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

Calculating dependencies ... done!
Dependency resolution took 0.90 s (backtrack: 0/20).


The following USE changes are necessary to proceed:
 (see "package.use" in the portage(5) man page for more details)
# required by app-crypt/seahorse-47.0.1-r2::gentoo
# required by =app-crypt/seahorse-47.0.1-r2 (argument)
>=app-crypt/gcr-3.41.2-r2:0 vala

!!! The ebuild selected to satisfy "app-crypt/gcr:0[vala]" has unmet requirements.
- app-crypt/gcr-3.41.2-r2::gentoo USE="X -gtk -gtk-doc -introspection (-systemd) -test -vala -wayland"

  The following REQUIRED_USE flag constraints are unsatisfied:
    vala? ( introspection )

  The above constraints are a subset of the following complete expression:
    gtk-doc? ( introspection ) vala? ( introspection )

(dependency required by "app-crypt/seahorse-47.0.1-r2::gentoo" [ebuild])
(dependency required by "=app-crypt/seahorse-47.0.1-r2" [argument])