OKAY IT HALF WORKS

Co-Authored-By: Ne_Eo <NeeEoo@users.noreply.github.com>

source/funkin/backend/system/macros/CustomFieldMacro.hx

@@ -0,0 +1,52 @@
+package funkin.backend.system.macros;
+
+#if macro
+import haxe.macro.Context;
+import haxe.macro.Expr;
+import haxe.macro.Compiler;
+
+using StringTools;
+
+/**
+ * Macro used to add custom fields to classes without having to override the entire file.
+ */
+class CustomFieldMacro {
+	public static function init() {
+		Compiler.addGlobalMetadata("lime.utils", '@:build(funkin.backend.system.macros.UsingHandler.build("lime.utils.AssetLibrary", "tag", "funkin.backend.assets.AssetSource"))');
+	}
+
+	// TODO: Add support for default values
+	public static function build(lib:String, fieldName:String, type:String) {
+		var fields = Context.getBuildFields();
+		var clRef = Context.getLocalClass();
+		if (clRef == null) return fields;
+		var cl = clRef.get();
+
+		var key = cl.module;
+		var fkey = cl.module + "." + cl.name;
+
+		if(fkey != lib) {
+			return fields;
+		}
+
+		var fields = Context.getBuildFields();
+
+		fields.push({
+			name: fieldName,
+			access: [APublic],
+			kind: FVar(getTPath(type)),
+			pos: Context.currentPos()
+		});
+
+		return fields;
+	}
+
+	public static function getTPath(type:String) {
+		var arr = type.split(".");
+		return TPath({
+			pack: arr.slice(0, arr.length - 1),
+			name: arr[arr.length - 1]
+		});
+	}
+}
+#end

source/funkin/backend/system/macros/Macros.hx

@@ -45,6 +45,8 @@ class Macros {
 	public static function initMacros() {
 		if(Context.defined("hl"))
 			HashLinkFixer.init();
+
+		CustomFieldsMacro.init();
 	}
 }
 #end