Merge branch 'maint'
[git] / read-tree.c
1 /*
2  * GIT - The information manager from hell
3  *
4  * Copyright (C) Linus Torvalds, 2005
5  */
6 #define DBRT_DEBUG 1
7
8 #include "cache.h"
9
10 #include "object.h"
11 #include "tree.h"
12 #include <sys/time.h>
13 #include <signal.h>
14
15 static int reset = 0;
16 static int merge = 0;
17 static int update = 0;
18 static int index_only = 0;
19 static int nontrivial_merge = 0;
20 static int trivial_merges_only = 0;
21 static int aggressive = 0;
22 static int verbose_update = 0;
23 static volatile int progress_update = 0;
24
25 static int head_idx = -1;
26 static int merge_size = 0;
27
28 static struct object_list *trees = NULL;
29
30 static struct cache_entry df_conflict_entry = { 
31 };
32
33 static struct tree_entry_list df_conflict_list = {
34         .name = NULL,
35         .next = &df_conflict_list
36 };
37
38 typedef int (*merge_fn_t)(struct cache_entry **src);
39
40 static int entcmp(char *name1, int dir1, char *name2, int dir2)
41 {
42         int len1 = strlen(name1);
43         int len2 = strlen(name2);
44         int len = len1 < len2 ? len1 : len2;
45         int ret = memcmp(name1, name2, len);
46         unsigned char c1, c2;
47         if (ret)
48                 return ret;
49         c1 = name1[len];
50         c2 = name2[len];
51         if (!c1 && dir1)
52                 c1 = '/';
53         if (!c2 && dir2)
54                 c2 = '/';
55         ret = (c1 < c2) ? -1 : (c1 > c2) ? 1 : 0;
56         if (c1 && c2 && !ret)
57                 ret = len1 - len2;
58         return ret;
59 }
60
61 static int unpack_trees_rec(struct tree_entry_list **posns, int len,
62                             const char *base, merge_fn_t fn, int *indpos)
63 {
64         int baselen = strlen(base);
65         int src_size = len + 1;
66         do {
67                 int i;
68                 char *first;
69                 int firstdir = 0;
70                 int pathlen;
71                 unsigned ce_size;
72                 struct tree_entry_list **subposns;
73                 struct cache_entry **src;
74                 int any_files = 0;
75                 int any_dirs = 0;
76                 char *cache_name;
77                 int ce_stage;
78
79                 /* Find the first name in the input. */
80
81                 first = NULL;
82                 cache_name = NULL;
83
84                 /* Check the cache */
85                 if (merge && *indpos < active_nr) {
86                         /* This is a bit tricky: */
87                         /* If the index has a subdirectory (with
88                          * contents) as the first name, it'll get a
89                          * filename like "foo/bar". But that's after
90                          * "foo", so the entry in trees will get
91                          * handled first, at which point we'll go into
92                          * "foo", and deal with "bar" from the index,
93                          * because the base will be "foo/". The only
94                          * way we can actually have "foo/bar" first of
95                          * all the things is if the trees don't
96                          * contain "foo" at all, in which case we'll
97                          * handle "foo/bar" without going into the
98                          * directory, but that's fine (and will return
99                          * an error anyway, with the added unknown
100                          * file case.
101                          */
102
103                         cache_name = active_cache[*indpos]->name;
104                         if (strlen(cache_name) > baselen &&
105                             !memcmp(cache_name, base, baselen)) {
106                                 cache_name += baselen;
107                                 first = cache_name;
108                         } else {
109                                 cache_name = NULL;
110                         }
111                 }
112
113 #if DBRT_DEBUG > 1
114                 if (first)
115                         printf("index %s\n", first);
116 #endif
117                 for (i = 0; i < len; i++) {
118                         if (!posns[i] || posns[i] == &df_conflict_list)
119                                 continue;
120 #if DBRT_DEBUG > 1
121                         printf("%d %s\n", i + 1, posns[i]->name);
122 #endif
123                         if (!first || entcmp(first, firstdir,
124                                              posns[i]->name, 
125                                              posns[i]->directory) > 0) {
126                                 first = posns[i]->name;
127                                 firstdir = posns[i]->directory;
128                         }
129                 }
130                 /* No name means we're done */
131                 if (!first)
132                         return 0;
133
134                 pathlen = strlen(first);
135                 ce_size = cache_entry_size(baselen + pathlen);
136
137                 src = xcalloc(src_size, sizeof(struct cache_entry *));
138
139                 subposns = xcalloc(len, sizeof(struct tree_list_entry *));
140
141                 if (cache_name && !strcmp(cache_name, first)) {
142                         any_files = 1;
143                         src[0] = active_cache[*indpos];
144                         remove_cache_entry_at(*indpos);
145                 }
146
147                 for (i = 0; i < len; i++) {
148                         struct cache_entry *ce;
149
150                         if (!posns[i] ||
151                             (posns[i] != &df_conflict_list &&
152                              strcmp(first, posns[i]->name))) {
153                                 continue;
154                         }
155
156                         if (posns[i] == &df_conflict_list) {
157                                 src[i + merge] = &df_conflict_entry;
158                                 continue;
159                         }
160
161                         if (posns[i]->directory) {
162                                 any_dirs = 1;
163                                 parse_tree(posns[i]->item.tree);
164                                 subposns[i] = posns[i]->item.tree->entries;
165                                 posns[i] = posns[i]->next;
166                                 src[i + merge] = &df_conflict_entry;
167                                 continue;
168                         }
169
170                         if (!merge)
171                                 ce_stage = 0;
172                         else if (i + 1 < head_idx)
173                                 ce_stage = 1;
174                         else if (i + 1 > head_idx)
175                                 ce_stage = 3;
176                         else
177                                 ce_stage = 2;
178
179                         ce = xcalloc(1, ce_size);
180                         ce->ce_mode = create_ce_mode(posns[i]->mode);
181                         ce->ce_flags = create_ce_flags(baselen + pathlen,
182                                                        ce_stage);
183                         memcpy(ce->name, base, baselen);
184                         memcpy(ce->name + baselen, first, pathlen + 1);
185
186                         any_files = 1;
187
188                         memcpy(ce->sha1, posns[i]->item.any->sha1, 20);
189                         src[i + merge] = ce;
190                         subposns[i] = &df_conflict_list;
191                         posns[i] = posns[i]->next;
192                 }
193                 if (any_files) {
194                         if (merge) {
195                                 int ret;
196
197 #if DBRT_DEBUG > 1
198                                 printf("%s:\n", first);
199                                 for (i = 0; i < src_size; i++) {
200                                         printf(" %d ", i);
201                                         if (src[i])
202                                                 printf("%s\n", sha1_to_hex(src[i]->sha1));
203                                         else
204                                                 printf("\n");
205                                 }
206 #endif
207                                 ret = fn(src);
208                                 
209 #if DBRT_DEBUG > 1
210                                 printf("Added %d entries\n", ret);
211 #endif
212                                 *indpos += ret;
213                         } else {
214                                 for (i = 0; i < src_size; i++) {
215                                         if (src[i]) {
216                                                 add_cache_entry(src[i], ADD_CACHE_OK_TO_ADD|ADD_CACHE_SKIP_DFCHECK);
217                                         }
218                                 }
219                         }
220                 }
221                 if (any_dirs) {
222                         char *newbase = xmalloc(baselen + 2 + pathlen);
223                         memcpy(newbase, base, baselen);
224                         memcpy(newbase + baselen, first, pathlen);
225                         newbase[baselen + pathlen] = '/';
226                         newbase[baselen + pathlen + 1] = '\0';
227                         if (unpack_trees_rec(subposns, len, newbase, fn,
228                                              indpos))
229                                 return -1;
230                         free(newbase);
231                 }
232                 free(subposns);
233                 free(src);
234         } while (1);
235 }
236
237 static void reject_merge(struct cache_entry *ce)
238 {
239         die("Entry '%s' would be overwritten by merge. Cannot merge.", 
240             ce->name);
241 }
242
243 /* Unlink the last component and attempt to remove leading
244  * directories, in case this unlink is the removal of the
245  * last entry in the directory -- empty directories are removed.
246  */
247 static void unlink_entry(char *name)
248 {
249         char *cp, *prev;
250
251         if (unlink(name))
252                 return;
253         prev = NULL;
254         while (1) {
255                 int status;
256                 cp = strrchr(name, '/');
257                 if (prev)
258                         *prev = '/';
259                 if (!cp)
260                         break;
261
262                 *cp = 0;
263                 status = rmdir(name);
264                 if (status) {
265                         *cp = '/';
266                         break;
267                 }
268                 prev = cp;
269         }
270 }
271
272 static void progress_interval(int signum)
273 {
274         progress_update = 1;
275 }
276
277 static void setup_progress_signal(void)
278 {
279         struct sigaction sa;
280         struct itimerval v;
281
282         memset(&sa, 0, sizeof(sa));
283         sa.sa_handler = progress_interval;
284         sigemptyset(&sa.sa_mask);
285         sa.sa_flags = SA_RESTART;
286         sigaction(SIGALRM, &sa, NULL);
287
288         v.it_interval.tv_sec = 1;
289         v.it_interval.tv_usec = 0;
290         v.it_value = v.it_interval;
291         setitimer(ITIMER_REAL, &v, NULL);
292 }
293
294 static void check_updates(struct cache_entry **src, int nr)
295 {
296         static struct checkout state = {
297                 .base_dir = "",
298                 .force = 1,
299                 .quiet = 1,
300                 .refresh_cache = 1,
301         };
302         unsigned short mask = htons(CE_UPDATE);
303         unsigned last_percent = 200, cnt = 0, total = 0;
304
305         if (update && verbose_update) {
306                 for (total = cnt = 0; cnt < nr; cnt++) {
307                         struct cache_entry *ce = src[cnt];
308                         if (!ce->ce_mode || ce->ce_flags & mask)
309                                 total++;
310                 }
311
312                 /* Don't bother doing this for very small updates */
313                 if (total < 250)
314                         total = 0;
315
316                 if (total) {
317                         fprintf(stderr, "Checking files out...\n");
318                         setup_progress_signal();
319                         progress_update = 1;
320                 }
321                 cnt = 0;
322         }
323
324         while (nr--) {
325                 struct cache_entry *ce = *src++;
326
327                 if (total) {
328                         if (!ce->ce_mode || ce->ce_flags & mask) {
329                                 unsigned percent;
330                                 cnt++;
331                                 percent = (cnt * 100) / total;
332                                 if (percent != last_percent ||
333                                     progress_update) {
334                                         fprintf(stderr, "%4u%% (%u/%u) done\r",
335                                                 percent, cnt, total);
336                                         last_percent = percent;
337                                 }
338                         }
339                 }
340                 if (!ce->ce_mode) {
341                         if (update)
342                                 unlink_entry(ce->name);
343                         continue;
344                 }
345                 if (ce->ce_flags & mask) {
346                         ce->ce_flags &= ~mask;
347                         if (update)
348                                 checkout_entry(ce, &state, NULL);
349                 }
350         }
351         if (total) {
352                 signal(SIGALRM, SIG_IGN);
353                 fputc('\n', stderr);
354         }
355 }
356
357 static int unpack_trees(merge_fn_t fn)
358 {
359         int indpos = 0;
360         unsigned len = object_list_length(trees);
361         struct tree_entry_list **posns;
362         int i;
363         struct object_list *posn = trees;
364         merge_size = len;
365
366         if (len) {
367                 posns = xmalloc(len * sizeof(struct tree_entry_list *));
368                 for (i = 0; i < len; i++) {
369                         posns[i] = ((struct tree *) posn->item)->entries;
370                         posn = posn->next;
371                 }
372                 if (unpack_trees_rec(posns, len, "", fn, &indpos))
373                         return -1;
374         }
375
376         if (trivial_merges_only && nontrivial_merge)
377                 die("Merge requires file-level merging");
378
379         check_updates(active_cache, active_nr);
380         return 0;
381 }
382
383 static int list_tree(unsigned char *sha1)
384 {
385         struct tree *tree = parse_tree_indirect(sha1);
386         if (!tree)
387                 return -1;
388         object_list_append(&tree->object, &trees);
389         return 0;
390 }
391
392 static int same(struct cache_entry *a, struct cache_entry *b)
393 {
394         if (!!a != !!b)
395                 return 0;
396         if (!a && !b)
397                 return 1;
398         return a->ce_mode == b->ce_mode && 
399                 !memcmp(a->sha1, b->sha1, 20);
400 }
401
402
403 /*
404  * When a CE gets turned into an unmerged entry, we
405  * want it to be up-to-date
406  */
407 static void verify_uptodate(struct cache_entry *ce)
408 {
409         struct stat st;
410
411         if (index_only)
412                 return;
413
414         if (!lstat(ce->name, &st)) {
415                 unsigned changed = ce_match_stat(ce, &st, 1);
416                 if (!changed)
417                         return;
418                 errno = 0;
419         }
420         if (reset) {
421                 ce->ce_flags |= htons(CE_UPDATE);
422                 return;
423         }
424         if (errno == ENOENT)
425                 return;
426         die("Entry '%s' not uptodate. Cannot merge.", ce->name);
427 }
428
429 static int merged_entry(struct cache_entry *merge, struct cache_entry *old)
430 {
431         merge->ce_flags |= htons(CE_UPDATE);
432         if (old) {
433                 /*
434                  * See if we can re-use the old CE directly?
435                  * That way we get the uptodate stat info.
436                  *
437                  * This also removes the UPDATE flag on
438                  * a match.
439                  */
440                 if (same(old, merge)) {
441                         *merge = *old;
442                 } else {
443                         verify_uptodate(old);
444                 }
445         }
446         merge->ce_flags &= ~htons(CE_STAGEMASK);
447         add_cache_entry(merge, ADD_CACHE_OK_TO_ADD);
448         return 1;
449 }
450
451 static int deleted_entry(struct cache_entry *ce, struct cache_entry *old)
452 {
453         if (old)
454                 verify_uptodate(old);
455         ce->ce_mode = 0;
456         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
457         return 1;
458 }
459
460 static int keep_entry(struct cache_entry *ce)
461 {
462         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
463         return 1;
464 }
465
466 #if DBRT_DEBUG
467 static void show_stage_entry(FILE *o,
468                              const char *label, const struct cache_entry *ce)
469 {
470         if (!ce)
471                 fprintf(o, "%s (missing)\n", label);
472         else
473                 fprintf(o, "%s%06o %s %d\t%s\n",
474                         label,
475                         ntohl(ce->ce_mode),
476                         sha1_to_hex(ce->sha1),
477                         ce_stage(ce),
478                         ce->name);
479 }
480 #endif
481
482 static int threeway_merge(struct cache_entry **stages)
483 {
484         struct cache_entry *index;
485         struct cache_entry *head; 
486         struct cache_entry *remote = stages[head_idx + 1];
487         int count;
488         int head_match = 0;
489         int remote_match = 0;
490
491         int df_conflict_head = 0;
492         int df_conflict_remote = 0;
493
494         int any_anc_missing = 0;
495         int no_anc_exists = 1;
496         int i;
497
498         for (i = 1; i < head_idx; i++) {
499                 if (!stages[i])
500                         any_anc_missing = 1;
501                 else
502                         no_anc_exists = 0;
503         }
504
505         index = stages[0];
506         head = stages[head_idx];
507
508         if (head == &df_conflict_entry) {
509                 df_conflict_head = 1;
510                 head = NULL;
511         }
512
513         if (remote == &df_conflict_entry) {
514                 df_conflict_remote = 1;
515                 remote = NULL;
516         }
517
518         /* First, if there's a #16 situation, note that to prevent #13
519          * and #14. 
520          */
521         if (!same(remote, head)) {
522                 for (i = 1; i < head_idx; i++) {
523                         if (same(stages[i], head)) {
524                                 head_match = i;
525                         }
526                         if (same(stages[i], remote)) {
527                                 remote_match = i;
528                         }
529                 }
530         }
531
532         /* We start with cases where the index is allowed to match
533          * something other than the head: #14(ALT) and #2ALT, where it
534          * is permitted to match the result instead.
535          */
536         /* #14, #14ALT, #2ALT */
537         if (remote && !df_conflict_head && head_match && !remote_match) {
538                 if (index && !same(index, remote) && !same(index, head))
539                         reject_merge(index);
540                 return merged_entry(remote, index);
541         }
542         /*
543          * If we have an entry in the index cache, then we want to
544          * make sure that it matches head.
545          */
546         if (index && !same(index, head)) {
547                 reject_merge(index);
548         }
549
550         if (head) {
551                 /* #5ALT, #15 */
552                 if (same(head, remote))
553                         return merged_entry(head, index);
554                 /* #13, #3ALT */
555                 if (!df_conflict_remote && remote_match && !head_match)
556                         return merged_entry(head, index);
557         }
558
559         /* #1 */
560         if (!head && !remote && any_anc_missing)
561                 return 0;
562
563         /* Under the new "aggressive" rule, we resolve mostly trivial
564          * cases that we historically had git-merge-one-file resolve.
565          */
566         if (aggressive) {
567                 int head_deleted = !head && !df_conflict_head;
568                 int remote_deleted = !remote && !df_conflict_remote;
569                 /*
570                  * Deleted in both.
571                  * Deleted in one and unchanged in the other.
572                  */
573                 if ((head_deleted && remote_deleted) ||
574                     (head_deleted && remote && remote_match) ||
575                     (remote_deleted && head && head_match)) {
576                         if (index)
577                                 return deleted_entry(index, index);
578                         return 0;
579                 }
580                 /*
581                  * Added in both, identically.
582                  */
583                 if (no_anc_exists && head && remote && same(head, remote))
584                         return merged_entry(head, index);
585
586         }
587
588         /* Below are "no merge" cases, which require that the index be
589          * up-to-date to avoid the files getting overwritten with
590          * conflict resolution files. 
591          */
592         if (index) {
593                 verify_uptodate(index);
594         }
595
596         nontrivial_merge = 1;
597
598         /* #2, #3, #4, #6, #7, #9, #11. */
599         count = 0;
600         if (!head_match || !remote_match) {
601                 for (i = 1; i < head_idx; i++) {
602                         if (stages[i]) {
603                                 keep_entry(stages[i]);
604                                 count++;
605                                 break;
606                         }
607                 }
608         }
609 #if DBRT_DEBUG
610         else {
611                 fprintf(stderr, "read-tree: warning #16 detected\n");
612                 show_stage_entry(stderr, "head   ", stages[head_match]);
613                 show_stage_entry(stderr, "remote ", stages[remote_match]);
614         }
615 #endif
616         if (head) { count += keep_entry(head); }
617         if (remote) { count += keep_entry(remote); }
618         return count;
619 }
620
621 /*
622  * Two-way merge.
623  *
624  * The rule is to "carry forward" what is in the index without losing
625  * information across a "fast forward", favoring a successful merge
626  * over a merge failure when it makes sense.  For details of the
627  * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
628  *
629  */
630 static int twoway_merge(struct cache_entry **src)
631 {
632         struct cache_entry *current = src[0];
633         struct cache_entry *oldtree = src[1], *newtree = src[2];
634
635         if (merge_size != 2)
636                 return error("Cannot do a twoway merge of %d trees",
637                              merge_size);
638
639         if (current) {
640                 if ((!oldtree && !newtree) || /* 4 and 5 */
641                     (!oldtree && newtree &&
642                      same(current, newtree)) || /* 6 and 7 */
643                     (oldtree && newtree &&
644                      same(oldtree, newtree)) || /* 14 and 15 */
645                     (oldtree && newtree &&
646                      !same(oldtree, newtree) && /* 18 and 19*/
647                      same(current, newtree))) {
648                         return keep_entry(current);
649                 }
650                 else if (oldtree && !newtree && same(current, oldtree)) {
651                         /* 10 or 11 */
652                         return deleted_entry(oldtree, current);
653                 }
654                 else if (oldtree && newtree &&
655                          same(current, oldtree) && !same(current, newtree)) {
656                         /* 20 or 21 */
657                         return merged_entry(newtree, current);
658                 }
659                 else {
660                         /* all other failures */
661                         if (oldtree)
662                                 reject_merge(oldtree);
663                         if (current)
664                                 reject_merge(current);
665                         if (newtree)
666                                 reject_merge(newtree);
667                         return -1;
668                 }
669         }
670         else if (newtree)
671                 return merged_entry(newtree, current);
672         else
673                 return deleted_entry(oldtree, current);
674 }
675
676 /*
677  * One-way merge.
678  *
679  * The rule is:
680  * - take the stat information from stage0, take the data from stage1
681  */
682 static int oneway_merge(struct cache_entry **src)
683 {
684         struct cache_entry *old = src[0];
685         struct cache_entry *a = src[1];
686
687         if (merge_size != 1)
688                 return error("Cannot do a oneway merge of %d trees",
689                              merge_size);
690
691         if (!a)
692                 return deleted_entry(old, NULL);
693         if (old && same(old, a)) {
694                 if (reset) {
695                         struct stat st;
696                         if (lstat(old->name, &st) ||
697                             ce_match_stat(old, &st, 1))
698                                 old->ce_flags |= htons(CE_UPDATE);
699                 }
700                 return keep_entry(old);
701         }
702         return merged_entry(a, NULL);
703 }
704
705 static int read_cache_unmerged(void)
706 {
707         int i, deleted;
708         struct cache_entry **dst;
709
710         read_cache();
711         dst = active_cache;
712         deleted = 0;
713         for (i = 0; i < active_nr; i++) {
714                 struct cache_entry *ce = active_cache[i];
715                 if (ce_stage(ce)) {
716                         deleted++;
717                         continue;
718                 }
719                 if (deleted)
720                         *dst = ce;
721                 dst++;
722         }
723         active_nr -= deleted;
724         return deleted;
725 }
726
727 static const char read_tree_usage[] = "git-read-tree (<sha> | -m [--aggressive] [-u | -i] <sha1> [<sha2> [<sha3>]])";
728
729 static struct cache_file cache_file;
730
731 int main(int argc, char **argv)
732 {
733         int i, newfd, stage = 0;
734         unsigned char sha1[20];
735         merge_fn_t fn = NULL;
736
737         setup_git_directory();
738         git_config(git_default_config);
739
740         newfd = hold_index_file_for_update(&cache_file, get_index_file());
741         if (newfd < 0)
742                 die("unable to create new cachefile");
743
744         git_config(git_default_config);
745
746         merge = 0;
747         reset = 0;
748         for (i = 1; i < argc; i++) {
749                 const char *arg = argv[i];
750
751                 /* "-u" means "update", meaning that a merge will update
752                  * the working tree.
753                  */
754                 if (!strcmp(arg, "-u")) {
755                         update = 1;
756                         continue;
757                 }
758
759                 if (!strcmp(arg, "-v")) {
760                         verbose_update = 1;
761                         continue;
762                 }
763
764                 /* "-i" means "index only", meaning that a merge will
765                  * not even look at the working tree.
766                  */
767                 if (!strcmp(arg, "-i")) {
768                         index_only = 1;
769                         continue;
770                 }
771
772                 /* This differs from "-m" in that we'll silently ignore unmerged entries */
773                 if (!strcmp(arg, "--reset")) {
774                         if (stage || merge)
775                                 usage(read_tree_usage);
776                         reset = 1;
777                         merge = 1;
778                         stage = 1;
779                         read_cache_unmerged();
780                         continue;
781                 }
782
783                 if (!strcmp(arg, "--trivial")) {
784                         trivial_merges_only = 1;
785                         continue;
786                 }
787
788                 if (!strcmp(arg, "--aggressive")) {
789                         aggressive = 1;
790                         continue;
791                 }
792
793                 /* "-m" stands for "merge", meaning we start in stage 1 */
794                 if (!strcmp(arg, "-m")) {
795                         if (stage || merge)
796                                 usage(read_tree_usage);
797                         if (read_cache_unmerged())
798                                 die("you need to resolve your current index first");
799                         stage = 1;
800                         merge = 1;
801                         continue;
802                 }
803
804                 /* using -u and -i at the same time makes no sense */
805                 if (1 < index_only + update)
806                         usage(read_tree_usage);
807
808                 if (get_sha1(arg, sha1))
809                         die("Not a valid object name %s", arg);
810                 if (list_tree(sha1) < 0)
811                         die("failed to unpack tree object %s", arg);
812                 stage++;
813         }
814         if ((update||index_only) && !merge)
815                 usage(read_tree_usage);
816
817         if (merge) {
818                 if (stage < 2)
819                         die("just how do you expect me to merge %d trees?", stage-1);
820                 switch (stage - 1) {
821                 case 1:
822                         fn = oneway_merge;
823                         break;
824                 case 2:
825                         fn = twoway_merge;
826                         break;
827                 case 3:
828                         fn = threeway_merge;
829                         break;
830                 default:
831                         fn = threeway_merge;
832                         break;
833                 }
834
835                 if (stage - 1 >= 3)
836                         head_idx = stage - 2;
837                 else
838                         head_idx = 1;
839         }
840
841         unpack_trees(fn);
842         if (write_cache(newfd, active_cache, active_nr) ||
843             commit_index_file(&cache_file))
844                 die("unable to write new index file");
845         return 0;
846 }