Date & time pickers (external piece)

Status: implemented as day-piece-datetime, an external Day Piece registered link-time into each backend’s renderer slice without touching day: the first external piece with renderers for all seven toolkits (including its own ArkUI NDK shim). TWO pieces (date_picker(Signal<DayDate>) and time_picker(Signal<DayTime>)) because a single combined date-time control exists on only 3 of the 7 toolkits (NSDatePicker, UIDatePicker.dateAndTime, QDateTimeEdit), while separate date and time controls realize natively on all of them. Combined selection is composition: row((date_picker(d), time_picker(t))).

Authoring

use day_piece_datetime::{DayDate, DayTime, date_picker, time_picker};

let date = Signal::new(DayDate::new(2026, 7, 18).unwrap());
let time = Signal::new(DayTime::new(9, 30, 0).unwrap());

column((
    date_picker(date),                       // Compact (default): field → platform chooser
    date_picker(date).inline(),              // Inline: embedded calendar / wheels
    date_picker(date)
        .min(DayDate::new(2026, 1, 1).unwrap())
        .max(DayDate::new(2026, 12, 31).unwrap()),
    time_picker(time).seconds(true),         // seconds honored on AppKit/Qt only
))

The bound signal is two-way: a user pick writes it; the app writing it updates the native control. Values are civil (zoneless): DayDate { year, month, day } (proleptic Gregorian, validated constructors, Display/parse_iso speak ISO-8601) and DayTime { hour, minute, second }. Day carries no time-zone database: an app that needs zoned instants attaches the zone itself (DayDate::today() derives from the system clock in UTC). Interchange across native boundaries is epoch days / seconds-of-day; every renderer pins its control’s calendar to proleptic-Gregorian UTC so the civil value never shifts by zone, while the locale stays the user’s: month and weekday names render localized by the platform.

min/max bound the date natively where the control supports it, and the piece clamps every pick regardless; an out-of-range synthetic set lands on the nearest bound.

Styles: the shared subset

Two intents (+ Automatic, which is Compact everywhere today):

• Compact — a field/button showing the value that summons a transient chooser. The chooser’s chrome is the platform’s own: a popover on iOS, a modal Material dialog on Android, a calendar-popup on Qt, a flyout on Windows. Same gesture contract, different chrome (by design).
• Inline — an embedded calendar / clock / wheels.

Anything finer (wheels-vs-calendar, dialog-vs-popover) is platform identity Day does not paper over (DESIGN.md §2: native-at-home beats identical-everywhere).

Per-toolkit realization

day_piece_datetime::support() reports the compiled backend’s tier.

What the unified pieces do NOT promise

• Identical chrome — Android’s chooser is a modal dialog, iOS’s a popover, Qt’s a popup.
• Seconds everywhere — .seconds(true) is honored on AppKit and Qt (the two toolkits whose controls have a seconds field) and is a no-op elsewhere.
• A combined date+time single control — compose the two pieces; a date_time_picker convenience that upgrades to the native combined control on AppKit/UIKit/Qt is a possible v2.
• Range / multi-date selection — v2 territory (UICalendarView, MaterialDatePicker range, CalendarView multi-select).
• Native min/max on every surface — GTK’s GtkCalendar and ArkUI’s calendar picker have no bounds API; there the piece’s own clamp bounds the value (the visual grid stays free), and a clamped pick snaps the control back on the echo patch.

Scripting

Every picker accepts Event::TextChanged carrying an ISO value as a synthetic set, so dayscript’s existing input: step drives any picker on any backend, and ISO readouts bound to the signals assert locale-independently:

- input: { id: date-compact, text: "2026-11-05" }
- assert_text: { id: date-value, text: "2026-11-05" }
- input: { id: time-compact, text: "14:45" }

Limits

• Android’s Material dialogs live on the activity’s FragmentManager; a dialog left open survives the piece (it dismisses with the activity, and re-opening is guarded by tag).
• ArkUI hour-cycle follows the node default (USE_MILITARY_TIME unset); wiring it to the system hour-cycle preference is a follow-up.
• DayTime’s Display shows seconds exactly when nonzero ("09:30" / "09:30:07"); assert accordingly in scripts.