cachix-action

Build software only once using Nix with the help of Cachix.

This action will configure Cachix and invoke nix-build.

Why do I need this

Because you'd like for your CI to be fast. Let me explain.

Directory-based caching on a typical CI doesn't work well for Nix.

/nix/store is a global storage of everything Nix operates on. These are your sources, patches, tarballs, packages, configuration.

A directory-based cache requires downloading a whole store, including the irrelevant parts. cachix-action will only fetch what's needed by configuring a Nix binary cache.

When the build is done, cachix-action only has to upload the new store paths, rather than syncing the whole store.

Purging paths from a directory-based cache is not feasible because it'd have to be aware of all branches and their respective contents somehow.

Usage

1. Login to Cachix and create a new cache.

   1. Follow getting started to create your signing key
   2. Backup the signing key in the process.

2. As an admin of your github repository:

   1. Click on Settings
   2. Click on Secrets (If missing, you need to sign up first for actions beta)
   3. Add your signing key value under name CACHIX_SIGNING_KEY.

3. Create .github/workflows/test.yml in your repo with the following contents:

name: "Test"
on:
  pull_request:
  push:
jobs:
  tests:
    runs-on: ubuntu-latest
    steps:
    - uses: actions/checkout@v1
    - uses: cachix/install-nix-action@v6
    - uses: cachix/cachix-action@v2
      with:
        name: mycache
        signingKey: '${{ secrets.CACHIX_SIGNING_KEY }}'
        # Only needed for private caches
        authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'

Alternatively, you can use this action to only configure cachix for substitution:

...
    - uses: cachix/cachix-action@v2
      with:
        name: mycache
        skipNixBuild: true
        # Only needed for private caches
        authToken: '${{ secrets.CACHIX_AUTH_TOKEN }}'
...

See action.yml for all options.

---

Hacking

Install the dependencies

$ yarn install

Build the typescript

$ yarn build

Run the tests ✔️

$ yarn test