fix(react): render a custom tooltip body before the moved tooltip paints

.changeset/react-tooltip-body-sync.md

@@ -0,0 +1,5 @@
+---
+'@tanstack/react-charts': patch
+---
+
+Render a custom tooltip body in the same task as the tooltip moves, so a pointer move no longer paints the previous point's body at the new position.

packages/react-charts/src/Chart.test.tsx

@@ -343,15 +343,24 @@ describe('React adapter', () => {
     })
     const scene = createChartScene(definition, { width: 480, height: 260 })
     for (const point of scene.points) {
-      await act(async () =>
+      const move = () =>
         svg.dispatchEvent(
           new MouseEvent('pointermove', {
             bubbles: true,
             clientX: point.x,
             clientY: point.y,
           }),
-        ),
+        )
+      Object.assign(globalThis, { IS_REACT_ACT_ENVIRONMENT: false })
+      try {
+        move()
+      } finally {
+        Object.assign(globalThis, { IS_REACT_ACT_ENVIRONMENT: true })
+      }
+      expect(target.querySelector('[data-testid="primary"]')?.textContent).toBe(
+        point.groupLabel,
       )
+      await act(async () => move())
       expect(target.querySelector('[data-testid="primary"]')?.textContent).toBe(
         point.groupLabel,
       )

packages/react-charts/src/tooltip.test.tsx

@@ -121,4 +121,144 @@ describe('tooltip state ownership', () => {
       }
     },
   )
+
+  it('commits the body before the browser paints an interaction', async () => {
+    const definition = defineChart({
+      marks: [
+        dot(
+          [
+            { x: 0, y: 1 },
+            { x: 1, y: 2 },
+          ],
+          { x: 'x', y: 'y' },
+        ),
+      ],
+      scales: {
+        x: { scale: scaleLinear().domain([0, 1]) },
+        y: { scale: scaleLinear().domain([0, 3]) },
+      },
+      tooltip: { use: tooltip },
+    })
+    const container = document.createElement('div')
+    document.body.append(container)
+    const root = createRoot(container)
+    const errors = vi.spyOn(console, 'error')
+    const render = (width: number) =>
+      act(async () =>
+        root.render(
+          <Chart
+            definition={definition}
+            width={width}
+            height={260}
+            ariaLabel="chart"
+            renderTooltipBody={({ primaryPoint }) => (
+              <span data-body>{primaryPoint?.datum.y}</span>
+            )}
+          />,
+        ),
+      )
+    try {
+      await render(480)
+      const svg = container.querySelector('svg')
+      if (!svg) throw new Error('Missing SVG')
+      await act(async () =>
+        svg.dispatchEvent(new FocusEvent('focusin', { bubbles: true })),
+      )
+      expect(container.querySelector('[data-body]')?.textContent).toBe('1')
+      Object.assign(globalThis, { IS_REACT_ACT_ENVIRONMENT: false })
+      try {
+        svg.dispatchEvent(
+          new KeyboardEvent('keydown', { key: 'ArrowRight', bubbles: true }),
+        )
+      } finally {
+        Object.assign(globalThis, { IS_REACT_ACT_ENVIRONMENT: true })
+      }
+      expect(container.querySelector('[data-body]')?.textContent).toBe('2')
+      await render(520)
+      expect(container.querySelector('[data-body]')?.textContent).toBe('2')
+    } finally {
+      try {
+        await act(async () => root.unmount())
+        expect(errors).not.toHaveBeenCalled()
+      } finally {
+        errors.mockRestore()
+        container.remove()
+      }
+    }
+  })
+
+  it.each([
+    ['layout', 'setup'],
+    ['layout', 'cleanup'],
+    ['passive', 'setup'],
+    ['passive', 'cleanup'],
+  ] as const)(
+    'accepts a dismissal from the body %s effect %s',
+    async (phase, step) => {
+      const definition = defineChart({
+        marks: [
+          dot(
+            [
+              { x: 0, y: 1 },
+              { x: 1, y: 2 },
+            ],
+            { x: 'x', y: 'y' },
+          ),
+        ],
+        scales: {
+          x: { scale: scaleLinear().domain([0, 1]) },
+          y: { scale: scaleLinear().domain([0, 3]) },
+        },
+        tooltip: { use: tooltip },
+      })
+      const useEffect =
+        phase === 'layout' ? React.useLayoutEffect : React.useEffect
+      function Body({ dismiss }: { dismiss: () => void }) {
+        const [armed, setArmed] = React.useState(false)
+        useEffect(() => {
+          if (step === 'setup' && armed) dismiss()
+          if (step === 'cleanup' && !armed) return () => dismiss()
+        }, [armed, dismiss])
+        return (
+          <button data-body type="button" onClick={() => setArmed(true)}>
+            dismiss
+          </button>
+        )
+      }
+      const container = document.createElement('div')
+      document.body.append(container)
+      const root = createRoot(container)
+      const errors = vi.spyOn(console, 'error')
+      try {
+        await act(async () =>
+          root.render(
+            <Chart
+              definition={definition}
+              width={480}
+              height={260}
+              ariaLabel="chart"
+              renderTooltipBody={({ dismiss }) => <Body dismiss={dismiss} />}
+            />,
+          ),
+        )
+        const svg = container.querySelector('svg')
+        if (!svg) throw new Error('Missing SVG')
+        await act(async () =>
+          svg.dispatchEvent(new FocusEvent('focusin', { bubbles: true })),
+        )
+        const button = container.querySelector<HTMLElement>('[data-body]')
+        if (!button) throw new Error('Missing tooltip body')
+        await act(async () => button.click())
+        expect(container.querySelector('[data-body]')).toBeNull()
+      } finally {
+        try {
+          await act(async () => root.unmount())
+          expect(errors).not.toHaveBeenCalled()
+        } finally {
+          errors.mockRestore()
+          container.remove()
+        }
+      }
+    },
+  )
 })

packages/react-charts/src/tooltip.tsx

@@ -1,7 +1,7 @@
 'use client'
 
 import * as React from 'react'
-import { createPortal } from 'react-dom'
+import { createPortal, flushSync } from 'react-dom'
 import type {
   ChartTooltipBodyContext,
   ChartTooltipBodyTarget,
@@ -135,6 +135,25 @@ export function CanvasChart<
   )
 }
 
+const useIsomorphicLayoutEffect =
+  typeof document === 'undefined' ? React.useEffect : React.useLayoutEffect
+
+let hostCommit = false
+
+function HostCommitStart() {
+  useIsomorphicLayoutEffect(() => {
+    hostCommit = true
+  })
+  return null
+}
+
+function HostCommitEnd() {
+  useIsomorphicLayoutEffect(() => {
+    hostCommit = false
+  })
+  return null
+}
+
 function TooltipBody<
   TDatum,
   TXValue extends ChartValue,
@@ -163,7 +182,8 @@ function TooltipBody<
   > | null>(null)
   const onChange = React.useCallback(
     (nextTarget: ChartTooltipBodyTarget<TDatum, TXValue, TYValue> | null) => {
-      setTarget(nextTarget)
+      if (nextTarget === null || hostCommit) setTarget(nextTarget)
+      else flushSync(() => setTarget(nextTarget))
     },
     [],
   )
@@ -173,7 +193,9 @@ function TooltipBody<
   const chart = React.useMemo(() => children(notify), [children, notify])
   return (
     <>
+      <HostCommitStart />
       {chart}
+      <HostCommitEnd />
       {renderTooltipBody && target
         ? createPortal(
             renderTooltipBody({