prevent recursion in php-syntax-propertize-extend-region

Similar to problem #277, I am receiving the error

   (error "parse-sexp-propertize-function did not move syntax-propertize--done")

due to recursion depth being exceeded.  I am using the current git branch of
emacs.  Seems that re-search function can now trigger
syntax-propertize-extend-region-functions to be called again, which in turn
triggers the same call to php-syntax-propertize-extend-region.  This stops
recursion when parameters already being processed are passed to
php-syntax-propertize-extend-region.  This fixes the error and seems to improve
handling of large files, though I have not yet profiled it.

Author: Herbert Jones

php-mode.el

@@ -974,26 +974,37 @@ this ^ lineup"
     (goto-char (point-max)))
   (c-put-char-property (1- (point)) 'syntax-table (string-to-syntax "|")))
 
+(defvar-local php-mode--propertize-extend-region-current nil
+  "Prevent undesirable recursion in PHP-SYNTAX-PROPERTIZE-EXTEND-REGION")
+
 (defun php-syntax-propertize-extend-region (start end)
   "Extend the propertize region if START or END falls inside a PHP heredoc."
-  (let ((new-start)
-        (new-end))
-    (goto-char start)
-    (when (re-search-backward php-heredoc-start-re nil t)
-      (let ((maybe (point)))
-        (when (and (re-search-forward
-                    (php-heredoc-end-re (match-string 0)) nil t)
-                   (> (point) start))
-          (setq new-start maybe))))
-    (goto-char end)
-    (when (re-search-backward php-heredoc-start-re nil t)
-      (if (re-search-forward
-           (php-heredoc-end-re (match-string 0)) nil t)
-          (when (> (point) end)
-            (setq new-end (point)))
-        (setq new-end (point-max))))
-    (when (or new-start new-end)
-      (cons (or new-start start) (or new-end end)))))
+  (let ((pair (cons start end)))
+    (when (not (member pair php-mode--propertize-extend-region-current))
+      ;; re-search functions may trigger
+      ;; syntax-propertize-extend-region-functions to be called again, which in
+      ;; turn call this to be called again.
+      (push pair php-mode--propertize-extend-region-current)
+      (unwind-protect
+          (let ((new-start)
+                (new-end))
+            (goto-char start)
+            (when (re-search-backward php-heredoc-start-re nil t)
+              (let ((maybe (point)))
+                (when (and (re-search-forward (php-heredoc-end-re (match-string 0)) nil t)
+                           (> (point) start))
+                  (setq new-start maybe))))
+            (goto-char end)
+            (when (re-search-backward php-heredoc-start-re nil t)
+              (if (re-search-forward (php-heredoc-end-re (match-string 0)) nil t)
+                  (when (> (point) end)
+                    (setq new-end (point)))
+                (setq new-end (point-max))))
+            (when (or new-start new-end)
+              (cons (or new-start start) (or new-end end))))
+        ;; Cleanup
+        (setq php-mode--propertize-extend-region-current
+              (delete pair php-mode--propertize-extend-region-current))))))
 
 (easy-menu-define php-mode-menu php-mode-map "PHP Mode Commands"
   (cons "PHP" (c-lang-const c-mode-menu php)))