I thought of another problem with the wrapper class solution: if we need to 
actually backport a newer version of the class from, e.g., Poky master, then 
there is now no natural place for it since it is occupied by the wrapper class. 
That means we would either have to rename the backported class, or put it 
somewhere else than in “classes”. It also means backporting a class requires 
the wrapper class to be modified.

Here is a question for Richard: what do you think of an idea I had to add 
support in bitbake for extending classes? I do not mean to add something like 
bbclassappend, as I know that is troublesome. My idea instead is something like 
the prefuncs/postfuncs that we have for functions. I.e., before actually doing 
the inherit of a class foo, bitbake would inherit anything specified in 
BBCLASS_PRE_INHERIT:foo, and after inheriting the class it would automatically 
inherit anything in BBCLASS_POST_INHERIT:foo.  That way one can simply extend a 
class through normal variable operations, making it easy to do, e.g., in the 
distro configuration.

//Peter

From: [email protected] 
<[email protected]> On Behalf Of Peter Kjellerstedt
Sent: den 20 oktober 2021 03:32
To: Jose Quaresma <[email protected]>
Cc: OE-core <[email protected]>
Subject: Re: [OE-core] [PATCH] externalsrc.bbclass: Allow externalsrc to be 
extended with extra classes

Well, I had not considered that option. I can’t say I am to keen on having 
wrapper classes with the same name as the upstream classes as I think it leads 
to confusion. And the solution doesn’t scale very well (what if two layers want 
to override the same class?). But on the positive side it works for any class 
without requiring changes to OE-Core. And I guess the latter wins. I wish there 
was a more bitbakey way to add to classes though (bbclassappend anyone? 😉).

//Peter

From: Jose Quaresma <[email protected]<mailto:[email protected]>>
Sent: den 19 oktober 2021 19:15
To: Peter Kjellerstedt 
<[email protected]<mailto:[email protected]>>
Cc: OE-core 
<[email protected]<mailto:[email protected]>>
Subject: Re: [OE-core] [PATCH] externalsrc.bbclass: Allow externalsrc to be 
extended with extra classes

Hi Peter,

require the class on the new one will do the same
and we don't need any changes for that
but I may not be seeing everything

require ${COREBASE}/meta/classes/externalsrc.bbclass

Jose

Peter Kjellerstedt 
<[email protected]<mailto:[email protected]>> escreveu no 
dia terça, 19/10/2021 à(s) 18:03:
The EXTERNALSRC_EXTENSIONS variable holds a list of additional classes
that will be inherited when externalsrc is inherited.

Signed-off-by: Peter Kjellerstedt 
<[email protected]<mailto:[email protected]>>
---

We have had a local copy of this class for a long time since we need
to make it suppport a local class when checking BBCLASSEXTEND. And
now we wanted to add some more functionality that should be active
when externalsrc is in use. So instead of forking the class even
more, I thought it would be better to make the upstream class
extendable. The solution was inspired by USERADDEXTENSION in
useradd.bbclass.

 meta/classes/externalsrc.bbclass | 5 +++++
 meta/conf/documentation.conf     | 1 +
 2 files changed, 6 insertions(+)

diff --git a/meta/classes/externalsrc.bbclass b/meta/classes/externalsrc.bbclass
index abfe24bace..488d75760f 100644
--- a/meta/classes/externalsrc.bbclass
+++ b/meta/classes/externalsrc.bbclass
@@ -265,3 +265,8 @@ def srctree_configure_hash_files(d):
     return ' '.join(out_items)

 EXPORT_FUNCTIONS do_buildclean
+
+# Use the following to extend externalsrc with custom functionality
+EXTERNALSRC_EXTENSIONS ??= ""
+
+inherit ${EXTERNALSRC_EXTENSIONS}
diff --git a/meta/conf/documentation.conf b/meta/conf/documentation.conf
index 80ad8e10d5..6d5b734b02 100644
--- a/meta/conf/documentation.conf
+++ b/meta/conf/documentation.conf
@@ -160,6 +160,7 @@ EXTENDPE[doc] = "Used with file and pathnames to create a 
prefix for a recipe's
 EXTENDPKGV[doc] = "The full package version specification as it appears on the 
final packages produced by a recipe."
 EXTERNALSRC[doc] = "If externalsrc.bbclass is inherited, this variable points 
to the source tree, which is outside of the OpenEmbedded build system."
 EXTERNALSRC_BUILD[doc] = "If externalsrc.bbclass is inherited, this variable 
points to the directory in which the recipe's source code is built, which is 
outside of the OpenEmbedded build system."
+EXTERNALSRC_EXTENSIONS[doc] = "A list of additional classes that will be 
inherited when externalsrc is inherited."
 EXTRA_IMAGE_FEATURES[doc] = "The list of additional features to include in an 
image. Configure this variable in the conf/local.conf file in the Build 
Directory."
 EXTRA_IMAGEDEPENDS[doc] = "A list of recipes to build that do not provide 
packages for installing into the root filesystem. Use this variable to list 
recipes that are required to build the final image, but not needed in the root 
filesystem."
 EXTRA_OECMAKE[doc] = "Additional cmake options."


--
Best regards,

José Quaresma
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