Fail build if GraalVM reachability metadata repository is enabled, but no repository has been configured.

[amizurov]

Is your feature request related to a problem? Please describe.
Hi, folks we are happy with using GraalVM native-image feature for our microservices, but we faced with some inconvenient behaviour with graalvm-reachability data. The main problem here is that our builds can run under a proxy which required an installed CA certificate. If someone forgets about this, the build will be green and everything will look fine, only this error will be in the log:

[ERROR] Failed to download from https://github.com/oracle/graalvm-reachability-metadata/releases/download/0.3.1/graalvm-reachability-metadata-0.3.1.zip: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target
[WARNING] GraalVM reachability metadata repository is enabled, but no repository has been configured

But when you run a program or an integration test, you will find that some classes are not available due to lack of reachability-metadata, in which case it is not easy to find the root cause.

Plugin config snippet:

...
<configuration>
      <classesDirectory>${project.build.outputDirectory}</classesDirectory>
      <metadataRepository>
             <version>0.3.1</version>
             <enabled>true</enabled>
       </metadataRepository>
</configuration>
...

Describe the solution you'd like
It's would be nice if we could to fail the build if reachability metadata repository is enabled but not configured.
Maybe such option is already present but we didn't find it. Thanks.

[dpozinen]

This would be a great addition, because this metadata is a mandatory requirement and is basically akin to a missing dependency. I would go so far as to say this should be the default behavior