fix: delay column width recalculation until all rows have index (#7165)…

… (#7168)

packages/grid/src/vaadin-grid.js

@@ -535,18 +535,28 @@ class Grid extends ElementMixin(
     }
   }
 
-  /** @private */
-  __hasRowsWithClientHeight() {
-    return !!Array.from(this.$.items.children).filter((row) => row.clientHeight).length;
-  }
-
   /** @protected */
   __itemsReceived() {
-    if (
-      this._recalculateColumnWidthOnceLoadingFinished &&
-      !this._cache.isLoading() &&
-      this.__hasRowsWithClientHeight()
-    ) {
+    if (!this._recalculateColumnWidthOnceLoadingFinished || this._cache.isLoading()) {
+      return;
+    }
+
+    // Delay recalculation if any rows are missing an index.
+    // This can happen during the grid's initialization if the recalculation is triggered
+    // as a result of the data provider responding synchronously to a page request created
+    // in the middle of the virtualizer update loop. In this case, rows after the one that
+    // triggered the page request may not have an index property yet. The lack of index
+    // prevents _onDataProviderPageReceived from requesting children for these rows,
+    // resulting in loading state being set to false and the recalculation beginning
+    // before all the data is loaded. Note, rows without index get updated in later iterations
+    // of the virtualizer update loop, ensuring the grid eventually reaches a stable state.
+    const hasRowsWithUndefinedIndex = [...this.$.items.children].some((row) => row.index === undefined);
+    if (hasRowsWithUndefinedIndex) {
+      return;
+    }
+
+    const hasRowsWithClientHeight = [...this.$.items.children].some((row) => row.clientHeight > 0);
+    if (hasRowsWithClientHeight) {
       this._recalculateColumnWidthOnceLoadingFinished = false;
       this.recalculateColumnWidths();
     }

packages/grid/test/column-auto-width.test.js

@@ -1,5 +1,5 @@
 import { expect } from '@esm-bundle/chai';
-import { fixtureSync, nextFrame, oneEvent } from '@vaadin/testing-helpers';
+import { aTimeout, fixtureSync, nextFrame, oneEvent } from '@vaadin/testing-helpers';
 import sinon from 'sinon';
 import '../vaadin-grid.js';
 import '../vaadin-grid-column-group.js';
@@ -240,7 +240,7 @@ describe('async recalculateWidth columns', () => {
     `);
   });
 
-  it('should recalculate column widths when child items loaded', () => {
+  it('should recalculate column widths when child items are loaded synchronously', () => {
     const data = [
       {
         name: 'foo',
@@ -264,6 +264,38 @@ describe('async recalculateWidth columns', () => {
     flushGrid(grid);
     expect(grid._recalculateColumnWidths.called).to.be.true;
   });
+
+  describe('initially empty grid', () => {
+    let recalculateColumnWidthsSpy, dataProvider;
+
+    beforeEach(() => {
+      recalculateColumnWidthsSpy = sinon.spy(grid, 'recalculateColumnWidths');
+      dataProvider = (_params, callback) => callback([], 0);
+      grid.dataProvider = (params, callback) => dataProvider(params, callback);
+      flushGrid(grid);
+      recalculateColumnWidthsSpy.resetHistory();
+    });
+
+    it('should recalculate column widths when child items are loaded asynchonously', async () => {
+      const items = [{ name: 'Item-0' }, { name: 'Item-1', children: [{ name: 'Item-1-0' }] }];
+
+      dataProvider = ({ parentItem }, callback) => {
+        if (parentItem) {
+          setTimeout(() => callback(parentItem.children, parentItem.children.length));
+        } else {
+          callback(items.slice(0, grid.size), grid.size);
+        }
+      };
+
+      grid.expandItem(items[1]);
+      grid.size = 2;
+      flushGrid(grid);
+
+      expect(recalculateColumnWidthsSpy.called).to.be.false;
+      await aTimeout(0);
+      expect(recalculateColumnWidthsSpy.calledOnce).to.be.true;
+    });
+  });
 });
 
 describe('column group', () => {