bahaghari: use npins for pinning nixpkgs branches

This makes it possible for easier way to contribute with non-flakes
usage.

subprojects/bahaghari/flake.nix

@@ -2,15 +2,16 @@
   description = "Specialized set of Nix modules for generating and applying themes.";
 
   inputs = {
-    nixpkgs.url = "github:NixOS/nixpkgs/nixpkgs-unstable";
     flake-utils.url = "github:numtide/flake-utils";
   };
 
-  outputs = inputs@{ self, nixpkgs, ... }:
-    let systems = inputs.flake-utils.lib.defaultSystems;
+  outputs = inputs@{ self, ... }:
+    let
+      systems = inputs.flake-utils.lib.defaultSystems;
+      sources = import ./npins;
     in inputs.flake-utils.lib.eachSystem systems
       (system: {
         devShells.default =
-          import ./shell.nix { pkgs = import nixpkgs { inherit system; }; };
+          import ./shell.nix { pkgs = import sources.nixos-stable { inherit system; }; };
       }) // import ./default.nix { };
 }

subprojects/bahaghari/npins/default.nix

@@ -0,0 +1,80 @@
+# Generated by npins. Do not modify; will be overwritten regularly
+let
+  data = builtins.fromJSON (builtins.readFile ./sources.json);
+  version = data.version;
+
+  mkSource =
+    spec:
+    assert spec ? type;
+    let
+      path =
+        if spec.type == "Git" then
+          mkGitSource spec
+        else if spec.type == "GitRelease" then
+          mkGitSource spec
+        else if spec.type == "PyPi" then
+          mkPyPiSource spec
+        else if spec.type == "Channel" then
+          mkChannelSource spec
+        else
+          builtins.throw "Unknown source type ${spec.type}";
+    in
+    spec // { outPath = path; };
+
+  mkGitSource =
+    {
+      repository,
+      revision,
+      url ? null,
+      hash,
+      branch ? null,
+      ...
+    }:
+    assert repository ? type;
+    # At the moment, either it is a plain git repository (which has an url), or it is a GitHub/GitLab repository
+    # In the latter case, there we will always be an url to the tarball
+    if url != null then
+      (builtins.fetchTarball {
+        inherit url;
+        sha256 = hash; # FIXME: check nix version & use SRI hashes
+      })
+    else
+      assert repository.type == "Git";
+      let
+        urlToName =
+          url: rev:
+          let
+            matched = builtins.match "^.*/([^/]*)(\\.git)?$" repository.url;
+
+            short = builtins.substring 0 7 rev;
+
+            appendShort = if (builtins.match "[a-f0-9]*" rev) != null then "-${short}" else "";
+          in
+          "${if matched == null then "source" else builtins.head matched}${appendShort}";
+        name = urlToName repository.url revision;
+      in
+      builtins.fetchGit {
+        url = repository.url;
+        rev = revision;
+        inherit name;
+        # hash = hash;
+      };
+
+  mkPyPiSource =
+    { url, hash, ... }:
+    builtins.fetchurl {
+      inherit url;
+      sha256 = hash;
+    };
+
+  mkChannelSource =
+    { url, hash, ... }:
+    builtins.fetchTarball {
+      inherit url;
+      sha256 = hash;
+    };
+in
+if version == 3 then
+  builtins.mapAttrs (_: mkSource) data.pins
+else
+  throw "Unsupported format version ${toString version} in sources.json. Try running `npins upgrade`"

subprojects/bahaghari/npins/sources.json

@@ -0,0 +1,29 @@
+{
+  "pins": {
+    "nixos-stable": {
+      "type": "Git",
+      "repository": {
+        "type": "GitHub",
+        "owner": "NixOS",
+        "repo": "nixpkgs"
+      },
+      "branch": "nixos-24.05",
+      "revision": "b3b2b28c1daa04fe2ae47c21bb76fd226eac4ca1",
+      "url": "https://github.com/NixOS/nixpkgs/archive/b3b2b28c1daa04fe2ae47c21bb76fd226eac4ca1.tar.gz",
+      "hash": "06jxcg73ymibvfg3czmq856f84bkhxhqgwa51mf87xprjz74zxks"
+    },
+    "nixos-unstable": {
+      "type": "Git",
+      "repository": {
+        "type": "GitHub",
+        "owner": "NixOS",
+        "repo": "nixpkgs"
+      },
+      "branch": "nixos-unstable",
+      "revision": "57610d2f8f0937f39dbd72251e9614b1561942d8",
+      "url": "https://github.com/NixOS/nixpkgs/archive/57610d2f8f0937f39dbd72251e9614b1561942d8.tar.gz",
+      "hash": "0k8az8vmfdk1n8xlza252sqk0hm1hfc7g67adin6jxqaab2s34n9"
+    }
+  },
+  "version": 3
+}

subprojects/bahaghari/shell.nix

@@ -1,7 +1,19 @@
-{ pkgs ? import <nixpkgs> { } }:
+let
+  sources = import ./npins;
+in
+{ pkgs ? import sources.nixos-stable { } }:
 
 with pkgs;
 
 mkShell {
-  inputsFrom = [ nix ];
+  inputsFrom = [
+    nix
+  ];
+
+  packages = [
+    npins
+
+    treefmt
+    nixpkgs-fmt
+  ];
 }

subprojects/bahaghari/tests/default.nix

@@ -1,7 +1,10 @@
 # This is the unit cases for our Nix project.
-{ pkgs ? import <nixpkgs> { } }:
-
+{ branch ? "nixos-stable" }:
 
+let
+  sources = import ../npins;
+  pkgs = import sources.${branch} { };
+in
 {
   lib = import ./lib { inherit pkgs; };
   #modules = import ./modules { inherit pkgs; };