jbang --java 17 when default is java 11 build integration fails

[maxandersen]

Describe the bug
Have java 11 in system path.
Run jbang --java 17 https://gist.github.com/rivasdiaz/f2e9efd1bf2079f0101f865846af2502 and you get error about

Caused by: io.quarkus.builder.BuildException: Build failure: Build failed due to errors
        [error]: Build step io.quarkus.arc.deployment.ConfigBuildStep#generateConfigClasses threw an exception: java.lang.UnsupportedClassVersionError: MavenStatsConfig has been compiled by a more recent version of the Java Runtime (class file version 61.0), this version of the Java Runtime only recognizes class file versions up to 55.0
        at java.base/java.lang.ClassLoader.defineClass1(Native Method)
        at java.base/java.lang.ClassLoader.defineClass(ClassLoader.java:1017)
        at io.quarkus.bootstrap.classloading.QuarkusClassLoader.loadClass(QuarkusClassLoader.java:445)
        at io.quarkus.bootstrap.classloading.QuarkusClassLoader.loadClass(QuarkusClassLoader.java:405)
        at io.quarkus.deployment.configuration.ConfigMappingUtils.toClass(ConfigMappingUtils.java:93)
        at io.quarkus.deployment.configuration.ConfigMappingUtils.generateConfigClasses(ConfigMappingUtils.java:51)

as if it compiles with java 17 but then falls back to running quarkus build integration with java 11...

solution would be to run that integration externally when jbang is running with lower version.

or at least help with info to user on what is happening.

[quintesse]

Well, that's logical, the user might specify --java 17 but that doesn't mean that JBang itself runs with that version. JBang can't know what version you specified until it parsed those options and by then it's too late :-)
You can use JBANG_DEFAULT_JAVA_VERSION=17 jbang .... but that's of course not very user-friendly.
It's one of the reasons we really need to make that integration stuff run externally (as you mention).
Until then we might be able to give a better message indeed.

[maxandersen]

Yeah it's logical; but I tell you that even though i wrote the damn thing it took me about 15 tries of trying out tons of stuff before it clicked :)

[nandorholozsnyak]

I've just bumped into the same problem, Java 8 set as default version to run JBang, Java 11 set in the script and during the build error happens, just with different versions.
Any progress or idea on it?

[maxandersen]

no progress on it yet, but we know the solution.

1. for now detect the java version mismatch and inform/warn the user
2. change integration to run in external process when java versions doesn't match

[quintesse]

See #1290 :-)