From 6979d476e5d51b6be13ad9d6483569f66ef7c3cb Mon Sep 17 00:00:00 2001
From: Dominic Gannaway <trueadm@users.noreply.github.com>
Date: Thu, 16 Jan 2025 11:49:02 +0000
Subject: [PATCH] wip

---
 .../src/internal/client/dom/blocks/boundary.js    | 15 +++++++++------
 packages/svelte/src/internal/client/runtime.js    |  5 ++++-
 2 files changed, 13 insertions(+), 7 deletions(-)

diff --git a/packages/svelte/src/internal/client/dom/blocks/boundary.js b/packages/svelte/src/internal/client/dom/blocks/boundary.js
index 87070fa65e..c5043559c8 100644
--- a/packages/svelte/src/internal/client/dom/blocks/boundary.js
+++ b/packages/svelte/src/internal/client/dom/blocks/boundary.js
@@ -1,7 +1,7 @@
 /** @import { Effect, Source, TemplateNode, } from '#client' */
 
 import { UNINITIALIZED } from '../../../../constants.js';
-import { AWAIT_EFFECT, BOUNDARY_EFFECT, EFFECT_TRANSPARENT, PENDING } from '../../constants.js';
+import { AWAIT_EFFECT, BOUNDARY_EFFECT, EFFECT_TRANSPARENT, INERT, PENDING } from '../../constants.js';
 import { derived } from '../../reactivity/deriveds.js';
 import {
 	block,
@@ -254,8 +254,11 @@ export function trigger_async_boundary(effect, trigger) {
  */
 export function await_derived(fn) {
 	var current = active_effect;
-	/** @type {Source<V | typeof PENDING>} */
-	var value = source(PENDING);
+	/** @type {Source<V | typeof UNINITIALIZED>} */
+	var value = source(UNINITIALIZED);
+	// We mark the source signal as inert as it's value
+	// can throw if in an async pending state
+	value.f ^= INERT;
 	/** @type {Promise<V> | typeof UNINITIALIZED} */
 	var previous_promise = UNINITIALIZED;
 	var derived_promise = derived(fn);
@@ -276,9 +279,6 @@ export function await_derived(fn) {
 
 		if (should_suspend) {
 			set_is_within_await(true);
-			untrack(() => {
-				set(value, PENDING);
-			});
 			trigger_async_boundary(current, ASYNC_INCREMENT);
 
 			// If we're updating, then we need to flush the boundary microtasks
@@ -287,6 +287,9 @@ export function await_derived(fn) {
 			}
 
 			promise.then((v) => {
+				if (previous_promise !== promise) {
+					return;
+				}
 				set(value, v);
 				trigger_async_boundary(current, ASYNC_DECREMENT);
 			});
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 03bbe34625..4f7457376e 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -1035,7 +1035,10 @@ export function get(signal) {
 
 	value = signal.v;
 
-	if (value === PENDING) {
+	if (
+		(flags & INERT) !== 0 &&
+		(is_within_await || (active_effect !== null && (active_effect.f & INERT) !== 0))
+	) {
 		throw PENDING;
 	}