These are the packages that would be merged, in order:

Calculating dependencies ... done!
Dependency resolution took 1.55 s (backtrack: 0/20).

[ebuild     U  ] dev-util/spirv-headers-1.4.363.0::gentoo [1.4.341.0::gentoo] 581 KiB
[ebuild     U  ] dev-util/spirv-tools-1.4.363.0::gentoo [1.4.341.0::gentoo] USE="-test" 3474 KiB
[ebuild  N     ] dev-util/glslang-1.4.363.0:0/16.6::gentoo  4528 KiB

Total: 3 packages (2 upgrades, 1 new), Size of downloads: 8582 KiB