feat: allow every children in `template` tags (#15007)

* feat: allow every children in `template` tags

* Update .changeset/dry-mails-return.md

---------

Co-authored-by: Rich Harris <rich.harris@vercel.com>

.changeset/dry-mails-return.md

@@ -0,0 +1,5 @@
+---
+'svelte': minor
+---
+
+feat: allow `<template>` elements to contain any child

packages/svelte/src/html-tree-validation.js

@@ -186,6 +186,8 @@ export function is_tag_valid_with_ancestor(child_tag, ancestors, child_loc, ance
 export function is_tag_valid_with_parent(child_tag, parent_tag, child_loc, parent_loc) {
 	if (child_tag.includes('-') || parent_tag?.includes('-')) return null; // custom elements can be anything
 
+	if (parent_tag === 'template') return null; // no errors or warning should be thrown in immediate children of template tags
+
 	const disallowed = disallowed_children[parent_tag];
 
 	const child = child_loc ? `\`<${child_tag}>\` (${child_loc})` : `\`<${child_tag}>\``;

packages/svelte/tests/validator/samples/invalid-node-placement-template/errors.json

@@ -0,0 +1 @@
+[]

packages/svelte/tests/validator/samples/invalid-node-placement-template/input.svelte

@@ -0,0 +1,6 @@
+<template>
+	<tr>
+		<td></td>
+		<td></td>
+	</tr>
+</template>