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

Calculating dependencies ... done!
Dependency resolution took 0.97 s (backtrack: 0/20).

[ebuild  N     ] dev-libs/mimalloc-3.4.5:0/3::gentoo  USE="-debug -test" 1391 KiB

Total: 1 package (1 new), Size of downloads: 1391 KiB