neovim: Use vim-crystal from nixpkgs/master

Nix flakes makes it easy to mix and match packages from any git
repository, which includes being able to use multiple nixpkgs branches.

flake.lock

@@ -363,6 +363,22 @@
         "type": "github"
       }
     },
+    "nixpkgs-master": {
+      "locked": {
+        "lastModified": 1686254953,
+        "narHash": "sha256-TlfkVPJQiVt5K2+pm1uhpvxkyloWu1xPOTxoVBi4tQc=",
+        "owner": "NixOS",
+        "repo": "nixpkgs",
+        "rev": "cc4e1f69ed9c4cce1abc6a9ef0a91b71c4a52004",
+        "type": "github"
+      },
+      "original": {
+        "owner": "NixOS",
+        "ref": "master",
+        "repo": "nixpkgs",
+        "type": "github"
+      }
+    },
     "root": {
       "inputs": {
         "crystal-flake": "crystal-flake",
@@ -371,6 +387,7 @@
         "hyprland": "hyprland",
         "nix-gaming": "nix-gaming",
         "nixpkgs": "nixpkgs",
+        "nixpkgs-master": "nixpkgs-master",
         "stylix": "stylix"
       }
     },

flake.nix

@@ -28,6 +28,7 @@
 
   inputs = {
     nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    nixpkgs-master.url = "github:NixOS/nixpkgs/master";
 
     home-manager = {
       url = "github:nix-community/home-manager/master";

modules/neovim/default.nix

@@ -1,4 +1,6 @@
-{pkgs, ...}: {
+{pkgs, nixpkgs-master, ...}: let
+  VARIABLES = import ../../src/variables.nix;
+in {
   programs.neovim.enable = true;
 
   home-manager.sharedModules = [
@@ -222,6 +224,7 @@
           csv-vim
           rust-vim
           neoformat
+          nixpkgs-master.legacyPackages.${VARIABLES.system}.vimPlugins.vim-crystal
         ];
       };
     }