Hi folks, just to clarify: it appears that while you can override the outputs of a buildRustPackage derivation, it isn’t possible to override the inputs (i.e. dependencies). Please let me know if I’m wrong about this (and feel free to revert my edits to the wiki page which note this).
I struggled quite a bit with this before giving up, going so far as to reify the Cargo.lock using fromTOML, patching it, then writing it back out with remarshal, and using cargo-edit to patch the dependencies’ Cargo.toml files. My use case involves an A->B->C dependency where I need to replace “C”, so the Cargo.toml in “B” needs to be rewritten.
Specifically, I’m trying to swap out the ring cryptography library with IBM’s fork which has support for powerpc64le (PR to merge upstream). I picked tiny as an example case but pretty much anything written in Rust that uses cryptography or HTTPs relies on ring. The goal here was not to have to run cargo update for every single rust package that uses ring (or that can use it in place of openssl). This is a large and rapidly growing number of packages. It ought to be possible to calculate the new checksum for ring once, and then patch that value in using non-network-accessing operations, inside of nix derivations.
I ended up in never-ending fights with cargo, which really wants to do things its way. The closest I ever got always managed to end with something like
error: the lock file /build/source/Cargo.lock needs to be updated but --frozen was passed to prevent this
If there is a way around this please do let me know. Until then my working assumption is that cargo simply doesn’t support the kinds of magic that nix has gotten me addicted to using. The only way forward here appears to be to skip cargo and have nix drive the build process with crate2nix.