fix(napi-derive): async task void output type (#1795)

crates/backend/src/typegen/struct.rs

@@ -36,9 +36,14 @@ impl ToTypeDef for NapiImpl {
   fn to_type_def(&self) -> Option<TypeDef> {
     if let Some(output_type) = &self.task_output_type {
       TASK_STRUCTS.with(|t| {
+        let resolved_type = ty_to_ts_type(output_type, false, true, false).0;
         t.borrow_mut().insert(
           self.name.to_string(),
-          ty_to_ts_type(output_type, false, true, false).0,
+          if resolved_type == "undefined" {
+            "void".to_owned()
+          } else {
+            resolved_type
+          },
         );
       });
     }

crates/macro/src/parser/mod.rs

@@ -1033,9 +1033,7 @@ impl ConvertToAST for syn::ItemImpl {
           if let Some((_, t, _)) = &self.trait_ {
             if let Some(PathSegment { ident, .. }) = t.segments.last() {
               if ident == "Task" && m.ident == "JsValue" {
-                if let Type::Path(_) = &m.ty {
+                task_output_type = Some(m.ty.clone());
-                  task_output_type = Some(m.ty.clone());
-                }
               } else if ident == "Generator" {
                 if let Type::Path(_) = &m.ty {
                   if m.ident == "Yield" {

examples/napi/__tests__/__snapshots__/typegen.spec.ts.md

@@ -246,6 +246,8 @@ Generated by [AVA](https://avajs.dev).
     ␊
     export function asyncReduceBuffer(buf: Buffer): Promise<number>␊
     ␊
+    export function asyncTaskVoidReturn(): Promise<void>␊
+    ␊
     export interface B {␊
       bar: number␊
     }␊

examples/napi/index.d.ts

@@ -236,6 +236,8 @@ export function asyncPlus100(p: Promise<number>): Promise<number>
 
 export function asyncReduceBuffer(buf: Buffer): Promise<number>
 
+export function asyncTaskVoidReturn(): Promise<void>
+
 export interface B {
   bar: number
 }

examples/napi/src/task.rs

@@ -28,3 +28,24 @@ fn without_abort_controller(a: u32, b: u32) -> AsyncTask<DelaySum> {
 fn with_abort_controller(a: u32, b: u32, signal: AbortSignal) -> AsyncTask<DelaySum> {
   AsyncTask::with_signal(DelaySum(a, b), signal)
 }
+
+struct AsyncTaskVoidReturn {}
+
+#[napi]
+impl Task for AsyncTaskVoidReturn {
+  type JsValue = ();
+  type Output = ();
+
+  fn compute(&mut self) -> Result<Self::Output> {
+    Ok(())
+  }
+
+  fn resolve(&mut self, _env: Env, output: Self::Output) -> Result<Self::JsValue> {
+    Ok(output)
+  }
+}
+
+#[napi]
+fn async_task_void_return() -> AsyncTask<AsyncTaskVoidReturn> {
+  AsyncTask::new(AsyncTaskVoidReturn {})
+}