yarn2nix

yarn2nix [path/to/yarn.lock]
yarn2nix --template [path/to/package.json]

Convert a `yarn.lock` into a synonymous nix expression.
If no path is given, search for `./yarn.lock`.
In the second invocation generate a template for your `package.json`.

Features

• Purely transform yarn.lock files into very minimal, line-diffable nix expressions.
• Nix is used to its fullest. Every package is a derivation, whole dependency subtrees are shared in an optimal way, even between projects.
• The ability to resolve git dependencies by prefetching their repos and including the hashes.
• Completely local transformation if there are no git dependencies (can be used inside nix-build, no large file check-in).
• Extremely fast.
• Nice code that can be easily extended, new repositories introduced, adapt to new versions of the yarn.lock format.
• Comes with a nix library that uses the power of overlays to make overriding dependencies possible.

Probably a few more.

Example Output

The HackMD project is an elaborate npm package with hundreds of dependencies. yarn2nix flawlessly parses the current (2017-12) yarn.lock file distributed with the project, including resolving their manual git forks of multiple npm packages:

dist/build/yarn2nix/yarn2nix ~/tmp/hackmd/yarn.lock | wc
   5306   17068  280246
cat ~/tmp/hackmd/yarn.lock | wc
   7667   11307  266652

The output of this conversion can be seen here. Also note that git dependencies are resolved correctly.

Pushing it through the provided library of nix functions, we get a complete build of HackMD dependencies, using the project template (generated with --template), we also build HackMD. Included executables will be in node_modules/.bin as expected and correctly link to their respective library paths in the nix store, for example:

 ls /nix/store/2jc8b4q9i2cvx7pamv5r8md45prrvx4f-hackmd-0.5.1-0.5.1/node_modules/.bin/markdown-it --help
Usage: ls [OPTION]... [FILE]...
List information about the FILEs (the current directory by default).

Building

$ nix-build
$ result/bin/yarn2nix

Development

$ nix-shell
nix-shell> hpack
nix-shell> cabal build