In some cases we explicitly want to unset an accessible attribute; for
instance, an accessible property is gated on a widget property, and if
the widget property gets unset, the accessible property should be reset.
We're currently overloading NULL to mean both "this value is undefined,
and should be reset to its default" and "the value collection failed".
Let's do error reporting right, by using GError to mean "the collection
failed, for this specific reason"; then, we can use a NULL return value
to signal that the accessible attribute should be reset to its default
value.
This is only relevant for pointer-sized attribute values: strings,
references, and reference lists; numeric, boolean, tristate, and token
values either cannot be undefined, or have a specific "undefined" value.
Show a tab for accessibility information.
This shows the role and the accessible attributes
(states, properties, relations).
For now, changing the values is not possible, and
we only show the explicitly set values. In the future,
we want to show the attributes that are relevant for
the role, regardless of whether they are set or not,
and allow changing some of the attributes (the ones
that are not fully managed by GTK itself).
We're stopping activity mode when finalizing, which will change
accessible state; this will create a GtkATContext, and since GtkWidget
drops its GtkATContext on dispose(), we're going to end up leaking it on
the floor:
```
2,007 (64 direct, 1,943 indirect) bytes in 1 blocks are definitely lost in loss record 36,242 of 36,944
at 0x483977F: malloc (vg_replace_malloc.c:307)
by 0x5222105: g_malloc (gmem.c:106)
by 0x523E222: g_slice_alloc (gslice.c:1025)
by 0x523E261: g_slice_alloc0 (gslice.c:1051)
by 0x534B398: g_type_create_instance (gtype.c:1849)
by 0x53302EE: g_object_new_internal (gobject.c:1937)
by 0x53312AF: g_object_new_valist (gobject.c:2262)
by 0x532FEE8: g_object_new (gobject.c:1780)
by 0x4B3F942: gtk_test_at_context_new (gtktestatcontext.c:107)
by 0x491CC50: gtk_at_context_create (gtkatcontext.c:380)
by 0x4BFEDA0: gtk_widget_accessible_get_at_context (gtkwidget.c:8127)
by 0x4906079: gtk_accessible_get_at_context (gtkaccessible.c:83)
by 0x490618F: gtk_accessible_update_state (gtkaccessible.c:137)
by 0x4ACBA6D: gtk_progress_bar_act_mode_leave (gtkprogressbar.c:690)
by 0x4ACB4F8: gtk_progress_bar_finalize (gtkprogressbar.c:564)
```
We're also unparenting widgets and changing styles, which is another
potential source of leaks and side effects.
Track what we really need to send for inset shadows, which are used
as a border replacement in many cases.
Fishbowl says I can draw around 200-300 more switches per frame like
this too.
We must initialize the properties in init, since they
are expected to be there ab initio, and we can't call
gtk_accessible_update_property from finalize - it causes
us to recreate an at context and badness follows.
