gitview: Move the console error messages to message dialog
[git] / builtin-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 #include "builtin.h"
15
16 static int reset = 0;
17 static int merge = 0;
18 static int update = 0;
19 static int index_only = 0;
20 static int nontrivial_merge = 0;
21 static int trivial_merges_only = 0;
22 static int aggressive = 0;
23 static int verbose_update = 0;
24 static volatile int progress_update = 0;
25
26 static int head_idx = -1;
27 static int merge_size = 0;
28
29 static struct object_list *trees = NULL;
30
31 static struct cache_entry df_conflict_entry = { 
32 };
33
34 static struct tree_entry_list df_conflict_list = {
35         .name = NULL,
36         .next = &df_conflict_list
37 };
38
39 typedef int (*merge_fn_t)(struct cache_entry **src);
40
41 static int entcmp(char *name1, int dir1, char *name2, int dir2)
42 {
43         int len1 = strlen(name1);
44         int len2 = strlen(name2);
45         int len = len1 < len2 ? len1 : len2;
46         int ret = memcmp(name1, name2, len);
47         unsigned char c1, c2;
48         if (ret)
49                 return ret;
50         c1 = name1[len];
51         c2 = name2[len];
52         if (!c1 && dir1)
53                 c1 = '/';
54         if (!c2 && dir2)
55                 c2 = '/';
56         ret = (c1 < c2) ? -1 : (c1 > c2) ? 1 : 0;
57         if (c1 && c2 && !ret)
58                 ret = len1 - len2;
59         return ret;
60 }
61
62 static int unpack_trees_rec(struct tree_entry_list **posns, int len,
63                             const char *base, merge_fn_t fn, int *indpos)
64 {
65         int baselen = strlen(base);
66         int src_size = len + 1;
67         do {
68                 int i;
69                 char *first;
70                 int firstdir = 0;
71                 int pathlen;
72                 unsigned ce_size;
73                 struct tree_entry_list **subposns;
74                 struct cache_entry **src;
75                 int any_files = 0;
76                 int any_dirs = 0;
77                 char *cache_name;
78                 int ce_stage;
79
80                 /* Find the first name in the input. */
81
82                 first = NULL;
83                 cache_name = NULL;
84
85                 /* Check the cache */
86                 if (merge && *indpos < active_nr) {
87                         /* This is a bit tricky: */
88                         /* If the index has a subdirectory (with
89                          * contents) as the first name, it'll get a
90                          * filename like "foo/bar". But that's after
91                          * "foo", so the entry in trees will get
92                          * handled first, at which point we'll go into
93                          * "foo", and deal with "bar" from the index,
94                          * because the base will be "foo/". The only
95                          * way we can actually have "foo/bar" first of
96                          * all the things is if the trees don't
97                          * contain "foo" at all, in which case we'll
98                          * handle "foo/bar" without going into the
99                          * directory, but that's fine (and will return
100                          * an error anyway, with the added unknown
101                          * file case.
102                          */
103
104                         cache_name = active_cache[*indpos]->name;
105                         if (strlen(cache_name) > baselen &&
106                             !memcmp(cache_name, base, baselen)) {
107                                 cache_name += baselen;
108                                 first = cache_name;
109                         } else {
110                                 cache_name = NULL;
111                         }
112                 }
113
114 #if DBRT_DEBUG > 1
115                 if (first)
116                         printf("index %s\n", first);
117 #endif
118                 for (i = 0; i < len; i++) {
119                         if (!posns[i] || posns[i] == &df_conflict_list)
120                                 continue;
121 #if DBRT_DEBUG > 1
122                         printf("%d %s\n", i + 1, posns[i]->name);
123 #endif
124                         if (!first || entcmp(first, firstdir,
125                                              posns[i]->name, 
126                                              posns[i]->directory) > 0) {
127                                 first = posns[i]->name;
128                                 firstdir = posns[i]->directory;
129                         }
130                 }
131                 /* No name means we're done */
132                 if (!first)
133                         return 0;
134
135                 pathlen = strlen(first);
136                 ce_size = cache_entry_size(baselen + pathlen);
137
138                 src = xcalloc(src_size, sizeof(struct cache_entry *));
139
140                 subposns = xcalloc(len, sizeof(struct tree_list_entry *));
141
142                 if (cache_name && !strcmp(cache_name, first)) {
143                         any_files = 1;
144                         src[0] = active_cache[*indpos];
145                         remove_cache_entry_at(*indpos);
146                 }
147
148                 for (i = 0; i < len; i++) {
149                         struct cache_entry *ce;
150
151                         if (!posns[i] ||
152                             (posns[i] != &df_conflict_list &&
153                              strcmp(first, posns[i]->name))) {
154                                 continue;
155                         }
156
157                         if (posns[i] == &df_conflict_list) {
158                                 src[i + merge] = &df_conflict_entry;
159                                 continue;
160                         }
161
162                         if (posns[i]->directory) {
163                                 any_dirs = 1;
164                                 parse_tree(posns[i]->item.tree);
165                                 subposns[i] = posns[i]->item.tree->entries;
166                                 posns[i] = posns[i]->next;
167                                 src[i + merge] = &df_conflict_entry;
168                                 continue;
169                         }
170
171                         if (!merge)
172                                 ce_stage = 0;
173                         else if (i + 1 < head_idx)
174                                 ce_stage = 1;
175                         else if (i + 1 > head_idx)
176                                 ce_stage = 3;
177                         else
178                                 ce_stage = 2;
179
180                         ce = xcalloc(1, ce_size);
181                         ce->ce_mode = create_ce_mode(posns[i]->mode);
182                         ce->ce_flags = create_ce_flags(baselen + pathlen,
183                                                        ce_stage);
184                         memcpy(ce->name, base, baselen);
185                         memcpy(ce->name + baselen, first, pathlen + 1);
186
187                         any_files = 1;
188
189                         memcpy(ce->sha1, posns[i]->item.any->sha1, 20);
190                         src[i + merge] = ce;
191                         subposns[i] = &df_conflict_list;
192                         posns[i] = posns[i]->next;
193                 }
194                 if (any_files) {
195                         if (merge) {
196                                 int ret;
197
198 #if DBRT_DEBUG > 1
199                                 printf("%s:\n", first);
200                                 for (i = 0; i < src_size; i++) {
201                                         printf(" %d ", i);
202                                         if (src[i])
203                                                 printf("%s\n", sha1_to_hex(src[i]->sha1));
204                                         else
205                                                 printf("\n");
206                                 }
207 #endif
208                                 ret = fn(src);
209                                 
210 #if DBRT_DEBUG > 1
211                                 printf("Added %d entries\n", ret);
212 #endif
213                                 *indpos += ret;
214                         } else {
215                                 for (i = 0; i < src_size; i++) {
216                                         if (src[i]) {
217                                                 add_cache_entry(src[i], ADD_CACHE_OK_TO_ADD|ADD_CACHE_SKIP_DFCHECK);
218                                         }
219                                 }
220                         }
221                 }
222                 if (any_dirs) {
223                         char *newbase = xmalloc(baselen + 2 + pathlen);
224                         memcpy(newbase, base, baselen);
225                         memcpy(newbase + baselen, first, pathlen);
226                         newbase[baselen + pathlen] = '/';
227                         newbase[baselen + pathlen + 1] = '\0';
228                         if (unpack_trees_rec(subposns, len, newbase, fn,
229                                              indpos))
230                                 return -1;
231                         free(newbase);
232                 }
233                 free(subposns);
234                 free(src);
235         } while (1);
236 }
237
238 static void reject_merge(struct cache_entry *ce)
239 {
240         die("Entry '%s' would be overwritten by merge. Cannot merge.", 
241             ce->name);
242 }
243
244 /* Unlink the last component and attempt to remove leading
245  * directories, in case this unlink is the removal of the
246  * last entry in the directory -- empty directories are removed.
247  */
248 static void unlink_entry(char *name)
249 {
250         char *cp, *prev;
251
252         if (unlink(name))
253                 return;
254         prev = NULL;
255         while (1) {
256                 int status;
257                 cp = strrchr(name, '/');
258                 if (prev)
259                         *prev = '/';
260                 if (!cp)
261                         break;
262
263                 *cp = 0;
264                 status = rmdir(name);
265                 if (status) {
266                         *cp = '/';
267                         break;
268                 }
269                 prev = cp;
270         }
271 }
272
273 static void progress_interval(int signum)
274 {
275         progress_update = 1;
276 }
277
278 static void setup_progress_signal(void)
279 {
280         struct sigaction sa;
281         struct itimerval v;
282
283         memset(&sa, 0, sizeof(sa));
284         sa.sa_handler = progress_interval;
285         sigemptyset(&sa.sa_mask);
286         sa.sa_flags = SA_RESTART;
287         sigaction(SIGALRM, &sa, NULL);
288
289         v.it_interval.tv_sec = 1;
290         v.it_interval.tv_usec = 0;
291         v.it_value = v.it_interval;
292         setitimer(ITIMER_REAL, &v, NULL);
293 }
294
295 static void check_updates(struct cache_entry **src, int nr)
296 {
297         static struct checkout state = {
298                 .base_dir = "",
299                 .force = 1,
300                 .quiet = 1,
301                 .refresh_cache = 1,
302         };
303         unsigned short mask = htons(CE_UPDATE);
304         unsigned last_percent = 200, cnt = 0, total = 0;
305
306         if (update && verbose_update) {
307                 for (total = cnt = 0; cnt < nr; cnt++) {
308                         struct cache_entry *ce = src[cnt];
309                         if (!ce->ce_mode || ce->ce_flags & mask)
310                                 total++;
311                 }
312
313                 /* Don't bother doing this for very small updates */
314                 if (total < 250)
315                         total = 0;
316
317                 if (total) {
318                         fprintf(stderr, "Checking files out...\n");
319                         setup_progress_signal();
320                         progress_update = 1;
321                 }
322                 cnt = 0;
323         }
324
325         while (nr--) {
326                 struct cache_entry *ce = *src++;
327
328                 if (total) {
329                         if (!ce->ce_mode || ce->ce_flags & mask) {
330                                 unsigned percent;
331                                 cnt++;
332                                 percent = (cnt * 100) / total;
333                                 if (percent != last_percent ||
334                                     progress_update) {
335                                         fprintf(stderr, "%4u%% (%u/%u) done\r",
336                                                 percent, cnt, total);
337                                         last_percent = percent;
338                                 }
339                         }
340                 }
341                 if (!ce->ce_mode) {
342                         if (update)
343                                 unlink_entry(ce->name);
344                         continue;
345                 }
346                 if (ce->ce_flags & mask) {
347                         ce->ce_flags &= ~mask;
348                         if (update)
349                                 checkout_entry(ce, &state, NULL);
350                 }
351         }
352         if (total) {
353                 signal(SIGALRM, SIG_IGN);
354                 fputc('\n', stderr);
355         }
356 }
357
358 static int unpack_trees(merge_fn_t fn)
359 {
360         int indpos = 0;
361         unsigned len = object_list_length(trees);
362         struct tree_entry_list **posns;
363         int i;
364         struct object_list *posn = trees;
365         merge_size = len;
366
367         if (len) {
368                 posns = xmalloc(len * sizeof(struct tree_entry_list *));
369                 for (i = 0; i < len; i++) {
370                         posns[i] = ((struct tree *) posn->item)->entries;
371                         posn = posn->next;
372                 }
373                 if (unpack_trees_rec(posns, len, "", fn, &indpos))
374                         return -1;
375         }
376
377         if (trivial_merges_only && nontrivial_merge)
378                 die("Merge requires file-level merging");
379
380         check_updates(active_cache, active_nr);
381         return 0;
382 }
383
384 static int list_tree(unsigned char *sha1)
385 {
386         struct tree *tree = parse_tree_indirect(sha1);
387         if (!tree)
388                 return -1;
389         object_list_append(&tree->object, &trees);
390         return 0;
391 }
392
393 static int same(struct cache_entry *a, struct cache_entry *b)
394 {
395         if (!!a != !!b)
396                 return 0;
397         if (!a && !b)
398                 return 1;
399         return a->ce_mode == b->ce_mode && 
400                 !memcmp(a->sha1, b->sha1, 20);
401 }
402
403
404 /*
405  * When a CE gets turned into an unmerged entry, we
406  * want it to be up-to-date
407  */
408 static void verify_uptodate(struct cache_entry *ce)
409 {
410         struct stat st;
411
412         if (index_only || reset)
413                 return;
414
415         if (!lstat(ce->name, &st)) {
416                 unsigned changed = ce_match_stat(ce, &st, 1);
417                 if (!changed)
418                         return;
419                 errno = 0;
420         }
421         if (reset) {
422                 ce->ce_flags |= htons(CE_UPDATE);
423                 return;
424         }
425         if (errno == ENOENT)
426                 return;
427         die("Entry '%s' not uptodate. Cannot merge.", ce->name);
428 }
429
430 /*
431  * We do not want to remove or overwrite a working tree file that
432  * is not tracked.
433  */
434 static void verify_absent(const char *path, const char *action)
435 {
436         struct stat st;
437
438         if (index_only || reset || !update)
439                 return;
440         if (!lstat(path, &st))
441                 die("Untracked working tree file '%s' "
442                     "would be %s by merge.", path, action);
443 }
444
445 static int merged_entry(struct cache_entry *merge, struct cache_entry *old)
446 {
447         merge->ce_flags |= htons(CE_UPDATE);
448         if (old) {
449                 /*
450                  * See if we can re-use the old CE directly?
451                  * That way we get the uptodate stat info.
452                  *
453                  * This also removes the UPDATE flag on
454                  * a match.
455                  */
456                 if (same(old, merge)) {
457                         *merge = *old;
458                 } else {
459                         verify_uptodate(old);
460                 }
461         }
462         else
463                 verify_absent(merge->name, "overwritten");
464
465         merge->ce_flags &= ~htons(CE_STAGEMASK);
466         add_cache_entry(merge, ADD_CACHE_OK_TO_ADD);
467         return 1;
468 }
469
470 static int deleted_entry(struct cache_entry *ce, struct cache_entry *old)
471 {
472         if (old)
473                 verify_uptodate(old);
474         else
475                 verify_absent(ce->name, "removed");
476         ce->ce_mode = 0;
477         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
478         return 1;
479 }
480
481 static int keep_entry(struct cache_entry *ce)
482 {
483         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD);
484         return 1;
485 }
486
487 #if DBRT_DEBUG
488 static void show_stage_entry(FILE *o,
489                              const char *label, const struct cache_entry *ce)
490 {
491         if (!ce)
492                 fprintf(o, "%s (missing)\n", label);
493         else
494                 fprintf(o, "%s%06o %s %d\t%s\n",
495                         label,
496                         ntohl(ce->ce_mode),
497                         sha1_to_hex(ce->sha1),
498                         ce_stage(ce),
499                         ce->name);
500 }
501 #endif
502
503 static int threeway_merge(struct cache_entry **stages)
504 {
505         struct cache_entry *index;
506         struct cache_entry *head; 
507         struct cache_entry *remote = stages[head_idx + 1];
508         int count;
509         int head_match = 0;
510         int remote_match = 0;
511         const char *path = NULL;
512
513         int df_conflict_head = 0;
514         int df_conflict_remote = 0;
515
516         int any_anc_missing = 0;
517         int no_anc_exists = 1;
518         int i;
519
520         for (i = 1; i < head_idx; i++) {
521                 if (!stages[i])
522                         any_anc_missing = 1;
523                 else {
524                         if (!path)
525                                 path = stages[i]->name;
526                         no_anc_exists = 0;
527                 }
528         }
529
530         index = stages[0];
531         head = stages[head_idx];
532
533         if (head == &df_conflict_entry) {
534                 df_conflict_head = 1;
535                 head = NULL;
536         }
537
538         if (remote == &df_conflict_entry) {
539                 df_conflict_remote = 1;
540                 remote = NULL;
541         }
542
543         if (!path && index)
544                 path = index->name;
545         if (!path && head)
546                 path = head->name;
547         if (!path && remote)
548                 path = remote->name;
549
550         /* First, if there's a #16 situation, note that to prevent #13
551          * and #14.
552          */
553         if (!same(remote, head)) {
554                 for (i = 1; i < head_idx; i++) {
555                         if (same(stages[i], head)) {
556                                 head_match = i;
557                         }
558                         if (same(stages[i], remote)) {
559                                 remote_match = i;
560                         }
561                 }
562         }
563
564         /* We start with cases where the index is allowed to match
565          * something other than the head: #14(ALT) and #2ALT, where it
566          * is permitted to match the result instead.
567          */
568         /* #14, #14ALT, #2ALT */
569         if (remote && !df_conflict_head && head_match && !remote_match) {
570                 if (index && !same(index, remote) && !same(index, head))
571                         reject_merge(index);
572                 return merged_entry(remote, index);
573         }
574         /*
575          * If we have an entry in the index cache, then we want to
576          * make sure that it matches head.
577          */
578         if (index && !same(index, head)) {
579                 reject_merge(index);
580         }
581
582         if (head) {
583                 /* #5ALT, #15 */
584                 if (same(head, remote))
585                         return merged_entry(head, index);
586                 /* #13, #3ALT */
587                 if (!df_conflict_remote && remote_match && !head_match)
588                         return merged_entry(head, index);
589         }
590
591         /* #1 */
592         if (!head && !remote && any_anc_missing)
593                 return 0;
594
595         /* Under the new "aggressive" rule, we resolve mostly trivial
596          * cases that we historically had git-merge-one-file resolve.
597          */
598         if (aggressive) {
599                 int head_deleted = !head && !df_conflict_head;
600                 int remote_deleted = !remote && !df_conflict_remote;
601                 /*
602                  * Deleted in both.
603                  * Deleted in one and unchanged in the other.
604                  */
605                 if ((head_deleted && remote_deleted) ||
606                     (head_deleted && remote && remote_match) ||
607                     (remote_deleted && head && head_match)) {
608                         if (index)
609                                 return deleted_entry(index, index);
610                         else if (path)
611                                 verify_absent(path, "removed");
612                         return 0;
613                 }
614                 /*
615                  * Added in both, identically.
616                  */
617                 if (no_anc_exists && head && remote && same(head, remote))
618                         return merged_entry(head, index);
619
620         }
621
622         /* Below are "no merge" cases, which require that the index be
623          * up-to-date to avoid the files getting overwritten with
624          * conflict resolution files. 
625          */
626         if (index) {
627                 verify_uptodate(index);
628         }
629         else if (path)
630                 verify_absent(path, "overwritten");
631
632         nontrivial_merge = 1;
633
634         /* #2, #3, #4, #6, #7, #9, #11. */
635         count = 0;
636         if (!head_match || !remote_match) {
637                 for (i = 1; i < head_idx; i++) {
638                         if (stages[i]) {
639                                 keep_entry(stages[i]);
640                                 count++;
641                                 break;
642                         }
643                 }
644         }
645 #if DBRT_DEBUG
646         else {
647                 fprintf(stderr, "read-tree: warning #16 detected\n");
648                 show_stage_entry(stderr, "head   ", stages[head_match]);
649                 show_stage_entry(stderr, "remote ", stages[remote_match]);
650         }
651 #endif
652         if (head) { count += keep_entry(head); }
653         if (remote) { count += keep_entry(remote); }
654         return count;
655 }
656
657 /*
658  * Two-way merge.
659  *
660  * The rule is to "carry forward" what is in the index without losing
661  * information across a "fast forward", favoring a successful merge
662  * over a merge failure when it makes sense.  For details of the
663  * "carry forward" rule, please see <Documentation/git-read-tree.txt>.
664  *
665  */
666 static int twoway_merge(struct cache_entry **src)
667 {
668         struct cache_entry *current = src[0];
669         struct cache_entry *oldtree = src[1], *newtree = src[2];
670
671         if (merge_size != 2)
672                 return error("Cannot do a twoway merge of %d trees",
673                              merge_size);
674
675         if (current) {
676                 if ((!oldtree && !newtree) || /* 4 and 5 */
677                     (!oldtree && newtree &&
678                      same(current, newtree)) || /* 6 and 7 */
679                     (oldtree && newtree &&
680                      same(oldtree, newtree)) || /* 14 and 15 */
681                     (oldtree && newtree &&
682                      !same(oldtree, newtree) && /* 18 and 19*/
683                      same(current, newtree))) {
684                         return keep_entry(current);
685                 }
686                 else if (oldtree && !newtree && same(current, oldtree)) {
687                         /* 10 or 11 */
688                         return deleted_entry(oldtree, current);
689                 }
690                 else if (oldtree && newtree &&
691                          same(current, oldtree) && !same(current, newtree)) {
692                         /* 20 or 21 */
693                         return merged_entry(newtree, current);
694                 }
695                 else {
696                         /* all other failures */
697                         if (oldtree)
698                                 reject_merge(oldtree);
699                         if (current)
700                                 reject_merge(current);
701                         if (newtree)
702                                 reject_merge(newtree);
703                         return -1;
704                 }
705         }
706         else if (newtree)
707                 return merged_entry(newtree, current);
708         else
709                 return deleted_entry(oldtree, current);
710 }
711
712 /*
713  * One-way merge.
714  *
715  * The rule is:
716  * - take the stat information from stage0, take the data from stage1
717  */
718 static int oneway_merge(struct cache_entry **src)
719 {
720         struct cache_entry *old = src[0];
721         struct cache_entry *a = src[1];
722
723         if (merge_size != 1)
724                 return error("Cannot do a oneway merge of %d trees",
725                              merge_size);
726
727         if (!a)
728                 return deleted_entry(old, old);
729         if (old && same(old, a)) {
730                 if (reset) {
731                         struct stat st;
732                         if (lstat(old->name, &st) ||
733                             ce_match_stat(old, &st, 1))
734                                 old->ce_flags |= htons(CE_UPDATE);
735                 }
736                 return keep_entry(old);
737         }
738         return merged_entry(a, old);
739 }
740
741 static int read_cache_unmerged(void)
742 {
743         int i, deleted;
744         struct cache_entry **dst;
745
746         read_cache();
747         dst = active_cache;
748         deleted = 0;
749         for (i = 0; i < active_nr; i++) {
750                 struct cache_entry *ce = active_cache[i];
751                 if (ce_stage(ce)) {
752                         deleted++;
753                         continue;
754                 }
755                 if (deleted)
756                         *dst = ce;
757                 dst++;
758         }
759         active_nr -= deleted;
760         return deleted;
761 }
762
763 static const char read_tree_usage[] = "git-read-tree (<sha> | -m [--aggressive] [-u | -i] <sha1> [<sha2> [<sha3>]])";
764
765 static struct cache_file cache_file;
766
767 int cmd_read_tree(int argc, const char **argv, char **envp)
768 {
769         int i, newfd, stage = 0;
770         unsigned char sha1[20];
771         merge_fn_t fn = NULL;
772
773         setup_git_directory();
774         git_config(git_default_config);
775
776         newfd = hold_index_file_for_update(&cache_file, get_index_file());
777         if (newfd < 0)
778                 die("unable to create new cachefile");
779
780         git_config(git_default_config);
781
782         merge = 0;
783         reset = 0;
784         for (i = 1; i < argc; i++) {
785                 const char *arg = argv[i];
786
787                 /* "-u" means "update", meaning that a merge will update
788                  * the working tree.
789                  */
790                 if (!strcmp(arg, "-u")) {
791                         update = 1;
792                         continue;
793                 }
794
795                 if (!strcmp(arg, "-v")) {
796                         verbose_update = 1;
797                         continue;
798                 }
799
800                 /* "-i" means "index only", meaning that a merge will
801                  * not even look at the working tree.
802                  */
803                 if (!strcmp(arg, "-i")) {
804                         index_only = 1;
805                         continue;
806                 }
807
808                 /* This differs from "-m" in that we'll silently ignore unmerged entries */
809                 if (!strcmp(arg, "--reset")) {
810                         if (stage || merge)
811                                 usage(read_tree_usage);
812                         reset = 1;
813                         merge = 1;
814                         stage = 1;
815                         read_cache_unmerged();
816                         continue;
817                 }
818
819                 if (!strcmp(arg, "--trivial")) {
820                         trivial_merges_only = 1;
821                         continue;
822                 }
823
824                 if (!strcmp(arg, "--aggressive")) {
825                         aggressive = 1;
826                         continue;
827                 }
828
829                 /* "-m" stands for "merge", meaning we start in stage 1 */
830                 if (!strcmp(arg, "-m")) {
831                         if (stage || merge)
832                                 usage(read_tree_usage);
833                         if (read_cache_unmerged())
834                                 die("you need to resolve your current index first");
835                         stage = 1;
836                         merge = 1;
837                         continue;
838                 }
839
840                 /* using -u and -i at the same time makes no sense */
841                 if (1 < index_only + update)
842                         usage(read_tree_usage);
843
844                 if (get_sha1(arg, sha1))
845                         die("Not a valid object name %s", arg);
846                 if (list_tree(sha1) < 0)
847                         die("failed to unpack tree object %s", arg);
848                 stage++;
849         }
850         if ((update||index_only) && !merge)
851                 usage(read_tree_usage);
852
853         if (merge) {
854                 if (stage < 2)
855                         die("just how do you expect me to merge %d trees?", stage-1);
856                 switch (stage - 1) {
857                 case 1:
858                         fn = oneway_merge;
859                         break;
860                 case 2:
861                         fn = twoway_merge;
862                         break;
863                 case 3:
864                         fn = threeway_merge;
865                         break;
866                 default:
867                         fn = threeway_merge;
868                         break;
869                 }
870
871                 if (stage - 1 >= 3)
872                         head_idx = stage - 2;
873                 else
874                         head_idx = 1;
875         }
876
877         unpack_trees(fn);
878         if (write_cache(newfd, active_cache, active_nr) ||
879             commit_index_file(&cache_file))
880                 die("unable to write new index file");
881         return 0;
882 }