.gitignore

.bundle/
.overcommit.yml
vendor/

README.md

How to verify:

1. Install nix
2. Clone this gist and install overcommit twice in nix-shell:

git clone https://gist.github.com/ento/a77fb97f581bdea4ed27c845107308bf
# or git@gist.github.com:a77fb97f581bdea4ed27c845107308bf.git
cd a77fb97f581bdea4ed27c845107308bf
nix-shell
overcommit --install
overcommit --install # this fails
[ -w .git/hooks/overcommit-hook ] && echo "Master hook is writable" || echo "Master hooks is not writable"

Gemfile

# frozen_string_literal: true

source "https://rubygems.org"

group :development do
  gem 'overcommit'
end

Gemfile.lock

GEM
  remote: https://rubygems.org/
  specs:
    childprocess (0.9.0)
      ffi (~> 1.0, >= 1.0.11)
    ffi (1.9.25)
    iniparse (1.4.4)
    overcommit (0.46.0)
      childprocess (~> 0.6, >= 0.6.3)
      iniparse (~> 1.4)

PLATFORMS
  ruby

DEPENDENCIES
  overcommit

BUNDLED WITH
   1.16.3

gemset.nix

{
  childprocess = {
    dependencies = ["ffi"];
    source = {
      remotes = ["https://rubygems.org"];
      sha256 = "0a61922kmvcxyj5l70fycapr87gz1dzzlkfpq85rfqk5vdh3d28p";
      type = "gem";
    };
    version = "0.9.0";
  };
  ffi = {
    source = {
      remotes = ["https://rubygems.org"];
      sha256 = "0jpm2dis1j7zvvy3lg7axz9jml316zrn7s0j59vyq3qr127z0m7q";
      type = "gem";
    };
    version = "1.9.25";
  };
  iniparse = {
    source = {
      remotes = ["https://rubygems.org"];
      sha256 = "1xbik6838gfh5yq9ahh1m7dzszxlk0g7x5lvhb8amk60mafkrgws";
      type = "gem";
    };
    version = "1.4.4";
  };
  overcommit = {
    dependencies = ["childprocess" "iniparse"];
    source = {
      remotes = ["https://rubygems.org"];
      sha256 = "0jfgpprjkq7hkyk7z0wc8difnnzmvmkin0b3bgsmnh6vvpyrz0mn";
      type = "gem";
    };
    version = "0.46.0";
  };
}

Makefile

all: gemset.nix

gemset.nix: Gemfile
	nix-shell -p bundix --run 'bundix --magic --lock'

shell.nix

{ pkgs ? import <nixpkgs> {} }:
let
  gems = pkgs.bundlerEnv {
    name = "overcommit-nix-mcve";
    ruby = pkgs.ruby_2_5;
    gemdir = ./.;
    groups = ["default" "development" "test"];
  };
in
pkgs.mkShell {
  buildInputs = [
    pkgs.ruby_2_5
    gems
  ];
}