private static IEnumerable <ISource> FilesUnder(this IVsProject inProject, DTE dte, VSConstants.VSITEMID id)
{
Option <ISource> file = inProject.TryFindFile(dte, id);
IEnumerable <ISource> result =
file.OfType <SourceFile>() is Some <SourceFile> some ? new [] { some.Content }.Concat(inProject.GetSourceFiles(some.Content.Dte, some.Content.ItemId))
: file is Some <ISource> general ? new[] { general.Content }
: inProject.GetSourceFiles(dte, id);
return(result);
}