Message11950

test_gc_jy produces warnings in Java 9

WARNING: Illegal reflective access by org.python.modules.gc (file:.../jython-dev.jar) to field java.util.ArrayList.elementData

A cut-down version of the test only running GCTests_Jy_TraverseByReflection is a good basis for debugging. Launching the test as:
dist\bin\jython -J--illegal-access=debug -m test.regrtest -v test_gc_jy
will show where the illegal access happens, at the call to setAccessible in org.python.modules.gc.traverseByReflectionIntern.

I'm peeling this off from #2656 in order to park it. I don't consider this a blocker for 2.7.2, but it is a long-term Java roadmap issue. Before the available JVMs prohibit access to private fields (at the moment they just produce an ugly message), our implementation of gc will need a re-think. The ugly message is not encountered unless the optional gc module is invoked, which must mean the user is prepared for a tussle with JVM internals.