severity: warning
include this/file/does/not/exist.inc
or
include a/file/from/another/layer.inc
If an include file doesn't reside in the same layer, it creates an external dependency on something that is likely beyond the control of the layer. It will create breakage if the other layer changes the name and/or the path of the include file.
Or the include simply doesn't exit at all.
Fix the include path or
# nooelint: oelint.file.includenotfound
include a/file/from/another/layer.inc
in case the include file is from another layer.