Timex.Timezone.local/0 fails with :could_not_resolve_timezone in the hour after DST starts

[dyxyl]

Steps to reproduce

Call Timex.Timezone.local/0 when the system time is within 1 hour after DST starts (the missing hour of local time). For example, at ~U[2024-03-31 01:13:41.097331Z] when TZ=Europe/London.

Description of issue

I would expect Timex.Timezone.local/0 to return the DST timezone like it does in the hour that follows the failing case.

Instead, it returns a :could_not_resolve_timezone error.

Timex.Timezone.local/0 calls Timex.Timezone.local/1 with the current UTC. The documentation for Timex.Timezone.local/1 doesn't say if the argument is in UTC or local time.

Here is an example session with timex 3.7.11 and TZ=Europe/London. (2) and (3) show it working before DST starts. (4), (5) and (6) show it failing during the changeover. (7) and (8) show it working again after the changeover.

iex(1)> Application.ensure_all_started(:timex)
{:ok,
 [:crypto, :asn1, :public_key, :ssl, :unicode_util_compat, :idna, :mimerl,
  :certifi, :syntax_tools, :parse_trans, :ssl_verify_fun, :metrics, :hackney,
  :tzdata, :combine, :expo, :gettext, :timex]}
iex(2)> Timex.Timezone.local
#<TimezoneInfo(Europe/London - GMT (+00:00:00))>
iex(3)> Timex.now
~U[2024-03-31 00:58:30.182979Z]
iex(4)> Timex.now
~U[2024-03-31 01:13:41.097331Z]
iex(5)> Timex.Timezone.local
{:error, {:could_not_resolve_timezone, "Europe/London", 63879066824, :wall}}
iex(6)> Timex.now
~U[2024-03-31 01:13:54.824859Z]
iex(7)> Timex.now
~U[2024-03-31 02:01:56.322685Z]
iex(8)> Timex.Timezone.local
#<TimezoneInfo(Europe/London - BST (+01:00:00))>
iex(9)> Application.started_applications
[
  {:timex,
   ~c"Timex is a rich, comprehensive Date/Time library for Elixir projects, with full timezone support via the :tzdata package.\nIf you need to manipulate dates, times, datetimes, timestamps, etc., then Timex is for you!\n",
   ~c"3.7.11"},
  {:gettext, ~c"Internationalization and localization through gettext",
   ~c"0.23.1"},
  {:expo,
   ~c"Low-level Gettext file handling (.po/.pot/.mo file writer and parser).",
   ~c"0.4.1"},
  {:combine, ~c"A parser combinator library for Elixir projects.", ~c"0.10.0"},
  {:tzdata, ~c"Tzdata is a parser and library for the tz database.\n",
   ~c"1.1.1"},
  {:hackney, ~c"simple HTTP client", ~c"1.20.1"},
  {:metrics, ~c"A generic interface to different metrics systems in Erlang.",
   ~c"1.0.1"},
  {:ssl_verify_fun, ~c"SSL verification library", ~c"1.1.7"},
  {:parse_trans, ~c"Parse transform library", ~c"3.4.1"},
  {:syntax_tools, ~c"Syntax tools", ~c"3.0.1"},
  {:certifi, ~c"CA bundle adapted from Mozilla by https://certifi.io",
   ~c"2.12.0"},
  {:mimerl, ~c"Library to handle mimetypes", ~c"1.2.0"},
  {:idna, ~c"A pure Erlang IDNA implementation", ~c"6.1.1"},
  {:unicode_util_compat, ~c"unicode_util compatibility library for Erlang < 20",
   ~c"0.7.0"},
  {:ssl, ~c"Erlang/OTP SSL application", ~c"10.9.1.3"},
  {:public_key, ~c"Public key infrastructure", ~c"1.13.3.2"},
  {:asn1, ~c"The Erlang ASN1 compiler version 5.0.21.1", ~c"5.0.21.1"},
  {:crypto, ~c"CRYPTO", ~c"5.1.4.2"},
  {:logger, ~c"logger", ~c"1.15.7"},
  {:iex, ~c"iex", ~c"1.15.7"},
  {:elixir, ~c"elixir", ~c"1.15.7"},
  {:compiler, ~c"ERTS  CXC 138 10", ~c"8.2.6.4"},
  {:stdlib, ~c"ERTS  CXC 138 10", ~c"4.3.1.3"},
  {:kernel, ~c"ERTS  CXC 138 10", ~c"8.5.4.2"}
]
iex(10)>