fixes

packages/svelte/src/compiler/phases/3-transform/server/transform-server.js

@@ -35,7 +35,6 @@ import { sanitize_template_string } from '../../../utils/sanitize_template_strin
 import {
 	BLOCK_ANCHOR,
 	BLOCK_CLOSE,
-	BLOCK_CLOSE_ELSE,
 	BLOCK_OPEN,
 	BLOCK_OPEN_ELSE
 } from '../../../../internal/server/hydration.js';
@@ -1343,7 +1342,6 @@ const template_visitors = {
 	},
 	EachBlock(node, context) {
 		const state = context.state;
-		state.template.push(block_open);
 
 		const each_node_meta = node.metadata;
 		const collection = /** @type {import('estree').Expression} */ (context.visit(node.expression));
@@ -1379,26 +1377,27 @@ const template_visitors = {
 			b.block(each)
 		);
 
-		const close = b.stmt(b.assignment('+=', b.id('$$payload.out'), b.literal(BLOCK_CLOSE)));
-
 		if (node.fallback) {
+			const open = b.stmt(b.assignment('+=', b.id('$$payload.out'), b.literal(BLOCK_OPEN)));
+
 			const fallback = /** @type {import('estree').BlockStatement} */ (
 				context.visit(node.fallback)
 			);
 
-			fallback.body.push(
-				b.stmt(b.assignment('+=', b.id('$$payload.out'), b.literal(BLOCK_CLOSE_ELSE)))
+			fallback.body.unshift(
+				b.stmt(b.assignment('+=', b.id('$$payload.out'), b.literal(BLOCK_OPEN_ELSE)))
 			);
 
 			state.template.push(
 				b.if(
 					b.binary('!==', b.member(array_id, b.id('length')), b.literal(0)),
-					b.block([for_loop, close]),
+					b.block([open, for_loop]),
 					fallback
-				)
+				),
+				block_close
 			);
 		} else {
-			state.template.push(for_loop, close);
+			state.template.push(block_open, for_loop, block_open);
 		}
 	},
 	IfBlock(node, context) {

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

@@ -11,7 +11,7 @@ import {
 import { block, branch, pause_effect, resume_effect } from '../../reactivity/effects.js';
 import { DEV } from 'esm-env';
 import { queue_micro_task } from '../task.js';
-import { hydrate_node, hydrating, set_hydrate_node } from '../hydration.js';
+import { hydrate_next, hydrate_node, hydrating, set_hydrate_node } from '../hydration.js';
 import { mutable_source, set, source } from '../../reactivity/sources.js';
 
 const PENDING = 0;
@@ -28,6 +28,10 @@ const CATCH = 2;
  * @returns {void}
  */
 export function await_block(anchor, get_input, pending_fn, then_fn, catch_fn) {
+	if (hydrating) {
+		hydrate_next();
+	}
+
 	var runes = is_runes();
 	var component_context = current_component_context;
 
@@ -148,7 +152,6 @@ export function await_block(anchor, get_input, pending_fn, then_fn, catch_fn) {
 	});
 
 	if (hydrating) {
-		anchor = hydrate_node.nextSibling;
-		set_hydrate_node(anchor);
+		anchor = hydrate_node;
 	}
 }

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

@@ -5,16 +5,15 @@ import {
 	EACH_IS_STRICT_EQUALS,
 	EACH_ITEM_REACTIVE,
 	EACH_KEYED,
-	HYDRATION_END_ELSE,
+	HYDRATION_START_ELSE,
 	HYDRATION_START
 } from '../../../../constants.js';
 import {
+	hydrate_next,
 	hydrate_node,
 	hydrate_nodes,
-	hydrate_start,
 	hydrating,
 	set_hydrate_node,
-	set_hydrate_open,
 	set_hydrating
 } from '../hydration.js';
 import { clear_text_content, empty } from '../operations.js';
@@ -107,6 +106,11 @@ function pause_effects(state, items, controlled_anchor, items_map) {
  * @returns {void}
  */
 export function each(anchor, flags, get_collection, get_key, render_fn, fallback_fn = null) {
+	// console.log('each', { anchor });
+	if (hydrating) {
+		hydrate_next();
+	}
+
 	/** @type {import('#client').EachState} */
 	var state = { flags, items: new Map(), first: null };
 
@@ -155,11 +159,11 @@ export function each(anchor, flags, get_collection, get_key, render_fn, fallback
 		let mismatch = false;
 
 		if (hydrating) {
-			var is_else = /** @type {Comment} */ (anchor).data === HYDRATION_END_ELSE;
+			var is_else = /** @type {Comment} */ (anchor).data === HYDRATION_START_ELSE;
 
 			if (is_else !== (length === 0) || hydrate_node === undefined) {
 				// hydration mismatch — remove the server-rendered DOM and start over
-				remove(hydrate_nodes);
+				// remove(hydrate_nodes);
 				set_hydrating(false);
 				mismatch = true;
 			}
@@ -168,7 +172,7 @@ export function each(anchor, flags, get_collection, get_key, render_fn, fallback
 		// this is separate to the previous block because `hydrating` might change
 		if (hydrating) {
 			/** @type {Node} */
-			var child_anchor = hydrate_node;
+			var child_anchor = hydrate_node; // TODO do we still need child_anchors, in a world without `effect.dom`?
 
 			/** @type {import('#client').EachItem | null} */
 			var prev = null;
@@ -188,15 +192,15 @@ export function each(anchor, flags, get_collection, get_key, render_fn, fallback
 					break;
 				}
 
-				set_hydrate_open(child_anchor);
+				hydrate_next();
 
 				var value = array[i];
 				var key = get_key(value, i);
 				item = create_item(child_anchor, state, prev, null, value, key, i, render_fn, flags);
 				state.items.set(key, item);
 				var close = hydrate_node.nextSibling; // TODO validate. or replace `<!--]--><!--[-->` with `<!---->`
-				set_hydrate_node(close);
-				child_anchor = /** @type {Comment} */ (close.nextSibling);
+				// hydrate_next();
+				child_anchor = /** @type {Comment} */ (hydrate_next());
 
 				prev = item;
 			}
@@ -237,9 +241,10 @@ export function each(anchor, flags, get_collection, get_key, render_fn, fallback
 	});
 
 	if (hydrating) {
-		anchor = hydrate_node.nextSibling;
-		set_hydrate_node(anchor);
+		anchor = hydrate_node;
 	}
+
+	// console.log('each', { anchor });
 }
 
 /**

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

@@ -1,9 +1,10 @@
+/** @import { TemplateNode } from '#client' */
 import { EFFECT_TRANSPARENT } from '../../constants.js';
 import {
+	hydrate_next,
 	hydrate_node,
 	hydrate_nodes,
 	hydrating,
-	set_hydrate_node,
 	set_hydrating
 } from '../hydration.js';
 import { remove } from '../reconciler.js';
@@ -11,7 +12,7 @@ import { block, branch, pause_effect, resume_effect } from '../../reactivity/eff
 import { HYDRATION_START_ELSE } from '../../../../constants.js';
 
 /**
- * @param {Comment} anchor
+ * @param {TemplateNode} anchor
  * @param {() => boolean} get_condition
  * @param {(anchor: Node) => import('#client').Dom} consequent_fn
  * @param {null | ((anchor: Node) => import('#client').Dom)} [alternate_fn]
@@ -25,6 +26,10 @@ export function if_block(
 	alternate_fn = null,
 	elseif = false
 ) {
+	if (hydrating) {
+		hydrate_next();
+	}
+
 	/** @type {import('#client').Effect | null} */
 	var consequent_effect = null;
 
@@ -43,7 +48,7 @@ export function if_block(
 		let mismatch = false;
 
 		if (hydrating) {
-			const is_else = anchor.data === HYDRATION_START_ELSE;
+			const is_else = /** @type {Comment} */ (anchor).data === HYDRATION_START_ELSE;
 
 			if (condition === is_else) {
 				// Hydration mismatch: remove everything inside the anchor and start fresh.
@@ -87,7 +92,6 @@ export function if_block(
 	}, flags);
 
 	if (hydrating) {
-		anchor = hydrate_node.nextSibling;
-		set_hydrate_node(anchor);
+		anchor = hydrate_node;
 	}
 }

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

@@ -5,6 +5,7 @@ import {
 	dev_current_component_function,
 	set_dev_current_component_function
 } from '../../runtime.js';
+import { hydrate_next, hydrate_node, hydrating } from '../hydration.js';
 
 /**
  * @template {(node: import('#client').TemplateNode, ...args: any[]) => import('#client').Dom} SnippetFn
@@ -14,6 +15,10 @@ import {
  * @returns {void}
  */
 export function snippet(anchor, get_snippet, ...args) {
+	if (hydrating) {
+		hydrate_next();
+	}
+
 	/** @type {SnippetFn | null | undefined} */
 	var snippet;
 
@@ -32,6 +37,10 @@ export function snippet(anchor, get_snippet, ...args) {
 			snippet_effect = branch(() => /** @type {SnippetFn} */ (snippet)(anchor, ...args));
 		}
 	}, EFFECT_TRANSPARENT);
+
+	if (hydrating) {
+		anchor = hydrate_node;
+	}
 }
 
 /**

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

@@ -1,6 +1,6 @@
 /** @import { TemplateNode, Dom, Effect } from '#client' */
 import { block, branch, pause_effect } from '../../reactivity/effects.js';
-import { hydrate_node, hydrating, set_hydrate_node } from '../hydration.js';
+import { hydrate_next, hydrate_node, hydrating } from '../hydration.js';
 
 /**
  * @template P
@@ -11,6 +11,10 @@ import { hydrate_node, hydrating, set_hydrate_node } from '../hydration.js';
  * @returns {void}
  */
 export function component(anchor, get_component, render_fn) {
+	if (hydrating) {
+		hydrate_next();
+	}
+
 	/** @type {C} */
 	let component;
 
@@ -31,7 +35,6 @@ export function component(anchor, get_component, render_fn) {
 	});
 
 	if (hydrating) {
-		anchor = hydrate_node.nextSibling;
-		set_hydrate_node(anchor);
+		anchor = hydrate_node;
 	}
 }

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

@@ -12,18 +12,9 @@ export function set_hydrating(value) {
 	hydrating = value;
 }
 
-/** @type {Comment} */
-export let hydrate_open;
-
 /** @type {TemplateNode} */
 export let hydrate_node;
 
-/** @param {Comment} node */
-export function set_hydrate_open(node) {
-	hydrate_open = node;
-	hydrate_node = node.nextSibling;
-}
-
 /** @param {TemplateNode} node */
 export function set_hydrate_node(node) {
 	hydrate_node = node;
@@ -42,8 +33,7 @@ export let hydrate_start;
 
 /** @param {import('#client').TemplateNode[]} nodes */
 export function set_hydrate_nodes(nodes) {
-	hydrate_nodes = nodes;
-	hydrate_start = nodes && nodes[0];
+	throw new Error('TODO');
 }
 
 /**
@@ -52,11 +42,7 @@ export function set_hydrate_nodes(nodes) {
  * TODO it might be worth storing this value separately rather than retrieving it with `previousSibling`
  */
 export function get_start() {
-	return hydrate_open;
-
-	return /** @type {import('#client').TemplateNode} */ (
-		hydrate_start.previousSibling ?? hydrate_start
-	);
+	return hydrate_node;
 }
 
 /**
@@ -64,9 +50,10 @@ export function get_start() {
  * @param {TemplateNode} node
  */
 export function hydrate_anchor(node) {
-	if (node.nodeType === 8 && /** @type {Comment} */ (node).data === HYDRATION_START) {
-		set_hydrate_open(/** @type {Comment} */ (node));
-	}
-
 	return node;
 }
+
+export function hydrate_next() {
+	hydrate_node = /** @type {TemplateNode} */ (hydrate_node.nextSibling);
+	return hydrate_node;
+}

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

@@ -1,5 +1,11 @@
 /** @import { Effect, TemplateNode } from '#client' */
-import { hydrate_anchor, hydrate_node, hydrating, set_hydrate_node } from './hydration.js';
+import {
+	hydrate_anchor,
+	hydrate_next,
+	hydrate_node,
+	hydrating,
+	set_hydrate_node
+} from './hydration.js';
 import { DEV } from 'esm-env';
 import { init_array_prototype_warnings } from '../dev/equality.js';
 import { current_effect } from '../runtime.js';
@@ -67,7 +73,7 @@ export function child(node) {
 
 	// Child can be null if we have an element with a single child, like `<p>{text}</p>`, where `text` is empty
 	if (child === null) {
-		return hydrate_node.appendChild(empty());
+		child = hydrate_node.appendChild(empty());
 	}
 
 	set_hydrate_node(child);
@@ -91,6 +97,8 @@ export function first_child(fragment, is_text) {
 		return first;
 	}
 
+	// hydrate_next();
+
 	// if an {expression} is empty during SSR, there might be no
 	// text node to hydrate — we must therefore create one
 	if (is_text && hydrate_node?.nodeType !== 3) {
@@ -102,10 +110,16 @@ export function first_child(fragment, is_text) {
 		}
 
 		hydrate_node?.before(text);
+		set_hydrate_node(text);
 		return text;
 	}
 
-	return hydrate_anchor(hydrate_node);
+	// console.log('first_child', {
+	// 	hydrate_node,
+	// 	content: hydrate_node.data ?? hydrate_node.outerHTML
+	// });
+
+	return hydrate_node;
 }
 
 /**

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

@@ -1,16 +1,9 @@
 /** @import { Effect, EffectNodes, TemplateNode } from '#client' */
-import {
-	get_start,
-	hydrate_node,
-	hydrate_nodes,
-	hydrate_start,
-	hydrating,
-	set_hydrate_node
-} from './hydration.js';
+import { get_start, hydrate_next, hydrate_node, hydrating, set_hydrate_node } from './hydration.js';
 import { empty } from './operations.js';
 import { create_fragment_from_html } from './reconciler.js';
 import { current_effect } from '../runtime.js';
-import { HYDRATION_END, TEMPLATE_FRAGMENT, TEMPLATE_USE_IMPORT_NODE } from '../../../constants.js';
+import { TEMPLATE_FRAGMENT, TEMPLATE_USE_IMPORT_NODE } from '../../../constants.js';
 import { queue_micro_task } from './task.js';
 
 /**
@@ -42,8 +35,7 @@ export function template(content, flags) {
 
 	return () => {
 		if (hydrating) {
-			assign_nodes(get_start(), null);
-
+			assign_nodes(hydrate_node, null);
 			return hydrate_node;
 		}
 
@@ -117,7 +109,7 @@ export function ns_template(content, flags, ns = 'svg') {
 		if (hydrating) {
 			assign_nodes(get_start(), null);
 
-			return hydrate_start;
+			return hydrate_node;
 		}
 
 		if (!node) {
@@ -228,6 +220,8 @@ export function text(anchor) {
 
 	var node = hydrate_node;
 
+	// console.log('text', { hydrate_node });
+
 	if (node.nodeType !== 3) {
 		// if an {expression} is empty during SSR, `hydrate_nodes` will be empty.
 		// we need to insert an empty text node
@@ -244,7 +238,7 @@ export function comment() {
 	if (hydrating) {
 		assign_nodes(get_start(), null);
 
-		return hydrate_start;
+		return hydrate_node;
 	}
 
 	var frag = document.createDocumentFragment();
@@ -266,8 +260,10 @@ export function comment() {
 export function append(anchor, dom) {
 	if (hydrating) {
 		/** @type {Effect & { nodes: EffectNodes }} */ (current_effect).nodes.end = hydrate_node;
+		hydrate_next();
 
 		// console.log('effect.nodes', current_effect.nodes);
+		// console.log(dom);
 
 		// // next node should be a <!--]-->
 		// var next = hydrate_node.nextSibling;

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

@@ -4,9 +4,11 @@ import { HYDRATION_ERROR, HYDRATION_START, PassiveDelegatedEvents } from '../../
 import { flush_sync, push, pop, current_component_context } from './runtime.js';
 import { effect_root, branch } from './reactivity/effects.js';
 import {
+	hydrate_next,
 	hydrate_nodes,
+	hydrating,
+	set_hydrate_node,
 	set_hydrate_nodes,
-	set_hydrate_open,
 	set_hydrating
 } from './dom/hydration.js';
 import { array_from } from './utils.js';
@@ -56,6 +58,10 @@ export function set_text(text, value) {
  * @param {null | ((anchor: Comment) => void)} fallback_fn
  */
 export function slot(anchor, slot_fn, slot_props, fallback_fn) {
+	if (hydrating) {
+		hydrate_next();
+	}
+
 	if (slot_fn === undefined) {
 		if (fallback_fn !== null) {
 			fallback_fn(anchor);
@@ -128,6 +134,7 @@ export function hydrate(component, options) {
 
 	const target = options.target;
 	const previous_hydrate_nodes = hydrate_nodes;
+	const was_hydrating = hydrating;
 
 	try {
 		// Don't flush previous effects to ensure order of outer effects stays consistent
@@ -146,7 +153,8 @@ export function hydrate(component, options) {
 				throw HYDRATION_ERROR;
 			}
 
-			set_hydrate_open(/** @type {Comment} */ (anchor));
+			set_hydrate_node(/** @type {Comment} */ (anchor));
+			hydrate_next();
 
 			const instance = _mount(component, { ...options, anchor });
 
@@ -172,8 +180,7 @@ export function hydrate(component, options) {
 
 		throw error;
 	} finally {
-		set_hydrating(!!previous_hydrate_nodes);
-		set_hydrate_nodes(previous_hydrate_nodes);
+		set_hydrating(was_hydrating);
 		reset_head_anchor();
 	}
 }

packages/svelte/src/internal/server/hydration.js

@@ -1,7 +1,6 @@
 import {
 	HYDRATION_ANCHOR,
 	HYDRATION_END,
-	HYDRATION_END_ELSE,
 	HYDRATION_START,
 	HYDRATION_START_ELSE
 } from '../../constants.js';
@@ -10,4 +9,3 @@ export const BLOCK_OPEN = `<!--${HYDRATION_START}-->`;
 export const BLOCK_OPEN_ELSE = `<!--${HYDRATION_START_ELSE}-->`;
 export const BLOCK_CLOSE = `<!--${HYDRATION_END}-->`;
 export const BLOCK_ANCHOR = `<!--${HYDRATION_ANCHOR}-->`;
-export const BLOCK_CLOSE_ELSE = `<!--${HYDRATION_END_ELSE}-->`;

playgrounds/demo/vite.config.js

@@ -11,7 +11,7 @@ export default defineConfig({
 		inspect(),
 		svelte({
 			compilerOptions: {
-				hmr: true
+				hmr: false
 			}
 		})
 	],