fix(cdk/text-field): autosize text areas using the placeholder

scripts/check-mdc-tests-config.ts

@@ -77,7 +77,7 @@ export const config = {
       'should calculate the outline gaps inside the shadow DOM',
       'should be legacy appearance if no default options provided',
       'should be legacy appearance if empty default options provided',
-      'should not calculate wrong content height due to long placeholders',
+      'should adjust height due to long placeholders',
       'should work in a tab',
       'should work in a step'
     ],

src/cdk/text-field/autosize.spec.ts

@@ -50,7 +50,7 @@ describe('CdkTextareaAutosize', () => {
   it('should resize the textarea based on its content', () => {
     let previousHeight = textarea.clientHeight;
 
-    fixture.componentInstance.content = `
+    textarea.value = `
     Once upon a midnight dreary, while I pondered, weak and weary,
     Over many a quaint and curious volume of forgotten lore—
         While I nodded, nearly napping, suddenly there came a tapping,
@@ -68,7 +68,7 @@ describe('CdkTextareaAutosize', () => {
         .toBe(textarea.scrollHeight, 'Expected textarea height to match its scrollHeight');
 
     previousHeight = textarea.clientHeight;
-    fixture.componentInstance.content += `
+    textarea.value += `
         Ah, distinctly I remember it was in the bleak December;
     And each separate dying ember wrought its ghost upon the floor.
         Eagerly I wished the morrow;—vainly I had sought to borrow
@@ -85,6 +85,38 @@ describe('CdkTextareaAutosize', () => {
         .toBe(textarea.scrollHeight, 'Expected textarea height to match its scrollHeight');
   });
 
+  it('should keep the placeholder size if the value is shorter than the placeholder', () => {
+    fixture = TestBed.createComponent(AutosizeTextAreaWithContent);
+
+    textarea = fixture.nativeElement.querySelector('textarea');
+    autosize = fixture.debugElement.query(By.css('textarea'))!
+        .injector.get<CdkTextareaAutosize>(CdkTextareaAutosize);
+
+    fixture.componentInstance.placeholder = `
+    Once upon a midnight dreary, while I pondered, weak and weary,
+    Over many a quaint and curious volume of forgotten lore—
+        While I nodded, nearly napping, suddenly there came a tapping,
+    As of some one gently rapping, rapping at my chamber door.
+    “’Tis some visitor,” I muttered, “tapping at my chamber door—
+                Only this and nothing more.”`;
+
+    fixture.detectChanges();
+
+    expect(textarea.clientHeight)
+        .toBe(textarea.scrollHeight, 'Expected textarea height to match its scrollHeight');
+
+    let previousHeight = textarea.clientHeight;
+
+    textarea.value = 'a';
+
+    // Manually call resizeToFitContent instead of faking an `input` event.
+    fixture.detectChanges();
+    autosize.resizeToFitContent();
+
+    expect(textarea.clientHeight)
+        .toBe(previousHeight, 'Expected textarea height not to have changed');
+  });
+
   it('should set a min-height based on minRows', () => {
     expect(textarea.style.minHeight).toBeFalsy();
 
@@ -161,7 +193,7 @@ describe('CdkTextareaAutosize', () => {
   });
 
   it('should calculate the proper height based on the specified amount of max rows', () => {
-    fixture.componentInstance.content = [1, 2, 3, 4, 5, 6, 7, 8].join('\n');
+    textarea.value = [1, 2, 3, 4, 5, 6, 7, 8].join('\n');
     fixture.detectChanges();
     autosize.resizeToFitContent();
 
@@ -196,6 +228,27 @@ describe('CdkTextareaAutosize', () => {
       .toBe(textarea.scrollHeight, 'Expected textarea height to match its scrollHeight');
   });
 
+  it('should properly resize to placeholder on init', () => {
+    // Manually create the test component in this test, because in this test the first change
+    // detection should be triggered after a multiline placeholder is set.
+    fixture = TestBed.createComponent(AutosizeTextAreaWithContent);
+    textarea = fixture.nativeElement.querySelector('textarea');
+    autosize = fixture.debugElement.query(By.css('textarea'))!
+        .injector.get<CdkTextareaAutosize>(CdkTextareaAutosize);
+
+    fixture.componentInstance.placeholder = `
+      Line
+      Line
+      Line
+      Line
+      Line`;
+
+    fixture.detectChanges();
+
+    expect(textarea.clientHeight)
+      .toBe(textarea.scrollHeight, 'Expected textarea height to match its scrollHeight');
+  });
+
   it('should resize when an associated form control value changes', fakeAsync(() => {
     const fixtureWithForms = TestBed.createComponent(AutosizeTextareaWithNgModel);
     textarea = fixtureWithForms.nativeElement.querySelector('textarea');
@@ -298,14 +351,15 @@ const textareaStyleReset = `
 @Component({
   template: `
     <textarea cdkTextareaAutosize [cdkAutosizeMinRows]="minRows" [cdkAutosizeMaxRows]="maxRows"
-        #autosize="cdkTextareaAutosize">{{content}}</textarea>`,
+        #autosize="cdkTextareaAutosize" [placeholder]="placeholder">{{content}}</textarea>`,
   styles: [textareaStyleReset],
 })
 class AutosizeTextAreaWithContent {
   @ViewChild('autosize') autosize: CdkTextareaAutosize;
   minRows: number | null = null;
   maxRows: number | null = null;
   content: string = '';
+  placeholder: string = '';
 }
 
 @Component({

src/cdk/text-field/autosize.ts

@@ -88,8 +88,19 @@ export class CdkTextareaAutosize implements AfterViewInit, DoCheck, OnDestroy {
     }
   }
 
+  @Input()
+  get placeholder(): string { return this._textareaElement.placeholder; }
+  set placeholder(value: string) {
+    this._cachedPlaceholderHeight = undefined;
+    this._textareaElement.placeholder = value;
+    this._cacheTextareaPlaceholderHeight();
+  }
+
+
   /** Cached height of a textarea with a single row. */
   private _cachedLineHeight: number;
+  /** Cached height of a textarea with only the placeholder. */
+  private _cachedPlaceholderHeight?: number;
 
   /** Used to reference correct document/window */
   protected _document?: Document;
@@ -195,6 +206,30 @@ export class CdkTextareaAutosize implements AfterViewInit, DoCheck, OnDestroy {
     this._setMaxHeight();
   }
 
+  private _measureScrollHeight(): number {
+    // Reset the textarea height to auto in order to shrink back to its default size.
+    // Also temporarily force overflow:hidden, so scroll bars do not interfere with calculations.
+    this._textareaElement.classList.add(this._measuringClass);
+    // The measuring class includes a 2px padding to workaround an issue with Chrome,
+    // so we account for that extra space here by subtracting 4 (2px top + 2px bottom).
+    const scrollHeight = this._textareaElement.scrollHeight - 4;
+    this._textareaElement.classList.remove(this._measuringClass);
+
+    return scrollHeight;
+  }
+
+  private _cacheTextareaPlaceholderHeight(): void {
+    if (this._cachedPlaceholderHeight) {
+      return;
+    }
+
+    const value = this._textareaElement.value;
+
+    this._textareaElement.value = this._textareaElement.placeholder;
+    this._cachedPlaceholderHeight = this._measureScrollHeight();
+    this._textareaElement.value = value;
+  }
+
   ngDoCheck() {
     if (this._platform.isBrowser) {
       this.resizeToFitContent();
@@ -213,6 +248,7 @@ export class CdkTextareaAutosize implements AfterViewInit, DoCheck, OnDestroy {
     }
 
     this._cacheTextareaLineHeight();
+    this._cacheTextareaPlaceholderHeight();
 
     // If we haven't determined the line-height yet, we know we're still hidden and there's no point
     // in checking the height of the textarea.
@@ -228,24 +264,14 @@ export class CdkTextareaAutosize implements AfterViewInit, DoCheck, OnDestroy {
       return;
     }
 
-    const placeholderText = textarea.placeholder;
-
-    // Reset the textarea height to auto in order to shrink back to its default size.
-    // Also temporarily force overflow:hidden, so scroll bars do not interfere with calculations.
-    // Long placeholders that are wider than the textarea width may lead to a bigger scrollHeight
-    // value. To ensure that the scrollHeight is not bigger than the content, the placeholders
-    // need to be removed temporarily.
-    textarea.classList.add(this._measuringClass);
-    textarea.placeholder = '';
+    const scrollHeight = this._measureScrollHeight();
 
     // The measuring class includes a 2px padding to workaround an issue with Chrome,
     // so we account for that extra space here by subtracting 4 (2px top + 2px bottom).
-    const height = textarea.scrollHeight - 4;
+    const height = Math.max(scrollHeight, this._cachedPlaceholderHeight || 0);
 
     // Use the scrollHeight to know how large the textarea *would* be if fit its entire value.
     textarea.style.height = `${height}px`;
-    textarea.classList.remove(this._measuringClass);
-    textarea.placeholder = placeholderText;
 
     this._ngZone.runOutsideAngular(() => {
       if (typeof requestAnimationFrame !== 'undefined') {

src/material/input/input.spec.ts

@@ -1719,7 +1719,7 @@ describe('MatFormField default options', () => {
 });
 
 describe('MatInput with textarea autosize', () => {
-  it('should not calculate wrong content height due to long placeholders', () => {
+  it('should adjust height due to long placeholders', () => {
     const fixture = createComponent(AutosizeTextareaWithLongPlaceholder);
     fixture.detectChanges();
 
@@ -1735,8 +1735,8 @@ describe('MatInput with textarea autosize', () => {
 
     autosize.resizeToFitContent(true);
 
-    expect(textarea.clientHeight).toBe(heightWithLongPlaceholder,
-        'Expected the textarea height to be the same with a long placeholder.');
+    expect(textarea.clientHeight).toBeLessThan(heightWithLongPlaceholder,
+        'Expected the textarea height to be shorter with a long placeholder.');
   });
 
   it('should work in a tab', () => {

tools/public_api_guard/cdk/text-field.d.ts

@@ -31,6 +31,8 @@ export declare class CdkTextareaAutosize implements AfterViewInit, DoCheck, OnDe
     set maxRows(value: number);
     get minRows(): number;
     set minRows(value: number);
+    get placeholder(): string;
+    set placeholder(value: string);
     constructor(_elementRef: ElementRef<HTMLElement>, _platform: Platform, _ngZone: NgZone,
     document?: any);
     _noopInputHandler(): void;
@@ -44,7 +46,7 @@ export declare class CdkTextareaAutosize implements AfterViewInit, DoCheck, OnDe
     static ngAcceptInputType_enabled: BooleanInput;
     static ngAcceptInputType_maxRows: NumberInput;
     static ngAcceptInputType_minRows: NumberInput;
-    static ɵdir: i0.ɵɵDirectiveDefWithMeta<CdkTextareaAutosize, "textarea[cdkTextareaAutosize]", ["cdkTextareaAutosize"], { "minRows": "cdkAutosizeMinRows"; "maxRows": "cdkAutosizeMaxRows"; "enabled": "cdkTextareaAutosize"; }, {}, never>;
+    static ɵdir: i0.ɵɵDirectiveDefWithMeta<CdkTextareaAutosize, "textarea[cdkTextareaAutosize]", ["cdkTextareaAutosize"], { "minRows": "cdkAutosizeMinRows"; "maxRows": "cdkAutosizeMaxRows"; "enabled": "cdkTextareaAutosize"; "placeholder": "placeholder"; }, {}, never>;
     static ɵfac: i0.ɵɵFactoryDef<CdkTextareaAutosize, [null, null, null, { optional: true; }]>;
 }