Consistent support for EnumSet subclasses in CollectionFactory

Issue: SPR-17619

spring-core/src/main/java/org/springframework/core/CollectionFactory.java

 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -195,7 +195,7 @@ public final class CollectionFactory {
 				throw new IllegalArgumentException("Unsupported Collection interface: " + collectionType.getName());
 			}
 		}
-		else if (EnumSet.class == collectionType) {
+		else if (EnumSet.class.isAssignableFrom(collectionType)) {
 			Assert.notNull(elementType, "Cannot create EnumSet for unknown element type");
 			// Cast is necessary for compilation in Eclipse 4.4.1.
 			return (Collection<E>) EnumSet.noneOf(asEnumType(elementType));

spring-core/src/test/java/org/springframework/core/CollectionFactoryTests.java

 /*
- * Copyright 2002-2017 the original author or authors.
+ * Copyright 2002-2018 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -35,11 +35,11 @@ import java.util.TreeMap;
 import java.util.TreeSet;
 
 import org.junit.Test;
+
 import org.springframework.util.LinkedMultiValueMap;
 import org.springframework.util.MultiValueMap;
 
-import static org.hamcrest.CoreMatchers.*;
-import static org.hamcrest.Matchers.empty;
+import static org.hamcrest.Matchers.*;
 import static org.junit.Assert.*;
 import static org.springframework.core.CollectionFactory.*;
 
@@ -104,7 +104,7 @@ public class CollectionFactoryTests {
 	 * {@link CollectionFactory#createApproximateMap(Object, int)}
 	 * is not type-safe.
 	 * <p>The reasoning is similar that described in
-	 * {@link #createApproximateCollectionIsNotTypeSafe()}.
+	 * {@link #createApproximateCollectionIsNotTypeSafeForEnumSet}.
 	 */
 	@Test
 	public void createApproximateMapIsNotTypeSafeForEnumMap() {
@@ -242,6 +242,12 @@ public class CollectionFactoryTests {
 		assertThat(createCollection(EnumSet.class, Color.class, 0), is(instanceOf(EnumSet.class)));
 	}
 
+	@Test  // SPR-17619
+	public void createsEnumSetSubclass() {
+		EnumSet<Color> enumSet = EnumSet.noneOf(Color.class);
+		assertThat(createCollection(enumSet.getClass(), Color.class, 0), is(instanceOf(enumSet.getClass())));
+	}
+
 	@Test(expected = IllegalArgumentException.class)
 	public void rejectsInvalidElementTypeForEnumSet() {
 		createCollection(EnumSet.class, Object.class, 0);
@@ -297,7 +303,8 @@ public class CollectionFactoryTests {
 	}
 
 
-	static enum Color {
+	enum Color {
 		RED, BLUE;
 	}
+
 }