Function is_freedesktop_theme_available 

pub fn is_freedesktop_theme_available(theme: &str) -> bool

Check whether a freedesktop icon theme is installed on this system.

Looks for the theme’s index.theme file in the standard XDG icon directories ($XDG_DATA_DIRS/icons/<theme>/ and $XDG_DATA_HOME/icons/<theme>/).

Always returns false on non-Linux platforms.