doc.c 29.6 KB
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/* Record indices of function doc strings stored in a file. -*- coding: utf-8 -*-
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Copyright (C) 1985-1986, 1993-1995, 1997-2017 Free Software Foundation,
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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 <https://www.gnu.org/licenses/>.  */
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#include <config.h>
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#include <errno.h>
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#include <sys/types.h>
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#include <sys/file.h>	/* Must be after sys/types.h for USG.  */
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#include <fcntl.h>
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#include <unistd.h>

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#include <c-ctype.h>

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#include "lisp.h"
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#include "character.h"
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#include "coding.h"
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#include "buffer.h"
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#include "disptab.h"
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#include "intervals.h"
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#include "keymap.h"
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/* Buffer used for reading from documentation file.  */
static char *get_doc_string_buffer;
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static ptrdiff_t get_doc_string_buffer_size;
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static unsigned char *read_bytecode_pointer;

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static char const sibling_etc[] = "../etc/";

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/* `readchar' in lread.c calls back here to fetch the next byte.
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   If UNREADFLAG is 1, we unread a byte.  */

int
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read_bytecode_char (bool unreadflag)
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{
  if (unreadflag)
    {
      read_bytecode_pointer--;
      return 0;
    }
  return *read_bytecode_pointer++;
}

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/* Extract a doc string from a file.  FILEPOS says where to get it.
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   If it is an integer, use that position in the standard DOC file.
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   If it is (FILE . INTEGER), use FILE as the file name
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   and INTEGER as the position in that file.
   But if INTEGER is negative, make it positive.
   (A negative integer is used for user variables, so we can distinguish
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   them without actually fetching the doc string.)

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   If the location does not point to the beginning of a docstring
   (e.g. because the file has been modified and the location is stale),
   return nil.

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   If UNIBYTE, always make a unibyte string.
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   If DEFINITION, assume this is for reading
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   a dynamic function definition; convert the bytestring
   and the constants vector with appropriate byte handling,
   and return a cons cell.  */
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Lisp_Object
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get_doc_string (Lisp_Object filepos, bool unibyte, bool definition)
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{
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  char *from, *to, *name, *p, *p1;
  int fd;
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  int offset;
  EMACS_INT position;
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  Lisp_Object file, tem, pos;
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  ptrdiff_t count;
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  USE_SAFE_ALLOCA;
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  if (INTEGERP (filepos))
    {
      file = Vdoc_file_name;
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      pos = filepos;
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    }
  else if (CONSP (filepos))
    {
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      file = XCAR (filepos);
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      pos = XCDR (filepos);
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    }
  else
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    return Qnil;

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  position = eabs (XINT (pos));
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  if (!STRINGP (Vdoc_directory))
    return Qnil;

  if (!STRINGP (file))
    return Qnil;
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  /* Put the file name in NAME as a C string.
     If it is relative, combine it with Vdoc_directory.  */

  tem = Ffile_name_absolute_p (file);
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  file = ENCODE_FILE (file);
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  Lisp_Object docdir
    = NILP (tem) ? ENCODE_FILE (Vdoc_directory) : empty_unibyte_string;
  ptrdiff_t docdir_sizemax = SBYTES (docdir) + 1;
#ifndef CANNOT_DUMP
  docdir_sizemax = max (docdir_sizemax, sizeof sibling_etc);
#endif
  name = SAFE_ALLOCA (docdir_sizemax + SBYTES (file));
  lispstpcpy (lispstpcpy (name, docdir), file);
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  fd = emacs_open (name, O_RDONLY, 0);
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  if (fd < 0)
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    {
#ifndef CANNOT_DUMP
      if (!NILP (Vpurify_flag))
	{
	  /* Preparing to dump; DOC file is probably not installed.
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	     So check in ../etc.  */
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	  lispstpcpy (stpcpy (name, sibling_etc), file);
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	  fd = emacs_open (name, O_RDONLY, 0);
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	}
#endif
      if (fd < 0)
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	{
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	  if (errno == EMFILE || errno == ENFILE)
	    report_file_error ("Read error on documentation file", file);

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	  SAFE_FREE ();
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	  AUTO_STRING (cannot_open, "Cannot open doc string file \"");
	  AUTO_STRING (quote_nl, "\"\n");
	  return concat3 (cannot_open, file, quote_nl);
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	}
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    }
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  count = SPECPDL_INDEX ();
  record_unwind_protect_int (close_file_unwind, fd);
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  /* Seek only to beginning of disk block.  */
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  /* Make sure we read at least 1024 bytes before `position'
     so we can check the leading text for consistency.  */
  offset = min (position, max (1024, position % (8 * 1024)));
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  if (TYPE_MAXIMUM (off_t) < position
      || lseek (fd, position - offset, 0) < 0)
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    error ("Position %"pI"d out of range in doc string file \"%s\"",
	   position, name);
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  /* Read the doc string into get_doc_string_buffer.
     P points beyond the data just read.  */
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  p = get_doc_string_buffer;
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  while (1)
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    {
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      ptrdiff_t space_left = (get_doc_string_buffer_size - 1
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			      - (p - get_doc_string_buffer));
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      int nread;

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      /* Allocate or grow the buffer if we need to.  */
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      if (space_left <= 0)
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	{
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	  ptrdiff_t in_buffer = p - get_doc_string_buffer;
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	  get_doc_string_buffer
	    = xpalloc (get_doc_string_buffer, &get_doc_string_buffer_size,
		       16 * 1024, -1, 1);
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	  p = get_doc_string_buffer + in_buffer;
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	  space_left = (get_doc_string_buffer_size - 1
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			- (p - get_doc_string_buffer));
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	}

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      /* Read a disk block at a time.
         If we read the same block last time, maybe skip this?  */
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      if (space_left > 1024 * 8)
	space_left = 1024 * 8;
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      nread = emacs_read_quit (fd, p, space_left);
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      if (nread < 0)
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	report_file_error ("Read error on documentation file", file);
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      p[nread] = 0;
      if (!nread)
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	break;
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      if (p == get_doc_string_buffer)
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	p1 = strchr (p + offset, '\037');
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      else
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	p1 = strchr (p, '\037');
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      if (p1)
	{
	  *p1 = 0;
	  p = p1;
	  break;
	}
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      p += nread;
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    }
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  unbind_to (count, Qnil);
  SAFE_FREE ();
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  /* Sanity checking.  */
  if (CONSP (filepos))
    {
      int test = 1;
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      /* A dynamic docstring should be either at the very beginning of a "#@
	 comment" or right after a dynamic docstring delimiter (in case we
	 pack several such docstrings within the same comment).  */
      if (get_doc_string_buffer[offset - test] != '\037')
	{
	  if (get_doc_string_buffer[offset - test++] != ' ')
	    return Qnil;
	  while (get_doc_string_buffer[offset - test] >= '0'
		 && get_doc_string_buffer[offset - test] <= '9')
	    test++;
	  if (get_doc_string_buffer[offset - test++] != '@'
	      || get_doc_string_buffer[offset - test] != '#')
	    return Qnil;
	}
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    }
  else
    {
      int test = 1;
      if (get_doc_string_buffer[offset - test++] != '\n')
	return Qnil;
      while (get_doc_string_buffer[offset - test] > ' ')
	test++;
      if (get_doc_string_buffer[offset - test] != '\037')
	return Qnil;
    }

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  /* Scan the text and perform quoting with ^A (char code 1).
     ^A^A becomes ^A, ^A0 becomes a null char, and ^A_ becomes a ^_.  */
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  from = get_doc_string_buffer + offset;
  to = get_doc_string_buffer + offset;
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  while (from != p)
    {
      if (*from == 1)
	{
	  int c;

	  from++;
	  c = *from++;
	  if (c == 1)
	    *to++ = c;
	  else if (c == '0')
	    *to++ = 0;
	  else if (c == '_')
	    *to++ = 037;
	  else
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	    {
	      unsigned char uc = c;
	      error ("\
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Invalid data in documentation file -- %c followed by code %03o",
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		     1, uc);
	    }
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	}
      else
	*to++ = *from++;
    }

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  /* If DEFINITION, read from this buffer
     the same way we would read bytes from a file.  */
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  if (definition)
    {
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      read_bytecode_pointer = (unsigned char *) get_doc_string_buffer + offset;
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      return Fread (Qlambda);
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    }

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  if (unibyte)
    return make_unibyte_string (get_doc_string_buffer + offset,
				to - (get_doc_string_buffer + offset));
  else
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    {
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      /* The data determines whether the string is multibyte.  */
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      ptrdiff_t nchars
	= multibyte_chars_in_text (((unsigned char *) get_doc_string_buffer
				    + offset),
				   to - (get_doc_string_buffer + offset));
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      return make_string_from_bytes (get_doc_string_buffer + offset,
				     nchars,
				     to - (get_doc_string_buffer + offset));
    }
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}

/* Get a string from position FILEPOS and pass it through the Lisp reader.
   We use this for fetching the bytecode string and constants vector
   of a compiled function from the .elc file.  */

Lisp_Object
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read_doc_string (Lisp_Object filepos)
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{
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  return get_doc_string (filepos, 0, 1);
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}

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static bool
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reread_doc_file (Lisp_Object file)
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{
  if (NILP (file))
    Fsnarf_documentation (Vdoc_file_name);
  else
    Fload (file, Qt, Qt, Qt, Qnil);
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  return 1;
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}

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DEFUN ("documentation", Fdocumentation, Sdocumentation, 1, 2, 0,
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       doc: /* Return the documentation string of FUNCTION.
Unless a non-nil second argument RAW is given, the
string is passed through `substitute-command-keys'.  */)
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  (Lisp_Object function, Lisp_Object raw)
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{
  Lisp_Object fun;
  Lisp_Object funcar;
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  Lisp_Object doc;
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  bool try_reload = 1;
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 documentation:
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  doc = Qnil;
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  if (SYMBOLP (function))
    {
      Lisp_Object tem = Fget (function, Qfunction_documentation);
      if (!NILP (tem))
	return Fdocumentation_property (function, Qfunction_documentation,
					raw);
    }

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  fun = Findirect_function (function, Qnil);
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  if (NILP (fun))
    xsignal1 (Qvoid_function, function);
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  if (CONSP (fun) && EQ (XCAR (fun), Qmacro))
    fun = XCDR (fun);
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  if (SUBRP (fun))
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    doc = make_number (XSUBR (fun)->doc);
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  else if (MODULE_FUNCTIONP (fun))
    doc = XMODULE_FUNCTION (fun)->documentation;
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  else if (COMPILEDP (fun))
    {
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      if (PVSIZE (fun) <= COMPILED_DOC_STRING)
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	return Qnil;
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      else
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	{
	  Lisp_Object tem = AREF (fun, COMPILED_DOC_STRING);
	  if (STRINGP (tem))
	    doc = tem;
	  else if (NATNUMP (tem) || CONSP (tem))
	    doc = tem;
	  else
	    return Qnil;
	}
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    }
  else if (STRINGP (fun) || VECTORP (fun))
    {
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      return build_string ("Keyboard macro.");
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    }
  else if (CONSP (fun))
    {
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      funcar = XCAR (fun);
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      if (!SYMBOLP (funcar))
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	xsignal1 (Qinvalid_function, fun);
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      else if (EQ (funcar, Qkeymap))
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	return build_string ("Prefix command (definition is a keymap associating keystrokes with commands).");
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      else if (EQ (funcar, Qlambda)
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	       || (EQ (funcar, Qclosure) && (fun = XCDR (fun), 1))
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	       || EQ (funcar, Qautoload))
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	{
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	  Lisp_Object tem1 = Fcdr (Fcdr (fun));
	  Lisp_Object tem = Fcar (tem1);
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	  if (STRINGP (tem))
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	    doc = tem;
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	  /* Handle a doc reference--but these never come last
	     in the function body, so reject them if they are last.  */
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	  else if ((NATNUMP (tem) || (CONSP (tem) && INTEGERP (XCDR (tem))))
		   && !NILP (XCDR (tem1)))
	    doc = tem;
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	  else
	    return Qnil;
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	}
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      else
	goto oops;
    }
  else
    {
    oops:
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      xsignal1 (Qinvalid_function, fun);
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    }
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  /* If DOC is 0, it's typically because of a dumped file missing
     from the DOC file (bug in src/Makefile.in).  */
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  if (EQ (doc, make_number (0)))
    doc = Qnil;
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  if (INTEGERP (doc) || CONSP (doc))
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    {
      Lisp_Object tem;
      tem = get_doc_string (doc, 0, 0);
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      if (NILP (tem) && try_reload)
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	{
	  /* The file is newer, we need to reset the pointers.  */
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	  try_reload = reread_doc_file (Fcar_safe (doc));
	  if (try_reload)
	    {
	      try_reload = 0;
	      goto documentation;
	    }
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	}
      else
	doc = tem;
    }
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  if (NILP (raw))
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    doc = Fsubstitute_command_keys (doc);
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  return doc;
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}

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DEFUN ("documentation-property", Fdocumentation_property,
       Sdocumentation_property, 2, 3, 0,
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       doc: /* Return the documentation string that is SYMBOL's PROP property.
Third argument RAW omitted or nil means pass the result through
`substitute-command-keys' if it is a string.

This differs from `get' in that it can refer to strings stored in the
`etc/DOC' file; and that it evaluates documentation properties that
aren't strings.  */)
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  (Lisp_Object symbol, Lisp_Object prop, Lisp_Object raw)
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{
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  bool try_reload = 1;
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  Lisp_Object tem;
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 documentation_property:
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  tem = Fget (symbol, prop);
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  if (EQ (tem, make_number (0)))
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    tem = Qnil;
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  if (INTEGERP (tem) || (CONSP (tem) && INTEGERP (XCDR (tem))))
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    {
      Lisp_Object doc = tem;
      tem = get_doc_string (tem, 0, 0);
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      if (NILP (tem) && try_reload)
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	{
	  /* The file is newer, we need to reset the pointers.  */
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	  try_reload = reread_doc_file (Fcar_safe (doc));
	  if (try_reload)
	    {
	      try_reload = 0;
	      goto documentation_property;
	    }
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	}
    }
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  else if (!STRINGP (tem))
    /* Feval protects its argument.  */
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    tem = Feval (tem, Qnil);
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  if (NILP (raw) && STRINGP (tem))
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    tem = Fsubstitute_command_keys (tem);
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  return tem;
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}

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/* Scanning the DOC files and placing docstring offsets into functions.  */

static void
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store_function_docstring (Lisp_Object obj, EMACS_INT offset)
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{
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  /* Don't use indirect_function here, or defaliases will apply their
     docstrings to the base functions (Bug#2603).  */
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  Lisp_Object fun = SYMBOLP (obj) ? XSYMBOL (obj)->u.s.function : obj;
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  /* The type determines where the docstring is stored.  */

  /* If it's a lisp form, stick it in the form.  */
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  if (CONSP (fun) && EQ (XCAR (fun), Qmacro))
    fun = XCDR (fun);
  if (CONSP (fun))
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    {
      Lisp_Object tem;

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      tem = XCAR (fun);
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      if (EQ (tem, Qlambda) || EQ (tem, Qautoload)
	  || (EQ (tem, Qclosure) && (fun = XCDR (fun), 1)))
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	{
	  tem = Fcdr (Fcdr (fun));
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	  if (CONSP (tem) && INTEGERP (XCAR (tem)))
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	    /* FIXME: This modifies typically pure hash-cons'd data, so its
	       correctness is quite delicate.  */
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	    XSETCAR (tem, make_number (offset));
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	}
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    }

  /* Lisp_Subrs have a slot for it.  */
  else if (SUBRP (fun))
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    XSUBR (fun)->doc = offset;
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  /* Bytecode objects sometimes have slots for it.  */
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  else if (COMPILEDP (fun))
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    {
      /* This bytecode object must have a slot for the
	 docstring, since we've found a docstring for it.  */
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      if (PVSIZE (fun) > COMPILED_DOC_STRING)
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	ASET (fun, COMPILED_DOC_STRING, make_number (offset));
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      else
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	{
	  AUTO_STRING (format, "No docstring slot for %s");
	  CALLN (Fmessage, format,
		 (SYMBOLP (obj)
		  ? SYMBOL_NAME (obj)
		  : build_string ("<anonymous>")));
	}
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    }
}


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DEFUN ("Snarf-documentation", Fsnarf_documentation, Ssnarf_documentation,
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       1, 1, 0,
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       doc: /* Used during Emacs initialization to scan the `etc/DOC...' file.
This searches the `etc/DOC...' file for doc strings and
records them in function and variable definitions.
The function takes one argument, FILENAME, a string;
it specifies the file name (without a directory) of the DOC file.
That file is found in `../etc' now; later, when the dumped Emacs is run,
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the same file name is found in the `doc-directory'.  */)
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  (Lisp_Object filename)
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{
  int fd;
  char buf[1024 + 1];
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  int filled;
  EMACS_INT pos;
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  Lisp_Object sym;
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  char *p, *name;
  bool skip_file = 0;
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  ptrdiff_t count;
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  char const *dirname;
  ptrdiff_t dirlen;
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  /* Preloaded defcustoms using custom-initialize-delay are added to
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     this list, but kept unbound.  See https://debbugs.gnu.org/11565  */
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  Lisp_Object delayed_init =
    find_symbol_value (intern ("custom-delayed-init-variables"));

  if (EQ (delayed_init, Qunbound)) delayed_init = Qnil;
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  CHECK_STRING (filename);
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  if
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#ifndef CANNOT_DUMP
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    (!NILP (Vpurify_flag))
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#else /* CANNOT_DUMP */
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      (0)
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#endif /* CANNOT_DUMP */
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    {
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      dirname = sibling_etc;
      dirlen = sizeof sibling_etc - 1;
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    }
  else
    {
      CHECK_STRING (Vdoc_directory);
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      dirname = SSDATA (Vdoc_directory);
      dirlen = SBYTES (Vdoc_directory);
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    }
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  count = SPECPDL_INDEX ();
  USE_SAFE_ALLOCA;
  name = SAFE_ALLOCA (dirlen + SBYTES (filename) + 1);
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  lispstpcpy (stpcpy (name, dirname), filename); 	/*** Add this line ***/
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  /* Vbuild_files is nil when temacs is run, and non-nil after that.  */
  if (NILP (Vbuild_files))
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    {
      static char const *const buildobj[] =
	{
	  #include "buildobj.h"
	};
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      int i = ARRAYELTS (buildobj);
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      while (0 <= --i)
	Vbuild_files = Fcons (build_string (buildobj[i]), Vbuild_files);
      Vbuild_files = Fpurecopy (Vbuild_files);
    }
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  fd = emacs_open (name, O_RDONLY, 0);
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  if (fd < 0)
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    {
      int open_errno = errno;
      report_file_errno ("Opening doc string file", build_string (name),
			 open_errno);
    }
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  record_unwind_protect_int (close_file_unwind, fd);
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  Vdoc_file_name = filename;
  filled = 0;
  pos = 0;
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  while (true)
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    {
      if (filled < 512)
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	filled += emacs_read_quit (fd, &buf[filled], sizeof buf - 1 - filled);
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      if (!filled)
	break;

      buf[filled] = 0;
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      char *end = buf + (filled < 512 ? filled : filled - 128);
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      p = memchr (buf, '\037', end - buf);
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      /* p points to ^_Ffunctionname\n or ^_Vvarname\n or ^_Sfilename\n.  */
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      if (p)
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	{
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	  end = strchr (p, '\n');
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          /* See if this is a file name, and if it is a file in build-files.  */
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          if (p[1] == 'S')
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            {
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              skip_file = 0;
              if (end - p > 4 && end[-2] == '.'
                  && (end[-1] == 'o' || end[-1] == 'c'))
                {
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                  ptrdiff_t len = end - p - 2;
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                  char *fromfile = SAFE_ALLOCA (len + 1);
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                  memcpy (fromfile, &p[2], len);
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                  fromfile[len] = 0;
                  if (fromfile[len-1] == 'c')
                    fromfile[len-1] = 'o';

                  skip_file = NILP (Fmember (build_string (fromfile),
                                             Vbuild_files));
                }
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            }

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	  sym = oblookup (Vobarray, p + 2,
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			  multibyte_chars_in_text ((unsigned char *) p + 2,
						   end - p - 2),
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			  end - p - 2);
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	  /* Check skip_file so that when a function is defined several
	     times in different files (typically, once in xterm, once in
	     w32term, ...), we only pay attention to the one that
	     matters.  */
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	  if (! skip_file && SYMBOLP (sym))
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	    {
	      /* Attach a docstring to a variable?  */
	      if (p[1] == 'V')
		{
		  /* Install file-position as variable-documentation property
		     and make it negative for a user-variable
		     (doc starts with a `*').  */
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                  if (!NILP (Fboundp (sym))
                      || !NILP (Fmemq (sym, delayed_init)))
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                    Fput (sym, Qvariable_documentation,
                          make_number ((pos + end + 1 - buf)
                                       * (end[1] == '*' ? -1 : 1)));
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		}

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	      /* Attach a docstring to a function?  */
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	      else if (p[1] == 'F')
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                {
                  if (!NILP (Ffboundp (sym)))
                    store_function_docstring (sym, pos + end + 1 - buf);
                }
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	      else if (p[1] == 'S')
		; /* Just a source file name boundary marker.  Ignore it.  */

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	      else
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		error ("DOC file invalid at position %"pI"d", pos);
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	    }
	}
      pos += end - buf;
      filled -= end - buf;
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      memmove (buf, end, filled);
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    }
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  SAFE_FREE ();
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  return unbind_to (count, Qnil);
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}

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/* Return true if text quoting style should default to quote `like this'.  */
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static bool
default_to_grave_quoting_style (void)
{
  if (!text_quoting_flag)
    return true;
  if (! DISP_TABLE_P (Vstandard_display_table))
    return false;
  Lisp_Object dv = DISP_CHAR_VECTOR (XCHAR_TABLE (Vstandard_display_table),
				     LEFT_SINGLE_QUOTATION_MARK);
  return (VECTORP (dv) && ASIZE (dv) == 1
	  && EQ (AREF (dv, 0), make_number ('`')));
}

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/* Return the current effective text quoting style.  */
enum text_quoting_style
text_quoting_style (void)
{
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  if (NILP (Vtext_quoting_style)
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      ? default_to_grave_quoting_style ()
      : EQ (Vtext_quoting_style, Qgrave))
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    return GRAVE_QUOTING_STYLE;
  else if (EQ (Vtext_quoting_style, Qstraight))
    return STRAIGHT_QUOTING_STYLE;
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  else
    return CURVE_QUOTING_STYLE;
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}

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DEFUN ("substitute-command-keys", Fsubstitute_command_keys,
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       Ssubstitute_command_keys, 1, 1, 0,
       doc: /* Substitute key descriptions for command names in STRING.
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Each substring of the form \\=\\[COMMAND] is replaced by either a
keystroke sequence that invokes COMMAND, or "M-x COMMAND" if COMMAND
is not on any keys.

Each substring of the form \\=\\{MAPVAR} is replaced by a summary of
the value of MAPVAR as a keymap.  This summary is similar to the one
produced by `describe-bindings'.  The summary ends in two newlines
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\(used by the helper function `help-make-xrefs' to find the end of the
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summary).

Each substring of the form \\=\\<MAPVAR> specifies the use of MAPVAR
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as the keymap for future \\=\\[COMMAND] substrings.
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Each grave accent \\=` is replaced by left quote, and each apostrophe \\='
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is replaced by right quote.  Left and right quote characters are
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specified by `text-quoting-style'.
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\\=\\= quotes the following character and is discarded; thus, \\=\\=\\=\\= puts \\=\\=
into the output, \\=\\=\\=\\[ puts \\=\\[ into the output, and \\=\\=\\=` puts \\=` into the
output.
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Return the original STRING if no substitutions are made.
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Otherwise, return a new string.  */)
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  (Lisp_Object string)
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{
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  char *buf;
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  bool changed = false;
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  bool nonquotes_changed = false;
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  unsigned char *strp;
  char *bufp;
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  ptrdiff_t idx;
  ptrdiff_t bsize;
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  Lisp_Object tem;
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  Lisp_Object keymap;
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  unsigned char const *start;
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  ptrdiff_t length, length_byte;
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  Lisp_Object name;
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  ptrdiff_t nchars;
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  if (NILP (string))
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    return Qnil;

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  /* If STRING contains non-ASCII unibyte data, process its
     properly-encoded multibyte equivalent instead.  This simplifies
     the implementation and is OK since substitute-command-keys is
     intended for use only on text strings.  Keep STRING around, since
     it will be returned if no changes occur.  */
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  Lisp_Object str = Fstring_make_multibyte (string);
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  enum text_quoting_style quoting_style = text_quoting_style ();
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  nchars = 0;

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  /* KEYMAP is either nil (which means search all the active keymaps)
     or a specified local map (which means search just that and the
     global map).  If non-nil, it might come from Voverriding_local_map,
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     or from a \\<mapname> construct in STRING itself..  */
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  keymap = Voverriding_local_map;
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  ptrdiff_t strbytes = SBYTES (str);
  bsize = strbytes;
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  /* Fixed-size stack buffer.  */
  char sbuf[MAX_ALLOCA];
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  /* Heap-allocated buffer, if any.  */
  char *abuf;
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  /* Extra room for expansion due to replacing ‘\[]’ with ‘M-x ’.  */
  enum { EXTRA_ROOM = sizeof "M-x " - sizeof "\\[]" };

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  ptrdiff_t count = SPECPDL_INDEX ();

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  if (bsize <= sizeof sbuf - EXTRA_ROOM)
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    {
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      abuf = NULL;
      buf = sbuf;
      bsize = sizeof sbuf;
    }
  else
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    {
      buf = abuf = xpalloc (NULL, &bsize, EXTRA_ROOM, STRING_BYTES_BOUND, 1);
      record_unwind_protect_ptr (xfree, abuf);
    }
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  bufp = buf;

  strp = SDATA (str);
  while (strp < SDATA (str) + strbytes)
    {
      unsigned char *close_bracket;

      if (strp[0] == '\\' && strp[1] == '='
	  && strp + 2 < SDATA (str) + strbytes)
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	{
	  /* \= quotes the next character;
	     thus, to put in \[ without its special meaning, use \=\[.  */
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	  changed = nonquotes_changed = true;
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	  strp += 2;
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	  /* Fall through to copy one char.  */
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	}
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      else if (strp[0] == '\\' && strp[1] == '['
	       && (close_bracket
		   = memchr (strp + 2, ']',
			     SDATA (str) + strbytes - (strp + 2))))
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	{
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	  bool follow_remap = 1;
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	  start = strp + 2;
	  length_byte = close_bracket - start;
	  idx = close_bracket + 1 - SDATA (str);
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	  name = Fintern (make_string ((char *) start, length_byte), Qnil);
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	do_remap:
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	  tem = Fwhere_is_internal (name, keymap, Qt, Qnil, Qnil);
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	  if (VECTORP (tem) && ASIZE (tem) > 1
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	      && EQ (AREF (tem, 0), Qremap) && SYMBOLP (AREF (tem, 1))
	      && follow_remap)
	    {
	      name = AREF (tem, 1);
	      follow_remap = 0;
	      goto do_remap;
	    }

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	  /* Fwhere_is_internal can GC, so take relocation of string
	     contents into account.  */
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	  strp = SDATA (str) + idx;
	  start = strp - length_byte - 1;
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	  if (NILP (tem))	/* but not on any keys */
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	    {
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	      memcpy (bufp, "M-x ", 4);
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	      bufp += 4;
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	      nchars += 4;
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	      length = multibyte_chars_in_text (start, length_byte);
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	      goto subst;
	    }
	  else
	    {			/* function is on a key */
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	      tem = Fkey_description (tem, Qnil);
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	      goto subst_string;
	    }
	}
      /* \{foo} is replaced with a summary of the keymap (symbol-value foo).
	 \<foo> just sets the keymap used for \[cmd].  */
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      else if (strp[0] == '\\' && (strp[1] == '{' || strp[1] == '<')
	       && (close_bracket
		   = memchr (strp + 2, strp[1] == '{' ? '}' : '>',
			     SDATA (str) + strbytes - (strp + 2))))
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	{
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	 {
859
	  bool generate_summary = strp[1] == '{';
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	  /* This is for computing the SHADOWS arg for describe_map_tree.  */
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	  Lisp_Object active_maps = Fcurrent_active_maps (Qnil, Qnil);
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	  ptrdiff_t count = SPECPDL_INDEX ();
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	  start = strp + 2;
	  length_byte = close_bracket - start;
	  idx = close_bracket + 1 - SDATA (str);
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	  /* Get the value of the keymap in TEM, or nil if undefined.
	     Do this while still in the user's current buffer
	     in case it is a local variable.  */
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	  name = Fintern (make_string ((char *) start, length_byte), Qnil);
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	  tem = Fboundp (name);
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	  if (! NILP (tem))
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	    {
	      tem = Fsymbol_value (name);
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