Bug summary

When trying to save figure with GTK4 on Mac, the file format is always pgf regardless what we have selected. Furthermore, if the saving pgf fails, an error box is displayed and cannot be closed. I tried to investigate what was happening there but haven't fixed it yet. (See additional information)

No matter what we have selected, format is always pgf when saving

Code for reproduction

import numpy as np
import matplotlib.pyplot as plt
import matplotlib as mpl

print(mpl.__file__)
print(mpl.__version__)
mpl.use('gtk4agg')

# evenly sampled time at 200ms intervals
t = np.arange(0., 5., 0.2)
# red dashes, blue squares and green triangles
plt.plot(t, t, 'r--', t, t**2, 'bs', t, t**3, 'g^')
plt.show()

Actual outcome

Save fig fails

Expected outcome

Save fig success

Additional information

pygobject 3.44.1
gtk4: stable 4.12.0

For the "always pgf" bug:

/lib/matplotlib/backends/backend_gtk4.py line 361

dialog.set_choice('format', formats[default_format])

should be

dialog.set_choice('format', formats[0])

full code snippet:
dialog is a Gtk.FileChooserNative instance.

formats = [formats[default_format], *formats[:default_format],
                   *formats[default_format+1:]]
dialog.add_choice('format', 'File format', formats, formats)
dialog.set_choice('format', formats[default_format])

dialog.set_current_folder(Gio.File.new_for_path(
    os.path.expanduser(mpl.rcParams['savefig.directory'])))
dialog.set_current_name(self.canvas.get_default_filename())

However, after fixing this, it always resolve to PNG (the correct default choice.) I suspect dialog.add_choice() cannot work correctly on Mac or doesn't work anymore.

The easiest fix is extracting the file extension via dialog.get_file() which is already at line 372 in /lib/matplotlib/backends/backend_gtk4.py line 361

P. S.
I tried to replace it with Gtk.FileChooserNative.get_filter(), but it doesn't work and it's probably a confirmed bug in GTK4https://gitlab.gnome.org/GNOME/gtk/-/issues/1820

Operating system

Mac

Matplotlib Version

3.8.0.dev1829+g3d2d0727ec.d20230818

Matplotlib Backend

gtk4agg

Python version

3.9.6

Jupyter version

No response

Installation

None