From 24ac097a639c0ef8c961bb5ed8a237e22c42eaae Mon Sep 17 00:00:00 2001
From: Ella <ella@vandurpe.com>
Date: Fri, 6 Oct 2023 14:38:23 +0300
Subject: [PATCH] List: fix forward merging of nested list

---
 .../src/list-item/hooks/use-merge.js          | 43 ++++++-------
 test/e2e/specs/editor/blocks/list.spec.js     | 64 ++++++++++++-------
 2 files changed, 62 insertions(+), 45 deletions(-)

diff --git a/packages/block-library/src/list-item/hooks/use-merge.js b/packages/block-library/src/list-item/hooks/use-merge.js
index 6b456a2a742bdb..cda1f0c02d3a88 100644
--- a/packages/block-library/src/list-item/hooks/use-merge.js
+++ b/packages/block-library/src/list-item/hooks/use-merge.js
@@ -76,6 +76,24 @@ export default function useMerge( clientId, onMerge ) {
 	}
 
 	return ( forward ) => {
+		function mergeWithNested( clientIdA, clientIdB ) {
+			registry.batch( () => {
+				// When merging a sub list item with a higher next list item, we
+				// also need to move any nested list items. Check if there's a
+				// listed list, and append its nested list items to the current
+				// list.
+				const [ nestedListClientId ] = getBlockOrder( clientIdB );
+				if ( nestedListClientId ) {
+					moveBlocksToPosition(
+						getBlockOrder( nestedListClientId ),
+						nestedListClientId,
+						getBlockRootClientId( clientIdA )
+					);
+				}
+				mergeBlocks( clientIdA, clientIdB );
+			} );
+		}
+
 		if ( forward ) {
 			const nextBlockClientId = getNextId( clientId );
 
@@ -87,14 +105,7 @@ export default function useMerge( clientId, onMerge ) {
 			if ( getParentListItemId( nextBlockClientId ) ) {
 				outdentListItem( nextBlockClientId );
 			} else {
-				registry.batch( () => {
-					moveBlocksToPosition(
-						getBlockOrder( nextBlockClientId ),
-						nextBlockClientId,
-						getPreviousBlockClientId( nextBlockClientId )
-					);
-					mergeBlocks( clientId, nextBlockClientId );
-				} );
+				mergeWithNested( clientId, nextBlockClientId );
 			}
 		} else {
 			// Merging is only done from the top level. For lowel levels, the
@@ -104,21 +115,7 @@ export default function useMerge( clientId, onMerge ) {
 				outdentListItem( clientId );
 			} else if ( previousBlockClientId ) {
 				const trailingId = getTrailingId( previousBlockClientId );
-				registry.batch( () => {
-					// When merging a list item with a previous trailing list
-					// item, we also need to move any nested list items. First,
-					// check if there's a listed list. If there's a nested list,
-					// append its nested list items to the trailing list.
-					const [ nestedListClientId ] = getBlockOrder( clientId );
-					if ( nestedListClientId ) {
-						moveBlocksToPosition(
-							getBlockOrder( nestedListClientId ),
-							nestedListClientId,
-							getBlockRootClientId( trailingId )
-						);
-					}
-					mergeBlocks( trailingId, clientId );
-				} );
+				mergeWithNested( trailingId, clientId );
 			} else {
 				onMerge( forward );
 			}
diff --git a/test/e2e/specs/editor/blocks/list.spec.js b/test/e2e/specs/editor/blocks/list.spec.js
index f4396982bb997f..741e4a210d2f73 100644
--- a/test/e2e/specs/editor/blocks/list.spec.js
+++ b/test/e2e/specs/editor/blocks/list.spec.js
@@ -1361,11 +1361,8 @@ test.describe( 'List (@firefox)', () => {
 <!-- /wp:list -->` );
 	} );
 
-	test( 'should merge two list items with nested lists', async ( {
-		editor,
-		page,
-	} ) => {
-		await editor.insertBlock( {
+	test.describe( 'should merge two list items with nested lists', () => {
+		const start = {
 			name: 'core/list',
 			innerBlocks: [
 				{
@@ -1399,22 +1396,8 @@ test.describe( 'List (@firefox)', () => {
 					],
 				},
 			],
-		} );
-
-		// Navigate to the third item.
-		await page.keyboard.press( 'ArrowDown' );
-		await page.keyboard.press( 'ArrowDown' );
-		await page.keyboard.press( 'ArrowDown' );
-		await page.keyboard.press( 'ArrowDown' );
-		await page.keyboard.press( 'ArrowDown' );
-		await page.keyboard.press( 'ArrowDown' );
-
-		await page.keyboard.press( 'Backspace' );
-
-		// Test caret position.
-		await page.keyboard.type( '‸' );
-
-		await expect.poll( editor.getBlocks ).toMatchObject( [
+		};
+		const end = [
 			{
 				name: 'core/list',
 				innerBlocks: [
@@ -1439,6 +1422,43 @@ test.describe( 'List (@firefox)', () => {
 					},
 				],
 			},
-		] );
+		];
+
+		test( 'Backspace', async ( { editor, page } ) => {
+			await editor.insertBlock( start );
+
+			// Navigate to the start of the third item.
+			await page.keyboard.press( 'ArrowDown' );
+			await page.keyboard.press( 'ArrowDown' );
+			await page.keyboard.press( 'ArrowDown' );
+			await page.keyboard.press( 'ArrowDown' );
+			await page.keyboard.press( 'ArrowDown' );
+			await page.keyboard.press( 'ArrowDown' );
+
+			await page.keyboard.press( 'Backspace' );
+
+			// Test caret position.
+			await page.keyboard.type( '‸' );
+
+			await expect.poll( editor.getBlocks ).toMatchObject( end );
+		} );
+
+		test( 'Delete (forward)', async ( { editor, page } ) => {
+			await editor.insertBlock( start );
+
+			// Navigate to the end of the second item.
+			await page.keyboard.press( 'ArrowDown' );
+			await page.keyboard.press( 'ArrowDown' );
+			await page.keyboard.press( 'ArrowDown' );
+			await page.keyboard.press( 'ArrowDown' );
+			await page.keyboard.press( 'ArrowRight' );
+
+			await page.keyboard.press( 'Delete' );
+
+			// Test caret position.
+			await page.keyboard.type( '‸' );
+
+			await expect.poll( editor.getBlocks ).toMatchObject( end );
+		} );
 	} );
 } );