about summary refs log tree commit diff
path: root/third_party/git/builtin/checkout.c
blob: 6123f732a2c84f975c576e7077a0c6da369e6b31 (plain) (blame)
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
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
1448
1449
1450
1451
1452
1453
1454
1455
1456
1457
1458
1459
1460
1461
1462
1463
1464
1465
1466
1467
1468
1469
1470
1471
1472
1473
1474
1475
1476
1477
1478
1479
1480
1481
1482
1483
1484
1485
1486
1487
1488
1489
1490
1491
1492
1493
1494
1495
1496
1497
1498
1499
1500
1501
1502
1503
1504
1505
1506
1507
1508
1509
1510
1511
1512
1513
1514
1515
1516
1517
1518
1519
1520
1521
1522
1523
1524
1525
1526
1527
1528
1529
1530
1531
1532
1533
1534
1535
1536
1537
1538
1539
1540
1541
1542
1543
1544
1545
1546
1547
1548
1549
1550
1551
1552
1553
1554
1555
1556
1557
1558
1559
1560
1561
1562
1563
1564
1565
1566
1567
1568
1569
1570
1571
1572
1573
1574
1575
1576
1577
1578
1579
1580
1581
1582
1583
1584
1585
1586
1587
1588
1589
1590
1591
1592
1593
1594
1595
1596
1597
1598
1599
1600
1601
1602
1603
1604
1605
1606
1607
1608
1609
1610
1611
1612
1613
1614
1615
1616
1617
1618
1619
1620
1621
1622
1623
1624
1625
1626
1627
1628
1629
1630
1631
1632
1633
1634
1635
1636
1637
1638
1639
1640
1641
1642
1643
1644
1645
1646
1647
1648
1649
1650
1651
1652
1653
1654
1655
1656
1657
1658
1659
1660
1661
1662
1663
1664
1665
1666
1667
1668
1669
1670
1671
1672
1673
1674
1675
1676
1677
1678
1679
1680
1681
1682
1683
1684
1685
1686
1687
1688
1689
1690
1691
1692
1693
1694
1695
1696
1697
1698
1699
1700
1701
1702
1703
1704
1705
1706
1707
1708
1709
1710
1711
1712
1713
1714
1715
1716
1717
1718
1719
1720
1721
1722
1723
1724
1725
1726
1727
1728
1729
1730
1731
1732
1733
1734
1735
1736
1737
1738
1739
1740
1741
1742
1743
1744
1745
1746
1747
1748
1749
1750
1751
1752
1753
1754
1755
1756
1757
1758
1759
1760
1761
1762
1763
1764
1765
1766
1767
1768
1769
1770
1771
1772
1773
1774
1775
1776
1777
1778
1779
1780
1781
1782
1783
1784
1785
1786
1787
1788
1789
1790
1791
1792
1793
1794
1795
1796
1797
1798
1799
1800
1801
#define USE_THE_INDEX_COMPATIBILITY_MACROS
#include "builtin.h"
#include "advice.h"
#include "blob.h"
#include "branch.h"
#include "cache-tree.h"
#include "checkout.h"
#include "commit.h"
#include "config.h"
#include "diff.h"
#include "dir.h"
#include "ll-merge.h"
#include "lockfile.h"
#include "merge-recursive.h"
#include "object-store.h"
#include "parse-options.h"
#include "refs.h"
#include "remote.h"
#include "resolve-undo.h"
#include "revision.h"
#include "run-command.h"
#include "submodule.h"
#include "submodule-config.h"
#include "tree.h"
#include "tree-walk.h"
#include "unpack-trees.h"
#include "wt-status.h"
#include "xdiff-interface.h"

static const char * const checkout_usage[] = {
	N_("git checkout [<options>] <branch>"),
	N_("git checkout [<options>] [<branch>] -- <file>..."),
	NULL,
};

static const char * const switch_branch_usage[] = {
	N_("git switch [<options>] [<branch>]"),
	NULL,
};

static const char * const restore_usage[] = {
	N_("git restore [<options>] [--source=<branch>] <file>..."),
	NULL,
};

struct checkout_opts {
	int patch_mode;
	int quiet;
	int merge;
	int force;
	int force_detach;
	int implicit_detach;
	int writeout_stage;
	int overwrite_ignore;
	int ignore_skipworktree;
	int ignore_other_worktrees;
	int show_progress;
	int count_checkout_paths;
	int overlay_mode;
	int dwim_new_local_branch;
	int discard_changes;
	int accept_ref;
	int accept_pathspec;
	int switch_branch_doing_nothing_is_ok;
	int only_merge_on_switching_branches;
	int can_switch_when_in_progress;
	int orphan_from_empty_tree;
	int empty_pathspec_ok;
	int checkout_index;
	int checkout_worktree;
	const char *ignore_unmerged_opt;
	int ignore_unmerged;

	const char *new_branch;
	const char *new_branch_force;
	const char *new_orphan_branch;
	int new_branch_log;
	enum branch_track track;
	struct diff_options diff_options;
	char *conflict_style;

	int branch_exists;
	const char *prefix;
	struct pathspec pathspec;
	const char *from_treeish;
	struct tree *source_tree;
};

static int post_checkout_hook(struct commit *old_commit, struct commit *new_commit,
			      int changed)
{
	return run_hook_le(NULL, "post-checkout",
			   oid_to_hex(old_commit ? &old_commit->object.oid : &null_oid),
			   oid_to_hex(new_commit ? &new_commit->object.oid : &null_oid),
			   changed ? "1" : "0", NULL);
	/* "new_commit" can be NULL when checking out from the index before
	   a commit exists. */

}

static int update_some(const struct object_id *oid, struct strbuf *base,
		const char *pathname, unsigned mode, int stage, void *context)
{
	int len;
	struct cache_entry *ce;
	int pos;

	if (S_ISDIR(mode))
		return READ_TREE_RECURSIVE;

	len = base->len + strlen(pathname);
	ce = make_empty_cache_entry(&the_index, len);
	oidcpy(&ce->oid, oid);
	memcpy(ce->name, base->buf, base->len);
	memcpy(ce->name + base->len, pathname, len - base->len);
	ce->ce_flags = create_ce_flags(0) | CE_UPDATE;
	ce->ce_namelen = len;
	ce->ce_mode = create_ce_mode(mode);

	/*
	 * If the entry is the same as the current index, we can leave the old
	 * entry in place. Whether it is UPTODATE or not, checkout_entry will
	 * do the right thing.
	 */
	pos = cache_name_pos(ce->name, ce->ce_namelen);
	if (pos >= 0) {
		struct cache_entry *old = active_cache[pos];
		if (ce->ce_mode == old->ce_mode &&
		    oideq(&ce->oid, &old->oid)) {
			old->ce_flags |= CE_UPDATE;
			discard_cache_entry(ce);
			return 0;
		}
	}

	add_cache_entry(ce, ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
	return 0;
}

static int read_tree_some(struct tree *tree, const struct pathspec *pathspec)
{
	read_tree_recursive(the_repository, tree, "", 0, 0,
			    pathspec, update_some, NULL);

	/* update the index with the given tree's info
	 * for all args, expanding wildcards, and exit
	 * with any non-zero return code.
	 */
	return 0;
}

static int skip_same_name(const struct cache_entry *ce, int pos)
{
	while (++pos < active_nr &&
	       !strcmp(active_cache[pos]->name, ce->name))
		; /* skip */
	return pos;
}

static int check_stage(int stage, const struct cache_entry *ce, int pos,
		       int overlay_mode)
{
	while (pos < active_nr &&
	       !strcmp(active_cache[pos]->name, ce->name)) {
		if (ce_stage(active_cache[pos]) == stage)
			return 0;
		pos++;
	}
	if (!overlay_mode)
		return 0;
	if (stage == 2)
		return error(_("path '%s' does not have our version"), ce->name);
	else
		return error(_("path '%s' does not have their version"), ce->name);
}

static int check_stages(unsigned stages, const struct cache_entry *ce, int pos)
{
	unsigned seen = 0;
	const char *name = ce->name;

	while (pos < active_nr) {
		ce = active_cache[pos];
		if (strcmp(name, ce->name))
			break;
		seen |= (1 << ce_stage(ce));
		pos++;
	}
	if ((stages & seen) != stages)
		return error(_("path '%s' does not have all necessary versions"),
			     name);
	return 0;
}

static int checkout_stage(int stage, const struct cache_entry *ce, int pos,
			  const struct checkout *state, int *nr_checkouts,
			  int overlay_mode)
{
	while (pos < active_nr &&
	       !strcmp(active_cache[pos]->name, ce->name)) {
		if (ce_stage(active_cache[pos]) == stage)
			return checkout_entry(active_cache[pos], state,
					      NULL, nr_checkouts);
		pos++;
	}
	if (!overlay_mode) {
		unlink_entry(ce);
		return 0;
	}
	if (stage == 2)
		return error(_("path '%s' does not have our version"), ce->name);
	else
		return error(_("path '%s' does not have their version"), ce->name);
}

static int checkout_merged(int pos, const struct checkout *state, int *nr_checkouts)
{
	struct cache_entry *ce = active_cache[pos];
	const char *path = ce->name;
	mmfile_t ancestor, ours, theirs;
	int status;
	struct object_id oid;
	mmbuffer_t result_buf;
	struct object_id threeway[3];
	unsigned mode = 0;

	memset(threeway, 0, sizeof(threeway));
	while (pos < active_nr) {
		int stage;
		stage = ce_stage(ce);
		if (!stage || strcmp(path, ce->name))
			break;
		oidcpy(&threeway[stage - 1], &ce->oid);
		if (stage == 2)
			mode = create_ce_mode(ce->ce_mode);
		pos++;
		ce = active_cache[pos];
	}
	if (is_null_oid(&threeway[1]) || is_null_oid(&threeway[2]))
		return error(_("path '%s' does not have necessary versions"), path);

	read_mmblob(&ancestor, &threeway[0]);
	read_mmblob(&ours, &threeway[1]);
	read_mmblob(&theirs, &threeway[2]);

	/*
	 * NEEDSWORK: re-create conflicts from merges with
	 * merge.renormalize set, too
	 */
	status = ll_merge(&result_buf, path, &ancestor, "base",
			  &ours, "ours", &theirs, "theirs",
			  state->istate, NULL);
	free(ancestor.ptr);
	free(ours.ptr);
	free(theirs.ptr);
	if (status < 0 || !result_buf.ptr) {
		free(result_buf.ptr);
		return error(_("path '%s': cannot merge"), path);
	}

	/*
	 * NEEDSWORK:
	 * There is absolutely no reason to write this as a blob object
	 * and create a phony cache entry.  This hack is primarily to get
	 * to the write_entry() machinery that massages the contents to
	 * work-tree format and writes out which only allows it for a
	 * cache entry.  The code in write_entry() needs to be refactored
	 * to allow us to feed a <buffer, size, mode> instead of a cache
	 * entry.  Such a refactoring would help merge_recursive as well
	 * (it also writes the merge result to the object database even
	 * when it may contain conflicts).
	 */
	if (write_object_file(result_buf.ptr, result_buf.size, blob_type, &oid))
		die(_("Unable to add merge result for '%s'"), path);
	free(result_buf.ptr);
	ce = make_transient_cache_entry(mode, &oid, path, 2);
	if (!ce)
		die(_("make_cache_entry failed for path '%s'"), path);
	status = checkout_entry(ce, state, NULL, nr_checkouts);
	discard_cache_entry(ce);
	return status;
}

static void mark_ce_for_checkout_overlay(struct cache_entry *ce,
					 char *ps_matched,
					 const struct checkout_opts *opts)
{
	ce->ce_flags &= ~CE_MATCHED;
	if (!opts->ignore_skipworktree && ce_skip_worktree(ce))
		return;
	if (opts->source_tree && !(ce->ce_flags & CE_UPDATE))
		/*
		 * "git checkout tree-ish -- path", but this entry
		 * is in the original index but is not in tree-ish
		 * or does not match the pathspec; it will not be
		 * checked out to the working tree.  We will not do
		 * anything to this entry at all.
		 */
		return;
	/*
	 * Either this entry came from the tree-ish we are
	 * checking the paths out of, or we are checking out
	 * of the index.
	 *
	 * If it comes from the tree-ish, we already know it
	 * matches the pathspec and could just stamp
	 * CE_MATCHED to it from update_some(). But we still
	 * need ps_matched and read_tree_recursive (and
	 * eventually tree_entry_interesting) cannot fill
	 * ps_matched yet. Once it can, we can avoid calling
	 * match_pathspec() for _all_ entries when
	 * opts->source_tree != NULL.
	 */
	if (ce_path_match(&the_index, ce, &opts->pathspec, ps_matched))
		ce->ce_flags |= CE_MATCHED;
}

static void mark_ce_for_checkout_no_overlay(struct cache_entry *ce,
					    char *ps_matched,
					    const struct checkout_opts *opts)
{
	ce->ce_flags &= ~CE_MATCHED;
	if (!opts->ignore_skipworktree && ce_skip_worktree(ce))
		return;
	if (ce_path_match(&the_index, ce, &opts->pathspec, ps_matched)) {
		ce->ce_flags |= CE_MATCHED;
		if (opts->source_tree && !(ce->ce_flags & CE_UPDATE))
			/*
			 * In overlay mode, but the path is not in
			 * tree-ish, which means we should remove it
			 * from the index and the working tree.
			 */
			ce->ce_flags |= CE_REMOVE | CE_WT_REMOVE;
	}
}

static int checkout_worktree(const struct checkout_opts *opts)
{
	struct checkout state = CHECKOUT_INIT;
	int nr_checkouts = 0, nr_unmerged = 0;
	int errs = 0;
	int pos;

	state.force = 1;
	state.refresh_cache = 1;
	state.istate = &the_index;

	enable_delayed_checkout(&state);
	for (pos = 0; pos < active_nr; pos++) {
		struct cache_entry *ce = active_cache[pos];
		if (ce->ce_flags & CE_MATCHED) {
			if (!ce_stage(ce)) {
				errs |= checkout_entry(ce, &state,
						       NULL, &nr_checkouts);
				continue;
			}
			if (opts->writeout_stage)
				errs |= checkout_stage(opts->writeout_stage,
						       ce, pos,
						       &state,
						       &nr_checkouts, opts->overlay_mode);
			else if (opts->merge)
				errs |= checkout_merged(pos, &state,
							&nr_unmerged);
			pos = skip_same_name(ce, pos) - 1;
		}
	}
	remove_marked_cache_entries(&the_index, 1);
	remove_scheduled_dirs();
	errs |= finish_delayed_checkout(&state, &nr_checkouts);

	if (opts->count_checkout_paths) {
		if (nr_unmerged)
			fprintf_ln(stderr, Q_("Recreated %d merge conflict",
					      "Recreated %d merge conflicts",
					      nr_unmerged),
				   nr_unmerged);
		if (opts->source_tree)
			fprintf_ln(stderr, Q_("Updated %d path from %s",
					      "Updated %d paths from %s",
					      nr_checkouts),
				   nr_checkouts,
				   find_unique_abbrev(&opts->source_tree->object.oid,
						      DEFAULT_ABBREV));
		else if (!nr_unmerged || nr_checkouts)
			fprintf_ln(stderr, Q_("Updated %d path from the index",
					      "Updated %d paths from the index",
					      nr_checkouts),
				   nr_checkouts);
	}

	return errs;
}

static int checkout_paths(const struct checkout_opts *opts,
			  const char *revision)
{
	int pos;
	static char *ps_matched;
	struct object_id rev;
	struct commit *head;
	int errs = 0;
	struct lock_file lock_file = LOCK_INIT;
	int checkout_index;

	trace2_cmd_mode(opts->patch_mode ? "patch" : "path");

	if (opts->track != BRANCH_TRACK_UNSPECIFIED)
		die(_("'%s' cannot be used with updating paths"), "--track");

	if (opts->new_branch_log)
		die(_("'%s' cannot be used with updating paths"), "-l");

	if (opts->ignore_unmerged && opts->patch_mode)
		die(_("'%s' cannot be used with updating paths"),
		    opts->ignore_unmerged_opt);

	if (opts->force_detach)
		die(_("'%s' cannot be used with updating paths"), "--detach");

	if (opts->merge && opts->patch_mode)
		die(_("'%s' cannot be used with %s"), "--merge", "--patch");

	if (opts->ignore_unmerged && opts->merge)
		die(_("'%s' cannot be used with %s"),
		    opts->ignore_unmerged_opt, "-m");

	if (opts->new_branch)
		die(_("Cannot update paths and switch to branch '%s' at the same time."),
		    opts->new_branch);

	if (!opts->checkout_worktree && !opts->checkout_index)
		die(_("neither '%s' or '%s' is specified"),
		    "--staged", "--worktree");

	if (!opts->checkout_worktree && !opts->from_treeish)
		die(_("'%s' must be used when '%s' is not specified"),
		    "--worktree", "--source");

	if (opts->checkout_index && !opts->checkout_worktree &&
	    opts->writeout_stage)
		die(_("'%s' or '%s' cannot be used with %s"),
		    "--ours", "--theirs", "--staged");

	if (opts->checkout_index && !opts->checkout_worktree &&
	    opts->merge)
		die(_("'%s' or '%s' cannot be used with %s"),
		    "--merge", "--conflict", "--staged");

	if (opts->patch_mode) {
		const char *patch_mode;

		if (opts->checkout_index && opts->checkout_worktree)
			patch_mode = "--patch=checkout";
		else if (opts->checkout_index && !opts->checkout_worktree)
			patch_mode = "--patch=reset";
		else if (!opts->checkout_index && opts->checkout_worktree)
			patch_mode = "--patch=worktree";
		else
			BUG("either flag must have been set, worktree=%d, index=%d",
			    opts->checkout_worktree, opts->checkout_index);
		return run_add_interactive(revision, patch_mode, &opts->pathspec);
	}

	repo_hold_locked_index(the_repository, &lock_file, LOCK_DIE_ON_ERROR);
	if (read_cache_preload(&opts->pathspec) < 0)
		return error(_("index file corrupt"));

	if (opts->source_tree)
		read_tree_some(opts->source_tree, &opts->pathspec);

	ps_matched = xcalloc(opts->pathspec.nr, 1);

	/*
	 * Make sure all pathspecs participated in locating the paths
	 * to be checked out.
	 */
	for (pos = 0; pos < active_nr; pos++)
		if (opts->overlay_mode)
			mark_ce_for_checkout_overlay(active_cache[pos],
						     ps_matched,
						     opts);
		else
			mark_ce_for_checkout_no_overlay(active_cache[pos],
							ps_matched,
							opts);

	if (report_path_error(ps_matched, &opts->pathspec)) {
		free(ps_matched);
		return 1;
	}
	free(ps_matched);

	/* "checkout -m path" to recreate conflicted state */
	if (opts->merge)
		unmerge_marked_index(&the_index);

	/* Any unmerged paths? */
	for (pos = 0; pos < active_nr; pos++) {
		const struct cache_entry *ce = active_cache[pos];
		if (ce->ce_flags & CE_MATCHED) {
			if (!ce_stage(ce))
				continue;
			if (opts->ignore_unmerged) {
				if (!opts->quiet)
					warning(_("path '%s' is unmerged"), ce->name);
			} else if (opts->writeout_stage) {
				errs |= check_stage(opts->writeout_stage, ce, pos, opts->overlay_mode);
			} else if (opts->merge) {
				errs |= check_stages((1<<2) | (1<<3), ce, pos);
			} else {
				errs = 1;
				error(_("path '%s' is unmerged"), ce->name);
			}
			pos = skip_same_name(ce, pos) - 1;
		}
	}
	if (errs)
		return 1;

	/* Now we are committed to check them out */
	if (opts->checkout_worktree)
		errs |= checkout_worktree(opts);

	/*
	 * Allow updating the index when checking out from the index.
	 * This is to save new stat info.
	 */
	if (opts->checkout_worktree && !opts->checkout_index && !opts->source_tree)
		checkout_index = 1;
	else
		checkout_index = opts->checkout_index;

	if (checkout_index) {
		if (write_locked_index(&the_index, &lock_file, COMMIT_LOCK))
			die(_("unable to write new index file"));
	} else {
		/*
		 * NEEDSWORK: if --worktree is not specified, we
		 * should save stat info of checked out files in the
		 * index to avoid the next (potentially costly)
		 * refresh. But it's a bit tricker to do...
		 */
		rollback_lock_file(&lock_file);
	}

	read_ref_full("HEAD", 0, &rev, NULL);
	head = lookup_commit_reference_gently(the_repository, &rev, 1);

	errs |= post_checkout_hook(head, head, 0);
	return errs;
}

static void show_local_changes(struct object *head,
			       const struct diff_options *opts)
{
	struct rev_info rev;
	/* I think we want full paths, even if we're in a subdirectory. */
	repo_init_revisions(the_repository, &rev, NULL);
	rev.diffopt.flags = opts->flags;
	rev.diffopt.output_format |= DIFF_FORMAT_NAME_STATUS;
	diff_setup_done(&rev.diffopt);
	add_pending_object(&rev, head, NULL);
	run_diff_index(&rev, 0);
}

static void describe_detached_head(const char *msg, struct commit *commit)
{
	struct strbuf sb = STRBUF_INIT;

	if (!parse_commit(commit))
		pp_commit_easy(CMIT_FMT_ONELINE, commit, &sb);
	if (print_sha1_ellipsis()) {
		fprintf(stderr, "%s %s... %s\n", msg,
			find_unique_abbrev(&commit->object.oid, DEFAULT_ABBREV), sb.buf);
	} else {
		fprintf(stderr, "%s %s %s\n", msg,
			find_unique_abbrev(&commit->object.oid, DEFAULT_ABBREV), sb.buf);
	}
	strbuf_release(&sb);
}

static int reset_tree(struct tree *tree, const struct checkout_opts *o,
		      int worktree, int *writeout_error)
{
	struct unpack_trees_options opts;
	struct tree_desc tree_desc;

	memset(&opts, 0, sizeof(opts));
	opts.head_idx = -1;
	opts.update = worktree;
	opts.skip_unmerged = !worktree;
	opts.reset = 1;
	opts.merge = 1;
	opts.fn = oneway_merge;
	opts.verbose_update = o->show_progress;
	opts.src_index = &the_index;
	opts.dst_index = &the_index;
	parse_tree(tree);
	init_tree_desc(&tree_desc, tree->buffer, tree->size);
	switch (unpack_trees(1, &tree_desc, &opts)) {
	case -2:
		*writeout_error = 1;
		/*
		 * We return 0 nevertheless, as the index is all right
		 * and more importantly we have made best efforts to
		 * update paths in the work tree, and we cannot revert
		 * them.
		 */
		/* fallthrough */
	case 0:
		return 0;
	default:
		return 128;
	}
}

struct branch_info {
	const char *name; /* The short name used */
	const char *path; /* The full name of a real branch */
	struct commit *commit; /* The named commit */
	/*
	 * if not null the branch is detached because it's already
	 * checked out in this checkout
	 */
	char *checkout;
};

static void setup_branch_path(struct branch_info *branch)
{
	struct strbuf buf = STRBUF_INIT;

	strbuf_branchname(&buf, branch->name, INTERPRET_BRANCH_LOCAL);
	if (strcmp(buf.buf, branch->name))
		branch->name = xstrdup(buf.buf);
	strbuf_splice(&buf, 0, 0, "refs/heads/", 11);
	branch->path = strbuf_detach(&buf, NULL);
}

static int merge_working_tree(const struct checkout_opts *opts,
			      struct branch_info *old_branch_info,
			      struct branch_info *new_branch_info,
			      int *writeout_error)
{
	int ret;
	struct lock_file lock_file = LOCK_INIT;
	struct tree *new_tree;

	hold_locked_index(&lock_file, LOCK_DIE_ON_ERROR);
	if (read_cache_preload(NULL) < 0)
		return error(_("index file corrupt"));

	resolve_undo_clear();
	if (opts->new_orphan_branch && opts->orphan_from_empty_tree) {
		if (new_branch_info->commit)
			BUG("'switch --orphan' should never accept a commit as starting point");
		new_tree = parse_tree_indirect(the_hash_algo->empty_tree);
	} else
		new_tree = get_commit_tree(new_branch_info->commit);
	if (opts->discard_changes) {
		ret = reset_tree(new_tree, opts, 1, writeout_error);
		if (ret)
			return ret;
	} else {
		struct tree_desc trees[2];
		struct tree *tree;
		struct unpack_trees_options topts;

		memset(&topts, 0, sizeof(topts));
		topts.head_idx = -1;
		topts.src_index = &the_index;
		topts.dst_index = &the_index;

		setup_unpack_trees_porcelain(&topts, "checkout");

		refresh_cache(REFRESH_QUIET);

		if (unmerged_cache()) {
			error(_("you need to resolve your current index first"));
			return 1;
		}

		/* 2-way merge to the new branch */
		topts.initial_checkout = is_cache_unborn();
		topts.update = 1;
		topts.merge = 1;
		topts.quiet = opts->merge && old_branch_info->commit;
		topts.verbose_update = opts->show_progress;
		topts.fn = twoway_merge;
		if (opts->overwrite_ignore) {
			topts.dir = xcalloc(1, sizeof(*topts.dir));
			topts.dir->flags |= DIR_SHOW_IGNORED;
			setup_standard_excludes(topts.dir);
		}
		tree = parse_tree_indirect(old_branch_info->commit ?
					   &old_branch_info->commit->object.oid :
					   the_hash_algo->empty_tree);
		init_tree_desc(&trees[0], tree->buffer, tree->size);
		parse_tree(new_tree);
		tree = new_tree;
		init_tree_desc(&trees[1], tree->buffer, tree->size);

		ret = unpack_trees(2, trees, &topts);
		clear_unpack_trees_porcelain(&topts);
		if (ret == -1) {
			/*
			 * Unpack couldn't do a trivial merge; either
			 * give up or do a real merge, depending on
			 * whether the merge flag was used.
			 */
			struct tree *result;
			struct tree *work;
			struct tree *old_tree;
			struct merge_options o;
			struct strbuf sb = STRBUF_INIT;

			if (!opts->merge)
				return 1;

			/*
			 * Without old_branch_info->commit, the below is the same as
			 * the two-tree unpack we already tried and failed.
			 */
			if (!old_branch_info->commit)
				return 1;
			old_tree = get_commit_tree(old_branch_info->commit);

			if (repo_index_has_changes(the_repository, old_tree, &sb))
				die(_("cannot continue with staged changes in "
				      "the following files:\n%s"), sb.buf);
			strbuf_release(&sb);

			if (repo_index_has_changes(the_repository,
						   get_commit_tree(old_branch_info->commit),
						   &sb))
				warning(_("staged changes in the following files may be lost: %s"),
					sb.buf);
			strbuf_release(&sb);

			/* Do more real merge */

			/*
			 * We update the index fully, then write the
			 * tree from the index, then merge the new
			 * branch with the current tree, with the old
			 * branch as the base. Then we reset the index
			 * (but not the working tree) to the new
			 * branch, leaving the working tree as the
			 * merged version, but skipping unmerged
			 * entries in the index.
			 */

			add_files_to_cache(NULL, NULL, 0);
			/*
			 * NEEDSWORK: carrying over local changes
			 * when branches have different end-of-line
			 * normalization (or clean+smudge rules) is
			 * a pain; plumb in an option to set
			 * o.renormalize?
			 */
			init_merge_options(&o, the_repository);
			o.verbosity = 0;
			work = write_tree_from_memory(&o);

			ret = reset_tree(new_tree,
					 opts, 1,
					 writeout_error);
			if (ret)
				return ret;
			o.ancestor = old_branch_info->name;
			o.branch1 = new_branch_info->name;
			o.branch2 = "local";
			ret = merge_trees(&o,
					  new_tree,
					  work,
					  old_tree,
					  &result);
			if (ret < 0)
				exit(128);
			ret = reset_tree(new_tree,
					 opts, 0,
					 writeout_error);
			strbuf_release(&o.obuf);
			if (ret)
				return ret;
		}
	}

	if (!active_cache_tree)
		active_cache_tree = cache_tree();

	if (!cache_tree_fully_valid(active_cache_tree))
		cache_tree_update(&the_index, WRITE_TREE_SILENT | WRITE_TREE_REPAIR);

	if (write_locked_index(&the_index, &lock_file, COMMIT_LOCK))
		die(_("unable to write new index file"));

	if (!opts->discard_changes && !opts->quiet && new_branch_info->commit)
		show_local_changes(&new_branch_info->commit->object, &opts->diff_options);

	return 0;
}

static void report_tracking(struct branch_info *new_branch_info)
{
	struct strbuf sb = STRBUF_INIT;
	struct branch *branch = branch_get(new_branch_info->name);

	if (!format_tracking_info(branch, &sb, AHEAD_BEHIND_FULL))
		return;
	fputs(sb.buf, stdout);
	strbuf_release(&sb);
}

static void update_refs_for_switch(const struct checkout_opts *opts,
				   struct branch_info *old_branch_info,
				   struct branch_info *new_branch_info)
{
	struct strbuf msg = STRBUF_INIT;
	const char *old_desc, *reflog_msg;
	if (opts->new_branch) {
		if (opts->new_orphan_branch) {
			char *refname;

			refname = mkpathdup("refs/heads/%s", opts->new_orphan_branch);
			if (opts->new_branch_log &&
			    !should_autocreate_reflog(refname)) {
				int ret;
				struct strbuf err = STRBUF_INIT;

				ret = safe_create_reflog(refname, 1, &err);
				if (ret) {
					fprintf(stderr, _("Can not do reflog for '%s': %s\n"),
						opts->new_orphan_branch, err.buf);
					strbuf_release(&err);
					free(refname);
					return;
				}
				strbuf_release(&err);
			}
			free(refname);
		}
		else
			create_branch(the_repository,
				      opts->new_branch, new_branch_info->name,
				      opts->new_branch_force ? 1 : 0,
				      opts->new_branch_force ? 1 : 0,
				      opts->new_branch_log,
				      opts->quiet,
				      opts->track);
		new_branch_info->name = opts->new_branch;
		setup_branch_path(new_branch_info);
	}

	old_desc = old_branch_info->name;
	if (!old_desc && old_branch_info->commit)
		old_desc = oid_to_hex(&old_branch_info->commit->object.oid);

	reflog_msg = getenv("GIT_REFLOG_ACTION");
	if (!reflog_msg)
		strbuf_addf(&msg, "checkout: moving from %s to %s",
			old_desc ? old_desc : "(invalid)", new_branch_info->name);
	else
		strbuf_insert(&msg, 0, reflog_msg, strlen(reflog_msg));

	if (!strcmp(new_branch_info->name, "HEAD") && !new_branch_info->path && !opts->force_detach) {
		/* Nothing to do. */
	} else if (opts->force_detach || !new_branch_info->path) {	/* No longer on any branch. */
		update_ref(msg.buf, "HEAD", &new_branch_info->commit->object.oid, NULL,
			   REF_NO_DEREF, UPDATE_REFS_DIE_ON_ERR);
		if (!opts->quiet) {
			if (old_branch_info->path &&
			    advice_detached_head && !opts->force_detach)
				detach_advice(new_branch_info->name);
			describe_detached_head(_("HEAD is now at"), new_branch_info->commit);
		}
	} else if (new_branch_info->path) {	/* Switch branches. */
		if (create_symref("HEAD", new_branch_info->path, msg.buf) < 0)
			die(_("unable to update HEAD"));
		if (!opts->quiet) {
			if (old_branch_info->path && !strcmp(new_branch_info->path, old_branch_info->path)) {
				if (opts->new_branch_force)
					fprintf(stderr, _("Reset branch '%s'\n"),
						new_branch_info->name);
				else
					fprintf(stderr, _("Already on '%s'\n"),
						new_branch_info->name);
			} else if (opts->new_branch) {
				if (opts->branch_exists)
					fprintf(stderr, _("Switched to and reset branch '%s'\n"), new_branch_info->name);
				else
					fprintf(stderr, _("Switched to a new branch '%s'\n"), new_branch_info->name);
			} else {
				fprintf(stderr, _("Switched to branch '%s'\n"),
					new_branch_info->name);
			}
		}
		if (old_branch_info->path && old_branch_info->name) {
			if (!ref_exists(old_branch_info->path) && reflog_exists(old_branch_info->path))
				delete_reflog(old_branch_info->path);
		}
	}
	remove_branch_state(the_repository, !opts->quiet);
	strbuf_release(&msg);
	if (!opts->quiet &&
	    (new_branch_info->path || (!opts->force_detach && !strcmp(new_branch_info->name, "HEAD"))))
		report_tracking(new_branch_info);
}

static int add_pending_uninteresting_ref(const char *refname,
					 const struct object_id *oid,
					 int flags, void *cb_data)
{
	add_pending_oid(cb_data, refname, oid, UNINTERESTING);
	return 0;
}

static void describe_one_orphan(struct strbuf *sb, struct commit *commit)
{
	strbuf_addstr(sb, "  ");
	strbuf_add_unique_abbrev(sb, &commit->object.oid, DEFAULT_ABBREV);
	strbuf_addch(sb, ' ');
	if (!parse_commit(commit))
		pp_commit_easy(CMIT_FMT_ONELINE, commit, sb);
	strbuf_addch(sb, '\n');
}

#define ORPHAN_CUTOFF 4
static void suggest_reattach(struct commit *commit, struct rev_info *revs)
{
	struct commit *c, *last = NULL;
	struct strbuf sb = STRBUF_INIT;
	int lost = 0;
	while ((c = get_revision(revs)) != NULL) {
		if (lost < ORPHAN_CUTOFF)
			describe_one_orphan(&sb, c);
		last = c;
		lost++;
	}
	if (ORPHAN_CUTOFF < lost) {
		int more = lost - ORPHAN_CUTOFF;
		if (more == 1)
			describe_one_orphan(&sb, last);
		else
			strbuf_addf(&sb, _(" ... and %d more.\n"), more);
	}

	fprintf(stderr,
		Q_(
		/* The singular version */
		"Warning: you are leaving %d commit behind, "
		"not connected to\n"
		"any of your branches:\n\n"
		"%s\n",
		/* The plural version */
		"Warning: you are leaving %d commits behind, "
		"not connected to\n"
		"any of your branches:\n\n"
		"%s\n",
		/* Give ngettext() the count */
		lost),
		lost,
		sb.buf);
	strbuf_release(&sb);

	if (advice_detached_head)
		fprintf(stderr,
			Q_(
			/* The singular version */
			"If you want to keep it by creating a new branch, "
			"this may be a good time\nto do so with:\n\n"
			" git branch <new-branch-name> %s\n\n",
			/* The plural version */
			"If you want to keep them by creating a new branch, "
			"this may be a good time\nto do so with:\n\n"
			" git branch <new-branch-name> %s\n\n",
			/* Give ngettext() the count */
			lost),
			find_unique_abbrev(&commit->object.oid, DEFAULT_ABBREV));
}

/*
 * We are about to leave commit that was at the tip of a detached
 * HEAD.  If it is not reachable from any ref, this is the last chance
 * for the user to do so without resorting to reflog.
 */
static void orphaned_commit_warning(struct commit *old_commit, struct commit *new_commit)
{
	struct rev_info revs;
	struct object *object = &old_commit->object;

	repo_init_revisions(the_repository, &revs, NULL);
	setup_revisions(0, NULL, &revs, NULL);

	object->flags &= ~UNINTERESTING;
	add_pending_object(&revs, object, oid_to_hex(&object->oid));

	for_each_ref(add_pending_uninteresting_ref, &revs);
	if (new_commit)
		add_pending_oid(&revs, "HEAD",
				&new_commit->object.oid,
				UNINTERESTING);

	if (prepare_revision_walk(&revs))
		die(_("internal error in revision walk"));
	if (!(old_commit->object.flags & UNINTERESTING))
		suggest_reattach(old_commit, &revs);
	else
		describe_detached_head(_("Previous HEAD position was"), old_commit);

	/* Clean up objects used, as they will be reused. */
	clear_commit_marks_all(ALL_REV_FLAGS);
}

static int switch_branches(const struct checkout_opts *opts,
			   struct branch_info *new_branch_info)
{
	int ret = 0;
	struct branch_info old_branch_info;
	void *path_to_free;
	struct object_id rev;
	int flag, writeout_error = 0;
	int do_merge = 1;

	trace2_cmd_mode("branch");

	memset(&old_branch_info, 0, sizeof(old_branch_info));
	old_branch_info.path = path_to_free = resolve_refdup("HEAD", 0, &rev, &flag);
	if (old_branch_info.path)
		old_branch_info.commit = lookup_commit_reference_gently(the_repository, &rev, 1);
	if (!(flag & REF_ISSYMREF))
		old_branch_info.path = NULL;

	if (old_branch_info.path)
		skip_prefix(old_branch_info.path, "refs/heads/", &old_branch_info.name);

	if (opts->new_orphan_branch && opts->orphan_from_empty_tree) {
		if (new_branch_info->name)
			BUG("'switch --orphan' should never accept a commit as starting point");
		new_branch_info->commit = NULL;
		new_branch_info->name = "(empty)";
		do_merge = 1;
	}

	if (!new_branch_info->name) {
		new_branch_info->name = "HEAD";
		new_branch_info->commit = old_branch_info.commit;
		if (!new_branch_info->commit)
			die(_("You are on a branch yet to be born"));
		parse_commit_or_die(new_branch_info->commit);

		if (opts->only_merge_on_switching_branches)
			do_merge = 0;
	}

	if (do_merge) {
		ret = merge_working_tree(opts, &old_branch_info, new_branch_info, &writeout_error);
		if (ret) {
			free(path_to_free);
			return ret;
		}
	}

	if (!opts->quiet && !old_branch_info.path && old_branch_info.commit && new_branch_info->commit != old_branch_info.commit)
		orphaned_commit_warning(old_branch_info.commit, new_branch_info->commit);

	update_refs_for_switch(opts, &old_branch_info, new_branch_info);

	ret = post_checkout_hook(old_branch_info.commit, new_branch_info->commit, 1);
	free(path_to_free);
	return ret || writeout_error;
}

static int git_checkout_config(const char *var, const char *value, void *cb)
{
	if (!strcmp(var, "diff.ignoresubmodules")) {
		struct checkout_opts *opts = cb;
		handle_ignore_submodules_arg(&opts->diff_options, value);
		return 0;
	}

	if (starts_with(var, "submodule."))
		return git_default_submodule_config(var, value, NULL);

	return git_xmerge_config(var, value, NULL);
}

static void setup_new_branch_info_and_source_tree(
	struct branch_info *new_branch_info,
	struct checkout_opts *opts,
	struct object_id *rev,
	const char *arg)
{
	struct tree **source_tree = &opts->source_tree;
	struct object_id branch_rev;

	new_branch_info->name = arg;
	setup_branch_path(new_branch_info);

	if (!check_refname_format(new_branch_info->path, 0) &&
	    !read_ref(new_branch_info->path, &branch_rev))
		oidcpy(rev, &branch_rev);
	else
		new_branch_info->path = NULL; /* not an existing branch */

	new_branch_info->commit = lookup_commit_reference_gently(the_repository, rev, 1);
	if (!new_branch_info->commit) {
		/* not a commit */
		*source_tree = parse_tree_indirect(rev);
	} else {
		parse_commit_or_die(new_branch_info->commit);
		*source_tree = get_commit_tree(new_branch_info->commit);
	}
}

static int parse_branchname_arg(int argc, const char **argv,
				int dwim_new_local_branch_ok,
				struct branch_info *new_branch_info,
				struct checkout_opts *opts,
				struct object_id *rev,
				int *dwim_remotes_matched)
{
	const char **new_branch = &opts->new_branch;
	int argcount = 0;
	const char *arg;
	int dash_dash_pos;
	int has_dash_dash = 0;
	int i;

	/*
	 * case 1: git checkout <ref> -- [<paths>]
	 *
	 *   <ref> must be a valid tree, everything after the '--' must be
	 *   a path.
	 *
	 * case 2: git checkout -- [<paths>]
	 *
	 *   everything after the '--' must be paths.
	 *
	 * case 3: git checkout <something> [--]
	 *
	 *   (a) If <something> is a commit, that is to
	 *       switch to the branch or detach HEAD at it.  As a special case,
	 *       if <something> is A...B (missing A or B means HEAD but you can
	 *       omit at most one side), and if there is a unique merge base
	 *       between A and B, A...B names that merge base.
	 *
	 *   (b) If <something> is _not_ a commit, either "--" is present
	 *       or <something> is not a path, no -t or -b was given, and
	 *       and there is a tracking branch whose name is <something>
	 *       in one and only one remote (or if the branch exists on the
	 *       remote named in checkout.defaultRemote), then this is a
	 *       short-hand to fork local <something> from that
	 *       remote-tracking branch.
	 *
	 *   (c) Otherwise, if "--" is present, treat it like case (1).
	 *
	 *   (d) Otherwise :
	 *       - if it's a reference, treat it like case (1)
	 *       - else if it's a path, treat it like case (2)
	 *       - else: fail.
	 *
	 * case 4: git checkout <something> <paths>
	 *
	 *   The first argument must not be ambiguous.
	 *   - If it's *only* a reference, treat it like case (1).
	 *   - If it's only a path, treat it like case (2).
	 *   - else: fail.
	 *
	 */
	if (!argc)
		return 0;

	if (!opts->accept_pathspec) {
		if (argc > 1)
			die(_("only one reference expected"));
		has_dash_dash = 1; /* helps disambiguate */
	}

	arg = argv[0];
	dash_dash_pos = -1;
	for (i = 0; i < argc; i++) {
		if (opts->accept_pathspec && !strcmp(argv[i], "--")) {
			dash_dash_pos = i;
			break;
		}
	}
	if (dash_dash_pos == 0)
		return 1; /* case (2) */
	else if (dash_dash_pos == 1)
		has_dash_dash = 1; /* case (3) or (1) */
	else if (dash_dash_pos >= 2)
		die(_("only one reference expected, %d given."), dash_dash_pos);
	opts->count_checkout_paths = !opts->quiet && !has_dash_dash;

	if (!strcmp(arg, "-"))
		arg = "@{-1}";

	if (get_oid_mb(arg, rev)) {
		/*
		 * Either case (3) or (4), with <something> not being
		 * a commit, or an attempt to use case (1) with an
		 * invalid ref.
		 *
		 * It's likely an error, but we need to find out if
		 * we should auto-create the branch, case (3).(b).
		 */
		int recover_with_dwim = dwim_new_local_branch_ok;

		int could_be_checkout_paths = !has_dash_dash &&
			check_filename(opts->prefix, arg);

		if (!has_dash_dash && !no_wildcard(arg))
			recover_with_dwim = 0;

		/*
		 * Accept "git checkout foo", "git checkout foo --"
		 * and "git switch foo" as candidates for dwim.
		 */
		if (!(argc == 1 && !has_dash_dash) &&
		    !(argc == 2 && has_dash_dash) &&
		    opts->accept_pathspec)
			recover_with_dwim = 0;

		if (recover_with_dwim) {
			const char *remote = unique_tracking_name(arg, rev,
								  dwim_remotes_matched);
			if (remote) {
				if (could_be_checkout_paths)
					die(_("'%s' could be both a local file and a tracking branch.\n"
					      "Please use -- (and optionally --no-guess) to disambiguate"),
					    arg);
				*new_branch = arg;
				arg = remote;
				/* DWIMmed to create local branch, case (3).(b) */
			} else {
				recover_with_dwim = 0;
			}
		}

		if (!recover_with_dwim) {
			if (has_dash_dash)
				die(_("invalid reference: %s"), arg);
			return argcount;
		}
	}

	/* we can't end up being in (2) anymore, eat the argument */
	argcount++;
	argv++;
	argc--;

	setup_new_branch_info_and_source_tree(new_branch_info, opts, rev, arg);

	if (!opts->source_tree)                   /* case (1): want a tree */
		die(_("reference is not a tree: %s"), arg);

	if (!has_dash_dash) {	/* case (3).(d) -> (1) */
		/*
		 * Do not complain the most common case
		 *	git checkout branch
		 * even if there happen to be a file called 'branch';
		 * it would be extremely annoying.
		 */
		if (argc)
			verify_non_filename(opts->prefix, arg);
	} else if (opts->accept_pathspec) {
		argcount++;
		argv++;
		argc--;
	}

	return argcount;
}

static int switch_unborn_to_new_branch(const struct checkout_opts *opts)
{
	int status;
	struct strbuf branch_ref = STRBUF_INIT;

	trace2_cmd_mode("unborn");

	if (!opts->new_branch)
		die(_("You are on a branch yet to be born"));
	strbuf_addf(&branch_ref, "refs/heads/%s", opts->new_branch);
	status = create_symref("HEAD", branch_ref.buf, "checkout -b");
	strbuf_release(&branch_ref);
	if (!opts->quiet)
		fprintf(stderr, _("Switched to a new branch '%s'\n"),
			opts->new_branch);
	return status;
}

static void die_expecting_a_branch(const struct branch_info *branch_info)
{
	struct object_id oid;
	char *to_free;

	if (dwim_ref(branch_info->name, strlen(branch_info->name), &oid, &to_free) == 1) {
		const char *ref = to_free;

		if (skip_prefix(ref, "refs/tags/", &ref))
			die(_("a branch is expected, got tag '%s'"), ref);
		if (skip_prefix(ref, "refs/remotes/", &ref))
			die(_("a branch is expected, got remote branch '%s'"), ref);
		die(_("a branch is expected, got '%s'"), ref);
	}
	if (branch_info->commit)
		die(_("a branch is expected, got commit '%s'"), branch_info->name);
	/*
	 * This case should never happen because we already die() on
	 * non-commit, but just in case.
	 */
	die(_("a branch is expected, got '%s'"), branch_info->name);
}

static void die_if_some_operation_in_progress(void)
{
	struct wt_status_state state;

	memset(&state, 0, sizeof(state));
	wt_status_get_state(the_repository, &state, 0);

	if (state.merge_in_progress)
		die(_("cannot switch branch while merging\n"
		      "Consider \"git merge --quit\" "
		      "or \"git worktree add\"."));
	if (state.am_in_progress)
		die(_("cannot switch branch in the middle of an am session\n"
		      "Consider \"git am --quit\" "
		      "or \"git worktree add\"."));
	if (state.rebase_interactive_in_progress || state.rebase_in_progress)
		die(_("cannot switch branch while rebasing\n"
		      "Consider \"git rebase --quit\" "
		      "or \"git worktree add\"."));
	if (state.cherry_pick_in_progress)
		die(_("cannot switch branch while cherry-picking\n"
		      "Consider \"git cherry-pick --quit\" "
		      "or \"git worktree add\"."));
	if (state.revert_in_progress)
		die(_("cannot switch branch while reverting\n"
		      "Consider \"git revert --quit\" "
		      "or \"git worktree add\"."));
	if (state.bisect_in_progress)
		warning(_("you are switching branch while bisecting"));
}

static int checkout_branch(struct checkout_opts *opts,
			   struct branch_info *new_branch_info)
{
	if (opts->pathspec.nr)
		die(_("paths cannot be used with switching branches"));

	if (opts->patch_mode)
		die(_("'%s' cannot be used with switching branches"),
		    "--patch");

	if (opts->overlay_mode != -1)
		die(_("'%s' cannot be used with switching branches"),
		    "--[no]-overlay");

	if (opts->writeout_stage)
		die(_("'%s' cannot be used with switching branches"),
		    "--ours/--theirs");

	if (opts->force && opts->merge)
		die(_("'%s' cannot be used with '%s'"), "-f", "-m");

	if (opts->discard_changes && opts->merge)
		die(_("'%s' cannot be used with '%s'"), "--discard-changes", "--merge");

	if (opts->force_detach && opts->new_branch)
		die(_("'%s' cannot be used with '%s'"),
		    "--detach", "-b/-B/--orphan");

	if (opts->new_orphan_branch) {
		if (opts->track != BRANCH_TRACK_UNSPECIFIED)
			die(_("'%s' cannot be used with '%s'"), "--orphan", "-t");
		if (opts->orphan_from_empty_tree && new_branch_info->name)
			die(_("'%s' cannot take <start-point>"), "--orphan");
	} else if (opts->force_detach) {
		if (opts->track != BRANCH_TRACK_UNSPECIFIED)
			die(_("'%s' cannot be used with '%s'"), "--detach", "-t");
	} else if (opts->track == BRANCH_TRACK_UNSPECIFIED)
		opts->track = git_branch_track;

	if (new_branch_info->name && !new_branch_info->commit)
		die(_("Cannot switch branch to a non-commit '%s'"),
		    new_branch_info->name);

	if (!opts->switch_branch_doing_nothing_is_ok &&
	    !new_branch_info->name &&
	    !opts->new_branch &&
	    !opts->force_detach)
		die(_("missing branch or commit argument"));

	if (!opts->implicit_detach &&
	    !opts->force_detach &&
	    !opts->new_branch &&
	    !opts->new_branch_force &&
	    new_branch_info->name &&
	    !new_branch_info->path)
		die_expecting_a_branch(new_branch_info);

	if (!opts->can_switch_when_in_progress)
		die_if_some_operation_in_progress();

	if (new_branch_info->path && !opts->force_detach && !opts->new_branch &&
	    !opts->ignore_other_worktrees) {
		int flag;
		char *head_ref = resolve_refdup("HEAD", 0, NULL, &flag);
		if (head_ref &&
		    (!(flag & REF_ISSYMREF) || strcmp(head_ref, new_branch_info->path)))
			die_if_checked_out(new_branch_info->path, 1);
		free(head_ref);
	}

	if (!new_branch_info->commit && opts->new_branch) {
		struct object_id rev;
		int flag;

		if (!read_ref_full("HEAD", 0, &rev, &flag) &&
		    (flag & REF_ISSYMREF) && is_null_oid(&rev))
			return switch_unborn_to_new_branch(opts);
	}
	return switch_branches(opts, new_branch_info);
}

static struct option *add_common_options(struct checkout_opts *opts,
					 struct option *prevopts)
{
	struct option options[] = {
		OPT__QUIET(&opts->quiet, N_("suppress progress reporting")),
		{ OPTION_CALLBACK, 0, "recurse-submodules", NULL,
			    "checkout", "control recursive updating of submodules",
			    PARSE_OPT_OPTARG, option_parse_recurse_submodules_worktree_updater },
		OPT_BOOL(0, "progress", &opts->show_progress, N_("force progress reporting")),
		OPT_BOOL('m', "merge", &opts->merge, N_("perform a 3-way merge with the new branch")),
		OPT_STRING(0, "conflict", &opts->conflict_style, N_("style"),
			   N_("conflict style (merge or diff3)")),
		OPT_END()
	};
	struct option *newopts = parse_options_concat(prevopts, options);
	free(prevopts);
	return newopts;
}

static struct option *add_common_switch_branch_options(
	struct checkout_opts *opts, struct option *prevopts)
{
	struct option options[] = {
		OPT_BOOL('d', "detach", &opts->force_detach, N_("detach HEAD at named commit")),
		OPT_SET_INT('t', "track",  &opts->track, N_("set upstream info for new branch"),
			BRANCH_TRACK_EXPLICIT),
		OPT__FORCE(&opts->force, N_("force checkout (throw away local modifications)"),
			   PARSE_OPT_NOCOMPLETE),
		OPT_STRING(0, "orphan", &opts->new_orphan_branch, N_("new-branch"), N_("new unparented branch")),
		OPT_BOOL_F(0, "overwrite-ignore", &opts->overwrite_ignore,
			   N_("update ignored files (default)"),
			   PARSE_OPT_NOCOMPLETE),
		OPT_BOOL(0, "ignore-other-worktrees", &opts->ignore_other_worktrees,
			 N_("do not check if another worktree is holding the given ref")),
		OPT_END()
	};
	struct option *newopts = parse_options_concat(prevopts, options);
	free(prevopts);
	return newopts;
}

static struct option *add_checkout_path_options(struct checkout_opts *opts,
						struct option *prevopts)
{
	struct option options[] = {
		OPT_SET_INT_F('2', "ours", &opts->writeout_stage,
			      N_("checkout our version for unmerged files"),
			      2, PARSE_OPT_NONEG),
		OPT_SET_INT_F('3', "theirs", &opts->writeout_stage,
			      N_("checkout their version for unmerged files"),
			      3, PARSE_OPT_NONEG),
		OPT_BOOL('p', "patch", &opts->patch_mode, N_("select hunks interactively")),
		OPT_BOOL(0, "ignore-skip-worktree-bits", &opts->ignore_skipworktree,
			 N_("do not limit pathspecs to sparse entries only")),
		OPT_END()
	};
	struct option *newopts = parse_options_concat(prevopts, options);
	free(prevopts);
	return newopts;
}

static int checkout_main(int argc, const char **argv, const char *prefix,
			 struct checkout_opts *opts, struct option *options,
			 const char * const usagestr[])
{
	struct branch_info new_branch_info;
	int dwim_remotes_matched = 0;
	int parseopt_flags = 0;

	memset(&new_branch_info, 0, sizeof(new_branch_info));
	opts->overwrite_ignore = 1;
	opts->prefix = prefix;
	opts->show_progress = -1;

	git_config(git_checkout_config, opts);

	opts->track = BRANCH_TRACK_UNSPECIFIED;

	if (!opts->accept_pathspec && !opts->accept_ref)
		BUG("make up your mind, you need to take _something_");
	if (opts->accept_pathspec && opts->accept_ref)
		parseopt_flags = PARSE_OPT_KEEP_DASHDASH;

	argc = parse_options(argc, argv, prefix, options,
			     usagestr, parseopt_flags);

	if (opts->show_progress < 0) {
		if (opts->quiet)
			opts->show_progress = 0;
		else
			opts->show_progress = isatty(2);
	}

	if (opts->conflict_style) {
		opts->merge = 1; /* implied */
		git_xmerge_config("merge.conflictstyle", opts->conflict_style, NULL);
	}
	if (opts->force) {
		opts->discard_changes = 1;
		opts->ignore_unmerged_opt = "--force";
		opts->ignore_unmerged = 1;
	}

	if ((!!opts->new_branch + !!opts->new_branch_force + !!opts->new_orphan_branch) > 1)
		die(_("-b, -B and --orphan are mutually exclusive"));

	if (opts->overlay_mode == 1 && opts->patch_mode)
		die(_("-p and --overlay are mutually exclusive"));

	if (opts->checkout_index >= 0 || opts->checkout_worktree >= 0) {
		if (opts->checkout_index < 0)
			opts->checkout_index = 0;
		if (opts->checkout_worktree < 0)
			opts->checkout_worktree = 0;
	} else {
		if (opts->checkout_index < 0)
			opts->checkout_index = -opts->checkout_index - 1;
		if (opts->checkout_worktree < 0)
			opts->checkout_worktree = -opts->checkout_worktree - 1;
	}
	if (opts->checkout_index < 0 || opts->checkout_worktree < 0)
		BUG("these flags should be non-negative by now");
	/*
	 * convenient shortcut: "git restore --staged" equals
	 * "git restore --staged --source HEAD"
	 */
	if (!opts->from_treeish && opts->checkout_index && !opts->checkout_worktree)
		opts->from_treeish = "HEAD";

	/*
	 * From here on, new_branch will contain the branch to be checked out,
	 * and new_branch_force and new_orphan_branch will tell us which one of
	 * -b/-B/--orphan is being used.
	 */
	if (opts->new_branch_force)
		opts->new_branch = opts->new_branch_force;

	if (opts->new_orphan_branch)
		opts->new_branch = opts->new_orphan_branch;

	/* --track without -b/-B/--orphan should DWIM */
	if (opts->track != BRANCH_TRACK_UNSPECIFIED && !opts->new_branch) {
		const char *argv0 = argv[0];
		if (!argc || !strcmp(argv0, "--"))
			die(_("--track needs a branch name"));
		skip_prefix(argv0, "refs/", &argv0);
		skip_prefix(argv0, "remotes/", &argv0);
		argv0 = strchr(argv0, '/');
		if (!argv0 || !argv0[1])
			die(_("missing branch name; try -b"));
		opts->new_branch = argv0 + 1;
	}

	/*
	 * Extract branch name from command line arguments, so
	 * all that is left is pathspecs.
	 *
	 * Handle
	 *
	 *  1) git checkout <tree> -- [<paths>]
	 *  2) git checkout -- [<paths>]
	 *  3) git checkout <something> [<paths>]
	 *
	 * including "last branch" syntax and DWIM-ery for names of
	 * remote branches, erroring out for invalid or ambiguous cases.
	 */
	if (argc && opts->accept_ref) {
		struct object_id rev;
		int dwim_ok =
			!opts->patch_mode &&
			opts->dwim_new_local_branch &&
			opts->track == BRANCH_TRACK_UNSPECIFIED &&
			!opts->new_branch;
		int n = parse_branchname_arg(argc, argv, dwim_ok,
					     &new_branch_info, opts, &rev,
					     &dwim_remotes_matched);
		argv += n;
		argc -= n;
	} else if (!opts->accept_ref && opts->from_treeish) {
		struct object_id rev;

		if (get_oid_mb(opts->from_treeish, &rev))
			die(_("could not resolve %s"), opts->from_treeish);

		setup_new_branch_info_and_source_tree(&new_branch_info,
						      opts, &rev,
						      opts->from_treeish);

		if (!opts->source_tree)
			die(_("reference is not a tree: %s"), opts->from_treeish);
	}

	if (opts->accept_pathspec && !opts->empty_pathspec_ok && !argc &&
	    !opts->patch_mode)	/* patch mode is special */
		die(_("you must specify path(s) to restore"));

	if (argc) {
		parse_pathspec(&opts->pathspec, 0,
			       opts->patch_mode ? PATHSPEC_PREFIX_ORIGIN : 0,
			       prefix, argv);

		if (!opts->pathspec.nr)
			die(_("invalid path specification"));

		/*
		 * Try to give more helpful suggestion.
		 * new_branch && argc > 1 will be caught later.
		 */
		if (opts->new_branch && argc == 1)
			die(_("'%s' is not a commit and a branch '%s' cannot be created from it"),
				argv[0], opts->new_branch);

		if (opts->force_detach)
			die(_("git checkout: --detach does not take a path argument '%s'"),
			    argv[0]);

		if (1 < !!opts->writeout_stage + !!opts->force + !!opts->merge)
			die(_("git checkout: --ours/--theirs, --force and --merge are incompatible when\n"
			      "checking out of the index."));
	}

	if (opts->new_branch) {
		struct strbuf buf = STRBUF_INIT;

		if (opts->new_branch_force)
			opts->branch_exists = validate_branchname(opts->new_branch, &buf);
		else
			opts->branch_exists =
				validate_new_branchname(opts->new_branch, &buf, 0);
		strbuf_release(&buf);
	}

	UNLEAK(opts);
	if (opts->patch_mode || opts->pathspec.nr) {
		int ret = checkout_paths(opts, new_branch_info.name);
		if (ret && dwim_remotes_matched > 1 &&
		    advice_checkout_ambiguous_remote_branch_name)
			advise(_("'%s' matched more than one remote tracking branch.\n"
				 "We found %d remotes with a reference that matched. So we fell back\n"
				 "on trying to resolve the argument as a path, but failed there too!\n"
				 "\n"
				 "If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
				 "you can do so by fully qualifying the name with the --track option:\n"
				 "\n"
				 "    git checkout --track origin/<name>\n"
				 "\n"
				 "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
				 "one remote, e.g. the 'origin' remote, consider setting\n"
				 "checkout.defaultRemote=origin in your config."),
			       argv[0],
			       dwim_remotes_matched);
		return ret;
	} else {
		return checkout_branch(opts, &new_branch_info);
	}
}

int cmd_checkout(int argc, const char **argv, const char *prefix)
{
	struct checkout_opts opts;
	struct option *options;
	struct option checkout_options[] = {
		OPT_STRING('b', NULL, &opts.new_branch, N_("branch"),
			   N_("create and checkout a new branch")),
		OPT_STRING('B', NULL, &opts.new_branch_force, N_("branch"),
			   N_("create/reset and checkout a branch")),
		OPT_BOOL('l', NULL, &opts.new_branch_log, N_("create reflog for new branch")),
		OPT_BOOL(0, "guess", &opts.dwim_new_local_branch,
			 N_("second guess 'git checkout <no-such-branch>' (default)")),
		OPT_BOOL(0, "overlay", &opts.overlay_mode, N_("use overlay mode (default)")),
		OPT_END()
	};
	int ret;

	memset(&opts, 0, sizeof(opts));
	opts.dwim_new_local_branch = 1;
	opts.switch_branch_doing_nothing_is_ok = 1;
	opts.only_merge_on_switching_branches = 0;
	opts.accept_ref = 1;
	opts.accept_pathspec = 1;
	opts.implicit_detach = 1;
	opts.can_switch_when_in_progress = 1;
	opts.orphan_from_empty_tree = 0;
	opts.empty_pathspec_ok = 1;
	opts.overlay_mode = -1;
	opts.checkout_index = -2;    /* default on */
	opts.checkout_worktree = -2; /* default on */

	options = parse_options_dup(checkout_options);
	options = add_common_options(&opts, options);
	options = add_common_switch_branch_options(&opts, options);
	options = add_checkout_path_options(&opts, options);

	ret = checkout_main(argc, argv, prefix, &opts,
			    options, checkout_usage);
	FREE_AND_NULL(options);
	return ret;
}

int cmd_switch(int argc, const char **argv, const char *prefix)
{
	struct checkout_opts opts;
	struct option *options = NULL;
	struct option switch_options[] = {
		OPT_STRING('c', "create", &opts.new_branch, N_("branch"),
			   N_("create and switch to a new branch")),
		OPT_STRING('C', "force-create", &opts.new_branch_force, N_("branch"),
			   N_("create/reset and switch to a branch")),
		OPT_BOOL(0, "guess", &opts.dwim_new_local_branch,
			 N_("second guess 'git switch <no-such-branch>'")),
		OPT_BOOL(0, "discard-changes", &opts.discard_changes,
			 N_("throw away local modifications")),
		OPT_END()
	};
	int ret;

	memset(&opts, 0, sizeof(opts));
	opts.dwim_new_local_branch = 1;
	opts.accept_ref = 1;
	opts.accept_pathspec = 0;
	opts.switch_branch_doing_nothing_is_ok = 0;
	opts.only_merge_on_switching_branches = 1;
	opts.implicit_detach = 0;
	opts.can_switch_when_in_progress = 0;
	opts.orphan_from_empty_tree = 1;
	opts.overlay_mode = -1;

	options = parse_options_dup(switch_options);
	options = add_common_options(&opts, options);
	options = add_common_switch_branch_options(&opts, options);

	ret = checkout_main(argc, argv, prefix, &opts,
			    options, switch_branch_usage);
	FREE_AND_NULL(options);
	return ret;
}

int cmd_restore(int argc, const char **argv, const char *prefix)
{
	struct checkout_opts opts;
	struct option *options;
	struct option restore_options[] = {
		OPT_STRING('s', "source", &opts.from_treeish, "<tree-ish>",
			   N_("which tree-ish to checkout from")),
		OPT_BOOL('S', "staged", &opts.checkout_index,
			   N_("restore the index")),
		OPT_BOOL('W', "worktree", &opts.checkout_worktree,
			   N_("restore the working tree (default)")),
		OPT_BOOL(0, "ignore-unmerged", &opts.ignore_unmerged,
			 N_("ignore unmerged entries")),
		OPT_BOOL(0, "overlay", &opts.overlay_mode, N_("use overlay mode")),
		OPT_END()
	};
	int ret;

	memset(&opts, 0, sizeof(opts));
	opts.accept_ref = 0;
	opts.accept_pathspec = 1;
	opts.empty_pathspec_ok = 0;
	opts.overlay_mode = 0;
	opts.checkout_index = -1;    /* default off */
	opts.checkout_worktree = -2; /* default on */
	opts.ignore_unmerged_opt = "--ignore-unmerged";

	options = parse_options_dup(restore_options);
	options = add_common_options(&opts, options);
	options = add_checkout_path_options(&opts, options);

	ret = checkout_main(argc, argv, prefix, &opts,
			    options, restore_usage);
	FREE_AND_NULL(options);
	return ret;
}