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 "run-command.h"
  13 #include "diff.h"
  14 #include "refs.h"
  15 #include "commit.h"
  16 #include "diffcore.h"
  17 #include "revision.h"
  18 #include "unpack-trees.h"
  19 #include "cache-tree.h"
  20 #include "dir.h"
  21 #include "utf8.h"
  22 #include "log-tree.h"
  23 #include "color.h"
  24 #include "rerere.h"
  25 #include "help.h"
  26 #include "merge-recursive.h"
  27 #include "resolve-undo.h"
  28 #include "remote.h"
  29
  30 #define DEFAULT_TWOHEAD (1<<0)
  31 #define DEFAULT_OCTOPUS (1<<1)
  32 #define NO_FAST_FORWARD (1<<2)
  33 #define NO_TRIVIAL      (1<<3)
  34
  35 struct strategy {
  36         const char *name;
  37         unsigned attr;
  38 };
  39
  40 static const char * const builtin_merge_usage[] = {
  41         "git merge [options] [<commit>...]",
  42         "git merge [options] <msg> HEAD <commit>",
  43         "git merge --abort",
  44         NULL
  45 };
  46
  47 static int show_diffstat = 1, shortlog_len, squash;
  48 static int option_commit = 1, allow_fast_forward = 1;
  49 static int fast_forward_only;
  50 static int allow_trivial = 1, have_message;
  51 static struct strbuf merge_msg;
  52 static struct commit_list *remoteheads;
  53 static struct strategy **use_strategies;
  54 static size_t use_strategies_nr, use_strategies_alloc;
  55 static const char **xopts;
  56 static size_t xopts_nr, xopts_alloc;
  57 static const char *branch;
  58 static char *branch_mergeoptions;
  59 static int option_renormalize;
  60 static int verbosity;
  61 static int allow_rerere_auto;
  62 static int abort_current_merge;
  63 static int show_progress = -1;
  64 static int default_to_upstream;
  65
  66 static struct strategy all_strategy[] = {
  67         { "recursive",  DEFAULT_TWOHEAD | NO_TRIVIAL },
  68         { "octopus",    DEFAULT_OCTOPUS },
  69         { "resolve",    0 },
  70         { "ours",       NO_FAST_FORWARD | NO_TRIVIAL },
  71         { "subtree",    NO_FAST_FORWARD | NO_TRIVIAL },
  72 };
  73
  74 static const char *pull_twohead, *pull_octopus;
  75
  76 static int option_parse_message(const struct option *opt,
  77                                 const char *arg, int unset)
  78 {
  79         struct strbuf *buf = opt->value;
  80
  81         if (unset)
  82                 strbuf_setlen(buf, 0);
  83         else if (arg) {
  84                 strbuf_addf(buf, "%s%s", buf->len ? "\n\n" : "", arg);
  85                 have_message = 1;
  86         } else
  87                 return error(_("switch `m' requires a value"));
  88         return 0;
  89 }
  90
  91 static struct strategy *get_strategy(const char *name)
  92 {
  93         int i;
  94         struct strategy *ret;
  95         static struct cmdnames main_cmds, other_cmds;
  96         static int loaded;
  97
  98         if (!name)
  99                 return NULL;
 100
 101         for (i = 0; i < ARRAY_SIZE(all_strategy); i++)
 102                 if (!strcmp(name, all_strategy[i].name))
 103                         return &all_strategy[i];
 104
 105         if (!loaded) {
 106                 struct cmdnames not_strategies;
 107                 loaded = 1;
 108
 109                 memset(&not_strategies, 0, sizeof(struct cmdnames));
 110                 load_command_list("git-merge-", &main_cmds, &other_cmds);
 111                 for (i = 0; i < main_cmds.cnt; i++) {
 112                         int j, found = 0;
 113                         struct cmdname *ent = main_cmds.names[i];
 114                         for (j = 0; j < ARRAY_SIZE(all_strategy); j++)
 115                                 if (!strncmp(ent->name, all_strategy[j].name, ent->len)
 116                                                 && !all_strategy[j].name[ent->len])
 117                                         found = 1;
 118                         if (!found)
 119                                 add_cmdname(&not_strategies, ent->name, ent->len);
 120                 }
 121                 exclude_cmds(&main_cmds, &not_strategies);
 122         }
 123         if (!is_in_cmdlist(&main_cmds, name) && !is_in_cmdlist(&other_cmds, name)) {
 124                 fprintf(stderr, _("Could not find merge strategy '%s'.\n"), name);
 125                 fprintf(stderr, _("Available strategies are:"));
 126                 for (i = 0; i < main_cmds.cnt; i++)
 127                         fprintf(stderr, " %s", main_cmds.names[i]->name);
 128                 fprintf(stderr, ".\n");
 129                 if (other_cmds.cnt) {
 130                         fprintf(stderr, _("Available custom strategies are:"));
 131                         for (i = 0; i < other_cmds.cnt; i++)
 132                                 fprintf(stderr, " %s", other_cmds.names[i]->name);
 133                         fprintf(stderr, ".\n");
 134                 }
 135                 exit(1);
 136         }
 137
 138         ret = xcalloc(1, sizeof(struct strategy));
 139         ret->name = xstrdup(name);
 140         ret->attr = NO_TRIVIAL;
 141         return ret;
 142 }
 143
 144 static void append_strategy(struct strategy *s)
 145 {
 146         ALLOC_GROW(use_strategies, use_strategies_nr + 1, use_strategies_alloc);
 147         use_strategies[use_strategies_nr++] = s;
 148 }
 149
 150 static int option_parse_strategy(const struct option *opt,
 151                                  const char *name, int unset)
 152 {
 153         if (unset)
 154                 return 0;
 155
 156         append_strategy(get_strategy(name));
 157         return 0;
 158 }
 159
 160 static int option_parse_x(const struct option *opt,
 161                           const char *arg, int unset)
 162 {
 163         if (unset)
 164                 return 0;
 165
 166         ALLOC_GROW(xopts, xopts_nr + 1, xopts_alloc);
 167         xopts[xopts_nr++] = xstrdup(arg);
 168         return 0;
 169 }
 170
 171 static int option_parse_n(const struct option *opt,
 172                           const char *arg, int unset)
 173 {
 174         show_diffstat = unset;
 175         return 0;
 176 }
 177
 178 static struct option builtin_merge_options[] = {
 179         { OPTION_CALLBACK, 'n', NULL, NULL, NULL,
 180                 "do not show a diffstat at the end of the merge",
 181                 PARSE_OPT_NOARG, option_parse_n },
 182         OPT_BOOLEAN(0, "stat", &show_diffstat,
 183                 "show a diffstat at the end of the merge"),
 184         OPT_BOOLEAN(0, "summary", &show_diffstat, "(synonym to --stat)"),
 185         { OPTION_INTEGER, 0, "log", &shortlog_len, "n",
 186           "add (at most <n>) entries from shortlog to merge commit message",
 187           PARSE_OPT_OPTARG, NULL, DEFAULT_MERGE_LOG_LEN },
 188         OPT_BOOLEAN(0, "squash", &squash,
 189                 "create a single commit instead of doing a merge"),
 190         OPT_BOOLEAN(0, "commit", &option_commit,
 191                 "perform a commit if the merge succeeds (default)"),
 192         OPT_BOOLEAN(0, "ff", &allow_fast_forward,
 193                 "allow fast-forward (default)"),
 194         OPT_BOOLEAN(0, "ff-only", &fast_forward_only,
 195                 "abort if fast-forward is not possible"),
 196         OPT_RERERE_AUTOUPDATE(&allow_rerere_auto),
 197         OPT_CALLBACK('s', "strategy", &use_strategies, "strategy",
 198                 "merge strategy to use", option_parse_strategy),
 199         OPT_CALLBACK('X', "strategy-option", &xopts, "option=value",
 200                 "option for selected merge strategy", option_parse_x),
 201         OPT_CALLBACK('m', "message", &merge_msg, "message",
 202                 "merge commit message (for a non-fast-forward merge)",
 203                 option_parse_message),
 204         OPT__VERBOSITY(&verbosity),
 205         OPT_BOOLEAN(0, "abort", &abort_current_merge,
 206                 "abort the current in-progress merge"),
 207         OPT_SET_INT(0, "progress", &show_progress, "force progress reporting", 1),
 208         OPT_END()
 209 };
 210
 211 /* Cleans up metadata that is uninteresting after a succeeded merge. */
 212 static void drop_save(void)
 213 {
 214         unlink(git_path("MERGE_HEAD"));
 215         unlink(git_path("MERGE_MSG"));
 216         unlink(git_path("MERGE_MODE"));
 217 }
 218
 219 static int save_state(unsigned char *stash)
 220 {
 221         int len;
 222         struct child_process cp;
 223         struct strbuf buffer = STRBUF_INIT;
 224         const char *argv[] = {"stash", "create", NULL};
 225
 226         memset(&cp, 0, sizeof(cp));
 227         cp.argv = argv;
 228         cp.out = -1;
 229         cp.git_cmd = 1;
 230
 231         if (start_command(&cp))
 232                 die(_("could not run stash."));
 233         len = strbuf_read(&buffer, cp.out, 1024);
 234         close(cp.out);
 235
 236         if (finish_command(&cp) || len < 0)
 237                 die(_("stash failed"));
 238         else if (!len)          /* no changes */
 239                 return -1;
 240         strbuf_setlen(&buffer, buffer.len-1);
 241         if (get_sha1(buffer.buf, stash))
 242                 die(_("not a valid object: %s"), buffer.buf);
 243         return 0;
 244 }
 245
 246 static void read_empty(unsigned const char *sha1, int verbose)
 247 {
 248         int i = 0;
 249         const char *args[7];
 250
 251         args[i++] = "read-tree";
 252         if (verbose)
 253                 args[i++] = "-v";
 254         args[i++] = "-m";
 255         args[i++] = "-u";
 256         args[i++] = EMPTY_TREE_SHA1_HEX;
 257         args[i++] = sha1_to_hex(sha1);
 258         args[i] = NULL;
 259
 260         if (run_command_v_opt(args, RUN_GIT_CMD))
 261                 die(_("read-tree failed"));
 262 }
 263
 264 static void reset_hard(unsigned const char *sha1, int verbose)
 265 {
 266         int i = 0;
 267         const char *args[6];
 268
 269         args[i++] = "read-tree";
 270         if (verbose)
 271                 args[i++] = "-v";
 272         args[i++] = "--reset";
 273         args[i++] = "-u";
 274         args[i++] = sha1_to_hex(sha1);
 275         args[i] = NULL;
 276
 277         if (run_command_v_opt(args, RUN_GIT_CMD))
 278                 die(_("read-tree failed"));
 279 }
 280
 281 static void restore_state(const unsigned char *head,
 282                           const unsigned char *stash)
 283 {
 284         struct strbuf sb = STRBUF_INIT;
 285         const char *args[] = { "stash", "apply", NULL, NULL };
 286
 287         if (is_null_sha1(stash))
 288                 return;
 289
 290         reset_hard(head, 1);
 291
 292         args[2] = sha1_to_hex(stash);
 293
 294         /*
 295          * It is OK to ignore error here, for example when there was
 296          * nothing to restore.
 297          */
 298         run_command_v_opt(args, RUN_GIT_CMD);
 299
 300         strbuf_release(&sb);
 301         refresh_cache(REFRESH_QUIET);
 302 }
 303
 304 /* This is called when no merge was necessary. */
 305 static void finish_up_to_date(const char *msg)
 306 {
 307         if (verbosity >= 0)
 308                 printf("%s%s\n", squash ? _(" (nothing to squash)") : "", msg);
 309         drop_save();
 310 }
 311
 312 static void squash_message(struct commit *commit)
 313 {
 314         struct rev_info rev;
 315         struct strbuf out = STRBUF_INIT;
 316         struct commit_list *j;
 317         int fd;
 318         struct pretty_print_context ctx = {0};
 319
 320         printf(_("Squash commit -- not updating HEAD\n"));
 321         fd = open(git_path("SQUASH_MSG"), O_WRONLY | O_CREAT, 0666);
 322         if (fd < 0)
 323                 die_errno(_("Could not write to '%s'"), git_path("SQUASH_MSG"));
 324
 325         init_revisions(&rev, NULL);
 326         rev.ignore_merges = 1;
 327         rev.commit_format = CMIT_FMT_MEDIUM;
 328
 329         commit->object.flags |= UNINTERESTING;
 330         add_pending_object(&rev, &commit->object, NULL);
 331
 332         for (j = remoteheads; j; j = j->next)
 333                 add_pending_object(&rev, &j->item->object, NULL);
 334
 335         setup_revisions(0, NULL, &rev, NULL);
 336         if (prepare_revision_walk(&rev))
 337                 die(_("revision walk setup failed"));
 338
 339         ctx.abbrev = rev.abbrev;
 340         ctx.date_mode = rev.date_mode;
 341         ctx.fmt = rev.commit_format;
 342
 343         strbuf_addstr(&out, "Squashed commit of the following:\n");
 344         while ((commit = get_revision(&rev)) != NULL) {
 345                 strbuf_addch(&out, '\n');
 346                 strbuf_addf(&out, "commit %s\n",
 347                         sha1_to_hex(commit->object.sha1));
 348                 pretty_print_commit(&ctx, commit, &out);
 349         }
 350         if (write(fd, out.buf, out.len) < 0)
 351                 die_errno(_("Writing SQUASH_MSG"));
 352         if (close(fd))
 353                 die_errno(_("Finishing SQUASH_MSG"));
 354         strbuf_release(&out);
 355 }
 356
 357 static void finish(struct commit *head_commit,
 358                    const unsigned char *new_head, const char *msg)
 359 {
 360         struct strbuf reflog_message = STRBUF_INIT;
 361         const unsigned char *head = head_commit->object.sha1;
 362
 363         if (!msg)
 364                 strbuf_addstr(&reflog_message, getenv("GIT_REFLOG_ACTION"));
 365         else {
 366                 if (verbosity >= 0)
 367                         printf("%s\n", msg);
 368                 strbuf_addf(&reflog_message, "%s: %s",
 369                         getenv("GIT_REFLOG_ACTION"), msg);
 370         }
 371         if (squash) {
 372                 squash_message(head_commit);
 373         } else {
 374                 if (verbosity >= 0 && !merge_msg.len)
 375                         printf(_("No merge message -- not updating HEAD\n"));
 376                 else {
 377                         const char *argv_gc_auto[] = { "gc", "--auto", NULL };
 378                         update_ref(reflog_message.buf, "HEAD",
 379                                 new_head, head, 0,
 380                                 DIE_ON_ERR);
 381                         /*
 382                          * We ignore errors in 'gc --auto', since the
 383                          * user should see them.
 384                          */
 385                         run_command_v_opt(argv_gc_auto, RUN_GIT_CMD);
 386                 }
 387         }
 388         if (new_head && show_diffstat) {
 389                 struct diff_options opts;
 390                 diff_setup(&opts);
 391                 opts.output_format |=
 392                         DIFF_FORMAT_SUMMARY | DIFF_FORMAT_DIFFSTAT;
 393                 opts.detect_rename = DIFF_DETECT_RENAME;
 394                 if (diff_setup_done(&opts) < 0)
 395                         die(_("diff_setup_done failed"));
 396                 diff_tree_sha1(head, new_head, "", &opts);
 397                 diffcore_std(&opts);
 398                 diff_flush(&opts);
 399         }
 400
 401         /* Run a post-merge hook */
 402         run_hook(NULL, "post-merge", squash ? "1" : "0", NULL);
 403
 404         strbuf_release(&reflog_message);
 405 }
 406
 407 /* Get the name for the merge commit's message. */
 408 static void merge_name(const char *remote, struct strbuf *msg)
 409 {
 410         struct object *remote_head;
 411         unsigned char branch_head[20], buf_sha[20];
 412         struct strbuf buf = STRBUF_INIT;
 413         struct strbuf bname = STRBUF_INIT;
 414         const char *ptr;
 415         char *found_ref;
 416         int len, early;
 417
 418         strbuf_branchname(&bname, remote);
 419         remote = bname.buf;
 420
 421         memset(branch_head, 0, sizeof(branch_head));
 422         remote_head = peel_to_type(remote, 0, NULL, OBJ_COMMIT);
 423         if (!remote_head)
 424                 die(_("'%s' does not point to a commit"), remote);
 425
 426         if (dwim_ref(remote, strlen(remote), branch_head, &found_ref) > 0) {
 427                 if (!prefixcmp(found_ref, "refs/heads/")) {
 428                         strbuf_addf(msg, "%s\t\tbranch '%s' of .\n",
 429                                     sha1_to_hex(branch_head), remote);
 430                         goto cleanup;
 431                 }
 432                 if (!prefixcmp(found_ref, "refs/remotes/")) {
 433                         strbuf_addf(msg, "%s\t\tremote-tracking branch '%s' of .\n",
 434                                     sha1_to_hex(branch_head), remote);
 435                         goto cleanup;
 436                 }
 437         }
 438
 439         /* See if remote matches <name>^^^.. or <name>~<number> */
 440         for (len = 0, ptr = remote + strlen(remote);
 441              remote < ptr && ptr[-1] == '^';
 442              ptr--)
 443                 len++;
 444         if (len)
 445                 early = 1;
 446         else {
 447                 early = 0;
 448                 ptr = strrchr(remote, '~');
 449                 if (ptr) {
 450                         int seen_nonzero = 0;
 451
 452                         len++; /* count ~ */
 453                         while (*++ptr && isdigit(*ptr)) {
 454                                 seen_nonzero |= (*ptr != '0');
 455                                 len++;
 456                         }
 457                         if (*ptr)
 458                                 len = 0; /* not ...~<number> */
 459                         else if (seen_nonzero)
 460                                 early = 1;
 461                         else if (len == 1)
 462                                 early = 1; /* "name~" is "name~1"! */
 463                 }
 464         }
 465         if (len) {
 466                 struct strbuf truname = STRBUF_INIT;
 467                 strbuf_addstr(&truname, "refs/heads/");
 468                 strbuf_addstr(&truname, remote);
 469                 strbuf_setlen(&truname, truname.len - len);
 470                 if (resolve_ref(truname.buf, buf_sha, 1, NULL)) {
 471                         strbuf_addf(msg,
 472                                     "%s\t\tbranch '%s'%s of .\n",
 473                                     sha1_to_hex(remote_head->sha1),
 474                                     truname.buf + 11,
 475                                     (early ? " (early part)" : ""));
 476                         strbuf_release(&truname);
 477                         goto cleanup;
 478                 }
 479         }
 480
 481         if (!strcmp(remote, "FETCH_HEAD") &&
 482                         !access(git_path("FETCH_HEAD"), R_OK)) {
 483                 FILE *fp;
 484                 struct strbuf line = STRBUF_INIT;
 485                 char *ptr;
 486
 487                 fp = fopen(git_path("FETCH_HEAD"), "r");
 488                 if (!fp)
 489                         die_errno(_("could not open '%s' for reading"),
 490                                   git_path("FETCH_HEAD"));
 491                 strbuf_getline(&line, fp, '\n');
 492                 fclose(fp);
 493                 ptr = strstr(line.buf, "\tnot-for-merge\t");
 494                 if (ptr)
 495                         strbuf_remove(&line, ptr-line.buf+1, 13);
 496                 strbuf_addbuf(msg, &line);
 497                 strbuf_release(&line);
 498                 goto cleanup;
 499         }
 500         strbuf_addf(msg, "%s\t\tcommit '%s'\n",
 501                 sha1_to_hex(remote_head->sha1), remote);
 502 cleanup:
 503         strbuf_release(&buf);
 504         strbuf_release(&bname);
 505 }
 506
 507 static void parse_branch_merge_options(char *bmo)
 508 {
 509         const char **argv;
 510         int argc;
 511
 512         if (!bmo)
 513                 return;
 514         argc = split_cmdline(bmo, &argv);
 515         if (argc < 0)
 516                 die(_("Bad branch.%s.mergeoptions string: %s"), branch,
 517                     split_cmdline_strerror(argc));
 518         argv = xrealloc(argv, sizeof(*argv) * (argc + 2));
 519         memmove(argv + 1, argv, sizeof(*argv) * (argc + 1));
 520         argc++;
 521         argv[0] = "branch.*.mergeoptions";
 522         parse_options(argc, argv, NULL, builtin_merge_options,
 523                       builtin_merge_usage, 0);
 524         free(argv);
 525 }
 526
 527 static int git_merge_config(const char *k, const char *v, void *cb)
 528 {
 529         if (branch && !prefixcmp(k, "branch.") &&
 530                 !prefixcmp(k + 7, branch) &&
 531                 !strcmp(k + 7 + strlen(branch), ".mergeoptions")) {
 532                 free(branch_mergeoptions);
 533                 branch_mergeoptions = xstrdup(v);
 534                 return 0;
 535         }
 536
 537         if (!strcmp(k, "merge.diffstat") || !strcmp(k, "merge.stat"))
 538                 show_diffstat = git_config_bool(k, v);
 539         else if (!strcmp(k, "pull.twohead"))
 540                 return git_config_string(&pull_twohead, k, v);
 541         else if (!strcmp(k, "pull.octopus"))
 542                 return git_config_string(&pull_octopus, k, v);
 543         else if (!strcmp(k, "merge.renormalize"))
 544                 option_renormalize = git_config_bool(k, v);
 545         else if (!strcmp(k, "merge.log") || !strcmp(k, "merge.summary")) {
 546                 int is_bool;
 547                 shortlog_len = git_config_bool_or_int(k, v, &is_bool);
 548                 if (!is_bool && shortlog_len < 0)
 549                         return error(_("%s: negative length %s"), k, v);
 550                 if (is_bool && shortlog_len)
 551                         shortlog_len = DEFAULT_MERGE_LOG_LEN;
 552                 return 0;
 553         } else if (!strcmp(k, "merge.ff")) {
 554                 int boolval = git_config_maybe_bool(k, v);
 555                 if (0 <= boolval) {
 556                         allow_fast_forward = boolval;
 557                 } else if (v && !strcmp(v, "only")) {
 558                         allow_fast_forward = 1;
 559                         fast_forward_only = 1;
 560                 } /* do not barf on values from future versions of git */
 561                 return 0;
 562         } else if (!strcmp(k, "merge.defaulttoupstream")) {
 563                 default_to_upstream = git_config_bool(k, v);
 564                 return 0;
 565         }
 566         return git_diff_ui_config(k, v, cb);
 567 }
 568
 569 static int read_tree_trivial(unsigned char *common, unsigned char *head,
 570                              unsigned char *one)
 571 {
 572         int i, nr_trees = 0;
 573         struct tree *trees[MAX_UNPACK_TREES];
 574         struct tree_desc t[MAX_UNPACK_TREES];
 575         struct unpack_trees_options opts;
 576
 577         memset(&opts, 0, sizeof(opts));
 578         opts.head_idx = 2;
 579         opts.src_index = &the_index;
 580         opts.dst_index = &the_index;
 581         opts.update = 1;
 582         opts.verbose_update = 1;
 583         opts.trivial_merges_only = 1;
 584         opts.merge = 1;
 585         trees[nr_trees] = parse_tree_indirect(common);
 586         if (!trees[nr_trees++])
 587                 return -1;
 588         trees[nr_trees] = parse_tree_indirect(head);
 589         if (!trees[nr_trees++])
 590                 return -1;
 591         trees[nr_trees] = parse_tree_indirect(one);
 592         if (!trees[nr_trees++])
 593                 return -1;
 594         opts.fn = threeway_merge;
 595         cache_tree_free(&active_cache_tree);
 596         for (i = 0; i < nr_trees; i++) {
 597                 parse_tree(trees[i]);
 598                 init_tree_desc(t+i, trees[i]->buffer, trees[i]->size);
 599         }
 600         if (unpack_trees(nr_trees, t, &opts))
 601                 return -1;
 602         return 0;
 603 }
 604
 605 static void write_tree_trivial(unsigned char *sha1)
 606 {
 607         if (write_cache_as_tree(sha1, 0, NULL))
 608                 die(_("git write-tree failed to write a tree"));
 609 }
 610
 611 static const char *merge_argument(struct commit *commit)
 612 {
 613         if (commit)
 614                 return sha1_to_hex(commit->object.sha1);
 615         else
 616                 return EMPTY_TREE_SHA1_HEX;
 617 }
 618
 619 int try_merge_command(const char *strategy, size_t xopts_nr,
 620                       const char **xopts, struct commit_list *common,
 621                       const char *head_arg, struct commit_list *remotes)
 622 {
 623         const char **args;
 624         int i = 0, x = 0, ret;
 625         struct commit_list *j;
 626         struct strbuf buf = STRBUF_INIT;
 627
 628         args = xmalloc((4 + xopts_nr + commit_list_count(common) +
 629                         commit_list_count(remotes)) * sizeof(char *));
 630         strbuf_addf(&buf, "merge-%s", strategy);
 631         args[i++] = buf.buf;
 632         for (x = 0; x < xopts_nr; x++) {
 633                 char *s = xmalloc(strlen(xopts[x])+2+1);
 634                 strcpy(s, "--");
 635                 strcpy(s+2, xopts[x]);
 636                 args[i++] = s;
 637         }
 638         for (j = common; j; j = j->next)
 639                 args[i++] = xstrdup(merge_argument(j->item));
 640         args[i++] = "--";
 641         args[i++] = head_arg;
 642         for (j = remotes; j; j = j->next)
 643                 args[i++] = xstrdup(merge_argument(j->item));
 644         args[i] = NULL;
 645         ret = run_command_v_opt(args, RUN_GIT_CMD);
 646         strbuf_release(&buf);
 647         i = 1;
 648         for (x = 0; x < xopts_nr; x++)
 649                 free((void *)args[i++]);
 650         for (j = common; j; j = j->next)
 651                 free((void *)args[i++]);
 652         i += 2;
 653         for (j = remotes; j; j = j->next)
 654                 free((void *)args[i++]);
 655         free(args);
 656         discard_cache();
 657         if (read_cache() < 0)
 658                 die(_("failed to read the cache"));
 659         resolve_undo_clear();
 660
 661         return ret;
 662 }
 663
 664 static int try_merge_strategy(const char *strategy, struct commit_list *common,
 665                               struct commit *head, const char *head_arg)
 666 {
 667         int index_fd;
 668         struct lock_file *lock = xcalloc(1, sizeof(struct lock_file));
 669
 670         index_fd = hold_locked_index(lock, 1);
 671         refresh_cache(REFRESH_QUIET);
 672         if (active_cache_changed &&
 673                         (write_cache(index_fd, active_cache, active_nr) ||
 674                          commit_locked_index(lock)))
 675                 return error(_("Unable to write index."));
 676         rollback_lock_file(lock);
 677
 678         if (!strcmp(strategy, "recursive") || !strcmp(strategy, "subtree")) {
 679                 int clean, x;
 680                 struct commit *result;
 681                 struct lock_file *lock = xcalloc(1, sizeof(struct lock_file));
 682                 int index_fd;
 683                 struct commit_list *reversed = NULL;
 684                 struct merge_options o;
 685                 struct commit_list *j;
 686
 687                 if (remoteheads->next) {
 688                         error(_("Not handling anything other than two heads merge."));
 689                         return 2;
 690                 }
 691
 692                 init_merge_options(&o);
 693                 if (!strcmp(strategy, "subtree"))
 694                         o.subtree_shift = "";
 695
 696                 o.renormalize = option_renormalize;
 697                 o.show_rename_progress =
 698                         show_progress == -1 ? isatty(2) : show_progress;
 699
 700                 for (x = 0; x < xopts_nr; x++)
 701                         if (parse_merge_opt(&o, xopts[x]))
 702                                 die(_("Unknown option for merge-recursive: -X%s"), xopts[x]);
 703
 704                 o.branch1 = head_arg;
 705                 o.branch2 = remoteheads->item->util;
 706
 707                 for (j = common; j; j = j->next)
 708                         commit_list_insert(j->item, &reversed);
 709
 710                 index_fd = hold_locked_index(lock, 1);
 711                 clean = merge_recursive(&o, head,
 712                                 remoteheads->item, reversed, &result);
 713                 if (active_cache_changed &&
 714                                 (write_cache(index_fd, active_cache, active_nr) ||
 715                                  commit_locked_index(lock)))
 716                         die (_("unable to write %s"), get_index_file());
 717                 rollback_lock_file(lock);
 718                 return clean ? 0 : 1;
 719         } else {
 720                 return try_merge_command(strategy, xopts_nr, xopts,
 721                                                 common, head_arg, remoteheads);
 722         }
 723 }
 724
 725 static void count_diff_files(struct diff_queue_struct *q,
 726                              struct diff_options *opt, void *data)
 727 {
 728         int *count = data;
 729
 730         (*count) += q->nr;
 731 }
 732
 733 static int count_unmerged_entries(void)
 734 {
 735         int i, ret = 0;
 736
 737         for (i = 0; i < active_nr; i++)
 738                 if (ce_stage(active_cache[i]))
 739                         ret++;
 740
 741         return ret;
 742 }
 743
 744 int checkout_fast_forward(const unsigned char *head, const unsigned char *remote)
 745 {
 746         struct tree *trees[MAX_UNPACK_TREES];
 747         struct unpack_trees_options opts;
 748         struct tree_desc t[MAX_UNPACK_TREES];
 749         int i, fd, nr_trees = 0;
 750         struct dir_struct dir;
 751         struct lock_file *lock_file = xcalloc(1, sizeof(struct lock_file));
 752
 753         refresh_cache(REFRESH_QUIET);
 754
 755         fd = hold_locked_index(lock_file, 1);
 756
 757         memset(&trees, 0, sizeof(trees));
 758         memset(&opts, 0, sizeof(opts));
 759         memset(&t, 0, sizeof(t));
 760         memset(&dir, 0, sizeof(dir));
 761         dir.flags |= DIR_SHOW_IGNORED;
 762         dir.exclude_per_dir = ".gitignore";
 763         opts.dir = &dir;
 764
 765         opts.head_idx = 1;
 766         opts.src_index = &the_index;
 767         opts.dst_index = &the_index;
 768         opts.update = 1;
 769         opts.verbose_update = 1;
 770         opts.merge = 1;
 771         opts.fn = twoway_merge;
 772         setup_unpack_trees_porcelain(&opts, "merge");
 773
 774         trees[nr_trees] = parse_tree_indirect(head);
 775         if (!trees[nr_trees++])
 776                 return -1;
 777         trees[nr_trees] = parse_tree_indirect(remote);
 778         if (!trees[nr_trees++])
 779                 return -1;
 780         for (i = 0; i < nr_trees; i++) {
 781                 parse_tree(trees[i]);
 782                 init_tree_desc(t+i, trees[i]->buffer, trees[i]->size);
 783         }
 784         if (unpack_trees(nr_trees, t, &opts))
 785                 return -1;
 786         if (write_cache(fd, active_cache, active_nr) ||
 787                 commit_locked_index(lock_file))
 788                 die(_("unable to write new index file"));
 789         return 0;
 790 }
 791
 792 static void split_merge_strategies(const char *string, struct strategy **list,
 793                                    int *nr, int *alloc)
 794 {
 795         char *p, *q, *buf;
 796
 797         if (!string)
 798                 return;
 799
 800         buf = xstrdup(string);
 801         q = buf;
 802         for (;;) {
 803                 p = strchr(q, ' ');
 804                 if (!p) {
 805                         ALLOC_GROW(*list, *nr + 1, *alloc);
 806                         (*list)[(*nr)++].name = xstrdup(q);
 807                         free(buf);
 808                         return;
 809                 } else {
 810                         *p = '\0';
 811                         ALLOC_GROW(*list, *nr + 1, *alloc);
 812                         (*list)[(*nr)++].name = xstrdup(q);
 813                         q = ++p;
 814                 }
 815         }
 816 }
 817
 818 static void add_strategies(const char *string, unsigned attr)
 819 {
 820         struct strategy *list = NULL;
 821         int list_alloc = 0, list_nr = 0, i;
 822
 823         memset(&list, 0, sizeof(list));
 824         split_merge_strategies(string, &list, &list_nr, &list_alloc);
 825         if (list) {
 826                 for (i = 0; i < list_nr; i++)
 827                         append_strategy(get_strategy(list[i].name));
 828                 return;
 829         }
 830         for (i = 0; i < ARRAY_SIZE(all_strategy); i++)
 831                 if (all_strategy[i].attr & attr)
 832                         append_strategy(&all_strategy[i]);
 833
 834 }
 835
 836 static void write_merge_msg(void)
 837 {
 838         int fd = open(git_path("MERGE_MSG"), O_WRONLY | O_CREAT, 0666);
 839         if (fd < 0)
 840                 die_errno(_("Could not open '%s' for writing"),
 841                           git_path("MERGE_MSG"));
 842         if (write_in_full(fd, merge_msg.buf, merge_msg.len) != merge_msg.len)
 843                 die_errno(_("Could not write to '%s'"), git_path("MERGE_MSG"));
 844         close(fd);
 845 }
 846
 847 static void read_merge_msg(void)
 848 {
 849         strbuf_reset(&merge_msg);
 850         if (strbuf_read_file(&merge_msg, git_path("MERGE_MSG"), 0) < 0)
 851                 die_errno(_("Could not read from '%s'"), git_path("MERGE_MSG"));
 852 }
 853
 854 static void run_prepare_commit_msg(void)
 855 {
 856         write_merge_msg();
 857         run_hook(get_index_file(), "prepare-commit-msg",
 858                  git_path("MERGE_MSG"), "merge", NULL, NULL);
 859         read_merge_msg();
 860 }
 861
 862 static int merge_trivial(struct commit *head)
 863 {
 864         unsigned char result_tree[20], result_commit[20];
 865         struct commit_list *parent = xmalloc(sizeof(*parent));
 866
 867         write_tree_trivial(result_tree);
 868         printf(_("Wonderful.\n"));
 869         parent->item = head;
 870         parent->next = xmalloc(sizeof(*parent->next));
 871         parent->next->item = remoteheads->item;
 872         parent->next->next = NULL;
 873         run_prepare_commit_msg();
 874         commit_tree(merge_msg.buf, result_tree, parent, result_commit, NULL);
 875         finish(head, result_commit, "In-index merge");
 876         drop_save();
 877         return 0;
 878 }
 879
 880 static int finish_automerge(struct commit *head,
 881                             struct commit_list *common,
 882                             unsigned char *result_tree,
 883                             const char *wt_strategy)
 884 {
 885         struct commit_list *parents = NULL, *j;
 886         struct strbuf buf = STRBUF_INIT;
 887         unsigned char result_commit[20];
 888
 889         free_commit_list(common);
 890         if (allow_fast_forward) {
 891                 parents = remoteheads;
 892                 commit_list_insert(head, &parents);
 893                 parents = reduce_heads(parents);
 894         } else {
 895                 struct commit_list **pptr = &parents;
 896
 897                 pptr = &commit_list_insert(head,
 898                                 pptr)->next;
 899                 for (j = remoteheads; j; j = j->next)
 900                         pptr = &commit_list_insert(j->item, pptr)->next;
 901         }
 902         free_commit_list(remoteheads);
 903         strbuf_addch(&merge_msg, '\n');
 904         run_prepare_commit_msg();
 905         commit_tree(merge_msg.buf, result_tree, parents, result_commit, NULL);
 906         strbuf_addf(&buf, "Merge made by the '%s' strategy.", wt_strategy);
 907         finish(head, result_commit, buf.buf);
 908         strbuf_release(&buf);
 909         drop_save();
 910         return 0;
 911 }
 912
 913 static int suggest_conflicts(int renormalizing)
 914 {
 915         FILE *fp;
 916         int pos;
 917
 918         fp = fopen(git_path("MERGE_MSG"), "a");
 919         if (!fp)
 920                 die_errno(_("Could not open '%s' for writing"),
 921                           git_path("MERGE_MSG"));
 922         fprintf(fp, "\nConflicts:\n");
 923         for (pos = 0; pos < active_nr; pos++) {
 924                 struct cache_entry *ce = active_cache[pos];
 925
 926                 if (ce_stage(ce)) {
 927                         fprintf(fp, "\t%s\n", ce->name);
 928                         while (pos + 1 < active_nr &&
 929                                         !strcmp(ce->name,
 930                                                 active_cache[pos + 1]->name))
 931                                 pos++;
 932                 }
 933         }
 934         fclose(fp);
 935         rerere(allow_rerere_auto);
 936         printf(_("Automatic merge failed; "
 937                         "fix conflicts and then commit the result.\n"));
 938         return 1;
 939 }
 940
 941 static struct commit *is_old_style_invocation(int argc, const char **argv,
 942                                               const unsigned char *head)
 943 {
 944         struct commit *second_token = NULL;
 945         if (argc > 2) {
 946                 unsigned char second_sha1[20];
 947
 948                 if (get_sha1(argv[1], second_sha1))
 949                         return NULL;
 950                 second_token = lookup_commit_reference_gently(second_sha1, 0);
 951                 if (!second_token)
 952                         die(_("'%s' is not a commit"), argv[1]);
 953                 if (hashcmp(second_token->object.sha1, head))
 954                         return NULL;
 955         }
 956         return second_token;
 957 }
 958
 959 static int evaluate_result(void)
 960 {
 961         int cnt = 0;
 962         struct rev_info rev;
 963
 964         /* Check how many files differ. */
 965         init_revisions(&rev, "");
 966         setup_revisions(0, NULL, &rev, NULL);
 967         rev.diffopt.output_format |=
 968                 DIFF_FORMAT_CALLBACK;
 969         rev.diffopt.format_callback = count_diff_files;
 970         rev.diffopt.format_callback_data = &cnt;
 971         run_diff_files(&rev, 0);
 972
 973         /*
 974          * Check how many unmerged entries are
 975          * there.
 976          */
 977         cnt += count_unmerged_entries();
 978
 979         return cnt;
 980 }
 981
 982 /*
 983  * Pretend as if the user told us to merge with the tracking
 984  * branch we have for the upstream of the current branch
 985  */
 986 static int setup_with_upstream(const char ***argv)
 987 {
 988         struct branch *branch = branch_get(NULL);
 989         int i;
 990         const char **args;
 991
 992         if (!branch)
 993                 die(_("No current branch."));
 994         if (!branch->remote)
 995                 die(_("No remote for the current branch."));
 996         if (!branch->merge_nr)
 997                 die(_("No default upstream defined for the current branch."));
 998
 999         args = xcalloc(branch->merge_nr + 1, sizeof(char *));
1000         for (i = 0; i < branch->merge_nr; i++) {
1001                 if (!branch->merge[i]->dst)
1002                         die(_("No remote tracking branch for %s from %s"),
1003                             branch->merge[i]->src, branch->remote_name);
1004                 args[i] = branch->merge[i]->dst;
1005         }
1006         args[i] = NULL;
1007         *argv = args;
1008         return i;
1009 }
1010
1011 int cmd_merge(int argc, const char **argv, const char *prefix)
1012 {
1013         unsigned char result_tree[20];
1014         unsigned char stash[20];
1015         unsigned char head_sha1[20];
1016         struct commit *head_commit;
1017         struct strbuf buf = STRBUF_INIT;
1018         const char *head_arg;
1019         int flag, i;
1020         int best_cnt = -1, merge_was_ok = 0, automerge_was_ok = 0;
1021         struct commit_list *common = NULL;
1022         const char *best_strategy = NULL, *wt_strategy = NULL;
1023         struct commit_list **remotes = &remoteheads;
1024
1025         if (argc == 2 && !strcmp(argv[1], "-h"))
1026                 usage_with_options(builtin_merge_usage, builtin_merge_options);
1027
1028         /*
1029          * Check if we are _not_ on a detached HEAD, i.e. if there is a
1030          * current branch.
1031          */
1032         branch = resolve_ref("HEAD", head_sha1, 0, &flag);
1033         if (branch && !prefixcmp(branch, "refs/heads/"))
1034                 branch += 11;
1035         if (!branch || is_null_sha1(head_sha1))
1036                 head_commit = NULL;
1037         else
1038                 head_commit = lookup_commit_or_die(head_sha1, "HEAD");
1039
1040         git_config(git_merge_config, NULL);
1041
1042         if (branch_mergeoptions)
1043                 parse_branch_merge_options(branch_mergeoptions);
1044         argc = parse_options(argc, argv, prefix, builtin_merge_options,
1045                         builtin_merge_usage, 0);
1046
1047         if (verbosity < 0 && show_progress == -1)
1048                 show_progress = 0;
1049
1050         if (abort_current_merge) {
1051                 int nargc = 2;
1052                 const char *nargv[] = {"reset", "--merge", NULL};
1053
1054                 if (!file_exists(git_path("MERGE_HEAD")))
1055                         die(_("There is no merge to abort (MERGE_HEAD missing)."));
1056
1057                 /* Invoke 'git reset --merge' */
1058                 return cmd_reset(nargc, nargv, prefix);
1059         }
1060
1061         if (read_cache_unmerged())
1062                 die_resolve_conflict("merge");
1063
1064         if (file_exists(git_path("MERGE_HEAD"))) {
1065                 /*
1066                  * There is no unmerged entry, don't advise 'git
1067                  * add/rm <file>', just 'git commit'.
1068                  */
1069                 if (advice_resolve_conflict)
1070                         die(_("You have not concluded your merge (MERGE_HEAD exists).\n"
1071                                   "Please, commit your changes before you can merge."));
1072                 else
1073                         die(_("You have not concluded your merge (MERGE_HEAD exists)."));
1074         }
1075         if (file_exists(git_path("CHERRY_PICK_HEAD"))) {
1076                 if (advice_resolve_conflict)
1077                         die(_("You have not concluded your cherry-pick (CHERRY_PICK_HEAD exists).\n"
1078                             "Please, commit your changes before you can merge."));
1079                 else
1080                         die(_("You have not concluded your cherry-pick (CHERRY_PICK_HEAD exists)."));
1081         }
1082         resolve_undo_clear();
1083
1084         if (verbosity < 0)
1085                 show_diffstat = 0;
1086
1087         if (squash) {
1088                 if (!allow_fast_forward)
1089                         die(_("You cannot combine --squash with --no-ff."));
1090                 option_commit = 0;
1091         }
1092
1093         if (!allow_fast_forward && fast_forward_only)
1094                 die(_("You cannot combine --no-ff with --ff-only."));
1095
1096         if (!abort_current_merge) {
1097                 if (!argc && default_to_upstream)
1098                         argc = setup_with_upstream(&argv);
1099                 else if (argc == 1 && !strcmp(argv[0], "-"))
1100                         argv[0] = "@{-1}";
1101         }
1102         if (!argc)
1103                 usage_with_options(builtin_merge_usage,
1104                         builtin_merge_options);
1105
1106         /*
1107          * This could be traditional "merge <msg> HEAD <commit>..."  and
1108          * the way we can tell it is to see if the second token is HEAD,
1109          * but some people might have misused the interface and used a
1110          * committish that is the same as HEAD there instead.
1111          * Traditional format never would have "-m" so it is an
1112          * additional safety measure to check for it.
1113          */
1114
1115         if (!have_message && head_commit &&
1116             is_old_style_invocation(argc, argv, head_commit->object.sha1)) {
1117                 strbuf_addstr(&merge_msg, argv[0]);
1118                 head_arg = argv[1];
1119                 argv += 2;
1120                 argc -= 2;
1121         } else if (!head_commit) {
1122                 struct object *remote_head;
1123                 /*
1124                  * If the merged head is a valid one there is no reason
1125                  * to forbid "git merge" into a branch yet to be born.
1126                  * We do the same for "git pull".
1127                  */
1128                 if (argc != 1)
1129                         die(_("Can merge only exactly one commit into "
1130                                 "empty head"));
1131                 if (squash)
1132                         die(_("Squash commit into empty head not supported yet"));
1133                 if (!allow_fast_forward)
1134                         die(_("Non-fast-forward commit does not make sense into "
1135                             "an empty head"));
1136                 remote_head = peel_to_type(argv[0], 0, NULL, OBJ_COMMIT);
1137                 if (!remote_head)
1138                         die(_("%s - not something we can merge"), argv[0]);
1139                 read_empty(remote_head->sha1, 0);
1140                 update_ref("initial pull", "HEAD", remote_head->sha1, NULL, 0,
1141                                 DIE_ON_ERR);
1142                 return 0;
1143         } else {
1144                 struct strbuf merge_names = STRBUF_INIT;
1145
1146                 /* We are invoked directly as the first-class UI. */
1147                 head_arg = "HEAD";
1148
1149                 /*
1150                  * All the rest are the commits being merged;
1151                  * prepare the standard merge summary message to
1152                  * be appended to the given message.  If remote
1153                  * is invalid we will die later in the common
1154                  * codepath so we discard the error in this
1155                  * loop.
1156                  */
1157                 for (i = 0; i < argc; i++)
1158                         merge_name(argv[i], &merge_names);
1159
1160                 if (!have_message || shortlog_len) {
1161                         fmt_merge_msg(&merge_names, &merge_msg, !have_message,
1162                                       shortlog_len);
1163                         if (merge_msg.len)
1164                                 strbuf_setlen(&merge_msg, merge_msg.len - 1);
1165                 }
1166         }
1167
1168         if (!head_commit || !argc)
1169                 usage_with_options(builtin_merge_usage,
1170                         builtin_merge_options);
1171
1172         strbuf_addstr(&buf, "merge");
1173         for (i = 0; i < argc; i++)
1174                 strbuf_addf(&buf, " %s", argv[i]);
1175         setenv("GIT_REFLOG_ACTION", buf.buf, 0);
1176         strbuf_reset(&buf);
1177
1178         for (i = 0; i < argc; i++) {
1179                 struct object *o;
1180                 struct commit *commit;
1181
1182                 o = peel_to_type(argv[i], 0, NULL, OBJ_COMMIT);
1183                 if (!o)
1184                         die(_("%s - not something we can merge"), argv[i]);
1185                 commit = lookup_commit(o->sha1);
1186                 commit->util = (void *)argv[i];
1187                 remotes = &commit_list_insert(commit, remotes)->next;
1188
1189                 strbuf_addf(&buf, "GITHEAD_%s", sha1_to_hex(o->sha1));
1190                 setenv(buf.buf, argv[i], 1);
1191                 strbuf_reset(&buf);
1192         }
1193
1194         if (!use_strategies) {
1195                 if (!remoteheads->next)
1196                         add_strategies(pull_twohead, DEFAULT_TWOHEAD);
1197                 else
1198                         add_strategies(pull_octopus, DEFAULT_OCTOPUS);
1199         }
1200
1201         for (i = 0; i < use_strategies_nr; i++) {
1202                 if (use_strategies[i]->attr & NO_FAST_FORWARD)
1203                         allow_fast_forward = 0;
1204                 if (use_strategies[i]->attr & NO_TRIVIAL)
1205                         allow_trivial = 0;
1206         }
1207
1208         if (!remoteheads->next)
1209                 common = get_merge_bases(head_commit, remoteheads->item, 1);
1210         else {
1211                 struct commit_list *list = remoteheads;
1212                 commit_list_insert(head_commit, &list);
1213                 common = get_octopus_merge_bases(list);
1214                 free(list);
1215         }
1216
1217         update_ref("updating ORIG_HEAD", "ORIG_HEAD", head_commit->object.sha1,
1218                    NULL, 0, DIE_ON_ERR);
1219
1220         if (!common)
1221                 ; /* No common ancestors found. We need a real merge. */
1222         else if (!remoteheads->next && !common->next &&
1223                         common->item == remoteheads->item) {
1224                 /*
1225                  * If head can reach all the merge then we are up to date.
1226                  * but first the most common case of merging one remote.
1227                  */
1228                 finish_up_to_date("Already up-to-date.");
1229                 return 0;
1230         } else if (allow_fast_forward && !remoteheads->next &&
1231                         !common->next &&
1232                         !hashcmp(common->item->object.sha1, head_commit->object.sha1)) {
1233                 /* Again the most common case of merging one remote. */
1234                 struct strbuf msg = STRBUF_INIT;
1235                 struct object *o;
1236                 char hex[41];
1237
1238                 strcpy(hex, find_unique_abbrev(head_commit->object.sha1, DEFAULT_ABBREV));
1239
1240                 if (verbosity >= 0)
1241                         printf(_("Updating %s..%s\n"),
1242                                 hex,
1243                                 find_unique_abbrev(remoteheads->item->object.sha1,
1244                                 DEFAULT_ABBREV));
1245                 strbuf_addstr(&msg, "Fast-forward");
1246                 if (have_message)
1247                         strbuf_addstr(&msg,
1248                                 " (no commit created; -m option ignored)");
1249                 o = peel_to_type(sha1_to_hex(remoteheads->item->object.sha1),
1250                         0, NULL, OBJ_COMMIT);
1251                 if (!o)
1252                         return 1;
1253
1254                 if (checkout_fast_forward(head_commit->object.sha1, remoteheads->item->object.sha1))
1255                         return 1;
1256
1257                 finish(head_commit, o->sha1, msg.buf);
1258                 drop_save();
1259                 return 0;
1260         } else if (!remoteheads->next && common->next)
1261                 ;
1262                 /*
1263                  * We are not doing octopus and not fast-forward.  Need
1264                  * a real merge.
1265                  */
1266         else if (!remoteheads->next && !common->next && option_commit) {
1267                 /*
1268                  * We are not doing octopus, not fast-forward, and have
1269                  * only one common.
1270                  */
1271                 refresh_cache(REFRESH_QUIET);
1272                 if (allow_trivial && !fast_forward_only) {
1273                         /* See if it is really trivial. */
1274                         git_committer_info(IDENT_ERROR_ON_NO_NAME);
1275                         printf(_("Trying really trivial in-index merge...\n"));
1276                         if (!read_tree_trivial(common->item->object.sha1,
1277                                         head_commit->object.sha1, remoteheads->item->object.sha1))
1278                                 return merge_trivial(head_commit);
1279                         printf(_("Nope.\n"));
1280                 }
1281         } else {
1282                 /*
1283                  * An octopus.  If we can reach all the remote we are up
1284                  * to date.
1285                  */
1286                 int up_to_date = 1;
1287                 struct commit_list *j;
1288
1289                 for (j = remoteheads; j; j = j->next) {
1290                         struct commit_list *common_one;
1291
1292                         /*
1293                          * Here we *have* to calculate the individual
1294                          * merge_bases again, otherwise "git merge HEAD^
1295                          * HEAD^^" would be missed.
1296                          */
1297                         common_one = get_merge_bases(head_commit, j->item, 1);
1298                         if (hashcmp(common_one->item->object.sha1,
1299                                 j->item->object.sha1)) {
1300                                 up_to_date = 0;
1301                                 break;
1302                         }
1303                 }
1304                 if (up_to_date) {
1305                         finish_up_to_date("Already up-to-date. Yeeah!");
1306                         return 0;
1307                 }
1308         }
1309
1310         if (fast_forward_only)
1311                 die(_("Not possible to fast-forward, aborting."));
1312
1313         /* We are going to make a new commit. */
1314         git_committer_info(IDENT_ERROR_ON_NO_NAME);
1315
1316         /*
1317          * At this point, we need a real merge.  No matter what strategy
1318          * we use, it would operate on the index, possibly affecting the
1319          * working tree, and when resolved cleanly, have the desired
1320          * tree in the index -- this means that the index must be in
1321          * sync with the head commit.  The strategies are responsible
1322          * to ensure this.
1323          */
1324         if (use_strategies_nr == 1 ||
1325             /*
1326              * Stash away the local changes so that we can try more than one.
1327              */
1328             save_state(stash))
1329                 hashcpy(stash, null_sha1);
1330
1331         for (i = 0; i < use_strategies_nr; i++) {
1332                 int ret;
1333                 if (i) {
1334                         printf(_("Rewinding the tree to pristine...\n"));
1335                         restore_state(head_commit->object.sha1, stash);
1336                 }
1337                 if (use_strategies_nr != 1)
1338                         printf(_("Trying merge strategy %s...\n"),
1339                                 use_strategies[i]->name);
1340                 /*
1341                  * Remember which strategy left the state in the working
1342                  * tree.
1343                  */
1344                 wt_strategy = use_strategies[i]->name;
1345
1346                 ret = try_merge_strategy(use_strategies[i]->name,
1347                                          common, head_commit, head_arg);
1348                 if (!option_commit && !ret) {
1349                         merge_was_ok = 1;
1350                         /*
1351                          * This is necessary here just to avoid writing
1352                          * the tree, but later we will *not* exit with
1353                          * status code 1 because merge_was_ok is set.
1354                          */
1355                         ret = 1;
1356                 }
1357
1358                 if (ret) {
1359                         /*
1360                          * The backend exits with 1 when conflicts are
1361                          * left to be resolved, with 2 when it does not
1362                          * handle the given merge at all.
1363                          */
1364                         if (ret == 1) {
1365                                 int cnt = evaluate_result();
1366
1367                                 if (best_cnt <= 0 || cnt <= best_cnt) {
1368                                         best_strategy = use_strategies[i]->name;
1369                                         best_cnt = cnt;
1370                                 }
1371                         }
1372                         if (merge_was_ok)
1373                                 break;
1374                         else
1375                                 continue;
1376                 }
1377
1378                 /* Automerge succeeded. */
1379                 write_tree_trivial(result_tree);
1380                 automerge_was_ok = 1;
1381                 break;
1382         }
1383
1384         /*
1385          * If we have a resulting tree, that means the strategy module
1386          * auto resolved the merge cleanly.
1387          */
1388         if (automerge_was_ok)
1389                 return finish_automerge(head_commit, common, result_tree,
1390                                         wt_strategy);
1391
1392         /*
1393          * Pick the result from the best strategy and have the user fix
1394          * it up.
1395          */
1396         if (!best_strategy) {
1397                 restore_state(head_commit->object.sha1, stash);
1398                 if (use_strategies_nr > 1)
1399                         fprintf(stderr,
1400                                 _("No merge strategy handled the merge.\n"));
1401                 else
1402                         fprintf(stderr, _("Merge with strategy %s failed.\n"),
1403                                 use_strategies[0]->name);
1404                 return 2;
1405         } else if (best_strategy == wt_strategy)
1406                 ; /* We already have its result in the working tree. */
1407         else {
1408                 printf(_("Rewinding the tree to pristine...\n"));
1409                 restore_state(head_commit->object.sha1, stash);
1410                 printf(_("Using the %s to prepare resolving by hand.\n"),
1411                         best_strategy);
1412                 try_merge_strategy(best_strategy, common, head_commit, head_arg);
1413         }
1414
1415         if (squash)
1416                 finish(head_commit, NULL, NULL);
1417         else {
1418                 int fd;
1419                 struct commit_list *j;
1420
1421                 for (j = remoteheads; j; j = j->next)
1422                         strbuf_addf(&buf, "%s\n",
1423                                 sha1_to_hex(j->item->object.sha1));
1424                 fd = open(git_path("MERGE_HEAD"), O_WRONLY | O_CREAT, 0666);
1425                 if (fd < 0)
1426                         die_errno(_("Could not open '%s' for writing"),
1427                                   git_path("MERGE_HEAD"));
1428                 if (write_in_full(fd, buf.buf, buf.len) != buf.len)
1429                         die_errno(_("Could not write to '%s'"), git_path("MERGE_HEAD"));
1430                 close(fd);
1431                 strbuf_addch(&merge_msg, '\n');
1432                 write_merge_msg();
1433                 fd = open(git_path("MERGE_MODE"), O_WRONLY | O_CREAT | O_TRUNC, 0666);
1434                 if (fd < 0)
1435                         die_errno(_("Could not open '%s' for writing"),
1436                                   git_path("MERGE_MODE"));
1437                 strbuf_reset(&buf);
1438                 if (!allow_fast_forward)
1439                         strbuf_addf(&buf, "no-ff");
1440                 if (write_in_full(fd, buf.buf, buf.len) != buf.len)
1441                         die_errno(_("Could not write to '%s'"), git_path("MERGE_MODE"));
1442                 close(fd);
1443         }
1444
1445         if (merge_was_ok) {
1446                 fprintf(stderr, _("Automatic merge went well; "
1447                         "stopped before committing as requested\n"));
1448                 return 0;
1449         } else
1450                 return suggest_conflicts(option_renormalize);
1451 }