[OE-core] Custom CLASSOVERRIDE and a "sub-sysroot" for JavaScript

[chris.laplante at agilent.com]

Hi Richard,

> > I have a few concerns/questions:
> > [a] Is the basic premise of a custom CLASSOVERRIDE supported by
> > Yocto? Our situation seems a bit weird, because our emscripten
> > recipes are still sort of “target” recipes, so I feel a bit funny
> > completely wiping CLASSOVERRIDE.
> 
> I assume this class extension only applies for target recipes?
> 
> If so, why not append ":class-emscripten" to CLASSOVERRIDE rather than
> overwrite it? We support multiple overrides.

Makes sense, I'll give it a try. 

> > [b] At the very least, I know I did something wrong, because
> > sometimes we get weird warnings like:
> >
> > WARNING: app-emscripten-1.0+gitAUTOINC+1d1073e7c4-r0 do_compile:
> > Manifest /home/user/yocto/build/tmp/sstate-control/manifest-
> > x86_64_x86_64-nativesdk-library-emscripten.populate_sysroot not found
> > in my_mach cortexa9t2hf-neon cortexa9t2hf-vfp cortexa9hf-neon
> > cortexa9hf-vfp armv7at2hf-neon armv7ahf-neon armv7at2hf-vfp armv7ahf-
> > vfp armv6thf-vfp armv6hf-vfp armv5tehf-vfp armv5ehf-vfp armv5thf-vfp
> > armv5hf-vfp allarch x86_64_x86_64-nativesdk (variant '')?
> >
> > ... usually followed by a build failure in “app-emscripten” because
> > “library-emscripten:do_populate_sysroot” indeed didn’t run. Related
> > to [a] or perhaps the stamp-extra-info lines?
> 
> I'd say the stamp-extra-info lines. Why do you think you want those?

To be honest, I'm not completely sure. I based this class off of native.bbclass and nativesdk.bbclass and they both do it. I have little idea what stamp-extra-info actually does.  


> > [c] Is there a better way to do the “sub-sysroot” (/usr/js)? Would
> > multilib cover this whole use case?  (2)
> 
> No, it wouldn't since multilib assumes the headers are one set with two
> sets of binaries/libs. You are doing something quite similar to the
> multilib class extension though.

OK, so the basic strategy seems OK then? 

Thanks again for your expertise,
Chris