fix(datepicker): keyboard fixes (enter matches click behavior & correct up and down arrow behavior in year mode).

Author: mmalerba

src/lib/datepicker/calendar.ts

@@ -312,6 +312,7 @@ export class MatCalendar<D> implements AfterContentInit, OnDestroy, OnChanges {
       case ENTER:
         if (this._dateFilterForViews(this._activeDate)) {
           this._dateSelected(this._activeDate);
+          this._userSelected();
           // Prevent unexpected default actions such as form submission.
           event.preventDefault();
         }
@@ -375,23 +376,17 @@ export class MatCalendar<D> implements AfterContentInit, OnDestroy, OnChanges {
    * calendar table.
    */
   private _prevMonthInSameCol(date: D): D {
-    // Determine how many months to jump forward given that there are 2 empty slots at the beginning
-    // of each year.
-    let increment = this._dateAdapter.getMonth(date) <= 4 ? -5 :
-        (this._dateAdapter.getMonth(date) >= 7 ? -7 : -12);
-    return this._dateAdapter.addCalendarMonths(date, increment);
+    // Decrement by 4 since there are 4 months per row.
+    return this._dateAdapter.addCalendarMonths(date, -4);
   }
 
   /**
    * Determine the date for the month that comes after the given month in the same column in the
    * calendar table.
    */
   private _nextMonthInSameCol(date: D): D {
-    // Determine how many months to jump forward given that there are 2 empty slots at the beginning
-    // of each year.
-    let increment = this._dateAdapter.getMonth(date) <= 4 ? 7 :
-        (this._dateAdapter.getMonth(date) >= 7 ? 5 : 12);
-    return this._dateAdapter.addCalendarMonths(date, increment);
+    // Increment by 4 since there are 4 months per row.
+    return this._dateAdapter.addCalendarMonths(date, 4);
   }
 
   /**