Get typespecs for Code.compile_string() module

Questions / Help
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1

Hello! Is it possible to get the typespecs for a module that is compiled at runtime via Code.complie_string()? For example, if I run

compiled_module, _bytecode = Code.compile_string(
  """
  defmodule UserDefinedGreeter do
    @spec call(name :: String.t()) :: {:return, String.t()}
    def call(name) do
      {:return, "Hey " <> name}
    end
  end
  """
)

I end up with a UserDefinedGreeter module and I can e.g. call UserDefinedGreeter.call("foo"). However, I can’t seem to access that call typespec.

  • Code.Typespec.fetch_types(UserDefinedGreeter) returns :error
  • Kernel.Typespec.beam_specs(UserDefinedGreeter) returns nil

Is there an option I’m overlooking, or a different way to compile Elixir code at runtime that will result in the typespecs being accessible?

1 Like
2

Those functions retrieve information from the byte code on disk I believe, and therefore will fail for dynamically compiled modules.

I think you may find this post to be helpful. At least to understand the issue better.

4 Likes
3

Ah good to know — it looks like there might be a possible workaround in the post you linked. I’ll follow up there, thanks!

4

From that post you linked:

It turns out I can pass the bytecode to Code.Typespec.fetch_specs directly. So from the original example, this should work:

_compiled_module, bytecode = Code.compile_string(
  """
  defmodule UserDefinedGreeter do
    @spec call(name :: String.t()) :: {:return, String.t()}
    def call(name) do
      {:return, "Hey " <> name}
    end
  end
  """
)
Code.Typespec.fetch_specs(bytecode)
1 Like