fix(material-experimental/mdc-input): only apply styling when inside a form field

Currently `mat-form-field` brings in the styles for `MatInput`. but the problem is that
they target a class that is applied even to inputs that aren't inside a form field.

These changes aim to prevent CSS from bleeding out by only styling inputs inside a `mat-form-field`.

Fixes #21871.

Author: crisbeto

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

@@ -130,6 +130,7 @@ describe('MDC-based MatChipInput', () => {
 
     it('should set input styling classes', () => {
       expect(inputNativeElement.classList).toContain('mat-mdc-input-element');
+      expect(inputNativeElement.classList).toContain('mat-mdc-form-field-control');
       expect(inputNativeElement.classList).toContain('mat-mdc-chip-input');
       expect(inputNativeElement.classList).toContain('mdc-text-field__input');
     });

src/material-experimental/mdc-chips/chip-input.ts

@@ -17,8 +17,10 @@ import {
   Input,
   OnChanges,
   OnDestroy,
+  Optional,
   Output
 } from '@angular/core';
+import {MatFormField, MAT_FORM_FIELD} from '@angular/material-experimental/mdc-form-field';
 import {MatChipsDefaultOptions, MAT_CHIPS_DEFAULT_OPTIONS} from './chip-default-options';
 import {MatChipGrid} from './chip-grid';
 import {MatChipTextControl} from './chip-text-control';
@@ -127,9 +129,14 @@ export class MatChipInput implements MatChipTextControl, AfterContentInit, OnCha
 
   constructor(
     protected _elementRef: ElementRef<HTMLInputElement>,
-    @Inject(MAT_CHIPS_DEFAULT_OPTIONS) private _defaultOptions: MatChipsDefaultOptions) {
-    this.inputElement = this._elementRef.nativeElement as HTMLInputElement;
-  }
+    @Inject(MAT_CHIPS_DEFAULT_OPTIONS) private _defaultOptions: MatChipsDefaultOptions,
+    @Optional() @Inject(MAT_FORM_FIELD) formField?: MatFormField) {
+      this.inputElement = this._elementRef.nativeElement as HTMLInputElement;
+
+      if (formField) {
+        this.inputElement.classList.add('mat-mdc-form-field-control');
+      }
+    }
 
   ngOnChanges() {
     this._chipGrid.stateChanges.next();

src/material-experimental/mdc-form-field/_form-field-native-select.scss

@@ -17,7 +17,7 @@ $mat-form-field-select-horizontal-end-padding: $mat-form-field-select-arrow-widt
   // Remove the native select down arrow and ensure that the native appearance
   // does not conflict with the form-field. e.g. Focus indication of the native
   // select is undesired since we handle focus as part of the form-field.
-  select.mat-mdc-input-element {
+  select.mat-mdc-form-field-control {
     -moz-appearance: none;
     -webkit-appearance: none;
     background-color: transparent;
@@ -82,7 +82,7 @@ $mat-form-field-select-horizontal-end-padding: $mat-form-field-select-arrow-widt
 
     // Add padding on the end of the native select so that the content does not
     // overlap with the Material Design arrow.
-    .mat-mdc-input-element {
+    .mat-mdc-form-field-control {
       padding-right: $mat-form-field-select-horizontal-end-padding;
       [dir='rtl'] & {
         padding-right: 0;
@@ -104,7 +104,7 @@ $mat-form-field-select-horizontal-end-padding: $mat-form-field-select-arrow-widt
     $dropdown-icon-color: rgba(mdc-theme-color.prop-value(on-surface), 0.54);
     $disabled-dropdown-icon-color: rgba(mdc-theme-color.prop-value(on-surface), 0.38);
 
-    select.mat-mdc-input-element {
+    select.mat-mdc-form-field-control {
       // On dark themes we set the native `select` color to some shade of white,
       // however the color propagates to all of the `option` elements, which are
       // always on a white background inside the dropdown, causing them to blend in.

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

@@ -74,7 +74,7 @@
 
     // MDC uses the `subtitle1` level for the input label and value, but the spec shows `body1` as
     // the correct level.
-    .mat-mdc-input-element,
+    .mat-mdc-form-field-control,
     .mat-mdc-form-field label,
     .mat-mdc-form-field-text-prefix,
     .mat-mdc-form-field-text-suffix {

src/material-experimental/mdc-form-field/_mdc-text-field-structure-overrides.scss

@@ -8,7 +8,7 @@
   // Unset the border set by MDC. We move the border (which serves as the Material Design
   // text-field bottom line) into its own element. This is necessary because we want the
   // bottom-line to span across the whole form-field (including prefixes and suffixes).
-  .mat-mdc-input-element {
+  .mat-mdc-form-field-control {
     border: none;
   }
 
@@ -25,8 +25,8 @@
   // not work for us since we support arbitrary form field controls which don't necessarily
   // use an `input` element. We organize the vertical spacing on the infix container.
   .mdc-text-field--no-label:not(.mdc-text-field--textarea)
-  .mat-mdc-input-element.mdc-text-field__input,
-  .mat-mdc-text-field-wrapper .mat-mdc-input-element {
+  .mat-mdc-form-field-control.mdc-text-field__input,
+  .mat-mdc-text-field-wrapper .mat-mdc-form-field-control {
     height: auto;
   }
 

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

@@ -896,6 +896,17 @@ describe('MatMdcInput without forms', () => {
     expect(formField.classList).toContain('mat-warn');
   }));
 
+  it('should set a class on the input depending on whether it is in a form field', fakeAsync(() => {
+    const fixture = createComponent(MatInputInsideOutsideFormField);
+    fixture.detectChanges();
+
+    const inFormField = fixture.nativeElement.querySelector('.inside');
+    const outsideFormField = fixture.nativeElement.querySelector('.outside');
+
+    expect(inFormField.classList).toContain('mat-mdc-form-field-control');
+    expect(outsideFormField.classList).not.toContain('mat-mdc-form-field-control');
+  }));
+
 });
 
 describe('MatMdcInput with forms', () => {
@@ -1800,3 +1811,15 @@ class CustomMatInputAccessor {
 class MatInputWithColor {
   color: ThemePalette;
 }
+
+
+@Component({
+  template: `
+    <mat-form-field>
+      <input class="inside" matNativeControl>
+    </mat-form-field>
+
+    <input class="outside" matNativeControl>
+  `
+})
+class MatInputInsideOutsideFormField {}

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

@@ -19,13 +19,17 @@ import {MatInput as BaseMatInput} from '@angular/material/input';
       input[matNativeControl], textarea[matNativeControl]`,
   exportAs: 'matInput',
   host: {
-    'class': 'mat-mdc-input-element mdc-text-field__input',
-    // The BaseMatInput parent class adds `mat-input-element` and `mat-form-field-autofill-control`
-    // to the CSS classlist, but this should not be added for this MDC equivalent input.
+    'class': 'mat-mdc-input-element',
+    // The BaseMatInput parent class adds `mat-input-element`, `mat-form-field-control` and
+    // `mat-form-field-autofill-control` to the CSS class list, but this should not be added for
+    // this MDC equivalent input.
     '[class.mat-form-field-autofill-control]': 'false',
     '[class.mat-input-element]': 'false',
+    '[class.mat-form-field-control]': 'false',
     '[class.mat-input-server]': '_isServer',
     '[class.mat-mdc-textarea-input]': '_isTextarea',
+    '[class.mat-mdc-form-field-control]': '_isInFormField',
+    '[class.mdc-text-field__input]': '_isInFormField',
     // Native input properties that are overwritten by Angular inputs need to be synced with
     // the native input element. Otherwise property bindings for those don't work.
     '[id]': 'id',

src/material/input/input.ts

@@ -107,6 +107,9 @@ export class MatInput extends _MatInputMixinBase implements MatFormFieldControl<
   /** Whether the component is a textarea. */
   readonly _isTextarea: boolean;
 
+  /** Whether the input is inside of a form field. */
+  readonly _isInFormField: boolean;
+
   /**
    * Implemented as part of MatFormFieldControl.
    * @docs-private
@@ -282,6 +285,7 @@ export class MatInput extends _MatInputMixinBase implements MatFormFieldControl<
     this._isServer = !this._platform.isBrowser;
     this._isNativeSelect = nodeName === 'select';
     this._isTextarea = nodeName === 'textarea';
+    this._isInFormField = !!_formField;
 
     if (this._isNativeSelect) {
       this.controlType = (element as HTMLSelectElement).multiple ? 'mat-native-select-multiple' :

tools/public_api_guard/material/input.d.ts

@@ -8,6 +8,7 @@ export declare class MatInput extends _MatInputMixinBase implements MatFormField
     protected _disabled: boolean;
     protected _elementRef: ElementRef<HTMLInputElement | HTMLSelectElement | HTMLTextAreaElement>;
     protected _id: string;
+    readonly _isInFormField: boolean;
     readonly _isNativeSelect: boolean;
     readonly _isServer: boolean;
     readonly _isTextarea: boolean;