[OE-core] SRC_URI computing order

[Eric Bénard]

Hi Richard,

I saw your patch fixing FILESPATH's and Kergoth's one fixing
PACKAGECONFIG processing order and I think I'm also facing an order
problem when SRC_URI is computed.

So when building SRC_URI when two layers have bbappend which apply
patches : the SRC_URI seems to be built using an order I fail to
understand somewhere instead of priority or the overrides' order.

The use case is a System on Module and its custom motherboard :
- meta-fsl-arm :
* linux-imx_xyz.bb :
SRC_URI = "patchgeneric1 ..."

- meta-som-support :
* conf/machine/mysom.conf

* linux-imx_xyz.bbappend :
SRC_URI_append_mysom = "patchsom1 patchsom2 ..."

- meta-custommotherboard (SOM + Cunstom Motherboard) :
* conf/machine/myproduct.conf
MACHINEOVERRIDES_prepend = "mysom:"
include conf/machine/mysom.conf

* linux-imx_xyz.bbappend :
SRC_URI_append_myproduct = "patchproduct1 patchproduct2 ..."

in the end I get :
SRC_URI = "patchgeneric1 ... patchsoc1 ... patchproduct1 ...
patchsom1 ..."

and of course as patchproduct* are supposed to apply on top of
patchsoc* the patch fail to apply.

I didn't found a way to build SRC_URI in the order I would like (I
tested : changing MACHINEOVERRIDES 's order, changing layers' priority,
changing machine's name to see if that was an alphabetical order ...).

In the end the only thing which worked was to add an (empty by default)
variable in som's SRC_URI and filling this variables from the
custommotherboard's bbappend.

Is the behaviour I'm seeing expected or is there something wrong in my
setup ?

Thanks,
Eric