refactor(useDate): fix stale V0DateAdapter references and add type tests

- Update all references to renamed Vuetify0DateAdapter class
- Replace == null with isNullOrUndefined() utility
- Add type-level regression tests for overload protection
- Fix createDateContext type signature in docs

Author: johnleider

apps/docs/src/pages/composables/plugins/use-date.md

@@ -105,7 +105,7 @@ const isSameMonth = adapter.isSameMonth(today, inFiveDays)
 
 - **Details**
 
-  - `adapter`: Custom date adapter (default: `V0DateAdapter` using Temporal API)
+  - `adapter`: Custom date adapter (default: `Vuetify0DateAdapter` using Temporal API)
   - `locale`: Default locale for formatting (default: 'en-US' or from `useLocale`)
   - `localeMap`: Mapping from short locale codes to Intl locale strings
   - `namespace`: Context namespace for dependency injection (default: 'v0:date')
@@ -277,10 +277,8 @@ The `formatByString()` method supports these tokens:
 
 - **Type**
   ```ts
-  function createDateContext<
-    T extends Temporal.PlainDateTime = Temporal.PlainDateTime,
-    E extends DateContext<T> = DateContext<T>
-  > (options: DateContextOptions<T>): ContextTrinity<E>
+  function createDateContext (options?: DateContextOptionsDefault): ContextTrinity<DateContext<Temporal.PlainDateTime>>
+  function createDateContext<T> (options: DateContextOptionsWithAdapter<T>): ContextTrinity<DateContext<T>>
   ```
 
 - **Details**

packages/0/src/composables/useDate/adapters/v0.ts

@@ -78,7 +78,7 @@ export class Vuetify0DateAdapter implements DateAdapter<PlainDateTime> {
    * hydration via `<ClientOnly>` (Nuxt) or `v-if` + `onMounted` pattern.
    */
   date (value?: unknown): PlainDateTime | null {
-    if (value == null) {
+    if (isNullOrUndefined(value)) {
       // SSR safety: Temporal.Now requires browser environment
       return IN_BROWSER
         ? Temporal.Now.plainDateTimeISO()
@@ -190,7 +190,7 @@ export class Vuetify0DateAdapter implements DateAdapter<PlainDateTime> {
   }
 
   isValid (date: unknown): boolean {
-    if (date == null) return false
+    if (isNullOrUndefined(date)) return false
 
     if (date instanceof Temporal.PlainDateTime) return true
     if (date instanceof Temporal.PlainDate) return true

packages/0/src/composables/useDate/index.bench.ts

@@ -1,10 +1,10 @@
 import { Temporal } from '@js-temporal/polyfill'
 import { bench, describe } from 'vitest'
-import { V0DateAdapter } from './adapters/v0'
+import { Vuetify0DateAdapter } from './adapters/v0'
 
 describe('useDate benchmarks', () => {
-  describe('V0DateAdapter', () => {
-    const adapter = new V0DateAdapter()
+  describe('Vuetify0DateAdapter', () => {
+    const adapter = new Vuetify0DateAdapter()
     const testDate = Temporal.PlainDateTime.from('2024-06-15T10:30:00')
 
     describe('construction', () => {

packages/0/src/composables/useDate/index.test.ts

@@ -1,4 +1,4 @@
-import { describe, it, expect, beforeEach } from 'vitest'
+import { describe, it, expect, beforeEach, expectTypeOf } from 'vitest'
 import { Temporal } from '@js-temporal/polyfill'
 import { createDate, createDateContext, createDateFallback, createDatePlugin, useDate } from './index'
 import { Vuetify0DateAdapter } from './adapters/v0'
@@ -1374,4 +1374,38 @@ describe('useDate', () => {
       wrapper.unmount()
     })
   })
+
+  describe('type safety (compile-time)', () => {
+    it('should infer correct types for overloads', () => {
+      // Default adapter: returns DateContext<Temporal.PlainDateTime>
+      const defaultCtx = createDate()
+      expectTypeOf(defaultCtx.adapter.date()).toEqualTypeOf<Temporal.PlainDateTime | null>()
+
+      // Custom adapter with explicit type: infers T from adapter
+      const customAdapter = new Vuetify0DateAdapter()
+      const customCtx = createDate({ adapter: customAdapter })
+      expectTypeOf(customCtx.adapter.date()).toEqualTypeOf<Temporal.PlainDateTime | null>()
+
+      // Context trinity returns correct type
+      const [, , ctx] = createDateContext()
+      expectTypeOf(ctx.adapter.date()).toEqualTypeOf<Temporal.PlainDateTime | null>()
+
+      // useDate returns default type
+      const usedCtx = useDate()
+      expectTypeOf(usedCtx.adapter.date()).toEqualTypeOf<Temporal.PlainDateTime | null>()
+    })
+
+    // Type-level tests: these verify TypeScript rejects invalid calls
+    // The @ts-expect-error comments ensure these FAIL to compile if removed
+    it('should reject invalid overload usage at compile time', () => {
+      // @ts-expect-error - T provided without adapter should fail
+      createDate<Date>()
+
+      // @ts-expect-error - T provided without adapter should fail
+      createDateContext<Date>()
+
+      // @ts-expect-error - T provided without adapter should fail
+      createDatePlugin<Date>()
+    })
+  })
 })

packages/0/src/composables/useDate/index.ts

@@ -86,9 +86,9 @@ export interface DateOptionsWithAdapter<T> extends DateOptionsBase {
   adapter: DateAdapter<T>
 }
 
-/** Options when using the default V0DateAdapter */
+/** Options when using the default Vuetify0DateAdapter */
 export interface DateOptionsDefault extends DateOptionsBase {
-  /** When omitted, V0DateAdapter is used */
+  /** When omitted, Vuetify0DateAdapter is used */
   adapter?: undefined
 }
 
@@ -214,7 +214,7 @@ function createDateInternal<T> (
 }
 
 /**
- * Creates a new date context with the default V0DateAdapter.
+ * Creates a new date context with the default Vuetify0DateAdapter.
  *
  * @param options Optional locale configuration.
  * @returns A date context using Temporal.PlainDateTime.
@@ -282,7 +282,7 @@ export function createDateFallback (): DateContext<DefaultDateType> {
 }
 
 /**
- * Creates a new date context trinity with the default V0DateAdapter.
+ * Creates a new date context trinity with the default Vuetify0DateAdapter.
  *
  * @param options Optional locale and namespace configuration.
  * @returns A trinity [useContext, provideContext, defaultContext].
@@ -333,7 +333,7 @@ export function createDateContext<T = DefaultDateType> (
 }
 
 /**
- * Creates a new date plugin with the default V0DateAdapter.
+ * Creates a new date plugin with the default Vuetify0DateAdapter.
  *
  * @param options Optional locale and namespace configuration.
  * @returns A Vue plugin.
@@ -378,8 +378,7 @@ export function createDatePlugin<T = DefaultDateType> (
 ) {
   const { namespace = 'v0:date', ...options } = _options
 
-  // Preserve custom adapter if provided, otherwise use default
-  // Safe cast: discriminated union check ensures correct overload selection
+  // Type narrowing required for overload resolution (cannot be extracted without losing type safety)
   const [, provideDateContext, context] = 'adapter' in options && options.adapter !== undefined
     ? createDateContext({ namespace, ...options } as DateContextOptionsWithAdapter<T>)
     : createDateContext({ namespace, ...options } as DateContextOptionsDefault) as unknown as ContextTrinity<DateContext<T>>
@@ -396,7 +395,7 @@ export function createDatePlugin<T = DefaultDateType> (
  * Returns the current date context.
  *
  * When called inside a component with a provided date context (via plugin or provider),
- * returns that context. Otherwise, returns a fallback context with V0DateAdapter.
+ * returns that context. Otherwise, returns a fallback context with Vuetify0DateAdapter.
  *
  * @param namespace The namespace to look up (defaults to 'v0:date').
  * @returns The current date context.