fix(material/form-field): add hasFloatingLabel input and update classes if mat-label is added and removed dynamically

Currently, when `mat-Label` is added dynamically initially its not visible in DOM, this fix will add/remove classes  for the same.

Fixes #29939

Author: mistrykaran91

goldens/material/form-field/index.api.md

@@ -16,8 +16,10 @@ import * as i2 from '@angular/cdk/bidi';
 import { InjectionToken } from '@angular/core';
 import { NgControl } from '@angular/forms';
 import { Observable } from 'rxjs';
+import { OnChanges } from '@angular/core';
 import { OnDestroy } from '@angular/core';
 import { QueryList } from '@angular/core';
+import { SimpleChanges } from '@angular/core';
 
 // @public
 export type FloatLabelType = 'always' | 'auto';

goldens/material/input/index.api.md

@@ -25,6 +25,7 @@ import { OnChanges } from '@angular/core';
 import { OnDestroy } from '@angular/core';
 import { Platform } from '@angular/cdk/platform';
 import { QueryList } from '@angular/core';
+import { SimpleChanges } from '@angular/core';
 import { Subject } from 'rxjs';
 import { WritableSignal } from '@angular/core';
 

src/material/form-field/directives/notched-outline.ts

@@ -13,6 +13,8 @@ import {
   ElementRef,
   Input,
   NgZone,
+  OnChanges,
+  SimpleChanges,
   ViewChild,
   ViewEncapsulation,
   inject,
@@ -36,21 +38,27 @@ import {
   changeDetection: ChangeDetectionStrategy.OnPush,
   encapsulation: ViewEncapsulation.None,
 })
-export class MatFormFieldNotchedOutline implements AfterViewInit {
+export class MatFormFieldNotchedOutline implements AfterViewInit, OnChanges {
   private _elementRef = inject<ElementRef<HTMLElement>>(ElementRef);
   private _ngZone = inject(NgZone);
 
   /** Whether the notch should be opened. */
   @Input('matFormFieldNotchedOutlineOpen') open: boolean = false;
 
+  /** Whether the floating label is present. */
+  @Input('matFormFieldHasFloatingLabel') hasFloatingLabel: boolean = false;
+
   @ViewChild('notch') _notch: ElementRef<HTMLElement>;
 
-  ngAfterViewInit(): void {
-    const element = this._elementRef.nativeElement;
-    const label = element.querySelector<HTMLElement>('.mdc-floating-label');
+  /** Gets the HTML element for the floating label. */
+  get element(): HTMLElement {
+    return this._elementRef.nativeElement;
+  }
 
+  ngAfterViewInit(): void {
+    const label = this.element.querySelector<HTMLElement>('.mdc-floating-label');
     if (label) {
-      element.classList.add('mdc-notched-outline--upgraded');
+      this.element.classList.add('mdc-notched-outline--upgraded');
 
       if (typeof requestAnimationFrame === 'function') {
         label.style.transitionDuration = '0s';
@@ -59,7 +67,18 @@ export class MatFormFieldNotchedOutline implements AfterViewInit {
         });
       }
     } else {
-      element.classList.add('mdc-notched-outline--no-label');
+      this.element.classList.add('mdc-notched-outline--no-label');
+    }
+  }
+
+  ngOnChanges(changes: SimpleChanges) {
+    if (
+      changes['hasFloatingLabel'] &&
+      this.hasFloatingLabel &&
+      this.element.classList.contains('mdc-notched-outline--no-label')
+    ) {
+      this.element.classList.add('mdc-notched-outline--upgraded');
+      this.element.classList.remove('mdc-notched-outline--no-label');
     }
   }
 

src/material/form-field/form-field.html

@@ -50,7 +50,10 @@
   }
   <div class="mat-mdc-form-field-flex">
     @if (_hasOutline()) {
-      <div matFormFieldNotchedOutline [matFormFieldNotchedOutlineOpen]="_shouldLabelFloat()">
+      <div
+        matFormFieldNotchedOutline
+        [matFormFieldNotchedOutlineOpen]="_shouldLabelFloat()"
+        [matFormFieldHasFloatingLabel]="_hasFloatingLabel()">
         @if (!_forceDisplayInfixLabel()) {
           <ng-template [ngTemplateOutlet]="labelTemplate"></ng-template>
         }

src/material/input/input.spec.ts

@@ -625,6 +625,27 @@ describe('MatMdcInput without forms', () => {
     expect(input.getAttribute('aria-describedby')).toBe(`initial ${hintId}`);
   }));
 
+  it('should show outline label correctly based on initial condition to false', fakeAsync(() => {
+    const fixture = TestBed.createComponent(MatInputOutlineWithConditionalLabel);
+    fixture.detectChanges();
+    tick(16);
+
+    const notchedOutline: HTMLElement = fixture.debugElement.query(
+      By.css('.mdc-notched-outline'),
+    ).nativeElement;
+
+    expect(notchedOutline.classList).toContain('mdc-notched-outline--no-label');
+    expect(notchedOutline.classList).not.toContain('mdc-notched-outline--upgraded');
+
+    fixture.componentInstance.showLabel = true;
+    fixture.changeDetectorRef.markForCheck();
+    fixture.detectChanges();
+    tick(16);
+
+    expect(notchedOutline.classList).not.toContain('mdc-notched-outline--no-label');
+    expect(notchedOutline.classList).toContain('mdc-notched-outline--upgraded');
+  }));
+
   it('supports user binding to aria-describedby', fakeAsync(() => {
     const fixture = TestBed.createComponent(MatInputWithSubscriptAndAriaDescribedBy);
 
@@ -2170,6 +2191,22 @@ class MatInputWithAppearance {
   appearance: MatFormFieldAppearance;
 }
 
+@Component({
+  template: `
+    <mat-form-field appearance="outline">
+    @if(showLabel) {
+      <mat-label>My Label</mat-label>
+    }
+      <input matInput placeholder="Placeholder">
+    </mat-form-field>
+  `,
+  imports: [MatInputModule],
+})
+class MatInputOutlineWithConditionalLabel {
+  @ViewChild(MatFormField) formField: MatFormField;
+  showLabel: boolean = false;
+}
+
 @Component({
   template: `
     <mat-form-field [subscriptSizing]="sizing">