Use pre-commit hook from pre-commit-hooks.nix

.gitignore

@@ -1,2 +1,3 @@
-wordclock_credentials.py
+/.pre-commit-config.yaml
 __pycache__
+wordclock_credentials.py

.pre-commit-config.yaml

@@ -1,6 +0,0 @@
-repos:
-  - repo: https://github.com/psf/black
-    rev: stable
-    hooks:
-      - id: black
-        language_version: python3

default.nix

@@ -0,0 +1,11 @@
+let
+  nix-pre-commit-hooks = import (builtins.fetchTarball "https://github.com/cachix/pre-commit-hooks.nix/tarball/master");
+in
+{
+  pre-commit-check = nix-pre-commit-hooks.run {
+    src = ./.;
+    hooks = {
+      black.enable = true;
+    };
+  };
+}

shell.nix

@@ -2,13 +2,9 @@
 
 pkgs.mkShell {
   nativeBuildInputs = with pkgs; [
-    gitAndTools.pre-commit
-    (python3.withPackages(ps: [ ps.virtualenv ]))
+    nixpkgs-fmt
   ];
   shellHook = ''
-    # black’s pre-commit hook builds a wheel (zip file) for black and fails
-    # when the timestamp is lower than 1980 (due to zip limitations)
-    export SOURCE_DATE_EPOCH=315532800
-    pre-commit install -f >/dev/null
+    ${(import ./default.nix).pre-commit-check.shellHook}
   '';
 }