feat(material-experimental/mdc-form-field): Add option for dynamic su…

src/dev-app/mdc-input/mdc-input-demo.html

@@ -415,6 +415,81 @@ <h4>Textarea</h4>
   </mat-card-content>
 </mat-card>
 
+<mat-card class="demo-card demo-basic">
+  <mat-toolbar color="primary">Dynamic Subscript Sizing</mat-toolbar>
+  <mat-card-content>
+    <p>
+      One validation
+      <mat-form-field appearance="fill" [color]="color" subscriptSizing="dynamic">
+        <mat-label>Fill appearance</mat-label>
+        <input matInput [(ngModel)]="fillAppearance" required>
+        <mat-error>This field is required</mat-error>
+      </mat-form-field>
+    </p>
+
+    <p>
+      One very long validation that wraps
+      <mat-form-field appearance="fill" [color]="color" subscriptSizing="dynamic"
+          style="width: 212px">
+        <mat-label>Fill appearance</mat-label>
+        <input matInput [(ngModel)]="fillAppearance" required>
+        <mat-error>This field is extremely, very much, absolutely positively required so do not forget it!</mat-error>
+      </mat-form-field>
+    </p>
+
+    <p>
+      One hint and one validation
+      <mat-form-field appearance="fill" [color]="color" subscriptSizing="dynamic">
+        <mat-label>Fill appearance</mat-label>
+        <input matInput [(ngModel)]="fillAppearance" required>
+        <mat-error>This field is required</mat-error>
+        <mat-hint>Please type something here</mat-hint>
+      </mat-form-field>
+    </p>
+
+    <p>
+      Multiple errors
+      <mat-form-field appearance="fill" [color]="color" subscriptSizing="dynamic">
+        <mat-label>Fill appearance</mat-label>
+        <input matInput [(ngModel)]="fillAppearance" required>
+        <mat-error>AAA</mat-error>
+        <mat-error>BBB</mat-error>
+        <mat-error>CCC</mat-error>
+      </mat-form-field>
+    </p>
+
+    <p>
+      Multiple hints
+      <mat-form-field appearance="fill" [color]="color" subscriptSizing="dynamic">
+        <mat-label>Fill appearance</mat-label>
+        <input matInput>
+        <mat-hint>aaa</mat-hint>
+        <mat-hint>bbb</mat-hint>
+        <mat-hint>ccc</mat-hint>
+      </mat-form-field>
+    </p>
+
+    <p>
+      Multiple hints with differing alignment
+      <mat-form-field appearance="fill" [color]="color" subscriptSizing="dynamic">
+        <mat-label>Fill appearance</mat-label>
+        <input matInput>
+        <mat-hint>aaa</mat-hint>
+        <mat-hint align="end">bbb</mat-hint>
+        <mat-hint align="end">ccc</mat-hint>
+      </mat-form-field>
+    </p>
+
+    <p>
+      No hints or errors
+      <mat-form-field appearance="fill" [color]="color" subscriptSizing="dynamic">
+        <mat-label>Fill appearance</mat-label>
+        <input matInput>
+      </mat-form-field>
+    </p>
+  </mat-card-content>
+</mat-card>
+
 <mat-card class="demo-card demo-basic">
   <mat-toolbar color="primary">Number Inputs</mat-toolbar>
   <mat-card-content>

src/material-experimental/mdc-form-field/_form-field-subscript.scss

@@ -23,12 +23,23 @@
     padding: 0 mdc-textfield-variables.$padding-horizontal;
   }
 
+  .mat-mdc-form-field-subscript-dynamic-size {
+    .mat-mdc-form-field-hint-wrapper,
+    .mat-mdc-form-field-error-wrapper {
+      position: static;
+    }
+  }
+
   .mat-mdc-form-field-bottom-align::before {
     content: '';
     display: inline-block;
     height: 16px;
   }
 
+  .mat-mdc-form-field-bottom-align.mat-mdc-form-field-subscript-dynamic-size::before {
+    content: unset;
+  }
+
   .mat-mdc-form-field-hint-end {
     order: 1;
   }

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

@@ -71,6 +71,7 @@
 </div>
 
 <div class="mat-mdc-form-field-subscript-wrapper mat-mdc-form-field-bottom-align"
+     [class.mat-mdc-form-field-subscript-dynamic-size]="subscriptSizing === 'dynamic'"
      [ngSwitch]="_getDisplayedMessages()">
   <div class="mat-mdc-form-field-error-wrapper" *ngSwitchCase="'error'"
        [@transitionMessages]="_subscriptAnimationState">

src/material-experimental/mdc-form-field/form-field.ts

@@ -61,6 +61,9 @@ export type FloatLabelType = 'always' | 'auto';
 /** Possible appearance styles for the form field. */
 export type MatFormFieldAppearance = 'fill' | 'outline';
 
+/** Behaviors for how the subscript height is set. */
+export type SubscriptSizing = 'fixed' | 'dynamic';
+
 /**
  * Represents the default options for the form field that can be configured
  * using the `MAT_FORM_FIELD_DEFAULT_OPTIONS` injection token.
@@ -69,6 +72,7 @@ export interface MatFormFieldDefaultOptions {
   appearance?: MatFormFieldAppearance;
   hideRequiredMarker?: boolean;
   floatLabel?: FloatLabelType;
+  subscriptSizing?: SubscriptSizing;
 }
 
 /**
@@ -87,6 +91,9 @@ const DEFAULT_APPEARANCE: MatFormFieldAppearance = 'fill';
 /** Default appearance used by the form-field. */
 const DEFAULT_FLOAT_LABEL: FloatLabelType = 'auto';
 
+/** Default way that the suffix element height is set. */
+const DEFAULT_SUBSCRIPT_SIZING: SubscriptSizing = 'fixed';
+
 /**
  * Default transform for docked floating labels in a MDC text-field. This value has been
  * extracted from the MDC text-field styles because we programmatically modify the docked
@@ -206,6 +213,20 @@ export class MatFormField
   }
   private _appearance: MatFormFieldAppearance = DEFAULT_APPEARANCE;
 
+  /**
+   * Whether the form field should reserve space for one line of hint/error text (default)
+   * or to have the spacing grow from 0px as needed based on the size of the hint/error content.
+   * Note that when using dynamic sizing, layout shifts will occur when hint/error text changes.
+   */
+  @Input()
+  get subscriptSizing(): SubscriptSizing {
+    return this._subscriptSizing || this._defaults?.subscriptSizing || DEFAULT_SUBSCRIPT_SIZING;
+  }
+  set subscriptSizing(value: SubscriptSizing) {
+    this._subscriptSizing = value || this._defaults?.subscriptSizing || DEFAULT_SUBSCRIPT_SIZING;
+  }
+  private _subscriptSizing: SubscriptSizing = DEFAULT_SUBSCRIPT_SIZING;
+
   /** Text for the form field hint. */
   @Input()
   get hintLabel(): string {

src/material-experimental/mdc-input/input.spec.ts

@@ -32,6 +32,7 @@ import {
   MatFormField,
   MatFormFieldAppearance,
   MatFormFieldModule,
+  SubscriptSizing,
 } from '@angular/material-experimental/mdc-form-field';
 import {MatIconModule} from '@angular/material/icon';
 import {By} from '@angular/platform-browser';
@@ -1406,6 +1407,47 @@ describe('MatFormField default options', () => {
     expect(fixture.componentInstance.formField.hideRequiredMarker).toBe(true);
     expect(fixture.componentInstance.formField.appearance).toBe('outline');
   });
+
+  it('defaults subscriptSizing to false', () => {
+    const fixture = createComponent(MatInputWithSubscriptSizing);
+    fixture.detectChanges();
+
+    const subscriptElement = fixture.nativeElement.querySelector(
+      '.mat-mdc-form-field-subscript-wrapper',
+    );
+
+    expect(fixture.componentInstance.formField.subscriptSizing).toBe('fixed');
+    expect(subscriptElement.classList.contains('mat-mdc-form-field-subscript-dynamic-size')).toBe(
+      false,
+    );
+
+    fixture.componentInstance.sizing = 'dynamic';
+    fixture.detectChanges();
+
+    expect(fixture.componentInstance.formField.subscriptSizing).toBe('dynamic');
+    expect(subscriptElement.classList.contains('mat-mdc-form-field-subscript-dynamic-size')).toBe(
+      true,
+    );
+  });
+
+  it('changes the default value of subscriptSizing', () => {
+    const fixture = createComponent(MatInputWithSubscriptSizing, [
+      {
+        provide: MAT_FORM_FIELD_DEFAULT_OPTIONS,
+        useValue: {
+          subscriptSizing: 'dynamic',
+        },
+      },
+    ]);
+
+    fixture.detectChanges();
+    expect(fixture.componentInstance.formField.subscriptSizing).toBe('dynamic');
+    expect(
+      fixture.nativeElement
+        .querySelector('.mat-mdc-form-field-subscript-wrapper')
+        .classList.contains('mat-mdc-form-field-subscript-dynamic-size'),
+    ).toBe(true);
+  });
 });
 
 function configureTestingModule(
@@ -1815,6 +1857,19 @@ class MatInputWithAppearance {
   appearance: MatFormFieldAppearance;
 }
 
+@Component({
+  template: `
+    <mat-form-field [subscriptSizing]="sizing">
+      <mat-label>My Label</mat-label>
+      <input matInput placeholder="Placeholder" required>
+    </mat-form-field>
+  `,
+})
+class MatInputWithSubscriptSizing {
+  @ViewChild(MatFormField) formField: MatFormField;
+  sizing: SubscriptSizing;
+}
+
 @Component({
   template: `
     <mat-form-field>