Backend generates useless companion class for inner objects

[smarter]

The following code:

object Outer {
  object Inner
}

generates the following files with scalac:

Outer.class  Outer$.class  Outer$Inner$.class

and the following files with Dotty:

Outer.class  Outer.hasTasty  Outer$.class  Outer$Inner.class  Outer$Inner$.class

The Outer.hasTasty is expected but the Outer$Inner.class isn't, it doesn't seem to contain much:

% cfr 'Outer$Inner.class'
/*
 * Decompiled with CFR 0_120.
 */
public final class Outer$Inner {
}

Could we avoid generating these companions? On case-insenstive filesystems they can be harmful: #2673 (comment)

[smarter]

DarkDimius added exp:novice and removed exp:expert labels 9 minutes ago

I think for something to be novice-level it needs to be obvious how to fix, or you need to give some instructions on how someone could fix it ;).

[abeln]

I'd be happy to take a look at this if given some pointers.

[DarkDimius]

@abeln, backend has a single entry-point to decide where to output files: method getFileForClassfile. I'd intercept this method in debugger and see when is it called for the generated class and why.

[smarter]

Also we have some docs on the backend you might find helpful: http://dotty.epfl.ch/docs/contributing/backend.html and http://dotty.epfl.ch/docs/internals/backend.html