Guard clauses in "with" cause Dialyzer warnings (in Elixir 1.5)

[Cohedrin]

Environment

• elixir 1.5.1
• OTP 20.0
• Operating system: OSX

Current behavior

Adding a guard clause inside of an else block of a with statement causes dialyzer to raise an warning

Example:

  def with_else do
    with :ok <- ok_or_error(),
         :ok <- ok_or_other_error(),
         :ok <- ok_or_tuple_error(),
         :ok <- ok_or_tuple_list_error() do
      :ok
    else
      :error ->
        :error
      :other_error ->
        :other_error
      {:error, msg} when is_list(msg) ->
        :error
      {:error, _msg} ->
        :error
    end
  end

Will raise a warning Guard test is_list(msg@1::'err') can never succeed

Expected behavior

No warning is raised, this was the behavior on 1.4.x

I've added a failing test case here for this issue.

Notes

• This is related to Dialyzer warnings with 1.5 using with/else statements #6378, but was not solved by 288fb9e.
• I've added a failing test case here for this issue