zsh: set environment variables in zshenv instead of zprofile

This patch fixes two issues:

1. The file in which environment variables are set is inconsistent.
  - This file sets them in zprofile when programs.zsh.enable is not
  set.
  - Zsh module sets them in zshenv when programs.zsh.enable is set.

2. Setting environment variables in zprofile overrides what users set
in .zshenv.  See these[1] home-manager[2] issues[3].

/etc/profile is also changed to /etc/set-environment. Here is a
comparison:

Using /etc/profile:
- Pros
  - config.environment.shellInit is sourced in all zsh
- Cons
  - config.environment.loginShellInit is also sourced in non-login zsh
  - config.programs.bash.shellInit is also sourced in all zsh
  - config.programs.bash.loginShellInit is also sourced in all zsh

Using /etc/set-environment:
- Pros
  - config.programs.bash.shellInit is not sourced in any zsh
  - config.programs.bash.loginShellInit is not sourced in any zsh
- Cons
  - config.environment.shellInit is not sourced in any zsh
  - config.environment.loginShellInit is not sourced in any zsh

[1]: https://github.com/nix-community/home-manager/issues/2751#issuecomment-1048682643
[2]: https://github.com/nix-community/home-manager/issues/2991
[3]: https://github.com/nix-community/home-manager/issues/3681#issuecomment-1436054233

nixos/doc/manual/release-notes/rl-2305.section.md

@@ -187,6 +187,8 @@ In addition to numerous new and upgraded packages, this release has the followin
   The `{aclUse,superUser,disableActions}` attributes have been renamed, `pluginsConfig` now also accepts an attribute set of booleans, passing plain PHP is deprecated.
   Same applies to `acl` which now also accepts structured settings.
 
+- The `zsh` package changes the way to set environment variables on NixOS systems where `programs.zsh.enable` equals `false`.  It now sources `/etc/set-environment` when reading the system-level `zshenv` file.  Before, it sourced `/etc/profile` when reading the system-level `zprofile` file.
+
 - The `wordpress` service now takes configuration via the `services.wordpress.sites.<name>.settings` attribute set, `extraConfig` is still available to append  additional text to `wp-config.php`.
 
 - To reduce closure size in `nixos/modules/profiles/minimal.nix` profile disabled installation documentations and manuals. Also disabled `logrotate` and `udisks2` services.

pkgs/shells/zsh/default.nix

@@ -42,7 +42,7 @@ stdenv.mkDerivation {
     "--enable-multibyte"
     "--with-tcsetpgrp"
     "--enable-pcre"
-    "--enable-zprofile=${placeholder "out"}/etc/zprofile"
+    "--enable-zshenv=${placeholder "out"}/etc/zshenv"
     "--disable-site-fndir"
   ] ++ lib.optionals (stdenv.hostPlatform != stdenv.buildPlatform && !stdenv.hostPlatform.isStatic) [
     # Also see: https://github.com/buildroot/buildroot/commit/2f32e668aa880c2d4a2cce6c789b7ca7ed6221ba
@@ -64,34 +64,36 @@ stdenv.mkDerivation {
   postInstall = ''
     make install.info install.html
     mkdir -p $out/etc/
-    cat > $out/etc/zprofile <<EOF
+    cat > $out/etc/zshenv <<EOF
 if test -e /etc/NIXOS; then
-  if test -r /etc/zprofile; then
+  if test -r /etc/zshenv; then
-    . /etc/zprofile
+    . /etc/zshenv
   else
     emulate bash
     alias shopt=false
-    . /etc/profile
+    if [ -z "$__NIXOS_SET_ENVIRONMENT_DONE" ]; then
+      . /etc/set-environment
+    fi
     unalias shopt
     emulate zsh
   fi
-  if test -r /etc/zprofile.local; then
+  if test -r /etc/zshenv.local; then
-    . /etc/zprofile.local
+    . /etc/zshenv.local
   fi
 else
-  # on non-nixos we just source the global /etc/zprofile as if we did
+  # on non-nixos we just source the global /etc/zshenv as if we did
   # not use the configure flag
-  if test -r /etc/zprofile; then
+  if test -r /etc/zshenv; then
-    . /etc/zprofile
+    . /etc/zshenv
   fi
 fi
 EOF
     ${if stdenv.hostPlatform == stdenv.buildPlatform then ''
-      $out/bin/zsh -c "zcompile $out/etc/zprofile"
+      $out/bin/zsh -c "zcompile $out/etc/zshenv"
     '' else ''
-      ${lib.getBin buildPackages.zsh}/bin/zsh -c "zcompile $out/etc/zprofile"
+      ${lib.getBin buildPackages.zsh}/bin/zsh -c "zcompile $out/etc/zshenv"
     ''}
-    mv $out/etc/zprofile $out/etc/zprofile_zwc_is_used
+    mv $out/etc/zshenv $out/etc/zshenv_zwc_is_used
 
     rm $out/bin/zsh-${version}
     mkdir -p $out/share/doc/