`undefined function __aliases__/1` in 1.19.0-rc.1+OTP28.1 when importing module with regex in defstruct

[hkrutzer]

Elixir and Erlang/OTP versions

Erlang/OTP 28 [erts-16.1] [source] [64-bit] [smp:14:14] [ds:14:14:10] [async-threads:1] [jit]

Elixir 1.19.0-rc.1 (f642b30) (compiled with Erlang/OTP 28)

Operating system

macos

Current behavior

defmodule Test do
  defstruct(
    my_regex: ~r/^hi$/
  )

  def init() do
    %__MODULE__{}
  end
end

IO.inspect(Test.init())

> elixir test.exs
error: undefined function __aliases__/1 (expected Test to define such a function or for it to be imported, but none are available)
└─ test.exs: Test.init/1

** (CompileError) test.exs: cannot compile module Test (errors have been logged)

Expected behavior

> elixir --version
Erlang/OTP 27 [erts-15.2.7] [source] [64-bit] [smp:14:14] [ds:14:14:10] [async-threads:1] [jit]

Elixir 1.18.4 (compiled with Erlang/OTP 27)

> elixir test.exs
%Test{my_regex: ~r/^hi$/}

[sabiwara]

Thanks @hkrutzer for the report! 💜

Hum, I'm not sure if we can support this, but perhaps we should fail with a similar error as having a ref field 💭

iex> defmodule LichWeb.BoxJson do
       defstruct foo: make_ref()
     end
** (ArgumentError) invalid value for struct field foo, cannot escape #Reference<0.415929174.1843658753.247575>. The supported values are: lists, tuples, maps, atoms, numbers, bitstrings, PIDs and remote functions in the format &Mod.fun/arity

[hkrutzer]

Hum, I'm not sure if we can support this

It is what it is 🙂. But I had to reduce this test module from a much larger one where it's not clear the compilation is failing due to the regex; so at least a better error would help a lot.

[josevalim]

I pushed a fix but it had unintended complications in that it either introduces subtlities during struct introspection or makes them more expensive. So I will revert and improve the error message. :)

[hkrutzer]

Thanks @sabiwara @josevalim :) I don't suppose this is expected to come back in the future? Example of where I use this: I have a struct that represents some configurable input validation, where there is a default that matches e.g. a certain type of zipcode (I can solve this in a different way of course).

[josevalim]

It is unfortunately, a bit tricky to support this right now. We plan to introduce typed structs in the future, and maybe then we’ll have an opportunity to introduce this future, but I wouldn’t count on it, sorry. :(