build.sbt should do Unsupported Platform test

[LeeTibbert]

Arman,

Under the rubric of "moving errors closer to the application developer", what do you
think about build.sbt doing the "UnsupportedPlatform" check.

Confessing my limitations in public again, I could not figure out that
the linktime missing symbol for "UnsupportedPlatformException" currently
expected & wanted in the 'main' branch when running on macOS actually
meant "Not Yet on this platform".

I have not tried it yet, but, given encouragement, I could.

1. Have build.sbt check the System property "os.name"
2. do the downcasing to compare to Linux or macOS.
3. Have sbt itself throw a RunTimeException("Lee you are at it again!")

That gives pretty immediate feedback, which needs little sussing out.

[armanbilge]

Thanks for raising this. I agree, the unsupported platform error could be a lot clearer in meaning. A couple thoughts:

1. When I proposed the UnsupportedPlatformError, I actually was not thinking about an epollcat developer. I was thinking about an application developer, who is using epollcat as a library. In which case, no matter what we do in our build.sbt, it will not help them.

2. Although our build.sbt can warn if it is being run on an unsupported platform, I do not think it should throw a fatal error. There is no reason someone cannot develop epollcat on a non-supported platform: after all, to run the scala compiler you need only a JDK. They won't be able to run tests locally, but CI assumes much of that responsibility anyway. It's far from ideal, but I do not want to rule this out.