Turn off dependency tracking for compilation on release, closes #1982

Author: José Valim

CHANGELOG.md

@@ -10,6 +10,7 @@
   * [ExUnit] `:include` in ExUnit only has effect if a test was previously excluded with `:exclude`
   * [ExUnit] Only run `setup_all` and `teardown_all` if there are tests in the case
   * [Kernel] Ensure bitstring modifier arguments are expanded
+  * [Kernel] Ensure compiler does not block on missing modules
 
 * Deprecations
   * [Kernel] `is_alive/0` is deprecated in favor of `Node.alive?`

lib/elixir/lib/kernel/error_handler.ex

@@ -22,7 +22,15 @@ defmodule Kernel.ErrorHandler do
         parent <- { :waiting, self(), ref, module }
         :erlang.garbage_collect(self)
         receive do
-          { ^ref, :release } -> :ok
+          { ^ref, :ready } ->
+            :ok
+          { ^ref, :release } ->
+            # On release, get rid of the compiler pid,
+            # no further allow elixir_ensure_compiled directives
+            # and revert to the original error handler.
+            :erlang.erase(:elixir_compiler_pid)
+            :erlang.erase(:elixir_ensure_compiled)
+            :erlang.process_flag(:error_handler, :error_handler)
         end
     end
   end

lib/elixir/lib/kernel/parallel_compiler.ex

@@ -65,7 +65,7 @@ defmodule Kernel.ParallelCompiler do
   # Release waiting processes
   defp spawn_compilers([h|t], original, output, callbacks, waiting, queued, schedulers, result) when is_pid(h) do
     { ^h, ref, _ } = List.keyfind(waiting, h, 0)
-    h <- { ref, :release }
+    h <- { ref, :ready }
     waiting = List.keydelete(waiting, h, 0)
     spawn_compilers(t, original, output, callbacks, waiting, queued, schedulers, result)
   end
@@ -76,8 +76,12 @@ defmodule Kernel.ParallelCompiler do
 
     { pid, ref } =
       :erlang.spawn_monitor fn ->
-        :erlang.put(:elixir_compiler_pid, parent)
+        # Notify Code.ensure_compiled/2 that we should
+        # attempt to compile the module by doing a dispatch.
         :erlang.put(:elixir_ensure_compiled, true)
+
+        # Set the elixir_compiler_pid used by our custom Kernel.ErrorHandler.
+        :erlang.put(:elixir_compiler_pid, parent)
         :erlang.process_flag(:error_handler, Kernel.ErrorHandler)
 
         exit(try do