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docs: guard detached layout reads in scroll-spy #74

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Merged
ClementBobin merged 1 commit into from
Oct 16, 2026
Merged

docs: guard detached layout reads in scroll-spy #74

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16 changes: 11 additions & 5 deletions showcase/src/wasmJsMain/kotlin/dev/kindling/showcase/docs/Site.kt
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Original file line number Diff line number Diff line change
Expand Up @@ -229,21 +229,23 @@ private fun PageContent(page: DocPage?, loc: Loc, dark: Boolean, flat: List<DocP
// Scroll-spy: the last heading that has reached the top of the viewport (or the last one at the bottom).
val activeHeading by remember(headings) {
derivedStateOf {
val top = viewport?.takeIf { it.isAttached }?.positionInRoot()?.y ?: 0f
val top = viewport.safeY() ?: 0f
val atEnd = scroll.maxValue > 0 && scroll.value >= scroll.maxValue - 4
var active = headings.firstOrNull()?.first
for ((index, _) in headings) {
val c = coords[index]?.takeIf { it.isAttached } ?: continue
if (c.positionInRoot().y - top <= 110f) active = index else break
val y = coords[index].safeY() ?: continue
if (y - top <= 110f) active = index else break
}
if (atEnd) headings.lastOrNull()?.first ?: active else active
}
}
val scrollTo: (Int) -> Unit = { index ->
val target = coords[index]
val top = viewport
if (target != null && target.isAttached && top != null) {
val y = target.positionInRoot().y - top.positionInRoot().y
val ty = target.safeY()
val vy = top.safeY()
if (ty != null && vy != null) {
val y = ty - vy
scope.launch { scroll.animateScrollTo((scroll.value + y - 24f).toInt().coerceAtLeast(0)) }
}
}
Expand Down Expand Up @@ -381,3 +383,7 @@ private fun SearchOverlay(pages: List<DocPage>, onClose: () -> Unit, onPick: (St
}
}
}

/** Position in the root, or null when the layout is detached (it can be removed between the check and the read). */
private fun LayoutCoordinates?.safeY(): Float? =
if (this == null || !isAttached) null else try { positionInRoot().y } catch (_: IllegalArgumentException) { null }
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