Function in_cache_arg_position 

pub fn in_cache_arg_position(text: &str, offset: usize) -> bool

v0.140 (ADR 0163): the cursor is at an argument-name position inside a @cache( … ) — the innermost open paren is opened by the cache annotation (@cache, not a bare cache( call), and the current argument segment (since the last ,) has no : yet (a name position, not a value one).