summaryrefslogtreecommitdiff
path: root/src/undo.c
blob: adc12193fd43388b0f718f3aae7d60ee5632c40c (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
/* undo handling for GNU Emacs.
   Copyright (C) 1990, 1993, 1994, 2000, 2001, 2002, 2003, 2004,
                 2005, 2006, 2007  Free Software Foundation, Inc.

This file is part of GNU Emacs.

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

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

You should have received a copy of the GNU General Public License
along with GNU Emacs; see the file COPYING.  If not, write to
the Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor,
Boston, MA 02110-1301, USA.  */


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

/* Limits controlling how much undo information to keep.  */

EMACS_INT undo_limit;
EMACS_INT undo_strong_limit;

Lisp_Object Vundo_outer_limit;

/* Function to call when undo_outer_limit is exceeded.  */

Lisp_Object Vundo_outer_limit_function;

/* Last buffer for which undo information was recorded.  */
Lisp_Object last_undo_buffer;

Lisp_Object Qinhibit_read_only;

/* Marker for function call undo list elements.  */

Lisp_Object Qapply;

/* The first time a command records something for undo.
   it also allocates the undo-boundary object
   which will be added to the list at the end of the command.
   This ensures we can't run out of space while trying to make
   an undo-boundary.  */
Lisp_Object pending_boundary;

/* Record point as it was at beginning of this command (if necessary)
   And prepare the undo info for recording a change.
   PT is the position of point that will naturally occur as a result of the
   undo record that will be added just after this command terminates.  */

static void
record_point (pt)
     int pt;
{
  int at_boundary;

  /* Allocate a cons cell to be the undo boundary after this command.  */
  if (NILP (pending_boundary))
    pending_boundary = Fcons (Qnil, Qnil);

  if (!BUFFERP (last_undo_buffer)
      || current_buffer != XBUFFER (last_undo_buffer))
    Fundo_boundary ();
  XSETBUFFER (last_undo_buffer, current_buffer);

  if (CONSP (current_buffer->undo_list))
    {
      /* Set AT_BOUNDARY to 1 only when we have nothing other than
         marker adjustment before undo boundary.  */

      Lisp_Object tail = current_buffer->undo_list, elt;

      while (1)
	{
	  if (NILP (tail))
	    elt = Qnil;
	  else
	    elt = XCAR (tail);
	  if (NILP (elt) || ! (CONSP (elt) && MARKERP (XCAR (elt))))
	    break;
	  tail = XCDR (tail);
	}
      at_boundary = NILP (elt);
    }
  else
    at_boundary = 1;

  if (MODIFF <= SAVE_MODIFF)
    record_first_change ();

  /* If we are just after an undo boundary, and
     point wasn't at start of deleted range, record where it was.  */
  if (at_boundary
      && BUFFERP (last_point_position_buffer)
      /* If we're called from batch mode, this could be nil.  */
      && current_buffer == XBUFFER (last_point_position_buffer))
    {
      /* If we have switched windows, use the point value
	 from the window we are in.  */
      if (! EQ (last_point_position_window, selected_window))
	last_point_position = marker_position (XWINDOW (selected_window)->pointm);

      if (last_point_position != pt)
	current_buffer->undo_list
	  = Fcons (make_number (last_point_position), current_buffer->undo_list);
    }
}

/* Record an insertion that just happened or is about to happen,
   for LENGTH characters at position BEG.
   (It is possible to record an insertion before or after the fact
   because we don't need to record the contents.)  */

void
record_insert (beg, length)
     int beg, length;
{
  Lisp_Object lbeg, lend;

  if (EQ (current_buffer->undo_list, Qt))
    return;

  record_point (beg);

  /* If this is following another insertion and consecutive with it
     in the buffer, combine the two.  */
  if (CONSP (current_buffer->undo_list))
    {
      Lisp_Object elt;
      elt = XCAR (current_buffer->undo_list);
      if (CONSP (elt)
	  && INTEGERP (XCAR (elt))
	  && INTEGERP (XCDR (elt))
	  && XINT (XCDR (elt)) == beg)
	{
	  XSETCDR (elt, make_number (beg + length));
	  return;
	}
    }

  XSETFASTINT (lbeg, beg);
  XSETINT (lend, beg + length);
  current_buffer->undo_list = Fcons (Fcons (lbeg, lend),
                                     current_buffer->undo_list);
}

/* Record that a deletion is about to take place,
   of the characters in STRING, at location BEG.  */

void
record_delete (beg, string)
     int beg;
     Lisp_Object string;
{
  Lisp_Object sbeg;

  if (EQ (current_buffer->undo_list, Qt))
    return;

  if (PT == beg + SCHARS (string))
    {
      XSETINT (sbeg, -beg);
      record_point (PT);
    }
  else
    {
      XSETFASTINT (sbeg, beg);
      record_point (beg);
    }

  current_buffer->undo_list
    = Fcons (Fcons (string, sbeg), current_buffer->undo_list);
}

/* Record the fact that MARKER is about to be adjusted by ADJUSTMENT.
   This is done only when a marker points within text being deleted,
   because that's the only case where an automatic marker adjustment
   won't be inverted automatically by undoing the buffer modification.  */

void
record_marker_adjustment (marker, adjustment)
     Lisp_Object marker;
     int adjustment;
{
  if (EQ (current_buffer->undo_list, Qt))
    return;

  /* Allocate a cons cell to be the undo boundary after this command.  */
  if (NILP (pending_boundary))
    pending_boundary = Fcons (Qnil, Qnil);

  if (!BUFFERP (last_undo_buffer)
      || current_buffer != XBUFFER (last_undo_buffer))
    Fundo_boundary ();
  XSETBUFFER (last_undo_buffer, current_buffer);

  current_buffer->undo_list
    = Fcons (Fcons (marker, make_number (adjustment)),
	     current_buffer->undo_list);
}

/* Record that a replacement is about to take place,
   for LENGTH characters at location BEG.
   The replacement must not change the number of characters.  */

void
record_change (beg, length)
     int beg, length;
{
  record_delete (beg, make_buffer_string (beg, beg + length, 1));
  record_insert (beg, length);
}

/* Record that an unmodified buffer is about to be changed.
   Record the file modification date so that when undoing this entry
   we can tell whether it is obsolete because the file was saved again.  */

void
record_first_change ()
{
  Lisp_Object high, low;
  struct buffer *base_buffer = current_buffer;

  if (EQ (current_buffer->undo_list, Qt))
    return;

  if (!BUFFERP (last_undo_buffer)
      || current_buffer != XBUFFER (last_undo_buffer))
    Fundo_boundary ();
  XSETBUFFER (last_undo_buffer, current_buffer);

  if (base_buffer->base_buffer)
    base_buffer = base_buffer->base_buffer;

  XSETFASTINT (high, (base_buffer->modtime >> 16) & 0xffff);
  XSETFASTINT (low, base_buffer->modtime & 0xffff);
  current_buffer->undo_list = Fcons (Fcons (Qt, Fcons (high, low)), current_buffer->undo_list);
}

/* Record a change in property PROP (whose old value was VAL)
   for LENGTH characters starting at position BEG in BUFFER.  */

void
record_property_change (beg, length, prop, value, buffer)
     int beg, length;
     Lisp_Object prop, value, buffer;
{
  Lisp_Object lbeg, lend, entry;
  struct buffer *obuf = current_buffer;
  int boundary = 0;

  if (EQ (XBUFFER (buffer)->undo_list, Qt))
    return;

  /* Allocate a cons cell to be the undo boundary after this command.  */
  if (NILP (pending_boundary))
    pending_boundary = Fcons (Qnil, Qnil);

  if (!EQ (buffer, last_undo_buffer))
    boundary = 1;
  last_undo_buffer = buffer;

  /* Switch temporarily to the buffer that was changed.  */
  current_buffer = XBUFFER (buffer);

  if (boundary)
    Fundo_boundary ();

  if (MODIFF <= SAVE_MODIFF)
    record_first_change ();

  XSETINT (lbeg, beg);
  XSETINT (lend, beg + length);
  entry = Fcons (Qnil, Fcons (prop, Fcons (value, Fcons (lbeg, lend))));
  current_buffer->undo_list = Fcons (entry, current_buffer->undo_list);

  current_buffer = obuf;
}

DEFUN ("undo-boundary", Fundo_boundary, Sundo_boundary, 0, 0, 0,
       doc: /* Mark a boundary between units of undo.
An undo command will stop at this point,
but another undo command will undo to the previous boundary.  */)
     ()
{
  Lisp_Object tem;
  if (EQ (current_buffer->undo_list, Qt))
    return Qnil;
  tem = Fcar (current_buffer->undo_list);
  if (!NILP (tem))
    {
      /* One way or another, cons nil onto the front of the undo list.  */
      if (!NILP (pending_boundary))
	{
	  /* If we have preallocated the cons cell to use here,
	     use that one.  */
	  XSETCDR (pending_boundary, current_buffer->undo_list);
	  current_buffer->undo_list = pending_boundary;
	  pending_boundary = Qnil;
	}
      else
	current_buffer->undo_list = Fcons (Qnil, current_buffer->undo_list);
    }
  return Qnil;
}

/* At garbage collection time, make an undo list shorter at the end,
   returning the truncated list.  How this is done depends on the
   variables undo-limit, undo-strong-limit and undo-outer-limit.
   In some cases this works by calling undo-outer-limit-function.  */

void
truncate_undo_list (b)
     struct buffer *b;
{
  Lisp_Object list;
  Lisp_Object prev, next, last_boundary;
  int size_so_far = 0;

  /* Make sure that calling undo-outer-limit-function
     won't cause another GC.  */
  int count = inhibit_garbage_collection ();

  /* Make the buffer current to get its local values of variables such
     as undo_limit.  Also so that Vundo_outer_limit_function can
     tell which buffer to operate on.  */
  record_unwind_protect (set_buffer_if_live, Fcurrent_buffer ());
  set_buffer_internal (b);

  list = b->undo_list;

  prev = Qnil;
  next = list;
  last_boundary = Qnil;

  /* If the first element is an undo boundary, skip past it.  */
  if (CONSP (next) && NILP (XCAR (next)))
    {
      /* Add in the space occupied by this element and its chain link.  */
      size_so_far += sizeof (struct Lisp_Cons);

      /* Advance to next element.  */
      prev = next;
      next = XCDR (next);
    }

  /* Always preserve at least the most recent undo record
     unless it is really horribly big.

     Skip, skip, skip the undo, skip, skip, skip the undo,
     Skip, skip, skip the undo, skip to the undo bound'ry.  */

  while (CONSP (next) && ! NILP (XCAR (next)))
    {
      Lisp_Object elt;
      elt = XCAR (next);

      /* Add in the space occupied by this element and its chain link.  */
      size_so_far += sizeof (struct Lisp_Cons);
      if (CONSP (elt))
	{
	  size_so_far += sizeof (struct Lisp_Cons);
	  if (STRINGP (XCAR (elt)))
	    size_so_far += (sizeof (struct Lisp_String) - 1
			    + SCHARS (XCAR (elt)));
	}

      /* Advance to next element.  */
      prev = next;
      next = XCDR (next);
    }

  /* If by the first boundary we have already passed undo_outer_limit,
     we're heading for memory full, so offer to clear out the list.  */
  if (INTEGERP (Vundo_outer_limit)
      && size_so_far > XINT (Vundo_outer_limit)
      && !NILP (Vundo_outer_limit_function))
    {
      Lisp_Object temp = last_undo_buffer, tem;

      /* Normally the function this calls is undo-outer-limit-truncate.  */
      tem = call1 (Vundo_outer_limit_function, make_number (size_so_far));
      if (! NILP (tem))
	{
	  /* The function is responsible for making
	     any desired changes in buffer-undo-list.  */
	  unbind_to (count, Qnil);
	  return;
	}
      /* That function probably used the minibuffer, and if so, that
	 changed last_undo_buffer.  Change it back so that we don't
	 force next change to make an undo boundary here.  */
      last_undo_buffer = temp;
    }

  if (CONSP (next))
    last_boundary = prev;

  /* Keep additional undo data, if it fits in the limits.  */
  while (CONSP (next))
    {
      Lisp_Object elt;
      elt = XCAR (next);

      /* When we get to a boundary, decide whether to truncate
	 either before or after it.  The lower threshold, undo_limit,
	 tells us to truncate after it.  If its size pushes past
	 the higher threshold undo_strong_limit, we truncate before it.  */
      if (NILP (elt))
	{
	  if (size_so_far > undo_strong_limit)
	    break;
	  last_boundary = prev;
	  if (size_so_far > undo_limit)
	    break;
	}

      /* Add in the space occupied by this element and its chain link.  */
      size_so_far += sizeof (struct Lisp_Cons);
      if (CONSP (elt))
	{
	  size_so_far += sizeof (struct Lisp_Cons);
	  if (STRINGP (XCAR (elt)))
	    size_so_far += (sizeof (struct Lisp_String) - 1
			    + SCHARS (XCAR (elt)));
	}

      /* Advance to next element.  */
      prev = next;
      next = XCDR (next);
    }

  /* If we scanned the whole list, it is short enough; don't change it.  */
  if (NILP (next))
    ;
  /* Truncate at the boundary where we decided to truncate.  */
  else if (!NILP (last_boundary))
    XSETCDR (last_boundary, Qnil);
  /* There's nothing we decided to keep, so clear it out.  */
  else
    b->undo_list = Qnil;

  unbind_to (count, Qnil);
}

DEFUN ("primitive-undo", Fprimitive_undo, Sprimitive_undo, 2, 2, 0,
       doc: /* Undo N records from the front of the list LIST.
Return what remains of the list.  */)
     (n, list)
     Lisp_Object n, list;
{
  struct gcpro gcpro1, gcpro2;
  Lisp_Object next;
  int count = SPECPDL_INDEX ();
  register int arg;
  Lisp_Object oldlist;
  int did_apply = 0;

#if 0  /* This is a good feature, but would make undo-start
	  unable to do what is expected.  */
  Lisp_Object tem;

  /* If the head of the list is a boundary, it is the boundary
     preceding this command.  Get rid of it and don't count it.  */
  tem = Fcar (list);
  if (NILP (tem))
    list = Fcdr (list);
#endif

  CHECK_NUMBER (n);
  arg = XINT (n);
  next = Qnil;
  GCPRO2 (next, list);
  /* I don't think we need to gcpro oldlist, as we use it only
     to check for EQ.  ++kfs  */

  /* In a writable buffer, enable undoing read-only text that is so
     because of text properties.  */
  if (NILP (current_buffer->read_only))
    specbind (Qinhibit_read_only, Qt);

  /* Don't let `intangible' properties interfere with undo.  */
  specbind (Qinhibit_point_motion_hooks, Qt);

  oldlist = current_buffer->undo_list;

  while (arg > 0)
    {
      while (CONSP (list))
	{
	  next = XCAR (list);
	  list = XCDR (list);
	  /* Exit inner loop at undo boundary.  */
	  if (NILP (next))
	    break;
	  /* Handle an integer by setting point to that value.  */
	  if (INTEGERP (next))
	    SET_PT (clip_to_bounds (BEGV, XINT (next), ZV));
	  else if (CONSP (next))
	    {
	      Lisp_Object car, cdr;

	      car = XCAR (next);
	      cdr = XCDR (next);
	      if (EQ (car, Qt))
		{
		  /* Element (t high . low) records previous modtime.  */
		  Lisp_Object high, low;
		  int mod_time;
		  struct buffer *base_buffer = current_buffer;

		  high = Fcar (cdr);
		  low = Fcdr (cdr);
		  mod_time = (XFASTINT (high) << 16) + XFASTINT (low);

		  if (current_buffer->base_buffer)
		    base_buffer = current_buffer->base_buffer;

		  /* If this records an obsolete save
		     (not matching the actual disk file)
		     then don't mark unmodified.  */
		  if (mod_time != base_buffer->modtime)
		    continue;
#ifdef CLASH_DETECTION
		  Funlock_buffer ();
#endif /* CLASH_DETECTION */
		  Fset_buffer_modified_p (Qnil);
		}
	      else if (EQ (car, Qnil))
		{
		  /* Element (nil PROP VAL BEG . END) is property change.  */
		  Lisp_Object beg, end, prop, val;

		  prop = Fcar (cdr);
		  cdr = Fcdr (cdr);
		  val = Fcar (cdr);
		  cdr = Fcdr (cdr);
		  beg = Fcar (cdr);
		  end = Fcdr (cdr);

		  if (XINT (beg) < BEGV || XINT (end) > ZV)
		    error ("Changes to be undone are outside visible portion of buffer");
		  Fput_text_property (beg, end, prop, val, Qnil);
		}
	      else if (INTEGERP (car) && INTEGERP (cdr))
		{
		  /* Element (BEG . END) means range was inserted.  */

		  if (XINT (car) < BEGV
		      || XINT (cdr) > ZV)
		    error ("Changes to be undone are outside visible portion of buffer");
		  /* Set point first thing, so that undoing this undo
		     does not send point back to where it is now.  */
		  Fgoto_char (car);
		  Fdelete_region (car, cdr);
		}
	      else if (EQ (car, Qapply))
		{
		  /* Element (apply FUN . ARGS) means call FUN to undo.  */
		  struct buffer *save_buffer = current_buffer;

		  car = Fcar (cdr);
		  cdr = Fcdr (cdr);
		  if (INTEGERP (car))
		    {
		      /* Long format: (apply DELTA START END FUN . ARGS).  */
		      Lisp_Object delta = car;
		      Lisp_Object start = Fcar (cdr);
		      Lisp_Object end   = Fcar (Fcdr (cdr));
		      Lisp_Object start_mark = Fcopy_marker (start, Qnil);
		      Lisp_Object end_mark   = Fcopy_marker (end, Qt);

		      cdr = Fcdr (Fcdr (cdr));
		      apply1 (Fcar (cdr), Fcdr (cdr));

		      /* Check that the function did what the entry said it
			 would do.  */
		      if (!EQ (start, Fmarker_position (start_mark))
			  || (XINT (delta) + XINT (end)
			      != marker_position (end_mark)))
			error ("Changes to be undone by function different than announced");
		      Fset_marker (start_mark, Qnil, Qnil);
		      Fset_marker (end_mark, Qnil, Qnil);
		    }
		  else
		    apply1 (car, cdr);

		  if (save_buffer != current_buffer)
		    error ("Undo function switched buffer");
		  did_apply = 1;
		}
	      else if (STRINGP (car) && INTEGERP (cdr))
		{
		  /* Element (STRING . POS) means STRING was deleted.  */
		  Lisp_Object membuf;
		  int pos = XINT (cdr);

		  membuf = car;
		  if (pos < 0)
		    {
		      if (-pos < BEGV || -pos > ZV)
			error ("Changes to be undone are outside visible portion of buffer");
		      SET_PT (-pos);
		      Finsert (1, &membuf);
		    }
		  else
		    {
		      if (pos < BEGV || pos > ZV)
			error ("Changes to be undone are outside visible portion of buffer");
		      SET_PT (pos);

		      /* Now that we record marker adjustments
			 (caused by deletion) for undo,
			 we should always insert after markers,
			 so that undoing the marker adjustments
			 put the markers back in the right place.  */
		      Finsert (1, &membuf);
		      SET_PT (pos);
		    }
		}
	      else if (MARKERP (car) && INTEGERP (cdr))
		{
		  /* (MARKER . INTEGER) means a marker MARKER
		     was adjusted by INTEGER.  */
		  if (XMARKER (car)->buffer)
		    Fset_marker (car,
				 make_number (marker_position (car) - XINT (cdr)),
				 Fmarker_buffer (car));
		}
	    }
	}
      arg--;
    }


  /* Make sure an apply entry produces at least one undo entry,
     so the test in `undo' for continuing an undo series
     will work right.  */
  if (did_apply
      && EQ (oldlist, current_buffer->undo_list))
    current_buffer->undo_list
      = Fcons (list3 (Qapply, Qcdr, Qnil), current_buffer->undo_list);

  UNGCPRO;
  return unbind_to (count, list);
}

void
syms_of_undo ()
{
  Qinhibit_read_only = intern ("inhibit-read-only");
  staticpro (&Qinhibit_read_only);

  Qapply = intern ("apply");
  staticpro (&Qapply);

  pending_boundary = Qnil;
  staticpro (&pending_boundary);

  defsubr (&Sprimitive_undo);
  defsubr (&Sundo_boundary);

  DEFVAR_INT ("undo-limit", &undo_limit,
	      doc: /* Keep no more undo information once it exceeds this size.
This limit is applied when garbage collection happens.
When a previous command increases the total undo list size past this
value, the earlier commands that came before it are forgotten.

The size is counted as the number of bytes occupied,
which includes both saved text and other data.  */);
  undo_limit = 20000;

  DEFVAR_INT ("undo-strong-limit", &undo_strong_limit,
	      doc: /* Don't keep more than this much size of undo information.
This limit is applied when garbage collection happens.
When a previous command increases the total undo list size past this
value, that command and the earlier commands that came before it are forgotten.
However, the most recent buffer-modifying command's undo info
is never discarded for this reason.

The size is counted as the number of bytes occupied,
which includes both saved text and other data.  */);
  undo_strong_limit = 30000;

  DEFVAR_LISP ("undo-outer-limit", &Vundo_outer_limit,
	      doc: /* Outer limit on size of undo information for one command.
At garbage collection time, if the current command has produced
more than this much undo information, it discards the info and displays
a warning.  This is a last-ditch limit to prevent memory overflow.

The size is counted as the number of bytes occupied, which includes
both saved text and other data.  A value of nil means no limit.  In
this case, accumulating one huge undo entry could make Emacs crash as
a result of memory overflow.

In fact, this calls the function which is the value of
`undo-outer-limit-function' with one argument, the size.
The text above describes the behavior of the function
that variable usually specifies.  */);
  Vundo_outer_limit = make_number (3000000);

  DEFVAR_LISP ("undo-outer-limit-function", &Vundo_outer_limit_function,
	       doc: /* Function to call when an undo list exceeds `undo-outer-limit'.
This function is called with one argument, the current undo list size
for the most recent command (since the last undo boundary).
If the function returns t, that means truncation has been fully handled.
If it returns nil, the other forms of truncation are done.

Garbage collection is inhibited around the call to this function,
so it must make sure not to do a lot of consing.  */);
  Vundo_outer_limit_function = Qnil;
}

/* arch-tag: d546ee01-4aed-4ffb-bb8b-eefaae50d38a
   (do not change this comment) */