Don't print the underlying type for @opaque

Closes #2612

Author: ericmj

lib/iex/lib/iex/introspection.ex

@@ -311,6 +311,12 @@ defmodule IEx.Introspection do
     Enum.map(specs, &{tag, &1})
   end
 
+  defp print_type({:opaque, type}) do
+    {:::, _, [ast, _]} = Kernel.Typespec.type_to_ast(type)
+    IO.puts IEx.color(:eval_info, "@opaque #{Macro.to_string(ast)}")
+    true
+  end
+
   defp print_type({kind, type}) do
     ast = Kernel.Typespec.type_to_ast(type)
     IO.puts IEx.color(:eval_info, "@#{kind} #{Macro.to_string(ast)}")

lib/iex/test/iex/helpers_test.exs

@@ -60,6 +60,9 @@ defmodule IEx.HelpersTest do
     assert "@type t() :: " <> _
            = capture_io(fn -> t Enum.t end)
     assert capture_io(fn -> t Enum.t end) == capture_io(fn -> t Enum.t/0 end)
+
+    assert "@opaque t()\n" = capture_io(fn -> t Regex.t end)
+    assert capture_io(fn -> t Regex.t end) == capture_io(fn -> t Regex.t/0 end)
   end
 
   test "s helper" do