bug(mat-form-field): mat-error is not displayed properly in nested @if

[JoshThunar]

Description

When mat-form-field contains mat-error with a simple @if, then it is rendered properly. However, if we nest @if, error will be squished inside the form, instead of being present in mat-mdc-form-field-subscript-wrapper.

<mat-form-field appearance="outline">
  <input formControlName="bbb" matInput/>
      @if ( true ) {
        <mat-error>Nice error</mat-error>
      }
</mat-form-field>

Reproduction

https://stackblitz.com/edit/stackblitz-starters-nhxdncvv?file=src%2Fmain.ts

Expected Behavior

Renders properly:

@if( true ) {
  <mat-error>Nice error</mat-error>
}

Actual Behavior

Doesn't render properly:

@if( true ) {
  @if ( true ) {
    <mat-error>Terrible error</mat-error>
  }
}

Environment

• Angular: 21
• CDK/Material: 21

[crisbeto]

It's an issue with content projection. See #54035.