Layer priorities influencing default version selection

[Paul Eggleton <paul.eggleton@linux.intel.com>]

Hi all,

Andrea pointed out a situation where he has seen the layer priority overriding 
version selection, and I've been able to confirm it.

Basically, if you have a recipe with a lower version in a layer with a higher 
priority it selects the lower version. What's more after digging further I 
found there were some rather anomalous interactions with the version logic and 
BBCLASSEXTEND. Here's an example using Poky:

1. Firstly, copy meta/recipes-support/curl to meta-yocto/recipes-support, then 
rename the version in meta-yocto so that its version is 7.20.0. At this point 
both meta/ and meta-yocto/ have the same layer priority of 5.

2.  "bitbake -s | grep ^curl" reports:
curl                                               :7.21.7-r0                          
curl-native                                        :7.21.7-r0                          
curl-nativesdk                                     :7.21.7-r0                          

3. Now increase the layer priority in meta-yocto/conf/layer.conf to 6, and run  
"bitbake -s | grep ^curl" again:
curl                                               :7.20.0-r0                          
curl-native                                        :7.21.7-r0                          
curl-nativesdk                                     :7.21.7-r0                          

So the latest version here is a lie, this is not the latest version available. 
Furthermore it seems not to have affected the BBCLASSEXTENDs.

4. Now add PREFERRED_VERSION_curl = "7.21.7" to conf/layer.conf and run 
"bitbake -s | grep ^curl" again:
curl                                 :7.20.0-r0                :7.21.7-r0
curl-native                    :7.21.7-r0                          
curl-nativesdk               :7.21.7-r0                          

So it can clearly see the other recipe, it just doesn't acknowledge it until 
you force the matter.

This is all rather undesirable behaviour IMHO - even if the BBCLASSEXTEND and 
reported "latest version available" issues were corrected, I think the policy 
of "latest version wins unless DEFAULT_PREFERENCE or PREFERRED_VERSION says 
otherwise" should not be affected by layer priority.

Thoughts?

Cheers,
Paul

(PS: this is not unique to Poky, Andrea and I first reproduced this with 
Angstrom using bitbake master.)

-- 

Paul Eggleton
Intel Open Source Technology Centre