7.6.0 to 7.6.1 breaks DST boundary startOf('day')

[HowieSquires]

After upgrading from 7.6.0 to 7.7.0 for the latest 2025 DST boundaries, I noticed that one of the Jest tests we run has broken.

Previously
spacetime('2024-03-31 01:00', 'Europe/London').startOf('day')

would return -

2024-03-31 00:00

However, it's now returning -

2024-03-31 01:00.

I played between the other updates between 7.6.0 and 7.7.0 and noticed the error occurs between 7.6.0 and 7.6.1.

[HowieSquires]

@spencermountain Further to this:

spacetime('2024-03-31 01:00', 'Europe/London').format('iso') = 2024-03-31 00:00

spacetime('2024-03-31 02:00', 'Europe/London').format('iso') = 2024-03-31 00:00

spacetime('2024-03-31 03:00', 'Europe/London').format('iso') = 2024-03-31 02:00

This is strange behaviour as the second one using 02:00 should either be 01:00 or stay at 02:00.

[spencermountain]

hey Howie, yep - this looks like this issue where we struggle to know the exact hour, within 1 hour of a DST change. This is because we're using native js dates internally, to represent remote dates, and there's a small overlap where we can't resolve it.
Sorry about that. was hoping to fix it in 2024, but it's a real tough one.
cheers

[HowieSquires]

@spencermountain Is it not a case of fixing the breaking change between 7.6.0 and 7.6.1? I'm not sure what changed?

[spencermountain]

Ya, I think it's maybe the date of the daylight savings change that could have changed between the versions. I haven't checked this, but the DST change is on that day, and it looks to be an hour off.
Cheers