Module caches  Copy item path  Source  DefIdCache  In-memory cache for queries whose key is a DefId DefaultCache  In-memory cache for queries whose keys aren’t suitable for any of the
more specialized kinds of cache. Backed by a sharded hashmap. SingleCache  In-memory cache for queries whose key type only has one value (e.g. ()).
The cache therefore only needs to store one query return value. VecCache In-memory cache for queries whose keys are densely-numbered IDs
(e.g CrateNum, LocalDefId), and can therefore be used as indices
into a dense vector of cached values. QueryCache  Trait for types that serve as an in-memory cache for query results,
for a given key (argument) type and value (return) type.