summaryrefslogtreecommitdiff
path: root/unpack-trees.c
blob: 32251018b20da26b2587b656ff012b5e59e74b2b (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
#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"
 
#define DBRT_DEBUG 1
 
struct tree_entry_list {
	struct tree_entry_list *next;
	unsigned int mode;
	const char *name;
	const unsigned char *sha1;
};
 
static struct tree_entry_list *create_tree_entry_list(struct tree_desc *desc)
{
	struct name_entry one;
	struct tree_entry_list *ret = NULL;
	struct tree_entry_list **list_p = &ret;
 
	while (tree_entry(desc, &one)) {
		struct tree_entry_list *entry;
 
		entry = xmalloc(sizeof(struct tree_entry_list));
		entry->name = one.path;
		entry->sha1 = one.sha1;
		entry->mode = one.mode;
		entry->next = NULL;
 
		*list_p = entry;
		list_p = &entry->next;
	}
	return ret;
}
 
static int entcmp(const char *name1, int dir1, const char *name2, int dir2)
{
	int len1 = strlen(name1);
	int len2 = strlen(name2);
	int len = len1 < len2 ? len1 : len2;
	int ret = memcmp(name1, name2, len);
	unsigned char c1, c2;
	if (ret)
		return ret;
	c1 = name1[len];
	c2 = name2[len];
	if (!c1 && dir1)
		c1 = '/';
	if (!c2 && dir2)
		c2 = '/';
	ret = (c1 < c2) ? -1 : (c1 > c2) ? 1 : 0;
	if (c1 && c2 && !ret)
		ret = len1 - len2;
	return ret;
}
 
static inline void remove_entry(int remove)
{
	if (remove >= 0)
		remove_cache_entry_at(remove);
}
 
static int unpack_trees_rec(struct tree_entry_list **posns, int len,
			    const char *base, struct unpack_trees_options *o,
			    struct tree_entry_list *df_conflict_list)
{
	int remove;
	int baselen = strlen(base);
	int src_size = len + 1;
	int i_stk = i_stk;
	int retval = 0;
 
	if (o->dir)
		i_stk = push_exclude_per_directory(o->dir, base, strlen(base));
 
	do {
		int i;
		const char *first;
		int firstdir = 0;
		int pathlen;
		unsigned ce_size;
		struct tree_entry_list **subposns;
		struct cache_entry **src;
		int any_files = 0;
		int any_dirs = 0;
		char *cache_name;
		int ce_stage;
 
		/* Find the first name in the input. */
 
		first = NULL;
		cache_name = NULL;
 
		/* Check the cache */
		if (o->merge && o->pos < active_nr) {
			/* This is a bit tricky: */
			/* If the index has a subdirectory (with
			 * contents) as the first name, it'll get a
			 * filename like "foo/bar". But that's after
			 * "foo", so the entry in trees will get
			 * handled first, at which point we'll go into
			 * "foo", and deal with "bar" from the index,
			 * because the base will be "foo/". The only
			 * way we can actually have "foo/bar" first of
			 * all the things is if the trees don't
			 * contain "foo" at all, in which case we'll
			 * handle "foo/bar" without going into the
			 * directory, but that's fine (and will return
			 * an error anyway, with the added unknown
			 * file case.
			 */
 
			cache_name = active_cache[o->pos]->name;
			if (strlen(cache_name) > baselen &&
			    !memcmp(cache_name, base, baselen)) {
				cache_name += baselen;
				first = cache_name;
			} else {
				cache_name = NULL;
			}
		}
 
#if DBRT_DEBUG > 1
		if (first)
			printf("index %s\n", first);
#endif
		for (i = 0; i < len; i++) {
			if (!posns[i] || posns[i] == df_conflict_list)
				continue;
#if DBRT_DEBUG > 1
			printf("%d %s\n", i + 1, posns[i]->name);
#endif
			if (!first || entcmp(first, firstdir,
					     posns[i]->name,
					     S_ISDIR(posns[i]->mode)) > 0) {
				first = posns[i]->name;
				firstdir = S_ISDIR(posns[i]->mode);
			}
		}
		/* No name means we're done */
		if (!first)
			goto leave_directory;
 
		pathlen = strlen(first);
		ce_size = cache_entry_size(baselen + pathlen);
 
		src = xcalloc(src_size, sizeof(struct cache_entry *));
 
		subposns = xcalloc(len, sizeof(struct tree_list_entry *));
 
		remove = -1;
		if (cache_name && !strcmp(cache_name, first)) {
			any_files = 1;
			src[0] = active_cache[o->pos];
			remove = o->pos;
		}
 
		for (i = 0; i < len; i++) {
			struct cache_entry *ce;
 
			if (!posns[i] ||
			    (posns[i] != df_conflict_list &&
			     strcmp(first, posns[i]->name))) {
				continue;
			}
 
			if (posns[i] == df_conflict_list) {
				src[i + o->merge] = o->df_conflict_entry;
				continue;
			}
 
			if (S_ISDIR(posns[i]->mode)) {
				struct tree *tree = lookup_tree(posns[i]->sha1);
				struct tree_desc t;
				any_dirs = 1;
				parse_tree(tree);
				init_tree_desc(&t, tree->buffer, tree->size);
				subposns[i] = create_tree_entry_list(&t);
				posns[i] = posns[i]->next;
				src[i + o->merge] = o->df_conflict_entry;
				continue;
			}
 
			if (!o->merge)
				ce_stage = 0;
			else if (i + 1 < o->head_idx)
				ce_stage = 1;
			else if (i + 1 > o->head_idx)
				ce_stage = 3;
			else
				ce_stage = 2;
 
			ce = xcalloc(1, ce_size);
			ce->ce_mode = create_ce_mode(posns[i]->mode);
			ce->ce_flags = create_ce_flags(baselen + pathlen,
						       ce_stage);
			memcpy(ce->name, base, baselen);
			memcpy(ce->name + baselen, first, pathlen + 1);
 
			any_files = 1;
 
			hashcpy(ce->sha1, posns[i]->sha1);
			src[i + o->merge] = ce;
			subposns[i] = df_conflict_list;
			posns[i] = posns[i]->next;
		}
		if (any_files) {
			if (o->merge) {
				int ret;
 
#if DBRT_DEBUG > 1
				printf("%s:\n", first);
				for (i = 0; i < src_size; i++) {
					printf(" %d ", i);
					if (src[i])
						printf("%s\n", sha1_to_hex(src[i]->sha1));
					else
						printf("\n");
				}
#endif
				ret = o->fn(src, o, remove);
 
#if DBRT_DEBUG > 1
				printf("Added %d entries\n", ret);
#endif
				o->pos += ret;
			} else {
				remove_entry(remove);
				for (i = 0; i < src_size; i++) {
					if (src[i]) {
						add_cache_entry(src[i], ADD_CACHE_OK_TO_ADD|ADD_CACHE_SKIP_DFCHECK);
					}
				}
			}
		}
		if (any_dirs) {
			char *newbase = xmalloc(baselen + 2 + pathlen);
			memcpy(newbase, base, baselen);
			memcpy(newbase + baselen, first, pathlen);
			newbase[baselen + pathlen] = '/';
			newbase[baselen + pathlen + 1] = '\0';
			if (unpack_trees_rec(subposns, len, newbase, o,
					     df_conflict_list)) {
				retval = -1;
				goto leave_directory;
			}
			free(newbase);
		}
		free(subposns);
		free(src);
	} while (1);
 
 leave_directory:
	if (o->dir)
		pop_exclude_per_directory(o->dir, i_stk);
	return retval;
}
 
/* Unlink the last component and attempt to remove leading
 * directories, in case this unlink is the removal of the
 * last entry in the directory -- empty directories are removed.
 */
static void unlink_entry(char *name, char *last_symlink)
{
	char *cp, *prev;
 
	if (has_symlink_leading_path(name, last_symlink))
		return;
	if (unlink(name))
		return;
	prev = NULL;
	while (1) {
		int status;
		cp = strrchr(name, '/');
		if (prev)
			*prev = '/';
		if (!cp)
			break;
 
		*cp = 0;
		status = rmdir(name);
		if (status) {
			*cp = '/';
			break;
		}
		prev = cp;
	}
}
 
static struct checkout state;
static void check_updates(struct cache_entry **src, int nr,
			struct unpack_trees_options *o)
{
	unsigned short mask = htons(CE_UPDATE);
	unsigned cnt = 0, total = 0;
	struct progress progress;
	char last_symlink[PATH_MAX];
 
	if (o->update && o->verbose_update) {
		for (total = cnt = 0; cnt < nr; cnt++) {
			struct cache_entry *ce = src[cnt];
			if (!ce->ce_mode || ce->ce_flags & mask)
				total++;
		}
 
		start_progress_delay(&progress, "Checking out files",
				     total, 50, 2);
		cnt = 0;
	}
 
	*last_symlink = '\0';
	while (nr--) {
		struct cache_entry *ce = *src++;
 
		if (total)
			if (!ce->ce_mode || ce->ce_flags & mask)
				display_progress(&progress, ++cnt);
		if (!ce->ce_mode) {
			if (o->update)
				unlink_entry(ce->name, last_symlink);
			continue;
		}
		if (ce->ce_flags & mask) {
			ce->ce_flags &= ~mask;
			if (o->update) {
				checkout_entry(ce, &state, NULL);
				*last_symlink = '\0';
			}
		}
	}
	if (total)
		stop_progress(&progress);;
}
 
int unpack_trees(unsigned len, struct tree_desc *t, struct unpack_trees_options *o)
{
	struct tree_entry_list **posns;
	int i;
	struct tree_entry_list df_conflict_list;
	static struct cache_entry *dfc;
 
	memset(&df_conflict_list, 0, sizeof(df_conflict_list));
	df_conflict_list.next = &df_conflict_list;
	memset(&state, 0, sizeof(state));
	state.base_dir = "";
	state.force = 1;
	state.quiet = 1;
	state.refresh_cache = 1;
 
	o->merge_size = len;
 
	if (!dfc)
		dfc = xcalloc(1, sizeof(struct cache_entry) + 1);
	o->df_conflict_entry = dfc;
 
	if (len) {
		posns = xmalloc(len * sizeof(struct tree_entry_list *));
		for (i = 0; i < len; i++)
			posns[i] = create_tree_entry_list(t+i);
 
		if (unpack_trees_rec(posns, len, o->prefix ? o->prefix : "",
				     o, &df_conflict_list))
			return -1;
	}
 
	if (o->trivial_merges_only && o->nontrivial_merge)
		die("Merge requires file-level merging");
 
	check_updates(active_cache, active_nr, o);
	return 0;
}
 
/* Here come the merge functions */
 
static void reject_merge(struct cache_entry *ce)
{
	die("Entry '%s' would be overwritten by merge. Cannot merge.",
	    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 void verify_uptodate(struct cache_entry *ce,
		struct unpack_trees_options *o)
{
	struct stat st;
 
	if (o->index_only || o->reset)
		return;
 
	if (!lstat(ce->name, &st)) {
		unsigned changed = ce_match_stat(ce, &st, 1);
		if (!changed)
			return;
		/*
		 * 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(ntohl(ce->ce_mode)))
			return;
		errno = 0;
	}
	if (errno == ENOENT)
		return;
	die("Entry '%s' not uptodate. Cannot merge.", ce->name);
}
 
static void invalidate_ce_path(struct cache_entry *ce)
{
	if (ce)
		cache_tree_invalidate_path(active_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 pos, i;
	struct dir_struct d;
	char *pathbuf;
	int cnt = 0;
	unsigned char sha1[20];
 
	if (S_ISGITLINK(ntohl(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);
	pos = cache_name_pos(ce->name, namelen);
	if (0 <= pos)
		return cnt; /* we have it as nondirectory */
	pos = -pos - 1;
	for (i = pos; i < active_nr; i++) {
		struct cache_entry *ce = active_cache[i];
		int len = ce_namelen(ce);
		if (len < namelen ||
		    strncmp(ce->name, ce->name, namelen) ||
		    ce->name[namelen] != '/')
			break;
		/*
		 * ce->name is an entry in the subdirectory.
		 */
		if (!ce_stage(ce)) {
			verify_uptodate(ce, o);
			ce->ce_mode = 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)
		die("Updating '%s' would lose untracked files in it",
		    ce->name);
	free(pathbuf);
	return cnt;
}
 
/*
 * We do not want to remove or overwrite a working tree file that
 * is not tracked, unless it is ignored.
 */
static void 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;
 
	if (has_symlink_leading_path(ce->name, NULL))
		return;
 
	if (!lstat(ce->name, &st)) {
		int cnt;
 
		if (o->dir && excluded(o->dir, ce->name))
			/*
			 * ce->name is explicitly excluded, so it is Ok to
			 * overwrite it.
			 */
			return;
		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.
			 */
			cnt = verify_clean_subdirectory(ce, action, o);
 
			/*
			 * If this removed entries from the index,
			 * what that means is:
			 *
			 * (1) the caller unpack_trees_rec() 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 += cnt;
			return;
		}
 
		/*
		 * The previous round may already have decided to
		 * delete this path, which is in a subdirectory that
		 * is being replaced with a blob.
		 */
		cnt = cache_name_pos(ce->name, strlen(ce->name));
		if (0 <= cnt) {
			struct cache_entry *ce = active_cache[cnt];
			if (!ce_stage(ce) && !ce->ce_mode)
				return;
		}
 
		die("Untracked working tree file '%s' "
		    "would be %s by merge.", ce->name, action);
	}
}
 
static int merged_entry(struct cache_entry *merge, struct cache_entry *old,
		struct unpack_trees_options *o)
{
	merge->ce_flags |= htons(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.
		 */
		if (same(old, merge)) {
			*merge = *old;
		} else {
			verify_uptodate(old, o);
			invalidate_ce_path(old);
		}
	}
	else {
		verify_absent(merge, "overwritten", o);
		invalidate_ce_path(merge);
	}
 
	merge->ce_flags &= ~htons(CE_STAGEMASK);
	add_cache_entry(merge, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
	return 1;
}
 
static int deleted_entry(struct cache_entry *ce, struct cache_entry *old,
		struct unpack_trees_options *o)
{
	if (old)
		verify_uptodate(old, o);
	else
		verify_absent(ce, "removed", o);
	ce->ce_mode = 0;
	add_cache_entry(ce, ADD_CACHE_OK_TO_ADD|ADD_CACHE_OK_TO_REPLACE);
	invalidate_ce_path(ce);
	return 1;
}
 
static int keep_entry(struct cache_entry *ce, struct unpack_trees_options *o)
{
	add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
	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,
			ntohl(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,
		int remove)
{
	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))
			reject_merge(index);
		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)) {
		reject_merge(index);
	}
 
	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) {
		remove_entry(remove);
		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)) {
			remove_entry(remove);
			if (index)
				return deleted_entry(index, index, o);
			else if (ce && !head_deleted)
				verify_absent(ce, "removed", o);
			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) {
		verify_uptodate(index, o);
	}
 
	remove_entry(remove);
	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,
		int remove)
{
	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 */
			remove_entry(remove);
			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 */
			remove_entry(remove);
			if (oldtree)
				reject_merge(oldtree);
			if (current)
				reject_merge(current);
			if (newtree)
				reject_merge(newtree);
			return -1;
		}
	}
	else if (newtree)
		return merged_entry(newtree, current, o);
	remove_entry(remove);
	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,
		int remove)
{
	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)
		die("Entry '%s' overlaps.  Cannot bind.", a->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,
		int remove)
{
	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) {
		remove_entry(remove);
		return deleted_entry(old, old, o);
	}
	if (old && same(old, a)) {
		if (o->reset) {
			struct stat st;
			if (lstat(old->name, &st) ||
			    ce_match_stat(old, &st, 1))
				old->ce_flags |= htons(CE_UPDATE);
		}
		return keep_entry(old, o);
	}
	return merged_entry(a, old, o);
}