How to make zsh search configuration in $XDG_CONFIG_HOME

Looking to make my ~ a cleaner place, I would like to move as much user configuration files into $XDG_CONFIG_HOME, which is ~/.config by default. So I would like to store all my zsh user files in $XDG_CONFIG_HOME/zsh/. So far already have this:

% ls $XDG_CONFIG_HOME/zsh/
histfile  zsh_cache zshrc

Easy, you just have to fill your ~/.zshrc. Now the trickiest part seems to make zsh read directly $XDG_CONFIG_HOME/zsh/zshrc without sourcing it from ~/.zshrc. How would you proceed?

Solution

One may edit /etc/zsh/zshenv to set $XDG_CONFIG_HOME directories and $ZDOTDIR. This require write privilegies on this files though.

So provided that $HOME is defined when zsh read it (I don't know if it's the case), you may add to your /etc/zsh/zshenv:

if [[ -z "$XDG_CONFIG_HOME" ]]
then
        export XDG_CONFIG_HOME="$HOME/.config/"
fi

if [[ -d "$XDG_CONFIG_HOME/zsh" ]]
then
        export ZDOTDIR="$XDG_CONFIG_HOME/zsh/"
fi