lazy Future construction for AsyncDerived

leptos_server/src/resource.rs

@@ -12,7 +12,8 @@ use futures::Future;
 use hydration_context::SerializedDataId;
 use reactive_graph::{
     computed::{
-        ArcAsyncDerived, ArcMemo, AsyncDerived, AsyncDerivedFuture, AsyncState,
+        ArcAsyncDerived, ArcAsyncDerivedFuture, ArcMemo, AsyncDerived,
+        AsyncDerivedFuture, AsyncState,
     },
     graph::{Source, ToAnySource, ToAnySubscriber},
     owner::Owner,
@@ -157,6 +158,7 @@ where
     T::SerErr: Debug,
     T::DeErr: Debug,
 {
+    #[track_caller]
     pub fn new_with_encoding<S, Fut>(
         source: impl Fn() -> S + Send + Sync + 'static,
         fetcher: impl Fn(S) -> Fut + Send + Sync + 'static,
@@ -241,7 +243,7 @@ where
     T: Clone + 'static,
 {
     type Output = T;
-    type IntoFuture = AsyncDerivedFuture<T>;
+    type IntoFuture = ArcAsyncDerivedFuture<T>;
 
     fn into_future(self) -> Self::IntoFuture {
         self.data.into_future()
@@ -281,6 +283,7 @@ where
     T::SerErr: Debug,
     T::DeErr: Debug,
 {
+    #[track_caller]
     pub fn new<S, Fut>(
         source: impl Fn() -> S + Send + Sync + 'static,
         fetcher: impl Fn(S) -> Fut + Send + Sync + 'static,
@@ -300,6 +303,7 @@ where
     T::SerErr: Debug,
     T::DeErr: Debug,
 {
+    #[track_caller]
     pub fn new_serde<S, Fut>(
         source: impl Fn() -> S + Send + Sync + 'static,
         fetcher: impl Fn(S) -> Fut + Send + Sync + 'static,
@@ -320,6 +324,7 @@ where
     T::SerErr: Debug,
     T::DeErr: Debug,
 {
+    #[track_caller]
     pub fn new_serde_wb<S, Fut>(
         source: impl Fn() -> S + Send + Sync + 'static,
         fetcher: impl Fn(S) -> Fut + Send + Sync + 'static,
@@ -340,6 +345,7 @@ where
     T::SerErr: Debug,
     T::DeErr: Debug,
 {
+    #[track_caller]
     pub fn new_miniserde<S, Fut>(
         source: impl Fn() -> S + Send + Sync + 'static,
         fetcher: impl Fn(S) -> Fut + Send + Sync + 'static,
@@ -360,6 +366,7 @@ where
     T::SerErr: Debug,
     T::DeErr: Debug,
 {
+    #[track_caller]
     pub fn new_serde_lite<S, Fut>(
         source: impl Fn() -> S + Send + Sync + 'static,
         fetcher: impl Fn(S) -> Fut + Send + Sync + 'static,
@@ -380,6 +387,7 @@ where
     T::SerErr: Debug,
     T::DeErr: Debug,
 {
+    #[track_caller]
     pub fn new_rkyv<S, Fut>(
         source: impl Fn() -> S + Send + Sync + 'static,
         fetcher: impl Fn(S) -> Fut + Send + Sync + 'static,
@@ -400,6 +408,7 @@ where
     T::SerErr: Debug,
     T::DeErr: Debug,
 {
+    #[track_caller]
     pub fn new_with_encoding<S, Fut>(
         source: impl Fn() -> S + Send + Sync + 'static,
         fetcher: impl Fn(S) -> Fut + Send + Sync + 'static,
@@ -425,6 +434,7 @@ where
     type Output = T;
     type IntoFuture = AsyncDerivedFuture<T>;
 
+    #[track_caller]
     fn into_future(self) -> Self::IntoFuture {
         self.data.into_future()
     }

reactive_graph/src/computed/async_derived/future_impls.rs

@@ -1,10 +1,12 @@
-use super::{ArcAsyncDerived, AsyncState};
+use super::{ArcAsyncDerived, AsyncDerived, AsyncState};
 use crate::{
     graph::{AnySource, ToAnySource},
     signal::guards::Plain,
-    traits::Track,
+    traits::{DefinedAt, Track},
+    unwrap_signal,
 };
 use or_poisoned::OrPoisoned;
+use pin_project_lite::pin_project;
 use std::{
     future::{Future, IntoFuture},
     pin::Pin,
@@ -14,13 +16,13 @@ use std::{
 
 /// A [`Future`] that is ready when an [`ArcAsyncDerived`] is finished loading or reloading,
 /// but does not contain its value.
-pub struct AsyncDerivedReadyFuture<T> {
+pub struct ArcAsyncDerivedReadyFuture<T> {
     pub(crate) source: AnySource,
     pub(crate) value: Arc<RwLock<AsyncState<T>>>,
     pub(crate) wakers: Arc<RwLock<Vec<Waker>>>,
 }
 
-impl<T: 'static> Future for AsyncDerivedReadyFuture<T> {
+impl<T: 'static> Future for ArcAsyncDerivedReadyFuture<T> {
     type Output = ();
 
     fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
@@ -38,7 +40,7 @@ impl<T: 'static> Future for AsyncDerivedReadyFuture<T> {
 
 /// A [`Future`] that is ready when an [`ArcAsyncDerived`] is finished loading or reloading,
 /// and contains its value.
-pub struct AsyncDerivedFuture<T> {
+pub struct ArcAsyncDerivedFuture<T> {
     source: AnySource,
     value: Arc<RwLock<AsyncState<T>>>,
     wakers: Arc<RwLock<Vec<Waker>>>,
@@ -49,10 +51,10 @@ where
     T: Clone + 'static,
 {
     type Output = T;
-    type IntoFuture = AsyncDerivedFuture<T>;
+    type IntoFuture = ArcAsyncDerivedFuture<T>;
 
     fn into_future(self) -> Self::IntoFuture {
-        AsyncDerivedFuture {
+        ArcAsyncDerivedFuture {
             source: self.to_any_source(),
             value: Arc::clone(&self.value),
             wakers: Arc::clone(&self.wakers),
@@ -62,7 +64,7 @@ where
 
 // this is implemented to output T by cloning it because read guards should not be held across
 // .await points, and it's way too easy to trip up by doing that!
-impl<T> Future for AsyncDerivedFuture<T>
+impl<T> Future for ArcAsyncDerivedFuture<T>
 where
     T: Clone + 'static,
 {
@@ -82,3 +84,52 @@ where
         }
     }
 }
+
+pin_project! {
+    /// A [`Future`] that is ready when an [`AsyncDerived`] is finished loading or reloading,
+    /// and contains its value.
+    pub struct AsyncDerivedFuture<T> {
+        this: AsyncDerived<T>,
+        #[pin]
+        inner: Option<ArcAsyncDerivedFuture<T>>,
+    }
+}
+
+impl<T> IntoFuture for AsyncDerived<T>
+where
+    T: Send + Sync + Clone + 'static,
+{
+    type Output = T;
+    type IntoFuture = AsyncDerivedFuture<T>;
+
+    fn into_future(self) -> Self::IntoFuture {
+        AsyncDerivedFuture {
+            this: self,
+            inner: None,
+        }
+    }
+}
+
+// this is implemented to output T by cloning it because read guards should not be held across
+// .await points, and it's way too easy to trip up by doing that!
+impl<T> Future for AsyncDerivedFuture<T>
+where
+    T: Send + Sync + Clone + 'static,
+{
+    type Output = T;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let mut this = self.project();
+        if this.inner.is_none() {
+            let stored = *this.this;
+            this.inner.set(Some(
+                stored
+                    .inner
+                    .get()
+                    .unwrap_or_else(unwrap_signal!(stored))
+                    .into_future(),
+            ));
+        }
+        this.inner.as_pin_mut().unwrap().poll(cx)
+    }
+}