Don't apply DST offset in parseISO when parsing date, fixes #1449

scripts/test/dst.sh

@@ -10,6 +10,7 @@ export PATH="$(yarn bin):$PATH"
 export NODE_ENV=test
 
 env TZ=America/Sao_Paulo babel-node ./test/dst/parseISO/basic.js
+env TZ=Australia/Sydney babel-node ./test/dst/parseISO/sydney.js
 env TZ=Pacific/Apia babel-node ./test/dst/parseISO/samoa.js
 env TZ=Asia/Damascus babel-node ./test/dst/eachDayOfInterval/basic.js
 env TZ=America/Santiago babel-node ./test/dst/addBusinessDays/basic.js

src/parseISO/index.js

@@ -138,7 +138,11 @@ export default function parseISO(argument, dirtyOptions) {
 
     // Adjust time when it's coming from DST
     var fullTimeDateNextDay = new Date(fullTime)
-    fullTimeDateNextDay.setDate(fullTimeDate.getDate() + 1)
+    if (offset > 0) {
+      fullTimeDateNextDay.setDate(fullTimeDate.getDate() + 1)
+    } else {
+      fullTimeDateNextDay.setDate(fullTimeDate.getDate() - 1)
+    }
     var offsetDiff =
       getTimezoneOffsetInMilliseconds(fullTimeDateNextDay) - offset
     if (offsetDiff > 0) {

test/dst/parseISO/sydney.js

@@ -0,0 +1,12 @@
+// This is basic DST test for parseISO
+
+import parseISO from '../../../src/parseISO'
+import assert from 'assert'
+
+if (process.env.TZ !== 'Australia/Sydney')
+  throw new Error('The test must be run with TZ=Australia/Sydney')
+
+if (parseInt(process.version.match(/^v(\d+)\./)[1]) < 10)
+  throw new Error('The test must be run on Node.js version >= 10')
+
+assert.equal(parseISO('2019-10-06').getDate(), 6)