bug#4512: 23.1; html-mode C-c C-f on runs of <P>

[Kevin Ryde]

In a html-mode buffer with runs of successive <P> tags, like

    (progn
      (switch-to-buffer "foo")
      (dotimes (i 5000) (insert (format "<p> abc\n" i)))
      (goto-char (point-min))
      (html-mode))

pressing C-c C-f gets an error

    Variable binding depth exceeds max-specpdl-size

instead of going forward.  The way C-c C-f `sgml-skip-tag-forward'
requires a closing </P> etc is no doubt what's wanted for sgml, but for
the looser html it'd be good if it recognised some closing tags are
optional.

--- sgml-mode.el.~1.140.~       2009-08-22 07:48:30.000000000 +1000
+++ sgml-mode.el        2009-09-22 08:42:35.000000000 +1000
@@ -840,6 +840,14 @@
   ;; FIXME: Use sgml-get-context or something similar.
   ;; It currently might jump to an unrelated </P> if the <P>
   ;; we're skipping has no matching </P>.
+
+  ;; FIXME: For html-mode a closing </P> is optional, and others like
+  ;; </TR> similarly.  This code or some `html-skip-tag-forward'
+  ;; should recognise a new <P> ends a previous <P>, and with some
+  ;; precedence levels among <TR>, <TD>, <P>, etc.  Currently the
+  ;; recursion in the `while' below means runs of successive <P> error
+  ;; out exceeding max-specpdl-size.
+  
   (let ((return t))
     (with-syntax-table sgml-tag-syntax-table
       (while (>= arg 1)


In GNU Emacs 23.1.1 (i486-pc-linux-gnu, GTK+ Version 2.16.5)
 of 2009-08-03 on raven, modified by Debian
configured using `configure  '--build=i486-linux-gnu' '--host=i486-linux-gnu' 
'--prefix=/usr' '--sharedstatedir=/var/lib' '--libexecdir=/usr/lib' 
'--localstatedir=/var/lib' '--infodir=/usr/share/info' 
'--mandir=/usr/share/man' '--with-pop=yes' 
'--enable-locallisppath=/etc/emacs23:/etc/emacs:/usr/local/share/emacs/23.1/site-lisp:/usr/local/share/emacs/site-lisp:/usr/share/emacs/23.1/site-lisp:/usr/share/emacs/site-lisp:/usr/share/emacs/23.1/leim'
 '--with-x=yes' '--with-x-toolkit=gtk' '--with-toolkit-scroll-bars' 
'build_alias=i486-linux-gnu' 'host_alias=i486-linux-gnu' 'CFLAGS=-DDEBIAN -g 
-O2' 'LDFLAGS=-g' 'CPPFLAGS=''

Important settings:
  value of $LC_ALL: nil
  value of $LC_COLLATE: nil
  value of $LC_CTYPE: nil
  value of $LC_MESSAGES: nil
  value of $LC_MONETARY: nil
  value of $LC_NUMERIC: nil
  value of $LC_TIME: nil
  value of $LANG: en_AU
  value of $XMODIFIERS: nil
  locale-coding-system: iso-latin-1-unix
  default-enable-multibyte-characters: t