(syntax-ppss-flush-cache): Fix corner boundary case.

Suggested by Martin Rudalics <rudalics@gmx.at>.

1 files changed, 9 insertions, 5 deletions

diff --git a/lisp/emacs-lisp/syntax.el b/lisp/emacs-lisp/syntax.el
index 126c8d50dd9..6c897319433 100644
--- a/lisp/emacs-lisp/syntax.el
+++ b/lisp/emacs-lisp/syntax.el
@@ -83,10 +83,14 @@ point (where the PPSS is equivalent to nil).")
     (setq syntax-ppss-cache (cdr syntax-ppss-cache)))
   ;; Throw away `last' value if made invalid.
   (when (< beg (or (car syntax-ppss-last) 0))
-    (if (< beg (or (car (nth 10 syntax-ppss-last))
-                   (nth 9 syntax-ppss-last)
-                   (nth 2 syntax-ppss-last)
-                   0))
+    ;; If syntax-begin-function jumped to BEG, then the old state at BEG can
+    ;; depend on the text after BEG (which is presumably changed).  So if
+    ;; BEG=(car (nth 10 syntax-ppss-last)) don't reuse that data because the
+    ;; assumed nil state at BEG may not be valid any more.
+    (if (<= beg (or (car (nth 10 syntax-ppss-last))
+                    (nth 9 syntax-ppss-last)
+                    (nth 2 syntax-ppss-last)
+                    0))
         (setq syntax-ppss-last nil)
       (setcar syntax-ppss-last nil)))
   ;; Unregister if there's no cache left.  Sadly this doesn't work
@@ -293,5 +297,5 @@ Point is at POS when this function returns."
 
 (provide 'syntax)
 
-;;; arch-tag: 302f1eeb-e77c-4680-a8c5-c543e01161a5
+;; arch-tag: 302f1eeb-e77c-4680-a8c5-c543e01161a5
 ;;; syntax.el ends here