nix-gitlab-ci/README.md

# Nix Gitlab CI

Flake module which allows generating a `.gitlab-ci.yml` from Nix.

This allows easily using any Nix package in CI.

Also makes it possible to split CI parts in a separate module which can be imported in multiple projects.

## Usage

```nix
# flake.nix
{
  ...
  inputs.nix-gitlab-ci.url = "gitlab:TECHNOFAB/nix-gitlab-ci/<version>?dir=lib";  # recommendation: pin to the latest release/version
  
  outputs = {...}: flake-parts.lib.mkFlake {...} {
    imports = [
      inputs.nix-gitlab-ci.flakeModule
    ];
    ...
    
    perSystem = {pkgs, ...}: {
      # ci is a shortcut and creates a "default" pipeline
      ci = {
        stages = ["test"];
        jobs = {
          "test" = {
            stage = "test";
            nix.deps = [pkgs.unixtools.ping];
            script = [
              "ping -c 5 8.8.8.8"
            ];
          };
        };
      };
      # runs on a merge request for example
      pipelines."merge_request_event" = {
        stages = ["some_stage"];
        jobs = { ... };
      };
      ...
    }
  }
}
```

```yaml
# .gitlab-ci.yml
include:
  - component: gitlab.com/TECHNOFAB/nix-gitlab-ci/nix-gitlab-ci@<version>  # recommendation: pin to the latest release/version (don't use "main" etc.)
    inputs:
      version: <version>  # docker image tag, use the same version as a above
```

## Utilities

### Disable Caching temporarily

To disable any of the provided caches for a pipeline one can set `NIX_CI_DISABLE_CACHE` to
anything non-empty (eg. "yes") when triggering the pipeline.

The `build:nix-ci` job has a different special environment variable `NIX_CI_FORCE_BUILD`
(useful if the generated pipeline in the cache is outdated, this will build it again).

### Run Jobs locally

You can run any job's script (+ before and after) locally with Nix for easier testing:

```sh
#                                /  pipeline name, like "default"
nix run .#gitlab-ci:pipeline:<pipeline name>:job:<name>
```

There is also `.#gitlab-ci:pipeline:<pipeline name>:job-deps:<name>` which generates and exports the required environment variables for each job:

- PATH (with all deps)
- any custom env variables which contain store paths to not break stuff when switching archs

## Thanks to

Some parts of this implementation are adapted/inspired from https://gitlab.com/Cynerd/gitlab-ci-nix