Two way sync V0 (#282)

* Unfinished two-way sync API

* In-memory two-way sync complete

* Move PatchSet application into ChangeProcessor thread, where it can be synchronous

* Stop InstanceMap's signals when a ServeSession terminates

* Apply patch in ChangeProcessor

* Feature flag

* Fix error in ChangeProcessor due to wrong drop order

plugin/src/ApiContext.lua

@@ -156,11 +156,22 @@ function ApiContext:read(ids)
 end
 
 function ApiContext:write(patch)
-	local url = ("%s/write"):format(self.__baseUrl)
-	local body = Http.jsonEncode({
+	local url = ("%s/api/write"):format(self.__baseUrl)
+
+	local body = {
 		sessionId = self.__sessionId,
-		patch = patch,
-	})
+		removed = patch.removed,
+		updated = patch.updated,
+	}
+
+	-- Only add the 'added' field if the table is non-empty, or else Roblox's
+	-- JSON implementation will turn the table into an array instead of an
+	-- object, causing API validation to fail.
+	if next(patch.added) ~= nil then
+		body.added = patch.added
+	end
+
+	body = Http.jsonEncode(body)
 
 	return Http.post(url, body)
 		:andThen(rejectFailedRequests)

plugin/src/DevSettings.lua

@@ -25,7 +25,7 @@ local VALUES = {
 			[Environment.Test] = true,
 		},
 	},
-	ExperimentalTwoWaySync = {
+	UnstableTwoWaySync = {
 		type = "BoolValue",
 		values = {
 			[Environment.User] = false,
@@ -141,7 +141,7 @@ function DevSettings:shouldTypecheck()
 end
 
 function DevSettings:twoWaySyncEnabled()
-	return getValue("ExperimentalTwoWaySync")
+	return getValue("UnstableTwoWaySync")
 end
 
 function _G.ROJO_DEV_CREATE()

plugin/src/InstanceMap.lua

@@ -20,6 +20,16 @@ function InstanceMap.new(onInstanceChanged)
 	return setmetatable(self, InstanceMap)
 end
 
+--[[
+	Disconnect all connections and release all instance references.
+]]
+function InstanceMap:stop()
+	-- I think this is safe.
+	for instance in pairs(self.fromInstances) do
+		self:removeInstance(instance)
+	end
+end
+
 function InstanceMap:__fmtDebug(output)
 	output:writeLine("InstanceMap {{")
 	output:indent()
@@ -145,7 +155,9 @@ function InstanceMap:__disconnectSignals(instance)
 	local signals = self.instancesToSignal[instance]
 
 	if signals ~= nil then
-		-- In the general case, we avoid
+		-- In most cases, we only have a single signal, so we avoid keeping
+		-- around the extra table. ValueBase objects force us to use multiple
+		-- signals to emulate the Instance.Changed event, however.
 		if typeof(signals) == "table" then
 			for _, signal in ipairs(signals) do
 				signal:Disconnect()

plugin/src/ServeSession.lua

@@ -189,6 +189,7 @@ end
 function ServeSession:__stopInternal(err)
 	self:__setStatus(Status.Disconnected, err)
 	self.__apiContext:disconnect()
+	self.__instanceMap:stop()
 end
 
 function ServeSession:__setStatus(status, detail)