textprop.c

/* Interface code for dealing with text properties.
   Copyright (C) 1993, 1994, 1995, 1997, 1999, 2000, 2001, 2002, 2003,
                 2004, 2005, 2006, 2007, 2008, 2009 Free Software Foundation, Inc.

This file is part of GNU Emacs.

GNU Emacs is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.

GNU Emacs is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
GNU General Public License for more details.

You should have received a copy of the GNU General Public License
along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */

#include <config.h>
#include "lisp.h"
#include "intervals.h"
#include "buffer.h"
#include "window.h"

#ifndef NULL
#define NULL (void *)0
#endif

/* Test for membership, allowing for t (actually any non-cons) to mean the
   universal set.  */

#define TMEM(sym, set) (CONSP (set) ? ! NILP (Fmemq (sym, set)) : ! NILP (set))


/* NOTES:  previous- and next- property change will have to skip
  zero-length intervals if they are implemented.  This could be done
  inside next_interval and previous_interval.

  set_properties needs to deal with the interval property cache.

  It is assumed that for any interval plist, a property appears
  only once on the list.  Although some code i.e., remove_properties,
  handles the more general case, the uniqueness of properties is
  necessary for the system to remain consistent.  This requirement
  is enforced by the subrs installing properties onto the intervals.  */


/* Types of hooks.  */
Lisp_Object Qmouse_left;
Lisp_Object Qmouse_entered;
Lisp_Object Qpoint_left;
Lisp_Object Qpoint_entered;
Lisp_Object Qcategory;
Lisp_Object Qlocal_map;

/* Visual properties text (including strings) may have.  */
Lisp_Object Qforeground, Qbackground, Qfont, Qunderline, Qstipple;
Lisp_Object Qinvisible, Qread_only, Qintangible, Qmouse_face;
Lisp_Object Qminibuffer_prompt;

/* Sticky properties */
Lisp_Object Qfront_sticky, Qrear_nonsticky;

/* If o1 is a cons whose cdr is a cons, return non-zero and set o2 to
   the o1's cdr.  Otherwise, return zero.  This is handy for
   traversing plists.  */
#define PLIST_ELT_P(o1, o2) (CONSP (o1) && ((o2)=XCDR (o1), CONSP (o2)))

Lisp_Object Vinhibit_point_motion_hooks;
Lisp_Object Vdefault_text_properties;
Lisp_Object Vchar_property_alias_alist;
Lisp_Object Vtext_property_default_nonsticky;

/* verify_interval_modification saves insertion hooks here
   to be run later by report_interval_modification.  */
Lisp_Object interval_insert_behind_hooks;
Lisp_Object interval_insert_in_front_hooks;

static void text_read_only P_ ((Lisp_Object)) NO_RETURN;


/* Signal a `text-read-only' error.  This function makes it easier
   to capture that error in GDB by putting a breakpoint on it.  */

static void
text_read_only (propval)
     Lisp_Object propval;
{
  if (STRINGP (propval))
    xsignal1 (Qtext_read_only, propval);

  xsignal0 (Qtext_read_only);
}



/* Extract the interval at the position pointed to by BEGIN from
   OBJECT, a string or buffer.  Additionally, check that the positions
   pointed to by BEGIN and END are within the bounds of OBJECT, and
   reverse them if *BEGIN is greater than *END.  The objects pointed
   to by BEGIN and END may be integers or markers; if the latter, they
   are coerced to integers.

   When OBJECT is a string, we increment *BEGIN and *END
   to make them origin-one.

   Note that buffer points don't correspond to interval indices.
   For example, point-max is 1 greater than the index of the last
   character.  This difference is handled in the caller, which uses
   the validated points to determine a length, and operates on that.
   Exceptions are Ftext_properties_at, Fnext_property_change, and
   Fprevious_property_change which call this function with BEGIN == END.
   Handle this case specially.

   If FORCE is soft (0), it's OK to return NULL_INTERVAL.  Otherwise,
   create an interval tree for OBJECT if one doesn't exist, provided
   the object actually contains text.  In the current design, if there
   is no text, there can be no text properties.  */

#define soft 0
#define hard 1

INTERVAL
validate_interval_range (object, begin, end, force)
     Lisp_Object object, *begin, *end;
     int force;
{
  register INTERVAL i;
  int searchpos;

  CHECK_STRING_OR_BUFFER (object);
  CHECK_NUMBER_COERCE_MARKER (*begin);
  CHECK_NUMBER_COERCE_MARKER (*end);

  /* If we are asked for a point, but from a subr which operates
     on a range, then return nothing.  */
  if (EQ (*begin, *end) && begin != end)
    return NULL_INTERVAL;

  if (XINT (*begin) > XINT (*end))
    {
      Lisp_Object n;
      n = *begin;
      *begin = *end;
      *end = n;
    }

  if (BUFFERP (object))
    {
      register struct buffer *b = XBUFFER (object);

      if (!(BUF_BEGV (b) <= XINT (*begin) && XINT (*begin) <= XINT (*end)
	    && XINT (*end) <= BUF_ZV (b)))
	args_out_of_range (*begin, *end);
      i = BUF_INTERVALS (b);

      /* If there's no text, there are no properties.  */
      if (BUF_BEGV (b) == BUF_ZV (b))
	return NULL_INTERVAL;

      searchpos = XINT (*begin);
    }
  else
    {
      int len = SCHARS (object);

      if (! (0 <= XINT (*begin) && XINT (*begin) <= XINT (*end)
	     && XINT (*end) <= len))
	args_out_of_range (*begin, *end);
      XSETFASTINT (*begin, XFASTINT (*begin));
      if (begin != end)
	XSETFASTINT (*end, XFASTINT (*end));
      i = STRING_INTERVALS (object);

      if (len == 0)
	return NULL_INTERVAL;

      searchpos = XINT (*begin);
    }

  if (NULL_INTERVAL_P (i))
    return (force ? create_root_interval (object) : i);

  return find_interval (i, searchpos);
}

/* Validate LIST as a property list.  If LIST is not a list, then
   make one consisting of (LIST nil).  Otherwise, verify that LIST
   is even numbered and thus suitable as a plist.  */

static Lisp_Object
validate_plist (list)
     Lisp_Object list;
{
  if (NILP (list))
    return Qnil;

  if (CONSP (list))
    {
      register int i;
      register Lisp_Object tail;
      for (i = 0, tail = list; CONSP (tail); i++)
	{
	  tail = XCDR (tail);
	  QUIT;
	}
      if (i & 1)
	error ("Odd length text property list");
      return list;
    }

  return Fcons (list, Fcons (Qnil, Qnil));
}

/* Return nonzero if interval I has all the properties,
   with the same values, of list PLIST.  */

static int
interval_has_all_properties (plist, i)
     Lisp_Object plist;
     INTERVAL i;
{
  register Lisp_Object tail1, tail2, sym1;
  register int found;

  /* Go through each element of PLIST.  */
  for (tail1 = plist; CONSP (tail1); tail1 = Fcdr (XCDR (tail1)))
    {
      sym1 = XCAR (tail1);
      found = 0;

      /* Go through I's plist, looking for sym1 */
      for (tail2 = i->plist; CONSP (tail2); tail2 = Fcdr (XCDR (tail2)))
	if (EQ (sym1, XCAR (tail2)))
	  {
	    /* Found the same property on both lists.  If the
	       values are unequal, return zero.  */
	    if (! EQ (Fcar (XCDR (tail1)), Fcar (XCDR (tail2))))
	      return 0;

	    /* Property has same value on both lists;  go to next one.  */
	    found = 1;
	    break;
	  }

      if (! found)
	return 0;
    }

  return 1;
}

/* Return nonzero if the plist of interval I has any of the
   properties of PLIST, regardless of their values.  */

static INLINE int
interval_has_some_properties (plist, i)
     Lisp_Object plist;
     INTERVAL i;
{
  register Lisp_Object tail1, tail2, sym;

  /* Go through each element of PLIST.  */
  for (tail1 = plist; CONSP (tail1); tail1 = Fcdr (XCDR (tail1)))
    {
      sym = XCAR (tail1);

      /* Go through i's plist, looking for tail1 */
      for (tail2 = i->plist; CONSP (tail2); tail2 = Fcdr (XCDR (tail2)))
	if (EQ (sym, XCAR (tail2)))
	  return 1;
    }

  return 0;
}

/* Return nonzero if the plist of interval I has any of the
   property names in LIST, regardless of their values.  */

static INLINE int
interval_has_some_properties_list (list, i)
     Lisp_Object list;
     INTERVAL i;
{
  register Lisp_Object tail1, tail2, sym;

  /* Go through each element of LIST.  */
  for (tail1 = list; CONSP (tail1); tail1 = XCDR (tail1))
    {
      sym = Fcar (tail1);

      /* Go through i's plist, looking for tail1 */
      for (tail2 = i->plist; CONSP (tail2); tail2 = XCDR (XCDR (tail2)))
	if (EQ (sym, XCAR (tail2)))
	  return 1;
    }

  return 0;
}

/* Changing the plists of individual intervals.  */

/* Return the value of PROP in property-list PLIST, or Qunbound if it
   has none.  */
static Lisp_Object
property_value (plist, prop)
     Lisp_Object plist, prop;
{
  Lisp_Object value;

  while (PLIST_ELT_P (plist, value))
    if (EQ (XCAR (plist), prop))
      return XCAR (value);
    else
      plist = XCDR (value);

  return Qunbound;
}

/* Set the properties of INTERVAL to PROPERTIES,
   and record undo info for the previous values.
   OBJECT is the string or buffer that INTERVAL belongs to.  */

static void
set_properties (properties, interval, object)
     Lisp_Object properties, object;
     INTERVAL interval;
{
  Lisp_Object sym, value;

  if (BUFFERP (object))
    {
      /* For each property in the old plist which is missing from PROPERTIES,
	 or has a different value in PROPERTIES, make an undo record.  */
      for (sym = interval->plist;
	   PLIST_ELT_P (sym, value);
	   sym = XCDR (value))
	if (! EQ (property_value (properties, XCAR (sym)),
		  XCAR (value)))
	  {
	    record_property_change (interval->position, LENGTH (interval),
				    XCAR (sym), XCAR (value),
				    object);
	  }

      /* For each new property that has no value at all in the old plist,
	 make an undo record binding it to nil, so it will be removed.  */
      for (sym = properties;
	   PLIST_ELT_P (sym, value);
	   sym = XCDR (value))
	if (EQ (property_value (interval->plist, XCAR (sym)), Qunbound))
	  {
	    record_property_change (interval->position, LENGTH (interval),
				    XCAR (sym), Qnil,
				    object);
	  }
    }

  /* Store new properties.  */
  interval->plist = Fcopy_sequence (properties);
}

/* Add the properties of PLIST to the interval I, or set
   the value of I's property to the value of the property on PLIST
   if they are different.

   OBJECT should be the string or buffer the interval is in.

   Return nonzero if this changes I (i.e., if any members of PLIST
   are actually added to I's plist) */

static int
add_properties (plist, i, object)
     Lisp_Object plist;
     INTERVAL i;
     Lisp_Object object;
{
  Lisp_Object tail1, tail2, sym1, val1;
  register int changed = 0;
  register int found;
  struct gcpro gcpro1, gcpro2, gcpro3;

  tail1 = plist;
  sym1 = Qnil;
  val1 = Qnil;
  /* No need to protect OBJECT, because we can GC only in the case
     where it is a buffer, and live buffers are always protected.
     I and its plist are also protected, via OBJECT.  */
  GCPRO3 (tail1, sym1, val1);

  /* Go through each element of PLIST.  */
  for (tail1 = plist; CONSP (tail1); tail1 = Fcdr (XCDR (tail1)))
    {
      sym1 = XCAR (tail1);
      val1 = Fcar (XCDR (tail1));
      found = 0;

      /* Go through I's plist, looking for sym1 */
      for (tail2 = i->plist; CONSP (tail2); tail2 = Fcdr (XCDR (tail2)))
	if (EQ (sym1, XCAR (tail2)))
	  {
	    /* No need to gcpro, because tail2 protects this
	       and it must be a cons cell (we get an error otherwise).  */
	    register Lisp_Object this_cdr;

	    this_cdr = XCDR (tail2);
	    /* Found the property.  Now check its value.  */
	    found = 1;

	    /* The properties have the same value on both lists.
	       Continue to the next property.  */
	    if (EQ (val1, Fcar (this_cdr)))
	      break;

	    /* Record this change in the buffer, for undo purposes.  */
	    if (BUFFERP (object))
	      {
		record_property_change (i->position, LENGTH (i),
					sym1, Fcar (this_cdr), object);
	      }

	    /* I's property has a different value -- change it */
	    Fsetcar (this_cdr, val1);
	    changed++;
	    break;
	  }

      if (! found)
	{
	  /* Record this change in the buffer, for undo purposes.  */
	  if (BUFFERP (object))
	    {
	      record_property_change (i->position, LENGTH (i),
				      sym1, Qnil, object);
	    }
	  i->plist = Fcons (sym1, Fcons (val1, i->plist));
	  changed++;
	}
    }

  UNGCPRO;

  return changed;
}

/* For any members of PLIST, or LIST,
   which are properties of I, remove them from I's plist.
   (If PLIST is non-nil, use that, otherwise use LIST.)
   OBJECT is the string or buffer containing I.  */

static int
remove_properties (plist, list, i, object)
     Lisp_Object plist, list;
     INTERVAL i;
     Lisp_Object object;
{
  register Lisp_Object tail1, tail2, sym, current_plist;
  register int changed = 0;

  /* Nonzero means tail1 is a plist, otherwise it is a list.  */
  int use_plist;

  current_plist = i->plist;

  if (! NILP (plist))
    tail1 = plist, use_plist = 1;
  else
    tail1 = list, use_plist = 0;

  /* Go through each element of LIST or PLIST.  */
  while (CONSP (tail1))
    {
      sym = XCAR (tail1);

      /* First, remove the symbol if it's at the head of the list */
      while (CONSP (current_plist) && EQ (sym, XCAR (current_plist)))
	{
	  if (BUFFERP (object))
	    record_property_change (i->position, LENGTH (i),
				    sym, XCAR (XCDR (current_plist)),
				    object);

	  current_plist = XCDR (XCDR (current_plist));
	  changed++;
	}

      /* Go through I's plist, looking for SYM.  */
      tail2 = current_plist;
      while (! NILP (tail2))
	{
	  register Lisp_Object this;
	  this = XCDR (XCDR (tail2));
	  if (CONSP (this) && EQ (sym, XCAR (this)))
	    {
	      if (BUFFERP (object))
		record_property_change (i->position, LENGTH (i),
					sym, XCAR (XCDR (this)), object);

	      Fsetcdr (XCDR (tail2), XCDR (XCDR (this)));
	      changed++;
	    }
	  tail2 = this;
	}

      /* Advance thru TAIL1 one way or the other.  */
      tail1 = XCDR (tail1);
      if (use_plist && CONSP (tail1))
	tail1 = XCDR (tail1);
    }

  if (changed)
    i->plist = current_plist;
  return changed;
}

#if 0
/* Remove all properties from interval I.  Return non-zero
   if this changes the interval.  */

static INLINE int
erase_properties (i)
     INTERVAL i;
{
  if (NILP (i->plist))
    return 0;

  i->plist = Qnil;
  return 1;
}
#endif

/* Returns the interval of POSITION in OBJECT.
   POSITION is BEG-based.  */

INTERVAL
interval_of (position, object)
     int position;
     Lisp_Object object;
{
  register INTERVAL i;
  int beg, end;

  if (NILP (object))
    XSETBUFFER (object, current_buffer);
  else if (EQ (object, Qt))
    return NULL_INTERVAL;

  CHECK_STRING_OR_BUFFER (object);

  if (BUFFERP (object))
    {
      register struct buffer *b = XBUFFER (object);

      beg = BUF_BEGV (b);
      end = BUF_ZV (b);
      i = BUF_INTERVALS (b);
    }
  else
    {
      beg = 0;
      end = SCHARS (object);
      i = STRING_INTERVALS (object);
    }

  if (!(beg <= position && position <= end))
    args_out_of_range (make_number (position), make_number (position));
  if (beg == end || NULL_INTERVAL_P (i))
    return NULL_INTERVAL;

  return find_interval (i, position);
}

DEFUN ("text-properties-at", Ftext_properties_at,
       Stext_properties_at, 1, 2, 0,
       doc: /* Return the list of properties of the character at POSITION in OBJECT.
If the optional second argument OBJECT is a buffer (or nil, which means
the current buffer), POSITION is a buffer position (integer or marker).
If OBJECT is a string, POSITION is a 0-based index into it.
If POSITION is at the end of OBJECT, the value is nil.  */)
     (position, object)
     Lisp_Object position, object;
{
  register INTERVAL i;

  if (NILP (object))
    XSETBUFFER (object, current_buffer);

  i = validate_interval_range (object, &position, &position, soft);
  if (NULL_INTERVAL_P (i))
    return Qnil;
  /* If POSITION is at the end of the interval,
     it means it's the end of OBJECT.
     There are no properties at the very end,
     since no character follows.  */
  if (XINT (position) == LENGTH (i) + i->position)
    return Qnil;

  return i->plist;
}

DEFUN ("get-text-property", Fget_text_property, Sget_text_property, 2, 3, 0,
       doc: /* Return the value of POSITION's property PROP, in OBJECT.
OBJECT is optional and defaults to the current buffer.
If POSITION is at the end of OBJECT, the value is nil.  */)
     (position, prop, object)
     Lisp_Object position, object;
     Lisp_Object prop;
{
  return textget (Ftext_properties_at (position, object), prop);
}

/* Return the value of char's property PROP, in OBJECT at POSITION.
   OBJECT is optional and defaults to the current buffer.
   If OVERLAY is non-0, then in the case that the returned property is from
   an overlay, the overlay found is returned in *OVERLAY, otherwise nil is
   returned in *OVERLAY.
   If POSITION is at the end of OBJECT, the value is nil.
   If OBJECT is a buffer, then overlay properties are considered as well as
   text properties.
   If OBJECT is a window, then that window's buffer is used, but
   window-specific overlays are considered only if they are associated
   with OBJECT. */
Lisp_Object
get_char_property_and_overlay (position, prop, object, overlay)
     Lisp_Object position, object;
     register Lisp_Object prop;
     Lisp_Object *overlay;
{
  struct window *w = 0;

  CHECK_NUMBER_COERCE_MARKER (position);

  if (NILP (object))
    XSETBUFFER (object, current_buffer);

  if (WINDOWP (object))
    {
      w = XWINDOW (object);
      object = w->buffer;
    }
  if (BUFFERP (object))
    {
      int noverlays;
      Lisp_Object *overlay_vec;
      struct buffer *obuf = current_buffer;

      if (XINT (position) < BUF_BEGV (XBUFFER (object))
	  || XINT (position) > BUF_ZV (XBUFFER (object)))
	xsignal1 (Qargs_out_of_range, position);

      set_buffer_temp (XBUFFER (object));

      GET_OVERLAYS_AT (XINT (position), overlay_vec, noverlays, NULL, 0);
      noverlays = sort_overlays (overlay_vec, noverlays, w);

      set_buffer_temp (obuf);

      /* Now check the overlays in order of decreasing priority.  */
      while (--noverlays >= 0)
	{
	  Lisp_Object tem = Foverlay_get (overlay_vec[noverlays], prop);
	  if (!NILP (tem))
	    {
	      if (overlay)
		/* Return the overlay we got the property from.  */
		*overlay = overlay_vec[noverlays];
	      return tem;
	    }
	}
    }

  if (overlay)
    /* Indicate that the return value is not from an overlay.  */
    *overlay = Qnil;

  /* Not a buffer, or no appropriate overlay, so fall through to the
     simpler case.  */
  return Fget_text_property (position, prop, object);
}

DEFUN ("get-char-property", Fget_char_property, Sget_char_property, 2, 3, 0,
       doc: /* Return the value of POSITION's property PROP, in OBJECT.
Both overlay properties and text properties are checked.
OBJECT is optional and defaults to the current buffer.
If POSITION is at the end of OBJECT, the value is nil.
If OBJECT is a buffer, then overlay properties are considered as well as
text properties.
If OBJECT is a window, then that window's buffer is used, but window-specific
overlays are considered only if they are associated with OBJECT.  */)
     (position, prop, object)
     Lisp_Object position, object;
     register Lisp_Object prop;
{
  return get_char_property_and_overlay (position, prop, object, 0);
}

DEFUN ("get-char-property-and-overlay", Fget_char_property_and_overlay,
       Sget_char_property_and_overlay, 2, 3, 0,
       doc: /* Like `get-char-property', but with extra overlay information.
The value is a cons cell.  Its car is the return value of `get-char-property'
with the same arguments--that is, the value of POSITION's property
PROP in OBJECT.  Its cdr is the overlay in which the property was
found, or nil, if it was found as a text property or not found at all.

OBJECT is optional and defaults to the current buffer.  OBJECT may be
a string, a buffer or a window.  For strings, the cdr of the return
value is always nil, since strings do not have overlays.  If OBJECT is
a window, then that window's buffer is used, but window-specific
overlays are considered only if they are associated with OBJECT.  If
POSITION is at the end of OBJECT, both car and cdr are nil.  */)
     (position, prop, object)
     Lisp_Object position, object;
     register Lisp_Object prop;
{
  Lisp_Object overlay;
  Lisp_Object val
    = get_char_property_and_overlay (position, prop, object, &overlay);
  return Fcons (val, overlay);
}


DEFUN ("next-char-property-change", Fnext_char_property_change,
       Snext_char_property_change, 1, 2, 0,
       doc: /* Return the position of next text property or overlay change.
This scans characters forward in the current buffer from POSITION till
it finds a change in some text property, or the beginning or end of an
overlay, and returns the position of that.
If none is found up to (point-max), the function returns (point-max).

If the optional second argument LIMIT is non-nil, don't search
past position LIMIT; return LIMIT if nothing is found before LIMIT.
LIMIT is a no-op if it is greater than (point-max).  */)
     (position, limit)
     Lisp_Object position, limit;
{
  Lisp_Object temp;

  temp = Fnext_overlay_change (position);
  if (! NILP (limit))
    {
      CHECK_NUMBER_COERCE_MARKER (limit);
      if (XINT (limit) < XINT (temp))
	temp = limit;
    }
  return Fnext_property_change (position, Qnil, temp);
}

DEFUN ("previous-char-property-change", Fprevious_char_property_change,
       Sprevious_char_property_change, 1, 2, 0,
       doc: /* Return the position of previous text property or overlay change.
Scans characters backward in the current buffer from POSITION till it
finds a change in some text property, or the beginning or end of an
overlay, and returns the position of that.
If none is found since (point-min), the function returns (point-min).

If the optional second argument LIMIT is non-nil, don't search
past position LIMIT; return LIMIT if nothing is found before LIMIT.
LIMIT is a no-op if it is less than (point-min).  */)
     (position, limit)
     Lisp_Object position, limit;
{
  Lisp_Object temp;

  temp = Fprevious_overlay_change (position);
  if (! NILP (limit))
    {
      CHECK_NUMBER_COERCE_MARKER (limit);
      if (XINT (limit) > XINT (temp))
	temp = limit;
    }
  return Fprevious_property_change (position, Qnil, temp);
}


DEFUN ("next-single-char-property-change", Fnext_single_char_property_change,
       Snext_single_char_property_change, 2, 4, 0,
       doc: /* Return the position of next text property or overlay change for a specific property.
Scans characters forward from POSITION till it finds
a change in the PROP property, then returns the position of the change.
If the optional third argument OBJECT is a buffer (or nil, which means
the current buffer), POSITION is a buffer position (integer or marker).
If OBJECT is a string, POSITION is a 0-based index into it.

In a string, scan runs to the end of the string.
In a buffer, it runs to (point-max), and the value cannot exceed that.

The property values are compared with `eq'.
If the property is constant all the way to the end of OBJECT, return the
last valid position in OBJECT.
If the optional fourth argument LIMIT is non-nil, don't search
past position LIMIT; return LIMIT if nothing is found before LIMIT.  */)
     (position, prop, object, limit)
     Lisp_Object prop, position, object, limit;
{
  if (STRINGP (object))
    {
      position = Fnext_single_property_change (position, prop, object, limit);
      if (NILP (position))
	{
	  if (NILP (limit))
	    position = make_number (SCHARS (object));
	  else
	    {
	      CHECK_NUMBER (limit);
	      position = limit;
	    }
	}
    }
  else
    {
      Lisp_Object initial_value, value;
      int count = SPECPDL_INDEX ();

      if (! NILP (object))
	CHECK_BUFFER (object);

      if (BUFFERP (object) && current_buffer != XBUFFER (object))
	{
	  record_unwind_protect (Fset_buffer, Fcurrent_buffer ());
	  Fset_buffer (object);
	}

      CHECK_NUMBER_COERCE_MARKER (position);

      initial_value = Fget_char_property (position, prop, object);

      if (NILP (limit))
	XSETFASTINT (limit, ZV);
      else
	CHECK_NUMBER_COERCE_MARKER (limit);

      if (XFASTINT (position) >= XFASTINT (limit))
	{
	  position = limit;
	  if (XFASTINT (position) > ZV)
	    XSETFASTINT (position, ZV);
	}
      else
	while (1)
	  {
	    position = Fnext_char_property_change (position, limit);
	    if (XFASTINT (position) >= XFASTINT (limit))
	      {
		position = limit;
		break;
	      }

	    value = Fget_char_property (position, prop, object);
	    if (!EQ (value, initial_value))
	      break;
	  }

      unbind_to (count, Qnil);
    }

  return position;
}

DEFUN ("previous-single-char-property-change",
       Fprevious_single_char_property_change,
       Sprevious_single_char_property_change, 2, 4, 0,
       doc: /* Return the position of previous text property or overlay change for a specific property.
Scans characters backward from POSITION till it finds
a change in the PROP property, then returns the position of the change.
If the optional third argument OBJECT is a buffer (or nil, which means
the current buffer), POSITION is a buffer position (integer or marker).
If OBJECT is a string, POSITION is a 0-based index into it.

In a string, scan runs to the start of the string.
In a buffer, it runs to (point-min), and the value cannot be less than that.

The property values are compared with `eq'.
If the property is constant all the way to the start of OBJECT, return the
first valid position in OBJECT.
If the optional fourth argument LIMIT is non-nil, don't search
back past position LIMIT; return LIMIT if nothing is found before LIMIT.  */)
     (position, prop, object, limit)
     Lisp_Object prop, position, object, limit;
{
  if (STRINGP (object))
    {
      position = Fprevious_single_property_change (position, prop, object, limit);
      if (NILP (position))
	{
	  if (NILP (limit))
	    position = make_number (0);
	  else
	    {
	      CHECK_NUMBER (limit);
	      position = limit;
	    }
	}
    }
  else
    {
      int count = SPECPDL_INDEX ();

      if (! NILP (object))
	CHECK_BUFFER (object);

      if (BUFFERP (object) && current_buffer != XBUFFER (object))
	{
	  record_unwind_protect (Fset_buffer, Fcurrent_buffer ());
	  Fset_buffer (object);
	}

      CHECK_NUMBER_COERCE_MARKER (position);

      if (NILP (limit))
	XSETFASTINT (limit, BEGV);
      else
	CHECK_NUMBER_COERCE_MARKER (limit);

      if (XFASTINT (position) <= XFASTINT (limit))
	{
	  position = limit;
	  if (XFASTINT (position) < BEGV)
	    XSETFASTINT (position, BEGV);
	}
      else
	{
	  Lisp_Object initial_value
	    = Fget_char_property (make_number (XFASTINT (position) - 1),
				  prop, object);

	  while (1)
	    {
	      position = Fprevious_char_property_change (position, limit);

	      if (XFASTINT (position) <= XFASTINT (limit))
		{
		  position = limit;
		  break;
		}
	      else
		{
		  Lisp_Object value
		    = Fget_char_property (make_number (XFASTINT (position) - 1),
					  prop, object);

		  if (!EQ