Dates before 1581 are not read correctly

[manuth]

Affected Version

SilverStripe 4.4

phpunit/phpunit            5.7.27 The PHP Unit Testing framework.
silverstripe-themes/simple 3.2.0  The SilverStripe simple theme (default SilverStripe 3 theme)
silverstripe/recipe-cms    4.4.4  SilverStripe recipe for fully featured page and asset content editing
silverstripe/recipe-plugin 1.3.0  Helper plugin to install SilverStripe recipes

Description

Dates before 1581-01-01 are neither stored nor read correctly.

Steps to Reproduce

1. Create a page type with a Date field in the $db array
2. Create a SilverStripe\Forms\DateField using the getCMSFields() method
3. In the CMS set the date to 1580-12-17
4. Hit "Save"

Expected Behavior

The date value should equal 1580-12-17

Actual Behavior

The date displayed in the CMS is 1580-11-27

[manuth]

Also dates in the future (higher than 2040-04-01 like, for example 2040-04-02) are affected.

[robbieaverill]

Possibly related: #8844

[phptek]

Prob related to the introduction of the Julian Calendar in 1584?

[manuth]

Alright so I could verify that IntlDateFormatter is the source of the problem which formats the incorrect date. Sadly I couldn't find any issue about this sort of trouble - honestly I didn't even know what words to google as English isn't my main language.

Anyway I could also find out that IntlDateFormatter works correctly in combination with IntlCalendar!
So.... guys... it would be awesome if you could make DBDate using IntlCalendar instead of strtotime.

Example:

$year = 1580;
$month = 1;
$day = 20;

$calendar = IntlCalendar::createInstance(null, self::ISO_LOCALE);
$calendar->set(IntlCalendar::FIELD_YEAR, $year);
$calendar->set(IntlCalendar::FIELD_MONTH, $month - 1);
$calendar->set(IntlCalendar::FIELD_DAY_OF_MONTH, $day);
echo $formatter->format($calendar); // echos '1580-01-20'

[manuth]

@phptek I really don't know why the IntlDateFormatter wouldn't be able to do so.
Also that wouldn't explain why dates exactly before 1580-12-17 and exactly after 2040-04-01 aren't working.

However using IntlCalendar seems to solve this issue.