add nix-prefetch-source (#21734)

pkgs/tools/package-management/nix-update-source/default.nix

···
+{ lib, pkgs, fetchFromGitHub, python3Packages, nix-prefetch-scripts }:
+python3Packages.buildPythonApplication rec {
+  version = "0.2.1";
+  name = "nix-update-source-${version}";
+  src = fetchFromGitHub {
+    owner = "timbertson";
+    repo = "nix-update-source";
+    rev = "version-${version}";
+    sha256 = "1w3aj0kjp8zhxkzqxnm5srrsqsvrmxhn4sqkr4kjffh61jg8jq8a";
+  };
+  propagatedBuildInputs = [ nix-prefetch-scripts ];
+  passthru = {
+    fetch = path:
+      let
+        fetchers = {
+          # whitelist of allowed fetchers
+          inherit (pkgs) fetchgit fetchurl fetchFromGitHub;
+        };
+        json = lib.importJSON path;
+        fetchFn = builtins.getAttr json.fetch.fn fetchers;
+        src = fetchFn json.fetch.args;
+      in
+      json // { inherit src; };
+  };
+  meta = {
+    description = "Utility to autimate updating of nix derivation sources";
+    maintainers = with lib.maintainers; [ timbertson ];
+  };
+}

pkgs/top-level/all-packages.nix

···
     nix-prefetch-zip
     nix-prefetch-scripts;
 
+  nix-update-source = callPackage ../tools/package-management/nix-update-source {};
+
   nix-template-rpm = callPackage ../build-support/templaterpm { inherit (pythonPackages) python toposort; };
 
   nix-repl = callPackage ../tools/package-management/nix-repl { };