Add Nix flake as a build system

.gitignore

@@ -71,3 +71,6 @@ tcl
 
 # Ignore Jupyter Notebook related temp files
 .ipynb_checkpoints/
+
+# Nix
+/result*

default.nix

@@ -0,0 +1,3 @@
+(import (fetchTarball https://github.com/edolstra/flake-compat/archive/b4a34015c698c7793d592d66adbab377907a2be8.tar.gz) {
+  src = builtins.fetchGit ./.;
+}).defaultNix

flake.nix

@@ -0,0 +1,25 @@
+{
+  description = "Parse and compare all the package versions and all the ranges. From debian, npm, pypi, ruby and more. Process all the version range specs and expressions.";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
+  };
+
+  outputs = { self, nixpkgs }: ({
+    overlays.default = import ./overlay.nix;
+  }) // (
+    let
+      supportedSystems = [ "aarch64-darwin" "aarch64-linux" "x86_64-darwin" "x86_64-linux" ];
+      forAllSystems = f: nixpkgs.lib.genAttrs supportedSystems (system: f system);
+      nixpkgsFor = forAllSystems (system: self.overlays.default null nixpkgs.legacyPackages.${system});
+    in
+    {
+      packages = forAllSystems (system: rec {
+        python3Packages = {
+          inherit (nixpkgsFor.${system}.python3Packages) univers;
+        };
+        default = python3Packages.univers;
+      });
+    }
+  );
+}

overlay.nix

@@ -0,0 +1,42 @@
+final: prev: rec {
+  python3 = prev.python3.override {
+    packageOverrides = final: prev:
+      {
+        univers = python3Packages.callPackage
+          ({ lib
+           , buildPythonPackage
+           , git
+           , setuptools-scm
+           , attrs
+           , packaging
+           , pyparsing
+           , semantic-version
+           , semver
+           , black
+           , commoncode
+           , pytestCheckHook
+           , saneyaml
+           }: buildPythonPackage rec {
+            name = "univers";
+
+            src = ./.;
+
+            nativeBuildInputs = [ git setuptools-scm ];
+            propagatedBuildInputs = [ attrs packaging pyparsing semantic-version semver ];
+            checkInputs = [ black commoncode pytestCheckHook saneyaml ];
+
+            dontConfigure = true; # ./configure tries to setup virtualenv and downloads dependencies
+
+            pythonImportsCheck = [ "univers" ];
+
+            meta = with lib; {
+              description = "Library for parsing version ranges and expressions";
+              homepage = "https://github.com/nexB/univers";
+              license = with licenses; [ asl20 bsd3 mit ];
+            };
+          })
+          { };
+      };
+  };
+  python3Packages = prev.recurseIntoAttrs python3.pkgs;
+}

shell.nix

@@ -0,0 +1,3 @@
+(import (fetchTarball https://github.com/edolstra/flake-compat/archive/b4a34015c698c7793d592d66adbab377907a2be8.tar.gz) {
+  src = builtins.fetchGit ./.;
+}).shellNix