fix(charts): flip tall tooltips below the cursor when needed for space

[JoshuaKGoldberg]

Chart tooltip tops previously were a based on a max of either the existing position (- an offset) vs. the CHART_TOOLTIP_VIEWPORT_OFFSET. That works as long as there's room above the chart/cursor for all of it. But as seen in LOGS-851, if there isn't, then the tooltip weirdly hangs below where you'd expect it to.

Now, when a tooltip is too tall to fit above the cursor, it renders below the cursor instead, flipping the arrow up via the existing arrow-top class.

Before	After

Closes LOGS-851.

[linear-code]

LOGS-851

[scttcper]

not totally sure the tests are worth it

[JoshuaKGoldberg]

👍 I can remove them, I am not passionate about keeping tricky JSDom mock testing.

[sentry]

Bug: The chart tooltip positioning logic lacks a check for the bottom viewport boundary, allowing tall tooltips to render off-screen when triggered near the bottom of a chart.
_{Severity: MEDIUM}

Suggested Fix

Add a boundary check for the bottom of the viewport. After calculating topPos, check if topPos + tipHeight + chartBoundingRect.top exceeds window.innerHeight. If it does, adjust topPos to ensure the tooltip's bottom edge is clamped to the viewport boundary, preventing it from rendering off-screen.

Prompt for AI Agent

Review the code at the location below. A potential bug has been identified by an AI
agent. Verify if this is a real issue. If it is, propose a fix; if not, explain why it's
not valid.

Location: static/app/components/charts/components/tooltip.tsx#L437-L439

Potential issue: The tooltip positioning logic in the `position` function was updated to
prevent the tooltip from being clipped by the top of the viewport by flipping it below
the cursor. However, this new logic at `topPos = Number(pos[1]) + 20` does not include a
corresponding check for the bottom edge of the viewport. When a chart generates a tall
tooltip (e.g., from many series) and the user's cursor is near the bottom of the chart,
the tooltip can be positioned partially or entirely off-screen, making its content
inaccessible.

_{Did we get this right? 👍 / 👎 to inform future reviews.}

[cursor]

Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[cursor]

Flipped tooltip still clips viewport

Medium Severity

When the above-cursor placement would clip the viewport top, the tooltip moves to pos[1] + 20 with arrow-top, but there is no check that the new top clears CHART_TOOLTIP_VIEWPORT_OFFSET. If the chart’s bounding rect extends above the viewport, the below placement can remain clipped while the removed Math.max clamp used to keep it on screen.

 

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[JoshuaKGoldberg]

If the user has scrolled all the way down, they can scroll back up.