use niv

nix/sources.json

@@ -1,4 +1,16 @@
 {
+    "niv": {
+        "branch": "master",
+        "description": "Easy dependency management for Nix projects",
+        "homepage": "https://github.com/nmattia/niv",
+        "owner": "nmattia",
+        "repo": "niv",
+        "rev": "e0ca65c81a2d7a4d82a189f1e23a48d59ad42070",
+        "sha256": "1pq9nh1d8nn3xvbdny8fafzw87mj7gsmp6pxkdl65w2g18rmcmzx",
+        "type": "tarball",
+        "url": "https://github.com/nmattia/niv/archive/e0ca65c81a2d7a4d82a189f1e23a48d59ad42070.tar.gz",
+        "url_template": "https://github.com/<owner>/<repo>/archive/<rev>.tar.gz"
+    },
     "nixpkgs": {
         "branch": "nixpkgs-unstable",
         "description": "Nix Packages collection",

shell.nix

@@ -59,6 +59,11 @@ let
 
     # faster builds - see https://github.com/rtfeldman/roc/blob/trunk/BUILDING_FROM_SOURCE.md#use-lld-for-the-linker
     llvmPkgs.lld
+
+    # meta-tools
+    # note: niv manages its own nixpkgs so it doesn't need pkgs.callPackage. Do
+    # `cachix use niv` to get cached builds!
+    (import sources.niv { }).niv
   ];
 in pkgs.mkShell {
   buildInputs = inputs ++ darwinInputs ++ linuxInputs;