Use Nix to manage the development environment

.envrc

@@ -0,0 +1,84 @@
+####################################
+# Environment setup for Nix shells #
+####################################
+
+# From https://github.com/direnv/direnv/wiki/Nix#persistent-cached-shell
+#
+# Usage: use_nix [...]
+#
+# Load environment variables from `nix-shell`.
+# If you have a `default.nix` or `shell.nix` one of these will be used and
+# the derived environment will be stored at ./.direnv/env-<hash>
+# and symlink to it will be created at ./.direnv/default.
+# Dependencies are added to the GC roots, such that the environment remains persistent.
+#
+# Packages can also be specified directly via e.g `use nix -p ocaml`,
+# however those will not be added to the GC roots.
+#
+# The resulting environment is cached for better performance.
+#
+# To trigger switch to a different environment:
+# `rm -f .direnv/default`
+#
+# To derive a new environment:
+# `rm -rf .direnv/env-$(md5sum {shell,default}.nix 2> /dev/null | cut -c -32)`
+#
+# To remove cache:
+# `rm -f .direnv/dump-*`
+#
+# To remove all environments:
+# `rm -rf .direnv/env-*`
+#
+# To remove only old environments:
+# `find .direnv -name 'env-*' -and -not -name `readlink .direnv/default` -exec rm -rf {} +`
+#
+use_nix() {
+    set -e
+
+    local shell="shell.nix"
+    if [[ ! -f "${shell}" ]]; then
+        shell="default.nix"
+    fi
+
+    if [[ ! -f "${shell}" ]]; then
+        fail "use nix: shell.nix or default.nix not found in the folder"
+    fi
+
+    local dir="${PWD}"/.direnv
+    local default="${dir}/default"
+    if [[ ! -L "${default}" ]] || [[ ! -d `readlink "${default}"` ]]; then
+        local wd="${dir}/env-`md5sum "${shell}" | cut -c -32`" # TODO: Hash also the nixpkgs version?
+        mkdir -p "${wd}"
+
+        local drv="${wd}/env.drv"
+        if [[ ! -f "${drv}" ]]; then
+            log_status "use nix: deriving new environment"
+            IN_NIX_SHELL=1 nix-instantiate --add-root "${drv}" --indirect "${shell}" > /dev/null
+            nix-store -r `nix-store --query --references "${drv}"` --add-root "${wd}/dep" --indirect > /dev/null
+        fi
+
+        rm -f "${default}"
+        ln -s `basename "${wd}"` "${default}"
+    fi
+
+    local drv=`readlink -f "${default}/env.drv"`
+    local dump="${dir}/dump-`md5sum ".envrc" | cut -c -32`-`md5sum ${drv} | cut -c -32`"
+
+    if [[ ! -f "${dump}" ]] || [[ "${XDG_CONFIG_DIR}/direnv/direnvrc" -nt "${dump}" ]]; then
+        log_status "use nix: updating cache"
+
+        old=`find ${dir} -name 'dump-*'`
+        nix-shell "${drv}" --show-trace "$@" --run 'direnv dump' > "${dump}"
+        rm -f ${old}
+    fi
+
+    direnv_load cat "${dump}"
+
+    watch_file "${default}"
+    watch_file shell.nix
+    if [[ ${shell} == "default.nix" ]]; then
+        watch_file default.nix
+    fi
+}
+
+use nix

.gitignore

@@ -1,18 +1,37 @@
-# Application artifacts (Elixir)
+##
+## Application artifacts
+##
+
+# direnv cache for Nix shells
+/.direnv/
+
+# Elixir build directory
 /_build/
+
+# Elixir dependencies
 /deps/
 /.fetch
+
+# Elixir binary files
 *.beam
 *.ez
-typed_struct-*.tar
+/typed_struct-*.tar
+/typed_struct
 
 # Test coverage and documentation
 /cover/
 /doc/
 
-# Editor artifacts
+##
+## Editor artifacts
+##
+
 /.elixir_ls/
 /.history/
 
-# Crash dumps
+##
+## Crash dumps
+##
+
+# Erang VM
 erl_crash.dump

shell.nix

@@ -0,0 +1,49 @@
+{ pkgs ? import <nixpkgs> {} }:
+
+with pkgs;
+
+let
+  inherit (lib) optional optionals;
+
+  erlangDrv = { mkDerivation }:
+    mkDerivation rec {
+      version = "21.0";
+      # Use `nix-prefetch-github --rev OTP-<version> erlang otp` to update.
+      sha256 = "0khprgawmbdpn9b8jw2kksmvs6b45mibpjralsc0ggxym1397vm8";
+
+      prePatch = ''
+        substituteInPlace configure.in --replace '`sw_vers -productVersion`' '10.10'
+      '';
+    };
+
+  elixirDrv = { mkDerivation }:
+    mkDerivation rec {
+      version = "1.7.3";
+      # Use `nix-prefetch-github --rev v<version> elixir-lang elixir` to update.
+      sha256 = "0d7rj4khmvy76z12njzwzknm1j9rhjadgj9k1chjd4gnjffkb1aa";
+      minimumOTPVersion = "19";
+    };
+
+  erlang = (beam.lib.callErlang erlangDrv { wxGTK = wxGTK30; }).override {
+    # Temporary fix to enable use on OS X El Capitan.
+    enableKernelPoll = if stdenv.isDarwin then false else true;
+  };
+
+  rebar = pkgs.rebar.override { inherit erlang; };
+
+  elixir = beam.lib.callElixir elixirDrv {
+    inherit erlang rebar;
+    debugInfo = true;
+  };
+in
+
+mkShell {
+  buildInputs = [ elixir git ]
+    ++ optional stdenv.isLinux libnotify # For ExUnit Notifier on Linux.
+    ++ optional stdenv.isDarwin terminal-notifier # For ExUnit Notifier on macOS.
+    ++ optionals stdenv.isDarwin (with darwin.apple_sdk.frameworks; [
+      # For file_system on macOS.
+      CoreFoundation
+      CoreServices
+    ]);
+}