[Block Editor]: Fix caret position on block merging (#34169)

* [Block Editor]: Fix caret position on block merging

* add e2e tests

* update e2e tests

packages/block-editor/src/store/actions.js

@@ -885,7 +885,8 @@ export function* mergeBlocks( firstBlockClientId, secondBlockClientId ) {
 				},
 			},
 			...blocksWithTheSameType.slice( 1 ),
-		]
+		],
+		0 // If we don't pass the `indexToSelect` it will default to the last block.
 	);
 }
 

packages/block-editor/src/store/reducer.js

@@ -1281,9 +1281,9 @@ function selectionHelper( state = {}, action ) {
 				return state;
 			}
 
-			const indexToSelect =
-				action.indexToSelect || action.blocks.length - 1;
-			const blockToSelect = action.blocks[ indexToSelect ];
+			const blockToSelect =
+				action.blocks[ action.indexToSelect ] ||
+				action.blocks[ action.blocks.length - 1 ];
 
 			if ( ! blockToSelect ) {
 				return {};

packages/block-editor/src/store/test/reducer.js

@@ -2397,6 +2397,30 @@ describe( 'state', () => {
 			expect( state.selectionEnd ).toEqual( expected.selectionEnd );
 		} );
 
+		it( 'should replace the selected block when is explicitly passed (`indexToSelect`)', () => {
+			const original = deepFreeze( {
+				selectionStart: { clientId: 'chicken' },
+				selectionEnd: { clientId: 'chicken' },
+			} );
+			const action = {
+				type: 'REPLACE_BLOCKS',
+				clientIds: [ 'chicken' ],
+				blocks: [
+					{ clientId: 'rigas' },
+					{ clientId: 'chicken' },
+					{ clientId: 'wings' },
+				],
+				indexToSelect: 0,
+			};
+			const state = selection( original, action );
+			expect( state ).toEqual(
+				expect.objectContaining( {
+					selectionStart: { clientId: 'rigas' },
+					selectionEnd: { clientId: 'rigas' },
+				} )
+			);
+		} );
+
 		it( 'should reset if replacing with empty set', () => {
 			const original = deepFreeze( {
 				selectionStart: { clientId: 'chicken' },

packages/e2e-tests/specs/editor/various/splitting-merging.test.js

@@ -226,4 +226,50 @@ describe( 'splitting and merging blocks', () => {
 
 		expect( await getEditedPostContent() ).toMatchSnapshot();
 	} );
+
+	describe( 'test restore selection when merge produces more than one block', () => {
+		it( 'on forward delete', async () => {
+			await insertBlock( 'Paragraph' );
+			await page.keyboard.type( 'hi' );
+			await insertBlock( 'List' );
+			await page.keyboard.type( 'item 1' );
+			await page.keyboard.press( 'Enter' );
+			await page.keyboard.type( 'item 2' );
+			await pressKeyTimes( 'ArrowUp', 2 );
+			await page.keyboard.press( 'Delete' );
+			// Carret should be in the first block and at the proper position.
+			await page.keyboard.type( '-' );
+			expect( await getEditedPostContent() ).toMatchInlineSnapshot( `
+			"<!-- wp:paragraph -->
+			<p>hi-item 1</p>
+			<!-- /wp:paragraph -->
+
+			<!-- wp:paragraph -->
+			<p>item 2</p>
+			<!-- /wp:paragraph -->"
+		` );
+		} );
+		it( 'on backspace', async () => {
+			await insertBlock( 'Paragraph' );
+			await page.keyboard.type( 'hi' );
+			await insertBlock( 'List' );
+			await page.keyboard.type( 'item 1' );
+			await page.keyboard.press( 'Enter' );
+			await page.keyboard.type( 'item 2' );
+			await page.keyboard.press( 'ArrowUp' );
+			await pressKeyTimes( 'ArrowLeft', 6 );
+			await page.keyboard.press( 'Backspace' );
+			// Carret should be in the first block and at the proper position.
+			await page.keyboard.type( '-' );
+			expect( await getEditedPostContent() ).toMatchInlineSnapshot( `
+			"<!-- wp:paragraph -->
+			<p>hi-item 1</p>
+			<!-- /wp:paragraph -->
+
+			<!-- wp:paragraph -->
+			<p>item 2</p>
+			<!-- /wp:paragraph -->"
+		` );
+		} );
+	} );
 } );