fix: invalidate `@const` tags based on visible references in legacy mode (#18041)

closes #17992

.changeset/const-tags.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: invalidate `@const` tags based on visible references in legacy mode

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);
 			}
 		}

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>
+			`
+		);
+	}
+});

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}