tools: add nix-ast-dump

[inclyc]

also add an ast dump utility, produces indented output:

[user@system]$ build/nix-ast-dump ~flakes/shell.nix
 ExprLambda: ({ pkgs ? (let lock = (((builtins).fromJSON ((builtins).readFile ~flakes/flake.lock))).nodes.nixpkgs.locked; nixpkgs = (fetchTarball { sha256 = (lock).narHash; url = ("https://github.com/nixos/nixpkgs/archive/" + (lock).rev + ".tar.gz"); }); in (import nixpkgs { overlays = [ ]; })), ... }: ((pkgs).mkShell { NIX_CONFIG = "extra-experimental-features = nix-command flakes repl-flake"; nativeBuildInputs = (with pkgs; [ (nix) (home-manager) (git) (sops) (gnupg) (age) ]); }))
  ExprLet: (let lock = (((builtins).fromJSON ((builtins).readFile ~flakes/flake.lock))).nodes.nixpkgs.locked; nixpkgs = (fetchTarball { sha256 = (lock).narHash; url = ("https://github.com/nixos/nixpkgs/archive/" + (lock).rev + ".tar.gz"); }); in (import nixpkgs { overlays = [ ]; }))
   ExprAttrs: { lock = (((builtins).fromJSON ((builtins).readFile ~flakes/flake.lock))).nodes.nixpkgs.locked; nixpkgs = (fetchTarball { sha256 = (lock).narHash; url = ("https://github.com/nixos/nixpkgs/archive/" + (lock).rev + ".tar.gz"); }); }
    ExprSelect: (((builtins).fromJSON ((builtins).readFile ~flakes/flake.lock))).nodes.nixpkgs.locked
     ExprCall: ((builtins).fromJSON ((builtins).readFile ~flakes/flake.lock))
      ExprCall: ((builtins).readFile ~flakes/flake.lock)
       ExprPath: ~flakes/flake.lock
       ExprSelect: (builtins).readFile
        ExprVar: builtins
      ExprSelect: (builtins).fromJSON
       ExprVar: builtins
    ExprCall: (fetchTarball { sha256 = (lock).narHash; url = ("https://github.com/nixos/nixpkgs/archive/" + (lock).rev + ".tar.gz"); })
     ExprAttrs: { sha256 = (lock).narHash; url = ("https://github.com/nixos/nixpkgs/archive/" + (lock).rev + ".tar.gz"); }
      ExprConcatStrings: ("https://github.com/nixos/nixpkgs/archive/" + (lock).rev + ".tar.gz")
       ExprString: "https://github.com/nixos/nixpkgs/archive/"
       ExprSelect: (lock).rev
        ExprVar: lock
       ExprString: ".tar.gz"
      ExprSelect: (lock).narHash
       ExprVar: lock
     ExprVar: fetchTarball
   ExprCall: (import nixpkgs { overlays = [ ]; })
    ExprVar: nixpkgs
    ExprAttrs: { overlays = [ ]; }
     ExprList: [ ]
    ExprVar: import
  ExprCall: ((pkgs).mkShell { NIX_CONFIG = "extra-experimental-features = nix-command flakes repl-flake"; nativeBuildInputs = (with pkgs; [ (nix) (home-manager) (git) (sops) (gnupg) (age) ]); })
   ExprAttrs: { NIX_CONFIG = "extra-experimental-features = nix-command flakes repl-flake"; nativeBuildInputs = (with pkgs; [ (nix) (home-manager) (git) (sops) (gnupg) (age) ]); }
    ExprString: "extra-experimental-features = nix-command flakes repl-flake"
    ExprWith: (with pkgs; [ (nix) (home-manager) (git) (sops) (gnupg) (age) ])
     ExprVar: pkgs
     ExprList: [ (nix) (home-manager) (git) (sops) (gnupg) (age) ]
      ExprVar: nix
      ExprVar: home-manager
      ExprVar: git
      ExprVar: sops
      ExprVar: gnupg
      ExprVar: age
   ExprSelect: (pkgs).mkShell
    ExprVar: pkgs

# Shell for bootstrapping flake-enabled nix and other tooling
{ pkgs ? # If pkgs is not defined, instanciate nixpkgs from locked commit
  let
    lock = (builtins.fromJSON (builtins.readFile ./flake.lock)).nodes.nixpkgs.locked;
    nixpkgs = fetchTarball {
      url = "https://github.com/nixos/nixpkgs/archive/${lock.rev}.tar.gz";
      sha256 = lock.narHash;
    };
  in
  import nixpkgs { overlays = [ ]; }
, ...
}: pkgs.mkShell {
  NIX_CONFIG = "extra-experimental-features = nix-command flakes repl-flake";
  nativeBuildInputs = with pkgs; [
    nix
    home-manager
    git

    sops
    gnupg
    age
  ];
}

[inclyc]

TODO: add regression tests.