fix(editor): behavior of deleting at the start of line (#12787)

Close BS-3182, #12736 




#### PR Dependency Tree


* **PR #12787** 👈

This tree was auto-generated by
[Charcoal](https://github.com/danerwilliams/charcoal)

<!-- This is an auto-generated comment: release notes by coderabbit.ai
-->

## Summary by CodeRabbit

- **Bug Fixes**
- Improved the behavior when deleting empty lines and merging blocks,
ensuring more accurate handling of block deletion and cursor focus in
various scenarios.
- **Tests**
- Added new end-to-end tests to verify correct deletion of lines in
edgeless text and paragraph blocks, including checks for block removal
and cursor position.
- Introduced a utility function to retrieve block IDs for testing
purposes.

<!-- end of auto-generated comment: release notes by coderabbit.ai -->

tests/blocksuite/e2e/edgeless/edgeless-text.spec.ts

@@ -11,6 +11,8 @@ import {
   edgelessCommonSetup,
   enterPlaygroundRoom,
   getEdgelessSelectedRect,
+  getIds,
+  getInlineSelectionIndex,
   getPageSnapshot,
   initEmptyEdgelessState,
   pasteByKeyboard,
@@ -21,6 +23,8 @@ import {
   pressBackspace,
   pressEnter,
   pressEscape,
+  pressShiftTab,
+  pressTab,
   redoByKeyboard,
   selectAllByKeyboard,
   setEdgelessTool,
@@ -552,6 +556,52 @@ test.describe('edgeless text block', () => {
       1
     );
   });
+
+  test('edgeless text should be able to delete line', async ({ page }) => {
+    await dblclickView(page, [100, -100]);
+    // 5: aaa
+    // 6:     bbb
+    // 7: ccc|
+    {
+      await type(page, 'aaa');
+      await pressEnter(page);
+      await pressTab(page);
+      await type(page, 'bbb');
+      await pressEnter(page);
+      await pressShiftTab(page);
+      await type(page, 'ccc');
+    }
+
+    // 5: aaa
+    // 6:     bbb|
+    await pressBackspace(page, 4);
+    expect(await getIds(page)).not.toContain(7);
+    await assertBlockTextContent(page, 5, 'aaa');
+    await assertBlockTextContent(page, 6, 'bbb');
+    expect(await getInlineSelectionIndex(page)).toBe(3);
+
+    // 5: |aaa
+    // 6:     bbb
+    {
+      await pressArrowUp(page);
+      await pressArrowLeft(page, 3);
+      await pressBackspace(page);
+    }
+
+    await assertBlockTextContent(page, 5, 'aaa');
+    await assertBlockTextContent(page, 6, 'bbb');
+    expect(await getInlineSelectionIndex(page)).toBe(0);
+
+    // 6: |bbb
+    {
+      await pressArrowRight(page, 3);
+      await pressBackspace(page, 4);
+    }
+
+    expect(await getIds(page)).not.toContain(7);
+    await assertBlockTextContent(page, 6, 'bbb');
+    expect(await getInlineSelectionIndex(page)).toBe(0);
+  });
 });
 
 test('press backspace at the start of first line when edgeless text exist', async ({

tests/blocksuite/e2e/paragraph.spec.ts

@@ -8,7 +8,9 @@ import {
   enterPlaygroundRoom,
   focusRichText,
   focusTitle,
+  getBlockIds,
   getIndexCoordinate,
+  getInlineSelectionIndex,
   getPageSnapshot,
   initEmptyEdgelessState,
   initEmptyParagraphState,
@@ -44,6 +46,7 @@ import {
   assertBlockChildrenIds,
   assertBlockCount,
   assertBlockSelections,
+  assertBlockTextContent,
   assertBlockType,
   assertClassName,
   assertDivider,
@@ -734,6 +737,45 @@ test('delete at start of paragraph with content', async ({ page }) => {
   await assertRichTexts(page, ['123', '456']);
 });
 
+test('delete empty line should work correctly', async ({ page }) => {
+  await enterPlaygroundRoom(page);
+  await initEmptyParagraphState(page);
+  await focusRichText(page);
+
+  // 2: aaa
+  // 3:     bbb
+  // 4: ccc|
+  {
+    await type(page, 'aaa');
+    await pressEnter(page);
+    await pressTab(page);
+    await type(page, 'bbb');
+    await pressEnter(page);
+    await pressShiftTab(page);
+    await type(page, 'ccc');
+  }
+
+  // 2: aaa
+  // 3:     bbb|
+  await pressBackspace(page, 4);
+  expect(await getBlockIds(page)).not.toContain(4);
+  await assertBlockTextContent(page, 2, 'aaa');
+  await assertBlockTextContent(page, 3, 'bbb');
+  expect(await getInlineSelectionIndex(page)).toBe(3);
+
+  // title: |aaa
+  // 3: bbb
+  {
+    await pressArrowUp(page);
+    await pressArrowLeft(page, 3);
+    await pressBackspace(page);
+  }
+  await expect(page.locator('doc-title')).toContainText('aaa');
+  expect(await getBlockIds(page)).not.toContain(2);
+  await assertBlockTextContent(page, 3, 'bbb');
+  expect(await getInlineSelectionIndex(page)).toBe(0);
+});
+
 test('get focus from page title enter', async ({ page }) => {
   await enterPlaygroundRoom(page);
   await initEmptyParagraphState(page);

tests/blocksuite/e2e/utils/actions/block.ts

@@ -23,3 +23,9 @@ export async function updateBlockType(
   );
   await waitNextFrame(page, 400);
 }
+
+export async function getBlockIds(page: Page) {
+  return page.evaluate(() => {
+    return window.host.std.store.getAllModels().map(m => m.id);
+  });
+}