Support @TempDir constructor injection for Java record classes (#4279)

The `@TempDir` annotation on a constructor parameter is copied to the
generated `final` instance field. This caused it top be picked up by
`TempDirectory` for instance field injection which then failed because
the field was `final`. This change now checks if a test class is an
instance of a record type and skips instance field injection. Since
records cannot have any instance fields besides the ones generated from
their constructor, there's no need to inject values into any of them.

Author: marcphilipp

junit-jupiter-engine/src/main/java/org/junit/jupiter/engine/extension/TempDirectory.java

@@ -19,6 +19,7 @@
 import static org.junit.platform.commons.support.AnnotationSupport.findAnnotatedFields;
 import static org.junit.platform.commons.support.AnnotationSupport.findAnnotation;
 import static org.junit.platform.commons.support.ReflectionSupport.makeAccessible;
+import static org.junit.platform.commons.util.ReflectionUtils.isRecordObject;
 
 import java.io.File;
 import java.io.IOException;
@@ -135,7 +136,9 @@ private void injectStaticFields(ExtensionContext context, Class<?> testClass) {
 	}
 
 	private void injectInstanceFields(ExtensionContext context, Object instance) {
-		injectFields(context, instance, instance.getClass(), ModifierSupport::isNotStatic);
+		if (!isRecordObject(instance)) {
+			injectFields(context, instance, instance.getClass(), ModifierSupport::isNotStatic);
+		}
 	}
 
 	private void injectFields(ExtensionContext context, Object testInstance, Class<?> testClass,

junit-platform-commons/src/main/java/org/junit/platform/commons/util/ReflectionUtils.java

@@ -365,6 +365,25 @@ public static boolean isInnerClass(Class<?> clazz) {
 		return !isStatic(clazz) && clazz.isMemberClass();
 	}
 
+	/**
+	 * {@return whether the supplied {@code object} is an instance of a record class}
+	 * @since 1.12
+	 */
+	@API(status = INTERNAL, since = "1.12")
+	public static boolean isRecordObject(Object object) {
+		return object != null && isRecordClass(object.getClass());
+	}
+
+	/**
+	 * {@return whether the supplied {@code clazz} is a record class}
+	 * @since 1.12
+	 */
+	@API(status = INTERNAL, since = "1.12")
+	public static boolean isRecordClass(Class<?> clazz) {
+		Class<?> superclass = clazz.getSuperclass();
+		return superclass != null && "java.lang.Record".equals(superclass.getName());
+	}
+
 	/**
 	 * Determine if the return type of the supplied method is primitive {@code void}.
 	 *

jupiter-tests/src/test/java/org/junit/jupiter/engine/extension/TempDirectoryPerDeclarationTests.java

@@ -164,6 +164,12 @@ void resolvesSeparateTempDirsForEachAnnotationDeclaration(TestInstance.Lifecycle
 		assertThat(testATempDirs).doesNotContainEntry("afterEach2", testBTempDirs.get("afterEach2"));
 	}
 
+	@Test
+	void supportsConstructorInjectionOnRecords() {
+		executeTestsForClass(TempDirRecordTestCase.class).testEvents()//
+				.assertStatistics(stats -> stats.started(1).succeeded(1));
+	}
+
 	@Test
 	@DisplayName("does not prevent constructor parameter resolution")
 	void tempDirectoryDoesNotPreventConstructorParameterResolution() {
@@ -1527,4 +1533,12 @@ void test(@SuppressWarnings("unused") @TempDir Path tempDir) {
 
 	}
 
+	@SuppressWarnings("JUnitMalformedDeclaration")
+	record TempDirRecordTestCase(@TempDir Path tempDir) {
+		@Test
+		void shouldExists() {
+			assertTrue(Files.exists(tempDir));
+		}
+	}
+
 }

platform-tests/src/test/java/org/junit/platform/commons/util/ReflectionUtilsTests.java

@@ -285,6 +285,23 @@ void getInterfaceMethodIfPossible() throws Exception {
 			assertThat(interfaceMethod.getDeclaringClass()).isEqualTo(Closeable.class);
 		}
 
+		@Test
+		void isRecordObject() {
+			assertTrue(ReflectionUtils.isRecordObject(new SomeRecord(1)));
+			assertFalse(ReflectionUtils.isRecordObject(new ClassWithOneCustomConstructor("")));
+			assertFalse(ReflectionUtils.isRecordObject(null));
+		}
+
+		@Test
+		void isRecordClass() {
+			assertTrue(ReflectionUtils.isRecordClass(SomeRecord.class));
+			assertFalse(ReflectionUtils.isRecordClass(ClassWithOneCustomConstructor.class));
+			assertFalse(ReflectionUtils.isRecordClass(Object.class));
+		}
+
+		record SomeRecord(int n) {
+		}
+
 		static class ClassWithVoidAndNonVoidMethods {
 
 			void voidMethod() {