gistfile1.txt

[ebuild   R   *] sys-kernel/spl-9999::gentoo  USE="-custom-cflags -debug" 0 KiB
[ebuild   R   ~] app-emulation/virtualbox-modules-5.2.12::gentoo  USE="-pax_kernel" 0 KiB
[ebuild   R   *] sys-fs/zfs-kmod-9999::gentoo  USE="rootfs -custom-cflags -debug" 0 KiB
[ebuild   R   ~] x11-drivers/nvidia-drivers-396.24:0/396::gentoo  USE="X acpi driver gtk3 kms multilib tools uvm -compat -pax_kernel -static-libs -wayland" ABI_X86="32 (64) (-x32)" 0 KiB
[ebuild   R   ~] net-vpn/wireguard-0.0.20180531::gentoo  USE="module tools -debug -module-src" 0 KiB
[blocks B      ] sys-kernel/spl ("sys-kernel/spl" is blocking sys-fs/zfs-kmod-9999)

Total: 5 packages (5 reinstalls), Size of downloads: 0 KiB
Conflict: 1 block (1 unsatisfied)

 * Error: The above package list contains packages which cannot be
 * installed at the same time on the same system.

  (sys-kernel/spl-9999:0/0::gentoo, ebuild scheduled for merge) pulled in by
    sys-kernel/spl:0 required by @module-rebuild

  (sys-fs/zfs-kmod-9999:0/0::gentoo, ebuild scheduled for merge) pulled in by
    sys-fs/zfs-kmod:0 required by @module-rebuild


For more information about Blocked Packages, please refer to the following
section of the Gentoo Linux x86 Handbook (architecture is irrelevant):

https://wiki.gentoo.org/wiki/Handbook:X86/Working/Portage#Blocked_packages