GTK: Migrate to GTK4

[AesaraB]

It's about time, isn't it?

I'll update this issue as I better understand the codebase and libraries. For now, we're starting with the guide found in GTK's documentation.

Tasks

• Update codebase to GTK 3.24
  • Stop relying on depreciated symbols (GTK 3.24)
    • This in and of itself should fix a bunch of bugs (and add in new ones, yay)
    • Side goal: since we're going through all of these files, maybe start documenting things better.
• Stop using depreciated symbols (GTK 4)

[AesaraB]

Issue #1161 may occur due to the use of depreciated function Gdk.Device.grab()

[AesaraB]

Since basically all of Gdk.Screen is depreciated with Gdk.Display, I'm hoping that focusing on that class first will improve Wayland usability.

[AesaraB]

Comment 1

Yeah, this is much easier with compiled languages. Here we can only see the deprecations through at runtime.

But you should not need to switch to GTK 4, you should be able to enable the deprecation warnings (silenced by default) with the following patch:

--- a/mypaint.py
+++ b/mypaint.py
@@ -26,6 +26,9 @@ import os.path
 from os.path import join, isdir, dirname, abspath
 import re
 import logging
+import warnings
+import gi
+warnings.simplefilter('default', gi.PyGIDeprecationWarning)
 
 logger = logging.getLogger('mypaint')
 if sys.version_info >= (3,):

There are also some deprecations which need to be enabled with G_ENABLE_DIAGNOSTIC=1 as per the migration guide.

(Though for some reason I am not getting all the warnings I would expect. Edit: asked on pygobject chat.)

---

There was a feature request for mypy to find deprecations using static analysis but it fizzled out due to a lack of standard deprecation markings. Looks like those has been accepted since in PEP-0702 but it will take time until they are recognized by tooling. And since we do not do static analysis currently, we would need to start first. Also since the bindings are generated at runtime, we would need to employ pygobject/pygobject-stubs#165.

Comment 2

Quoting Neui from the GNOME Python chat:

Use Python Development mode which shows DeprecationWarning globally (default is to hide them except __main__). PyGObject uses the Python DeprecationWarning for deprecated library stuff instead of the PyGObject-specific PyGIDeprecationWarning used by PyGObject specific overrides and stuff (it seems, from reading the code). This is what it looks like with Gtk.Alignment.new for example:

test-deprecation.py:7: DeprecationWarning: Gtk.Alignment.new is deprecated
  alignment = Gtk.Alignment.new(1, 1, 1, 1)