IllegalAccessException when mocking package-private Spring controller

Issue description

Hello, I'm trying to mock a Spring controller using the new @SpringBean annotation and then call the mapped method using TestRestTemplate (also tried MockMvc with same results). This works only if the controller java class is public, but the test fails with IllegalAccessException if I change the access to package-private.

Bellow is a minimal Spring Boot project (I can provide a repo with an easy-to-run version if needed). I also tried using different tool versions, such as JDK 11, Spring Boot 2.0, Groovy 2.4 or adding a cglib dependency instead of relying on the default Byte Buddy with no difference.

How to reproduce

main/java:

@SpringBootApplication
public class Application {
    public static void main(String[] args) {
        SpringApplication.run(Application.class, args);
    }
}

@RestController
/* public */ class HelloController { // works with public, fails without
    @GetMapping("/hello")
    public String hello() {
        return "hello";
    }
}

test/groovy

@SpringBootTest(webEnvironment = RANDOM_PORT)
class HelloControllerTest extends Specification {

    @SpringBean
    HelloController controller = Mock()

    @Autowired
    TestRestTemplate rest

    def "should mock it"() {
        given:
        controller.hello() >> "goodbye"

        expect:
        rest.getForObject("/hello", String) == "goodbye"
    }
}

Resulting exception:

java.lang.IllegalAccessException: Class org.spockframework.spring.mock.DelegatingInterceptor can not access a member of class mock.HelloController with modifiers "public"
	at sun.reflect.Reflection.ensureMemberAccess(Reflection.java:102) ~[na:1.8.0_144]
	at java.lang.reflect.AccessibleObject.slowCheckMemberAccess(AccessibleObject.java:296) ~[na:1.8.0_144]
	at java.lang.reflect.AccessibleObject.checkAccess(AccessibleObject.java:288) ~[na:1.8.0_144]
	at java.lang.reflect.Method.invoke(Method.java:491) ~[na:1.8.0_144]
	at org.spockframework.spring.mock.DelegatingInterceptor.intercept(DelegatingInterceptor.java:53) ~[spock-spring-1.2-groovy-2.5.jar:1.2]
	at org.spockframework.mock.runtime.ByteBuddyInterceptorAdapter.interceptNonAbstract(ByteBuddyInterceptorAdapter.java:35) ~[spock-core-1.2-groovy-2.5.jar:1.2]
	at mock.HelloController$SpockMock$280894713.hello(Unknown Source) ~[na:na]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_144]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_144]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_144]
	at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_144]
	at org.springframework.web.method.support.InvocableHandlerMethod.doInvoke(InvocableHandlerMethod.java:215) ~[spring-web-5.1.2.RELEASE.jar:5.1.2.RELEASE]
	at org.springframework.web.method.support.InvocableHandlerMethod.invokeForRequest(InvocableHandlerMethod.java:142) ~[spring-web-5.1.2.RELEASE.jar:5.1.2.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:102) ~[spring-webmvc-5.1.2.RELEASE.jar:5.1.2.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:895) ~[spring-webmvc-5.1.2.RELEASE.jar:5.1.2.RELEASE]
	at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:800) ~[spring-webmvc-5.1.2.RELEASE.jar:5.1.2.RELEASE]
	at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:87) ~[spring-webmvc-5.1.2.RELEASE.jar:5.1.2.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:1038) ~[spring-webmvc-5.1.2.RELEASE.jar:5.1.2.RELEASE]
	at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:942) ~[spring-webmvc-5.1.2.RELEASE.jar:5.1.2.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:998) ~[spring-webmvc-5.1.2.RELEASE.jar:5.1.2.RELEASE]
	at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:890) ~[spring-webmvc-5.1.2.RELEASE.jar:5.1.2.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:634) ~[tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.springframework.web.servlet.FrameworkServlet.service(FrameworkServlet.java:875) ~[spring-webmvc-5.1.2.RELEASE.jar:5.1.2.RELEASE]
	at javax.servlet.http.HttpServlet.service(HttpServlet.java:741) ~[tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:231) ~[tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:53) ~[tomcat-embed-websocket-9.0.12.jar:9.0.12]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.springframework.web.filter.RequestContextFilter.doFilterInternal(RequestContextFilter.java:99) ~[spring-web-5.1.2.RELEASE.jar:5.1.2.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.2.RELEASE.jar:5.1.2.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.springframework.web.filter.FormContentFilter.doFilterInternal(FormContentFilter.java:92) ~[spring-web-5.1.2.RELEASE.jar:5.1.2.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.2.RELEASE.jar:5.1.2.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.springframework.web.filter.HiddenHttpMethodFilter.doFilterInternal(HiddenHttpMethodFilter.java:93) ~[spring-web-5.1.2.RELEASE.jar:5.1.2.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.2.RELEASE.jar:5.1.2.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.springframework.web.filter.CharacterEncodingFilter.doFilterInternal(CharacterEncodingFilter.java:200) ~[spring-web-5.1.2.RELEASE.jar:5.1.2.RELEASE]
	at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:107) ~[spring-web-5.1.2.RELEASE.jar:5.1.2.RELEASE]
	at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:193) ~[tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:166) ~[tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:199) ~[tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96) [tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:490) [tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:139) [tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:92) [tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:74) [tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:343) [tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:408) [tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66) [tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:770) [tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1415) [tomcat-embed-core-9.0.12.jar:9.0.12]
	at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49) [tomcat-embed-core-9.0.12.jar:9.0.12]
	at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1149) [na:1.8.0_144]
	at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:624) [na:1.8.0_144]
	at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61) [tomcat-embed-core-9.0.12.jar:9.0.12]
	at java.lang.Thread.run(Thread.java:748) [na:1.8.0_144]

Additional Environment information

Java/JDK

jdk1.8.0_144

Build tool version

Gradle

4.10.2

Build-tool dependencies used

Gradle

plugins {
    id 'java'
    id 'groovy'
    id 'org.springframework.boot' version '2.1.0.RELEASE'
    id 'io.spring.dependency-management' version '1.0.6.RELEASE'
}

repositories {
    mavenCentral()
}

dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-web'
    testImplementation 'org.springframework.boot:spring-boot-starter-test'
    testImplementation 'org.spockframework:spock-spring:1.2-groovy-2.5'
}

Start at org.spockframework.spring.mock.DelegatingInterceptor.intercept, referenced at line 53 in the stack trace, and reproduce the package-private HelloController case with @SpringBean and TestRestTemplate. Compare it with the public-controller case; done means the mapped call succeeds without making HelloController public and the regression is covered by a test.