src/doc.c

   1 /* Record indices of function doc strings stored in a file.
   2
   3 Copyright (C) 1985-1986, 1993-1995, 1997-2014 Free Software Foundation,
   4 Inc.
   5
   6 This file is part of GNU Emacs.
   7
   8 GNU Emacs is free software: you can redistribute it and/or modify
   9 it under the terms of the GNU General Public License as published by
  10 the Free Software Foundation, either version 3 of the License, or
  11 (at your option) any later version.
  12
  13 GNU Emacs is distributed in the hope that it will be useful,
  14 but WITHOUT ANY WARRANTY; without even the implied warranty of
  15 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  16 GNU General Public License for more details.
  17
  18 You should have received a copy of the GNU General Public License
  19 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
  20
  21
  22 #include <config.h>
  23
  24 #include <errno.h>
  25 #include <sys/types.h>
  26 #include <sys/file.h>   /* Must be after sys/types.h for USG.  */
  27 #include <fcntl.h>
  28 #include <unistd.h>
  29
  30 #include <c-ctype.h>
  31
  32 #include "lisp.h"
  33 #include "character.h"
  34 #include "buffer.h"
  35 #include "keyboard.h"
  36 #include "keymap.h"
  37
  38 Lisp_Object Qfunction_documentation;
  39
  40 /* Buffer used for reading from documentation file.  */
  41 static char *get_doc_string_buffer;
  42 static ptrdiff_t get_doc_string_buffer_size;
  43
  44 static unsigned char *read_bytecode_pointer;
  45
  46 /* `readchar' in lread.c calls back here to fetch the next byte.
  47    If UNREADFLAG is 1, we unread a byte.  */
  48
  49 int
  50 read_bytecode_char (bool unreadflag)
  51 {
  52   if (unreadflag)
  53     {
  54       read_bytecode_pointer--;
  55       return 0;
  56     }
  57   return *read_bytecode_pointer++;
  58 }
  59
  60 /* Extract a doc string from a file.  FILEPOS says where to get it.
  61    If it is an integer, use that position in the standard DOC file.
  62    If it is (FILE . INTEGER), use FILE as the file name
  63    and INTEGER as the position in that file.
  64    But if INTEGER is negative, make it positive.
  65    (A negative integer is used for user variables, so we can distinguish
  66    them without actually fetching the doc string.)
  67
  68    If the location does not point to the beginning of a docstring
  69    (e.g. because the file has been modified and the location is stale),
  70    return nil.
  71
  72    If UNIBYTE, always make a unibyte string.
  73
  74    If DEFINITION, assume this is for reading
  75    a dynamic function definition; convert the bytestring
  76    and the constants vector with appropriate byte handling,
  77    and return a cons cell.  */
  78
  79 Lisp_Object
  80 get_doc_string (Lisp_Object filepos, bool unibyte, bool definition)
  81 {
  82   char *from, *to, *name, *p, *p1;
  83   int fd;
  84   ptrdiff_t minsize;
  85   int offset;
  86   EMACS_INT position;
  87   Lisp_Object file, tem, pos;
  88   ptrdiff_t count;
  89   USE_SAFE_ALLOCA;
  90
  91   if (INTEGERP (filepos))
  92     {
  93       file = Vdoc_file_name;
  94       pos = filepos;
  95     }
  96   else if (CONSP (filepos))
  97     {
  98       file = XCAR (filepos);
  99       pos = XCDR (filepos);
 100     }
 101   else
 102     return Qnil;
 103
 104   position = eabs (XINT (pos));
 105
 106   if (!STRINGP (Vdoc_directory))
 107     return Qnil;
 108
 109   if (!STRINGP (file))
 110     return Qnil;
 111
 112   /* Put the file name in NAME as a C string.
 113      If it is relative, combine it with Vdoc_directory.  */
 114
 115   tem = Ffile_name_absolute_p (file);
 116   file = ENCODE_FILE (file);
 117   if (NILP (tem))
 118     {
 119       Lisp_Object docdir = ENCODE_FILE (Vdoc_directory);
 120       minsize = SCHARS (docdir);
 121       /* sizeof ("../etc/") == 8 */
 122       if (minsize < 8)
 123         minsize = 8;
 124       name = SAFE_ALLOCA (minsize + SCHARS (file) + 8);
 125       strcpy (name, SSDATA (docdir));
 126       strcat (name, SSDATA (file));
 127     }
 128   else
 129     {
 130       name = SSDATA (file);
 131     }
 132
 133   fd = emacs_open (name, O_RDONLY, 0);
 134   if (fd < 0)
 135     {
 136 #ifndef CANNOT_DUMP
 137       if (!NILP (Vpurify_flag))
 138         {
 139           /* Preparing to dump; DOC file is probably not installed.
 140              So check in ../etc.  */
 141           strcpy (name, "../etc/");
 142           strcat (name, SSDATA (file));
 143
 144           fd = emacs_open (name, O_RDONLY, 0);
 145         }
 146 #endif
 147       if (fd < 0)
 148         {
 149           SAFE_FREE ();
 150           return concat3 (build_string ("Cannot open doc string file \""),
 151                           file, build_string ("\"\n"));
 152         }
 153     }
 154   count = SPECPDL_INDEX ();
 155   record_unwind_protect_int (close_file_unwind, fd);
 156
 157   /* Seek only to beginning of disk block.  */
 158   /* Make sure we read at least 1024 bytes before `position'
 159      so we can check the leading text for consistency.  */
 160   offset = min (position, max (1024, position % (8 * 1024)));
 161   if (TYPE_MAXIMUM (off_t) < position
 162       || lseek (fd, position - offset, 0) < 0)
 163     error ("Position %"pI"d out of range in doc string file \"%s\"",
 164            position, name);
 165
 166   /* Read the doc string into get_doc_string_buffer.
 167      P points beyond the data just read.  */
 168
 169   p = get_doc_string_buffer;
 170   while (1)
 171     {
 172       ptrdiff_t space_left = (get_doc_string_buffer_size - 1
 173                               - (p - get_doc_string_buffer));
 174       int nread;
 175
 176       /* Allocate or grow the buffer if we need to.  */
 177       if (space_left <= 0)
 178         {
 179           ptrdiff_t in_buffer = p - get_doc_string_buffer;
 180           get_doc_string_buffer
 181             = xpalloc (get_doc_string_buffer, &get_doc_string_buffer_size,
 182                        16 * 1024, -1, 1);
 183           p = get_doc_string_buffer + in_buffer;
 184           space_left = (get_doc_string_buffer_size - 1
 185                         - (p - get_doc_string_buffer));
 186         }
 187
 188       /* Read a disk block at a time.
 189          If we read the same block last time, maybe skip this?  */
 190       if (space_left > 1024 * 8)
 191         space_left = 1024 * 8;
 192       nread = emacs_read (fd, p, space_left);
 193       if (nread < 0)
 194         report_file_error ("Read error on documentation file", file);
 195       p[nread] = 0;
 196       if (!nread)
 197         break;
 198       if (p == get_doc_string_buffer)
 199         p1 = strchr (p + offset, '\037');
 200       else
 201         p1 = strchr (p, '\037');
 202       if (p1)
 203         {
 204           *p1 = 0;
 205           p = p1;
 206           break;
 207         }
 208       p += nread;
 209     }
 210   unbind_to (count, Qnil);
 211   SAFE_FREE ();
 212
 213   /* Sanity checking.  */
 214   if (CONSP (filepos))
 215     {
 216       int test = 1;
 217       /* A dynamic docstring should be either at the very beginning of a "#@
 218          comment" or right after a dynamic docstring delimiter (in case we
 219          pack several such docstrings within the same comment).  */
 220       if (get_doc_string_buffer[offset - test] != '\037')
 221         {
 222           if (get_doc_string_buffer[offset - test++] != ' ')
 223             return Qnil;
 224           while (get_doc_string_buffer[offset - test] >= '0'
 225                  && get_doc_string_buffer[offset - test] <= '9')
 226             test++;
 227           if (get_doc_string_buffer[offset - test++] != '@'
 228               || get_doc_string_buffer[offset - test] != '#')
 229             return Qnil;
 230         }
 231     }
 232   else
 233     {
 234       int test = 1;
 235       if (get_doc_string_buffer[offset - test++] != '\n')
 236         return Qnil;
 237       while (get_doc_string_buffer[offset - test] > ' ')
 238         test++;
 239       if (get_doc_string_buffer[offset - test] != '\037')
 240         return Qnil;
 241     }
 242
 243   /* Scan the text and perform quoting with ^A (char code 1).
 244      ^A^A becomes ^A, ^A0 becomes a null char, and ^A_ becomes a ^_.  */
 245   from = get_doc_string_buffer + offset;
 246   to = get_doc_string_buffer + offset;
 247   while (from != p)
 248     {
 249       if (*from == 1)
 250         {
 251           int c;
 252
 253           from++;
 254           c = *from++;
 255           if (c == 1)
 256             *to++ = c;
 257           else if (c == '0')
 258             *to++ = 0;
 259           else if (c == '_')
 260             *to++ = 037;
 261           else
 262             {
 263               unsigned char uc = c;
 264               error ("\
 265 Invalid data in documentation file -- %c followed by code %03o",
 266                      1, uc);
 267             }
 268         }
 269       else
 270         *to++ = *from++;
 271     }
 272
 273   /* If DEFINITION, read from this buffer
 274      the same way we would read bytes from a file.  */
 275   if (definition)
 276     {
 277       read_bytecode_pointer = (unsigned char *) get_doc_string_buffer + offset;
 278       return Fread (Qlambda);
 279     }
 280
 281   if (unibyte)
 282     return make_unibyte_string (get_doc_string_buffer + offset,
 283                                 to - (get_doc_string_buffer + offset));
 284   else
 285     {
 286       /* The data determines whether the string is multibyte.  */
 287       ptrdiff_t nchars
 288         = multibyte_chars_in_text (((unsigned char *) get_doc_string_buffer
 289                                     + offset),
 290                                    to - (get_doc_string_buffer + offset));
 291       return make_string_from_bytes (get_doc_string_buffer + offset,
 292                                      nchars,
 293                                      to - (get_doc_string_buffer + offset));
 294     }
 295 }
 296
 297 /* Get a string from position FILEPOS and pass it through the Lisp reader.
 298    We use this for fetching the bytecode string and constants vector
 299    of a compiled function from the .elc file.  */
 300
 301 Lisp_Object
 302 read_doc_string (Lisp_Object filepos)
 303 {
 304   return get_doc_string (filepos, 0, 1);
 305 }
 306
 307 static bool
 308 reread_doc_file (Lisp_Object file)
 309 {
 310 #if 0
 311   Lisp_Object reply, prompt[3];
 312   struct gcpro gcpro1;
 313   GCPRO1 (file);
 314   prompt[0] = build_string ("File ");
 315   prompt[1] = NILP (file) ? Vdoc_file_name : file;
 316   prompt[2] = build_string (" is out of sync.  Reload? ");
 317   reply = Fy_or_n_p (Fconcat (3, prompt));
 318   UNGCPRO;
 319   if (NILP (reply))
 320     return 0;
 321 #endif
 322
 323   if (NILP (file))
 324     Fsnarf_documentation (Vdoc_file_name);
 325   else
 326     Fload (file, Qt, Qt, Qt, Qnil);
 327
 328   return 1;
 329 }
 330
 331 DEFUN ("documentation", Fdocumentation, Sdocumentation, 1, 2, 0,
 332        doc: /* Return the documentation string of FUNCTION.
 333 Unless a non-nil second argument RAW is given, the
 334 string is passed through `substitute-command-keys'.  */)
 335   (Lisp_Object function, Lisp_Object raw)
 336 {
 337   Lisp_Object fun;
 338   Lisp_Object funcar;
 339   Lisp_Object doc;
 340   bool try_reload = 1;
 341
 342  documentation:
 343
 344   doc = Qnil;
 345
 346   if (SYMBOLP (function))
 347     {
 348       Lisp_Object tem = Fget (function, Qfunction_documentation);
 349       if (!NILP (tem))
 350         return Fdocumentation_property (function, Qfunction_documentation,
 351                                         raw);
 352     }
 353
 354   fun = Findirect_function (function, Qnil);
 355   if (CONSP (fun) && EQ (XCAR (fun), Qmacro))
 356     fun = XCDR (fun);
 357   if (SUBRP (fun))
 358     {
 359       if (XSUBR (fun)->doc == 0)
 360         return Qnil;
 361       /* FIXME: This is not portable, as it assumes that string
 362          pointers have the top bit clear.  */
 363       else if ((intptr_t) XSUBR (fun)->doc >= 0)
 364         doc = build_string (XSUBR (fun)->doc);
 365       else
 366         doc = make_number ((intptr_t) XSUBR (fun)->doc);
 367     }
 368   else if (COMPILEDP (fun))
 369     {
 370       if ((ASIZE (fun) & PSEUDOVECTOR_SIZE_MASK) <= COMPILED_DOC_STRING)
 371         return Qnil;
 372       else
 373         {
 374           Lisp_Object tem = AREF (fun, COMPILED_DOC_STRING);
 375           if (STRINGP (tem))
 376             doc = tem;
 377           else if (NATNUMP (tem) || CONSP (tem))
 378             doc = tem;
 379           else
 380             return Qnil;
 381         }
 382     }
 383   else if (STRINGP (fun) || VECTORP (fun))
 384     {
 385       return build_string ("Keyboard macro.");
 386     }
 387   else if (CONSP (fun))
 388     {
 389       funcar = XCAR (fun);
 390       if (!SYMBOLP (funcar))
 391         xsignal1 (Qinvalid_function, fun);
 392       else if (EQ (funcar, Qkeymap))
 393         return build_string ("Prefix command (definition is a keymap associating keystrokes with commands).");
 394       else if (EQ (funcar, Qlambda)
 395                || (EQ (funcar, Qclosure) && (fun = XCDR (fun), 1))
 396                || EQ (funcar, Qautoload))
 397         {
 398           Lisp_Object tem1 = Fcdr (Fcdr (fun));
 399           Lisp_Object tem = Fcar (tem1);
 400           if (STRINGP (tem))
 401             doc = tem;
 402           /* Handle a doc reference--but these never come last
 403              in the function body, so reject them if they are last.  */
 404           else if ((NATNUMP (tem) || (CONSP (tem) && INTEGERP (XCDR (tem))))
 405                    && !NILP (XCDR (tem1)))
 406             doc = tem;
 407           else
 408             return Qnil;
 409         }
 410       else
 411         goto oops;
 412     }
 413   else
 414     {
 415     oops:
 416       xsignal1 (Qinvalid_function, fun);
 417     }
 418
 419   /* If DOC is 0, it's typically because of a dumped file missing
 420      from the DOC file (bug in src/Makefile.in).  */
 421   if (EQ (doc, make_number (0)))
 422     doc = Qnil;
 423   if (INTEGERP (doc) || CONSP (doc))
 424     {
 425       Lisp_Object tem;
 426       tem = get_doc_string (doc, 0, 0);
 427       if (NILP (tem) && try_reload)
 428         {
 429           /* The file is newer, we need to reset the pointers.  */
 430           struct gcpro gcpro1, gcpro2;
 431           GCPRO2 (function, raw);
 432           try_reload = reread_doc_file (Fcar_safe (doc));
 433           UNGCPRO;
 434           if (try_reload)
 435             {
 436               try_reload = 0;
 437               goto documentation;
 438             }
 439         }
 440       else
 441         doc = tem;
 442     }
 443
 444   if (NILP (raw))
 445     doc = Fsubstitute_command_keys (doc);
 446   return doc;
 447 }
 448
 449 DEFUN ("documentation-property", Fdocumentation_property,
 450        Sdocumentation_property, 2, 3, 0,
 451        doc: /* Return the documentation string that is SYMBOL's PROP property.
 452 Third argument RAW omitted or nil means pass the result through
 453 `substitute-command-keys' if it is a string.
 454
 455 This differs from `get' in that it can refer to strings stored in the
 456 `etc/DOC' file; and that it evaluates documentation properties that
 457 aren't strings.  */)
 458   (Lisp_Object symbol, Lisp_Object prop, Lisp_Object raw)
 459 {
 460   bool try_reload = 1;
 461   Lisp_Object tem;
 462
 463  documentation_property:
 464
 465   tem = Fget (symbol, prop);
 466   if (EQ (tem, make_number (0)))
 467     tem = Qnil;
 468   if (INTEGERP (tem) || (CONSP (tem) && INTEGERP (XCDR (tem))))
 469     {
 470       Lisp_Object doc = tem;
 471       tem = get_doc_string (tem, 0, 0);
 472       if (NILP (tem) && try_reload)
 473         {
 474           /* The file is newer, we need to reset the pointers.  */
 475           struct gcpro gcpro1, gcpro2, gcpro3;
 476           GCPRO3 (symbol, prop, raw);
 477           try_reload = reread_doc_file (Fcar_safe (doc));
 478           UNGCPRO;
 479           if (try_reload)
 480             {
 481               try_reload = 0;
 482               goto documentation_property;
 483             }
 484         }
 485     }
 486   else if (!STRINGP (tem))
 487     /* Feval protects its argument.  */
 488     tem = Feval (tem, Qnil);
 489
 490   if (NILP (raw) && STRINGP (tem))
 491     tem = Fsubstitute_command_keys (tem);
 492   return tem;
 493 }
 494 \f
 495 /* Scanning the DOC files and placing docstring offsets into functions.  */
 496
 497 static void
 498 store_function_docstring (Lisp_Object obj, ptrdiff_t offset)
 499 {
 500   /* Don't use indirect_function here, or defaliases will apply their
 501      docstrings to the base functions (Bug#2603).  */
 502   Lisp_Object fun = SYMBOLP (obj) ? XSYMBOL (obj)->function : obj;
 503
 504   /* The type determines where the docstring is stored.  */
 505
 506   /* Lisp_Subrs have a slot for it.  */
 507   if (SUBRP (fun))
 508     {
 509       intptr_t negative_offset = - offset;
 510       XSUBR (fun)->doc = (char *) negative_offset;
 511     }
 512
 513   /* If it's a lisp form, stick it in the form.  */
 514   else if (CONSP (fun))
 515     {
 516       Lisp_Object tem;
 517
 518       tem = XCAR (fun);
 519       if (EQ (tem, Qlambda) || EQ (tem, Qautoload)
 520           || (EQ (tem, Qclosure) && (fun = XCDR (fun), 1)))
 521         {
 522           tem = Fcdr (Fcdr (fun));
 523           if (CONSP (tem) && INTEGERP (XCAR (tem)))
 524             /* FIXME: This modifies typically pure hash-cons'd data, so its
 525                correctness is quite delicate.  */
 526             XSETCAR (tem, make_number (offset));
 527         }
 528       else if (EQ (tem, Qmacro))
 529         store_function_docstring (XCDR (fun), offset);
 530     }
 531
 532   /* Bytecode objects sometimes have slots for it.  */
 533   else if (COMPILEDP (fun))
 534     {
 535       /* This bytecode object must have a slot for the
 536          docstring, since we've found a docstring for it.  */
 537       if ((ASIZE (fun) & PSEUDOVECTOR_SIZE_MASK) > COMPILED_DOC_STRING)
 538         ASET (fun, COMPILED_DOC_STRING, make_number (offset));
 539     }
 540 }
 541
 542
 543 DEFUN ("Snarf-documentation", Fsnarf_documentation, Ssnarf_documentation,
 544        1, 1, 0,
 545        doc: /* Used during Emacs initialization to scan the `etc/DOC...' file.
 546 This searches the `etc/DOC...' file for doc strings and
 547 records them in function and variable definitions.
 548 The function takes one argument, FILENAME, a string;
 549 it specifies the file name (without a directory) of the DOC file.
 550 That file is found in `../etc' now; later, when the dumped Emacs is run,
 551 the same file name is found in the `doc-directory'.  */)
 552   (Lisp_Object filename)
 553 {
 554   int fd;
 555   char buf[1024 + 1];
 556   int filled;
 557   EMACS_INT pos;
 558   Lisp_Object sym;
 559   char *p, *name;
 560   bool skip_file = 0;
 561   ptrdiff_t count;
 562
 563   CHECK_STRING (filename);
 564
 565   if
 566 #ifndef CANNOT_DUMP
 567     (!NILP (Vpurify_flag))
 568 #else /* CANNOT_DUMP */
 569       (0)
 570 #endif /* CANNOT_DUMP */
 571     {
 572       name = alloca (SCHARS (filename) + 14);
 573       strcpy (name, "../etc/");
 574     }
 575   else
 576     {
 577       CHECK_STRING (Vdoc_directory);
 578       name = alloca (SCHARS (filename) + SCHARS (Vdoc_directory) + 1);
 579       strcpy (name, SSDATA (Vdoc_directory));
 580     }
 581   strcat (name, SSDATA (filename));     /*** Add this line ***/
 582
 583   /* Vbuild_files is nil when temacs is run, and non-nil after that.  */
 584   if (NILP (Vbuild_files))
 585     {
 586       static char const *const buildobj[] =
 587         {
 588           #include "buildobj.h"
 589         };
 590       int i = sizeof buildobj / sizeof *buildobj;
 591       while (0 <= --i)
 592         Vbuild_files = Fcons (build_string (buildobj[i]), Vbuild_files);
 593       Vbuild_files = Fpurecopy (Vbuild_files);
 594     }
 595
 596   fd = emacs_open (name, O_RDONLY, 0);
 597   if (fd < 0)
 598     {
 599       int open_errno = errno;
 600       report_file_errno ("Opening doc string file", build_string (name),
 601                          open_errno);
 602     }
 603   count = SPECPDL_INDEX ();
 604   record_unwind_protect_int (close_file_unwind, fd);
 605   Vdoc_file_name = filename;
 606   filled = 0;
 607   pos = 0;
 608   while (1)
 609     {
 610       register char *end;
 611       if (filled < 512)
 612         filled += emacs_read (fd, &buf[filled], sizeof buf - 1 - filled);
 613       if (!filled)
 614         break;
 615
 616       buf[filled] = 0;
 617       end = buf + (filled < 512 ? filled : filled - 128);
 618       p = memchr (buf, '\037', end - buf);
 619       /* p points to ^_Ffunctionname\n or ^_Vvarname\n or ^_Sfilename\n.  */
 620       if (p)
 621         {
 622           end = strchr (p, '\n');
 623
 624           /* See if this is a file name, and if it is a file in build-files.  */
 625           if (p[1] == 'S')
 626             {
 627               skip_file = 0;
 628               if (end - p > 4 && end[-2] == '.'
 629                   && (end[-1] == 'o' || end[-1] == 'c'))
 630                 {
 631                   ptrdiff_t len = end - p - 2;
 632                   char *fromfile = alloca (len + 1);
 633                   memcpy (fromfile, &p[2], len);
 634                   fromfile[len] = 0;
 635                   if (fromfile[len-1] == 'c')
 636                     fromfile[len-1] = 'o';
 637
 638                   skip_file = NILP (Fmember (build_string (fromfile),
 639                                              Vbuild_files));
 640                 }
 641             }
 642
 643           sym = oblookup (Vobarray, p + 2,
 644                           multibyte_chars_in_text ((unsigned char *) p + 2,
 645                                                    end - p - 2),
 646                           end - p - 2);
 647           /* Check skip_file so that when a function is defined several
 648              times in different files (typically, once in xterm, once in
 649              w32term, ...), we only pay attention to the one that
 650              matters.  */
 651           if (! skip_file && SYMBOLP (sym))
 652             {
 653               /* Attach a docstring to a variable?  */
 654               if (p[1] == 'V')
 655                 {
 656                   /* Install file-position as variable-documentation property
 657                      and make it negative for a user-variable
 658                      (doc starts with a `*').  */
 659                   if (!NILP (Fboundp (sym)))
 660                     Fput (sym, Qvariable_documentation,
 661                           make_number ((pos + end + 1 - buf)
 662                                        * (end[1] == '*' ? -1 : 1)));
 663                 }
 664
 665               /* Attach a docstring to a function?  */
 666               else if (p[1] == 'F')
 667                 {
 668                   if (!NILP (Ffboundp (sym)))
 669                     store_function_docstring (sym, pos + end + 1 - buf);
 670                 }
 671               else if (p[1] == 'S')
 672                 ; /* Just a source file name boundary marker.  Ignore it.  */
 673
 674               else
 675                 error ("DOC file invalid at position %"pI"d", pos);
 676             }
 677         }
 678       pos += end - buf;
 679       filled -= end - buf;
 680       memmove (buf, end, filled);
 681     }
 682   return unbind_to (count, Qnil);
 683 }
 684 \f
 685 DEFUN ("substitute-command-keys", Fsubstitute_command_keys,
 686        Ssubstitute_command_keys, 1, 1, 0,
 687        doc: /* Substitute key descriptions for command names in STRING.
 688 Each substring of the form \\=\\[COMMAND] is replaced by either a
 689 keystroke sequence that invokes COMMAND, or "M-x COMMAND" if COMMAND
 690 is not on any keys.
 691
 692 Each substring of the form \\=\\{MAPVAR} is replaced by a summary of
 693 the value of MAPVAR as a keymap.  This summary is similar to the one
 694 produced by `describe-bindings'.  The summary ends in two newlines
 695 \(used by the helper function `help-make-xrefs' to find the end of the
 696 summary).
 697
 698 Each substring of the form \\=\\<MAPVAR> specifies the use of MAPVAR
 699 as the keymap for future \\=\\[COMMAND] substrings.
 700 \\=\\= quotes the following character and is discarded;
 701 thus, \\=\\=\\=\\= puts \\=\\= into the output, and \\=\\=\\=\\[ puts \\=\\[ into the output.
 702
 703 Return the original STRING if no substitutions are made.
 704 Otherwise, return a new string, without any text properties.  */)
 705   (Lisp_Object string)
 706 {
 707   char *buf;
 708   bool changed = 0;
 709   unsigned char *strp;
 710   char *bufp;
 711   ptrdiff_t idx;
 712   ptrdiff_t bsize;
 713   Lisp_Object tem;
 714   Lisp_Object keymap;
 715   unsigned char *start;
 716   ptrdiff_t length, length_byte;
 717   Lisp_Object name;
 718   struct gcpro gcpro1, gcpro2, gcpro3, gcpro4;
 719   bool multibyte;
 720   ptrdiff_t nchars;
 721
 722   if (NILP (string))
 723     return Qnil;
 724
 725   CHECK_STRING (string);
 726   tem = Qnil;
 727   keymap = Qnil;
 728   name = Qnil;
 729   GCPRO4 (string, tem, keymap, name);
 730
 731   multibyte = STRING_MULTIBYTE (string);
 732   nchars = 0;
 733
 734   /* KEYMAP is either nil (which means search all the active keymaps)
 735      or a specified local map (which means search just that and the
 736      global map).  If non-nil, it might come from Voverriding_local_map,
 737      or from a \\<mapname> construct in STRING itself..  */
 738   keymap = Voverriding_local_map;
 739
 740   bsize = SBYTES (string);
 741   bufp = buf = xmalloc (bsize);
 742
 743   strp = SDATA (string);
 744   while (strp < SDATA (string) + SBYTES (string))
 745     {
 746       if (strp[0] == '\\' && strp[1] == '=')
 747         {
 748           /* \= quotes the next character;
 749              thus, to put in \[ without its special meaning, use \=\[.  */
 750           changed = 1;
 751           strp += 2;
 752           if (multibyte)
 753             {
 754               int len;
 755
 756               STRING_CHAR_AND_LENGTH (strp, len);
 757               if (len == 1)
 758                 *bufp = *strp;
 759               else
 760                 memcpy (bufp, strp, len);
 761               strp += len;
 762               bufp += len;
 763               nchars++;
 764             }
 765           else
 766             *bufp++ = *strp++, nchars++;
 767         }
 768       else if (strp[0] == '\\' && strp[1] == '[')
 769         {
 770           ptrdiff_t start_idx;
 771           bool follow_remap = 1;
 772
 773           changed = 1;
 774           strp += 2;            /* skip \[ */
 775           start = strp;
 776           start_idx = start - SDATA (string);
 777
 778           while ((strp - SDATA (string)
 779                   < SBYTES (string))
 780                  && *strp != ']')
 781             strp++;
 782           length_byte = strp - start;
 783
 784           strp++;               /* skip ] */
 785
 786           /* Save STRP in IDX.  */
 787           idx = strp - SDATA (string);
 788           name = Fintern (make_string ((char *) start, length_byte), Qnil);
 789
 790         do_remap:
 791           tem = Fwhere_is_internal (name, keymap, Qt, Qnil, Qnil);
 792
 793           if (VECTORP (tem) && ASIZE (tem) > 1
 794               && EQ (AREF (tem, 0), Qremap) && SYMBOLP (AREF (tem, 1))
 795               && follow_remap)
 796             {
 797               name = AREF (tem, 1);
 798               follow_remap = 0;
 799               goto do_remap;
 800             }
 801
 802           /* Note the Fwhere_is_internal can GC, so we have to take
 803              relocation of string contents into account.  */
 804           strp = SDATA (string) + idx;
 805           start = SDATA (string) + start_idx;
 806
 807           if (NILP (tem))       /* but not on any keys */
 808             {
 809               ptrdiff_t offset = bufp - buf;
 810               if (STRING_BYTES_BOUND - 4 < bsize)
 811                 string_overflow ();
 812               buf = xrealloc (buf, bsize += 4);
 813               bufp = buf + offset;
 814               memcpy (bufp, "M-x ", 4);
 815               bufp += 4;
 816               nchars += 4;
 817               if (multibyte)
 818                 length = multibyte_chars_in_text (start, length_byte);
 819               else
 820                 length = length_byte;
 821               goto subst;
 822             }
 823           else
 824             {                   /* function is on a key */
 825               tem = Fkey_description (tem, Qnil);
 826               goto subst_string;
 827             }
 828         }
 829       /* \{foo} is replaced with a summary of the keymap (symbol-value foo).
 830          \<foo> just sets the keymap used for \[cmd].  */
 831       else if (strp[0] == '\\' && (strp[1] == '{' || strp[1] == '<'))
 832         {
 833           struct buffer *oldbuf;
 834           ptrdiff_t start_idx;
 835           /* This is for computing the SHADOWS arg for describe_map_tree.  */
 836           Lisp_Object active_maps = Fcurrent_active_maps (Qnil, Qnil);
 837           Lisp_Object earlier_maps;
 838           ptrdiff_t count = SPECPDL_INDEX ();
 839
 840           changed = 1;
 841           strp += 2;            /* skip \{ or \< */
 842           start = strp;
 843           start_idx = start - SDATA (string);
 844
 845           while ((strp - SDATA (string) < SBYTES (string))
 846                  && *strp != '}' && *strp != '>')
 847             strp++;
 848
 849           length_byte = strp - start;
 850           strp++;                       /* skip } or > */
 851
 852           /* Save STRP in IDX.  */
 853           idx = strp - SDATA (string);
 854
 855           /* Get the value of the keymap in TEM, or nil if undefined.
 856              Do this while still in the user's current buffer
 857              in case it is a local variable.  */
 858           name = Fintern (make_string ((char *) start, length_byte), Qnil);
 859           tem = Fboundp (name);
 860           if (! NILP (tem))
 861             {
 862               tem = Fsymbol_value (name);
 863               if (! NILP (tem))
 864                 {
 865                   tem = get_keymap (tem, 0, 1);
 866                   /* Note that get_keymap can GC.  */
 867                   strp = SDATA (string) + idx;
 868                   start = SDATA (string) + start_idx;
 869                 }
 870             }
 871
 872           /* Now switch to a temp buffer.  */
 873           oldbuf = current_buffer;
 874           set_buffer_internal (XBUFFER (Vprin1_to_string_buffer));
 875           /* This is for an unusual case where some after-change
 876              function uses 'format' or 'prin1' or something else that
 877              will thrash Vprin1_to_string_buffer we are using.  */
 878           specbind (Qinhibit_modification_hooks, Qt);
 879
 880           if (NILP (tem))
 881             {
 882               name = Fsymbol_name (name);
 883               insert_string ("\nUses keymap `");
 884               insert_from_string (name, 0, 0,
 885                                   SCHARS (name),
 886                                   SBYTES (name), 1);
 887               insert_string ("', which is not currently defined.\n");
 888               if (start[-1] == '<') keymap = Qnil;
 889             }
 890           else if (start[-1] == '<')
 891             keymap = tem;
 892           else
 893             {
 894               /* Get the list of active keymaps that precede this one.
 895                  If this one's not active, get nil.  */
 896               earlier_maps = Fcdr (Fmemq (tem, Freverse (active_maps)));
 897               describe_map_tree (tem, 1, Fnreverse (earlier_maps),
 898                                  Qnil, 0, 1, 0, 0, 1);
 899             }
 900           tem = Fbuffer_string ();
 901           Ferase_buffer ();
 902           set_buffer_internal (oldbuf);
 903           unbind_to (count, Qnil);
 904
 905         subst_string:
 906           start = SDATA (tem);
 907           length = SCHARS (tem);
 908           length_byte = SBYTES (tem);
 909         subst:
 910           {
 911             ptrdiff_t offset = bufp - buf;
 912             if (STRING_BYTES_BOUND - length_byte < bsize)
 913               string_overflow ();
 914             buf = xrealloc (buf, bsize += length_byte);
 915             bufp = buf + offset;
 916             memcpy (bufp, start, length_byte);
 917             bufp += length_byte;
 918             nchars += length;
 919             /* Check STRING again in case gc relocated it.  */
 920             strp = SDATA (string) + idx;
 921           }
 922         }
 923       else if (! multibyte)             /* just copy other chars */
 924         *bufp++ = *strp++, nchars++;
 925       else
 926         {
 927           int len;
 928
 929           STRING_CHAR_AND_LENGTH (strp, len);
 930           if (len == 1)
 931             *bufp = *strp;
 932           else
 933             memcpy (bufp, strp, len);
 934           strp += len;
 935           bufp += len;
 936           nchars++;
 937         }
 938     }
 939
 940   if (changed)                  /* don't bother if nothing substituted */
 941     tem = make_string_from_bytes (buf, nchars, bufp - buf);
 942   else
 943     tem = string;
 944   xfree (buf);
 945   RETURN_UNGCPRO (tem);
 946 }
 947 \f
 948 void
 949 syms_of_doc (void)
 950 {
 951   DEFSYM (Qfunction_documentation, "function-documentation");
 952
 953   DEFVAR_LISP ("internal-doc-file-name", Vdoc_file_name,
 954                doc: /* Name of file containing documentation strings of built-in symbols.  */);
 955   Vdoc_file_name = Qnil;
 956
 957   DEFVAR_LISP ("build-files", Vbuild_files,
 958                doc: /* A list of files used to build this Emacs binary.  */);
 959   Vbuild_files = Qnil;
 960
 961   defsubr (&Sdocumentation);
 962   defsubr (&Sdocumentation_property);
 963   defsubr (&Ssnarf_documentation);
 964   defsubr (&Ssubstitute_command_keys);
 965 }