pub fn merge(&mut self, new: Self) {
        for (selector, name) in new.selectors {
            self.selectors
                .entry(selector.clone())
                .and_modify(|e| {
                    assert_eq!(
                        e, &name,
                        "Function name mismatch for selector '{:?}'",
                        selector
                    )
                })
                .or_insert(name);
        }
    }
Merges new selectors into the existing set.
core/bin/selector_generator/src/selectors.rs