fix hydration

Author: Rich-Harris

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

@@ -7,6 +7,7 @@ import {
 	pause_effect,
 	resume_effect
 } from '../../reactivity/effects.js';
+import { hydrate_node, hydrating } from '../hydration.js';
 import { create_text, should_defer_append } from '../operations.js';
 
 /**
@@ -18,7 +19,7 @@ import { create_text, should_defer_append } from '../operations.js';
  */
 export class BranchManager {
 	/** @type {TemplateNode} */
-	#anchor;
+	anchor;
 
 	/** @type {Map<Batch, Key>} */
 	#batches = new Map();
@@ -34,7 +35,7 @@ export class BranchManager {
 	 * @param {TemplateNode} anchor
 	 */
 	constructor(anchor) {
-		this.#anchor = anchor;
+		this.anchor = anchor;
 	}
 
 	#commit = () => {
@@ -58,7 +59,7 @@ export class BranchManager {
 			/** @type {TemplateNode} */ (offscreen.fragment.lastChild).remove();
 
 			// ...and append the fragment
-			this.#anchor.before(offscreen.fragment);
+			this.anchor.before(offscreen.fragment);
 		}
 
 		this.#batches.delete(batch);
@@ -132,6 +133,10 @@ export class BranchManager {
 
 			batch.add_callback(this.#commit);
 		} else {
+			if (hydrating) {
+				this.anchor = hydrate_node;
+			}
+
 			this.#commit();
 		}
 	}

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

@@ -29,9 +29,6 @@ export function if_block(node, fn, elseif = false) {
 
 	var anchor = node;
 
-	/** @type {typeof UNINITIALIZED | boolean | null} */
-	var condition = UNINITIALIZED;
-
 	var flags = elseif ? EFFECT_TRANSPARENT : 0;
 
 	var has_branch = false;
@@ -44,12 +41,9 @@ export function if_block(node, fn, elseif = false) {
 	var branches = new BranchManager(anchor);
 
 	const update_branch = (
-		/** @type {boolean | null} */ new_condition,
+		/** @type {boolean} */ condition,
 		/** @type {null | ((anchor: Node) => void)} */ fn
 	) => {
-		/** Whether or not there was a hydration mismatch. Needs to be a `let` or else it isn't treeshaken out */
-		let mismatch = false;
-
 		if (hydrating) {
 			const is_else = read_hydration_instruction(anchor) === HYDRATION_START_ELSE;
 
@@ -59,24 +53,24 @@ export function if_block(node, fn, elseif = false) {
 				anchor = skip_nodes();
 
 				set_hydrate_node(anchor);
+				branches.anchor = anchor;
+
 				set_hydrating(false);
-				mismatch = true;
+				branches.ensure(condition, fn ?? noop);
+				set_hydrating(true);
+
+				return;
 			}
 		}
 
-		branches.ensure(new_condition, fn ?? noop);
-
-		if (mismatch) {
-			// continue in hydration mode
-			set_hydrating(true);
-		}
+		branches.ensure(condition, fn ?? noop);
 	};
 
 	block(() => {
 		has_branch = false;
 		fn(set_branch);
 		if (!has_branch) {
-			update_branch(null, null);
+			update_branch(false, null);
 		}
 	}, flags);