flake: 🥐 add nix development shell

flake.nix

@@ -0,0 +1,56 @@
+{
+  description = "A nix development shell and build environment for galileo";
+
+  inputs = {
+    nixpkgs.url = "github:NixOS/nixpkgs/nixos-unstable";
+    flake-utils.url = "github:numtide/flake-utils";
+    rust-overlay = {
+      url = "github:oxalica/rust-overlay";
+      inputs = {
+        nixpkgs.follows = "nixpkgs";
+        flake-utils.follows = "flake-utils";
+      };
+    };
+    crane = {
+      url = "github:ipetkov/crane";
+      inputs = { nixpkgs.follows = "nixpkgs"; };
+    };
+  };
+
+  outputs = { nixpkgs, flake-utils, rust-overlay, crane, ... }:
+    flake-utils.lib.eachDefaultSystem
+      (system:
+        let
+          # Set up for Rust builds, pinned to the Rust toolchain version in the Penumbra repository
+          overlays = [ (import rust-overlay) ];
+          pkgs = import nixpkgs { inherit system overlays; };
+          rustToolchain = pkgs.rust-bin.fromRustupToolchainFile ./rust-toolchain.toml;
+          craneLib = (crane.mkLib pkgs).overrideToolchain rustToolchain;
+          src = craneLib.cleanCargoSource (craneLib.path ./.);
+          # Important environment variables so that the build can find the necessary libraries
+          PKG_CONFIG_PATH="${pkgs.openssl.dev}/lib/pkgconfig";
+          LIBCLANG_PATH="${pkgs.libclang.lib}/lib";
+        in with pkgs; with pkgs.lib; let
+	galileo = (craneLib.buildPackage {
+            inherit src system PKG_CONFIG_PATH LIBCLANG_PATH;
+            pname = "galileo";
+            version = "0.1.0";
+            nativeBuildInputs = [ pkg-config ];
+            buildInputs = [ clang openssl ];
+	    # A lockfile is not used in this repository.
+            cargoVendorDir = null;
+        }).overrideAttrs (_: { doCheck = false; }); # Disable tests to improve build times
+	in {
+	  inherit galileo;
+	  devShells.default = craneLib.devShell {
+            inherit LIBCLANG_PATH;
+            inputsFrom = [ galileo ];
+            packages = [ cargo-watch cargo-nextest ];
+            shellHook = ''
+              export LIBCLANG_PATH=${LIBCLANG_PATH}
+              export RUST_SRC_PATH=${pkgs.rustPlatform.rustLibSrc} # Required for rust-analyzer
+            '';
+	  };
+	}
+      );
+}