create separate effect type for async deriveds, as they are not blocks

packages/svelte/src/internal/client/constants.js

@@ -23,6 +23,7 @@ export const EFFECT_PRESERVED = 1 << 21; // effects with this flag should not be
 
 // Flags used for async
 export const REACTION_IS_UPDATING = 1 << 22;
+export const EFFECT_ASYNC = 1 << 23;
 
 export const STATE_SYMBOL = Symbol('$state');
 export const STATE_SYMBOL_METADATA = Symbol('$state metadata');

packages/svelte/src/internal/client/dev/debug.js

@@ -7,6 +7,7 @@ import {
 	CLEAN,
 	DERIVED,
 	EFFECT,
+	EFFECT_ASYNC,
 	MAYBE_DIRTY,
 	RENDER_EFFECT,
 	ROOT_EFFECT
@@ -39,6 +40,8 @@ export function log_effect_tree(effect) {
 		label = 'boundary';
 	} else if ((flags & BLOCK_EFFECT) !== 0) {
 		label = 'block';
+	} else if ((flags & EFFECT_ASYNC) !== 0) {
+		label = 'async';
 	} else if ((flags & BRANCH_EFFECT) !== 0) {
 		label = 'branch';
 	} else if ((flags & RENDER_EFFECT) !== 0) {

packages/svelte/src/internal/client/reactivity/deriveds.js

@@ -5,6 +5,7 @@ import {
 	DERIVED,
 	DESTROYED,
 	DIRTY,
+	EFFECT_ASYNC,
 	EFFECT_PRESERVED,
 	MAYBE_DIRTY,
 	UNOWNED
@@ -22,7 +23,7 @@ import {
 import { equals, safe_equals } from './equality.js';
 import * as e from '../errors.js';
 import * as w from '../warnings.js';
-import { block, destroy_effect } from './effects.js';
+import { block, destroy_effect, render_effect } from './effects.js';
 import { inspect_effects, internal_set, set_inspect_effects, source } from './sources.js';
 import { get_stack } from '../dev/tracing.js';
 import { tracing_mode_flag } from '../../flags/index.js';
@@ -107,8 +108,7 @@ export function async_derived(fn, location) {
 	/** @type {(() => void) | null} */
 	var unsuspend = null;
 
-	// TODO this isn't a block
+	render_effect(() => {
-	block(() => {
 		if (DEV) from_async_derived = active_effect;
 		var current = (promise = fn());
 		if (DEV) from_async_derived = null;
@@ -151,7 +151,7 @@ export function async_derived(fn, location) {
 				}
 			}
 		);
-	}, EFFECT_PRESERVED);
+	}, EFFECT_ASYNC | EFFECT_PRESERVED);
 
 	return new Promise(async (fulfil) => {
 		// if the effect re-runs before the initial promise

packages/svelte/src/internal/client/reactivity/effects.js

@@ -335,8 +335,8 @@ export function legacy_pre_effect_reset() {
  * @param {() => void | (() => void)} fn
  * @returns {Effect}
  */
-export function render_effect(fn) {
+export function render_effect(fn, flags = 0) {
-	return create_effect(RENDER_EFFECT, fn, true);
+	return create_effect(RENDER_EFFECT | flags, fn, true);
 }
 
 /**

packages/svelte/src/internal/client/reactivity/sources.js

@@ -28,7 +28,8 @@ import {
 	UNOWNED,
 	MAYBE_DIRTY,
 	BLOCK_EFFECT,
-	ROOT_EFFECT
+	ROOT_EFFECT,
+	EFFECT_ASYNC
 } from '../constants.js';
 import * as e from '../errors.js';
 import { legacy_mode_flag, tracing_mode_flag } from '../../flags/index.js';
@@ -150,7 +151,7 @@ export function set(source, value) {
 		active_reaction !== null &&
 		!untracking &&
 		is_runes() &&
-		(active_reaction.f & (DERIVED | BLOCK_EFFECT)) !== 0 &&
+		(active_reaction.f & (DERIVED | BLOCK_EFFECT | EFFECT_ASYNC)) !== 0 &&
 		// If the source was created locally within the current derived, then
 		// we allow the mutation.
 		(derived_sources === null || !derived_sources.includes(source))

packages/svelte/src/internal/client/runtime.js

@@ -24,7 +24,8 @@ import {
 	LEGACY_DERIVED_PROP,
 	DISCONNECTED,
 	BOUNDARY_EFFECT,
-	REACTION_IS_UPDATING
+	REACTION_IS_UPDATING,
+	EFFECT_ASYNC
 } from './constants.js';
 import {
 	flush_idle_tasks,
@@ -820,7 +821,7 @@ function process_effects(effect, effects = [], boundary) {
 		var sibling = current_effect.next;
 
 		if (!is_skippable_branch && (flags & INERT) === 0) {
-			if (boundary !== undefined && (flags & (BLOCK_EFFECT | BRANCH_EFFECT)) === 0) {
+			if (boundary !== undefined && (flags & (BLOCK_EFFECT | BRANCH_EFFECT | EFFECT_ASYNC)) === 0) {
 				// Inside a boundary, defer everything except block/branch effects
 				boundary.add_effect(current_effect);
 			} else if ((flags & BOUNDARY_EFFECT) !== 0) {