Hi, a user found an issue when attempting to use my Ultraviolet library: Unexpected Dialyzer issue · Issue #1 · dcrck/ultraviolet · GitHub

defmodule MyModule do
  require Logger

  def testing do
    sport_color = "pink"

    case Ultraviolet.new(sport_color) do
      {:error, m} -> Logger.error("should_not_happen", reason: m)
      {:ok, color} -> color
    end
  end
end

error :

lib/my_module.ex:9:pattern_match
The pattern can never match the type.

Pattern:
{:ok, _color}

Type:
{:error, _}

________________________________________________________________________________
done (warnings were emitted)
Halting VM with exit status 2

Here’s a repository where I can reproduce the issue:

The warning doesn’t really make much sense to me, as I’ve used Color.new() in a variety of tests without encountering error cases, so I don’t know why dialyzer would see no path forward but the error case for a case I’ve definitely tested. Regardless, I’ve been working at this for a few hours now and I can’t seem to resolve this issue. Here’s what I’ve tried so far:

• fixing all the dialyzer warnings / errors in Ultraviolet. While the published version still has warnings, the main branch does not. I’ve edited mix.exs on the example repository to point to my local copy with all the warnings resolved.
• expanded the metaprogramming construct I use to generate function signatures for the W3CX11 named colors.
• overriding the function to force a return type of {:ok, %Color{}} in an attempt to get something working.

None of these seem to work. Does anyone have any suggestions for how I might solve this problem? Thanks!