Convert {constants} returned by CurrentFilename in Inno Setup

Question

What to do to get nice, full filename from the code below:

;bugfixes
Source: "Bugfixes\CombatGameConstants.json"; DestDir: "{code:battletechDataDir}\constants";\
    Flags: uninsneveruninstall; Components: DataBugfixes; BeforeInstall: BackupFile()

and the BackupFile() procedure:

procedure BackupFile();
var fileToBackup : String;
begin
  { if backup file already exists skip creation, otherwise rename the file to file.backup }
  fileToBackup := CurrentFilename(); { get destination file name }
  if not FileExists(fileToBackup + '.backup') then
  begin
    if not RenameFile(fileToBackup, fileToBackup + '.backup') then
      MsgBox('Creation backup file for ' + fileToBackup + ' failed!', mbInformation, MB_OK);
  end;
end;

This does not convert {code:battletechDataDir} into full path – CurrentFileName() returns me {code:battletechDataDir}\constants\{code:battletechDataDir}\constants. So either how to convert that {code:battletechDataDir} into directory, or backup given file other way?

Answer 1

You can use ExpandConstant function:

fileToBackup := ExpandConstant(CurrentFilename()); { get destination file name }

---

Though CurrentFilename is intended for use with wildcard source. With a fixed file name, you might as well refer to the file explicitly:

fileToBackup := battletechDataDir('') + '\constants\CombatGameConstants.json';