fix(form-field): incorrect assumptions about page direction

These changes undo the changes from #15415 because they were making incorrect assumptions about the page starting off as LTR, and they were calling `updateOutlineGap` with an outdated value for the direction. This is causing issues like #17390.

I'm not totally sure what was being fixed by these changes, because the test that was added didn't fail even if I reverted all of the changes. From what I can tell the problem #15415 was trying to solve was that the outline gap might be updated too early on a direction change, before the browser has had the chance to recalculate the layout. These changes switch to recalculating inside a `requestAnimationFrame` after direction changes, in order to give the browser enough time to recalculate the layout.

Fixes #17390.

Author: crisbeto

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

@@ -232,15 +232,6 @@ export class MatFormField extends _MatFormFieldMixinBase
   /** Whether the Angular animations are enabled. */
   _animationsEnabled: boolean;
 
-  /* Holds the previous direction emitted by directionality service change emitter.
-     This is used in updateOutlineGap() method to update the width and position of the gap in the
-     outline. Only relevant for the outline appearance. The direction is getting updated in the
-     UI after directionality service change emission. So the outlines gaps are getting
-     updated in updateOutlineGap() method before connectionContainer child direction change
-     in UI. We may get wrong calculations. So we are storing the previous direction to get the
-     correct outline calculations*/
-  private _previousDirection: Direction = 'ltr';
-
   /**
    * @deprecated
    * @breaking-change 8.0.0
@@ -356,8 +347,13 @@ export class MatFormField extends _MatFormFieldMixinBase
 
     if (this._dir) {
       this._dir.change.pipe(takeUntil(this._destroyed)).subscribe(() => {
-        this.updateOutlineGap();
-        this._previousDirection = this._dir.value;
+        if (typeof requestAnimationFrame === 'function') {
+          this._ngZone.runOutsideAngular(() => {
+            requestAnimationFrame(() => this.updateOutlineGap());
+          });
+        } else {
+          this.updateOutlineGap();
+        }
       });
     }
   }
@@ -580,7 +576,7 @@ export class MatFormField extends _MatFormFieldMixinBase
 
   /** Gets the start end of the rect considering the current directionality. */
   private _getStartEnd(rect: ClientRect): number {
-    return this._previousDirection === 'rtl' ? rect.right : rect.left;
+    return (this._dir && this._dir.value === 'rtl') ? rect.right : rect.left;
   }
 
   /** Checks whether the form field is attached to the DOM. */

src/material/input/input.spec.ts

@@ -15,7 +15,7 @@ import {
   ViewEncapsulation,
   ElementRef,
 } from '@angular/core';
-import {ComponentFixture, fakeAsync, flush, TestBed} from '@angular/core/testing';
+import {ComponentFixture, fakeAsync, flush, TestBed, tick} from '@angular/core/testing';
 import {
   FormControl,
   FormGroup,
@@ -1444,7 +1444,7 @@ describe('MatInput with appearance', () => {
     fakeDirectionality.value = 'rtl';
     fakeDirectionality.change.next('rtl');
     outlineFixture.detectChanges();
-    flush();
+    tick(16.6); // Angular replaces requestAnimationFrame calls with 16.6ms timeouts in tests.
     outlineFixture.detectChanges();
 
     expect(outlineFixture.componentInstance.formField.updateOutlineGap).toHaveBeenCalled();
@@ -1479,7 +1479,7 @@ describe('MatInput with appearance', () => {
       fakeDirectionality.value = 'rtl';
       fakeDirectionality.change.next('rtl');
       outlineFixture.detectChanges();
-      flush();
+      tick(16.6); // Angular replaces requestAnimationFrame calls with 16.6ms timeouts in tests.
       outlineFixture.detectChanges();
 
       let wrapperElement = outlineFixture.nativeElement;
@@ -1493,7 +1493,7 @@ describe('MatInput with appearance', () => {
       fakeDirectionality.value = 'ltr';
       fakeDirectionality.change.next('ltr');
       outlineFixture.detectChanges();
-      flush();
+      tick(16.6);
       outlineFixture.detectChanges();
 
       wrapperElement = outlineFixture.nativeElement;