The rust language highlighting lexers used by Geany are part of the [Scintilla](https://www.scintilla.org/) project and the symbol parsers are part of the [uctags](https://github.com/universal-ctags/ctags) project.

First you need to check if those upstreams have been changed, and if not then raise a request to them. Better you do that directly, you know Rust, the Geany team not so much.

When the upstreams have been upgraded then a pull request can be made to include them into Geany.

@SiegeLord thanks, closed fixed