There has been an evolution in how one defines pallets in the Substrate framework over time, and this has left the ecosystem in a state where useful pallets exist in different versions.
This begs the question
is it safe to mix pallets built using distinct FRAME macros in the same runtime?
In other words, if it all builds, can one assume there is no extra risk or problems coming from the mixing itself?
It should be okay to mix pallets from the old and new macros. We had this for a while when we were migrating pallets to the new macros.
End of the day, the underlying generated Rust code is the same, just the syntax for defining a pallet is different.
I think pretty much everyone's using the new macro system (rather than the older decl macros that used to exist). I would see if there's an alternative pallet if you're still seeing the old decl ones as maybe it's not been updated because the ecosystem has moved on to something better. If you've got specific examples maybe we can highlight modern day equivalents.
In the nodes we were running we were able to mix the two versions safely while we were working on getting all of our pallets upgraded.
