[OE-core] How to set PACKAGECONFIG + proposal

[Enrico Scholz]

Hi,

recent packaging uses lots of different ways how PACKAGECONFIG is set:

a)  PACKAGECONFIG ??= "<something>"

b)  PACKAGECONFIG ?= "<something>"

and similar variations for special classes

c)  PACKAGECONFIG_class-target ??= "<something>"

d)  PACKAGECONFIG_class-target ?= "<something>"

Sample c) causes problems (see 8994ff6650a4c4c2f0b07e5ee6a5f889270151e5)
and at least me does not see why it is going wrong.  It is unclear to me
either why some packages uses a), other b).

To avoid nasty surprises; I would prefer to avoid cases c) and d) or
even ban the usage of '?=' completely when assigning _overrides.

As "<something>" is calculated sometimes in non trivial ways and contains
requirements instead of user configurable features, I suggest to write

  DEFAULT_PACKAGECONFIG = "<something>"
  DEFAULT_PACKAGECONFIG_class-target = "<something>"

  PACKAGECONFIG ??= "${DEFAULT_PACKAGECONFIG}"
 
at least when case c) or d) were used.  Using '??=' or '?=' is debatable
but should be consistent across the distribution.


Opinions?



Enrico