Let’s say I have next controller where {:error, _, _} action result processed by FallbackController:

defmodule SomeProjectWeb.Api.V1.SessionController do
  use SomeProjectWeb, :controller

  alias SomeProject.Session
  alias SomeProject.Session.Otp
  alias SomeProjectWeb.Api.V1.CastAndValidateRenderError
  alias SomeProjectWeb.Api.V1.FallbackController
  alias SomeProjectWeb.Api.V1.{CommonSchema, SessionSchema}

  plug(OpenApiSpex.Plug.CastAndValidate, render_error: CastAndValidateRenderError)

  action_fallback(FallbackController)

  tags(["session"])

  def action(conn, _) do
    apply(__MODULE__, action_name(conn), [conn, conn.params, conn.body_params])
  end

  operation(:otp_create,
    summary: "otp_create summary",
    description: "otp_create description",
    requestBody: {
      "request body description",
      "application/json",
      SessionSchema.OtpCreateRequest,
      required: true
    },
    responses: [
      ok: {
        "ok description",
        "application/json",
        SessionSchema.OtpCreateResponse
      },
      unauthorized: "...",
      unprocessable_entity: {
        "Unprocessable Content, ...",
        "application/json",
        %Schema{
          allOf: [
            CommonSchema.ErrorResponse,
            %Schema{
              type: :object,
              properties: %{
                code: %Schema{
                  enum: [
                    :no_otp_delivery_channel,
                    :runout_signup_account
                  ]
                }
              }
            }
          ]
        }
      },
      internal_server_error: {
        "Internal Server Error, ...",
        "application/json",
        %Schema{
          allOf: [
            CommonSchema.ErrorResponse,
            %Schema{
              type: :object,
              properties: %{
                code: %Schema{
                  enum: [
                    :external_api,
                    :demo_account_manager
                  ]
                }
              }
            }
          ]
        }
      }
    ]
  )

  def otp_create(conn, _params, %{user_email: email} = _body_params) do
    case SomeProject.DemoAccountManager.retrieve(email) do
      {:ok, i_account} ->
        case SomeProject.ExternalApi.create_otp(i_account) do
          {200, %{"success" => 1, "type" => "email", "from" => email}} ->
            otp = Session.create_otp(%{i_account: i_account, demo: true})

            render(conn, otp_id: otp.id, type: "email", from: email)

          {500, %{"faultcode" => "channel-error"}} ->
            {:error, :unprocessable_entity, :no_otp_delivery_channel}

          _ ->
            {:error, :internal_server_error, :external_api}
        end

      {:error, :runout} ->
        {:error, :unprocessable_entity, :runout_signup_account}

      {:error, _} ->
        {:error, :internal_server_error, :demo_account_manager}
    end
  end
end

For now, I manually sync possible error codes for each result with relative result schema. That is diffidently not convenient and will lead to unsync in the future.

I want to implement some type of module macro that will collect and group all its functions :error results and introduce the helper function to access them.
So I could replace:

      internal_server_error: {
        "Internal Server Error, ...",
        "application/json",
        %Schema{
          allOf: [
            CommonSchema.ErrorResponse,
            %Schema{
              type: :object,
              properties: %{
                code: %Schema{
                  enum: [
                    :external_api,
                    :demo_account_manager
                  ]
                }
              }
            }
          ]
        }
      }

with:

      internal_server_error: {
        "Internal Server Error, ...",
        "application/json",
        %Schema{
          allOf: [
            CommonSchema.ErrorResponse,
            %Schema{
              type: :object,
              properties: %{
                code: %Schema{
                  enum: error_codes(:otp_create, :internal_server_error)
                }
              }
            }
          ]
        }
      }

(for sure such the final helper function could produce a more significant piece of repetitive code, but here I want to highlight its core functionality)

What is the best way to implement such functionality?