Currently, serializing the config struct uses the default json encoder. It's supposed to be human-consumable, so use the PrettyEncoder instead.
Make sure that the normal json decoder ignores whitespace though.

Eventually(tm)

Store the screen id in the Workspace struct instead of in a Deck under WindowManager. Probably also wrap Screen in a struct that provides width+height, since I assume those two Xlib calls for every single Layout.apply is expensive.

XServer::get_event should handle most(if not all) of the event types.
It should also wrap the important/relevant members of the event into an enum it returns. Also, fix your naming - match on a ButtonPress, cast to XButtonPressedEvent, and return a ButtonPressed? That's terrible.

Currently, you can only reload the config. This is actually pretty sweet. Unfortunately, that's pretty much useless during dev since you still have to cold reload for code changes.

Make the entire WindowManager struct derive Encodable/Decodable, serialize it to a swapfile, execvp the new binary, load in the old WindowManager.

Alternatively, we could just scan the XOrg window heirarchy on boot to see what to add. It's a lot less work, but would put all windows in the same workspace and forget about lots of other important info.

(Basically just #1) Handle all the varients of the enum get_events() returns. Especially window mapping and stuff.

Current, Config::setup is confusing to read. It looks like the loop that creates the workspace jump hotkeys forgets to initialize the None value, while in reality it never touches a KeyBind, only Key. Making parse_keybind explicit would show that the workspace loop onlys touches Keys, and the Config fields are KeyBinds instead.

Yes, I'm aware these are terrible names.

KeyMod is a bitfield. I parse C-S-k into (CONTROL | SHIFT).bits() with a lookup and shifting 1<<k, which 1) would trigger undefined behavior if the lookup table is too long 2) would break with a different endianness.

Change the lookup table into [("C-",CONTROL),("S-",SHIFT)] and add in the tuple's bits() value instead.

Specific rules that are automagically applied depending on the window's name. Like how spectrwm does it, except serialized to a proper data structure.

I copied over the key.rs file I wrote from the wtftw fork, but need to add a callback queue. The queue should probably be a member of the WindowManager class - its constructor already is passed the ConfigLock

WindowManager currently spams the hell out of Rc. That's bad and expensive - use &-references and unsafe set_lifetime to avoid that.
Also, make WindowManager's windows member be Vec<(Window,Pos)> instead of just Window (or maybe wrap it in a struct with that info?), needed in order to also store information about the pos and size...and if it's in master or not, and hidden?