Fix DST issue (closes #972, closes #992)

scripts/test/dst.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+
+# The script runs the DST tests.
+#
+# It's a part of the test process.
+
+set -ex
+
+export PATH="$(yarn bin):$PATH"
+
+env TZ=America/Sao_Paulo babel-node ./test/dst/toDate/basic.js
+env TZ=Pacific/Apia babel-node ./test/dst/toDate/samoa.js

scripts/test/travis.sh

@@ -21,6 +21,8 @@ then
 
   yarn test -- --single-run
 
+  ./scripts/test/dst.sh
+
   prebuild
   ./scripts/test/tz.sh
 

src/toDate/index.js

@@ -186,11 +186,20 @@ export default function toDate(argument, dirtyOptions) {
         return new Date(NaN)
       }
     } else {
-      // get offset accurate to hour in timezones that change offset
-      offset = getTimezoneOffsetInMilliseconds(new Date(timestamp + time))
-      offset = getTimezoneOffsetInMilliseconds(
-        new Date(timestamp + time + offset)
-      )
+      var fullTime = timestamp + time
+      var fullTimeDate = new Date(fullTime)
+
+      offset = getTimezoneOffsetInMilliseconds(fullTimeDate)
+
+      // Adjust time when it's coming from DST
+      var fullTimeDateNextDay = new Date(fullTime)
+      fullTimeDateNextDay.setDate(fullTimeDate.getDate() + 1)
+      var offsetDiff =
+        getTimezoneOffsetInMilliseconds(fullTimeDateNextDay) -
+        getTimezoneOffsetInMilliseconds(fullTimeDate)
+      if (offsetDiff > 0) {
+        offset += offsetDiff
+      }
     }
 
     return new Date(timestamp + time + offset)

test/dst/toDate/basic.js

@@ -0,0 +1,30 @@
+// This is basic DST test for toDate
+
+import toDate from '../../../src/toDate'
+import assert from 'assert'
+
+if (process.env.TZ !== 'America/Sao_Paulo')
+  throw new Error('The test must be run with TZ=America/Sao_Paulo')
+
+if (parseInt(process.version.match(/^v(\d+)\./)[1]) < 10)
+  throw new Error('The test must be run on Node.js version >= 10')
+
+// Test DST start edge
+assert.equal(toDate('2018-11-03').getDate(), 3)
+assert.equal(toDate('2018-11-04').getDate(), 4) // DST start
+assert.equal(toDate('2018-11-05').getDate(), 5)
+
+// Test DST end edge
+assert.equal(toDate('2019-02-15').getDate(), 15)
+assert.equal(toDate('2019-02-16').getDate(), 16) // DST end
+assert.equal(toDate('2019-02-17').getDate(), 17)
+
+// Test creation of nonexistent time
+assert.equal(
+  toDate('2018-11-04T00:00').toString(),
+  'Sun Nov 04 2018 01:00:00 GMT-0200 (Brasilia Summer Time)'
+)
+assert.equal(
+  toDate('2018-11-04T00:30').toString(),
+  'Sun Nov 04 2018 01:30:00 GMT-0200 (Brasilia Summer Time)'
+)

test/dst/toDate/samoa.js

@@ -0,0 +1,16 @@
+// This is basic DST test for toDate
+
+import toDate from '../../../src/toDate'
+import assert from 'assert'
+
+if (process.env.TZ !== 'Pacific/Apia')
+  throw new Error('The test must be run with TZ=Pacific/Apia')
+
+if (parseInt(process.version.match(/^v(\d+)\./)[1]) < 10)
+  throw new Error('The test must be run on Node.js version >= 10')
+
+assert.equal(toDate('2011-12-30').getDate(), 31)
+assert.equal(
+  toDate('2011-12-30T03:30').toString(),
+  'Sat Dec 31 2011 03:30:00 GMT+1400 (Apia Daylight Time)'
+)