`Comeonin.Argon2.check_pass/2` always return `{:error, binary()}` according to Dialyzer

[hauleth]

I know it isn't true, but still, this is the warning I have when I am using Comeonin.Argon2.check_pass/2 with with macro:

apps/kokon/lib/kokon/accounts/sessions.ex:36: The pattern {'ok', _user@2} can never match the type {'error',<<_:64,_:_*8>>}

My code is:

# apps/kokon/lib/kokon/accounts/sessions.ex
@spec create(email(), Password.password) :: {:ok, Session.t} | :error
def create(email, password) do
  user =
    User
    |> where(email: ^email)
    |> Repo.one

  with {:ok, user}    <- Password.check(user, password), # Line 36 from dialyse warning
       {:ok, session} <- Session.new(user) |> Repo.insert
  do
    {:ok, session}
  else
    {:error, reason} ->
      Logger.warn(fn ->
        "Failed to create user session: #{inspect reason}"
      end)

      :error
    _ -> :error
  end
end

And Password module has defdelegate to Comeonin.Argon2.check_pass/2:

@type password :: binary()
@type user :: %{password_hash: hash()}

@hasher Application.get_env(:kokon, __MODULE__, []) |> Keyword.fetch!(:hasher)

@spec check(user() | nil, password()) :: {:ok, user()} | {:error, binary()}
defdelegate check(user, password), to: @hasher, as: :check_pass

This error is quite irritating as GitLab CI do not build cache after failed jobs even when allow_failure is set to true, so my Dialyzer's PLT files aren't cached (and it is quite expensive operation in matter of time.

[riverrun]

If you haven't done so already, could you open a dialyzer issue? Hopefully, they can give us more information about how to solve this problem.

[hauleth]

@riverrun to be honest I do not know to which repo this should go:

• Elixir - as I believe this issue with code generation (I have had similar issue with other fragment where I have been generating functions inside for comprehension)
• OTP - as this is where Dialyzer code resides
• Dialyxir - as this is ran through it

[riverrun]

Try dialyxir first. If nothing else, there might be a way to silence the errors, like adding an annotation to the check_pass function.

[riverrun]

Do you have any news about this issue?

[riverrun]

Closing this issue for now. If you have any further updates to this, feel free to reopen this issue.

[NobbZ]

This is a bug in riverrun/argon2_elixir and gets fixed by riverrun/argon2_elixir#21.