[BUG] `gdk::Paintable.snapshot()` doesn't accept `gtk::Snapshot`

[rmnvgr]

Bug description

The gdk::Paintable.snapshot() method doesn't accept a reference to a gtk::Snapshot. The compiler complains with this:

error[E0308]: mismatched types
  --> src/main.rs:74:40
   |
74 |                     paintable.snapshot(&snapshot, width.into(), height.into());
   |                                        ^^^^^^^^^ expected struct `gtk4::gdk4::Snapshot`, found struct `gtk4::Snapshot`
   |
   = note: expected reference `&gtk4::gdk4::Snapshot`
              found reference `&gtk4::Snapshot`

For more information about this error, try `rustc --explain E0308`.

It expects a gdk::Snapshot, which gtk::Snapshot is according to the docs.

I call it with this code:

let snapshot = gtk::Snapshot::new();
paintable.snapshot(&snapshot, width, height);

Replacing &snapshot by snapshot.upcast_ref() gets rid of the error.

[A6GibKm]

From my side, the two things that are desirable in practice are

• Being able to call the gtk::Snapshot methods on the gdk::Snapshot provided by the snapshot vfunc on widgets and paintables
• Be able to pass gtk::Snapshots to the snapshot vfuncs

[bilelmoussaoui]

The easiest fix I can think of is to make all those methods take a AsRef<gdk::Snapshot> & implement that trait on both :-)

[bilelmoussaoui]

An alternative would be moving the methods from gtk::Snapshot to a trait and implement that trait for gdk::Snapshot that though won't allow passing a gtk::Snapshot to a method that expects a gdk::Snapshot so we kind of need both.

[bilelmoussaoui]

An alternative would be moving the methods from gtk::Snapshot to a trait and implement that trait for gdk::Snapshot that though won't allow passing a gtk::Snapshot to a method that expects a gdk::Snapshot so we kind of need both.

What I don't like about this approach is that it requires manually implementing all the methods of gtk::Snapshot... Because gir only generates a AsRef relation when it is a fundamental type and uses IsA if it is an object(which is the case here).

I wonder if it would make sense to have some kind of config for setting that you want an AsRef instead of IsA somewhere in gir.

[sdroege]

Be able to pass gtk::Snapshots to the snapshot vfuncs

That's easily fixed by marking gdk::Snapshot not as final type and have the trait be generated.

Being able to call the gtk::Snapshot methods on the gdk::Snapshot provided by the snapshot vfunc on widgets and paintables

That looks like a problem. gtk::Snapshot is actually a different type (a subclass of gdk::Snapshot) and it has some additional internal state. I don't think you can call the gtk::Snapshot API on every gdk::Snapshot, in case others than gtk::Snapshot exist at some point as non-abstract types.