git.oblomov.eu Git - git/blob - 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 "commit.h"
  18 #include "diffcore.h"
  19 #include "revision.h"
  20 #include "unpack-trees.h"
  21 #include "cache-tree.h"
  22 #include "dir.h"
  23 #include "utf8.h"
  24 #include "log-tree.h"
  25 #include "color.h"
  26 #include "rerere.h"
  27 #include "help.h"
  28 #include "merge-recursive.h"
  29 #include "resolve-undo.h"
  30 #include "remote.h"
  31 #include "fmt-merge-msg.h"
  32 #include "gpg-interface.h"
  33 #include "sequencer.h"
  34 #include "string-list.h"
  35
  36 #define DEFAULT_TWOHEAD (1<<0)
  37 #define DEFAULT_OCTOPUS (1<<1)
  38 #define NO_FAST_FORWARD (1<<2)
  39 #define NO_TRIVIAL      (1<<3)
  40
  41 struct strategy {
  42         const char *name;
  43         unsigned attr;
  44 };
  45
  46 static const char * const builtin_merge_usage[] = {
  47         N_("git merge [<options>] [<commit>...]"),
  48         N_("git merge --abort"),
  49         N_("git merge --continue"),
  50         NULL
  51 };
  52
  53 static int show_diffstat = 1, shortlog_len = -1, squash;
  54 static int option_commit = 1;
  55 static int option_edit = -1;
  56 static int allow_trivial = 1, have_message, verify_signatures;
  57 static int overwrite_ignore = 1;
  58 static struct strbuf merge_msg = STRBUF_INIT;
  59 static struct strategy **use_strategies;
  60 static size_t use_strategies_nr, use_strategies_alloc;
  61 static const char **xopts;
  62 static size_t xopts_nr, xopts_alloc;
  63 static const char *branch;
  64 static char *branch_mergeoptions;
  65 static int option_renormalize;
  66 static int verbosity;
  67 static int allow_rerere_auto;
  68 static int abort_current_merge;
  69 static int continue_current_merge;
  70 static int allow_unrelated_histories;
  71 static int show_progress = -1;
  72 static int default_to_upstream = 1;
  73 static const char *sign_commit;
  74
  75 static struct strategy all_strategy[] = {
  76         { "recursive",  DEFAULT_TWOHEAD | NO_TRIVIAL },
  77         { "octopus",    DEFAULT_OCTOPUS },
  78         { "resolve",    0 },
  79         { "ours",       NO_FAST_FORWARD | NO_TRIVIAL },
  80         { "subtree",    NO_FAST_FORWARD | NO_TRIVIAL },
  81 };
  82
  83 static const char *pull_twohead, *pull_octopus;
  84
  85 enum ff_type {
  86         FF_NO,
  87         FF_ALLOW,
  88         FF_ONLY
  89 };
  90
  91 static enum ff_type fast_forward = FF_ALLOW;
  92
  93 static int option_parse_message(const struct option *opt,
  94                                 const char *arg, int unset)
  95 {
  96         struct strbuf *buf = opt->value;
  97
  98         if (unset)
  99                 strbuf_setlen(buf, 0);
 100         else if (arg) {
 101                 strbuf_addf(buf, "%s%s", buf->len ? "\n\n" : "", arg);
 102                 have_message = 1;
 103         } else
 104                 return error(_("switch `m' requires a value"));
 105         return 0;
 106 }
 107
 108 static struct strategy *get_strategy(const char *name)
 109 {
 110         int i;
 111         struct strategy *ret;
 112         static struct cmdnames main_cmds, other_cmds;
 113         static int loaded;
 114
 115         if (!name)
 116                 return NULL;
 117
 118         for (i = 0; i < ARRAY_SIZE(all_strategy); i++)
 119                 if (!strcmp(name, all_strategy[i].name))
 120                         return &all_strategy[i];
 121
 122         if (!loaded) {
 123                 struct cmdnames not_strategies;
 124                 loaded = 1;
 125
 126                 memset(&not_strategies, 0, sizeof(struct cmdnames));
 127                 load_command_list("git-merge-", &main_cmds, &other_cmds);
 128                 for (i = 0; i < main_cmds.cnt; i++) {
 129                         int j, found = 0;
 130                         struct cmdname *ent = main_cmds.names[i];
 131                         for (j = 0; j < ARRAY_SIZE(all_strategy); j++)
 132                                 if (!strncmp(ent->name, all_strategy[j].name, ent->len)
 133                                                 && !all_strategy[j].name[ent->len])
 134                                         found = 1;
 135                         if (!found)
 136                                 add_cmdname(&not_strategies, ent->name, ent->len);
 137                 }
 138                 exclude_cmds(&main_cmds, &not_strategies);
 139         }
 140         if (!is_in_cmdlist(&main_cmds, name) && !is_in_cmdlist(&other_cmds, name)) {
 141                 fprintf(stderr, _("Could not find merge strategy '%s'.\n"), name);
 142                 fprintf(stderr, _("Available strategies are:"));
 143                 for (i = 0; i < main_cmds.cnt; i++)
 144                         fprintf(stderr, " %s", main_cmds.names[i]->name);
 145                 fprintf(stderr, ".\n");
 146                 if (other_cmds.cnt) {
 147                         fprintf(stderr, _("Available custom strategies are:"));
 148                         for (i = 0; i < other_cmds.cnt; i++)
 149                                 fprintf(stderr, " %s", other_cmds.names[i]->name);
 150                         fprintf(stderr, ".\n");
 151                 }
 152                 exit(1);
 153         }
 154
 155         ret = xcalloc(1, sizeof(struct strategy));
 156         ret->name = xstrdup(name);
 157         ret->attr = NO_TRIVIAL;
 158         return ret;
 159 }
 160
 161 static void append_strategy(struct strategy *s)
 162 {
 163         ALLOC_GROW(use_strategies, use_strategies_nr + 1, use_strategies_alloc);
 164         use_strategies[use_strategies_nr++] = s;
 165 }
 166
 167 static int option_parse_strategy(const struct option *opt,
 168                                  const char *name, int unset)
 169 {
 170         if (unset)
 171                 return 0;
 172
 173         append_strategy(get_strategy(name));
 174         return 0;
 175 }
 176
 177 static int option_parse_x(const struct option *opt,
 178                           const char *arg, int unset)
 179 {
 180         if (unset)
 181                 return 0;
 182
 183         ALLOC_GROW(xopts, xopts_nr + 1, xopts_alloc);
 184         xopts[xopts_nr++] = xstrdup(arg);
 185         return 0;
 186 }
 187
 188 static int option_parse_n(const struct option *opt,
 189                           const char *arg, int unset)
 190 {
 191         show_diffstat = unset;
 192         return 0;
 193 }
 194
 195 static struct option builtin_merge_options[] = {
 196         { OPTION_CALLBACK, 'n', NULL, NULL, NULL,
 197                 N_("do not show a diffstat at the end of the merge"),
 198                 PARSE_OPT_NOARG, option_parse_n },
 199         OPT_BOOL(0, "stat", &show_diffstat,
 200                 N_("show a diffstat at the end of the merge")),
 201         OPT_BOOL(0, "summary", &show_diffstat, N_("(synonym to --stat)")),
 202         { OPTION_INTEGER, 0, "log", &shortlog_len, N_("n"),
 203           N_("add (at most <n>) entries from shortlog to merge commit message"),
 204           PARSE_OPT_OPTARG, NULL, DEFAULT_MERGE_LOG_LEN },
 205         OPT_BOOL(0, "squash", &squash,
 206                 N_("create a single commit instead of doing a merge")),
 207         OPT_BOOL(0, "commit", &option_commit,
 208                 N_("perform a commit if the merge succeeds (default)")),
 209         OPT_BOOL('e', "edit", &option_edit,
 210                 N_("edit message before committing")),
 211         OPT_SET_INT(0, "ff", &fast_forward, N_("allow fast-forward (default)"), FF_ALLOW),
 212         { OPTION_SET_INT, 0, "ff-only", &fast_forward, NULL,
 213                 N_("abort if fast-forward is not possible"),
 214                 PARSE_OPT_NOARG | PARSE_OPT_NONEG, NULL, FF_ONLY },
 215         OPT_RERERE_AUTOUPDATE(&allow_rerere_auto),
 216         OPT_BOOL(0, "verify-signatures", &verify_signatures,
 217                 N_("verify that the named commit has a valid GPG signature")),
 218         OPT_CALLBACK('s', "strategy", &use_strategies, N_("strategy"),
 219                 N_("merge strategy to use"), option_parse_strategy),
 220         OPT_CALLBACK('X', "strategy-option", &xopts, N_("option=value"),
 221                 N_("option for selected merge strategy"), option_parse_x),
 222         OPT_CALLBACK('m', "message", &merge_msg, N_("message"),
 223                 N_("merge commit message (for a non-fast-forward merge)"),
 224                 option_parse_message),
 225         OPT__VERBOSITY(&verbosity),
 226         OPT_BOOL(0, "abort", &abort_current_merge,
 227                 N_("abort the current in-progress merge")),
 228         OPT_BOOL(0, "continue", &continue_current_merge,
 229                 N_("continue the current in-progress merge")),
 230         OPT_BOOL(0, "allow-unrelated-histories", &allow_unrelated_histories,
 231                  N_("allow merging unrelated histories")),
 232         OPT_SET_INT(0, "progress", &show_progress, N_("force progress reporting"), 1),
 233         { OPTION_STRING, 'S', "gpg-sign", &sign_commit, N_("key-id"),
 234           N_("GPG sign commit"), PARSE_OPT_OPTARG, NULL, (intptr_t) "" },
 235         OPT_BOOL(0, "overwrite-ignore", &overwrite_ignore, N_("update ignored files (default)")),
 236         OPT_END()
 237 };
 238
 239 /* Cleans up metadata that is uninteresting after a succeeded merge. */
 240 static void drop_save(void)
 241 {
 242         unlink(git_path_merge_head());
 243         unlink(git_path_merge_msg());
 244         unlink(git_path_merge_mode());
 245 }
 246
 247 static int save_state(struct object_id *stash)
 248 {
 249         int len;
 250         struct child_process cp = CHILD_PROCESS_INIT;
 251         struct strbuf buffer = STRBUF_INIT;
 252         const char *argv[] = {"stash", "create", NULL};
 253
 254         cp.argv = argv;
 255         cp.out = -1;
 256         cp.git_cmd = 1;
 257
 258         if (start_command(&cp))
 259                 die(_("could not run stash."));
 260         len = strbuf_read(&buffer, cp.out, 1024);
 261         close(cp.out);
 262
 263         if (finish_command(&cp) || len < 0)
 264                 die(_("stash failed"));
 265         else if (!len)          /* no changes */
 266                 return -1;
 267         strbuf_setlen(&buffer, buffer.len-1);
 268         if (get_oid(buffer.buf, stash))
 269                 die(_("not a valid object: %s"), buffer.buf);
 270         return 0;
 271 }
 272
 273 static void read_empty(unsigned const char *sha1, int verbose)
 274 {
 275         int i = 0;
 276         const char *args[7];
 277
 278         args[i++] = "read-tree";
 279         if (verbose)
 280                 args[i++] = "-v";
 281         args[i++] = "-m";
 282         args[i++] = "-u";
 283         args[i++] = EMPTY_TREE_SHA1_HEX;
 284         args[i++] = sha1_to_hex(sha1);
 285         args[i] = NULL;
 286
 287         if (run_command_v_opt(args, RUN_GIT_CMD))
 288                 die(_("read-tree failed"));
 289 }
 290
 291 static void reset_hard(unsigned const char *sha1, int verbose)
 292 {
 293         int i = 0;
 294         const char *args[6];
 295
 296         args[i++] = "read-tree";
 297         if (verbose)
 298                 args[i++] = "-v";
 299         args[i++] = "--reset";
 300         args[i++] = "-u";
 301         args[i++] = sha1_to_hex(sha1);
 302         args[i] = NULL;
 303
 304         if (run_command_v_opt(args, RUN_GIT_CMD))
 305                 die(_("read-tree failed"));
 306 }
 307
 308 static void restore_state(const struct object_id *head,
 309                           const struct object_id *stash)
 310 {
 311         struct strbuf sb = STRBUF_INIT;
 312         const char *args[] = { "stash", "apply", NULL, NULL };
 313
 314         if (is_null_oid(stash))
 315                 return;
 316
 317         reset_hard(head->hash, 1);
 318
 319         args[2] = oid_to_hex(stash);
 320
 321         /*
 322          * It is OK to ignore error here, for example when there was
 323          * nothing to restore.
 324          */
 325         run_command_v_opt(args, RUN_GIT_CMD);
 326
 327         strbuf_release(&sb);
 328         refresh_cache(REFRESH_QUIET);
 329 }
 330
 331 /* This is called when no merge was necessary. */
 332 static void finish_up_to_date(const char *msg)
 333 {
 334         if (verbosity >= 0)
 335                 printf("%s%s\n", squash ? _(" (nothing to squash)") : "", msg);
 336         drop_save();
 337 }
 338
 339 static void squash_message(struct commit *commit, struct commit_list *remoteheads)
 340 {
 341         struct rev_info rev;
 342         struct strbuf out = STRBUF_INIT;
 343         struct commit_list *j;
 344         struct pretty_print_context ctx = {0};
 345
 346         printf(_("Squash commit -- not updating HEAD\n"));
 347
 348         init_revisions(&rev, NULL);
 349         rev.ignore_merges = 1;
 350         rev.commit_format = CMIT_FMT_MEDIUM;
 351
 352         commit->object.flags |= UNINTERESTING;
 353         add_pending_object(&rev, &commit->object, NULL);
 354
 355         for (j = remoteheads; j; j = j->next)
 356                 add_pending_object(&rev, &j->item->object, NULL);
 357
 358         setup_revisions(0, NULL, &rev, NULL);
 359         if (prepare_revision_walk(&rev))
 360                 die(_("revision walk setup failed"));
 361
 362         ctx.abbrev = rev.abbrev;
 363         ctx.date_mode = rev.date_mode;
 364         ctx.fmt = rev.commit_format;
 365
 366         strbuf_addstr(&out, "Squashed commit of the following:\n");
 367         while ((commit = get_revision(&rev)) != NULL) {
 368                 strbuf_addch(&out, '\n');
 369                 strbuf_addf(&out, "commit %s\n",
 370                         oid_to_hex(&commit->object.oid));
 371                 pretty_print_commit(&ctx, commit, &out);
 372         }
 373         write_file_buf(git_path_squash_msg(), out.buf, out.len);
 374         strbuf_release(&out);
 375 }
 376
 377 static void finish(struct commit *head_commit,
 378                    struct commit_list *remoteheads,
 379                    const struct object_id *new_head, const char *msg)
 380 {
 381         struct strbuf reflog_message = STRBUF_INIT;
 382         const struct object_id *head = &head_commit->object.oid;
 383
 384         if (!msg)
 385                 strbuf_addstr(&reflog_message, getenv("GIT_REFLOG_ACTION"));
 386         else {
 387                 if (verbosity >= 0)
 388                         printf("%s\n", msg);
 389                 strbuf_addf(&reflog_message, "%s: %s",
 390                         getenv("GIT_REFLOG_ACTION"), msg);
 391         }
 392         if (squash) {
 393                 squash_message(head_commit, remoteheads);
 394         } else {
 395                 if (verbosity >= 0 && !merge_msg.len)
 396                         printf(_("No merge message -- not updating HEAD\n"));
 397                 else {
 398                         const char *argv_gc_auto[] = { "gc", "--auto", NULL };
 399                         update_ref(reflog_message.buf, "HEAD",
 400                                 new_head->hash, head->hash, 0,
 401                                 UPDATE_REFS_DIE_ON_ERR);
 402                         /*
 403                          * We ignore errors in 'gc --auto', since the
 404                          * user should see them.
 405                          */
 406                         close_all_packs();
 407                         run_command_v_opt(argv_gc_auto, RUN_GIT_CMD);
 408                 }
 409         }
 410         if (new_head && show_diffstat) {
 411                 struct diff_options opts;
 412                 diff_setup(&opts);
 413                 opts.stat_width = -1; /* use full terminal width */
 414                 opts.stat_graph_width = -1; /* respect statGraphWidth config */
 415                 opts.output_format |=
 416                         DIFF_FORMAT_SUMMARY | DIFF_FORMAT_DIFFSTAT;
 417                 opts.detect_rename = DIFF_DETECT_RENAME;
 418                 diff_setup_done(&opts);
 419                 diff_tree_oid(head, new_head, "", &opts);
 420                 diffcore_std(&opts);
 421                 diff_flush(&opts);
 422         }
 423
 424         /* Run a post-merge hook */
 425         run_hook_le(NULL, "post-merge", squash ? "1" : "0", NULL);
 426
 427         strbuf_release(&reflog_message);
 428 }
 429
 430 /* Get the name for the merge commit's message. */
 431 static void merge_name(const char *remote, struct strbuf *msg)
 432 {
 433         struct commit *remote_head;
 434         struct object_id branch_head;
 435         struct strbuf buf = STRBUF_INIT;
 436         struct strbuf bname = STRBUF_INIT;
 437         const char *ptr;
 438         char *found_ref;
 439         int len, early;
 440
 441         strbuf_branchname(&bname, remote, 0);
 442         remote = bname.buf;
 443
 444         oidclr(&branch_head);
 445         remote_head = get_merge_parent(remote);
 446         if (!remote_head)
 447                 die(_("'%s' does not point to a commit"), remote);
 448
 449         if (dwim_ref(remote, strlen(remote), branch_head.hash, &found_ref) > 0) {
 450                 if (starts_with(found_ref, "refs/heads/")) {
 451                         strbuf_addf(msg, "%s\t\tbranch '%s' of .\n",
 452                                     oid_to_hex(&branch_head), remote);
 453                         goto cleanup;
 454                 }
 455                 if (starts_with(found_ref, "refs/tags/")) {
 456                         strbuf_addf(msg, "%s\t\ttag '%s' of .\n",
 457                                     oid_to_hex(&branch_head), remote);
 458                         goto cleanup;
 459                 }
 460                 if (starts_with(found_ref, "refs/remotes/")) {
 461                         strbuf_addf(msg, "%s\t\tremote-tracking branch '%s' of .\n",
 462                                     oid_to_hex(&branch_head), remote);
 463                         goto cleanup;
 464                 }
 465         }
 466
 467         /* See if remote matches <name>^^^.. or <name>~<number> */
 468         for (len = 0, ptr = remote + strlen(remote);
 469              remote < ptr && ptr[-1] == '^';
 470              ptr--)
 471                 len++;
 472         if (len)
 473                 early = 1;
 474         else {
 475                 early = 0;
 476                 ptr = strrchr(remote, '~');
 477                 if (ptr) {
 478                         int seen_nonzero = 0;
 479
 480                         len++; /* count ~ */
 481                         while (*++ptr && isdigit(*ptr)) {
 482                                 seen_nonzero |= (*ptr != '0');
 483                                 len++;
 484                         }
 485                         if (*ptr)
 486                                 len = 0; /* not ...~<number> */
 487                         else if (seen_nonzero)
 488                                 early = 1;
 489                         else if (len == 1)
 490                                 early = 1; /* "name~" is "name~1"! */
 491                 }
 492         }
 493         if (len) {
 494                 struct strbuf truname = STRBUF_INIT;
 495                 strbuf_addf(&truname, "refs/heads/%s", remote);
 496                 strbuf_setlen(&truname, truname.len - len);
 497                 if (ref_exists(truname.buf)) {
 498                         strbuf_addf(msg,
 499                                     "%s\t\tbranch '%s'%s of .\n",
 500                                     oid_to_hex(&remote_head->object.oid),
 501                                     truname.buf + 11,
 502                                     (early ? " (early part)" : ""));
 503                         strbuf_release(&truname);
 504                         goto cleanup;
 505                 }
 506                 strbuf_release(&truname);
 507         }
 508
 509         if (remote_head->util) {
 510                 struct merge_remote_desc *desc;
 511                 desc = merge_remote_util(remote_head);
 512                 if (desc && desc->obj && desc->obj->type == OBJ_TAG) {
 513                         strbuf_addf(msg, "%s\t\t%s '%s'\n",
 514                                     oid_to_hex(&desc->obj->oid),
 515                                     typename(desc->obj->type),
 516                                     remote);
 517                         goto cleanup;
 518                 }
 519         }
 520
 521         strbuf_addf(msg, "%s\t\tcommit '%s'\n",
 522                 oid_to_hex(&remote_head->object.oid), remote);
 523 cleanup:
 524         strbuf_release(&buf);
 525         strbuf_release(&bname);
 526 }
 527
 528 static void parse_branch_merge_options(char *bmo)
 529 {
 530         const char **argv;
 531         int argc;
 532
 533         if (!bmo)
 534                 return;
 535         argc = split_cmdline(bmo, &argv);
 536         if (argc < 0)
 537                 die(_("Bad branch.%s.mergeoptions string: %s"), branch,
 538                     split_cmdline_strerror(argc));
 539         REALLOC_ARRAY(argv, argc + 2);
 540         MOVE_ARRAY(argv + 1, argv, argc + 1);
 541         argc++;
 542         argv[0] = "branch.*.mergeoptions";
 543         parse_options(argc, argv, NULL, builtin_merge_options,
 544                       builtin_merge_usage, 0);
 545         free(argv);
 546 }
 547
 548 static int git_merge_config(const char *k, const char *v, void *cb)
 549 {
 550         int status;
 551
 552         if (branch && starts_with(k, "branch.") &&
 553                 starts_with(k + 7, branch) &&
 554                 !strcmp(k + 7 + strlen(branch), ".mergeoptions")) {
 555                 free(branch_mergeoptions);
 556                 branch_mergeoptions = xstrdup(v);
 557                 return 0;
 558         }
 559
 560         if (!strcmp(k, "merge.diffstat") || !strcmp(k, "merge.stat"))
 561                 show_diffstat = git_config_bool(k, v);
 562         else if (!strcmp(k, "pull.twohead"))
 563                 return git_config_string(&pull_twohead, k, v);
 564         else if (!strcmp(k, "pull.octopus"))
 565                 return git_config_string(&pull_octopus, k, v);
 566         else if (!strcmp(k, "merge.renormalize"))
 567                 option_renormalize = git_config_bool(k, v);
 568         else if (!strcmp(k, "merge.ff")) {
 569                 int boolval = git_config_maybe_bool(k, v);
 570                 if (0 <= boolval) {
 571                         fast_forward = boolval ? FF_ALLOW : FF_NO;
 572                 } else if (v && !strcmp(v, "only")) {
 573                         fast_forward = FF_ONLY;
 574                 } /* do not barf on values from future versions of git */
 575                 return 0;
 576         } else if (!strcmp(k, "merge.defaulttoupstream")) {
 577                 default_to_upstream = git_config_bool(k, v);
 578                 return 0;
 579         } else if (!strcmp(k, "commit.gpgsign")) {
 580                 sign_commit = git_config_bool(k, v) ? "" : NULL;
 581                 return 0;
 582         }
 583
 584         status = fmt_merge_msg_config(k, v, cb);
 585         if (status)
 586                 return status;
 587         status = git_gpg_config(k, v, NULL);
 588         if (status)
 589                 return status;
 590         return git_diff_ui_config(k, v, cb);
 591 }
 592
 593 static int read_tree_trivial(struct object_id *common, struct object_id *head,
 594                              struct object_id *one)
 595 {
 596         int i, nr_trees = 0;
 597         struct tree *trees[MAX_UNPACK_TREES];
 598         struct tree_desc t[MAX_UNPACK_TREES];
 599         struct unpack_trees_options opts;
 600
 601         memset(&opts, 0, sizeof(opts));
 602         opts.head_idx = 2;
 603         opts.src_index = &the_index;
 604         opts.dst_index = &the_index;
 605         opts.update = 1;
 606         opts.verbose_update = 1;
 607         opts.trivial_merges_only = 1;
 608         opts.merge = 1;
 609         trees[nr_trees] = parse_tree_indirect(common);
 610         if (!trees[nr_trees++])
 611                 return -1;
 612         trees[nr_trees] = parse_tree_indirect(head);
 613         if (!trees[nr_trees++])
 614                 return -1;
 615         trees[nr_trees] = parse_tree_indirect(one);
 616         if (!trees[nr_trees++])
 617                 return -1;
 618         opts.fn = threeway_merge;
 619         cache_tree_free(&active_cache_tree);
 620         for (i = 0; i < nr_trees; i++) {
 621                 parse_tree(trees[i]);
 622                 init_tree_desc(t+i, trees[i]->buffer, trees[i]->size);
 623         }
 624         if (unpack_trees(nr_trees, t, &opts))
 625                 return -1;
 626         return 0;
 627 }
 628
 629 static void write_tree_trivial(struct object_id *oid)
 630 {
 631         if (write_cache_as_tree(oid->hash, 0, NULL))
 632                 die(_("git write-tree failed to write a tree"));
 633 }
 634
 635 static int try_merge_strategy(const char *strategy, struct commit_list *common,
 636                               struct commit_list *remoteheads,
 637                               struct commit *head)
 638 {
 639         static struct lock_file lock;
 640         const char *head_arg = "HEAD";
 641
 642         hold_locked_index(&lock, LOCK_DIE_ON_ERROR);
 643         refresh_cache(REFRESH_QUIET);
 644         if (active_cache_changed &&
 645             write_locked_index(&the_index, &lock, COMMIT_LOCK))
 646                 return error(_("Unable to write index."));
 647         rollback_lock_file(&lock);
 648
 649         if (!strcmp(strategy, "recursive") || !strcmp(strategy, "subtree")) {
 650                 int clean, x;
 651                 struct commit *result;
 652                 struct commit_list *reversed = NULL;
 653                 struct merge_options o;
 654                 struct commit_list *j;
 655
 656                 if (remoteheads->next) {
 657                         error(_("Not handling anything other than two heads merge."));
 658                         return 2;
 659                 }
 660
 661                 init_merge_options(&o);
 662                 if (!strcmp(strategy, "subtree"))
 663                         o.subtree_shift = "";
 664
 665                 o.renormalize = option_renormalize;
 666                 o.show_rename_progress =
 667                         show_progress == -1 ? isatty(2) : show_progress;
 668
 669                 for (x = 0; x < xopts_nr; x++)
 670                         if (parse_merge_opt(&o, xopts[x]))
 671                                 die(_("Unknown option for merge-recursive: -X%s"), xopts[x]);
 672
 673                 o.branch1 = head_arg;
 674                 o.branch2 = merge_remote_util(remoteheads->item)->name;
 675
 676                 for (j = common; j; j = j->next)
 677                         commit_list_insert(j->item, &reversed);
 678
 679                 hold_locked_index(&lock, LOCK_DIE_ON_ERROR);
 680                 clean = merge_recursive(&o, head,
 681                                 remoteheads->item, reversed, &result);
 682                 if (clean < 0)
 683                         exit(128);
 684                 if (active_cache_changed &&
 685                     write_locked_index(&the_index, &lock, COMMIT_LOCK))
 686                         die (_("unable to write %s"), get_index_file());
 687                 rollback_lock_file(&lock);
 688                 return clean ? 0 : 1;
 689         } else {
 690                 return try_merge_command(strategy, xopts_nr, xopts,
 691                                                 common, head_arg, remoteheads);
 692         }
 693 }
 694
 695 static void count_diff_files(struct diff_queue_struct *q,
 696                              struct diff_options *opt, void *data)
 697 {
 698         int *count = data;
 699
 700         (*count) += q->nr;
 701 }
 702
 703 static int count_unmerged_entries(void)
 704 {
 705         int i, ret = 0;
 706
 707         for (i = 0; i < active_nr; i++)
 708                 if (ce_stage(active_cache[i]))
 709                         ret++;
 710
 711         return ret;
 712 }
 713
 714 static void add_strategies(const char *string, unsigned attr)
 715 {
 716         int i;
 717
 718         if (string) {
 719                 struct string_list list = STRING_LIST_INIT_DUP;
 720                 struct string_list_item *item;
 721                 string_list_split(&list, string, ' ', -1);
 722                 for_each_string_list_item(item, &list)
 723                         append_strategy(get_strategy(item->string));
 724                 string_list_clear(&list, 0);
 725                 return;
 726         }
 727         for (i = 0; i < ARRAY_SIZE(all_strategy); i++)
 728                 if (all_strategy[i].attr & attr)
 729                         append_strategy(&all_strategy[i]);
 730
 731 }
 732
 733 static void read_merge_msg(struct strbuf *msg)
 734 {
 735         const char *filename = git_path_merge_msg();
 736         strbuf_reset(msg);
 737         if (strbuf_read_file(msg, filename, 0) < 0)
 738                 die_errno(_("Could not read from '%s'"), filename);
 739 }
 740
 741 static void write_merge_state(struct commit_list *);
 742 static void abort_commit(struct commit_list *remoteheads, const char *err_msg)
 743 {
 744         if (err_msg)
 745                 error("%s", err_msg);
 746         fprintf(stderr,
 747                 _("Not committing merge; use 'git commit' to complete the merge.\n"));
 748         write_merge_state(remoteheads);
 749         exit(1);
 750 }
 751
 752 static const char merge_editor_comment[] =
 753 N_("Please enter a commit message to explain why this merge is necessary,\n"
 754    "especially if it merges an updated upstream into a topic branch.\n"
 755    "\n"
 756    "Lines starting with '%c' will be ignored, and an empty message aborts\n"
 757    "the commit.\n");
 758
 759 static void write_merge_heads(struct commit_list *);
 760 static void prepare_to_commit(struct commit_list *remoteheads)
 761 {
 762         struct strbuf msg = STRBUF_INIT;
 763         strbuf_addbuf(&msg, &merge_msg);
 764         strbuf_addch(&msg, '\n');
 765         if (squash)
 766                 BUG("the control must not reach here under --squash");
 767         if (0 < option_edit)
 768                 strbuf_commented_addf(&msg, _(merge_editor_comment), comment_line_char);
 769         write_merge_heads(remoteheads);
 770         write_file_buf(git_path_merge_msg(), msg.buf, msg.len);
 771         if (run_commit_hook(0 < option_edit, get_index_file(), "prepare-commit-msg",
 772                             git_path_merge_msg(), "merge", NULL))
 773                 abort_commit(remoteheads, NULL);
 774         if (0 < option_edit) {
 775                 if (launch_editor(git_path_merge_msg(), NULL, NULL))
 776                         abort_commit(remoteheads, NULL);
 777         }
 778         read_merge_msg(&msg);
 779         strbuf_stripspace(&msg, 0 < option_edit);
 780         if (!msg.len)
 781                 abort_commit(remoteheads, _("Empty commit message."));
 782         strbuf_release(&merge_msg);
 783         strbuf_addbuf(&merge_msg, &msg);
 784         strbuf_release(&msg);
 785 }
 786
 787 static int merge_trivial(struct commit *head, struct commit_list *remoteheads)
 788 {
 789         struct object_id result_tree, result_commit;
 790         struct commit_list *parents, **pptr = &parents;
 791         static struct lock_file lock;
 792
 793         hold_locked_index(&lock, LOCK_DIE_ON_ERROR);
 794         refresh_cache(REFRESH_QUIET);
 795         if (active_cache_changed &&
 796             write_locked_index(&the_index, &lock, COMMIT_LOCK))
 797                 return error(_("Unable to write index."));
 798         rollback_lock_file(&lock);
 799
 800         write_tree_trivial(&result_tree);
 801         printf(_("Wonderful.\n"));
 802         pptr = commit_list_append(head, pptr);
 803         pptr = commit_list_append(remoteheads->item, pptr);
 804         prepare_to_commit(remoteheads);
 805         if (commit_tree(merge_msg.buf, merge_msg.len, result_tree.hash, parents,
 806                         result_commit.hash, NULL, sign_commit))
 807                 die(_("failed to write commit object"));
 808         finish(head, remoteheads, &result_commit, "In-index merge");
 809         drop_save();
 810         return 0;
 811 }
 812
 813 static int finish_automerge(struct commit *head,
 814                             int head_subsumed,
 815                             struct commit_list *common,
 816                             struct commit_list *remoteheads,
 817                             struct object_id *result_tree,
 818                             const char *wt_strategy)
 819 {
 820         struct commit_list *parents = NULL;
 821         struct strbuf buf = STRBUF_INIT;
 822         struct object_id result_commit;
 823
 824         free_commit_list(common);
 825         parents = remoteheads;
 826         if (!head_subsumed || fast_forward == FF_NO)
 827                 commit_list_insert(head, &parents);
 828         strbuf_addch(&merge_msg, '\n');
 829         prepare_to_commit(remoteheads);
 830         if (commit_tree(merge_msg.buf, merge_msg.len, result_tree->hash, parents,
 831                         result_commit.hash, NULL, sign_commit))
 832                 die(_("failed to write commit object"));
 833         strbuf_addf(&buf, "Merge made by the '%s' strategy.", wt_strategy);
 834         finish(head, remoteheads, &result_commit, buf.buf);
 835         strbuf_release(&buf);
 836         drop_save();
 837         return 0;
 838 }
 839
 840 static int suggest_conflicts(void)
 841 {
 842         const char *filename;
 843         FILE *fp;
 844         struct strbuf msgbuf = STRBUF_INIT;
 845
 846         filename = git_path_merge_msg();
 847         fp = xfopen(filename, "a");
 848
 849         append_conflicts_hint(&msgbuf);
 850         fputs(msgbuf.buf, fp);
 851         strbuf_release(&msgbuf);
 852         fclose(fp);
 853         rerere(allow_rerere_auto);
 854         printf(_("Automatic merge failed; "
 855                         "fix conflicts and then commit the result.\n"));
 856         return 1;
 857 }
 858
 859 static int evaluate_result(void)
 860 {
 861         int cnt = 0;
 862         struct rev_info rev;
 863
 864         /* Check how many files differ. */
 865         init_revisions(&rev, "");
 866         setup_revisions(0, NULL, &rev, NULL);
 867         rev.diffopt.output_format |=
 868                 DIFF_FORMAT_CALLBACK;
 869         rev.diffopt.format_callback = count_diff_files;
 870         rev.diffopt.format_callback_data = &cnt;
 871         run_diff_files(&rev, 0);
 872
 873         /*
 874          * Check how many unmerged entries are
 875          * there.
 876          */
 877         cnt += count_unmerged_entries();
 878
 879         return cnt;
 880 }
 881
 882 /*
 883  * Pretend as if the user told us to merge with the remote-tracking
 884  * branch we have for the upstream of the current branch
 885  */
 886 static int setup_with_upstream(const char ***argv)
 887 {
 888         struct branch *branch = branch_get(NULL);
 889         int i;
 890         const char **args;
 891
 892         if (!branch)
 893                 die(_("No current branch."));
 894         if (!branch->remote_name)
 895                 die(_("No remote for the current branch."));
 896         if (!branch->merge_nr)
 897                 die(_("No default upstream defined for the current branch."));
 898
 899         args = xcalloc(st_add(branch->merge_nr, 1), sizeof(char *));
 900         for (i = 0; i < branch->merge_nr; i++) {
 901                 if (!branch->merge[i]->dst)
 902                         die(_("No remote-tracking branch for %s from %s"),
 903                             branch->merge[i]->src, branch->remote_name);
 904                 args[i] = branch->merge[i]->dst;
 905         }
 906         args[i] = NULL;
 907         *argv = args;
 908         return i;
 909 }
 910
 911 static void write_merge_heads(struct commit_list *remoteheads)
 912 {
 913         struct commit_list *j;
 914         struct strbuf buf = STRBUF_INIT;
 915
 916         for (j = remoteheads; j; j = j->next) {
 917                 struct object_id *oid;
 918                 struct commit *c = j->item;
 919                 if (c->util && merge_remote_util(c)->obj) {
 920                         oid = &merge_remote_util(c)->obj->oid;
 921                 } else {
 922                         oid = &c->object.oid;
 923                 }
 924                 strbuf_addf(&buf, "%s\n", oid_to_hex(oid));
 925         }
 926         write_file_buf(git_path_merge_head(), buf.buf, buf.len);
 927
 928         strbuf_reset(&buf);
 929         if (fast_forward == FF_NO)
 930                 strbuf_addstr(&buf, "no-ff");
 931         write_file_buf(git_path_merge_mode(), buf.buf, buf.len);
 932 }
 933
 934 static void write_merge_state(struct commit_list *remoteheads)
 935 {
 936         write_merge_heads(remoteheads);
 937         strbuf_addch(&merge_msg, '\n');
 938         write_file_buf(git_path_merge_msg(), merge_msg.buf, merge_msg.len);
 939 }
 940
 941 static int default_edit_option(void)
 942 {
 943         static const char name[] = "GIT_MERGE_AUTOEDIT";
 944         const char *e = getenv(name);
 945         struct stat st_stdin, st_stdout;
 946
 947         if (have_message)
 948                 /* an explicit -m msg without --[no-]edit */
 949                 return 0;
 950
 951         if (e) {
 952                 int v = git_config_maybe_bool(name, e);
 953                 if (v < 0)
 954                         die(_("Bad value '%s' in environment '%s'"), e, name);
 955                 return v;
 956         }
 957
 958         /* Use editor if stdin and stdout are the same and is a tty */
 959         return (!fstat(0, &st_stdin) &&
 960                 !fstat(1, &st_stdout) &&
 961                 isatty(0) && isatty(1) &&
 962                 st_stdin.st_dev == st_stdout.st_dev &&
 963                 st_stdin.st_ino == st_stdout.st_ino &&
 964                 st_stdin.st_mode == st_stdout.st_mode);
 965 }
 966
 967 static struct commit_list *reduce_parents(struct commit *head_commit,
 968                                           int *head_subsumed,
 969                                           struct commit_list *remoteheads)
 970 {
 971         struct commit_list *parents, **remotes;
 972
 973         /*
 974          * Is the current HEAD reachable from another commit being
 975          * merged?  If so we do not want to record it as a parent of
 976          * the resulting merge, unless --no-ff is given.  We will flip
 977          * this variable to 0 when we find HEAD among the independent
 978          * tips being merged.
 979          */
 980         *head_subsumed = 1;
 981
 982         /* Find what parents to record by checking independent ones. */
 983         parents = reduce_heads(remoteheads);
 984
 985         remoteheads = NULL;
 986         remotes = &remoteheads;
 987         while (parents) {
 988                 struct commit *commit = pop_commit(&parents);
 989                 if (commit == head_commit)
 990                         *head_subsumed = 0;
 991                 else
 992                         remotes = &commit_list_insert(commit, remotes)->next;
 993         }
 994         return remoteheads;
 995 }
 996
 997 static void prepare_merge_message(struct strbuf *merge_names, struct strbuf *merge_msg)
 998 {
 999         struct fmt_merge_msg_opts opts;
1000
1001         memset(&opts, 0, sizeof(opts));
1002         opts.add_title = !have_message;
1003         opts.shortlog_len = shortlog_len;
1004         opts.credit_people = (0 < option_edit);
1005
1006         fmt_merge_msg(merge_names, merge_msg, &opts);
1007         if (merge_msg->len)
1008                 strbuf_setlen(merge_msg, merge_msg->len - 1);
1009 }
1010
1011 static void handle_fetch_head(struct commit_list **remotes, struct strbuf *merge_names)
1012 {
1013         const char *filename;
1014         int fd, pos, npos;
1015         struct strbuf fetch_head_file = STRBUF_INIT;
1016
1017         if (!merge_names)
1018                 merge_names = &fetch_head_file;
1019
1020         filename = git_path_fetch_head();
1021         fd = open(filename, O_RDONLY);
1022         if (fd < 0)
1023                 die_errno(_("could not open '%s' for reading"), filename);
1024
1025         if (strbuf_read(merge_names, fd, 0) < 0)
1026                 die_errno(_("could not read '%s'"), filename);
1027         if (close(fd) < 0)
1028                 die_errno(_("could not close '%s'"), filename);
1029
1030         for (pos = 0; pos < merge_names->len; pos = npos) {
1031                 struct object_id oid;
1032                 char *ptr;
1033                 struct commit *commit;
1034
1035                 ptr = strchr(merge_names->buf + pos, '\n');
1036                 if (ptr)
1037                         npos = ptr - merge_names->buf + 1;
1038                 else
1039                         npos = merge_names->len;
1040
1041                 if (npos - pos < GIT_SHA1_HEXSZ + 2 ||
1042                     get_oid_hex(merge_names->buf + pos, &oid))
1043                         commit = NULL; /* bad */
1044                 else if (memcmp(merge_names->buf + pos + GIT_SHA1_HEXSZ, "\t\t", 2))
1045                         continue; /* not-for-merge */
1046                 else {
1047                         char saved = merge_names->buf[pos + GIT_SHA1_HEXSZ];
1048                         merge_names->buf[pos + GIT_SHA1_HEXSZ] = '\0';
1049                         commit = get_merge_parent(merge_names->buf + pos);
1050                         merge_names->buf[pos + GIT_SHA1_HEXSZ] = saved;
1051                 }
1052                 if (!commit) {
1053                         if (ptr)
1054                                 *ptr = '\0';
1055                         die(_("not something we can merge in %s: %s"),
1056                             filename, merge_names->buf + pos);
1057                 }
1058                 remotes = &commit_list_insert(commit, remotes)->next;
1059         }
1060
1061         if (merge_names == &fetch_head_file)
1062                 strbuf_release(&fetch_head_file);
1063 }
1064
1065 static struct commit_list *collect_parents(struct commit *head_commit,
1066                                            int *head_subsumed,
1067                                            int argc, const char **argv,
1068                                            struct strbuf *merge_msg)
1069 {
1070         int i;
1071         struct commit_list *remoteheads = NULL;
1072         struct commit_list **remotes = &remoteheads;
1073         struct strbuf merge_names = STRBUF_INIT, *autogen = NULL;
1074
1075         if (merge_msg && (!have_message || shortlog_len))
1076                 autogen = &merge_names;
1077
1078         if (head_commit)
1079                 remotes = &commit_list_insert(head_commit, remotes)->next;
1080
1081         if (argc == 1 && !strcmp(argv[0], "FETCH_HEAD")) {
1082                 handle_fetch_head(remotes, autogen);
1083                 remoteheads = reduce_parents(head_commit, head_subsumed, remoteheads);
1084         } else {
1085                 for (i = 0; i < argc; i++) {
1086                         struct commit *commit = get_merge_parent(argv[i]);
1087                         if (!commit)
1088                                 help_unknown_ref(argv[i], "merge",
1089                                                  _("not something we can merge"));
1090                         remotes = &commit_list_insert(commit, remotes)->next;
1091                 }
1092                 remoteheads = reduce_parents(head_commit, head_subsumed, remoteheads);
1093                 if (autogen) {
1094                         struct commit_list *p;
1095                         for (p = remoteheads; p; p = p->next)
1096                                 merge_name(merge_remote_util(p->item)->name, autogen);
1097                 }
1098         }
1099
1100         if (autogen) {
1101                 prepare_merge_message(autogen, merge_msg);
1102                 strbuf_release(autogen);
1103         }
1104
1105         return remoteheads;
1106 }
1107
1108 int cmd_merge(int argc, const char **argv, const char *prefix)
1109 {
1110         struct object_id result_tree, stash, head_oid;
1111         struct commit *head_commit;
1112         struct strbuf buf = STRBUF_INIT;
1113         int i, ret = 0, head_subsumed;
1114         int best_cnt = -1, merge_was_ok = 0, automerge_was_ok = 0;
1115         struct commit_list *common = NULL;
1116         const char *best_strategy = NULL, *wt_strategy = NULL;
1117         struct commit_list *remoteheads, *p;
1118         void *branch_to_free;
1119         int orig_argc = argc;
1120
1121         if (argc == 2 && !strcmp(argv[1], "-h"))
1122                 usage_with_options(builtin_merge_usage, builtin_merge_options);
1123
1124         /*
1125          * Check if we are _not_ on a detached HEAD, i.e. if there is a
1126          * current branch.
1127          */
1128         branch = branch_to_free = resolve_refdup("HEAD", 0, head_oid.hash, NULL);
1129         if (branch && starts_with(branch, "refs/heads/"))
1130                 branch += 11;
1131         if (!branch || is_null_oid(&head_oid))
1132                 head_commit = NULL;
1133         else
1134                 head_commit = lookup_commit_or_die(&head_oid, "HEAD");
1135
1136         init_diff_ui_defaults();
1137         git_config(git_merge_config, NULL);
1138
1139         if (branch_mergeoptions)
1140                 parse_branch_merge_options(branch_mergeoptions);
1141         argc = parse_options(argc, argv, prefix, builtin_merge_options,
1142                         builtin_merge_usage, 0);
1143         if (shortlog_len < 0)
1144                 shortlog_len = (merge_log_config > 0) ? merge_log_config : 0;
1145
1146         if (verbosity < 0 && show_progress == -1)
1147                 show_progress = 0;
1148
1149         if (abort_current_merge) {
1150                 int nargc = 2;
1151                 const char *nargv[] = {"reset", "--merge", NULL};
1152
1153                 if (orig_argc != 2)
1154                         usage_msg_opt(_("--abort expects no arguments"),
1155                               builtin_merge_usage, builtin_merge_options);
1156
1157                 if (!file_exists(git_path_merge_head()))
1158                         die(_("There is no merge to abort (MERGE_HEAD missing)."));
1159
1160                 /* Invoke 'git reset --merge' */
1161                 ret = cmd_reset(nargc, nargv, prefix);
1162                 goto done;
1163         }
1164
1165         if (continue_current_merge) {
1166                 int nargc = 1;
1167                 const char *nargv[] = {"commit", NULL};
1168
1169                 if (orig_argc != 2)
1170                         usage_msg_opt(_("--continue expects no arguments"),
1171                               builtin_merge_usage, builtin_merge_options);
1172
1173                 if (!file_exists(git_path_merge_head()))
1174                         die(_("There is no merge in progress (MERGE_HEAD missing)."));
1175
1176                 /* Invoke 'git commit' */
1177                 ret = cmd_commit(nargc, nargv, prefix);
1178                 goto done;
1179         }
1180
1181         if (read_cache_unmerged())
1182                 die_resolve_conflict("merge");
1183
1184         if (file_exists(git_path_merge_head())) {
1185                 /*
1186                  * There is no unmerged entry, don't advise 'git
1187                  * add/rm <file>', just 'git commit'.
1188                  */
1189                 if (advice_resolve_conflict)
1190                         die(_("You have not concluded your merge (MERGE_HEAD exists).\n"
1191                                   "Please, commit your changes before you merge."));
1192                 else
1193                         die(_("You have not concluded your merge (MERGE_HEAD exists)."));
1194         }
1195         if (file_exists(git_path_cherry_pick_head())) {
1196                 if (advice_resolve_conflict)
1197                         die(_("You have not concluded your cherry-pick (CHERRY_PICK_HEAD exists).\n"
1198                             "Please, commit your changes before you merge."));
1199                 else
1200                         die(_("You have not concluded your cherry-pick (CHERRY_PICK_HEAD exists)."));
1201         }
1202         resolve_undo_clear();
1203
1204         if (verbosity < 0)
1205                 show_diffstat = 0;
1206
1207         if (squash) {
1208                 if (fast_forward == FF_NO)
1209                         die(_("You cannot combine --squash with --no-ff."));
1210                 option_commit = 0;
1211         }
1212
1213         if (!argc) {
1214                 if (default_to_upstream)
1215                         argc = setup_with_upstream(&argv);
1216                 else
1217                         die(_("No commit specified and merge.defaultToUpstream not set."));
1218         } else if (argc == 1 && !strcmp(argv[0], "-")) {
1219                 argv[0] = "@{-1}";
1220         }
1221
1222         if (!argc)
1223                 usage_with_options(builtin_merge_usage,
1224                         builtin_merge_options);
1225
1226         if (!head_commit) {
1227                 /*
1228                  * If the merged head is a valid one there is no reason
1229                  * to forbid "git merge" into a branch yet to be born.
1230                  * We do the same for "git pull".
1231                  */
1232                 struct object_id *remote_head_oid;
1233                 if (squash)
1234                         die(_("Squash commit into empty head not supported yet"));
1235                 if (fast_forward == FF_NO)
1236                         die(_("Non-fast-forward commit does not make sense into "
1237                             "an empty head"));
1238                 remoteheads = collect_parents(head_commit, &head_subsumed,
1239                                               argc, argv, NULL);
1240                 if (!remoteheads)
1241                         die(_("%s - not something we can merge"), argv[0]);
1242                 if (remoteheads->next)
1243                         die(_("Can merge only exactly one commit into empty head"));
1244                 remote_head_oid = &remoteheads->item->object.oid;
1245                 read_empty(remote_head_oid->hash, 0);
1246                 update_ref("initial pull", "HEAD", remote_head_oid->hash,
1247                            NULL, 0, UPDATE_REFS_DIE_ON_ERR);
1248                 goto done;
1249         }
1250
1251         /*
1252          * All the rest are the commits being merged; prepare
1253          * the standard merge summary message to be appended
1254          * to the given message.
1255          */
1256         remoteheads = collect_parents(head_commit, &head_subsumed,
1257                                       argc, argv, &merge_msg);
1258
1259         if (!head_commit || !argc)
1260                 usage_with_options(builtin_merge_usage,
1261                         builtin_merge_options);
1262
1263         if (verify_signatures) {
1264                 for (p = remoteheads; p; p = p->next) {
1265                         struct commit *commit = p->item;
1266                         char hex[GIT_MAX_HEXSZ + 1];
1267                         struct signature_check signature_check;
1268                         memset(&signature_check, 0, sizeof(signature_check));
1269
1270                         check_commit_signature(commit, &signature_check);
1271
1272                         find_unique_abbrev_r(hex, commit->object.oid.hash, DEFAULT_ABBREV);
1273                         switch (signature_check.result) {
1274                         case 'G':
1275                                 break;
1276                         case 'U':
1277                                 die(_("Commit %s has an untrusted GPG signature, "
1278                                       "allegedly by %s."), hex, signature_check.signer);
1279                         case 'B':
1280                                 die(_("Commit %s has a bad GPG signature "
1281                                       "allegedly by %s."), hex, signature_check.signer);
1282                         default: /* 'N' */
1283                                 die(_("Commit %s does not have a GPG signature."), hex);
1284                         }
1285                         if (verbosity >= 0 && signature_check.result == 'G')
1286                                 printf(_("Commit %s has a good GPG signature by %s\n"),
1287                                        hex, signature_check.signer);
1288
1289                         signature_check_clear(&signature_check);
1290                 }
1291         }
1292
1293         strbuf_addstr(&buf, "merge");
1294         for (p = remoteheads; p; p = p->next)
1295                 strbuf_addf(&buf, " %s", merge_remote_util(p->item)->name);
1296         setenv("GIT_REFLOG_ACTION", buf.buf, 0);
1297         strbuf_reset(&buf);
1298
1299         for (p = remoteheads; p; p = p->next) {
1300                 struct commit *commit = p->item;
1301                 strbuf_addf(&buf, "GITHEAD_%s",
1302                             oid_to_hex(&commit->object.oid));
1303                 setenv(buf.buf, merge_remote_util(commit)->name, 1);
1304                 strbuf_reset(&buf);
1305                 if (fast_forward != FF_ONLY &&
1306                     merge_remote_util(commit) &&
1307                     merge_remote_util(commit)->obj &&
1308                     merge_remote_util(commit)->obj->type == OBJ_TAG)
1309                         fast_forward = FF_NO;
1310         }
1311
1312         if (option_edit < 0)
1313                 option_edit = default_edit_option();
1314
1315         if (!use_strategies) {
1316                 if (!remoteheads)
1317                         ; /* already up-to-date */
1318                 else if (!remoteheads->next)
1319                         add_strategies(pull_twohead, DEFAULT_TWOHEAD);
1320                 else
1321                         add_strategies(pull_octopus, DEFAULT_OCTOPUS);
1322         }
1323
1324         for (i = 0; i < use_strategies_nr; i++) {
1325                 if (use_strategies[i]->attr & NO_FAST_FORWARD)
1326                         fast_forward = FF_NO;
1327                 if (use_strategies[i]->attr & NO_TRIVIAL)
1328                         allow_trivial = 0;
1329         }
1330
1331         if (!remoteheads)
1332                 ; /* already up-to-date */
1333         else if (!remoteheads->next)
1334                 common = get_merge_bases(head_commit, remoteheads->item);
1335         else {
1336                 struct commit_list *list = remoteheads;
1337                 commit_list_insert(head_commit, &list);
1338                 common = get_octopus_merge_bases(list);
1339                 free(list);
1340         }
1341
1342         update_ref("updating ORIG_HEAD", "ORIG_HEAD", head_commit->object.oid.hash,
1343                    NULL, 0, UPDATE_REFS_DIE_ON_ERR);
1344
1345         if (remoteheads && !common) {
1346                 /* No common ancestors found. */
1347                 if (!allow_unrelated_histories)
1348                         die(_("refusing to merge unrelated histories"));
1349                 /* otherwise, we need a real merge. */
1350         } else if (!remoteheads ||
1351                  (!remoteheads->next && !common->next &&
1352                   common->item == remoteheads->item)) {
1353                 /*
1354                  * If head can reach all the merge then we are up to date.
1355                  * but first the most common case of merging one remote.
1356                  */
1357                 finish_up_to_date(_("Already up-to-date."));
1358                 goto done;
1359         } else if (fast_forward != FF_NO && !remoteheads->next &&
1360                         !common->next &&
1361                         !oidcmp(&common->item->object.oid, &head_commit->object.oid)) {
1362                 /* Again the most common case of merging one remote. */
1363                 struct strbuf msg = STRBUF_INIT;
1364                 struct commit *commit;
1365
1366                 if (verbosity >= 0) {
1367                         printf(_("Updating %s..%s\n"),
1368                                find_unique_abbrev(head_commit->object.oid.hash,
1369                                                   DEFAULT_ABBREV),
1370                                find_unique_abbrev(remoteheads->item->object.oid.hash,
1371                                                   DEFAULT_ABBREV));
1372                 }
1373                 strbuf_addstr(&msg, "Fast-forward");
1374                 if (have_message)
1375                         strbuf_addstr(&msg,
1376                                 " (no commit created; -m option ignored)");
1377                 commit = remoteheads->item;
1378                 if (!commit) {
1379                         ret = 1;
1380                         goto done;
1381                 }
1382
1383                 if (checkout_fast_forward(&head_commit->object.oid,
1384                                           &commit->object.oid,
1385                                           overwrite_ignore)) {
1386                         ret = 1;
1387                         goto done;
1388                 }
1389
1390                 finish(head_commit, remoteheads, &commit->object.oid, msg.buf);
1391                 drop_save();
1392                 goto done;
1393         } else if (!remoteheads->next && common->next)
1394                 ;
1395                 /*
1396                  * We are not doing octopus and not fast-forward.  Need
1397                  * a real merge.
1398                  */
1399         else if (!remoteheads->next && !common->next && option_commit) {
1400                 /*
1401                  * We are not doing octopus, not fast-forward, and have
1402                  * only one common.
1403                  */
1404                 refresh_cache(REFRESH_QUIET);
1405                 if (allow_trivial && fast_forward != FF_ONLY) {
1406                         /* See if it is really trivial. */
1407                         git_committer_info(IDENT_STRICT);
1408                         printf(_("Trying really trivial in-index merge...\n"));
1409                         if (!read_tree_trivial(&common->item->object.oid,
1410                                                &head_commit->object.oid,
1411                                                &remoteheads->item->object.oid)) {
1412                                 ret = merge_trivial(head_commit, remoteheads);
1413                                 goto done;
1414                         }
1415                         printf(_("Nope.\n"));
1416                 }
1417         } else {
1418                 /*
1419                  * An octopus.  If we can reach all the remote we are up
1420                  * to date.
1421                  */
1422                 int up_to_date = 1;
1423                 struct commit_list *j;
1424
1425                 for (j = remoteheads; j; j = j->next) {
1426                         struct commit_list *common_one;
1427
1428                         /*
1429                          * Here we *have* to calculate the individual
1430                          * merge_bases again, otherwise "git merge HEAD^
1431                          * HEAD^^" would be missed.
1432                          */
1433                         common_one = get_merge_bases(head_commit, j->item);
1434                         if (oidcmp(&common_one->item->object.oid, &j->item->object.oid)) {
1435                                 up_to_date = 0;
1436                                 break;
1437                         }
1438                 }
1439                 if (up_to_date) {
1440                         finish_up_to_date(_("Already up-to-date. Yeeah!"));
1441                         goto done;
1442                 }
1443         }
1444
1445         if (fast_forward == FF_ONLY)
1446                 die(_("Not possible to fast-forward, aborting."));
1447
1448         /* We are going to make a new commit. */
1449         git_committer_info(IDENT_STRICT);
1450
1451         /*
1452          * At this point, we need a real merge.  No matter what strategy
1453          * we use, it would operate on the index, possibly affecting the
1454          * working tree, and when resolved cleanly, have the desired
1455          * tree in the index -- this means that the index must be in
1456          * sync with the head commit.  The strategies are responsible
1457          * to ensure this.
1458          */
1459         if (use_strategies_nr == 1 ||
1460             /*
1461              * Stash away the local changes so that we can try more than one.
1462              */
1463             save_state(&stash))
1464                 oidclr(&stash);
1465
1466         for (i = 0; i < use_strategies_nr; i++) {
1467                 int ret;
1468                 if (i) {
1469                         printf(_("Rewinding the tree to pristine...\n"));
1470                         restore_state(&head_commit->object.oid, &stash);
1471                 }
1472                 if (use_strategies_nr != 1)
1473                         printf(_("Trying merge strategy %s...\n"),
1474                                 use_strategies[i]->name);
1475                 /*
1476                  * Remember which strategy left the state in the working
1477                  * tree.
1478                  */
1479                 wt_strategy = use_strategies[i]->name;
1480
1481                 ret = try_merge_strategy(use_strategies[i]->name,
1482                                          common, remoteheads,
1483                                          head_commit);
1484                 if (!option_commit && !ret) {
1485                         merge_was_ok = 1;
1486                         /*
1487                          * This is necessary here just to avoid writing
1488                          * the tree, but later we will *not* exit with
1489                          * status code 1 because merge_was_ok is set.
1490                          */
1491                         ret = 1;
1492                 }
1493
1494                 if (ret) {
1495                         /*
1496                          * The backend exits with 1 when conflicts are
1497                          * left to be resolved, with 2 when it does not
1498                          * handle the given merge at all.
1499                          */
1500                         if (ret == 1) {
1501                                 int cnt = evaluate_result();
1502
1503                                 if (best_cnt <= 0 || cnt <= best_cnt) {
1504                                         best_strategy = use_strategies[i]->name;
1505                                         best_cnt = cnt;
1506                                 }
1507                         }
1508                         if (merge_was_ok)
1509                                 break;
1510                         else
1511                                 continue;
1512                 }
1513
1514                 /* Automerge succeeded. */
1515                 write_tree_trivial(&result_tree);
1516                 automerge_was_ok = 1;
1517                 break;
1518         }
1519
1520         /*
1521          * If we have a resulting tree, that means the strategy module
1522          * auto resolved the merge cleanly.
1523          */
1524         if (automerge_was_ok) {
1525                 ret = finish_automerge(head_commit, head_subsumed,
1526                                        common, remoteheads,
1527                                        &result_tree, wt_strategy);
1528                 goto done;
1529         }
1530
1531         /*
1532          * Pick the result from the best strategy and have the user fix
1533          * it up.
1534          */
1535         if (!best_strategy) {
1536                 restore_state(&head_commit->object.oid, &stash);
1537                 if (use_strategies_nr > 1)
1538                         fprintf(stderr,
1539                                 _("No merge strategy handled the merge.\n"));
1540                 else
1541                         fprintf(stderr, _("Merge with strategy %s failed.\n"),
1542                                 use_strategies[0]->name);
1543                 ret = 2;
1544                 goto done;
1545         } else if (best_strategy == wt_strategy)
1546                 ; /* We already have its result in the working tree. */
1547         else {
1548                 printf(_("Rewinding the tree to pristine...\n"));
1549                 restore_state(&head_commit->object.oid, &stash);
1550                 printf(_("Using the %s to prepare resolving by hand.\n"),
1551                         best_strategy);
1552                 try_merge_strategy(best_strategy, common, remoteheads,
1553                                    head_commit);
1554         }
1555
1556         if (squash)
1557                 finish(head_commit, remoteheads, NULL, NULL);
1558         else
1559                 write_merge_state(remoteheads);
1560
1561         if (merge_was_ok)
1562                 fprintf(stderr, _("Automatic merge went well; "
1563                         "stopped before committing as requested\n"));
1564         else
1565                 ret = suggest_conflicts();
1566
1567 done:
1568         free(branch_to_free);
1569         return ret;
1570 }