From edcbb0e6403e5b90e72c3ef1f46a938a52cc2d53 Mon Sep 17 00:00:00 2001
From: Rich Harris <rich.harris@vercel.com>
Date: Wed, 1 Apr 2026 04:36:26 -0400
Subject: [PATCH] fix: invalidate `@const` tags based on visible references in
 legacy mode (#18041)

closes #17992
---
 .changeset/const-tags.md                      |  5 +++
 .../2-analyze/visitors/shared/function.js     |  2 +-
 .../const-tag-depends-on-const-tag/_config.js | 34 +++++++++++++++++++
 .../main.svelte                               | 15 ++++++++
 4 files changed, 55 insertions(+), 1 deletion(-)
 create mode 100644 .changeset/const-tags.md
 create mode 100644 packages/svelte/tests/runtime-legacy/samples/const-tag-depends-on-const-tag/_config.js
 create mode 100644 packages/svelte/tests/runtime-legacy/samples/const-tag-depends-on-const-tag/main.svelte

diff --git a/.changeset/const-tags.md b/.changeset/const-tags.md
new file mode 100644
index 0000000000..82765c5038
--- /dev/null
+++ b/.changeset/const-tags.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: invalidate `@const` tags based on visible references in legacy mode
diff --git a/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/function.js b/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/function.js
index 4d93cd44e0..7bdb2243f2 100644
--- a/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/function.js
+++ b/packages/svelte/src/compiler/phases/2-analyze/visitors/shared/function.js
@@ -10,7 +10,7 @@ export function visit_function(node, context) {
 		for (const [name] of context.state.scope.references) {
 			const binding = context.state.scope.get(name);
 
-			if (binding && binding.scope.function_depth < context.state.scope.function_depth) {
+			if (binding && binding.scope !== context.state.scope) {
 				context.state.expression.references.add(binding);
 			}
 		}
diff --git a/packages/svelte/tests/runtime-legacy/samples/const-tag-depends-on-const-tag/_config.js b/packages/svelte/tests/runtime-legacy/samples/const-tag-depends-on-const-tag/_config.js
new file mode 100644
index 0000000000..6282d36f75
--- /dev/null
+++ b/packages/svelte/tests/runtime-legacy/samples/const-tag-depends-on-const-tag/_config.js
@@ -0,0 +1,34 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	html: `
+		<input>
+		<p>hello</p>
+		<p>hello</p>
+	`,
+
+	ssrHtml: `
+		<input value="hello">
+		<p>hello</p>
+		<p>hello</p>
+	`,
+
+	async test({ assert, target }) {
+		const [input] = target.querySelectorAll('input');
+
+		flushSync(() => {
+			input.value = 'goodbye';
+			input.dispatchEvent(new InputEvent('input', { bubbles: true }));
+		});
+
+		assert.htmlEqual(
+			target.innerHTML,
+			`
+				<input>
+				<p>goodbye</p>
+				<p>goodbye</p>
+			`
+		);
+	}
+});
diff --git a/packages/svelte/tests/runtime-legacy/samples/const-tag-depends-on-const-tag/main.svelte b/packages/svelte/tests/runtime-legacy/samples/const-tag-depends-on-const-tag/main.svelte
new file mode 100644
index 0000000000..a32010717c
--- /dev/null
+++ b/packages/svelte/tests/runtime-legacy/samples/const-tag-depends-on-const-tag/main.svelte
@@ -0,0 +1,15 @@
+<svelte:options runes={false} />
+
+<script>
+	let message = 'hello';
+</script>
+
+<input bind:value={message} />
+
+{#if true}
+	{@const m1 = message}
+	{@const m2 = (() => m1)()}
+
+	<p>{m1}</p>
+	<p>{m2}</p>
+{/if}