`groovy:execute` on Java 11 gives `WARNING: Illegal reflective access`

[bobtiernay-okta]

Using:

$java -version

openjdk version "11.0.4" 2019-07-16 LTS
OpenJDK Runtime Environment Corretto-11.0.4.11.1 (build 11.0.4+11-LTS)
OpenJDK 64-Bit Server VM Corretto-11.0.4.11.1 (build 11.0.4+11-LTS, mixed mode)

executing the following:

$ mvn -N groovy:execute

with:

<plugin>
    <groupId>org.codehaus.gmaven</groupId>
    <artifactId>groovy-maven-plugin</artifactId>
    <version>2.1.1</version>
    <executions>
        <execution>
            <id>default-cli</id>
            <configuration>
                <source>${root.dir}/src/main/groovy/project.groovy</source>
                <scriptpath>
                    <path>${root.dir}/src/main/groovy</path>
                </scriptpath>
            </configuration>
        </execution>
    </executions>
</plugin>

gives:

[INFO] Scanning for projects...
...
[INFO]
[INFO] --- groovy-maven-plugin:2.1.1:execute (default-cli) @ lake ---
WARNING: An illegal reflective access operation has occurred
WARNING: Illegal reflective access by org.codehaus.groovy.reflection.CachedClass (file:/Users/btiernay/.m2/repository/org/codehaus/groovy/groovy-all/2.4.9/groovy-all-2.4.9.jar) to method java.lang.Object.finalize()
WARNING: Please consider reporting this to the maintainers of org.codehaus.groovy.reflection.CachedClass
WARNING: Use --illegal-access=warn to enable warnings of further illegal reflective access operations
WARNING: All illegal access operations will be denied in a future release
...

Which is likely related to https://issues.apache.org/jira/browse/GROOVY-8339.

I'm wondering if there is a way to pass the --illegal-access=warn compiler option to prevent this, perhaps with a new plugin configuration?

[jdillon]

I am not really sure how Java 11 works in this respect, mostly only know that Java 11 breaks a lot of things so I am still mostly using Java 8. But I can probably get some time to take a closer look and maybe look at what a more modern groovy version has in terms of compiler flags.

[jbliznak]

As @bobtiernay-okta identified the root cause is groovy issue so the workaround is to override groovy-all version in plugin declaration with version 3.0.0-beta-1 or newer, following https://github.com/groovy/gmaven/blob/gmaven-2.x/groovy-maven-plugin/src/site/markdown/index.md :

<plugin>
    <groupId>org.codehaus.gmaven</groupId>
    <artifactId>groovy-maven-plugin</artifactId>
    <version>2.1.1</version>
    <executions>
        <execution>
            ...
        </execution>
    </executions>
    <dependencies>
        <dependency>
            <groupId>org.codehaus.groovy</groupId>
            <artifactId>groovy-all</artifactId>
            <version>3.0.0-beta-3</version>
            <type>pom</type>
        </dependency>
    </dependencies>
</plugin>

@jdillon probably just update the version and change type to pom at https://github.com/groovy/gmaven/blob/gmaven-2.x/gmaven-adapter-impl/pom.xml#L58 but as I don't have much insight in groovy I can't tell whether it could break something else or not, however, the warning is gone.