From ebbb5dd65556101a0be19c78344447039eaa0263 Mon Sep 17 00:00:00 2001
From: Dominic Gannaway <trueadm@users.noreply.github.com>
Date: Mon, 8 Jan 2024 12:59:12 +0000
Subject: [PATCH] fix: improve internal signal dependency checking logic
 (#10111)

---
 .changeset/olive-kangaroos-brake.md           |  5 +++++
 .../svelte/src/internal/client/runtime.js     | 14 ++++++++----
 .../samples/each-updates/_config.js           |  2 +-
 .../samples/text-effect-multi-deps/_config.js | 22 +++++++++++++++++++
 .../text-effect-multi-deps/main.svelte        | 12 ++++++++++
 5 files changed, 50 insertions(+), 5 deletions(-)
 create mode 100644 .changeset/olive-kangaroos-brake.md
 create mode 100644 packages/svelte/tests/runtime-runes/samples/text-effect-multi-deps/_config.js
 create mode 100644 packages/svelte/tests/runtime-runes/samples/text-effect-multi-deps/main.svelte

diff --git a/.changeset/olive-kangaroos-brake.md b/.changeset/olive-kangaroos-brake.md
new file mode 100644
index 0000000000..68f3d40704
--- /dev/null
+++ b/.changeset/olive-kangaroos-brake.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: improve internal signal dependency checking logic
diff --git a/packages/svelte/src/internal/client/runtime.js b/packages/svelte/src/internal/client/runtime.js
index 946a6c3196..1e5301a970 100644
--- a/packages/svelte/src/internal/client/runtime.js
+++ b/packages/svelte/src/internal/client/runtime.js
@@ -349,15 +349,21 @@ function execute_signal_fn(signal) {
 		if (current_dependencies !== null) {
 			let i;
 			if (dependencies !== null) {
-				const dep_length = dependencies.length;
+				// Include any dependencies up until the current_dependencies_index.
+				const full_dependencies =
+					current_dependencies_index === 0
+						? dependencies
+						: dependencies.slice(0, current_dependencies_index).concat(current_dependencies);
+				const dep_length = full_dependencies.length;
 				// If we have more than 16 elements in the array then use a Set for faster performance
 				// TODO: evaluate if we should always just use a Set or not here?
-				const current_dependencies_set = dep_length > 16 ? new Set(current_dependencies) : null;
+				const current_dependencies_set = dep_length > 16 ? new Set(full_dependencies) : null;
+
 				for (i = current_dependencies_index; i < dep_length; i++) {
-					const dependency = dependencies[i];
+					const dependency = full_dependencies[i];
 					if (
 						(current_dependencies_set !== null && !current_dependencies_set.has(dependency)) ||
-						!current_dependencies.includes(dependency)
+						!full_dependencies.includes(dependency)
 					) {
 						remove_consumer(signal, dependency, false);
 					}
diff --git a/packages/svelte/tests/runtime-runes/samples/each-updates/_config.js b/packages/svelte/tests/runtime-runes/samples/each-updates/_config.js
index a6cdafd20f..13b0b4aed7 100644
--- a/packages/svelte/tests/runtime-runes/samples/each-updates/_config.js
+++ b/packages/svelte/tests/runtime-runes/samples/each-updates/_config.js
@@ -33,7 +33,7 @@ export default test({
 
 		assert.htmlEqual(
 			target.innerHTML,
-			`<p>test costs $1</p><p>test 2 costs $2000</p><p>test costs $1</p><p>test 2 costs $2000</p><button>add</button><button>change</button><button>reload</button>`
+			`<p>test costs $1</p><p>test 2 costs $2</p><p>test costs $1</p><p>test 2 costs $2</p><button>add</button><button>change</button><button>reload</button>`
 		);
 	}
 });
diff --git a/packages/svelte/tests/runtime-runes/samples/text-effect-multi-deps/_config.js b/packages/svelte/tests/runtime-runes/samples/text-effect-multi-deps/_config.js
new file mode 100644
index 0000000000..7dba287f5a
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/text-effect-multi-deps/_config.js
@@ -0,0 +1,22 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `<p>0 - 0</p><button>+</button`,
+
+	async test({ assert, target }) {
+		const [btn1] = target.querySelectorAll('button');
+
+		flushSync(() => {
+			btn1.click();
+		});
+
+		assert.htmlEqual(target.innerHTML, `<p>1 - 1</p><button>+</button`);
+
+		flushSync(() => {
+			btn1.click();
+		});
+
+		assert.htmlEqual(target.innerHTML, `<p>2 - 2</p><button>+</button`);
+	}
+});
diff --git a/packages/svelte/tests/runtime-runes/samples/text-effect-multi-deps/main.svelte b/packages/svelte/tests/runtime-runes/samples/text-effect-multi-deps/main.svelte
new file mode 100644
index 0000000000..6550153736
--- /dev/null
+++ b/packages/svelte/tests/runtime-runes/samples/text-effect-multi-deps/main.svelte
@@ -0,0 +1,12 @@
+<script>
+	let x = $state({a: 0, b:0});
+	let count = 0;
+</script>
+
+<p>{x.a} - {x.b}</p>
+
+<button onclick={() => {
+	const a = ++count;
+	x = {a, b: a};
+}}>+</button>
+