Every interactive zsh sources /etc/zshrc (see STARTUP/SHUTDOWN FILES in zshautll(1))
Therefor every interactive zsh process will respect the content of these variables.
Using `export` will also lead to child processes inheriting this value.
This leads to problems, if other interactive shells are spawned such as bash,
because they use an incomptabible history format (without timestamps).
There seems to be also cases, where the local HISTSIZE in ~/.zshrc is
not sourced but /etc/zshrc, which leads to history truncation in other shells.
This reverts commit 766207ca1d.
We need to solve the problem with `environment.profileRelativeEnvVars`.
The best workaround is to make profileRelativeEnvVars prepend paths.
NixOS has a pervasive dependency on bash. For instance, the X11
session script sources /etc/profile to get a reasonable
environment. Thus we should not provide an option to disable bash.
Also, enabling zsh no longer sets ‘users.defaultUserShell’ to zsh, to
prevent a collision with bash's definition of the same
option. (Changing the default shell is also something that should be
left to the user.)
Using pkgs.lib on the spine of module evaluation is problematic
because the pkgs argument depends on the result of module
evaluation. To prevent an infinite recursion, pkgs and some of the
modules are evaluated twice, which is inefficient. Using ‘with lib’
prevents this problem.
