fix: display label as tooltip title on stickiness graph

[ghoti143]

Problem

As described in #22209, the <LineGraph /> component wasn't properly rendering tooltip titles in the context of the stickiness graph. This was due to the fact that the filter interval was undefined so the IntervalType defaulted to day.

posthog/frontend/src/scenes/insights/InsightTooltip/InsightTooltip.tsx

Line 105 in 00bab5e

? `${getFormattedDate(date, seriesData?.[0]?.filter?.interval)} (${

posthog/frontend/src/scenes/insights/InsightTooltip/insightTooltipUtils.tsx

Line 90 in 261a2f5

export function getFormattedDate(input?: string | number, interval: IntervalType = 'day'): string {

Changes

As described in #22440 (comment), the interval value is not present in the api response. Even if it was present, however, it could be argued that 3 weeks (EDT), 4 weeks (UTC), and 2 days (PDT) are not good titles (the presence of the timezone makes no sense in this context). Thus it was decided to avoid the date formatting all together when the date value is numeric by returning the label value from the altTitle function. This is the same value used on the graph's X axis.

Below are some comparisons showing the difference b/w PostHog:master and ghoti143:bug-tooltip-title

Stickiness graph grouped by week

PostHog:master

ghoti143:bug-tooltip-title

Stickiness graph grouped by day

PostHog:master

ghoti143:bug-tooltip-title

Stickiness graph grouped by hour

PostHog:master

ghoti143:bug-tooltip-title

Does this work well for both Cloud and self-hosted?

Yes

How did you test this code?

Manually tested the Trends graph to ensure that it still renders the titles using the getFormattedDate() function and doesn't display the labels.

[Twixes]

Excellent improvement, thank you!