Add check-order script

Author: lassik

admin/check-order.el

@@ -0,0 +1,24 @@
+;; If a child mode is derived from a parent mode, the child must be
+;; listed before the parent. Otherwise the parent will shadow the
+;; child and the child will never match.
+
+;; Note that information about parent-child relationships is only
+;; available for modes that have been loaded into Emacs. For a
+;; comprehensive check, all modes recognized by language-id need to be
+;; loaded into Emacs.
+
+(cl-reduce (lambda (modes-so-far language)
+             (let ((language-modes (cdr language)))
+               (cl-reduce (lambda (modes-so-far mode)
+                            (message "%S" modes-so-far)
+                            (let ((mode (if (listp mode) (car mode) mode)))
+                              (cl-assert (symbolp mode))
+                              (let ((parent (apply #'provided-mode-derived-p
+                                                   mode modes-so-far)))
+                                (when (and parent (not (equal parent mode)))
+                                  (error "%S is shadowed by %S" mode parent)))
+                              (cons mode modes-so-far)))
+                          language-modes
+                          :initial-value modes-so-far)))
+           language-id--definitions
+           :initial-value '())