---
title: "Developing Packages with Rix"
output: rmarkdown::html_vignette
vignette: >
  %\VignetteIndexEntry{Developing packages with rix}
  %\VignetteEngine{knitr::rmarkdown}
  %\VignetteEncoding{UTF-8}
---

```{r, include = FALSE}
knitr::opts_chunk$set(
  collapse = TRUE,
  comment = "#>"
)
```

## Why bring `{rix}` into your package workflow?

This vignette walks through a recommended development loop for package
authors:

1. Declare the package dependencies with `{rix}`.
2. Commit the resulting `default.nix` to the repository.
3. Use the same definition locally and in CI/CD (for example GitHub
   Actions).
4. Refresh the snapshot frequently so that you notice upstream changes
   early.

## Declaring your package environment

Start by calling `rix()` from your package root. List the R packages and
system tools that your package requires for development, testing, or
vignette builds:

```{r, eval = FALSE}
rix(
  r_ver = "bleeding-edge",
  r_pkgs = c(
    "devtools", "rcmdcheck", "roxygen2", # package development helpers
    "jsonlite", "httr"                    # package runtime deps
  ),
  system_pkgs = c("pandoc"), # or anything else
  ide = "none",
  path = "default.nix",
  overwrite = TRUE
)
```

A few tips when shaping the environment:

- Prefer `r_ver = "bleeding-edge"` (or at least a very recent
  date). This aligns your local setup with what users will experience
  soon and surfaces compatibility problems early.
  See `vignette("bleeding-edge")` for more
  details on using `"bleeding-edge"`.
- If you use a fixed date, then keep `date` current. Updating it every few 
  weeks lets you track CRAN, nixpkgs, and system toolchain updates. 
  If the new snapshot fails you can fix issues right away instead of 
  facing a large backlog later, or you could always revert to an earlier
  working date.

## Committing the environment to your repository

Place the `default.nix` file at the root of the package repository so
that contributors can run:

```sh
nix-shell
```

This drops them into a shell with the right environment for contributing.

To simplify onboarding, document in `README.md` (or a contributing guide)
that contributors should run `nix-shell` before working on the
package. 

Because the environment is pinned, collaborators and CI jobs execute the
same versions of your dependencies, eliminating “works on my machine”
bugs.

## Keeping the snapshot fresh

You could setp up a CI action to update the environment frequently, which would
then trigger unit tests on CI as well. If the tests fail you can immediately address 
incompatibilities introduced by recent CRAN changes.

## Using `{rix}` in GitHub Actions

Because `default.nix` captures the entire toolchain, you should use it as
the basis for your CI workflow. Below is a minimal GitHub Actions configuration
thatruns your package’s unit tests:

```yaml
on:
  push:
    branches: [main, master]
  pull_request:
    branches: [main, master]

name: devtools-tests-via-r-nix

permissions:
  contents: read

jobs:
  devtools_test:
    runs-on: ${{ matrix.os }}
    strategy:
      matrix:
        os: [macos-latest, ubuntu-latest]
    env:
      GITHUB_PAT: ${{ secrets.GITHUB_TOKEN }}

    steps:
      - uses: actions/checkout@v4

      - name: Create this folder to silence warning
        run: mkdir -p ~/.nix-defexpr/channels

      - name: Create .Renviron
        run: |
          echo "GITHUB_PAT=${{ secrets.GITHUB_TOKEN }}" >> ~/.Renviron
        shell: bash

      - uses: cachix/install-nix-action@v31
        with:
          nix_path: nixpkgs=https://github.com/rstats-on-nix/nixpkgs/archive/refs/heads/r-daily.tar.gz

      - uses: cachix/cachix-action@v14
        with:
          name: rstats-on-nix

      - name: devtools::test() via nix-shell
        run: nix-shell --run "Rscript -e \"devtools::test(stop_on_failure = TRUE)\""

```

The workflow builds the same shell you use locally and uses our `rstats-on-nix`
binary cache for fast, reproducible builds. Any failure signals that
newly published CRAN may be incompatible. Having the tests run on a schedule
is a safe way to catch them very early and avoid the dreaded 2 weeks notice 
from CRAN to fix your package!

## Summary

By defining your package environment with `{rix}`, committing the
`default.nix`, and reusing it across local development and CI/CD, you
build confidence that your package remains compatible with the evolving
R ecosystem. Regularly updating the snapshot keeps you close to the
latest CRAN state while still benefiting from the reproducibility that
Nix provides.