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

Calculating dependencies ... done!
Dependency resolution took 1.01 s (backtrack: 0/20).

[ebuild  N     ] acct-group/mosquitto-0-r3::gentoo  0 KiB
[ebuild  N     ] dev-libs/cJSON-1.7.19::gentoo  USE="-test" 348 KiB
[ebuild  N     ] acct-user/mosquitto-0-r3::gentoo  0 KiB
[ebuild  N     ] app-misc/mosquitto-2.0.22::gentoo  USE="bridge persistence srv ssl -examples (-systemd) -tcpd -test -websockets" 788 KiB

Total: 4 packages (4 new), Size of downloads: 1135 KiB