chore: unify async logic (#17731)

We have a bunch of repeated logic around incrementing/decrementing
pending states. This DRYs it out to unblock some forthcoming changes
around scheduling

packages/svelte/src/internal/client/dom/blocks/async.js

@@ -1,6 +1,5 @@
 /** @import { Blocker, TemplateNode, Value } from '#client' */
-import { flatten } from '../../reactivity/async.js';
+import { flatten, increment_pending } from '../../reactivity/async.js';
-import { Batch, current_batch } from '../../reactivity/batch.js';
 import { get } from '../../runtime.js';
 import {
 	hydrate_next,
@@ -10,7 +9,6 @@ import {
 	set_hydrating,
 	skip_nodes
 } from '../hydration.js';
-import { get_boundary } from './boundary.js';
 
 /**
  * @param {TemplateNode} node
@@ -44,12 +42,7 @@ export function async(node, blockers = [], expressions = [], fn) {
 		return;
 	}
 
-	var boundary = get_boundary();
+	const decrement_pending = increment_pending();
-	var batch = /** @type {Batch} */ (current_batch);
-	var blocking = boundary.is_rendered();
-
-	boundary.update_pending_count(1);
-	batch.increment(blocking);
 
 	if (was_hydrating) {
 		var previous_hydrate_node = hydrate_node;
@@ -72,8 +65,7 @@ export function async(node, blockers = [], expressions = [], fn) {
 				set_hydrating(false);
 			}
 
-			boundary.update_pending_count(-1);
+			decrement_pending();
-			batch.decrement(blocking);
 		}
 	});
 }

packages/svelte/src/internal/client/dom/blocks/boundary.js

@@ -452,10 +452,6 @@ export class Boundary {
 	}
 }
 
-export function get_boundary() {
-	return /** @type {Boundary} */ (/** @type {Effect} */ (active_effect).b);
-}
-
 export function pending() {
 	if (active_effect === null) {
 		e.effect_pending_outside_reaction();

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

@@ -8,7 +8,7 @@ import {
 	set_component_context,
 	set_dev_stack
 } from '../context.js';
-import { get_boundary } from '../dom/blocks/boundary.js';
+import { Boundary } from '../dom/blocks/boundary.js';
 import { invoke_error_boundary } from '../error-handling.js';
 import {
 	active_effect,
@@ -224,12 +224,7 @@ export function unset_context() {
 export function run(thunks) {
 	const restore = capture();
 
-	var boundary = get_boundary();
+	const decrement_pending = increment_pending();
-	var batch = /** @type {Batch} */ (current_batch);
-	var blocking = boundary.is_rendered();
-
-	boundary.update_pending_count(1);
-	batch.increment(blocking);
 
 	var active = /** @type {Effect} */ (active_effect);
 
@@ -286,10 +281,7 @@ export function run(thunks) {
 		// wait one more tick, so that template effects are
 		// guaranteed to run before `$effect(...)`
 		.then(() => Promise.resolve())
-		.finally(() => {
+		.finally(decrement_pending);
-			boundary.update_pending_count(-1);
-			batch.decrement(blocking);
-		});
 
 	return blockers;
 }
@@ -300,3 +292,17 @@ export function run(thunks) {
 export function wait(blockers) {
 	return Promise.all(blockers.map((b) => b.promise));
 }
+
+export function increment_pending() {
+	var boundary = /** @type {Boundary} */ (/** @type {Effect} */ (active_effect).b);
+	var batch = /** @type {Batch} */ (current_batch);
+	var blocking = boundary.is_rendered();
+
+	boundary.update_pending_count(1);
+	batch.increment(blocking);
+
+	return () => {
+		boundary.update_pending_count(-1);
+		batch.decrement(blocking);
+	};
+}

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

@@ -40,7 +40,7 @@ import { Boundary } from '../dom/blocks/boundary.js';
 import { component_context } from '../context.js';
 import { UNINITIALIZED } from '../../../constants.js';
 import { batch_values, current_batch } from './batch.js';
-import { unset_context } from './async.js';
+import { increment_pending, unset_context } from './async.js';
 import { deferred, includes, noop } from '../../shared/utils.js';
 import { set_signal_status, update_derived_status } from './status.js';
 
@@ -111,8 +111,6 @@ export function async_derived(fn, label, location) {
 		e.async_derived_orphan();
 	}
 
-	var boundary = /** @type {Boundary} */ (parent.b);
-
 	var promise = /** @type {Promise<V>} */ (/** @type {unknown} */ (undefined));
 	var signal = source(/** @type {V} */ (UNINITIALIZED));
 
@@ -156,10 +154,7 @@ export function async_derived(fn, label, location) {
 		var batch = /** @type {Batch} */ (current_batch);
 
 		if (should_suspend) {
-			var blocking = boundary.is_rendered();
+			var decrement_pending = increment_pending();
-
-			boundary.update_pending_count(1);
-			batch.increment(blocking);
 
 			deferreds.get(batch)?.reject(STALE_REACTION);
 			deferreds.delete(batch); // delete to ensure correct order in Map iteration below
@@ -208,9 +203,8 @@ export function async_derived(fn, label, location) {
 				}
 			}
 
-			if (should_suspend) {
+			if (decrement_pending) {
-				boundary.update_pending_count(-1);
+				decrement_pending();
-				batch.decrement(blocking);
 			}
 		};
 

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

@@ -40,8 +40,8 @@ import { DEV } from 'esm-env';
 import { define_property } from '../../shared/utils.js';
 import { get_next_sibling } from '../dom/operations.js';
 import { component_context, dev_current_component_function, dev_stack } from '../context.js';
-import { Batch, current_batch, schedule_effect } from './batch.js';
+import { Batch, schedule_effect } from './batch.js';
-import { flatten } from './async.js';
+import { flatten, increment_pending } from './async.js';
 import { without_reactive_context } from '../dom/elements/bindings/shared.js';
 import { set_signal_status } from './status.js';
 
@@ -376,14 +376,16 @@ export function template_effect(fn, sync = [], async = [], blockers = []) {
  * @param {Blocker[]} blockers
  */
 export function deferred_template_effect(fn, sync = [], async = [], blockers = []) {
-	var batch = /** @type {Batch} */ (current_batch);
+	if (async.length > 0 || blockers.length > 0) {
-	var is_async = async.length > 0 || blockers.length > 0;
+		var decrement_pending = increment_pending();
-
+	}
-	if (is_async) batch.increment(true);
 
 	flatten(blockers, sync, async, (values) => {
 		create_effect(EFFECT, () => fn(...values.map(get)), false);
-		if (is_async) batch.decrement(true);
+
+		if (decrement_pending) {
+			decrement_pending();
+		}
 	});
 }