Can't define a private on_load function

[marianoguerra]

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Environment

• Elixir & Erlang/OTP versions (elixir --version):

Erlang/OTP 23 [erts-11.1] [source] [64-bit] [smp:8:8] [ds:8:8:10] [async-threads:1] [hipe]
Elixir 1.10.4 (compiled with Erlang/OTP 23)

• Operating system: Ubuntu 20.04

Current behavior

Include code samples, errors and stacktraces if appropriate.

This elixir module:

defmodule MyMod do
  @on_load :on_load

  defp on_load do
    IO.puts "hi!"
  end
end

fails to compile with error mymod.ex:1: expected @on_load function on_load/0 to be defined as "def", got "defp"

This erlang module compiles:

-module(my_mod).
-on_load(on_load/0).

on_load() ->
    io:format("hi!~n").

Erlang docs about on_load say: "It is not necessary to export the function"

Expected behavior

I would expect the elixir code to compile.

The change to make it work is to add an extra clause here:

elixir/lib/elixir/src/elixir_module.erl

Line 197 in 3415f90

{_, def, _, _} ->

matching defp too.

It's ok to close this issue if it's a design decision for the language, but I think on_load functions are better when private since it doesn't make sense for example to load a nif by calling the on_load function manually after module load, which is one of the main use cases for on_load.

[josevalim]

IIRC earlier Erlang versions required them to be public, so we did the same validation. We need to see since when this restriction was removed from Erlang.

[marianoguerra]

The note is already in 17.0: https://github.com/erlang/otp/blob/07b8f441ca711f9812fad9e9115bab3c3aa92f79/system/doc/reference_manual/code_loading.xml#L148 I can trace it farther back but probably Elixir expects OTP >= 17?

Here's the tag: https://github.com/erlang/otp/releases/tag/OTP-17.0

[josevalim]

Yup, we should be fine! Latest requires 21+.