Iterate on plugin reconciler

- Renamed setProperty to setCanonicalProperty, which is more usefully
  descriptive. Also added a detailed comment.
- Fixed reconciler behavior with regards to removing known instances
  when $ignoreUnknownInstances is set

plugin/src/Reconciler.lua

@@ -1,6 +1,6 @@
 local InstanceMap = require(script.Parent.InstanceMap)
 local Logging = require(script.Parent.Logging)
-local setProperty = require(script.Parent.setProperty)
+local setCanonicalProperty = require(script.Parent.setCanonicalProperty)
 local rojoValueToRobloxValue = require(script.Parent.rojoValueToRobloxValue)
 
 local Reconciler = {}
@@ -43,10 +43,10 @@ function Reconciler:reconcile(virtualInstancesById, id, instance)
 	self.instanceMap:insert(id, instance)
 
 	-- Some instances don't like being named, even if their name already matches
-	setProperty(instance, "Name", virtualInstance.Name)
+	setCanonicalProperty(instance, "Name", virtualInstance.Name)
 
 	for key, value in pairs(virtualInstance.Properties) do
-		setProperty(instance, key, rojoValueToRobloxValue(value))
+		setCanonicalProperty(instance, key, rojoValueToRobloxValue(value))
 	end
 
 	local existingChildren = instance:GetChildren()
@@ -81,10 +81,17 @@ function Reconciler:reconcile(virtualInstancesById, id, instance)
 		end
 	end
 
-	if self:__shouldClearUnknownInstances(virtualInstance) then
-		for existingChildInstance in pairs(unvisitedExistingChildren) do
-			self.instanceMap:removeInstance(existingChildInstance)
-			existingChildInstance:Destroy()
+	local shouldClearUnknown = self:__shouldClearUnknownChildren(virtualInstance)
+
+	for existingChildInstance in pairs(unvisitedExistingChildren) do
+		local childId = self.instanceMap.fromInstances[existingChildInstance]
+
+		if childId == nil then
+			if shouldClearUnknown then
+				existingChildInstance:Destroy()
+			end
+		else
+			self.instanceMap:destroyInstance(existingChildInstance)
 		end
 	end
 
@@ -100,13 +107,13 @@ function Reconciler:reconcile(virtualInstancesById, id, instance)
 
 		-- Some instances, like services, don't like having their Parent
 		-- property poked, even if we're setting it to the same value.
-		setProperty(instance, "Parent", parent)
+		setCanonicalProperty(instance, "Parent", parent)
 	end
 
 	return instance
 end
 
-function Reconciler:__shouldClearUnknownInstances(virtualInstance)
+function Reconciler:__shouldClearUnknownChildren(virtualInstance)
 	if virtualInstance.Metadata ~= nil then
 		return not virtualInstance.Metadata.ignoreUnknownInstances
 	else
@@ -120,16 +127,16 @@ function Reconciler:__reify(virtualInstancesById, id, parent)
 	local instance = Instance.new(virtualInstance.ClassName)
 
 	for key, value in pairs(virtualInstance.Properties) do
-		setProperty(instance, key, rojoValueToRobloxValue(value))
+		setCanonicalProperty(instance, key, rojoValueToRobloxValue(value))
 	end
 
-	instance.Name = virtualInstance.Name
+	setCanonicalProperty(instance, "Name", virtualInstance.Name)
 
 	for _, childId in ipairs(virtualInstance.Children) do
 		self:__reify(virtualInstancesById, childId, instance)
 	end
 
-	setProperty(instance, "Parent", parent)
+	setCanonicalProperty(instance, "Parent", parent)
 	self.instanceMap:insert(id, instance)
 
 	return instance

plugin/src/Reconciler.spec.lua

@@ -0,0 +1,218 @@
+local Reconciler = require(script.Parent.Reconciler)
+
+return function()
+	it("should leave instances alone if there's nothing specified", function()
+		local instance = Instance.new("Folder")
+		instance.Name = "TestFolder"
+
+		local instanceId = "test-id"
+		local virtualInstancesById = {
+			[instanceId] = {
+				Name = "TestFolder",
+				ClassName = "Folder",
+				Children = {},
+				Properties = {},
+			},
+		}
+
+		local reconciler = Reconciler.new()
+		reconciler:reconcile(virtualInstancesById, instanceId, instance)
+	end)
+
+	it("should assign names from virtual instances", function()
+		local instance = Instance.new("Folder")
+		instance.Name = "InitialName"
+
+		local instanceId = "test-id"
+		local virtualInstancesById = {
+			[instanceId] = {
+				Name = "NewName",
+				ClassName = "Folder",
+				Children = {},
+				Properties = {},
+			},
+		}
+
+		local reconciler = Reconciler.new()
+		reconciler:reconcile(virtualInstancesById, instanceId, instance)
+
+		expect(instance.Name).to.equal("NewName")
+	end)
+
+	it("should assign properties from virtual instances", function()
+		local instance = Instance.new("IntValue")
+		instance.Name = "TestValue"
+		instance.Value = 5
+
+		local instanceId = "test-id"
+		local virtualInstancesById = {
+			[instanceId] = {
+				Name = "TestValue",
+				ClassName = "IntValue",
+				Children = {},
+				Properties = {
+					Value = {
+						Type = "Int32",
+						Value = 9
+					}
+				},
+			},
+		}
+
+		local reconciler = Reconciler.new()
+		reconciler:reconcile(virtualInstancesById, instanceId, instance)
+
+		expect(instance.Value).to.equal(9)
+	end)
+
+	it("should wipe unknown children by default", function()
+		local parent = Instance.new("Folder")
+		parent.Name = "Parent"
+
+		local child = Instance.new("Folder")
+		child.Name = "Child"
+
+		local parentId = "test-id"
+		local virtualInstancesById = {
+			[parentId] = {
+				Name = "Parent",
+				ClassName = "Folder",
+				Children = {},
+				Properties = {},
+			},
+		}
+
+		local reconciler = Reconciler.new()
+		reconciler:reconcile(virtualInstancesById, parentId, parent)
+
+		expect(#parent:GetChildren()).to.equal(0)
+	end)
+
+	it("should preserve unknown children if ignoreUnknownInstances is set", function()
+		local parent = Instance.new("Folder")
+		parent.Name = "Parent"
+
+		local child = Instance.new("Folder")
+		child.Parent = parent
+		child.Name = "Child"
+
+		local parentId = "test-id"
+		local virtualInstancesById = {
+			[parentId] = {
+				Name = "Parent",
+				ClassName = "Folder",
+				Children = {},
+				Properties = {},
+				Metadata = {
+					ignoreUnknownInstances = true,
+				},
+			},
+		}
+
+		local reconciler = Reconciler.new()
+		reconciler:reconcile(virtualInstancesById, parentId, parent)
+
+		expect(child.Parent).to.equal(parent)
+		expect(#parent:GetChildren()).to.equal(1)
+	end)
+
+	it("should remove known removed children", function()
+		local parent = Instance.new("Folder")
+		parent.Name = "Parent"
+
+		local child = Instance.new("Folder")
+		child.Parent = parent
+		child.Name = "Child"
+
+		local parentId = "parent-id"
+		local childId = "child-id"
+
+		local reconciler = Reconciler.new()
+
+		local virtualInstancesById = {
+			[parentId] = {
+				Name = "Parent",
+				ClassName = "Folder",
+				Children = {childId},
+				Properties = {},
+			},
+			[childId] = {
+				Name = "Child",
+				ClassName = "Folder",
+				Children = {},
+				Properties = {},
+			},
+		}
+		reconciler:reconcile(virtualInstancesById, parentId, parent)
+
+		expect(child.Parent).to.equal(parent)
+		expect(#parent:GetChildren()).to.equal(1)
+
+		local newVirtualInstances = {
+			[parentId] = {
+				Name = "Parent",
+				ClassName = "Folder",
+				Children = {},
+				Properties = {},
+			},
+			[childId] = nil,
+		}
+		reconciler:reconcile(newVirtualInstances, parentId, parent)
+
+		expect(child.Parent).to.equal(nil)
+		expect(#parent:GetChildren()).to.equal(0)
+	end)
+
+	it("should remove known removed children if ignoreUnknownInstances is set", function()
+		local parent = Instance.new("Folder")
+		parent.Name = "Parent"
+
+		local child = Instance.new("Folder")
+		child.Parent = parent
+		child.Name = "Child"
+
+		local parentId = "parent-id"
+		local childId = "child-id"
+
+		local reconciler = Reconciler.new()
+
+		local virtualInstancesById = {
+			[parentId] = {
+				Name = "Parent",
+				ClassName = "Folder",
+				Children = {childId},
+				Properties = {},
+				Metadata = {
+					ignoreUnknownInstances = true,
+				},
+			},
+			[childId] = {
+				Name = "Child",
+				ClassName = "Folder",
+				Children = {},
+				Properties = {},
+			},
+		}
+		reconciler:reconcile(virtualInstancesById, parentId, parent)
+
+		expect(child.Parent).to.equal(parent)
+		expect(#parent:GetChildren()).to.equal(1)
+
+		local newVirtualInstances = {
+			[parentId] = {
+				Name = "Parent",
+				ClassName = "Folder",
+				Children = {},
+				Properties = {},
+				Metadata = {
+					ignoreUnknownInstances = true,
+				},
+			},
+			[childId] = nil,
+		}
+		reconciler:reconcile(newVirtualInstances, parentId, parent)
+
+		expect(child.Parent).to.equal(nil)
+		expect(#parent:GetChildren()).to.equal(0)
+	end)
+end

plugin/src/setCanonicalProperty.lua

@@ -1,10 +1,17 @@
 local Logging = require(script.Parent.Logging)
 
 --[[
-	Attempts to set a property on the given instance, correctly handling
-	'virtual properties', which aren't reflected directly to Lua.
+	Attempts to set a property on the given instance.
+
+	This method deals in terms of what Rojo calls 'canonical properties', which
+	don't necessarily exist either in serialization or in Lua-reflected APIs,
+	but may be present in the API dump.
+
+	Ideally, canonical properties map 1:1 with properties we can assign, but in
+	some cases like LocalizationTable contents and CollectionService tags, we
+	have to read/write properties a little differently.
 ]]
-local function setProperty(instance, key, value)
+local function setCanonicalProperty(instance, key, value)
 	-- The 'Contents' property of LocalizationTable isn't directly exposed, but
 	-- has corresponding (deprecated) getters and setters.
 	if instance.ClassName == "LocalizationTable" and key == "Contents" then
@@ -42,4 +49,4 @@ local function setProperty(instance, key, value)
 	return true
 end
 
-return setProperty
+return setCanonicalProperty