aboutsummaryrefslogtreecommitdiff
path: root/unpack-trees.c
blob: e3c3fa12aaa80389868e5a26fa97b09d1dd61528 (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
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
#define NO_THE_INDEX_COMPATIBILITY_MACROS
#include "cache.h"
#include "dir.h"
#include "tree.h"
#include "tree-walk.h"
#include "cache-tree.h"
#include "unpack-trees.h"
#include "progress.h"
#include "refs.h"

/*
 * Error messages expected by scripts out of plumbing commands such as
 * read-tree.  Non-scripted Porcelain is not required to use these messages
 * and in fact are encouraged to reword them to better suit their particular
 * situation better.  See how "git checkout" replaces not_uptodate_file to
 * explain why it does not allow switching between branches when you have
 * local changes, for example.
 */
static struct unpack_trees_error_msgs unpack_plumbing_errors = {
	/* would_overwrite */
	"Entry '%s' would be overwritten by merge. Cannot merge.",

	/* not_uptodate_file */
	"Entry '%s' not uptodate. Cannot merge.",

	/* not_uptodate_dir */
	"Updating '%s' would lose untracked files in it",

	/* would_lose_untracked */
	"Untracked working tree file '%s' would be %s by merge.",

	/* bind_overlap */
	"Entry '%s' overlaps with '%s'.  Cannot bind.",
};

#define ERRORMSG(o,fld) \
	( ((o) && (o)->msgs.fld) \
	? ((o)->msgs.fld) \
	: (unpack_plumbing_errors.fld) )

static void add_entry(struct unpack_trees_options *o, struct cache_entry *ce,
	unsigned int set, unsigned int clear)
{
	unsigned int size = ce_size(ce);
	struct cache_entry *new = xmalloc(size);

	clear |= CE_HASHED | CE_UNHASHED;

	memcpy(new, ce, size);
	new->next = NULL;
	new->ce_flags = (new->ce_flags & ~clear) | set;
	add_index_entry(&o->result, new, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE|ADD_CACHE_SKIP_DFCHECK);
}

/*
 * Unlink the last component and schedule the leading directories for
 * removal, such that empty directories get removed.
 */
static void unlink_entry(struct cache_entry *ce)
{
	if (has_symlink_or_noent_leading_path(ce->name, ce_namelen(ce)))
		return;
	if (unlink(ce->name))
		return;
	schedule_dir_for_removal(ce->name, ce_namelen(ce));
}

static struct checkout state;
static int check_updates(struct unpack_trees_options *o)
{
	unsigned cnt = 0, total = 0;
	struct progress *progress = NULL;
	struct index_state *index = &o->result;
	int i;
	int errs = 0;

	if (o->update && o->verbose_update) {
		for (total = cnt = 0; cnt < index->cache_nr; cnt++) {
			struct cache_entry *ce = index->cache[cnt];
			if (ce->ce_flags & (CE_UPDATE | CE_REMOVE))
				total++;
		}

		progress = start_progress_delay("Checking out files",
						total, 50, 1);
		cnt = 0;
	}

	for (i = 0; i < index->cache_nr; i++) {
		struct cache_entry *ce = index->cache[i];

		if (ce->ce_flags & CE_REMOVE) {
			display_progress(progress, ++cnt);
			if (o->update)
				unlink_entry(ce);
			remove_index_entry_at(&o->result, i);
			i--;
			continue;
		}
	}
	remove_scheduled_dirs();

	for (i = 0; i < index->cache_nr; i++) {
		struct cache_entry *ce = index->cache[i];

		if (ce->ce_flags & CE_UPDATE) {
			display_progress(progress, ++cnt);
			ce->ce_flags &= ~CE_UPDATE;
			if (o->update) {
				errs |= checkout_entry(ce, &state, NULL);
			}
		}
	}
	stop_progress(&progress);
	return errs != 0;
}

static inline int call_unpack_fn(struct cache_entry **src, struct unpack_trees_options *o)
{
	int ret = o->fn(src, o);
	if (ret > 0)
		ret = 0;
	return ret;
}

static int unpack_index_entry(struct cache_entry *ce, struct unpack_trees_options *o)
{
	struct cache_entry *src[5] = { ce, };

	o->pos++;
	if (ce_stage(ce)) {
		if (o->skip_unmerged) {
			add_entry(o, ce, 0, 0);
			return 0;
		}
	}
	return call_unpack_fn(src, o);
}

int traverse_trees_recursive(int n, unsigned long dirmask, unsigned long df_conflicts, struct name_entry *names, struct traverse_info *info)
{
	int i;
	struct tree_desc t[MAX_UNPACK_TREES];
	struct traverse_info newinfo;
	struct name_entry *p;

	p = names;
	while (!p->mode)
		p++;

	newinfo = *info;
	newinfo.prev = info;
	newinfo.name = *p;
	newinfo.pathlen += tree_entry_len(p->path, p->sha1) + 1;
	newinfo.conflicts |= df_conflicts;

	for (i = 0; i < n; i++, dirmask >>= 1) {
		const unsigned char *sha1 = NULL;
		if (dirmask & 1)
			sha1 = names[i].sha1;
		fill_tree_descriptor(t+i, sha1);
	}
	return traverse_trees(n, t, &newinfo);
}

/*
 * Compare the traverse-path to the cache entry without actually
 * having to generate the textual representation of the traverse
 * path.
 *
 * NOTE! This *only* compares up to the size of the traverse path
 * itself - the caller needs to do the final check for the cache
 * entry having more data at the end!
 */
static int do_compare_entry(const struct cache_entry *ce, const struct traverse_info *info, const struct name_entry *n)
{
	int len, pathlen, ce_len;
	const char *ce_name;

	if (info->prev) {
		int cmp = do_compare_entry(ce, info->prev, &info->name);
		if (cmp)
			return cmp;
	}
	pathlen = info->pathlen;
	ce_len = ce_namelen(ce);

	/* If ce_len < pathlen then we must have previously hit "name == directory" entry */
	if (ce_len < pathlen)
		return -1;

	ce_len -= pathlen;
	ce_name = ce->name + pathlen;

	len = tree_entry_len(n->path, n->sha1);
	return df_name_compare(ce_name, ce_len, S_IFREG, n->path, len, n->mode);
}

static int compare_entry(const struct cache_entry *ce, const struct traverse_info *info, const struct name_entry *n)
{
	int cmp = do_compare_entry(ce, info, n);
	if (cmp)
		return cmp;

	/*
	 * Even if the beginning compared identically, the ce should
	 * compare as bigger than a directory leading up to it!
	 */
	return ce_namelen(ce) > traverse_path_len(info, n);
}

static struct cache_entry *create_ce_entry(const struct traverse_info *info, const struct name_entry *n, int stage)
{
	int len = traverse_path_len(info, n);
	struct cache_entry *ce = xcalloc(1, cache_entry_size(len));

	ce->ce_mode = create_ce_mode(n->mode);
	ce->ce_flags = create_ce_flags(len, stage);
	hashcpy(ce->sha1, n->sha1);
	make_traverse_path(ce->name, info, n);

	return ce;
}

static int unpack_nondirectories(int n, unsigned long mask,
				 unsigned long dirmask,
				 struct cache_entry **src,
				 const struct name_entry *names,
				 const struct traverse_info *info)
{
	int i;
	struct unpack_trees_options *o = info->data;
	unsigned long conflicts;

	/* Do we have *only* directories? Nothing to do */
	if (mask == dirmask && !src[0])
		return 0;

	conflicts = info->conflicts;
	if (o->merge)
		conflicts >>= 1;
	conflicts |= dirmask;

	/*
	 * Ok, we've filled in up to any potential index entry in src[0],
	 * now do the rest.
	 */
	for (i = 0; i < n; i++) {
		int stage;
		unsigned int bit = 1ul << i;
		if (conflicts & bit) {
			src[i + o->merge] = o->df_conflict_entry;
			continue;
		}
		if (!(mask & bit))
			continue;
		if (!o->merge)
			stage = 0;
		else if (i + 1 < o->head_idx)
			stage = 1;
		else if (i + 1 > o->head_idx)
			stage = 3;
		else
			stage = 2;
		src[i + o->merge] = create_ce_entry(info, names + i, stage);
	}

	if (o->merge)
		return call_unpack_fn(src, o);

	n += o->merge;
	for (i = 0; i < n; i++)
		add_entry(o, src[i], 0, 0);
	return 0;
}

static int unpack_callback(int n, unsigned long mask, unsigned long dirmask, struct name_entry *names, struct traverse_info *info)
{
	struct cache_entry *src[MAX_UNPACK_TREES + 1] = { NULL, };
	struct unpack_trees_options *o = info->data;
	const struct name_entry *p = names;

	/* Find first entry with a real name (we could use "mask" too) */
	while (!p->mode)
		p++;

	/* Are we supposed to look at the index too? */
	if (o->merge) {
		while (o->pos < o->src_index->cache_nr) {
			struct cache_entry *ce = o->src_index->cache[o->pos];
			int cmp = compare_entry(ce, info, p);
			if (cmp < 0) {
				if (unpack_index_entry(ce, o) < 0)
					return -1;
				continue;
			}
			if (!cmp) {
				o->pos++;
				if (ce_stage(ce)) {
					/*
					 * If we skip unmerged index entries, we'll skip this
					 * entry *and* the tree entries associated with it!
					 */
					if (o->skip_unmerged) {
						add_entry(o, ce, 0, 0);
						return mask;
					}
				}
				src[0] = ce;
			}
			break;
		}
	}

	if (unpack_nondirectories(n, mask, dirmask, src, names, info) < 0)
		return -1;

	/* Now handle any directories.. */
	if (dirmask) {
		unsigned long conflicts = mask & ~dirmask;
		if (o->merge) {
			conflicts <<= 1;
			if (src[0])
				conflicts |= 1;
		}
		if (traverse_trees_recursive(n, dirmask, conflicts,
					     names, info) < 0)
			return -1;
		return mask;
	}

	return mask;
}

static int unpack_failed(struct unpack_trees_options *o, const char *message)
{
	discard_index(&o->result);
	if (!o->gently) {
		if (message)
			return error("%s", message);
		return -1;
	}
	return -1;
}

/*
 * N-way merge "len" trees.  Returns 0 on success, -1 on failure to manipulate the
 * resulting index, -2 on failure to reflect the changes to the work tree.
 */
int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options *o)
{
	int ret;
	static struct cache_entry *dfc;

	if (len > MAX_UNPACK_TREES)
		die("unpack_trees takes at most %d trees", MAX_UNPACK_TREES);
	memset(&state, 0, sizeof(state));
	state.base_dir = "";
	state.force = 1;
	state.quiet = 1;
	state.refresh_cache = 1;

	memset(&o->result, 0, sizeof(o->result));
	o->result.initialized = 1;
	if (o->src_index)
		o->result.timestamp = o->src_index->timestamp;
	o->merge_size = len;

	if (!dfc)
		dfc = xcalloc(1, cache_entry_size(0));
	o->df_conflict_entry = dfc;

	if (len) {
		const char *prefix = o->prefix ? o->prefix : "";
		struct traverse_info info;

		setup_traverse_info(&info, prefix);
		info.fn = unpack_callback;
		info.data = o;

		if (traverse_trees(len, t, &info) < 0)
			return unpack_failed(o, NULL);
	}

	/* Any left-over entries in the index? */
	if (o->merge) {
		while (o->pos < o->src_index->cache_nr) {
			struct cache_entry *ce = o->src_index->cache[o->pos];
			if (unpack_index_entry(ce, o) < 0)
				return unpack_failed(o, NULL);
		}
	}

	if (o->trivial_merges_only && o->nontrivial_merge)
		return unpack_failed(o, "Merge requires file-level merging");

	o->src_index = NULL;
	ret = check_updates(o) ? (-2) : 0;
	if (o->dst_index)
		*o->dst_index = o->result;
	return ret;
}

/* Here come the merge functions */

static int reject_merge(struct cache_entry *ce, struct unpack_trees_options *o)
{
	return error(ERRORMSG(o, would_overwrite), ce->name);
}

static int same(struct cache_entry *a, struct cache_entry *b)
{
	if (!!a != !!b)
		return 0;
	if (!a && !b)
		return 1;
	return a->ce_mode == b->ce_mode &&
	       !hashcmp(a->sha1, b->sha1);
}


/*
 * When a CE gets turned into an unmerged entry, we
 * want it to be up-to-date
 */
static int verify_uptodate(struct cache_entry *ce,
		struct unpack_trees_options *o)
{
	struct stat st;

	if (o->index_only || o->reset)
		return 0;

	if (!lstat(ce->name, &st)) {
		unsigned changed = ie_match_stat(o->src_index, ce, &st, CE_MATCH_IGNORE_VALID);
		if (!changed)
			return 0;
		/*
		 * NEEDSWORK: the current default policy is to allow
		 * submodule to be out of sync wrt the supermodule
		 * index.  This needs to be tightened later for
		 * submodules that are marked to be automatically
		 * checked out.
		 */
		if (S_ISGITLINK(ce->ce_mode))
			return 0;
		errno = 0;
	}
	if (errno == ENOENT)
		return 0;
	return o->gently ? -1 :
		error(ERRORMSG(o, not_uptodate_file), ce->name);
}

static void invalidate_ce_path(struct cache_entry *ce, struct unpack_trees_options *o)
{
	if (ce)
		cache_tree_invalidate_path(o->src_index->cache_tree, ce->name);
}

/*
 * Check that checking out ce->sha1 in subdir ce->name is not
 * going to overwrite any working files.
 *
 * Currently, git does not checkout subprojects during a superproject
 * checkout, so it is not going to overwrite anything.
 */
static int verify_clean_submodule(struct cache_entry *ce, const char *action,
				      struct unpack_trees_options *o)
{
	return 0;
}

static int verify_clean_subdirectory(struct cache_entry *ce, const char *action,
				      struct unpack_trees_options *o)
{
	/*
	 * we are about to extract "ce->name"; we would not want to lose
	 * anything in the existing directory there.
	 */
	int namelen;
	int i;
	struct dir_struct d;
	char *pathbuf;
	int cnt = 0;
	unsigned char sha1[20];

	if (S_ISGITLINK(ce->ce_mode) &&
	    resolve_gitlink_ref(ce->name, "HEAD", sha1) == 0) {
		/* If we are not going to update the submodule, then
		 * we don't care.
		 */
		if (!hashcmp(sha1, ce->sha1))
			return 0;
		return verify_clean_submodule(ce, action, o);
	}

	/*
	 * First let's make sure we do not have a local modification
	 * in that directory.
	 */
	namelen = strlen(ce->name);
	for (i = o->pos; i < o->src_index->cache_nr; i++) {
		struct cache_entry *ce2 = o->src_index->cache[i];
		int len = ce_namelen(ce2);
		if (len < namelen ||
		    strncmp(ce->name, ce2->name, namelen) ||
		    ce2->name[namelen] != '/')
			break;
		/*
		 * ce2->name is an entry in the subdirectory.
		 */
		if (!ce_stage(ce2)) {
			if (verify_uptodate(ce2, o))
				return -1;
			add_entry(o, ce2, CE_REMOVE, 0);
		}
		cnt++;
	}

	/*
	 * Then we need to make sure that we do not lose a locally
	 * present file that is not ignored.
	 */
	pathbuf = xmalloc(namelen + 2);
	memcpy(pathbuf, ce->name, namelen);
	strcpy(pathbuf+namelen, "/");

	memset(&d, 0, sizeof(d));
	if (o->dir)
		d.exclude_per_dir = o->dir->exclude_per_dir;
	i = read_directory(&d, ce->name, pathbuf, namelen+1, NULL);
	if (i)
		return o->gently ? -1 :
			error(ERRORMSG(o, not_uptodate_dir), ce->name);
	free(pathbuf);
	return cnt;
}

/*
 * This gets called when there was no index entry for the tree entry 'dst',
 * but we found a file in the working tree that 'lstat()' said was fine,
 * and we're on a case-insensitive filesystem.
 *
 * See if we can find a case-insensitive match in the index that also
 * matches the stat information, and assume it's that other file!
 */
static int icase_exists(struct unpack_trees_options *o, struct cache_entry *dst, struct stat *st)
{
	struct cache_entry *src;

	src = index_name_exists(o->src_index, dst->name, ce_namelen(dst), 1);
	return src && !ie_match_stat(o->src_index, src, st, CE_MATCH_IGNORE_VALID);
}

/*
 * We do not want to remove or overwrite a working tree file that
 * is not tracked, unless it is ignored.
 */
static int verify_absent(struct cache_entry *ce, const char *action,
			 struct unpack_trees_options *o)
{
	struct stat st;

	if (o->index_only || o->reset || !o->update)
		return 0;

	if (has_symlink_or_noent_leading_path(ce->name, ce_namelen(ce)))
		return 0;

	if (!lstat(ce->name, &st)) {
		int ret;
		int dtype = ce_to_dtype(ce);
		struct cache_entry *result;

		/*
		 * It may be that the 'lstat()' succeeded even though
		 * target 'ce' was absent, because there is an old
		 * entry that is different only in case..
		 *
		 * Ignore that lstat() if it matches.
		 */
		if (ignore_case && icase_exists(o, ce, &st))
			return 0;

		if (o->dir && excluded(o->dir, ce->name, &dtype))
			/*
			 * ce->name is explicitly excluded, so it is Ok to
			 * overwrite it.
			 */
			return 0;
		if (S_ISDIR(st.st_mode)) {
			/*
			 * We are checking out path "foo" and
			 * found "foo/." in the working tree.
			 * This is tricky -- if we have modified
			 * files that are in "foo/" we would lose
			 * it.
			 */
			ret = verify_clean_subdirectory(ce, action, o);
			if (ret < 0)
				return ret;

			/*
			 * If this removed entries from the index,
			 * what that means is:
			 *
			 * (1) the caller unpack_callback() saw path/foo
			 * in the index, and it has not removed it because
			 * it thinks it is handling 'path' as blob with
			 * D/F conflict;
			 * (2) we will return "ok, we placed a merged entry
			 * in the index" which would cause o->pos to be
			 * incremented by one;
			 * (3) however, original o->pos now has 'path/foo'
			 * marked with "to be removed".
			 *
			 * We need to increment it by the number of
			 * deleted entries here.
			 */
			o->pos += ret;
			return 0;
		}

		/*
		 * The previous round may already have decided to
		 * delete this path, which is in a subdirectory that
		 * is being replaced with a blob.
		 */
		result = index_name_exists(&o->result, ce->name, ce_namelen(ce), 0);
		if (result) {
			if (result->ce_flags & CE_REMOVE)
				return 0;
		}

		return o->gently ? -1 :
			error(ERRORMSG(o, would_lose_untracked), ce->name, action);
	}
	return 0;
}

static int merged_entry(struct cache_entry *merge, struct cache_entry *old,
		struct unpack_trees_options *o)
{
	int update = CE_UPDATE;

	if (old) {
		/*
		 * See if we can re-use the old CE directly?
		 * That way we get the uptodate stat info.
		 *
		 * This also removes the UPDATE flag on a match; otherwise
		 * we will end up overwriting local changes in the work tree.
		 */
		if (same(old, merge)) {
			copy_cache_entry(merge, old);
			update = 0;
		} else {
			if (verify_uptodate(old, o))
				return -1;
			invalidate_ce_path(old, o);
		}
	}
	else {
		if (verify_absent(merge, "overwritten", o))
			return -1;
		invalidate_ce_path(merge, o);
	}

	add_entry(o, merge, update, CE_STAGEMASK);
	return 1;
}

static int deleted_entry(struct cache_entry *ce, struct cache_entry *old,
		struct unpack_trees_options *o)
{
	/* Did it exist in the index? */
	if (!old) {
		if (verify_absent(ce, "removed", o))
			return -1;
		return 0;
	}
	if (verify_uptodate(old, o))
		return -1;
	add_entry(o, ce, CE_REMOVE, 0);
	invalidate_ce_path(ce, o);
	return 1;
}

static int keep_entry(struct cache_entry *ce, struct unpack_trees_options *o)
{
	add_entry(o, ce, 0, 0);
	return 1;
}

#if DBRT_DEBUG
static void show_stage_entry(FILE *o,
			     const char *label, const struct cache_entry *ce)
{
	if (!ce)
		fprintf(o, "%s (missing)\n", label);
	else
		fprintf(o, "%s%06o %s %d\t%s\n",
			label,
			ce->ce_mode,
			sha1_to_hex(ce->sha1),
			ce_stage(ce),
			ce->name);
}
#endif

int threeway_merge(struct cache_entry **stages, struct unpack_trees_options *o)
{
	struct cache_entry *index;
	struct cache_entry *head;
	struct cache_entry *remote = stages[o->head_idx + 1];
	int count;
	int head_match = 0;
	int remote_match = 0;

	int df_conflict_head = 0;
	int df_conflict_remote = 0;

	int any_anc_missing = 0;
	int no_anc_exists = 1;
	int i;

	for (i = 1; i < o->head_idx; i++) {
		if (!stages[i] || stages[i] == o->df_conflict_entry)
			any_anc_missing = 1;
		else
			no_anc_exists = 0;
	}

	index = stages[0];
	head = stages[o->head_idx];

	if (head == o->df_conflict_entry) {
		df_conflict_head = 1;
		head = NULL;
	}

	if (remote == o->df_conflict_entry) {
		df_conflict_remote = 1;
		remote = NULL;
	}

	/* First, if there's a #16 situation, note that to prevent #13
	 * and #14.
	 */
	if (!same(remote, head)) {
		for (i = 1; i < o->head_idx; i++) {
			if (same(stages[i], head)) {
				head_match = i;
			}
			if (same(stages[i], remote)) {
				remote_match = i;
			}
		}
	}

	/* We start with cases where the index is allowed to match
	 * something other than the head: #14(ALT) and #2ALT, where it
	 * is permitted to match the result instead.
	 */
	/* #14, #14ALT, #2ALT */
	if (remote && !df_conflict_head && head_match && !remote_match) {
		if (index && !same(index, remote) && !same(index, head))
			return o->gently ? -1 : reject_merge(index, o);
		return merged_entry(remote, index, o);
	}
	/*
	 * If we have an entry in the index cache, then we want to
	 * make sure that it matches head.
	 */
	if (index && !same(index, head))
		return o->gently ? -1 : reject_merge(index, o);

	if (head) {
		/* #5ALT, #15 */
		if (same(head, remote))
			return merged_entry(head, index, o);
		/* #13, #3ALT */
		if (!df_conflict_remote && remote_match && !head_match)
			return merged_entry(head, index, o);
	}

	/* #1 */
	if (!head && !remote && any_anc_missing)
		return 0;

	/* Under the new "aggressive" rule, we resolve mostly trivial
	 * cases that we historically had git-merge-one-file resolve.
	 */
	if (o->aggressive) {
		int head_deleted = !head && !df_conflict_head;
		int remote_deleted = !remote && !df_conflict_remote;
		struct cache_entry *ce = NULL;

		if (index)
			ce = index;
		else if (head)
			ce = head;
		else if (remote)
			ce = remote;
		else {
			for (i = 1; i < o->head_idx; i++) {
				if (stages[i] && stages[i] != o->df_conflict_entry) {
					ce = stages[i];
					break;
				}
			}
		}

		/*
		 * Deleted in both.
		 * Deleted in one and unchanged in the other.
		 */
		if ((head_deleted && remote_deleted) ||
		    (head_deleted && remote && remote_match) ||
		    (remote_deleted && head && head_match)) {
			if (index)
				return deleted_entry(index, index, o);
			if (ce && !head_deleted) {
				if (verify_absent(ce, "removed", o))
					return -1;
			}
			return 0;
		}
		/*
		 * Added in both, identically.
		 */
		if (no_anc_exists && head && remote && same(head, remote))
			return merged_entry(head, index, o);

	}

	/* Below are "no merge" cases, which require that the index be
	 * up-to-date to avoid the files getting overwritten with
	 * conflict resolution files.
	 */
	if (index) {
		if (verify_uptodate(index, o))
			return -1;
	}

	o->nontrivial_merge = 1;

	/* #2, #3, #4, #6, #7, #9, #10, #11. */
	count = 0;
	if (!head_match || !remote_match) {
		for (i = 1; i < o->head_idx; i++) {
			if (stages[i] && stages[i] != o->df_conflict_entry) {
				keep_entry(stages[i], o);
				count++;
				break;
			}
		}
	}
#if DBRT_DEBUG
	else {
		fprintf(stderr, "read-tree: warning #16 detected\n");
		show_stage_entry(stderr, "head   ", stages[head_match]);
		show_stage_entry(stderr, "remote ", stages[remote_match]);
	}
#endif
	if (head) { count += keep_entry(head, o); }
	if (remote) { count += keep_entry(remote, o); }
	return count;
}

/*
 * Two-way merge.
 *
 * The rule is to "carry forward" what is in the index without losing
 * information across a "fast forward", favoring a successful merge
 * over a merge failure when it makes sense.  For details of the
 * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
 *
 */
int twoway_merge(struct cache_entry **src, struct unpack_trees_options *o)
{
	struct cache_entry *current = src[0];
	struct cache_entry *oldtree = src[1];
	struct cache_entry *newtree = src[2];

	if (o->merge_size != 2)
		return error("Cannot do a twoway merge of %d trees",
			     o->merge_size);

	if (oldtree == o->df_conflict_entry)
		oldtree = NULL;
	if (newtree == o->df_conflict_entry)
		newtree = NULL;

	if (current) {
		if ((!oldtree && !newtree) || /* 4 and 5 */
		    (!oldtree && newtree &&
		     same(current, newtree)) || /* 6 and 7 */
		    (oldtree && newtree &&
		     same(oldtree, newtree)) || /* 14 and 15 */
		    (oldtree && newtree &&
		     !same(oldtree, newtree) && /* 18 and 19 */
		     same(current, newtree))) {
			return keep_entry(current, o);
		}
		else if (oldtree && !newtree && same(current, oldtree)) {
			/* 10 or 11 */
			return deleted_entry(oldtree, current, o);
		}
		else if (oldtree && newtree &&
			 same(current, oldtree) && !same(current, newtree)) {
			/* 20 or 21 */
			return merged_entry(newtree, current, o);
		}
		else {
			/* all other failures */
			if (oldtree)
				return o->gently ? -1 : reject_merge(oldtree, o);
			if (current)
				return o->gently ? -1 : reject_merge(current, o);
			if (newtree)
				return o->gently ? -1 : reject_merge(newtree, o);
			return -1;
		}
	}
	else if (newtree) {
		if (oldtree && !o->initial_checkout) {
			/*
			 * deletion of the path was staged;
			 */
			if (same(oldtree, newtree))
				return 1;
			return reject_merge(oldtree, o);
		}
		return merged_entry(newtree, current, o);
	}
	return deleted_entry(oldtree, current, o);
}

/*
 * Bind merge.
 *
 * Keep the index entries at stage0, collapse stage1 but make sure
 * stage0 does not have anything there.
 */
int bind_merge(struct cache_entry **src,
		struct unpack_trees_options *o)
{
	struct cache_entry *old = src[0];
	struct cache_entry *a = src[1];

	if (o->merge_size != 1)
		return error("Cannot do a bind merge of %d trees\n",
			     o->merge_size);
	if (a && old)
		return o->gently ? -1 :
			error(ERRORMSG(o, bind_overlap), a->name, old->name);
	if (!a)
		return keep_entry(old, o);
	else
		return merged_entry(a, NULL, o);
}

/*
 * One-way merge.
 *
 * The rule is:
 * - take the stat information from stage0, take the data from stage1
 */
int oneway_merge(struct cache_entry **src, struct unpack_trees_options *o)
{
	struct cache_entry *old = src[0];
	struct cache_entry *a = src[1];

	if (o->merge_size != 1)
		return error("Cannot do a oneway merge of %d trees",
			     o->merge_size);

	if (!a)
		return deleted_entry(old, old, o);

	if (old && same(old, a)) {
		int update = 0;
		if (o->reset) {
			struct stat st;
			if (lstat(old->name, &st) ||
			    ie_match_stat(o->src_index, old, &st, CE_MATCH_IGNORE_VALID))
				update |= CE_UPDATE;
		}
		add_entry(o, old, update, 0);
		return 0;
	}
	return merged_entry(a, old, o);
}