hydrate objects constructed from GtkBuilder

This runs JS constructors on objects that were not constructed from JavaScript. This is effectively objects constructed from GtkBuilder.

This is done by tracking all objects currently being constructed in a variable named `ConstructContext`. If an object's `TypeInfo`'s `instance_init` method (see https://docs.gtk.org/gobject/struct.TypeInfo.html) while it's gType is not the currently being constructed type (i.e. the last element of `ConstructContext`), it is assumed that the object is being constructed from GtkBuilder and the object's constructor is called, but instead of creating a new `GObject`, the constructed object's `gi:ref` (pointer) is passed instead, and the javascript "construction" continues.

src/types/object.js

@@ -98,8 +98,22 @@ function defineClassStructMethods(target, info) {
   }
 }
 
-/** @type number | null */
-export let _HydratingObject = null;
+/** @type bigint | null */
+let HydratingObject = null;
+
+/**
+ * @param {bigint | null} object
+ */
+export function _setHydratingObject(object) {
+  HydratingObject = object;
+}
+
+/**
+ * An array of GTypes being currently constructed. This is to catch JS objects
+ * whose instance_init is called.
+ * @type bigint[]
+ */
+export const ConstructContext = [];
 
 export function createObject(info, gType) {
   const ParentClass = getParentClass(info) ?? Object;
@@ -109,22 +123,31 @@ export function createObject(info, gType) {
       super(props);
 
       if (gType == GType.OBJECT) {
-        if (_HydratingObject === null) {
-          const gType = Reflect.getOwnMetadata("gi:gtype", this.constructor);
+        const klass = this.constructor;
+
+        if (HydratingObject === null) {
+          const gType = Reflect.getOwnMetadata("gi:gtype", klass);
 
           if (!gType) {
             throw new Error("Tried to construct an object without a GType");
           }
 
+          ConstructContext.push(gType);
+
           Reflect.defineMetadata("gi:ref", g.object.new(gType, null), this);
           Object.entries(props).forEach(([key, value]) => {
             this[key] = value;
           });
+
+          ConstructContext.pop();
         } else {
-          Reflect.defineMetadata("gi:ref", _HydratingObject, this);
+          Reflect.defineMetadata("gi:ref", HydratingObject, this);
 
-          _HydratingObject = null;
+          HydratingObject = null;
         }
+
+        const init_fn = Reflect.getMetadata("gi:instance_init", klass);
+        if (init_fn) init_fn.call(this);
       }
     }
   };