> Assuming you have a KTextEditor::Document around, the right way to do it
> would be:
>   KTextEditor::VariableInterface* iface =
>     qobject_cast<KTextEditor::VariableInterface*>(doc);
>
>   if (iface) {
>     QString indentWidth = iface->variable("indent-width");
>     ...
>   }
> In other words, you can query the documents for arbitrary variables. You
> don't have to parse it yourself, it's for free.

If the document is opened in KDevelop, one can do
  IDocument *doc = ICore::self()->documentController()->documentForUrl(url);
  KTextEditor::Document *textdoc = doc->textDocument();
but I'd assume source formatter plugin also needs to reformat the files which 
aren't opened (like all files in the project)?