veloren/nix/README.md

## Read this first!

Since this repo uses a new Nix feature called "Flakes", it is recommended to enable it.
It massively improves the `nix` CLI UX, and adds many useful features.
We include instructions for Nix without flakes enabled, but using flakes is the recommended way.

See the [NixOS wiki](https://nixos.wiki/wiki/Flakes) for information on how to enable and use flakes.

It is recommended to first setup the [Cachix](https://cachix.org) cache to save time with builds:
```shell
nix shell nixpkgs#cachix -c cachix use veloren-nix
# or if you don't have flakes:
nix-shell -p cachix --run "cachix use veloren-nix"
```

As this repository uses `git-lfs`, please make sure `git-lfs` is in your path.
If you have a locally cloned repo, you can make sure it is setup with:
```shell
git lfs install --local && git lfs fetch && git lfs checkout
```
This should be automatically done if you use the development shell.

## Usage for players

### With flakes

If you just want to run the game without installing it, you can do so with:
```shell
# Voxygen (the default):
nix run gitlab:veloren/veloren
# Server CLI:
nix run gitlab:veloren/veloren#veloren-server-cli
# or if you have a local repo
nix run .
nix run .#veloren-server-cli
```

To install the game into your user profile:
```shell
# Voxygen:
nix profile install gitlab:veloren/veloren
# Server CLI:
nix profile install giltab:veloren/veloren#veloren-server-cli
# or if you have a local repo:
nix profile install .
nix profile install .#veloren-server-cli
```

To install (for example) Voxygen on your system, the NixOS configuration (if you use a flake based setup) could look something like this:
```nix
{ description = "NixOS configuration with flakes";

  inputs.veloren.url = gitlab:veloren/veloren;

  outputs = { self, nixpkgs, veloren }: {
    nixosConfigurations.<your-hostname> = nixpkgs.lib.nixosSystem rec {
      system = <your-system-arch>;
      # ...
      modules = [
        # add to your overlay so that the packages appear in pkgs
        # for subsequent modules
        ({...}: {
          nixpkgs.overlays = [
            # ...
            (final: prev: {
              inherit (veloren.packages."${system}") veloren-voxygen;
            })
          ];

          # You can also add the flake to your registry
          nix.registry.veloren.flake = veloren;
          # with this, you can run latest master
          # regardless of version installed like this:
          # nix run veloren/master
        })

        # some module
        ({ pkgs, ... }: {
          environment.systemPackages = [
            pkgs.veloren-voxygen
          ];
        })
        # ...
      ];
    };
  };
}
```

### Without flakes

You can do this to run the game without installing it (you will need a local clone of the repo though):
```shell
# build the game
nix-build nix/default.nix
# run it
./result/bin/veloren-voxygen
# or for server cli
./result-2/bin/veloren-server-cli
```

To install Voxygen and server CLI into user profile:
```shell
nix-env -f nix/default.nix -i
```

### Notes for non-NixOS setups

You'll need to use [nixGL](https://github.com/guibou/nixGL) to be able to run the game (after installing it):
```shell
# For Intel and AMD:
nixGLIntel veloren-voxygen
# For Nvidia:
nixGLNvidia veloren-voxygen
```

## Usage for developers

The development shell automatically setups the Cachix cache for you, so it is recommended to be in the dev shell always.
If you have the Cachix cache setup in `~/.config/nix/nix.conf` (as described in the beginning of this document), then this isn't a necessity.

### With flakes

To enter a shell environment with the necessary tools:
```shell
nix develop
```

### Without flakes

To enter the development shell:
```shell
nix-shell nix/shell.nix
```

### Direnv

This only works if you have flakes. There is an issue with the git-lfs hook in `shellHook` erroring out with `use nix`, so you'll have to enable flakes if you want to use the `envrc` file included.

If you have [direnv](https://direnv.net) and [nix-direnv](https://github.com/nix-community/nix-direnv) on your system, you can copy the `envrc` file to the root of the repository as `.envrc`:
```shell
cp nix/envrc .envrc
```

## Managing dependencies

### With flakes

If a specific revision is specified in `flake.nix`, you will have to update that first, either by specifying a new desired revision or by removing it.

You can update the dependencies individually or all at once from the root of the project:
```shell
# only nixpkgs
nix flake update --update-input nixpkgs
# everything
nix flake update --recreate-lock-file
```

### Without flakes

It is inadvised to update revisions without the use of `nix flake update` as it's both tedious and error-prone to attempt setting all fields to their correct values in both `flake.nix` and `flake.lock`, but if you need to do it for testing, `flake.lock` is where legacy nix commands get the input revisions from (through `flake-compat`), regardless of what is specified in `flake.nix` (see https://github.com/edolstra/flake-compat/issues/10). 

Modify the relevant `rev` field in `flake.lock` to what you need - you can use `nix-prefetch-git` to find an up-to-date revision. Leave the `narHash` entry as is and attempt a rebuild to find out what its value should be.

### Generating Cargo.nix

Enter the development shell.

To update `Cargo.nix` (and `crate-hashes.json`) using latest `Cargo.lock`, run:
```shell
crate2nix generate -f ../Cargo.toml
```

### Rust toolchain

If the `rust-toolchain` file is updated, you will need to update the `sha256` hash in the `nix/rustPkgs.nix` file.

Trying to build the derivation should give you the correct hash to put in.

## Formatting

Use [nixpkgs-fmt](https://github.com/nix-community/nixpkgs-fmt) to format files.

To format every Nix file:
```shell
nixpkgs-fmt flake.nix nix/*.nix
# or
nixpkgs-fmt **/**.nix
```