chore: remove anchor node from each block items (#11836)

* fix: improve each block runtime heuristics be removing anchor text node

* change message

* conflict

* merge

* fix bug

* Update .changeset/stale-nails-listen.md

---------

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

.changeset/stale-nails-listen.md

@@ -0,0 +1,5 @@
+---
+"svelte": patch
+---
+
+chore: remove anchor node from each block items

packages/svelte/src/internal/client/dom/blocks/each.js

@@ -85,7 +85,6 @@ function pause_effects(items, controlled_anchor, items_map) {
 			var item = items[i];
 			if (!is_controlled) {
 				items_map.delete(item.k);
-				item.o.remove();
 				link(item.prev, item.next);
 			}
 			destroy_effect(item.e, !is_controlled);
@@ -182,11 +181,10 @@ export function each(anchor, flags, get_collection, get_key, render_fn, fallback
 					break;
 				}
 
-				var child_open = /** @type {Comment} */ (child_anchor);
 				child_anchor = hydrate_anchor(child_anchor);
 				var value = array[i];
 				var key = get_key(value, i);
-				item = create_item(child_open, child_anchor, prev, null, value, key, i, render_fn, flags);
+				item = create_item(child_anchor, prev, null, value, key, i, render_fn, flags);
 				state.items.set(key, item);
 				child_anchor = /** @type {Comment} */ (child_anchor.nextSibling);
 
@@ -293,22 +291,9 @@ function reconcile(array, state, anchor, render_fn, flags, get_key) {
 		item = items.get(key);
 
 		if (item === undefined) {
-			var child_open = empty();
-			var child_anchor = current ? current.o : anchor;
-
-			child_anchor.before(child_open);
-
-			prev = create_item(
-				child_open,
-				child_anchor,
-				prev,
-				prev.next,
-				value,
-				key,
-				i,
-				render_fn,
-				flags
-			);
+			var child_anchor = current ? get_first_node(current.e) : anchor;
+
+			prev = create_item(child_anchor, prev, prev.next, value, key, i, render_fn, flags);
 
 			items.set(key, prev);
 
@@ -451,7 +436,6 @@ function update_item(item, value, index, type) {
 
 /**
  * @template V
- * @param {Comment | Text} open
  * @param {Node} anchor
  * @param {import('#client').EachItem | import('#client').EachState} prev
  * @param {import('#client').EachItem | null} next
@@ -462,7 +446,7 @@ function update_item(item, value, index, type) {
  * @param {number} flags
  * @returns {import('#client').EachItem}
  */
-function create_item(open, anchor, prev, next, value, key, index, render_fn, flags) {
+function create_item(anchor, prev, next, value, key, index, render_fn, flags) {
 	var previous_each_item = current_each_item;
 
 	try {
@@ -480,7 +464,6 @@ function create_item(open, anchor, prev, next, value, key, index, render_fn, fla
 			a: null,
 			// @ts-expect-error
 			e: null,
-			o: open,
 			prev,
 			next
 		};
@@ -497,16 +480,52 @@ function create_item(open, anchor, prev, next, value, key, index, render_fn, fla
 	}
 }
 
+/**
+ * @param {import('#client').TemplateNode} dom
+ * @param {import("#client").Effect} effect
+ * @returns {import('#client').TemplateNode}
+ */
+function get_adjusted_first_node(dom, effect) {
+	if ((dom.nodeType === 3 && /** @type {Text} */ (dom).data === '') || dom.nodeType === 8) {
+		var adjusted = effect.first;
+		var next;
+		while (adjusted !== null) {
+			next = adjusted.first;
+			if (adjusted.dom !== null) {
+				break;
+			} else if (next === null) {
+				return /** @type {import('#client').TemplateNode} */ (dom.previousSibling);
+			}
+			adjusted = next;
+		}
+		return get_first_node(/** @type {import("#client").Effect} */ (adjusted));
+	}
+	return dom;
+}
+
+/**
+ *
+ * @param {import('#client').Effect} effect
+ * @returns {import('#client').TemplateNode}
+ */
+function get_first_node(effect) {
+	var dom = effect.dom;
+	if (is_array(dom)) {
+		return get_adjusted_first_node(dom[0], effect);
+	}
+	return get_adjusted_first_node(/** @type {import('#client').TemplateNode} **/ (dom), effect);
+}
+
 /**
  * @param {import('#client').EachItem} item
  * @param {import('#client').EachItem | null} next
  * @param {Text | Element | Comment} anchor
  */
 function move(item, next, anchor) {
-	var end = item.next ? item.next.o : anchor;
-	var dest = next ? next.o : anchor;
+	var end = item.next ? get_first_node(item.next.e) : anchor;
+	var dest = next ? get_first_node(next.e) : anchor;
 
-	var node = /** @type {import('#client').TemplateNode} */ (item.o);
+	var node = get_first_node(item.e);
 
 	while (node !== end) {
 		var next_node = /** @type {import('#client').TemplateNode} */ (node.nextSibling);

packages/svelte/src/internal/client/dom/blocks/svelte-element.js

@@ -47,7 +47,6 @@ function swap_block_dom(effect, from, to) {
  * @returns {void}
  */
 export function element(node, get_tag, is_svg, render_fn, get_namespace, location) {
-	const parent_effect = /** @type {import('#client').Effect} */ (current_effect);
 	const filename = DEV && location && current_component_context?.function.filename;
 
 	/** @type {string | null} */
@@ -64,6 +63,18 @@ export function element(node, get_tag, is_svg, render_fn, get_namespace, locatio
 	/** @type {import('#client').Effect | null} */
 	let effect;
 
+	const parent_effect = /** @type {import('#client').Effect} */ (current_effect);
+
+	// Remove the the hydrated effect dom entry for our dynamic element
+	if (hydrating && is_array(parent_effect.dom)) {
+		var remove_index = parent_effect.dom.indexOf(
+			/** @type {import('#client').TemplateNode} */ (element)
+		);
+		if (remove_index !== -1) {
+			parent_effect.dom.splice(remove_index, 1);
+		}
+	}
+
 	/**
 	 * The keyed `{#each ...}` item block, if any, that this element is inside.
 	 * We track this so we can set it when changing the element, allowing any
@@ -72,6 +83,7 @@ export function element(node, get_tag, is_svg, render_fn, get_namespace, locatio
 	let each_item_block = current_each_item;
 
 	block(() => {
+		const element_effect = /** @type {import('#client').Effect} */ (current_effect);
 		const next_tag = get_tag() || null;
 		const ns = get_namespace
 			? get_namespace()
@@ -124,6 +136,13 @@ export function element(node, get_tag, is_svg, render_fn, get_namespace, locatio
 					};
 				}
 
+				if (prev_element && !hydrating) {
+					swap_block_dom(element_effect, prev_element, element);
+					prev_element.remove();
+				} else {
+					push_template_node(element, element_effect);
+				}
+
 				if (render_fn) {
 					// If hydrating, use the existing ssr comment as the anchor so that the
 					// inner open and close methods can pick up the existing nodes correctly
@@ -144,15 +163,6 @@ export function element(node, get_tag, is_svg, render_fn, get_namespace, locatio
 
 				anchor.before(element);
 
-				if (!hydrating) {
-					if (prev_element) {
-						swap_block_dom(parent_effect, prev_element, element);
-						prev_element.remove();
-					} else {
-						push_template_node(element, parent_effect);
-					}
-				}
-
 				// See below
 				return noop;
 			});

packages/svelte/src/internal/client/types.d.ts

@@ -85,8 +85,6 @@ export type EachItem = {
 	i: number | Source<number>;
 	/** key */
 	k: unknown;
-	/** anchor for items inserted before this */
-	o: Comment | Text;
 	prev: EachItem | EachState;
 	next: EachItem | null;
 };