If for some reason we're missing java.lang.Object mapping during import, fail eagerly

[ktoso]

Due to dependencies behaving weirdly in plugins the JavaKit dependency was not pulled unless more things were spelled out explicitly...

This resulted in a generated file like:

@JavaClass("org.apache.commons.io.FilenameUtils")
open class FilenameUtils {
  @JavaMethod
  @_nonoverride public convenience init(environment: JNIEnvironment? = nil)
}

which will fail to compile because we need the:

@JavaClass("org.apache.commons.io.FilenameUtils")
open class FilenameUtils: JavaObject {
  @JavaMethod
  @_nonoverride public convenience init(environment: JNIEnvironment? = nil)
}

form.

If we're ever generating code and we're missing JavaObject we should just immediately crash rather than hide the error futher along the build as it can be hard to diagnose what actually went wrong -- but it was a missing dependency on the swift-java file that declared java.lang.object.

[madsodgaard]

When does this exactly happen? The user tries to generate wrappers for Java classes that has no superclasses (other than JavaObject) and has not specified a dependency on JavaKit (which defines JavaObject). Is that a SwiftPM dependency missing or a missing dependency in the --depends-on flag?