File 1853-allow_negative_dates.patch of Package erlang
From ea128074537192dc3b7ff7e134eb69df76f7302a Mon Sep 17 00:00:00 2001
From: Daniel Kukula <daniel.kuku@gmail.com>
Date: Thu, 11 Dec 2025 19:36:10 +0100
Subject: [PATCH 3/4] allow_negative_dates
---
lib/stdlib/src/calendar.erl | 72 ++++++--
lib/stdlib/test/calendar_SUITE.erl | 164 +++++++++++++++++-
lib/stdlib/test/calendar_prop_SUITE.erl | 18 +-
.../test/property_test/calendar_prop.erl | 37 +++-
4 files changed, 264 insertions(+), 27 deletions(-)
diff --git a/lib/stdlib/src/calendar.erl b/lib/stdlib/src/calendar.erl
index db6c5bed1e..589d457f4a 100644
--- a/lib/stdlib/src/calendar.erl
+++ b/lib/stdlib/src/calendar.erl
@@ -44,10 +44,12 @@ Protestant parts of Germany and the Netherlands adopted it in 1698, England
followed in 1752, and Russia in 1918 (the October revolution of 1917 took place
in November according to the Gregorian calendar).
-The Gregorian calendar in this module is extended back to year 0. For a given
-date, the _gregorian days_ is the number of days up to and including the date
-specified. Similarly, the _gregorian seconds_ for a specified date and time is
-the number of seconds up to and including the specified date and time.
+The Gregorian calendar in this module is extended back to year 0 and also
+supports negative years (proleptic Gregorian calendar). For a given date, the
+_gregorian days_ is the number of days up to and including the date specified.
+Negative years use astronomical year numbering where year 0 = 1 BCE, year -1 =
+2 BCE, etc. Similarly, the _gregorian seconds_ for a specified date and time
+is the number of seconds up to and including the specified date and time.
For computing differences between epochs in time, use the functions counting
gregorian days or seconds. If epochs are specified as local time, they must be
@@ -161,7 +163,7 @@ The year using the Gregorian calendar.
Year cannot be abbreviated. For example, 93 denotes year 93, not 1993. The valid
range depends on the underlying operating system.
""".
--type year() :: non_neg_integer().
+-type year() :: integer().
-type year1970() :: 1970..10000. % should probably be 1970..
-type month() :: 1..12.
-type day() :: 1..31.
@@ -229,7 +231,7 @@ The time unit used by the rfc3339 conversion functions.
Year :: year(),
Month :: month(),
Day :: day(),
- Days :: non_neg_integer().
+ Days :: integer().
date_to_gregorian_days(Year, Month, Day) when is_integer(Day), Day > 0 ->
%% Neri-Schneider algorithm.
%% Shift year so March is first month (simplifies leap year handling).
@@ -247,7 +249,7 @@ specified date.
""".
-spec date_to_gregorian_days(Date) -> Days when
Date :: date(),
- Days :: non_neg_integer().
+ Days :: integer().
date_to_gregorian_days({Year, Month, Day}) ->
date_to_gregorian_days(Year, Month, Day).
@@ -263,7 +265,7 @@ specified date and time.
""".
-spec datetime_to_gregorian_seconds(DateTime) -> Seconds when
DateTime :: datetime(),
- Seconds :: non_neg_integer().
+ Seconds :: integer().
datetime_to_gregorian_seconds({Date, Time}) ->
?SECONDS_PER_DAY*date_to_gregorian_days(Date) +
time_to_seconds(Time).
@@ -280,7 +282,7 @@ datetime_to_gregorian_seconds({Date, Time}) ->
Month :: month(),
Day :: day().
day_of_the_week(Year, Month, Day) ->
- (date_to_gregorian_days(Year, Month, Day) + 5) rem 7 + 1.
+ mod(date_to_gregorian_days(Year, Month, Day) + 5, 7) + 1.
-doc """
Computes the day of the week from the specified `Year`, `Month`, and `Day`.
@@ -296,7 +298,7 @@ day_of_the_week({Year, Month, Day}) ->
%%
-doc "Computes the date from the specified number of gregorian days.".
-spec gregorian_days_to_date(Days) -> date() when
- Days :: non_neg_integer().
+ Days :: integer().
gregorian_days_to_date(Days) ->
%% Neri-Schneider algorithm.
%% Shift to March 1, year 0 epoch.
@@ -318,10 +320,14 @@ gregorian_days_to_date(Days) ->
%%
-doc "Computes the date and time from the specified number of gregorian seconds.".
-spec gregorian_seconds_to_datetime(Seconds) -> datetime() when
- Seconds :: non_neg_integer().
-gregorian_seconds_to_datetime(Secs) when Secs >= 0 ->
- Days = Secs div ?SECONDS_PER_DAY,
- Rest = Secs rem ?SECONDS_PER_DAY,
+ Seconds :: integer().
+gregorian_seconds_to_datetime(Secs) ->
+ Days0 = Secs div ?SECONDS_PER_DAY,
+ Rest0 = Secs rem ?SECONDS_PER_DAY,
+ {Days, Rest} = case Rest0 < 0 of
+ true -> {Days0 - 1, Rest0 + ?SECONDS_PER_DAY};
+ false -> {Days0, Rest0}
+ end,
{gregorian_days_to_date(Days), seconds_to_time(Rest)}.
@@ -330,11 +336,11 @@ gregorian_seconds_to_datetime(Secs) when Secs >= 0 ->
-doc "Checks if the specified year is a leap year.".
-spec is_leap_year(Year) -> boolean() when
Year :: year().
-is_leap_year(Y) when is_integer(Y), Y >= 0 ->
+is_leap_year(Y) when is_integer(Y) ->
is_leap_year1(Y).
-spec is_leap_year1(year()) -> boolean().
-is_leap_year1(Year) when Year rem 4 =:= 0, Year rem 100 > 0 ->
+is_leap_year1(Year) when Year rem 4 =:= 0, Year rem 100 =/= 0 ->
true;
is_leap_year1(Year) when Year rem 400 =:= 0 ->
true;
@@ -397,7 +403,7 @@ iso_week_number({Year, Month, Day}) ->
Year :: year(),
Month :: month(),
LastDay :: ldom().
-last_day_of_the_month(Y, M) when is_integer(Y), Y >= 0 ->
+last_day_of_the_month(Y, M) when is_integer(Y) ->
last_day_of_the_month1(Y, M).
-spec last_day_of_the_month1(year(),month()) -> ldom().
@@ -596,6 +602,17 @@ rfc3339_to_system_time(List, Options) when is_list(List) ->
rfc3339_to_system_time_list(List, Options).
%% _T is the character separating the date and the time:
+%% Handle negative years (ISO 8601 extended format: -YYYY-MM-DD)
+rfc3339_to_system_time_bin(
+ <<$-, Year0:4/binary, $-, Month0:2/binary, $-, Day0:2/binary, _T,
+ Hour0:2/binary, $:, Min0:2/binary, $:, Sec0:2/binary, TimeStr/binary>> = DateTimeBin, Options) ->
+ Hour = binary_to_integer(Hour0),
+ Min = binary_to_integer(Min0),
+ Sec = binary_to_integer(Sec0),
+ Year = -binary_to_integer(Year0),
+ Month = binary_to_integer(Month0),
+ Day = binary_to_integer(Day0),
+ rfc3339_to_system_time_1(DateTimeBin, Options, Year, Month, Day, Hour, Min, Sec, binary_to_list(TimeStr));
rfc3339_to_system_time_bin(
<<Year0:4/binary, $-, Month0:2/binary, $-, Day0:2/binary, _T,
Hour0:2/binary, $:, Min0:2/binary, $:, Sec0:2/binary, TimeStr/binary>> = DateTimeBin, Options) ->
@@ -608,6 +625,17 @@ rfc3339_to_system_time_bin(
rfc3339_to_system_time_1(DateTimeBin, Options, Year, Month, Day, Hour, Min, Sec, binary_to_list(TimeStr)).
%% _T is the character separating the date and the time:
+%% Handle negative years (ISO 8601 extended format: -YYYY-MM-DD)
+rfc3339_to_system_time_list(
+ [$-, Y1, Y2, Y3, Y4, $-, Mon1, Mon2, $-, D1, D2, _T,
+ H1, H2, $:, Min1, Min2, $:, S1, S2 | TimeStr] = DateTimeString, Options) ->
+ Hour = list_to_integer([H1, H2]),
+ Min = list_to_integer([Min1, Min2]),
+ Sec = list_to_integer([S1, S2]),
+ Year = -list_to_integer([Y1, Y2, Y3, Y4]),
+ Month = list_to_integer([Mon1, Mon2]),
+ Day = list_to_integer([D1, D2]),
+ rfc3339_to_system_time_1(DateTimeString, Options, Year, Month, Day, Hour, Min, Sec, TimeStr);
rfc3339_to_system_time_list(
[Y1, Y2, Y3, Y4, $-, Mon1, Mon2, $-, D1, D2, _T,
H1, H2, $:, Min1, Min2, $:, S1, S2 | TimeStr] = DateTimeString, Options) ->
@@ -892,7 +920,7 @@ valid_date(Y, M, D) when is_integer(Y), is_integer(M), is_integer(D) ->
valid_date1(Y, M, D).
-spec valid_date1(integer(), integer(), integer()) -> boolean().
-valid_date1(Y, M, D) when Y >= 0, M > 0, M < 13, D > 0 ->
+valid_date1(Y, M, D) when is_integer(Y), M > 0, M < 13, D > 0 ->
D =< last_day_of_the_month(Y, M);
valid_date1(_, _, _) ->
false.
@@ -921,7 +949,10 @@ gregorian_days_of_iso_w01_1(Year) ->
D0101 + 7 - DOW + 1
end.
-check(_Arg, _Options, Secs) when Secs >= - ?SECONDS_FROM_0_TO_1970,
+%% Restrict RFC3339 to years -9999..9999 (4-digit format)
+-define(SECONDS_FROM_MINUS_9999_TO_1970, 377705116800).
+
+check(_Arg, _Options, Secs) when Secs >= -?SECONDS_FROM_MINUS_9999_TO_1970,
Secs < ?SECONDS_FROM_0_TO_10000 ->
ok;
check(Arg, Options, _Secs) ->
@@ -1020,6 +1051,9 @@ pad2(N) when N < 10 ->
pad2(N) ->
integer_to_list(N).
+pad4(N) when N < 0 ->
+ %% Negative years: format as -YYYY (ISO 8601 extended format)
+ [$- | pad4(-N)];
pad4(N) when N < 10 ->
[$0, $0, $0 | integer_to_list(N)];
pad4(N) when N < 100 ->
diff --git a/lib/stdlib/test/calendar_SUITE.erl b/lib/stdlib/test/calendar_SUITE.erl
index 82f3590283..d0b128fa0c 100644
--- a/lib/stdlib/test/calendar_SUITE.erl
+++ b/lib/stdlib/test/calendar_SUITE.erl
@@ -28,10 +28,14 @@
gregorian_days/1,
big_gregorian_days/1,
gregorian_days_edge_cases/1,
+ negative_gregorian_days/1,
gregorian_seconds/1,
+ negative_gregorian_seconds/1,
day_of_the_week/1,
day_of_the_week_calibrate/1,
+ negative_day_of_the_week/1,
leap_years/1,
+ negative_leap_years/1,
last_day_of_the_month/1,
local_time_to_universal_time_dst/1,
iso_week_number/1,
@@ -50,7 +54,9 @@ all() ->
day_of_the_week_calibrate, leap_years,
last_day_of_the_month, local_time_to_universal_time_dst,
iso_week_number, system_time, rfc3339, big_gregorian_days,
- gregorian_days_edge_cases].
+ gregorian_days_edge_cases, negative_gregorian_days,
+ negative_gregorian_seconds, negative_leap_years,
+ negative_day_of_the_week].
groups() ->
[].
@@ -156,6 +162,150 @@ check_roundtrip_samples() ->
Days = calendar:date_to_gregorian_days(Date)
end, lists:seq(0, 4000000, 10000)).
+%% Tests negative dates (dates before year 0).
+%% Uses astronomical year numbering: year 0 = 1 BCE, year -1 = 2 BCE, etc.
+negative_gregorian_days(Config) when is_list(Config) ->
+ %% Test day before epoch (Dec 31, year -1)
+ -1 = calendar:date_to_gregorian_days({-1, 12, 31}),
+ {-1, 12, 31} = calendar:gregorian_days_to_date(-1),
+
+ %% Test year -1 boundaries (year -1 is NOT a leap year: -1 rem 4 = -1)
+ %% Year -1 has 365 days: Jan 1 is day -365, Dec 31 is day -1
+ -365 = calendar:date_to_gregorian_days({-1, 1, 1}),
+ {-1, 1, 1} = calendar:gregorian_days_to_date(-365),
+
+ %% Test year -4 (leap year: -4 rem 4 = 0, -4 rem 100 = -4)
+ true = calendar:is_leap_year(-4),
+ -1461 = calendar:date_to_gregorian_days({-4, 1, 1}),
+ {-4, 1, 1} = calendar:gregorian_days_to_date(-1461),
+ -1096 = calendar:date_to_gregorian_days({-4, 12, 31}), % 366 days in year -4
+ -1402 = calendar:date_to_gregorian_days({-4, 2, 29}), % Leap day
+ {-4, 2, 29} = calendar:gregorian_days_to_date(-1402),
+
+ %% Test year -100 (NOT a leap year: divisible by 100)
+ false = calendar:is_leap_year(-100),
+ -36466 = calendar:date_to_gregorian_days({-100, 2, 28}),
+ {-100, 2, 28} = calendar:gregorian_days_to_date(-36466),
+ -36465 = calendar:date_to_gregorian_days({-100, 3, 1}),
+ {-100, 3, 1} = calendar:gregorian_days_to_date(-36465),
+
+ %% Test year -400 (IS a leap year: divisible by 400)
+ true = calendar:is_leap_year(-400),
+ -146038 = calendar:date_to_gregorian_days({-400, 2, 29}),
+ {-400, 2, 29} = calendar:gregorian_days_to_date(-146038),
+
+ %% Test roundtrip for negative days
+ check_negative_roundtrip_samples(),
+
+ %% Test valid_date for negative years
+ true = calendar:valid_date({-1, 12, 31}),
+ true = calendar:valid_date({-4, 2, 29}),
+ false = calendar:valid_date({-1, 2, 29}), % -1 is not a leap year
+ true = calendar:valid_date({-400, 2, 29}),
+ false = calendar:valid_date({-100, 2, 29}),
+
+ %% Test last_day_of_the_month for negative years
+ 29 = calendar:last_day_of_the_month(-4, 2),
+ 28 = calendar:last_day_of_the_month(-1, 2),
+ 29 = calendar:last_day_of_the_month(-400, 2),
+ 28 = calendar:last_day_of_the_month(-100, 2),
+
+ ok.
+
+%% Helper: check roundtrip for negative days
+check_negative_roundtrip_samples() ->
+ %% Sample every 10000 days from -1000000 to 0
+ lists:foreach(
+ fun(Days) ->
+ Date = calendar:gregorian_days_to_date(Days),
+ Days = calendar:date_to_gregorian_days(Date)
+ end, lists:seq(-1000000, 0, 10000)).
+
+%% Tests negative gregorian seconds (times before year 0).
+negative_gregorian_seconds(Config) when is_list(Config) ->
+ %% One second before midnight on Jan 1, year 0
+ -1 = calendar:datetime_to_gregorian_seconds({{-1, 12, 31}, {23, 59, 59}}),
+ {{-1, 12, 31}, {23, 59, 59}} = calendar:gregorian_seconds_to_datetime(-1),
+
+ %% Midnight on Dec 31, year -1
+ -86400 = calendar:datetime_to_gregorian_seconds({{-1, 12, 31}, {0, 0, 0}}),
+ {{-1, 12, 31}, {0, 0, 0}} = calendar:gregorian_seconds_to_datetime(-86400),
+
+ %% Start of year -1
+ -31536000 = calendar:datetime_to_gregorian_seconds({{-1, 1, 1}, {0, 0, 0}}),
+ {{-1, 1, 1}, {0, 0, 0}} = calendar:gregorian_seconds_to_datetime(-31536000),
+
+ %% Test a time in the middle of a negative day
+ {{-1, 12, 31}, {12, 30, 45}} = calendar:gregorian_seconds_to_datetime(-41355),
+
+ %% Test roundtrip for various negative seconds
+ lists:foreach(
+ fun(Secs) ->
+ DateTime = calendar:gregorian_seconds_to_datetime(Secs),
+ Secs = calendar:datetime_to_gregorian_seconds(DateTime)
+ end, lists:seq(-100000000, 0, 1234567)),
+
+ ok.
+
+%% Tests leap year detection for negative years.
+negative_leap_years(Config) when is_list(Config) ->
+ %% Year -1 is NOT a leap year (-1 rem 4 = -1)
+ false = calendar:is_leap_year(-1),
+ %% Year -2 is NOT a leap year
+ false = calendar:is_leap_year(-2),
+ %% Year -3 is NOT a leap year
+ false = calendar:is_leap_year(-3),
+ %% Year -4 IS a leap year (-4 rem 4 = 0, -4 rem 100 = -4)
+ true = calendar:is_leap_year(-4),
+ %% Year -8 IS a leap year
+ true = calendar:is_leap_year(-8),
+ %% Year -100 is NOT a leap year (divisible by 100, not by 400)
+ false = calendar:is_leap_year(-100),
+ %% Year -200 is NOT a leap year
+ false = calendar:is_leap_year(-200),
+ %% Year -300 is NOT a leap year
+ false = calendar:is_leap_year(-300),
+ %% Year -400 IS a leap year (divisible by 400)
+ true = calendar:is_leap_year(-400),
+ %% Year -800 IS a leap year
+ true = calendar:is_leap_year(-800),
+ %% Year -500 is NOT a leap year
+ false = calendar:is_leap_year(-500),
+
+ %% Check leap years from -1000 to 0
+ check_negative_leap_years(-1000, 0),
+
+ ok.
+
+%% Helper: verify leap year logic for negative years
+check_negative_leap_years(Year, EndYear) when Year < EndYear ->
+ Expected = (Year rem 4 =:= 0) andalso
+ ((Year rem 100 =/= 0) orelse (Year rem 400 =:= 0)),
+ Expected = calendar:is_leap_year(Year),
+ check_negative_leap_years(Year + 1, EndYear);
+check_negative_leap_years(_, _) ->
+ ok.
+
+%% Tests day_of_the_week for negative dates
+negative_day_of_the_week(Config) when is_list(Config) ->
+ %% Jan 1, year 0 is a Saturday (day 6)
+ 6 = calendar:day_of_the_week({0, 1, 1}),
+ %% Dec 31, year -1 should be Friday (day 5)
+ 5 = calendar:day_of_the_week({-1, 12, 31}),
+ %% Dec 30, year -1 should be Thursday (day 4)
+ 4 = calendar:day_of_the_week({-1, 12, 30}),
+
+ %% Verify 7-day cycle works for negative dates
+ lists:foreach(
+ fun(Days) ->
+ DOW1 = calendar:day_of_the_week(calendar:gregorian_days_to_date(Days)),
+ DOW2 = calendar:day_of_the_week(calendar:gregorian_days_to_date(Days + 7)),
+ true = (DOW1 =:= DOW2),
+ true = (DOW1 >= 1 andalso DOW1 =< 7)
+ end, lists:seq(-100000, 0, 1000)),
+
+ ok.
+
%% Tests that datetime_to_gregorian_seconds and
%% gregorian_seconds_to_date are each others inverses for a sampled
%% number of seconds from ?START_YEAR-01-01 up to ?END_YEAR-01-01: We check
@@ -305,6 +455,7 @@ rfc3339(Config) when is_list(Config) ->
roundtrip_fmt_rfc3339_z(253402300799*1_000_000+999_999, Mys),
"9999-12-31T23:59:59.999999999Z" =
roundtrip_fmt_rfc3339_z(253402300799*1_000_000_000+999_999_999, Ns),
+ %% Year 10000 is out of range (restricted to -9999..9999)
{'EXIT', _} = (catch do_format_z(253402300799+1, [])),
{'EXIT', _} = (catch do_parse("9999-12-31T23:59:60Z", [])),
{'EXIT', _} = (catch do_format_z(253402300799*1_000_000_000+999_999_999+1, Ns)),
@@ -338,6 +489,17 @@ rfc3339(Config) when is_list(Config) ->
"1970-01-01T00:00:00.000001Z" =
test_parse("1970-01-01T00:00:00.000001Z", Mys),
+ %% Negative years (ISO 8601 extended format)
+ "-0001-01-01T00:00:00Z" = test_parse("-0001-01-01T00:00:00Z"),
+ "-0001-12-31T23:59:59Z" = test_parse("-0001-12-31T23:59:59Z"),
+ "-0004-02-29T12:30:45Z" = test_parse("-0004-02-29T12:30:45Z"), % leap year
+ "-0100-06-15T00:00:00Z" = test_parse("-0100-06-15T00:00:00Z"),
+ "-0400-02-29T00:00:00Z" = test_parse("-0400-02-29T00:00:00Z"), % leap year (div 400)
+ %% Binary input for negative years
+ "-0001-01-01T00:00:00Z" = test_parse(<<"-0001-01-01T00:00:00Z">>),
+ "-0004-02-29T12:30:45Z" = test_parse(<<"-0004-02-29T12:30:45Z">>),
+
+
test_time(erlang:system_time(second), []),
test_time(erlang:system_time(second), Z),
test_time(erlang:system_time(second), Z ++ S),
diff --git a/lib/stdlib/test/calendar_prop_SUITE.erl b/lib/stdlib/test/calendar_prop_SUITE.erl
index 0d91134623..efef81a901 100644
--- a/lib/stdlib/test/calendar_prop_SUITE.erl
+++ b/lib/stdlib/test/calendar_prop_SUITE.erl
@@ -29,7 +29,9 @@
gregorian_days_roundtrip/1,
gregorian_days_monotonic/1,
day_of_week_cycle/1,
- year_length/1]).
+ year_length/1,
+ negative_leap_year/1,
+ gregorian_seconds_roundtrip/1]).
suite() ->
[{ct_hooks,[ts_install_cth]}].
@@ -41,7 +43,9 @@ all() ->
gregorian_days_roundtrip,
gregorian_days_monotonic,
day_of_week_cycle,
- year_length].
+ year_length,
+ negative_leap_year,
+ gregorian_seconds_roundtrip].
groups() ->
[].
@@ -92,3 +96,13 @@ year_length(Config) when is_list(Config) ->
ct_property_test:quickcheck(
calendar_prop:year_length(),
Config).
+
+negative_leap_year(Config) when is_list(Config) ->
+ ct_property_test:quickcheck(
+ calendar_prop:negative_leap_year(),
+ Config).
+
+gregorian_seconds_roundtrip(Config) when is_list(Config) ->
+ ct_property_test:quickcheck(
+ calendar_prop:gregorian_seconds_roundtrip(),
+ Config).
diff --git a/lib/stdlib/test/property_test/calendar_prop.erl b/lib/stdlib/test/property_test/calendar_prop.erl
index e968bea7b5..2a72f6c94d 100644
--- a/lib/stdlib/test/property_test/calendar_prop.erl
+++ b/lib/stdlib/test/property_test/calendar_prop.erl
@@ -90,10 +90,11 @@ loss(SystemTime, nanosecond) -> SystemTime rem 1_000_000_000;
loss(SystemTime, native) -> loss(erlang:convert_time_unit(SystemTime, native, nanosecond), nanosecond).
%% Property: date_to_gregorian_days and gregorian_days_to_date are inverses
+%% Includes negative days (dates before year 0)
gregorian_days_roundtrip() ->
?FORALL(
Days,
- integer(0, 4_000_000), % Covers year 0 to ~10950
+ integer(-1_000_000, 4_000_000), % Covers year ~-2738 to ~10950
begin
Date = calendar:gregorian_days_to_date(Days),
Days =:= calendar:date_to_gregorian_days(Date)
@@ -115,10 +116,11 @@ gregorian_days_monotonic() ->
).
%% Property: day_of_the_week cycles correctly (1-7, Monday-Sunday)
+%% Includes negative days (dates before year 0)
day_of_week_cycle() ->
?FORALL(
Days,
- integer(0, 1_000_000),
+ integer(-500_000, 1_000_000),
begin
DOW1 = calendar:day_of_the_week(calendar:gregorian_days_to_date(Days)),
DOW2 = calendar:day_of_the_week(calendar:gregorian_days_to_date(Days + 7)),
@@ -127,10 +129,11 @@ day_of_week_cycle() ->
).
%% Property: leap years have 366 days, non-leap years have 365 days
+%% Includes negative years
year_length() ->
?FORALL(
Year,
- integer(0, 10000),
+ integer(-2000, 10000),
begin
Jan1 = calendar:date_to_gregorian_days(Year, 1, 1),
Dec31 = calendar:date_to_gregorian_days(Year, 12, 31),
@@ -143,9 +146,9 @@ year_length() ->
end
).
-%% Generator for valid dates
+%% Generator for valid dates (including negative years)
valid_date() ->
- ?LET(Year, integer(0, 9999),
+ ?LET(Year, integer(-2000, 9999),
?LET(Month, integer(1, 12),
?LET(Day, integer(1, calendar:last_day_of_the_month(Year, Month)),
{Year, Month, Day}))).
@@ -161,3 +164,27 @@ next_day(Year, Month, Day) ->
true ->
{Year + 1, 1, 1}
end.
+
+%% Property: leap year rules work correctly for negative years
+negative_leap_year() ->
+ ?FORALL(
+ Year,
+ integer(-10000, -1),
+ begin
+ IsLeap = calendar:is_leap_year(Year),
+ Expected = (Year rem 4 =:= 0) andalso
+ ((Year rem 100 =/= 0) orelse (Year rem 400 =:= 0)),
+ IsLeap =:= Expected
+ end
+ ).
+
+%% Property: gregorian_seconds roundtrip works for negative seconds
+gregorian_seconds_roundtrip() ->
+ ?FORALL(
+ Secs,
+ integer(-100_000_000, 100_000_000),
+ begin
+ DateTime = calendar:gregorian_seconds_to_datetime(Secs),
+ Secs =:= calendar:datetime_to_gregorian_seconds(DateTime)
+ end
+ ).
--
2.51.0
