Scoping issue with Set types - delphi

Question

I have 3 units This is my main unit....
uses
Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.ExtCtrls, Vcl.StdCtrls;
type
TForm1 = class(TForm)
Button1: TButton;
Panel1: TPanel;
Panel2: TPanel;
Panel3: TPanel;
procedure FormShow(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
end;
var
Form1: TForm1;
implementation
Uses Unit2;
{$R *.dfm}
procedure TForm1.FormShow(Sender: TObject);
begin
Panel1.Visible := oiNone in form2.Settings.OptVars;
Panel2.Visible := oiHint in form2.Settings.OptVars;
Panel3.Visible := oiStat in form2.Settings.OptVars;
end;
end.
This is the second unit - used by the first.
unit Unit2;
interface
uses
Winapi.Windows, Winapi.Messages, System.SysUtils, System.Variants, System.Classes, Vcl.Graphics,
Vcl.Controls, Vcl.Forms, Vcl.Dialogs, Vcl.StdCtrls, Unit3;
type
TForm2 = class(TForm)
CheckBox1: TCheckBox;
CheckBox2: TCheckBox;
CheckBox3: TCheckBox;
procedure FormCreate(Sender: TObject);
procedure FormDestroy(Sender: TObject);
private
{ Private declarations }
public
{ Public declarations }
Settings: TSettings;
end;
var
Form2: TForm2;
implementation
{$R *.dfm}
procedure TForm2.FormCreate(Sender: TObject);
begin
Settings := TSettings.Create;
Checkbox1.Checked := oiNone in Settings.OptVars;
CheckBox2.Checked := oiHint in Settings.OptVars;
CheckBox3.Checked := oiStat in Settings.OptVars;
end;
procedure TForm2.FormDestroy(Sender: TObject);
begin
Settings.Free;
end;
end.
and this is the unit which is used by the second unit and contains the Set type which is used by both other units.
unit Unit3;
interface
Uses
winAPI.windows,system.classes;
Type
TOptions = Set Of (oiNone, oiHint, oiStat);
TSettings = class
private
fMyOption: TOptions;
public
Constructor Create;
Destructor Destroy;
property OptVars: TOptions read fMyOption write fMyOption;
end;
implementation
constructor TSettings.Create;
begin
fMyOption := [oiNone, oiHint, oiStat];
end;
destructor TSettings.Destroy;
begin
end;
end.
In the second unit, the items oiNone,oiHint, oiStat are accessible and within scope.
In the first unit, the items oiNone, oiHint and oiStat are not accessible and within scope although the Settings.OpVars which is a TOption data type is accessible.
I cannot think of a better way to describe my problem. If you put these into a project you should see the issue.

Answer 1

Update
After the latest edit it is clear that my first hunch was correct. You weren't using the unit that declares the type. The names have changed, but with the current edit your problem is that the main unit does not use Unit3.
You need to reference the unit that declares the set type, and its enumerated type. Add UnusedItemsReg to your uses clause in the third unit.
If you have done that then the only other explanation I can imagine is that you compile with scoped enums enabled. But I'm clutching at straws now.
I would definitely recommend that you declare the enumerated type as a named type in its own right. Certainly if you use scoped enums then you'll need to do that. But sooner or later you'll want to have that type available.
type
TOption = (oiNone, oiHint, oiStat);
TOptions = set of TOption;
If you do use scoped enums then you'll refer to then like this:
TOption.oiNone

Answer 2

You need Unit3 in the (a) uses clause of the main unit. Otherwise it cannot see type TOptions. That is a requirement of Delphi for visibility. It does not use the implicit references that you seem to be seeking.