Are there any Wayland compositor 'toolkits'? 
I'm thinking something that lets you design your own compositor by writing limited code and configuration.
Not locked into a specific paradigm and more capable than just "customize this off-the-shelf WM", but less work than rolling your own with a bunch of libraries.
(Customizable WMs *may* be suitable answers, if you can customize both their appearance and behaviour far enough that a user would not be able to identify the underlying WM from using a customized installation, as an imperfect yardstick.)
@natty From what I know of both, what I'm looking for would be sitting somewhere in the middle between those two
@joepie91 smithay might fit your purpose
@TyberiusPrime Unfortunately that is very much "rolling your own with a bunch of libraries"
@joepie91 sorry. Don't know of anything higher level. The docs suggest it will eventually get there: "The window management and drawing logic is however at this time not provided (but helpers for this are planned for future version)."
@joepie91 wlroots?
@ckie That's still definitely in the "rolling your own" camp. I'm more looking for something that's firmly outside of the "For Software Developers" category.
@joepie91@pixie.town The way river works might interest you? River has a compositor that's independent of what it calls a "layout generator" which is an external program which manages window positioning. River manages (and enforces) tags and outputs, but window positioning itself within an output is entirely delegated.
It seems there's a big rewrite on its way that includes renaming the role of layout generator to window manager, with all that implies (for example, among the functionality removed from the compositor in that pr is tags)
@z This looks a lot closer than most, thanks! From a quick look it's a bit too restricted for what I'm looking for (being tiling-only) but it's definitely quite close to the category I'm looking for.
@joepie91@pixie.town I think "tiling only" is a trap. The faq has a "my windows are not tiled!" that mentions this happens without a layout generator. Not sure myself if a current layout generator can just handle floating windows atm but this sounds like something that will be very possible with 0.4 (the rewrite).
@joepie91 I’m not sure if this would be the easiest thing to do in Wayland. I don’t think it’s necessarily designed for composability like this
But I would be happy to be proven wrong
@Byte Wayland is just the protocol that applications and the compositor speak to each other basically; it doesn't introduce any constraints on how the compositor can work (unlike X) so I don't see any reason why this wouldn't be possible on a theoretical level
@joepie91@pixie.town somewhere on the scale from Smithay to XMonad?