Deprecate $HOME/.xkb path in favor of XDG_CONFIG_HOME/xkb

[bam80]

So our lookup path sequence becomes - in that order:

• XDG_CONFIG_HOME/xkb

• $HOME/.xkb
  ...

I think $HOME/.xkb is not necessary any more,
the random dotstyle-configs/dirs in $HOME are deprecated nowadays, being fully replaced by XDG_CONFIG_HOME path which renders to something like ${XDG_CONFIG_HOME:-$HOME/.config}:

$XDG_CONFIG_HOME defines the base directory relative to which user-specific configuration files should be stored. If $XDG_CONFIG_HOME is either not set or empty, a default equal to $HOME/.config should be used.

https://specifications.freedesktop.org/basedir-spec/latest/#variables

So I would suggest just drop $HOME/.xkb as legacy one to teach people good practice.

Originally posted by @bam80 in #162 (comment)

[wismill]

While I agree ~/.config/xkb is a better configuration location, I’m not sure “teach people good practice” is a good argument to introduce such a breaking change.

It would break the keyboard configuration of people relying on this and it’s quite difficult to debug if one is not familiar with XKB. Indeed, some people may install their files in ~/.xkb following instructions but without any knowledge of XKB. Even for more experienced people, debugging this may be time-consuming.

Added to that, XDG Base Directory Specification is more a convention than a standard, so it’s difficult to know if all setups using xkbcommon support it.

Supporting ~/.xkb config folder has no maintenance cost for us and its lookup really marginally impacts performance, so “teach people good practice” seems a weak argument and patronizing.

We already promote the XDG specification by looking its directories up first.

CC @whot, since you authored #162.

[bam80]

I believe the change is inevitable. The XDG's Specification is a standard de-facto for quite a long time, and our lib has already adopted it.
Any app which had legacy path for configs at some point in the past doesn't have to keep that forever.

Alternatively, we could declare that legacy path as deprecated for some time in the docs/release notes, and then remove after.

[whot]

Ack for deprecating it in the documentation (potentially mostly hiding it) but removal of the functionality is just going to cause potential breakage for now good technical reason.

$HOME/.xkb was supported before the addition of the xdg directories.

[bam80]

I would ask to make runtime DEPRECATED!-marked log output etc. whenever the legacy path is encountered.

[bam80]

deprecating it in the documentation (potentially mostly hiding it)

Hiding is not good. We should emphasize the path support could be deleted any time in the future versions.