Illustrate Scala Issues with Dependencies

[promiseofcake]

When using java_proto_library targets from https://github.com/pubref/rules_protobuf @ v.0.7.1

In our java_binary target we need only to provide the path to the //proto:c dependency for compilation / runtime with --strict_java_deps=ERROR enabled.

For a scala_binary, I would expect to only need to do the same, but it seems the output of our //proto:c is providing jars in a way that java_library will pick them up as exports but scala_ will not.

Situation is the same as: promiseofcake/bazel-scala-test#2, (Issue: bazelbuild/rules_scala#235) except in this case we don't have control over the target to be able to export all the necessary dependencies.

[promiseofcake]

Example error:

$ bazel build --strict_java_deps=ERROR //src/main/scala/com/promiseofcake/sample:sample 
INFO: Analysed target //src/main/scala/com/promiseofcake/sample:sample.
INFO: Found 1 target...
ERROR: /Users/lucas/Workspace/repos/promiseofcake/pubref-java-proto-deps/src/main/scala/com/promiseofcake/sample/BUILD:3:1: scala //src/main/scala/com/promiseofcake/sample:sample failed (Exit 1): scalac failed: error executing command 
  (cd /private/var/tmp/_bazel_lucas/bc5a6721c7ab98ca01a2928cb6103bf1/execroot/__main__ && \
  exec env - \
  bazel-out/host/bin/external/io_bazel_rules_scala/src/java/io/bazel/rulesscala/scalac/scalac @bazel-out/darwin_x86_64-fastbuild/bin/src/main/scala/com/promiseofcake/sample/sample_worker_input)
error: Target 'Unknown label of file bazel-out/darwin_x86_64-fastbuild/bin/proto/libb-hjar.jar which came from //proto:c' is used but isn't explicitly declared, please add it to the deps.
You can use the following buildozer command:
buildozer 'add deps Unknown label of file bazel-out/darwin_x86_64-fastbuild/bin/proto/libb-hjar.jar which came from //proto:c' //src/main/scala/com/promiseofcake/sample:sample
error: Target 'Unknown label of file bazel-out/darwin_x86_64-fastbuild/genfiles/proto/_ijar/a_compile_imports/external/com_google_protobuf_protobuf_java/jar/protobuf-java-3.1.0-ijar.jar which came from //proto:c' is used but isn't explicitly declared, please add it to the deps.
You can use the following buildozer command:
buildozer 'add deps Unknown label of file bazel-out/darwin_x86_64-fastbuild/genfiles/proto/_ijar/a_compile_imports/external/com_google_protobuf_protobuf_java/jar/protobuf-java-3.1.0-ijar.jar which came from //proto:c' //src/main/scala/com/promiseofcake/sample:sample
error: Target 'Unknown label of file bazel-out/darwin_x86_64-fastbuild/bin/proto/liba-hjar.jar which came from //proto:c' is used but isn't explicitly declared, please add it to the deps.
You can use the following buildozer command:
buildozer 'add deps Unknown label of file bazel-out/darwin_x86_64-fastbuild/bin/proto/liba-hjar.jar which came from //proto:c' //src/main/scala/com/promiseofcake/sample:sample
three errors found
three errors found
java.lang.RuntimeException: Build failed
        at io.bazel.rulesscala.scalac.ScalacProcessor.compileScalaSources(ScalacProcessor.java:256)
        at io.bazel.rulesscala.scalac.ScalacProcessor.processRequest(ScalacProcessor.java:68)
        at io.bazel.rulesscala.worker.GenericWorker.run(GenericWorker.java:125)
        at io.bazel.rulesscala.scalac.ScalaCInvoker.main(ScalaCInvoker.java:41)
Target //src/main/scala/com/promiseofcake/sample:sample failed to build
INFO: Elapsed time: 3.344s, Critical Path: 3.17s
FAILED: Build did NOT complete successfully