From 41cdbafc40caf21083a40bf86aeadaefab3771b1 Mon Sep 17 00:00:00 2001
From: Dominic Gannaway <trueadm@users.noreply.github.com>
Date: Mon, 19 Feb 2024 12:24:35 +0000
Subject: [PATCH] fix: improve effect over-fire on store subscription init
 (#10535)

---
 .changeset/cool-roses-trade.md                |  5 +++++
 .../svelte/src/internal/client/runtime.js     |  3 +++
 .../store-subscribe-effect-init/_config.js    | 22 +++++++++++++++++++
 .../store-subscribe-effect-init/log.js        |  2 ++
 .../store-subscribe-effect-init/main.svelte   | 18 +++++++++++++++
 5 files changed, 50 insertions(+)
 create mode 100644 .changeset/cool-roses-trade.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/store-subscribe-effect-init/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/store-subscribe-effect-init/log.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/store-subscribe-effect-init/main.svelte

diff --git a/.changeset/cool-roses-trade.md b/.changeset/cool-roses-trade.md
new file mode 100644
index 0000000000..ae05a8f8b4
--- /dev/null
+++ b/.changeset/cool-roses-trade.md
@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+fix: improve effect over-fire on store subscription init
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index dbcffed933..8db5cfa54f 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -1210,8 +1210,11 @@ export function set_signal_value(signal, value) {
 		//
 		// $effect(() => x++)
 		//
+		// We additionally want to skip this logic for when ignore_mutation_validation is
+		// true, as stores write to source signal on initialization.
 		if (
 			is_runes(null) &&
+			!ignore_mutation_validation &&
 			current_effect !== null &&
 			current_effect.c === null &&
 			(current_effect.f & CLEAN) !== 0
diff --git a/packages/svelte/tests/runtime-runes/samples/store-subscribe-effect-init/_config.js b/packages/svelte/tests/runtime-runes/samples/store-subscribe-effect-init/_config.js
new file mode 100644
index 0000000000..13ada44925
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/store-subscribe-effect-init/_config.js
@@ -0,0 +1,22 @@
+import { test } from '../../test';
+import { log } from './log.js';
+
+export default test({
+	html: `<button>increment</button>`,
+
+	before_test() {
+		log.length = 0;
+	},
+
+	async test({ assert, target }) {
+		const btn = target.querySelector('button');
+
+		assert.deepEqual(log, [1]);
+
+		await btn?.click();
+		assert.deepEqual(log, [1, 2]);
+
+		await btn?.click();
+		assert.deepEqual(log, [1, 2, 3]);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/store-subscribe-effect-init/log.js b/packages/svelte/tests/runtime-runes/samples/store-subscribe-effect-init/log.js
new file mode 100644
index 0000000000..d3df521f4d
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/store-subscribe-effect-init/log.js
@@ -0,0 +1,2 @@
+/** @type {any[]} */
+export const log = [];
diff --git a/packages/svelte/tests/runtime-runes/samples/store-subscribe-effect-init/main.svelte b/packages/svelte/tests/runtime-runes/samples/store-subscribe-effect-init/main.svelte
new file mode 100644
index 0000000000..27c07d779c
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/store-subscribe-effect-init/main.svelte
@@ -0,0 +1,18 @@
+<script>
+	import { untrack } from 'svelte';
+	import { writable } from 'svelte/store';
+	import { log } from './log';
+
+	const storeCount = writable(0)
+	let count = $state(0);
+
+	$effect(() => {
+		$storeCount;
+		untrack(() => {
+			count++;
+			log.push(count);
+		});
+	});
+</script>
+
+<button on:click={() => $storeCount++}>increment</button>