(font-lock-default-fontify-region): Fix subtle

off-by-one problem that could force re-fontifying the whole buffer.
(font-lock-remove-keywords): New function.
(font-lock-add-keywords): Use the new function to ensure idempotence.

1 files changed, 20 insertions, 1 deletions

diff --git a/lisp/font-lock.el b/lisp/font-lock.el
index ab3f84f18be..d96058ba12b 100644
--- a/lisp/font-lock.el
+++ b/lisp/font-lock.el
@@ -753,12 +753,24 @@ see the variables `c-font-lock-extra-types', `c++-font-lock-extra-types',
          ;; Otherwise if Font Lock mode is on, set or add the keywords now.
          (if (eq append 'set)
              (setq font-lock-keywords keywords)
+           (font-lock-remove-keywords keywords)
            (let ((old (if (eq (car-safe font-lock-keywords) t)
                           (cdr font-lock-keywords)
                         font-lock-keywords)))
              (setq font-lock-keywords (if append
                                           (append old keywords)
                                         (append keywords old))))))))
+
+;;;###autoload
+(defun font-lock-remove-keywords (keywords)
+  "Remove highlighting KEYWORDS from the current buffer."
+  (setq font-lock-keywords (copy-list font-lock-keywords))
+  (dolist (keyword keywords)
+    (setq font-lock-keywords
+          (delete keyword
+                  (delete (font-lock-compile-keyword keyword)
+                          font-lock-keywords)))))
+
 
 ;;; Global Font Lock mode.
 
@@ -1096,8 +1108,15 @@ The value of this variable is used when Font Lock mode is turned on."
           ;; check to see if we should expand the beg/end area for
           ;; proper multiline matches
           (setq beg (if (get-text-property beg 'font-lock-multiline)
+                        ;; if the text-property is non-nil, (1+ beg)
+                        ;; is valid.  We need to use (1+ beg) for the
+                        ;; case where (get-text-property (1- beg)) is nil
+                        ;; in which case we want to keep BEG but
+                        ;; previous-single-property-change will return
+                        ;; the previous change (if any) rather than
+                        ;; the one at BEG.
                         (or (previous-single-property-change
-                             beg 'font-lock-multiline)
+                             (1+ beg) 'font-lock-multiline)
                             (point-min))
                       beg))
           (setq end (or (text-property-any end (point-max)