Feature: Warn against creating packages and classes with file names illegal on Windows

[Sciss]

On Windows, there are reserved file names, including, among others, aux, Aux, aux.*, Aux.*, con, ... (full list). Thus when building on a Windows machine, you probably run into an OS error when scalac tries to write these files. See #4781.

However, you can perfectly create those files on other OS such as Linux or macOS. But when trying to extract those files on a Windows computer, it fails.

I would thus suggest, perhaps in conjunction with #4781, to warn or even error on those file names on any operating system. That way you prevent somebody from building an entire library based on com.foo.aux.Aux (which I just did) and finding out much later that it causes problems (example: extracting the scaladoc jar).

[som-snytt]

Maybe -Xlint:special-names, where the new -Wconf will make it easy to suppress in case Aux is a pattern.

-d artifact.jar avoids writing Aux.class to the file system. Scaladoc could do the same (if it doesn't already). My expectation is that a user on Windows never extracts Scaladoc but configs the IDE to use the doc.jar or src.jar.

Alternatively, encode Aux as $I$hate$windows$Aux. No one is put out by + as $plus.

Alternatively, a Scalafix that rewrites Aux to Auks and adds type Aux = Auks to your custom Predef.