Global shortcuts can trigger Plasma Api via dbus. Like it's done for taking a screenshot with Spectactle. Unfortunately this doesn't work for any dbus related Shortcuts. Mapping Plasma internal commands (e.g. switch between applications) works though.

Install spectacle and press the <PrintSc> button.
"x86_64-linux"Linux 4.14.29, NixOS, 18.09pre133621.56fb68dcef4 (Jellyfish)yesnonix-env (Nix) 2.0"nixos""nixpkgs-18.09pre133875.182dd989461"/nix/var/nix/profiles/per-user/root/channels/nixos/nixpkgsAny workaround here? Having to open the application every time to take screenshots at the moment.
On pressing print
dbus-monitor
signal time=1563646220.996644 sender=:1.8 -> destination=(null destination) serial=2684 path=/component/khotkeys; interface=org.kde.kglobalaccel.Component; member=globalShortcutPressed
string "khotkeys"
string "{0e9b02f6-499a-4339-aa10-474aeb4f10dc}"
int64 14753311
xsession:
D-Bus call: "org.kde.Spectacle" : "/" : "StartAgent" : ()
system details:
spectacle 19.04.1
nixos-unstable
Linux 4.19.58 #1-NixOS SMP Wed Jul 10 07:53:48 UTC 2019 x86_64 GNU/Linux
Try installing the nixos package with attribute name qt5.full. Prior to installing that package I had the same issue. Afterwards, it worked.
Try installing the nixos package with attribute name qt5.full. Prior to installing that package I had the same issue. Afterwards, it worked.
Will try and write an update here
PS: @johnalotoski's solution worked. What's the solution here? To add the missing qt5 inputs to the spectacle package?
Works for me with adding qt5.qttools to system packages.
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Most helpful comment
Try installing the nixos package with attribute name qt5.full. Prior to installing that package I had the same issue. Afterwards, it worked.