Okay I just properly took a look at this, and some of the sibling responses are only partially correct. It's not symbol names that change, but the crate does ap

Okay I just properly took a look at this, and some of the sibling responses are only partially correct. It's not symbol names that change, but the crate does appear to have a hash used to sanity-check against this. I used these sources: // a.rs #![crate_type = "lib"] pub struct Foo { pub x: i32 } // b.rs #![crate_type = "lib"] extern crate a; pub fn foo() -> a::Foo { a::Foo {} } // c.rs extern crate b; fn main() { println!("{}", b::foo().x); } The field `x` from crate `a` was originally not there, and added after compiling crate `b`. The error when trying to compile crate `c` was: error[E0460]: found possibly newer version of crate `a` which `b` depends on --> c.rs:1:1 | 1 | extern crate b; | ^^^^^^^^^^^^^^^ | = note: perhaps that crate needs to be recompiled? = note: crate `a` path #1: liba.rlib = note: crate `b` path #1: libb.rlib