Path: utzoo!utgpu!watmath!uunet!tut.cis.ohio-state.edu!PURDUE.EDU!trinkle
From: trinkle@PURDUE.EDU
Newsgroups: gnu.emacs.bug
Subject: Possible infinite loop in forward-paragraph (GNU Emacs 18.52)
Message-ID: <8901231725.AA03733@bors.cs.purdue.edu>
Date: 23 Jan 89 17:25:04 GMT
Sender: daemon@tut.cis.ohio-state.edu
Distribution: gnu
Organization: GNUs Not Usenet
Lines: 83


Index:
	lisp/paragraphs.el GNU Emacs 18.52

Description:
	This bug exists in 18.51 and 18.52 GNU Emacs.  If, in tex-mode,
	you have a buffer with nothing by paragraph-separaters,
	(backward-paragraph) will go into an infinite loop.

Repeat-By:
	Create a file foo.tex with the following contents:

------------------------------cut here------------------------------
\begin{..}
\item ...
\item ...
\item ...
\item ...
\end{...}

\begin{..}
\item ...
\item ...
\item ...
\item ...
\end{...}

\begin{..}
\item ...
\item ...
\item ...
\item ...
\end{...}
------------------------------cut here------------------------------

	Start GNU Emacs and visit foo.tex.  This should load tex-mode.
	Go to the end of the buffer and do a backward-paragraph
	(probably bound to META-[).  GNU Emacs will go into an
	infinite loop.  The problem is in forward-paragraph when doing
	a backward-paragraph search (arg = -1). If a paragraph-start
	match is found, then there is a while loop that keeps doing a
	(forward-line 1) while (looking-at paragraph-separate).
	Unfortunately there is no check for (eobp).  In a file with
	nothing but paragraph-separate lines, this will cause an
	infinite loop.

Fix:
	If there is a check for (eobp), things seem to work just fine.
	This garuantees that the while loop will never be an infinite
	loop. Replace

  		 (not (bobp)))
  	      (re-search-backward paragraph-start nil t))
  	    ;; Found one.
  	    (progn
! 	      (while (looking-at paragraph-separate)
  		(forward-line 1))
  	      (if (eq (char-after (- (point) 2)) ?\n)
  		  (forward-line -1)))
  	  ;; No starter or separator line => use buffer beg.
  	  (goto-char (point-min))))
        (setq arg (1+ arg)))
      (while (> arg 0)

	with

  		 (not (bobp)))
  	      (re-search-backward paragraph-start nil t))
  	    ;; Found one.
  	    (progn
! 	      (while (and (looking-at paragraph-separate) (not (eobp)))
  		(forward-line 1))
  	      (if (eq (char-after (- (point) 2)) ?\n)
  		  (forward-line -1)))
  	  ;; No starter or separator line => use buffer beg.
  	  (goto-char (point-min))))
        (setq arg (1+ arg)))
      (while (> arg 0)

Daniel Trinkle			trinkle@cs.purdue.edu
Dept. of Computer Sciences	{backbone}!purdue!trinkle
Purdue University		317-494-7844
West Lafayette, IN 47907