Fix scroll jumps in multi-list SolidVirtualList scenarios

[paxee]

Problem

Commit 290bcbd added forceUpdate to Virtual.updateUniqueIds to ensure dataSource changes are reflected immediately in single-list scenarios, fixing stale rendering and covering growing/shrinking lists. However, in applications with multiple SolidVirtualList instances (e.g., multiple virtualized lists in a single parent component), this caused unintended scroll jumps. Parent re-renders triggered the createEffect for dataSourceIds in all instances, calling updateUniqueIds and forceUpdate even when their dataSource was unchanged, leading to unnecessary range updates and scroll position shifts.

Approach

To maintain the benefits of 290bcbd (immediate updates for modified lists) while preventing scroll jumps in multi-list setups, I've optimized SolidVirtualList’s reactivity to ensure updateUniqueIds is only called when a list’s dataSource IDs change. I also improved initial rendering to avoid unnecessary updates.

Changes

• Memoized dataSource: Added memoizedDataSource using createMemo to prevent dataSourceIds recomputation when the dataSource prop reference changes but content is identical.
• Added prevIds Signal: Introduced a prevIds signal to track previous dataSourceIds. The createEffect now checks if dataSourceIds differs from prevIds before calling updateUniqueIds, preventing unnecessary forceUpdate calls.

Impact

• Fixes scroll jumps in multi-list scenarios by ensuring only the modified list updates its range.
• Preserves 290bcbd’s fix for immediate updates in single-list scenarios.
• Improves performance by reducing unnecessary reactivity and range calculations.
• Compatible with all use cases, including single and multi-list setups.

Test

• Tested with multiple SolidVirtualList instances in a parent component which shares a common state data store.
• Verified that updating one list’s dataSource does not affect others’ scroll positions.
• Confirmed no regressions in single-list scenarios (e.g., dataSource updates redraw correctly per 290bcbd).

Notes

• The fix uses Solid’s reactivity in SolidVirtualList for efficiency. Alternatively, the prevIds logic could be moved to Virtual.updateUniqueIds for framework-agnostic use, but this is less idiomatic for SolidJS.
• Future improvements could include debouncing ResizeObserver in VirtualListItem for added stability.
• Continuation of 290bcbd.