Undo parent for MultipleParentsClassLoader (#2312)

66998ea inadvertently undid a change from 9bc9be6, which breaks behavior under some classloaders that special case mockito classes. Use of an explicit parent with `MultipleParentsClassLoader` appears to be discouraged in the documentation also.

Co-authored-by: Charles Munger <clm@google.com>
Co-authored-by: Tim van der Lippe <tvanderlippe@google.com>

src/main/java/org/mockito/internal/creation/bytebuddy/SubclassBytecodeGenerator.java

@@ -136,7 +136,7 @@ public <T> Class<? extends T> mockClass(MockFeatures<T> features) {
         if (shouldIncludeContextLoader) {
             loaderBuilder = loaderBuilder.appendMostSpecific(contextLoader);
         }
-        ClassLoader classLoader = loaderBuilder.build(MockMethodInterceptor.class.getClassLoader());
+        ClassLoader classLoader = loaderBuilder.build();
 
         // If Mockito does not need to create a new class loader and if a mock is not based on a JDK
         // type, we attempt

src/test/java/org/mockitousage/bugs/creation/PackagePrivateWithContextClassLoaderTest.java

@@ -9,6 +9,11 @@
 import static org.mockito.Mockito.when;
 import static org.mockito.Mockito.withSettings;
 
+import java.io.ByteArrayOutputStream;
+import java.io.File;
+import java.io.IOException;
+import java.io.InputStream;
+import java.lang.reflect.Method;
 import org.junit.After;
 import org.junit.Before;
 import org.junit.Test;
@@ -18,11 +23,12 @@ public class PackagePrivateWithContextClassLoaderTest {
 
     private ClassLoader oldContextClassloader;
 
-    public static class PublicClass {
-
+    public abstract static class PublicClass {
         int packagePrivateMethod() {
             return 0;
         }
+
+        abstract void packagePrivateAbstractMethod();
     }
 
     public interface PublicInterface {}
@@ -67,4 +73,102 @@ public void should_be_able_to_mock_package_private_extra_interface() throws Exce
                                 PublicInterface.class,
                                 withSettings().extraInterfaces(PackagePrivateInterface.class));
     }
+
+    /**
+     * In this test we have a class that delegates loading of mockito/JDK classes to its parent,
+     * but defines in its own for others. If mockito selects the defining classloader of the mock
+     * to the classloader of mockito, calling the abstract package-private method will fail - the
+     * defining classloader of the mocked type's package is different from the generated mock class
+     * package. Because the nonDelegatingLoader is a child of mockito's loader, it's more specific
+     * and should be preferred.
+     */
+    @Test
+    public void classloader_with_parent_but_does_not_delegate() throws Exception {
+        ClassLoader nonDelegatingLoader = new NotAlwaysDelegatingClassLoader();
+        Thread.currentThread().setContextClassLoader(nonDelegatingLoader);
+        Class<?> loaded =
+                Class.forName(LoadedByCustomLoader.class.getName(), false, nonDelegatingLoader);
+        Method attemptMock = loaded.getDeclaredMethod("attemptMock");
+        attemptMock.invoke(null);
+    }
+
+    public static class LoadedByCustomLoader {
+        public static void attemptMock() {
+            PublicClass mock = mock(PublicClass.class);
+            mock.packagePrivateAbstractMethod();
+        }
+    }
+
+    /**
+     * This classloader has a parent, but doesn't always delegate to it.
+     */
+    public static final class NotAlwaysDelegatingClassLoader extends ClassLoader {
+
+        /**
+         * Initial size of buffer used to read class data.
+         */
+        /*  Note: should be enough for most classes, and is not a hard limit. */
+        private static final int BUF_SIZE = 4096;
+
+        public NotAlwaysDelegatingClassLoader() {
+            super(NotAlwaysDelegatingClassLoader.class.getClassLoader());
+        }
+
+        @Override
+        protected Class<?> loadClass(String name, boolean resolve) throws ClassNotFoundException {
+            // First, check if the class has already been loaded. If not, load it
+            // ourselves or delegate to the parent.
+            Class<?> result = findLoadedClass(name);
+            if (result == null) {
+                // All classes defined in this testsuite should be loaded by this classloader,
+                // but any other class (e.g. those coming from java.* or org.mockito.* packages)
+                // will be loaded by the parent.
+                if (name.startsWith("org.mockitousage.")) {
+                    result = findClass(name);
+                } else {
+                    return super.loadClass(name, resolve);
+                }
+            }
+            if (resolve) {
+                resolveClass(result);
+            }
+            return result;
+        }
+
+        @Override
+        public Class<?> findClass(String className) throws ClassNotFoundException {
+            try {
+                // Create a package for this class, unless it's in the default package.
+                int dotpos = className.lastIndexOf('.');
+                if (dotpos != -1) {
+                    String pkgname = className.substring(0, dotpos);
+                    if (getPackage(pkgname) == null) {
+                        definePackage(pkgname, null, null, null, null, null, null, null);
+                    }
+                }
+                String resourceName = className.replace('.', File.separatorChar) + ".class";
+                InputStream input = getSystemResourceAsStream(resourceName);
+                if (input == null) {
+                    throw new ClassNotFoundException("Couldn't find resource " + resourceName);
+                }
+                byte[] classData = loadClassData(input);
+                return defineClass(className, classData, 0, classData.length, null);
+            } catch (IOException e) {
+                throw new ClassNotFoundException("Cannot load " + className, e);
+            }
+        }
+
+        /**
+         * Load class data from a given input stream.
+         */
+        private byte[] loadClassData(InputStream input) throws IOException {
+            ByteArrayOutputStream output = new ByteArrayOutputStream(BUF_SIZE);
+            byte[] buffer = new byte[BUF_SIZE];
+            int readCount;
+            while ((readCount = input.read(buffer, 0, BUF_SIZE)) >= 0) {
+                output.write(buffer, 0, readCount);
+            }
+            return output.toByteArray();
+        }
+    }
 }