Use Nix flake

.gitignore

@@ -1,3 +1,4 @@
 /.envrc
+/.direnv
 /vendor/bundle
 /Gemfile.lock

default.nix

@@ -0,0 +1,11 @@
+# flake-compat shim for usage without flakes
+(import
+  (
+    let lock = builtins.fromJSON (builtins.readFile ./flake.lock); in
+    fetchTarball {
+      url = lock.nodes.flake-compat.locked.url or "https://github.com/edolstra/flake-compat/archive/${lock.nodes.flake-compat.locked.rev}.tar.gz";
+      sha256 = lock.nodes.flake-compat.locked.narHash;
+    }
+  )
+  { src = ./.; }
+).defaultNix

flake.nix

@@ -0,0 +1,57 @@
+{
+  inputs = {
+    nixpkgs.url = "github:nixos/nixpkgs/master";
+
+    # cross-platform convenience
+    flake-utils.url = "github:numtide/flake-utils";
+
+    # backwards compatibility with nix-build and nix-shell
+    flake-compat.url = "https://flakehub.com/f/edolstra/flake-compat/1.tar.gz";
+  };
+
+  outputs = { self, nixpkgs, flake-utils, flake-compat }:
+    # resolve for all platforms in turn
+    flake-utils.lib.eachDefaultSystem (system:
+      let
+        # packages for this system platform
+        pkgs = nixpkgs.legacyPackages.${system};
+
+        # control versions
+        ruby = pkgs.ruby_3_3;
+        llvm = pkgs.llvmPackages_16;
+        gcc = pkgs.gcc13;
+      in {
+        devShell = pkgs.llvm.stdenv.mkDerivation {
+          name = "devshell";
+
+          buildInputs = with pkgs; [
+            ruby
+            libyaml.dev
+
+            # TODO: some gems insist on using `gcc` on Linux, satisfy them for now:
+            # - json
+            # - protobuf
+            # - ruby-prof
+            gcc
+          ];
+
+          shellHook = ''
+            # get major.minor.0 ruby version
+            export RUBY_VERSION="$(ruby -e 'puts RUBY_VERSION.gsub(/\d+$/, "0")')"
+
+            # make gem install work in-project, compatibly with bundler
+            export GEM_HOME="$(pwd)/vendor/bundle/ruby/$RUBY_VERSION"
+
+            # make bundle work in-project
+            export BUNDLE_PATH="$(pwd)/vendor/bundle"
+
+            # enable calling gem scripts without bundle exec
+            export PATH="$GEM_HOME/bin:$PATH"
+
+            # enable implicitly resolving gems to bundled version
+            export RUBYGEMS_GEMDEPS="$(pwd)/Gemfile"
+          '';
+        };
+      }
+    );
+}

shell.nix

@@ -1,22 +1,11 @@
-{
-  pkgs ? import <nixpkgs> {},
-  pinned ? import(fetchTarball("https://github.com/NixOS/nixpkgs/archive/47b604b07d1e.tar.gz")) {},
-}:
-let
-  ruby = pinned.ruby_3_3;
-  llvm = pinned.llvmPackages_16;
-in llvm.stdenv.mkDerivation {
-  name = "shell";
-
-  buildInputs = [
-    ruby
-    pinned.libyaml.dev
-  ];
-
-  shellHook = ''
-    export RUBY_VERSION="$(ruby -e 'puts RUBY_VERSION.gsub(/\d+$/, "0")')"
-    export GEM_HOME="$(pwd)/vendor/bundle/ruby/$RUBY_VERSION"
-    export BUNDLE_PATH="$(pwd)/vendor/bundle"
-    export PATH="$GEM_HOME/bin:$PATH"
-  '';
-}
+# flake-compat shim for usage without flakes
+(import
+  (
+    let lock = builtins.fromJSON (builtins.readFile ./flake.lock); in
+    fetchTarball {
+      url = lock.nodes.flake-compat.locked.url or "https://github.com/edolstra/flake-compat/archive/${lock.nodes.flake-compat.locked.rev}.tar.gz";
+      sha256 = lock.nodes.flake-compat.locked.narHash;
+    }
+  )
+  { src = ./.; }
+).shellNix