fix: restore depth guard in getParentBlockInfo to prevent RangeError (blo-1103)

packages/core/src/api/blockManipulation/commands/mergeBlocks/mergeBlocks.test.ts

@@ -2,7 +2,7 @@ import { describe, expect, it } from "vitest";
 
 import { getBlockInfoFromTransaction } from "../../../getBlockInfoFromPos.js";
 import { setupTestEnv } from "../../setupTestEnv.js";
-import { mergeBlocksCommand } from "./mergeBlocks.js";
+import { getParentBlockInfo, mergeBlocksCommand } from "./mergeBlocks.js";
 
 const getEditor = setupTestEnv();
 
@@ -77,6 +77,20 @@ describe("Test mergeBlocks", () => {
     expect(anchorIsAtOldFirstBlockEndPos).toBeTruthy();
   });
 
+  it("getParentBlockInfo returns undefined for top-level block", () => {
+    getEditor().setTextCursorPosition("paragraph-0");
+
+    const beforePos = getPosBeforeSelectedBlock();
+    const doc = getEditor()._tiptapEditor.state.doc;
+    const $pos = doc.resolve(beforePos);
+
+    expect($pos.depth - 1).toBeLessThan(1);
+
+    const result = getParentBlockInfo(doc, beforePos);
+
+    expect(result).toBeUndefined();
+  });
+
   // We expect a no-op for each of the remaining tests as merging should only
   // happen for blocks which both have inline content. We also expect
   // `mergeBlocks` to return false as TipTap commands should do that instead of

packages/core/src/api/blockManipulation/commands/mergeBlocks/mergeBlocks.ts

@@ -16,6 +16,11 @@ export const getParentBlockInfo = (
 ): BlockInfo | undefined => {
   const $pos = doc.resolve(beforePos);
   const depth = $pos.depth - 1;
+
+  if (depth < 1) {
+    return undefined;
+  }
+
   const parentBeforePos = $pos.before(depth);
   const parentNode = doc.resolve(parentBeforePos).nodeAfter;