When a do_patch operation fails for Linux-yocto, it recommends running 'bitbake -c devshell Linux-yocto' to troubleshoot/fix the error. However, With Dylan and later, running the suggested command gives the same error instead of opening a development terminal. To see this in practice, you will need to break a machine by modifying an .scc file such that another included .scc file is not found. The file not found causes the do_patch to fail, which prints the "Patch failures can be resolved in the devshell (bitbak -c devshell ${PN})" However, since devshell runs after do_patch, and do_patch fails, there is no way into the devshell. This bug is not to report a broken do_patch (it should have been broken), but is to report the invalid help message printed when an error does occur.
devshell.bbclass sets do_devshell to run after do_patch, so it seems that a broken patch could block devshell from executing for any recipe, not just the kernel. We could change devshell to be run after do_unpack instead, but then that would break some people's workflow if they expect to start with the patched source as they do currently. We do have another option here - we have a proper shell-based interactive patch resolution feature that is enabled by setting PATCHRESOLVE to "user". Since kernel-yocto.bbclass has its own custom do_patch it may not currenly work with this however; perhaps the best solution would be to make it work with that if it doesn't and change the message (which is specific to kernel-yocto.bbclass) to recommend using that rather than devshell which won't work anyway.
For now, we'll get the message update and worry about changing the devshell dependencies in 1.9. Changing the status to "in design".