Merge successive non-leaf blocks resulting from untab

Summary:
When untab results in two consecutive non-leaf blocks of the same type, it causes various bugs & issues on certain further operations.

- Implement an operation to merge two consecutive blocks in the block map by adding all the children of the next block to the given (previous) block & removing the next block.
- Use this operation during untab for the case where children were moved up & there are two consecutive non-leaf blocks (see before & after videos in test plan)

Merge operation:
https://pxl.cl/hsS9

Untab resulting in merge:
https://pxl.cl/hsSg

(these two examples are implemented as tests )

Reviewed By: vdurmont

Differential Revision: D9834729

fbshipit-source-id: 5352763266e3b5fbb030b329015298bd669a4a4f

Author: niveditc

src/model/modifier/exploration/DraftTreeOperations.js

@@ -433,11 +433,70 @@ const moveChildUp = (blockMap: BlockMap, key: string): BlockMap => {
   return newBlockMap;
 };
 
+/**
+ * This is a utility method to merge two non-leaf blocks into one. The next block's
+ * children are added to the provided block & the next block is deleted.
+ *
+ * This operation respects the tree data invariants - it expects and returns a
+ * valid tree.
+ */
+const mergeBlocks = (blockMap: BlockMap, key: string): BlockMap => {
+  verifyTree(blockMap);
+  // current block must be a non-leaf
+  let block = blockMap.get(key);
+  invariant(block !== null, 'block must exist in block map');
+  invariant(block.getChildKeys().count() > 0, 'block must be a non-leaf');
+  // next block must exist & be a non-leaf
+  const nextBlockKey = block.getNextSiblingKey();
+  invariant(nextBlockKey != null, 'block must have a next block');
+  const nextBlock = blockMap.get(nextBlockKey);
+  invariant(nextBlock != null, 'next block must exist in block map');
+  invariant(
+    nextBlock.getChildKeys().count() > 0,
+    'next block must be a non-leaf',
+  );
+
+  const childKeys = block.getChildKeys().concat(nextBlock.getChildKeys());
+  block = block.merge({
+    nextSibling: nextBlock.getNextSiblingKey(),
+    children: childKeys,
+  });
+  const nextChildren = childKeys.map((k, i) =>
+    blockMap.get(k).merge({
+      parent: key,
+      prevSibling: i - 1 < 0 ? null : childKeys.get(i - 1),
+      nextSibling: i + 1 === childKeys.count() ? null : childKeys.get(i + 1),
+    }),
+  );
+
+  const nextNextBlockKey = nextBlock.getNextSiblingKey();
+  const blocks = blockMap.toSeq();
+  const newBlockMap = blocks
+    .takeUntil(b => b.getKey() === key)
+    .concat(
+      [[block.getKey(), block]],
+      nextChildren.map(b => [b.getKey(), b]),
+      nextNextBlockKey != null
+        ? [
+            [
+              nextNextBlockKey,
+              blockMap.get(nextNextBlockKey).merge({prevSibling: key}),
+            ],
+          ]
+        : [],
+      blocks.skipUntil(b => b.getKey() === nextNextBlockKey).rest(),
+    )
+    .toOrderedMap();
+  verifyTree(newBlockMap);
+  return newBlockMap;
+};
+
 module.exports = {
   updateParentChild,
   replaceParentChild,
   updateSibling,
   createNewParent,
   updateAsSiblingsChild,
   moveChildUp,
+  mergeBlocks,
 };

src/model/modifier/exploration/NestedRichTextEditorUtil.js

@@ -422,6 +422,7 @@ const NestedRichTextEditorUtil: RichTextUtils = {
 
       // on untab, we also want to unnest any sibling blocks that become two levels deep
       // ensure that block's old parent does not have a non-leaf as its first child.
+      let childWasUntabbed = false;
       if (parentKey != null) {
         let parent = blockMap.get(parentKey);
         while (parent != null) {
@@ -437,6 +438,26 @@ const NestedRichTextEditorUtil: RichTextUtils = {
           } else {
             blockMap = DraftTreeOperations.moveChildUp(blockMap, firstChildKey);
             parent = blockMap.get(parentKey);
+            childWasUntabbed = true;
+          }
+        }
+      }
+
+      // now, we may be in a state with two non-leaf blocks of the same type
+      // next to each other
+      if (childWasUntabbed && parentKey != null) {
+        const parent = blockMap.get(parentKey);
+        const prevSiblingKey =
+          parent != null // parent may have been deleted
+            ? parent.getPrevSiblingKey()
+            : null;
+        if (prevSiblingKey != null && parent.getChildKeys().count() > 0) {
+          const prevSibling = blockMap.get(prevSiblingKey);
+          if (prevSibling != null && prevSibling.getChildKeys().count() > 0) {
+            blockMap = DraftTreeOperations.mergeBlocks(
+              blockMap,
+              prevSiblingKey,
+            );
           }
         }
       }

src/model/modifier/exploration/__tests__/DraftTreeOperations-test.js

@@ -544,3 +544,66 @@ const blockMap10 = Immutable.OrderedMap({
 test('test moving only child up deletes parent 3', () => {
   expect(DraftTreeOperations.moveChildUp(blockMap10, 'B')).toMatchSnapshot();
 });
+
+const blockMap11 = Immutable.OrderedMap({
+  A: new ContentBlockNode({
+    key: 'A',
+    parent: null,
+    text: 'alpha',
+    children: Immutable.List([]),
+    prevSibling: null,
+    nextSibling: 'X',
+  }),
+  X: new ContentBlockNode({
+    key: 'X',
+    parent: null,
+    text: '',
+    children: Immutable.List(['B', 'C']),
+    prevSibling: 'A',
+    nextSibling: 'Y',
+  }),
+  B: new ContentBlockNode({
+    key: 'B',
+    parent: 'X',
+    text: 'beta',
+    children: Immutable.List([]),
+    prevSibling: null,
+    nextSibling: 'C',
+  }),
+  C: new ContentBlockNode({
+    key: 'C',
+    parent: 'X',
+    text: 'charlie',
+    children: Immutable.List([]),
+    prevSibling: 'B',
+    nextSibling: null,
+  }),
+  Y: new ContentBlockNode({
+    key: 'Y',
+    parent: null,
+    text: '',
+    children: Immutable.List(['D', 'E']),
+    prevSibling: 'X',
+    nextSibling: null,
+  }),
+  D: new ContentBlockNode({
+    key: 'D',
+    parent: 'Y',
+    text: 'delta',
+    children: Immutable.List([]),
+    prevSibling: null,
+    nextSibling: 'E',
+  }),
+  E: new ContentBlockNode({
+    key: 'E',
+    parent: 'Y',
+    text: 'epsilon',
+    children: Immutable.List([]),
+    prevSibling: 'D',
+    nextSibling: null,
+  }),
+});
+
+test('test merging blocks', () => {
+  expect(DraftTreeOperations.mergeBlocks(blockMap11, 'X')).toMatchSnapshot();
+});

src/model/modifier/exploration/__tests__/NestedRichTextEditorUtil-test.js

@@ -645,6 +645,84 @@ test('onTab (untab) unnests non-leaf next sibling', () => {
   );
 });
 
+const contentBlockNodes5 = [
+  new ContentBlockNode({
+    key: 'A',
+    parent: null,
+    text: 'alpha',
+    children: Immutable.List([]),
+    prevSibling: null,
+    nextSibling: 'X',
+    type: 'ordered-list-item',
+  }),
+  new ContentBlockNode({
+    key: 'X',
+    parent: null,
+    text: '',
+    children: Immutable.List(['B', 'Y', 'E']),
+    prevSibling: 'A',
+    nextSibling: null,
+    type: 'ordered-list-item',
+  }),
+  new ContentBlockNode({
+    key: 'B',
+    parent: 'X',
+    text: 'beta',
+    children: Immutable.List([]),
+    prevSibling: null,
+    nextSibling: 'Y',
+    type: 'ordered-list-item',
+  }),
+  new ContentBlockNode({
+    key: 'Y',
+    parent: 'X',
+    text: '',
+    children: Immutable.List(['C', 'D']),
+    prevSibling: 'B',
+    nextSibling: 'E',
+    type: 'ordered-list-item',
+  }),
+  new ContentBlockNode({
+    key: 'C',
+    parent: 'Y',
+    text: 'charlie',
+    children: Immutable.List([]),
+    prevSibling: null,
+    nextSibling: 'D',
+    type: 'ordered-list-item',
+  }),
+  new ContentBlockNode({
+    key: 'D',
+    parent: 'Y',
+    text: 'delta',
+    children: Immutable.List([]),
+    prevSibling: 'C',
+    nextSibling: null,
+    type: 'ordered-list-item',
+  }),
+  new ContentBlockNode({
+    key: 'E',
+    parent: 'X',
+    text: 'epsilon',
+    children: Immutable.List([]),
+    prevSibling: 'Y',
+    nextSibling: null,
+    type: 'ordered-list-item',
+  }),
+];
+
+test('onTab (untab) merges adjacent non-leaf blocks', () => {
+  assertNestedUtilOperation(
+    editorState =>
+      onTab({preventDefault: () => {}, shiftKey: true}, editorState, 2),
+    {
+      anchorKey: 'B',
+      focusKey: 'B',
+    },
+    contentBlockNodes5,
+  );
+});
+
 // TODO (T32099101)
 test('onSplitParent must split a nested block retaining parent', () => {
   expect(true).toBe(true);