Import inside `defmodule`

[petrkozorezov]

I'm trying to use dune with elixir-nx/Nx and getting the following error about import.

iex(12)> defmodule ExtendedAllowlist do
...(12)>   use Dune.Allowlist, extend: Dune.Allowlist.Default
...(12)>
...(12)>   allow Nx, :all
...(12)>   allow Nx.Defn, :all
...(12)> end
{:module, ExtendedAllowlist,
 <<70, 79, 82, 49, 0, 0, 211, 244, 66, 69, 65, 77, 65, 116, 85, 56, 0, 0, 38,
   94, 0, 0, 3, 217, 24, 69, 108, 105, 120, 105, 114, 46, 69, 120, 116, 101,
   110, 100, 101, 100, 65, 108, 108, 111, 119, 108, 105, ...>>, :ok}

iex(13)> Dune.eval_string("defmodule Foo do import Nx.Defn; defn foo(n) do Nx.power(n, 2) end end; Foo.foo(3)", allowlist: ExtendedAllowlist)
%Dune.Failure{
  type: :module_restricted,
  message: "** (DuneRestrictedError) the following syntax is restricted inside defmodule:\n         import Nx.Defn",
  stdio: ""
}

[sabiwara]

Hello @petrkozorezov , thank you for the report 💜

import falls into this section of the README:

would need to be reimplemented in an alternative way and therefore need a consequent amount of work that hasn't been done yet

I will keep the issue open, I actually started to look into it at some point but I'm not sure when I will be able to make progress. It will be needed to support external macros that aren't part of the Kernel module.

[sabiwara]

Hi again @petrkozorezov.
I also realized that the specific case of Nx.Defn wouldn't work even if import was supported, because defn would need an actual module in order to define functions.
As explained here, Dune cannot provide real modules because they would break isolation, it can only fake the basic behavior of a module to some extend.