summaryrefslogtreecommitdiff
path: root/notes-merge.c
blob: e804db2d02820c3ba762eebbbe7b465a487d83b8 (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
#include "cache.h"
#include "commit.h"
#include "refs.h"
#include "diff.h"
#include "diffcore.h"
#include "xdiff-interface.h"
#include "ll-merge.h"
#include "dir.h"
#include "notes.h"
#include "notes-merge.h"
#include "strbuf.h"
#include "notes-utils.h"

struct notes_merge_pair {
	unsigned char obj[20], base[20], local[20], remote[20];
};

void init_notes_merge_options(struct notes_merge_options *o)
{
	memset(o, 0, sizeof(struct notes_merge_options));
	strbuf_init(&(o->commit_msg), 0);
	o->verbosity = NOTES_MERGE_VERBOSITY_DEFAULT;
}

static int path_to_sha1(const char *path, unsigned char *sha1)
{
	char hex_sha1[40];
	int i = 0;
	while (*path && i < 40) {
		if (*path != '/')
			hex_sha1[i++] = *path;
		path++;
	}
	if (*path || i != 40)
		return -1;
	return get_sha1_hex(hex_sha1, sha1);
}

static int verify_notes_filepair(struct diff_filepair *p, unsigned char *sha1)
{
	switch (p->status) {
	case DIFF_STATUS_MODIFIED:
		assert(p->one->mode == p->two->mode);
		assert(!is_null_sha1(p->one->sha1));
		assert(!is_null_sha1(p->two->sha1));
		break;
	case DIFF_STATUS_ADDED:
		assert(is_null_sha1(p->one->sha1));
		break;
	case DIFF_STATUS_DELETED:
		assert(is_null_sha1(p->two->sha1));
		break;
	default:
		return -1;
	}
	assert(!strcmp(p->one->path, p->two->path));
	return path_to_sha1(p->one->path, sha1);
}

static struct notes_merge_pair *find_notes_merge_pair_pos(
		struct notes_merge_pair *list, int len, unsigned char *obj,
		int insert_new, int *occupied)
{
	/*
	 * Both diff_tree_remote() and diff_tree_local() tend to process
	 * merge_pairs in ascending order. Therefore, cache last returned
	 * index, and search sequentially from there until the appropriate
	 * position is found.
	 *
	 * Since inserts only happen from diff_tree_remote() (which mainly
	 * _appends_), we don't care that inserting into the middle of the
	 * list is expensive (using memmove()).
	 */
	static int last_index;
	int i = last_index < len ? last_index : len - 1;
	int prev_cmp = 0, cmp = -1;
	while (i >= 0 && i < len) {
		cmp = hashcmp(obj, list[i].obj);
		if (!cmp) /* obj belongs @ i */
			break;
		else if (cmp < 0 && prev_cmp <= 0) /* obj belongs < i */
			i--;
		else if (cmp < 0) /* obj belongs between i-1 and i */
			break;
		else if (cmp > 0 && prev_cmp >= 0) /* obj belongs > i */
			i++;
		else /* if (cmp > 0) */ { /* obj belongs between i and i+1 */
			i++;
			break;
		}
		prev_cmp = cmp;
	}
	if (i < 0)
		i = 0;
	/* obj belongs at, or immediately preceding, index i (0 <= i <= len) */

	if (!cmp)
		*occupied = 1;
	else {
		*occupied = 0;
		if (insert_new && i < len) {
			memmove(list + i + 1, list + i,
				(len - i) * sizeof(struct notes_merge_pair));
			memset(list + i, 0, sizeof(struct notes_merge_pair));
		}
	}
	last_index = i;
	return list + i;
}

static unsigned char uninitialized[20] =
	"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff" \
	"\xff\xff\xff\xff\xff\xff\xff\xff\xff\xff";

static struct notes_merge_pair *diff_tree_remote(struct notes_merge_options *o,
						 const unsigned char *base,
						 const unsigned char *remote,
						 int *num_changes)
{
	struct diff_options opt;
	struct notes_merge_pair *changes;
	int i, len = 0;

	trace_printf("\tdiff_tree_remote(base = %.7s, remote = %.7s)\n",
	       sha1_to_hex(base), sha1_to_hex(remote));

	diff_setup(&opt);
	DIFF_OPT_SET(&opt, RECURSIVE);
	opt.output_format = DIFF_FORMAT_NO_OUTPUT;
	diff_setup_done(&opt);
	diff_tree_sha1(base, remote, "", &opt);
	diffcore_std(&opt);

	changes = xcalloc(diff_queued_diff.nr, sizeof(struct notes_merge_pair));

	for (i = 0; i < diff_queued_diff.nr; i++) {
		struct diff_filepair *p = diff_queued_diff.queue[i];
		struct notes_merge_pair *mp;
		int occupied;
		unsigned char obj[20];

		if (verify_notes_filepair(p, obj)) {
			trace_printf("\t\tCannot merge entry '%s' (%c): "
			       "%.7s -> %.7s. Skipping!\n", p->one->path,
			       p->status, sha1_to_hex(p->one->sha1),
			       sha1_to_hex(p->two->sha1));
			continue;
		}
		mp = find_notes_merge_pair_pos(changes, len, obj, 1, &occupied);
		if (occupied) {
			/* We've found an addition/deletion pair */
			assert(!hashcmp(mp->obj, obj));
			if (is_null_sha1(p->one->sha1)) { /* addition */
				assert(is_null_sha1(mp->remote));
				hashcpy(mp->remote, p->two->sha1);
			} else if (is_null_sha1(p->two->sha1)) { /* deletion */
				assert(is_null_sha1(mp->base));
				hashcpy(mp->base, p->one->sha1);
			} else
				assert(!"Invalid existing change recorded");
		} else {
			hashcpy(mp->obj, obj);
			hashcpy(mp->base, p->one->sha1);
			hashcpy(mp->local, uninitialized);
			hashcpy(mp->remote, p->two->sha1);
			len++;
		}
		trace_printf("\t\tStored remote change for %s: %.7s -> %.7s\n",
		       sha1_to_hex(mp->obj), sha1_to_hex(mp->base),
		       sha1_to_hex(mp->remote));
	}
	diff_flush(&opt);
	free_pathspec(&opt.pathspec);

	*num_changes = len;
	return changes;
}

static void diff_tree_local(struct notes_merge_options *o,
			    struct notes_merge_pair *changes, int len,
			    const unsigned char *base,
			    const unsigned char *local)
{
	struct diff_options opt;
	int i;

	trace_printf("\tdiff_tree_local(len = %i, base = %.7s, local = %.7s)\n",
	       len, sha1_to_hex(base), sha1_to_hex(local));

	diff_setup(&opt);
	DIFF_OPT_SET(&opt, RECURSIVE);
	opt.output_format = DIFF_FORMAT_NO_OUTPUT;
	diff_setup_done(&opt);
	diff_tree_sha1(base, local, "", &opt);
	diffcore_std(&opt);

	for (i = 0; i < diff_queued_diff.nr; i++) {
		struct diff_filepair *p = diff_queued_diff.queue[i];
		struct notes_merge_pair *mp;
		int match;
		unsigned char obj[20];

		if (verify_notes_filepair(p, obj)) {
			trace_printf("\t\tCannot merge entry '%s' (%c): "
			       "%.7s -> %.7s. Skipping!\n", p->one->path,
			       p->status, sha1_to_hex(p->one->sha1),
			       sha1_to_hex(p->two->sha1));
			continue;
		}
		mp = find_notes_merge_pair_pos(changes, len, obj, 0, &match);
		if (!match) {
			trace_printf("\t\tIgnoring local-only change for %s: "
			       "%.7s -> %.7s\n", sha1_to_hex(obj),
			       sha1_to_hex(p->one->sha1),
			       sha1_to_hex(p->two->sha1));
			continue;
		}

		assert(!hashcmp(mp->obj, obj));
		if (is_null_sha1(p->two->sha1)) { /* deletion */
			/*
			 * Either this is a true deletion (1), or it is part
			 * of an A/D pair (2), or D/A pair (3):
			 *
			 * (1) mp->local is uninitialized; set it to null_sha1
			 * (2) mp->local is not uninitialized; don't touch it
			 * (3) mp->local is uninitialized; set it to null_sha1
			 *     (will be overwritten by following addition)
			 */
			if (!hashcmp(mp->local, uninitialized))
				hashclr(mp->local);
		} else if (is_null_sha1(p->one->sha1)) { /* addition */
			/*
			 * Either this is a true addition (1), or it is part
			 * of an A/D pair (2), or D/A pair (3):
			 *
			 * (1) mp->local is uninitialized; set to p->two->sha1
			 * (2) mp->local is uninitialized; set to p->two->sha1
			 * (3) mp->local is null_sha1;     set to p->two->sha1
			 */
			assert(is_null_sha1(mp->local) ||
			       !hashcmp(mp->local, uninitialized));
			hashcpy(mp->local, p->two->sha1);
		} else { /* modification */
			/*
			 * This is a true modification. p->one->sha1 shall
			 * match mp->base, and mp->local shall be uninitialized.
			 * Set mp->local to p->two->sha1.
			 */
			assert(!hashcmp(p->one->sha1, mp->base));
			assert(!hashcmp(mp->local, uninitialized));
			hashcpy(mp->local, p->two->sha1);
		}
		trace_printf("\t\tStored local change for %s: %.7s -> %.7s\n",
		       sha1_to_hex(mp->obj), sha1_to_hex(mp->base),
		       sha1_to_hex(mp->local));
	}
	diff_flush(&opt);
	free_pathspec(&opt.pathspec);
}

static void check_notes_merge_worktree(struct notes_merge_options *o)
{
	if (!o->has_worktree) {
		/*
		 * Must establish NOTES_MERGE_WORKTREE.
		 * Abort if NOTES_MERGE_WORKTREE already exists
		 */
		if (file_exists(git_path(NOTES_MERGE_WORKTREE)) &&
		    !is_empty_dir(git_path(NOTES_MERGE_WORKTREE))) {
			if (advice_resolve_conflict)
				die("You have not concluded your previous "
				    "notes merge (%s exists).\nPlease, use "
				    "'git notes merge --commit' or 'git notes "
				    "merge --abort' to commit/abort the "
				    "previous merge before you start a new "
				    "notes merge.", git_path("NOTES_MERGE_*"));
			else
				die("You have not concluded your notes merge "
				    "(%s exists).", git_path("NOTES_MERGE_*"));
		}

		if (safe_create_leading_directories(git_path(
				NOTES_MERGE_WORKTREE "/.test")))
			die_errno("unable to create directory %s",
				  git_path(NOTES_MERGE_WORKTREE));
		o->has_worktree = 1;
	} else if (!file_exists(git_path(NOTES_MERGE_WORKTREE)))
		/* NOTES_MERGE_WORKTREE should already be established */
		die("missing '%s'. This should not happen",
		    git_path(NOTES_MERGE_WORKTREE));
}

static void write_buf_to_worktree(const unsigned char *obj,
				  const char *buf, unsigned long size)
{
	int fd;
	char *path = git_path(NOTES_MERGE_WORKTREE "/%s", sha1_to_hex(obj));
	if (safe_create_leading_directories(path))
		die_errno("unable to create directory for '%s'", path);
	if (file_exists(path))
		die("found existing file at '%s'", path);

	fd = open(path, O_WRONLY | O_TRUNC | O_CREAT, 0666);
	if (fd < 0)
		die_errno("failed to open '%s'", path);

	while (size > 0) {
		long ret = write_in_full(fd, buf, size);
		if (ret < 0) {
			/* Ignore epipe */
			if (errno == EPIPE)
				break;
			die_errno("notes-merge");
		} else if (!ret) {
			die("notes-merge: disk full?");
		}
		size -= ret;
		buf += ret;
	}

	close(fd);
}

static void write_note_to_worktree(const unsigned char *obj,
				   const unsigned char *note)
{
	enum object_type type;
	unsigned long size;
	void *buf = read_sha1_file(note, &type, &size);

	if (!buf)
		die("cannot read note %s for object %s",
		    sha1_to_hex(note), sha1_to_hex(obj));
	if (type != OBJ_BLOB)
		die("blob expected in note %s for object %s",
		    sha1_to_hex(note), sha1_to_hex(obj));
	write_buf_to_worktree(obj, buf, size);
	free(buf);
}

static int ll_merge_in_worktree(struct notes_merge_options *o,
				struct notes_merge_pair *p)
{
	mmbuffer_t result_buf;
	mmfile_t base, local, remote;
	int status;

	read_mmblob(&base, p->base);
	read_mmblob(&local, p->local);
	read_mmblob(&remote, p->remote);

	status = ll_merge(&result_buf, sha1_to_hex(p->obj), &base, NULL,
			  &local, o->local_ref, &remote, o->remote_ref, NULL);

	free(base.ptr);
	free(local.ptr);
	free(remote.ptr);

	if ((status < 0) || !result_buf.ptr)
		die("Failed to execute internal merge");

	write_buf_to_worktree(p->obj, result_buf.ptr, result_buf.size);
	free(result_buf.ptr);

	return status;
}

static int merge_one_change_manual(struct notes_merge_options *o,
				   struct notes_merge_pair *p,
				   struct notes_tree *t)
{
	const char *lref = o->local_ref ? o->local_ref : "local version";
	const char *rref = o->remote_ref ? o->remote_ref : "remote version";

	trace_printf("\t\t\tmerge_one_change_manual(obj = %.7s, base = %.7s, "
	       "local = %.7s, remote = %.7s)\n",
	       sha1_to_hex(p->obj), sha1_to_hex(p->base),
	       sha1_to_hex(p->local), sha1_to_hex(p->remote));

	/* add "Conflicts:" section to commit message first time through */
	if (!o->has_worktree)
		strbuf_addstr(&(o->commit_msg), "\n\nConflicts:\n");

	strbuf_addf(&(o->commit_msg), "\t%s\n", sha1_to_hex(p->obj));

	if (o->verbosity >= 2)
		printf("Auto-merging notes for %s\n", sha1_to_hex(p->obj));
	check_notes_merge_worktree(o);
	if (is_null_sha1(p->local)) {
		/* D/F conflict, checkout p->remote */
		assert(!is_null_sha1(p->remote));
		if (o->verbosity >= 1)
			printf("CONFLICT (delete/modify): Notes for object %s "
				"deleted in %s and modified in %s. Version from %s "
				"left in tree.\n",
				sha1_to_hex(p->obj), lref, rref, rref);
		write_note_to_worktree(p->obj, p->remote);
	} else if (is_null_sha1(p->remote)) {
		/* D/F conflict, checkout p->local */
		assert(!is_null_sha1(p->local));
		if (o->verbosity >= 1)
			printf("CONFLICT (delete/modify): Notes for object %s "
				"deleted in %s and modified in %s. Version from %s "
				"left in tree.\n",
				sha1_to_hex(p->obj), rref, lref, lref);
		write_note_to_worktree(p->obj, p->local);
	} else {
		/* "regular" conflict, checkout result of ll_merge() */
		const char *reason = "content";
		if (is_null_sha1(p->base))
			reason = "add/add";
		assert(!is_null_sha1(p->local));
		assert(!is_null_sha1(p->remote));
		if (o->verbosity >= 1)
			printf("CONFLICT (%s): Merge conflict in notes for "
				"object %s\n", reason, sha1_to_hex(p->obj));
		ll_merge_in_worktree(o, p);
	}

	trace_printf("\t\t\tremoving from partial merge result\n");
	remove_note(t, p->obj);

	return 1;
}

static int merge_one_change(struct notes_merge_options *o,
			    struct notes_merge_pair *p, struct notes_tree *t)
{
	/*
	 * Return 0 if change is successfully resolved (stored in notes_tree).
	 * Return 1 is change results in a conflict (NOT stored in notes_tree,
	 * but instead written to NOTES_MERGE_WORKTREE with conflict markers).
	 */
	switch (o->strategy) {
	case NOTES_MERGE_RESOLVE_MANUAL:
		return merge_one_change_manual(o, p, t);
	case NOTES_MERGE_RESOLVE_OURS:
		if (o->verbosity >= 2)
			printf("Using local notes for %s\n",
						sha1_to_hex(p->obj));
		/* nothing to do */
		return 0;
	case NOTES_MERGE_RESOLVE_THEIRS:
		if (o->verbosity >= 2)
			printf("Using remote notes for %s\n",
						sha1_to_hex(p->obj));
		if (add_note(t, p->obj, p->remote, combine_notes_overwrite))
			die("BUG: combine_notes_overwrite failed");
		return 0;
	case NOTES_MERGE_RESOLVE_UNION:
		if (o->verbosity >= 2)
			printf("Concatenating local and remote notes for %s\n",
							sha1_to_hex(p->obj));
		if (add_note(t, p->obj, p->remote, combine_notes_concatenate))
			die("failed to concatenate notes "
			    "(combine_notes_concatenate)");
		return 0;
	case NOTES_MERGE_RESOLVE_CAT_SORT_UNIQ:
		if (o->verbosity >= 2)
			printf("Concatenating unique lines in local and remote "
				"notes for %s\n", sha1_to_hex(p->obj));
		if (add_note(t, p->obj, p->remote, combine_notes_cat_sort_uniq))
			die("failed to concatenate notes "
			    "(combine_notes_cat_sort_uniq)");
		return 0;
	}
	die("Unknown strategy (%i).", o->strategy);
}

static int merge_changes(struct notes_merge_options *o,
			 struct notes_merge_pair *changes, int *num_changes,
			 struct notes_tree *t)
{
	int i, conflicts = 0;

	trace_printf("\tmerge_changes(num_changes = %i)\n", *num_changes);
	for (i = 0; i < *num_changes; i++) {
		struct notes_merge_pair *p = changes + i;
		trace_printf("\t\t%.7s: %.7s -> %.7s/%.7s\n",
		       sha1_to_hex(p->obj), sha1_to_hex(p->base),
		       sha1_to_hex(p->local), sha1_to_hex(p->remote));

		if (!hashcmp(p->base, p->remote)) {
			/* no remote change; nothing to do */
			trace_printf("\t\t\tskipping (no remote change)\n");
		} else if (!hashcmp(p->local, p->remote)) {
			/* same change in local and remote; nothing to do */
			trace_printf("\t\t\tskipping (local == remote)\n");
		} else if (!hashcmp(p->local, uninitialized) ||
			   !hashcmp(p->local, p->base)) {
			/* no local change; adopt remote change */
			trace_printf("\t\t\tno local change, adopted remote\n");
			if (add_note(t, p->obj, p->remote,
				     combine_notes_overwrite))
				die("BUG: combine_notes_overwrite failed");
		} else {
			/* need file-level merge between local and remote */
			trace_printf("\t\t\tneed content-level merge\n");
			conflicts += merge_one_change(o, p, t);
		}
	}

	return conflicts;
}

static int merge_from_diffs(struct notes_merge_options *o,
			    const unsigned char *base,
			    const unsigned char *local,
			    const unsigned char *remote, struct notes_tree *t)
{
	struct notes_merge_pair *changes;
	int num_changes, conflicts;

	trace_printf("\tmerge_from_diffs(base = %.7s, local = %.7s, "
	       "remote = %.7s)\n", sha1_to_hex(base), sha1_to_hex(local),
	       sha1_to_hex(remote));

	changes = diff_tree_remote(o, base, remote, &num_changes);
	diff_tree_local(o, changes, num_changes, base, local);

	conflicts = merge_changes(o, changes, &num_changes, t);
	free(changes);

	if (o->verbosity >= 4)
		printf(t->dirty ?
		       "Merge result: %i unmerged notes and a dirty notes tree\n" :
		       "Merge result: %i unmerged notes and a clean notes tree\n",
		       conflicts);

	return conflicts ? -1 : 1;
}

int notes_merge(struct notes_merge_options *o,
		struct notes_tree *local_tree,
		unsigned char *result_sha1)
{
	unsigned char local_sha1[20], remote_sha1[20];
	struct commit *local, *remote;
	struct commit_list *bases = NULL;
	const unsigned char *base_sha1, *base_tree_sha1;
	int result = 0;

	assert(o->local_ref && o->remote_ref);
	assert(!strcmp(o->local_ref, local_tree->ref));
	hashclr(result_sha1);

	trace_printf("notes_merge(o->local_ref = %s, o->remote_ref = %s)\n",
	       o->local_ref, o->remote_ref);

	/* Dereference o->local_ref into local_sha1 */
	if (read_ref_full(o->local_ref, local_sha1, 0, NULL))
		die("Failed to resolve local notes ref '%s'", o->local_ref);
	else if (!check_refname_format(o->local_ref, 0) &&
		is_null_sha1(local_sha1))
		local = NULL; /* local_sha1 == null_sha1 indicates unborn ref */
	else if (!(local = lookup_commit_reference(local_sha1)))
		die("Could not parse local commit %s (%s)",
		    sha1_to_hex(local_sha1), o->local_ref);
	trace_printf("\tlocal commit: %.7s\n", sha1_to_hex(local_sha1));

	/* Dereference o->remote_ref into remote_sha1 */
	if (get_sha1(o->remote_ref, remote_sha1)) {
		/*
		 * Failed to get remote_sha1. If o->remote_ref looks like an
		 * unborn ref, perform the merge using an empty notes tree.
		 */
		if (!check_refname_format(o->remote_ref, 0)) {
			hashclr(remote_sha1);
			remote = NULL;
		} else {
			die("Failed to resolve remote notes ref '%s'",
			    o->remote_ref);
		}
	} else if (!(remote = lookup_commit_reference(remote_sha1))) {
		die("Could not parse remote commit %s (%s)",
		    sha1_to_hex(remote_sha1), o->remote_ref);
	}
	trace_printf("\tremote commit: %.7s\n", sha1_to_hex(remote_sha1));

	if (!local && !remote)
		die("Cannot merge empty notes ref (%s) into empty notes ref "
		    "(%s)", o->remote_ref, o->local_ref);
	if (!local) {
		/* result == remote commit */
		hashcpy(result_sha1, remote_sha1);
		goto found_result;
	}
	if (!remote) {
		/* result == local commit */
		hashcpy(result_sha1, local_sha1);
		goto found_result;
	}
	assert(local && remote);

	/* Find merge bases */
	bases = get_merge_bases(local, remote, 1);
	if (!bases) {
		base_sha1 = null_sha1;
		base_tree_sha1 = EMPTY_TREE_SHA1_BIN;
		if (o->verbosity >= 4)
			printf("No merge base found; doing history-less merge\n");
	} else if (!bases->next) {
		base_sha1 = bases->item->object.sha1;
		base_tree_sha1 = bases->item->tree->object.sha1;
		if (o->verbosity >= 4)
			printf("One merge base found (%.7s)\n",
				sha1_to_hex(base_sha1));
	} else {
		/* TODO: How to handle multiple merge-bases? */
		base_sha1 = bases->item->object.sha1;
		base_tree_sha1 = bases->item->tree->object.sha1;
		if (o->verbosity >= 3)
			printf("Multiple merge bases found. Using the first "
				"(%.7s)\n", sha1_to_hex(base_sha1));
	}

	if (o->verbosity >= 4)
		printf("Merging remote commit %.7s into local commit %.7s with "
			"merge-base %.7s\n", sha1_to_hex(remote->object.sha1),
			sha1_to_hex(local->object.sha1),
			sha1_to_hex(base_sha1));

	if (!hashcmp(remote->object.sha1, base_sha1)) {
		/* Already merged; result == local commit */
		if (o->verbosity >= 2)
			printf("Already up-to-date!\n");
		hashcpy(result_sha1, local->object.sha1);
		goto found_result;
	}
	if (!hashcmp(local->object.sha1, base_sha1)) {
		/* Fast-forward; result == remote commit */
		if (o->verbosity >= 2)
			printf("Fast-forward\n");
		hashcpy(result_sha1, remote->object.sha1);
		goto found_result;
	}

	result = merge_from_diffs(o, base_tree_sha1, local->tree->object.sha1,
				  remote->tree->object.sha1, local_tree);

	if (result != 0) { /* non-trivial merge (with or without conflicts) */
		/* Commit (partial) result */
		struct commit_list *parents = NULL;
		commit_list_insert(remote, &parents); /* LIFO order */
		commit_list_insert(local, &parents);
		create_notes_commit(local_tree, parents,
				    o->commit_msg.buf, o->commit_msg.len,
				    result_sha1);
	}

found_result:
	free_commit_list(bases);
	strbuf_release(&(o->commit_msg));
	trace_printf("notes_merge(): result = %i, result_sha1 = %.7s\n",
	       result, sha1_to_hex(result_sha1));
	return result;
}

int notes_merge_commit(struct notes_merge_options *o,
		       struct notes_tree *partial_tree,
		       struct commit *partial_commit,
		       unsigned char *result_sha1)
{
	/*
	 * Iterate through files in .git/NOTES_MERGE_WORKTREE and add all
	 * found notes to 'partial_tree'. Write the updated notes tree to
	 * the DB, and commit the resulting tree object while reusing the
	 * commit message and parents from 'partial_commit'.
	 * Finally store the new commit object SHA1 into 'result_sha1'.
	 */
	DIR *dir;
	struct dirent *e;
	struct strbuf path = STRBUF_INIT;
	const char *buffer = get_commit_buffer(partial_commit);
	const char *msg = strstr(buffer, "\n\n");
	int baselen;

	strbuf_addstr(&path, git_path(NOTES_MERGE_WORKTREE));
	if (o->verbosity >= 3)
		printf("Committing notes in notes merge worktree at %s\n",
			path.buf);

	if (!msg || msg[2] == '\0')
		die("partial notes commit has empty message");
	msg += 2;

	dir = opendir(path.buf);
	if (!dir)
		die_errno("could not open %s", path.buf);

	strbuf_addch(&path, '/');
	baselen = path.len;
	while ((e = readdir(dir)) != NULL) {
		struct stat st;
		unsigned char obj_sha1[20], blob_sha1[20];

		if (is_dot_or_dotdot(e->d_name))
			continue;

		if (strlen(e->d_name) != 40 || get_sha1_hex(e->d_name, obj_sha1)) {
			if (o->verbosity >= 3)
				printf("Skipping non-SHA1 entry '%s%s'\n",
					path.buf, e->d_name);
			continue;
		}

		strbuf_addstr(&path, e->d_name);
		/* write file as blob, and add to partial_tree */
		if (stat(path.buf, &st))
			die_errno("Failed to stat '%s'", path.buf);
		if (index_path(blob_sha1, path.buf, &st, HASH_WRITE_OBJECT))
			die("Failed to write blob object from '%s'", path.buf);
		if (add_note(partial_tree, obj_sha1, blob_sha1, NULL))
			die("Failed to add resolved note '%s' to notes tree",
			    path.buf);
		if (o->verbosity >= 4)
			printf("Added resolved note for object %s: %s\n",
				sha1_to_hex(obj_sha1), sha1_to_hex(blob_sha1));
		strbuf_setlen(&path, baselen);
	}

	create_notes_commit(partial_tree, partial_commit->parents,
			    msg, strlen(msg), result_sha1);
	unuse_commit_buffer(partial_commit, buffer);
	if (o->verbosity >= 4)
		printf("Finalized notes merge commit: %s\n",
			sha1_to_hex(result_sha1));
	strbuf_release(&path);
	closedir(dir);
	return 0;
}

int notes_merge_abort(struct notes_merge_options *o)
{
	/*
	 * Remove all files within .git/NOTES_MERGE_WORKTREE. We do not remove
	 * the .git/NOTES_MERGE_WORKTREE directory itself, since it might be
	 * the current working directory of the user.
	 */
	struct strbuf buf = STRBUF_INIT;
	int ret;

	strbuf_addstr(&buf, git_path(NOTES_MERGE_WORKTREE));
	if (o->verbosity >= 3)
		printf("Removing notes merge worktree at %s/*\n", buf.buf);
	ret = remove_dir_recursively(&buf, REMOVE_DIR_KEEP_TOPLEVEL);
	strbuf_release(&buf);
	return ret;
}