Function expr_references_ident 

pub fn expr_references_ident(expr: &Spanned<Expr>, name: &str) -> bool

True iff expr (recursively) mentions name as an Ident/ Resolved reference. Used by the caller-guard extractor to filter out enclosing predicates that don’t constrain the variable passed at the countdown-param position — those predicates name caller locals that aren’t in scope inside the callee.