anchor.diff:          let arg = (results.TryGetResult <@ FindPackageVersionsArgs.NuGet @>,
                      results.TryGetResult <@ FindPackageVersionsArgs.NuGet_Legacy @>)
                     |> legacyOption results "(omit, option is the new default argument)" "nuget"
  -        match arg with
  -        | Some(id) -> id
  -        | _ -> results.GetResult <@ FindPackageVersionsArgs.NuGet @>
  +        require arg (fun _ -> results.GetResult <@ FindPackageVersionsArgs.NuGet @>)
       let sources =
           let arg = (results.TryGetResult <@ FindPackageVersionsArgs.Source @>,
                      results.TryGetResult <@ FindPackageVersionsArgs.Source_Legacy @>)
  
positive.code:         failObsolete oldSyntax newSyntax
      | (_, _) -> None
  
  let add (results : ParseResults<_>) =
      let packageName =
          let arg = (results.TryGetResult <@ AddArgs.NuGet @>,
                     results.TryGetResult <@ AddArgs.NuGet_Legacy @>)
                    |> legacyOption results "(omit, option is the new default argument)" "nuget"
          match arg with
          | Some(id) -> id
          | _ -> results.GetResult <@ AddArgs.NuGet @>
      let version =
          let arg = (results.TryGetResult <@ AddArgs.Version @>,
                     results.TryGetResult <@ AddArgs.Version_Legacy @>)
  
negative.code:         let arg = (results.TryGetResult <@ PushArgs.Package @>,
                     results.TryGetResult <@ PushArgs.Package_Legacy @>)
                    |> legacyOption results "(omit, option is the new default argument)" "file"
          require arg (fun _ -> results.GetResult <@ PushArgs.Package @>)
      let url =
          (results.TryGetResult <@ PushArgs.Url @>,
           results.TryGetResult <@ PushArgs.Url_Legacy @>)
  