refactor(material/tooltip): fix strict property initialization errors

Updates the code to be compatible with strict property initialization.

Author: crisbeto

src/material/tooltip/tooltip.spec.ts

@@ -1575,8 +1575,8 @@ class BasicTooltipDemo {
   showTooltipClass = false;
   tooltipDisabled = false;
   touchGestures: TooltipTouchGestures = 'auto';
-  @ViewChild(MatTooltip) tooltip: MatTooltip;
-  @ViewChild('button') button: ElementRef<HTMLButtonElement>;
+  @ViewChild(MatTooltip) tooltip!: MatTooltip;
+  @ViewChild('button') button!: ElementRef<HTMLButtonElement>;
 }
 
 @Component({
@@ -1596,7 +1596,7 @@ class ScrollableTooltipDemo {
   message: string = initialTooltipMessage;
   showButton: boolean = true;
 
-  @ViewChild(CdkScrollable) scrollingContainer: CdkScrollable;
+  @ViewChild(CdkScrollable) scrollingContainer!: CdkScrollable;
 
   scrollDown() {
     const scrollingContainerEl = this.scrollingContainer.getElementRef().nativeElement;
@@ -1658,8 +1658,8 @@ class DataBoundAriaLabelTooltip {
   imports: [MatTooltipModule, OverlayModule],
 })
 class TooltipOnTextFields {
-  @ViewChild('input') input: ElementRef<HTMLInputElement>;
-  @ViewChild('textarea') textarea: ElementRef<HTMLTextAreaElement>;
+  @ViewChild('input') input!: ElementRef<HTMLInputElement>;
+  @ViewChild('textarea') textarea!: ElementRef<HTMLTextAreaElement>;
   touchGestures: TooltipTouchGestures = 'auto';
 }
 
@@ -1674,7 +1674,7 @@ class TooltipOnTextFields {
   imports: [MatTooltipModule, OverlayModule],
 })
 class TooltipOnDraggableElement {
-  @ViewChild('button') button: ElementRef;
+  @ViewChild('button') button!: ElementRef;
   touchGestures: TooltipTouchGestures = 'auto';
 }
 
@@ -1684,8 +1684,8 @@ class TooltipOnDraggableElement {
 })
 class TooltipDemoWithoutPositionBinding {
   message: string = initialTooltipMessage;
-  @ViewChild(MatTooltip) tooltip: MatTooltip;
-  @ViewChild('button') button: ElementRef<HTMLButtonElement>;
+  @ViewChild(MatTooltip) tooltip!: MatTooltip;
+  @ViewChild('button') button!: ElementRef<HTMLButtonElement>;
 }
 
 @Component({
@@ -1694,8 +1694,8 @@ class TooltipDemoWithoutPositionBinding {
 })
 class TooltipDemoWithoutTooltipClassBinding {
   message = initialTooltipMessage;
-  @ViewChild(MatTooltip) tooltip: MatTooltip;
-  @ViewChild('button') button: ElementRef<HTMLButtonElement>;
+  @ViewChild(MatTooltip) tooltip!: MatTooltip;
+  @ViewChild('button') button!: ElementRef<HTMLButtonElement>;
 }
 
 @Component({
@@ -1706,8 +1706,8 @@ class TooltipDemoWithoutTooltipClassBinding {
 })
 class TooltipDemoWithTooltipClassBinding {
   message: string = initialTooltipMessage;
-  @ViewChild(MatTooltip) tooltip: MatTooltip;
-  @ViewChild('button') button: ElementRef<HTMLButtonElement>;
+  @ViewChild(MatTooltip) tooltip!: MatTooltip;
+  @ViewChild('button') button!: ElementRef<HTMLButtonElement>;
 }
 
 @Component({
@@ -1717,8 +1717,8 @@ class TooltipDemoWithTooltipClassBinding {
 })
 class WideTooltipDemo {
   message = 'Test';
-  @ViewChild(MatTooltip) tooltip: MatTooltip;
-  @ViewChild('button') button: ElementRef<HTMLButtonElement>;
+  @ViewChild(MatTooltip) tooltip!: MatTooltip;
+  @ViewChild('button') button!: ElementRef<HTMLButtonElement>;
 }
 
 /** Asserts whether a tooltip directive has a tooltip instance. */

src/material/tooltip/tooltip.ts

@@ -195,22 +195,22 @@ export class MatTooltip implements OnDestroy, AfterViewInit {
     optional: true,
   });
 
-  _overlayRef: OverlayRef | null;
-  _tooltipInstance: TooltipComponent | null;
+  _overlayRef: OverlayRef | null = null;
+  _tooltipInstance: TooltipComponent | null = null;
   _overlayPanelClass: string[] | undefined; // Used for styling internally.
 
-  private _portal: ComponentPortal<TooltipComponent>;
+  private _portal!: ComponentPortal<TooltipComponent>;
   private _position: TooltipPosition = 'below';
   private _positionAtOrigin: boolean = false;
   private _disabled: boolean = false;
-  private _tooltipClass: string | string[] | Set<string> | {[key: string]: unknown};
+  private _tooltipClass!: string | string[] | Set<string> | {[key: string]: unknown};
   private _viewInitialized = false;
   private _pointerExitEventsInitialized = false;
   private readonly _tooltipComponent = TooltipComponent;
   private _viewportMargin = 8;
-  private _currentPosition: TooltipPosition;
+  private _currentPosition!: TooltipPosition;
   private readonly _cssClassPrefix: string = 'mat-mdc';
-  private _ariaDescriptionPending: boolean;
+  private _ariaDescriptionPending = false;
   private _dirSubscribed = false;
 
   /** Allows the user to define the position of the tooltip relative to the parent element */
@@ -279,7 +279,7 @@ export class MatTooltip implements OnDestroy, AfterViewInit {
     this._showDelay = coerceNumberProperty(value);
   }
 
-  private _showDelay: number;
+  private _showDelay!: number;
 
   /** The default delay in ms before hiding the tooltip after hide is called */
   @Input('matTooltipHideDelay')
@@ -295,7 +295,7 @@ export class MatTooltip implements OnDestroy, AfterViewInit {
     }
   }
 
-  private _hideDelay: number;
+  private _hideDelay!: number;
 
   /**
    * How touch gestures should be handled by the tooltip. On touch devices the tooltip directive
@@ -970,10 +970,10 @@ export class TooltipComponent implements OnDestroy {
   _isMultiline = false;
 
   /** Message to display in the tooltip */
-  message: string;
+  message!: string;
 
   /** Classes to be added to the tooltip. Supports the same syntax as `ngClass`. */
-  tooltipClass: string | string[] | Set<string> | {[key: string]: unknown};
+  tooltipClass!: string | string[] | Set<string> | {[key: string]: unknown};
 
   /** The timeout ID of any current timer set to show the tooltip */
   private _showTimeoutId: ReturnType<typeof setTimeout> | undefined;
@@ -982,10 +982,10 @@ export class TooltipComponent implements OnDestroy {
   private _hideTimeoutId: ReturnType<typeof setTimeout> | undefined;
 
   /** Element that caused the tooltip to open. */
-  _triggerElement: HTMLElement;
+  _triggerElement!: HTMLElement;
 
   /** Amount of milliseconds to delay the closing sequence. */
-  _mouseLeaveHideDelay: number;
+  _mouseLeaveHideDelay!: number;
 
   /** Whether animations are currently disabled. */
   private _animationsDisabled = _animationsDisabled();
@@ -996,7 +996,7 @@ export class TooltipComponent implements OnDestroy {
     // the DOM which can happen before `ngAfterViewInit`.
     static: true,
   })
-  _tooltip: ElementRef<HTMLElement>;
+  _tooltip!: ElementRef<HTMLElement>;
 
   /** Whether interactions on the page should close the tooltip */
   private _closeOnInteraction = false;

src/material/tooltip/tooltip.zone.spec.ts

@@ -72,7 +72,7 @@ class ScrollableTooltipDemo {
   message: string = initialTooltipMessage;
   showButton: boolean = true;
 
-  @ViewChild(CdkScrollable) scrollingContainer: CdkScrollable;
+  @ViewChild(CdkScrollable) scrollingContainer!: CdkScrollable;
 
   scrollDown() {
     const scrollingContainerEl = this.scrollingContainer.getElementRef().nativeElement;