nixos/zsh-syntax-highlighting: refactor

nixos/modules/programs/zsh/zsh-syntax-highlighting.nix

@@ -54,25 +54,25 @@ in
   config = mkIf cfg.enable {
     environment.systemPackages = with pkgs; [ zsh-syntax-highlighting ];
 
-      programs.zsh.interactiveShellInit = with pkgs; with builtins; ''
+    assertions = [
-        source ${zsh-syntax-highlighting}/share/zsh-syntax-highlighting/zsh-syntax-highlighting.zsh
+      {
-
+        assertion = length(attrNames cfg.patterns) > 0 -> elem "pattern" cfg.highlighters;
-        ${optionalString (length(cfg.highlighters) > 0)
+        message = ''
-          "ZSH_HIGHLIGHT_HIGHLIGHTERS=(${concatStringsSep " " cfg.highlighters})"
+          When highlighting patterns, "pattern" needs to be included in the list of highlighters.
-        }
-
-        ${let
-            n = attrNames cfg.patterns;
-          in
-            optionalString (length(n) > 0)
-              (assert(elem "pattern" cfg.highlighters); (foldl (
-                a: b:
-                  ''
-                    ${a}
-                    ZSH_HIGHLIGHT_PATTERNS+=('${b}' '${attrByPath [b] "" cfg.patterns}')
-                  ''
-              ) "") n)
-        }
         '';
+      }
+    ];
+
+    programs.zsh.interactiveShellInit = with pkgs;
+      lib.concatStringsSep "\n" ([
+        "source ${zsh-syntax-highlighting}/share/zsh-syntax-highlighting/zsh-syntax-highlighting.zsh"
+      ] ++ optional (length(cfg.highlighters) > 0)
+        "ZSH_HIGHLIGHT_HIGHLIGHTERS=(${concatStringsSep " " cfg.highlighters})"
+        ++ optionals (length(attrNames cfg.patterns) > 0)
+          (mapAttrsToList (
+            pattern: design:
+            "ZSH_HIGHLIGHT_PATTERNS+=('${pattern}' '${design}')"
+          ) cfg.patterns)
+      );
   };
 }