Type Alias PromotionSources 

pub type PromotionSources = HashMap<String, Vec<String>>;

The sources[] of every promotion in a folded log, keyed by promotion ID. Rules (5) and (6) below join against it, and doctor builds the same map while it scans so both answer a hand-edited log identically.

Aliased Type

pub struct PromotionSources { /* private fields */ }