Add support for an XKB extensions directory

[wismill]

libxkbcommon introduced flexibility by enabling multiple XKB lookup paths. However, there is no easy way to distribute packages that provide XKB data: such packages usually resort to modify the root XKB directory, which is not good.

I propose to added another XKB path lookup for XKB extensions, XKB_CONFIG_EXTENSIONS_PATH, which would default to /usr/share/xkeyboard-config.d (exact path subject to bikeshedding). Then each subdirectory of the XKB extensions directory, listed in lexicographic order, is appended to the XKB include paths.

Package should use the variable xkb_extensions_path provided by the pkg-config file of either libxkbcommon or xkeyboard-config.

Rules can be extended by using a partial rules file <ruleset>.post, e.g. to add an option.

---

Example: package xkb-layout-xxx provides a partial registry file evdev.xml and a symbols file xxx. It installs them as follow:

• /usr/share/xkeyboard-config.d/xxx/rules/evdev.xml
• /usr/share/xkeyboard-config.d/xxx/symbols/xxx
  Further files such as license and README can be installed too, if relevant.

[joel-porquet]

Maintainer of xkb-altgr-weur for ArchLinux/AUR here. The proposal sounds great, although I'm not enough of a XKB expert to assess if it may have potential flaws. What's for sure is that the current way of adding layouts is horrible (having to modify the root directory) so anything that would help with that is welcome!

[wismill]

Published in release 1.13.0. See the doc Packaging keyboard layouts.