Further work on Bug#28889

* lisp/net/tramp.el (tramp-set-syntax): New defun.
(tramp-syntax): Use it.  Change :package-version.  (Bug#28889)

lisp/net/tramp.el

@@ -674,13 +674,18 @@ Do not change the value by `setq', it must be changed only by
 `custom-set-variables'.  See also `tramp-change-syntax'."
   :group 'tramp
   :version "26.1"
-  :package-version '(Tramp . "2.3.2")
+  :package-version '(Tramp . "2.3.3")
   :type '(choice (const :tag "Default" default)
 		 (const :tag "Ange-FTP" simplified)
 		 (const :tag "XEmacs" separate))
   :require 'tramp
   :initialize 'custom-initialize-set
-  :set (lambda (symbol value)
+  :set 'tramp-set-syntax)
+
+(defun tramp-set-syntax (symbol value)
+  "Set SYMBOL to value VALUE.
+Used in user option `tramp-syntax'.  There are further variables
+to be set, depending on VALUE."
   ;; Check allowed values.
   (unless (memq value (tramp-syntax-values))
     (tramp-compat-user-error "Wrong `tramp-syntax' %s" tramp-syntax))
@@ -709,13 +714,14 @@ Do not change the value by `setq', it must be changed only by
 	  tramp-completion-file-name-regexp
           (tramp-build-completion-file-name-regexp)))
   ;; Rearrange file name handlers.
-	 (tramp-register-file-name-handlers)))
+  (tramp-register-file-name-handlers))
 
 ;; Initialize the Tramp syntax variables.  We want to override initial
-;; values of `tramp-file-name-regexp' and
-;; `tramp-completion-file-name-regexp'.
+;; value of `tramp-file-name-regexp'.  Other Tramp syntax variables
+;; must be initialized as well to proper values.  We do not call
+;; `custom-set-variable', this would load Tramp via custom.el.
 (eval-after-load 'tramp
-  '(custom-set-variables `(tramp-syntax ',(tramp-compat-tramp-syntax))))
+  '(tramp-set-syntax 'tramp-syntax (tramp-compat-tramp-syntax)))
 
 (defun tramp-syntax-values ()
   "Return possible values of `tramp-syntax', a list"