#nix #flake

---
Nix flakes are source trees containing a file `flake.nix` at their root. The file `flake.nix` provides a standardized way to provide [[Zettelkast/Index/Nix]] artifacts. It's like a package manager for [[Zettelkast/Index/Nix]]. A flake can be dependent on other Flakes and it's possible to pin dependencies to exact revisions by using a `flake.lock` file.

Nix flake evaluation is hermetic, meaning that it produces the same result wherever it's built.k

The feature can be enabled in `~/.config/nix/nix.conf`:

```
experimental-features = nix-command flakes
```

To initialize in a repo: `nix flake init`.

In flakes dependencies have to be specified explicitly and MUST be locked to specific versions therefore it's no longer allowed to use the nixpkgs found in `NIX_PATH` by referencing it like `<nixpkgs>`.

Output of a Flake is an arbitrary [[Zettelkast/Index/Nix]] value such as a package, [[NixOS]] module or library function.
Commands `nix build` and `nix shell` will build the output `packages.<system>.default` unless we specify another output, for example: `nix shell .#checks.aarch64-linux.build`.


**Inputs**
```
{
  inputs = {
    # GitHub repository as the data source, specifying the master branch.
    # This is the most common input format.
    nixpkgs.url = "github:Mic92/nixpkgs/master";
    # Git URL, applicable to any Git repository using the https/ssh protocol.
    git-example.url = "git+https://git.somehost.tld/user/path?ref=branch";
    # Git URL by tag, applicable to any Git repository using the https/ssh protocol.
    git-example-tag.url = "git+https://git.somehost.tld/user/path?tag=x.y.x";
    # Github URL by pull request.
    git-pr.url = "github:NixOS/nixpkgs?ref=pull/349351/head";
    # Git URL with submodules, applicable to any Git repository using the https/ssh protocol. 
    git-example-submodule.url = "git+https://git.somehost.tld/user/path?submodules=1";
    # Archive File URL, needed in case your input use LFS.
    # Regular git input doesn't support LFS yet.
    git-example-lfs.url = "https://codeberg.org/solver-orgz/treedome/archive/master.tar.gz";
    # Similar to fetching a Git repository, but using the ssh protocol
    # with key authentication. Also uses the shallow=1 parameter
    # to avoid copying the .git directory.
    ssh-git-example.url = "git+ssh://git@github.com/ryan4yin/nix-secrets.git?shallow=1";
    # It's also possible to directly depend on a local Git repository.
    git-directory-example.url = "git+file:/path/to/repo?shallow=1";
    # Using the `dir` parameter to specify a subdirectory.
    nixpkgs.url = "github:foo/bar?dir=shu";
    # Local folder (if using an absolute path, the 'path:' prefix can be omitted).
    directory-example.url = "path:/path/to/repo";

    # If the data source is not a flake, set flake=false.
    # `flake=false` is usually used to include additional source code,
    #   configuration files, etc.
    # In Nix code, you can directly reference files within
    #   it using "${inputs.bar}/xxx/xxx" notation.
    # For example, import "${inputs.bar}/xxx/xxx.nix" to import a specific nix file,
    # or use "${inputs.bar}/xx/xx" as a path parameter for certain options.
    bar = {
      url = "github:foo/bar/branch";
      flake = false;
    };

    sops-nix = {
      url = "github:Mic92/sops-nix";
      # `follows` is the inheritance syntax within inputs.
      # Here, it ensures that sops-nix's `inputs.nixpkgs` aligns with
      # the current flake's inputs.nixpkgs,
      # avoiding inconsistencies in the dependency's nixpkgs version.
      inputs.nixpkgs.follows = "nixpkgs";
    };

    # Lock the flake to a specific commit.
    nix-doom-emacs = {
      url = "github:vlaci/nix-doom-emacs?rev=238b18d7b2c8239f676358634bfb32693d3706f3";
      flake = false;
    };
  };

  outputs = { self, ... }@inputs: { ... };
}
```

---
[Flakes Wiki](https://nixos.wiki/wiki/Flakes)