TYPO3 Core

Hi,

to get the surrounding facts straight:

- You have a DB field that is not capable of storing time zone information (date)
- You create a date with timezone information
- You store that field and the timezone information is obviously lost
- When retrieving the data due to the lost timezone information the date is now wrong (which worked before by accident in case you created a date in the default timezone or anything "close enough")

The change to convert all dates to UTC is meant to ensure consistent date handling throughout the core - especially because date fields don't have timezone information - when displaying those dates later, we need "something" to assume as base. This could be:

- UTC always
- the php timezone
- the mysql / server timezone
- the timezone you set manually when creating the date
- the timezone on the client side (because he used a javascript datepicker)

only one of these options is in my eyes "safe" - and that is UTC always. To fix your issue I'd just use new \DateTime('2016-07-13', DateTimeZone::UTC); - or am I missing something?

For migration of "old" stored dates I'd directly use an mysql script doing something along https://dev.mysql.com/doc/refman/5.7/en/date-and-time-functions.html#function_convert-tz

I have a date field in the database. No matter what I do, when I read it, I always get the date, which is in the database, no matter what time zone it was before, like always UTC.
A pure date is always independent of time zones for me (human logic, not PHP logic). So I still do not understand if I want to save a datetime object to a date field, why there has to be a conversion, the only thing that can happen during the conversion is that the date is broken. There is no advantage in any case.
With the datetime type it is not necessary to create it in UTC because TYPO3 converts it to default timezone when reading from database. This is confusing and inconsistent. I understand this in principle but I mean it is wrong.

And what about existing projects? I knew about the fact that TYPO3 stores dates time-zone independent or in other words, that TYPO3 does not convert dates before writing data to databse and therefore i wrote my code without converting anything / creating Dates in UTC.
Now I would have to adjust code in each project and unittests do no longer work anymore and I can not ensure that my changes work.

In summary: it should not be converted if the database field is a "date" (not datetime) field. The backconversion to the original date is not possible.
The use of the conversion should be switchable in the installtool to ensure the compatibility to already existing projects which handle conversions by themselfes.