Difficulty using `buildRustPackage` with a `src` containing multiple cargo workspaces

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1

Context

I have a repository structured like the following:

repo
├── workspace-a
├── workspace-b
└── workspace-c

Where each workspace has its own Cargo.lock and multiple crates.

The crate I would like to build a package for is repo/workspace-a/foo. The foo crate depends on multiple crates from all three workspaces using the [path] attribute to refer to them.

The Error

I’m running into some odd errors when attempting to use the rustPlatform.buildRustPackage function to build a nix package for my foo crate.

My nix expr looks something like this:

{ stdenv, rustPlatform, ... }:
rustPlatform.buildRustPackage rec {
  pname = "foo";
  version = "0.1.0";
  src = fetchGit {
    url = "ssh://git@github.com/owner/repo.git";
    rev = "8b1128c4d827e17f6d794f9f8a885240ce83630b";
  };
  cargoSha256 = "17ldqr5asrdcsh4l29m3b5r37r5d0b3npq1lrgjmxb6vlx6a36qh";
}

Where the cargoSha256 is currently made up. I’m expecting to get an error where nix tells me that it found a different hash from the one provided at which point I’ll add the proper hash, but I haven’t managed to get this far yet.

After building with:

nix-build -E '(import <nixpkgs> {}).callPackage ./foo.nix {}'

And the output I get is along these lines:

these derivations will be built:
  /nix/store/iqms4hbij486rjccrq7dwjr5s18q6978-foo-0.1.0-vendor.tar.gz.drv
  /nix/store/h1xp9mwcgbf6l2fjwrkrkzh6nd4sp124-foo-0.1.0.drv
building '/nix/store/iqms4hbij486rjccrq7dwjr5s18q6978-foo-0.1.0-vendor.tar.gz.drv'...
unpacking sources
unpacking source archive /nix/store/2hpv2w99kpqja78wwi6k0ja9fh2nkw5d-source
source root is source
patching sources
building

ERROR: The Cargo.lock file doesn't exist

Cargo.lock is needed to make sure that cargoSha256 doesn't change
when the registry is updated.

builder for '/nix/store/iqms4hbij486rjccrq7dwjr5s18q6978-foo-0.1.0-vendor.tar.gz.drv' failed with exit code 1
cannot build derivation '/nix/store/h1xp9mwcgbf6l2fjwrkrkzh6nd4sp124-foo-0.1.0.drv': 1 dependencies couldn't be built
error: build of '/nix/store/h1xp9mwcgbf6l2fjwrkrkzh6nd4sp124-foo-0.1.0.drv' failed

I have ensured that each of the workspaces has their respective Cargo.lock file in the repository at the specified commit, so I don’t believe this to be the problem.

Solution Attempt

My first suspicion was that the builder possibly could not find the necessary package within the repository, so I tried changing the sourceRoot directory to the workspace containing foo. Despite knowing that this would omit some of the other crate dependencies I needed within the repo, I thought the nix builder might at least find the Cargo.lock in the workspace this time, however I got an earlier error this time:

these derivations will be built:                                                                                                                                                                                                               
  /nix/store/3aw08jgr6g82l626ilvzmjfkwldh7yz9-foo-0.1.0-vendor.tar.gz.drv                                                                                                                                                                 
  /nix/store/2pb3hgil3lq23hjhfgzyivnck8jddcja-foo-0.1.0.drv                                                                                                                                                                               
building '/nix/store/3aw08jgr6g82l626ilvzmjfkwldh7yz9-foo-0.1.0-vendor.tar.gz.drv'...                                                                                                                                                    
unpacking sources                                                                                                                                                                                                                              
unpacking source archive /nix/store/2hpv2w99kpqja78wwi6k0ja9fh2nkw5d-source                                                                                                                                                                    
source root is /nix/store/2hpv2w99kpqja78wwi6k0ja9fh2nkw5d-source                                                                                                                                                                              
chmod: changing permissions of '/nix/store/2hpv2w99kpqja78wwi6k0ja9fh2nkw5d-source': Operation not permitted                                                                                                                                   
chmod: changing permissions of '/nix/store/2hpv2w99kpqja78wwi6k0ja9fh2nkw5d-source/.github': Operation not permitted                                                                                                                           
chmod: changing permissions of '/nix/store/2hpv2w99kpqja78wwi6k0ja9fh2nkw5d-source/.github/workflows': Operation not permitted                               
# lots more errors like this for every file in the repo, then
builder for '/nix/store/snld264c3lgp4w456al9kfswg54pknbv-foo-0.1.0-vendor.tar.gz.drv' failed with exit code 1
cannot build derivation '/nix/store/w7bs9ssjyz7lx4s863rdjqqzb66ag4km-foo-0.1.0.drv': 1 dependencies couldn't be built
error: build of '/nix/store/w7bs9ssjyz7lx4s863rdjqqzb66ag4km-foo-0.1.0.drv' failed

I’m unsure what to make of all the chmod attempts, but it seems like this is also the wrong approach.

Questions

Is there some way that I can specify the location of the crate foo and/or its Cargo.lock file within the $src repo that will still allow the crate to refer to its dependencies from the other two workspaces? I noticed that there is a cargoBuildFlags attribute and thought that perhaps I could use it to specify the --manifest-path ${src}/workspace-a/foo/Cargo.toml, however the error above appears to occur before the cargo build even begins.

Or perhaps it is possible that the ERROR: The Cargo.lock file doesn't exist could have a different cause altogether?

Any advice appreciated!

PS

Apologies for the placeholder names! The actual repo I’m building is a private Rust project, otherwise I’d link directly to it.

2

sourceRoot should work, looks like your issue is that it’s trying to write to the src derivation

chmod: changing permissions of '/nix/store/2hpv2w99kpqja78wwi6k0ja9fh2nkw5d-source': Operation not permitted

which isn’t allowed (it’s read only). Normally, this isn’t an issue as the workflow is usually:

unpackPhase # dumps src into /build, which is writable
cd $sourceRoot # sourceRoot is inherited from unpackPhase, which gets it from src
3

Thanks for the response!

Ahhh interesting, do you have any intuition on why it might be trying to write to the src derivation? For reference, this is exactly how I was pointing it to the subdir:

sourceRoot = "${src}/workspace-a/foo";

Perhaps I should be using some /build output related path instead?

4

when doing interpolation with a derivation, you will get the store path, so your sourceRoot expands to:

sourceRoot = "/nix/store/<hash>-source/workspace-a/foo";

which will be read only. you want something like:

  src = fetchGit {
    name = "foo";
    ...
  };

  sourceRoot = "foo/workspace-a/bar";
2 Likes
5

Thanks @jonringer, this was the hint I needed!

Starting the string with source appears to start from the default source location. So, the following appears to be working in my case (at least so far - I have a new round of errors):

sourceRoot = "source/workspace-a";
2 Likes
6

for fetchFromGitHub (and probably others) that is the case, it has the default name = "source", so your sourceRoot by default will point to source.

other fetchers such as fetchurl will take the base name. E.g. my-package-3.0.4.tar.gz → sourceRoot=mypackage-3.0.4

2 Likes