No API to retrieve enforced_keys on a struct

[lukaszsamson]

Elixir and Erlang/OTP versions

any

Operating system

any

Current behavior

When a language server is returning completions with struct keys it would be nice to highlight the enforced ones. There is currently no API to retrieve that info. The @enforce_keys attribute is compile time only, there is no trace of that left in EEP48 docs.

Expected behavior

A metadata entry with enforced keys in documentation for the :__struct__ function

[josevalim]

It is available on __info__(:struct) also based if the field has a default or not.

[lukaszsamson]

If so then it's not what I'd expect to see

Interactive Elixir (1.18.3) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> Date.__info__(:struct)
[
  %{default: nil, field: :year},
  %{default: nil, field: :month},
  %{default: nil, field: :day},
  %{default: Calendar.ISO, field: :calendar}
]
iex(2)> %Date{}
** (ArgumentError) the following keys must also be given when building struct Date: [:year, :month, :day]
    (elixir 1.18.3) expanding struct: Date.__struct__/1
    iex:2: (file)

[josevalim]

Hrm, could it be main only or am I hallucinating?

[olunusib]

Seems there used to be a required boolean key, but it was removed in e3bad83#diff-2749d1ae144d00522b8cc4c216006f3cf7ca6eeb79b4d3f70bc6124a09f861a3L216-R216? With an older version:

Interactive Elixir (1.17.3) - press Ctrl+C to exit (type h() ENTER for help)
iex(1)> Date.__info__(:struct)
[
  %{field: :year, required: true},
  %{field: :month, required: true},
  %{field: :day, required: true},
  %{field: :calendar, required: false}
]

[josevalim]

Ah, thank you, that's it. We have plans to make the default key optional once we introduce typed structs. That's because once we introduce typed structs, a required field should not really have a default value, otherwise if you say field :age, integer(), required: true and then it defaults to nil, it means the type is actually integer() or nil. Therefore this will be tackled by #13881.