format-patch: allow --interdiff to apply to a lone-patch
[git] / builtin / merge.c
1 /*
2  * Builtin "git merge"
3  *
4  * Copyright (c) 2008 Miklos Vajna <vmiklos@frugalware.org>
5  *
6  * Based on git-merge.sh by Junio C Hamano.
7  */
8
9 #include "cache.h"
10 #include "config.h"
11 #include "parse-options.h"
12 #include "builtin.h"
13 #include "lockfile.h"
14 #include "run-command.h"
15 #include "diff.h"
16 #include "refs.h"
17 #include "refspec.h"
18 #include "commit.h"
19 #include "diffcore.h"
20 #include "revision.h"
21 #include "unpack-trees.h"
22 #include "cache-tree.h"
23 #include "dir.h"
24 #include "utf8.h"
25 #include "log-tree.h"
26 #include "color.h"
27 #include "rerere.h"
28 #include "help.h"
29 #include "merge-recursive.h"
30 #include "resolve-undo.h"
31 #include "remote.h"
32 #include "fmt-merge-msg.h"
33 #include "gpg-interface.h"
34 #include "sequencer.h"
35 #include "string-list.h"
36 #include "packfile.h"
37 #include "tag.h"
38 #include "alias.h"
39
40 #define DEFAULT_TWOHEAD (1<<0)
41 #define DEFAULT_OCTOPUS (1<<1)
42 #define NO_FAST_FORWARD (1<<2)
43 #define NO_TRIVIAL      (1<<3)
44
45 struct strategy {
46         const char *name;
47         unsigned attr;
48 };
49
50 static const char * const builtin_merge_usage[] = {
51         N_("git merge [<options>] [<commit>...]"),
52         N_("git merge --abort"),
53         N_("git merge --continue"),
54         NULL
55 };
56
57 static int show_diffstat = 1, shortlog_len = -1, squash;
58 static int option_commit = 1;
59 static int option_edit = -1;
60 static int allow_trivial = 1, have_message, verify_signatures;
61 static int overwrite_ignore = 1;
62 static struct strbuf merge_msg = STRBUF_INIT;
63 static struct strategy **use_strategies;
64 static size_t use_strategies_nr, use_strategies_alloc;
65 static const char **xopts;
66 static size_t xopts_nr, xopts_alloc;
67 static const char *branch;
68 static char *branch_mergeoptions;
69 static int option_renormalize;
70 static int verbosity;
71 static int allow_rerere_auto;
72 static int abort_current_merge;
73 static int continue_current_merge;
74 static int allow_unrelated_histories;
75 static int show_progress = -1;
76 static int default_to_upstream = 1;
77 static int signoff;
78 static const char *sign_commit;
79 static int verify_msg = 1;
80
81 static struct strategy all_strategy[] = {
82         { "recursive",  DEFAULT_TWOHEAD | NO_TRIVIAL },
83         { "octopus",    DEFAULT_OCTOPUS },
84         { "resolve",    0 },
85         { "ours",       NO_FAST_FORWARD | NO_TRIVIAL },
86         { "subtree",    NO_FAST_FORWARD | NO_TRIVIAL },
87 };
88
89 static const char *pull_twohead, *pull_octopus;
90
91 enum ff_type {
92         FF_NO,
93         FF_ALLOW,
94         FF_ONLY
95 };
96
97 static enum ff_type fast_forward = FF_ALLOW;
98
99 static int option_parse_message(const struct option *opt,
100                                 const char *arg, int unset)
101 {
102         struct strbuf *buf = opt->value;
103
104         if (unset)
105                 strbuf_setlen(buf, 0);
106         else if (arg) {
107                 strbuf_addf(buf, "%s%s", buf->len ? "\n\n" : "", arg);
108                 have_message = 1;
109         } else
110                 return error(_("switch `m' requires a value"));
111         return 0;
112 }
113
114 static struct strategy *get_strategy(const char *name)
115 {
116         int i;
117         struct strategy *ret;
118         static struct cmdnames main_cmds, other_cmds;
119         static int loaded;
120
121         if (!name)
122                 return NULL;
123
124         for (i = 0; i < ARRAY_SIZE(all_strategy); i++)
125                 if (!strcmp(name, all_strategy[i].name))
126                         return &all_strategy[i];
127
128         if (!loaded) {
129                 struct cmdnames not_strategies;
130                 loaded = 1;
131
132                 memset(&not_strategies, 0, sizeof(struct cmdnames));
133                 load_command_list("git-merge-", &main_cmds, &other_cmds);
134                 for (i = 0; i < main_cmds.cnt; i++) {
135                         int j, found = 0;
136                         struct cmdname *ent = main_cmds.names[i];
137                         for (j = 0; j < ARRAY_SIZE(all_strategy); j++)
138                                 if (!strncmp(ent->name, all_strategy[j].name, ent->len)
139                                                 && !all_strategy[j].name[ent->len])
140                                         found = 1;
141                         if (!found)
142                                 add_cmdname(&not_strategies, ent->name, ent->len);
143                 }
144                 exclude_cmds(&main_cmds, &not_strategies);
145         }
146         if (!is_in_cmdlist(&main_cmds, name) && !is_in_cmdlist(&other_cmds, name)) {
147                 fprintf(stderr, _("Could not find merge strategy '%s'.\n"), name);
148                 fprintf(stderr, _("Available strategies are:"));
149                 for (i = 0; i < main_cmds.cnt; i++)
150                         fprintf(stderr, " %s", main_cmds.names[i]->name);
151                 fprintf(stderr, ".\n");
152                 if (other_cmds.cnt) {
153                         fprintf(stderr, _("Available custom strategies are:"));
154                         for (i = 0; i < other_cmds.cnt; i++)
155                                 fprintf(stderr, " %s", other_cmds.names[i]->name);
156                         fprintf(stderr, ".\n");
157                 }
158                 exit(1);
159         }
160
161         ret = xcalloc(1, sizeof(struct strategy));
162         ret->name = xstrdup(name);
163         ret->attr = NO_TRIVIAL;
164         return ret;
165 }
166
167 static void append_strategy(struct strategy *s)
168 {
169         ALLOC_GROW(use_strategies, use_strategies_nr + 1, use_strategies_alloc);
170         use_strategies[use_strategies_nr++] = s;
171 }
172
173 static int option_parse_strategy(const struct option *opt,
174                                  const char *name, int unset)
175 {
176         if (unset)
177                 return 0;
178
179         append_strategy(get_strategy(name));
180         return 0;
181 }
182
183 static int option_parse_x(const struct option *opt,
184                           const char *arg, int unset)
185 {
186         if (unset)
187                 return 0;
188
189         ALLOC_GROW(xopts, xopts_nr + 1, xopts_alloc);
190         xopts[xopts_nr++] = xstrdup(arg);
191         return 0;
192 }
193
194 static int option_parse_n(const struct option *opt,
195                           const char *arg, int unset)
196 {
197         show_diffstat = unset;
198         return 0;
199 }
200
201 static struct option builtin_merge_options[] = {
202         { OPTION_CALLBACK, 'n', NULL, NULL, NULL,
203                 N_("do not show a diffstat at the end of the merge"),
204                 PARSE_OPT_NOARG, option_parse_n },
205         OPT_BOOL(0, "stat", &show_diffstat,
206                 N_("show a diffstat at the end of the merge")),
207         OPT_BOOL(0, "summary", &show_diffstat, N_("(synonym to --stat)")),
208         { OPTION_INTEGER, 0, "log", &shortlog_len, N_("n"),
209           N_("add (at most <n>) entries from shortlog to merge commit message"),
210           PARSE_OPT_OPTARG, NULL, DEFAULT_MERGE_LOG_LEN },
211         OPT_BOOL(0, "squash", &squash,
212                 N_("create a single commit instead of doing a merge")),
213         OPT_BOOL(0, "commit", &option_commit,
214                 N_("perform a commit if the merge succeeds (default)")),
215         OPT_BOOL('e', "edit", &option_edit,
216                 N_("edit message before committing")),
217         OPT_SET_INT(0, "ff", &fast_forward, N_("allow fast-forward (default)"), FF_ALLOW),
218         OPT_SET_INT_F(0, "ff-only", &fast_forward,
219                       N_("abort if fast-forward is not possible"),
220                       FF_ONLY, PARSE_OPT_NONEG),
221         OPT_RERERE_AUTOUPDATE(&allow_rerere_auto),
222         OPT_BOOL(0, "verify-signatures", &verify_signatures,
223                 N_("verify that the named commit has a valid GPG signature")),
224         OPT_CALLBACK('s', "strategy", &use_strategies, N_("strategy"),
225                 N_("merge strategy to use"), option_parse_strategy),
226         OPT_CALLBACK('X', "strategy-option", &xopts, N_("option=value"),
227                 N_("option for selected merge strategy"), option_parse_x),
228         OPT_CALLBACK('m', "message", &merge_msg, N_("message"),
229                 N_("merge commit message (for a non-fast-forward merge)"),
230                 option_parse_message),
231         OPT__VERBOSITY(&verbosity),
232         OPT_BOOL(0, "abort", &abort_current_merge,
233                 N_("abort the current in-progress merge")),
234         OPT_BOOL(0, "continue", &continue_current_merge,
235                 N_("continue the current in-progress merge")),
236         OPT_BOOL(0, "allow-unrelated-histories", &allow_unrelated_histories,
237                  N_("allow merging unrelated histories")),
238         OPT_SET_INT(0, "progress", &show_progress, N_("force progress reporting"), 1),
239         { OPTION_STRING, 'S', "gpg-sign", &sign_commit, N_("key-id"),
240           N_("GPG sign commit"), PARSE_OPT_OPTARG, NULL, (intptr_t) "" },
241         OPT_BOOL(0, "overwrite-ignore", &overwrite_ignore, N_("update ignored files (default)")),
242         OPT_BOOL(0, "signoff", &signoff, N_("add Signed-off-by:")),
243         OPT_BOOL(0, "verify", &verify_msg, N_("verify commit-msg hook")),
244         OPT_END()
245 };
246
247 /* Cleans up metadata that is uninteresting after a succeeded merge. */
248 static void drop_save(void)
249 {
250         unlink(git_path_merge_head(the_repository));
251         unlink(git_path_merge_msg(the_repository));
252         unlink(git_path_merge_mode(the_repository));
253 }
254
255 static int save_state(struct object_id *stash)
256 {
257         int len;
258         struct child_process cp = CHILD_PROCESS_INIT;
259         struct strbuf buffer = STRBUF_INIT;
260         const char *argv[] = {"stash", "create", NULL};
261         int rc = -1;
262
263         cp.argv = argv;
264         cp.out = -1;
265         cp.git_cmd = 1;
266
267         if (start_command(&cp))
268                 die(_("could not run stash."));
269         len = strbuf_read(&buffer, cp.out, 1024);
270         close(cp.out);
271
272         if (finish_command(&cp) || len < 0)
273                 die(_("stash failed"));
274         else if (!len)          /* no changes */
275                 goto out;
276         strbuf_setlen(&buffer, buffer.len-1);
277         if (get_oid(buffer.buf, stash))
278                 die(_("not a valid object: %s"), buffer.buf);
279         rc = 0;
280 out:
281         strbuf_release(&buffer);
282         return rc;
283 }
284
285 static void read_empty(const struct object_id *oid, int verbose)
286 {
287         int i = 0;
288         const char *args[7];
289
290         args[i++] = "read-tree";
291         if (verbose)
292                 args[i++] = "-v";
293         args[i++] = "-m";
294         args[i++] = "-u";
295         args[i++] = empty_tree_oid_hex();
296         args[i++] = oid_to_hex(oid);
297         args[i] = NULL;
298
299         if (run_command_v_opt(args, RUN_GIT_CMD))
300                 die(_("read-tree failed"));
301 }
302
303 static void reset_hard(const struct object_id *oid, int verbose)
304 {
305         int i = 0;
306         const char *args[6];
307
308         args[i++] = "read-tree";
309         if (verbose)
310                 args[i++] = "-v";
311         args[i++] = "--reset";
312         args[i++] = "-u";
313         args[i++] = oid_to_hex(oid);
314         args[i] = NULL;
315
316         if (run_command_v_opt(args, RUN_GIT_CMD))
317                 die(_("read-tree failed"));
318 }
319
320 static void restore_state(const struct object_id *head,
321                           const struct object_id *stash)
322 {
323         struct strbuf sb = STRBUF_INIT;
324         const char *args[] = { "stash", "apply", NULL, NULL };
325
326         if (is_null_oid(stash))
327                 return;
328
329         reset_hard(head, 1);
330
331         args[2] = oid_to_hex(stash);
332
333         /*
334          * It is OK to ignore error here, for example when there was
335          * nothing to restore.
336          */
337         run_command_v_opt(args, RUN_GIT_CMD);
338
339         strbuf_release(&sb);
340         refresh_cache(REFRESH_QUIET);
341 }
342
343 /* This is called when no merge was necessary. */
344 static void finish_up_to_date(const char *msg)
345 {
346         if (verbosity >= 0)
347                 printf("%s%s\n", squash ? _(" (nothing to squash)") : "", msg);
348         drop_save();
349 }
350
351 static void squash_message(struct commit *commit, struct commit_list *remoteheads)
352 {
353         struct rev_info rev;
354         struct strbuf out = STRBUF_INIT;
355         struct commit_list *j;
356         struct pretty_print_context ctx = {0};
357
358         printf(_("Squash commit -- not updating HEAD\n"));
359
360         init_revisions(&rev, NULL);
361         rev.ignore_merges = 1;
362         rev.commit_format = CMIT_FMT_MEDIUM;
363
364         commit->object.flags |= UNINTERESTING;
365         add_pending_object(&rev, &commit->object, NULL);
366
367         for (j = remoteheads; j; j = j->next)
368                 add_pending_object(&rev, &j->item->object, NULL);
369
370         setup_revisions(0, NULL, &rev, NULL);
371         if (prepare_revision_walk(&rev))
372                 die(_("revision walk setup failed"));
373
374         ctx.abbrev = rev.abbrev;
375         ctx.date_mode = rev.date_mode;
376         ctx.fmt = rev.commit_format;
377
378         strbuf_addstr(&out, "Squashed commit of the following:\n");
379         while ((commit = get_revision(&rev)) != NULL) {
380                 strbuf_addch(&out, '\n');
381                 strbuf_addf(&out, "commit %s\n",
382                         oid_to_hex(&commit->object.oid));
383                 pretty_print_commit(&ctx, commit, &out);
384         }
385         write_file_buf(git_path_squash_msg(the_repository), out.buf, out.len);
386         strbuf_release(&out);
387 }
388
389 static void finish(struct commit *head_commit,
390                    struct commit_list *remoteheads,
391                    const struct object_id *new_head, const char *msg)
392 {
393         struct strbuf reflog_message = STRBUF_INIT;
394         const struct object_id *head = &head_commit->object.oid;
395
396         if (!msg)
397                 strbuf_addstr(&reflog_message, getenv("GIT_REFLOG_ACTION"));
398         else {
399                 if (verbosity >= 0)
400                         printf("%s\n", msg);
401                 strbuf_addf(&reflog_message, "%s: %s",
402                         getenv("GIT_REFLOG_ACTION"), msg);
403         }
404         if (squash) {
405                 squash_message(head_commit, remoteheads);
406         } else {
407                 if (verbosity >= 0 && !merge_msg.len)
408                         printf(_("No merge message -- not updating HEAD\n"));
409                 else {
410                         const char *argv_gc_auto[] = { "gc", "--auto", NULL };
411                         update_ref(reflog_message.buf, "HEAD", new_head, head,
412                                    0, UPDATE_REFS_DIE_ON_ERR);
413                         /*
414                          * We ignore errors in 'gc --auto', since the
415                          * user should see them.
416                          */
417                         close_all_packs(the_repository->objects);
418                         run_command_v_opt(argv_gc_auto, RUN_GIT_CMD);
419                 }
420         }
421         if (new_head && show_diffstat) {
422                 struct diff_options opts;
423                 diff_setup(&opts);
424                 opts.stat_width = -1; /* use full terminal width */
425                 opts.stat_graph_width = -1; /* respect statGraphWidth config */
426                 opts.output_format |=
427                         DIFF_FORMAT_SUMMARY | DIFF_FORMAT_DIFFSTAT;
428                 opts.detect_rename = DIFF_DETECT_RENAME;
429                 diff_setup_done(&opts);
430                 diff_tree_oid(head, new_head, "", &opts);
431                 diffcore_std(&opts);
432                 diff_flush(&opts);
433         }
434
435         /* Run a post-merge hook */
436         run_hook_le(NULL, "post-merge", squash ? "1" : "0", NULL);
437
438         strbuf_release(&reflog_message);
439 }
440
441 /* Get the name for the merge commit's message. */
442 static void merge_name(const char *remote, struct strbuf *msg)
443 {
444         struct commit *remote_head;
445         struct object_id branch_head;
446         struct strbuf buf = STRBUF_INIT;
447         struct strbuf bname = STRBUF_INIT;
448         struct merge_remote_desc *desc;
449         const char *ptr;
450         char *found_ref;
451         int len, early;
452
453         strbuf_branchname(&bname, remote, 0);
454         remote = bname.buf;
455
456         oidclr(&branch_head);
457         remote_head = get_merge_parent(remote);
458         if (!remote_head)
459                 die(_("'%s' does not point to a commit"), remote);
460
461         if (dwim_ref(remote, strlen(remote), &branch_head, &found_ref) > 0) {
462                 if (starts_with(found_ref, "refs/heads/")) {
463                         strbuf_addf(msg, "%s\t\tbranch '%s' of .\n",
464                                     oid_to_hex(&branch_head), remote);
465                         goto cleanup;
466                 }
467                 if (starts_with(found_ref, "refs/tags/")) {
468                         strbuf_addf(msg, "%s\t\ttag '%s' of .\n",
469                                     oid_to_hex(&branch_head), remote);
470                         goto cleanup;
471                 }
472                 if (starts_with(found_ref, "refs/remotes/")) {
473                         strbuf_addf(msg, "%s\t\tremote-tracking branch '%s' of .\n",
474                                     oid_to_hex(&branch_head), remote);
475                         goto cleanup;
476                 }
477         }
478
479         /* See if remote matches <name>^^^.. or <name>~<number> */
480         for (len = 0, ptr = remote + strlen(remote);
481              remote < ptr && ptr[-1] == '^';
482              ptr--)
483                 len++;
484         if (len)
485                 early = 1;
486         else {
487                 early = 0;
488                 ptr = strrchr(remote, '~');
489                 if (ptr) {
490                         int seen_nonzero = 0;
491
492                         len++; /* count ~ */
493                         while (*++ptr && isdigit(*ptr)) {
494                                 seen_nonzero |= (*ptr != '0');
495                                 len++;
496                         }
497                         if (*ptr)
498                                 len = 0; /* not ...~<number> */
499                         else if (seen_nonzero)
500                                 early = 1;
501                         else if (len == 1)
502                                 early = 1; /* "name~" is "name~1"! */
503                 }
504         }
505         if (len) {
506                 struct strbuf truname = STRBUF_INIT;
507                 strbuf_addf(&truname, "refs/heads/%s", remote);
508                 strbuf_setlen(&truname, truname.len - len);
509                 if (ref_exists(truname.buf)) {
510                         strbuf_addf(msg,
511                                     "%s\t\tbranch '%s'%s of .\n",
512                                     oid_to_hex(&remote_head->object.oid),
513                                     truname.buf + 11,
514                                     (early ? " (early part)" : ""));
515                         strbuf_release(&truname);
516                         goto cleanup;
517                 }
518                 strbuf_release(&truname);
519         }
520
521         desc = merge_remote_util(remote_head);
522         if (desc && desc->obj && desc->obj->type == OBJ_TAG) {
523                 strbuf_addf(msg, "%s\t\t%s '%s'\n",
524                             oid_to_hex(&desc->obj->oid),
525                             type_name(desc->obj->type),
526                             remote);
527                 goto cleanup;
528         }
529
530         strbuf_addf(msg, "%s\t\tcommit '%s'\n",
531                 oid_to_hex(&remote_head->object.oid), remote);
532 cleanup:
533         strbuf_release(&buf);
534         strbuf_release(&bname);
535 }
536
537 static void parse_branch_merge_options(char *bmo)
538 {
539         const char **argv;
540         int argc;
541
542         if (!bmo)
543                 return;
544         argc = split_cmdline(bmo, &argv);
545         if (argc < 0)
546                 die(_("Bad branch.%s.mergeoptions string: %s"), branch,
547                     split_cmdline_strerror(argc));
548         REALLOC_ARRAY(argv, argc + 2);
549         MOVE_ARRAY(argv + 1, argv, argc + 1);
550         argc++;
551         argv[0] = "branch.*.mergeoptions";
552         parse_options(argc, argv, NULL, builtin_merge_options,
553                       builtin_merge_usage, 0);
554         free(argv);
555 }
556
557 static int git_merge_config(const char *k, const char *v, void *cb)
558 {
559         int status;
560
561         if (branch && starts_with(k, "branch.") &&
562                 starts_with(k + 7, branch) &&
563                 !strcmp(k + 7 + strlen(branch), ".mergeoptions")) {
564                 free(branch_mergeoptions);
565                 branch_mergeoptions = xstrdup(v);
566                 return 0;
567         }
568
569         if (!strcmp(k, "merge.diffstat") || !strcmp(k, "merge.stat"))
570                 show_diffstat = git_config_bool(k, v);
571         else if (!strcmp(k, "merge.verifysignatures"))
572                 verify_signatures = git_config_bool(k, v);
573         else if (!strcmp(k, "pull.twohead"))
574                 return git_config_string(&pull_twohead, k, v);
575         else if (!strcmp(k, "pull.octopus"))
576                 return git_config_string(&pull_octopus, k, v);
577         else if (!strcmp(k, "merge.renormalize"))
578                 option_renormalize = git_config_bool(k, v);
579         else if (!strcmp(k, "merge.ff")) {
580                 int boolval = git_parse_maybe_bool(v);
581                 if (0 <= boolval) {
582                         fast_forward = boolval ? FF_ALLOW : FF_NO;
583                 } else if (v && !strcmp(v, "only")) {
584                         fast_forward = FF_ONLY;
585                 } /* do not barf on values from future versions of git */
586                 return 0;
587         } else if (!strcmp(k, "merge.defaulttoupstream")) {
588                 default_to_upstream = git_config_bool(k, v);
589                 return 0;
590         } else if (!strcmp(k, "commit.gpgsign")) {
591                 sign_commit = git_config_bool(k, v) ? "" : NULL;
592                 return 0;
593         }
594
595         status = fmt_merge_msg_config(k, v, cb);
596         if (status)
597                 return status;
598         status = git_gpg_config(k, v, NULL);
599         if (status)
600                 return status;
601         return git_diff_ui_config(k, v, cb);
602 }
603
604 static int read_tree_trivial(struct object_id *common, struct object_id *head,
605                              struct object_id *one)
606 {
607         int i, nr_trees = 0;
608         struct tree *trees[MAX_UNPACK_TREES];
609         struct tree_desc t[MAX_UNPACK_TREES];
610         struct unpack_trees_options opts;
611
612         memset(&opts, 0, sizeof(opts));
613         opts.head_idx = 2;
614         opts.src_index = &the_index;
615         opts.dst_index = &the_index;
616         opts.update = 1;
617         opts.verbose_update = 1;
618         opts.trivial_merges_only = 1;
619         opts.merge = 1;
620         trees[nr_trees] = parse_tree_indirect(common);
621         if (!trees[nr_trees++])
622                 return -1;
623         trees[nr_trees] = parse_tree_indirect(head);
624         if (!trees[nr_trees++])
625                 return -1;
626         trees[nr_trees] = parse_tree_indirect(one);
627         if (!trees[nr_trees++])
628                 return -1;
629         opts.fn = threeway_merge;
630         cache_tree_free(&active_cache_tree);
631         for (i = 0; i < nr_trees; i++) {
632                 parse_tree(trees[i]);
633                 init_tree_desc(t+i, trees[i]->buffer, trees[i]->size);
634         }
635         if (unpack_trees(nr_trees, t, &opts))
636                 return -1;
637         return 0;
638 }
639
640 static void write_tree_trivial(struct object_id *oid)
641 {
642         if (write_cache_as_tree(oid, 0, NULL))
643                 die(_("git write-tree failed to write a tree"));
644 }
645
646 static int try_merge_strategy(const char *strategy, struct commit_list *common,
647                               struct commit_list *remoteheads,
648                               struct commit *head)
649 {
650         struct lock_file lock = LOCK_INIT;
651         const char *head_arg = "HEAD";
652
653         hold_locked_index(&lock, LOCK_DIE_ON_ERROR);
654         refresh_cache(REFRESH_QUIET);
655         if (write_locked_index(&the_index, &lock,
656                                COMMIT_LOCK | SKIP_IF_UNCHANGED))
657                 return error(_("Unable to write index."));
658
659         if (!strcmp(strategy, "recursive") || !strcmp(strategy, "subtree")) {
660                 int clean, x;
661                 struct commit *result;
662                 struct commit_list *reversed = NULL;
663                 struct merge_options o;
664                 struct commit_list *j;
665
666                 if (remoteheads->next) {
667                         error(_("Not handling anything other than two heads merge."));
668                         return 2;
669                 }
670
671                 init_merge_options(&o);
672                 if (!strcmp(strategy, "subtree"))
673                         o.subtree_shift = "";
674
675                 o.renormalize = option_renormalize;
676                 o.show_rename_progress =
677                         show_progress == -1 ? isatty(2) : show_progress;
678
679                 for (x = 0; x < xopts_nr; x++)
680                         if (parse_merge_opt(&o, xopts[x]))
681                                 die(_("Unknown option for merge-recursive: -X%s"), xopts[x]);
682
683                 o.branch1 = head_arg;
684                 o.branch2 = merge_remote_util(remoteheads->item)->name;
685
686                 for (j = common; j; j = j->next)
687                         commit_list_insert(j->item, &reversed);
688
689                 hold_locked_index(&lock, LOCK_DIE_ON_ERROR);
690                 clean = merge_recursive(&o, head,
691                                 remoteheads->item, reversed, &result);
692                 if (clean < 0)
693                         exit(128);
694                 if (write_locked_index(&the_index, &lock,
695                                        COMMIT_LOCK | SKIP_IF_UNCHANGED))
696                         die (_("unable to write %s"), get_index_file());
697                 return clean ? 0 : 1;
698         } else {
699                 return try_merge_command(strategy, xopts_nr, xopts,
700                                                 common, head_arg, remoteheads);
701         }
702 }
703
704 static void count_diff_files(struct diff_queue_struct *q,
705                              struct diff_options *opt, void *data)
706 {
707         int *count = data;
708
709         (*count) += q->nr;
710 }
711
712 static int count_unmerged_entries(void)
713 {
714         int i, ret = 0;
715
716         for (i = 0; i < active_nr; i++)
717                 if (ce_stage(active_cache[i]))
718                         ret++;
719
720         return ret;
721 }
722
723 static void add_strategies(const char *string, unsigned attr)
724 {
725         int i;
726
727         if (string) {
728                 struct string_list list = STRING_LIST_INIT_DUP;
729                 struct string_list_item *item;
730                 string_list_split(&list, string, ' ', -1);
731                 for_each_string_list_item(item, &list)
732                         append_strategy(get_strategy(item->string));
733                 string_list_clear(&list, 0);
734                 return;
735         }
736         for (i = 0; i < ARRAY_SIZE(all_strategy); i++)
737                 if (all_strategy[i].attr & attr)
738                         append_strategy(&all_strategy[i]);
739
740 }
741
742 static void read_merge_msg(struct strbuf *msg)
743 {
744         const char *filename = git_path_merge_msg(the_repository);
745         strbuf_reset(msg);
746         if (strbuf_read_file(msg, filename, 0) < 0)
747                 die_errno(_("Could not read from '%s'"), filename);
748 }
749
750 static void write_merge_state(struct commit_list *);
751 static void abort_commit(struct commit_list *remoteheads, const char *err_msg)
752 {
753         if (err_msg)
754                 error("%s", err_msg);
755         fprintf(stderr,
756                 _("Not committing merge; use 'git commit' to complete the merge.\n"));
757         write_merge_state(remoteheads);
758         exit(1);
759 }
760
761 static const char merge_editor_comment[] =
762 N_("Please enter a commit message to explain why this merge is necessary,\n"
763    "especially if it merges an updated upstream into a topic branch.\n"
764    "\n"
765    "Lines starting with '%c' will be ignored, and an empty message aborts\n"
766    "the commit.\n");
767
768 static void write_merge_heads(struct commit_list *);
769 static void prepare_to_commit(struct commit_list *remoteheads)
770 {
771         struct strbuf msg = STRBUF_INIT;
772         strbuf_addbuf(&msg, &merge_msg);
773         strbuf_addch(&msg, '\n');
774         if (squash)
775                 BUG("the control must not reach here under --squash");
776         if (0 < option_edit)
777                 strbuf_commented_addf(&msg, _(merge_editor_comment), comment_line_char);
778         if (signoff)
779                 append_signoff(&msg, ignore_non_trailer(msg.buf, msg.len), 0);
780         write_merge_heads(remoteheads);
781         write_file_buf(git_path_merge_msg(the_repository), msg.buf, msg.len);
782         if (run_commit_hook(0 < option_edit, get_index_file(), "prepare-commit-msg",
783                             git_path_merge_msg(the_repository), "merge", NULL))
784                 abort_commit(remoteheads, NULL);
785         if (0 < option_edit) {
786                 if (launch_editor(git_path_merge_msg(the_repository), NULL, NULL))
787                         abort_commit(remoteheads, NULL);
788         }
789
790         if (verify_msg && run_commit_hook(0 < option_edit, get_index_file(),
791                                           "commit-msg",
792                                           git_path_merge_msg(the_repository), NULL))
793                 abort_commit(remoteheads, NULL);
794
795         read_merge_msg(&msg);
796         strbuf_stripspace(&msg, 0 < option_edit);
797         if (!msg.len)
798                 abort_commit(remoteheads, _("Empty commit message."));
799         strbuf_release(&merge_msg);
800         strbuf_addbuf(&merge_msg, &msg);
801         strbuf_release(&msg);
802 }
803
804 static int merge_trivial(struct commit *head, struct commit_list *remoteheads)
805 {
806         struct object_id result_tree, result_commit;
807         struct commit_list *parents, **pptr = &parents;
808         struct lock_file lock = LOCK_INIT;
809
810         hold_locked_index(&lock, LOCK_DIE_ON_ERROR);
811         refresh_cache(REFRESH_QUIET);
812         if (write_locked_index(&the_index, &lock,
813                                COMMIT_LOCK | SKIP_IF_UNCHANGED))
814                 return error(_("Unable to write index."));
815
816         write_tree_trivial(&result_tree);
817         printf(_("Wonderful.\n"));
818         pptr = commit_list_append(head, pptr);
819         pptr = commit_list_append(remoteheads->item, pptr);
820         prepare_to_commit(remoteheads);
821         if (commit_tree(merge_msg.buf, merge_msg.len, &result_tree, parents,
822                         &result_commit, NULL, sign_commit))
823                 die(_("failed to write commit object"));
824         finish(head, remoteheads, &result_commit, "In-index merge");
825         drop_save();
826         return 0;
827 }
828
829 static int finish_automerge(struct commit *head,
830                             int head_subsumed,
831                             struct commit_list *common,
832                             struct commit_list *remoteheads,
833                             struct object_id *result_tree,
834                             const char *wt_strategy)
835 {
836         struct commit_list *parents = NULL;
837         struct strbuf buf = STRBUF_INIT;
838         struct object_id result_commit;
839
840         free_commit_list(common);
841         parents = remoteheads;
842         if (!head_subsumed || fast_forward == FF_NO)
843                 commit_list_insert(head, &parents);
844         strbuf_addch(&merge_msg, '\n');
845         prepare_to_commit(remoteheads);
846         if (commit_tree(merge_msg.buf, merge_msg.len, result_tree, parents,
847                         &result_commit, NULL, sign_commit))
848                 die(_("failed to write commit object"));
849         strbuf_addf(&buf, "Merge made by the '%s' strategy.", wt_strategy);
850         finish(head, remoteheads, &result_commit, buf.buf);
851         strbuf_release(&buf);
852         drop_save();
853         return 0;
854 }
855
856 static int suggest_conflicts(void)
857 {
858         const char *filename;
859         FILE *fp;
860         struct strbuf msgbuf = STRBUF_INIT;
861
862         filename = git_path_merge_msg(the_repository);
863         fp = xfopen(filename, "a");
864
865         append_conflicts_hint(&msgbuf);
866         fputs(msgbuf.buf, fp);
867         strbuf_release(&msgbuf);
868         fclose(fp);
869         rerere(allow_rerere_auto);
870         printf(_("Automatic merge failed; "
871                         "fix conflicts and then commit the result.\n"));
872         return 1;
873 }
874
875 static int evaluate_result(void)
876 {
877         int cnt = 0;
878         struct rev_info rev;
879
880         /* Check how many files differ. */
881         init_revisions(&rev, "");
882         setup_revisions(0, NULL, &rev, NULL);
883         rev.diffopt.output_format |=
884                 DIFF_FORMAT_CALLBACK;
885         rev.diffopt.format_callback = count_diff_files;
886         rev.diffopt.format_callback_data = &cnt;
887         run_diff_files(&rev, 0);
888
889         /*
890          * Check how many unmerged entries are
891          * there.
892          */
893         cnt += count_unmerged_entries();
894
895         return cnt;
896 }
897
898 /*
899  * Pretend as if the user told us to merge with the remote-tracking
900  * branch we have for the upstream of the current branch
901  */
902 static int setup_with_upstream(const char ***argv)
903 {
904         struct branch *branch = branch_get(NULL);
905         int i;
906         const char **args;
907
908         if (!branch)
909                 die(_("No current branch."));
910         if (!branch->remote_name)
911                 die(_("No remote for the current branch."));
912         if (!branch->merge_nr)
913                 die(_("No default upstream defined for the current branch."));
914
915         args = xcalloc(st_add(branch->merge_nr, 1), sizeof(char *));
916         for (i = 0; i < branch->merge_nr; i++) {
917                 if (!branch->merge[i]->dst)
918                         die(_("No remote-tracking branch for %s from %s"),
919                             branch->merge[i]->src, branch->remote_name);
920                 args[i] = branch->merge[i]->dst;
921         }
922         args[i] = NULL;
923         *argv = args;
924         return i;
925 }
926
927 static void write_merge_heads(struct commit_list *remoteheads)
928 {
929         struct commit_list *j;
930         struct strbuf buf = STRBUF_INIT;
931
932         for (j = remoteheads; j; j = j->next) {
933                 struct object_id *oid;
934                 struct commit *c = j->item;
935                 struct merge_remote_desc *desc;
936
937                 desc = merge_remote_util(c);
938                 if (desc && desc->obj) {
939                         oid = &desc->obj->oid;
940                 } else {
941                         oid = &c->object.oid;
942                 }
943                 strbuf_addf(&buf, "%s\n", oid_to_hex(oid));
944         }
945         write_file_buf(git_path_merge_head(the_repository), buf.buf, buf.len);
946
947         strbuf_reset(&buf);
948         if (fast_forward == FF_NO)
949                 strbuf_addstr(&buf, "no-ff");
950         write_file_buf(git_path_merge_mode(the_repository), buf.buf, buf.len);
951         strbuf_release(&buf);
952 }
953
954 static void write_merge_state(struct commit_list *remoteheads)
955 {
956         write_merge_heads(remoteheads);
957         strbuf_addch(&merge_msg, '\n');
958         write_file_buf(git_path_merge_msg(the_repository), merge_msg.buf,
959                        merge_msg.len);
960 }
961
962 static int default_edit_option(void)
963 {
964         static const char name[] = "GIT_MERGE_AUTOEDIT";
965         const char *e = getenv(name);
966         struct stat st_stdin, st_stdout;
967
968         if (have_message)
969                 /* an explicit -m msg without --[no-]edit */
970                 return 0;
971
972         if (e) {
973                 int v = git_parse_maybe_bool(e);
974                 if (v < 0)
975                         die(_("Bad value '%s' in environment '%s'"), e, name);
976                 return v;
977         }
978
979         /* Use editor if stdin and stdout are the same and is a tty */
980         return (!fstat(0, &st_stdin) &&
981                 !fstat(1, &st_stdout) &&
982                 isatty(0) && isatty(1) &&
983                 st_stdin.st_dev == st_stdout.st_dev &&
984                 st_stdin.st_ino == st_stdout.st_ino &&
985                 st_stdin.st_mode == st_stdout.st_mode);
986 }
987
988 static struct commit_list *reduce_parents(struct commit *head_commit,
989                                           int *head_subsumed,
990                                           struct commit_list *remoteheads)
991 {
992         struct commit_list *parents, **remotes;
993
994         /*
995          * Is the current HEAD reachable from another commit being
996          * merged?  If so we do not want to record it as a parent of
997          * the resulting merge, unless --no-ff is given.  We will flip
998          * this variable to 0 when we find HEAD among the independent
999          * tips being merged.
1000          */
1001         *head_subsumed = 1;
1002
1003         /* Find what parents to record by checking independent ones. */
1004         parents = reduce_heads(remoteheads);
1005         free_commit_list(remoteheads);
1006
1007         remoteheads = NULL;
1008         remotes = &remoteheads;
1009         while (parents) {
1010                 struct commit *commit = pop_commit(&parents);
1011                 if (commit == head_commit)
1012                         *head_subsumed = 0;
1013                 else
1014                         remotes = &commit_list_insert(commit, remotes)->next;
1015         }
1016         return remoteheads;
1017 }
1018
1019 static void prepare_merge_message(struct strbuf *merge_names, struct strbuf *merge_msg)
1020 {
1021         struct fmt_merge_msg_opts opts;
1022
1023         memset(&opts, 0, sizeof(opts));
1024         opts.add_title = !have_message;
1025         opts.shortlog_len = shortlog_len;
1026         opts.credit_people = (0 < option_edit);
1027
1028         fmt_merge_msg(merge_names, merge_msg, &opts);
1029         if (merge_msg->len)
1030                 strbuf_setlen(merge_msg, merge_msg->len - 1);
1031 }
1032
1033 static void handle_fetch_head(struct commit_list **remotes, struct strbuf *merge_names)
1034 {
1035         const char *filename;
1036         int fd, pos, npos;
1037         struct strbuf fetch_head_file = STRBUF_INIT;
1038
1039         if (!merge_names)
1040                 merge_names = &fetch_head_file;
1041
1042         filename = git_path_fetch_head(the_repository);
1043         fd = open(filename, O_RDONLY);
1044         if (fd < 0)
1045                 die_errno(_("could not open '%s' for reading"), filename);
1046
1047         if (strbuf_read(merge_names, fd, 0) < 0)
1048                 die_errno(_("could not read '%s'"), filename);
1049         if (close(fd) < 0)
1050                 die_errno(_("could not close '%s'"), filename);
1051
1052         for (pos = 0; pos < merge_names->len; pos = npos) {
1053                 struct object_id oid;
1054                 char *ptr;
1055                 struct commit *commit;
1056
1057                 ptr = strchr(merge_names->buf + pos, '\n');
1058                 if (ptr)
1059                         npos = ptr - merge_names->buf + 1;
1060                 else
1061                         npos = merge_names->len;
1062
1063                 if (npos - pos < GIT_SHA1_HEXSZ + 2 ||
1064                     get_oid_hex(merge_names->buf + pos, &oid))
1065                         commit = NULL; /* bad */
1066                 else if (memcmp(merge_names->buf + pos + GIT_SHA1_HEXSZ, "\t\t", 2))
1067                         continue; /* not-for-merge */
1068                 else {
1069                         char saved = merge_names->buf[pos + GIT_SHA1_HEXSZ];
1070                         merge_names->buf[pos + GIT_SHA1_HEXSZ] = '\0';
1071                         commit = get_merge_parent(merge_names->buf + pos);
1072                         merge_names->buf[pos + GIT_SHA1_HEXSZ] = saved;
1073                 }
1074                 if (!commit) {
1075                         if (ptr)
1076                                 *ptr = '\0';
1077                         die(_("not something we can merge in %s: %s"),
1078                             filename, merge_names->buf + pos);
1079                 }
1080                 remotes = &commit_list_insert(commit, remotes)->next;
1081         }
1082
1083         if (merge_names == &fetch_head_file)
1084                 strbuf_release(&fetch_head_file);
1085 }
1086
1087 static struct commit_list *collect_parents(struct commit *head_commit,
1088                                            int *head_subsumed,
1089                                            int argc, const char **argv,
1090                                            struct strbuf *merge_msg)
1091 {
1092         int i;
1093         struct commit_list *remoteheads = NULL;
1094         struct commit_list **remotes = &remoteheads;
1095         struct strbuf merge_names = STRBUF_INIT, *autogen = NULL;
1096
1097         if (merge_msg && (!have_message || shortlog_len))
1098                 autogen = &merge_names;
1099
1100         if (head_commit)
1101                 remotes = &commit_list_insert(head_commit, remotes)->next;
1102
1103         if (argc == 1 && !strcmp(argv[0], "FETCH_HEAD")) {
1104                 handle_fetch_head(remotes, autogen);
1105                 remoteheads = reduce_parents(head_commit, head_subsumed, remoteheads);
1106         } else {
1107                 for (i = 0; i < argc; i++) {
1108                         struct commit *commit = get_merge_parent(argv[i]);
1109                         if (!commit)
1110                                 help_unknown_ref(argv[i], "merge",
1111                                                  _("not something we can merge"));
1112                         remotes = &commit_list_insert(commit, remotes)->next;
1113                 }
1114                 remoteheads = reduce_parents(head_commit, head_subsumed, remoteheads);
1115                 if (autogen) {
1116                         struct commit_list *p;
1117                         for (p = remoteheads; p; p = p->next)
1118                                 merge_name(merge_remote_util(p->item)->name, autogen);
1119                 }
1120         }
1121
1122         if (autogen) {
1123                 prepare_merge_message(autogen, merge_msg);
1124                 strbuf_release(autogen);
1125         }
1126
1127         return remoteheads;
1128 }
1129
1130 static int merging_a_throwaway_tag(struct commit *commit)
1131 {
1132         char *tag_ref;
1133         struct object_id oid;
1134         int is_throwaway_tag = 0;
1135
1136         /* Are we merging a tag? */
1137         if (!merge_remote_util(commit) ||
1138             !merge_remote_util(commit)->obj ||
1139             merge_remote_util(commit)->obj->type != OBJ_TAG)
1140                 return is_throwaway_tag;
1141
1142         /*
1143          * Now we know we are merging a tag object.  Are we downstream
1144          * and following the tags from upstream?  If so, we must have
1145          * the tag object pointed at by "refs/tags/$T" where $T is the
1146          * tagname recorded in the tag object.  We want to allow such
1147          * a "just to catch up" merge to fast-forward.
1148          *
1149          * Otherwise, we are playing an integrator's role, making a
1150          * merge with a throw-away tag from a contributor with
1151          * something like "git pull $contributor $signed_tag".
1152          * We want to forbid such a merge from fast-forwarding
1153          * by default; otherwise we would not keep the signature
1154          * anywhere.
1155          */
1156         tag_ref = xstrfmt("refs/tags/%s",
1157                           ((struct tag *)merge_remote_util(commit)->obj)->tag);
1158         if (!read_ref(tag_ref, &oid) &&
1159             !oidcmp(&oid, &merge_remote_util(commit)->obj->oid))
1160                 is_throwaway_tag = 0;
1161         else
1162                 is_throwaway_tag = 1;
1163         free(tag_ref);
1164         return is_throwaway_tag;
1165 }
1166
1167 int cmd_merge(int argc, const char **argv, const char *prefix)
1168 {
1169         struct object_id result_tree, stash, head_oid;
1170         struct commit *head_commit;
1171         struct strbuf buf = STRBUF_INIT;
1172         int i, ret = 0, head_subsumed;
1173         int best_cnt = -1, merge_was_ok = 0, automerge_was_ok = 0;
1174         struct commit_list *common = NULL;
1175         const char *best_strategy = NULL, *wt_strategy = NULL;
1176         struct commit_list *remoteheads, *p;
1177         void *branch_to_free;
1178         int orig_argc = argc;
1179
1180         if (argc == 2 && !strcmp(argv[1], "-h"))
1181                 usage_with_options(builtin_merge_usage, builtin_merge_options);
1182
1183         /*
1184          * Check if we are _not_ on a detached HEAD, i.e. if there is a
1185          * current branch.
1186          */
1187         branch = branch_to_free = resolve_refdup("HEAD", 0, &head_oid, NULL);
1188         if (branch)
1189                 skip_prefix(branch, "refs/heads/", &branch);
1190
1191         init_diff_ui_defaults();
1192         git_config(git_merge_config, NULL);
1193
1194         if (!branch || is_null_oid(&head_oid))
1195                 head_commit = NULL;
1196         else
1197                 head_commit = lookup_commit_or_die(&head_oid, "HEAD");
1198
1199         if (branch_mergeoptions)
1200                 parse_branch_merge_options(branch_mergeoptions);
1201         argc = parse_options(argc, argv, prefix, builtin_merge_options,
1202                         builtin_merge_usage, 0);
1203         if (shortlog_len < 0)
1204                 shortlog_len = (merge_log_config > 0) ? merge_log_config : 0;
1205
1206         if (verbosity < 0 && show_progress == -1)
1207                 show_progress = 0;
1208
1209         if (abort_current_merge) {
1210                 int nargc = 2;
1211                 const char *nargv[] = {"reset", "--merge", NULL};
1212
1213                 if (orig_argc != 2)
1214                         usage_msg_opt(_("--abort expects no arguments"),
1215                               builtin_merge_usage, builtin_merge_options);
1216
1217                 if (!file_exists(git_path_merge_head(the_repository)))
1218                         die(_("There is no merge to abort (MERGE_HEAD missing)."));
1219
1220                 /* Invoke 'git reset --merge' */
1221                 ret = cmd_reset(nargc, nargv, prefix);
1222                 goto done;
1223         }
1224
1225         if (continue_current_merge) {
1226                 int nargc = 1;
1227                 const char *nargv[] = {"commit", NULL};
1228
1229                 if (orig_argc != 2)
1230                         usage_msg_opt(_("--continue expects no arguments"),
1231                               builtin_merge_usage, builtin_merge_options);
1232
1233                 if (!file_exists(git_path_merge_head(the_repository)))
1234                         die(_("There is no merge in progress (MERGE_HEAD missing)."));
1235
1236                 /* Invoke 'git commit' */
1237                 ret = cmd_commit(nargc, nargv, prefix);
1238                 goto done;
1239         }
1240
1241         if (read_cache_unmerged())
1242                 die_resolve_conflict("merge");
1243
1244         if (file_exists(git_path_merge_head(the_repository))) {
1245                 /*
1246                  * There is no unmerged entry, don't advise 'git
1247                  * add/rm <file>', just 'git commit'.
1248                  */
1249                 if (advice_resolve_conflict)
1250                         die(_("You have not concluded your merge (MERGE_HEAD exists).\n"
1251                                   "Please, commit your changes before you merge."));
1252                 else
1253                         die(_("You have not concluded your merge (MERGE_HEAD exists)."));
1254         }
1255         if (file_exists(git_path_cherry_pick_head(the_repository))) {
1256                 if (advice_resolve_conflict)
1257                         die(_("You have not concluded your cherry-pick (CHERRY_PICK_HEAD exists).\n"
1258                             "Please, commit your changes before you merge."));
1259                 else
1260                         die(_("You have not concluded your cherry-pick (CHERRY_PICK_HEAD exists)."));
1261         }
1262         resolve_undo_clear();
1263
1264         if (verbosity < 0)
1265                 show_diffstat = 0;
1266
1267         if (squash) {
1268                 if (fast_forward == FF_NO)
1269                         die(_("You cannot combine --squash with --no-ff."));
1270                 option_commit = 0;
1271         }
1272
1273         if (!argc) {
1274                 if (default_to_upstream)
1275                         argc = setup_with_upstream(&argv);
1276                 else
1277                         die(_("No commit specified and merge.defaultToUpstream not set."));
1278         } else if (argc == 1 && !strcmp(argv[0], "-")) {
1279                 argv[0] = "@{-1}";
1280         }
1281
1282         if (!argc)
1283                 usage_with_options(builtin_merge_usage,
1284                         builtin_merge_options);
1285
1286         if (!head_commit) {
1287                 /*
1288                  * If the merged head is a valid one there is no reason
1289                  * to forbid "git merge" into a branch yet to be born.
1290                  * We do the same for "git pull".
1291                  */
1292                 struct object_id *remote_head_oid;
1293                 if (squash)
1294                         die(_("Squash commit into empty head not supported yet"));
1295                 if (fast_forward == FF_NO)
1296                         die(_("Non-fast-forward commit does not make sense into "
1297                             "an empty head"));
1298                 remoteheads = collect_parents(head_commit, &head_subsumed,
1299                                               argc, argv, NULL);
1300                 if (!remoteheads)
1301                         die(_("%s - not something we can merge"), argv[0]);
1302                 if (remoteheads->next)
1303                         die(_("Can merge only exactly one commit into empty head"));
1304                 remote_head_oid = &remoteheads->item->object.oid;
1305                 read_empty(remote_head_oid, 0);
1306                 update_ref("initial pull", "HEAD", remote_head_oid, NULL, 0,
1307                            UPDATE_REFS_DIE_ON_ERR);
1308                 goto done;
1309         }
1310
1311         /*
1312          * All the rest are the commits being merged; prepare
1313          * the standard merge summary message to be appended
1314          * to the given message.
1315          */
1316         remoteheads = collect_parents(head_commit, &head_subsumed,
1317                                       argc, argv, &merge_msg);
1318
1319         if (!head_commit || !argc)
1320                 usage_with_options(builtin_merge_usage,
1321                         builtin_merge_options);
1322
1323         if (verify_signatures) {
1324                 for (p = remoteheads; p; p = p->next) {
1325                         struct commit *commit = p->item;
1326                         char hex[GIT_MAX_HEXSZ + 1];
1327                         struct signature_check signature_check;
1328                         memset(&signature_check, 0, sizeof(signature_check));
1329
1330                         check_commit_signature(commit, &signature_check);
1331
1332                         find_unique_abbrev_r(hex, &commit->object.oid, DEFAULT_ABBREV);
1333                         switch (signature_check.result) {
1334                         case 'G':
1335                                 break;
1336                         case 'U':
1337                                 die(_("Commit %s has an untrusted GPG signature, "
1338                                       "allegedly by %s."), hex, signature_check.signer);
1339                         case 'B':
1340                                 die(_("Commit %s has a bad GPG signature "
1341                                       "allegedly by %s."), hex, signature_check.signer);
1342                         default: /* 'N' */
1343                                 die(_("Commit %s does not have a GPG signature."), hex);
1344                         }
1345                         if (verbosity >= 0 && signature_check.result == 'G')
1346                                 printf(_("Commit %s has a good GPG signature by %s\n"),
1347                                        hex, signature_check.signer);
1348
1349                         signature_check_clear(&signature_check);
1350                 }
1351         }
1352
1353         strbuf_addstr(&buf, "merge");
1354         for (p = remoteheads; p; p = p->next)
1355                 strbuf_addf(&buf, " %s", merge_remote_util(p->item)->name);
1356         setenv("GIT_REFLOG_ACTION", buf.buf, 0);
1357         strbuf_reset(&buf);
1358
1359         for (p = remoteheads; p; p = p->next) {
1360                 struct commit *commit = p->item;
1361                 strbuf_addf(&buf, "GITHEAD_%s",
1362                             oid_to_hex(&commit->object.oid));
1363                 setenv(buf.buf, merge_remote_util(commit)->name, 1);
1364                 strbuf_reset(&buf);
1365                 if (fast_forward != FF_ONLY && merging_a_throwaway_tag(commit))
1366                         fast_forward = FF_NO;
1367         }
1368
1369         if (option_edit < 0)
1370                 option_edit = default_edit_option();
1371
1372         if (!use_strategies) {
1373                 if (!remoteheads)
1374                         ; /* already up-to-date */
1375                 else if (!remoteheads->next)
1376                         add_strategies(pull_twohead, DEFAULT_TWOHEAD);
1377                 else
1378                         add_strategies(pull_octopus, DEFAULT_OCTOPUS);
1379         }
1380
1381         for (i = 0; i < use_strategies_nr; i++) {
1382                 if (use_strategies[i]->attr & NO_FAST_FORWARD)
1383                         fast_forward = FF_NO;
1384                 if (use_strategies[i]->attr & NO_TRIVIAL)
1385                         allow_trivial = 0;
1386         }
1387
1388         if (!remoteheads)
1389                 ; /* already up-to-date */
1390         else if (!remoteheads->next)
1391                 common = get_merge_bases(head_commit, remoteheads->item);
1392         else {
1393                 struct commit_list *list = remoteheads;
1394                 commit_list_insert(head_commit, &list);
1395                 common = get_octopus_merge_bases(list);
1396                 free(list);
1397         }
1398
1399         update_ref("updating ORIG_HEAD", "ORIG_HEAD",
1400                    &head_commit->object.oid, NULL, 0, UPDATE_REFS_DIE_ON_ERR);
1401
1402         if (remoteheads && !common) {
1403                 /* No common ancestors found. */
1404                 if (!allow_unrelated_histories)
1405                         die(_("refusing to merge unrelated histories"));
1406                 /* otherwise, we need a real merge. */
1407         } else if (!remoteheads ||
1408                  (!remoteheads->next && !common->next &&
1409                   common->item == remoteheads->item)) {
1410                 /*
1411                  * If head can reach all the merge then we are up to date.
1412                  * but first the most common case of merging one remote.
1413                  */
1414                 finish_up_to_date(_("Already up to date."));
1415                 goto done;
1416         } else if (fast_forward != FF_NO && !remoteheads->next &&
1417                         !common->next &&
1418                         !oidcmp(&common->item->object.oid, &head_commit->object.oid)) {
1419                 /* Again the most common case of merging one remote. */
1420                 struct strbuf msg = STRBUF_INIT;
1421                 struct commit *commit;
1422
1423                 if (verbosity >= 0) {
1424                         printf(_("Updating %s..%s\n"),
1425                                find_unique_abbrev(&head_commit->object.oid,
1426                                                   DEFAULT_ABBREV),
1427                                find_unique_abbrev(&remoteheads->item->object.oid,
1428                                                   DEFAULT_ABBREV));
1429                 }
1430                 strbuf_addstr(&msg, "Fast-forward");
1431                 if (have_message)
1432                         strbuf_addstr(&msg,
1433                                 " (no commit created; -m option ignored)");
1434                 commit = remoteheads->item;
1435                 if (!commit) {
1436                         ret = 1;
1437                         goto done;
1438                 }
1439
1440                 if (checkout_fast_forward(&head_commit->object.oid,
1441                                           &commit->object.oid,
1442                                           overwrite_ignore)) {
1443                         ret = 1;
1444                         goto done;
1445                 }
1446
1447                 finish(head_commit, remoteheads, &commit->object.oid, msg.buf);
1448                 drop_save();
1449                 goto done;
1450         } else if (!remoteheads->next && common->next)
1451                 ;
1452                 /*
1453                  * We are not doing octopus and not fast-forward.  Need
1454                  * a real merge.
1455                  */
1456         else if (!remoteheads->next && !common->next && option_commit) {
1457                 /*
1458                  * We are not doing octopus, not fast-forward, and have
1459                  * only one common.
1460                  */
1461                 refresh_cache(REFRESH_QUIET);
1462                 if (allow_trivial && fast_forward != FF_ONLY) {
1463                         /* See if it is really trivial. */
1464                         git_committer_info(IDENT_STRICT);
1465                         printf(_("Trying really trivial in-index merge...\n"));
1466                         if (!read_tree_trivial(&common->item->object.oid,
1467                                                &head_commit->object.oid,
1468                                                &remoteheads->item->object.oid)) {
1469                                 ret = merge_trivial(head_commit, remoteheads);
1470                                 goto done;
1471                         }
1472                         printf(_("Nope.\n"));
1473                 }
1474         } else {
1475                 /*
1476                  * An octopus.  If we can reach all the remote we are up
1477                  * to date.
1478                  */
1479                 int up_to_date = 1;
1480                 struct commit_list *j;
1481
1482                 for (j = remoteheads; j; j = j->next) {
1483                         struct commit_list *common_one;
1484
1485                         /*
1486                          * Here we *have* to calculate the individual
1487                          * merge_bases again, otherwise "git merge HEAD^
1488                          * HEAD^^" would be missed.
1489                          */
1490                         common_one = get_merge_bases(head_commit, j->item);
1491                         if (oidcmp(&common_one->item->object.oid, &j->item->object.oid)) {
1492                                 up_to_date = 0;
1493                                 break;
1494                         }
1495                 }
1496                 if (up_to_date) {
1497                         finish_up_to_date(_("Already up to date. Yeeah!"));
1498                         goto done;
1499                 }
1500         }
1501
1502         if (fast_forward == FF_ONLY)
1503                 die(_("Not possible to fast-forward, aborting."));
1504
1505         /* We are going to make a new commit. */
1506         git_committer_info(IDENT_STRICT);
1507
1508         /*
1509          * At this point, we need a real merge.  No matter what strategy
1510          * we use, it would operate on the index, possibly affecting the
1511          * working tree, and when resolved cleanly, have the desired
1512          * tree in the index -- this means that the index must be in
1513          * sync with the head commit.  The strategies are responsible
1514          * to ensure this.
1515          */
1516         if (use_strategies_nr == 1 ||
1517             /*
1518              * Stash away the local changes so that we can try more than one.
1519              */
1520             save_state(&stash))
1521                 oidclr(&stash);
1522
1523         for (i = 0; i < use_strategies_nr; i++) {
1524                 int ret;
1525                 if (i) {
1526                         printf(_("Rewinding the tree to pristine...\n"));
1527                         restore_state(&head_commit->object.oid, &stash);
1528                 }
1529                 if (use_strategies_nr != 1)
1530                         printf(_("Trying merge strategy %s...\n"),
1531                                 use_strategies[i]->name);
1532                 /*
1533                  * Remember which strategy left the state in the working
1534                  * tree.
1535                  */
1536                 wt_strategy = use_strategies[i]->name;
1537
1538                 ret = try_merge_strategy(use_strategies[i]->name,
1539                                          common, remoteheads,
1540                                          head_commit);
1541                 if (!option_commit && !ret) {
1542                         merge_was_ok = 1;
1543                         /*
1544                          * This is necessary here just to avoid writing
1545                          * the tree, but later we will *not* exit with
1546                          * status code 1 because merge_was_ok is set.
1547                          */
1548                         ret = 1;
1549                 }
1550
1551                 if (ret) {
1552                         /*
1553                          * The backend exits with 1 when conflicts are
1554                          * left to be resolved, with 2 when it does not
1555                          * handle the given merge at all.
1556                          */
1557                         if (ret == 1) {
1558                                 int cnt = evaluate_result();
1559
1560                                 if (best_cnt <= 0 || cnt <= best_cnt) {
1561                                         best_strategy = use_strategies[i]->name;
1562                                         best_cnt = cnt;
1563                                 }
1564                         }
1565                         if (merge_was_ok)
1566                                 break;
1567                         else
1568                                 continue;
1569                 }
1570
1571                 /* Automerge succeeded. */
1572                 write_tree_trivial(&result_tree);
1573                 automerge_was_ok = 1;
1574                 break;
1575         }
1576
1577         /*
1578          * If we have a resulting tree, that means the strategy module
1579          * auto resolved the merge cleanly.
1580          */
1581         if (automerge_was_ok) {
1582                 ret = finish_automerge(head_commit, head_subsumed,
1583                                        common, remoteheads,
1584                                        &result_tree, wt_strategy);
1585                 goto done;
1586         }
1587
1588         /*
1589          * Pick the result from the best strategy and have the user fix
1590          * it up.
1591          */
1592         if (!best_strategy) {
1593                 restore_state(&head_commit->object.oid, &stash);
1594                 if (use_strategies_nr > 1)
1595                         fprintf(stderr,
1596                                 _("No merge strategy handled the merge.\n"));
1597                 else
1598                         fprintf(stderr, _("Merge with strategy %s failed.\n"),
1599                                 use_strategies[0]->name);
1600                 ret = 2;
1601                 goto done;
1602         } else if (best_strategy == wt_strategy)
1603                 ; /* We already have its result in the working tree. */
1604         else {
1605                 printf(_("Rewinding the tree to pristine...\n"));
1606                 restore_state(&head_commit->object.oid, &stash);
1607                 printf(_("Using the %s to prepare resolving by hand.\n"),
1608                         best_strategy);
1609                 try_merge_strategy(best_strategy, common, remoteheads,
1610                                    head_commit);
1611         }
1612
1613         if (squash)
1614                 finish(head_commit, remoteheads, NULL, NULL);
1615         else
1616                 write_merge_state(remoteheads);
1617
1618         if (merge_was_ok)
1619                 fprintf(stderr, _("Automatic merge went well; "
1620                         "stopped before committing as requested\n"));
1621         else
1622                 ret = suggest_conflicts();
1623
1624 done:
1625         free(branch_to_free);
1626         return ret;
1627 }