Summary

I’m trying to create a macro that takes in input a module name and automatically creates a defdelegate for each function defined in that module.

Example

defmodule MyApp.TargetModule1 do
  def foo(name, opts \\ []) do
    name <> to_string(opts)
  end

  def bar(name) do
    String.uppercase(name)
  end
end

defmodule MyApp.TargetModule2 do
  def baz(name) do
    "Ciao" <> name
  end
end


defmodule MyApp.DelegateModule do
  delegate_all MyApp.TargetModule1
  # the line above will generate the following:
  # defdelegate foo(name, opts \\ []), to: MyApp.TargetModule1
  # defdelegate bar(name), to: MyApp.TargetModule1

  delegate_all MyApp.TargetModule2
  # the line above will generate the following:
  # defdelegate baz(name), to: MyApp.TargetModule2
end

What I’ve done so far

I achieved this using Code.fetch_docs/1 and Code.Typespec.fetch_specs/1 but unfortunately these functions won’t work unless the .beam file isn’t already written on disk so when I modify any target module I get the :module_not_found error.

I know I can get the function list with MyApp.TargetModule1.__info__(:functions) but this will return a simple list of functions and arities without arguments names and possibly default arguments.

Questions

I already looked into ExUnit.DocTest but it also uses Code.fetch_docs/1 and I don’t know how does it work! Tests are compiled after the main lib files?

How can I get function signature (possibly also specs and documentations) from a module at runtime?