fix: flush batches whenever an async value resolves (#16912)

* fix: flush batches whenever an async value resolves

* move some code around

* unnecessary

Author: Rich-Harris

.changeset/metal-parents-train.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: flush batches whenever an async value resolves

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

@@ -52,8 +52,6 @@ export function flatten(sync, async, fn) {
 
 	Promise.all(async.map((expression) => async_derived(expression)))
 		.then((result) => {
-			batch?.activate();
-
 			restore();
 
 			try {

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

@@ -178,6 +178,8 @@ export class Batch {
 			flush_queued_effects(render_effects);
 			flush_queued_effects(effects);
 
+			previous_batch = null;
+
 			this.#deferred?.resolve();
 		} else {
 			this.#defer_effects(this.#render_effects);
@@ -280,17 +282,6 @@ export class Batch {
 
 	deactivate() {
 		current_batch = null;
-		previous_batch = null;
-
-		for (const update of effect_pending_updates) {
-			effect_pending_updates.delete(update);
-			update();
-
-			if (current_batch !== null) {
-				// only do one at a time
-				break;
-			}
-		}
 	}
 
 	flush() {
@@ -307,6 +298,16 @@ export class Batch {
 		}
 
 		this.deactivate();
+
+		for (const update of effect_pending_updates) {
+			effect_pending_updates.delete(update);
+			update();
+
+			if (current_batch !== null) {
+				// only do one at a time
+				break;
+			}
+		}
 	}
 
 	/**
@@ -375,21 +376,17 @@ export class Batch {
 	decrement() {
 		this.#pending -= 1;
 
-		if (this.#pending === 0) {
-			for (const e of this.#dirty_effects) {
-				set_signal_status(e, DIRTY);
-				schedule_effect(e);
-			}
-
-			for (const e of this.#maybe_dirty_effects) {
-				set_signal_status(e, MAYBE_DIRTY);
-				schedule_effect(e);
-			}
+		for (const e of this.#dirty_effects) {
+			set_signal_status(e, DIRTY);
+			schedule_effect(e);
+		}
 
-			this.flush();
-		} else {
-			this.deactivate();
+		for (const e of this.#maybe_dirty_effects) {
+			set_signal_status(e, MAYBE_DIRTY);
+			schedule_effect(e);
 		}
+
+		this.flush();
 	}
 
 	/** @param {() => void} fn */