nix_for_rustaceans/slides/slides.md

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marp: true
lang: en-US
title: Reproducible development environments with Nix
theme: nix_talk
transition: fade
paginate: true
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---

# Reproducible development environments with Nix

#### Kateřina "Kate" Churanová

---

# What is Nix

- Purely functional programming language
- Package manager
- multiplatform (Linux, Mac OS, BSD-ish)

---

# What is Nix NOT

- Easy to learn
- Well documented
- Opinionated

---
# What is it for

- Access to huge repository of various packages
- Declarative way to define builds and build enviroment and their configuration
- Coexistence of various versions of software and libraries on the same system

*Every simple configuration language will eventually end up being turing complete*

---

# Nix derivation

- "Package"
- evaluates to store derivation in `/nix/store/`
- `2n45ikclc8d5fhzkvg1197qlc2zk3s64-rustc-1.77.2.drv`
<!-- This prevents conflicts and allows various versions to be installed at ones. -->

---

# Nix flake

- Unstable, but widely used
- New way of creating nix derivations
- Lock file version pinning
- Allows reproducibility

---

```nix
{
  inputs = {
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
  };
  outputs =
    { self, nixpkgs }:
    {
      packages.x86_64-linux.default = nixpkgs.legacyPackages.x86_64-linux.hello;
      packages.x86_64-linux.foobar = nixpkgs.legacyPackages.x86_64-linux.fortune;
    };
}
```

---

![bg width:80%](../assets/pictures/flake_relations.svg)

---

# Nix developer shell

- `nix develop`
- builds all flake dependencies, but not the flake itself
- sets up the development environment

---

# Nix direnv

- https://github.com/nix-community/nix-direnv
- Activates developer shell automatically

---

# Frameworks

- Pure nix solution is usable, but tedious with ugly boilerplate
- [Numtide: flake-utils](https://github.com/ursi/numtide-flake-utils)
- [Hercules CI: Flake Parts](https://flake.parts/)

<!-- Both are fairly lightweight and remove boilerplate. -->

---

# Flake parts - Minimal modular framework

## Dev environment management

- Devshell
- Devenv

## Rust project building

- NCI (Nix cargo integration)

---

# Basic flake parts project

```nix
{
  inputs = {
    flake-parts.url = "github:hercules-ci/flake-parts";
    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
  };

  outputs = inputs@{ flake-parts, ... }:
    flake-parts.lib.mkFlake { inherit inputs; } {
      imports = [
        # Modules go here
      ];
      systems = [ "x86_64-linux" "aarch64-linux" "aarch64-darwin" "x86_64-darwin" ];
      perSystem = { config, self', inputs', pkgs, system, ... }: {
        packages.default = pkgs.hello;
      };
    };
}
```

---

# Fun begins with Rust

### flake.nix

```nix
  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
    nci = {
      url = "github:yusdacra/nix-cargo-integration";
      inputs.nixpkgs.follows = "nixpkgs";
    };
    flake-parts = {
      url = "github:hercules-ci/flake-parts";
      inputs.nixpkgs-lib.follows = "nixpkgs";
    };
  };
```

---

```nix
outputs = inputs @ {
    flake-parts,
    nci,
    ...
  }:
    flake-parts.lib.mkFlake {inherit inputs;} {
      systems = ["x86_64-linux"];
      imports = [
        nci.flakeModule
        ./crates.nix
      ];
      perSystem = {
        pkgs,
        config,
        ...
      }: let
        crateName = "my-crate"
        crateOutputs = config.nci.outputs.${crateName};
      in {
        devShells.default = crateOutputs.devShell;
        packages.default = crateOutputs.packages.release;
      };
    };
```

---

### crates.nix

```nix
{...}: {
  perSystem = {
    pkgs,
    config,
    ...
  }: let
    crateName = "my-crate";
  in {
    nci.projects."simple".path = ./.;
    nci.crates.${crateName} = {};
  };
}
```

---

# Why all of this though?

- Reproducible environment with pinned Rust version
- Predictable dependencies
- Plenty of other tools for your disposal
- Extremely simple generation of lightweight OCI containers

---

```nix
          packages.container = pkgs.dockerTools.streamLayeredImage {
            name = crateName;
            tag = "latest";
            contents = [ ];
            config = {
              Cmd = [ "${crateOutputs.packages.release}/bin/my-crate" ];
            };
          };
```

---

# Other learning materials
### Fasterthanlime's series on Rust development with Nix
[https://fasterthanli.me/series/building-a-rust-service-with-nix](https://fasterthanli.me/series/building-a-rust-service-with-nix) 
### Nix pills
[https://nixos.org/guides/nix-pills/](https://nixos.org/guides/nix-pills/)
### This presentation and examples
[https://code.nolog.cz/shine/nix_for_rustaceans](https://code.nolog.cz/shine/nix_for_rustaceans)