Add helpers for default/empty datetime value

[johnjamesjacoby]

Typing 0000-00-00 00:00:00 is error prone, and tedious.

There are a few dozen usages of it sprinkled through-out WordPress. Hundreds of plugins also.

I offer up the idea of 2 helper functions:

• __return_empty_datetime() that simply returns 0000-00-00 00:00:00
• is_empty_datetime( $datetime = '' ) to check if a variable is empty() or 0000-00-00 00:00:00

[johnjamesjacoby]

Beware: the NO_ZERO_DATES MySQL mode rabbit hole is very deep.

WordPress doesn't use null as a default value in datetime columns for legacy reasons, and I'm not suggesting we try to support it here. Mostly, I am just sick of typing 0000-00-00 00:00:00 in my own related code, and rewriting the same helpers for avoiding empty datetime values.

[johnbillion]

+1

[johnjamesjacoby]

Somewhat related to #41785...

If there were such a helper function, it could include a MySQL version check, and own the default return value based on that and whatever MySQL modes happen to be set.

Add helper functions for default datetime value and check for empty datetime value.

Trac ticket: https://core.trac.wordpress.org/ticket/46210