Bug 15134 - DST/BST not correct for dates prior to 1970
Summary: DST/BST not correct for dates prior to 1970
Status: NEW
Alias: None
Product: Class Libraries
Classification: Mono
Component: System ()
Version: unspecified
Hardware: Macintosh Mac OS
: --- normal
Target Milestone: Untriaged
Assignee: Bugzilla
Depends on:
Reported: 2013-10-02 15:03 UTC by Jon Goldberger [MSFT]
Modified: 2015-02-03 13:28 UTC (History)
6 users (show)

Is this bug a regression?: ---
Last known good build:

test project (11.96 KB, application/zip)
2013-10-02 15:03 UTC, Jon Goldberger [MSFT]
Version info (1.34 KB, text/plain)
2013-10-02 15:03 UTC, Jon Goldberger [MSFT]

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Description Jon Goldberger [MSFT] 2013-10-02 15:03:21 UTC
Created attachment 5040 [details]
test project

I'm using DateTime.ToLocalTime() in an iOS library and it's returning
unexpected results. The time doesn't seem to change to match the timezone
but the Kind is being set to Local.

I've posted an example on StackOverflow.com

Is this expected behaviour?

After further investigation this appears to be confined to dates before
1970 (note that BST started in 1916).

Please find attached:

- A sample project that outputs all the timezone and datetime
information (rename .zipped to .zip)
- A screenshot of it running on my mac (iOS Simulator)
- A copy of my 'About' information.

This is to be a very serious problem and means that all 'Date of births' in
my app are shown incorrectly as they are derived from UTC date strings.

In the screenshot you'll notice that the 'Daylight savings time for year
1970' is incorrect.
Comment 1 Jon Goldberger [MSFT] 2013-10-02 15:03:41 UTC
Created attachment 5041 [details]
Version info
Comment 3 Rolf Bjarne Kvinge [MSFT] 2013-10-03 17:34:12 UTC
Paolo, looks like this commit you made a long time ago is the source of this bug:


Here is a test case: https://gist.github.com/rolfbjarne/e599168fe2aba6b47353 - executing it will clearly show that there is no summertime information from before 1970.
Comment 5 Paolo Molaro 2013-10-28 11:07:41 UTC
While we implement a complete fix for this, you can use the following workaround for DateTime.ToLocalTime():

  Datetime localdate = TimeZoneInfo.ConvertTime (utcdate, TimeZoneInfo.Utc, TimeZoneInfo.Local);
Comment 6 chris 2013-10-28 11:17:46 UTC
Hi Paolo,

The workaround does not work. It results in the same issue.

I've added the following lines to the original sample project. 

// 1960 (2)
utcDateTime = new DateTime (1960, 07, 15, 15, 00, 00, DateTimeKind.Utc);
utcTimeString = utcDateTime.ToString ();
var localdate = TimeZoneInfo.ConvertTime (utcDateTime, TimeZoneInfo.Utc,TimeZoneInfo.Local);
localTimeString = localdate.ToString ();

Both the localTimeString and utcTimeString result in "7/15/1960 3:00:00 PM", which is incorrect. localTimeString should be "7/15/1960 4:00:00 PM"
Comment 7 Paolo Molaro 2013-10-29 04:07:45 UTC
Chris: what is the mono version and the platform version this is being run on?
TimeZoneInfo needs the zoneinfo data to be available (Android, Linux, OSX).
I had tested the workaround on my system with a date from 1918 and it was fine.
Comment 8 chris 2013-10-29 06:12:48 UTC
Hi Paolo,

I'm running under iOS and have tested in both simulator and device.

I have updated my system since the original version information was attached, so here it is again:

=== Xamarin Studio ===

Version 4.0.13 (build 38)
Installation UUID: 4e7a8b28-b1e8-4f65-9910-dd21d038725e
	Mono 3.2.3 ((no/8d3b4b7)
	GTK+ 2.24.20 theme: Raleigh
	GTK# (
	Package version: 302030000

=== Apple Developer Tools ===

Xcode 5.0.1 (3335.23)
Build 5A2053

=== Xamarin.iOS ===

Version: (Business Edition)
Hash: 57edee2
Build date: 2013-04-10 18:05:51-0400

=== Xamarin.Android ===

Version: 4.8.3 (Starter Edition)
Android SDK: /Users/chriskoiak/Library/Developer/Xamarin/android-sdk-mac_x86
	Supported Android versions:
		2.1   (API level 7)
		2.2   (API level 8)
		2.3   (API level 10)
		3.1   (API level 12)
		4.0   (API level 14)
		4.0.3 (API level 15)
		4.2   (API level 17)
Java SDK: /usr
No Java runtime present, requesting install.

=== Xamarin.Mac ===

Xamarin.Mac: Not Installed

=== Build Information ===

Release ID: 400130038
Git revision: 07afec667f7be5d0ee511eb7115bbac6377fbae8
Build date: 2013-09-24 08:53:29+0000
Xamarin addins: 61140345a5b109633a94409edcbc7a4c19a425c6

=== Operating System ===

Mac OS X 10.9.0
Darwin Chriss-MacBook-Pro-2.local 13.0.0 Darwin Kernel Version 13.0.0
    Thu Sep 19 22:22:27 PDT 2013
    root:xnu-2422.1.72~6/RELEASE_X86_64 x86_64