bug(mat-table): Material Table tries to render rows on reorder when rows are not exists

[lopatnov]

Is this a regression?

• Yes, this behavior used to work in the previous version

The previous version in which this bug was not present was

No response

Description

When columns in mat-table re-order by moveItemInArray and dataSource is loading, so it's undefined, the error is happened in table.mjs, in _getAllRenderRows function in this lines of code:

// For each data object, get the list of rows that should be rendered, represented by the
// respective `RenderRow` object which is the pair of `data` and `CdkRowDef`.
for (let i = 0; i < this._data.length; i++) {

Because this._data is undefined.
The error is: TypeError: Cannot read properties of undefined (reading 'length')

Reproduction

StackBlitz link: not ready
Steps to reproduce:

1. Configure <mat-table> tag with cdkDropList cdkDropListOrientation="horizontal" attribute
2. Configure columns <mat-header-cell> tag with cdkDrag attribute
3. Make some time for loading dataSource and update columns order by moveItemInArray function
4. You should see an error in provided code of mat-table

Expected Behavior

Expected that mat-table should work normally with undefined dataSource. If source is empty, no rows exists, it's simple. Why I need to write some workaround like <mat-table [dataSource]="dataSource || []"? It's one of weakness of mat-table. And I think while data didn't load, it shouldn't start to render rows.

Actual Behavior

mat-table tries to render undefined rows, so error happened. After this error mat-table work in unexpected way. For example becomes something wrong with fixed columns. They became hidden one by one.

Environment

• Angular: 19.1.0

• CDK/Material: 19.1.0

• Browser(s): Chrome Version 134.0.6998.178 (Official Build) (64-bit)

• Operating System (e.g. Windows, macOS, Ubuntu): Windows 11

• "@angular/cdk": "^19.1.0",

• "@angular/common": "^19.1.1",

• "@angular/compiler": "^19.1.1",

• "@angular/core": "^19.1.1",

• "@angular/forms": "^19.1.1",

• "@angular/material": "^19.1.0",

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