Unnest the first non-leaf child

Summary:
We don't want to leave behind doubly nested children if their preceding block is untabbed. Here we iterate to make sure that the next block is never left with a non-leaf first child.

Diagram of this operation, also implemented in the test below:
https://pxl.cl/hs20

Reviewed By: vdurmont

Differential Revision: D9826012

fbshipit-source-id: 1c14c5091ce89ddee3e80b2a7e9eef9d4759c320

src/model/modifier/exploration/NestedRichTextEditorUtil.js

@@ -419,6 +419,27 @@ const NestedRichTextEditorUtil: RichTextUtils = {
         );
         blockMap = DraftTreeOperations.moveChildUp(blockMap, key);
       }
+
+      // 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.
+      if (parentKey != null) {
+        let parent = blockMap.get(parentKey);
+        while (parent != null) {
+          const children = parent.getChildKeys();
+          const firstChildKey = children.first();
+          invariant(
+            firstChildKey != null,
+            'parent must have at least one child',
+          );
+          const firstChild = blockMap.get(firstChildKey);
+          if (firstChild.getChildKeys().count() === 0) {
+            break;
+          } else {
+            blockMap = DraftTreeOperations.moveChildUp(blockMap, firstChildKey);
+            parent = blockMap.get(parentKey);
+          }
+        }
+      }
     }
     content = editorState.getCurrentContent().merge({
       blockMap: blockMap,

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

@@ -585,6 +585,66 @@ test('onTab (untab) on a middle child splits the block at that child', () => {
   );
 });
 
+const contentBlockNodes4 = [
+  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']),
+    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']),
+    prevSibling: 'B',
+    nextSibling: null,
+    type: 'ordered-list-item',
+  }),
+  new ContentBlockNode({
+    key: 'C',
+    parent: 'Y',
+    text: 'charlie',
+    children: Immutable.List([]),
+    prevSibling: null,
+    nextSibling: null,
+    type: 'ordered-list-item',
+  }),
+];
+
+test('onTab (untab) unnests non-leaf next sibling', () => {
+  assertNestedUtilOperation(
+    editorState =>
+      onTab({preventDefault: () => {}, shiftKey: true}, editorState, 2),
+    {
+      anchorKey: 'B',
+      focusKey: 'B',
+    },
+    contentBlockNodes4,
+  );
+});
+
 // TODO (T32099101)
 test('onSplitParent must split a nested block retaining parent', () => {
   expect(true).toBe(true);

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

@@ -1903,6 +1903,128 @@ Object {
 }
 `;
 
+exports[`onTab (untab) unnests non-leaf next sibling 1`] = `
+Object {
+  "A": Object {
+    "characterList": Array [
+      Object {
+        "entity": null,
+        "style": Array [],
+      },
+      Object {
+        "entity": null,
+        "style": Array [],
+      },
+      Object {
+        "entity": null,
+        "style": Array [],
+      },
+      Object {
+        "entity": null,
+        "style": Array [],
+      },
+      Object {
+        "entity": null,
+        "style": Array [],
+      },
+    ],
+    "children": Array [],
+    "data": Object {},
+    "depth": 0,
+    "key": "A",
+    "nextSibling": "B",
+    "parent": null,
+    "prevSibling": null,
+    "text": "alpha",
+    "type": "ordered-list-item",
+  },
+  "B": Object {
+    "characterList": Array [
+      Object {
+        "entity": null,
+        "style": Array [],
+      },
+      Object {
+        "entity": null,
+        "style": Array [],
+      },
+      Object {
+        "entity": null,
+        "style": Array [],
+      },
+      Object {
+        "entity": null,
+        "style": Array [],
+      },
+    ],
+    "children": Array [],
+    "data": Object {},
+    "depth": 0,
+    "key": "B",
+    "nextSibling": "Y",
+    "parent": null,
+    "prevSibling": "A",
+    "text": "beta",
+    "type": "ordered-list-item",
+  },
+  "C": Object {
+    "characterList": Array [
+      Object {
+        "entity": null,
+        "style": Array [],
+      },
+      Object {
+        "entity": null,
+        "style": Array [],
+      },
+      Object {
+        "entity": null,
+        "style": Array [],
+      },
+      Object {
+        "entity": null,
+        "style": Array [],
+      },
+      Object {
+        "entity": null,
+        "style": Array [],
+      },
+      Object {
+        "entity": null,
+        "style": Array [],
+      },
+      Object {
+        "entity": null,
+        "style": Array [],
+      },
+    ],
+    "children": Array [],
+    "data": Object {},
+    "depth": 0,
+    "key": "C",
+    "nextSibling": null,
+    "parent": "Y",
+    "prevSibling": null,
+    "text": "charlie",
+    "type": "ordered-list-item",
+  },
+  "Y": Object {
+    "characterList": Array [],
+    "children": Array [
+      "C",
+    ],
+    "data": Object {},
+    "depth": 0,
+    "key": "Y",
+    "nextSibling": null,
+    "parent": null,
+    "prevSibling": "B",
+    "text": "",
+    "type": "ordered-list-item",
+  },
+}
+`;
+
 exports[`onTab when siblings are at the same depth creates a new parent 1`] = `
 Object {
   "A": Object {