Is it possible to filter/require installation path

Question

So I wonder if it is possible to allow user to enter only ASCII as installation path? (warn him and make input path again) (problem is application we install is old and can not work with Cyrillic paths so we need to restrict user on installation stage)

Answer 1

To restrict the user input for the application directory for the Basic Latin character set you may use the following code. The code only checks if any char of the selected directory name doesn't exceed the Basic Latin character set range. If that happens, an error message is shown and the user is forced to stay on the directory selection page. The remaining folder name validation (based on the file system naming conventions) is left on Inno Setup internals, as it already was:

[Setup]
AppName=My Program
AppVersion=1.5
DefaultDirName={pf}\My Program

[Code]
function IsCharValid(Value: Char): Boolean;
begin
  Result := Ord(Value) <= $007F;
end;

function IsDirNameValid(const Value: string): Boolean;
var
  I: Integer;
begin
  Result := False;
  for I := 1 to Length(Value) do
    if not IsCharValid(Value[I]) then
      Exit;
  Result := True;
end;

function NextButtonClick(CurPageID: Integer): Boolean;
begin
  Result := True;

  if (CurPageID = wpSelectDir) and 
    not IsDirNameValid(WizardForm.DirEdit.Text) then
  begin
    Result := False;
    MsgBox('There is an invalid char in the selected directory name. ' +
      'Directory path may contain only chars that are valid for the ' +
      'file system naming conventions and only in the range of the ' +
      'Basic Latin character set.', mbError, MB_OK);
  end;
end;