Function find_all_ret_expressions 

pub fn find_all_ret_expressions<'hir, F>(
    _cx: &LateContext<'_>,
    expr: &'hir Expr<'hir>,
    callback: F,
) -> bool
where
    F: FnMut(&'hir Expr<'hir>) -> bool,

calls callback on every expression that could be the return value of expr.

returns false if expr contains ? or if callback ever return false.