(add-hook): Implement `permanent-local-hook' property.

1 files changed, 11 insertions, 1 deletions

diff --git a/lisp/subr.el b/lisp/subr.el
index ca479de2687..5a7f88f76dd 100644
--- a/lisp/subr.el
+++ b/lisp/subr.el
@@ -1103,7 +1103,17 @@ function, it is changed to a list of functions."
                 (append hook-value (list function))
               (cons function hook-value))))
     ;; Set the actual variable
-    (if local (set hook hook-value) (set-default hook hook-value))))
+    (if local
+        (progn
+          ;; If HOOK isn't a permanent local,
+          ;; but FUNCTION wants to survive a change of modes,
+          ;; mark HOOK as partially permanent.
+          (and (symbolp function)
+               (get function 'permanent-local-hook)
+               (not (get hook 'permanent-local))
+               (put hook 'permanent-local 'permanent-local-hook))
+          (set hook hook-value))
+      (set-default hook hook-value))))
 
 (defun remove-hook (hook function &optional local)
   "Remove from the value of HOOK the function FUNCTION.