GtkTreeView should open and close nested items with unmodified arrow keys

Submitted by Nate Graham @Pointedstick

Assigned to gtk..@..tk.org

Link to original bug (#775731)

Description

Fedora 25 + GNOME 3.22 + Wayland

Various programs use GtkTreeView to display nested content, like evolution and baobab. One frustration in all of these programs is that keyboard navigation does not open nested items with the unmodified right arrow key, or close nested items with the unmodified left arrow key when the root node is selected. Instead, the shift modifier key must be held down when pushing the relevant arrow key.

There are three problems with this:

1. It's hidden and user-unfriendly; the fact that you need to press the shift key is not documented or exposed anywhere.
2. It's unnecessary; The plain arrow keys aren't doing anything else, so there's no need to bury the functionality behind a modifier key.
3. It's contrary to expectations and the way tree views work in basically every other widget toolkit across every computing platform I've ever used.

Here are two bugs I filed against other programs to implement this, not knowing that GtkTreeView was the culprit: https://bugzilla.gnome.org/show_bug.cgi?id=775370 https://bugzilla.gnome.org/show_bug.cgi?id=731689

Version: 3.22.x