refactor: replace first operator usages

Replaces all usages of the `first` operator with `take(1)` in order to avoid some cryptic errors that `first` throws when the observable completes before it has emitted a value.

Author: crisbeto

src/cdk/a11y/focus-trap.ts

@@ -17,7 +17,7 @@ import {
 } from '@angular/core';
 import {coerceBooleanProperty} from '@angular/cdk/coercion';
 import {Platform} from '@angular/cdk/platform';
-import {first} from 'rxjs/operators/first';
+import {take} from 'rxjs/operators/take';
 import {InteractivityChecker} from './interactivity-checker';
 
 
@@ -283,7 +283,7 @@ export class FocusTrap {
     if (this._ngZone.isStable) {
       fn();
     } else {
-      this._ngZone.onStable.asObservable().pipe(first()).subscribe(fn);
+      this._ngZone.onStable.asObservable().pipe(take(1)).subscribe(fn);
     }
   }
 }

src/cdk/a11y/list-key-manager.spec.ts

@@ -1,5 +1,5 @@
 import {DOWN_ARROW, TAB, UP_ARROW} from '@angular/cdk/keycodes';
-import {first} from 'rxjs/operators/first';
+import {take} from 'rxjs/operators/take';
 import {QueryList} from '@angular/core';
 import {fakeAsync, tick} from '@angular/core/testing';
 import {createKeyboardEvent} from '../testing/event-objects';
@@ -196,7 +196,7 @@ describe('Key managers', () => {
 
       it('should emit tabOut when the tab key is pressed', () => {
         let spy = jasmine.createSpy('tabOut spy');
-        keyManager.tabOut.pipe(first()).subscribe(spy);
+        keyManager.tabOut.pipe(take(1)).subscribe(spy);
         keyManager.onKeydown(fakeKeyEvents.tab);
 
         expect(spy).toHaveBeenCalled();

src/cdk/overlay/overlay-ref.ts

@@ -12,7 +12,7 @@ import {OverlayConfig} from './overlay-config';
 import {OverlayKeyboardDispatcher} from './keyboard/overlay-keyboard-dispatcher';
 import {Observable} from 'rxjs/Observable';
 import {Subject} from 'rxjs/Subject';
-import {first} from 'rxjs/operators/first';
+import {take} from 'rxjs/operators/take';
 
 
 /**
@@ -69,7 +69,7 @@ export class OverlayRef implements PortalOutlet {
     // Update the position once the zone is stable so that the overlay will be fully rendered
     // before attempting to position it, as the position may depend on the size of the rendered
     // content.
-    this._ngZone.onStable.asObservable().pipe(first()).subscribe(() => {
+    this._ngZone.onStable.asObservable().pipe(take(1)).subscribe(() => {
       this.updatePosition();
     });
 

src/lib/autocomplete/autocomplete-trigger.ts

@@ -18,7 +18,7 @@ import {
 } from '@angular/cdk/overlay';
 import {TemplatePortal} from '@angular/cdk/portal';
 import {filter} from 'rxjs/operators/filter';
-import {first} from 'rxjs/operators/first';
+import {take} from 'rxjs/operators/take';
 import {switchMap} from 'rxjs/operators/switchMap';
 import {tap} from 'rxjs/operators/tap';
 import {delay} from 'rxjs/operators/delay';
@@ -368,7 +368,7 @@ export class MatAutocompleteTrigger implements ControlValueAccessor, OnDestroy {
    * stream every time the option list changes.
    */
   private _subscribeToClosingActions(): Subscription {
-    const firstStable = this._zone.onStable.asObservable().pipe(first());
+    const firstStable = this._zone.onStable.asObservable().pipe(take(1));
     const optionChanges = this.autocomplete.options.changes.pipe(
       tap(() => this._positionStrategy.recalculateLastPosition()),
       // Defer emitting to the stream until the next tick, because changing
@@ -387,7 +387,7 @@ export class MatAutocompleteTrigger implements ControlValueAccessor, OnDestroy {
           return this.panelClosingActions;
         }),
         // when the first closing event occurs...
-        first()
+        take(1)
       )
       // set the value, close the panel, and complete.
       .subscribe(event => this._setValueAndClose(event));

src/lib/datepicker/calendar.ts

@@ -36,7 +36,7 @@ import {
   SimpleChanges,
 } from '@angular/core';
 import {DateAdapter, MAT_DATE_FORMATS, MatDateFormats} from '@angular/material/core';
-import {first} from 'rxjs/operators/first';
+import {take} from 'rxjs/operators/take';
 import {Subscription} from 'rxjs/Subscription';
 import {createMissingDateImplError} from './datepicker-errors';
 import {MatDatepickerIntl} from './datepicker-intl';
@@ -261,7 +261,7 @@ export class MatCalendar<D> implements AfterContentInit, OnDestroy, OnChanges {
   /** Focuses the active cell after the microtask queue is empty. */
   _focusActiveCell() {
     this._ngZone.runOutsideAngular(() => {
-      this._ngZone.onStable.asObservable().pipe(first()).subscribe(() => {
+      this._ngZone.onStable.asObservable().pipe(take(1)).subscribe(() => {
         this._elementRef.nativeElement.querySelector('.mat-calendar-body-active').focus();
       });
     });

src/lib/datepicker/datepicker.ts

@@ -18,7 +18,7 @@ import {
   ScrollStrategy,
 } from '@angular/cdk/overlay';
 import {ComponentPortal} from '@angular/cdk/portal';
-import {first} from 'rxjs/operators/first';
+import {take} from 'rxjs/operators/take';
 import {
   AfterContentInit,
   ChangeDetectionStrategy,
@@ -338,7 +338,7 @@ export class MatDatepicker<D> implements OnDestroy {
       componentRef.instance.datepicker = this;
 
       // Update the position once the calendar has rendered.
-      this._ngZone.onStable.asObservable().pipe(first()).subscribe(() => {
+      this._ngZone.onStable.asObservable().pipe(take(1)).subscribe(() => {
         this._popupRef.updatePosition();
       });
     }

src/lib/dialog/dialog-ref.ts

@@ -8,7 +8,7 @@
 
 import {OverlayRef, GlobalPositionStrategy} from '@angular/cdk/overlay';
 import {filter} from 'rxjs/operators/filter';
-import {first} from 'rxjs/operators/first';
+import {take} from 'rxjs/operators/take';
 import {DialogPosition} from './dialog-config';
 import {Observable} from 'rxjs/Observable';
 import {Subject} from 'rxjs/Subject';
@@ -50,7 +50,7 @@ export class MatDialogRef<T> {
     // Emit when opening animation completes
     _containerInstance._animationStateChanged.pipe(
       filter(event => event.phaseName === 'done' && event.toState === 'enter'),
-      first()
+      take(1)
     )
     .subscribe(() => {
       this._afterOpen.next();
@@ -60,7 +60,7 @@ export class MatDialogRef<T> {
     // Dispose overlay when closing animation is complete
     _containerInstance._animationStateChanged.pipe(
       filter(event => event.phaseName === 'done' && event.toState === 'exit'),
-      first()
+      take(1)
     )
     .subscribe(() => {
       this._overlayRef.dispose();
@@ -80,7 +80,7 @@ export class MatDialogRef<T> {
     // Transition the backdrop in parallel to the dialog.
     this._containerInstance._animationStateChanged.pipe(
       filter(event => event.phaseName === 'start'),
-      first()
+      take(1)
     )
     .subscribe(() => {
       this._beforeClose.next(dialogResult);

src/lib/form-field/form-field.ts

@@ -8,7 +8,7 @@
 
 import {animate, state, style, transition, trigger} from '@angular/animations';
 import {coerceBooleanProperty} from '@angular/cdk/coercion';
-import {first} from 'rxjs/operators/first';
+import {take} from 'rxjs/operators/take';
 import {startWith} from 'rxjs/operators/startWith';
 import {
   AfterContentChecked,
@@ -237,7 +237,7 @@ export class MatFormField implements AfterViewInit, AfterContentInit, AfterConte
       this._showAlwaysAnimate = true;
       this._floatPlaceholder = 'always';
 
-      fromEvent(this._placeholder.nativeElement, 'transitionend').pipe(first()).subscribe(() => {
+      fromEvent(this._placeholder.nativeElement, 'transitionend').pipe(take(1)).subscribe(() => {
         this._showAlwaysAnimate = false;
       });
 

src/lib/icon/icon.ts

@@ -6,7 +6,7 @@
  * found in the LICENSE file at https://angular.io/license
  */
 
-import {first} from 'rxjs/operators/first';
+import {take} from 'rxjs/operators/take';
 import {
   Attribute,
   ChangeDetectionStrategy,
@@ -132,7 +132,7 @@ export class MatIcon extends _MatIconMixinBase implements OnChanges, OnInit, Can
       if (this.svgIcon) {
         const [namespace, iconName] = this._splitIconName(this.svgIcon);
 
-        this._iconRegistry.getNamedSvgIcon(iconName, namespace).pipe(first()).subscribe(
+        this._iconRegistry.getNamedSvgIcon(iconName, namespace).pipe(take(1)).subscribe(
           svg => this._setSvgElement(svg),
           (err: Error) => console.log(`Error retrieving icon: ${err.message}`)
         );

src/lib/menu/menu-directive.ts

@@ -12,7 +12,7 @@ import {Direction} from '@angular/cdk/bidi';
 import {ESCAPE, LEFT_ARROW, RIGHT_ARROW} from '@angular/cdk/keycodes';
 import {startWith} from 'rxjs/operators/startWith';
 import {switchMap} from 'rxjs/operators/switchMap';
-import {first} from 'rxjs/operators/first';
+import {take} from 'rxjs/operators/take';
 import {
   AfterContentInit,
   ChangeDetectionStrategy,
@@ -189,7 +189,7 @@ export class MatMenu implements AfterContentInit, MatMenuPanel, OnDestroy {
 
     return this._ngZone.onStable
       .asObservable()
-      .pipe(first(), switchMap(() => this._hovered()));
+      .pipe(take(1), switchMap(() => this._hovered()));
   }
 
   /** Handle a keyboard event from the menu, delegating to the appropriate action. */

src/lib/select/select.ts

@@ -19,7 +19,7 @@ import {
   ViewportRuler,
 } from '@angular/cdk/overlay';
 import {filter} from 'rxjs/operators/filter';
-import {first} from 'rxjs/operators/first';
+import {take} from 'rxjs/operators/take';
 import {map} from 'rxjs/operators/map';
 import {startWith} from 'rxjs/operators/startWith';
 import {takeUntil} from 'rxjs/operators/takeUntil';
@@ -530,7 +530,7 @@ export class MatSelect extends _MatSelectMixinBase implements AfterContentInit,
     this._changeDetectorRef.markForCheck();
 
     // Set the font size on the panel element once it exists.
-    this._ngZone.onStable.asObservable().pipe(first()).subscribe(() => {
+    this._ngZone.onStable.asObservable().pipe(take(1)).subscribe(() => {
       if (this._triggerFontSize && this.overlayDir.overlayRef &&
           this.overlayDir.overlayRef.overlayElement) {
         this.overlayDir.overlayRef.overlayElement.style.fontSize = `${this._triggerFontSize}px`;
@@ -714,7 +714,7 @@ export class MatSelect extends _MatSelectMixinBase implements AfterContentInit,
    * Callback that is invoked when the overlay panel has been attached.
    */
   _onAttached(): void {
-    this.overlayDir.positionChange.pipe(first()).subscribe(() => {
+    this.overlayDir.positionChange.pipe(take(1)).subscribe(() => {
       this._changeDetectorRef.detectChanges();
       this._calculateOverlayOffsetX();
       this.panel.nativeElement.scrollTop = this._scrollTop;

src/lib/sidenav/drawer.ts

@@ -33,7 +33,7 @@ import {
 import {DOCUMENT} from '@angular/platform-browser';
 import {merge} from 'rxjs/observable/merge';
 import {filter} from 'rxjs/operators/filter';
-import {first} from 'rxjs/operators/first';
+import {take} from 'rxjs/operators/take';
 import {startWith} from 'rxjs/operators/startWith';
 import {takeUntil} from 'rxjs/operators/takeUntil';
 import {map} from 'rxjs/operators/map';
@@ -346,7 +346,7 @@ export class MatDrawer implements AfterContentInit, OnDestroy {
     // TODO(crisbeto): This promise is here for backwards-compatibility.
     // It should be removed next time we do breaking changes in the drawer.
     return new Promise<any>(resolve => {
-      this.openedChange.pipe(first()).subscribe(open => {
+      this.openedChange.pipe(take(1)).subscribe(open => {
         resolve(new MatDrawerToggleResult(open ? 'open' : 'close', true));
       });
     });
@@ -517,7 +517,7 @@ export class MatDrawerContainer implements AfterContentInit, OnDestroy {
     // NOTE: We need to wait for the microtask queue to be empty before validating,
     // since both drawers may be swapping positions at the same time.
     drawer.onPositionChanged.pipe(takeUntil(this._drawers.changes)).subscribe(() => {
-      this._ngZone.onMicrotaskEmpty.asObservable().pipe(first()).subscribe(() => {
+      this._ngZone.onMicrotaskEmpty.asObservable().pipe(take(1)).subscribe(() => {
         this._validateDrawers();
       });
     });

src/lib/snack-bar/snack-bar-container.ts

@@ -32,7 +32,7 @@ import {
   ComponentPortal,
   CdkPortalOutlet,
 } from '@angular/cdk/portal';
-import {first} from 'rxjs/operators/first';
+import {take} from 'rxjs/operators/take';
 import {AnimationCurves, AnimationDurations} from '@angular/material/core';
 import {Observable} from 'rxjs/Observable';
 import {Subject} from 'rxjs/Subject';
@@ -177,7 +177,7 @@ export class MatSnackBarContainer extends BasePortalOutlet implements OnDestroy
    * errors where we end up removing an element which is in the middle of an animation.
    */
   private _completeExit() {
-    this._ngZone.onMicrotaskEmpty.asObservable().pipe(first()).subscribe(() => {
+    this._ngZone.onMicrotaskEmpty.asObservable().pipe(take(1)).subscribe(() => {
       this._onExit.next();
       this._onExit.complete();
     });

src/lib/snack-bar/snack-bar.ts

@@ -17,7 +17,7 @@ import {MatSnackBarContainer} from './snack-bar-container';
 import {MatSnackBarRef} from './snack-bar-ref';
 import {BreakpointObserver, Breakpoints} from '@angular/cdk/layout';
 import {takeUntil} from 'rxjs/operators/takeUntil';
-import {first} from 'rxjs/operators/first';
+import {take} from 'rxjs/operators/take';
 
 
 /**
@@ -153,7 +153,7 @@ export class MatSnackBar {
     // appropriate. This class is applied to the overlay element because the overlay must expand to
     // fill the width of the screen for full width snackbars.
     this._breakpointObserver.observe(Breakpoints.Handset).pipe(
-      takeUntil(overlayRef.detachments().pipe(first()))
+      takeUntil(overlayRef.detachments().pipe(take(1)))
     ).subscribe(state => {
       if (state.matches) {
         overlayRef.overlayElement.classList.add('mat-snack-bar-handset');

src/lib/tooltip/tooltip.ts

@@ -24,7 +24,7 @@ import {
 } from '@angular/cdk/overlay';
 import {Platform} from '@angular/cdk/platform';
 import {ComponentPortal} from '@angular/cdk/portal';
-import {first} from 'rxjs/operators/first';
+import {take} from 'rxjs/operators/take';
 import {ScrollDispatcher} from '@angular/cdk/scrolling';
 import {
   ChangeDetectionStrategy,
@@ -387,7 +387,7 @@ export class MatTooltip implements OnDestroy {
       this._tooltipInstance.message = this.message;
       this._tooltipInstance._markForCheck();
 
-      this._ngZone.onMicrotaskEmpty.asObservable().pipe(first()).subscribe(() => {
+      this._ngZone.onMicrotaskEmpty.asObservable().pipe(take(1)).subscribe(() => {
         if (this._tooltipInstance) {
           this._overlayRef!.updatePosition();
         }

tools/package-tools/rollup-globals.ts

@@ -73,6 +73,7 @@ export const rollupGlobals = {
   'rxjs/operators/debounceTime': 'Rx.Observable',
   'rxjs/operators/takeUntil': 'Rx.Observable',
   'rxjs/operators/first': 'Rx.Observable',
+  'rxjs/operators/take': 'Rx.Observable',
   'rxjs/operators/filter': 'Rx.Observable',
   'rxjs/operators/map': 'Rx.Observable',
   'rxjs/operators/tap': 'Rx.Observable',