allow specifing the version using nix-build nix --arg version '"0.1.0"'

run `nix-build nix` to build without flakes

flake.nix

@@ -1,3 +1,5 @@
+# ml2 ts=2 sts=2 sw=2
+
 {
   description = "A simple Go package";
 
@@ -22,34 +24,14 @@
       # Nixpkgs instantiated for supported system types.
       nixpkgsFor = forAllSystems (system: import nixpkgs { inherit system; });
 
-    in
+    in {
-    {
-
       # Provide some binary packages for selected system types.
       packages = forAllSystems (system:
       let
         pkgs = nixpkgsFor.${system};
       in
       {
-          tt = pkgs.buildGoModule {
+        tt = pkgs.callPackage ./nix/package.nix { version = version; };
-            pname = "tt";
-            inherit version;
-            # In 'nix develop', we don't need a copy of the source tree
-            # in the Nix store.
-            src = ./.;
-
-            # This hash locks the dependencies of this package. It is
-            # necessary because of how Go requires network access to resolve
-            # VCS.  See https://www.tweag.io/blog/2021-03-04-gomod2nix/ for
-            # details. Normally one can build with a fake hash and rely on native Go
-            # mechanisms to tell you what the hash should be or determine what
-            # it should be "out-of-band" with other tooling (eg. gomod2nix).
-            # To begin with it is recommended to set this, but one must
-            # remember to bump this hash when your dependencies change.
-            # vendorHash = pkgs.lib.fakeHash;
-
-            vendorHash = "sha256-cpjMZr+kP+XyXRxK4YI/lGHl97IROFVVz8DrID0vi6E=";
-          };
       });
 
       # Add dependencies that are only needed for development

nix/default.nix

@@ -0,0 +1,4 @@
+# ml2 ts=2 sts=2 sw=2
+
+with import <nixpkgs> {};
+{version ? "HEAD"}: callPackage ./package.nix {inherit version;}

nix/package.nix

@@ -0,0 +1,21 @@
+# ml2 ts=2 sts=2 sw=2
+{buildGoModule, version ? "HEAD"}: buildGoModule {
+  pname = "tt";
+  inherit version;
+
+  # In 'nix develop', we don't need a copy of the source tree
+  # in the Nix store.
+  src = ./..;
+
+  # This hash locks the dependencies of this package. It is
+  # necessary because of how Go requires network access to resolve
+  # VCS.  See https://www.tweag.io/blog/2021-03-04-gomod2nix/ for
+  # details. Normally one can build with a fake hash and rely on native Go
+  # mechanisms to tell you what the hash should be or determine what
+  # it should be "out-of-band" with other tooling (eg. gomod2nix).
+  # To begin with it is recommended to set this, but one must
+  # remember to bump this hash when your dependencies change.
+  # vendorHash = pkgs.lib.fakeHash;
+
+  vendorHash = "sha256-cpjMZr+kP+XyXRxK4YI/lGHl97IROFVVz8DrID0vi6E=";
+}