fix: memoize Suspense readiness to avoid rerendering children/fallback

leptos/src/suspense_component.rs

@@ -1,5 +1,7 @@
 use leptos_dom::{DynChild, HydrationCtx, IntoView};
 use leptos_macro::component;
+#[cfg(any(feature = "csr", feature = "hydrate"))]
+use leptos_reactive::SignalGet;
 use leptos_reactive::{
     create_memo, provide_context, SignalGetUntracked, SuspenseContext,
 };
@@ -93,14 +95,17 @@ where
 
     let current_id = HydrationCtx::next_component();
 
+    #[cfg(any(feature = "csr", feature = "hydrate"))]
+    let ready = context.ready();
+
     let child = DynChild::new({
         move || {
             // pull lazy memo before checking if context is ready
             let children_rendered = children.get_untracked();
 
             #[cfg(any(feature = "csr", feature = "hydrate"))]
             {
-                if context.ready() {
+                if ready.get() {
                     children_rendered
                 } else {
                     fallback.get_untracked()

leptos/src/transition.rs

@@ -99,7 +99,9 @@ where
                         cfg!(feature = "csr") && first_run.get();
                     let is_first_run =
                         is_first_run(first_run, &suspense_context);
-                    first_run.set(false);
+                    if was_first_run {
+                        first_run.set(false)
+                    }
 
                     if let Some(prev_children) = &*prev_child.borrow() {
                         if is_first_run || was_first_run {

leptos_reactive/src/suspense.rs

@@ -1,9 +1,9 @@
 //! Types that handle asynchronous data loading via `<Suspense/>`.
 
 use crate::{
-    create_isomorphic_effect, create_rw_signal, create_signal, oco::Oco,
-    queue_microtask, signal::SignalGet, store_value, ReadSignal, RwSignal,
-    SignalSet, SignalUpdate, StoredValue, WriteSignal,
+    create_isomorphic_effect, create_memo, create_rw_signal, create_signal,
+    oco::Oco, queue_microtask, signal::SignalGet, store_value, Memo,
+    ReadSignal, RwSignal, SignalSet, SignalUpdate, StoredValue, WriteSignal,
 };
 use futures::Future;
 use std::{cell::RefCell, collections::VecDeque, pin::Pin, rc::Rc};
@@ -154,10 +154,9 @@ impl SuspenseContext {
     }
 
     /// Tests whether all of the pending resources have resolved.
-    pub fn ready(&self) -> bool {
-        self.pending_resources
-            .try_with(|n| *n == 0)
-            .unwrap_or(false)
+    pub fn ready(&self) -> Memo<bool> {
+        let pending = self.pending_resources;
+        create_memo(move |_| pending.try_with(|n| *n == 0).unwrap_or(false))
     }
 }
 

router/src/components/outlet.rs

@@ -72,7 +72,7 @@ pub fn Outlet() -> impl IntoView {
                 move |prev| {
                     let outlet = outlet.get();
                     let is_fallback =
-                        !global_suspense.with_inner(SuspenseContext::ready);
+                        !global_suspense.with_inner(|c| c.ready().get());
                     if prev.is_none() {
                         set_current_view.set(outlet);
                     } else if !is_fallback {
@@ -81,7 +81,7 @@ pub fn Outlet() -> impl IntoView {
                             move || {
                                 let is_fallback = untrack(move || {
                                     !global_suspense
-                                        .with_inner(SuspenseContext::ready)
+                                        .with_inner(|c| c.ready().get())
                                 });
                                 if !is_fallback {
                                     set_current_view.set(outlet);

router/src/components/routes.rs

@@ -451,16 +451,15 @@ fn root_route(
 
         create_effect(move |prev| {
             let root = root_view.get();
-            let is_fallback =
-                !global_suspense.with_inner(SuspenseContext::ready);
+            let is_fallback = !global_suspense.with_inner(|c| c.ready().get());
             if prev.is_none() {
                 set_current_view.set(root);
             } else if !is_fallback {
                 queue_microtask({
                     let global_suspense = global_suspense.clone();
                     move || {
                         let is_fallback = untrack(move || {
-                            !global_suspense.with_inner(SuspenseContext::ready)
+                            !global_suspense.with_inner(|c| c.ready().get())
                         });
                         if !is_fallback {
                             set_current_view.set(root);