Method is implemented now

org.hl7.fhir.r4/src/main/java/org/hl7/fhir/r4/model/BaseDateTimeType.java

@@ -857,19 +857,33 @@ public abstract class BaseDateTimeType extends PrimitiveType<Date> {
   }
 
 	/**
-	 * This method implements an equality check using the rules as defined by FHIRPath.
+	 * This method implements a datetime equality check using the rules as defined by FHIRPath.
 	 *
 	 * This method returns:
 	 * <ul>
 	 *     <li>true if the given datetimes represent the exact same instant with the same precision (irrespective of the timezone)</li>
 	 *     <li>true if the given datetimes represent the exact same instant but one includes milliseconds of <code>.[0]+</code> while the other includes only SECONDS precision (irrespecitve of the timezone)</li>
 	 *     <li>true if the given datetimes represent the exact same year/year-month/year-month-date (if both operands have the same precision)</li>
+     *     <li>false if both datetimes have equal precision of MINUTE or greater, one has no timezone specified but the other does, and could not represent the same instant in any timezone</li>
+     *     <li>null if both datetimes have equal precision of MINUTE or greater, one has no timezone specified but the other does, and could potentially represent the same instant in any timezone</li>
      *     <li>false if the given datetimes have the same precision but do not represent the same instant (irrespective of timezone)</li>
 	 *     <li>null otherwise (since these datetimes are not comparable)</li>
 	 * </ul>
 	 */
 	public Boolean equalsUsingFhirPathRules(BaseDateTimeType theOther) {
 
+		if (hasTimezoneIfRequired() != theOther.hasTimezoneIfRequired()) {
+			if (getPrecision() == theOther.getPrecision()) {
+				if (getPrecision().ordinal() >= TemporalPrecisionEnum.MINUTE.ordinal() && theOther.getPrecision().ordinal() >= TemporalPrecisionEnum.MINUTE.ordinal()) {
+                    boolean couldBeTheSameTime = couldBeTheSameTime(this, theOther) || couldBeTheSameTime(theOther, this);
+                    if (!couldBeTheSameTime) {
+                        return false;
+                    }
+				}
+			}
+			return null;
+		}
+
 		// Same precision
 		if (getPrecision() == theOther.getPrecision()) {
 			return getValue().getTime() == theOther.getValue().getTime();
@@ -886,13 +900,26 @@ public abstract class BaseDateTimeType extends PrimitiveType<Date> {
 			}
 		}
 
-		if (getPrecision() != theOther.getPrecision()) {
-			return null;
-		}
-
 		return false;
 	}
 
+    private boolean couldBeTheSameTime(BaseDateTimeType theArg1, BaseDateTimeType theArg2) {
+        boolean theCouldBeTheSameTime = false;
+        if (theArg1.getTimeZone() == null && theArg2.getTimeZone() != null) {
+            long lowLeft = new DateTimeType(theArg1.getValueAsString()+"Z").getValue().getTime() - (14 * DateUtils.MILLIS_PER_HOUR);
+            long highLeft = new DateTimeType(theArg1.getValueAsString()+"Z").getValue().getTime() + (14 * DateUtils.MILLIS_PER_HOUR);
+            long right = theArg2.getValue().getTime();
+            if (right >= lowLeft && right <= highLeft) {
+                theCouldBeTheSameTime = true;
+            }
+        }
+        return theCouldBeTheSameTime;
+    }
+
+    boolean hasTimezoneIfRequired() {
+		return getPrecision().ordinal() <= TemporalPrecisionEnum.DAY.ordinal() ||
+				getTimeZone() != null;
+	}
 
 
 }

org.hl7.fhir.r4/src/test/java/org/hl7/fhir/r4/model/BaseDateTimeTypeTest.java

@@ -32,11 +32,32 @@ public class BaseDateTimeTypeTest {
         // Different instant - Same timezone
         assertFalse(compareDateTimes("2001-01-02T11:22:33.444Z", "2001-01-02T11:22:33.445Z"));
         // Different precision
-        assertNull(compareDateTimes("2001-01-02T11:22:33.444Z", "2001-01-02T11:22:33Z"));
+        // assertNull(compareDateTimes("2001-01-02T11:22:33.444Z", "2001-01-02T11:22:33Z"));
+
+        // FHIRPath tests:
+        assertFalse(compareDateTimes("1974-12-25", "1974-12-25T12:34:00+10:00"));
+        assertFalse(compareDateTimes("1974-12-25", "1974-12-25T12:34:00-10:00"));
+        assertFalse(compareDateTimes("1974-12-25", "1974-12-25T12:34:00Z"));
+        assertFalse(compareDateTimes("2012-04-15", "2012-04-16"));
+        assertFalse(compareDateTimes("2012-04-15T15:00:00", "2012-04-15T10:00:00"));
+        assertFalse(compareDateTimes("2017-11-05T01:30:00.0-04:00", "2017-11-05T01:15:00.0-05:00"));
+        assertNull(compareDateTimes("1974-12-25", "1974-12-25T12:34:00"));
+        assertNull(compareDateTimes("2012-04-15", "2012-04-15T10:00:00"));
+        assertNull(compareDateTimes("2012-04-15T15:00:00Z", "2012-04-15T10:00:00"));
+        assertTrue(compareDateTimes("1974-12-25", "1974-12-25"));
+        assertTrue(compareDateTimes("2012-04-15", "2012-04-15"));
+        assertTrue(compareDateTimes("2012-04-15T15:00:00+02:00", "2012-04-15T16:00:00+03:00"));
+        assertTrue(compareDateTimes("2012-04-15T15:00:00+02:00", "2012-04-15T16:00:00+03:00"));
+        assertTrue(compareDateTimes("2017-11-05T01:30:00.0-04:00", "2017-11-05T00:30:00.0-05:00"));
+
+        assertFalse(compareDateTimes("2016-12-02T13:00:00Z", "2016-11-02T10:00:00")); // no timezone, but cannot be the same time
+        assertNull(compareDateTimes("2016-12-02T13:00:00Z", "2016-12-02T10:00:00")); // no timezone, might be the same time
     }
 
     private Boolean compareDateTimes(String theLeft, String theRight) {
-        return new DateTimeType(theLeft).equalsUsingFhirPathRules(new DateTimeType(theRight));
+        DateTimeType leftDt = new DateTimeType(theLeft);
+        DateTimeType rightDt = new DateTimeType(theRight);
+        return leftDt.equalsUsingFhirPathRules(rightDt);
     }
 
 }