Fix Mock does not intercept package-private methods in OSGi correctly

docs/release_notes.adoc

@@ -16,6 +16,7 @@ include::include.adoc[]
 * Fix argument mismatch descriptions for varargs methods by expanding varargs instead of reporting `<too few arguments>` spockPull:2315[]
 * Fix Pattern flags being dropped when `java.util.regex.Pattern` instances are used in Spock regex conditions spockIssue:2298[]
 * Fix `MockitoMockMaker` throws NPE on null object spockIssue:2337[]
+* Fix Mock does not intercept package-private methods in OSGi correctly spockIssue:2384[]
 
 === Breaking Changes
 

spock-core/src/main/java/org/spockframework/mock/runtime/ByteBuddyMockFactory.java

@@ -29,7 +29,6 @@
 import net.bytebuddy.dynamic.Transformer;
 import net.bytebuddy.dynamic.loading.ClassInjector;
 import net.bytebuddy.dynamic.loading.ClassLoadingStrategy;
-import net.bytebuddy.dynamic.loading.MultipleParentClassLoader;
 import net.bytebuddy.dynamic.scaffold.TypeValidation;
 import net.bytebuddy.implementation.FieldAccessor;
 import net.bytebuddy.implementation.FixedValue;
@@ -96,19 +95,36 @@ class ByteBuddyMockFactory {
    * A mock is considered local, if all additional interfaces of the mock (including {@link ISpockMockObject}) are
    * loadable by the target class' classloader.
    *
-   * @param targetClass The to-be-mocked class
+   * @param targetClass          The to-be-mocked class
    * @param additionalInterfaces Additional interfaces of the to-be-mocked type
    * @return true, if this is a local mock. Otherwise false
    */
   @VisibleForTesting
   static boolean isLocalMock(Class<?> targetClass, Collection<Class<?>> additionalInterfaces) {
-    // Inspired by https://github.com/mockito/mockito/blob/99426415c0ceb30e55216c3934854528c83f410e/mockito-core/src/main/java/org/mockito/internal/creation/bytebuddy/SubclassBytecodeGenerator.java#L165-L166
-    ClassLoader cl = new MultipleParentClassLoader.Builder()
-      .appendMostSpecific(targetClass)
-      .appendMostSpecific(additionalInterfaces)
-      .appendMostSpecific(ISpockMockObject.class)
-      .build();
-    return cl == targetClass.getClassLoader();
+    ClassLoader targetLoader = targetClass.getClassLoader();
+    if (targetLoader == null) {
+      targetLoader = ClassLoader.getSystemClassLoader();
+    }
+    Class<?> spockMockClass = loadClassIfAvailableInClassLoader(targetLoader, ISpockMockObject.class);
+    if (spockMockClass != ISpockMockObject.class) {
+      //The ISpockMockObject is not visible to the targetLoader, so we can't be local.
+      return false;
+    }
+    for (Class<?> ifClass : additionalInterfaces) {
+      Class<?> ifClassOfTarget = loadClassIfAvailableInClassLoader(targetLoader, ifClass);
+      if (ifClassOfTarget != ifClass) {
+        return false;
+      }
+    }
+    return true;
+  }
+
+  private static Class<?> loadClassIfAvailableInClassLoader(ClassLoader loader, Class<?> clazz) {
+    try {
+      return loader.loadClass(clazz.getName());
+    } catch (ClassNotFoundException e) {
+      return null;
+    }
   }
 
   Object createMock(IMockMaker.IMockCreationSettings settings) {

spock-specs/src/test/groovy/org/spockframework/smoke/mock/osgi/OsgiPackagePrivateMemberMockSpec.groovy

@@ -0,0 +1,54 @@
+/*
+ * Copyright 2026 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
+ *      https://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.spockframework.smoke.mock.osgi
+
+
+import spock.lang.Issue
+import spock.lang.Specification
+import spock.util.EmbeddedSpecRunner
+
+class OsgiPackagePrivateMemberMockSpec extends Specification {
+  def runner = new EmbeddedSpecRunner(new OsgiTestClassLoader(this.class.classLoader))
+
+  @SuppressWarnings('UnnecessaryQualifiedReference')
+  @Issue("https://github.com/spockframework/spock/issues/2384")
+  def "OSGi package private mock shall be mockable with ByteBuddy"() {
+    when:
+    def res = runner.runSpecBody("""
+    def mock = Mock(org.spockframework.smoke.mock.osgi.testclasses.PkgPrivateMemberClass, mockMaker: spock.mock.MockMakers.byteBuddy) {
+        packagePrivate() >> "mocked"
+    }
+
+    def "mock is called when invoked from Java code"() {
+        when:
+        def result = new org.spockframework.smoke.mock.osgi.testclasses.InvocationFromJava(mock).invoke()
+
+        then:
+        result == "mocked"
+    }
+
+    def "mock is called when invoked directly from Groovy"() {
+        when:
+        def result = mock.packagePrivate()
+
+        then:
+        result == "mocked"
+    }
+""")
+
+    then:
+    res.testsSucceededCount == 2
+  }
+}

spock-specs/src/test/groovy/org/spockframework/smoke/mock/osgi/OsgiTestClassLoader.groovy

@@ -0,0 +1,63 @@
+/*
+ * Copyright 2026 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
+ *      https://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.spockframework.smoke.mock.osgi
+
+import groovy.transform.CompileStatic
+
+import static java.util.Objects.requireNonNull
+
+/**
+ * Fakes an OSGi like ClassLoader env, by not using the parent ClassLoader semantics.
+ */
+@CompileStatic
+class OsgiTestClassLoader extends ClassLoader {
+  private final ClassLoader hostCl
+
+  OsgiTestClassLoader(ClassLoader hostCl) {
+    super(null)
+    this.hostCl = requireNonNull(hostCl)
+  }
+
+  @Override
+  protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
+    if (!name.startsWith("org.spockframework.smoke.mock.osgi.testclasses")) {
+      return hostCl.loadClass(name)
+    }
+    super.loadClass(name, resolve)
+  }
+
+  @Override
+  protected Class<?> findClass(String name) throws ClassNotFoundException {
+    def clsFilePath = name
+    clsFilePath = clsFilePath.replace(".", "/")
+    clsFilePath += ".class"
+    def is = hostCl.getResourceAsStream(clsFilePath)
+    if (is == null) {
+      throw new ClassNotFoundException(name)
+    }
+    def clsData = is.getBytes()
+    return defineClass(name, clsData, 0, clsData.length)
+  }
+
+  @Override
+  URL getResource(String name) {
+    return hostCl.getResource(name)
+  }
+
+  @Override
+  Enumeration<URL> getResources(String name) throws IOException {
+    return hostCl.getResources(name)
+  }
+}

spock-specs/src/test/groovy/org/spockframework/smoke/mock/osgi/testclasses/InvocationFromJava.java

@@ -0,0 +1,27 @@
+/*
+ * Copyright 2026 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
+ *      https://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.spockframework.smoke.mock.osgi.testclasses;
+
+public class InvocationFromJava {
+  PkgPrivateMemberClass obj;
+
+  public InvocationFromJava(PkgPrivateMemberClass obj) {
+    this.obj = obj;
+  }
+
+  public Object invoke() {
+    return obj.packagePrivate();
+  }
+}

spock-specs/src/test/groovy/org/spockframework/smoke/mock/osgi/testclasses/PkgPrivateMemberClass.java

@@ -0,0 +1,22 @@
+/*
+ * Copyright 2026 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
+ *      https://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.spockframework.smoke.mock.osgi.testclasses;
+
+public class PkgPrivateMemberClass {
+
+  String packagePrivate() {
+    return "original";
+  }
+}