Give permanent-local property to per-buffer variables without defaults.

* doc/emacs/custom.texi (Examining): Update C-h v message.

* lisp/bindings.el: Assign a non-nil permanent-local property to
per-buffer variables which lack a default value.

* lisp/help-fns.el (describe-variable): In the "automatically becomes
local" notice, take note of permanent-local variables.

Fixes: debbugs:11930

1 files changed, 14 insertions, 1 deletions

diff --git a/lisp/bindings.el b/lisp/bindings.el
index e0bea34cd0a..97450f788aa 100644
--- a/lisp/bindings.el
+++ b/lisp/bindings.el
@@ -650,9 +650,22 @@ okay.  See `mode-line-format'.")
         user-error ;; That's the main one!
         ))
 
-
 (make-variable-buffer-local 'indent-tabs-mode)
 
+;; These per-buffer variables are never reset by
+;; `kill-all-local-variables', because they have no default value.
+;; For consistency, we give them the `permanent-local' property, even
+;; though `kill-all-local-variables' does not actually consult it.
+
+(mapcar (lambda (sym) (put sym 'permanent-local t))
+	'(buffer-file-name default-directory buffer-backed-up
+	  buffer-saved-size buffer-auto-save-file-name
+	  buffer-read-only buffer-undo-list mark-active
+	  point-before-scroll buffer-file-truename
+	  buffer-file-format buffer-auto-save-file-format
+	  buffer-display-count buffer-display-time
+	  enable-multibyte-characters))
+
 ;; We have base64, md5 and sha1 functions built in now.
 (provide 'base64)
 (provide 'md5)