For more details see comments on D10724

Thanks for review.

Can't we reuse this same code from kcoreaddons? Maybe kcoreaddons can offer a macro that does this?

As hinted in the commit message, plan is to have some ECM macro instead, but only for 5.45 in a month, to not hurry macro signature design. Soon up for discussion though.

Current draft/working prototype results in code like the following for CMakeLists.txt (replacing the complete current code to set up things with CMAKE_AUTOMOC_MACRO_NAMES & :CMAKE_AUTOMOC_DEPEND_FILTERS):

include(ECMSetupQtPluginMacros)

ecm_setup_qtplugin_macros(
    JSON_NONE
        "K_EXPORT_PLASMA_SERVICE"
        "K_EXPORT_PLASMA_APPLET"
        "K_EXPORT_PLASMA_PACKAGE"
        "K_EXPORT_PLASMA_APPLETSCRIPTENGINE"
        "K_EXPORT_PLASMA_DATAENGINESCRIPTENGINE"
        "K_EXPORT_PLASMA_DATAENGINE"
    JSON_ARG2
        "K_EXPORT_PLASMA_PACKAGE_WITH_JSON"
    JSON_ARG3
        "K_EXPORT_PLASMA_SERVICE_WITH_JSON"
        "K_EXPORT_PLASMA_APPLET_WITH_JSON"
        "K_EXPORT_PLASMA_APPLETSCRIPTENGINE_WITH_JSON"
        "K_EXPORT_PLASMA_DATAENGINESCRIPTENGINE_WITH_JSON"
        "K_EXPORT_PLASMA_CONTAINMENTACTIONS_WITH_JSON"
        "K_EXPORT_PLASMA_DATAENGINE_WITH_JSON"
    CONFIG_VARIABLE
         PACKAGE_SETUP_AUTOMOC_MACROS
)

and in the KF5PlasmaConfig.cmake.in then just need some

@PACKAGE_SETUP_AUTOMOC_MACROS@

The complete code copies as now in the patch are just a temporary solution by purpose, to already fix the issue, but without rushed new public API.

Given there was no principal objection and this code is following the pattern of D10724, going to push now as well, so it gets some more field-testing before next weeks tagging.