[Audit] useDate - ensure adapter system matches Vuetify

[johnleider]

Summary

Ensure useDate adapter system matches Vuetify 3's date-io pattern.

Research Findings

v0 Architecture

• Adapter Pattern: Generic DateAdapter<T> interface (62 methods)
• Default Adapter: Vuetify0DateAdapter using TC39 Temporal API with @js-temporal/polyfill
• Trinity Pattern: Full support via createDateContext() and createDatePlugin()
• Locale Integration: Auto-syncs with useLocale() composable
• SSR-Safe: Temporal.Now checks IN_BROWSER; returns epoch on server

Vuetify 3 Architecture

• Adapter Pattern: DateAdapter<T> interface (52 methods)
• Default Adapter: VuetifyDateAdapter using native JavaScript Date
• date-io Ecosystem: Supports dayjs, luxon, date-fns, moment via @date-io/* packages
• No Trinity Pattern: Simple factory function

Feature Comparison

v0 Has (Vuetify 3 Lacks)

Feature	v0 Method	Impact
Seconds support	getSeconds(), addSeconds(), setSeconds()	Time-precise operations
Years arithmetic	addYears()	Direct year manipulation
Granular comparisons	isAfterMonth(), isBeforeDay(), etc.	12+ comparison methods
Days in month	getDaysInMonth()	Calendar calculations
Month/Year arrays	getMonthArray(), getYearRange()	Picker generation
Format helpers	getFormatHelperText(), getMeridiemText()	Localization hints
12-hour check	is12HourCycleInCurrentLocale()	AM/PM detection
String parsing	parse() with format	Custom format parsing
Token formatting	formatByString()	YYYY, MM, DD tokens
Date/time merge	mergeDateAndTime()	Combining components

Vuetify 3 Has (v0 Lacks)

Feature	Impact
date-io ecosystem	dayjs, luxon, date-fns, moment adapters
Timezone support	Via luxon/dayjs adapters
Week calculation strategies	firstDayOfYear, firstWeekSize by locale

Adapter Compatibility

v0's DateAdapter is a SUPERSET of date-io's IUtils interface. Vuetify 3's is a SUBSET.

Tasks

• Create adapter factory pattern for community date-io adapters
• Build reference adapters: @vuetify/v0-date-dayjs, @vuetify/v0-date-luxon, @vuetify/v0-date-fns
• Document adapter creation guide
• Consider bridge package for Vuetify 3 compatibility layer
• Evaluate keeping Temporal as default vs switching to date-io base

Files

• v0 core: packages/0/src/composables/useDate/index.ts
• v0 adapter: packages/0/src/composables/useDate/adapters/adapter.ts
• v0 implementation: packages/0/src/composables/useDate/adapters/v0.ts
• Vuetify 3: packages/vuetify/src/composables/date/

[J-Sek]

Default Vuetify adapter implements addMonths with day reset (sets it to 1). It is different from any other date-io adapter. Temporal (v0) keeps the day. We can ensure AI does not break it in a rush by merging #133

[johnleider]

Updated Analysis (Mar 11)

Full method-by-method comparison done (see specs/composables/useDate-comparison.md).

Key findings:

• v0's DateAdapter is a strict superset: 86 methods vs Vuetify's 48
• v0 uses Temporal API (immutable), Vuetify uses native Date (mutable)
• Not directly swappable — different signatures and return types
• Compatibility wrapper could bridge them

v0 needs:

• date-fns adapter
• Luxon adapter
• Day.js adapter (nice-to-have)

Out of scope (Vuetify-level):

• Moment.js adapter (deprecated)
• js-joda adapter (niche)
• useDateFormat() composable
• weekInfo() locale lookup table
• Custom format function support

Details in #116.