Function expand_sigil 

pub fn expand_sigil(
    query: &str,
    alias_lookup: &dyn Fn(&str) -> Option<Vec<String>>,
) -> Option<SigilExpansion>

Expand an alias query like @todo or @config/section. Returns None if the query doesn’t start with @ or the alias is unknown.

alias_lookup resolves an alias name to its target paths.