Leap year period calculation issue when start date = 29/02

[Vashev-S]

Leap year period calculation issue when start date = 29/02

[pithu]

Isn't that more a theoretical discussion ? Period of one year can be 365 or 366 days. From 2024-02-28 to 2025-02-28 is one year and from 2024-02-29 to 2025-03-01 its one year and one day. IMHO the result is correct. Nevertheless our upstream project threeten and in the java api you get the same results. So this probably more a discussion for the java community.

[Vashev-S]

You gave me some thought , thanks.

But for me it is not just theoretical. I want to find whole year form 2024-02-29.
The result looks strange, Isn't it?

// Very strange result 
const start = LocalDate.parse('2024-02-29')
const end = start.plusYears(1); // '2025-02-28'
start.until(end) // P11M30D

// Another example
const start = LocalDate.parse('2024-02-29')
const end =  LocalDate.parse('2024-03-01')
start.until(end) // P1Y1D

//This one is 100% accurate
const start = LocalDate.parse('2024-02-28')
const end = start.plusYears(1); // '2024-02-28'
start.until(end) // P1Y

Perhaps I missunderstund how leap years calculation works, but where is P1Y if we start counting from 02.29 ?

[pithu]

Indeed, i agree that Period and Date calculation can produce strange results in case of leap years. Especially your first example looks weird. But the second makes sense imo. Eg LocalDate.parse('2024-02-29').until(LocalDate.parse('2028-02-29')).toString() is P4Y and LocalDate.parse('2024-02-29').until(LocalDate.parse('2028-03-01')).toString() is P4Y1D.
In general i would say its impossible to map an amount of days to a consistent period of years, month and days of month, because years and month do not have a fixed amount of days.

[Vashev-S]

I totaly agree that second example make sense.

But I still belive in bug in the first example.

Next condition must be equal with any X and Z
"X + (Z - Z) = X"

const start = LocalDate.parse(X)
const end =  start.plusYears(Z);

const reclaculatedStart = end.plusYears(-Z);

checkEqualty(start , reclaculatedStart ); // Must be true in any case

But somehow it doesn't work with "X = '02-29-....'" and "1 <= Z < 4"

const start = LocalDate.parse('2024-02-29')
const end = start.plusYears(1); // '2025-02-28'

const recalcedStart = end.plusYears(-1);  // '2024-02-28'

I would be REALY happy if you will find misstake in my thoughts.

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