Error handling

Matching Elixir conventions, Tuist server functions should return success and errors as values in form of {:ok, result} and {:error, reason} tuples.
In order for us to leverage automatic error handling, we follow a standardized error format that is used across both domain and interface logic.

Error format

1. Any successful function execution should return {:ok, result}, where result can be any value.
2. Any error where the function execution is not successful should return {:error, reason}, where reason is a string describing the error.

For generic errors, the reason should be an atom describing the error code:

1. :unauthenticated - There is no authenticated user.
2. :unauthorized - The authenticated user is not authorized to perform the requested action.
3. :not_found - The requested resource was not found.

[!NOTE] In our controller error handling, :unauthenticated maps to HTTP error 401 and :unauthorized maps to HTTP error 403. This does not match the HTTP status code name, but matches the cause of the error more closely.

For input errors, the preference is to return an %Ecto.Changeset{} containing the error messages pertaining to the related input fields.
For all other errors, reason should be a string describing the error.

These error formats allow us to handle errors in a consistent way across domain logic and controllers, making it possible to simply return the errors inside our controller actions and have automatic formatting and status code handling.

Controller example

with {:ok, account} <- get_account(handle), # returns {:ok, account} or {:error, :not_found}
     :ok <- can(conn.assigns.current_user, :update, account, :organization), # returns :ok or {:error, :unauthorized}
     {:ok, account} <- Accounts.update_account(account, params) do # returns {:ok, account} or {:error, changeset}
  conn
  |> put_status(:ok)
  |> json(%{id: account.id, handle: account.name})
end

Since the with clause returns all non-matching values as-is, the error paths will be passed onto the controller which will handle them generically.