nix-build action

This nix-build action is an opinionated all-inclusive action that will

• Checkout your code
• Install a Nix language interpreter and daemon
• Setup artifacts caching
• Automatically run nix-build with heuristics applied

---

Usage

Here's a simple sample to get you started:

name: "CI"

on:
  pull_request:
  push:

jobs:
  build:
    name: Build (${{ matrix.os }})
    strategy:
      fail-fast: false
      matrix:
        os:
          - ubuntu-24.04
          - macos-13 # most recent x86_64
          - macos-15 # most recent aarch64
    runs-on: ${{ matrix.os }}
    steps:
      - uses: samueldr-wip/nix-build-release.nix-action@latest

Note

Prefer pinning to a released version, rather than following the latest branch.

This applies to all actions.

This sample will effectively run nix-build ./release.nix or nix-build ./default.nix at the root of your repository.

By default the artifacts will be sent to the cache, allowing future builds to resume from existing transitive builds (if relevant).

---

nix-build heuristics

Heuristics is a big word for basically a small few options.

The first of the following files found will be nix-build't:

• release.nix
• default.nix

*This mirrors an older, yet still relevant, convention with Nix projects, where the default.nix may expose a more involved API, and the release.nix expression is used as a well-known way to build the expected outputs.

---

Configuring the action

There are a couple inputs you can provide to this action.

Be mindful about interactions between some inputs. Read the script and the action to better understand how they interact.

expression-file

The expression file to build.

When missing, it will try in order: [ ./release.nix ./default.nix ].

attributes

Attributes to build from the expression.

When missing, it will follow the default Nix semantics around build outputs.

nix-expression

When provided, nix-build will pass the given value to the standard input, and build that instead of expression-file.

nix-build-extra-arguments

When provided, the call to nix-build will use these appended extra arguments.

Warning

Beware of string splitting semantics!

nix-path

When provided, NIX_PATH will be set to this value.

checkout-repo

Default: true

Whether the repository will be checked-out automatically with the actions/checkout action.

Use false to bring your own checkout action alternative.

installer-action

Default: lix-gha-installer-action

Installer action to use.

Supports the following: [ "lix-gha-installer-action" "none" ].

Use none to bring your own.

cache-action

Default: DeterminateSystems/magic-nix-cache

Cache action to use.

Supports the following: [ "DeterminateSystems/magic-nix-cache" "none" ].

Use none to disable or bring your own.

---

FAQ

Can I use the ___ action instead?

Maybe!

As of right now, all steps (except building) are conditional.

If you don't want to use the actions/checkout to checkout your repo, set checkout-repo to false.

Similarly, all other actions are implemented as if they were an enum type, with the none value available to disable the step entirely.

Contributions welcome for alternative steps.

I want to upload the build to a binary cache

It is not supported at this moment, though a desired feature.

Contributions welcome to add support.

I want upload outputs to a release

This is not a desired feature, as it involves knowing too much about the intended use-case.

Instead, you can safely add additional steps to upload artifacts to releases, just like you would otherwise.

My release.nix is big and OOMs at eval

Try making a matrix out of it, and use the attributes input to build one attribute at a time.

This will also provide some parallelism, but unless done carefully, will not manage dependencies between attributes.

What about Flakes?

Currently unsupported, as I'm not using them myself. I don't think I could properly support the nuances of Flakes since I don't know them.

Contributions welcome to support Flakes appropriately.