GInterface methods (e.g. GFile.getPath) missing on instances, only present on prototype

[romgrk]

Summary

Methods that come from a GInterface are not present on object instances — they only exist on the interface's prototype. For example a Gio.File returned by Gio.File.newForPath() (a GLocalFile, which implements the GFile interface) exposes only the base GObject methods; file.getPath, file.enumerateChildren, file.getBasename, etc. are all undefined.

The methods do exist on Gio.File.prototype, so they can be invoked with .call(), but they are not mixed into the instance's prototype chain.

Reproduction

const gi = require('node-gtk');
const Gio = gi.require('Gio', '2.0');

const f = Gio.File.newForPath('/tmp/example.txt');
console.log('typeof f.getPath           :', typeof f.getPath);
console.log('typeof f.getBasename       :', typeof f.getBasename);
console.log('typeof Gio.File.prototype.getPath:', typeof Gio.File.prototype.getPath);
console.log('via prototype.call         :', Gio.File.prototype.getPath.call(f));

Actual

typeof f.getPath           : undefined
typeof f.getBasename       : undefined
typeof Gio.File.prototype.getPath: function
via prototype.call         : /tmp/example.txt

Expected

f.getPath() should work directly, i.e. interface methods should be available on instances of types implementing that interface.

Notes

• This also affects objects handed back from other APIs, e.g. the GFile retrieved via fileInfo.getAttributeObject('standard::file') from a GtkDirectoryList.
• Concrete-class methods are unaffected — GFileInfo, GFileEnumerator, GtkDirectoryList etc. expose their own methods on instances normally.
• The concrete type here (GLocalFile) is a private/non-introspectable type, so node-gtk wraps the instance using the declared return type GFile (the interface). The interface's methods don't get applied to the instance.
• Workaround: Gio.File.prototype.<method>.call(instance, ...).

Environment

• node-gtk 2.0.0
• node v22.22.3
• GTK 4.22.4, GLib 2.88.1