Ignore Kotlin annotations when creating test context cache key

Every classes that's compiled by Kotlin is annotated with
kotlin.Metadata. The attributes of this annotation always differ so
if they are used in the cache key, context caching will effectively
be disabled.

This commit updates the key used by ImportsContextCustomizer to
ignore the kotlin.Metadata annotation. Additionally, to align with
with Java where annotations in java.lang.annotation are ignored,
annotations in kotlin.annotation are also ignored.

Closes gh-7101

spring-boot-test/pom.xml

@@ -112,6 +112,12 @@
 			<optional>true</optional>
 		</dependency>
 		<!-- Test -->
+		<dependency>
+			<groupId>org.jetbrains.kotlin</groupId>
+			<artifactId>kotlin-runtime</artifactId>
+			<version>1.0.4</version>
+			<scope>test</scope>
+		</dependency>
 		<dependency>
 			<groupId>org.apache.tomcat.embed</groupId>
 			<artifactId>tomcat-embed-core</artifactId>

spring-boot-test/src/main/java/org/springframework/boot/test/context/ImportsContextCustomizer.java

@@ -207,10 +207,10 @@ public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry)
 
 	/**
 	 * The key used to ensure correct application context caching. Keys are generated
-	 * based on <em>all</em> the annotations used with the test. We must use something
-	 * broader than just {@link Import @Import} annotations since an {@code @Import} may
-	 * use an {@link ImportSelector} which could make decisions based on anything
-	 * available from {@link AnnotationMetadata}.
+	 * based on <em>all</em> the annotations used with the test that aren't core Java or
+	 * Kotlin annotations. We must use something broader than just {@link Import @Import}
+	 * annotations since an {@code @Import} may use an {@link ImportSelector} which could
+	 * make decisions based on anything available from {@link AnnotationMetadata}.
 	 */
 	static class ContextCustomizerKey {
 
@@ -239,14 +239,24 @@ private void collectClassAnnotations(Class<?> classType,
 		private void collectElementAnnotations(AnnotatedElement element,
 				Set<Annotation> annotations, Set<Class<?>> seen) {
 			for (Annotation annotation : element.getDeclaredAnnotations()) {
-				if (!AnnotationUtils.isInJavaLangAnnotationPackage(annotation)) {
+				if (!AnnotationUtils.isInJavaLangAnnotationPackage(annotation)
+						&& !isIgnoredKotlinAnnotation(annotation)) {
 					annotations.add(annotation);
 					collectClassAnnotations(annotation.annotationType(), annotations,
 							seen);
 				}
 			}
 		}
 
+		private boolean isIgnoredKotlinAnnotation(Annotation annotation) {
+			return "kotlin.Metadata".equals(annotation.annotationType().getName())
+					|| isInKotlinAnnotationPackage(annotation);
+		}
+
+		private boolean isInKotlinAnnotationPackage(Annotation annotation) {
+			return annotation.annotationType().getName().startsWith("kotlin.annotation.");
+		}
+
 		@Override
 		public int hashCode() {
 			return this.annotations.hashCode();

spring-boot-test/src/test/java/org/springframework/boot/test/context/ImportsContextCustomizerTests.java

@@ -0,0 +1,48 @@
+/*
+ * Copyright 2012-2016 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.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.test.context;
+
+import kotlin.Metadata;
+import org.junit.Test;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests for {@link ImportsContextCustomizer}.
+ *
+ * @author Andy Wilkinson
+ */
+public class ImportsContextCustomizerTests {
+
+	@Test
+	public void customizersForTestClassesWithDifferentKotlinMetadataAreEqual() {
+		assertThat(new ImportsContextCustomizer(FirstKotlinAnnotatedTestClass.class))
+				.isEqualTo(new ImportsContextCustomizer(
+						SecondKotlinAnnotatedTestClass.class));
+	}
+
+	@Metadata(d2 = "foo")
+	static class FirstKotlinAnnotatedTestClass {
+
+	}
+
+	@Metadata(d2 = "bar")
+	static class SecondKotlinAnnotatedTestClass {
+
+	}
+
+}