[codex] fix historical timezone endOf regression

package.json

@@ -5,7 +5,8 @@
   "main": "dayjs.min.js",
   "types": "index.d.ts",
   "scripts": {
-    "test": "TZ=Pacific/Auckland npm run test-tz && TZ=Europe/London npm run test-tz && TZ=America/Whitehorse npm run test-tz && npm run test-tz && jest --coverage --coverageThreshold='{ \"global\": { \"lines\": 100} }'",
+    "test": "TZ=Pacific/Auckland npm run test-tz && TZ=Europe/London npm run test-tz && TZ=America/Whitehorse npm run test-tz && TZ=Asia/Singapore npm run test-issue3003 && npm run test-tz && jest --coverage --coverageThreshold='{ \"global\": { \"lines\": 100} }'",
+    "test-issue3003": "jest test/issues/issue3003.test.js --runInBand --coverage=false",
     "test-tz": "date && jest test/timezone.test --coverage=false",
     "lint": "./node_modules/.bin/eslint src/* test/* build/*",
     "prettier": "prettier --write \"docs/**/*.md\"",

src/index.js

@@ -146,42 +146,78 @@ class Dayjs {
   startOf(units, startOf) { // startOf -> endOf
     const isStartOf = !Utils.u(startOf) ? startOf : true
     const unit = Utils.p(units)
-    const instanceFactory = (d, m) => {
-      const ins = Utils.w(this.$u ?
-        Date.UTC(this.$y, m, d) : new Date(this.$y, m, d), this)
-      return isStartOf ? ins : ins.endOf(C.D)
+    const hasCustomOffset = !this.$u && !Utils.u(this.$offset)
+    const instanceFactory = (y, m, d) => Utils.w(this.$u ?
+      Date.UTC(y, m, d) : new Date(y, m, d), this)
+    const instanceFactorySet = (method, args) => {
+      const date = this.toDate()
+      date[method].apply(date, args) // eslint-disable-line prefer-spread
+      return Utils.w(date, this)
     }
-    const instanceFactorySet = (method, slice) => {
+    const instanceFactorySetOffset = (method, slice) => {
       const argumentStart = [0, 0, 0, 0]
       const argumentEnd = [23, 59, 59, 999]
-      return Utils.w(this.toDate()[method].apply( // eslint-disable-line prefer-spread
-        this.toDate('s'),
-        (isStartOf ? argumentStart : argumentEnd).slice(slice)
-      ), this)
+      const date = this.toDate('s')
+      // eslint-disable-next-line prefer-spread
+      date[method].apply(date, (isStartOf ? argumentStart : argumentEnd).slice(slice))
+      return Utils.w(date, this)
     }
+    const instanceFactoryEnd = instance => Utils.w(instance.valueOf() - 1, this)
     const { $W, $M, $D } = this
     const utcPad = `set${this.$u ? 'UTC' : ''}`
+    if (hasCustomOffset) {
+      switch (unit) {
+        case C.Y:
+          return isStartOf ? instanceFactory(this.$y, 0, 1) :
+            instanceFactory(this.$y, 11, 31).endOf(C.D)
+        case C.M:
+          return isStartOf ? instanceFactory(this.$y, $M, 1) :
+            instanceFactory(this.$y, $M + 1, 0).endOf(C.D)
+        case C.W: {
+          const weekStart = this.$locale().weekStart || 0
+          const gap = ($W < weekStart ? $W + 7 : $W) - weekStart
+          return isStartOf ? instanceFactory(this.$y, $M, $D - gap) :
+            instanceFactory(this.$y, $M, $D + (6 - gap)).endOf(C.D)
+        }
+        case C.D:
+        case C.DATE:
+          return instanceFactorySetOffset(`${utcPad}Hours`, 0)
+        case C.H:
+          return instanceFactorySetOffset(`${utcPad}Minutes`, 1)
+        case C.MIN:
+          return instanceFactorySetOffset(`${utcPad}Seconds`, 2)
+        case C.S:
+          return instanceFactorySetOffset(`${utcPad}Milliseconds`, 3)
+        default:
+          return this.clone()
+      }
+    }
     switch (unit) {
       case C.Y:
-        return isStartOf ? instanceFactory(1, 0) :
-          instanceFactory(31, 11)
+        return isStartOf ? instanceFactory(this.$y, 0, 1) :
+          instanceFactoryEnd(instanceFactory(this.$y + 1, 0, 1))
       case C.M:
-        return isStartOf ? instanceFactory(1, $M) :
-          instanceFactory(0, $M + 1)
+        return isStartOf ? instanceFactory(this.$y, $M, 1) :
+          instanceFactoryEnd(instanceFactory(this.$y, $M + 1, 1))
       case C.W: {
         const weekStart = this.$locale().weekStart || 0
         const gap = ($W < weekStart ? $W + 7 : $W) - weekStart
-        return instanceFactory(isStartOf ? $D - gap : $D + (6 - gap), $M)
+        return isStartOf ? instanceFactory(this.$y, $M, $D - gap) :
+          instanceFactoryEnd(instanceFactory(this.$y, $M, $D + (7 - gap)))
       }
       case C.D:
       case C.DATE:
-        return instanceFactorySet(`${utcPad}Hours`, 0)
+        return isStartOf ? instanceFactory(this.$y, $M, $D) :
+          instanceFactoryEnd(instanceFactory(this.$y, $M, $D + 1))
       case C.H:
-        return instanceFactorySet(`${utcPad}Minutes`, 1)
+        return isStartOf ? instanceFactorySet(`${utcPad}Minutes`, [0, 0, 0]) :
+          instanceFactoryEnd(instanceFactorySet(`${utcPad}Minutes`, [60, 0, 0]))
       case C.MIN:
-        return instanceFactorySet(`${utcPad}Seconds`, 2)
+        return isStartOf ? instanceFactorySet(`${utcPad}Seconds`, [0, 0]) :
+          instanceFactoryEnd(instanceFactorySet(`${utcPad}Seconds`, [60, 0]))
       case C.S:
-        return instanceFactorySet(`${utcPad}Milliseconds`, 3)
+        return isStartOf ? instanceFactorySet(`${utcPad}Milliseconds`, [0]) :
+          instanceFactoryEnd(instanceFactorySet(`${utcPad}Milliseconds`, [1000]))
       default:
         return this.clone()
     }

test/issues/issue3003.test.js

@@ -0,0 +1,22 @@
+import dayjs from '../../src'
+
+// Run this file with TZ=Asia/Singapore or TZ=Asia/Kuala_Lumpur.
+describe('issue 3003', () => {
+  it('returns the correct number of days in month across midnight offset shifts', () => {
+    expect(dayjs('1981-12-01').daysInMonth()).toBe(31)
+  })
+
+  it('keeps endOf("month") on the last local day', () => {
+    const endOfMonth = dayjs('1981-12-01').endOf('month')
+
+    expect(endOfMonth.month()).toBe(11)
+    expect(endOfMonth.date()).toBe(31)
+  })
+
+  it('keeps endOf("day") on the same local day when midnight shifts', () => {
+    const endOfDay = dayjs('1981-12-31').endOf('day')
+
+    expect(endOfDay.month()).toBe(11)
+    expect(endOfDay.date()).toBe(31)
+  })
+})

test/plugin/utc-utcOffset.test.js

@@ -150,6 +150,48 @@ test('utc startOf', () => {
     .toBe(1500465600000)
 })
 
+test('offset mode startOf/endOf matches moment for larger and smaller units', () => {
+  const d = '2019-09-11T12:34:56.789Z'
+  const units = ['year', 'hour', 'minute', 'second']
+
+  units.forEach((unit) => {
+    expect(dayjs(d).utcOffset(480).startOf(unit).valueOf())
+      .toBe(moment(d).utcOffset(480).startOf(unit).valueOf())
+    expect(dayjs(d).utcOffset(480).endOf(unit).valueOf())
+      .toBe(moment(d).utcOffset(480).endOf(unit).valueOf())
+  })
+
+  const original = dayjs(d).utcOffset(480)
+  expect(original.startOf('otherString').valueOf()).toBe(original.valueOf())
+  expect(original.endOf('otherString').valueOf()).toBe(original.valueOf())
+})
+
+test('offset mode startOf/endOf week respects locale weekStart', () => {
+  moment.updateLocale('offset-week-start', { week: { dow: 3 } })
+
+  const sunday = '2019-09-01T12:00:00Z'
+  const friday = '2019-09-06T12:00:00Z'
+  const locale = { name: 'offset-week-start', weekStart: 3 }
+
+  expect(dayjs(sunday).utcOffset(480).locale(locale).startOf('week')
+    .valueOf())
+    .toBe(moment(sunday).utcOffset(480).locale('offset-week-start').startOf('week')
+      .valueOf())
+  expect(dayjs(sunday).utcOffset(480).locale(locale).endOf('week')
+    .valueOf())
+    .toBe(moment(sunday).utcOffset(480).locale('offset-week-start').endOf('week')
+      .valueOf())
+
+  expect(dayjs(friday).utcOffset(480).locale(locale).startOf('week')
+    .valueOf())
+    .toBe(moment(friday).utcOffset(480).locale('offset-week-start').startOf('week')
+      .valueOf())
+  expect(dayjs(friday).utcOffset(480).locale(locale).endOf('week')
+    .valueOf())
+    .toBe(moment(friday).utcOffset(480).locale('offset-week-start').endOf('week')
+      .valueOf())
+})
+
 test('cloning dates modified with utcOffset', () => {
   const djs = dayjs('2023-10-29T00:00:00+03:00')