DateTimePatch: keep DateTime.__eq__ behavior from DateTime 2

We have too much code depending on this behavior, so we keep this patch
for now.

product/ERP5Type/patches/DateTimePatch.py

@@ -35,6 +35,15 @@ SyntaxError, DateError, TimeError, localtime, time
 
 STATE_KEY = 'str'
 
+# DateTime 3 changed the __eq__ behavior and d1 == d2 only if they have the same same
+# timezone. With DateTime 2 two dates from different timezones representing the same
+# time were equal. This patch keeps the behavior from DateTime 2.
+# See zopefoundation/DateTime commit fff6d04 (Various cleanups, improve unpickling
+# speed and distinguish between equal representations and references to equal points
+# in time., 2011-05-06)
+DateTimeKlass.__eq__ = DateTimeKlass.equalTo
+
+
 # ERP5 Patch for different pickle implementation, to optimize for disk usage.
 # We had different __getstate__ implementations, so we need __setstate__ to support
 # loading these formats that might be present in ZODBs.

[Kazuhiko Shiozaki]

@jerome This change introduces the following behaviour on Zope4.

• code

portal = context.getPortalObject()
web_page = portal.web_page_module.newContent(
  portal_type='Web Page',
  temp_object=True,
)
web_page.setEffectiveDate(DateTime(0))
print web_page.getEffectiveDate()
print web_page.hasEffectiveDate()
return printed

• Zope2 result

1970/01/01 01:00:00 GMT+1
True

• Zope4 result

None
False

It is caused by DateTime.equalTo at https://github.com/zopefoundation/DateTime/commit/b9ddd8b9f9c8ba89fcab749a1871871706e7c2c0#diff-778daecbfbef655fab523b4aaa62847e40260011204ee3202a063367e3f35f91R1247 and Setter.__call__ at https://lab.nexedi.com/nexedi/erp5/blob/7ac33e16956cbd4684fdefbf35d25fcfff39350f/product/ERP5Type/Accessor/Base.py#L74-75 (and similar code in Tester.__call__).

I can understand that the change in DateTime is introduced for Python3 sorting, but I think the code should be rather the following to keep Python2's sort behaviour, i.e. None is always first.

def equalTo(self, t):
  if t is None:
    return False # instead of 't = 0'
  ...
def greaterThanEqualTo(self, t):
  if t is None:
    return True # instead of 't = 0'
  ...
def lessThanEqualTo(self, t):
  if t is None:
    return False # instead of 't = 0'
  ...

Or we should 'fix' in our Accessor code ?

[Kazuhiko Shiozaki]

Let's continue on !1800 (closed)