Bind all possible ex cmd abbreviations

Means that :de expands to delete

evil-ex.el

@@ -585,13 +585,20 @@ in case of incomplete or unknown commands."
 
 (defun evil-ex-define-cmd (cmd function)
   "Bind the function FUNCTION to the command CMD."
-  (if (string-match "\\[\\(.*\\)\\]" cmd)
-      (let ((abbrev (replace-match "" nil t cmd))
-            (full (replace-match "\\1" nil nil cmd)))
-        (evil--add-to-alist evil-ex-commands
-                            full function
-                            abbrev full))
-    (evil--add-to-alist evil-ex-commands cmd function)))
+  (cond ((not (string-match-p "\\[" cmd))
+         (evil--add-to-alist evil-ex-commands cmd function))
+        ((string-match "\\]\\(.+\\)" cmd)
+         (user-error "Trailing characters in cmd definition: %s"
+                     (match-string 1 cmd)))
+        ((not (string-match-p "\\]" cmd))
+         (user-error "Missing ] in cmd definition: %s" cmd))
+        (t (string-match "\\(.*\\)\\[\\(.*\\)\\]" cmd)
+           (let ((mandatory (match-string 1 cmd))
+                 (optional  (match-string 2 cmd)))
+             (dotimes (n (1+ (length optional)))
+               (evil--add-to-alist evil-ex-commands
+                                   (concat mandatory (substring optional 0 n))
+                                   function))))))
 
 (defmacro evil-ex-define-argument-type (arg-type doc &rest body)
   "Define a new handler for argument-type ARG-TYPE.