react-day-picker v8 -> v9 Errors in the shadcn Calendar

A shadcn Calendar is a thin wrapper around react-day-picker. The react-day-picker 9.0.0 release (mid-2024) reshaped almost every public prop name, the classNames key system, the components-override surface, and the formatter contract. Every v8 prop name still parses as valid JSX in v9 (selectedDays, disabledDays, modifiers={[...]}, components={{ Caption }}), but the v9 DayPicker simply ignores them. The symptom is therefore SILENT : the page compiles, the calendar mounts, and nothing happens (no selection, no styles, no custom caption). TypeScript narrows the typed errors to a single rule on mode ; the rest manifests as visual breakage.

This skill maps each v8 syntax shape onto its v9 replacement, lists the TypeScript error messages that surface for the typed cases, and documents the canonical recovery flow when the shadcn-side components/ui/calendar.tsx itself pre-dates the v9 release.

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