Move registry to rebar3, since it needs it itself to be bootstrapped.

This makes rebar3 build a bit more hermetic. Next stage is to pull in
rebar3 plugins dependencies for bootstrap to pick up.

pkgs/development/tools/build-managers/rebar3/default.nix

@@ -1,8 +1,13 @@
-{ stdenv, fetchurl, erlang }:
+{ stdenv, fetchurl, erlang, tree, fetchFromGitHub }:
 
 
 let
   version = "3.0.0-beta.4";
+  registrySnapshot = import ./registrySnapshot.nix { inherit fetchFromGitHub; };
+  setupRegistry = ''
+    mkdir -p _build/default/{lib,plugins,packages}/ ./.cache/rebar3/hex/default/
+    zcat ${registrySnapshot}/registry.ets.gz > .cache/rebar3/hex/default/registry
+  '';
 in
 stdenv.mkDerivation {
   name = "rebar3-${version}";
@@ -13,8 +18,11 @@ stdenv.mkDerivation {
   };
 
   buildInputs = [ erlang ];
+  inherit setupRegistry;
+
 
   buildPhase = ''
+    ${setupRegistry}
     HOME=. escript bootstrap
   '';
   installPhase = ''

pkgs/development/tools/build-managers/rebar3/registrySnapshot.nix

@@ -0,0 +1,8 @@
+{ fetchFromGitHub }:
+
+fetchFromGitHub {
+  owner = "gleber";
+  repo = "hex-pm-registry-snapshots";
+  rev = "48147b0";
+  sha256 = "0ibfnhrhbka4n6wkhs99fpy3sjab54ip37jgvx2hcfhfr4pxhbxw";
+}