How to list all the modules of a certain submodule via macro?

There're modules in a certain directory and sub-directories of my project which I want to parse and save into a variable at compile time via a macro

defmodule MyApp.MySubmodules.Mod1 do
    @doc "this module does AA"
  #
end

defmodule MyApp.MySubmodules.Mod2 do
    @doc "this is for CC"
  #
end

# ...

defmodule MyApp.MySubmodules.Mod3 do
    @doc "something afdsafdsfds"

  #
end

defmodule MyApp.MySubmodules.Xyz.Mod4 do
    @doc "blah-blah-blah-blah"

  #
end

And

defmodule MyApp.MainModule do
  use MyModuleParse

end

This would create a module attribute via macro

@my_modules %{
    mod1: "this module does AA",
    mod2: "this is for CC",
    mod3: "something afdsafdsfds",
    xyz_mod4: "blah-blah-blah-blah"
}

The idea is to be able to enumerate certain modules at the compile time and present them to a user on an html page. And do it without having to do copy-paste manually into MyApp.MainModule each time I change, add or delete a module.

How to implement this?

Firstly, how to list all of the modules given a certain path -- MyApp.MySubmodules? Then, how to read @doc of one?

Via a macro.

If you take a look at the ex_doc package, you can see some of their tricks, including Code.fetch_docs/1, e.g.

iex> Code.fetch_docs(Integer)
{:docs_v1, 2, :elixir, "text/markdown",
 %{
   "en" => "Functions for working with integers.\n\nSome functions that " <> _etc
 }, %{},
 [
   {{:function, :digits, 2}, 171, ["digits(integer, base \\\\ 10)"],
    %{
      "en" => "Returns the ordered digits for the given `integer`..." <> _etc
    }, %{defaults: 1}},
   # ... etc...
 ]}

That can output a LOT of information, but I think it has everything you need: the @moduledoc stuff is first, then it's followed by a list of the @doc blocks for each function.

You might need to use some calls to Code.ensure_loaded/1 (or its friends) because your "summary" module requires that these other modules be compiled BEFORE it can perform this kind of introspection on them.