1300110 - DateTime doesn't clear cache for different time zones with same tz-adjustment

Status: RESOLVED INCOMPLETE

(Core :: JavaScript Engine, defect, P3)

Description

[André Bargull [:anba]]

Attachment: testDateTime.cpp

This optimization [1] isn't correct. Two time zones may use the same offset, but still have different time zone rules, e.g. America/Denver and America/Phoenix. The attached test case is currently failing for America/Los_Angeles and America/Phoenix, but that's caused by bug 830304. 

[1] http://hg.mozilla.org/mozilla-central/file/d5f20820c805/js/src/vm/DateTime.cpp#l158

Comment 1

[André Bargull [:anba]]

Attachment: testDateTime.cpp

There is a similar issue in DateObject::fillLocalTimeSlots(), updated the test case accordingly.

[1] http://hg.mozilla.org/mozilla-central/file/d5f20820c805/js/src/jsdate.cpp#l1253

Comment 3

[Matthew Gaudet (he/him) [:mgaudet]]

All the referenced code seems gone now.

Comment 4

[André Bargull [:anba]]

The code now lives here: https://searchfox.org/mozilla-central/rev/c09764753ea40725eb50decad2c51edecbd33308/js/src/vm/DateTime.cpp#202

Comment 5

[Matthew Gaudet (he/him) [:mgaudet]]

Ah! -- worth resuscitating this one then?

Comment 6

[André Bargull [:anba]]

Hmm, I think we should at least add a comment to that line of code to explain the current situation. Things have slightly changed since this bug has been filed:

• The public JSAPI function JS::ResetTimeZone will always trigger a time zone update, even if the offset is unchanged. (That means the test code attached to this bug doesn't show this issue anymore.)
• Only when the internal js::ResetTimeZoneInternal function is called from JS::Realm::init for our periodic time zone modification checks, the bug described here can be observed.
• Bug 1343826 added support to receive time zone change messages from the OS, so it shouldn't actually be necessary anymore for JS::Realm::init to check for time zone changes. At least as long as bug 1343826 covers all supported OSes and it works correctly -- and it doesn't quite seem to work on Ubuntu when manually modifying the time zone through the system settings. STR:
  • Open dev-tools and evaluate new Intl.DateTimeFormat().resolvedOptions().timeZone.
  • Change system time zone, for example from Europe/Berlin to Europe/Paris.
  • Switch back to the dev-tools console and evaluate new Intl.DateTimeFormat().resolvedOptions().timeZone again.
  • For me it's both times returning Europe/Berlin. Chromium correctly returns Europe/Paris after changing the time zone.