Explicitly announce structs

Before this patch, we could announce a struct too early,
only when __struct__/0 was defined (and not __struct__/1)
leading to deadlocks in the compiler. We fixed the bug and
made struct announcements to avoid future bugs.

Closes #4844

Signed-off-by: José Valim <jose.valim@plataformatec.com.br>

Author: José Valim

lib/elixir/lib/kernel.ex

@@ -3473,7 +3473,7 @@ defmodule Kernel do
       end
 
       unquote(builder)
-
+      Kernel.Utils.announce_struct(__MODULE__)
       fields
     end
   end

lib/elixir/lib/kernel/utils.ex

@@ -84,4 +84,11 @@ defmodule Kernel.Utils do
      List.wrap(Module.get_attribute(module, :enforce_keys)),
      Module.get_attribute(module, :derive)}
   end
+
+  def announce_struct(module) do
+    case :erlang.get(:elixir_compiler_pid) do
+      :undefined -> :ok
+      pid -> send(pid, {:struct_available, module})
+    end
+  end
 end

lib/elixir/src/elixir_def.erl

@@ -105,8 +105,6 @@ store_definition(Meta, Line, Kind, CheckClauses, Name, Args, Guards, Body, KeepL
   store_each(CheckClauses, Kind, File, Location, Module, DefaultsLength, Function),
   [store_each(false, Kind, File, Location, Module, 0,
     default_function_for(Kind, Name, Default)) || Default <- Defaults],
-
-  make_struct_available(Kind, Module, Name, Args),
   {Name, Arity}.
 
 %% @on_definition
@@ -117,16 +115,6 @@ run_on_definition_callbacks(Kind, Line, Module, Name, Args, Guards, Expr, E) ->
   _ = [Mod:Fun(Env, Kind, Name, Args, Guards, Expr) || {Mod, Fun} <- Callbacks],
   ok.
 
-make_struct_available(def, Module, '__struct__', []) ->
-  case erlang:get(elixir_compiler_pid) of
-    undefined -> ok;
-    Pid ->
-      Pid ! {struct_available, Module},
-      ok
-  end;
-make_struct_available(_, _, _, _) ->
-  ok.
-
 %% Retrieve location from meta file (if Key == keep)
 %% or @file, otherwise nil
 

lib/elixir/test/elixir/fixtures/parallel_struct/bar.ex

@@ -1,4 +1,3 @@
 defmodule Bar do
-  defstruct name: ""
-  def foo?(%Foo{}), do: true
+  defstruct name: "", foo: %Foo{}
 end