fix(datepicker): throw when value is set to invalid type

BREAKING CHANGE: You must now use an actual Date object rather than a
string when setting the value of the datepicker programmatically
(through value, ngModel, or formControl).

Author: mmalerba

src/lib/core/datetime/date-adapter.ts

@@ -156,6 +156,13 @@ export abstract class DateAdapter<D> {
    */
   abstract getISODateString(date: D): string;
 
+  /**
+   * Checks whether the given value is a date object of type `D`.
+   * @param value The value to check.
+   * @returns Whether the value is a date object of type `D`.
+   */
+  abstract isDateObject(value: any): boolean;
+
   /**
    * Sets the locale used for all dates.
    * @param locale The new locale.

src/lib/core/datetime/native-date-adapter.ts

@@ -192,6 +192,10 @@ export class NativeDateAdapter extends DateAdapter<Date> {
     ].join('-');
   }
 
+  isDateObject(value: any) {
+    return value instanceof Date;
+  }
+
   /** Creates a date but allows the month and date to overflow. */
   private _createDateWithOverflow(year: number, month: number, date: number) {
     let result = new Date(year, month, date);

src/lib/datepicker/datepicker-input.ts

@@ -99,12 +99,14 @@ export class MdDatepickerInput<D> implements AfterContentInit, ControlValueAcces
         this._dateFormats.parse.dateInput);
   }
   set value(value: D | null) {
-    let date = this._dateAdapter.parse(value, this._dateFormats.parse.dateInput);
+    if (value != null && !this._dateAdapter.isDateObject(value)) {
+      throw new Error('Datepicker: value not recognized as a date object by DateAdapter.');
+    }
     let oldDate = this.value;
     this._renderer.setProperty(this._elementRef.nativeElement, 'value',
-        date ? this._dateAdapter.format(date, this._dateFormats.display.dateInput) : '');
-    if (!this._dateAdapter.sameDate(oldDate, date)) {
-      this._valueChange.emit(date);
+        value ? this._dateAdapter.format(value, this._dateFormats.display.dateInput) : '');
+    if (!this._dateAdapter.sameDate(oldDate, value)) {
+      this._valueChange.emit(value);
     }
   }
 

src/lib/datepicker/datepicker.spec.ts

@@ -189,6 +189,14 @@ describe('MdDatepicker', () => {
         expect(attachToRef.nativeElement.tagName.toLowerCase())
             .toBe('input', 'popup should be attached to native input');
       });
+
+      it('should throw when given wrong data type', () => {
+        testComponent.date = '1/1/2017' as any;
+
+        expect(() => fixture.detectChanges()).toThrow();
+
+        testComponent.date = null;
+      });
     });
 
     describe('datepicker with too many inputs', () => {
@@ -767,7 +775,7 @@ describe('MdDatepicker', () => {
 class StandardDatepicker {
   touch = false;
   disabled = false;
-  date = new Date(2020, JAN, 1);
+  date: Date | null = new Date(2020, JAN, 1);
   @ViewChild('d') datepicker: MdDatepicker<Date>;
   @ViewChild(MdDatepickerInput) datepickerInput: MdDatepickerInput<Date>;
 }