wip

packages/svelte/src/compiler/phases/2-analyze/visitors/SvelteBoundary.js

@@ -2,7 +2,7 @@
 /** @import { Context } from '../types' */
 import * as e from '../../../errors.js';
 
-const valid = ['onerror', 'failed'];
+const valid = ['onerror', 'failed', 'pending'];
 
 /**
  * @param {AST.SvelteBoundary} node

packages/svelte/src/compiler/phases/3-transform/client/visitors/SvelteBoundary.js

@@ -39,7 +39,10 @@ export function SvelteBoundary(node, context) {
 
 	// Capture the `failed` implicit snippet prop
 	for (const child of node.fragment.nodes) {
-		if (child.type === 'SnippetBlock' && child.expression.name === 'failed') {
+		if (
+			child.type === 'SnippetBlock' &&
+			(child.expression.name === 'failed' || child.expression.name === 'pending')
+		) {
 			// we need to delay the visit of the snippets in case they access a ConstTag that is declared
 			// after the snippets so that the visitor for the const tag can be updated
 			snippets_visits.push(() => {

packages/svelte/src/index-client.js

@@ -191,3 +191,5 @@ export {
 } from './internal/client/runtime.js';
 
 export { createRawSnippet } from './internal/client/dom/blocks/snippet.js';
+
+export { suspend, unsuspend } from './internal/client/dom/blocks/boundary.js';

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

@@ -1,7 +1,13 @@
 /** @import { Effect, TemplateNode, } from '#client' */
 
-import { BOUNDARY_EFFECT, EFFECT_TRANSPARENT } from '../../constants.js';
-import { block, branch, destroy_effect, pause_effect } from '../../reactivity/effects.js';
+import { BOUNDARY_EFFECT, EFFECT_TRANSPARENT, INERT } from '../../constants.js';
+import {
+	block,
+	branch,
+	destroy_effect,
+	pause_effect,
+	resume_effect
+} from '../../reactivity/effects.js';
 import {
 	active_effect,
 	active_reaction,
@@ -20,8 +26,12 @@ import {
 	remove_nodes,
 	set_hydrate_node
 } from '../hydration.js';
+import { get_next_sibling } from '../operations.js';
 import { queue_micro_task } from '../task.js';
 
+const SUSPEND_INCREMENT = Symbol();
+const SUSPEND_DECREMENT = Symbol();
+
 /**
  * @param {Effect} boundary
  * @param {() => void} fn
@@ -49,6 +59,7 @@ function with_boundary(boundary, fn) {
  * @param {{
  * 	 onerror?: (error: unknown, reset: () => void) => void,
  *   failed?: (anchor: Node, error: () => unknown, reset: () => () => void) => void
+ *   pending?: (anchor: Node) => void
  * }} props
  * @param {((anchor: Node) => void)} boundary_fn
  * @returns {void}
@@ -58,14 +69,95 @@ export function boundary(node, props, boundary_fn) {
 
 	/** @type {Effect} */
 	var boundary_effect;
+	/** @type {Effect | null} */
+	var suspended_effect = null;
+	/** @type {DocumentFragment | null} */
+	var suspended_fragment = null;
+	var suspend_count = 0;
 
 	block(() => {
 		var boundary = /** @type {Effect} */ (active_effect);
 		var hydrate_open = hydrate_node;
 		var is_creating_fallback = false;
 
-		// We re-use the effect's fn property to avoid allocation of an additional field
-		boundary.fn = (/** @type {unknown}} */ error) => {
+		const render_snippet = (/** @type { () => void } */ snippet_fn) => {
+			// Render the snippet in a microtask
+			queue_micro_task(() => {
+				with_boundary(boundary, () => {
+					is_creating_fallback = true;
+
+					try {
+						boundary_effect = branch(() => {
+							snippet_fn();
+						});
+					} catch (error) {
+						handle_error(error, boundary, null, boundary.ctx);
+					}
+
+					reset_is_throwing_error();
+					is_creating_fallback = false;
+				});
+			});
+		};
+
+		// @ts-ignore We re-use the effect's fn property to avoid allocation of an additional field
+		boundary.fn = (/** @type {unknown} */ input) => {
+			let pending = props.pending;
+
+			if (input === SUSPEND_INCREMENT) {
+				if (!pending) {
+					return false;
+				}
+				suspend_count++;
+
+				if (suspended_effect === null) {
+					var effect = boundary_effect;
+					suspended_effect = boundary_effect;
+
+					pause_effect(suspended_effect, () => {
+						/** @type {TemplateNode | null} */
+						var node = effect.nodes_start;
+						var end = effect.nodes_end;
+						suspended_fragment = document.createDocumentFragment();
+
+						while (node !== null) {
+							/** @type {TemplateNode | null} */
+							var sibling =
+								node === end ? null : /** @type {TemplateNode} */ (get_next_sibling(node));
+
+							node.remove();
+							suspended_fragment.append(node);
+							node = sibling;
+						}
+					}, false);
+
+					render_snippet(() => {
+						pending(anchor);
+					});
+				}
+				return true;
+			}
+
+			if (input === SUSPEND_DECREMENT) {
+				if (!pending) {
+					return false;
+				}
+				suspend_count--;
+
+				if (suspend_count === 0 && suspended_effect !== null) {
+					if (boundary_effect) {
+						destroy_effect(boundary_effect);
+					}
+					boundary_effect = suspended_effect;
+					suspended_effect = null;
+					anchor.before(/** @type {DocumentFragment} */ (suspended_fragment));
+					resume_effect(boundary_effect);
+				}
+
+				return true;
+			}
+
+			var error = input;
 			var onerror = props.onerror;
 			let failed = props.failed;
 
@@ -96,26 +188,12 @@ export function boundary(node, props, boundary_fn) {
 			}
 
 			if (failed) {
-				// Render the `failed` snippet in a microtask
-				queue_micro_task(() => {
-					with_boundary(boundary, () => {
-						is_creating_fallback = true;
-
-						try {
-							boundary_effect = branch(() => {
-								failed(
-									anchor,
-									() => error,
-									() => reset
-								);
-							});
-						} catch (error) {
-							handle_error(error, boundary, null, boundary.ctx);
-						}
-
-						reset_is_throwing_error();
-						is_creating_fallback = false;
-					});
+				render_snippet(() => {
+					failed(
+						anchor,
+						() => error,
+						() => reset
+					);
 				});
 			}
 		};
@@ -132,3 +210,31 @@ export function boundary(node, props, boundary_fn) {
 		anchor = hydrate_node;
 	}
 }
+
+export function suspend() {
+	var current = active_effect;
+
+	while (current !== null) {
+		if ((current.f & BOUNDARY_EFFECT) !== 0) {
+			// @ts-ignore
+			if (current.fn(SUSPEND_INCREMENT)) {
+				return;
+			}
+		}
+		current = current.parent;
+	}
+}
+
+export function unsuspend() {
+	var current = active_effect;
+
+	while (current !== null) {
+		if ((current.f & BOUNDARY_EFFECT) !== 0) {
+			// @ts-ignore
+			if (current.fn(SUSPEND_DECREMENT)) {
+				return;
+			}
+		}
+		current = current.parent;
+	}
+}

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

@@ -129,7 +129,7 @@ export {
 	update_store,
 	mark_store_binding
 } from './reactivity/store.js';
-export { boundary } from './dom/blocks/boundary.js';
+export { boundary, suspend } from './dom/blocks/boundary.js';
 export { set_text } from './render.js';
 export {
 	get,

packages/svelte/src/internal/client/reactivity/effects.js

@@ -528,15 +528,20 @@ export function unlink_effect(effect) {
  * A paused effect does not update, and the DOM subtree becomes inert.
  * @param {Effect} effect
  * @param {() => void} [callback]
+ * @param {boolean} [destroy]
  */
-export function pause_effect(effect, callback) {
+export function pause_effect(effect, callback, destroy = true) {
 	/** @type {TransitionManager[]} */
 	var transitions = [];
 
-	pause_children(effect, transitions, true);
+	pause_children(effect, transitions, true, destroy);
 
 	run_out_transitions(transitions, () => {
-		destroy_effect(effect);
+		if (destroy) {
+			destroy_effect(effect);
+		} else {
+			execute_effect_teardown(effect);
+		}
 		if (callback) callback();
 	});
 }
@@ -561,8 +566,9 @@ export function run_out_transitions(transitions, fn) {
  * @param {Effect} effect
  * @param {TransitionManager[]} transitions
  * @param {boolean} local
+ * @param {boolean} [destroy]
  */
-export function pause_children(effect, transitions, local) {
+export function pause_children(effect, transitions, local, destroy = true) {
 	if ((effect.f & INERT) !== 0) return;
 	effect.f ^= INERT;
 
@@ -582,7 +588,7 @@ export function pause_children(effect, transitions, local) {
 		// TODO we don't need to call pause_children recursively with a linked list in place
 		// it's slightly more involved though as we have to account for `transparent` changing
 		// through the tree.
-		pause_children(child, transitions, transparent ? local : false);
+		pause_children(child, transitions, transparent ? local : false, destroy);
 		child = sibling;
 	}
 }
@@ -602,17 +608,21 @@ export function resume_effect(effect) {
  */
 function resume_children(effect, local) {
 	if ((effect.f & INERT) === 0) return;
+	effect.f ^= INERT;
+
+	// Ensure the effect is marked as clean again so that any dirty child
+	// effects can schedule themselves for execution
+	if ((effect.f & CLEAN) === 0) {
+		effect.f ^= CLEAN;
+	}
 
 	// If a dependency of this effect changed while it was paused,
-	// apply the change now
+	// schedule the effect to update
 	if (check_dirtiness(effect)) {
-		update_effect(effect);
+		set_signal_status(effect, DIRTY);
+		schedule_effect(effect);
 	}
 
-	// Ensure we toggle the flag after possibly updating the effect so that
-	// each block logic can correctly operate on inert items
-	effect.f ^= INERT;
-
 	var child = effect.first;
 
 	while (child !== null) {

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

@@ -776,7 +776,7 @@ export function schedule_effect(signal) {
 		var flags = effect.f;
 
 		if ((flags & (ROOT_EFFECT | BRANCH_EFFECT)) !== 0) {
-			if ((flags & CLEAN) === 0) return;
+			if ((flags & CLEAN) === 0) return
 			effect.f ^= CLEAN;
 		}
 	}