According to:-PSR-2 multiline array indentation missing
PSR-2 doesn't define how arrays should be indented, or if they should
even be indented at all, so PHPCS can't enforce any rules in this
area.
When I have asked about arrays in other areas of the standard, the
response was to treat them like a single object, and ignore them. So
many PHPCS checks for PSR-2 actually skip right over arrays and don't
do any checking inside them either.
So this isn't a bug, and it's also not something I can add to PHPCS
because PSR-2 doesn't define an array formatting standard.
Note:-
The same thing is stated in this thread too:- Question on proper Array syntax
There's no correct answer, beacuse the PSR is silent on the matter,
but I think your assumption is reasonable. It's certainly my practice.
Even if you check this thread:- Coding Style Guide Additions
It only states about adding ,
not about anything regarding adding spaces.
Arrays that span across multiple lines can have a trailing comma to
make sure that adding new rows does not change the previous row, as
well.