fix: provide more hydration mismatch coverage (#12755)

* fix: provide more hydration mismatch coverage

* tweak

* add test for safari borking stuff

* fix

* fix windows test

* failing test

* oops

* revert playground changes

* simplify

* template content hydration logic should really be separate from reset logic

* actually the test is incorrect, and now i cant seem to recreate what i saw before... hmm

* update comment to no longer mention templates

* failing test

* delete test for now

---------

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

.changeset/stupid-rivers-stare.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: provide more hydration mismatch coverage

packages/svelte/src/compiler/phases/3-transform/client/visitors/RegularElement.js

@@ -327,9 +327,8 @@ export function RegularElement(node, context) {
 	// set the value of `hydrate_node` to `node.content`
 	if (node.name === 'template') {
 		needs_reset = true;
-
+		child_state.init.push(b.stmt(b.call('$.hydrate_template', arg)));
 		arg = b.member(arg, b.id('content'));
-		child_state.init.push(b.stmt(b.call('$.reset', arg)));
 	}
 
 	process_children(trimmed, () => b.call('$.child', arg), true, {

packages/svelte/src/internal/client/dom/hydration.js

@@ -30,21 +30,38 @@ export let hydrate_node;
 
 /** @param {TemplateNode} node */
 export function set_hydrate_node(node) {
+	if (node === null) {
+		w.hydration_mismatch();
+		throw HYDRATION_ERROR;
+	}
+
 	return (hydrate_node = node);
 }
 
 export function hydrate_next() {
-	if (hydrate_node === null) {
+	return set_hydrate_node(/** @type {TemplateNode} */ (hydrate_node.nextSibling));
+}
+
+/** @param {TemplateNode} node */
+export function reset(node) {
+	if (!hydrating) return;
+
+	// If the node has remaining siblings, something has gone wrong
+	if (hydrate_node.nextSibling !== null) {
 		w.hydration_mismatch();
 		throw HYDRATION_ERROR;
 	}
-	return (hydrate_node = /** @type {TemplateNode} */ (hydrate_node.nextSibling));
+
+	hydrate_node = node;
 }
 
-/** @param {TemplateNode} node */
-export function reset(node) {
+/**
+ * @param {HTMLTemplateElement} template
+ */
+export function hydrate_template(template) {
 	if (hydrating) {
-		hydrate_node = node;
+		// @ts-expect-error TemplateNode doesn't include DocumentFragment, but it's actually fine
+		hydrate_node = template.content;
 	}
 }
 

packages/svelte/src/internal/client/index.js

@@ -66,7 +66,7 @@ export {
 	bind_focused
 } from './dom/elements/bindings/universal.js';
 export { bind_window_scroll, bind_window_size } from './dom/elements/bindings/window.js';
-export { next, reset } from './dom/hydration.js';
+export { hydrate_template, next, reset } from './dom/hydration.js';
 export {
 	once,
 	preventDefault,

packages/svelte/tests/hydration/samples/safari-borking/_config.js

@@ -0,0 +1,5 @@
+import { test } from '../../test';
+
+export default test({
+	expect_hydration_error: true
+});

packages/svelte/tests/hydration/samples/safari-borking/_expected.html

@@ -0,0 +1 @@
+<h1>call +636-555-3226 now</h1>

packages/svelte/tests/hydration/samples/safari-borking/_override.html

@@ -0,0 +1 @@
+<!--[--><h1>call <a href="tel:+636-555-3226">+636-555-3226</a> now</h1><!--]-->

packages/svelte/tests/hydration/samples/safari-borking/main.svelte

@@ -0,0 +1,5 @@
+<script>
+	const message = `call +636-555-3226 now`;
+</script>
+
+<h1>{message}</h1>

packages/svelte/tests/hydration/samples/surrounding-whitespace/_expected.html

@@ -0,0 +1,2 @@
+		<!-- unrelated comment -->
+		<!--[--><!--[-->hello<!--]--><!--]-->

packages/svelte/tests/hydration/test.ts

@@ -113,15 +113,16 @@ const { test, run } = suite<HydrationTest>(async (config, cwd) => {
 			throw new Error(`Unexpected errors: ${errors.join('\n')}`);
 		}
 
-		if (!override) {
-			const expected = read(`${cwd}/_expected.html`) ?? rendered.html;
-			flushSync();
-			assert.equal(target.innerHTML.trim(), expected.trim());
-		}
+		flushSync();
+
+		const normalize = (string: string) => string.trim().replace(/\r\n/g, '\n');
+
+		const expected = read(`${cwd}/_expected.html`) ?? rendered.html;
+		assert.equal(normalize(target.innerHTML), normalize(expected));
 
 		if (rendered.head) {
 			const expected = read(`${cwd}/_expected_head.html`) ?? rendered.head;
-			assert.equal(head.innerHTML.trim(), expected.trim());
+			assert.equal(normalize(head.innerHTML), normalize(expected));
 		}
 
 		if (config.snapshot) {

playgrounds/demo/ssr-dev.js

@@ -27,7 +27,9 @@ polka()
 
 		const html = transformed_template
 			.replace(`<!--ssr-head-->`, head)
-			.replace(`<!--ssr-body-->`, body);
+			.replace(`<!--ssr-body-->`, body)
+			// check that Safari doesn't break hydration
+			.replaceAll('+636-555-3226', '<a href="tel:+636-555-3226">+636-555-3226</a>');
 
 		res.writeHead(200, { 'Content-Type': 'text/html' }).end(html);
 	})