[MaterialDatePicker] Crash - Scroll to Min Year of CalendarConstraint

Resolves #981
Resolves #980

PiperOrigin-RevId: 296000173

Author: ymarian

lib/java/com/google/android/material/datepicker/CalendarConstraints.java

@@ -167,6 +167,21 @@ public void writeToParcel(Parcel dest, int flags) {
     dest.writeParcelable(validator, /* parcelableFlags = */ 0);
   }
 
+  /**
+   * Returns the given month if it's within the constraints or the closest bound if it's outside.
+   */
+  Month clamp(Month month) {
+    if (month.compareTo(start) < 0) {
+      return start;
+    }
+
+    if (month.compareTo(end) > 0) {
+      return end;
+    }
+
+    return month;
+  }
+
   /** Builder for {@link com.google.android.material.datepicker.CalendarConstraints}. */
   public static final class Builder {
 

lib/java/com/google/android/material/datepicker/YearGridAdapter.java

@@ -84,7 +84,9 @@ private OnClickListener createYearClickListener(final int year) {
     return new OnClickListener() {
       @Override
       public void onClick(View view) {
-        Month moveTo = Month.create(year, materialCalendar.getCurrentMonth().month);
+        Month current = Month.create(year, materialCalendar.getCurrentMonth().month);
+        CalendarConstraints calendarConstraints = materialCalendar.getCalendarConstraints();
+        Month moveTo = calendarConstraints.clamp(current);
         materialCalendar.setCurrentMonth(moveTo);
         materialCalendar.setSelector(CalendarSelector.DAY);
       }

lib/javatests/com/google/android/material/datepicker/CalendarConstraintsTest.java

@@ -15,6 +15,7 @@
  */
 package com.google.android.material.datepicker;
 
+import static com.google.common.truth.Truth.assertThat;
 import static org.junit.Assert.assertEquals;
 
 import com.google.android.material.internal.ParcelableTestUtils;
@@ -24,10 +25,9 @@
 import org.junit.rules.ExpectedException;
 import org.junit.runner.RunWith;
 import org.robolectric.RobolectricTestRunner;
-import org.robolectric.annotation.internal.DoNotInstrument;
 
+/** Tests for {@link CalendarConstraints} */
 @RunWith(RobolectricTestRunner.class)
-@DoNotInstrument
 public class CalendarConstraintsTest {
 
   private static final long FEB_2016 = Month.create(2016, Calendar.FEBRUARY).timeInMillis;
@@ -45,6 +45,52 @@ public void equalAfterParceling() {
     assertEquals(originalBounds, constructedBounds);
   }
 
+  @Test
+  public void clampMonth_when_InsideBounds() {
+    Month today = Month.today();
+    Month yearBefore = today.monthsLater(-12);
+    Month yearAfter = today.monthsLater(12);
+
+    long start = yearBefore.timeInMillis;
+    long end = yearAfter.timeInMillis;
+    CalendarConstraints calendarConstraints =
+        new CalendarConstraints.Builder().setStart(start).setEnd(end).build();
+
+    Month monthWithinBounds = yearAfter.monthsLater(-5);
+    assertThat(calendarConstraints.clamp(monthWithinBounds))
+        .isEqualTo(monthWithinBounds);
+  }
+
+  @Test
+  public void clampMonth_when_beforeLowerBound() {
+    Month today = Month.today();
+    Month yearBefore = today.monthsLater(-12);
+    Month yearAfter = today.monthsLater(12);
+
+    long start = yearBefore.timeInMillis;
+    long end = yearAfter.timeInMillis;
+    CalendarConstraints calendarConstraints =
+        new CalendarConstraints.Builder().setStart(start).setEnd(end).build();
+
+    assertThat(calendarConstraints.clamp(yearBefore.monthsLater(-5)))
+        .isEqualTo(yearBefore);
+  }
+
+  @Test
+  public void clampMonth_when_AfterUpperBound() {
+    Month today = Month.today();
+    Month yearBefore = today.monthsLater(-12);
+    Month yearAfter = today.monthsLater(12);
+
+    long start = yearBefore.timeInMillis;
+    long end = yearAfter.timeInMillis;
+    CalendarConstraints calendarConstraints =
+        new CalendarConstraints.Builder().setStart(start).setEnd(end).build();
+
+    assertThat(calendarConstraints.clamp(yearAfter.monthsLater(5)))
+        .isEqualTo(yearAfter);
+  }
+
   @Test
   public void currentDefaultsToTodayIfWithinBounds() {
     Month today = Month.today();