From f7ce3f6a9985d4a79ceca4a09a7baca51000ce79 Mon Sep 17 00:00:00 2001
From: Jan Vogt <jan.vogt+csenv@findeck.de>
Date: Wed, 25 Jun 2025 22:51:51 +0000
Subject: [PATCH 1/5] Add failing test for #16242

---
 .../samples/whitespace-before-child/Nested.svelte          | 1 +
 .../samples/whitespace-before-child/_override.html         | 2 ++
 .../hydration/samples/whitespace-before-child/main.svelte  | 7 +++++++
 3 files changed, 10 insertions(+)
 create mode 100644 packages/svelte/tests/hydration/samples/whitespace-before-child/Nested.svelte
 create mode 100644 packages/svelte/tests/hydration/samples/whitespace-before-child/_override.html
 create mode 100644 packages/svelte/tests/hydration/samples/whitespace-before-child/main.svelte

diff --git a/packages/svelte/tests/hydration/samples/whitespace-before-child/Nested.svelte b/packages/svelte/tests/hydration/samples/whitespace-before-child/Nested.svelte
new file mode 100644
index 000000000000..c230e50ebc61
--- /dev/null
+++ b/packages/svelte/tests/hydration/samples/whitespace-before-child/Nested.svelte
@@ -0,0 +1 @@
+<p>nested</p>
diff --git a/packages/svelte/tests/hydration/samples/whitespace-before-child/_override.html b/packages/svelte/tests/hydration/samples/whitespace-before-child/_override.html
new file mode 100644
index 000000000000..90ca4ef4b8c9
--- /dev/null
+++ b/packages/svelte/tests/hydration/samples/whitespace-before-child/_override.html
@@ -0,0 +1,2 @@
+<!--[-->
+<main><p>nested</p><!----></main><!--]-->
\ No newline at end of file
diff --git a/packages/svelte/tests/hydration/samples/whitespace-before-child/main.svelte b/packages/svelte/tests/hydration/samples/whitespace-before-child/main.svelte
new file mode 100644
index 000000000000..0aa292515099
--- /dev/null
+++ b/packages/svelte/tests/hydration/samples/whitespace-before-child/main.svelte
@@ -0,0 +1,7 @@
+<script>
+	// https://github.com/sveltejs/svelte/issues/16242
+	import Nested from './Nested.svelte';
+</script>
+<main>
+	<Nested />
+</main>

From b4200fa5f1ce8972677625557bd83e6b42b5d49d Mon Sep 17 00:00:00 2001
From: Jan Vogt <jan.vogt+csenv@findeck.de>
Date: Wed, 25 Jun 2025 22:52:59 +0000
Subject: [PATCH 2/5] Increase expectations for fix to #15819

one of the cases we CAN hydrate
---
 .../samples/cloudflare-mirage-borking-2/_config.js          | 6 ------
 .../samples/cloudflare-mirage-borking-2/_expected.html      | 1 -
 .../samples/cloudflare-mirage-borking-2/main.svelte         | 1 +
 3 files changed, 1 insertion(+), 7 deletions(-)
 delete mode 100644 packages/svelte/tests/hydration/samples/cloudflare-mirage-borking-2/_config.js
 delete mode 100644 packages/svelte/tests/hydration/samples/cloudflare-mirage-borking-2/_expected.html

diff --git a/packages/svelte/tests/hydration/samples/cloudflare-mirage-borking-2/_config.js b/packages/svelte/tests/hydration/samples/cloudflare-mirage-borking-2/_config.js
deleted file mode 100644
index 56ba73b06408..000000000000
--- a/packages/svelte/tests/hydration/samples/cloudflare-mirage-borking-2/_config.js
+++ /dev/null
@@ -1,6 +0,0 @@
-import { test } from '../../test';
-
-// https://github.com/sveltejs/svelte/issues/15819
-export default test({
-	expect_hydration_error: true
-});
diff --git a/packages/svelte/tests/hydration/samples/cloudflare-mirage-borking-2/_expected.html b/packages/svelte/tests/hydration/samples/cloudflare-mirage-borking-2/_expected.html
deleted file mode 100644
index 5179fb04a5f7..000000000000
--- a/packages/svelte/tests/hydration/samples/cloudflare-mirage-borking-2/_expected.html
+++ /dev/null
@@ -1 +0,0 @@
-<p>start</p><p>cond</p><!---->
diff --git a/packages/svelte/tests/hydration/samples/cloudflare-mirage-borking-2/main.svelte b/packages/svelte/tests/hydration/samples/cloudflare-mirage-borking-2/main.svelte
index bfb4f2cdb8cf..3f0097fb9ddd 100644
--- a/packages/svelte/tests/hydration/samples/cloudflare-mirage-borking-2/main.svelte
+++ b/packages/svelte/tests/hydration/samples/cloudflare-mirage-borking-2/main.svelte
@@ -1,4 +1,5 @@
 <script>
+	// https://github.com/sveltejs/svelte/issues/15819
 	const cond = true;
 </script>
 

From a28a11edda049436675ffc7b5b1a9638c09d36f6 Mon Sep 17 00:00:00 2001
From: Jan Vogt <jan.vogt+csenv@findeck.de>
Date: Wed, 25 Jun 2025 22:59:45 +0000
Subject: [PATCH 3/5] make hydration less whitespace sensitive

this fixes #16242 and allows to sucessfully hydrate #15851 as well.
---
 .changeset/curvy-colts-occur.md                      |  5 +++++
 packages/svelte/src/internal/client/dom/hydration.js | 10 ++++++++--
 2 files changed, 13 insertions(+), 2 deletions(-)
 create mode 100644 .changeset/curvy-colts-occur.md

diff --git a/.changeset/curvy-colts-occur.md b/.changeset/curvy-colts-occur.md
new file mode 100644
index 000000000000..3245e6638206
--- /dev/null
+++ b/.changeset/curvy-colts-occur.md
@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: make hydration less whitespace sensitive
diff --git a/packages/svelte/src/internal/client/dom/hydration.js b/packages/svelte/src/internal/client/dom/hydration.js
index 1f80b7922bc2..5ecdb1c236fb 100644
--- a/packages/svelte/src/internal/client/dom/hydration.js
+++ b/packages/svelte/src/internal/client/dom/hydration.js
@@ -1,6 +1,6 @@
 /** @import { TemplateNode } from '#client' */
 
-import { COMMENT_NODE } from '#client/constants';
+import { COMMENT_NODE, TEXT_NODE } from '#client/constants';
 import {
 	HYDRATION_END,
 	HYDRATION_ERROR,
@@ -41,7 +41,13 @@ export function set_hydrate_node(node) {
 }
 
 export function hydrate_next() {
-	return set_hydrate_node(/** @type {TemplateNode} */ (get_next_sibling(hydrate_node)));
+	var node = set_hydrate_node(/** @type {TemplateNode} */(get_next_sibling(hydrate_node)));
+	while (hydrate_node.nodeType === TEXT_NODE && !hydrate_node.nodeValue?.trim()) {
+		var next_sibling = get_next_sibling(hydrate_node)
+		hydrate_node.parentElement?.removeChild(hydrate_node)
+		node = set_hydrate_node(/** @type {TemplateNode} */(next_sibling))
+	}
+	return node
 }
 
 /** @param {TemplateNode} node */

From e9bd78259fb516554a6afab6cfa47b570fb98662 Mon Sep 17 00:00:00 2001
From: Jan Vogt <jan.vogt+csenv@findeck.de>
Date: Thu, 26 Jun 2025 01:27:36 +0000
Subject: [PATCH 4/5] fix await blocks

For some reason await blocks render html whitespace and
their custom hydration error handling seems to depend
on hydrating text nodes.
---
 .../src/internal/client/dom/blocks/await.js   |  2 +-
 .../src/internal/client/dom/hydration.js      | 20 +++++++++++++++++--
 2 files changed, 19 insertions(+), 3 deletions(-)

diff --git a/packages/svelte/src/internal/client/dom/blocks/await.js b/packages/svelte/src/internal/client/dom/blocks/await.js
index 47df5fc9a5f8..2c3e3af4a798 100644
--- a/packages/svelte/src/internal/client/dom/blocks/await.js
+++ b/packages/svelte/src/internal/client/dom/blocks/await.js
@@ -36,7 +36,7 @@ const CATCH = 2;
  */
 export function await_block(node, get_input, pending_fn, then_fn, catch_fn) {
 	if (hydrating) {
-		hydrate_next();
+		hydrate_next(true);
 	}
 
 	var anchor = node;
diff --git a/packages/svelte/src/internal/client/dom/hydration.js b/packages/svelte/src/internal/client/dom/hydration.js
index 5ecdb1c236fb..37492c80e298 100644
--- a/packages/svelte/src/internal/client/dom/hydration.js
+++ b/packages/svelte/src/internal/client/dom/hydration.js
@@ -40,9 +40,25 @@ export function set_hydrate_node(node) {
 	return (hydrate_node = node);
 }
 
-export function hydrate_next() {
+/**
+ * Moove to the next node to be hydrated. Empty text nodes will be skipped,
+ * unless `allow_text` is set to true.
+ *
+ * Skipping whitespace helps to sucessful hydrate even if some middleware added
+ * arbitrary whitespace into the html. This was at least twice an issue:
+ *
+ * - https://github.com/sveltejs/svelte/issues/15819
+ * - https://github.com/sveltejs/svelte/issues/16242
+ *
+ * Removing empty text nodes should be finde, as required text nodes will be
+ * added on demand. Doing so is necessary because an empty text on the server
+ * side will result in a missing text nodes as well.
+ *
+ * @param {boolean} allow_text
+ */
+export function hydrate_next(allow_text = false) {
 	var node = set_hydrate_node(/** @type {TemplateNode} */(get_next_sibling(hydrate_node)));
-	while (hydrate_node.nodeType === TEXT_NODE && !hydrate_node.nodeValue?.trim()) {
+	while (!allow_text && node.nodeType === TEXT_NODE && !node.nodeValue?.trim()) {
 		var next_sibling = get_next_sibling(hydrate_node)
 		hydrate_node.parentElement?.removeChild(hydrate_node)
 		node = set_hydrate_node(/** @type {TemplateNode} */(next_sibling))

From 94c47847b49a7e6be99c0219fae9d4834cd0d59b Mon Sep 17 00:00:00 2001
From: Jan Vogt <jan.vogt+csenv@findeck.de>
Date: Thu, 26 Jun 2025 07:39:01 +0000
Subject: [PATCH 5/5] prevent nix flake and direnv setup to leak

---
 .gitignore | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/.gitignore b/.gitignore
index d50343766485..6d05d789a674 100644
--- a/.gitignore
+++ b/.gitignore
@@ -14,9 +14,13 @@ coverage
 # dotenv environment variables file
 .env
 .env.test
+flake.nix
+flake.lock
+.envrc
 
 # build output
 .vercel
+.direnv
 
 # OS-specific
 .DS_Store

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