DateTime difference sometimes calculated incorrectly

[kirkmorrow]

void main() {
final x = DateTime(2022, 12, 31);
final y = DateTime(2023, 3, 12);
final z = DateTime(2023, 3, 13);
final foo = y.difference(x).inDays;
final bar = z.difference(x).inDays;
print(foo);
print(bar);
}

Result:
71
71

There are 71 days between Dec. 31st and March 12, but not March 13.

[kirkmorrow]

Further digging:

void main() {
void main() {
final x = DateTime(2023, 3, 12, 2);
final y = DateTime(2023, 3, 12, 3);
print(x.millisecondsSinceEpoch);
print(y.millisecondsSinceEpoch);
print(x.difference(y).inMicroseconds);
}

Result:
1678608000000
1678608000000
0

No time passes between 2am and 3am on March 12, 2023?

[lrhn]

Correct. Daylight saving starts at 2 AM, at which point the time zone changes so that it's now 3 AM.
No time passed between the two, it's the same point in time.

Use UTC time if you want to work with dates only.
The inDays really means "in multiples of 24 hours", and some calendar days have 23 or 25 hours.

So, working as designed. You can't ignore daylight saving when using local-time DateTimes.