Description of problem:
The grub.cfg created as a result of a fresh installation of Fedora 28 Beta on a spare MBR partition does not have a menuentry for systems on other partitions, such as other Linux and Windows systems. Running grub2-mkconfig from within the new system yields the same result.
Version-Release number of selected component (if applicable):
grub2 2.02-29.fc28 in Fedora 28 Beta
Steps to Reproduce:
1. Copy a Fedora 28 beta Workstation netinstall 64-bit image to a memory stick
2. Boot the memory stick on a workstation (BIOS and MBR partitioned disk)
3. Request install of a minimal system or a full Fedora Workstation (doesn't matter) onto a spare partition on the workstation.
4. Reboot installed system.
Observe that only the newly-installed system and its rescue entry are listed in the offered grub menu. Running grub2-mkconfig a further time within the installed system is no help, it produces the same grub.cfg.
Expect that in addition to the newly installed system, other pre-existing Fedora systems and Windows systems on other partitions will also have menuentry(s) and be bootable
This issue can be circumvented post-installation by installing the os-prober package and then re-running grub2-mkconfig -o /boot/grub2/grub.cfg .
Doing a rpm --query --requires for each of the grub2 2.02-29.fc28 packages shows no declared dependency on the os-prober package. This seems to be similar to the 2011 bug #678456.
I've added to the summary title of this bug to reflect this additional info.
Issue satisfactorily fixed by release of grub2 2.02-34 on 2018-04-23 which re-instated os-prober dependency.