FA-77336 / Calendar recurrence rules / Open access
Next due date for a recurring task after completions: series end · case 01
The final occurrence falling exactly on the end date is dropped.
ROOT CAUSE
The end bound is treated as exclusive.
VERIFIED REPAIR
At the series end decision use `end is not None and due > end`, leaving the other decision sites of the model unchanged.
Unsuccessful approach: The partial repair `end is not None and cd > end` tests the completion date rather than the next due date.
Case contract
A recurring task first due on first_due repeats every interval_days. Completions are processed in chronological order. mode "regenerate": the next due date is completion + interval. mode "schedule": completing advances to the next scheduled due date, skipping every scheduled date on or before the completion date. If the resulting due date passes until (inclusive bound, may be None), the task has no next due date (None).
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(first_due, interval_days, mode, completions, until):
due = dt.date.fromisoformat(first_due)
end = dt.date.fromisoformat(until) if until else None
step = dt.timedelta(days=interval_days)
for c in sorted(completions):
cd = dt.date.fromisoformat(c)
if mode == 'regenerate':
due = cd + step
else:
due = due + step
while due <= cd:
due += step
if end is not None and due >= end:
return None
return due.isoformat()
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression: late completion on next due',
['2024-01-01', 7, 'schedule', ['2024-01-08'], None],
'2024-01-15'),
('early completion regenerate', ['2024-01-10', 7, 'regenerate', ['2024-01-05'], None], '2024-01-12'),
('late completion regenerate', ['2024-01-10', 7, 'regenerate', ['2024-01-20'], None], '2024-01-27'),
('out of order schedule', ['2024-01-01', 7, 'schedule', ['2024-01-20', '2024-01-02'], None], '2024-01-22'),
('multiple missed schedule', ['2024-01-01', 3, 'schedule', ['2024-01-11'], None], '2024-01-13'),
('until exact', ['2024-01-01', 7, 'schedule', ['2024-01-01'], '2024-01-08'], '2024-01-08'),
('until passed', ['2024-01-01', 7, 'schedule', ['2024-01-01', '2024-01-08'], '2024-01-10'], None)],
[('late completion regenerate', ['2024-01-10', 7, 'regenerate', ['2024-01-20'], None], '2024-01-27'),
('out of order schedule', ['2024-01-01', 7, 'schedule', ['2024-01-20', '2024-01-02'], None], '2024-01-22'),
('multiple missed schedule', ['2024-01-01', 3, 'schedule', ['2024-01-11'], None], '2024-01-13'),
('until exact', ['2024-01-01', 7, 'schedule', ['2024-01-01'], '2024-01-08'], '2024-01-08'),
('until passed', ['2024-01-01', 7, 'schedule', ['2024-01-01', '2024-01-08'], '2024-01-10'], None),
('until regenerate', ['2024-02-01', 10, 'regenerate', ['2024-02-05'], '2024-02-15'], '2024-02-15'),
('no completions', ['2024-02-01', 10, 'schedule', [], None], '2024-02-01')],
[('multiple missed schedule', ['2024-01-01', 3, 'schedule', ['2024-01-11'], None], '2024-01-13'),
('until exact', ['2024-01-01', 7, 'schedule', ['2024-01-01'], '2024-01-08'], '2024-01-08'),
('until passed', ['2024-01-01', 7, 'schedule', ['2024-01-01', '2024-01-08'], '2024-01-10'], None),
('until regenerate', ['2024-02-01', 10, 'regenerate', ['2024-02-05'], '2024-02-15'], '2024-02-15'),
('no completions', ['2024-02-01', 10, 'schedule', [], None], '2024-02-01'),
('completion after until but due inside',
['2024-03-01', 30, 'schedule', ['2024-03-05'], '2024-03-31'],
'2024-03-31'),
('two schedule completions',
['2024-04-01', 14, 'schedule', ['2024-03-30', '2024-04-10'], None],
'2024-04-29')],
[('until passed', ['2024-01-01', 7, 'schedule', ['2024-01-01', '2024-01-08'], '2024-01-10'], None),
('until regenerate', ['2024-02-01', 10, 'regenerate', ['2024-02-05'], '2024-02-15'], '2024-02-15'),
('no completions', ['2024-02-01', 10, 'schedule', [], None], '2024-02-01'),
('completion after until but due inside',
['2024-03-01', 30, 'schedule', ['2024-03-05'], '2024-03-31'],
'2024-03-31'),
('two schedule completions',
['2024-04-01', 14, 'schedule', ['2024-03-30', '2024-04-10'], None],
'2024-04-29'),
('out of order regenerate',
['2024-04-01', 5, 'regenerate', ['2024-04-09', '2024-04-02'], None],
'2024-04-14'),
('regression: late completion on next due',
['2024-01-01', 7, 'schedule', ['2024-01-08'], None],
'2024-01-15')],
[('no completions', ['2024-02-01', 10, 'schedule', [], None], '2024-02-01'),
('completion after until but due inside',
['2024-03-01', 30, 'schedule', ['2024-03-05'], '2024-03-31'],
'2024-03-31'),
('two schedule completions',
['2024-04-01', 14, 'schedule', ['2024-03-30', '2024-04-10'], None],
'2024-04-29'),
('out of order regenerate',
['2024-04-01', 5, 'regenerate', ['2024-04-09', '2024-04-02'], None],
'2024-04-14'),
('regression: late completion on next due',
['2024-01-01', 7, 'schedule', ['2024-01-08'], None],
'2024-01-15'),
('early completion regenerate', ['2024-01-10', 7, 'regenerate', ['2024-01-05'], None], '2024-01-12'),
('late completion regenerate', ['2024-01-10', 7, 'regenerate', ['2024-01-20'], None], '2024-01-27'),
('until passed', ['2024-01-01', 7, 'schedule', ['2024-01-01', '2024-01-08'], '2024-01-10'], None)]]
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: late completion on next due | 2024-01-15 | 2024-01-15 | Passed |
| early completion regenerate | 2024-01-12 | 2024-01-12 | Passed |
| late completion regenerate | 2024-01-27 | 2024-01-27 | Passed |
| out of order schedule | 2024-01-22 | 2024-01-22 | Passed |
| multiple missed schedule | 2024-01-13 | 2024-01-13 | Passed |
| until exact | None | 2024-01-08 | Failed |
| until passed | None | None | Passed |
SHA-256 / dc376260c72867483427c95b9de795e1ff24441c0390708532f326c3c9860b40
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(first_due, interval_days, mode, completions, until):
due = dt.date.fromisoformat(first_due)
end = dt.date.fromisoformat(until) if until else None
step = dt.timedelta(days=interval_days)
for c in sorted(completions):
cd = dt.date.fromisoformat(c)
if mode == 'regenerate':
due = cd + step
else:
due = due + step
while due <= cd:
due += step
if end is not None and cd > end:
return None
return due.isoformat()
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression: late completion on next due',
['2024-01-01', 7, 'schedule', ['2024-01-08'], None],
'2024-01-15'),
('early completion regenerate', ['2024-01-10', 7, 'regenerate', ['2024-01-05'], None], '2024-01-12'),
('late completion regenerate', ['2024-01-10', 7, 'regenerate', ['2024-01-20'], None], '2024-01-27'),
('out of order schedule', ['2024-01-01', 7, 'schedule', ['2024-01-20', '2024-01-02'], None], '2024-01-22'),
('multiple missed schedule', ['2024-01-01', 3, 'schedule', ['2024-01-11'], None], '2024-01-13'),
('until exact', ['2024-01-01', 7, 'schedule', ['2024-01-01'], '2024-01-08'], '2024-01-08'),
('until passed', ['2024-01-01', 7, 'schedule', ['2024-01-01', '2024-01-08'], '2024-01-10'], None)],
[('late completion regenerate', ['2024-01-10', 7, 'regenerate', ['2024-01-20'], None], '2024-01-27'),
('out of order schedule', ['2024-01-01', 7, 'schedule', ['2024-01-20', '2024-01-02'], None], '2024-01-22'),
('multiple missed schedule', ['2024-01-01', 3, 'schedule', ['2024-01-11'], None], '2024-01-13'),
('until exact', ['2024-01-01', 7, 'schedule', ['2024-01-01'], '2024-01-08'], '2024-01-08'),
('until passed', ['2024-01-01', 7, 'schedule', ['2024-01-01', '2024-01-08'], '2024-01-10'], None),
('until regenerate', ['2024-02-01', 10, 'regenerate', ['2024-02-05'], '2024-02-15'], '2024-02-15'),
('no completions', ['2024-02-01', 10, 'schedule', [], None], '2024-02-01')],
[('multiple missed schedule', ['2024-01-01', 3, 'schedule', ['2024-01-11'], None], '2024-01-13'),
('until exact', ['2024-01-01', 7, 'schedule', ['2024-01-01'], '2024-01-08'], '2024-01-08'),
('until passed', ['2024-01-01', 7, 'schedule', ['2024-01-01', '2024-01-08'], '2024-01-10'], None),
('until regenerate', ['2024-02-01', 10, 'regenerate', ['2024-02-05'], '2024-02-15'], '2024-02-15'),
('no completions', ['2024-02-01', 10, 'schedule', [], None], '2024-02-01'),
('completion after until but due inside',
['2024-03-01', 30, 'schedule', ['2024-03-05'], '2024-03-31'],
'2024-03-31'),
('two schedule completions',
['2024-04-01', 14, 'schedule', ['2024-03-30', '2024-04-10'], None],
'2024-04-29')],
[('until passed', ['2024-01-01', 7, 'schedule', ['2024-01-01', '2024-01-08'], '2024-01-10'], None),
('until regenerate', ['2024-02-01', 10, 'regenerate', ['2024-02-05'], '2024-02-15'], '2024-02-15'),
('no completions', ['2024-02-01', 10, 'schedule', [], None], '2024-02-01'),
('completion after until but due inside',
['2024-03-01', 30, 'schedule', ['2024-03-05'], '2024-03-31'],
'2024-03-31'),
('two schedule completions',
['2024-04-01', 14, 'schedule', ['2024-03-30', '2024-04-10'], None],
'2024-04-29'),
('out of order regenerate',
['2024-04-01', 5, 'regenerate', ['2024-04-09', '2024-04-02'], None],
'2024-04-14'),
('regression: late completion on next due',
['2024-01-01', 7, 'schedule', ['2024-01-08'], None],
'2024-01-15')],
[('no completions', ['2024-02-01', 10, 'schedule', [], None], '2024-02-01'),
('completion after until but due inside',
['2024-03-01', 30, 'schedule', ['2024-03-05'], '2024-03-31'],
'2024-03-31'),
('two schedule completions',
['2024-04-01', 14, 'schedule', ['2024-03-30', '2024-04-10'], None],
'2024-04-29'),
('out of order regenerate',
['2024-04-01', 5, 'regenerate', ['2024-04-09', '2024-04-02'], None],
'2024-04-14'),
('regression: late completion on next due',
['2024-01-01', 7, 'schedule', ['2024-01-08'], None],
'2024-01-15'),
('early completion regenerate', ['2024-01-10', 7, 'regenerate', ['2024-01-05'], None], '2024-01-12'),
('late completion regenerate', ['2024-01-10', 7, 'regenerate', ['2024-01-20'], None], '2024-01-27'),
('until passed', ['2024-01-01', 7, 'schedule', ['2024-01-01', '2024-01-08'], '2024-01-10'], None)]]
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: late completion on next due | 2024-01-15 | 2024-01-15 | Passed |
| early completion regenerate | 2024-01-12 | 2024-01-12 | Passed |
| late completion regenerate | 2024-01-27 | 2024-01-27 | Passed |
| out of order schedule | 2024-01-22 | 2024-01-22 | Passed |
| multiple missed schedule | 2024-01-13 | 2024-01-13 | Passed |
| until exact | 2024-01-08 | 2024-01-08 | Passed |
| until passed | 2024-01-15 | None | Failed |
SHA-256 / 3fcf741d892cf91d6e3b763891be7354f4c5dd8fef350aef8e1ea1703dd1e3a3
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(first_due, interval_days, mode, completions, until):
due = dt.date.fromisoformat(first_due)
end = dt.date.fromisoformat(until) if until else None
step = dt.timedelta(days=interval_days)
for c in sorted(completions):
cd = dt.date.fromisoformat(c)
if mode == 'regenerate':
due = cd + step
else:
due = due + step
while due <= cd:
due += step
if end is not None and due > end:
return None
return due.isoformat()
def check(label, actual, expected):
observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
fixtures = [[('regression: late completion on next due',
['2024-01-01', 7, 'schedule', ['2024-01-08'], None],
'2024-01-15'),
('early completion regenerate', ['2024-01-10', 7, 'regenerate', ['2024-01-05'], None], '2024-01-12'),
('late completion regenerate', ['2024-01-10', 7, 'regenerate', ['2024-01-20'], None], '2024-01-27'),
('out of order schedule', ['2024-01-01', 7, 'schedule', ['2024-01-20', '2024-01-02'], None], '2024-01-22'),
('multiple missed schedule', ['2024-01-01', 3, 'schedule', ['2024-01-11'], None], '2024-01-13'),
('until exact', ['2024-01-01', 7, 'schedule', ['2024-01-01'], '2024-01-08'], '2024-01-08'),
('until passed', ['2024-01-01', 7, 'schedule', ['2024-01-01', '2024-01-08'], '2024-01-10'], None)],
[('late completion regenerate', ['2024-01-10', 7, 'regenerate', ['2024-01-20'], None], '2024-01-27'),
('out of order schedule', ['2024-01-01', 7, 'schedule', ['2024-01-20', '2024-01-02'], None], '2024-01-22'),
('multiple missed schedule', ['2024-01-01', 3, 'schedule', ['2024-01-11'], None], '2024-01-13'),
('until exact', ['2024-01-01', 7, 'schedule', ['2024-01-01'], '2024-01-08'], '2024-01-08'),
('until passed', ['2024-01-01', 7, 'schedule', ['2024-01-01', '2024-01-08'], '2024-01-10'], None),
('until regenerate', ['2024-02-01', 10, 'regenerate', ['2024-02-05'], '2024-02-15'], '2024-02-15'),
('no completions', ['2024-02-01', 10, 'schedule', [], None], '2024-02-01')],
[('multiple missed schedule', ['2024-01-01', 3, 'schedule', ['2024-01-11'], None], '2024-01-13'),
('until exact', ['2024-01-01', 7, 'schedule', ['2024-01-01'], '2024-01-08'], '2024-01-08'),
('until passed', ['2024-01-01', 7, 'schedule', ['2024-01-01', '2024-01-08'], '2024-01-10'], None),
('until regenerate', ['2024-02-01', 10, 'regenerate', ['2024-02-05'], '2024-02-15'], '2024-02-15'),
('no completions', ['2024-02-01', 10, 'schedule', [], None], '2024-02-01'),
('completion after until but due inside',
['2024-03-01', 30, 'schedule', ['2024-03-05'], '2024-03-31'],
'2024-03-31'),
('two schedule completions',
['2024-04-01', 14, 'schedule', ['2024-03-30', '2024-04-10'], None],
'2024-04-29')],
[('until passed', ['2024-01-01', 7, 'schedule', ['2024-01-01', '2024-01-08'], '2024-01-10'], None),
('until regenerate', ['2024-02-01', 10, 'regenerate', ['2024-02-05'], '2024-02-15'], '2024-02-15'),
('no completions', ['2024-02-01', 10, 'schedule', [], None], '2024-02-01'),
('completion after until but due inside',
['2024-03-01', 30, 'schedule', ['2024-03-05'], '2024-03-31'],
'2024-03-31'),
('two schedule completions',
['2024-04-01', 14, 'schedule', ['2024-03-30', '2024-04-10'], None],
'2024-04-29'),
('out of order regenerate',
['2024-04-01', 5, 'regenerate', ['2024-04-09', '2024-04-02'], None],
'2024-04-14'),
('regression: late completion on next due',
['2024-01-01', 7, 'schedule', ['2024-01-08'], None],
'2024-01-15')],
[('no completions', ['2024-02-01', 10, 'schedule', [], None], '2024-02-01'),
('completion after until but due inside',
['2024-03-01', 30, 'schedule', ['2024-03-05'], '2024-03-31'],
'2024-03-31'),
('two schedule completions',
['2024-04-01', 14, 'schedule', ['2024-03-30', '2024-04-10'], None],
'2024-04-29'),
('out of order regenerate',
['2024-04-01', 5, 'regenerate', ['2024-04-09', '2024-04-02'], None],
'2024-04-14'),
('regression: late completion on next due',
['2024-01-01', 7, 'schedule', ['2024-01-08'], None],
'2024-01-15'),
('early completion regenerate', ['2024-01-10', 7, 'regenerate', ['2024-01-05'], None], '2024-01-12'),
('late completion regenerate', ['2024-01-10', 7, 'regenerate', ['2024-01-20'], None], '2024-01-27'),
('until passed', ['2024-01-01', 7, 'schedule', ['2024-01-01', '2024-01-08'], '2024-01-10'], None)]]
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: late completion on next due | 2024-01-15 | 2024-01-15 | Passed |
| early completion regenerate | 2024-01-12 | 2024-01-12 | Passed |
| late completion regenerate | 2024-01-27 | 2024-01-27 | Passed |
| out of order schedule | 2024-01-22 | 2024-01-22 | Passed |
| multiple missed schedule | 2024-01-13 | 2024-01-13 | Passed |
| until exact | 2024-01-08 | 2024-01-08 | Passed |
| until passed | None | None | Passed |
SHA-256 / 578cd79215a645632945cc2c9c6defa62516ed70f39a2c464850220e3d44d5f3
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 2026-09-29T14:49:24.536755+00:00.
Case digest / e1e2e55a034d1a2dceaf9a482aa3510738468acb2a02491a01bc62483b480d0a