Support nesting Parent (#48)

* allow nesting parent property

* update changelog

* fix mock instances Parent property not being a proxy

* add tests

Closes #47

CHANGELOG.md

@@ -28,6 +28,8 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/).
   destroyed.
 - Error reporting should be improved with better formatting when effects invoke
   other effects and no more loss of stack traces.
+- Nesting parent properties now work, and they are now also checked for
+  duplicates like other properties.
 
 ### Removed
 

src/apply.luau

@@ -23,6 +23,9 @@ type Cache = {
         Array<(Instance) -> ()> -- action callbacks
     >,
 
+    -- what to parent the instance to after running actions
+    parent: unknown,
+
     -- cache to detect duplicate property setting at same nesting depth
     nested_debug: Map<
         number, -- depth
@@ -47,6 +50,7 @@ local function borrow_cache(): Cache
             actions = setmetatable({} :: any, { -- lazy init
                 __index = function(self, i) self[i] = {}; return self[i] end
             }),
+            parent = nil,
             nested_debug = setmetatable({} :: any, {
                 __index = function(self, i: number) self[i] = {}; return self[i] end
             }),
@@ -61,8 +65,6 @@ end
 
 local function process_properties(properties: Map<unknown, unknown>, instance: Instance, cache: Cache, depth: number)
     for property, value in properties do
-        if property == "Parent" then continue end
-
         if type(property) == "string" then
             if flags.strict then -- check for duplicate property assignment at nesting depth
                 if cache.nested_debug[depth][property] then
@@ -71,6 +73,11 @@ local function process_properties(properties: Map<unknown, unknown>, instance: I
                 cache.nested_debug[depth][property] = true
             end
 
+            if property == "Parent" then
+                cache.parent = value
+                continue
+            end
+
             if type(value) == "function" then 
                 if typeof((instance :: any)[property]) == "RBXScriptSignal" then
                     table.insert(cache.events, property) -- add event name to buffer
@@ -106,9 +113,6 @@ local function apply<T>(instance: T & Instance, properties: { [unknown]: unknown
         error "attempt to call a constructor returned by create() with no properties"
     end
 
-    -- queue parent assignment if any for last
-    local parent: unknown = properties.Parent 
-
     local caches = borrow_cache()
     local events = caches.events
     local actions = caches.actions
@@ -135,6 +139,7 @@ local function apply<T>(instance: T & Instance, properties: { [unknown]: unknown
         end
     end
 
+    local parent = caches.parent
     if parent then
         if type(parent) == "function" then
             implicit_effect.parent(instance, parent :: () -> Instance)
@@ -145,6 +150,7 @@ local function apply<T>(instance: T & Instance, properties: { [unknown]: unknown
 
     table.clear(events)
     for _, queued in next, actions do table.clear(queued) end
+    caches.parent = nil
     if flags.strict then table.clear(nested_debug) end
     table.clear(nested_stack)
 

test/mock.luau

@@ -86,6 +86,9 @@ local Instance = {} :: any do
     local proxies = {} :: { [Data]: userdata? }
     setmetatable(proxies :: any, { __mode = "v" })
 
+    -- allocate variables for the metamethods as __index and get_proxy cross refrences each other
+    local __index, __newindex
+
     local function get_data(userdata: userdata): Data
         local function f(userdata: userdata): ProxyMT
             return getmetatable(userdata :: any)
@@ -94,6 +97,19 @@ local Instance = {} :: any do
         return f(userdata).data
     end
 
+    local function get_proxy(data: Data): userdata
+        return proxies[data] or (function()
+            local userdata = newproxy(true)
+            local proxy = getmetatable(userdata)
+            proxy.proxy = userdata
+            proxy.data = data
+            proxy.__index = __index
+            proxy.__newindex = __newindex
+            proxies[data] = userdata   
+            return userdata
+        end)()
+    end
+
     local function is_instance(value: unknown): boolean
         local mt = getmetatable(value :: any)
         return mt and mt.data and mt.data.type == "Instance"
@@ -101,16 +117,16 @@ local Instance = {} :: any do
 
     local methods = {}
 
-    local function __index(userdata: userdata, property: string): ()
+    __index = function(userdata: userdata, property: string): ()
         local data = get_data(userdata)
         return if methods[property] then methods[property]
             elseif property == "Name" then data.name
-            elseif property == "Parent" then data.parent
+            elseif property == "Parent" then (data.parent and get_proxy(data.parent))
             elseif property == "Destroying" then data.destroying
             else data.properties[property] 
     end
 
-    local function __newindex(userdata: userdata, property: string, value: unknown)
+    __newindex = function(userdata: userdata, property: string, value: unknown)
         local data = get_data(userdata)
         if property == "Name" then
             if type(value) ~= "string" then error("name must be a string", 2) end
@@ -135,19 +151,6 @@ local Instance = {} :: any do
         end
     end
 
-    local function get_proxy(data: Data): userdata
-        return proxies[data] or (function()
-            local userdata = newproxy(true)
-            local proxy = getmetatable(userdata)
-            proxy.proxy = userdata
-            proxy.data = data
-            proxy.__index = __index
-            proxy.__newindex = __newindex
-            proxies[data] = userdata   
-            return userdata
-        end)()
-    end
-
     function Instance.new(class: string): Instance
         local data = {
             name = "UNNAMED",

test/tests.luau

@@ -759,6 +759,13 @@ TEST("create()", wrap_root(function()
         CHECK(text.Text == "test")
     end
 
+    do CASE "set nested parent"
+        local frame = create "Frame" {}
+        local text = create "TextLavel" { { Parent = frame } }
+        CHECK(frame:GetChildren()[1] == text)
+        CHECK(text.Parent == frame)
+    end
+
     do CASE "nested deferred"
         local text = create "TextLabel" {
             {