Inconsistent behavior for generated resource files

[azymnis]

Problem

Scala rules have issues with generated files that are part of resources. The problem is that we are using the file.path attribute to map the destination path for these files, instead of file.short_path.

How to reproduce

Suppose that we add the following rule to test/src/main/resources/scala/test/BUILD:

genrule(
    name = "generated-hello",
    outs = ["generated-hello.txt"],
    cmd = "echo 'hello' > $@",
    visibility = ["//visibility:public"],
)

and then we modify test/BUILD to be have this:

scala_library(
    name = "ResourcesStripScalaLib",
    srcs = ["src/main/scala/scala/test/ResourcesStripScalaLib.scala"],
    resources = [
        "//test/data:more.txt",
        "//test/data:foo.txt",
        "//test/src/main/resources/scala/test:more-hellos",
        "//test/src/main/resources/scala/test:more-byes",
        "//test/src/main/resources/scala/test:generated-hello",
        ],
    resource_strip_prefix = "test/",
)

Then running this bazel build test:ResourcesStripScalaLib will generate the following error:

java.lang.RuntimeException: Resource File bazel-out/local-fastbuild/genfiles/test/src/main/resources/scala/test/generated-hello.txt is not under the specified strip prefix test/
	at io.bazel.rulesscala.scalac.ScalacProcessor.getResourcePath(ScalacProcessor.java:313)
	at io.bazel.rulesscala.scalac.ScalacProcessor.copyResources(ScalacProcessor.java:295)
	at io.bazel.rulesscala.scalac.ScalacProcessor.processRequest(ScalacProcessor.java:74)
	at io.bazel.rulesscala.worker.GenericWorker.runPersistentWorker(GenericWorker.java:52)
	at io.bazel.rulesscala.worker.GenericWorker.run(GenericWorker.java:121)
	at io.bazel.rulesscala.scalac.ScalaCInvoker.main(ScalaCInvoker.java:41)
Target //test:ResourcesStripScalaLib failed to build

@johnynek @ittaiz I've got a PR baking that can fix this, will send shortly