Validate attribute removals, handle reserved failures separately from…

… invalid ones (#440)

rbx_dom_lua/src/customProperties.lua

@@ -26,6 +26,21 @@ local TERRAIN_MATERIAL_COLORS = {
 	Enum.Material.Pavement,
 }
 
+local function isAttributeNameValid(attributeName)
+	-- For SetAttribute to succeed, the attribute name must be less than or
+	-- equal to 100 characters...
+	return #attributeName <= 100
+		-- ...and must only contain alphanumeric characters, periods, hyphens,
+		-- underscores, or forward slashes.
+		and attributeName:match("[^%w%.%-_/]") == nil
+end
+
+local function isAttributeNameReserved(attributeName)
+	-- For SetAttribute to succeed, attribute names must not use the RBX
+	-- prefix, which is reserved by Roblox.
+	return attributeName:sub(1, 3) ~= "RBX"
+end
+
 -- Defines how to read and write properties that aren't directly scriptable.
 --
 -- The reflection database refers to these as having scriptability = "Custom"
@@ -40,26 +55,33 @@ return {
 				local didAllWritesSucceed = true
 
 				for attributeName, attributeValue in pairs(value) do
-					local isNameValid =
-						-- For our SetAttribute to succeed, the attribute name must be
-						-- less than or equal to 100 characters...
-						#attributeName <= 100
-						-- ...must only contain alphanumeric characters, periods, hyphens,
-						-- underscores, or forward slashes...
-						and attributeName:match("[^%w%.%-_/]") == nil
-						-- ... and must not use the RBX prefix, which is reserved by Roblox.
-						and attributeName:sub(1, 3) ~= "RBX"
-
-					if isNameValid then
-						instance:SetAttribute(attributeName, attributeValue)
-					else
+					if isAttributeNameReserved(attributeName) then
+						-- If the attribute name is reserved, then we don't
+						-- really care about reporting any failures about
+						-- it.
+						continue
+					end
+
+					if not isAttributeNameValid(attributeName) then
 						didAllWritesSucceed = false
+						continue
 					end
+
+					instance:SetAttribute(attributeName, attributeValue)
 				end
 
-				for key in pairs(existing) do
-					if value[key] == nil then
-						instance:SetAttribute(key, nil)
+				for existingAttributeName in pairs(existing) do
+					if isAttributeNameReserved(existingAttributeName) then
+						continue
+					end
+
+					if not isAttributeNameValid(existingAttributeName) then
+						didAllWritesSucceed = false
+						continue
+					end
+
+					if value[existingAttributeName] == nil then
+						instance:SetAttribute(existingAttributeName, nil)
 					end
 				end