fix: repair `href` attribute mismatches (#13032)

* fix: repair `href` attribute mismatches

The reasoning in #9662 turns out to be false: While it's true that the href would resolve to the same URL on the initial page, once you're doing a client-side navigation to a URL at a different depth, the relative path would now point to the wrong location. Therefore we need to repair href hydration mismatches

fixes https://github.com/sveltejs/kit/issues/12254

* remove test

* Revert "remove test"

This reverts commit fa43304329.

* fix test

* remove comment, since the rationale for skipping the attributes in question is covered by the one immediately below

* fix

* add test for <a> specifically

---------

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

.changeset/two-cats-approve.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: repair `href` attribute mismatches

packages/svelte/src/internal/client/dom/elements/attributes.js

@@ -89,7 +89,11 @@ export function set_attribute(element, attribute, value, skip_warning) {
 	if (hydrating) {
 		attributes[attribute] = element.getAttribute(attribute);
 
-		if (attribute === 'src' || attribute === 'href' || attribute === 'srcset') {
+		if (
+			attribute === 'src' ||
+			attribute === 'srcset' ||
+			(attribute === 'href' && element.nodeName === 'LINK')
+		) {
 			if (!skip_warning) {
 				check_src_in_dev_hydration(element, attribute, value);
 			}
@@ -388,7 +392,7 @@ function check_src_in_dev_hydration(element, attribute, value) {
 
 	w.hydration_attribute_changed(
 		attribute,
-		element.outerHTML.replace(element.innerHTML, '...'),
+		element.outerHTML.replace(element.innerHTML, element.innerHTML && '...'),
 		String(value)
 	);
 }

packages/svelte/tests/hydration/samples/ignore-mismatched-href/_config.js

@@ -10,10 +10,10 @@ export default test({
 	},
 
 	test(assert, target) {
-		assert.equal(target.querySelector('a')?.getAttribute('href'), '/bar');
+		assert.equal(target.querySelector('link')?.getAttribute('href'), '/bar');
 	},
 
 	errors: [
-		'The `href` attribute on `<a href="/bar">...</a>` changed its value between server and client renders. The client value, `/foo`, will be ignored in favour of the server value'
+		'The `href` attribute on `<link href="/bar">` changed its value between server and client renders. The client value, `/foo`, will be ignored in favour of the server value'
 	]
 });

packages/svelte/tests/hydration/samples/ignore-mismatched-href/main.svelte

@@ -2,4 +2,4 @@
 	let { browser } = $props();
 </script>
 
-<a href={browser ? '/foo': '/bar'}>foo</a>
+<link href={browser ? '/foo' : '/bar'} />

packages/svelte/tests/hydration/samples/img-src-mismatch/_config.js

@@ -12,6 +12,6 @@ export default test({
 		assert.htmlEqual(target.innerHTML, '<img src="server.jpg" alt="">');
 	},
 	errors: [
-		'The `src` attribute on `...<img src="server.jpg" alt="">` changed its value between server and client renders. The client value, `client.jpg`, will be ignored in favour of the server value'
+		'The `src` attribute on `<img src="server.jpg" alt="">` changed its value between server and client renders. The client value, `client.jpg`, will be ignored in favour of the server value'
 	]
 });

packages/svelte/tests/hydration/samples/repair-mismatched-a-href/_config.js

@@ -0,0 +1,11 @@
+import { test } from '../../test';
+
+export default test({
+	server_props: {
+		browser: false
+	},
+
+	props: {
+		browser: true
+	}
+});

packages/svelte/tests/hydration/samples/repair-mismatched-a-href/_expected.html

@@ -0,0 +1 @@
+<!--[--><a href="/foo">foo</a><!--]-->

packages/svelte/tests/hydration/samples/repair-mismatched-a-href/main.svelte

@@ -0,0 +1,5 @@
+<script>
+	let { browser } = $props();
+</script>
+
+<a href={browser ? '/foo' : '/bar'}>foo</a>