make elseif transparent for transition purposes

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

@@ -2548,22 +2548,24 @@ export const template_visitors = {
 			context.visit(node.consequent)
 		);
 
-		context.state.after_update.push(
-			b.stmt(
-				b.call(
-					'$.if',
-					context.state.node,
-					b.thunk(/** @type {import('estree').Expression} */ (context.visit(node.test))),
-					b.arrow([b.id('$$anchor')], consequent),
-					node.alternate
-						? b.arrow(
-								[b.id('$$anchor')],
-								/** @type {import('estree').BlockStatement} */ (context.visit(node.alternate))
-							)
-						: b.literal(null)
-				)
-			)
-		);
+		const args = [
+			context.state.node,
+			b.thunk(/** @type {import('estree').Expression} */ (context.visit(node.test))),
+			b.arrow([b.id('$$anchor')], consequent),
+			node.alternate
+				? b.arrow(
+						[b.id('$$anchor')],
+						/** @type {import('estree').BlockStatement} */ (context.visit(node.alternate))
+					)
+				: b.literal(null)
+		];
+
+		if (node.elseif) {
+			// the additional effect layer shouldn't affect local transitions
+			args.push(b.literal(true));
+		}
+
+		context.state.after_update.push(b.stmt(b.call('$.if', ...args)));
 	},
 	AwaitBlock(node, context) {
 		context.state.template.push('<!>');

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

@@ -9,6 +9,7 @@ export const DIRTY = 1 << 9;
 export const MAYBE_DIRTY = 1 << 10;
 export const INERT = 1 << 11;
 export const DESTROYED = 1 << 12;
+export const IS_ELSEIF = 1 << 13;
 
 export const ROOT_BLOCK = 0;
 export const IF_BLOCK = 1;

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

@@ -1,4 +1,4 @@
-import { IF_BLOCK, UNINITIALIZED } from '../../constants.js';
+import { IF_BLOCK, IS_ELSEIF, UNINITIALIZED } from '../../constants.js';
 import {
 	current_hydration_fragment,
 	hydrate_block_anchor,
@@ -37,9 +37,10 @@ function create_if_block() {
  * @param {() => boolean} condition_fn
  * @param {(anchor: Node) => void} consequent_fn
  * @param {null | ((anchor: Node) => void)} alternate_fn
+ * @param {boolean} [elseif]
  * @returns {void}
  */
-export function if_block(anchor_node, condition_fn, consequent_fn, alternate_fn) {
+export function if_block(anchor_node, condition_fn, consequent_fn, alternate_fn, elseif = false) {
 	const block = create_if_block();
 
 	hydrate_block_anchor(anchor_node);
@@ -153,6 +154,8 @@ export function if_block(anchor_node, condition_fn, consequent_fn, alternate_fn)
 		}
 	}, block);
 
+	if_effect.f |= IS_ELSEIF;
+
 	mismatch = false; // TODO not sure if we actually need this — belt and braces
 
 	if_effect.ondestroy = () => {

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

@@ -20,7 +20,8 @@ import {
 	EFFECT,
 	PRE_EFFECT,
 	DESTROYED,
-	INERT
+	INERT,
+	IS_ELSEIF
 } from '../constants.js';
 import { set } from './sources.js';
 import { noop } from '../../common.js';
@@ -300,7 +301,8 @@ function pause_children(effect, transitions, local) {
 
 	if (effect.effects) {
 		for (const child of effect.effects) {
-			pause_children(child, transitions, false);
+			var transparent = (child.f & IS_ELSEIF) !== 0 || (child.f & MANAGED) !== 0;
+			pause_children(child, transitions, transparent ? local : false);
 		}
 	}
 }
@@ -323,7 +325,8 @@ function resume_children(effect, local) {
 
 	if (effect.effects) {
 		for (const child of effect.effects) {
-			resume_children(child, false);
+			var transparent = (child.f & IS_ELSEIF) !== 0 || (child.f & MANAGED) !== 0;
+			resume_children(child, transparent ? local : false);
 		}
 	}