Updated Nix build environment for working with Nimbus

Other changes:

* For the macOS builds in Travis, attempt to install rocksdb through brew

.travis.yml

@@ -15,7 +15,8 @@ matrix:
 
     - os: osx
       before_install:
-        # - brew update
+        - brew update
+        - brew install rocksdb
         # - brew install gcc
 
         - git clone https://github.com/nim-lang/nim.git

README.md

@@ -15,8 +15,24 @@ Join the Status community chats:
 
 ## Building & Testing
 
+### Prerequisites
+
+Please install a recent version of Facebook's RocksDB following the instructions here:
+
+https://github.com/facebook/rocksdb/blob/master/INSTALL.md
+
 Currently Nimbus requires the latest development version of the Nim programming language. Follow the [installation steps](https://github.com/nim-lang/Nim) or use [choosenim](https://github.com/dom96/choosenim).
 
+### Obtaining the prerequisites through the Nix package manager
+
+Users of the [Nix package manager](https://nixos.org/nix/download.html) can install all prerequisites simply by running:
+
+``` bash
+nix-shell nimbus.nix
+```
+
+### Build
+
 You can build the package and run the tests using `nimble test`. You can run the example using `nim compile --run examples/decompile_smart_contract.nim`.
 
 ## License

default.nix

@@ -1,22 +1,10 @@
-{ pkgs ? import <nixpkgs> {} }:
-
 let
-  stdenv = pkgs.stdenv;
+  pkgs = import (builtins.fetchGit {
+     url = git://github.com/NixOS/nixpkgs;
+     rev = "8c6f9223d02c5123cbd364d6d56caca3c81416f0";
+  }) {};
 
 in
 
-stdenv.mkDerivation rec {
-  name = "nimbus-${version}";
-  version = "0.0.1";
-
-  meta = with stdenv.lib; {
-    description = "An Ethereum 2.0 Sharding Client for Resource-Restricted Devices";
-    homepage = https://github.com/status-im/nimbus;
-    license = [licenses.asl20];
-    platforms = platforms.unix;
-  };
-
-  src = ./.;
-  buildInputs = [pkgs.clang pkgs.nim pkgs.rocksdb pkgs.secp256k1 pkgs.cryptopp];
-}
+import ./nimbus.nix { inherit pkgs; }
 

devenv.nix

@@ -1,10 +0,0 @@
-let
-  pkgs = import (builtins.fetchGit {
-     url = git://github.com/NixOS/nixpkgs;
-     rev = "8c6f9223d02c5123cbd364d6d56caca3c81416f0";
-  }) {};
-
-in
-
-import ./default.nix { inherit pkgs; }
-

nim.nix

@@ -0,0 +1,67 @@
+{ stdenv, lib, makeWrapper, nodejs, openssl, pcre, readline, sqlite, nim }:
+
+stdenv.mkDerivation rec {
+  # This derivation may be a bit confusing at first, because it builds the Status'
+  # Nimbus branch of Nim using the standard Nim compiler provided by Nix.
+  #
+  # It's mostly a copy of the original Nim recipe, but uses git to obtain the
+  # sources and have a simplified `buildPhase`.
+  #
+  # For maintainance, you only need to bump the obtained git revision from time
+  # to time.
+
+  name = "status-nim";
+  version = "0.18.1";
+
+  src = fetchGit {
+    url = "git://github.com/status-im/Nim";
+    ref = "nimbus";
+
+    # Set this to the hash of the head commit in the nimbus branch:
+    rev = "d40fb5a6d3ed937d41fd0e72a27df8c397aae881";
+  };
+
+  doCheck = true;
+
+  enableParallelBuilding = true;
+
+  NIX_LDFLAGS = [
+    "-lcrypto"
+    "-lpcre"
+    "-lreadline"
+    "-lsqlite3"
+  ];
+
+  # 1. nodejs is only needed for tests
+  # 2. we could create a separate derivation for the "written in c" version of nim
+  #    used for bootstrapping, but koch insists on moving the nim compiler around
+  #    as part of building it, so it cannot be read-only
+
+  buildInputs  = [
+    makeWrapper nodejs nim
+    openssl pcre readline sqlite
+  ];
+
+  buildPhase   = ''
+    nim c --lib:"./lib" -d:release koch.nim
+    nim c --lib:"./lib" -d:release compiler/nim.nim && mv compiler/nim bin/
+  '';
+
+  installPhase = ''
+    install -Dt $out/bin bin/* koch
+    ./koch install $out
+    mv $out/nim/bin/* $out/bin/ && rmdir $out/nim/bin
+    mv $out/nim/*     $out/     && rmdir $out/nim
+    wrapProgram $out/bin/nim \
+      --suffix PATH : ${lib.makeBinPath [ stdenv.cc ]}
+  '';
+
+  meta = with stdenv.lib; {
+    description = "Status's build of Nim";
+    homepage = https://nim-lang.org/;
+    license = licenses.mit;
+    maintainers = with maintainers; [ ehmry peterhoeg ];
+    platforms = with platforms; linux ++ darwin; # arbitrary
+  };
+}
+

nimbus.nix

@@ -0,0 +1,23 @@
+{ pkgs ? import <nixpkgs> {  } }:
+
+let
+  stdenv = pkgs.stdenv;
+  nim = pkgs.callPackage ./nim.nix {};
+
+in
+
+stdenv.mkDerivation rec {
+  name = "nimbus-${version}";
+  version = "0.0.1";
+
+  meta = with stdenv.lib; {
+    description = "An Ethereum 2.0 Sharding Client for Resource-Restricted Devices";
+    homepage = https://github.com/status-im/nimbus;
+    license = [licenses.asl20];
+    platforms = platforms.unix;
+  };
+
+  src = ./.;
+  buildInputs = [pkgs.clang nim pkgs.rocksdb_lite];
+}
+