InnoSetup Uninstall by deleting the application folder

installer.iss

procedure CurUninstallStepChanged(CurUninstallStep: TUninstallStep);
begin

  // warn the user, that his working folder is going to be deleted and projects might get lost
  if (CurUninstallStep = usUninstall) then begin
  
    if MsgBox('***WARNING***'#13#10#13#10 +
        'The installation folder is [ '+ ExpandConstant('{app}') +' ].'#13#10 +
        'You are about to delete this folder and all its subfolders,'#13#10 +
        'including [ '+ ExpandConstant('{app}') +'\important_projects_folder ], which may contain your projects.'#13#10#13#10 +
        'This is your last chance to do a backup of your files.'#13#10#13#10 +
        'Do you want to proceed?'#13#10, mbConfirmation, MB_YESNO) = IDYES
    then begin
      // User clicked: YES

      // fix "read-only" status of all files and folders, else some things might remain after uninstallation
      ExecHidden('cmd.exe /c "attrib -R ' + appDir + '\*.* /s /d"');

      // Deletes the application directory and everything inside it.
      // This function will remove directories that are reparse points,
      // but it will not recursively delete files/directories inside them.
      DelTree(ExpandConstant('{app}'), True, True, True);

    end else begin
      // User clicked: No
      Abort;
    end;
  end;

end;