zsh: env var assertion for dotdir

Needs to be known at build time. Ensure user doesn't accidentally use
env var in `dotDir`

Signed-off-by: Austin Horstman <khaneliman12@gmail.com>

modules/programs/zsh/default.nix

@@ -344,9 +344,25 @@ in
     mkIf cfg.enable (
       lib.mkMerge [
         {
+          assertions = [
+            {
+              assertion = !lib.hasInfix "$" cfg.dotDir;
+              message = ''
+                programs.zsh.dotDir cannot contain shell variables as it is used for file creation at build time.
+                Current dotDir: ${cfg.dotDir}
+                Consider using an absolute path or home-manager config options instead.
+                You can replace shell variables with options like:
+                - config.home.homeDirectory (user's home directory)
+                - config.xdg.configHome (XDG config directory)
+                - config.xdg.dataHome (XDG data directory)
+                - config.xdg.cacheHome (XDG cache directory)
+              '';
+            }
+          ];
+
           warnings =
             lib.optionals
-              (cfg.dotDir != homeDir && !lib.hasPrefix "/" cfg.dotDir && !lib.hasPrefix "$" cfg.dotDir)
+              (cfg.dotDir != homeDir && !lib.hasPrefix "/" cfg.dotDir && !lib.hasInfix "$" cfg.dotDir)
               [
                 ''
                   Using relative paths in programs.zsh.dotDir is deprecated and will be removed in a future release.

tests/modules/programs/zsh/default.nix

@@ -4,7 +4,7 @@
   zsh-dotdir-absolute = import ./dotdir.nix "absolute";
   zsh-dotdir-default = import ./dotdir.nix "default";
   zsh-dotdir-relative = import ./dotdir.nix "relative";
-  zsh-dotdir-xdg-variable = import ./dotdir.nix "xdg-variable";
+  zsh-dotdir-shell-variable = import ./dotdir.nix "shell-variable";
   zsh-history-ignore-pattern = ./history-ignore-pattern.nix;
   zsh-history-path-absolute = import ./history-path.nix "absolute";
   zsh-history-path-default = import ./history-path.nix "default";

tests/modules/programs/zsh/dotdir.nix

@@ -18,7 +18,7 @@ let
       subDir
     else if case == "default" then
       options.programs.zsh.dotDir.default
-    else if case == "xdg-variable" then
+    else if case == "shell-variable" then
       "\${XDG_CONFIG_HOME:-\$HOME/.config}/zsh"
     else
       abort "Test condition not provided.";
@@ -48,12 +48,24 @@ in
       ''
     ];
 
-    nmt.script =
-      if case == "xdg-variable" then
+    test.asserts.assertions.expected = lib.optionals (case == "shell-variable") [
       ''
-          # For XDG variable case, check that shell variables are preserved in the generated shell code
-          # The fixed implementation should preserve variables without wrapping them in single quotes
-          assertFileContains home-files/.zshenv 'source ''${XDG_CONFIG_HOME:-''$HOME/.config}/zsh/.zshenv'
+        programs.zsh.dotDir cannot contain shell variables as it is used for file creation at build time.
+        Current dotDir: ''${XDG_CONFIG_HOME:-''$HOME/.config}/zsh
+        Consider using an absolute path or home-manager config options instead.
+        You can replace shell variables with options like:
+        - config.home.homeDirectory (user's home directory)
+        - config.xdg.configHome (XDG config directory)
+        - config.xdg.dataHome (XDG data directory)
+        - config.xdg.cacheHome (XDG cache directory)
+      ''
+    ];
+
+    nmt.script =
+      if case == "shell-variable" then
+        ''
+          # Shell variable case should fail assertion, no files to check
+          echo "Shell variable case should trigger assertion failure"
         ''
       else
         lib.concatStringsSep "\n" [