buffer.c 197 KB
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/* Buffer manipulation primitives for GNU Emacs.
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Copyright (C) 1985-1989, 1993-1995, 1997-2012 Free Software Foundation, Inc.
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This file is part of GNU Emacs.

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GNU Emacs is free software: you can redistribute it and/or modify
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it under the terms of the GNU General Public License as published by
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the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
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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
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along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
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#include <config.h>
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#include <sys/types.h>
#include <sys/stat.h>
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#include <sys/param.h>
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#include <errno.h>
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#include <stdio.h>
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#include <setjmp.h>
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#include <unistd.h>
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#include <verify.h>

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#include "lisp.h"
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#include "intervals.h"
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#include "window.h"
#include "commands.h"
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#include "character.h"
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#include "buffer.h"
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#include "region-cache.h"
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#include "indent.h"
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#include "blockinput.h"
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#include "keyboard.h"
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#include "keymap.h"
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#include "frame.h"
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struct buffer *current_buffer;		/* the current buffer */

/* First buffer in chain of all buffers (in reverse order of creation).
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   Threaded through ->header.next.buffer.  */
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struct buffer *all_buffers;

/* This structure holds the default values of the buffer-local variables
   defined with DEFVAR_PER_BUFFER, that have special slots in each buffer.
   The default value occupies the same slot in this structure
   as an individual buffer's value occupies in that buffer.
   Setting the default value also goes through the alist of buffers
   and stores into each buffer that does not say it has a local value.  */

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DECL_ALIGN (struct buffer, buffer_defaults);
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/* A Lisp_Object pointer to the above, used for staticpro */

static Lisp_Object Vbuffer_defaults;

/* This structure marks which slots in a buffer have corresponding
   default values in buffer_defaults.
   Each such slot has a nonzero value in this structure.
   The value has only one nonzero bit.

   When a buffer has its own local value for a slot,
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   the entry for that slot (found in the same slot in this structure)
   is turned on in the buffer's local_flags array.
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   If a slot in this structure is -1, then even though there may
   be a DEFVAR_PER_BUFFER for the slot, there is no default value for it;
   and the corresponding slot in buffer_defaults is not used.

   If a slot in this structure corresponding to a DEFVAR_PER_BUFFER is
   zero, that is a bug */

struct buffer buffer_local_flags;

/* This structure holds the names of symbols whose values may be
   buffer-local.  It is indexed and accessed in the same way as the above. */

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DECL_ALIGN (struct buffer, buffer_local_symbols);

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/* A Lisp_Object pointer to the above, used for staticpro */
static Lisp_Object Vbuffer_local_symbols;

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/* Return the symbol of the per-buffer variable at offset OFFSET in
   the buffer structure.  */

#define PER_BUFFER_SYMBOL(OFFSET) \
      (*(Lisp_Object *)((OFFSET) + (char *) &buffer_local_symbols))

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/* Maximum length of an overlay vector.  */
#define OVERLAY_COUNT_MAX						\
  ((ptrdiff_t) min (MOST_POSITIVE_FIXNUM,				\
		    min (PTRDIFF_MAX, SIZE_MAX) / sizeof (Lisp_Object)))

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/* Flags indicating which built-in buffer-local variables
   are permanent locals.  */
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static char buffer_permanent_local_flags[MAX_PER_BUFFER_VARS];
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/* Number of per-buffer variables used.  */

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int last_per_buffer_idx;
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static Lisp_Object Fset_buffer_major_mode (Lisp_Object);
static Lisp_Object Fdelete_overlay (Lisp_Object);
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static void call_overlay_mod_hooks (Lisp_Object list, Lisp_Object overlay,
                                    int after, Lisp_Object arg1,
                                    Lisp_Object arg2, Lisp_Object arg3);
static void swap_out_buffer_local_variables (struct buffer *b);
static void reset_buffer_local_variables (struct buffer *b, int permanent_too);
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/* Alist of all buffer names vs the buffers. */
/* This used to be a variable, but is no longer,
 to prevent lossage due to user rplac'ing this alist or its elements.  */
Lisp_Object Vbuffer_alist;

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static Lisp_Object Qkill_buffer_query_functions;
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/* Hook run before changing a major mode.  */
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static Lisp_Object Qchange_major_mode_hook;
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Lisp_Object Qfirst_change_hook;
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Lisp_Object Qbefore_change_functions;
Lisp_Object Qafter_change_functions;
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static Lisp_Object Qfundamental_mode, Qmode_class, Qpermanent_local;
static Lisp_Object Qpermanent_local_hook;
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static Lisp_Object Qprotected_field;
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static Lisp_Object QSFundamental;	/* A string "Fundamental" */
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static Lisp_Object Qkill_buffer_hook;
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static Lisp_Object Qbuffer_list_update_hook;
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static Lisp_Object Qget_file_buffer;
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static Lisp_Object Qoverlayp;
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Lisp_Object Qpriority, Qbefore_string, Qafter_string;
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static Lisp_Object Qevaporate;
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Lisp_Object Qmodification_hooks;
Lisp_Object Qinsert_in_front_hooks;
Lisp_Object Qinsert_behind_hooks;

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static void alloc_buffer_text (struct buffer *, ptrdiff_t);
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static void free_buffer_text (struct buffer *b);
static struct Lisp_Overlay * copy_overlays (struct buffer *, struct Lisp_Overlay *);
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static void modify_overlay (struct buffer *, ptrdiff_t, ptrdiff_t);
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static Lisp_Object buffer_lisp_local_variables (struct buffer *);
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/* For debugging; temporary.  See set_buffer_internal.  */
/* Lisp_Object Qlisp_mode, Vcheck_symbol; */

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void
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nsberror (Lisp_Object spec)
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{
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  if (STRINGP (spec))
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    error ("No buffer named %s", SDATA (spec));
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  error ("Invalid buffer argument");
}

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DEFUN ("buffer-live-p", Fbuffer_live_p, Sbuffer_live_p, 1, 1, 0,
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       doc: /* Return non-nil if OBJECT is a buffer which has not been killed.
Value is nil if OBJECT is not a buffer or if it has been killed.  */)
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  (Lisp_Object object)
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{
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  return ((BUFFERP (object) && ! NILP (BVAR (XBUFFER (object), name)))
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	  ? Qt : Qnil);
}

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DEFUN ("buffer-list", Fbuffer_list, Sbuffer_list, 0, 1, 0,
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       doc: /* Return a list of all existing live buffers.
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If the optional arg FRAME is a frame, we return the buffer list in the
proper order for that frame: the buffers show in FRAME come first,
followed by the rest of the buffers.  */)
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  (Lisp_Object frame)
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{
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  Lisp_Object general;
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  general = Fmapcar (Qcdr, Vbuffer_alist);

  if (FRAMEP (frame))
    {
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      Lisp_Object framelist, prevlist, tail;
      Lisp_Object args[3];
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      CHECK_FRAME (frame);
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      framelist = Fcopy_sequence (XFRAME (frame)->buffer_list);
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      prevlist = Fnreverse (Fcopy_sequence
			    (XFRAME (frame)->buried_buffer_list));
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      /* Remove from GENERAL any buffer that duplicates one in
         FRAMELIST or PREVLIST.  */
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      tail = framelist;
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      while (CONSP (tail))
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	{
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	  general = Fdelq (XCAR (tail), general);
	  tail = XCDR (tail);
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	}
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      tail = prevlist;
      while (CONSP (tail))
	{
	  general = Fdelq (XCAR (tail), general);
	  tail = XCDR (tail);
	}

      args[0] = framelist;
      args[1] = general;
      args[2] = prevlist;
      return Fnconc (3, args);
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    }
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  else
    return general;
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}

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/* Like Fassoc, but use Fstring_equal to compare
   (which ignores text properties),
   and don't ever QUIT.  */

static Lisp_Object
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assoc_ignore_text_properties (register Lisp_Object key, Lisp_Object list)
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{
  register Lisp_Object tail;
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  for (tail = list; CONSP (tail); tail = XCDR (tail))
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    {
      register Lisp_Object elt, tem;
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      elt = XCAR (tail);
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      tem = Fstring_equal (Fcar (elt), key);
      if (!NILP (tem))
	return elt;
    }
  return Qnil;
}

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DEFUN ("get-buffer", Fget_buffer, Sget_buffer, 1, 1, 0,
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       doc: /* Return the buffer named BUFFER-OR-NAME.
BUFFER-OR-NAME must be either a string or a buffer.  If BUFFER-OR-NAME
is a string and there is no buffer with that name, return nil.  If
BUFFER-OR-NAME is a buffer, return it as given.  */)
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  (register Lisp_Object buffer_or_name)
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{
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  if (BUFFERP (buffer_or_name))
    return buffer_or_name;
  CHECK_STRING (buffer_or_name);
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  return Fcdr (assoc_ignore_text_properties (buffer_or_name, Vbuffer_alist));
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}

DEFUN ("get-file-buffer", Fget_file_buffer, Sget_file_buffer, 1, 1, 0,
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       doc: /* Return the buffer visiting file FILENAME (a string).
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The buffer's `buffer-file-name' must match exactly the expansion of FILENAME.
If there is no such live buffer, return nil.
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See also `find-buffer-visiting'.  */)
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  (register Lisp_Object filename)
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{
  register Lisp_Object tail, buf, tem;
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  Lisp_Object handler;

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  CHECK_STRING (filename);
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  filename = Fexpand_file_name (filename, Qnil);

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  /* If the file name has special constructs in it,
     call the corresponding file handler.  */
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  handler = Ffind_file_name_handler (filename, Qget_file_buffer);
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  if (!NILP (handler))
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    {
      Lisp_Object handled_buf = call2 (handler, Qget_file_buffer,
				       filename);
      return BUFFERP (handled_buf) ? handled_buf : Qnil;
    }
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  for (tail = Vbuffer_alist; CONSP (tail); tail = XCDR (tail))
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    {
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      buf = Fcdr (XCAR (tail));
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      if (!BUFFERP (buf)) continue;
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      if (!STRINGP (BVAR (XBUFFER (buf), filename))) continue;
      tem = Fstring_equal (BVAR (XBUFFER (buf), filename), filename);
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      if (!NILP (tem))
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	return buf;
    }
  return Qnil;
}

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Lisp_Object
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get_truename_buffer (register Lisp_Object filename)
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{
  register Lisp_Object tail, buf, tem;

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  for (tail = Vbuffer_alist; CONSP (tail); tail = XCDR (tail))
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    {
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      buf = Fcdr (XCAR (tail));
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      if (!BUFFERP (buf)) continue;
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      if (!STRINGP (BVAR (XBUFFER (buf), file_truename))) continue;
      tem = Fstring_equal (BVAR (XBUFFER (buf), file_truename), filename);
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      if (!NILP (tem))
	return buf;
    }
  return Qnil;
}

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DEFUN ("get-buffer-create", Fget_buffer_create, Sget_buffer_create, 1, 1, 0,
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       doc: /* Return the buffer specified by BUFFER-OR-NAME, creating a new one if needed.
If BUFFER-OR-NAME is a string and a live buffer with that name exists,
return that buffer.  If no such buffer exists, create a new buffer with
that name and return it.  If BUFFER-OR-NAME starts with a space, the new
buffer does not keep undo information.

If BUFFER-OR-NAME is a buffer instead of a string, return it as given,
even if it is dead.  The return value is never nil.  */)
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  (register Lisp_Object buffer_or_name)
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{
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  register Lisp_Object buffer, name;
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  register struct buffer *b;

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  buffer = Fget_buffer (buffer_or_name);
  if (!NILP (buffer))
    return buffer;
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  if (SCHARS (buffer_or_name) == 0)
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    error ("Empty string for buffer name is not allowed");

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  b = allocate_buffer ();
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  /* An ordinary buffer uses its own struct buffer_text.  */
  b->text = &b->own_text;
  b->base_buffer = 0;

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  BUF_GAP_SIZE (b) = 20;
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  BLOCK_INPUT;
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  /* We allocate extra 1-byte at the tail and keep it always '\0' for
     anchoring a search.  */
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  alloc_buffer_text (b, BUF_GAP_SIZE (b) + 1);
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  UNBLOCK_INPUT;
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  if (! BUF_BEG_ADDR (b))
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    buffer_memory_full (BUF_GAP_SIZE (b) + 1);
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  b->pt = BEG;
  b->begv = BEG;
  b->zv = BEG;
  b->pt_byte = BEG_BYTE;
  b->begv_byte = BEG_BYTE;
  b->zv_byte = BEG_BYTE;

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  BUF_GPT (b) = BEG;
  BUF_GPT_BYTE (b) = BEG_BYTE;
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  BUF_Z (b) = BEG;
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  BUF_Z_BYTE (b) = BEG_BYTE;
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  BUF_MODIFF (b) = 1;
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  BUF_CHARS_MODIFF (b) = 1;
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  BUF_OVERLAY_MODIFF (b) = 1;
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  BUF_SAVE_MODIFF (b) = 1;
  BUF_INTERVALS (b) = 0;
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  BUF_UNCHANGED_MODIFIED (b) = 1;
  BUF_OVERLAY_UNCHANGED_MODIFIED (b) = 1;
  BUF_END_UNCHANGED (b) = 0;
  BUF_BEG_UNCHANGED (b) = 0;
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  *(BUF_GPT_ADDR (b)) = *(BUF_Z_ADDR (b)) = 0; /* Put an anchor '\0'.  */
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  b->text->inhibit_shrinking = 0;
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  b->newline_cache = 0;
  b->width_run_cache = 0;
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  BVAR (b, width_table) = Qnil;
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  b->prevent_redisplay_optimizations_p = 1;
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  /* Put this on the chain of all buffers including killed ones.  */
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  b->header.next.buffer = all_buffers;
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  all_buffers = b;

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  /* An ordinary buffer normally doesn't need markers
     to handle BEGV and ZV.  */
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  BVAR (b, pt_marker) = Qnil;
  BVAR (b, begv_marker) = Qnil;
  BVAR (b, zv_marker) = Qnil;
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  name = Fcopy_sequence (buffer_or_name);
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  STRING_SET_INTERVALS (name, NULL_INTERVAL);
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  BVAR (b, name) = name;
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  BVAR (b, undo_list) = (SREF (name, 0) != ' ') ? Qnil : Qt;
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  reset_buffer (b);
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  reset_buffer_local_variables (b, 1);
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  BVAR (b, mark) = Fmake_marker ();
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  BUF_MARKERS (b) = NULL;
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  /* Put this in the alist of all live buffers.  */
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  XSETBUFFER (buffer, b);
  Vbuffer_alist = nconc2 (Vbuffer_alist, Fcons (Fcons (name, buffer), Qnil));
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  /* And run buffer-list-update-hook.  */
  if (!NILP (Vrun_hooks))
    call1 (Vrun_hooks, Qbuffer_list_update_hook);
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  return buffer;
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}

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/* Return a list of overlays which is a copy of the overlay list
   LIST, but for buffer B.  */

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static struct Lisp_Overlay *
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copy_overlays (struct buffer *b, struct Lisp_Overlay *list)
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{
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  Lisp_Object buffer;
  struct Lisp_Overlay *result = NULL, *tail = NULL;
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  XSETBUFFER (buffer, b);

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  for (; list; list = list->next)
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    {
      Lisp_Object overlay, start, end, old_overlay;
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      ptrdiff_t charpos;
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      XSETMISC (old_overlay, list);
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      charpos = marker_position (OVERLAY_START (old_overlay));
      start = Fmake_marker ();
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      Fset_marker (start, make_number (charpos), buffer);
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      XMARKER (start)->insertion_type
	= XMARKER (OVERLAY_START (old_overlay))->insertion_type;

      charpos = marker_position (OVERLAY_END (old_overlay));
      end = Fmake_marker ();
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      Fset_marker (end, make_number (charpos), buffer);
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      XMARKER (end)->insertion_type
	= XMARKER (OVERLAY_END (old_overlay))->insertion_type;

      overlay = allocate_misc ();
      XMISCTYPE (overlay) = Lisp_Misc_Overlay;
      OVERLAY_START (overlay) = start;
      OVERLAY_END (overlay) = end;
      OVERLAY_PLIST (overlay) = Fcopy_sequence (OVERLAY_PLIST (old_overlay));
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      XOVERLAY (overlay)->next = NULL;
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      if (tail)
	tail = tail->next = XOVERLAY (overlay);
      else
	result = tail = XOVERLAY (overlay);
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    }

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  return result;
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}
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/* Clone per-buffer values of buffer FROM.

   Buffer TO gets the same per-buffer values as FROM, with the
   following exceptions: (1) TO's name is left untouched, (2) markers
   are copied and made to refer to TO, and (3) overlay lists are
   copied.  */

static void
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clone_per_buffer_values (struct buffer *from, struct buffer *to)
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{
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  Lisp_Object to_buffer;
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  int offset;

  XSETBUFFER (to_buffer, to);
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  /* buffer-local Lisp variables start at `undo_list',
     tho only the ones from `name' on are GC'd normally.  */
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  for (offset = PER_BUFFER_VAR_OFFSET (FIRST_FIELD_PER_BUFFER);
       offset <= PER_BUFFER_VAR_OFFSET (LAST_FIELD_PER_BUFFER);
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       offset += sizeof (Lisp_Object))
    {
      Lisp_Object obj;

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      /* Don't touch the `name' which should be unique for every buffer.  */
      if (offset == PER_BUFFER_VAR_OFFSET (name))
	continue;

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      obj = PER_BUFFER_VALUE (from, offset);
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      if (MARKERP (obj) && XMARKER (obj)->buffer == from)
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	{
	  struct Lisp_Marker *m = XMARKER (obj);
	  obj = Fmake_marker ();
	  XMARKER (obj)->insertion_type = m->insertion_type;
	  set_marker_both (obj, to_buffer, m->charpos, m->bytepos);
	}

      PER_BUFFER_VALUE (to, offset) = obj;
    }

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  memcpy (to->local_flags, from->local_flags, sizeof to->local_flags);
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  to->overlays_before = copy_overlays (to, from->overlays_before);
  to->overlays_after = copy_overlays (to, from->overlays_after);
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  /* Get (a copy of) the alist of Lisp-level local variables of FROM
     and install that in TO.  */
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  BVAR (to, local_var_alist) = buffer_lisp_local_variables (from);
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}

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/* If buffer B has markers to record PT, BEGV and ZV when it is not
   current, update these markers.  */

static void
record_buffer_markers (struct buffer *b)
{
  if (! NILP (BVAR (b, pt_marker)))
    {
      Lisp_Object buffer;

      eassert (!NILP (BVAR (b, begv_marker)));
      eassert (!NILP (BVAR (b, zv_marker)));

      XSETBUFFER (buffer, b);
      set_marker_both (BVAR (b, pt_marker), buffer, b->pt, b->pt_byte);
      set_marker_both (BVAR (b, begv_marker), buffer, b->begv, b->begv_byte);
      set_marker_both (BVAR (b, zv_marker), buffer, b->zv, b->zv_byte);
    }
}


/* If buffer B has markers to record PT, BEGV and ZV when it is not
   current, fetch these values into B->begv etc.  */

static void
fetch_buffer_markers (struct buffer *b)
{
  if (! NILP (BVAR (b, pt_marker)))
    {
      Lisp_Object m;

      eassert (!NILP (BVAR (b, begv_marker)));
      eassert (!NILP (BVAR (b, zv_marker)));

      m = BVAR (b, pt_marker);
      SET_BUF_PT_BOTH (b, marker_position (m), marker_byte_position (m));

      m = BVAR (b, begv_marker);
      SET_BUF_BEGV_BOTH (b, marker_position (m), marker_byte_position (m));

      m = BVAR (b, zv_marker);
      SET_BUF_ZV_BOTH (b, marker_position (m), marker_byte_position (m));
    }
}


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DEFUN ("make-indirect-buffer", Fmake_indirect_buffer, Smake_indirect_buffer,
       2, 3,
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       "bMake indirect buffer (to buffer): \nBName of indirect buffer: ",
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       doc: /* Create and return an indirect buffer for buffer BASE-BUFFER, named NAME.
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BASE-BUFFER should be a live buffer, or the name of an existing buffer.
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NAME should be a string which is not the name of an existing buffer.
Optional argument CLONE non-nil means preserve BASE-BUFFER's state,
such as major and minor modes, in the indirect buffer.
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CLONE nil means the indirect buffer's state is reset to default values.  */)
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  (Lisp_Object base_buffer, Lisp_Object name, Lisp_Object clone)
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{
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  Lisp_Object buf, tem;
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  struct buffer *b;
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  CHECK_STRING (name);
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  buf = Fget_buffer (name);
  if (!NILP (buf))
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    error ("Buffer name `%s' is in use", SDATA (name));
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  tem = base_buffer;
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  base_buffer = Fget_buffer (base_buffer);
  if (NILP (base_buffer))
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    error ("No such buffer: `%s'", SDATA (tem));
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  if (NILP (BVAR (XBUFFER (base_buffer), name)))
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    error ("Base buffer has been killed");
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  if (SCHARS (name) == 0)
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    error ("Empty string for buffer name is not allowed");

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  b = allocate_buffer ();
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  b->base_buffer = (XBUFFER (base_buffer)->base_buffer
		    ? XBUFFER (base_buffer)->base_buffer
		    : XBUFFER (base_buffer));
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  /* Use the base buffer's text object.  */
  b->text = b->base_buffer->text;

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  b->pt = b->base_buffer->pt;
  b->begv = b->base_buffer->begv;
  b->zv = b->base_buffer->zv;
  b->pt_byte = b->base_buffer->pt_byte;
  b->begv_byte = b->base_buffer->begv_byte;
  b->zv_byte = b->base_buffer->zv_byte;
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  b->newline_cache = 0;
  b->width_run_cache = 0;
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  BVAR (b, width_table) = Qnil;
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  /* Put this on the chain of all buffers including killed ones.  */
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  b->header.next.buffer = all_buffers;
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  all_buffers = b;

  name = Fcopy_sequence (name);
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  STRING_SET_INTERVALS (name, NULL_INTERVAL);
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  BVAR (b, name) = name;
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  reset_buffer (b);
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  reset_buffer_local_variables (b, 1);
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  /* Put this in the alist of all live buffers.  */
  XSETBUFFER (buf, b);
  Vbuffer_alist = nconc2 (Vbuffer_alist, Fcons (Fcons (name, buf), Qnil));

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  BVAR (b, mark) = Fmake_marker ();
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  /* The multibyte status belongs to the base buffer.  */
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  BVAR (b, enable_multibyte_characters) = BVAR (b->base_buffer, enable_multibyte_characters);
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  /* Make sure the base buffer has markers for its narrowing.  */
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  if (NILP (BVAR (b->base_buffer, pt_marker)))
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    {
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      eassert (NILP (BVAR (b->base_buffer, begv_marker)));
      eassert (NILP (BVAR (b->base_buffer, zv_marker)));
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      BVAR (b->base_buffer, pt_marker) = Fmake_marker ();
      set_marker_both (BVAR (b->base_buffer, pt_marker), base_buffer,
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		       b->base_buffer->pt,
		       b->base_buffer->pt_byte);

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      BVAR (b->base_buffer, begv_marker) = Fmake_marker ();
      set_marker_both (BVAR (b->base_buffer, begv_marker), base_buffer,
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		       b->base_buffer->begv,
		       b->base_buffer->begv_byte);

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      BVAR (b->base_buffer, zv_marker) = Fmake_marker ();
      set_marker_both (BVAR (b->base_buffer, zv_marker), base_buffer,
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		       b->base_buffer->zv,
		       b->base_buffer->zv_byte);
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      XMARKER (BVAR (b->base_buffer, zv_marker))->insertion_type = 1;
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    }

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  if (NILP (clone))
    {
      /* Give the indirect buffer markers for its narrowing.  */
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      BVAR (b, pt_marker) = Fmake_marker ();
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      set_marker_both (BVAR (b, pt_marker), buf, b->pt, b->pt_byte);
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      BVAR (b, begv_marker) = Fmake_marker ();
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      set_marker_both (BVAR (b, begv_marker), buf, b->begv, b->begv_byte);
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      BVAR (b, zv_marker) = Fmake_marker ();
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      set_marker_both (BVAR (b, zv_marker), buf, b->zv, b->zv_byte);
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      XMARKER (BVAR (b, zv_marker))->insertion_type = 1;
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    }
  else
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    {
      struct buffer *old_b = current_buffer;

      clone_per_buffer_values (b->base_buffer, b);
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      BVAR (b, filename) = Qnil;
      BVAR (b, file_truename) = Qnil;
      BVAR (b, display_count) = make_number (0);
      BVAR (b, backed_up) = Qnil;
      BVAR (b, auto_save_file_name) = Qnil;
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      set_buffer_internal_1 (b);
      Fset (intern ("buffer-save-without-query"), Qnil);
      Fset (intern ("buffer-file-number"), Qnil);
      Fset (intern ("buffer-stale-function"), Qnil);
      set_buffer_internal_1 (old_b);
    }
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  /* Run buffer-list-update-hook.  */
  if (!NILP (Vrun_hooks))
    call1 (Vrun_hooks, Qbuffer_list_update_hook);

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  return buf;
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}

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void
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delete_all_overlays (struct buffer *b)
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{
  Lisp_Object overlay;

  /* `reset_buffer' blindly sets the list of overlays to NULL, so we
     have to empty the list, otherwise we end up with overlays that
     think they belong to this buffer while the buffer doesn't know about
     them any more.  */
  while (b->overlays_before)
    {
      XSETMISC (overlay, b->overlays_before);
      Fdelete_overlay (overlay);
    }
  while (b->overlays_after)
    {
      XSETMISC (overlay, b->overlays_after);
      Fdelete_overlay (overlay);
    }
  eassert (b->overlays_before == NULL);
  eassert (b->overlays_after == NULL);
}

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/* Reinitialize everything about a buffer except its name and contents
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   and local variables.
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   If called on an already-initialized buffer, the list of overlays
   should be deleted before calling this function, otherwise we end up
   with overlays that claim to belong to the buffer but the buffer
   claims it doesn't belong to it.  */
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void
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reset_buffer (register struct buffer *b)
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{
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  BVAR (b, filename) = Qnil;
  BVAR (b, file_truename) = Qnil;
  BVAR (b, directory) = (current_buffer) ? BVAR (current_buffer, directory) : Qnil;
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  EMACS_SET_SECS_NSECS (b->modtime, 0, UNKNOWN_MODTIME_NSECS);
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  b->modtime_size = -1;
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  XSETFASTINT (BVAR (b, save_length), 0);
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  b->last_window_start = 1;
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  /* It is more conservative to start out "changed" than "unchanged".  */
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  b->clip_changed = 0;
  b->prevent_redisplay_optimizations_p = 1;
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  BVAR (b, backed_up) = Qnil;
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  BUF_AUTOSAVE_MODIFF (b) = 0;
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  b->auto_save_failure_time = 0;
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  BVAR (b, auto_save_file_name) = Qnil;
  BVAR (b, read_only) = Qnil;
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  b->overlays_before = NULL;
  b->overlays_after = NULL;
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  b->overlay_center = BEG;
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  BVAR (b, mark_active) = Qnil;
  BVAR (b, point_before_scroll) = Qnil;
  BVAR (b, file_format) = Qnil;
  BVAR (b, auto_save_file_format) = Qt;
  BVAR (b, last_selected_window) = Qnil;
  XSETINT (BVAR (b, display_count), 0);
  BVAR (b, display_time) = Qnil;
  BVAR (b, enable_multibyte_characters) = BVAR (&buffer_defaults, enable_multibyte_characters);
  BVAR (b, cursor_type) = BVAR (&buffer_defaults, cursor_type);
  BVAR (b, extra_line_spacing) = BVAR (&buffer_defaults, extra_line_spacing);
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  b->display_error_modiff = 0;
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}

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/* Reset buffer B's local variables info.
   Don't use this on a buffer that has already been in use;
   it does not treat permanent locals consistently.
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   Instead, use Fkill_all_local_variables.

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   If PERMANENT_TOO is 1, then we reset permanent
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   buffer-local variables.  If PERMANENT_TOO is 0,
   we preserve those.  */
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static void
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reset_buffer_local_variables (register struct buffer *b, int permanent_too)
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{
  register int offset;
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  int i;
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  /* Reset the major mode to Fundamental, together with all the
     things that depend on the major mode.
     default-major-mode is handled at a higher level.
     We ignore it here.  */
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  BVAR (b, major_mode) = Qfundamental_mode;
  BVAR (b, keymap) = Qnil;
  BVAR (b, mode_name) = QSFundamental;
  BVAR (b, minor_modes) = Qnil;
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  /* If the standard case table has been altered and invalidated,
     fix up its insides first.  */
  if (! (CHAR_TABLE_P (XCHAR_TABLE (Vascii_downcase_table)->extras[0])
	 && CHAR_TABLE_P (XCHAR_TABLE (Vascii_downcase_table)->extras[1])
	 && CHAR_TABLE_P (XCHAR_TABLE (Vascii_downcase_table)->extras[2])))
    Fset_standard_case_table (Vascii_downcase_table);

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  BVAR (b, downcase_table) = Vascii_downcase_table;
  BVAR (b, upcase_table) = XCHAR_TABLE (Vascii_downcase_table)->extras[0];
  BVAR (b, case_canon_table) = XCHAR_TABLE (Vascii_downcase_table)->extras[1];
  BVAR (b, case_eqv_table) = XCHAR_TABLE (Vascii_downcase_table)->extras[2];
  BVAR (b, invisibility_spec) = Qt;
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  /* Reset all (or most) per-buffer variables to their defaults.  */
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  if (permanent_too)
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    BVAR (b, local_var_alist) = Qnil;
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  else
    {
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      Lisp_Object tmp, prop, last = Qnil;
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      for (tmp = BVAR (b, local_var_alist); CONSP (tmp); tmp = XCDR (tmp))
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	if (!NILP (prop = Fget (XCAR (XCAR (tmp)), Qpermanent_local)))
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	  {
	    /* If permanent-local, keep it.  */
	    last = tmp;
	    if (EQ (prop, Qpermanent_local_hook))
	      {
		/* This is a partially permanent hook variable.
		   Preserve only the elements that want to be preserved.  */
		Lisp_Object list, newlist;
		list = XCDR (XCAR (tmp));
		if (!CONSP (list))
		  newlist = list;
		else
		  for (newlist = Qnil; CONSP (list); list = XCDR (list))
		    {
		      Lisp_Object elt = XCAR (list);
		      /* Preserve element ELT if it's t,
			 if it is a function with a `permanent-local-hook' property,
			 or if it's not a symbol.  */
		      if (! SYMBOLP (elt)
			  || EQ (elt, Qt)
			  || !NILP (Fget (elt, Qpermanent_local_hook)))
			newlist = Fcons (elt, newlist);
		    }
		XSETCDR (XCAR (tmp), Fnreverse (newlist));
	      }
	  }
	/* Delete this local variable.  */
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	else if (NILP (last))
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	  BVAR (b, local_var_alist) = XCDR (tmp);
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	else
	  XSETCDR (last, XCDR (tmp));
    }

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  for (i = 0; i < last_per_buffer_idx; ++i)
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    if (permanent_too || buffer_permanent_local_flags[i] == 0)
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      SET_PER_BUFFER_VALUE_P (b, i, 0);
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  /* For each slot that has a default value,
     copy that into the slot.  */

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  /* buffer-local Lisp variables start at `undo_list',
     tho only the ones from `name' on are GC'd normally.  */
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  for (offset = PER_BUFFER_VAR_OFFSET (FIRST_FIELD_PER_BUFFER);
       offset <= PER_BUFFER_VAR_OFFSET (LAST_FIELD_PER_BUFFER);
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       offset += sizeof (Lisp_Object))
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    {
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      int idx = PER_BUFFER_IDX (offset);
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      if ((idx > 0
	   && (permanent_too
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	       || buffer_permanent_local_flags[idx] == 0)))
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	PER_BUFFER_VALUE (b, offset) = PER_BUFFER_DEFAULT (offset);
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    }
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}