fix: error for rune usage in {@const} tag initialization

.changeset/polite-mirrors-arrive.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: error for rune usage in {@const} tag initialization

documentation/docs/98-reference/.generated/compile-errors.md

@@ -190,6 +190,12 @@ Cyclical dependency detected: %cycle%
 `{@const}` must be the immediate child of `{#snippet}`, `{#if}`, `{:else if}`, `{:else}`, `{#each}`, `{:then}`, `{:catch}`, `<svelte:fragment>`, `<svelte:boundary` or `<Component>`
 ```
 
+### const_tag_invalid_rune_usage
+
+```
+Can't use %name% as initialization of a `{@const}` tag
+```
+
 ### constant_assignment
 
 ```

packages/svelte/messages/compile-errors/template.md

@@ -120,6 +120,10 @@
 
 > `{@const}` must be the immediate child of `{#snippet}`, `{#if}`, `{:else if}`, `{:else}`, `{#each}`, `{:then}`, `{:catch}`, `<svelte:fragment>`, `<svelte:boundary` or `<Component>`
 
+## const_tag_invalid_rune_usage
+
+> Can't use %name% as initialization of a `{@const}` tag
+
 ## debug_tag_invalid_arguments
 
 > {@debug ...} arguments must be identifiers, not arbitrary expressions

packages/svelte/src/compiler/errors.js

@@ -896,6 +896,16 @@ export function const_tag_invalid_placement(node) {
 	e(node, 'const_tag_invalid_placement', `\`{@const}\` must be the immediate child of \`{#snippet}\`, \`{#if}\`, \`{:else if}\`, \`{:else}\`, \`{#each}\`, \`{:then}\`, \`{:catch}\`, \`<svelte:fragment>\`, \`<svelte:boundary\` or \`<Component>\`\nhttps://svelte.dev/e/const_tag_invalid_placement`);
 }
 
+/**
+ * Can't use %name% as initialization of a `{@const}` tag
+ * @param {null | number | NodeLike} node
+ * @param {string} name
+ * @returns {never}
+ */
+export function const_tag_invalid_rune_usage(node, name) {
+	e(node, 'const_tag_invalid_rune_usage', `Can't use ${name} as initialization of a \`{@const}\` tag\nhttps://svelte.dev/e/const_tag_invalid_rune_usage`);
+}
+
 /**
  * {@debug ...} arguments must be identifiers, not arbitrary expressions
  * @param {null | number | NodeLike} node

packages/svelte/src/compiler/phases/2-analyze/visitors/ConstTag.js

@@ -1,6 +1,7 @@
 /** @import { AST } from '#compiler' */
 /** @import { Context } from '../types' */
 import * as e from '../../../errors.js';
+import { get_rune } from '../../scope.js';
 import { validate_opening_tag } from './shared/utils.js';
 
 /**
@@ -12,6 +13,13 @@ export function ConstTag(node, context) {
 		validate_opening_tag(node, context.state, '@');
 	}
 
+	for (let declaration of node.declaration.declarations) {
+		const rune = get_rune(declaration.init, context.state.scope);
+		if (rune) {
+			e.const_tag_invalid_rune_usage(declaration.init, rune);
+		}
+	}
+
 	const parent = context.path.at(-1);
 	const grand_parent = context.path.at(-2);
 

packages/svelte/tests/validator/samples/const-tag-invalid-rune-usage/errors.json

@@ -0,0 +1,14 @@
+[
+	{
+		"code": "const_tag_invalid_rune_usage",
+		"message": "Can't use $derived as initialization of a `{@const}` tag",
+		"start": {
+			"line": 2,
+			"column": 15
+		},
+		"end": {
+			"line": 2,
+			"column": 26
+		}
+	}
+]

packages/svelte/tests/validator/samples/const-tag-invalid-rune-usage/input.svelte

@@ -0,0 +1,3 @@
+{#snippet test()}
+	{@const der = $derived(0)}
+{/snippet}