in case of @compile/module=<module>, jtreg prepends module name to source path location, so it's impossible to share source files b/w tests if they are in different directories.

one example -- https://bugs.openjdk.java.net/browse/JDK-8143238
in hotspot/test/compiler/jvmci, we have several tests which use hotspot/test/compiler/jvmci/common/CompilerToVMHelper.java. CompilerToVMHelper.java contains source code of jdk.vm.ci.hotspot.CompilerToVMHelper class, jdk.vm.ci module contains jdk.vm.ci.hotspot package.

the tests which use CompilerToVMHelper class are located in compiler/jvmci/compilerToVM/, compiler/jvmci/events/ and compiler/jvmci/ directories. Currently these test just compile java file using a relative path (@compile ../common/CompilerToVMHelper.java) and jdk.vm.ci.hotspot.CompilerToVMHelper classfile to BCP (using ClassFileInstaller and -Xbcp/a:.).

in jake, adding CompilerToVMHelper to BCP won't help, so we should use '@compile/module=jdk.vm.ci' instead, that forces us to move CompilerToVMHelper.java to jdk.vm.ci/jdk/vm/ci/hotspot/CompilerToVMHelper.java, but since jtreg search for modules directory in current directory and we have 3 different directories w/ tests which use CompilerToVMHelper, we have to have 3 copies of CompilerToVMHelper, which is not a very nice solution.

so I think it would be good if it'll be possible to have relative path in '@compile' actions even in case of '@compile/module'.