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

Calculating dependencies ... done!
Dependency resolution took 1.56 s (backtrack: 0/20).

[ebuild     UD ] dev-build/ninja-1.13.1::gentoo [1.13.2-r1::gentoo] USE="-doc -test" 286 KiB

Total: 1 package (1 downgrade), Size of downloads: 286 KiB