Warning about incorrect structure is misleading
`nimble install nigui` gives the following warning:
`Package 'nigui' has an incorrect structure. It should contain a single directory hierarchy for source files, named 'nigui', but file 'windows.nim' is in a directory named 'src/nigui/private/windows' instead. This will be an error in the future.`

The real issue in my case was, that in my nimble file `srcDir = "src"` was missing. After I added this, the warning is gone.