Hammox breaks when there is a @typep

[Gabriel Prá]

This code in type_engine.ex accepts only @type:

  defp get_type(type_list, type_name, arity) do
    case Enum.find(type_list, fn {:type, {name, _type, params}} ->
           name == type_name and length(params) == arity
         end) do
      nil -> {:error, {:type_not_found, {type_name, arity}}}
      type -> {:ok, type}
    end
  end

However, Typespecs accepts @type, @typep and @opaque (source). This causes hammox to break:

     ** (FunctionClauseError) no function clause matching in anonymous fn/1 in Hammox.TypeEngine.get_type/3

     The following arguments were given to anonymous fn/1 in Hammox.TypeEngine.get_type/3:

         # 1
         {:typep, {:names, {:remote_type, 133, [{:atom, 0, MapSet}, {:atom, 0, :t}, []]}, []}}

     stacktrace:
       (hammox 0.2.4) lib/hammox/type_engine.ex:695: anonymous fn/1 in Hammox.TypeEngine.get_type/3
       (elixir 1.10.2) lib/enum.ex:3305: Enum.find_list/3
       (hammox 0.2.4) lib/hammox/type_engine.ex:695: Hammox.TypeEngine.get_type/3
       (hammox 0.2.4) lib/hammox/type_engine.ex:656: Hammox.TypeEngine.resolve_remote_type/1
       (hammox 0.2.4) lib/hammox/type_engine.ex:621: Hammox.TypeEngine.match_type/2
       (hammox 0.2.4) lib/hammox.ex:312: Hammox.match_return_value/2
       (hammox 0.2.4) lib/hammox.ex:280: Hammox.match_call/3
       (hammox 0.2.4) lib/hammox.ex:264: anonymous fn/4 in Hammox.check_call/3
       (elixir 1.10.2) lib/enum.ex:3686: Enumerable.List.reduce/3
       (elixir 1.10.2) lib/enum.ex:2161: Enum.reduce_while/3
       (hammox 0.2.4) lib/hammox.ex:263: Hammox.check_call/3
       (hammox 0.2.4) lib/hammox.ex:256: Hammox.protected_code/3

In my case, I'm using Ecto.Multi.t() as the return value of a function, and this structure defines @typep: https://github.com/elixir-ecto/ecto/blob/v3.4.4/lib/ecto/multi.ex#L133

[Michał Szewczak]

Thanks for the report! This definitely needs fixing.