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Fix major incompatibility with tzdata 2026c (Morocco, Alberta Canada) #178

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Fix major incompatibility with tzdata 2026c (Morocco, Alberta Canada) #178

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6 changes: 6 additions & 0 deletions CHANGELOG.md
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Original file line number Diff line number Diff line change
@@ -1,5 +1,11 @@
# Changelog for Tzdata

### Fixed

- Fix Africa/Casablanca and Africa/El_Aaiun switching to permanent UTC six
months early in tzdata 2026c, and similar errors in some historical
transitions, caused by a zone line whose rules end before the line does.

### Changed

- Now supports version 4.x of hackney as well as 1.x
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80 changes: 55 additions & 25 deletions lib/tzdata/period_builder.ex
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Original file line number Diff line number Diff line change
Expand Up @@ -311,40 +311,70 @@ defmodule Tzdata.PeriodBuilder do
no_more_rules = rules_tail == []
no_more_years = tl(years) == []

# If we've hit the upper time boundary of this zone line, we do not need to examine any more
# rules for this rule set OR there are no more years to consider for this rule set
if last_included_rule || no_more_years && no_more_rules do
h_calc_next_zone_line(btz_data, period, until_utc, zone_line_tl, letter)
else
tail = cond do
# If there are no more rules for the year, continue with the next year
no_more_rules ->
cond do
# If we've hit the upper time boundary of this zone line, we do not need to examine any more
# rules for this rule set.
last_included_rule ->
h_calc_next_zone_line(btz_data, period, until_utc, zone_line_tl, letter)

# There are no more rules or years to consider, but the zone line has an explicit `until`
# that lies after the last rule transition. We still need to emit the remaining span (from
# the last transition up to the zone line's `until`, using the offset the last rule left in
# effect) before moving on to the next zone line. Recursing into calc_rule_periods/8 with an
# empty year list recomputes the zone line's `until` with that offset and handles the hand-off.
# Without this, the final span is dropped and the next zone line starts too early
# (e.g. Africa/Casablanca in tzdata 2026c: Morocco's rules end in March 2026 but the zone
# line runs until 20 September 2026, when the switch to permanent UTC actually happens).
no_more_years && no_more_rules && is_integer(upper_limit) ->
tail =
calc_rule_periods(
btz_data,
[zone_line | zone_line_tl],
until_utc,
utc_off,
rule.save,
years |> tl,
[],
zone_rules,
rule.letter
)
# Else continue with those rules
true ->
calc_periods_for_year(
btz_data,
[zone_line | zone_line_tl],
until_utc,
utc_off,
rule.save,
years,
zone_rules,
rules_tail,
rule.letter,
lower_limit
)
end
if period == nil, do: tail, else: [ period | tail ]

if period == nil, do: tail, else: [period | tail]

# There are no more rules or years and the zone line runs until :max. The current period is
# the last precompiled one; dynamic periods take over beyond this point.
no_more_years && no_more_rules ->
h_calc_next_zone_line(btz_data, period, until_utc, zone_line_tl, letter)

true ->
tail = cond do
# If there are no more rules for the year, continue with the next year
no_more_rules ->
calc_rule_periods(
btz_data,
[zone_line | zone_line_tl],
until_utc,
utc_off,
rule.save,
years |> tl,
zone_rules,
rule.letter
)
# Else continue with those rules
true ->
calc_periods_for_year(
btz_data,
[zone_line | zone_line_tl],
until_utc,
utc_off,
rule.save,
years,
zone_rules,
rules_tail,
rule.letter,
lower_limit
)
end
if period == nil, do: tail, else: [ period | tail ]
end
end

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72 changes: 72 additions & 0 deletions test/tz_period_builder_test.exs
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Expand Up @@ -472,6 +472,78 @@ defmodule Tzdata.PeriodBuilderTest do
assert invalid_periods == []
end

describe "zone line whose rules end before the zone line does (tzdata 2026c Morocco)" do
setup do
{:ok, map} = Tzdata.BasicDataMap.from_single_file_in_dir("test/tzdata_fixtures", "morocco_2026c")
{:ok, %{map: map}}
end

# In 2026c, Morocco's DST rules stop in March 2026, but the zone line using them
# runs until 20 September 2026, when Morocco switches to permanent UTC. Previously
# the builder ended the zone line at the last rule transition (March), dropping the
# +01 span from March to September and starting permanent UTC six months too early.
test "keeps the +01 span after the last rule and switches to permanent UTC on 2026-09-20", %{map: map} do
for zone <- ["Africa/Casablanca", "Africa/El_Aaiun"] do
[ramadan, west, permanent] = calc_periods(map, zone) |> Enum.take(-3)

# Ramadan 2026: back to +00 until the last Morocco rule fires
assert ramadan.utc_off + ramadan.std_off == 0
assert ramadan.until.utc == ~G[2026-03-22T02:00:00]

# The previously-dropped span: +01 from the last rule until the zone line ends
assert west == %{
std_off: 0,
utc_off: 3600,
zone_abbr: "+01",
from: %{
utc: ~G[2026-03-22T02:00:00],
standard: ~G[2026-03-22T03:00:00],
wall: ~G[2026-03-22T03:00:00]
},
until: %{
utc: ~G[2026-09-20T01:00:00],
standard: ~G[2026-09-20T02:00:00],
wall: ~G[2026-09-20T02:00:00]
}
}

# Permanent UTC from the zone line's end, forever
assert permanent == %{
std_off: 0,
utc_off: 0,
zone_abbr: "00",
from: %{
utc: ~G[2026-09-20T01:00:00],
standard: ~G[2026-09-20T01:00:00],
wall: ~G[2026-09-20T01:00:00]
},
until: %{utc: :max, standard: :max, wall: :max}
}
end
end

test "reports +01 (not UTC) in the middle of the dropped span", %{map: map} do
# 2026-06-15T12:00:00 UTC falls between the last rule (March) and the switch (September).
instant = ~G[2026-06-15T12:00:00]

for zone <- ["Africa/Casablanca", "Africa/El_Aaiun"] do
period =
calc_periods(map, zone)
|> Enum.find(fn p ->
p.from.utc != :min and p.until.utc != :max and
p.from.utc <= instant and instant < p.until.utc
end)

assert period.utc_off + period.std_off == 3600
end
end

test "produces no overlapping or backwards periods", %{map: map} do
test_for_overlaps(map, "Africa/Casablanca")
test_for_overlaps(map, "Africa/El_Aaiun")
end
end

test "Dublin with negative DST is handled correctly", %{map: map} do
periods = calc_periods(map, "Europe/Dublin")

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74 changes: 74 additions & 0 deletions test/tzdata_fixtures/morocco_2026c
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# Morocco rules and zones extracted verbatim from IANA tzdata 2026c (africa file).
# Fixture for regression-testing Morocco's switch to permanent UTC on 2026-09-20,
# where the zone line's rules end (2026 Mar) before the zone line itself does (2026 Sep).
# https://lists.iana.org/hyperkitty/list/tz-announce@iana.org/thread/NVHSX2PAQIT44U5FCCEVNJJYXQMMTJSA/

Rule Morocco 1939 only - Sep 12 0:00 1:00 -
Rule Morocco 1939 only - Nov 19 0:00 0 -
Rule Morocco 1940 only - Feb 25 0:00 1:00 -
Rule Morocco 1945 only - Nov 18 0:00 0 -
Rule Morocco 1950 only - Jun 11 0:00 1:00 -
Rule Morocco 1950 only - Oct 29 0:00 0 -
Rule Morocco 1967 only - Jun 3 12:00 1:00 -
Rule Morocco 1967 only - Oct 1 0:00 0 -
Rule Morocco 1974 only - Jun 24 0:00 1:00 -
Rule Morocco 1974 only - Sep 1 0:00 0 -
Rule Morocco 1976 1977 - May 1 0:00 1:00 -
Rule Morocco 1976 only - Aug 1 0:00 0 -
Rule Morocco 1977 only - Sep 28 0:00 0 -
Rule Morocco 1978 only - Jun 1 0:00 1:00 -
Rule Morocco 1978 only - Aug 4 0:00 0 -
Rule Morocco 2008 only - Jun 1 0:00 1:00 -
Rule Morocco 2008 only - Sep 1 0:00 0 -
Rule Morocco 2009 only - Jun 1 0:00 1:00 -
Rule Morocco 2009 only - Aug 21 0:00 0 -
Rule Morocco 2010 only - May 2 0:00 1:00 -
Rule Morocco 2010 only - Aug 8 0:00 0 -
Rule Morocco 2011 only - Apr 3 0:00 1:00 -
Rule Morocco 2011 only - Jul 31 0:00 0 -
Rule Morocco 2012 2013 - Apr lastSun 2:00 1:00 -
Rule Morocco 2012 only - Jul 20 3:00 0 -
Rule Morocco 2012 only - Aug 20 2:00 1:00 -
Rule Morocco 2012 only - Sep 30 3:00 0 -
Rule Morocco 2013 only - Jul 7 3:00 0 -
Rule Morocco 2013 only - Aug 10 2:00 1:00 -
Rule Morocco 2013 2018 - Oct lastSun 3:00 0 -
Rule Morocco 2014 2018 - Mar lastSun 2:00 1:00 -
Rule Morocco 2014 only - Jun 28 3:00 0 -
Rule Morocco 2014 only - Aug 2 2:00 1:00 -
Rule Morocco 2015 only - Jun 14 3:00 0 -
Rule Morocco 2015 only - Jul 19 2:00 1:00 -
Rule Morocco 2016 only - Jun 5 3:00 0 -
Rule Morocco 2016 only - Jul 10 2:00 1:00 -
Rule Morocco 2017 only - May 21 3:00 0 -
Rule Morocco 2017 only - Jul 2 2:00 1:00 -
Rule Morocco 2018 only - May 13 3:00 0 -
Rule Morocco 2018 only - Jun 17 2:00 1:00 -
Rule Morocco 2019 only - May 5 3:00 -1:00 -
Rule Morocco 2019 only - Jun 9 2:00 0 -
Rule Morocco 2020 only - Apr 19 3:00 -1:00 -
Rule Morocco 2020 only - May 31 2:00 0 -
Rule Morocco 2021 only - Apr 11 3:00 -1:00 -
Rule Morocco 2021 only - May 16 2:00 0 -
Rule Morocco 2022 only - Mar 27 3:00 -1:00 -
Rule Morocco 2022 only - May 8 2:00 0 -
Rule Morocco 2023 only - Mar 19 3:00 -1:00 -
Rule Morocco 2023 only - Apr 23 2:00 0 -
Rule Morocco 2024 only - Mar 10 3:00 -1:00 -
Rule Morocco 2024 only - Apr 14 2:00 0 -
Rule Morocco 2025 only - Feb 23 3:00 -1:00 -
Rule Morocco 2025 only - Apr 6 2:00 0 -
Rule Morocco 2026 only - Feb 15 3:00 -1:00 -
Rule Morocco 2026 only - Mar 22 2:00 0 -

Zone Africa/Casablanca -0:30:20 - LMT 1913 Oct 26
0:00 Morocco %z 1984 Mar 16
1:00 - %z 1986
0:00 Morocco %z 2018 Oct 28 3:00
1:00 Morocco %z 2026 Sep 20 2:00
0:00 - %z
Zone Africa/El_Aaiun -0:52:48 - LMT 1934 Jan # El Aaiún
-1:00 - %z 1976 Apr 14
0:00 Morocco %z 2018 Oct 28 3:00
1:00 Morocco %z 2026 Sep 20 2:00
0:00 - %z