feat(common): stricter types for DatePipe (#37447)

Make typing of DatePipe stricter to catch some misuses (such as passing
an Observable or an array) at compile time.

BREAKING CHANGE:
The signature of the `date` pipe now explicitly states which types are
accepted. This should only cause issues in corner cases, as any other
values would result in runtime exceptions.

PR Close #37447

packages/common/src/pipes/date_pipe.ts

@@ -171,7 +171,15 @@ export class DatePipe implements PipeTransform {
    * See [Setting your app locale](guide/i18n#setting-up-the-locale-of-your-app).
    * @returns A date string in the desired format.
    */
-  transform(value: any, format = 'mediumDate', timezone?: string, locale?: string): string|null {
+  transform(value: Date|string|number, format?: string, timezone?: string, locale?: string): string
+      |null;
+  transform(value: null|undefined, format?: string, timezone?: string, locale?: string): null;
+  transform(
+      value: Date|string|number|null|undefined, format?: string, timezone?: string,
+      locale?: string): string|null;
+  transform(
+      value: Date|string|number|null|undefined, format = 'mediumDate', timezone?: string,
+      locale?: string): string|null {
     if (value == null || value === '' || value !== value) return null;
 
     try {

packages/common/test/pipes/date_pipe_spec.ts

@@ -59,12 +59,20 @@ import {JitReflector} from '@angular/platform-browser-dynamic/src/compiler_refle
         expect(pipe.transform(Number.NaN)).toEqual(null);
       });
 
+      it('should return null for null', () => {
+        expect(pipe.transform(null)).toEqual(null);
+      });
+
+      it('should return null for undefined', () => {
+        expect(pipe.transform(undefined)).toEqual(null);
+      });
+
       it('should support ISO string without time', () => {
         expect(() => pipe.transform(isoStringWithoutTime)).not.toThrow();
       });
 
       it('should not support other objects', () => {
-        expect(() => pipe.transform({})).toThrowError(/InvalidPipeArgument/);
+        expect(() => pipe.transform({} as any)).toThrowError(/InvalidPipeArgument/);
       });
     });