fix: check for nil diffs

packages/charm-sync/src/__tests__/server.spec.luau

@@ -210,6 +210,26 @@ test("should serialize state", function()
 	assert(patch.isNone(payloads[1].data.a["5"]), "Expected index 5 to be serialized as string key")
 end)
 
+test("should not send unchanged state", function()
+	local client = {}
+	local a = Charm.atom(0)
+	local payloads
+
+	server.addSignalsToClient(client, { a = a })
+	server.connect(function(_, p)
+		payloads = p
+	end)
+
+	server.flush()
+	assert(payloads[1].type == "init", "Expected first payload to be init")
+	assert(payloads[1].data.a == 0, "Expected init payload to contain atom 'a'")
+
+	payloads = {}
+	a(0)
+	server.flush()
+	assert(#payloads == 0, "Expected no payloads to be sent for unchanged state")
+end)
+
 describe("historical", function()
 	beforeEach(function()
 		config.preserveHistory = true
@@ -344,6 +364,26 @@ describe("historical", function()
 		assert(payloads[4].type == "patch", "Expected fourth payload to be patch")
 		assert(payloads[4].data.b == 2, "Expected patch payload to contain atom 'b'")
 	end)
+
+	test("should not send unchanged state", function()
+		local client = {}
+		local a = Charm.atom(0)
+		local payloads
+
+		server.addSignalsToClient(client, { a = a })
+		server.connect(function(_, p)
+			payloads = p
+		end)
+
+		server.flush()
+		assert(payloads[1].type == "init", "Expected first payload to be init")
+		assert(payloads[1].data.a == 0, "Expected init payload to contain atom 'a'")
+
+		payloads = {}
+		a(0)
+		server.flush()
+		assert(#payloads == 0, "Expected no payloads to be sent for unchanged state")
+	end)
 end)
 
 return {}

packages/charm-sync/src/server.luau

@@ -75,24 +75,24 @@ local function trackReactive<T>(key: string, proxy: ReactiveProxy<T>)
 		return
 	end
 
-	local meta = getmetatable(proxy)
-	local snapshot = utils.deepCopy(meta.value)
+	local api = getmetatable(proxy)
+	local snapshot = utils.deepCopy(api.value)
 	local firstRun = true
 
 	local trackedState = {
 		target = proxy,
-		currentValue = meta.value,
+		currentValue = api.value,
 		lastSyncedValue = snapshot,
 		isReactive = true,
 	}
 
 	trackedState.dispose = Charm.effect(function()
-		meta.track()
+		api.track()
 		if not config.preserveHistory or firstRun then
 			firstRun = false
 		else
 			local oldSnapshot = snapshot
-			snapshot = utils.deepCopy(meta.value)
+			snapshot = utils.deepCopy(api.value)
 			table.insert(globalUpdates, {
 				key = key,
 				newValue = snapshot,
@@ -132,8 +132,8 @@ local function diffGlobalUpdateBuffer(): { any }
 	local patchCount = #globalUpdates
 	local patches = table.create(patchCount)
 
-	for index, update in globalUpdates do
-		patches[index] = patch.diff(update.oldValue, update.newValue)
+	for _, update in globalUpdates do
+		table.insert(patches, patch.diff(update.oldValue, update.newValue))
 	end
 
 	return patches
@@ -176,7 +176,7 @@ local function selectFromGlobalPatchList(client: any, globalPatches: { any }): {
 
 	-- If a pending signal was never updated, we still need to send its initial
 	-- state. This can happen if a signal was registered after its last change.
-	local initData: { [string]: any } = {}
+	local initData = {}
 
 	for key, status in clientKeys do
 		local trackedState = trackedStates[key]
@@ -194,7 +194,7 @@ local function selectFromGlobalPatchList(client: any, globalPatches: { any }): {
 	return payloads
 end
 
-local function diffGlobalState(): any
+local function diffGlobalState(): { [string]: any }?
 	local currentGlobalState: { [string]: any } = {}
 	local previousGlobalState: { [string]: any } = {}
 
@@ -211,7 +211,7 @@ local function diffGlobalState(): any
 	return patch.diff(previousGlobalState, currentGlobalState)
 end
 
-local function selectFromGlobalPatch(client: any, globalPatch: any): { SyncPayload }?
+local function selectFromGlobalPatch(client: any, globalPatch: { [string]: any }?): { SyncPayload }?
 	local clientKeys = clients[client]
 
 	if not clientKeys then
@@ -227,7 +227,7 @@ local function selectFromGlobalPatch(client: any, globalPatch: any): { SyncPaylo
 	for key, status in clientKeys do
 		local trackedState = trackedStates[key]
 
-		if status == LISTENING_FOR_CHANGES then
+		if status == LISTENING_FOR_CHANGES and globalPatch then
 			patchData[key] = globalPatch[key]
 		elseif status == PENDING_INITIAL_STATE then
 			initData[key] = trackedState.currentValue
@@ -323,11 +323,11 @@ local function flush()
 	end
 
 	local granular = config.preserveHistory
-	local globalPatch = if granular then diffGlobalUpdateBuffer() else diffGlobalState()
+	local globalPatch: { [any]: any }? = if granular then diffGlobalUpdateBuffer() else diffGlobalState()
 
 	for client in clients do
 		local payloads = if granular
-			then selectFromGlobalPatchList(client, globalPatch)
+			then selectFromGlobalPatchList(client, globalPatch :: { any })
 			else selectFromGlobalPatch(client, globalPatch)
 
 		if payloads and payloads[1] then

packages/charm/src/init.luau

@@ -6,7 +6,7 @@ export type Link = system.Link
 
 export type Atom<T = any> = (...((T) -> T) | T) -> T
 
-type ReactiveProxyMeta<T = {}> = {
+type ReactiveProxyApi<T = {}> = {
 	value: T,
 	track: () -> (),
 	set: (T | (T) -> ()?) -> (),
@@ -17,7 +17,7 @@ type ReactiveProxyProps<T = {}> = {
 	__signals: { [unknown]: () -> unknown },
 }
 
-export type ReactiveProxy<T = {}> = T & typeof(setmetatable({} :: ReactiveProxyProps<T>, {} :: ReactiveProxyMeta<T>))
+export type ReactiveProxy<T = {}> = T & typeof(setmetatable({} :: ReactiveProxyProps<T>, {} :: ReactiveProxyApi<T>))
 
 type EffectScopeNode = ReactiveNode & {
 	cleanups: { () -> () },
@@ -855,7 +855,7 @@ end
 ]]
 local function reactive<T>(initialValue: T & {}): (T, (update: (T) -> () | T?) -> ())
 	local track = signal(nil)
-	local proxyMeta = { value = initialValue, track = track }
+	local proxyApi = { value = initialValue, track = track }
 	local proxyMap = setmetatable({} :: { [{}]: any }, { __mode = "v" })
 
 	local function trackProperty(cache: { [any]: () -> any }, target: {}, key: any)
@@ -876,11 +876,11 @@ local function reactive<T>(initialValue: T & {}): (T, (update: (T) -> () | T?) -
 		proxyMap[target] = setmetatable({
 			__target = target,
 			__signals = setmetatable({}, { __mode = "v" }),
-		}, proxyMeta)
+		}, proxyApi)
 		return proxyMap[target]
 	end
 
-	function proxyMeta.__index(self: ReactiveProxy, key: any): any
+	function proxyApi.__index(self: ReactiveProxy, key: any): any
 		if activeSub then
 			trackProperty(self.__signals, self.__target, key)
 		end
@@ -888,8 +888,8 @@ local function reactive<T>(initialValue: T & {}): (T, (update: (T) -> () | T?) -
 		return if type(value) == "table" then createProxy(value) else value
 	end
 
-	function proxyMeta.__newindex(self: ReactiveProxy, key: any, value: any)
-		if type(value) == "table" and getmetatable(value) == proxyMeta then
+	function proxyApi.__newindex(self: ReactiveProxy, key: any, value: any)
+		if type(value) == "table" and getmetatable(value) == proxyApi then
 			value = value.__target
 		end
 		if self.__target[key] ~= value then
@@ -898,7 +898,7 @@ local function reactive<T>(initialValue: T & {}): (T, (update: (T) -> () | T?) -
 		end
 	end
 
-	function proxyMeta.__iter(self: ReactiveProxy)
+	function proxyApi.__iter(self: ReactiveProxy)
 		track()
 		local function iterator(target: {}, index: any)
 			local key, value = next(target, index)
@@ -907,12 +907,12 @@ local function reactive<T>(initialValue: T & {}): (T, (update: (T) -> () | T?) -
 		return iterator, self.__target
 	end
 
-	function proxyMeta.__len(self: ReactiveProxy)
+	function proxyApi.__len(self: ReactiveProxy)
 		track()
 		return #self.__target
 	end
 
-	function proxyMeta.set(update: ((T) -> ()) | T?)
+	function proxyApi.set(update: ((T) -> ()) | T?)
 		if type(update) == "function" then
 			update(initialValue)
 		elseif type(update) == "table" then
@@ -924,7 +924,7 @@ local function reactive<T>(initialValue: T & {}): (T, (update: (T) -> () | T?) -
 		trigger(track)
 	end
 
-	return createProxy(initialValue), proxyMeta.set
+	return createProxy(initialValue), proxyApi.set
 end
 
 --[[
@@ -938,10 +938,10 @@ end
 local function toRaw<T>(value: T): T
 	if type(value) == "table" and getmetatable(value) ~= nil then
 		local proxy: ReactiveProxy = value
-		local meta = getmetatable(proxy)
-		if meta.value == proxy.__target then
+		local api = getmetatable(proxy)
+		if api.value == proxy.__target then
 			-- Track the root proxy since nested proxies are already tracked
-			meta.track()
+			api.track()
 		end
 		return proxy.__target :: any
 	else