Cron appears to repeat a date #5675
Description
What version of Effect is running?
3.18.4
What steps can reproduce the bug?
This test case (pasted into Cron.test.ts if you want) I think demos the issue:
it.only.for([
["5 2 * * 4"]
])("equivalence test %s", ([str]) => {
const start = new Date("2020-01-01 0:00:01")
const end = new Date("2021-01-01 0:00:01")
const getYear = (generator: IterableIterator<Date>) => {
const res: Array<Date> = []
for (const date of generator) {
if (date > start && date < end) {
res.push(date)
} else {
return res
}
}
return res
}
const fwd = getYear(Cron.sequence(Cron.unsafeParse(str), start))
for (let i = 0; i < fwd.length; i++) {
console.log(fwd[i], fwd[i] - fwd[i - 1])
}
})What is the expected behavior?
I would expect this cron expression, which in plain english would repeat "at 02:05 on Thursday", to consistently repeat once every thursday at 2:05.
What do you see instead?
This is the sequence of generated instances, with the "milliseconds since the last cron run" printed in the second column.
2020-01-02T07:05:00.000Z NaN
2020-01-09T07:05:00.000Z 604800000
2020-01-16T07:05:00.000Z 604800000
2020-01-23T07:05:00.000Z 604800000
2020-01-30T07:05:00.000Z 604800000
2020-02-06T07:05:00.000Z 604800000
2020-02-13T07:05:00.000Z 604800000
2020-02-20T07:05:00.000Z 604800000
2020-02-27T07:05:00.000Z 604800000
2020-03-05T07:05:00.000Z 604800000
2020-03-12T07:05:00.000Z 604800000
2020-03-19T06:05:00.000Z 601200000
2020-03-26T06:05:00.000Z 604800000
2020-04-02T06:05:00.000Z 604800000
2020-04-09T06:05:00.000Z 604800000
2020-04-16T06:05:00.000Z 604800000
2020-04-23T06:05:00.000Z 604800000
2020-04-30T06:05:00.000Z 604800000
2020-05-07T06:05:00.000Z 604800000
2020-05-14T06:05:00.000Z 604800000
2020-05-21T06:05:00.000Z 604800000
2020-05-28T06:05:00.000Z 604800000
2020-06-04T06:05:00.000Z 604800000
2020-06-11T06:05:00.000Z 604800000
2020-06-18T06:05:00.000Z 604800000
2020-06-25T06:05:00.000Z 604800000
2020-07-02T06:05:00.000Z 604800000
2020-07-09T06:05:00.000Z 604800000
2020-07-16T06:05:00.000Z 604800000
2020-07-23T06:05:00.000Z 604800000
2020-07-30T06:05:00.000Z 604800000
2020-08-06T06:05:00.000Z 604800000
2020-08-13T06:05:00.000Z 604800000
2020-08-20T06:05:00.000Z 604800000
2020-08-27T06:05:00.000Z 604800000
2020-09-03T06:05:00.000Z 604800000
2020-09-10T06:05:00.000Z 604800000
2020-09-17T06:05:00.000Z 604800000
2020-09-24T06:05:00.000Z 604800000
2020-10-01T06:05:00.000Z 604800000
2020-10-08T06:05:00.000Z 604800000
2020-10-15T06:05:00.000Z 604800000
2020-10-22T06:05:00.000Z 604800000
2020-10-29T06:05:00.000Z 604800000
2020-11-05T06:05:00.000Z 604800000
2020-11-05T07:05:00.000Z 3600000
2020-11-12T07:05:00.000Z 604800000
2020-11-19T07:05:00.000Z 604800000
2020-11-26T07:05:00.000Z 604800000
2020-12-03T07:05:00.000Z 604800000
2020-12-10T07:05:00.000Z 604800000
2020-12-17T07:05:00.000Z 604800000
2020-12-24T07:05:00.000Z 604800000
2020-12-31T07:05:00.000Z 604800000
Note these lines:
2020-11-05T06:05:00.000Z 604800000
2020-11-05T07:05:00.000Z 3600000
2020-11-12T07:05:00.000Z 604800000
This is the odd behavior. The cron runs on November 5th at 6:05 utc, and then at 7:05 utc.
Yes, daylight savings changed in 2020 on November 1st, and that's probably the culprit, but this particular hour was not repeated, and you can test this with a variety of weekday expressions and you'll get the unusual repeated instance for all of them.
Additional information
This was done on my computer which is in EDT time zone. Parsing the cron expression as "utc" gives consistent (correct) results, with no repeated time.
Using a local timezone gives the unusual repeated results regardless of which day-of-week is specified.