Emit proper error if parsetools is not available

Author: José Valim

lib/mix/lib/mix/compilers/erlang.ex

@@ -96,6 +96,21 @@ defmodule Mix.Compilers.Erlang do
     end
   end
 
+  @doc """
+  Ensures the native Erlang application is available.
+  """
+  def ensure_application!(app, input) do
+    case Application.ensure_all_started(app) do
+      {:ok, _} ->
+        :ok
+      {:error, _} ->
+        Mix.raise "Could not compile #{inspect Path.relative_to_cwd(input)} because " <>
+                  "the application \"#{app}\" could not be found. This may happen if " <>
+                  "your package manager broke Erlang into multiple packages and may " <>
+                  "be fixed by installing the missing \"#{app}\" package for Erlang."
+    end
+  end
+
   @doc """
   Removes compiled files.
   """

lib/mix/lib/mix/tasks/compile.leex.ex

@@ -43,6 +43,7 @@ defmodule Mix.Tasks.Compile.Leex do
 
     Erlang.compile(manifest(), mappings, :xrl, :erl, opts[:force], fn
       input, output ->
+        Erlang.ensure_application!(:parsetools, input)
         options = options ++ [scannerfile: Erlang.to_erl_file(output), report: true]
         :leex.file(Erlang.to_erl_file(input), options)
     end)

lib/mix/lib/mix/tasks/compile.yecc.ex

@@ -43,6 +43,7 @@ defmodule Mix.Tasks.Compile.Yecc do
 
     Erlang.compile(manifest(), mappings, :yrl, :erl, opts[:force], fn
       input, output ->
+        Erlang.ensure_application!(:parsetools, input)
         options = options ++ [parserfile: Erlang.to_erl_file(output), report: true]
         :yecc.file(Erlang.to_erl_file(input), options)
     end)