Do not raise on foreign types, closes #10077

Author: josevalim

lib/iex/lib/iex/introspection.ex

@@ -735,9 +735,15 @@ defmodule IEx.Introspection do
   ## Helpers
 
   defp format_typespec(definition, kind, nesting) do
-    "@#{kind} #{Macro.to_string(definition)}"
-    |> Code.format_string!(line_length: IEx.width() - 2 * nesting)
-    |> IO.iodata_to_binary()
+    string = "@#{kind} #{Macro.to_string(definition)}"
+
+    try do
+      string
+      |> Code.format_string!(line_length: IEx.width() - 2 * nesting)
+      |> IO.iodata_to_binary()
+    rescue
+      _ -> string
+    end
     |> color_prefix_with_line()
     |> indent(nesting)
   end

lib/iex/test/iex/helpers_test.exs

@@ -853,6 +853,7 @@ defmodule IEx.HelpersTest do
       defmodule TypeSample do
         @typedoc "An ID with description."
         @type id_with_desc :: {number, String.t}
+        @type unquote(:"?")() :: :question_mark
       end
       """
 
@@ -872,6 +873,11 @@ defmodule IEx.HelpersTest do
 
                An ID with description.
                """
+
+        assert capture_io(fn -> t(TypeSample."?"()) end) == """
+               @type ?() :: :question_mark
+
+               """
       end)
     after
       cleanup_modules([TypeSample])