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 "parse-options.h"
  11 #include "builtin.h"
  12 #include "lockfile.h"
  13 #include "run-command.h"
  14 #include "diff.h"
  15 #include "refs.h"
  16 #include "commit.h"
  17 #include "diffcore.h"
  18 #include "revision.h"
  19 #include "unpack-trees.h"
  20 #include "cache-tree.h"
  21 #include "dir.h"
  22 #include "utf8.h"
  23 #include "log-tree.h"
  24 #include "color.h"
  25 #include "rerere.h"
  26 #include "help.h"
  27 #include "merge-recursive.h"
  28 #include "resolve-undo.h"
  29 #include "remote.h"
  30 #include "fmt-merge-msg.h"
  31 #include "gpg-interface.h"
  32 #include "sequencer.h"
  33
  34 #define DEFAULT_TWOHEAD (1<<0)
  35 #define DEFAULT_OCTOPUS (1<<1)
  36 #define NO_FAST_FORWARD (1<<2)
  37 #define NO_TRIVIAL      (1<<3)
  38
  39 struct strategy {
  40         const char *name;
  41         unsigned attr;
  42 };
  43
  44 static const char * const builtin_merge_usage[] = {
  45         N_("git merge [<options>] [<commit>...]"),
  46         N_("git merge [<options>] <msg> HEAD <commit>"),
  47         N_("git merge --abort"),
  48         NULL
  49 };
  50
  51 static int show_diffstat = 1, shortlog_len = -1, squash;
  52 static int option_commit = 1;
  53 static int option_edit = -1;
  54 static int allow_trivial = 1, have_message, verify_signatures;
  55 static int overwrite_ignore = 1;
  56 static struct strbuf merge_msg = STRBUF_INIT;
  57 static struct strategy **use_strategies;
  58 static size_t use_strategies_nr, use_strategies_alloc;
  59 static const char **xopts;
  60 static size_t xopts_nr, xopts_alloc;
  61 static const char *branch;
  62 static char *branch_mergeoptions;
  63 static int option_renormalize;
  64 static int verbosity;
  65 static int allow_rerere_auto;
  66 static int abort_current_merge;
  67 static int allow_unrelated_histories;
  68 static int show_progress = -1;
  69 static int default_to_upstream = 1;
  70 static const char *sign_commit;
  71
  72 static struct strategy all_strategy[] = {
  73         { "recursive",  DEFAULT_TWOHEAD | NO_TRIVIAL },
  74         { "octopus",    DEFAULT_OCTOPUS },
  75         { "resolve",    0 },
  76         { "ours",       NO_FAST_FORWARD | NO_TRIVIAL },
  77         { "subtree",    NO_FAST_FORWARD | NO_TRIVIAL },
  78 };
  79
  80 static const char *pull_twohead, *pull_octopus;
  81
  82 enum ff_type {
  83         FF_NO,
  84         FF_ALLOW,
  85         FF_ONLY
  86 };
  87
  88 static enum ff_type fast_forward = FF_ALLOW;
  89
  90 static int option_parse_message(const struct option *opt,
  91                                 const char *arg, int unset)
  92 {
  93         struct strbuf *buf = opt->value;
  94
  95         if (unset)
  96                 strbuf_setlen(buf, 0);
  97         else if (arg) {
  98                 strbuf_addf(buf, "%s%s", buf->len ? "\n\n" : "", arg);
  99                 have_message = 1;
 100         } else
 101                 return error(_("switch `m' requires a value"));
 102         return 0;
 103 }
 104
 105 static struct strategy *get_strategy(const char *name)
 106 {
 107         int i;
 108         struct strategy *ret;
 109         static struct cmdnames main_cmds, other_cmds;
 110         static int loaded;
 111
 112         if (!name)
 113                 return NULL;
 114
 115         for (i = 0; i < ARRAY_SIZE(all_strategy); i++)
 116                 if (!strcmp(name, all_strategy[i].name))
 117                         return &all_strategy[i];
 118
 119         if (!loaded) {
 120                 struct cmdnames not_strategies;
 121                 loaded = 1;
 122
 123                 memset(&not_strategies, 0, sizeof(struct cmdnames));
 124                 load_command_list("git-merge-", &main_cmds, &other_cmds);
 125                 for (i = 0; i < main_cmds.cnt; i++) {
 126                         int j, found = 0;
 127                         struct cmdname *ent = main_cmds.names[i];
 128                         for (j = 0; j < ARRAY_SIZE(all_strategy); j++)
 129                                 if (!strncmp(ent->name, all_strategy[j].name, ent->len)
 130                                                 && !all_strategy[j].name[ent->len])
 131                                         found = 1;
 132                         if (!found)
 133                                 add_cmdname(&not_strategies, ent->name, ent->len);
 134                 }
 135                 exclude_cmds(&main_cmds, &not_strategies);
 136         }
 137         if (!is_in_cmdlist(&main_cmds, name) && !is_in_cmdlist(&other_cmds, name)) {
 138                 fprintf(stderr, _("Could not find merge strategy '%s'.\n"), name);
 139                 fprintf(stderr, _("Available strategies are:"));
 140                 for (i = 0; i < main_cmds.cnt; i++)
 141                         fprintf(stderr, " %s", main_cmds.names[i]->name);
 142                 fprintf(stderr, ".\n");
 143                 if (other_cmds.cnt) {
 144                         fprintf(stderr, _("Available custom strategies are:"));
 145                         for (i = 0; i < other_cmds.cnt; i++)
 146                                 fprintf(stderr, " %s", other_cmds.names[i]->name);
 147                         fprintf(stderr, ".\n");
 148                 }
 149                 exit(1);
 150         }
 151
 152         ret = xcalloc(1, sizeof(struct strategy));
 153         ret->name = xstrdup(name);
 154         ret->attr = NO_TRIVIAL;
 155         return ret;
 156 }
 157
 158 static void append_strategy(struct strategy *s)
 159 {
 160         ALLOC_GROW(use_strategies, use_strategies_nr + 1, use_strategies_alloc);
 161         use_strategies[use_strategies_nr++] = s;
 162 }
 163
 164 static int option_parse_strategy(const struct option *opt,
 165                                  const char *name, int unset)
 166 {
 167         if (unset)
 168                 return 0;
 169
 170         append_strategy(get_strategy(name));
 171         return 0;
 172 }
 173
 174 static int option_parse_x(const struct option *opt,
 175                           const char *arg, int unset)
 176 {
 177         if (unset)
 178                 return 0;
 179
 180         ALLOC_GROW(xopts, xopts_nr + 1, xopts_alloc);
 181         xopts[xopts_nr++] = xstrdup(arg);
 182         return 0;
 183 }
 184
 185 static int option_parse_n(const struct option *opt,
 186                           const char *arg, int unset)
 187 {
 188         show_diffstat = unset;
 189         return 0;
 190 }
 191
 192 static struct option builtin_merge_options[] = {
 193         { OPTION_CALLBACK, 'n', NULL, NULL, NULL,
 194                 N_("do not show a diffstat at the end of the merge"),
 195                 PARSE_OPT_NOARG, option_parse_n },
 196         OPT_BOOL(0, "stat", &show_diffstat,
 197                 N_("show a diffstat at the end of the merge")),
 198         OPT_BOOL(0, "summary", &show_diffstat, N_("(synonym to --stat)")),
 199         { OPTION_INTEGER, 0, "log", &shortlog_len, N_("n"),
 200           N_("add (at most <n>) entries from shortlog to merge commit message"),
 201           PARSE_OPT_OPTARG, NULL, DEFAULT_MERGE_LOG_LEN },
 202         OPT_BOOL(0, "squash", &squash,
 203                 N_("create a single commit instead of doing a merge")),
 204         OPT_BOOL(0, "commit", &option_commit,
 205                 N_("perform a commit if the merge succeeds (default)")),
 206         OPT_BOOL('e', "edit", &option_edit,
 207                 N_("edit message before committing")),
 208         OPT_SET_INT(0, "ff", &fast_forward, N_("allow fast-forward (default)"), FF_ALLOW),
 209         { OPTION_SET_INT, 0, "ff-only", &fast_forward, NULL,
 210                 N_("abort if fast-forward is not possible"),
 211                 PARSE_OPT_NOARG | PARSE_OPT_NONEG, NULL, FF_ONLY },
 212         OPT_RERERE_AUTOUPDATE(&allow_rerere_auto),
 213         OPT_BOOL(0, "verify-signatures", &verify_signatures,
 214                 N_("verify that the named commit has a valid GPG signature")),
 215         OPT_CALLBACK('s', "strategy", &use_strategies, N_("strategy"),
 216                 N_("merge strategy to use"), option_parse_strategy),
 217         OPT_CALLBACK('X', "strategy-option", &xopts, N_("option=value"),
 218                 N_("option for selected merge strategy"), option_parse_x),
 219         OPT_CALLBACK('m', "message", &merge_msg, N_("message"),
 220                 N_("merge commit message (for a non-fast-forward merge)"),
 221                 option_parse_message),
 222         OPT__VERBOSITY(&verbosity),
 223         OPT_BOOL(0, "abort", &abort_current_merge,
 224                 N_("abort the current in-progress merge")),
 225         OPT_BOOL(0, "allow-unrelated-histories", &allow_unrelated_histories,
 226                  N_("allow merging unrelated histories")),
 227         OPT_SET_INT(0, "progress", &show_progress, N_("force progress reporting"), 1),
 228         { OPTION_STRING, 'S', "gpg-sign", &sign_commit, N_("key-id"),
 229           N_("GPG sign commit"), PARSE_OPT_OPTARG, NULL, (intptr_t) "" },
 230         OPT_BOOL(0, "overwrite-ignore", &overwrite_ignore, N_("update ignored files (default)")),
 231         OPT_END()
 232 };
 233
 234 /* Cleans up metadata that is uninteresting after a succeeded merge. */
 235 static void drop_save(void)
 236 {
 237         unlink(git_path_merge_head());
 238         unlink(git_path_merge_msg());
 239         unlink(git_path_merge_mode());
 240 }
 241
 242 static int save_state(unsigned char *stash)
 243 {
 244         int len;
 245         struct child_process cp = CHILD_PROCESS_INIT;
 246         struct strbuf buffer = STRBUF_INIT;
 247         const char *argv[] = {"stash", "create", NULL};
 248
 249         cp.argv = argv;
 250         cp.out = -1;
 251         cp.git_cmd = 1;
 252
 253         if (start_command(&cp))
 254                 die(_("could not run stash."));
 255         len = strbuf_read(&buffer, cp.out, 1024);
 256         close(cp.out);
 257
 258         if (finish_command(&cp) || len < 0)
 259                 die(_("stash failed"));
 260         else if (!len)          /* no changes */
 261                 return -1;
 262         strbuf_setlen(&buffer, buffer.len-1);
 263         if (get_sha1(buffer.buf, stash))
 264                 die(_("not a valid object: %s"), buffer.buf);
 265         return 0;
 266 }
 267
 268 static void read_empty(unsigned const char *sha1, int verbose)
 269 {
 270         int i = 0;
 271         const char *args[7];
 272
 273         args[i++] = "read-tree";
 274         if (verbose)
 275                 args[i++] = "-v";
 276         args[i++] = "-m";
 277         args[i++] = "-u";
 278         args[i++] = EMPTY_TREE_SHA1_HEX;
 279         args[i++] = sha1_to_hex(sha1);
 280         args[i] = NULL;
 281
 282         if (run_command_v_opt(args, RUN_GIT_CMD))
 283                 die(_("read-tree failed"));
 284 }
 285
 286 static void reset_hard(unsigned const char *sha1, int verbose)
 287 {
 288         int i = 0;
 289         const char *args[6];
 290
 291         args[i++] = "read-tree";
 292         if (verbose)
 293                 args[i++] = "-v";
 294         args[i++] = "--reset";
 295         args[i++] = "-u";
 296         args[i++] = sha1_to_hex(sha1);
 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 restore_state(const unsigned char *head,
 304                           const unsigned char *stash)
 305 {
 306         struct strbuf sb = STRBUF_INIT;
 307         const char *args[] = { "stash", "apply", NULL, NULL };
 308
 309         if (is_null_sha1(stash))
 310                 return;
 311
 312         reset_hard(head, 1);
 313
 314         args[2] = sha1_to_hex(stash);
 315
 316         /*
 317          * It is OK to ignore error here, for example when there was
 318          * nothing to restore.
 319          */
 320         run_command_v_opt(args, RUN_GIT_CMD);
 321
 322         strbuf_release(&sb);
 323         refresh_cache(REFRESH_QUIET);
 324 }
 325
 326 /* This is called when no merge was necessary. */
 327 static void finish_up_to_date(const char *msg)
 328 {
 329         if (verbosity >= 0)
 330                 printf("%s%s\n", squash ? _(" (nothing to squash)") : "", msg);
 331         drop_save();
 332 }
 333
 334 static void squash_message(struct commit *commit, struct commit_list *remoteheads)
 335 {
 336         struct rev_info rev;
 337         struct strbuf out = STRBUF_INIT;
 338         struct commit_list *j;
 339         struct pretty_print_context ctx = {0};
 340
 341         printf(_("Squash commit -- not updating HEAD\n"));
 342
 343         init_revisions(&rev, NULL);
 344         rev.ignore_merges = 1;
 345         rev.commit_format = CMIT_FMT_MEDIUM;
 346
 347         commit->object.flags |= UNINTERESTING;
 348         add_pending_object(&rev, &commit->object, NULL);
 349
 350         for (j = remoteheads; j; j = j->next)
 351                 add_pending_object(&rev, &j->item->object, NULL);
 352
 353         setup_revisions(0, NULL, &rev, NULL);
 354         if (prepare_revision_walk(&rev))
 355                 die(_("revision walk setup failed"));
 356
 357         ctx.abbrev = rev.abbrev;
 358         ctx.date_mode = rev.date_mode;
 359         ctx.fmt = rev.commit_format;
 360
 361         strbuf_addstr(&out, "Squashed commit of the following:\n");
 362         while ((commit = get_revision(&rev)) != NULL) {
 363                 strbuf_addch(&out, '\n');
 364                 strbuf_addf(&out, "commit %s\n",
 365                         oid_to_hex(&commit->object.oid));
 366                 pretty_print_commit(&ctx, commit, &out);
 367         }
 368         write_file_buf(git_path_squash_msg(), out.buf, out.len);
 369         strbuf_release(&out);
 370 }
 371
 372 static void finish(struct commit *head_commit,
 373                    struct commit_list *remoteheads,
 374                    const unsigned char *new_head, const char *msg)
 375 {
 376         struct strbuf reflog_message = STRBUF_INIT;
 377         const unsigned char *head = head_commit->object.oid.hash;
 378
 379         if (!msg)
 380                 strbuf_addstr(&reflog_message, getenv("GIT_REFLOG_ACTION"));
 381         else {
 382                 if (verbosity >= 0)
 383                         printf("%s\n", msg);
 384                 strbuf_addf(&reflog_message, "%s: %s",
 385                         getenv("GIT_REFLOG_ACTION"), msg);
 386         }
 387         if (squash) {
 388                 squash_message(head_commit, remoteheads);
 389         } else {
 390                 if (verbosity >= 0 && !merge_msg.len)
 391                         printf(_("No merge message -- not updating HEAD\n"));
 392                 else {
 393                         const char *argv_gc_auto[] = { "gc", "--auto", NULL };
 394                         update_ref(reflog_message.buf, "HEAD",
 395                                 new_head, head, 0,
 396                                 UPDATE_REFS_DIE_ON_ERR);
 397                         /*
 398                          * We ignore errors in 'gc --auto', since the
 399                          * user should see them.
 400                          */
 401                         close_all_packs();
 402                         run_command_v_opt(argv_gc_auto, RUN_GIT_CMD);
 403                 }
 404         }
 405         if (new_head && show_diffstat) {
 406                 struct diff_options opts;
 407                 diff_setup(&opts);
 408                 opts.stat_width = -1; /* use full terminal width */
 409                 opts.stat_graph_width = -1; /* respect statGraphWidth config */
 410                 opts.output_format |=
 411                         DIFF_FORMAT_SUMMARY | DIFF_FORMAT_DIFFSTAT;
 412                 opts.detect_rename = DIFF_DETECT_RENAME;
 413                 diff_setup_done(&opts);
 414                 diff_tree_sha1(head, new_head, "", &opts);
 415                 diffcore_std(&opts);
 416                 diff_flush(&opts);
 417         }
 418
 419         /* Run a post-merge hook */
 420         run_hook_le(NULL, "post-merge", squash ? "1" : "0", NULL);
 421
 422         strbuf_release(&reflog_message);
 423 }
 424
 425 /* Get the name for the merge commit's message. */
 426 static void merge_name(const char *remote, struct strbuf *msg)
 427 {
 428         struct commit *remote_head;
 429         unsigned char branch_head[20];
 430         struct strbuf buf = STRBUF_INIT;
 431         struct strbuf bname = STRBUF_INIT;
 432         const char *ptr;
 433         char *found_ref;
 434         int len, early;
 435
 436         strbuf_branchname(&bname, remote);
 437         remote = bname.buf;
 438
 439         memset(branch_head, 0, sizeof(branch_head));
 440         remote_head = get_merge_parent(remote);
 441         if (!remote_head)
 442                 die(_("'%s' does not point to a commit"), remote);
 443
 444         if (dwim_ref(remote, strlen(remote), branch_head, &found_ref) > 0) {
 445                 if (starts_with(found_ref, "refs/heads/")) {
 446                         strbuf_addf(msg, "%s\t\tbranch '%s' of .\n",
 447                                     sha1_to_hex(branch_head), remote);
 448                         goto cleanup;
 449                 }
 450                 if (starts_with(found_ref, "refs/tags/")) {
 451                         strbuf_addf(msg, "%s\t\ttag '%s' of .\n",
 452                                     sha1_to_hex(branch_head), remote);
 453                         goto cleanup;
 454                 }
 455                 if (starts_with(found_ref, "refs/remotes/")) {
 456                         strbuf_addf(msg, "%s\t\tremote-tracking branch '%s' of .\n",
 457                                     sha1_to_hex(branch_head), remote);
 458                         goto cleanup;
 459                 }
 460         }
 461
 462         /* See if remote matches <name>^^^.. or <name>~<number> */
 463         for (len = 0, ptr = remote + strlen(remote);
 464              remote < ptr && ptr[-1] == '^';
 465              ptr--)
 466                 len++;
 467         if (len)
 468                 early = 1;
 469         else {
 470                 early = 0;
 471                 ptr = strrchr(remote, '~');
 472                 if (ptr) {
 473                         int seen_nonzero = 0;
 474
 475                         len++; /* count ~ */
 476                         while (*++ptr && isdigit(*ptr)) {
 477                                 seen_nonzero |= (*ptr != '0');
 478                                 len++;
 479                         }
 480                         if (*ptr)
 481                                 len = 0; /* not ...~<number> */
 482                         else if (seen_nonzero)
 483                                 early = 1;
 484                         else if (len == 1)
 485                                 early = 1; /* "name~" is "name~1"! */
 486                 }
 487         }
 488         if (len) {
 489                 struct strbuf truname = STRBUF_INIT;
 490                 strbuf_addf(&truname, "refs/heads/%s", remote);
 491                 strbuf_setlen(&truname, truname.len - len);
 492                 if (ref_exists(truname.buf)) {
 493                         strbuf_addf(msg,
 494                                     "%s\t\tbranch '%s'%s of .\n",
 495                                     oid_to_hex(&remote_head->object.oid),
 496                                     truname.buf + 11,
 497                                     (early ? " (early part)" : ""));
 498                         strbuf_release(&truname);
 499                         goto cleanup;
 500                 }
 501                 strbuf_release(&truname);
 502         }
 503
 504         if (remote_head->util) {
 505                 struct merge_remote_desc *desc;
 506                 desc = merge_remote_util(remote_head);
 507                 if (desc && desc->obj && desc->obj->type == OBJ_TAG) {
 508                         strbuf_addf(msg, "%s\t\t%s '%s'\n",
 509                                     oid_to_hex(&desc->obj->oid),
 510                                     typename(desc->obj->type),
 511                                     remote);
 512                         goto cleanup;
 513                 }
 514         }
 515
 516         strbuf_addf(msg, "%s\t\tcommit '%s'\n",
 517                 oid_to_hex(&remote_head->object.oid), remote);
 518 cleanup:
 519         strbuf_release(&buf);
 520         strbuf_release(&bname);
 521 }
 522
 523 static void parse_branch_merge_options(char *bmo)
 524 {
 525         const char **argv;
 526         int argc;
 527
 528         if (!bmo)
 529                 return;
 530         argc = split_cmdline(bmo, &argv);
 531         if (argc < 0)
 532                 die(_("Bad branch.%s.mergeoptions string: %s"), branch,
 533                     split_cmdline_strerror(argc));
 534         REALLOC_ARRAY(argv, argc + 2);
 535         memmove(argv + 1, argv, sizeof(*argv) * (argc + 1));
 536         argc++;
 537         argv[0] = "branch.*.mergeoptions";
 538         parse_options(argc, argv, NULL, builtin_merge_options,
 539                       builtin_merge_usage, 0);
 540         free(argv);
 541 }
 542
 543 static int git_merge_config(const char *k, const char *v, void *cb)
 544 {
 545         int status;
 546
 547         if (branch && starts_with(k, "branch.") &&
 548                 starts_with(k + 7, branch) &&
 549                 !strcmp(k + 7 + strlen(branch), ".mergeoptions")) {
 550                 free(branch_mergeoptions);
 551                 branch_mergeoptions = xstrdup(v);
 552                 return 0;
 553         }
 554
 555         if (!strcmp(k, "merge.diffstat") || !strcmp(k, "merge.stat"))
 556                 show_diffstat = git_config_bool(k, v);
 557         else if (!strcmp(k, "pull.twohead"))
 558                 return git_config_string(&pull_twohead, k, v);
 559         else if (!strcmp(k, "pull.octopus"))
 560                 return git_config_string(&pull_octopus, k, v);
 561         else if (!strcmp(k, "merge.renormalize"))
 562                 option_renormalize = git_config_bool(k, v);
 563         else if (!strcmp(k, "merge.ff")) {
 564                 int boolval = git_config_maybe_bool(k, v);
 565                 if (0 <= boolval) {
 566                         fast_forward = boolval ? FF_ALLOW : FF_NO;
 567                 } else if (v && !strcmp(v, "only")) {
 568                         fast_forward = FF_ONLY;
 569                 } /* do not barf on values from future versions of git */
 570                 return 0;
 571         } else if (!strcmp(k, "merge.defaulttoupstream")) {
 572                 default_to_upstream = git_config_bool(k, v);
 573                 return 0;
 574         } else if (!strcmp(k, "commit.gpgsign")) {
 575                 sign_commit = git_config_bool(k, v) ? "" : NULL;
 576                 return 0;
 577         }
 578
 579         status = fmt_merge_msg_config(k, v, cb);
 580         if (status)
 581                 return status;
 582         status = git_gpg_config(k, v, NULL);
 583         if (status)
 584                 return status;
 585         return git_diff_ui_config(k, v, cb);
 586 }
 587
 588 static int read_tree_trivial(unsigned char *common, unsigned char *head,
 589                              unsigned char *one)
 590 {
 591         int i, nr_trees = 0;
 592         struct tree *trees[MAX_UNPACK_TREES];
 593         struct tree_desc t[MAX_UNPACK_TREES];
 594         struct unpack_trees_options opts;
 595
 596         memset(&opts, 0, sizeof(opts));
 597         opts.head_idx = 2;
 598         opts.src_index = &the_index;
 599         opts.dst_index = &the_index;
 600         opts.update = 1;
 601         opts.verbose_update = 1;
 602         opts.trivial_merges_only = 1;
 603         opts.merge = 1;
 604         trees[nr_trees] = parse_tree_indirect(common);
 605         if (!trees[nr_trees++])
 606                 return -1;
 607         trees[nr_trees] = parse_tree_indirect(head);
 608         if (!trees[nr_trees++])
 609                 return -1;
 610         trees[nr_trees] = parse_tree_indirect(one);
 611         if (!trees[nr_trees++])
 612                 return -1;
 613         opts.fn = threeway_merge;
 614         cache_tree_free(&active_cache_tree);
 615         for (i = 0; i < nr_trees; i++) {
 616                 parse_tree(trees[i]);
 617                 init_tree_desc(t+i, trees[i]->buffer, trees[i]->size);
 618         }
 619         if (unpack_trees(nr_trees, t, &opts))
 620                 return -1;
 621         return 0;
 622 }
 623
 624 static void write_tree_trivial(unsigned char *sha1)
 625 {
 626         if (write_cache_as_tree(sha1, 0, NULL))
 627                 die(_("git write-tree failed to write a tree"));
 628 }
 629
 630 static int try_merge_strategy(const char *strategy, struct commit_list *common,
 631                               struct commit_list *remoteheads,
 632                               struct commit *head, const char *head_arg)
 633 {
 634         static struct lock_file lock;
 635
 636         hold_locked_index(&lock, 1);
 637         refresh_cache(REFRESH_QUIET);
 638         if (active_cache_changed &&
 639             write_locked_index(&the_index, &lock, COMMIT_LOCK))
 640                 return error(_("Unable to write index."));
 641         rollback_lock_file(&lock);
 642
 643         if (!strcmp(strategy, "recursive") || !strcmp(strategy, "subtree")) {
 644                 int clean, x;
 645                 struct commit *result;
 646                 struct commit_list *reversed = NULL;
 647                 struct merge_options o;
 648                 struct commit_list *j;
 649
 650                 if (remoteheads->next) {
 651                         error(_("Not handling anything other than two heads merge."));
 652                         return 2;
 653                 }
 654
 655                 init_merge_options(&o);
 656                 if (!strcmp(strategy, "subtree"))
 657                         o.subtree_shift = "";
 658
 659                 o.renormalize = option_renormalize;
 660                 o.show_rename_progress =
 661                         show_progress == -1 ? isatty(2) : show_progress;
 662
 663                 for (x = 0; x < xopts_nr; x++)
 664                         if (parse_merge_opt(&o, xopts[x]))
 665                                 die(_("Unknown option for merge-recursive: -X%s"), xopts[x]);
 666
 667                 o.branch1 = head_arg;
 668                 o.branch2 = merge_remote_util(remoteheads->item)->name;
 669
 670                 for (j = common; j; j = j->next)
 671                         commit_list_insert(j->item, &reversed);
 672
 673                 hold_locked_index(&lock, 1);
 674                 clean = merge_recursive(&o, head,
 675                                 remoteheads->item, reversed, &result);
 676                 if (clean < 0)
 677                         exit(128);
 678                 if (active_cache_changed &&
 679                     write_locked_index(&the_index, &lock, COMMIT_LOCK))
 680                         die (_("unable to write %s"), get_index_file());
 681                 rollback_lock_file(&lock);
 682                 return clean ? 0 : 1;
 683         } else {
 684                 return try_merge_command(strategy, xopts_nr, xopts,
 685                                                 common, head_arg, remoteheads);
 686         }
 687 }
 688
 689 static void count_diff_files(struct diff_queue_struct *q,
 690                              struct diff_options *opt, void *data)
 691 {
 692         int *count = data;
 693
 694         (*count) += q->nr;
 695 }
 696
 697 static int count_unmerged_entries(void)
 698 {
 699         int i, ret = 0;
 700
 701         for (i = 0; i < active_nr; i++)
 702                 if (ce_stage(active_cache[i]))
 703                         ret++;
 704
 705         return ret;
 706 }
 707
 708 static void split_merge_strategies(const char *string, struct strategy **list,
 709                                    int *nr, int *alloc)
 710 {
 711         char *p, *q, *buf;
 712
 713         if (!string)
 714                 return;
 715
 716         buf = xstrdup(string);
 717         q = buf;
 718         for (;;) {
 719                 p = strchr(q, ' ');
 720                 if (!p) {
 721                         ALLOC_GROW(*list, *nr + 1, *alloc);
 722                         (*list)[(*nr)++].name = xstrdup(q);
 723                         free(buf);
 724                         return;
 725                 } else {
 726                         *p = '\0';
 727                         ALLOC_GROW(*list, *nr + 1, *alloc);
 728                         (*list)[(*nr)++].name = xstrdup(q);
 729                         q = ++p;
 730                 }
 731         }
 732 }
 733
 734 static void add_strategies(const char *string, unsigned attr)
 735 {
 736         struct strategy *list = NULL;
 737         int list_alloc = 0, list_nr = 0, i;
 738
 739         memset(&list, 0, sizeof(list));
 740         split_merge_strategies(string, &list, &list_nr, &list_alloc);
 741         if (list) {
 742                 for (i = 0; i < list_nr; i++)
 743                         append_strategy(get_strategy(list[i].name));
 744                 return;
 745         }
 746         for (i = 0; i < ARRAY_SIZE(all_strategy); i++)
 747                 if (all_strategy[i].attr & attr)
 748                         append_strategy(&all_strategy[i]);
 749
 750 }
 751
 752 static void read_merge_msg(struct strbuf *msg)
 753 {
 754         const char *filename = git_path_merge_msg();
 755         strbuf_reset(msg);
 756         if (strbuf_read_file(msg, filename, 0) < 0)
 757                 die_errno(_("Could not read from '%s'"), filename);
 758 }
 759
 760 static void write_merge_state(struct commit_list *);
 761 static void abort_commit(struct commit_list *remoteheads, const char *err_msg)
 762 {
 763         if (err_msg)
 764                 error("%s", err_msg);
 765         fprintf(stderr,
 766                 _("Not committing merge; use 'git commit' to complete the merge.\n"));
 767         write_merge_state(remoteheads);
 768         exit(1);
 769 }
 770
 771 static const char merge_editor_comment[] =
 772 N_("Please enter a commit message to explain why this merge is necessary,\n"
 773    "especially if it merges an updated upstream into a topic branch.\n"
 774    "\n"
 775    "Lines starting with '%c' will be ignored, and an empty message aborts\n"
 776    "the commit.\n");
 777
 778 static void prepare_to_commit(struct commit_list *remoteheads)
 779 {
 780         struct strbuf msg = STRBUF_INIT;
 781         strbuf_addbuf(&msg, &merge_msg);
 782         strbuf_addch(&msg, '\n');
 783         if (0 < option_edit)
 784                 strbuf_commented_addf(&msg, _(merge_editor_comment), comment_line_char);
 785         write_file_buf(git_path_merge_msg(), msg.buf, msg.len);
 786         if (run_commit_hook(0 < option_edit, get_index_file(), "prepare-commit-msg",
 787                             git_path_merge_msg(), "merge", NULL))
 788                 abort_commit(remoteheads, NULL);
 789         if (0 < option_edit) {
 790                 if (launch_editor(git_path_merge_msg(), NULL, NULL))
 791                         abort_commit(remoteheads, NULL);
 792         }
 793         read_merge_msg(&msg);
 794         strbuf_stripspace(&msg, 0 < option_edit);
 795         if (!msg.len)
 796                 abort_commit(remoteheads, _("Empty commit message."));
 797         strbuf_release(&merge_msg);
 798         strbuf_addbuf(&merge_msg, &msg);
 799         strbuf_release(&msg);
 800 }
 801
 802 static int merge_trivial(struct commit *head, struct commit_list *remoteheads)
 803 {
 804         unsigned char result_tree[20], result_commit[20];
 805         struct commit_list *parents, **pptr = &parents;
 806         static struct lock_file lock;
 807
 808         hold_locked_index(&lock, 1);
 809         refresh_cache(REFRESH_QUIET);
 810         if (active_cache_changed &&
 811             write_locked_index(&the_index, &lock, COMMIT_LOCK))
 812                 return error(_("Unable to write index."));
 813         rollback_lock_file(&lock);
 814
 815         write_tree_trivial(result_tree);
 816         printf(_("Wonderful.\n"));
 817         pptr = commit_list_append(head, pptr);
 818         pptr = commit_list_append(remoteheads->item, pptr);
 819         prepare_to_commit(remoteheads);
 820         if (commit_tree(merge_msg.buf, merge_msg.len, result_tree, parents,
 821                         result_commit, NULL, sign_commit))
 822                 die(_("failed to write commit object"));
 823         finish(head, remoteheads, result_commit, "In-index merge");
 824         drop_save();
 825         return 0;
 826 }
 827
 828 static int finish_automerge(struct commit *head,
 829                             int head_subsumed,
 830                             struct commit_list *common,
 831                             struct commit_list *remoteheads,
 832                             unsigned char *result_tree,
 833                             const char *wt_strategy)
 834 {
 835         struct commit_list *parents = NULL;
 836         struct strbuf buf = STRBUF_INIT;
 837         unsigned char result_commit[20];
 838
 839         free_commit_list(common);
 840         parents = remoteheads;
 841         if (!head_subsumed || fast_forward == FF_NO)
 842                 commit_list_insert(head, &parents);
 843         strbuf_addch(&merge_msg, '\n');
 844         prepare_to_commit(remoteheads);
 845         if (commit_tree(merge_msg.buf, merge_msg.len, result_tree, parents,
 846                         result_commit, NULL, sign_commit))
 847                 die(_("failed to write commit object"));
 848         strbuf_addf(&buf, "Merge made by the '%s' strategy.", wt_strategy);
 849         finish(head, remoteheads, result_commit, buf.buf);
 850         strbuf_release(&buf);
 851         drop_save();
 852         return 0;
 853 }
 854
 855 static int suggest_conflicts(void)
 856 {
 857         const char *filename;
 858         FILE *fp;
 859         struct strbuf msgbuf = STRBUF_INIT;
 860
 861         filename = git_path_merge_msg();
 862         fp = fopen(filename, "a");
 863         if (!fp)
 864                 die_errno(_("Could not open '%s' for writing"), filename);
 865
 866         append_conflicts_hint(&msgbuf);
 867         fputs(msgbuf.buf, fp);
 868         strbuf_release(&msgbuf);
 869         fclose(fp);
 870         rerere(allow_rerere_auto);
 871         printf(_("Automatic merge failed; "
 872                         "fix conflicts and then commit the result.\n"));
 873         return 1;
 874 }
 875
 876 static struct commit *is_old_style_invocation(int argc, const char **argv,
 877                                               const unsigned char *head)
 878 {
 879         struct commit *second_token = NULL;
 880         if (argc > 2) {
 881                 unsigned char second_sha1[20];
 882
 883                 if (get_sha1(argv[1], second_sha1))
 884                         return NULL;
 885                 second_token = lookup_commit_reference_gently(second_sha1, 0);
 886                 if (!second_token)
 887                         die(_("'%s' is not a commit"), argv[1]);
 888                 if (hashcmp(second_token->object.oid.hash, head))
 889                         return NULL;
 890         }
 891         return second_token;
 892 }
 893
 894 static int evaluate_result(void)
 895 {
 896         int cnt = 0;
 897         struct rev_info rev;
 898
 899         /* Check how many files differ. */
 900         init_revisions(&rev, "");
 901         setup_revisions(0, NULL, &rev, NULL);
 902         rev.diffopt.output_format |=
 903                 DIFF_FORMAT_CALLBACK;
 904         rev.diffopt.format_callback = count_diff_files;
 905         rev.diffopt.format_callback_data = &cnt;
 906         run_diff_files(&rev, 0);
 907
 908         /*
 909          * Check how many unmerged entries are
 910          * there.
 911          */
 912         cnt += count_unmerged_entries();
 913
 914         return cnt;
 915 }
 916
 917 /*
 918  * Pretend as if the user told us to merge with the remote-tracking
 919  * branch we have for the upstream of the current branch
 920  */
 921 static int setup_with_upstream(const char ***argv)
 922 {
 923         struct branch *branch = branch_get(NULL);
 924         int i;
 925         const char **args;
 926
 927         if (!branch)
 928                 die(_("No current branch."));
 929         if (!branch->remote_name)
 930                 die(_("No remote for the current branch."));
 931         if (!branch->merge_nr)
 932                 die(_("No default upstream defined for the current branch."));
 933
 934         args = xcalloc(st_add(branch->merge_nr, 1), sizeof(char *));
 935         for (i = 0; i < branch->merge_nr; i++) {
 936                 if (!branch->merge[i]->dst)
 937                         die(_("No remote-tracking branch for %s from %s"),
 938                             branch->merge[i]->src, branch->remote_name);
 939                 args[i] = branch->merge[i]->dst;
 940         }
 941         args[i] = NULL;
 942         *argv = args;
 943         return i;
 944 }
 945
 946 static void write_merge_state(struct commit_list *remoteheads)
 947 {
 948         struct commit_list *j;
 949         struct strbuf buf = STRBUF_INIT;
 950
 951         for (j = remoteheads; j; j = j->next) {
 952                 struct object_id *oid;
 953                 struct commit *c = j->item;
 954                 if (c->util && merge_remote_util(c)->obj) {
 955                         oid = &merge_remote_util(c)->obj->oid;
 956                 } else {
 957                         oid = &c->object.oid;
 958                 }
 959                 strbuf_addf(&buf, "%s\n", oid_to_hex(oid));
 960         }
 961         write_file_buf(git_path_merge_head(), buf.buf, buf.len);
 962         strbuf_addch(&merge_msg, '\n');
 963         write_file_buf(git_path_merge_msg(), merge_msg.buf, merge_msg.len);
 964
 965         strbuf_reset(&buf);
 966         if (fast_forward == FF_NO)
 967                 strbuf_addf(&buf, "no-ff");
 968         write_file_buf(git_path_merge_mode(), buf.buf, buf.len);
 969 }
 970
 971 static int default_edit_option(void)
 972 {
 973         static const char name[] = "GIT_MERGE_AUTOEDIT";
 974         const char *e = getenv(name);
 975         struct stat st_stdin, st_stdout;
 976
 977         if (have_message)
 978                 /* an explicit -m msg without --[no-]edit */
 979                 return 0;
 980
 981         if (e) {
 982                 int v = git_config_maybe_bool(name, e);
 983                 if (v < 0)
 984                         die(_("Bad value '%s' in environment '%s'"), e, name);
 985                 return v;
 986         }
 987
 988         /* Use editor if stdin and stdout are the same and is a tty */
 989         return (!fstat(0, &st_stdin) &&
 990                 !fstat(1, &st_stdout) &&
 991                 isatty(0) && isatty(1) &&
 992                 st_stdin.st_dev == st_stdout.st_dev &&
 993                 st_stdin.st_ino == st_stdout.st_ino &&
 994                 st_stdin.st_mode == st_stdout.st_mode);
 995 }
 996
 997 static struct commit_list *reduce_parents(struct commit *head_commit,
 998                                           int *head_subsumed,
 999                                           struct commit_list *remoteheads)
1000 {
1001         struct commit_list *parents, **remotes;
1002
1003         /*
1004          * Is the current HEAD reachable from another commit being
1005          * merged?  If so we do not want to record it as a parent of
1006          * the resulting merge, unless --no-ff is given.  We will flip
1007          * this variable to 0 when we find HEAD among the independent
1008          * tips being merged.
1009          */
1010         *head_subsumed = 1;
1011
1012         /* Find what parents to record by checking independent ones. */
1013         parents = reduce_heads(remoteheads);
1014
1015         remoteheads = NULL;
1016         remotes = &remoteheads;
1017         while (parents) {
1018                 struct commit *commit = pop_commit(&parents);
1019                 if (commit == head_commit)
1020                         *head_subsumed = 0;
1021                 else
1022                         remotes = &commit_list_insert(commit, remotes)->next;
1023         }
1024         return remoteheads;
1025 }
1026
1027 static void prepare_merge_message(struct strbuf *merge_names, struct strbuf *merge_msg)
1028 {
1029         struct fmt_merge_msg_opts opts;
1030
1031         memset(&opts, 0, sizeof(opts));
1032         opts.add_title = !have_message;
1033         opts.shortlog_len = shortlog_len;
1034         opts.credit_people = (0 < option_edit);
1035
1036         fmt_merge_msg(merge_names, merge_msg, &opts);
1037         if (merge_msg->len)
1038                 strbuf_setlen(merge_msg, merge_msg->len - 1);
1039 }
1040
1041 static void handle_fetch_head(struct commit_list **remotes, struct strbuf *merge_names)
1042 {
1043         const char *filename;
1044         int fd, pos, npos;
1045         struct strbuf fetch_head_file = STRBUF_INIT;
1046
1047         if (!merge_names)
1048                 merge_names = &fetch_head_file;
1049
1050         filename = git_path_fetch_head();
1051         fd = open(filename, O_RDONLY);
1052         if (fd < 0)
1053                 die_errno(_("could not open '%s' for reading"), filename);
1054
1055         if (strbuf_read(merge_names, fd, 0) < 0)
1056                 die_errno(_("could not read '%s'"), filename);
1057         if (close(fd) < 0)
1058                 die_errno(_("could not close '%s'"), filename);
1059
1060         for (pos = 0; pos < merge_names->len; pos = npos) {
1061                 unsigned char sha1[20];
1062                 char *ptr;
1063                 struct commit *commit;
1064
1065                 ptr = strchr(merge_names->buf + pos, '\n');
1066                 if (ptr)
1067                         npos = ptr - merge_names->buf + 1;
1068                 else
1069                         npos = merge_names->len;
1070
1071                 if (npos - pos < 40 + 2 ||
1072                     get_sha1_hex(merge_names->buf + pos, sha1))
1073                         commit = NULL; /* bad */
1074                 else if (memcmp(merge_names->buf + pos + 40, "\t\t", 2))
1075                         continue; /* not-for-merge */
1076                 else {
1077                         char saved = merge_names->buf[pos + 40];
1078                         merge_names->buf[pos + 40] = '\0';
1079                         commit = get_merge_parent(merge_names->buf + pos);
1080                         merge_names->buf[pos + 40] = saved;
1081                 }
1082                 if (!commit) {
1083                         if (ptr)
1084                                 *ptr = '\0';
1085                         die(_("not something we can merge in %s: %s"),
1086                             filename, merge_names->buf + pos);
1087                 }
1088                 remotes = &commit_list_insert(commit, remotes)->next;
1089         }
1090
1091         if (merge_names == &fetch_head_file)
1092                 strbuf_release(&fetch_head_file);
1093 }
1094
1095 static struct commit_list *collect_parents(struct commit *head_commit,
1096                                            int *head_subsumed,
1097                                            int argc, const char **argv,
1098                                            struct strbuf *merge_msg)
1099 {
1100         int i;
1101         struct commit_list *remoteheads = NULL;
1102         struct commit_list **remotes = &remoteheads;
1103         struct strbuf merge_names = STRBUF_INIT, *autogen = NULL;
1104
1105         if (merge_msg && (!have_message || shortlog_len))
1106                 autogen = &merge_names;
1107
1108         if (head_commit)
1109                 remotes = &commit_list_insert(head_commit, remotes)->next;
1110
1111         if (argc == 1 && !strcmp(argv[0], "FETCH_HEAD")) {
1112                 handle_fetch_head(remotes, autogen);
1113                 remoteheads = reduce_parents(head_commit, head_subsumed, remoteheads);
1114         } else {
1115                 for (i = 0; i < argc; i++) {
1116                         struct commit *commit = get_merge_parent(argv[i]);
1117                         if (!commit)
1118                                 help_unknown_ref(argv[i], "merge",
1119                                                  _("not something we can merge"));
1120                         remotes = &commit_list_insert(commit, remotes)->next;
1121                 }
1122                 remoteheads = reduce_parents(head_commit, head_subsumed, remoteheads);
1123                 if (autogen) {
1124                         struct commit_list *p;
1125                         for (p = remoteheads; p; p = p->next)
1126                                 merge_name(merge_remote_util(p->item)->name, autogen);
1127                 }
1128         }
1129
1130         if (autogen) {
1131                 prepare_merge_message(autogen, merge_msg);
1132                 strbuf_release(autogen);
1133         }
1134
1135         return remoteheads;
1136 }
1137
1138 int cmd_merge(int argc, const char **argv, const char *prefix)
1139 {
1140         unsigned char result_tree[20];
1141         unsigned char stash[20];
1142         unsigned char head_sha1[20];
1143         struct commit *head_commit;
1144         struct strbuf buf = STRBUF_INIT;
1145         const char *head_arg;
1146         int i, ret = 0, head_subsumed;
1147         int best_cnt = -1, merge_was_ok = 0, automerge_was_ok = 0;
1148         struct commit_list *common = NULL;
1149         const char *best_strategy = NULL, *wt_strategy = NULL;
1150         struct commit_list *remoteheads, *p;
1151         void *branch_to_free;
1152
1153         if (argc == 2 && !strcmp(argv[1], "-h"))
1154                 usage_with_options(builtin_merge_usage, builtin_merge_options);
1155
1156         /*
1157          * Check if we are _not_ on a detached HEAD, i.e. if there is a
1158          * current branch.
1159          */
1160         branch = branch_to_free = resolve_refdup("HEAD", 0, head_sha1, NULL);
1161         if (branch && starts_with(branch, "refs/heads/"))
1162                 branch += 11;
1163         if (!branch || is_null_sha1(head_sha1))
1164                 head_commit = NULL;
1165         else
1166                 head_commit = lookup_commit_or_die(head_sha1, "HEAD");
1167
1168         init_diff_ui_defaults();
1169         git_config(git_merge_config, NULL);
1170
1171         if (branch_mergeoptions)
1172                 parse_branch_merge_options(branch_mergeoptions);
1173         argc = parse_options(argc, argv, prefix, builtin_merge_options,
1174                         builtin_merge_usage, 0);
1175         if (shortlog_len < 0)
1176                 shortlog_len = (merge_log_config > 0) ? merge_log_config : 0;
1177
1178         if (verbosity < 0 && show_progress == -1)
1179                 show_progress = 0;
1180
1181         if (abort_current_merge) {
1182                 int nargc = 2;
1183                 const char *nargv[] = {"reset", "--merge", NULL};
1184
1185                 if (!file_exists(git_path_merge_head()))
1186                         die(_("There is no merge to abort (MERGE_HEAD missing)."));
1187
1188                 /* Invoke 'git reset --merge' */
1189                 ret = cmd_reset(nargc, nargv, prefix);
1190                 goto done;
1191         }
1192
1193         if (read_cache_unmerged())
1194                 die_resolve_conflict("merge");
1195
1196         if (file_exists(git_path_merge_head())) {
1197                 /*
1198                  * There is no unmerged entry, don't advise 'git
1199                  * add/rm <file>', just 'git commit'.
1200                  */
1201                 if (advice_resolve_conflict)
1202                         die(_("You have not concluded your merge (MERGE_HEAD exists).\n"
1203                                   "Please, commit your changes before you merge."));
1204                 else
1205                         die(_("You have not concluded your merge (MERGE_HEAD exists)."));
1206         }
1207         if (file_exists(git_path_cherry_pick_head())) {
1208                 if (advice_resolve_conflict)
1209                         die(_("You have not concluded your cherry-pick (CHERRY_PICK_HEAD exists).\n"
1210                             "Please, commit your changes before you merge."));
1211                 else
1212                         die(_("You have not concluded your cherry-pick (CHERRY_PICK_HEAD exists)."));
1213         }
1214         resolve_undo_clear();
1215
1216         if (verbosity < 0)
1217                 show_diffstat = 0;
1218
1219         if (squash) {
1220                 if (fast_forward == FF_NO)
1221                         die(_("You cannot combine --squash with --no-ff."));
1222                 option_commit = 0;
1223         }
1224
1225         if (!argc) {
1226                 if (default_to_upstream)
1227                         argc = setup_with_upstream(&argv);
1228                 else
1229                         die(_("No commit specified and merge.defaultToUpstream not set."));
1230         } else if (argc == 1 && !strcmp(argv[0], "-")) {
1231                 argv[0] = "@{-1}";
1232         }
1233
1234         if (!argc)
1235                 usage_with_options(builtin_merge_usage,
1236                         builtin_merge_options);
1237
1238         if (!head_commit) {
1239                 /*
1240                  * If the merged head is a valid one there is no reason
1241                  * to forbid "git merge" into a branch yet to be born.
1242                  * We do the same for "git pull".
1243                  */
1244                 unsigned char *remote_head_sha1;
1245                 if (squash)
1246                         die(_("Squash commit into empty head not supported yet"));
1247                 if (fast_forward == FF_NO)
1248                         die(_("Non-fast-forward commit does not make sense into "
1249                             "an empty head"));
1250                 remoteheads = collect_parents(head_commit, &head_subsumed,
1251                                               argc, argv, NULL);
1252                 if (!remoteheads)
1253                         die(_("%s - not something we can merge"), argv[0]);
1254                 if (remoteheads->next)
1255                         die(_("Can merge only exactly one commit into empty head"));
1256                 remote_head_sha1 = remoteheads->item->object.oid.hash;
1257                 read_empty(remote_head_sha1, 0);
1258                 update_ref("initial pull", "HEAD", remote_head_sha1,
1259                            NULL, 0, UPDATE_REFS_DIE_ON_ERR);
1260                 goto done;
1261         }
1262
1263         /*
1264          * This could be traditional "merge <msg> HEAD <commit>..."  and
1265          * the way we can tell it is to see if the second token is HEAD,
1266          * but some people might have misused the interface and used a
1267          * commit-ish that is the same as HEAD there instead.
1268          * Traditional format never would have "-m" so it is an
1269          * additional safety measure to check for it.
1270          */
1271         if (!have_message &&
1272             is_old_style_invocation(argc, argv, head_commit->object.oid.hash)) {
1273                 warning("old-style 'git merge <msg> HEAD <commit>' is deprecated.");
1274                 strbuf_addstr(&merge_msg, argv[0]);
1275                 head_arg = argv[1];
1276                 argv += 2;
1277                 argc -= 2;
1278                 remoteheads = collect_parents(head_commit, &head_subsumed,
1279                                               argc, argv, NULL);
1280         } else {
1281                 /* We are invoked directly as the first-class UI. */
1282                 head_arg = "HEAD";
1283
1284                 /*
1285                  * All the rest are the commits being merged; prepare
1286                  * the standard merge summary message to be appended
1287                  * to the given message.
1288                  */
1289                 remoteheads = collect_parents(head_commit, &head_subsumed,
1290                                               argc, argv, &merge_msg);
1291         }
1292
1293         if (!head_commit || !argc)
1294                 usage_with_options(builtin_merge_usage,
1295                         builtin_merge_options);
1296
1297         if (verify_signatures) {
1298                 for (p = remoteheads; p; p = p->next) {
1299                         struct commit *commit = p->item;
1300                         char hex[GIT_SHA1_HEXSZ + 1];
1301                         struct signature_check signature_check;
1302                         memset(&signature_check, 0, sizeof(signature_check));
1303
1304                         check_commit_signature(commit, &signature_check);
1305
1306                         find_unique_abbrev_r(hex, commit->object.oid.hash, DEFAULT_ABBREV);
1307                         switch (signature_check.result) {
1308                         case 'G':
1309                                 break;
1310                         case 'U':
1311                                 die(_("Commit %s has an untrusted GPG signature, "
1312                                       "allegedly by %s."), hex, signature_check.signer);
1313                         case 'B':
1314                                 die(_("Commit %s has a bad GPG signature "
1315                                       "allegedly by %s."), hex, signature_check.signer);
1316                         default: /* 'N' */
1317                                 die(_("Commit %s does not have a GPG signature."), hex);
1318                         }
1319                         if (verbosity >= 0 && signature_check.result == 'G')
1320                                 printf(_("Commit %s has a good GPG signature by %s\n"),
1321                                        hex, signature_check.signer);
1322
1323                         signature_check_clear(&signature_check);
1324                 }
1325         }
1326
1327         strbuf_addstr(&buf, "merge");
1328         for (p = remoteheads; p; p = p->next)
1329                 strbuf_addf(&buf, " %s", merge_remote_util(p->item)->name);
1330         setenv("GIT_REFLOG_ACTION", buf.buf, 0);
1331         strbuf_reset(&buf);
1332
1333         for (p = remoteheads; p; p = p->next) {
1334                 struct commit *commit = p->item;
1335                 strbuf_addf(&buf, "GITHEAD_%s",
1336                             oid_to_hex(&commit->object.oid));
1337                 setenv(buf.buf, merge_remote_util(commit)->name, 1);
1338                 strbuf_reset(&buf);
1339                 if (fast_forward != FF_ONLY &&
1340                     merge_remote_util(commit) &&
1341                     merge_remote_util(commit)->obj &&
1342                     merge_remote_util(commit)->obj->type == OBJ_TAG)
1343                         fast_forward = FF_NO;
1344         }
1345
1346         if (option_edit < 0)
1347                 option_edit = default_edit_option();
1348
1349         if (!use_strategies) {
1350                 if (!remoteheads)
1351                         ; /* already up-to-date */
1352                 else if (!remoteheads->next)
1353                         add_strategies(pull_twohead, DEFAULT_TWOHEAD);
1354                 else
1355                         add_strategies(pull_octopus, DEFAULT_OCTOPUS);
1356         }
1357
1358         for (i = 0; i < use_strategies_nr; i++) {
1359                 if (use_strategies[i]->attr & NO_FAST_FORWARD)
1360                         fast_forward = FF_NO;
1361                 if (use_strategies[i]->attr & NO_TRIVIAL)
1362                         allow_trivial = 0;
1363         }
1364
1365         if (!remoteheads)
1366                 ; /* already up-to-date */
1367         else if (!remoteheads->next)
1368                 common = get_merge_bases(head_commit, remoteheads->item);
1369         else {
1370                 struct commit_list *list = remoteheads;
1371                 commit_list_insert(head_commit, &list);
1372                 common = get_octopus_merge_bases(list);
1373                 free(list);
1374         }
1375
1376         update_ref("updating ORIG_HEAD", "ORIG_HEAD", head_commit->object.oid.hash,
1377                    NULL, 0, UPDATE_REFS_DIE_ON_ERR);
1378
1379         if (remoteheads && !common) {
1380                 /* No common ancestors found. */
1381                 if (!allow_unrelated_histories)
1382                         die(_("refusing to merge unrelated histories"));
1383                 /* otherwise, we need a real merge. */
1384         } else if (!remoteheads ||
1385                  (!remoteheads->next && !common->next &&
1386                   common->item == remoteheads->item)) {
1387                 /*
1388                  * If head can reach all the merge then we are up to date.
1389                  * but first the most common case of merging one remote.
1390                  */
1391                 finish_up_to_date(_("Already up-to-date."));
1392                 goto done;
1393         } else if (fast_forward != FF_NO && !remoteheads->next &&
1394                         !common->next &&
1395                         !oidcmp(&common->item->object.oid, &head_commit->object.oid)) {
1396                 /* Again the most common case of merging one remote. */
1397                 struct strbuf msg = STRBUF_INIT;
1398                 struct commit *commit;
1399
1400                 if (verbosity >= 0) {
1401                         char from[GIT_SHA1_HEXSZ + 1], to[GIT_SHA1_HEXSZ + 1];
1402                         find_unique_abbrev_r(from, head_commit->object.oid.hash,
1403                                               DEFAULT_ABBREV);
1404                         find_unique_abbrev_r(to, remoteheads->item->object.oid.hash,
1405                                               DEFAULT_ABBREV);
1406                         printf(_("Updating %s..%s\n"), from, to);
1407                 }
1408                 strbuf_addstr(&msg, "Fast-forward");
1409                 if (have_message)
1410                         strbuf_addstr(&msg,
1411                                 " (no commit created; -m option ignored)");
1412                 commit = remoteheads->item;
1413                 if (!commit) {
1414                         ret = 1;
1415                         goto done;
1416                 }
1417
1418                 if (checkout_fast_forward(head_commit->object.oid.hash,
1419                                           commit->object.oid.hash,
1420                                           overwrite_ignore)) {
1421                         ret = 1;
1422                         goto done;
1423                 }
1424
1425                 finish(head_commit, remoteheads, commit->object.oid.hash, msg.buf);
1426                 drop_save();
1427                 goto done;
1428         } else if (!remoteheads->next && common->next)
1429                 ;
1430                 /*
1431                  * We are not doing octopus and not fast-forward.  Need
1432                  * a real merge.
1433                  */
1434         else if (!remoteheads->next && !common->next && option_commit) {
1435                 /*
1436                  * We are not doing octopus, not fast-forward, and have
1437                  * only one common.
1438                  */
1439                 refresh_cache(REFRESH_QUIET);
1440                 if (allow_trivial && fast_forward != FF_ONLY) {
1441                         /* See if it is really trivial. */
1442                         git_committer_info(IDENT_STRICT);
1443                         printf(_("Trying really trivial in-index merge...\n"));
1444                         if (!read_tree_trivial(common->item->object.oid.hash,
1445                                                head_commit->object.oid.hash,
1446                                                remoteheads->item->object.oid.hash)) {
1447                                 ret = merge_trivial(head_commit, remoteheads);
1448                                 goto done;
1449                         }
1450                         printf(_("Nope.\n"));
1451                 }
1452         } else {
1453                 /*
1454                  * An octopus.  If we can reach all the remote we are up
1455                  * to date.
1456                  */
1457                 int up_to_date = 1;
1458                 struct commit_list *j;
1459
1460                 for (j = remoteheads; j; j = j->next) {
1461                         struct commit_list *common_one;
1462
1463                         /*
1464                          * Here we *have* to calculate the individual
1465                          * merge_bases again, otherwise "git merge HEAD^
1466                          * HEAD^^" would be missed.
1467                          */
1468                         common_one = get_merge_bases(head_commit, j->item);
1469                         if (oidcmp(&common_one->item->object.oid, &j->item->object.oid)) {
1470                                 up_to_date = 0;
1471                                 break;
1472                         }
1473                 }
1474                 if (up_to_date) {
1475                         finish_up_to_date(_("Already up-to-date. Yeeah!"));
1476                         goto done;
1477                 }
1478         }
1479
1480         if (fast_forward == FF_ONLY)
1481                 die(_("Not possible to fast-forward, aborting."));
1482
1483         /* We are going to make a new commit. */
1484         git_committer_info(IDENT_STRICT);
1485
1486         /*
1487          * At this point, we need a real merge.  No matter what strategy
1488          * we use, it would operate on the index, possibly affecting the
1489          * working tree, and when resolved cleanly, have the desired
1490          * tree in the index -- this means that the index must be in
1491          * sync with the head commit.  The strategies are responsible
1492          * to ensure this.
1493          */
1494         if (use_strategies_nr == 1 ||
1495             /*
1496              * Stash away the local changes so that we can try more than one.
1497              */
1498             save_state(stash))
1499                 hashclr(stash);
1500
1501         for (i = 0; i < use_strategies_nr; i++) {
1502                 int ret;
1503                 if (i) {
1504                         printf(_("Rewinding the tree to pristine...\n"));
1505                         restore_state(head_commit->object.oid.hash, stash);
1506                 }
1507                 if (use_strategies_nr != 1)
1508                         printf(_("Trying merge strategy %s...\n"),
1509                                 use_strategies[i]->name);
1510                 /*
1511                  * Remember which strategy left the state in the working
1512                  * tree.
1513                  */
1514                 wt_strategy = use_strategies[i]->name;
1515
1516                 ret = try_merge_strategy(use_strategies[i]->name,
1517                                          common, remoteheads,
1518                                          head_commit, head_arg);
1519                 if (!option_commit && !ret) {
1520                         merge_was_ok = 1;
1521                         /*
1522                          * This is necessary here just to avoid writing
1523                          * the tree, but later we will *not* exit with
1524                          * status code 1 because merge_was_ok is set.
1525                          */
1526                         ret = 1;
1527                 }
1528
1529                 if (ret) {
1530                         /*
1531                          * The backend exits with 1 when conflicts are
1532                          * left to be resolved, with 2 when it does not
1533                          * handle the given merge at all.
1534                          */
1535                         if (ret == 1) {
1536                                 int cnt = evaluate_result();
1537
1538                                 if (best_cnt <= 0 || cnt <= best_cnt) {
1539                                         best_strategy = use_strategies[i]->name;
1540                                         best_cnt = cnt;
1541                                 }
1542                         }
1543                         if (merge_was_ok)
1544                                 break;
1545                         else
1546                                 continue;
1547                 }
1548
1549                 /* Automerge succeeded. */
1550                 write_tree_trivial(result_tree);
1551                 automerge_was_ok = 1;
1552                 break;
1553         }
1554
1555         /*
1556          * If we have a resulting tree, that means the strategy module
1557          * auto resolved the merge cleanly.
1558          */
1559         if (automerge_was_ok) {
1560                 ret = finish_automerge(head_commit, head_subsumed,
1561                                        common, remoteheads,
1562                                        result_tree, wt_strategy);
1563                 goto done;
1564         }
1565
1566         /*
1567          * Pick the result from the best strategy and have the user fix
1568          * it up.
1569          */
1570         if (!best_strategy) {
1571                 restore_state(head_commit->object.oid.hash, stash);
1572                 if (use_strategies_nr > 1)
1573                         fprintf(stderr,
1574                                 _("No merge strategy handled the merge.\n"));
1575                 else
1576                         fprintf(stderr, _("Merge with strategy %s failed.\n"),
1577                                 use_strategies[0]->name);
1578                 ret = 2;
1579                 goto done;
1580         } else if (best_strategy == wt_strategy)
1581                 ; /* We already have its result in the working tree. */
1582         else {
1583                 printf(_("Rewinding the tree to pristine...\n"));
1584                 restore_state(head_commit->object.oid.hash, stash);
1585                 printf(_("Using the %s to prepare resolving by hand.\n"),
1586                         best_strategy);
1587                 try_merge_strategy(best_strategy, common, remoteheads,
1588                                    head_commit, head_arg);
1589         }
1590
1591         if (squash)
1592                 finish(head_commit, remoteheads, NULL, NULL);
1593         else
1594                 write_merge_state(remoteheads);
1595
1596         if (merge_was_ok)
1597                 fprintf(stderr, _("Automatic merge went well; "
1598                         "stopped before committing as requested\n"));
1599         else
1600                 ret = suggest_conflicts();
1601
1602 done:
1603         free(branch_to_free);
1604         return ret;
1605 }