docs: give a warning when you try to .dispatch() an action immediately (closes #2225)

leptos_reactive/src/lib.rs

@@ -125,7 +125,7 @@ use runtime::*;
 pub use runtime::{
     as_child_of_current_owner, batch, create_runtime, current_runtime,
     on_cleanup, run_as_child, set_current_runtime,
-    spawn_local_with_current_owner, spawn_local_with_owner,
+    spawn_local_with_current_owner, spawn_local_with_owner, try_batch,
     try_spawn_local_with_current_owner, try_spawn_local_with_owner,
     try_with_owner, untrack, untrack_with_diagnostics, with_current_owner,
     with_owner, Owner, RuntimeId, ScopedFuture,
@@ -143,7 +143,8 @@ pub use suspense::{GlobalSuspenseContext, SuspenseContext};
 pub use trigger::*;
 pub use watch::*;
 
-pub(crate) fn console_warn(s: &str) {
+#[doc(hidden)]
+pub fn console_warn(s: &str) {
     cfg_if::cfg_if! {
         if #[cfg(all(target_arch = "wasm32", any(feature = "csr", feature = "hydrate")))] {
             web_sys::console::warn_1(&wasm_bindgen::JsValue::from_str(s));

leptos_reactive/src/runtime.rs

@@ -1397,12 +1397,30 @@ impl Drop for SetObserverOnDrop {
 ///
 /// # Panics
 /// Panics if the runtime has already been disposed.
+///
+/// To avoid panicking under any circumstances, use [`try_batch`].
 #[cfg_attr(
     any(debug_assertions, features = "ssr"),
     instrument(level = "trace", skip_all,)
 )]
 #[inline(always)]
 pub fn batch<T>(f: impl FnOnce() -> T) -> T {
+    try_batch(f).expect(
+        "tried to run a batched update in a runtime that has been disposed",
+    )
+}
+
+/// Attempts to batch any reactive updates, preventing effects from running until the whole
+/// function has run. This allows you to prevent rerunning effects if multiple
+/// signal updates might cause the same effect to run.
+///
+/// Unlike [`batch`], this will not panic if the runtime has been disposed.
+#[cfg_attr(
+    any(debug_assertions, features = "ssr"),
+    instrument(level = "trace", skip_all,)
+)]
+#[inline(always)]
+pub fn try_batch<T>(f: impl FnOnce() -> T) -> Result<T, ReactiveSystemError> {
     with_runtime(move |runtime| {
         let batching = SetBatchingOnDrop(runtime.batching.get());
         runtime.batching.set(true);
@@ -1415,7 +1433,6 @@ pub fn batch<T>(f: impl FnOnce() -> T) -> T {
         runtime.run_effects();
         val
     })
-    .expect("tried to run a batched update in a runtime that has been disposed")
 }
 
 struct SetBatchingOnDrop(bool);

leptos_server/src/action.rs

@@ -1,7 +1,10 @@
 //use crate::{ServerFn, ServerFnError};
+#[cfg(debug_assertions)]
+use leptos_reactive::console_warn;
 use leptos_reactive::{
-    batch, create_rw_signal, is_suppressing_resource_load, signal_prelude::*,
-    spawn_local, store_value, use_context, ReadSignal, RwSignal, StoredValue,
+    create_rw_signal, is_suppressing_resource_load, signal_prelude::*,
+    spawn_local, store_value, try_batch, use_context, ReadSignal, RwSignal,
+    StoredValue,
 };
 use server_fn::{error::ServerFnUrlError, ServerFn, ServerFnError};
 use std::{cell::Cell, future::Future, pin::Pin, rc::Rc};
@@ -93,8 +96,18 @@ where
         any(debug_assertions, feature = "ssr"),
         tracing::instrument(level = "trace", skip_all,)
     )]
+    #[track_caller]
     pub fn dispatch(&self, input: I) {
-        self.0.with_value(|a| a.dispatch(input))
+        #[cfg(debug_assertions)]
+        let loc = std::panic::Location::caller();
+
+        self.0.with_value(|a| {
+            a.dispatch(
+                input,
+                #[cfg(debug_assertions)]
+                loc,
+            )
+        })
     }
 
     /// Create an [Action].
@@ -366,7 +379,11 @@ where
         any(debug_assertions, feature = "ssr"),
         tracing::instrument(level = "trace", skip_all,)
     )]
-    pub fn dispatch(&self, input: I) {
+    pub fn dispatch(
+        &self,
+        input: I,
+        #[cfg(debug_assertions)] loc: &'static std::panic::Location<'static>,
+    ) {
         if !is_suppressing_resource_load() {
             let fut = (self.action_fn)(&input);
             self.input.set(Some(input));
@@ -379,7 +396,7 @@ where
             pending_dispatches.set(pending_dispatches.get().saturating_sub(1));
             spawn_local(async move {
                 let new_value = fut.await;
-                batch(move || {
+                let res = try_batch(move || {
                     value.set(Some(new_value));
                     input.set(None);
                     version.update(|n| *n += 1);
@@ -389,6 +406,18 @@ where
                         pending.set(false);
                     }
                 });
+
+                if res.is_err() {
+                    #[cfg(debug_assertions)]
+                    console_warn(&format!(
+                        "At {loc}, you are dispatching an action in a runtime \
+                         that has already been disposed. This may be because \
+                         you are calling `.dispatch()` in the body of a \
+                         component, during initial server-side rendering. If \
+                         that's the case, you should probably be using \
+                         `create_resource` instead of `create_action`."
+                    ));
+                }
             })
         }
     }