Handle cyclic tables in debugger formatTable (#146)

CHANGELOG.md

@@ -20,6 +20,10 @@ The format is based on [Keep a Changelog][kac], and this project adheres to
 - `World:get()` now has fast paths for up to four components.
   - Getting one component is now more than 2x faster and this scales with more components.
 
+### Fixed
+
+- The debugger now gracefully handles cyclic tables.
+
 ## [0.9.0-beta.0] - 2024-11-15
 
 ### Added

lib/debugger/formatTable.luau

@@ -1,6 +1,7 @@
 local stringColor = "#dcdcaa"
 local numberColor = "#b0c4de"
 local keywordColor = "#c586c0"
+local dimmedColor = "#808080"
 
 function colorize(value, color)
 	if type(value) == "number" then
@@ -38,10 +39,17 @@ local FormatMode = {
 	Short = "Short",
 	Long = "Long",
 }
-local function formatTable(object, mode, _padLength, _depth)
+
+local function formatTable(object, mode, _padLength, _depth, _seen)
 	mode = mode or FormatMode.Short
 	_padLength = _padLength or 0
 	_depth = _depth or 1
+	_seen = _seen or {}
+
+	if _seen[object] then
+		return colorize("<cyclic>", dimmedColor)
+	end
+	_seen[object] = true
 
 	local max = if mode == FormatMode.Short then 7 else 1000
 
@@ -87,7 +95,7 @@ local function formatTable(object, mode, _padLength, _depth)
 				part ..= "[{..}]="
 			else
 				part ..= "["
-				part ..= formatTable(key, FormatMode.Short, #str + #part + _padLength, _depth + 1)
+				part ..= formatTable(key, FormatMode.Short, #str + #part + _padLength, _depth + 1, _seen)
 				part ..= "] = "
 			end
 		end
@@ -107,7 +115,7 @@ local function formatTable(object, mode, _padLength, _depth)
 			if mode == FormatMode.Short then
 				part ..= "{..}"
 			else
-				part ..= formatTable(value, FormatMode.Long, #str + #part + _padLength, _depth + 1)
+				part ..= formatTable(value, FormatMode.Long, #str + #part + _padLength, _depth + 1, _seen)
 			end
 		elseif mode == FormatMode.Long and (luaType == "userdata" or luaType == "vector") then
 			if robloxType == "CFrame" then
@@ -153,6 +161,8 @@ local function formatTable(object, mode, _padLength, _depth)
 		str ..= "}"
 	end
 
+	_seen[object] = nil
+
 	return str
 end