Fix hydration duplicate head tag issue sveltejs#7444

src/compiler/compile/render_dom/wrappers/Head.ts

@@ -36,7 +36,7 @@ export default class HeadWrapper extends Wrapper {
 		let nodes;
 		if (this.renderer.options.hydratable && this.fragment.nodes.length) {
 			nodes = block.get_unique_name('head_nodes');
-			block.chunks.claim.push(b`const ${nodes} = @query_selector_all('[data-svelte="${this.node.id}"]', @_document.head);`);
+			block.chunks.claim.push(b`const ${nodes} = @head_selector('${this.node.id}', @_document.head);`);
 		}
 
 		this.fragment.render(block, x`@_document.head` as unknown as Identifier, nodes);

src/compiler/compile/render_ssr/handlers/HtmlTag.ts

@@ -3,7 +3,13 @@ import RawMustacheTag from '../../nodes/RawMustacheTag';
 import { Expression } from 'estree';
 
 export default function(node: RawMustacheTag, renderer: Renderer, options: RenderOptions) {
-	if (options.hydratable) renderer.add_string('<!-- HTML_TAG_START -->');
+	if (options.hydratable) {
+		renderer.add_string(`<!-- HTML_TAG_START ${options.head_id ? `data-svelte="${options.head_id}" ` : ''}-->`);
+	}
+
 	renderer.add_expression(node.expression.node as Expression);
-	if (options.hydratable) renderer.add_string('<!-- HTML_TAG_END -->');
+
+	if (options.hydratable) {
+		renderer.add_string(`<!-- HTML_TAG_END ${options.head_id ? `data-svelte="${options.head_id}" ` : ''}-->`);
+	}
 }

src/runtime/internal/dom.ts

@@ -477,21 +477,24 @@ export function claim_space(nodes) {
 	return claim_text(nodes, ' ');
 }
 
-function find_comment(nodes, text, start) {
+function find_html_tag_comment(nodes, text, start) {
 	for (let i = start; i < nodes.length; i += 1) {
 		const node = nodes[i];
-		if (node.nodeType === 8 /* comment node */ && node.textContent.trim() === text) {
+		if (node.nodeType === 8 /* comment node */) {
+			const value = node.textContent.trim();
+			if (value === text || value.startsWith(text + ' data-svelte="') === true) {
 				return i;
 			}
 		}
+	}
 	return nodes.length;
 }
 
 
 export function claim_html_tag(nodes, is_svg: boolean) {
 	// find html opening tag
-	const start_index = find_comment(nodes, 'HTML_TAG_START', 0);
-	const end_index = find_comment(nodes, 'HTML_TAG_END', start_index);
+	const start_index = find_html_tag_comment(nodes, 'HTML_TAG_START', 0);
+	const end_index = find_html_tag_comment(nodes, 'HTML_TAG_END', start_index);
 	if (start_index === end_index) {
 		return new HtmlTagHydration(undefined, is_svg);
 	}
@@ -640,6 +643,25 @@ export function query_selector_all(selector: string, parent: HTMLElement = docum
 	return Array.from(parent.querySelectorAll(selector)) as ChildNodeArray;
 }
 
+export function head_selector(nodeId: string, head: HTMLElement) {
+	const result = [];
+	let started = 0;
+	for (const node of head.childNodes) {
+		if (node.nodeType === 8 /* comment node */ && node.textContent.trim() === `HTML_TAG_END data-svelte="${nodeId}"`) {
+			started -= 1;
+			result.push(node);
+		} else if (node.nodeType === 8 /* comment node */ && node.textContent.trim() === `HTML_TAG_START data-svelte="${nodeId}"`) {
+			started += 1;
+			result.push(node);
+		} else if (started > 0) {
+			result.push(node);
+		} else if (node.nodeType === 1 /* element node */ && (<Element>node).getAttribute('data-svelte') === nodeId) {
+			result.push(node);
+		}
+	}
+	return result;
+}
+
 export class HtmlTag {
 	private is_svg = false;
 	// parent for creating node

test/hydration/samples/head-html/Nested.svelte

@@ -0,0 +1,4 @@
+
+<svelte:head>
+	{@html '<meta name="nested_meta" content="nested_value">'}
+</svelte:head>

test/hydration/samples/head-html/_after_head.html

@@ -0,0 +1,7 @@
+<!-- HTML_TAG_START data-svelte="svelte-p6n9ep" -->
+<meta name="main_meta" content="main_value">
+<!-- HTML_TAG_END data-svelte="svelte-p6n9ep" -->
+
+<!-- HTML_TAG_START data-svelte="svelte-1ygcsvx" -->
+<meta name="nested_meta" content="nested_value">
+<!-- HTML_TAG_END data-svelte="svelte-1ygcsvx" -->

test/hydration/samples/head-html/_before_head.html

@@ -0,0 +1,7 @@
+<!-- HTML_TAG_START data-svelte="svelte-p6n9ep" -->
+<meta name="main_meta" content="main_value">
+<!-- HTML_TAG_END data-svelte="svelte-p6n9ep" -->
+
+<!-- HTML_TAG_START data-svelte="svelte-1ygcsvx" -->
+<meta name="nested_meta" content="nested_value">
+<!-- HTML_TAG_END data-svelte="svelte-1ygcsvx" -->

test/hydration/samples/head-html/main.svelte

@@ -0,0 +1,9 @@
+<script>
+	import Nested from './Nested.svelte';
+</script>
+
+<svelte:head>
+	{@html '<meta name="main_meta" content="main_value">'}
+</svelte:head>
+
+<Nested/>