Handle Class.getPackage() returning null for default package on Java 8

Fixes #4076.

junit-platform-commons/junit-platform-commons.gradle.kts

@@ -29,6 +29,7 @@ tasks.jar {
 
 tasks.codeCoverageClassesJar {
 	exclude("org/junit/platform/commons/util/ModuleUtils.class")
+	exclude("org/junit/platform/commons/util/PackageNameUtils.class")
 }
 
 eclipse {

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

@@ -0,0 +1,38 @@
+/*
+ * Copyright 2015-2024 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+
+package org.junit.platform.commons.util;
+
+import static org.junit.platform.commons.util.PackageUtils.DEFAULT_PACKAGE_NAME;
+
+/**
+ * Collection of utilities for working with package names.
+ *
+ * <h2>DISCLAIMER</h2>
+ *
+ * <p>These utilities are intended solely for usage within the JUnit framework
+ * itself. <strong>Any usage by external parties is not supported.</strong>
+ * Use at your own risk!
+ *
+ * @since 1.11.3
+ */
+class PackageNameUtils {
+
+	static String getPackageName(Class<?> clazz) {
+		Package p = clazz.getPackage();
+		if (p != null) {
+			return p.getName();
+		}
+		String className = clazz.getName();
+		int index = className.lastIndexOf('.');
+		return index == -1 ? DEFAULT_PACKAGE_NAME : className.substring(0, index);
+	}
+
+}

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

@@ -1903,7 +1903,8 @@ private static boolean isPackagePrivate(Member member) {
 	}
 
 	private static boolean declaredInSamePackage(Method m1, Method m2) {
-		return m1.getDeclaringClass().getPackage().getName().equals(m2.getDeclaringClass().getPackage().getName());
+		return PackageNameUtils.getPackageName(m1.getDeclaringClass()).equals(
+			PackageNameUtils.getPackageName(m2.getDeclaringClass()));
 	}
 
 	/**

junit-platform-commons/src/main/java9/org/junit/platform/commons/util/PackageNameUtils.java

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2015-2024 the original author or authors.
+ *
+ * All rights reserved. This program and the accompanying materials are
+ * made available under the terms of the Eclipse Public License v2.0 which
+ * accompanies this distribution and is available at
+ *
+ * https://www.eclipse.org/legal/epl-v20.html
+ */
+
+package org.junit.platform.commons.util;
+
+/**
+ * Collection of utilities for working with package names.
+ *
+ * <h2>DISCLAIMER</h2>
+ *
+ * <p>These utilities are intended solely for usage within the JUnit framework
+ * itself. <strong>Any usage by external parties is not supported.</strong>
+ * Use at your own risk!
+ *
+ * @since 1.11.3
+ */
+class PackageNameUtils {
+
+	static String getPackageName(Class<?> clazz) {
+		return clazz.getPackageName();
+	}
+
+}