add a nix environment to ensure a reproducible build

.envrc.default

@@ -0,0 +1,2 @@
+watch_file pyproject.toml
+use flake

.gitignore

@@ -1,3 +1,5 @@
+.envrc
+
 # Byte-compiled / optimized / DLL files
 __pycache__/
 *.py[cod]

.pre-commit-config.yaml

@@ -1,5 +1,4 @@
 ci:
-  skip: [pytest]
   autoupdate_schedule: monthly
   autoupdate_commit_msg: '[pre-commit.ci] pre-commit autoupdate'
 repos:
@@ -42,12 +41,4 @@ repos:
     hooks:
       - id: mypy
         exclude: tests
-  - repo: local
-    hooks:
-      - id: pytest
-        name: pytest
-        entry: pytest
-        language: python
-        pass_filenames: false
-        always_run: true
-fail_fast: true
+fail_fast: false

flake.nix

@@ -0,0 +1,56 @@
+{
+  description = "A very basic flake";
+
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs?ref=nixos-unstable";
+
+    pyproject-nix = {
+      url = "github:nix-community/pyproject.nix";
+      inputs.nixpkgs.follows = "nixpkgs";
+    };
+
+    flake-utils.url = "github:numtide/flake-utils";
+  };
+
+  outputs =
+    {
+      self,
+      nixpkgs,
+      pyproject-nix,
+      flake-utils,
+    }:
+    flake-utils.lib.eachDefaultSystem (
+      system:
+      let
+        pkgs = import nixpkgs { inherit system; };
+
+        project = pyproject-nix.lib.project.loadPyproject { projectRoot = ./.; };
+        python = pkgs.python312;
+      in
+      {
+        devShells.default =
+          let
+            attrs = project.renderers.withPackages {
+              inherit python;
+              extras = [ "tests" ];
+              extraPackages = python-pkgs: [ python-pkgs.ipykernel ];
+            };
+            pythonEnv = python.withPackages attrs;
+          in
+          pkgs.mkShell {
+            packages =
+              [ pythonEnv ]
+              ++ (with pkgs; [
+                ruff
+                pre-commit
+                rustc # for pre-commit ruff
+                cargo # for pre-commit ruff
+              ]);
+            shellHook = ''
+              export PYTHONPATH="$(pwd)/src"
+              export PIP_NO_BINARY="ruff"
+            '';
+          };
+      }
+    );
+}