injectionManager: Support overriding vfuncs

Overriding vfuncs can be useful, in particular when we convert
to ES modules, and exported symbols cannot easily be swapped out.

Adapt overrideMethod() to work correctly in that case as well.

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/2809>

js/extensions/extension.js

@@ -1,3 +1,5 @@
+const Gi = imports._gi;
+
 import {ExtensionBase, GettextWrapper} from './sharedInternals.js';
 
 const {extensionManager} = imports.ui.main;
@@ -48,7 +50,7 @@ export class InjectionManager {
      */
     overrideMethod(prototype, methodName, createOverrideFunc) {
         const originalMethod = this._saveMethod(prototype, methodName);
-        prototype[methodName] = createOverrideFunc(originalMethod);
+        this._installMethod(prototype, methodName, createOverrideFunc(originalMethod));
     }
 
     /**
@@ -66,7 +68,7 @@ export class InjectionManager {
         if (originalMethod === undefined)
             delete prototype[methodName];
         else
-            prototype[methodName] = originalMethod;
+            this._installMethod(prototype, methodName, originalMethod);
 
         savedProtoMethods.delete(methodName);
         if (savedProtoMethods.size === 0)
@@ -96,4 +98,13 @@ export class InjectionManager {
         savedProtoMethods.set(methodName, originalMethod);
         return originalMethod;
     }
+
+    _installMethod(prototype, methodName, method) {
+        if (methodName.startsWith('vfunc_')) {
+            const giPrototype = prototype[Gi.gobject_prototype_symbol];
+            giPrototype[Gi.hook_up_vfunc_symbol](methodName.slice(6), method);
+        } else {
+            prototype[methodName] = method;
+        }
+    }
 }

tests/unit/injectionManager.js

@@ -1,5 +1,7 @@
 const JsUnit = imports.jsUnit;
 
+import GObject from 'gi://GObject';
+
 import '../../js/ui/environment.js';
 
 import {InjectionManager} from '../../js/extensions/extension.js';
@@ -16,6 +18,23 @@ class Object1 {
     }
 }
 
+class GObject1 extends GObject.Object {
+    static [GObject.properties] = {
+        'plonked': GObject.ParamSpec.boolean(
+            'plonked', '', '',
+            GObject.ParamFlags.READWRITE,
+            false),
+    };
+
+    static {
+        GObject.registerClass(this);
+    }
+
+    plonk() {
+        this.set_property('plonked', true);
+    }
+}
+
 /**
  * @param {object} object to modify
  */
@@ -91,3 +110,28 @@ JsUnit.assertEquals(obj.getNumber(), 42);
 JsUnit.assertEquals(obj.getCount(), obj.count);
 JsUnit.assert(obj.count > 0);
 JsUnit.assertRaises(() => obj.getOtherNumber());
+
+// GObject injections
+const gobj = new GObject1();
+let vfuncCalled;
+
+injectionManager.overrideMethod(
+    GObject1.prototype, 'vfunc_set_property', originalMethod => {
+        return function (...args) {
+            // eslint-disable-next-line no-invalid-this
+            originalMethod.apply(this, args);
+            vfuncCalled = true;
+        };
+    });
+
+// gobj is now modified
+vfuncCalled = false;
+gobj.plonk();
+JsUnit.assertTrue(vfuncCalled);
+
+injectionManager.clear();
+
+// gobj is unmodified again
+vfuncCalled = false;
+gobj.plonk();
+JsUnit.assertFalse(vfuncCalled);