fix: improve outro behavior with transitions

.changeset/empty-bulldogs-exercise.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: improve outro behavior with transitions

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

@@ -1012,10 +1012,11 @@ export function mutate_store(store, expression, new_value) {
 
 /**
  * @param {import('./types.js').ComputationSignal} signal
+ * @param {import('./types.js').ComputationSignal} root
  * @param {boolean} inert
  * @returns {void}
  */
-export function mark_subtree_inert(signal, inert) {
+export function mark_subtree_inert(signal, root, inert, visited_blocks = new Set()) {
 	const flags = signal.f;
 	const is_already_inert = (flags & INERT) !== 0;
 	if (is_already_inert !== inert) {
@@ -1025,22 +1026,28 @@ export function mark_subtree_inert(signal, inert) {
 		}
 		// Nested if block effects
 		const block = signal.b;
-		if (block !== null) {
+		if (block !== null && !visited_blocks.has(block)) {
+			visited_blocks.add(block);
 			const type = block.t;
 			if (type === IF_BLOCK) {
+				const condition_effect = block.e;
+				const root_block = root.b?.p;
+				if (condition_effect !== null && root_block?.t === IF_BLOCK) {
+					mark_subtree_inert(condition_effect, root, inert);
+				}
 				const consequent_effect = block.ce;
 				if (consequent_effect !== null) {
-					mark_subtree_inert(consequent_effect, inert);
+					mark_subtree_inert(consequent_effect, root, inert, visited_blocks);
 				}
 				const alternate_effect = block.ae;
 				if (alternate_effect !== null) {
-					mark_subtree_inert(alternate_effect, inert);
+					mark_subtree_inert(alternate_effect, root, inert, visited_blocks);
 				}
 			} else if (type === EACH_BLOCK) {
 				const items = block.v;
 				for (let { e: each_item_effect } of items) {
 					if (each_item_effect !== null) {
-						mark_subtree_inert(each_item_effect, inert);
+						mark_subtree_inert(each_item_effect, root, inert, visited_blocks);
 					}
 				}
 			}
@@ -1050,7 +1057,7 @@ export function mark_subtree_inert(signal, inert) {
 	if (references !== null) {
 		let i;
 		for (i = 0; i < references.length; i++) {
-			mark_subtree_inert(references[i], inert);
+			mark_subtree_inert(references[i], root, inert, visited_blocks);
 		}
 	}
 }

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

@@ -371,22 +371,6 @@ function create_transition(dom, init, direction, effect) {
 		o() {
 			// @ts-ignore
 			const has_keyed_transition = dom.__animate;
-			const needs_reverse = direction === 'both' && curr_direction !== 'out';
-			curr_direction = 'out';
-			if (animation === null || cancelled) {
-				cancelled = false;
-				create_animation();
-			}
-			if (animation === null) {
-				transition.x();
-			} else {
-				dispatch_event(dom, 'outrostart');
-				if (needs_reverse) {
-					/** @type {Animation | TickAnimation} */ (animation).reverse();
-				} else {
-					/** @type {Animation | TickAnimation} */ (animation).play();
-				}
-			}
 			// If we're outroing an element that has an animation, then we need to fix
 			// its position to ensure it behaves nicely without causing layout shift.
 			if (has_keyed_transition) {
@@ -402,20 +386,46 @@ function create_transition(dom, init, direction, effect) {
 					dom.style.height = height;
 					const b = dom.getBoundingClientRect();
 					if (a.left !== b.left || a.top !== b.top) {
-						// Previously, in the Svelte 4, we'd just apply the transform the the DOM element. However,
-						// because we're now using Web Animations, we can't do that as it won't work properly if the
-						// animation is also making use of the same transformations. So instead, we apply an instantaneous
-						// animation and pause it on the first frame, just applying the same behavior.
-						const style = getComputedStyle(dom);
-						const transform = style.transform === 'none' ? '' : style.transform;
-						const frame = {
-							transform: `${transform} translate(${a.left - b.left}px, ${a.top - b.top}px)`
-						};
-						const animation = dom.animate([frame, frame], { duration: 1 });
-						animation.pause();
+						const translate = `translate(${a.left - b.left}px, ${a.top - b.top}px)`;
+						const existing_transform = style.transform;
+						if (existing_transform === 'none') {
+							dom.style.transform = translate;
+						} else {
+							// Previously, in the Svelte 4, we'd just apply the transform the the DOM element. However,
+							// because we're now using Web Animations, we can't do that as it won't work properly if the
+							// animation is also making use of the same transformations. So instead, we apply an
+							// instantaneous animation and pause it on the first frame, just applying the same behavior.
+							// We also need to take into consideration matrix transforms and how they might combine with
+							// an existing behavior that is already in progress (such as scale).
+							// > Follow the white rabbit.
+							const transform = existing_transform.startsWith('matrix(1,')
+								? translate
+								: `matrix(1,0,0,1,0,0)`;
+							const frame = {
+								transform
+							};
+							const animation = dom.animate([frame, frame], { duration: 1 });
+							animation.pause();
+						}
 					}
 				}
 			}
+			const needs_reverse = direction === 'both' && curr_direction !== 'out';
+			curr_direction = 'out';
+			if (animation === null || cancelled) {
+				cancelled = false;
+				create_animation();
+			}
+			if (animation === null) {
+				transition.x();
+			} else {
+				dispatch_event(dom, 'outrostart');
+				if (needs_reverse) {
+					/** @type {Animation | TickAnimation} */ (animation).reverse();
+				} else {
+					/** @type {Animation | TickAnimation} */ (animation).play();
+				}
+			}
 		},
 		// cancel
 		c() {
@@ -584,14 +594,15 @@ export function trigger_transitions(transitions, target_direction, from) {
 	const outros = [];
 	for (const transition of transitions) {
 		const direction = transition.r;
+		const effect = transition.e;
 		if (target_direction === 'in') {
 			if (direction === 'in' || direction === 'both') {
 				transition.in();
 			} else {
 				transition.c();
 			}
 			transition.d.inert = false;
-			mark_subtree_inert(transition.e, false);
+			mark_subtree_inert(effect, effect, false);
 		} else if (target_direction === 'key') {
 			if (direction === 'key') {
 				transition.p = transition.i(/** @type {DOMRect} */ (from));
@@ -603,7 +614,7 @@ export function trigger_transitions(transitions, target_direction, from) {
 				outros.push(transition.o);
 			}
 			transition.d.inert = true;
-			mark_subtree_inert(transition.e, true);
+			mark_subtree_inert(effect, effect, true);
 		}
 	}
 	if (outros.length > 0) {