to_string()));
+    }
     Ok((&self.data).len())
   }
 
@@ -63,6 +68,11 @@ impl Task for CountBufferLength {
     self.data.unref(env)?;
     env.create_uint32(output as _)
   }
+
+  fn reject(self, env: Env, err: Error) -> Result<Self::JsValue> {
+    self.data.unref(env)?;
+    Err(err)
+  }
 }
 
 #[js_function(1)]