Elixir: Fix impurity with Erlang.

The bash scripts of elixir contain some references to `erl'. This
patch wraps the scripts and extends PATH so `erl' is available.

Signed-off-by: Moritz Ulrich <moritz@tarn-vedra.de>

pkgs/development/interpreters/elixir/default.nix

@@ -1,4 +1,4 @@
-{ stdenv, fetchurl, erlang, rebar }:
+{ stdenv, fetchurl, erlang, rebar, makeWrapper, coreutils }:
 
 stdenv.mkDerivation {
   name = "elixir-0.10.1";
@@ -8,7 +8,7 @@ stdenv.mkDerivation {
     sha256 = "0gfr2bz3mw7ag9z2wb2g22n2vlyrp8dwy78fj9zi52kzl5w3vc3w";
   };
 
-  buildInputs = [ erlang rebar ];
+  buildInputs = [ erlang rebar makeWrapper ];
 
   preBuild = ''
     substituteInPlace rebar \
@@ -18,6 +18,17 @@ stdenv.mkDerivation {
       --replace "/usr/local" $out
   '';
 
+  postFixup = ''
+    # Elixirs binaries are shell scripts which run erl. This adds some
+    # stuff to PATH so the scripts run without problems.
+
+    for f in $out/bin/*
+    do
+      wrapProgram $f \
+      --prefix PATH ":" "${erlang}/bin:${coreutils}/bin"
+    done
+  '';
+
   meta = {
     homepage = "http://elixir-lang.org/";
     description = "Elixir is a functional, meta-programming aware language built on top of the Erlang VM.";