You sure you meant to reply to the follow-up to my comment? None of the hashes you mentioned is actually used by the compiler, except to detect changes wrt incr

You sure you meant to reply to the follow-up to my comment? None of the hashes you mentioned is actually used by the compiler, except to detect changes wrt incremental recompilation. (EDIT: and to catch recompiled crates, see: https://news.ycombinator.com/item?id=16004250 https://news.ycombinator.com/item?id=16004250) Distinguishing between crates is done solely through their name and -C metadata values provided by Cargo. Once crates are loaded by the compiler based on either their explicit path (via --extern) or by being a dependency of another dependency (and there the name and -C metadata prevent collisions), "two versions of the same crate" appears no different than "two different crates". The Rust compiler tends to "index" information (e.g. turning strings into various IDs) as quickly as possible, so a lot more semantics are "by identity" than "by syntax", and that helps when multiple identities may share a name. That includes compiling against already compiled crates, instead of header files you have serialized semantic types and functions, which all use proper identities to "name" anything they use in turn - you never have to be looking for a definition, or risk using the wrong one.