{
  description = "Neovim flake";

  inputs = {
    nixpkgs.url = "github:nixos/nixpkgs/nixos-unstable";
    flake-utils.url = "github:numtide/flake-utils";
  };

  outputs = { self, nixpkgs, flake-utils }:
    {
      overlay = final: prev:
        let
          pkgs = nixpkgs.legacyPackages.${prev.system};
        in
        rec {
          neovim = pkgs.neovim-unwrapped.overrideAttrs (oa: {
            version = "master";
            src = ../.;

            buildInputs = oa.buildInputs ++ pkgs.lib.optionals pkgs.stdenv.isDarwin (with pkgs.darwin.apple_sdk.frameworks; [
              CoreServices
            ]);
          });

          # a development binary to help debug issues
          neovim-debug =
            let
              stdenv = if pkgs.stdenv.isLinux then pkgs.llvmPackages_latest.stdenv else pkgs.stdenv;
            in
            ((neovim.override {
              lua = pkgs.luajit;
              inherit stdenv;
            }).overrideAttrs (oa: {

              dontStrip = true;
              NIX_CFLAGS_COMPILE = " -ggdb -Og";

              cmakeBuildType = "Debug";
              cmakeFlags = oa.cmakeFlags ++ [
                "-DMIN_LOG_LEVEL=0"
              ];

              disallowedReferences = [ ];
            }));

          # for neovim developers, beware of the slow binary
          neovim-developer =
            let
              lib = nixpkgs.lib;
              luacheck = pkgs.luaPackages.luacheck;
            in
            (neovim-debug.override ({ doCheck = pkgs.stdenv.isLinux; })).overrideAttrs (oa: {
              cmakeFlags = oa.cmakeFlags ++ [
                "-DLUACHECK_PRG=${luacheck}/bin/luacheck"
                "-DMIN_LOG_LEVEL=0"
                "-DENABLE_LTO=OFF"
              ] ++ pkgs.lib.optionals pkgs.stdenv.isLinux [
                # https://github.com/google/sanitizers/wiki/AddressSanitizerFlags
                # https://clang.llvm.org/docs/AddressSanitizer.html#symbolizing-the-reports
                "-DCLANG_ASAN_UBSAN=ON"
              ];
            });
        };
    } //
    flake-utils.lib.eachDefaultSystem (system:
      let
        pkgs = import nixpkgs {
          overlays = [ self.overlay ];
          inherit system;
        };

        lua = pkgs.lua5_1;

        pythonEnv = pkgs.python3.withPackages (ps: [
          ps.msgpack
          ps.flake8 # for 'make pylint'
        ]);
      in
      rec {

        packages = with pkgs; {
          default = neovim;
          inherit neovim neovim-debug neovim-developer;
        };

        checks = {
          pylint = pkgs.runCommandNoCC "pylint"
            {
              nativeBuildInputs = [ pythonEnv ];
              preferLocalBuild = true;
            } "make -C ${./..} pylint > $out";

          shlint = pkgs.runCommandNoCC "shlint"
            {
              nativeBuildInputs = [ pkgs.shellcheck ];
              preferLocalBuild = true;
            } "make -C ${./..} shlint > $out";
        };

        # kept for backwards-compatibility
        defaultPackage = pkgs.neovim;

        devShells = {
          default = pkgs.neovim-developer.overrideAttrs (oa: {

            buildInputs = with pkgs; oa.buildInputs ++ [
              cmake
              lua.pkgs.luacheck
              sumneko-lua-language-server
              pythonEnv
              include-what-you-use # for scripts/check-includes.py
              jq # jq for scripts/vim-patch.sh -r
              shellcheck # for `make shlint`
              doxygen # for script/gen_vimdoc.py
              clang-tools # for clangd to find the correct headers
            ];

            shellHook = oa.shellHook + ''
              export NVIM_PYTHON_LOG_LEVEL=DEBUG
              export NVIM_LOG_FILE=/tmp/nvim.log
              export ASAN_SYMBOLIZER_PATH=${pkgs.llvm_11}/bin/llvm-symbolizer

              # ASAN_OPTIONS=detect_leaks=1
              export ASAN_OPTIONS="log_path=./test.log:abort_on_error=1"
              export UBSAN_OPTIONS=print_stacktrace=1
              mkdir -p build/runtime/parser
              # nvim looks into CMAKE_INSTALL_DIR. Hack to avoid errors
              # when running the functionaltests
              mkdir -p outputs/out/share/nvim/syntax
              touch outputs/out/share/nvim/syntax/syntax.vim

              # for treesitter functionaltests
              mkdir -p runtime/parser
              cp -f ${pkgs.tree-sitter.builtGrammars.tree-sitter-c}/parser runtime/parser/c.so
            '';
          });
        };
      });
}