Add ChangeBatcher to plugin for two-way sync (#478)

* Implement ChangeBatcher

* Use ChangeBatcher for two-way sync

* Pause updates during patch application

* I can English good

* Break after encountering a nil Parent change

This prevents __flush from erroring out when an instance's Parent is
changed to nil and it has other property changes in the same batch.

* Update rbx_dom_lua

* Don't connect changed listeners in a running game

 #468 made me realize how bad of an idea this is in general...

* Update TestEZ and fix sibling Ref reification test

* Add ChangeBatcher tests

* Test instance unpausing by breaking functionality out to __cycle

* Break up the module a bit and improve tests

* Shuffle requires around and edit comment

* Break out more stuff, rename createChangePatch -> createPatchSet

* Make ChangeBatcher responsible for unpausing all paused instances

This somewhat improves the situation (of course, it would preferrable
to not have to hack around this problem with Source at all). It also
sets us up nicely if we come across any other properties that do
anything similar.

* Remove old reference to pausedBatchInstances

* Use RenderStepped instead of Heartbeat and trash multi-frame pauses

I probably should have done this in the first place...

ChangeBatcher still needs to unpause instances, but we don't need to
hold pauses for any longer than one cycle.

* Remove useless branch

* if not next(x) -> if next(x) == nil

* Add InstanceMap:unpauseAllInstances, use it in ChangeBatcher

* Move IsRunning check to InstanceMap:__maybeFireInstanceChanged

plugin/src/ChangeBatcher/createPatchSet.lua

@@ -0,0 +1,40 @@
+--[[
+	Take an InstanceMap and a dictionary mapping instances to sets of property
+	names. Populate a patch with the encoded values of all the given properties
+	on all the given instances (or, if any changes set Parent to nil, removals
+	of instances) and return the patch.
+]]
+
+local Log = require(script.Parent.Parent.Parent.Log)
+
+local PatchSet = require(script.Parent.Parent.PatchSet)
+
+local encodePatchUpdate = require(script.Parent.encodePatchUpdate)
+
+return function(instanceMap, propertyChanges)
+	local patch = PatchSet.newEmpty()
+
+	for instance, properties in pairs(propertyChanges) do
+		local instanceId = instanceMap.fromInstances[instance]
+
+		if instanceId == nil then
+			Log.warn("Ignoring change for instance {:?} as it is unknown to Rojo", instance)
+			continue
+		end
+
+		if properties.Parent then
+			if instance.Parent == nil then
+				table.insert(patch.removed, instanceId)
+			else
+				Log.warn("Cannot sync non-nil Parent property changes yet")
+			end
+		else
+			local update = encodePatchUpdate(instance, instanceId, properties)
+			table.insert(patch.updated, update)
+		end
+
+		propertyChanges[instance] = nil
+	end
+
+	return patch
+end

plugin/src/ChangeBatcher/createPatchSet.spec.lua

@@ -0,0 +1,74 @@
+return function()
+	local PatchSet = require(script.Parent.Parent.PatchSet)
+	local InstanceMap = require(script.Parent.Parent.InstanceMap)
+
+	local createPatchSet = require(script.Parent.createPatchSet)
+
+	it("should return a patch", function()
+		local patch = createPatchSet(InstanceMap.new(), {})
+
+		assert(PatchSet.validate(patch))
+	end)
+
+	it("should contain updates for every instance with property changes", function()
+		local instanceMap = InstanceMap.new()
+
+		local part1 = Instance.new("Part")
+		instanceMap:insert("PART_1", part1)
+
+		local part2 = Instance.new("Part")
+		instanceMap:insert("PART_2", part2)
+
+		local changes = {
+			[part1] = {
+				Position = true,
+				Size = true,
+				Color = true,
+			},
+			[part2] = {
+				CFrame = true,
+				Velocity = true,
+				Transparency = true,
+			},
+		}
+
+		local patch = createPatchSet(instanceMap, changes)
+
+		expect(#patch.updated).to.equal(2)
+	end)
+
+	it("should not contain any updates for removed instances", function()
+		local instanceMap = InstanceMap.new()
+
+		local part1 = Instance.new("Part")
+		instanceMap:insert("PART_1", part1)
+
+		local changes = {
+			[part1] = {
+				Parent = true,
+				Position = true,
+				Size = true,
+			},
+		}
+
+		local patch = createPatchSet(instanceMap, changes)
+
+		expect(#patch.removed).to.equal(1)
+		expect(#patch.updated).to.equal(0)
+	end)
+
+	it("should remove instances from the property change table", function()
+		local instanceMap = InstanceMap.new()
+
+		local part1 = Instance.new("Part")
+		instanceMap:insert("PART_1", part1)
+
+		local changes = {
+			[part1] = {},
+		}
+
+		createPatchSet(instanceMap, changes)
+
+		expect(next(changes)).to.equal(nil)
+	end)
+end

plugin/src/ChangeBatcher/encodePatchUpdate.lua

@@ -0,0 +1,39 @@
+local Log = require(script.Parent.Parent.Parent.Log)
+local RbxDom = require(script.Parent.Parent.Parent.RbxDom)
+
+local encodeProperty = require(script.Parent.encodeProperty)
+
+return function(instance, instanceId, properties)
+	local update = {
+		id = instanceId,
+		changedProperties = {},
+	}
+
+	for propertyName in pairs(properties) do
+		if propertyName == "Name" then
+			update.changedName = instance.Name
+		else
+			local descriptor = RbxDom.findCanonicalPropertyDescriptor(instance.ClassName, propertyName)
+
+			if not descriptor then
+				Log.debug("Could not sync back property {:?}.{}", instance, propertyName)
+				continue
+			end
+
+			local encodeSuccess, encodeResult = encodeProperty(instance, propertyName, descriptor)
+
+			if not encodeSuccess then
+				Log.debug("Could not sync back property {:?}.{}: {}", instance, propertyName, encodeResult)
+				continue
+			end
+
+			update.changedProperties[propertyName] = encodeResult
+		end
+	end
+
+	if next(update.changedProperties) == nil and update.changedName == nil then
+		return nil
+	end
+
+	return update
+end

plugin/src/ChangeBatcher/encodePatchUpdate.spec.lua

@@ -0,0 +1,62 @@
+return function()
+	local encodePatchUpdate = require(script.Parent.encodePatchUpdate)
+
+	it("should return an update when there are property changes", function()
+		local part = Instance.new("Part")
+		local properties = {
+			CFrame = true,
+			Color = true,
+		}
+		local update = encodePatchUpdate(part, "PART", properties)
+
+		expect(update.id).to.equal("PART")
+		expect(update.changedProperties.CFrame).to.be.ok()
+		expect(update.changedProperties.Color).to.be.ok()
+	end)
+
+	it("should return nil when there are no property changes", function()
+		local part = Instance.new("Part")
+		local properties = {
+			NonExistentProperty = true,
+		}
+		local update = encodePatchUpdate(part, "PART", properties)
+
+		expect(update).to.equal(nil)
+	end)
+
+	it("should set changedName in the update when the instance's Name changes", function()
+		local part = Instance.new("Part")
+		local properties = {
+			Name = true,
+		}
+
+		part.Name = "We'reGettingToTheCoolPart"
+
+		local update = encodePatchUpdate(part, "PART", properties)
+
+		expect(update.changedName).to.equal("We'reGettingToTheCoolPart")
+	end)
+
+	it("should correctly encode property values", function()
+		local part = Instance.new("Part")
+		local properties = {
+			Position = true,
+			Color = true,
+		}
+
+		part.Position = Vector3.new(0, 100, 0)
+		part.Color = Color3.new(0.8, 0.2, 0.9)
+
+		local update = encodePatchUpdate(part, "PART", properties)
+		local position = update.changedProperties.Position
+		local color = update.changedProperties.Color
+
+		expect(position.Vector3[1]).to.equal(0)
+		expect(position.Vector3[2]).to.equal(100)
+		expect(position.Vector3[3]).to.equal(0)
+
+		expect(color.Color3[1]).to.be.near(0.8, 0.01)
+		expect(color.Color3[2]).to.be.near(0.2, 0.01)
+		expect(color.Color3[3]).to.be.near(0.9, 0.01)
+	end)
+end

plugin/src/ChangeBatcher/encodeProperty.lua

@@ -0,0 +1,21 @@
+local Log = require(script.Parent.Parent.Parent.Log)
+local RbxDom = require(script.Parent.Parent.Parent.RbxDom)
+
+return function(instance, propertyName, propertyDescriptor)
+	local readSuccess, readResult = propertyDescriptor:read(instance)
+
+	if not readSuccess then
+		Log.warn("Could not sync back property {:?}.{}: {}", instance, propertyName, readResult)
+		return false, nil
+	end
+
+	local dataType = propertyDescriptor.dataType
+	local encodeSuccess, encodeResult = RbxDom.EncodedValue.encode(readResult, dataType)
+
+	if not encodeSuccess then
+		Log.warn("Could not sync back property {:?}.{}: {}", instance, propertyName, encodeResult)
+		return false, nil
+	end
+
+	return true, encodeResult
+end

plugin/src/ChangeBatcher/init.lua

@@ -0,0 +1,81 @@
+--[[
+	The ChangeBatcher is responsible for collecting and dispatching changes made
+	to tracked instances during two-way sync.
+]]
+
+local RunService = game:GetService("RunService")
+
+local PatchSet = require(script.Parent.PatchSet)
+
+local createPatchSet = require(script.createPatchSet)
+
+local ChangeBatcher = {}
+ChangeBatcher.__index = ChangeBatcher
+
+local BATCH_INTERVAL = 0.2
+
+function ChangeBatcher.new(instanceMap, onChangesFlushed)
+	local self
+
+	local renderSteppedConnection = RunService.RenderStepped:Connect(function(dt)
+		self:__cycle(dt)
+	end)
+
+	self = setmetatable({
+		__accumulator = 0,
+		__renderSteppedConnection = renderSteppedConnection,
+		__instanceMap = instanceMap,
+		__onChangesFlushed = onChangesFlushed,
+		__pendingPropertyChanges = {},
+	}, ChangeBatcher)
+
+	return self
+end
+
+function ChangeBatcher:stop()
+	self.__renderSteppedConnection:Disconnect()
+	self.__pendingPropertyChanges = {}
+end
+
+function ChangeBatcher:add(instance, propertyName)
+	local properties = self.__pendingPropertyChanges[instance]
+
+	if not properties then
+		properties = {}
+		self.__pendingPropertyChanges[instance] = properties
+	end
+
+	properties[propertyName] = true
+end
+
+function ChangeBatcher:__cycle(dt)
+	self.__accumulator += dt
+
+	if self.__accumulator >= BATCH_INTERVAL then
+		self.__accumulator -= BATCH_INTERVAL
+
+		local patch = self:__flush()
+
+		if patch then
+			self.__onChangesFlushed(patch)
+		end
+	end
+
+	self.__instanceMap:unpauseAllInstances()
+end
+
+function ChangeBatcher:__flush()
+	if next(self.__pendingPropertyChanges) == nil then
+		return nil
+	end
+
+	local patch = createPatchSet(self.__instanceMap, self.__pendingPropertyChanges)
+
+	if PatchSet.isEmpty(patch) then
+		return nil
+	end
+
+	return patch
+end
+
+return ChangeBatcher

plugin/src/ChangeBatcher/init.spec.lua

@@ -0,0 +1,101 @@
+return function()
+	local ChangeBatcher = require(script.Parent)
+	local InstanceMap = require(script.Parent.Parent.InstanceMap)
+	local PatchSet = require(script.Parent.Parent.PatchSet)
+
+	local noop = function() end
+
+	describe("new", function()
+		it("should create a new ChangeBatcher", function()
+			local instanceMap = InstanceMap.new()
+			local changeBatcher = ChangeBatcher.new(instanceMap, noop)
+
+			expect(changeBatcher.__pendingPropertyChanges).to.be.a("table")
+			expect(next(changeBatcher.__pendingPropertyChanges)).to.equal(nil)
+			expect(changeBatcher.__onChangesFlushed).to.equal(noop)
+			expect(changeBatcher.__instanceMap).to.equal(instanceMap)
+			expect(typeof(changeBatcher.__renderSteppedConnection)).to.equal("RBXScriptConnection")
+		end)
+	end)
+
+	describe("stop", function()
+		it("should disconnect the RenderStepped connection", function()
+			local changeBatcher = ChangeBatcher.new(InstanceMap.new(), noop)
+
+			changeBatcher:stop()
+
+			expect(changeBatcher.__renderSteppedConnection.Connected).to.equal(false)
+		end)
+	end)
+
+	describe("add", function()
+		it("should add property changes to be considered for the current batch", function()
+			local instanceMap = InstanceMap.new()
+			local changeBatcher = ChangeBatcher.new(instanceMap, noop)
+			local part = Instance.new("Part")
+
+			instanceMap:insert("PART", part)
+			changeBatcher:add(part, "Name")
+
+			local properties = changeBatcher.__pendingPropertyChanges[part]
+
+			expect(properties).to.be.a("table")
+			expect(properties.Name).to.be.ok()
+
+			changeBatcher:add(part, "Position")
+			expect(properties.Position).to.be.ok()
+		end)
+	end)
+
+	describe("__cycle", function()
+		it("should immediately unpause any paused instances after each cycle", function()
+			local instanceMap = InstanceMap.new()
+			local changeBatcher = ChangeBatcher.new(instanceMap, noop)
+			local part = Instance.new("Part")
+
+			instanceMap.pausedUpdateInstances[part] = true
+
+			changeBatcher:__cycle(0)
+
+			expect(instanceMap.pausedUpdateInstances[part]).to.equal(nil)
+		end)
+	end)
+
+	describe("__flush", function()
+		it("should return nil when there are no changes to process", function()
+			local changeBatcher = ChangeBatcher.new(InstanceMap.new(), noop)
+			expect(changeBatcher:__flush()).to.equal(nil)
+		end)
+
+		it("should return a patch when there are changes to process and the resulting patch is non-empty", function()
+			local instanceMap = InstanceMap.new()
+			local changeBatcher = ChangeBatcher.new(instanceMap, noop)
+			local part = Instance.new("Part")
+
+			instanceMap:insert("PART", part)
+
+			changeBatcher.__pendingPropertyChanges[part] = {
+				Position = true,
+				Name = true,
+			}
+
+			local patch = changeBatcher:__flush()
+
+			assert(PatchSet.validate(patch))
+		end)
+
+		it("should return nil when there are changes to process and the resulting patch is empty", function()
+			local instanceMap = InstanceMap.new()
+			local changeBatcher = ChangeBatcher.new(instanceMap, noop)
+			local part = Instance.new("Part")
+
+			instanceMap:insert("PART", part)
+
+			changeBatcher.__pendingPropertyChanges[part] = {
+				NonExistentProperty = true,
+			}
+
+			expect(changeBatcher:__flush()).to.equal(nil)
+		end)
+	end)
+end