Fix handling of DST jumps in Brazilian timezones in startOf/endOf, fixes

 #3132

src/lib/moment/start-end-of.js

@@ -1,19 +1,48 @@
 import { normalizeUnits } from '../units/aliases';
 
 export function startOf (units) {
+    var initialDate = this.date(),
+        checkForDST = true,
+        hour, clone;
+
     units = normalizeUnits(units);
+
+    // in week/isoWeek operations, jump to noon to make sure that we do not hit DST bugs when
+    // switching the weekday/isoWeekday and can collect a valid initialDate to use for comparison
+    // after the time is adjusted
+    if (units === 'week' || units === 'isoWeek') {
+        this.hours(12);
+    }
+
     // the following switch intentionally omits break keywords
     // to utilize falling through the cases.
     switch (units) {
         case 'year':
             this.month(0);
             /* falls through */
         case 'quarter':
+            // quarters is a special case
+            if (units === 'quarter') {
+                this.month(Math.floor(this.month() / 3) * 3);
+            }
+            /* falls through */
         case 'month':
             this.date(1);
+            // for month/quarter/year changes, no DST can interfere so we do not check for it
+            checkForDST = false;
             /* falls through */
         case 'week':
         case 'isoWeek':
+            // weeks are a special case
+            if (units === 'week') {
+                this.weekday(0);
+                initialDate = this.date();
+            }
+            if (units === 'isoWeek') {
+                this.isoWeekday(1);
+                initialDate = this.date();
+            }
+            /* falls through */
         case 'day':
         case 'date':
             this.hours(0);
@@ -28,17 +57,24 @@ export function startOf (units) {
             this.milliseconds(0);
     }
 
-    // weeks are a special case
-    if (units === 'week') {
-        this.weekday(0);
-    }
-    if (units === 'isoWeek') {
-        this.isoWeekday(1);
-    }
+    // check if day of month changed when setting the time
+    if (checkForDST && this.date() !== initialDate) {
+        // note: DST adjustments are assumed to occur in multiples of 1 hour (this is almost always the case)
+        // refer to http://www.timeanddate.com/time/aboutdst.html for the (rare) exceptions to this rule
 
-    // quarters are also special
-    if (units === 'quarter') {
-        this.month(Math.floor(this.month() / 3) * 3);
+        // depending on JS implementations, the time can jump 1day ahead or be in the past
+        if (this.date() > initialDate) {
+            this.date(initialDate);
+        } else {
+            // increment hour until cloned date == current date
+            hour = 1;
+            do {
+                clone = this.clone().add(hour++, 'hour');
+            } while (clone.date() < initialDate);
+
+            this.date(initialDate);
+            this.hours(clone.hours());
+        }
     }
 
     return this;
@@ -50,10 +86,50 @@ export function endOf (units) {
         return this;
     }
 
-    // 'date' is an alias for 'day', so it should be considered as such.
-    if (units === 'date') {
-        units = 'day';
+    // in week/isoWeek operations, jump to noon to make sure that we do not hit DST bugs when
+    // switching the weekday/isoWeekday
+    if (units === 'week' || units === 'isoWeek') {
+        this.hours(12);
+    }
+
+    // the following switch intentionally omits break keywords
+    // to utilize falling through the cases.
+    switch (units) {
+        case 'year':
+            this.month(11);
+            /* falls through */
+        case 'quarter':
+            // quarters is a special case
+            if (units === 'quarter') {
+                this.month((Math.floor(this.month() / 3) * 3) + 2);
+            }
+            /* falls through */
+        case 'month':
+            this.date(this.month() === 1 ? 28 : ([0, 2, 4, 6, 7, 9, 11].indexOf(this.month()) === -1 ? 30 : 31));
+            /* falls through */
+        case 'week':
+        case 'isoWeek':
+            // weeks are a special case
+            if (units === 'week') {
+                this.weekday(6);
+            }
+            if (units === 'isoWeek') {
+                this.isoWeekday(7);
+            }
+            /* falls through */
+        case 'day':
+        case 'date':
+            this.hours(23);
+            /* falls through */
+        case 'hour':
+            this.minutes(59);
+            /* falls through */
+        case 'minute':
+            this.seconds(59);
+            /* falls through */
+        case 'second':
+            this.milliseconds(999);
     }
 
-    return this.startOf(units).add(1, (units === 'isoWeek' ? 'week' : units)).subtract(1, 'ms');
+    return this;
 }

src/test/moment/start_end_of.js

@@ -186,7 +186,88 @@ test('end of day', function (assert) {
     assert.equal(m.hours(), 23, 'set the hours');
     assert.equal(m.minutes(), 59, 'set the minutes');
     assert.equal(m.seconds(), 59, 'set the seconds');
-    assert.equal(m.milliseconds(), 999, 'set the seconds');
+    assert.equal(m.milliseconds(), 999, 'set the milliseconds');
+});
+
+test('start/end of week with timezone on day DST switch occurs and weekstart being day of DST switch', function (assert) {
+    var oldOffset = moment.updateOffset,
+        fmt = 'YYYY-MM-DD HH:mm:ss.SSS',
+        m = moment('2017-10-15 02:03:04'),
+        expectedStart = '2017-10-15 01:00:00.000';
+
+    moment.updateOffset = function (mom, keepTime) {
+        // mimick Brazil DST which happens at midnight and in which 00:00:00 - 00:59:59 does not exist on Sunday 15th Oct 2017
+        if (mom.format(fmt) === '2017-10-15 00:00:00.000') {
+            mom.hour(1);
+        }
+    };
+
+    m.startOf('week');
+    assert.equal(m.format(fmt), expectedStart, 'start of week jumps correctly');
+
+    moment.updateOffset = oldOffset;
+});
+
+test('start/end of day with timezone on day DST switch occurs', function (assert) {
+    var oldOffset = moment.updateOffset,
+        fmt = 'YYYY-MM-DD HH:mm:ss.SSS',
+        m = moment('2017-10-15 02:03:04'),
+        m2 = moment('2017-10-15 02:03:04'),
+        expectedStart = '2017-10-15 01:00:00.000',
+        expectedEnd = '2017-10-15 23:59:59.999';
+
+    moment.updateOffset = function (mom, keepTime) {
+        // mimick Brazil DST which happens at midnight and in which 00:00:00 - 00:59:59 does not exist on Sunday 15th Oct 2017
+        if (mom.format(fmt) === '2017-10-15 00:00:00.000') {
+            mom.hour(1);
+        }
+    };
+
+    m.startOf('day');
+
+    assert.equal(m.format(fmt), expectedStart, 'start of day jumps correctly');
+
+    m.endOf('day');
+    m2.endOf('day');
+
+    assert.equal(m.format(fmt), expectedEnd, 'start + end of day jumps correctly');
+    assert.equal(m2.format(fmt), expectedEnd, 'end of day jumps correctly');
+
+    m.startOf('day');
+    assert.equal(m.format(fmt), expectedStart, 'start + end + start of day jumps correctly');
+
+    moment.updateOffset = oldOffset;
+});
+
+test('start/end of day with timezone on day before DST switch occurs', function (assert) {
+    var oldOffset = moment.updateOffset,
+        fmt = 'YYYY-MM-DD HH:mm:ss.SSS',
+        m = moment('2017-10-14 02:03:04'),
+        m2 = moment('2017-10-14 02:03:04'),
+        expectedStart = '2017-10-14 00:00:00.000',
+        expectedEnd = '2017-10-14 23:59:59.999';
+
+    moment.updateOffset = function (mom, keepTime) {
+        // mimick Brazil DST which happens at midnight and in which 00:00:00 - 00:59:59 does not exist on Sunday 15th Oct 2017
+        if (mom.format(fmt) === '2017-10-15 00:00:00.000') {
+            mom.hour(1);
+        }
+    };
+
+    m.startOf('day');
+
+    assert.equal(m.format(fmt), expectedStart, 'start of day jumps correctly');
+
+    m.endOf('day');
+    m2.endOf('day');
+
+    assert.equal(m.format(fmt), expectedEnd, 'start + end of day jumps correctly');
+    assert.equal(m2.format(fmt), expectedEnd, 'end of day jumps correctly');
+
+    m.startOf('day');
+    assert.equal(m.format(fmt), expectedStart, 'start + end + start of day jumps correctly');
+
+    moment.updateOffset = oldOffset;
 });
 
 test('start of date', function (assert) {