Override dependency

[marijanp]

Hello, I'm packaging a crate that is available on crates.io but not in nixpkgs using crane. I'm using crane's buildPackage and nixpkgs fetchCrate to fetch the sources. One of the dependencies of the package I'm trying to package downloads a bunch of files in its build.rs. I was able to figure out what these files are and now I would like to place them where they belong. Is there a way to override the dependency of the package somehow? Ideally I would add a postUnpack hook.

The dependency that fetches files from the internet is part of the workspace of the package I'm trying to build.

Thanks for your help in advance

[ipetkov]

It will largely depend on what that build script is doing and whether you can turn off the fetch part (assuming you can satisfy it's requirements by making the files available with a postUnpack script or equivalent).

If the build script unconditionally tries to touch the network, you'll need to either update it upstream, or have the derivation apply a patch before continuing with the build.

Hope this helps!

[ipetkov]

Studying the build.rs it reads the packages src directory to check whether the file is present. This is what makes me struggle. The source directory after the unpackPhase does not look at all like the actual github sources and I'm not able to inject the file where the build script is looking at it. The build.rs reads a src/file.zip, relative to the packages root directory.

It's worth noting that a build script's current working directory is the source directory of the build script’s package and not the source root that the derivation starts out with

---

I also tried to replace fetchCrate with fetchFromGitHub but then I run into toml parsing issues, and there are more problems with the repo like a missing Cargo.lock

There's some instructions for handling this documented here which might be helpful: https://crane.dev/faq/no-cargo-lock.html

[marijanp]

It's worth noting that a build script's current working directory is the source directory of the build script’s package and not the source root that the derivation starts out with

Is there a way to "patch" the build scripts working directory using crane?

[ipetkov]

Yes, all arguments are eventually lowered to mkDerivation, meaning you can set patches and the patchPhase will apply them to the source: https://nixos.org/manual/nixpkgs/stable/#ssec-patch-phase

Alternatively you can define a custom phase to patch things more "manually" (e.g. with a shell or sed script) if that works out better

[marijanp]

Ok I might need to make this clearer: I'm familiar with all the concepts in order to achieve patching.
The problem is: after the unpackPhase (using fetchCrate to obtain the sources) the source directory does not resemble the source directory encounter on the project's GitHub. Instead I'm left with:

|-- Cargo.lock
|-- Cargo.toml
`-- src
    |-- bin
    |   `-- crane-dummy-risc0-r0vm
    |       `-- main.rs
    `-- lib.rs

If I instead use fetchFromGithub crane misinterprets some templates which are part of that repository and when fromToml is called I get errors thrown by crane.

[ipetkov]

(using fetchCrate to obtain the sources) the source directory does not resemble the source directory encounter on the project's GitHub

fetchCrate pulls what's published to crates.io; cargo will normally only publish a crate's directory (modulo any explicit include/exclude definitions). If the crate is within a subdirectory it will likely not match what the project's repo looks like

Also you might be getting errors in trying to patch the dummfied sources during the buildDepsOnly derivation. If you are using buildPackage directly, consider setting something like:

let
  commonArgs = {
    # everything except for patching logic
  };
in
craneLib.buildPackage (commonArgs // {
  cargoArtifacts = craneLib.buildDepsOnly commonArgs;
  # patching logic goes here
});