javac unzips class files from jars on class path into output directory

[Doug Simon]

To be able to develop Graal on JDK 9, we're using the `--release 8` javac option and providing jar files for API that is either not in 9 or is not exported in 9. Here is a simplified form of a javac command:

javac -cp jdk.internal.vm.ci.jar:jdk.unsupported_sun.misc.Unsafe.jar -d bin/ --release 8 graal/org.graalvm.compiler.api.runtime/src/org/graalvm/compiler/api/runtime/*.java

where:

dsimon at kurz-3 ~/h/graal-core> ls graal/org.graalvm.compiler.api.runtime/src/org/graalvm/compiler/api/runtime/*.java
graal/org.graalvm.compiler.api.runtime/src/org/graalvm/compiler/api/runtime/GraalJVMCICompiler.java
graal/org.graalvm.compiler.api.runtime/src/org/graalvm/compiler/api/runtime/GraalRuntime.java

I expect 2 class files to be written to bin/. However, I see a number of files from jdk.internal.vm.ci.jar in bin:

dsimon at kurz-3 ~/h/graal-core> jar tf jdk.internal.vm.ci.jar | wc -l
     444
dsimon at kurz-3 ~/h/graal-core> find bin/jdk/vm/ci | wc -l
      55

I'm guessing that these are the classes in jdk.internal.vm.ci.jar referenced (transitively?) from the Graal sources.

Why is this happening? That is, why is javac extracting classes from a jar on the classpath and putting them in the output directory?

-Doug