Function defines_script 

pub fn defines_script(pkg_json: &str, script: &str) -> bool

Does package.json define script under “scripts”?

A brace-matched scan rather than a JSON parser: the only question is whether one key exists in one object, and a dependency-free binary is the point of this migration. Restricted to the “scripts” object so a same-named key elsewhere (a dependency called test, say) cannot answer for it.