in z3tracer/src/lexer.rs [271:283]
fn make_key(&mut self, key: u64, fresh: bool) -> QiKey {
let version = if fresh {
let e = self
.key_versions
.entry(key)
.and_modify(|e| *e += 1)
.or_insert(0);
*e
} else {
self.key_versions.get(&key).cloned().unwrap_or(0)
};
QiKey { key, version }
}