[gjs/gnome-3-34] GObject: Check implementing Gio.AsyncInitable

[Philip Chimento <pchimento src gnome org>]

commit ea19d16b0c497da509a41cf80889e771c4c3ce1c
Author: Philip Chimento <philip chimento gmail com>
Date:   Fri Nov 1 23:20:49 2019 -0700

    GObject: Check implementing Gio.AsyncInitable
    
    We want to avoid the situation in #287 altogether by making sure that
    you can't implement Gio.AsyncInitable in your object without
    implementing vfunc_init_async(), and print an error message that is more
    likely to tell you what the problem is.
    
    Since you _also_ can't implement vfunc_init_async() due to #72, we make
    the error message more broad than it needs to be; the error message
    should be changed to something like "You must define vfunc_init_async()
    in order to implement Gio.AsyncInitable."
    
    See #287.

 installed-tests/js/testGObjectInterface.js | 10 ++++++++++
 modules/overrides/GObject.js               |  9 +++++++++
 2 files changed, 19 insertions(+)
---
diff --git a/installed-tests/js/testGObjectInterface.js b/installed-tests/js/testGObjectInterface.js
index a6e0ffa2..2574d936 100644
--- a/installed-tests/js/testGObjectInterface.js
+++ b/installed-tests/js/testGObjectInterface.js
@@ -300,3 +300,13 @@ describe('GObject interface', function () {
             /\[object instance wrapper GType:Gjs_GObjectImplementingGObjectInterface jsobj@0x[a-f0-9]+ 
native@0x[a-f0-9]+\]/);
     });
 });
+
+describe('Specific class and interface checks', function () {
+    it('Gio.AsyncInitable must implement vfunc_async_init', function () {
+        expect(() => GObject.registerClass({
+            Implements: [Gio.Initable, Gio.AsyncInitable],
+        }, class BadAsyncInitable extends GObject.Object {
+            vfunc_init() {}
+        })).toThrow();
+    });
+});
diff --git a/modules/overrides/GObject.js b/modules/overrides/GObject.js
index 658d8fe6..0aece542 100644
--- a/modules/overrides/GObject.js
+++ b/modules/overrides/GObject.js
@@ -147,6 +147,15 @@ function _interfacePresent(required, klass) {
 }
 
 function _checkInterface(iface, proto) {
+    // Checks for specific interfaces
+
+    // Default vfunc_async_init() will run vfunc_init() in a thread and crash.
+    // Change error message when https://gitlab.gnome.org/GNOME/gjs/issues/72
+    // has been solved.
+    if (iface.$gtype.name === 'GAsyncInitable' &&
+        !Object.getOwnPropertyNames(proto).includes('vfunc_init_async'))
+        throw new Error("It's not currently possible to implement Gio.AsyncInitable.");
+
     // Check that proto implements all of this interface's required interfaces.
     // "proto" refers to the object's prototype (which implements the interface)
     // whereas "iface.prototype" is the interface's prototype (which may still