Simplify macro markers and add some tests

crates/neon-macros/src/export/function/mod.rs

@@ -42,19 +42,19 @@ pub(super) fn export(meta: meta::Meta, input: syn::ItemFn) -> proc_macro::TokenS
             .unwrap_or_else(|| quote::quote!(#name))
     });
 
-    // Import the value or JSON trait for conversion
-    let result_trait_name = if meta.json {
-        quote::format_ident!("NeonExportReturnJson")
+    // Tag whether we should JSON wrap results
+    let return_tag = if meta.json {
+        quote::format_ident!("NeonJsonTag")
     } else {
-        quote::format_ident!("NeonExportReturnValue")
+        quote::format_ident!("NeonValueTag")
     };
 
     // Convert the result
     // N.B.: Braces are intentionally included to avoid leaking trait to function body
     let result_extract = quote::quote!({
-        use neon::macro_internal::#result_trait_name;
+        use neon::macro_internal::{ToNeonMarker, #return_tag as NeonReturnTag};
 
-        res.try_neon_export_return(&mut cx)
+        (&res).to_neon_marker::<NeonReturnTag>().neon_into_js(&mut cx, res)
     });
 
     // Default export name as identity unless a name is provided
@@ -69,9 +69,9 @@ pub(super) fn export(meta: meta::Meta, input: syn::ItemFn) -> proc_macro::TokenS
             let (#(#tuple_fields,)*) = cx.args()?;
             let fut = #name(#context_arg #(#args),*);
             let fut = {
-                use neon::macro_internal::ToNeonFutureMarker;
+                use neon::macro_internal::{ToNeonMarker, NeonValueTag};
 
-                (&fut).to_neon_future_marker().make_result(&mut cx, fut)?
+                (&fut).to_neon_marker::<NeonValueTag>().into_neon_result(&mut cx, fut)?
             };
 
             neon::macro_internal::spawn(&mut cx, fut, |mut cx, res| #result_extract)

crates/neon/src/macro_internal/futures.rs

@@ -2,8 +2,8 @@ use std::future::Future;
 
 use crate::{
     context::{Context, Cx, TaskContext},
-    result::{JsResult, NeonResult},
-    types::{extract::TryIntoJs, JsValue},
+    result::JsResult,
+    types::JsValue,
 };
 
 pub fn spawn<'cx, F, S>(cx: &mut Cx<'cx>, fut: F, settle: S) -> JsResult<'cx, JsValue>
@@ -27,46 +27,3 @@ where
 
     Ok(promise.upcast())
 }
-
-pub trait ToNeonFutureMarker {
-    type Marker;
-
-    fn to_neon_future_marker(&self) -> Self::Marker;
-}
-
-impl<T, E> ToNeonFutureMarker for Result<T, E> {
-    type Marker = NeonFutureMarkerResult;
-
-    fn to_neon_future_marker(&self) -> Self::Marker {
-        NeonFutureMarkerResult
-    }
-}
-
-impl<T> ToNeonFutureMarker for &T {
-    type Marker = NeonFutureMarkerValue;
-
-    fn to_neon_future_marker(&self) -> Self::Marker {
-        NeonFutureMarkerValue
-    }
-}
-
-pub struct NeonFutureMarkerResult;
-pub struct NeonFutureMarkerValue;
-
-impl NeonFutureMarkerResult {
-    pub fn make_result<'cx, T, E>(self, cx: &mut Cx<'cx>, res: Result<T, E>) -> NeonResult<T>
-    where
-        E: TryIntoJs<'cx>,
-    {
-        res.or_else(|err| {
-            let err = err.try_into_js(cx)?;
-            cx.throw(err)
-        })
-    }
-}
-
-impl NeonFutureMarkerValue {
-    pub fn make_result<T>(self, _cx: &mut Cx, res: T) -> NeonResult<T> {
-        Ok(res)
-    }
-}

crates/neon/src/macro_internal/mod.rs

@@ -1,14 +1,19 @@
 //! Internals needed by macros. These have to be exported for the macros to work
 
+use std::marker::PhantomData;
+
 pub use linkme;
 
 use crate::{
-    context::{Cx, ModuleContext},
+    context::{Context, Cx, ModuleContext},
     handle::Handle,
     result::{JsResult, NeonResult},
     types::{extract::TryIntoJs, JsValue},
 };
 
+#[cfg(feature = "serde")]
+use crate::types::extract::Json;
+
 #[cfg(all(feature = "napi-6", feature = "futures"))]
 pub use self::futures::*;
 
@@ -23,46 +28,86 @@ pub static EXPORTS: [for<'cx> fn(&mut ModuleContext<'cx>) -> NeonResult<Export<'
 #[linkme::distributed_slice]
 pub static MAIN: [for<'cx> fn(ModuleContext<'cx>) -> NeonResult<()>];
 
-// Provides an identically named method to `NeonExportReturnJson` for easy swapping in macros
-pub trait NeonExportReturnValue<'cx> {
-    fn try_neon_export_return(self, cx: &mut Cx<'cx>) -> JsResult<'cx, JsValue>;
+// Wrapper for the value type and return type tags
+pub struct NeonMarker<Tag, Return>(PhantomData<Tag>, PhantomData<Return>);
+
+// Markers to determine the type of a value
+#[cfg(feature = "serde")]
+pub struct NeonJsonTag;
+pub struct NeonValueTag;
+pub struct NeonResultTag;
+
+pub trait ToNeonMarker {
+    type Return;
+
+    fn to_neon_marker<Tag>(&self) -> NeonMarker<Tag, Self::Return>;
 }
 
-impl<'cx, T> NeonExportReturnValue<'cx> for T
-where
-    T: TryIntoJs<'cx>,
-{
-    fn try_neon_export_return(self, cx: &mut Cx<'cx>) -> JsResult<'cx, JsValue> {
-        self.try_into_js(cx).map(|v| v.upcast())
+// Specialized implementation for `Result`
+impl<T, E> ToNeonMarker for Result<T, E> {
+    type Return = NeonResultTag;
+
+    fn to_neon_marker<Tag>(&self) -> NeonMarker<Tag, Self::Return> {
+        NeonMarker(PhantomData, PhantomData)
     }
 }
 
-#[cfg(feature = "serde")]
-// Trait used for specializing `Json` wrapping of `T` or `Result<T, _>` in macros
-// Leverages the [autoref specialization](https://github.com/dtolnay/case-studies/blob/master/autoref-specialization/README.md) technique
-pub trait NeonExportReturnJson<'cx> {
-    fn try_neon_export_return(self, cx: &mut Cx<'cx>) -> JsResult<'cx, JsValue>;
+// Default implementation that takes lower precedence due to autoref
+impl<T> ToNeonMarker for &T {
+    type Return = NeonValueTag;
+
+    fn to_neon_marker<Tag>(&self) -> NeonMarker<Tag, Self::Return> {
+        NeonMarker(PhantomData, PhantomData)
+    }
+}
+
+impl<Return> NeonMarker<NeonValueTag, Return> {
+    pub fn neon_into_js<'cx, T>(self, cx: &mut Cx<'cx>, v: T) -> JsResult<'cx, JsValue>
+    where
+        T: TryIntoJs<'cx>,
+    {
+        v.try_into_js(cx).map(|v| v.upcast())
+    }
 }
 
 #[cfg(feature = "serde")]
-// More specific behavior wraps `Result::Ok` in `Json`
-impl<'cx, T, E> NeonExportReturnJson<'cx> for Result<T, E>
-where
-    T: serde::Serialize,
-    E: TryIntoJs<'cx>,
-{
-    fn try_neon_export_return(self, cx: &mut Cx<'cx>) -> JsResult<'cx, JsValue> {
-        self.map(crate::types::extract::Json).try_into_js(cx)
+impl NeonMarker<NeonJsonTag, NeonValueTag> {
+    pub fn neon_into_js<'cx, T>(self, cx: &mut Cx<'cx>, v: T) -> JsResult<'cx, JsValue>
+    where
+        Json<T>: TryIntoJs<'cx>,
+    {
+        Json(v).try_into_js(cx).map(|v| v.upcast())
     }
 }
 
 #[cfg(feature = "serde")]
-// Due to autoref behavior, this is less specific than the other implementation
-impl<'cx, T> NeonExportReturnJson<'cx> for &T
-where
-    T: serde::Serialize,
-{
-    fn try_neon_export_return(self, cx: &mut Cx<'cx>) -> JsResult<'cx, JsValue> {
-        crate::types::extract::Json(self).try_into_js(cx)
+impl NeonMarker<NeonJsonTag, NeonResultTag> {
+    pub fn neon_into_js<'cx, T, E>(
+        self,
+        cx: &mut Cx<'cx>,
+        res: Result<T, E>,
+    ) -> JsResult<'cx, JsValue>
+    where
+        Result<Json<T>, E>: TryIntoJs<'cx>,
+    {
+        res.map(Json).try_into_js(cx).map(|v| v.upcast())
+    }
+}
+
+impl<Tag> NeonMarker<Tag, NeonValueTag> {
+    pub fn into_neon_result<T>(self, _cx: &mut Cx, v: T) -> NeonResult<T> {
+        Ok(v)
+    }
+}
+
+impl<Tag> NeonMarker<Tag, NeonResultTag> {
+    pub fn into_neon_result<'cx, T, E>(self, cx: &mut Cx<'cx>, res: Result<T, E>) -> NeonResult<T>
+    where
+        E: TryIntoJs<'cx>,
+    {
+        match res {
+            Ok(v) => Ok(v),
+            Err(err) => err.try_into_js(cx).and_then(|err| cx.throw(err)),
+        }
     }
 }

test/napi/src/js/futures.rs

@@ -2,7 +2,10 @@ use std::future::Future;
 
 use neon::{
     prelude::*,
-    types::{buffer::TypedArray, extract::Error},
+    types::{
+        buffer::TypedArray,
+        extract::{Error, Json, With, TryIntoJs},
+    },
 };
 
 use crate::runtime;
@@ -107,3 +110,28 @@ fn async_div(cx: &mut FunctionContext) -> NeonResult<impl Future<Output = Result
         Ok(a / b)
     })
 }
+
+#[neon::export(async)]
+fn async_with_events(
+    cx: &mut FunctionContext,
+    Json(data): Json<Vec<(f64, f64)>>,
+) -> NeonResult<impl Future<Output = impl for<'cx> TryIntoJs<'cx>>> {
+    fn emit(cx: &mut Cx, state: &str) -> NeonResult<()> {
+        cx.global::<JsObject>("process")?
+            .call_method_with(cx, "emit")?
+            .arg(cx.string("async_kitchen_sink"))
+            .arg(cx.string(state))
+            .exec(cx)
+    }
+
+    emit(cx, "start")?;
+
+    Ok(async move {
+        let res = data.into_iter().map(|(a, b)| a * b).collect::<Vec<_>>();
+
+        With(move |cx| -> NeonResult<_> {
+            emit(cx, "end")?;
+            Ok(res)
+        })
+    })
+}