[Setup]
AppName=My Program
AppVersion=1.5
DefaultDirName={pf}\My Program
DisableFinishedPage=yes
OutputDir=C:\Temp

[Code] 
var
  NeedRestartFlag: Boolean;

procedure CurStepChanged(CurStep: TSetupStep);
var
  ResultCode: Integer;
 begin
  if CurStep = ssInstall then
  begin
    if (FileExists('C:\Windows\System32\bash.exe')) then
    begin
      NeedRestartFlag := True
      Exec(ExpandConstant('dism.exe'), '/quiet /NoRestart /online /Enable-Feature /featurename:Microsoft-Windows-Subsystem-Linux', '', SW_HIDE, ewNoWait, ResultCode);
      Sleep(850)
    end
    else
    begin
      NeedRestartFlag := False
    end
  end;
end;

function NeedRestart(): Boolean;
begin
  if NeedRestartFlag then
  begin
    Log('Need restart');
    Result := True;
  end
    else
  begin
    Log('Do not need restart');
    Result := False;
  end;
end;