Shortcuts tweak

[wismill]

Currently each toolkit (Gtk, Qt, etc.) implements its strategy to deal with keyboard shortcuts on non-Latin layouts. See e.g.:

• Switching layout temporarily while modifier is held (xkeyboard-config)
• QXkbCommon::keysymToQtKey does not correctly handle punctuation with modifiers under some keyboard layouts (Qt)
• Cannot use keyboard shortcut Ctrl+Shift+N to create new folder on non-Latin keyboard layouts (Gtk)

Tweak keyboard shortcuts by adding the option to switch to a different group after pressing Control, Alt or Super. The target group can be set for each group, although the most common use case would probably be the same target for all layouts.

This also introduces the keymap compile options API.

This can be alternatively activated with the environment variable XKB_TARGET_SHORTCUT_LAYOUT¹. The target group is then the same for all groups. This allow to use the new feature even if the DE did not implement a UI to configure it.

TODO:

• Tests
• Support latch & lock?
• Doc
• Fix the new FIXMEs
• Move option API to other MR?
• Commit messages
• Remove environment variable support?
• Log entry

Footnotes

1. Actually the env variable will also activate this processing in clients for now, but this is a no-op, as the layout is set by the compositor, which would have already re-target it for shortcuts, if necessary. ↩

[wismill]

Note that there is another way of handling this: set the shortcut keysyms directly in the keymap (à la macOS), by defining new key types with e.g. map[Control] = levelX, etc. Some issues:

1. We need entries for every modifier combination.
2. We need the corresponding preserve entries, e.g. preserve[Control] = Control.
3. It is not easy to select the correct target layout using rules.

We could alleviate this by modifying the keymap on the fly from a given simple source → target layout mapping. Here we could have also fine-grained control on whether the punctuation keysym are affected or not, contrary to the current PR where it’s all-in or all-out.

A similar approach is to use the trick that we can have map[None] = level2 and use a mask with unmapped modifiers in the key type.