Timezone.convert("Etc/GMT...") inconsistent with DateTime+Tzdata

[vovayartsev]

This is largely a duplicate of #649, but slightly different

Steps to reproduce

in your mix.exs:

  defp deps do
    [
      {:timex,"3.7.6"},
      {:tzdata, "~> 1.1"}
    ]
  end

then in the console:

DateTime.now("Etc/GMT-4")    
{:ok, #DateTime<2021-09-02 21:30:46.545885+04:00 +04 Etc/GMT-4>}

tried in PostgreSQL and it's consistent with DateTime + Tzdata:

postgres=# select now() at time zone 'Etc/GMT-4'
 2021-09-02 21:30:57.241963

but Timex gives a very different result

Timex.now() |> Timex.Timezone.convert("Etc/GMT-4")
#DateTime<2021-09-02 13:31:50.793031-04:00 -04 Etc/GMT+4>

Description of issue

I was executing the lines above from Europe/Samara in the evening, around 21:30. My timezone is UTC+04:00 and the corresponding Etc area is Etc/GMT-4 (according to tz database wiki)

I was expecting Timex.now() |> Timex.Timezone.convert("Etc/GMT-4") to give me my local time (~21:30)