Inconsistent Y.XmlText.format behavior

[gblaketx]

Describe the bug Y.XmlText.format can strip attributes outside the range provided to the function. This behavior seems to happen specifically when the YDoc is initialized via applyUpdate from an encoded update.

To Reproduce This jest test reproduces the issue.

import * as Y from "yjs";

describe("inconsistentFormatBug", () => {
  it("1. Passes on fresh YDoc", () => {
    const yDoc = initializeYDoc();
    testYjsMerge(yDoc);
  });

  it("2. Fails on YDoc initialized via an encoded update", () => {
    const initialYDoc = initializeYDoc();
    const yDoc = new Y.Doc({ gc: false });
    Y.applyUpdate(yDoc, Y.encodeStateAsUpdate(initialYDoc));
    testYjsMerge(yDoc);
  });
});

function testYjsMerge(yDoc: Y.Doc) {
  const content = yDoc.get("text", Y.XmlText) as Y.XmlText;
  content.format(0, 6, { bold: null });
  content.format(6, 4, { type: "text" });

  expect(content.toDelta()).toEqual([
    {
      attributes: { type: "text" },
      insert: "Merge Test",
    },
    {
      attributes: { type: "text", italic: true },
      insert: " After",
    },
  ]);
}

function initializeYDoc(): Y.Doc {
  const yDoc = new Y.Doc({ gc: false });

  const content = yDoc.get("text", Y.XmlText) as Y.XmlText;
  content.insert(0, " After", { type: "text", italic: true });
  content.insert(0, "Test", { type: "text" });
  content.insert(0, "Merge ", { type: "text", bold: true });

  return yDoc;
}

The only difference between the setup for cases (1) and (2) is how the document is initialized, but they produce different results. In case (1), the format call is applied correctly. In case (2), it strips type attribute from the " After" text, even though it is outside of the provided range.

    {
      attributes: { type: "text" },
      insert: "Merge ",
    },
    {
      attributes: { type: "text" },
      insert: "Test",
    },
    {
      attributes: { italic: true },
      insert: " After",
    },

Expected behavior I would expect case (2) to behave like case (1) and not strip out the "type" attribute.

Environment Information

• node.js v16.19.1
• yjs v13.6.10

Additional context We are using yjs with slate-yjs and found this behavior was triggered by Slate merge_node operations on a newly loaded editor.

We found the issue in yjs v13.5.45 but have been able to repro it in v13.6.10 as well.

_{Huly®: YJS-408}

[dmonad]

Thanks for the report and the code for reproducing it!

This will be fixed in the next release.