Fix initializing of date with year < 100 in datepicker.

RELNOTES: Fix initializing of date with year < 100 in datepicker.
Before the fix: If you init the datepicker with date with year < 100 (eg.23) it will look like it works, but clicking on the grid cell will switch it 1900+ years (eg. 1923).
After the fix: The year < 100 is preserved through the interaction with the control.
-------------
Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=125713669

Author: joeltine

closure/goog/ui/datepicker.js

@@ -785,6 +785,8 @@ goog.ui.DatePicker.prototype.setDate_ = function(date, fireSelection) {
   // Set current month
   if (date) {
     this.activeMonth_.set(this.date_);
+    // Set years with two digits to their full year, not 19XX.
+    this.activeMonth_.setFullYear(this.date_.getFullYear());
     this.activeMonth_.setDate(1);
   }
 
@@ -1392,7 +1394,16 @@ goog.ui.DatePicker.prototype.updateCalendarGrid_ = function() {
     this.grid_[y] = [];
     for (var x = 0; x < 7; x++) {  // Weekdays
       this.grid_[y][x] = date.clone();
+      // Date.add breaks dates before year 100 by adding 1900 to the year
+      // value. As a workaround we store the year before the add and reapply it
+      // after (with special handling for January 1st).
+      var year = date.getFullYear();
       date.add(dayInterval);
+      if (date.getMonth() == 0 && date.getDate() == 1) {
+        // Increase year on January 1st.
+        year++;
+      }
+      date.setFullYear(year);
     }
   }
 

closure/goog/ui/datepicker_test.js

@@ -163,6 +163,25 @@ function testGetActiveMonth() {
       picker.getActiveMonth());
 }
 
+function testGetActiveMonthBeforeYear100() {
+  var date = new Date(23, 5, 5);
+  // Above statement will create date with year 1923, need to set full year
+  // explicitly.
+  date.setFullYear(23);
+
+  var expectedMonth = new goog.date.Date(23, 5, 1);
+  expectedMonth.setFullYear(23);
+
+  picker = new goog.ui.DatePicker(date);
+  var month = picker.getActiveMonth();
+  assertObjectEquals(expectedMonth, month);
+
+  month.setMonth(10);
+  assertObjectEquals(
+      'modifying the returned object is safe', expectedMonth,
+      picker.getActiveMonth());
+}
+
 function testGetDate() {
   picker = new goog.ui.DatePicker(new Date(2000, 0, 1));
   var date = picker.getDate();
@@ -177,6 +196,71 @@ function testGetDate() {
   assertNull('no date is selected', picker.getDate());
 }
 
+function testGetDateBeforeYear100() {
+  var inputDate = new Date(23, 5, 5);
+  // Above statement will create date with year 1923, need to set full year
+  // explicitly.
+  inputDate.setFullYear(23);
+  picker = new goog.ui.DatePicker(inputDate);
+  var date = picker.getDate();
+
+  var expectedDate = new goog.date.Date(23, 5, 5);
+  expectedDate.setFullYear(23);
+  assertObjectEquals(expectedDate, date);
+
+  picker.setDate(inputDate);
+  assertObjectEquals(expectedDate, picker.getDate());
+  var expectedMonth = new goog.date.Date(23, 5, 1);
+  expectedMonth.setFullYear(23);
+  assertObjectEquals(expectedMonth, picker.getActiveMonth());
+}
+
+function testGridForDecember23() {
+  // Initialize picker to December 23.
+  var inputDate = new Date(23, 11, 5);
+  // Above statement will create date with year 1923, need to set full year
+  // explicitly.
+  inputDate.setFullYear(23);
+  picker = new goog.ui.DatePicker(inputDate);
+  picker.create(sandbox);
+
+  // Grid start with last days of November 23, shows December 23 and first days
+  // of January 24.
+  for (var i = 0; i < 6; i++) {
+    for (var j = 0; j < 7; j++) {
+      var date = picker.getDateAt(i, j);
+      if (date.getMonth() == 0) {
+        assertEquals(24, date.getFullYear());
+      } else {
+        assertEquals(23, date.getFullYear());
+      }
+    }
+  }
+}
+
+function testGridForJanuary22() {
+  // Initialize picker to January 22.
+  var inputDate = new Date(22, 0, 5);
+  // Above statement will create date with year 1922, need to set full year
+  // explicitly.
+  inputDate.setFullYear(22);
+  picker = new goog.ui.DatePicker(inputDate);
+  picker.create(sandbox);
+
+  // Grid start with last days of December 21, shows January 22 and first days
+  // of February 22.
+  for (var i = 0; i < 6; i++) {
+    for (var j = 0; j < 7; j++) {
+      var date = picker.getDateAt(i, j);
+      if (date.getMonth() == 11) {
+        assertEquals(21, date.getFullYear());
+      } else {
+        assertEquals(22, date.getFullYear());
+      }
+    }
+  }
+}
+
 function testGetDateAt() {
   picker = new goog.ui.DatePicker();
   picker.create(sandbox);