src/undo.c

   1 /* undo handling for GNU Emacs.
   2    Copyright (C) 1990, 1993, 1994, 2000, 2001, 2002, 2003, 2004,
   3                  2005, 2006, 2007, 2008, 2009, 2010, 2011  Free Software Foundation, Inc.
   4
   5 This file is part of GNU Emacs.
   6
   7 GNU Emacs is free software: you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation, either version 3 of the License, or
  10 (at your option) any later version.
  11
  12 GNU Emacs is distributed in the hope that it will be useful,
  13 but WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  15 GNU General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GNU Emacs.  If not, see <http://www.gnu.org/licenses/>.  */
  19
  20
  21 #include <config.h>
  22 #include <setjmp.h>
  23 #include "lisp.h"
  24 #include "buffer.h"
  25 #include "commands.h"
  26 #include "window.h"
  27
  28 /* Limits controlling how much undo information to keep.  */
  29
  30 EMACS_INT undo_limit;
  31 EMACS_INT undo_strong_limit;
  32
  33 Lisp_Object Vundo_outer_limit;
  34
  35 /* Function to call when undo_outer_limit is exceeded.  */
  36
  37 Lisp_Object Vundo_outer_limit_function;
  38
  39 /* Last buffer for which undo information was recorded.  */
  40 /* BEWARE: This is not traced by the GC, so never dereference it!  */
  41 struct buffer *last_undo_buffer;
  42
  43 /* Position of point last time we inserted a boundary.  */
  44 struct buffer *last_boundary_buffer;
  45 EMACS_INT last_boundary_position;
  46
  47 Lisp_Object Qinhibit_read_only;
  48
  49 /* Marker for function call undo list elements.  */
  50
  51 Lisp_Object Qapply;
  52
  53 /* The first time a command records something for undo.
  54    it also allocates the undo-boundary object
  55    which will be added to the list at the end of the command.
  56    This ensures we can't run out of space while trying to make
  57    an undo-boundary.  */
  58 Lisp_Object pending_boundary;
  59
  60 /* Nonzero means do not record point in record_point.  */
  61
  62 int undo_inhibit_record_point;
  63
  64 /* Record point as it was at beginning of this command (if necessary)
  65    and prepare the undo info for recording a change.
  66    PT is the position of point that will naturally occur as a result of the
  67    undo record that will be added just after this command terminates.  */
  68
  69 static void
  70 record_point (pt)
  71      int pt;
  72 {
  73   int at_boundary;
  74
  75   /* Don't record position of pt when undo_inhibit_record_point holds.  */
  76   if (undo_inhibit_record_point)
  77     return;
  78
  79   /* Allocate a cons cell to be the undo boundary after this command.  */
  80   if (NILP (pending_boundary))
  81     pending_boundary = Fcons (Qnil, Qnil);
  82
  83   if ((current_buffer != last_undo_buffer)
  84       /* Don't call Fundo_boundary for the first change.  Otherwise we
  85          risk overwriting last_boundary_position in Fundo_boundary with
  86          PT of the current buffer and as a consequence not insert an
  87          undo boundary because last_boundary_position will equal pt in
  88          the test at the end of the present function (Bug#731).  */
  89       && (MODIFF > SAVE_MODIFF))
  90     Fundo_boundary ();
  91   last_undo_buffer = current_buffer;
  92
  93   if (CONSP (current_buffer->undo_list))
  94     {
  95       /* Set AT_BOUNDARY to 1 only when we have nothing other than
  96          marker adjustment before undo boundary.  */
  97
  98       Lisp_Object tail = current_buffer->undo_list, elt;
  99
 100       while (1)
 101         {
 102           if (NILP (tail))
 103             elt = Qnil;
 104           else
 105             elt = XCAR (tail);
 106           if (NILP (elt) || ! (CONSP (elt) && MARKERP (XCAR (elt))))
 107             break;
 108           tail = XCDR (tail);
 109         }
 110       at_boundary = NILP (elt);
 111     }
 112   else
 113     at_boundary = 1;
 114
 115   if (MODIFF <= SAVE_MODIFF)
 116     record_first_change ();
 117
 118   /* If we are just after an undo boundary, and
 119      point wasn't at start of deleted range, record where it was.  */
 120   if (at_boundary
 121       && current_buffer == last_boundary_buffer
 122       && last_boundary_position != pt)
 123     current_buffer->undo_list
 124       = Fcons (make_number (last_boundary_position), current_buffer->undo_list);
 125 }
 126
 127 /* Record an insertion that just happened or is about to happen,
 128    for LENGTH characters at position BEG.
 129    (It is possible to record an insertion before or after the fact
 130    because we don't need to record the contents.)  */
 131
 132 void
 133 record_insert (beg, length)
 134      int beg, length;
 135 {
 136   Lisp_Object lbeg, lend;
 137
 138   if (EQ (current_buffer->undo_list, Qt))
 139     return;
 140
 141   record_point (beg);
 142
 143   /* If this is following another insertion and consecutive with it
 144      in the buffer, combine the two.  */
 145   if (CONSP (current_buffer->undo_list))
 146     {
 147       Lisp_Object elt;
 148       elt = XCAR (current_buffer->undo_list);
 149       if (CONSP (elt)
 150           && INTEGERP (XCAR (elt))
 151           && INTEGERP (XCDR (elt))
 152           && XINT (XCDR (elt)) == beg)
 153         {
 154           XSETCDR (elt, make_number (beg + length));
 155           return;
 156         }
 157     }
 158
 159   XSETFASTINT (lbeg, beg);
 160   XSETINT (lend, beg + length);
 161   current_buffer->undo_list = Fcons (Fcons (lbeg, lend),
 162                                      current_buffer->undo_list);
 163 }
 164
 165 /* Record that a deletion is about to take place,
 166    of the characters in STRING, at location BEG.  */
 167
 168 void
 169 record_delete (beg, string)
 170      int beg;
 171      Lisp_Object string;
 172 {
 173   Lisp_Object sbeg;
 174
 175   if (EQ (current_buffer->undo_list, Qt))
 176     return;
 177
 178   if (PT == beg + SCHARS (string))
 179     {
 180       XSETINT (sbeg, -beg);
 181       record_point (PT);
 182     }
 183   else
 184     {
 185       XSETFASTINT (sbeg, beg);
 186       record_point (beg);
 187     }
 188
 189   current_buffer->undo_list
 190     = Fcons (Fcons (string, sbeg), current_buffer->undo_list);
 191 }
 192
 193 /* Record the fact that MARKER is about to be adjusted by ADJUSTMENT.
 194    This is done only when a marker points within text being deleted,
 195    because that's the only case where an automatic marker adjustment
 196    won't be inverted automatically by undoing the buffer modification.  */
 197
 198 void
 199 record_marker_adjustment (marker, adjustment)
 200      Lisp_Object marker;
 201      int adjustment;
 202 {
 203   if (EQ (current_buffer->undo_list, Qt))
 204     return;
 205
 206   /* Allocate a cons cell to be the undo boundary after this command.  */
 207   if (NILP (pending_boundary))
 208     pending_boundary = Fcons (Qnil, Qnil);
 209
 210   if (current_buffer != last_undo_buffer)
 211     Fundo_boundary ();
 212   last_undo_buffer = current_buffer;
 213
 214   current_buffer->undo_list
 215     = Fcons (Fcons (marker, make_number (adjustment)),
 216              current_buffer->undo_list);
 217 }
 218
 219 /* Record that a replacement is about to take place,
 220    for LENGTH characters at location BEG.
 221    The replacement must not change the number of characters.  */
 222
 223 void
 224 record_change (beg, length)
 225      int beg, length;
 226 {
 227   record_delete (beg, make_buffer_string (beg, beg + length, 1));
 228   record_insert (beg, length);
 229 }
 230 \f
 231 /* Record that an unmodified buffer is about to be changed.
 232    Record the file modification date so that when undoing this entry
 233    we can tell whether it is obsolete because the file was saved again.  */
 234
 235 void
 236 record_first_change ()
 237 {
 238   Lisp_Object high, low;
 239   struct buffer *base_buffer = current_buffer;
 240
 241   if (EQ (current_buffer->undo_list, Qt))
 242     return;
 243
 244   if (current_buffer != last_undo_buffer)
 245     Fundo_boundary ();
 246   last_undo_buffer = current_buffer;
 247
 248   if (base_buffer->base_buffer)
 249     base_buffer = base_buffer->base_buffer;
 250
 251   XSETFASTINT (high, (base_buffer->modtime >> 16) & 0xffff);
 252   XSETFASTINT (low, base_buffer->modtime & 0xffff);
 253   current_buffer->undo_list = Fcons (Fcons (Qt, Fcons (high, low)), current_buffer->undo_list);
 254 }
 255
 256 /* Record a change in property PROP (whose old value was VAL)
 257    for LENGTH characters starting at position BEG in BUFFER.  */
 258
 259 void
 260 record_property_change (beg, length, prop, value, buffer)
 261      int beg, length;
 262      Lisp_Object prop, value, buffer;
 263 {
 264   Lisp_Object lbeg, lend, entry;
 265   struct buffer *obuf = current_buffer, *buf = XBUFFER (buffer);
 266   int boundary = 0;
 267
 268   if (EQ (buf->undo_list, Qt))
 269     return;
 270
 271   /* Allocate a cons cell to be the undo boundary after this command.  */
 272   if (NILP (pending_boundary))
 273     pending_boundary = Fcons (Qnil, Qnil);
 274
 275   if (buf != last_undo_buffer)
 276     boundary = 1;
 277   last_undo_buffer = buf;
 278
 279   /* Switch temporarily to the buffer that was changed.  */
 280   current_buffer = buf;
 281
 282   if (boundary)
 283     Fundo_boundary ();
 284
 285   if (MODIFF <= SAVE_MODIFF)
 286     record_first_change ();
 287
 288   XSETINT (lbeg, beg);
 289   XSETINT (lend, beg + length);
 290   entry = Fcons (Qnil, Fcons (prop, Fcons (value, Fcons (lbeg, lend))));
 291   current_buffer->undo_list = Fcons (entry, current_buffer->undo_list);
 292
 293   current_buffer = obuf;
 294 }
 295
 296 DEFUN ("undo-boundary", Fundo_boundary, Sundo_boundary, 0, 0, 0,
 297        doc: /* Mark a boundary between units of undo.
 298 An undo command will stop at this point,
 299 but another undo command will undo to the previous boundary.  */)
 300      ()
 301 {
 302   Lisp_Object tem;
 303   if (EQ (current_buffer->undo_list, Qt))
 304     return Qnil;
 305   tem = Fcar (current_buffer->undo_list);
 306   if (!NILP (tem))
 307     {
 308       /* One way or another, cons nil onto the front of the undo list.  */
 309       if (!NILP (pending_boundary))
 310         {
 311           /* If we have preallocated the cons cell to use here,
 312              use that one.  */
 313           XSETCDR (pending_boundary, current_buffer->undo_list);
 314           current_buffer->undo_list = pending_boundary;
 315           pending_boundary = Qnil;
 316         }
 317       else
 318         current_buffer->undo_list = Fcons (Qnil, current_buffer->undo_list);
 319     }
 320   last_boundary_position = PT;
 321   last_boundary_buffer = current_buffer;
 322   return Qnil;
 323 }
 324
 325 /* At garbage collection time, make an undo list shorter at the end,
 326    returning the truncated list.  How this is done depends on the
 327    variables undo-limit, undo-strong-limit and undo-outer-limit.
 328    In some cases this works by calling undo-outer-limit-function.  */
 329
 330 void
 331 truncate_undo_list (b)
 332      struct buffer *b;
 333 {
 334   Lisp_Object list;
 335   Lisp_Object prev, next, last_boundary;
 336   int size_so_far = 0;
 337
 338   /* Make sure that calling undo-outer-limit-function
 339      won't cause another GC.  */
 340   int count = inhibit_garbage_collection ();
 341
 342   /* Make the buffer current to get its local values of variables such
 343      as undo_limit.  Also so that Vundo_outer_limit_function can
 344      tell which buffer to operate on.  */
 345   record_unwind_protect (set_buffer_if_live, Fcurrent_buffer ());
 346   set_buffer_internal (b);
 347
 348   list = b->undo_list;
 349
 350   prev = Qnil;
 351   next = list;
 352   last_boundary = Qnil;
 353
 354   /* If the first element is an undo boundary, skip past it.  */
 355   if (CONSP (next) && NILP (XCAR (next)))
 356     {
 357       /* Add in the space occupied by this element and its chain link.  */
 358       size_so_far += sizeof (struct Lisp_Cons);
 359
 360       /* Advance to next element.  */
 361       prev = next;
 362       next = XCDR (next);
 363     }
 364
 365   /* Always preserve at least the most recent undo record
 366      unless it is really horribly big.
 367
 368      Skip, skip, skip the undo, skip, skip, skip the undo,
 369      Skip, skip, skip the undo, skip to the undo bound'ry.  */
 370
 371   while (CONSP (next) && ! NILP (XCAR (next)))
 372     {
 373       Lisp_Object elt;
 374       elt = XCAR (next);
 375
 376       /* Add in the space occupied by this element and its chain link.  */
 377       size_so_far += sizeof (struct Lisp_Cons);
 378       if (CONSP (elt))
 379         {
 380           size_so_far += sizeof (struct Lisp_Cons);
 381           if (STRINGP (XCAR (elt)))
 382             size_so_far += (sizeof (struct Lisp_String) - 1
 383                             + SCHARS (XCAR (elt)));
 384         }
 385
 386       /* Advance to next element.  */
 387       prev = next;
 388       next = XCDR (next);
 389     }
 390
 391   /* If by the first boundary we have already passed undo_outer_limit,
 392      we're heading for memory full, so offer to clear out the list.  */
 393   if (INTEGERP (Vundo_outer_limit)
 394       && size_so_far > XINT (Vundo_outer_limit)
 395       && !NILP (Vundo_outer_limit_function))
 396     {
 397       Lisp_Object tem;
 398       struct buffer *temp = last_undo_buffer;
 399
 400       /* Normally the function this calls is undo-outer-limit-truncate.  */
 401       tem = call1 (Vundo_outer_limit_function, make_number (size_so_far));
 402       if (! NILP (tem))
 403         {
 404           /* The function is responsible for making
 405              any desired changes in buffer-undo-list.  */
 406           unbind_to (count, Qnil);
 407           return;
 408         }
 409       /* That function probably used the minibuffer, and if so, that
 410          changed last_undo_buffer.  Change it back so that we don't
 411          force next change to make an undo boundary here.  */
 412       last_undo_buffer = temp;
 413     }
 414
 415   if (CONSP (next))
 416     last_boundary = prev;
 417
 418   /* Keep additional undo data, if it fits in the limits.  */
 419   while (CONSP (next))
 420     {
 421       Lisp_Object elt;
 422       elt = XCAR (next);
 423
 424       /* When we get to a boundary, decide whether to truncate
 425          either before or after it.  The lower threshold, undo_limit,
 426          tells us to truncate after it.  If its size pushes past
 427          the higher threshold undo_strong_limit, we truncate before it.  */
 428       if (NILP (elt))
 429         {
 430           if (size_so_far > undo_strong_limit)
 431             break;
 432           last_boundary = prev;
 433           if (size_so_far > undo_limit)
 434             break;
 435         }
 436
 437       /* Add in the space occupied by this element and its chain link.  */
 438       size_so_far += sizeof (struct Lisp_Cons);
 439       if (CONSP (elt))
 440         {
 441           size_so_far += sizeof (struct Lisp_Cons);
 442           if (STRINGP (XCAR (elt)))
 443             size_so_far += (sizeof (struct Lisp_String) - 1
 444                             + SCHARS (XCAR (elt)));
 445         }
 446
 447       /* Advance to next element.  */
 448       prev = next;
 449       next = XCDR (next);
 450     }
 451
 452   /* If we scanned the whole list, it is short enough; don't change it.  */
 453   if (NILP (next))
 454     ;
 455   /* Truncate at the boundary where we decided to truncate.  */
 456   else if (!NILP (last_boundary))
 457     XSETCDR (last_boundary, Qnil);
 458   /* There's nothing we decided to keep, so clear it out.  */
 459   else
 460     b->undo_list = Qnil;
 461
 462   unbind_to (count, Qnil);
 463 }
 464 \f
 465 DEFUN ("primitive-undo", Fprimitive_undo, Sprimitive_undo, 2, 2, 0,
 466        doc: /* Undo N records from the front of the list LIST.
 467 Return what remains of the list.  */)
 468      (n, list)
 469      Lisp_Object n, list;
 470 {
 471   struct gcpro gcpro1, gcpro2;
 472   Lisp_Object next;
 473   int count = SPECPDL_INDEX ();
 474   register int arg;
 475   Lisp_Object oldlist;
 476   int did_apply = 0;
 477
 478 #if 0  /* This is a good feature, but would make undo-start
 479           unable to do what is expected.  */
 480   Lisp_Object tem;
 481
 482   /* If the head of the list is a boundary, it is the boundary
 483      preceding this command.  Get rid of it and don't count it.  */
 484   tem = Fcar (list);
 485   if (NILP (tem))
 486     list = Fcdr (list);
 487 #endif
 488
 489   CHECK_NUMBER (n);
 490   arg = XINT (n);
 491   next = Qnil;
 492   GCPRO2 (next, list);
 493   /* I don't think we need to gcpro oldlist, as we use it only
 494      to check for EQ.  ++kfs  */
 495
 496   /* In a writable buffer, enable undoing read-only text that is so
 497      because of text properties.  */
 498   if (NILP (current_buffer->read_only))
 499     specbind (Qinhibit_read_only, Qt);
 500
 501   /* Don't let `intangible' properties interfere with undo.  */
 502   specbind (Qinhibit_point_motion_hooks, Qt);
 503
 504   oldlist = current_buffer->undo_list;
 505
 506   while (arg > 0)
 507     {
 508       while (CONSP (list))
 509         {
 510           next = XCAR (list);
 511           list = XCDR (list);
 512           /* Exit inner loop at undo boundary.  */
 513           if (NILP (next))
 514             break;
 515           /* Handle an integer by setting point to that value.  */
 516           if (INTEGERP (next))
 517             SET_PT (clip_to_bounds (BEGV, XINT (next), ZV));
 518           else if (CONSP (next))
 519             {
 520               Lisp_Object car, cdr;
 521
 522               car = XCAR (next);
 523               cdr = XCDR (next);
 524               if (EQ (car, Qt))
 525                 {
 526                   /* Element (t high . low) records previous modtime.  */
 527                   Lisp_Object high, low;
 528                   int mod_time;
 529                   struct buffer *base_buffer = current_buffer;
 530
 531                   high = Fcar (cdr);
 532                   low = Fcdr (cdr);
 533                   mod_time = (XFASTINT (high) << 16) + XFASTINT (low);
 534
 535                   if (current_buffer->base_buffer)
 536                     base_buffer = current_buffer->base_buffer;
 537
 538                   /* If this records an obsolete save
 539                      (not matching the actual disk file)
 540                      then don't mark unmodified.  */
 541                   if (mod_time != base_buffer->modtime)
 542                     continue;
 543 #ifdef CLASH_DETECTION
 544                   Funlock_buffer ();
 545 #endif /* CLASH_DETECTION */
 546                   Fset_buffer_modified_p (Qnil);
 547                 }
 548               else if (EQ (car, Qnil))
 549                 {
 550                   /* Element (nil PROP VAL BEG . END) is property change.  */
 551                   Lisp_Object beg, end, prop, val;
 552
 553                   prop = Fcar (cdr);
 554                   cdr = Fcdr (cdr);
 555                   val = Fcar (cdr);
 556                   cdr = Fcdr (cdr);
 557                   beg = Fcar (cdr);
 558                   end = Fcdr (cdr);
 559
 560                   if (XINT (beg) < BEGV || XINT (end) > ZV)
 561                     error ("Changes to be undone are outside visible portion of buffer");
 562                   Fput_text_property (beg, end, prop, val, Qnil);
 563                 }
 564               else if (INTEGERP (car) && INTEGERP (cdr))
 565                 {
 566                   /* Element (BEG . END) means range was inserted.  */
 567
 568                   if (XINT (car) < BEGV
 569                       || XINT (cdr) > ZV)
 570                     error ("Changes to be undone are outside visible portion of buffer");
 571                   /* Set point first thing, so that undoing this undo
 572                      does not send point back to where it is now.  */
 573                   Fgoto_char (car);
 574                   Fdelete_region (car, cdr);
 575                 }
 576               else if (EQ (car, Qapply))
 577                 {
 578                   /* Element (apply FUN . ARGS) means call FUN to undo.  */
 579                   struct buffer *save_buffer = current_buffer;
 580
 581                   car = Fcar (cdr);
 582                   cdr = Fcdr (cdr);
 583                   if (INTEGERP (car))
 584                     {
 585                       /* Long format: (apply DELTA START END FUN . ARGS).  */
 586                       Lisp_Object delta = car;
 587                       Lisp_Object start = Fcar (cdr);
 588                       Lisp_Object end   = Fcar (Fcdr (cdr));
 589                       Lisp_Object start_mark = Fcopy_marker (start, Qnil);
 590                       Lisp_Object end_mark   = Fcopy_marker (end, Qt);
 591
 592                       cdr = Fcdr (Fcdr (cdr));
 593                       apply1 (Fcar (cdr), Fcdr (cdr));
 594
 595                       /* Check that the function did what the entry said it
 596                          would do.  */
 597                       if (!EQ (start, Fmarker_position (start_mark))
 598                           || (XINT (delta) + XINT (end)
 599                               != marker_position (end_mark)))
 600                         error ("Changes to be undone by function different than announced");
 601                       Fset_marker (start_mark, Qnil, Qnil);
 602                       Fset_marker (end_mark, Qnil, Qnil);
 603                     }
 604                   else
 605                     apply1 (car, cdr);
 606
 607                   if (save_buffer != current_buffer)
 608                     error ("Undo function switched buffer");
 609                   did_apply = 1;
 610                 }
 611               else if (STRINGP (car) && INTEGERP (cdr))
 612                 {
 613                   /* Element (STRING . POS) means STRING was deleted.  */
 614                   Lisp_Object membuf;
 615                   int pos = XINT (cdr);
 616
 617                   membuf = car;
 618                   if (pos < 0)
 619                     {
 620                       if (-pos < BEGV || -pos > ZV)
 621                         error ("Changes to be undone are outside visible portion of buffer");
 622                       SET_PT (-pos);
 623                       Finsert (1, &membuf);
 624                     }
 625                   else
 626                     {
 627                       if (pos < BEGV || pos > ZV)
 628                         error ("Changes to be undone are outside visible portion of buffer");
 629                       SET_PT (pos);
 630
 631                       /* Now that we record marker adjustments
 632                          (caused by deletion) for undo,
 633                          we should always insert after markers,
 634                          so that undoing the marker adjustments
 635                          put the markers back in the right place.  */
 636                       Finsert (1, &membuf);
 637                       SET_PT (pos);
 638                     }
 639                 }
 640               else if (MARKERP (car) && INTEGERP (cdr))
 641                 {
 642                   /* (MARKER . INTEGER) means a marker MARKER
 643                      was adjusted by INTEGER.  */
 644                   if (XMARKER (car)->buffer)
 645                     Fset_marker (car,
 646                                  make_number (marker_position (car) - XINT (cdr)),
 647                                  Fmarker_buffer (car));
 648                 }
 649             }
 650         }
 651       arg--;
 652     }
 653
 654
 655   /* Make sure an apply entry produces at least one undo entry,
 656      so the test in `undo' for continuing an undo series
 657      will work right.  */
 658   if (did_apply
 659       && EQ (oldlist, current_buffer->undo_list))
 660     current_buffer->undo_list
 661       = Fcons (list3 (Qapply, Qcdr, Qnil), current_buffer->undo_list);
 662
 663   UNGCPRO;
 664   return unbind_to (count, list);
 665 }
 666 \f
 667 void
 668 syms_of_undo ()
 669 {
 670   Qinhibit_read_only = intern_c_string ("inhibit-read-only");
 671   staticpro (&Qinhibit_read_only);
 672
 673   Qapply = intern_c_string ("apply");
 674   staticpro (&Qapply);
 675
 676   pending_boundary = Qnil;
 677   staticpro (&pending_boundary);
 678
 679   last_undo_buffer = NULL;
 680   last_boundary_buffer = NULL;
 681
 682   defsubr (&Sprimitive_undo);
 683   defsubr (&Sundo_boundary);
 684
 685   DEFVAR_INT ("undo-limit", &undo_limit,
 686               doc: /* Keep no more undo information once it exceeds this size.
 687 This limit is applied when garbage collection happens.
 688 When a previous command increases the total undo list size past this
 689 value, the earlier commands that came before it are forgotten.
 690
 691 The size is counted as the number of bytes occupied,
 692 which includes both saved text and other data.  */);
 693   undo_limit = 80000;
 694
 695   DEFVAR_INT ("undo-strong-limit", &undo_strong_limit,
 696               doc: /* Don't keep more than this much size of undo information.
 697 This limit is applied when garbage collection happens.
 698 When a previous command increases the total undo list size past this
 699 value, that command and the earlier commands that came before it are forgotten.
 700 However, the most recent buffer-modifying command's undo info
 701 is never discarded for this reason.
 702
 703 The size is counted as the number of bytes occupied,
 704 which includes both saved text and other data.  */);
 705   undo_strong_limit = 120000;
 706
 707   DEFVAR_LISP ("undo-outer-limit", &Vundo_outer_limit,
 708               doc: /* Outer limit on size of undo information for one command.
 709 At garbage collection time, if the current command has produced
 710 more than this much undo information, it discards the info and displays
 711 a warning.  This is a last-ditch limit to prevent memory overflow.
 712
 713 The size is counted as the number of bytes occupied, which includes
 714 both saved text and other data.  A value of nil means no limit.  In
 715 this case, accumulating one huge undo entry could make Emacs crash as
 716 a result of memory overflow.
 717
 718 In fact, this calls the function which is the value of
 719 `undo-outer-limit-function' with one argument, the size.
 720 The text above describes the behavior of the function
 721 that variable usually specifies.  */);
 722   Vundo_outer_limit = make_number (12000000);
 723
 724   DEFVAR_LISP ("undo-outer-limit-function", &Vundo_outer_limit_function,
 725                doc: /* Function to call when an undo list exceeds `undo-outer-limit'.
 726 This function is called with one argument, the current undo list size
 727 for the most recent command (since the last undo boundary).
 728 If the function returns t, that means truncation has been fully handled.
 729 If it returns nil, the other forms of truncation are done.
 730
 731 Garbage collection is inhibited around the call to this function,
 732 so it must make sure not to do a lot of consing.  */);
 733   Vundo_outer_limit_function = Qnil;
 734
 735   DEFVAR_BOOL ("undo-inhibit-record-point", &undo_inhibit_record_point,
 736                doc: /* Non-nil means do not record `point' in `buffer-undo-list'.  */);
 737   undo_inhibit_record_point = 0;
 738 }
 739
 740 /* arch-tag: d546ee01-4aed-4ffb-bb8b-eefaae50d38a
 741    (do not change this comment) */