problem in built-ins/Temporal/PlainDate/prototype/since/largestunit-higher-units.js

[FrankYFTang]

https://github.com/tc39/test262/blob/main/test/built-ins/Temporal/PlainDate/prototype/since/largestunit-higher-units.js

I have hard time to understand about the current expectaiton

const lastFeb20 = Temporal.PlainDate.from("2020-02-29");
const lastFeb21 = Temporal.PlainDate.from("2021-02-28");

lastFeb21.since(lastFeb20, { largestUnit: "years" }) => my implementation give me "P1Y"
lastFeb21.since(lastFeb20, { largestUnit: "months" }) => my implementation give me "P12M"

Could you explain to me why the exepectation are 11 months and 28 days here for these?

The current spec text is so complicate it is very difficult to tell how it work.

@ptomato @Ms2ger

[Ms2ger]

Agreed, this is a bug in the test/polyfill.

[justingrant]

I believe the previous implementation of this test matches the intended behavior of since, and the new test in this PR does not. Let's discuss over in tc39/proposal-temporal#1861 (review).