Fix 298633 (#3233)

Author: JiuqingSong

packages/roosterjs-content-model-plugins/lib/edit/deleteSteps/deleteList.ts

@@ -1,5 +1,13 @@
-import { getClosestAncestorBlockGroupIndex } from 'roosterjs-content-model-dom';
-import type { DeleteSelectionStep, ContentModelListItem } from 'roosterjs-content-model-types';
+import {
+    createListItem,
+    getClosestAncestorBlockGroupIndex,
+    mutateBlock,
+} from 'roosterjs-content-model-dom';
+import type {
+    DeleteSelectionStep,
+    ContentModelListItem,
+    ContentModelBlock,
+} from 'roosterjs-content-model-types';
 
 /**
  * @internal
@@ -10,21 +18,65 @@ export const deleteList: DeleteSelectionStep = context => {
     }
 
     const { paragraph, marker, path } = context.insertPoint;
+    const index = getClosestAncestorBlockGroupIndex<ContentModelListItem>(
+        path,
+        ['ListItem'],
+        ['TableCell', 'FormatContainer']
+    );
+    const item = path[index];
+    const parent = path[index + 1];
 
-    if (paragraph.segments[0] == marker) {
-        const index = getClosestAncestorBlockGroupIndex<ContentModelListItem>(
-            path,
-            ['ListItem'],
-            ['TableCell', 'FormatContainer']
-        );
-        const item = path[index] as ContentModelListItem | undefined;
-        const lastLevel = item?.levels[item.levels.length - 1];
-
-        if (lastLevel && item?.blocks[0] == paragraph) {
-            if (lastLevel.format.displayForDummyItem == 'block') {
-                item.levels.pop();
+    if (
+        item?.blockGroupType == 'ListItem' &&
+        item.levels.length > 0 &&
+        paragraph.segments[0] == marker &&
+        parent
+    ) {
+        const mutableList = mutateBlock(item);
+        const lastLevel = mutableList.levels[mutableList.levels.length - 1];
+        const listItemIndex = parent.blocks.indexOf(item);
+        const previousItem = parent.blocks[listItemIndex - 1];
+
+        // 1. If the last level is dummy, just remove it (legacy behavior)
+        // 2. If focus is at the beginning of list item and previous block is a list item with the same level count,
+        //    merge current list item into previous one
+        // 3. Otherwise, split the list item. Keep the blocks before the paragraph in the current list item,
+        //    move the rest to a new list item (if there are multiple levels) or directly to parent (if only one level)
+        if (lastLevel.format.displayForDummyItem == 'block') {
+            mutableList.levels.pop();
+
+            context.deleteResult = 'range';
+        } else if (
+            item.blocks[0] == paragraph &&
+            previousItem?.blockType == 'BlockGroup' &&
+            previousItem.blockGroupType == 'ListItem' &&
+            previousItem.levels.length == mutableList.levels.length
+        ) {
+            const mutablePreviousItem = mutateBlock(previousItem);
+
+            mutablePreviousItem.blocks.push(...mutableList.blocks);
+            mutateBlock(parent).blocks.splice(listItemIndex, 1);
+
+            context.deleteResult = 'range';
+        } else {
+            const removedBlocks = mutableList.blocks.splice(
+                mutableList.blocks.indexOf(paragraph),
+                mutableList.blocks.length
+            );
+
+            if (mutableList.levels.length > 1) {
+                const newListItem = createListItem(
+                    mutableList.levels.slice(0, -1),
+                    mutableList.format
+                );
+
+                newListItem.blocks = removedBlocks.map(
+                    block => mutateBlock(block) as ContentModelBlock
+                );
+
+                mutateBlock(parent).blocks.splice(listItemIndex + 1, 0, newListItem);
             } else {
-                lastLevel.format.displayForDummyItem = 'block';
+                mutateBlock(parent).blocks.splice(listItemIndex + 1, 0, ...removedBlocks);
             }
 
             context.deleteResult = 'range';