[Setup]
AppName=MyApp
AppVerName=MyApp
DefaultDirname={pf}\MyApp

[code]
function DoubleSlash(S: String): String;
var i: Integer;
begin
Result:='';
   while Length(S)>0 do begin
     i:=Pos('\', S);
     if i>0 then begin
       Result:= Result+Copy(S, 1, i-1)+'\\';
       Delete(S, 1, i);
     end else begin
       Result:= Result+S;
       SetLength(S, 0);
     end;;
   end;
end;

procedure CurStepChanged(CurStep: TSetupStep);
var s: string;
begin
if CurStep = ssPostInstall then begin
   s:= '-- This file uses UTF8 encoding without BOM'+#13+#10#13+#10+
       '-- Path to ISS Joiner'+#13#10+
       'joiner = "\"'+DoubleSlash(ExpandConstant('{app}\joiner.exe'))+'\""';
   SaveStringtoFile(ExpandConstant('{app}\MyLua.lua'), s, false)
end;
end;

[Setup]
AppName=MyApp
AppVerName=MyApp
DefaultDirname={pf}\MyApp

[code]
const
     CP_ACP = 0; CP_UTF8 = 65001;
          
Function MultiByteToWideChar(CodePage: UINT; dwFlags: DWORD; lpMultiByteStr: PAnsiChar; cbMultiByte: integer; lpWideCharStr: PAnsiChar; cchWideChar: integer): longint; external 'MultiByteToWideChar@kernel32.dll stdcall';
Function WideCharToMultiByte(CodePage: UINT; dwFlags: DWORD; lpWideCharStr: PAnsiChar; cchWideChar: integer; lpMultiByteStr: PAnsiChar; cbMultiByte: integer; lpDefaultChar: integer; lpUsedDefaultChar: integer): longint; external 'WideCharToMultiByte@kernel32.dll stdcall';

function AnsiToUtf8(strSource: string): string;
var nRet, nRet2: integer; WideCharBuf, MultiByteBuf: AnsiString;
begin
     SetLength(WideCharBuf, Length(strSource) * 2);
     SetLength(MultiByteBuf, Length(strSource) * 2);
     nRet:= MultiByteToWideChar(CP_ACP, 0, strSource, -1, WideCharBuf, Length(WideCharBuf));
     nRet2:= WideCharToMultiByte(CP_UTF8, 0, WideCharBuf, -1, MultiByteBuf, Length(MultiByteBuf), 0, 0);
     MultiByteBuf:= Copy(MultiByteBuf, 1, nRet2-1)
     Result:= MultiByteBuf;
end;

function DoubleSlash(S: String): String;
var i: Integer;
begin
Result:='';
     while Length(S)>0 do begin
       i:=Pos('\', S);
       if i>0 then begin
         Result:= Result+Copy(S, 1, i-1)+'\\';
         Delete(S, 1, i);
       end else begin
         Result:= Result+S;
         SetLength(S, 0);
       end;;
     end;
end;

procedure CurStepChanged(CurStep: TSetupStep);
var s: string;
begin
if CurStep = ssPostInstall then begin
     s:= '-- This file uses UTF8 encoding without BOM'+#13+#10#13+#10+
         '-- Path to ISS Joiner'+#13#10+
         'joiner = "\"'+DoubleSlash(ExpandConstant('{app}\joiner.exe'))+'\""';
     SaveStringtoFile(ExpandConstant('{app}\MyLua.lua'), AnsiToUtf8(s), false)
end;
end;