Re: [bitbake-devel][PATCH] bb: Add prefuncs and postfuncs ordering

On Sun, 2026-06-28 at 08:29 +0100, Richard Purdie via lists.openembedded.or=
g wrote:
> On Fri, 2026-06-26 at 11:00 -0600, Joshua Watt via lists.openembedded.org=
 wrote:
> > Adds the ability for functions specified in prefuncs and postfuncs to
> > specify the order in which they must execute. This allows specific
> > functions to indicate that they must run first or last (or second,
> > second to last, etc.) without needing all places in the code that
> > manipulate the function list to have to agree on how to order them
> > (a good example of this is sstate.bbclass and buildhistory.bbclass).
> >=20
> > Ordering is done similar to how python list indices work; 0 is always
> > sorted first, 1 is second, -2 is second to last, -1 is last, etc. In th=
e
> > event of functions having duplicate values, they are grouped together,
> > but keep their same relative ordering. If one or more functions do not
> > have an order assigned, they executed between the positive order
> > functions and the negative order functions, and keep their same relativ=
e
> > order (this means that existing behavior is preserved in the absence of
> > any ordering information).
> >=20
> > Signed-off-by: Joshua Watt <[email protected]>
>=20
> I've wondered about something like this for a long time, the trouble is
> it does not scale well and I've always concluded it wouldn't really
> help overall and solve the real problem.
>=20
> It solves an immediate issue of making one thing run first, or last. If
> a second comes along, it can just about handle that. The trouble is
> when you have three or more and they all want to be "last", or "first",
> you can't define that in the metadata. This just gets worse when you
> think of independent layers trying to pick numeric values. This is
> already a pain with layer priorities and I wish we'd never used
> numbers.
>=20
> You can already get some idea of ordering just by the +=3D and =3D+
> operations ordering the data, or reordering the variable contents using
> anon python.
>=20
> You could even define a filter function for the variable which could
> reorder things with a custom order function.
>=20
> So I'm probably against adding this level of complexity when we already
> have enough of it and it doesn't fully solve the issue anyway.
>=20
> If we did something, I'd probably look in the direction of "after" and
> "before" operations like tasks, trying to avoid some of the issues we
> have there.

I couldn't help thinking about this more, the syntax I was wondering
about was something along the lines of:

do_xxx[postfuncs] +=3D "functionC[after-functionB,after-functionA,before-fu=
nctionD]"

which is horrible, but at least explicit.

Cheers,

Richard