private static DiffResult Check(IReadOnlyList <TypeDefinition> olderTypes, IReadOnlyList <TypeDefinition> newerTypes)
{
var oWithNested = olderTypes.WithNested().ToImmutableList();
var nWithNested = newerTypes.WithNested().ToImmutableList();
var diffs = TopLevel.Diffs(oWithNested, nWithNested).ToImmutableList();
return(new DiffResult(diffs));
}