Flake-based direnv setup for nixOS users

.envrc

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+NBS_ONLY_LOAD_ENV_VARS=1 source env.sh
+
+if command -v nix > /dev/null
+then
+  export NIMBUS_NIX_ENV=1
+
+  cd nix
+  # watch_file tells direnv that changes to any of the watched files
+  # should trigger a re-evalution of the environment
+  watch_file flake.nix
+  watch_file flake.lock
+  watch_file shell.nix
+
+  mkdir -p .flake-profiles
+  eval "$(nix print-dev-env --profile ".flake-profiles/profile")"
+fi

nix/.gitignore

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+# Local file unique for each user
+.flake-profiles/

nix/flake.nix

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+{
+  description = "nimbus-eth2";
+
+  inputs = {
+    nixpkgs.url = github:NixOS/nixpkgs/nixos-21.11;
+    flake-utils.url = github:numtide/flake-utils;
+  };
+
+  outputs = { self, nixpkgs, flake-utils }:
+    flake-utils.lib.simpleFlake {
+      inherit self nixpkgs;
+      name = "nimbus-eth2";
+      shell = ./shell.nix;
+    };
+}

nix/shell.nix

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+{pkgs ? import <nixpkgs> {}}:
+with pkgs;
+  mkShell {
+    buildInputs =
+      [
+        figlet
+        git
+        gnumake
+        rocksdb
+      ]
+      ++ lib.optionals (!stdenv.isDarwin) [
+        lsb-release
+      ];
+
+    shellHook = ''
+      # By default, the Nix wrapper scripts for executing the system compilers
+      # will erase `-march=native` because this introduces impurity in the build.
+      # For the purposes of compiling Nimbus, this behavior is not desired:
+      export NIX_ENFORCE_NO_NATIVE=0
+
+      figlet "Welcome to Nimbus-eth1"
+    '';
+  }