license manifest files effectively disappear when do_rootfs is not rerun

["Christian Thießen" <christian.thiessen@airbus.com>]

(Cross-post: I first posted to https://lists.yoctoproject.org/g/yocto/message/58392, then realized that according to the poky readme this list is more appropriate. Sorry, beginner's mistake)

Dear list,
when building an image with a Yocto setup based on kirkstone, it seems I've come across an interesting corner case: The image built successfully, the build/tmp/deploy/licenses/${IMAGE}-${MACHINE} symlink got updated as expected, but that new directory contained only image_license.manifest. license.manifest and package.manifest were missing.
I've discovered that these latter files are generated by the image's do_rootfs task (ROOTFS_POSTPROCESS_COMMAND:prepend = "write_package_manifest; license_create_manifest; " in poky/meta/classes/license_image.bbclass). This task apparently did not need to be rerun in that particular build.
This behavior is at least a bit surprising to the user; bitbake claims to have run everything that needed to be run, completes successfully and then some files are just not there. It might be what happened here https://lists.yoctoproject.org/g/yocto/message/49600 too. For me, it broke a CI build that ran due to an environment change that didn't affect the image and then failed to deploy the manifest files. I could run bitbake with -C rootfs as a workaround, but that causes a warning and the problem could probably better be fixed within the oe-core classes. I'm not sure how though: Could the manifest generation be moved to a different point in the build, e.g. where image_license.manifest is generated? Or should build/tmp/deploy/licenses/${IMAGE}-${MACHINE} become a directory containing symlinks to files, instead of a symlink to a new directory, so that things that don't need to be updated can be retained? Maybe you have a completely different idea? I'll leave that up for discussion.
Thank you,

Christian Thießen