Would COMPATIBLE_IMAGE make sense?

["Jonas Vautherin" <jonas.vautherin@gmail.com>]

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I was thinking about my issue described here [1], and discovered the
variables called COMPATIBLE_MACHINE and COMPATIBLE_HOST, which "you can use
to stop recipes from being built for machines (/hosts) with which the
recipes are not compatible". And so I wondered if it would make sense to
add COMPATIBLE_IMAGE, for a similar purpose.

Let me explain my issue: I define different images in different layers (say
`first-project-image` and `second-project-image`), and in each of those
layers I create `.bbappends` to configure some packages. Typically
`hostapd` is used by both images, but with a different config file.

The thing is that when I run `bitbake first-project-image`, because
`second-project-image` is part of my bblayers.conf, then the
hostapd_%.bbappend from `second-project-image` is used and may have an
impact on `first-project-image`, which I don't want. I really want this
bbappend to only affect the image `second-project-image`.

One way I can see to deal with that is to realize that
`first-project-image` and `second-project-image` are two different
projects, and build them from two different BUILDDIRs. The thing I don't
like here is that all the packages are therefore downloaded and built
twice, which seems like a loss of time and space.

That's where I thought about COMPATIBLE_IMAGE. In the hostapd_%.bbappend of
`first-project-image`, I would set "COMPATIBLE_IMAGE =
'first-project-image'", and similarly for "COMPATIBLE_IMAGE =
'second-project-image'". So that I could still share a BUILDDIR between
different projects.

How bad of an idea is that?

Thanks in advance,
Jonas

[1]: https://stackoverflow.com/questions/68167244/image-specific-layers

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