This is way more complicated than it should be, because it requires
manually limiting the number of open file enumerators.
On the other hand, it exhaustively tests the items-changed emission of
all involved listmodels because those signals come in pretty much
randomly.
It's also 50% slower than the sync version, with the caeat that the sync
version only shows the UI after it's done loading, while this version
shows it right away.
This model just takes an object and a property name and recursively
looks it up. In particular, I want it for:
widget, widget.parent, widget.parent.parent, ...
The code gets rid of the GtkTreeView and replaces it with a GtkListBox.
Most of the logic is now done via GListModel subclasses.
A big change is that this new list is now tracking updates itself and
doesn't need to be manually updated. All code that used to cause rescans
or add forgotten objects to the tree has been removed.
If objects are missing from the object tree, the logic for tracking them
needs to be added.
This patch does multiple things:
1. Add a custom persistent per-row object.
2. Move all per-row API to that object. This means notifications are now
possible.
3. Add a "passthrough" construct-only property to the TreeListModel that
influences if the model returns these new object or passes through
the ones from the model.
This greatly simplifies the code needed to be written for widgetry,
because one can just connect the per-row object to the expanders that
expand and collapse rows.
As an added power feature, these objects can also be passed through
further models (like filter models).
It also adds kind of a hack to Adwaita to make the test look neat.
Let separators be declared as sidebars to have the same style as those
drawn by GtkStackSidebar. This also let them handle the selection-mode
class, whether they are assigned it or they descend from something in
selection mode.
Also drop setting the selection mode color for non-sidebar separators.
This is convenient when building a custom sidebar using a GtkSeparator
and to extend a sidebar to the title bar.
This is needed to work around headerbar sliding animation issues without
refactoring Adwaita's support of titlebars and headerbars as it may
break applications.
https://gitlab.gnome.org/GNOME/gtk/issues/1264
