[MINVOKER-182] Different groovy versions on test classpath can cause ClassCastException

**[Andrew Schurman](https://issues.apache.org/jira/secure/ViewProfile.jspa?name=aschurman)** opened **[MINVOKER-182](https://issues.apache.org/jira/browse/MINVOKER-182?redirect=false)** and commented

When `addTestClassPath` is set and you have a different version of groovy than invoker on your classpath, you will run into `ClassCastException` when
pre-/post- build hooks are run for tests. This occurs due to invoker creating groovy scripts in its version of groovy, but using a different version of groovy as the runtime (since test classpath elements are loaded first when `addTestClassPath=true`).

In my specific case, I had a transitive dependency on groovy 1.7, but invoker uses groovy 2.0. Being transitive does make it harder to spot, but
more importantly you may not have access to the dependency that depends on groovy. This could make swapping groovy versions impossible depending on the gap between versions.

Stack trace:

```
groovy.lang.GroovyRuntimeException: Failed to create Script instance for class: class Script1. Reason: java.lang.ClassCastException: Script1 cannot be
cast to groovy.lang.GroovyObject
at org.codehaus.groovy.runtime.InvokerHelper.createScript(InvokerHelper.java:443)
at groovy.lang.GroovyShell.parse(GroovyShell.java:625)
at groovy.lang.GroovyShell.evaluate(GroovyShell.java:516)
at groovy.lang.GroovyShell.evaluate(GroovyShell.java:556)
at groovy.lang.GroovyShell.evaluate(GroovyShell.java:527)
at org.apache.maven.shared.scriptinterpreter.GroovyScriptInterpreter.evaluateScript(GroovyScriptInterpreter.java:83)
at org.apache.maven.shared.scriptinterpreter.ScriptRunner.executeRun(ScriptRunner.java:249)
at org.apache.maven.shared.scriptinterpreter.ScriptRunner.run(ScriptRunner.java:177)
at org.apache.maven.plugin.invoker.AbstractInvokerMojo.runBuild(AbstractInvokerMojo.java:1692)
at org.apache.maven.plugin.invoker.AbstractInvokerMojo.runBuild(AbstractInvokerMojo.java:1360)
at org.apache.maven.plugin.invoker.AbstractInvokerMojo.runBuilds(AbstractInvokerMojo.java:1210)
at org.apache.maven.plugin.invoker.AbstractInvokerMojo.execute(AbstractInvokerMojo.java:723)
at org.apache.maven.plugin.DefaultBuildPluginManager.executeMojo(DefaultBuildPluginManager.java:101)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:209)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:153)
at org.apache.maven.lifecycle.internal.MojoExecutor.execute(MojoExecutor.java:145)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:84)
at org.apache.maven.lifecycle.internal.LifecycleModuleBuilder.buildProject(LifecycleModuleBuilder.java:59)
at org.apache.maven.lifecycle.internal.LifecycleStarter.singleThreadedBuild(LifecycleStarter.java:183)
at org.apache.maven.lifecycle.internal.LifecycleStarter.execute(LifecycleStarter.java:161)
at org.apache.maven.DefaultMaven.doExecute(DefaultMaven.java:320)
at org.apache.maven.DefaultMaven.execute(DefaultMaven.java:156)
at org.apache.maven.cli.MavenCli.execute(MavenCli.java:537)
at org.apache.maven.cli.MavenCli.doMain(MavenCli.java:196)
at org.apache.maven.cli.MavenCli.main(MavenCli.java:141)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:606)
at org.codehaus.plexus.classworlds.launcher.Launcher.launchEnhanced(Launcher.java:289)
at org.codehaus.plexus.classworlds.launcher.Launcher.launch(Launcher.java:229)
at org.codehaus.plexus.classworlds.launcher.Launcher.mainWithExitCode(Launcher.java:415)
at org.codehaus.plexus.classworlds.launcher.Launcher.main(Launcher.java:356)
Caused by: java.lang.ClassCastException: Script1 cannot be cast to groovy.lang.GroovyObject
at org.codehaus.groovy.runtime.InvokerHelper.createScript(InvokerHelper.java:421)
... 32 more
```

---

**Affects:** 1.8

**Issue Links:**
- [MINVOKER-274](https://issues.apache.org/jira/browse/MINVOKER-274) Use Groovy 3.x to prevent Java9+ warnings about Groovy 2.x using illegal reflection

1 votes, 7 watchers

Start with AbstractInvokerMojo.runBuild and the GroovyScriptInterpreter stack frames, then examine how addTestClassPath changes class loading for pre- and post-build hooks. Reproduce with a transitive Groovy version differing from the invoker's version; done means those hooks no longer fail with the reported ClassCastException.

Written by the indexing model from the issue text.