summaryrefslogtreecommitdiff
path: root/merge-ort.c
blob: d36a92b59b76fe49424ae97e4cd2777badb7e318 (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
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
1802
1803
1804
1805
1806
1807
1808
1809
1810
1811
1812
1813
1814
1815
1816
1817
1818
1819
1820
1821
1822
1823
1824
1825
1826
1827
1828
1829
1830
1831
1832
1833
1834
1835
1836
1837
1838
1839
1840
1841
1842
1843
1844
1845
1846
1847
1848
1849
1850
1851
1852
1853
1854
1855
1856
1857
1858
1859
1860
1861
1862
1863
1864
1865
1866
1867
1868
1869
1870
1871
1872
1873
1874
1875
1876
1877
1878
1879
1880
1881
1882
1883
1884
1885
1886
1887
1888
1889
1890
1891
1892
1893
1894
1895
1896
1897
1898
1899
1900
1901
1902
1903
1904
1905
1906
1907
1908
1909
1910
1911
1912
1913
1914
1915
1916
1917
1918
1919
1920
1921
1922
1923
1924
1925
1926
1927
1928
1929
1930
1931
1932
1933
1934
1935
1936
1937
1938
1939
1940
1941
1942
1943
1944
1945
1946
1947
1948
1949
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
1981
1982
1983
1984
1985
1986
1987
/*
 * "Ostensibly Recursive's Twin" merge strategy, or "ort" for short.  Meant
 * as a drop-in replacement for the "recursive" merge strategy, allowing one
 * to replace
 *
 *   git merge [-s recursive]
 *
 * with
 *
 *   git merge -s ort
 *
 * Note: git's parser allows the space between '-s' and its argument to be
 * missing.  (Should I have backronymed "ham", "alsa", "kip", "nap, "alvo",
 * "cale", "peedy", or "ins" instead of "ort"?)
 */

#include "cache.h"
#include "merge-ort.h"

#include "alloc.h"
#include "blob.h"
#include "cache-tree.h"
#include "commit.h"
#include "commit-reach.h"
#include "diff.h"
#include "diffcore.h"
#include "dir.h"
#include "object-store.h"
#include "strmap.h"
#include "tree.h"
#include "unpack-trees.h"
#include "xdiff-interface.h"

/*
 * We have many arrays of size 3.  Whenever we have such an array, the
 * indices refer to one of the sides of the three-way merge.  This is so
 * pervasive that the constants 0, 1, and 2 are used in many places in the
 * code (especially in arithmetic operations to find the other side's index
 * or to compute a relevant mask), but sometimes these enum names are used
 * to aid code clarity.
 *
 * See also 'filemask' and 'dirmask' in struct conflict_info; the "ith side"
 * referred to there is one of these three sides.
 */
enum merge_side {
	MERGE_BASE = 0,
	MERGE_SIDE1 = 1,
	MERGE_SIDE2 = 2
};

struct rename_info {
	/*
	 * pairs: pairing of filenames from diffcore_rename()
	 *
	 * Index 1 and 2 correspond to sides 1 & 2 as used in
	 * conflict_info.stages.  Index 0 unused.
	 */
	struct diff_queue_struct pairs[3];

	/*
	 * needed_limit: value needed for inexact rename detection to run
	 *
	 * If the current rename limit wasn't high enough for inexact
	 * rename detection to run, this records the limit needed.  Otherwise,
	 * this value remains 0.
	 */
	int needed_limit;
};

struct merge_options_internal {
	/*
	 * paths: primary data structure in all of merge ort.
	 *
	 * The keys of paths:
	 *   * are full relative paths from the toplevel of the repository
	 *     (e.g. "drivers/firmware/raspberrypi.c").
	 *   * store all relevant paths in the repo, both directories and
	 *     files (e.g. drivers, drivers/firmware would also be included)
	 *   * these keys serve to intern all the path strings, which allows
	 *     us to do pointer comparison on directory names instead of
	 *     strcmp; we just have to be careful to use the interned strings.
	 *     (Technically paths_to_free may track some strings that were
	 *      removed from froms paths.)
	 *
	 * The values of paths:
	 *   * either a pointer to a merged_info, or a conflict_info struct
	 *   * merged_info contains all relevant information for a
	 *     non-conflicted entry.
	 *   * conflict_info contains a merged_info, plus any additional
	 *     information about a conflict such as the higher orders stages
	 *     involved and the names of the paths those came from (handy
	 *     once renames get involved).
	 *   * a path may start "conflicted" (i.e. point to a conflict_info)
	 *     and then a later step (e.g. three-way content merge) determines
	 *     it can be cleanly merged, at which point it'll be marked clean
	 *     and the algorithm will ignore any data outside the contained
	 *     merged_info for that entry
	 *   * If an entry remains conflicted, the merged_info portion of a
	 *     conflict_info will later be filled with whatever version of
	 *     the file should be placed in the working directory (e.g. an
	 *     as-merged-as-possible variation that contains conflict markers).
	 */
	struct strmap paths;

	/*
	 * conflicted: a subset of keys->values from "paths"
	 *
	 * conflicted is basically an optimization between process_entries()
	 * and record_conflicted_index_entries(); the latter could loop over
	 * ALL the entries in paths AGAIN and look for the ones that are
	 * still conflicted, but since process_entries() has to loop over
	 * all of them, it saves the ones it couldn't resolve in this strmap
	 * so that record_conflicted_index_entries() can iterate just the
	 * relevant entries.
	 */
	struct strmap conflicted;

	/*
	 * paths_to_free: additional list of strings to free
	 *
	 * If keys are removed from "paths", they are added to paths_to_free
	 * to ensure they are later freed.  We avoid free'ing immediately since
	 * other places (e.g. conflict_info.pathnames[]) may still be
	 * referencing these paths.
	 */
	struct string_list paths_to_free;

	/*
	 * output: special messages and conflict notices for various paths
	 *
	 * This is a map of pathnames (a subset of the keys in "paths" above)
	 * to strbufs.  It gathers various warning/conflict/notice messages
	 * for later processing.
	 */
	struct strmap output;

	/*
	 * renames: various data relating to rename detection
	 */
	struct rename_info renames;

	/*
	 * current_dir_name: temporary var used in collect_merge_info_callback()
	 *
	 * Used to set merged_info.directory_name; see documentation for that
	 * variable and the requirements placed on that field.
	 */
	const char *current_dir_name;

	/* call_depth: recursion level counter for merging merge bases */
	int call_depth;
};

struct version_info {
	struct object_id oid;
	unsigned short mode;
};

struct merged_info {
	/* if is_null, ignore result.  otherwise result has oid & mode */
	struct version_info result;
	unsigned is_null:1;

	/*
	 * clean: whether the path in question is cleanly merged.
	 *
	 * see conflict_info.merged for more details.
	 */
	unsigned clean:1;

	/*
	 * basename_offset: offset of basename of path.
	 *
	 * perf optimization to avoid recomputing offset of final '/'
	 * character in pathname (0 if no '/' in pathname).
	 */
	size_t basename_offset;

	 /*
	  * directory_name: containing directory name.
	  *
	  * Note that we assume directory_name is constructed such that
	  *    strcmp(dir1_name, dir2_name) == 0 iff dir1_name == dir2_name,
	  * i.e. string equality is equivalent to pointer equality.  For this
	  * to hold, we have to be careful setting directory_name.
	  */
	const char *directory_name;
};

struct conflict_info {
	/*
	 * merged: the version of the path that will be written to working tree
	 *
	 * WARNING: It is critical to check merged.clean and ensure it is 0
	 * before reading any conflict_info fields outside of merged.
	 * Allocated merge_info structs will always have clean set to 1.
	 * Allocated conflict_info structs will have merged.clean set to 0
	 * initially.  The merged.clean field is how we know if it is safe
	 * to access other parts of conflict_info besides merged; if a
	 * conflict_info's merged.clean is changed to 1, the rest of the
	 * algorithm is not allowed to look at anything outside of the
	 * merged member anymore.
	 */
	struct merged_info merged;

	/* oids & modes from each of the three trees for this path */
	struct version_info stages[3];

	/* pathnames for each stage; may differ due to rename detection */
	const char *pathnames[3];

	/* Whether this path is/was involved in a directory/file conflict */
	unsigned df_conflict:1;

	/*
	 * Whether this path is/was involved in a non-content conflict other
	 * than a directory/file conflict (e.g. rename/rename, rename/delete,
	 * file location based on possible directory rename).
	 */
	unsigned path_conflict:1;

	/*
	 * For filemask and dirmask, the ith bit corresponds to whether the
	 * ith entry is a file (filemask) or a directory (dirmask).  Thus,
	 * filemask & dirmask is always zero, and filemask | dirmask is at
	 * most 7 but can be less when a path does not appear as either a
	 * file or a directory on at least one side of history.
	 *
	 * Note that these masks are related to enum merge_side, as the ith
	 * entry corresponds to side i.
	 *
	 * These values come from a traverse_trees() call; more info may be
	 * found looking at tree-walk.h's struct traverse_info,
	 * particularly the documentation above the "fn" member (note that
	 * filemask = mask & ~dirmask from that documentation).
	 */
	unsigned filemask:3;
	unsigned dirmask:3;

	/*
	 * Optimization to track which stages match, to avoid the need to
	 * recompute it in multiple steps. Either 0 or at least 2 bits are
	 * set; if at least 2 bits are set, their corresponding stages match.
	 */
	unsigned match_mask:3;
};

/*** Function Grouping: various utility functions ***/

/*
 * For the next three macros, see warning for conflict_info.merged.
 *
 * In each of the below, mi is a struct merged_info*, and ci was defined
 * as a struct conflict_info* (but we need to verify ci isn't actually
 * pointed at a struct merged_info*).
 *
 * INITIALIZE_CI: Assign ci to mi but only if it's safe; set to NULL otherwise.
 * VERIFY_CI: Ensure that something we assigned to a conflict_info* is one.
 * ASSIGN_AND_VERIFY_CI: Similar to VERIFY_CI but do assignment first.
 */
#define INITIALIZE_CI(ci, mi) do {                                           \
	(ci) = (!(mi) || (mi)->clean) ? NULL : (struct conflict_info *)(mi); \
} while (0)
#define VERIFY_CI(ci) assert(ci && !ci->merged.clean);
#define ASSIGN_AND_VERIFY_CI(ci, mi) do {    \
	(ci) = (struct conflict_info *)(mi);  \
	assert((ci) && !(mi)->clean);        \
} while (0)

static void free_strmap_strings(struct strmap *map)
{
	struct hashmap_iter iter;
	struct strmap_entry *entry;

	strmap_for_each_entry(map, &iter, entry) {
		free((char*)entry->key);
	}
}

static void clear_or_reinit_internal_opts(struct merge_options_internal *opti,
					  int reinitialize)
{
	void (*strmap_func)(struct strmap *, int) =
		reinitialize ? strmap_partial_clear : strmap_clear;

	/*
	 * We marked opti->paths with strdup_strings = 0, so that we
	 * wouldn't have to make another copy of the fullpath created by
	 * make_traverse_path from setup_path_info().  But, now that we've
	 * used it and have no other references to these strings, it is time
	 * to deallocate them.
	 */
	free_strmap_strings(&opti->paths);
	strmap_func(&opti->paths, 1);

	/*
	 * All keys and values in opti->conflicted are a subset of those in
	 * opti->paths.  We don't want to deallocate anything twice, so we
	 * don't free the keys and we pass 0 for free_values.
	 */
	strmap_func(&opti->conflicted, 0);

	/*
	 * opti->paths_to_free is similar to opti->paths; we created it with
	 * strdup_strings = 0 to avoid making _another_ copy of the fullpath
	 * but now that we've used it and have no other references to these
	 * strings, it is time to deallocate them.  We do so by temporarily
	 * setting strdup_strings to 1.
	 */
	opti->paths_to_free.strdup_strings = 1;
	string_list_clear(&opti->paths_to_free, 0);
	opti->paths_to_free.strdup_strings = 0;

	if (!reinitialize) {
		struct hashmap_iter iter;
		struct strmap_entry *e;

		/* Release and free each strbuf found in output */
		strmap_for_each_entry(&opti->output, &iter, e) {
			struct strbuf *sb = e->value;
			strbuf_release(sb);
			/*
			 * While strictly speaking we don't need to free(sb)
			 * here because we could pass free_values=1 when
			 * calling strmap_clear() on opti->output, that would
			 * require strmap_clear to do another
			 * strmap_for_each_entry() loop, so we just free it
			 * while we're iterating anyway.
			 */
			free(sb);
		}
		strmap_clear(&opti->output, 0);
	}
}

static int err(struct merge_options *opt, const char *err, ...)
{
	va_list params;
	struct strbuf sb = STRBUF_INIT;

	strbuf_addstr(&sb, "error: ");
	va_start(params, err);
	strbuf_vaddf(&sb, err, params);
	va_end(params);

	error("%s", sb.buf);
	strbuf_release(&sb);

	return -1;
}

__attribute__((format (printf, 4, 5)))
static void path_msg(struct merge_options *opt,
		     const char *path,
		     int omittable_hint, /* skippable under --remerge-diff */
		     const char *fmt, ...)
{
	va_list ap;
	struct strbuf *sb = strmap_get(&opt->priv->output, path);
	if (!sb) {
		sb = xmalloc(sizeof(*sb));
		strbuf_init(sb, 0);
		strmap_put(&opt->priv->output, path, sb);
	}

	va_start(ap, fmt);
	strbuf_vaddf(sb, fmt, ap);
	va_end(ap);

	strbuf_addch(sb, '\n');
}

/*** Function Grouping: functions related to collect_merge_info() ***/

static void setup_path_info(struct merge_options *opt,
			    struct string_list_item *result,
			    const char *current_dir_name,
			    int current_dir_name_len,
			    char *fullpath, /* we'll take over ownership */
			    struct name_entry *names,
			    struct name_entry *merged_version,
			    unsigned is_null,     /* boolean */
			    unsigned df_conflict, /* boolean */
			    unsigned filemask,
			    unsigned dirmask,
			    int resolved          /* boolean */)
{
	/* result->util is void*, so mi is a convenience typed variable */
	struct merged_info *mi;

	assert(!is_null || resolved);
	assert(!df_conflict || !resolved); /* df_conflict implies !resolved */
	assert(resolved == (merged_version != NULL));

	mi = xcalloc(1, resolved ? sizeof(struct merged_info) :
				   sizeof(struct conflict_info));
	mi->directory_name = current_dir_name;
	mi->basename_offset = current_dir_name_len;
	mi->clean = !!resolved;
	if (resolved) {
		mi->result.mode = merged_version->mode;
		oidcpy(&mi->result.oid, &merged_version->oid);
		mi->is_null = !!is_null;
	} else {
		int i;
		struct conflict_info *ci;

		ASSIGN_AND_VERIFY_CI(ci, mi);
		for (i = MERGE_BASE; i <= MERGE_SIDE2; i++) {
			ci->pathnames[i] = fullpath;
			ci->stages[i].mode = names[i].mode;
			oidcpy(&ci->stages[i].oid, &names[i].oid);
		}
		ci->filemask = filemask;
		ci->dirmask = dirmask;
		ci->df_conflict = !!df_conflict;
		if (dirmask)
			/*
			 * Assume is_null for now, but if we have entries
			 * under the directory then when it is complete in
			 * write_completed_directory() it'll update this.
			 * Also, for D/F conflicts, we have to handle the
			 * directory first, then clear this bit and process
			 * the file to see how it is handled -- that occurs
			 * near the top of process_entry().
			 */
			mi->is_null = 1;
	}
	strmap_put(&opt->priv->paths, fullpath, mi);
	result->string = fullpath;
	result->util = mi;
}

static int collect_merge_info_callback(int n,
				       unsigned long mask,
				       unsigned long dirmask,
				       struct name_entry *names,
				       struct traverse_info *info)
{
	/*
	 * n is 3.  Always.
	 * common ancestor (mbase) has mask 1, and stored in index 0 of names
	 * head of side 1  (side1) has mask 2, and stored in index 1 of names
	 * head of side 2  (side2) has mask 4, and stored in index 2 of names
	 */
	struct merge_options *opt = info->data;
	struct merge_options_internal *opti = opt->priv;
	struct string_list_item pi;  /* Path Info */
	struct conflict_info *ci; /* typed alias to pi.util (which is void*) */
	struct name_entry *p;
	size_t len;
	char *fullpath;
	const char *dirname = opti->current_dir_name;
	unsigned filemask = mask & ~dirmask;
	unsigned match_mask = 0; /* will be updated below */
	unsigned mbase_null = !(mask & 1);
	unsigned side1_null = !(mask & 2);
	unsigned side2_null = !(mask & 4);
	unsigned side1_matches_mbase = (!side1_null && !mbase_null &&
					names[0].mode == names[1].mode &&
					oideq(&names[0].oid, &names[1].oid));
	unsigned side2_matches_mbase = (!side2_null && !mbase_null &&
					names[0].mode == names[2].mode &&
					oideq(&names[0].oid, &names[2].oid));
	unsigned sides_match = (!side1_null && !side2_null &&
				names[1].mode == names[2].mode &&
				oideq(&names[1].oid, &names[2].oid));

	/*
	 * Note: When a path is a file on one side of history and a directory
	 * in another, we have a directory/file conflict.  In such cases, if
	 * the conflict doesn't resolve from renames and deletions, then we
	 * always leave directories where they are and move files out of the
	 * way.  Thus, while struct conflict_info has a df_conflict field to
	 * track such conflicts, we ignore that field for any directories at
	 * a path and only pay attention to it for files at the given path.
	 * The fact that we leave directories were they are also means that
	 * we do not need to worry about getting additional df_conflict
	 * information propagated from parent directories down to children
	 * (unlike, say traverse_trees_recursive() in unpack-trees.c, which
	 * sets a newinfo.df_conflicts field specifically to propagate it).
	 */
	unsigned df_conflict = (filemask != 0) && (dirmask != 0);

	/* n = 3 is a fundamental assumption. */
	if (n != 3)
		BUG("Called collect_merge_info_callback wrong");

	/*
	 * A bunch of sanity checks verifying that traverse_trees() calls
	 * us the way I expect.  Could just remove these at some point,
	 * though maybe they are helpful to future code readers.
	 */
	assert(mbase_null == is_null_oid(&names[0].oid));
	assert(side1_null == is_null_oid(&names[1].oid));
	assert(side2_null == is_null_oid(&names[2].oid));
	assert(!mbase_null || !side1_null || !side2_null);
	assert(mask > 0 && mask < 8);

	/* Determine match_mask */
	if (side1_matches_mbase)
		match_mask = (side2_matches_mbase ? 7 : 3);
	else if (side2_matches_mbase)
		match_mask = 5;
	else if (sides_match)
		match_mask = 6;

	/*
	 * Get the name of the relevant filepath, which we'll pass to
	 * setup_path_info() for tracking.
	 */
	p = names;
	while (!p->mode)
		p++;
	len = traverse_path_len(info, p->pathlen);

	/* +1 in both of the following lines to include the NUL byte */
	fullpath = xmalloc(len + 1);
	make_traverse_path(fullpath, len + 1, info, p->path, p->pathlen);

	/*
	 * If mbase, side1, and side2 all match, we can resolve early.  Even
	 * if these are trees, there will be no renames or anything
	 * underneath.
	 */
	if (side1_matches_mbase && side2_matches_mbase) {
		/* mbase, side1, & side2 all match; use mbase as resolution */
		setup_path_info(opt, &pi, dirname, info->pathlen, fullpath,
				names, names+0, mbase_null, 0,
				filemask, dirmask, 1);
		return mask;
	}

	/*
	 * Record information about the path so we can resolve later in
	 * process_entries.
	 */
	setup_path_info(opt, &pi, dirname, info->pathlen, fullpath,
			names, NULL, 0, df_conflict, filemask, dirmask, 0);

	ci = pi.util;
	VERIFY_CI(ci);
	ci->match_mask = match_mask;

	/* If dirmask, recurse into subdirectories */
	if (dirmask) {
		struct traverse_info newinfo;
		struct tree_desc t[3];
		void *buf[3] = {NULL, NULL, NULL};
		const char *original_dir_name;
		int i, ret;

		ci->match_mask &= filemask;
		newinfo = *info;
		newinfo.prev = info;
		newinfo.name = p->path;
		newinfo.namelen = p->pathlen;
		newinfo.pathlen = st_add3(newinfo.pathlen, p->pathlen, 1);
		/*
		 * If this directory we are about to recurse into cared about
		 * its parent directory (the current directory) having a D/F
		 * conflict, then we'd propagate the masks in this way:
		 *    newinfo.df_conflicts |= (mask & ~dirmask);
		 * But we don't worry about propagating D/F conflicts.  (See
		 * comment near setting of local df_conflict variable near
		 * the beginning of this function).
		 */

		for (i = MERGE_BASE; i <= MERGE_SIDE2; i++) {
			if (i == 1 && side1_matches_mbase)
				t[1] = t[0];
			else if (i == 2 && side2_matches_mbase)
				t[2] = t[0];
			else if (i == 2 && sides_match)
				t[2] = t[1];
			else {
				const struct object_id *oid = NULL;
				if (dirmask & 1)
					oid = &names[i].oid;
				buf[i] = fill_tree_descriptor(opt->repo,
							      t + i, oid);
			}
			dirmask >>= 1;
		}

		original_dir_name = opti->current_dir_name;
		opti->current_dir_name = pi.string;
		ret = traverse_trees(NULL, 3, t, &newinfo);
		opti->current_dir_name = original_dir_name;

		for (i = MERGE_BASE; i <= MERGE_SIDE2; i++)
			free(buf[i]);

		if (ret < 0)
			return -1;
	}

	return mask;
}

static int collect_merge_info(struct merge_options *opt,
			      struct tree *merge_base,
			      struct tree *side1,
			      struct tree *side2)
{
	int ret;
	struct tree_desc t[3];
	struct traverse_info info;
	const char *toplevel_dir_placeholder = "";

	opt->priv->current_dir_name = toplevel_dir_placeholder;
	setup_traverse_info(&info, toplevel_dir_placeholder);
	info.fn = collect_merge_info_callback;
	info.data = opt;
	info.show_all_errors = 1;

	parse_tree(merge_base);
	parse_tree(side1);
	parse_tree(side2);
	init_tree_desc(t + 0, merge_base->buffer, merge_base->size);
	init_tree_desc(t + 1, side1->buffer, side1->size);
	init_tree_desc(t + 2, side2->buffer, side2->size);

	ret = traverse_trees(NULL, 3, t, &info);

	return ret;
}

/*** Function Grouping: functions related to threeway content merges ***/

static int handle_content_merge(struct merge_options *opt,
				const char *path,
				const struct version_info *o,
				const struct version_info *a,
				const struct version_info *b,
				const char *pathnames[3],
				const int extra_marker_size,
				struct version_info *result)
{
	die("Not yet implemented");
}

/*** Function Grouping: functions related to detect_and_process_renames(), ***
 *** which are split into directory and regular rename detection sections. ***/

/*** Function Grouping: functions related to directory rename detection ***/

/*** Function Grouping: functions related to regular rename detection ***/

static int process_renames(struct merge_options *opt,
			   struct diff_queue_struct *renames)
{
	int clean_merge = 1, i;

	for (i = 0; i < renames->nr; ++i) {
		const char *oldpath = NULL, *newpath;
		struct diff_filepair *pair = renames->queue[i];
		struct conflict_info *oldinfo = NULL, *newinfo = NULL;
		struct strmap_entry *old_ent, *new_ent;
		unsigned int old_sidemask;
		int target_index, other_source_index;
		int source_deleted, collision, type_changed;
		const char *rename_branch = NULL, *delete_branch = NULL;

		old_ent = strmap_get_entry(&opt->priv->paths, pair->one->path);
		oldpath = old_ent->key;
		oldinfo = old_ent->value;

		new_ent = strmap_get_entry(&opt->priv->paths, pair->two->path);
		newpath = new_ent->key;
		newinfo = new_ent->value;

		/*
		 * diff_filepairs have copies of pathnames, thus we have to
		 * use standard 'strcmp()' (negated) instead of '=='.
		 */
		if (i + 1 < renames->nr &&
		    !strcmp(oldpath, renames->queue[i+1]->one->path)) {
			/* Handle rename/rename(1to2) or rename/rename(1to1) */
			const char *pathnames[3];
			struct version_info merged;
			struct conflict_info *base, *side1, *side2;
			unsigned was_binary_blob = 0;

			pathnames[0] = oldpath;
			pathnames[1] = newpath;
			pathnames[2] = renames->queue[i+1]->two->path;

			base = strmap_get(&opt->priv->paths, pathnames[0]);
			side1 = strmap_get(&opt->priv->paths, pathnames[1]);
			side2 = strmap_get(&opt->priv->paths, pathnames[2]);

			VERIFY_CI(base);
			VERIFY_CI(side1);
			VERIFY_CI(side2);

			if (!strcmp(pathnames[1], pathnames[2])) {
				/* Both sides renamed the same way */
				assert(side1 == side2);
				memcpy(&side1->stages[0], &base->stages[0],
				       sizeof(merged));
				side1->filemask |= (1 << MERGE_BASE);
				/* Mark base as resolved by removal */
				base->merged.is_null = 1;
				base->merged.clean = 1;

				/* We handled both renames, i.e. i+1 handled */
				i++;
				/* Move to next rename */
				continue;
			}

			/* This is a rename/rename(1to2) */
			clean_merge = handle_content_merge(opt,
							   pair->one->path,
							   &base->stages[0],
							   &side1->stages[1],
							   &side2->stages[2],
							   pathnames,
							   1 + 2 * opt->priv->call_depth,
							   &merged);
			if (!clean_merge &&
			    merged.mode == side1->stages[1].mode &&
			    oideq(&merged.oid, &side1->stages[1].oid))
				was_binary_blob = 1;
			memcpy(&side1->stages[1], &merged, sizeof(merged));
			if (was_binary_blob) {
				/*
				 * Getting here means we were attempting to
				 * merge a binary blob.
				 *
				 * Since we can't merge binaries,
				 * handle_content_merge() just takes one
				 * side.  But we don't want to copy the
				 * contents of one side to both paths.  We
				 * used the contents of side1 above for
				 * side1->stages, let's use the contents of
				 * side2 for side2->stages below.
				 */
				oidcpy(&merged.oid, &side2->stages[2].oid);
				merged.mode = side2->stages[2].mode;
			}
			memcpy(&side2->stages[2], &merged, sizeof(merged));

			side1->path_conflict = 1;
			side2->path_conflict = 1;
			/*
			 * TODO: For renames we normally remove the path at the
			 * old name.  It would thus seem consistent to do the
			 * same for rename/rename(1to2) cases, but we haven't
			 * done so traditionally and a number of the regression
			 * tests now encode an expectation that the file is
			 * left there at stage 1.  If we ever decide to change
			 * this, add the following two lines here:
			 *    base->merged.is_null = 1;
			 *    base->merged.clean = 1;
			 * and remove the setting of base->path_conflict to 1.
			 */
			base->path_conflict = 1;
			path_msg(opt, oldpath, 0,
				 _("CONFLICT (rename/rename): %s renamed to "
				   "%s in %s and to %s in %s."),
				 pathnames[0],
				 pathnames[1], opt->branch1,
				 pathnames[2], opt->branch2);

			i++; /* We handled both renames, i.e. i+1 handled */
			continue;
		}

		VERIFY_CI(oldinfo);
		VERIFY_CI(newinfo);
		target_index = pair->score; /* from collect_renames() */
		assert(target_index == 1 || target_index == 2);
		other_source_index = 3 - target_index;
		old_sidemask = (1 << other_source_index); /* 2 or 4 */
		source_deleted = (oldinfo->filemask == 1);
		collision = ((newinfo->filemask & old_sidemask) != 0);
		type_changed = !source_deleted &&
			(S_ISREG(oldinfo->stages[other_source_index].mode) !=
			 S_ISREG(newinfo->stages[target_index].mode));
		if (type_changed && collision) {
			/*
			 * special handling so later blocks can handle this...
			 *
			 * if type_changed && collision are both true, then this
			 * was really a double rename, but one side wasn't
			 * detected due to lack of break detection.  I.e.
			 * something like
			 *    orig: has normal file 'foo'
			 *    side1: renames 'foo' to 'bar', adds 'foo' symlink
			 *    side2: renames 'foo' to 'bar'
			 * In this case, the foo->bar rename on side1 won't be
			 * detected because the new symlink named 'foo' is
			 * there and we don't do break detection.  But we detect
			 * this here because we don't want to merge the content
			 * of the foo symlink with the foo->bar file, so we
			 * have some logic to handle this special case.  The
			 * easiest way to do that is make 'bar' on side1 not
			 * be considered a colliding file but the other part
			 * of a normal rename.  If the file is very different,
			 * well we're going to get content merge conflicts
			 * anyway so it doesn't hurt.  And if the colliding
			 * file also has a different type, that'll be handled
			 * by the content merge logic in process_entry() too.
			 *
			 * See also t6430, 'rename vs. rename/symlink'
			 */
			collision = 0;
		}
		if (source_deleted) {
			if (target_index == 1) {
				rename_branch = opt->branch1;
				delete_branch = opt->branch2;
			} else {
				rename_branch = opt->branch2;
				delete_branch = opt->branch1;
			}
		}

		assert(source_deleted || oldinfo->filemask & old_sidemask);

		/* Need to check for special types of rename conflicts... */
		if (collision && !source_deleted) {
			/* collision: rename/add or rename/rename(2to1) */
			const char *pathnames[3];
			struct version_info merged;

			struct conflict_info *base, *side1, *side2;
			unsigned clean;

			pathnames[0] = oldpath;
			pathnames[other_source_index] = oldpath;
			pathnames[target_index] = newpath;

			base = strmap_get(&opt->priv->paths, pathnames[0]);
			side1 = strmap_get(&opt->priv->paths, pathnames[1]);
			side2 = strmap_get(&opt->priv->paths, pathnames[2]);

			VERIFY_CI(base);
			VERIFY_CI(side1);
			VERIFY_CI(side2);

			clean = handle_content_merge(opt, pair->one->path,
						     &base->stages[0],
						     &side1->stages[1],
						     &side2->stages[2],
						     pathnames,
						     1 + 2 * opt->priv->call_depth,
						     &merged);

			memcpy(&newinfo->stages[target_index], &merged,
			       sizeof(merged));
			if (!clean) {
				path_msg(opt, newpath, 0,
					 _("CONFLICT (rename involved in "
					   "collision): rename of %s -> %s has "
					   "content conflicts AND collides "
					   "with another path; this may result "
					   "in nested conflict markers."),
					 oldpath, newpath);
			}
		} else if (collision && source_deleted) {
			/*
			 * rename/add/delete or rename/rename(2to1)/delete:
			 * since oldpath was deleted on the side that didn't
			 * do the rename, there's not much of a content merge
			 * we can do for the rename.  oldinfo->merged.is_null
			 * was already set, so we just leave things as-is so
			 * they look like an add/add conflict.
			 */

			newinfo->path_conflict = 1;
			path_msg(opt, newpath, 0,
				 _("CONFLICT (rename/delete): %s renamed "
				   "to %s in %s, but deleted in %s."),
				 oldpath, newpath, rename_branch, delete_branch);
		} else {
			/*
			 * a few different cases...start by copying the
			 * existing stage(s) from oldinfo over the newinfo
			 * and update the pathname(s).
			 */
			memcpy(&newinfo->stages[0], &oldinfo->stages[0],
			       sizeof(newinfo->stages[0]));
			newinfo->filemask |= (1 << MERGE_BASE);
			newinfo->pathnames[0] = oldpath;
			if (type_changed) {
				/* rename vs. typechange */
				/* Mark the original as resolved by removal */
				memcpy(&oldinfo->stages[0].oid, &null_oid,
				       sizeof(oldinfo->stages[0].oid));
				oldinfo->stages[0].mode = 0;
				oldinfo->filemask &= 0x06;
			} else if (source_deleted) {
				/* rename/delete */
				newinfo->path_conflict = 1;
				path_msg(opt, newpath, 0,
					 _("CONFLICT (rename/delete): %s renamed"
					   " to %s in %s, but deleted in %s."),
					 oldpath, newpath,
					 rename_branch, delete_branch);
			} else {
				/* normal rename */
				memcpy(&newinfo->stages[other_source_index],
				       &oldinfo->stages[other_source_index],
				       sizeof(newinfo->stages[0]));
				newinfo->filemask |= (1 << other_source_index);
				newinfo->pathnames[other_source_index] = oldpath;
			}
		}

		if (!type_changed) {
			/* Mark the original as resolved by removal */
			oldinfo->merged.is_null = 1;
			oldinfo->merged.clean = 1;
		}

	}

	return clean_merge;
}

static int compare_pairs(const void *a_, const void *b_)
{
	const struct diff_filepair *a = *((const struct diff_filepair **)a_);
	const struct diff_filepair *b = *((const struct diff_filepair **)b_);

	return strcmp(a->one->path, b->one->path);
}

/* Call diffcore_rename() to compute which files have changed on given side */
static void detect_regular_renames(struct merge_options *opt,
				   struct tree *merge_base,
				   struct tree *side,
				   unsigned side_index)
{
	struct diff_options diff_opts;
	struct rename_info *renames = &opt->priv->renames;

	repo_diff_setup(opt->repo, &diff_opts);
	diff_opts.flags.recursive = 1;
	diff_opts.flags.rename_empty = 0;
	diff_opts.detect_rename = DIFF_DETECT_RENAME;
	diff_opts.rename_limit = opt->rename_limit;
	if (opt->rename_limit <= 0)
		diff_opts.rename_limit = 1000;
	diff_opts.rename_score = opt->rename_score;
	diff_opts.show_rename_progress = opt->show_rename_progress;
	diff_opts.output_format = DIFF_FORMAT_NO_OUTPUT;
	diff_setup_done(&diff_opts);
	diff_tree_oid(&merge_base->object.oid, &side->object.oid, "",
		      &diff_opts);
	diffcore_std(&diff_opts);

	if (diff_opts.needed_rename_limit > renames->needed_limit)
		renames->needed_limit = diff_opts.needed_rename_limit;

	renames->pairs[side_index] = diff_queued_diff;

	diff_opts.output_format = DIFF_FORMAT_NO_OUTPUT;
	diff_queued_diff.nr = 0;
	diff_queued_diff.queue = NULL;
	diff_flush(&diff_opts);
}

/*
 * Get information of all renames which occurred in 'side_pairs', discarding
 * non-renames.
 */
static int collect_renames(struct merge_options *opt,
			   struct diff_queue_struct *result,
			   unsigned side_index)
{
	int i, clean = 1;
	struct diff_queue_struct *side_pairs;
	struct rename_info *renames = &opt->priv->renames;

	side_pairs = &renames->pairs[side_index];

	for (i = 0; i < side_pairs->nr; ++i) {
		struct diff_filepair *p = side_pairs->queue[i];

		if (p->status != 'R') {
			diff_free_filepair(p);
			continue;
		}

		/*
		 * p->score comes back from diffcore_rename_extended() with
		 * the similarity of the renamed file.  The similarity is
		 * was used to determine that the two files were related
		 * and are a rename, which we have already used, but beyond
		 * that we have no use for the similarity.  So p->score is
		 * now irrelevant.  However, process_renames() will need to
		 * know which side of the merge this rename was associated
		 * with, so overwrite p->score with that value.
		 */
		p->score = side_index;
		result->queue[result->nr++] = p;
	}

	return clean;
}

static int detect_and_process_renames(struct merge_options *opt,
				      struct tree *merge_base,
				      struct tree *side1,
				      struct tree *side2)
{
	struct diff_queue_struct combined;
	struct rename_info *renames = &opt->priv->renames;
	int s, clean = 1;

	memset(&combined, 0, sizeof(combined));

	detect_regular_renames(opt, merge_base, side1, MERGE_SIDE1);
	detect_regular_renames(opt, merge_base, side2, MERGE_SIDE2);

	ALLOC_GROW(combined.queue,
		   renames->pairs[1].nr + renames->pairs[2].nr,
		   combined.alloc);
	clean &= collect_renames(opt, &combined, MERGE_SIDE1);
	clean &= collect_renames(opt, &combined, MERGE_SIDE2);
	QSORT(combined.queue, combined.nr, compare_pairs);

	clean &= process_renames(opt, &combined);

	/* Free memory for renames->pairs[] and combined */
	for (s = MERGE_SIDE1; s <= MERGE_SIDE2; s++) {
		free(renames->pairs[s].queue);
		DIFF_QUEUE_CLEAR(&renames->pairs[s]);
	}
	if (combined.nr) {
		int i;
		for (i = 0; i < combined.nr; i++)
			diff_free_filepair(combined.queue[i]);
		free(combined.queue);
	}

	return clean;
}

/*** Function Grouping: functions related to process_entries() ***/

static int string_list_df_name_compare(const char *one, const char *two)
{
	int onelen = strlen(one);
	int twolen = strlen(two);
	/*
	 * Here we only care that entries for D/F conflicts are
	 * adjacent, in particular with the file of the D/F conflict
	 * appearing before files below the corresponding directory.
	 * The order of the rest of the list is irrelevant for us.
	 *
	 * To achieve this, we sort with df_name_compare and provide
	 * the mode S_IFDIR so that D/F conflicts will sort correctly.
	 * We use the mode S_IFDIR for everything else for simplicity,
	 * since in other cases any changes in their order due to
	 * sorting cause no problems for us.
	 */
	int cmp = df_name_compare(one, onelen, S_IFDIR,
				  two, twolen, S_IFDIR);
	/*
	 * Now that 'foo' and 'foo/bar' compare equal, we have to make sure
	 * that 'foo' comes before 'foo/bar'.
	 */
	if (cmp)
		return cmp;
	return onelen - twolen;
}

struct directory_versions {
	/*
	 * versions: list of (basename -> version_info)
	 *
	 * The basenames are in reverse lexicographic order of full pathnames,
	 * as processed in process_entries().  This puts all entries within
	 * a directory together, and covers the directory itself after
	 * everything within it, allowing us to write subtrees before needing
	 * to record information for the tree itself.
	 */
	struct string_list versions;

	/*
	 * offsets: list of (full relative path directories -> integer offsets)
	 *
	 * Since versions contains basenames from files in multiple different
	 * directories, we need to know which entries in versions correspond
	 * to which directories.  Values of e.g.
	 *     ""             0
	 *     src            2
	 *     src/moduleA    5
	 * Would mean that entries 0-1 of versions are files in the toplevel
	 * directory, entries 2-4 are files under src/, and the remaining
	 * entries starting at index 5 are files under src/moduleA/.
	 */
	struct string_list offsets;

	/*
	 * last_directory: directory that previously processed file found in
	 *
	 * last_directory starts NULL, but records the directory in which the
	 * previous file was found within.  As soon as
	 *    directory(current_file) != last_directory
	 * then we need to start updating accounting in versions & offsets.
	 * Note that last_directory is always the last path in "offsets" (or
	 * NULL if "offsets" is empty) so this exists just for quick access.
	 */
	const char *last_directory;

	/* last_directory_len: cached computation of strlen(last_directory) */
	unsigned last_directory_len;
};

static int tree_entry_order(const void *a_, const void *b_)
{
	const struct string_list_item *a = a_;
	const struct string_list_item *b = b_;

	const struct merged_info *ami = a->util;
	const struct merged_info *bmi = b->util;
	return base_name_compare(a->string, strlen(a->string), ami->result.mode,
				 b->string, strlen(b->string), bmi->result.mode);
}

static void write_tree(struct object_id *result_oid,
		       struct string_list *versions,
		       unsigned int offset,
		       size_t hash_size)
{
	size_t maxlen = 0, extra;
	unsigned int nr = versions->nr - offset;
	struct strbuf buf = STRBUF_INIT;
	struct string_list relevant_entries = STRING_LIST_INIT_NODUP;
	int i;

	/*
	 * We want to sort the last (versions->nr-offset) entries in versions.
	 * Do so by abusing the string_list API a bit: make another string_list
	 * that contains just those entries and then sort them.
	 *
	 * We won't use relevant_entries again and will let it just pop off the
	 * stack, so there won't be allocation worries or anything.
	 */
	relevant_entries.items = versions->items + offset;
	relevant_entries.nr = versions->nr - offset;
	QSORT(relevant_entries.items, relevant_entries.nr, tree_entry_order);

	/* Pre-allocate some space in buf */
	extra = hash_size + 8; /* 8: 6 for mode, 1 for space, 1 for NUL char */
	for (i = 0; i < nr; i++) {
		maxlen += strlen(versions->items[offset+i].string) + extra;
	}
	strbuf_grow(&buf, maxlen);

	/* Write each entry out to buf */
	for (i = 0; i < nr; i++) {
		struct merged_info *mi = versions->items[offset+i].util;
		struct version_info *ri = &mi->result;
		strbuf_addf(&buf, "%o %s%c",
			    ri->mode,
			    versions->items[offset+i].string, '\0');
		strbuf_add(&buf, ri->oid.hash, hash_size);
	}

	/* Write this object file out, and record in result_oid */
	write_object_file(buf.buf, buf.len, tree_type, result_oid);
	strbuf_release(&buf);
}

static void record_entry_for_tree(struct directory_versions *dir_metadata,
				  const char *path,
				  struct merged_info *mi)
{
	const char *basename;

	if (mi->is_null)
		/* nothing to record */
		return;

	basename = path + mi->basename_offset;
	assert(strchr(basename, '/') == NULL);
	string_list_append(&dir_metadata->versions,
			   basename)->util = &mi->result;
}

static void write_completed_directory(struct merge_options *opt,
				      const char *new_directory_name,
				      struct directory_versions *info)
{
	const char *prev_dir;
	struct merged_info *dir_info = NULL;
	unsigned int offset;

	/*
	 * Some explanation of info->versions and info->offsets...
	 *
	 * process_entries() iterates over all relevant files AND
	 * directories in reverse lexicographic order, and calls this
	 * function.  Thus, an example of the paths that process_entries()
	 * could operate on (along with the directories for those paths
	 * being shown) is:
	 *
	 *     xtract.c             ""
	 *     tokens.txt           ""
	 *     src/moduleB/umm.c    src/moduleB
	 *     src/moduleB/stuff.h  src/moduleB
	 *     src/moduleB/baz.c    src/moduleB
	 *     src/moduleB          src
	 *     src/moduleA/foo.c    src/moduleA
	 *     src/moduleA/bar.c    src/moduleA
	 *     src/moduleA          src
	 *     src                  ""
	 *     Makefile             ""
	 *
	 * info->versions:
	 *
	 *     always contains the unprocessed entries and their
	 *     version_info information.  For example, after the first five
	 *     entries above, info->versions would be:
	 *
	 *     	   xtract.c     <xtract.c's version_info>
	 *     	   token.txt    <token.txt's version_info>
	 *     	   umm.c        <src/moduleB/umm.c's version_info>
	 *     	   stuff.h      <src/moduleB/stuff.h's version_info>
	 *     	   baz.c        <src/moduleB/baz.c's version_info>
	 *
	 *     Once a subdirectory is completed we remove the entries in
	 *     that subdirectory from info->versions, writing it as a tree
	 *     (write_tree()).  Thus, as soon as we get to src/moduleB,
	 *     info->versions would be updated to
	 *
	 *     	   xtract.c     <xtract.c's version_info>
	 *     	   token.txt    <token.txt's version_info>
	 *     	   moduleB      <src/moduleB's version_info>
	 *
	 * info->offsets:
	 *
	 *     helps us track which entries in info->versions correspond to
	 *     which directories.  When we are N directories deep (e.g. 4
	 *     for src/modA/submod/subdir/), we have up to N+1 unprocessed
	 *     directories (+1 because of toplevel dir).  Corresponding to
	 *     the info->versions example above, after processing five entries
	 *     info->offsets will be:
	 *
	 *     	   ""           0
	 *     	   src/moduleB  2
	 *
	 *     which is used to know that xtract.c & token.txt are from the
	 *     toplevel dirctory, while umm.c & stuff.h & baz.c are from the
	 *     src/moduleB directory.  Again, following the example above,
	 *     once we need to process src/moduleB, then info->offsets is
	 *     updated to
	 *
	 *     	   ""           0
	 *     	   src          2
	 *
	 *     which says that moduleB (and only moduleB so far) is in the
	 *     src directory.
	 *
	 *     One unique thing to note about info->offsets here is that
	 *     "src" was not added to info->offsets until there was a path
	 *     (a file OR directory) immediately below src/ that got
	 *     processed.
	 *
	 * Since process_entry() just appends new entries to info->versions,
	 * write_completed_directory() only needs to do work if the next path
	 * is in a directory that is different than the last directory found
	 * in info->offsets.
	 */

	/*
	 * If we are working with the same directory as the last entry, there
	 * is no work to do.  (See comments above the directory_name member of
	 * struct merged_info for why we can use pointer comparison instead of
	 * strcmp here.)
	 */
	if (new_directory_name == info->last_directory)
		return;

	/*
	 * If we are just starting (last_directory is NULL), or last_directory
	 * is a prefix of the current directory, then we can just update
	 * info->offsets to record the offset where we started this directory
	 * and update last_directory to have quick access to it.
	 */
	if (info->last_directory == NULL ||
	    !strncmp(new_directory_name, info->last_directory,
		     info->last_directory_len)) {
		uintptr_t offset = info->versions.nr;

		info->last_directory = new_directory_name;
		info->last_directory_len = strlen(info->last_directory);
		/*
		 * Record the offset into info->versions where we will
		 * start recording basenames of paths found within
		 * new_directory_name.
		 */
		string_list_append(&info->offsets,
				   info->last_directory)->util = (void*)offset;
		return;
	}

	/*
	 * The next entry that will be processed will be within
	 * new_directory_name.  Since at this point we know that
	 * new_directory_name is within a different directory than
	 * info->last_directory, we have all entries for info->last_directory
	 * in info->versions and we need to create a tree object for them.
	 */
	dir_info = strmap_get(&opt->priv->paths, info->last_directory);
	assert(dir_info);
	offset = (uintptr_t)info->offsets.items[info->offsets.nr-1].util;
	if (offset == info->versions.nr) {
		/*
		 * Actually, we don't need to create a tree object in this
		 * case.  Whenever all files within a directory disappear
		 * during the merge (e.g. unmodified on one side and
		 * deleted on the other, or files were renamed elsewhere),
		 * then we get here and the directory itself needs to be
		 * omitted from its parent tree as well.
		 */
		dir_info->is_null = 1;
	} else {
		/*
		 * Write out the tree to the git object directory, and also
		 * record the mode and oid in dir_info->result.
		 */
		dir_info->is_null = 0;
		dir_info->result.mode = S_IFDIR;
		write_tree(&dir_info->result.oid, &info->versions, offset,
			   opt->repo->hash_algo->rawsz);
	}

	/*
	 * We've now used several entries from info->versions and one entry
	 * from info->offsets, so we get rid of those values.
	 */
	info->offsets.nr--;
	info->versions.nr = offset;

	/*
	 * Now we've taken care of the completed directory, but we need to
	 * prepare things since future entries will be in
	 * new_directory_name.  (In particular, process_entry() will be
	 * appending new entries to info->versions.)  So, we need to make
	 * sure new_directory_name is the last entry in info->offsets.
	 */
	prev_dir = info->offsets.nr == 0 ? NULL :
		   info->offsets.items[info->offsets.nr-1].string;
	if (new_directory_name != prev_dir) {
		uintptr_t c = info->versions.nr;
		string_list_append(&info->offsets,
				   new_directory_name)->util = (void*)c;
	}

	/* And, of course, we need to update last_directory to match. */
	info->last_directory = new_directory_name;
	info->last_directory_len = strlen(info->last_directory);
}

/* Per entry merge function */
static void process_entry(struct merge_options *opt,
			  const char *path,
			  struct conflict_info *ci,
			  struct directory_versions *dir_metadata)
{
	VERIFY_CI(ci);
	assert(ci->filemask >= 0 && ci->filemask <= 7);
	/* ci->match_mask == 7 was handled in collect_merge_info_callback() */
	assert(ci->match_mask == 0 || ci->match_mask == 3 ||
	       ci->match_mask == 5 || ci->match_mask == 6);

	if (ci->dirmask) {
		record_entry_for_tree(dir_metadata, path, &ci->merged);
		if (ci->filemask == 0)
			/* nothing else to handle */
			return;
		assert(ci->df_conflict);
	}

	if (ci->df_conflict) {
		die("Not yet implemented.");
	}

	/*
	 * NOTE: Below there is a long switch-like if-elseif-elseif... block
	 *       which the code goes through even for the df_conflict cases
	 *       above.  Well, it will once we don't die-not-implemented above.
	 */
	if (ci->match_mask) {
		ci->merged.clean = 1;
		if (ci->match_mask == 6) {
			/* stages[1] == stages[2] */
			ci->merged.result.mode = ci->stages[1].mode;
			oidcpy(&ci->merged.result.oid, &ci->stages[1].oid);
		} else {
			/* determine the mask of the side that didn't match */
			unsigned int othermask = 7 & ~ci->match_mask;
			int side = (othermask == 4) ? 2 : 1;

			ci->merged.result.mode = ci->stages[side].mode;
			ci->merged.is_null = !ci->merged.result.mode;
			oidcpy(&ci->merged.result.oid, &ci->stages[side].oid);

			assert(othermask == 2 || othermask == 4);
			assert(ci->merged.is_null ==
			       (ci->filemask == ci->match_mask));
		}
	} else if (ci->filemask >= 6 &&
		   (S_IFMT & ci->stages[1].mode) !=
		   (S_IFMT & ci->stages[2].mode)) {
		/*
		 * Two different items from (file/submodule/symlink)
		 */
		die("Not yet implemented.");
	} else if (ci->filemask >= 6) {
		/*
		 * TODO: Needs a two-way or three-way content merge, but we're
		 * just being lazy and copying the version from HEAD and
		 * leaving it as conflicted.
		 */
		ci->merged.clean = 0;
		ci->merged.result.mode = ci->stages[1].mode;
		oidcpy(&ci->merged.result.oid, &ci->stages[1].oid);
		/* When we fix above, we'll call handle_content_merge() */
		(void)handle_content_merge;
	} else if (ci->filemask == 3 || ci->filemask == 5) {
		/* Modify/delete */
		const char *modify_branch, *delete_branch;
		int side = (ci->filemask == 5) ? 2 : 1;
		int index = opt->priv->call_depth ? 0 : side;

		ci->merged.result.mode = ci->stages[index].mode;
		oidcpy(&ci->merged.result.oid, &ci->stages[index].oid);
		ci->merged.clean = 0;

		modify_branch = (side == 1) ? opt->branch1 : opt->branch2;
		delete_branch = (side == 1) ? opt->branch2 : opt->branch1;

		if (ci->path_conflict &&
		    oideq(&ci->stages[0].oid, &ci->stages[side].oid)) {
			/*
			 * This came from a rename/delete; no action to take,
			 * but avoid printing "modify/delete" conflict notice
			 * since the contents were not modified.
			 */
		} else {
			path_msg(opt, path, 0,
				 _("CONFLICT (modify/delete): %s deleted in %s "
				   "and modified in %s.  Version %s of %s left "
				   "in tree."),
				 path, delete_branch, modify_branch,
				 modify_branch, path);
		}
	} else if (ci->filemask == 2 || ci->filemask == 4) {
		/* Added on one side */
		int side = (ci->filemask == 4) ? 2 : 1;
		ci->merged.result.mode = ci->stages[side].mode;
		oidcpy(&ci->merged.result.oid, &ci->stages[side].oid);
		ci->merged.clean = !ci->df_conflict && !ci->path_conflict;
	} else if (ci->filemask == 1) {
		/* Deleted on both sides */
		ci->merged.is_null = 1;
		ci->merged.result.mode = 0;
		oidcpy(&ci->merged.result.oid, &null_oid);
		ci->merged.clean = !ci->path_conflict;
	}

	/*
	 * If still conflicted, record it separately.  This allows us to later
	 * iterate over just conflicted entries when updating the index instead
	 * of iterating over all entries.
	 */
	if (!ci->merged.clean)
		strmap_put(&opt->priv->conflicted, path, ci);
	record_entry_for_tree(dir_metadata, path, &ci->merged);
}

static void process_entries(struct merge_options *opt,
			    struct object_id *result_oid)
{
	struct hashmap_iter iter;
	struct strmap_entry *e;
	struct string_list plist = STRING_LIST_INIT_NODUP;
	struct string_list_item *entry;
	struct directory_versions dir_metadata = { STRING_LIST_INIT_NODUP,
						   STRING_LIST_INIT_NODUP,
						   NULL, 0 };

	if (strmap_empty(&opt->priv->paths)) {
		oidcpy(result_oid, opt->repo->hash_algo->empty_tree);
		return;
	}

	/* Hack to pre-allocate plist to the desired size */
	ALLOC_GROW(plist.items, strmap_get_size(&opt->priv->paths), plist.alloc);

	/* Put every entry from paths into plist, then sort */
	strmap_for_each_entry(&opt->priv->paths, &iter, e) {
		string_list_append(&plist, e->key)->util = e->value;
	}
	plist.cmp = string_list_df_name_compare;
	string_list_sort(&plist);

	/*
	 * Iterate over the items in reverse order, so we can handle paths
	 * below a directory before needing to handle the directory itself.
	 *
	 * This allows us to write subtrees before we need to write trees,
	 * and it also enables sane handling of directory/file conflicts
	 * (because it allows us to know whether the directory is still in
	 * the way when it is time to process the file at the same path).
	 */
	for (entry = &plist.items[plist.nr-1]; entry >= plist.items; --entry) {
		char *path = entry->string;
		/*
		 * NOTE: mi may actually be a pointer to a conflict_info, but
		 * we have to check mi->clean first to see if it's safe to
		 * reassign to such a pointer type.
		 */
		struct merged_info *mi = entry->util;

		write_completed_directory(opt, mi->directory_name,
					  &dir_metadata);
		if (mi->clean)
			record_entry_for_tree(&dir_metadata, path, mi);
		else {
			struct conflict_info *ci = (struct conflict_info *)mi;
			process_entry(opt, path, ci, &dir_metadata);
		}
	}

	if (dir_metadata.offsets.nr != 1 ||
	    (uintptr_t)dir_metadata.offsets.items[0].util != 0) {
		printf("dir_metadata.offsets.nr = %d (should be 1)\n",
		       dir_metadata.offsets.nr);
		printf("dir_metadata.offsets.items[0].util = %u (should be 0)\n",
		       (unsigned)(uintptr_t)dir_metadata.offsets.items[0].util);
		fflush(stdout);
		BUG("dir_metadata accounting completely off; shouldn't happen");
	}
	write_tree(result_oid, &dir_metadata.versions, 0,
		   opt->repo->hash_algo->rawsz);
	string_list_clear(&plist, 0);
	string_list_clear(&dir_metadata.versions, 0);
	string_list_clear(&dir_metadata.offsets, 0);
}

/*** Function Grouping: functions related to merge_switch_to_result() ***/

static int checkout(struct merge_options *opt,
		    struct tree *prev,
		    struct tree *next)
{
	/* Switch the index/working copy from old to new */
	int ret;
	struct tree_desc trees[2];
	struct unpack_trees_options unpack_opts;

	memset(&unpack_opts, 0, sizeof(unpack_opts));
	unpack_opts.head_idx = -1;
	unpack_opts.src_index = opt->repo->index;
	unpack_opts.dst_index = opt->repo->index;

	setup_unpack_trees_porcelain(&unpack_opts, "merge");

	/*
	 * NOTE: if this were just "git checkout" code, we would probably
	 * read or refresh the cache and check for a conflicted index, but
	 * builtin/merge.c or sequencer.c really needs to read the index
	 * and check for conflicted entries before starting merging for a
	 * good user experience (no sense waiting for merges/rebases before
	 * erroring out), so there's no reason to duplicate that work here.
	 */

	/* 2-way merge to the new branch */
	unpack_opts.update = 1;
	unpack_opts.merge = 1;
	unpack_opts.quiet = 0; /* FIXME: sequencer might want quiet? */
	unpack_opts.verbose_update = (opt->verbosity > 2);
	unpack_opts.fn = twoway_merge;
	if (1/* FIXME: opts->overwrite_ignore*/) {
		unpack_opts.dir = xcalloc(1, sizeof(*unpack_opts.dir));
		unpack_opts.dir->flags |= DIR_SHOW_IGNORED;
		setup_standard_excludes(unpack_opts.dir);
	}
	parse_tree(prev);
	init_tree_desc(&trees[0], prev->buffer, prev->size);
	parse_tree(next);
	init_tree_desc(&trees[1], next->buffer, next->size);

	ret = unpack_trees(2, trees, &unpack_opts);
	clear_unpack_trees_porcelain(&unpack_opts);
	dir_clear(unpack_opts.dir);
	FREE_AND_NULL(unpack_opts.dir);
	return ret;
}

static int record_conflicted_index_entries(struct merge_options *opt,
					   struct index_state *index,
					   struct strmap *paths,
					   struct strmap *conflicted)
{
	struct hashmap_iter iter;
	struct strmap_entry *e;
	int errs = 0;
	int original_cache_nr;

	if (strmap_empty(conflicted))
		return 0;

	original_cache_nr = index->cache_nr;

	/* Put every entry from paths into plist, then sort */
	strmap_for_each_entry(conflicted, &iter, e) {
		const char *path = e->key;
		struct conflict_info *ci = e->value;
		int pos;
		struct cache_entry *ce;
		int i;

		VERIFY_CI(ci);

		/*
		 * The index will already have a stage=0 entry for this path,
		 * because we created an as-merged-as-possible version of the
		 * file and checkout() moved the working copy and index over
		 * to that version.
		 *
		 * However, previous iterations through this loop will have
		 * added unstaged entries to the end of the cache which
		 * ignore the standard alphabetical ordering of cache
		 * entries and break invariants needed for index_name_pos()
		 * to work.  However, we know the entry we want is before
		 * those appended cache entries, so do a temporary swap on
		 * cache_nr to only look through entries of interest.
		 */
		SWAP(index->cache_nr, original_cache_nr);
		pos = index_name_pos(index, path, strlen(path));
		SWAP(index->cache_nr, original_cache_nr);
		if (pos < 0) {
			if (ci->filemask != 1)
				BUG("Conflicted %s but nothing in basic working tree or index; this shouldn't happen", path);
			cache_tree_invalidate_path(index, path);
		} else {
			ce = index->cache[pos];

			/*
			 * Clean paths with CE_SKIP_WORKTREE set will not be
			 * written to the working tree by the unpack_trees()
			 * call in checkout().  Our conflicted entries would
			 * have appeared clean to that code since we ignored
			 * the higher order stages.  Thus, we need override
			 * the CE_SKIP_WORKTREE bit and manually write those
			 * files to the working disk here.
			 *
			 * TODO: Implement this CE_SKIP_WORKTREE fixup.
			 */

			/*
			 * Mark this cache entry for removal and instead add
			 * new stage>0 entries corresponding to the
			 * conflicts.  If there are many conflicted entries, we
			 * want to avoid memmove'ing O(NM) entries by
			 * inserting the new entries one at a time.  So,
			 * instead, we just add the new cache entries to the
			 * end (ignoring normal index requirements on sort
			 * order) and sort the index once we're all done.
			 */
			ce->ce_flags |= CE_REMOVE;
		}

		for (i = MERGE_BASE; i <= MERGE_SIDE2; i++) {
			struct version_info *vi;
			if (!(ci->filemask & (1ul << i)))
				continue;
			vi = &ci->stages[i];
			ce = make_cache_entry(index, vi->mode, &vi->oid,
					      path, i+1, 0);
			add_index_entry(index, ce, ADD_CACHE_JUST_APPEND);
		}
	}

	/*
	 * Remove the unused cache entries (and invalidate the relevant
	 * cache-trees), then sort the index entries to get the conflicted
	 * entries we added to the end into their right locations.
	 */
	remove_marked_cache_entries(index, 1);
	QSORT(index->cache, index->cache_nr, cmp_cache_name_compare);

	return errs;
}

void merge_switch_to_result(struct merge_options *opt,
			    struct tree *head,
			    struct merge_result *result,
			    int update_worktree_and_index,
			    int display_update_msgs)
{
	assert(opt->priv == NULL);
	if (result->clean >= 0 && update_worktree_and_index) {
		struct merge_options_internal *opti = result->priv;

		if (checkout(opt, head, result->tree)) {
			/* failure to function */
			result->clean = -1;
			return;
		}

		if (record_conflicted_index_entries(opt, opt->repo->index,
						    &opti->paths,
						    &opti->conflicted)) {
			/* failure to function */
			result->clean = -1;
			return;
		}
	}

	if (display_update_msgs) {
		struct merge_options_internal *opti = result->priv;
		struct hashmap_iter iter;
		struct strmap_entry *e;
		struct string_list olist = STRING_LIST_INIT_NODUP;
		int i;

		/* Hack to pre-allocate olist to the desired size */
		ALLOC_GROW(olist.items, strmap_get_size(&opti->output),
			   olist.alloc);

		/* Put every entry from output into olist, then sort */
		strmap_for_each_entry(&opti->output, &iter, e) {
			string_list_append(&olist, e->key)->util = e->value;
		}
		string_list_sort(&olist);

		/* Iterate over the items, printing them */
		for (i = 0; i < olist.nr; ++i) {
			struct strbuf *sb = olist.items[i].util;

			printf("%s", sb->buf);
		}
		string_list_clear(&olist, 0);

		/* Also include needed rename limit adjustment now */
		diff_warn_rename_limit("merge.renamelimit",
				       opti->renames.needed_limit, 0);
	}

	merge_finalize(opt, result);
}

void merge_finalize(struct merge_options *opt,
		    struct merge_result *result)
{
	struct merge_options_internal *opti = result->priv;

	assert(opt->priv == NULL);

	clear_or_reinit_internal_opts(opti, 0);
	FREE_AND_NULL(opti);
}

/*** Function Grouping: helper functions for merge_incore_*() ***/

static inline void set_commit_tree(struct commit *c, struct tree *t)
{
	c->maybe_tree = t;
}

static struct commit *make_virtual_commit(struct repository *repo,
					  struct tree *tree,
					  const char *comment)
{
	struct commit *commit = alloc_commit_node(repo);

	set_merge_remote_desc(commit, comment, (struct object *)commit);
	set_commit_tree(commit, tree);
	commit->object.parsed = 1;
	return commit;
}

static void merge_start(struct merge_options *opt, struct merge_result *result)
{
	/* Sanity checks on opt */
	assert(opt->repo);

	assert(opt->branch1 && opt->branch2);

	assert(opt->detect_directory_renames >= MERGE_DIRECTORY_RENAMES_NONE &&
	       opt->detect_directory_renames <= MERGE_DIRECTORY_RENAMES_TRUE);
	assert(opt->rename_limit >= -1);
	assert(opt->rename_score >= 0 && opt->rename_score <= MAX_SCORE);
	assert(opt->show_rename_progress >= 0 && opt->show_rename_progress <= 1);

	assert(opt->xdl_opts >= 0);
	assert(opt->recursive_variant >= MERGE_VARIANT_NORMAL &&
	       opt->recursive_variant <= MERGE_VARIANT_THEIRS);

	/*
	 * detect_renames, verbosity, buffer_output, and obuf are ignored
	 * fields that were used by "recursive" rather than "ort" -- but
	 * sanity check them anyway.
	 */
	assert(opt->detect_renames >= -1 &&
	       opt->detect_renames <= DIFF_DETECT_COPY);
	assert(opt->verbosity >= 0 && opt->verbosity <= 5);
	assert(opt->buffer_output <= 2);
	assert(opt->obuf.len == 0);

	assert(opt->priv == NULL);

	/* Default to histogram diff.  Actually, just hardcode it...for now. */
	opt->xdl_opts = DIFF_WITH_ALG(opt, HISTOGRAM_DIFF);

	/* Initialization of opt->priv, our internal merge data */
	opt->priv = xcalloc(1, sizeof(*opt->priv));

	/*
	 * Although we initialize opt->priv->paths with strdup_strings=0,
	 * that's just to avoid making yet another copy of an allocated
	 * string.  Putting the entry into paths means we are taking
	 * ownership, so we will later free it.  paths_to_free is similar.
	 *
	 * In contrast, conflicted just has a subset of keys from paths, so
	 * we don't want to free those (it'd be a duplicate free).
	 */
	strmap_init_with_options(&opt->priv->paths, NULL, 0);
	strmap_init_with_options(&opt->priv->conflicted, NULL, 0);
	string_list_init(&opt->priv->paths_to_free, 0);

	/*
	 * keys & strbufs in output will sometimes need to outlive "paths",
	 * so it will have a copy of relevant keys.  It's probably a small
	 * subset of the overall paths that have special output.
	 */
	strmap_init(&opt->priv->output);
}

/*** Function Grouping: merge_incore_*() and their internal variants ***/

/*
 * Originally from merge_trees_internal(); heavily adapted, though.
 */
static void merge_ort_nonrecursive_internal(struct merge_options *opt,
					    struct tree *merge_base,
					    struct tree *side1,
					    struct tree *side2,
					    struct merge_result *result)
{
	struct object_id working_tree_oid;

	if (collect_merge_info(opt, merge_base, side1, side2) != 0) {
		/*
		 * TRANSLATORS: The %s arguments are: 1) tree hash of a merge
		 * base, and 2-3) the trees for the two trees we're merging.
		 */
		err(opt, _("collecting merge info failed for trees %s, %s, %s"),
		    oid_to_hex(&merge_base->object.oid),
		    oid_to_hex(&side1->object.oid),
		    oid_to_hex(&side2->object.oid));
		result->clean = -1;
		return;
	}

	result->clean = detect_and_process_renames(opt, merge_base,
						   side1, side2);
	process_entries(opt, &working_tree_oid);

	/* Set return values */
	result->tree = parse_tree_indirect(&working_tree_oid);
	/* existence of conflicted entries implies unclean */
	result->clean &= strmap_empty(&opt->priv->conflicted);
	if (!opt->priv->call_depth) {
		result->priv = opt->priv;
		opt->priv = NULL;
	}
}

/*
 * Originally from merge_recursive_internal(); somewhat adapted, though.
 */
static void merge_ort_internal(struct merge_options *opt,
			       struct commit_list *merge_bases,
			       struct commit *h1,
			       struct commit *h2,
			       struct merge_result *result)
{
	struct commit_list *iter;
	struct commit *merged_merge_bases;
	const char *ancestor_name;
	struct strbuf merge_base_abbrev = STRBUF_INIT;

	if (!merge_bases) {
		merge_bases = get_merge_bases(h1, h2);
		/* See merge-ort.h:merge_incore_recursive() declaration NOTE */
		merge_bases = reverse_commit_list(merge_bases);
	}

	merged_merge_bases = pop_commit(&merge_bases);
	if (merged_merge_bases == NULL) {
		/* if there is no common ancestor, use an empty tree */
		struct tree *tree;

		tree = lookup_tree(opt->repo, opt->repo->hash_algo->empty_tree);
		merged_merge_bases = make_virtual_commit(opt->repo, tree,
							 "ancestor");
		ancestor_name = "empty tree";
	} else if (merge_bases) {
		ancestor_name = "merged common ancestors";
	} else {
		strbuf_add_unique_abbrev(&merge_base_abbrev,
					 &merged_merge_bases->object.oid,
					 DEFAULT_ABBREV);
		ancestor_name = merge_base_abbrev.buf;
	}

	for (iter = merge_bases; iter; iter = iter->next) {
		const char *saved_b1, *saved_b2;
		struct commit *prev = merged_merge_bases;

		opt->priv->call_depth++;
		/*
		 * When the merge fails, the result contains files
		 * with conflict markers. The cleanness flag is
		 * ignored (unless indicating an error), it was never
		 * actually used, as result of merge_trees has always
		 * overwritten it: the committed "conflicts" were
		 * already resolved.
		 */
		saved_b1 = opt->branch1;
		saved_b2 = opt->branch2;
		opt->branch1 = "Temporary merge branch 1";
		opt->branch2 = "Temporary merge branch 2";
		merge_ort_internal(opt, NULL, prev, iter->item, result);
		if (result->clean < 0)
			return;
		opt->branch1 = saved_b1;
		opt->branch2 = saved_b2;
		opt->priv->call_depth--;

		merged_merge_bases = make_virtual_commit(opt->repo,
							 result->tree,
							 "merged tree");
		commit_list_insert(prev, &merged_merge_bases->parents);
		commit_list_insert(iter->item,
				   &merged_merge_bases->parents->next);

		clear_or_reinit_internal_opts(opt->priv, 1);
	}

	opt->ancestor = ancestor_name;
	merge_ort_nonrecursive_internal(opt,
					repo_get_commit_tree(opt->repo,
							     merged_merge_bases),
					repo_get_commit_tree(opt->repo, h1),
					repo_get_commit_tree(opt->repo, h2),
					result);
	strbuf_release(&merge_base_abbrev);
	opt->ancestor = NULL;  /* avoid accidental re-use of opt->ancestor */
}

void merge_incore_nonrecursive(struct merge_options *opt,
			       struct tree *merge_base,
			       struct tree *side1,
			       struct tree *side2,
			       struct merge_result *result)
{
	assert(opt->ancestor != NULL);
	merge_start(opt, result);
	merge_ort_nonrecursive_internal(opt, merge_base, side1, side2, result);
}

void merge_incore_recursive(struct merge_options *opt,
			    struct commit_list *merge_bases,
			    struct commit *side1,
			    struct commit *side2,
			    struct merge_result *result)
{
	/* We set the ancestor label based on the merge_bases */
	assert(opt->ancestor == NULL);

	merge_start(opt, result);
	merge_ort_internal(opt, merge_bases, side1, side2, result);
}