What version of Elixir are you using? I get no warnings when I compile in 1.14.1.

Regardless, since ends_at must be a NaiveDateTime, it’s better to be explicit about this in the function head as opposed to just checking that it isn’t nil:

def time_remaining(%NaiveDateTime{} = ends_at) do
  ...
end

or if you prefer when you can do the more verbose:

def time_remaining(ends_at) when is_struct(ends_at, NaiveDateTime) do
  ...
end

Deleting .elixir_ls folder solved it, thanks for taking the time to help me out here.

I haven’t seen this type of Dialyzer warning on a guard call before; but I have seen similar warnings for function parameters when Dialyzer thinks there’s no way for a given pattern match to possibly match a condition… which I sometimes do for a catch all function.

For example if I write something like the below, with no other calls to func_a/1:

def entry_func() do
  %{test: "Hi!"}
  |> func_a()
end

def func_a(%{} = param) do
  # do something
end

def func_a(_) do
  raise "Bad Param"
end

I will, with some regularity, see the ElixirLS Dialyzer warning that the second function head for func_a will never run… which looks like it could be similar to what you’re seeing. In this case Dialyzer isn’t exactly wrong… there’s no way for the second func_a/1 function head to match. But it’s not exactly helpful either because I may know now that in the future I might call it from somewhere else where the second function head is helpful.

Anyway, I can’t say for sure this is what you’re seeing, but it looks similar.