      'symbols))
   "Field names allowed in dune files.")
 
-(defvar dune-builtin-regex
+(defconst dune-builtin-regex
   (eval-when-compile
     (concat (regexp-opt
              '(;; Linking modes

     (2 dune-separator-face)
     (3 dune-separator-face))
    ("%{\\([^{}]*\\)}" 1 font-lock-variable-name-face keep)
    ("\\(:[a-zA-Z]+\\)\\b" 1 font-lock-builtin-face)
    ("\\(true\\|false\\)" 1 font-lock-constant-face)
    ("(\\(select\\)[[:space:]]+[^[:space:]]+[[:space:]]+\\(from\\)\\>"
     (1 font-lock-constant-face)

            "\\(?:\\_>\\|[[:space:]]\\)"))
  "Builtin sub-fields in dune")

(defconst dune-builtin-labels-regex
  (regexp-opt '("standard" "include") 'words)
  "Builtin :labels in dune")

(defvar dune-var-kind-regex
  (eval-when-compile
    (regexp-opt
