fix(badge): throw proper error when set on a non-element node

Currently if a `matBadge` is set on a non-element node, we eventually hit an error that can look cryptic. This changes add a proper error so it's easier to debug.

src/material/badge/badge.spec.ts

@@ -14,7 +14,7 @@ describe('MatBadge', () => {
     TestBed
         .configureTestingModule({
           imports: [MatBadgeModule],
-          declarations: [BadgeTestApp, PreExistingBadge, NestedBadge],
+          declarations: [BadgeTestApp, PreExistingBadge, NestedBadge, BadgeOnTemplate],
         })
         .compileComponents();
 
@@ -205,6 +205,12 @@ describe('MatBadge', () => {
     expect(fixture.componentInstance.badgeInstance.getBadgeElement()).toBe(badgeElement);
   });
 
+  it('should throw if badge is not attached to an element node', () => {
+    expect(() => {
+      TestBed.createComponent(BadgeOnTemplate);
+    }).toThrowError(/matBadge must be attached to an element node/);
+  });
+
 });
 
 /** Test component that contains a MatBadge. */
@@ -260,3 +266,12 @@ class PreExistingBadge {
 })
 class NestedBadge {
 }
+
+
+@Component({
+  template: `
+    <ng-template matBadge="1">Notifications</ng-template>
+  `
+})
+class BadgeOnTemplate {
+}

src/material/badge/badge.ts

@@ -19,6 +19,7 @@ import {
   Optional,
   Renderer2,
   SimpleChanges,
+  isDevMode,
 } from '@angular/core';
 import {CanDisable, CanDisableCtor, mixinDisabled, ThemePalette} from '@angular/material/core';
 import {ANIMATION_MODULE_TYPE} from '@angular/platform-browser/animations';
@@ -124,6 +125,13 @@ export class MatBadge extends _MatBadgeMixinBase implements OnDestroy, OnChanges
       private _renderer: Renderer2,
       @Optional() @Inject(ANIMATION_MODULE_TYPE) private _animationMode?: string) {
       super();
+
+      if (isDevMode()) {
+        const nativeElement = _elementRef.nativeElement;
+        if (nativeElement.nodeType !== nativeElement.ELEMENT_NODE) {
+          throw Error('matBadge must be attached to an element node.');
+        }
+      }
     }
 
   /** Whether the badge is above the host or not */