This is just unfortunate. It’s an aliasing violation to cast a pointer
to a pointer (and there’s no way round that), although in practice it
will not cause a problem. People do quite often compile with
`-Werror=strict-aliasing`, though, so fixing the warnings is helpful.
Warnings are of the form:
```
../../source/gnome-control-center/panels/keyboard/cc-keyboard-shortcut-dialog.c: In function ‘cc_keyboard_shortcut_dialog_finalize’:
../../source/gnome-control-center/panels/keyboard/cc-keyboard-shortcut-dialog.c:518:20: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
518 | g_clear_pointer ((GtkWindow**)&self->shortcut_editor, gtk_window_destroy);
/opt/gnome/install/include/glib-2.0/glib/gmacros.h:871:47: note: in definition of macro ‘G_STATIC_ASSERT’
871 | #define G_STATIC_ASSERT(expr) _Static_assert (expr, "Expression evaluates to false")
| ^~~~
../../source/gnome-control-center/panels/keyboard/cc-keyboard-shortcut-dialog.c:518:3: note: in expansion of macro ‘g_clear_pointer’
518 | g_clear_pointer ((GtkWindow**)&self->shortcut_editor, gtk_window_destroy);
| ^~~~~~~~~~~~~~~
In file included from /opt/gnome/install/include/glib-2.0/glib/gatomic.h:30,
from /opt/gnome/install/include/glib-2.0/glib/gthread.h:34,
from /opt/gnome/install/include/glib-2.0/glib/gasyncqueue.h:34,
from /opt/gnome/install/include/glib-2.0/glib.h:34:
../../source/gnome-control-center/panels/keyboard/cc-keyboard-shortcut-dialog.c:518:20: error: dereferencing type-punned pointer will break strict-aliasing rules [-Werror=strict-aliasing]
518 | g_clear_pointer ((GtkWindow**)&self->shortcut_editor, gtk_window_destroy);
/opt/gnome/install/include/glib-2.0/glib/glib-typeof.h:39:36: note: in definition of macro ‘glib_typeof’
39 | #define glib_typeof(t) __typeof__ (t)
| ^
../../source/gnome-control-center/panels/keyboard/cc-keyboard-shortcut-dialog.c:518:3: note: in expansion of macro ‘g_clear_pointer’
518 | g_clear_pointer ((GtkWindow**)&self->shortcut_editor, gtk_window_destroy);
| ^~~~~~~~~~~~~~~
cc1: all warnings being treated as errors
```
I believe it’s better to fix these by expanding out the
`g_clear_pointer()` call, than by changing the types of variables — the
latter approach means everything becomes a `GtkWidget` or a `GtkWindow`,
which loses type specificity. So this approach is in contrast to that
taken in commit 1bafd46ea3, for example.
Alternative approaches would be:
1. Add internal `cc_clear_window()` and `cc_clear_widget()` helpers
which do this in a single line without aliasing violations.
2. Enforce compiling with `-Wno-strict-aliasing` if strict aliasing is
not something that g-c-c maintainers want to care about (which would
be fine, aliasing checks probably won’t catch any bugs in this kind
of code).
Signed-off-by: Philip Withnall <pwithnall@gnome.org>
Fixes: #2563
ea014f24eb