yarn2nix

Converts yarn.lock files into nix expression.

1. Make yarn and yarn2nix available in your shell.

   cd $GIT_REPO
   nix-env -i yarn2nix -f .
   nix-env -i yarn -f .

2. Go to your project dir
3. If you have not generated a yarn.lock file before, run

   yarn install

4. Create a yarn.nix via:

   yarn2nix > yarn.nix

5. Create a default.nix to build your application (see the example below)

Requirements

Make sure to generate the lock file with yarn >= 1.10.1

Example default.nix

For example, for the front-end of weave's microservice reference application:

with (import <nixpkgs> {});
with (import /home/maarten/code/nixos/yarn2nix { inherit pkgs; });
rec {
  weave-front-end = mkYarnPackage {
    name = "weave-front-end";
    src = ./.;
    packageJSON = ./package.json;
    yarnLock = ./yarn.lock;
    # NOTE: this is optional and generated dynamically if omitted
    yarnNix = ./yarn.nix;
  };
}

note: you must modify /home/maarten/code/nixos/yarn2nix

To make this work nicely, I exposed the express server in server.js as a binary:

1. Add a bin entry to packages.json with the value server.js
2. Add #!/usr/bin/env node at the top of the file
3. chmod +x server.js

Testing the example

1. Run nix-build In the front-end directory. Copy the result path.
2. Create an isolated environment cd /tmp; nix-shell --pure -p bash.
3. /nix/store/some-path-to-frontend/bin/weave-demo-frontend

Run tests locally

./update-yarn-nix.sh
./tests/no-import-from-derivation/update-yarn-nix.sh
./run-tests.sh

Troubleshooting

nix-build fails with "found changes in the lockfile" error

yarn2nix runs on the beginning of build to ensure that yarn.lock is correct (and to collect nix-expressions if you haven't provided them). So, if there is something wrong, yarn2nix tries to change the lockfile, but fails and aborts, as it is run with --no-patch flag (as we can't let changes inside of nix-build).

It can sometimes give false-positives, so the solution at the moment is running yarn2nix --no-nix to patch the lockfile in place (the flag is just to avoid config spam, unless you're up to write yarn.nix).

License

yarn2nix is released under the terms of the GPL-3.0 license.