Event segments one day too short when timezone is set

[evanbrooks-codaio]

Check that this is really a bug

• I confirm

Reproduction link

https://codesandbox.io/p/sandbox/react-big-calendar-example-forked-wc6sts

Bug description

• Configure a localizer with a timezone to the east of the browser's current timezone.
• Create an event that spans multiple weeks
• Display a month view. Note that the event segments are not spanning correctly.

I believe this may be the same issue as #2425 , however it appears to happen consistently in any timezone, and consistently with either the moment or luxon localizers. feel free consolidate if this is a duplicate.

Expected Behavior

• Segments include the last day of the event.
• Segments extend to the last day of the week when multi-week

Actual Behavior

• Segments ends the day before the end of the event.
• Segments omit last day of the week when multi-week. (For example, ending on friday if the last day of the week is saturday).

react-big-calendar version

1.14.1

React version

18.2.0

Platform/Target and Browser Versions

macOS 14.4, Chrome 129

Validations

• Read the docs.
• Check that there isn't already an issue that request the same feature to avoid creating a duplicate.
• Make sure this is a react-big-calendar issue and not an implementation issue

Would you like to open a PR for this bug?

• I'm willing to open a PR

[evanbrooks-codaio]

The issue appears to be with the getBrowserTzOffset in the localizers, ie here for luxon. This configures the segmentOffset here and is used to explictly subtract the width of the segment here:

react-big-calendar/src/utils/eventLevels.js

Lines 26 to 28 in 856dddf

	// The segmentOffset is necessary when adjusting for timezones
	// ahead of the browser timezone
	span = Math.max(span - localizer.segmentOffset, 1)

It seems like this is subtracting "1" in situations where the segments are already correct. I've found that simply removing the segmentOffset appears to resolve the issue in my test case. I'm not sure exactly when it is necessary to subtract 1 (if ever?), but it seems to happening more often than it should.