missing mandatory field didn't error on bazel 0.2.3

[johnynek]

in the scala rules we have:

https://github.com/bazelbuild/rules_scala/blob/master/scala/scala.bzl#L410

"main_class": attr.string(mandatory=True),

despite that, on bazel 0.2.3, we don't get an error with a missing main_class attribute (which leads to confusing error messages when the manifest is incorrect and we try to run.

[brandjon]

I'm unable to reproduce using a toy example under either a recent version (0.4.0) or 0.2.3.

Looking at the line you linked, if you're talking about the scala_library rule, it doesn't have the mandatory flag on "main_class" (line 531), only scala_binary does. (I don't know Scala but I assume it's expected that a library wouldn't need a main class.) If you're having an issue with another rule where the mandatory flag isn't being respected, please reopen and provide an example failure. Thanks!