fix await blocks

For some reason await blocks render html whitespace and
their custom hydration error handling seems to depend
on hydrating text nodes.

Author: Jan Vogt

.envrc

@@ -0,0 +1 @@
+use flake

flake.lock

@@ -0,0 +1,9 @@
+{
+  inputs = { utils.url = "github:numtide/flake-utils"; };
+  outputs = { self, nixpkgs, utils }:
+    utils.lib.eachDefaultSystem (system:
+      let pkgs = nixpkgs.legacyPackages.${system};
+      in {
+        devShell = pkgs.mkShell { buildInputs = with pkgs; [ nodejs pnpm ]; };
+      });
+}

flake.nix

@@ -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;

packages/svelte/src/internal/client/dom/blocks/await.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/15819
+ *
+ * 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))