FA-76941 / Calendar recurrence rules / Open access
Yearly BYMONTH/BYMONTHDAY with leap-day skipping: leap rule · case 01
A February 29 series reports an instance in 2100.
ROOT CAUSE
The leap-year test ignores the century exception.
VERIFIED REPAIR
At the leap rule decision use `y % 4 == 0 and (y % 100 != 0 or y % 400 == 0)`, leaving the other decision sites of the model unchanged.
Unsuccessful approach: The partial repair `y % 4 == 0 and y % 100 != 0` excludes every century, including 2000 which is a leap year.
Case contract
FREQ=YEARLY on a fixed month and day. Years are dtstart.year + k*interval. A year in which the date does not exist (for example February 29 in a common year) is skipped, never clamped. Gregorian leap years: divisible by 4, except centuries not divisible by 400. Instances before dtstart are dropped and the series ends at until (inclusive). Return ISO dates.
Why this case matters
Recurring calendar series are expanded into concrete instances for display, reminders and conflict checks.
1 / The failure
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
import datetime as dt
import calendar
N = 1
observations = []
def solve(dtstart, month, day, interval, until):
start = tuple(int(x) for x in dtstart.split('-'))
last = tuple(int(x) for x in until.split('-'))
def is_leap(y):
return y % 4 == 0
out = []
for k in range(500):
y = start[0] + k * interval
if y > last[0]:
break
dim = [31, 29 if is_leap(y) else 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31][month - 1]
dd = day
if dd > dim:
continue
d = (y, month, dd)
if d < start:
continue
if d > last:
break
out.append('%04d-%02d-%02d' % d)
return out
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression: leap day across 2100',
['2092-02-29', 2, 29, 4, '2108-12-31'],
['2092-02-29', '2096-02-29', '2104-02-29', '2108-02-29']),
('leap day includes 2000',
['1996-02-29', 2, 29, 1, '2004-03-01'],
['1996-02-29', '2000-02-29', '2004-02-29']),
('anniversary before dtstart, interval 2',
['2024-06-01', 3, 15, 2, '2031-01-01'],
['2026-03-15', '2028-03-15', '2030-03-15']),
('until exactly on instance',
['2020-07-04', 7, 4, 1, '2023-07-04'],
['2020-07-04', '2021-07-04', '2022-07-04', '2023-07-04']),
('until year partial', ['2020-01-10', 12, 25, 1, '2022-06-30'], ['2020-12-25', '2021-12-25']),
('leap day from common year',
['2023-01-01', 2, 29, 1, '2033-01-01'],
['2024-02-29', '2028-02-29', '2032-02-29']),
('same month earlier day',
['2024-05-20', 5, 10, 1, '2027-12-31'],
['2025-05-10', '2026-05-10', '2027-05-10'])],
[('anniversary before dtstart, interval 2',
['2024-06-01', 3, 15, 2, '2031-01-01'],
['2026-03-15', '2028-03-15', '2030-03-15']),
('until exactly on instance',
['2020-07-04', 7, 4, 1, '2023-07-04'],
['2020-07-04', '2021-07-04', '2022-07-04', '2023-07-04']),
('until year partial', ['2020-01-10', 12, 25, 1, '2022-06-30'], ['2020-12-25', '2021-12-25']),
('leap day from common year',
['2023-01-01', 2, 29, 1, '2033-01-01'],
['2024-02-29', '2028-02-29', '2032-02-29']),
('same month earlier day',
['2024-05-20', 5, 10, 1, '2027-12-31'],
['2025-05-10', '2026-05-10', '2027-05-10']),
('dtstart on anniversary',
['2021-11-11', 11, 11, 3, '2031-11-11'],
['2021-11-11', '2024-11-11', '2027-11-11', '2030-11-11']),
('interval 4 leap-day from 2023', ['2023-03-01', 2, 29, 4, '2040-12-31'], []),
('regression: leap day across 2100',
['2092-02-29', 2, 29, 4, '2108-12-31'],
['2092-02-29', '2096-02-29', '2104-02-29', '2108-02-29']),
('leap day includes 2000',
['1996-02-29', 2, 29, 1, '2004-03-01'],
['1996-02-29', '2000-02-29', '2004-02-29'])],
[('until year partial', ['2020-01-10', 12, 25, 1, '2022-06-30'], ['2020-12-25', '2021-12-25']),
('leap day from common year',
['2023-01-01', 2, 29, 1, '2033-01-01'],
['2024-02-29', '2028-02-29', '2032-02-29']),
('same month earlier day',
['2024-05-20', 5, 10, 1, '2027-12-31'],
['2025-05-10', '2026-05-10', '2027-05-10']),
('dtstart on anniversary',
['2021-11-11', 11, 11, 3, '2031-11-11'],
['2021-11-11', '2024-11-11', '2027-11-11', '2030-11-11']),
('interval 4 leap-day from 2023', ['2023-03-01', 2, 29, 4, '2040-12-31'], []),
('year-end date',
['2019-12-31', 12, 31, 2, '2026-01-01'],
['2019-12-31', '2021-12-31', '2023-12-31', '2025-12-31']),
('century non-leap interval 1', ['2098-01-01', 2, 29, 1, '2105-01-01'], ['2104-02-29']),
('leap day includes 2000',
['1996-02-29', 2, 29, 1, '2004-03-01'],
['1996-02-29', '2000-02-29', '2004-02-29'])],
[('same month earlier day',
['2024-05-20', 5, 10, 1, '2027-12-31'],
['2025-05-10', '2026-05-10', '2027-05-10']),
('dtstart on anniversary',
['2021-11-11', 11, 11, 3, '2031-11-11'],
['2021-11-11', '2024-11-11', '2027-11-11', '2030-11-11']),
('interval 4 leap-day from 2023', ['2023-03-01', 2, 29, 4, '2040-12-31'], []),
('year-end date',
['2019-12-31', 12, 31, 2, '2026-01-01'],
['2019-12-31', '2021-12-31', '2023-12-31', '2025-12-31']),
('century non-leap interval 1', ['2098-01-01', 2, 29, 1, '2105-01-01'], ['2104-02-29']),
('regression: leap day across 2100',
['2092-02-29', 2, 29, 4, '2108-12-31'],
['2092-02-29', '2096-02-29', '2104-02-29', '2108-02-29']),
('leap day includes 2000',
['1996-02-29', 2, 29, 1, '2004-03-01'],
['1996-02-29', '2000-02-29', '2004-02-29'])],
[('interval 4 leap-day from 2023', ['2023-03-01', 2, 29, 4, '2040-12-31'], []),
('year-end date',
['2019-12-31', 12, 31, 2, '2026-01-01'],
['2019-12-31', '2021-12-31', '2023-12-31', '2025-12-31']),
('century non-leap interval 1', ['2098-01-01', 2, 29, 1, '2105-01-01'], ['2104-02-29']),
('regression: leap day across 2100',
['2092-02-29', 2, 29, 4, '2108-12-31'],
['2092-02-29', '2096-02-29', '2104-02-29', '2108-02-29']),
('leap day includes 2000',
['1996-02-29', 2, 29, 1, '2004-03-01'],
['1996-02-29', '2000-02-29', '2004-02-29']),
('anniversary before dtstart, interval 2',
['2024-06-01', 3, 15, 2, '2031-01-01'],
['2026-03-15', '2028-03-15', '2030-03-15']),
('until exactly on instance',
['2020-07-04', 7, 4, 1, '2023-07-04'],
['2020-07-04', '2021-07-04', '2022-07-04', '2023-07-04'])]]
for label, args, expected in fixtures[N-1]:
check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| regression: leap day across 2100 | ['2092-02-29', '2096-02-29', '2100-02-29', '2104-02-29', '2108-02-29'] | ['2092-02-29', '2096-02-29', '2104-02-29', '2108-02-29'] | Failed |
| leap day includes 2000 | ['1996-02-29', '2000-02-29', '2004-02-29'] | ['1996-02-29', '2000-02-29', '2004-02-29'] | Passed |
| anniversary before dtstart, interval 2 | ['2026-03-15', '2028-03-15', '2030-03-15'] | ['2026-03-15', '2028-03-15', '2030-03-15'] | Passed |
| until exactly on instance | ['2020-07-04', '2021-07-04', '2022-07-04', '2023-07-04'] | ['2020-07-04', '2021-07-04', '2022-07-04', '2023-07-04'] | Passed |
| until year partial | ['2020-12-25', '2021-12-25'] | ['2020-12-25', '2021-12-25'] | Passed |
| leap day from common year | ['2024-02-29', '2028-02-29', '2032-02-29'] | ['2024-02-29', '2028-02-29', '2032-02-29'] | Passed |
| same month earlier day | ['2025-05-10', '2026-05-10', '2027-05-10'] | ['2025-05-10', '2026-05-10', '2027-05-10'] | Passed |
SHA-256 / d3a71eb554b466e36f613925fc39b0a00c30c06a682ebcc46622aa145b47182a
2 / The unsuccessful fix
Exit 1"""Failure Map reference implementation. Python standard library only."""
import json
import datetime as dt
import calendar
N = 1
observations = []
def solve(dtstart, month, day, interval, until):
start = tuple(int(x) for x in dtstart.split('-'))
last = tuple(int(x) for x in until.split('-'))
def is_leap(y):
return y % 4 == 0 and y % 100 != 0
out = []
for k in range(500):
y = start[0] + k * interval
if y > last[0]:
break
dim = [31, 29 if is_leap(y) else 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31][month - 1]
dd = day
if dd > dim:
continue
d = (y, month, dd)
if d < start:
continue
if d > last:
break
out.append('%04d-%02d-%02d' % d)
return out
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression: leap day across 2100',
['2092-02-29', 2, 29, 4, '2108-12-31'],
['2092-02-29', '2096-02-29', '2104-02-29', '2108-02-29']),
('leap day includes 2000',
['1996-02-29', 2, 29, 1, '2004-03-01'],
['1996-02-29', '2000-02-29', '2004-02-29']),
('anniversary before dtstart, interval 2',
['2024-06-01', 3, 15, 2, '2031-01-01'],
['2026-03-15', '2028-03-15', '2030-03-15']),
('until exactly on instance',
['2020-07-04', 7, 4, 1, '2023-07-04'],
['2020-07-04', '2021-07-04', '2022-07-04', '2023-07-04']),
('until year partial', ['2020-01-10', 12, 25, 1, '2022-06-30'], ['2020-12-25', '2021-12-25']),
('leap day from common year',
['2023-01-01', 2, 29, 1, '2033-01-01'],
['2024-02-29', '2028-02-29', '2032-02-29']),
('same month earlier day',
['2024-05-20', 5, 10, 1, '2027-12-31'],
['2025-05-10', '2026-05-10', '2027-05-10'])],
[('anniversary before dtstart, interval 2',
['2024-06-01', 3, 15, 2, '2031-01-01'],
['2026-03-15', '2028-03-15', '2030-03-15']),
('until exactly on instance',
['2020-07-04', 7, 4, 1, '2023-07-04'],
['2020-07-04', '2021-07-04', '2022-07-04', '2023-07-04']),
('until year partial', ['2020-01-10', 12, 25, 1, '2022-06-30'], ['2020-12-25', '2021-12-25']),
('leap day from common year',
['2023-01-01', 2, 29, 1, '2033-01-01'],
['2024-02-29', '2028-02-29', '2032-02-29']),
('same month earlier day',
['2024-05-20', 5, 10, 1, '2027-12-31'],
['2025-05-10', '2026-05-10', '2027-05-10']),
('dtstart on anniversary',
['2021-11-11', 11, 11, 3, '2031-11-11'],
['2021-11-11', '2024-11-11', '2027-11-11', '2030-11-11']),
('interval 4 leap-day from 2023', ['2023-03-01', 2, 29, 4, '2040-12-31'], []),
('regression: leap day across 2100',
['2092-02-29', 2, 29, 4, '2108-12-31'],
['2092-02-29', '2096-02-29', '2104-02-29', '2108-02-29']),
('leap day includes 2000',
['1996-02-29', 2, 29, 1, '2004-03-01'],
['1996-02-29', '2000-02-29', '2004-02-29'])],
[('until year partial', ['2020-01-10', 12, 25, 1, '2022-06-30'], ['2020-12-25', '2021-12-25']),
('leap day from common year',
['2023-01-01', 2, 29, 1, '2033-01-01'],
['2024-02-29', '2028-02-29', '2032-02-29']),
('same month earlier day',
['2024-05-20', 5, 10, 1, '2027-12-31'],
['2025-05-10', '2026-05-10', '2027-05-10']),
('dtstart on anniversary',
['2021-11-11', 11, 11, 3, '2031-11-11'],
['2021-11-11', '2024-11-11', '2027-11-11', '2030-11-11']),
('interval 4 leap-day from 2023', ['2023-03-01', 2, 29, 4, '2040-12-31'], []),
('year-end date',
['2019-12-31', 12, 31, 2, '2026-01-01'],
['2019-12-31', '2021-12-31', '2023-12-31', '2025-12-31']),
('century non-leap interval 1', ['2098-01-01', 2, 29, 1, '2105-01-01'], ['2104-02-29']),
('leap day includes 2000',
['1996-02-29', 2, 29, 1, '2004-03-01'],
['1996-02-29', '2000-02-29', '2004-02-29'])],
[('same month earlier day',
['2024-05-20', 5, 10, 1, '2027-12-31'],
['2025-05-10', '2026-05-10', '2027-05-10']),
('dtstart on anniversary',
['2021-11-11', 11, 11, 3, '2031-11-11'],
['2021-11-11', '2024-11-11', '2027-11-11', '2030-11-11']),
('interval 4 leap-day from 2023', ['2023-03-01', 2, 29, 4, '2040-12-31'], []),
('year-end date',
['2019-12-31', 12, 31, 2, '2026-01-01'],
['2019-12-31', '2021-12-31', '2023-12-31', '2025-12-31']),
('century non-leap interval 1', ['2098-01-01', 2, 29, 1, '2105-01-01'], ['2104-02-29']),
('regression: leap day across 2100',
['2092-02-29', 2, 29, 4, '2108-12-31'],
['2092-02-29', '2096-02-29', '2104-02-29', '2108-02-29']),
('leap day includes 2000',
['1996-02-29', 2, 29, 1, '2004-03-01'],
['1996-02-29', '2000-02-29', '2004-02-29'])],
[('interval 4 leap-day from 2023', ['2023-03-01', 2, 29, 4, '2040-12-31'], []),
('year-end date',
['2019-12-31', 12, 31, 2, '2026-01-01'],
['2019-12-31', '2021-12-31', '2023-12-31', '2025-12-31']),
('century non-leap interval 1', ['2098-01-01', 2, 29, 1, '2105-01-01'], ['2104-02-29']),
('regression: leap day across 2100',
['2092-02-29', 2, 29, 4, '2108-12-31'],
['2092-02-29', '2096-02-29', '2104-02-29', '2108-02-29']),
('leap day includes 2000',
['1996-02-29', 2, 29, 1, '2004-03-01'],
['1996-02-29', '2000-02-29', '2004-02-29']),
('anniversary before dtstart, interval 2',
['2024-06-01', 3, 15, 2, '2031-01-01'],
['2026-03-15', '2028-03-15', '2030-03-15']),
('until exactly on instance',
['2020-07-04', 7, 4, 1, '2023-07-04'],
['2020-07-04', '2021-07-04', '2022-07-04', '2023-07-04'])]]
for label, args, expected in fixtures[N-1]:
check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| regression: leap day across 2100 | ['2092-02-29', '2096-02-29', '2104-02-29', '2108-02-29'] | ['2092-02-29', '2096-02-29', '2104-02-29', '2108-02-29'] | Passed |
| leap day includes 2000 | ['1996-02-29', '2004-02-29'] | ['1996-02-29', '2000-02-29', '2004-02-29'] | Failed |
| anniversary before dtstart, interval 2 | ['2026-03-15', '2028-03-15', '2030-03-15'] | ['2026-03-15', '2028-03-15', '2030-03-15'] | Passed |
| until exactly on instance | ['2020-07-04', '2021-07-04', '2022-07-04', '2023-07-04'] | ['2020-07-04', '2021-07-04', '2022-07-04', '2023-07-04'] | Passed |
| until year partial | ['2020-12-25', '2021-12-25'] | ['2020-12-25', '2021-12-25'] | Passed |
| leap day from common year | ['2024-02-29', '2028-02-29', '2032-02-29'] | ['2024-02-29', '2028-02-29', '2032-02-29'] | Passed |
| same month earlier day | ['2025-05-10', '2026-05-10', '2027-05-10'] | ['2025-05-10', '2026-05-10', '2027-05-10'] | Passed |
SHA-256 / 92d8f59f0388ddad7d70bf76b0d141e56bbb0889a8289fba535bdff1acd7bf77
3 / The verified repair
Exit 0"""Failure Map reference implementation. Python standard library only."""
import json
import datetime as dt
import calendar
N = 1
observations = []
def solve(dtstart, month, day, interval, until):
start = tuple(int(x) for x in dtstart.split('-'))
last = tuple(int(x) for x in until.split('-'))
def is_leap(y):
return y % 4 == 0 and (y % 100 != 0 or y % 400 == 0)
out = []
for k in range(500):
y = start[0] + k * interval
if y > last[0]:
break
dim = [31, 29 if is_leap(y) else 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31][month - 1]
dd = day
if dd > dim:
continue
d = (y, month, dd)
if d < start:
continue
if d > last:
break
out.append('%04d-%02d-%02d' % d)
return out
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression: leap day across 2100',
['2092-02-29', 2, 29, 4, '2108-12-31'],
['2092-02-29', '2096-02-29', '2104-02-29', '2108-02-29']),
('leap day includes 2000',
['1996-02-29', 2, 29, 1, '2004-03-01'],
['1996-02-29', '2000-02-29', '2004-02-29']),
('anniversary before dtstart, interval 2',
['2024-06-01', 3, 15, 2, '2031-01-01'],
['2026-03-15', '2028-03-15', '2030-03-15']),
('until exactly on instance',
['2020-07-04', 7, 4, 1, '2023-07-04'],
['2020-07-04', '2021-07-04', '2022-07-04', '2023-07-04']),
('until year partial', ['2020-01-10', 12, 25, 1, '2022-06-30'], ['2020-12-25', '2021-12-25']),
('leap day from common year',
['2023-01-01', 2, 29, 1, '2033-01-01'],
['2024-02-29', '2028-02-29', '2032-02-29']),
('same month earlier day',
['2024-05-20', 5, 10, 1, '2027-12-31'],
['2025-05-10', '2026-05-10', '2027-05-10'])],
[('anniversary before dtstart, interval 2',
['2024-06-01', 3, 15, 2, '2031-01-01'],
['2026-03-15', '2028-03-15', '2030-03-15']),
('until exactly on instance',
['2020-07-04', 7, 4, 1, '2023-07-04'],
['2020-07-04', '2021-07-04', '2022-07-04', '2023-07-04']),
('until year partial', ['2020-01-10', 12, 25, 1, '2022-06-30'], ['2020-12-25', '2021-12-25']),
('leap day from common year',
['2023-01-01', 2, 29, 1, '2033-01-01'],
['2024-02-29', '2028-02-29', '2032-02-29']),
('same month earlier day',
['2024-05-20', 5, 10, 1, '2027-12-31'],
['2025-05-10', '2026-05-10', '2027-05-10']),
('dtstart on anniversary',
['2021-11-11', 11, 11, 3, '2031-11-11'],
['2021-11-11', '2024-11-11', '2027-11-11', '2030-11-11']),
('interval 4 leap-day from 2023', ['2023-03-01', 2, 29, 4, '2040-12-31'], []),
('regression: leap day across 2100',
['2092-02-29', 2, 29, 4, '2108-12-31'],
['2092-02-29', '2096-02-29', '2104-02-29', '2108-02-29']),
('leap day includes 2000',
['1996-02-29', 2, 29, 1, '2004-03-01'],
['1996-02-29', '2000-02-29', '2004-02-29'])],
[('until year partial', ['2020-01-10', 12, 25, 1, '2022-06-30'], ['2020-12-25', '2021-12-25']),
('leap day from common year',
['2023-01-01', 2, 29, 1, '2033-01-01'],
['2024-02-29', '2028-02-29', '2032-02-29']),
('same month earlier day',
['2024-05-20', 5, 10, 1, '2027-12-31'],
['2025-05-10', '2026-05-10', '2027-05-10']),
('dtstart on anniversary',
['2021-11-11', 11, 11, 3, '2031-11-11'],
['2021-11-11', '2024-11-11', '2027-11-11', '2030-11-11']),
('interval 4 leap-day from 2023', ['2023-03-01', 2, 29, 4, '2040-12-31'], []),
('year-end date',
['2019-12-31', 12, 31, 2, '2026-01-01'],
['2019-12-31', '2021-12-31', '2023-12-31', '2025-12-31']),
('century non-leap interval 1', ['2098-01-01', 2, 29, 1, '2105-01-01'], ['2104-02-29']),
('leap day includes 2000',
['1996-02-29', 2, 29, 1, '2004-03-01'],
['1996-02-29', '2000-02-29', '2004-02-29'])],
[('same month earlier day',
['2024-05-20', 5, 10, 1, '2027-12-31'],
['2025-05-10', '2026-05-10', '2027-05-10']),
('dtstart on anniversary',
['2021-11-11', 11, 11, 3, '2031-11-11'],
['2021-11-11', '2024-11-11', '2027-11-11', '2030-11-11']),
('interval 4 leap-day from 2023', ['2023-03-01', 2, 29, 4, '2040-12-31'], []),
('year-end date',
['2019-12-31', 12, 31, 2, '2026-01-01'],
['2019-12-31', '2021-12-31', '2023-12-31', '2025-12-31']),
('century non-leap interval 1', ['2098-01-01', 2, 29, 1, '2105-01-01'], ['2104-02-29']),
('regression: leap day across 2100',
['2092-02-29', 2, 29, 4, '2108-12-31'],
['2092-02-29', '2096-02-29', '2104-02-29', '2108-02-29']),
('leap day includes 2000',
['1996-02-29', 2, 29, 1, '2004-03-01'],
['1996-02-29', '2000-02-29', '2004-02-29'])],
[('interval 4 leap-day from 2023', ['2023-03-01', 2, 29, 4, '2040-12-31'], []),
('year-end date',
['2019-12-31', 12, 31, 2, '2026-01-01'],
['2019-12-31', '2021-12-31', '2023-12-31', '2025-12-31']),
('century non-leap interval 1', ['2098-01-01', 2, 29, 1, '2105-01-01'], ['2104-02-29']),
('regression: leap day across 2100',
['2092-02-29', 2, 29, 4, '2108-12-31'],
['2092-02-29', '2096-02-29', '2104-02-29', '2108-02-29']),
('leap day includes 2000',
['1996-02-29', 2, 29, 1, '2004-03-01'],
['1996-02-29', '2000-02-29', '2004-02-29']),
('anniversary before dtstart, interval 2',
['2024-06-01', 3, 15, 2, '2031-01-01'],
['2026-03-15', '2028-03-15', '2030-03-15']),
('until exactly on instance',
['2020-07-04', 7, 4, 1, '2023-07-04'],
['2020-07-04', '2021-07-04', '2022-07-04', '2023-07-04'])]]
for label, args, expected in fixtures[N-1]:
check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
| Boundary fixture | Actual | Expected | Outcome |
|---|---|---|---|
| regression: leap day across 2100 | ['2092-02-29', '2096-02-29', '2104-02-29', '2108-02-29'] | ['2092-02-29', '2096-02-29', '2104-02-29', '2108-02-29'] | Passed |
| leap day includes 2000 | ['1996-02-29', '2000-02-29', '2004-02-29'] | ['1996-02-29', '2000-02-29', '2004-02-29'] | Passed |
| anniversary before dtstart, interval 2 | ['2026-03-15', '2028-03-15', '2030-03-15'] | ['2026-03-15', '2028-03-15', '2030-03-15'] | Passed |
| until exactly on instance | ['2020-07-04', '2021-07-04', '2022-07-04', '2023-07-04'] | ['2020-07-04', '2021-07-04', '2022-07-04', '2023-07-04'] | Passed |
| until year partial | ['2020-12-25', '2021-12-25'] | ['2020-12-25', '2021-12-25'] | Passed |
| leap day from common year | ['2024-02-29', '2028-02-29', '2032-02-29'] | ['2024-02-29', '2028-02-29', '2032-02-29'] | Passed |
| same month earlier day | ['2025-05-10', '2026-05-10', '2027-05-10'] | ['2025-05-10', '2026-05-10', '2027-05-10'] | Passed |
SHA-256 / 7a1cb20804979af7f04ed451c449747122471af0545b1505788e2793cccd735c
Verification & scope
Stipulated, bounded recurrence-expansion model evaluated offline on explicit fixtures; it is not a complete iCalendar implementation and makes no claim of standards conformance. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.
Observations recorded using Python 3.12.14 at 2026-09-29T14:49:20.977825+00:00.
Case digest / 4cfcbb98ed68c01ba228a8250b79b78e9ff1c7f3bf78b49977053f2fa73c3d4c