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 #include "fmt-merge-msg.h"
  30 #include "gpg-interface.h"
  31
  32 #define DEFAULT_TWOHEAD (1<<0)
  33 #define DEFAULT_OCTOPUS (1<<1)
  34 #define NO_FAST_FORWARD (1<<2)
  35 #define NO_TRIVIAL      (1<<3)
  36
  37 struct strategy {
  38         const char *name;
  39         unsigned attr;
  40 };
  41
  42 static const char * const builtin_merge_usage[] = {
  43         "git merge [options] [<commit>...]",
  44         "git merge [options] <msg> HEAD <commit>",
  45         "git merge --abort",
  46         NULL
  47 };
  48
  49 static int show_diffstat = 1, shortlog_len = -1, squash;
  50 static int option_commit = 1, allow_fast_forward = 1;
  51 static int fast_forward_only, option_edit = -1;
  52 static int allow_trivial = 1, have_message;
  53 static int overwrite_ignore = 1;
  54 static struct strbuf merge_msg = STRBUF_INIT;
  55 static struct strategy **use_strategies;
  56 static size_t use_strategies_nr, use_strategies_alloc;
  57 static const char **xopts;
  58 static size_t xopts_nr, xopts_alloc;
  59 static const char *branch;
  60 static char *branch_mergeoptions;
  61 static int option_renormalize;
  62 static int verbosity;
  63 static int allow_rerere_auto;
  64 static int abort_current_merge;
  65 static int show_progress = -1;
  66 static int default_to_upstream;
  67 static const char *sign_commit;
  68
  69 static struct strategy all_strategy[] = {
  70         { "recursive",  DEFAULT_TWOHEAD | NO_TRIVIAL },
  71         { "octopus",    DEFAULT_OCTOPUS },
  72         { "resolve",    0 },
  73         { "ours",       NO_FAST_FORWARD | NO_TRIVIAL },
  74         { "subtree",    NO_FAST_FORWARD | NO_TRIVIAL },
  75 };
  76
  77 static const char *pull_twohead, *pull_octopus;
  78
  79 static int option_parse_message(const struct option *opt,
  80                                 const char *arg, int unset)
  81 {
  82         struct strbuf *buf = opt->value;
  83
  84         if (unset)
  85                 strbuf_setlen(buf, 0);
  86         else if (arg) {
  87                 strbuf_addf(buf, "%s%s", buf->len ? "\n\n" : "", arg);
  88                 have_message = 1;
  89         } else
  90                 return error(_("switch `m' requires a value"));
  91         return 0;
  92 }
  93
  94 static struct strategy *get_strategy(const char *name)
  95 {
  96         int i;
  97         struct strategy *ret;
  98         static struct cmdnames main_cmds, other_cmds;
  99         static int loaded;
 100
 101         if (!name)
 102                 return NULL;
 103
 104         for (i = 0; i < ARRAY_SIZE(all_strategy); i++)
 105                 if (!strcmp(name, all_strategy[i].name))
 106                         return &all_strategy[i];
 107
 108         if (!loaded) {
 109                 struct cmdnames not_strategies;
 110                 loaded = 1;
 111
 112                 memset(&not_strategies, 0, sizeof(struct cmdnames));
 113                 load_command_list("git-merge-", &main_cmds, &other_cmds);
 114                 for (i = 0; i < main_cmds.cnt; i++) {
 115                         int j, found = 0;
 116                         struct cmdname *ent = main_cmds.names[i];
 117                         for (j = 0; j < ARRAY_SIZE(all_strategy); j++)
 118                                 if (!strncmp(ent->name, all_strategy[j].name, ent->len)
 119                                                 && !all_strategy[j].name[ent->len])
 120                                         found = 1;
 121                         if (!found)
 122                                 add_cmdname(&not_strategies, ent->name, ent->len);
 123                 }
 124                 exclude_cmds(&main_cmds, &not_strategies);
 125         }
 126         if (!is_in_cmdlist(&main_cmds, name) && !is_in_cmdlist(&other_cmds, name)) {
 127                 fprintf(stderr, _("Could not find merge strategy '%s'.\n"), name);
 128                 fprintf(stderr, _("Available strategies are:"));
 129                 for (i = 0; i < main_cmds.cnt; i++)
 130                         fprintf(stderr, " %s", main_cmds.names[i]->name);
 131                 fprintf(stderr, ".\n");
 132                 if (other_cmds.cnt) {
 133                         fprintf(stderr, _("Available custom strategies are:"));
 134                         for (i = 0; i < other_cmds.cnt; i++)
 135                                 fprintf(stderr, " %s", other_cmds.names[i]->name);
 136                         fprintf(stderr, ".\n");
 137                 }
 138                 exit(1);
 139         }
 140
 141         ret = xcalloc(1, sizeof(struct strategy));
 142         ret->name = xstrdup(name);
 143         ret->attr = NO_TRIVIAL;
 144         return ret;
 145 }
 146
 147 static void append_strategy(struct strategy *s)
 148 {
 149         ALLOC_GROW(use_strategies, use_strategies_nr + 1, use_strategies_alloc);
 150         use_strategies[use_strategies_nr++] = s;
 151 }
 152
 153 static int option_parse_strategy(const struct option *opt,
 154                                  const char *name, int unset)
 155 {
 156         if (unset)
 157                 return 0;
 158
 159         append_strategy(get_strategy(name));
 160         return 0;
 161 }
 162
 163 static int option_parse_x(const struct option *opt,
 164                           const char *arg, int unset)
 165 {
 166         if (unset)
 167                 return 0;
 168
 169         ALLOC_GROW(xopts, xopts_nr + 1, xopts_alloc);
 170         xopts[xopts_nr++] = xstrdup(arg);
 171         return 0;
 172 }
 173
 174 static int option_parse_n(const struct option *opt,
 175                           const char *arg, int unset)
 176 {
 177         show_diffstat = unset;
 178         return 0;
 179 }
 180
 181 static struct option builtin_merge_options[] = {
 182         { OPTION_CALLBACK, 'n', NULL, NULL, NULL,
 183                 "do not show a diffstat at the end of the merge",
 184                 PARSE_OPT_NOARG, option_parse_n },
 185         OPT_BOOLEAN(0, "stat", &show_diffstat,
 186                 "show a diffstat at the end of the merge"),
 187         OPT_BOOLEAN(0, "summary", &show_diffstat, "(synonym to --stat)"),
 188         { OPTION_INTEGER, 0, "log", &shortlog_len, "n",
 189           "add (at most <n>) entries from shortlog to merge commit message",
 190           PARSE_OPT_OPTARG, NULL, DEFAULT_MERGE_LOG_LEN },
 191         OPT_BOOLEAN(0, "squash", &squash,
 192                 "create a single commit instead of doing a merge"),
 193         OPT_BOOLEAN(0, "commit", &option_commit,
 194                 "perform a commit if the merge succeeds (default)"),
 195         OPT_BOOL('e', "edit", &option_edit,
 196                 "edit message before committing"),
 197         OPT_BOOLEAN(0, "ff", &allow_fast_forward,
 198                 "allow fast-forward (default)"),
 199         OPT_BOOLEAN(0, "ff-only", &fast_forward_only,
 200                 "abort if fast-forward is not possible"),
 201         OPT_RERERE_AUTOUPDATE(&allow_rerere_auto),
 202         OPT_CALLBACK('s', "strategy", &use_strategies, "strategy",
 203                 "merge strategy to use", option_parse_strategy),
 204         OPT_CALLBACK('X', "strategy-option", &xopts, "option=value",
 205                 "option for selected merge strategy", option_parse_x),
 206         OPT_CALLBACK('m', "message", &merge_msg, "message",
 207                 "merge commit message (for a non-fast-forward merge)",
 208                 option_parse_message),
 209         OPT__VERBOSITY(&verbosity),
 210         OPT_BOOLEAN(0, "abort", &abort_current_merge,
 211                 "abort the current in-progress merge"),
 212         OPT_SET_INT(0, "progress", &show_progress, "force progress reporting", 1),
 213         { OPTION_STRING, 'S', "gpg-sign", &sign_commit, "key id",
 214           "GPG sign commit", PARSE_OPT_OPTARG, NULL, (intptr_t) "" },
 215         OPT_BOOLEAN(0, "overwrite-ignore", &overwrite_ignore, "update ignored files (default)"),
 216         OPT_END()
 217 };
 218
 219 /* Cleans up metadata that is uninteresting after a succeeded merge. */
 220 static void drop_save(void)
 221 {
 222         unlink(git_path("MERGE_HEAD"));
 223         unlink(git_path("MERGE_MSG"));
 224         unlink(git_path("MERGE_MODE"));
 225 }
 226
 227 static int save_state(unsigned char *stash)
 228 {
 229         int len;
 230         struct child_process cp;
 231         struct strbuf buffer = STRBUF_INIT;
 232         const char *argv[] = {"stash", "create", NULL};
 233
 234         memset(&cp, 0, sizeof(cp));
 235         cp.argv = argv;
 236         cp.out = -1;
 237         cp.git_cmd = 1;
 238
 239         if (start_command(&cp))
 240                 die(_("could not run stash."));
 241         len = strbuf_read(&buffer, cp.out, 1024);
 242         close(cp.out);
 243
 244         if (finish_command(&cp) || len < 0)
 245                 die(_("stash failed"));
 246         else if (!len)          /* no changes */
 247                 return -1;
 248         strbuf_setlen(&buffer, buffer.len-1);
 249         if (get_sha1(buffer.buf, stash))
 250                 die(_("not a valid object: %s"), buffer.buf);
 251         return 0;
 252 }
 253
 254 static void read_empty(unsigned const char *sha1, int verbose)
 255 {
 256         int i = 0;
 257         const char *args[7];
 258
 259         args[i++] = "read-tree";
 260         if (verbose)
 261                 args[i++] = "-v";
 262         args[i++] = "-m";
 263         args[i++] = "-u";
 264         args[i++] = EMPTY_TREE_SHA1_HEX;
 265         args[i++] = sha1_to_hex(sha1);
 266         args[i] = NULL;
 267
 268         if (run_command_v_opt(args, RUN_GIT_CMD))
 269                 die(_("read-tree failed"));
 270 }
 271
 272 static void reset_hard(unsigned const char *sha1, int verbose)
 273 {
 274         int i = 0;
 275         const char *args[6];
 276
 277         args[i++] = "read-tree";
 278         if (verbose)
 279                 args[i++] = "-v";
 280         args[i++] = "--reset";
 281         args[i++] = "-u";
 282         args[i++] = sha1_to_hex(sha1);
 283         args[i] = NULL;
 284
 285         if (run_command_v_opt(args, RUN_GIT_CMD))
 286                 die(_("read-tree failed"));
 287 }
 288
 289 static void restore_state(const unsigned char *head,
 290                           const unsigned char *stash)
 291 {
 292         struct strbuf sb = STRBUF_INIT;
 293         const char *args[] = { "stash", "apply", NULL, NULL };
 294
 295         if (is_null_sha1(stash))
 296                 return;
 297
 298         reset_hard(head, 1);
 299
 300         args[2] = sha1_to_hex(stash);
 301
 302         /*
 303          * It is OK to ignore error here, for example when there was
 304          * nothing to restore.
 305          */
 306         run_command_v_opt(args, RUN_GIT_CMD);
 307
 308         strbuf_release(&sb);
 309         refresh_cache(REFRESH_QUIET);
 310 }
 311
 312 /* This is called when no merge was necessary. */
 313 static void finish_up_to_date(const char *msg)
 314 {
 315         if (verbosity >= 0)
 316                 printf("%s%s\n", squash ? _(" (nothing to squash)") : "", msg);
 317         drop_save();
 318 }
 319
 320 static void squash_message(struct commit *commit, struct commit_list *remoteheads)
 321 {
 322         struct rev_info rev;
 323         struct strbuf out = STRBUF_INIT;
 324         struct commit_list *j;
 325         const char *filename;
 326         int fd;
 327         struct pretty_print_context ctx = {0};
 328
 329         printf(_("Squash commit -- not updating HEAD\n"));
 330         filename = git_path("SQUASH_MSG");
 331         fd = open(filename, O_WRONLY | O_CREAT, 0666);
 332         if (fd < 0)
 333                 die_errno(_("Could not write to '%s'"), filename);
 334
 335         init_revisions(&rev, NULL);
 336         rev.ignore_merges = 1;
 337         rev.commit_format = CMIT_FMT_MEDIUM;
 338
 339         commit->object.flags |= UNINTERESTING;
 340         add_pending_object(&rev, &commit->object, NULL);
 341
 342         for (j = remoteheads; j; j = j->next)
 343                 add_pending_object(&rev, &j->item->object, NULL);
 344
 345         setup_revisions(0, NULL, &rev, NULL);
 346         if (prepare_revision_walk(&rev))
 347                 die(_("revision walk setup failed"));
 348
 349         ctx.abbrev = rev.abbrev;
 350         ctx.date_mode = rev.date_mode;
 351         ctx.fmt = rev.commit_format;
 352
 353         strbuf_addstr(&out, "Squashed commit of the following:\n");
 354         while ((commit = get_revision(&rev)) != NULL) {
 355                 strbuf_addch(&out, '\n');
 356                 strbuf_addf(&out, "commit %s\n",
 357                         sha1_to_hex(commit->object.sha1));
 358                 pretty_print_commit(&ctx, commit, &out);
 359         }
 360         if (write(fd, out.buf, out.len) < 0)
 361                 die_errno(_("Writing SQUASH_MSG"));
 362         if (close(fd))
 363                 die_errno(_("Finishing SQUASH_MSG"));
 364         strbuf_release(&out);
 365 }
 366
 367 static void finish(struct commit *head_commit,
 368                    struct commit_list *remoteheads,
 369                    const unsigned char *new_head, const char *msg)
 370 {
 371         struct strbuf reflog_message = STRBUF_INIT;
 372         const unsigned char *head = head_commit->object.sha1;
 373
 374         if (!msg)
 375                 strbuf_addstr(&reflog_message, getenv("GIT_REFLOG_ACTION"));
 376         else {
 377                 if (verbosity >= 0)
 378                         printf("%s\n", msg);
 379                 strbuf_addf(&reflog_message, "%s: %s",
 380                         getenv("GIT_REFLOG_ACTION"), msg);
 381         }
 382         if (squash) {
 383                 squash_message(head_commit, remoteheads);
 384         } else {
 385                 if (verbosity >= 0 && !merge_msg.len)
 386                         printf(_("No merge message -- not updating HEAD\n"));
 387                 else {
 388                         const char *argv_gc_auto[] = { "gc", "--auto", NULL };
 389                         update_ref(reflog_message.buf, "HEAD",
 390                                 new_head, head, 0,
 391                                 DIE_ON_ERR);
 392                         /*
 393                          * We ignore errors in 'gc --auto', since the
 394                          * user should see them.
 395                          */
 396                         run_command_v_opt(argv_gc_auto, RUN_GIT_CMD);
 397                 }
 398         }
 399         if (new_head && show_diffstat) {
 400                 struct diff_options opts;
 401                 diff_setup(&opts);
 402                 opts.stat_width = -1; /* use full terminal width */
 403                 opts.stat_graph_width = -1; /* respect statGraphWidth config */
 404                 opts.output_format |=
 405                         DIFF_FORMAT_SUMMARY | DIFF_FORMAT_DIFFSTAT;
 406                 opts.detect_rename = DIFF_DETECT_RENAME;
 407                 if (diff_setup_done(&opts) < 0)
 408                         die(_("diff_setup_done failed"));
 409                 diff_tree_sha1(head, new_head, "", &opts);
 410                 diffcore_std(&opts);
 411                 diff_flush(&opts);
 412         }
 413
 414         /* Run a post-merge hook */
 415         run_hook(NULL, "post-merge", squash ? "1" : "0", NULL);
 416
 417         strbuf_release(&reflog_message);
 418 }
 419
 420 /* Get the name for the merge commit's message. */
 421 static void merge_name(const char *remote, struct strbuf *msg)
 422 {
 423         struct commit *remote_head;
 424         unsigned char branch_head[20];
 425         struct strbuf buf = STRBUF_INIT;
 426         struct strbuf bname = STRBUF_INIT;
 427         const char *ptr;
 428         char *found_ref;
 429         int len, early;
 430
 431         strbuf_branchname(&bname, remote);
 432         remote = bname.buf;
 433
 434         memset(branch_head, 0, sizeof(branch_head));
 435         remote_head = get_merge_parent(remote);
 436         if (!remote_head)
 437                 die(_("'%s' does not point to a commit"), remote);
 438
 439         if (dwim_ref(remote, strlen(remote), branch_head, &found_ref) > 0) {
 440                 if (!prefixcmp(found_ref, "refs/heads/")) {
 441                         strbuf_addf(msg, "%s\t\tbranch '%s' of .\n",
 442                                     sha1_to_hex(branch_head), remote);
 443                         goto cleanup;
 444                 }
 445                 if (!prefixcmp(found_ref, "refs/tags/")) {
 446                         strbuf_addf(msg, "%s\t\ttag '%s' of .\n",
 447                                     sha1_to_hex(branch_head), remote);
 448                         goto cleanup;
 449                 }
 450                 if (!prefixcmp(found_ref, "refs/remotes/")) {
 451                         strbuf_addf(msg, "%s\t\tremote-tracking branch '%s' of .\n",
 452                                     sha1_to_hex(branch_head), remote);
 453                         goto cleanup;
 454                 }
 455         }
 456
 457         /* See if remote matches <name>^^^.. or <name>~<number> */
 458         for (len = 0, ptr = remote + strlen(remote);
 459              remote < ptr && ptr[-1] == '^';
 460              ptr--)
 461                 len++;
 462         if (len)
 463                 early = 1;
 464         else {
 465                 early = 0;
 466                 ptr = strrchr(remote, '~');
 467                 if (ptr) {
 468                         int seen_nonzero = 0;
 469
 470                         len++; /* count ~ */
 471                         while (*++ptr && isdigit(*ptr)) {
 472                                 seen_nonzero |= (*ptr != '0');
 473                                 len++;
 474                         }
 475                         if (*ptr)
 476                                 len = 0; /* not ...~<number> */
 477                         else if (seen_nonzero)
 478                                 early = 1;
 479                         else if (len == 1)
 480                                 early = 1; /* "name~" is "name~1"! */
 481                 }
 482         }
 483         if (len) {
 484                 struct strbuf truname = STRBUF_INIT;
 485                 strbuf_addstr(&truname, "refs/heads/");
 486                 strbuf_addstr(&truname, remote);
 487                 strbuf_setlen(&truname, truname.len - len);
 488                 if (ref_exists(truname.buf)) {
 489                         strbuf_addf(msg,
 490                                     "%s\t\tbranch '%s'%s of .\n",
 491                                     sha1_to_hex(remote_head->object.sha1),
 492                                     truname.buf + 11,
 493                                     (early ? " (early part)" : ""));
 494                         strbuf_release(&truname);
 495                         goto cleanup;
 496                 }
 497         }
 498
 499         if (!strcmp(remote, "FETCH_HEAD") &&
 500                         !access(git_path("FETCH_HEAD"), R_OK)) {
 501                 const char *filename;
 502                 FILE *fp;
 503                 struct strbuf line = STRBUF_INIT;
 504                 char *ptr;
 505
 506                 filename = git_path("FETCH_HEAD");
 507                 fp = fopen(filename, "r");
 508                 if (!fp)
 509                         die_errno(_("could not open '%s' for reading"),
 510                                   filename);
 511                 strbuf_getline(&line, fp, '\n');
 512                 fclose(fp);
 513                 ptr = strstr(line.buf, "\tnot-for-merge\t");
 514                 if (ptr)
 515                         strbuf_remove(&line, ptr-line.buf+1, 13);
 516                 strbuf_addbuf(msg, &line);
 517                 strbuf_release(&line);
 518                 goto cleanup;
 519         }
 520         strbuf_addf(msg, "%s\t\tcommit '%s'\n",
 521                 sha1_to_hex(remote_head->object.sha1), remote);
 522 cleanup:
 523         strbuf_release(&buf);
 524         strbuf_release(&bname);
 525 }
 526
 527 static void parse_branch_merge_options(char *bmo)
 528 {
 529         const char **argv;
 530         int argc;
 531
 532         if (!bmo)
 533                 return;
 534         argc = split_cmdline(bmo, &argv);
 535         if (argc < 0)
 536                 die(_("Bad branch.%s.mergeoptions string: %s"), branch,
 537                     split_cmdline_strerror(argc));
 538         argv = xrealloc(argv, sizeof(*argv) * (argc + 2));
 539         memmove(argv + 1, argv, sizeof(*argv) * (argc + 1));
 540         argc++;
 541         argv[0] = "branch.*.mergeoptions";
 542         parse_options(argc, argv, NULL, builtin_merge_options,
 543                       builtin_merge_usage, 0);
 544         free(argv);
 545 }
 546
 547 static int git_merge_config(const char *k, const char *v, void *cb)
 548 {
 549         int status;
 550
 551         if (branch && !prefixcmp(k, "branch.") &&
 552                 !prefixcmp(k + 7, branch) &&
 553                 !strcmp(k + 7 + strlen(branch), ".mergeoptions")) {
 554                 free(branch_mergeoptions);
 555                 branch_mergeoptions = xstrdup(v);
 556                 return 0;
 557         }
 558
 559         if (!strcmp(k, "merge.diffstat") || !strcmp(k, "merge.stat"))
 560                 show_diffstat = git_config_bool(k, v);
 561         else if (!strcmp(k, "pull.twohead"))
 562                 return git_config_string(&pull_twohead, k, v);
 563         else if (!strcmp(k, "pull.octopus"))
 564                 return git_config_string(&pull_octopus, k, v);
 565         else if (!strcmp(k, "merge.renormalize"))
 566                 option_renormalize = git_config_bool(k, v);
 567         else if (!strcmp(k, "merge.ff")) {
 568                 int boolval = git_config_maybe_bool(k, v);
 569                 if (0 <= boolval) {
 570                         allow_fast_forward = boolval;
 571                 } else if (v && !strcmp(v, "only")) {
 572                         allow_fast_forward = 1;
 573                         fast_forward_only = 1;
 574                 } /* do not barf on values from future versions of git */
 575                 return 0;
 576         } else if (!strcmp(k, "merge.defaulttoupstream")) {
 577                 default_to_upstream = git_config_bool(k, v);
 578                 return 0;
 579         }
 580
 581         status = fmt_merge_msg_config(k, v, cb);
 582         if (status)
 583                 return status;
 584         status = git_gpg_config(k, v, NULL);
 585         if (status)
 586                 return status;
 587         return git_diff_ui_config(k, v, cb);
 588 }
 589
 590 static int read_tree_trivial(unsigned char *common, unsigned char *head,
 591                              unsigned char *one)
 592 {
 593         int i, nr_trees = 0;
 594         struct tree *trees[MAX_UNPACK_TREES];
 595         struct tree_desc t[MAX_UNPACK_TREES];
 596         struct unpack_trees_options opts;
 597
 598         memset(&opts, 0, sizeof(opts));
 599         opts.head_idx = 2;
 600         opts.src_index = &the_index;
 601         opts.dst_index = &the_index;
 602         opts.update = 1;
 603         opts.verbose_update = 1;
 604         opts.trivial_merges_only = 1;
 605         opts.merge = 1;
 606         trees[nr_trees] = parse_tree_indirect(common);
 607         if (!trees[nr_trees++])
 608                 return -1;
 609         trees[nr_trees] = parse_tree_indirect(head);
 610         if (!trees[nr_trees++])
 611                 return -1;
 612         trees[nr_trees] = parse_tree_indirect(one);
 613         if (!trees[nr_trees++])
 614                 return -1;
 615         opts.fn = threeway_merge;
 616         cache_tree_free(&active_cache_tree);
 617         for (i = 0; i < nr_trees; i++) {
 618                 parse_tree(trees[i]);
 619                 init_tree_desc(t+i, trees[i]->buffer, trees[i]->size);
 620         }
 621         if (unpack_trees(nr_trees, t, &opts))
 622                 return -1;
 623         return 0;
 624 }
 625
 626 static void write_tree_trivial(unsigned char *sha1)
 627 {
 628         if (write_cache_as_tree(sha1, 0, NULL))
 629                 die(_("git write-tree failed to write a tree"));
 630 }
 631
 632 static const char *merge_argument(struct commit *commit)
 633 {
 634         if (commit)
 635                 return sha1_to_hex(commit->object.sha1);
 636         else
 637                 return EMPTY_TREE_SHA1_HEX;
 638 }
 639
 640 int try_merge_command(const char *strategy, size_t xopts_nr,
 641                       const char **xopts, struct commit_list *common,
 642                       const char *head_arg, struct commit_list *remotes)
 643 {
 644         const char **args;
 645         int i = 0, x = 0, ret;
 646         struct commit_list *j;
 647         struct strbuf buf = STRBUF_INIT;
 648
 649         args = xmalloc((4 + xopts_nr + commit_list_count(common) +
 650                         commit_list_count(remotes)) * sizeof(char *));
 651         strbuf_addf(&buf, "merge-%s", strategy);
 652         args[i++] = buf.buf;
 653         for (x = 0; x < xopts_nr; x++) {
 654                 char *s = xmalloc(strlen(xopts[x])+2+1);
 655                 strcpy(s, "--");
 656                 strcpy(s+2, xopts[x]);
 657                 args[i++] = s;
 658         }
 659         for (j = common; j; j = j->next)
 660                 args[i++] = xstrdup(merge_argument(j->item));
 661         args[i++] = "--";
 662         args[i++] = head_arg;
 663         for (j = remotes; j; j = j->next)
 664                 args[i++] = xstrdup(merge_argument(j->item));
 665         args[i] = NULL;
 666         ret = run_command_v_opt(args, RUN_GIT_CMD);
 667         strbuf_release(&buf);
 668         i = 1;
 669         for (x = 0; x < xopts_nr; x++)
 670                 free((void *)args[i++]);
 671         for (j = common; j; j = j->next)
 672                 free((void *)args[i++]);
 673         i += 2;
 674         for (j = remotes; j; j = j->next)
 675                 free((void *)args[i++]);
 676         free(args);
 677         discard_cache();
 678         if (read_cache() < 0)
 679                 die(_("failed to read the cache"));
 680         resolve_undo_clear();
 681
 682         return ret;
 683 }
 684
 685 static int try_merge_strategy(const char *strategy, struct commit_list *common,
 686                               struct commit_list *remoteheads,
 687                               struct commit *head, const char *head_arg)
 688 {
 689         int index_fd;
 690         struct lock_file *lock = xcalloc(1, sizeof(struct lock_file));
 691
 692         index_fd = hold_locked_index(lock, 1);
 693         refresh_cache(REFRESH_QUIET);
 694         if (active_cache_changed &&
 695                         (write_cache(index_fd, active_cache, active_nr) ||
 696                          commit_locked_index(lock)))
 697                 return error(_("Unable to write index."));
 698         rollback_lock_file(lock);
 699
 700         if (!strcmp(strategy, "recursive") || !strcmp(strategy, "subtree")) {
 701                 int clean, x;
 702                 struct commit *result;
 703                 struct lock_file *lock = xcalloc(1, sizeof(struct lock_file));
 704                 int index_fd;
 705                 struct commit_list *reversed = NULL;
 706                 struct merge_options o;
 707                 struct commit_list *j;
 708
 709                 if (remoteheads->next) {
 710                         error(_("Not handling anything other than two heads merge."));
 711                         return 2;
 712                 }
 713
 714                 init_merge_options(&o);
 715                 if (!strcmp(strategy, "subtree"))
 716                         o.subtree_shift = "";
 717
 718                 o.renormalize = option_renormalize;
 719                 o.show_rename_progress =
 720                         show_progress == -1 ? isatty(2) : show_progress;
 721
 722                 for (x = 0; x < xopts_nr; x++)
 723                         if (parse_merge_opt(&o, xopts[x]))
 724                                 die(_("Unknown option for merge-recursive: -X%s"), xopts[x]);
 725
 726                 o.branch1 = head_arg;
 727                 o.branch2 = merge_remote_util(remoteheads->item)->name;
 728
 729                 for (j = common; j; j = j->next)
 730                         commit_list_insert(j->item, &reversed);
 731
 732                 index_fd = hold_locked_index(lock, 1);
 733                 clean = merge_recursive(&o, head,
 734                                 remoteheads->item, reversed, &result);
 735                 if (active_cache_changed &&
 736                                 (write_cache(index_fd, active_cache, active_nr) ||
 737                                  commit_locked_index(lock)))
 738                         die (_("unable to write %s"), get_index_file());
 739                 rollback_lock_file(lock);
 740                 return clean ? 0 : 1;
 741         } else {
 742                 return try_merge_command(strategy, xopts_nr, xopts,
 743                                                 common, head_arg, remoteheads);
 744         }
 745 }
 746
 747 static void count_diff_files(struct diff_queue_struct *q,
 748                              struct diff_options *opt, void *data)
 749 {
 750         int *count = data;
 751
 752         (*count) += q->nr;
 753 }
 754
 755 static int count_unmerged_entries(void)
 756 {
 757         int i, ret = 0;
 758
 759         for (i = 0; i < active_nr; i++)
 760                 if (ce_stage(active_cache[i]))
 761                         ret++;
 762
 763         return ret;
 764 }
 765
 766 int checkout_fast_forward(const unsigned char *head, const unsigned char *remote)
 767 {
 768         struct tree *trees[MAX_UNPACK_TREES];
 769         struct unpack_trees_options opts;
 770         struct tree_desc t[MAX_UNPACK_TREES];
 771         int i, fd, nr_trees = 0;
 772         struct dir_struct dir;
 773         struct lock_file *lock_file = xcalloc(1, sizeof(struct lock_file));
 774
 775         refresh_cache(REFRESH_QUIET);
 776
 777         fd = hold_locked_index(lock_file, 1);
 778
 779         memset(&trees, 0, sizeof(trees));
 780         memset(&opts, 0, sizeof(opts));
 781         memset(&t, 0, sizeof(t));
 782         if (overwrite_ignore) {
 783                 memset(&dir, 0, sizeof(dir));
 784                 dir.flags |= DIR_SHOW_IGNORED;
 785                 setup_standard_excludes(&dir);
 786                 opts.dir = &dir;
 787         }
 788
 789         opts.head_idx = 1;
 790         opts.src_index = &the_index;
 791         opts.dst_index = &the_index;
 792         opts.update = 1;
 793         opts.verbose_update = 1;
 794         opts.merge = 1;
 795         opts.fn = twoway_merge;
 796         setup_unpack_trees_porcelain(&opts, "merge");
 797
 798         trees[nr_trees] = parse_tree_indirect(head);
 799         if (!trees[nr_trees++])
 800                 return -1;
 801         trees[nr_trees] = parse_tree_indirect(remote);
 802         if (!trees[nr_trees++])
 803                 return -1;
 804         for (i = 0; i < nr_trees; i++) {
 805                 parse_tree(trees[i]);
 806                 init_tree_desc(t+i, trees[i]->buffer, trees[i]->size);
 807         }
 808         if (unpack_trees(nr_trees, t, &opts))
 809                 return -1;
 810         if (write_cache(fd, active_cache, active_nr) ||
 811                 commit_locked_index(lock_file))
 812                 die(_("unable to write new index file"));
 813         return 0;
 814 }
 815
 816 static void split_merge_strategies(const char *string, struct strategy **list,
 817                                    int *nr, int *alloc)
 818 {
 819         char *p, *q, *buf;
 820
 821         if (!string)
 822                 return;
 823
 824         buf = xstrdup(string);
 825         q = buf;
 826         for (;;) {
 827                 p = strchr(q, ' ');
 828                 if (!p) {
 829                         ALLOC_GROW(*list, *nr + 1, *alloc);
 830                         (*list)[(*nr)++].name = xstrdup(q);
 831                         free(buf);
 832                         return;
 833                 } else {
 834                         *p = '\0';
 835                         ALLOC_GROW(*list, *nr + 1, *alloc);
 836                         (*list)[(*nr)++].name = xstrdup(q);
 837                         q = ++p;
 838                 }
 839         }
 840 }
 841
 842 static void add_strategies(const char *string, unsigned attr)
 843 {
 844         struct strategy *list = NULL;
 845         int list_alloc = 0, list_nr = 0, i;
 846
 847         memset(&list, 0, sizeof(list));
 848         split_merge_strategies(string, &list, &list_nr, &list_alloc);
 849         if (list) {
 850                 for (i = 0; i < list_nr; i++)
 851                         append_strategy(get_strategy(list[i].name));
 852                 return;
 853         }
 854         for (i = 0; i < ARRAY_SIZE(all_strategy); i++)
 855                 if (all_strategy[i].attr & attr)
 856                         append_strategy(&all_strategy[i]);
 857
 858 }
 859
 860 static void write_merge_msg(struct strbuf *msg)
 861 {
 862         const char *filename = git_path("MERGE_MSG");
 863         int fd = open(filename, O_WRONLY | O_CREAT, 0666);
 864         if (fd < 0)
 865                 die_errno(_("Could not open '%s' for writing"),
 866                           filename);
 867         if (write_in_full(fd, msg->buf, msg->len) != msg->len)
 868                 die_errno(_("Could not write to '%s'"), filename);
 869         close(fd);
 870 }
 871
 872 static void read_merge_msg(struct strbuf *msg)
 873 {
 874         const char *filename = git_path("MERGE_MSG");
 875         strbuf_reset(msg);
 876         if (strbuf_read_file(msg, filename, 0) < 0)
 877                 die_errno(_("Could not read from '%s'"), filename);
 878 }
 879
 880 static void write_merge_state(struct commit_list *);
 881 static void abort_commit(struct commit_list *remoteheads, const char *err_msg)
 882 {
 883         if (err_msg)
 884                 error("%s", err_msg);
 885         fprintf(stderr,
 886                 _("Not committing merge; use 'git commit' to complete the merge.\n"));
 887         write_merge_state(remoteheads);
 888         exit(1);
 889 }
 890
 891 static const char merge_editor_comment[] =
 892 N_("Please enter a commit message to explain why this merge is necessary,\n"
 893    "especially if it merges an updated upstream into a topic branch.\n"
 894    "\n"
 895    "Lines starting with '#' will be ignored, and an empty message aborts\n"
 896    "the commit.\n");
 897
 898 static void prepare_to_commit(struct commit_list *remoteheads)
 899 {
 900         struct strbuf msg = STRBUF_INIT;
 901         const char *comment = _(merge_editor_comment);
 902         strbuf_addbuf(&msg, &merge_msg);
 903         strbuf_addch(&msg, '\n');
 904         if (0 < option_edit)
 905                 strbuf_add_lines(&msg, "# ", comment, strlen(comment));
 906         write_merge_msg(&msg);
 907         run_hook(get_index_file(), "prepare-commit-msg",
 908                  git_path("MERGE_MSG"), "merge", NULL, NULL);
 909         if (0 < option_edit) {
 910                 if (launch_editor(git_path("MERGE_MSG"), NULL, NULL))
 911                         abort_commit(remoteheads, NULL);
 912         }
 913         read_merge_msg(&msg);
 914         stripspace(&msg, 0 < option_edit);
 915         if (!msg.len)
 916                 abort_commit(remoteheads, _("Empty commit message."));
 917         strbuf_release(&merge_msg);
 918         strbuf_addbuf(&merge_msg, &msg);
 919         strbuf_release(&msg);
 920 }
 921
 922 static int merge_trivial(struct commit *head, struct commit_list *remoteheads)
 923 {
 924         unsigned char result_tree[20], result_commit[20];
 925         struct commit_list *parent = xmalloc(sizeof(*parent));
 926
 927         write_tree_trivial(result_tree);
 928         printf(_("Wonderful.\n"));
 929         parent->item = head;
 930         parent->next = xmalloc(sizeof(*parent->next));
 931         parent->next->item = remoteheads->item;
 932         parent->next->next = NULL;
 933         prepare_to_commit(remoteheads);
 934         if (commit_tree(&merge_msg, result_tree, parent, result_commit, NULL,
 935                         sign_commit))
 936                 die(_("failed to write commit object"));
 937         finish(head, remoteheads, result_commit, "In-index merge");
 938         drop_save();
 939         return 0;
 940 }
 941
 942 static int finish_automerge(struct commit *head,
 943                             int head_subsumed,
 944                             struct commit_list *common,
 945                             struct commit_list *remoteheads,
 946                             unsigned char *result_tree,
 947                             const char *wt_strategy)
 948 {
 949         struct commit_list *parents = NULL;
 950         struct strbuf buf = STRBUF_INIT;
 951         unsigned char result_commit[20];
 952
 953         free_commit_list(common);
 954         parents = remoteheads;
 955         if (!head_subsumed || !allow_fast_forward)
 956                 commit_list_insert(head, &parents);
 957         strbuf_addch(&merge_msg, '\n');
 958         prepare_to_commit(remoteheads);
 959         if (commit_tree(&merge_msg, result_tree, parents, result_commit,
 960                         NULL, sign_commit))
 961                 die(_("failed to write commit object"));
 962         strbuf_addf(&buf, "Merge made by the '%s' strategy.", wt_strategy);
 963         finish(head, remoteheads, result_commit, buf.buf);
 964         strbuf_release(&buf);
 965         drop_save();
 966         return 0;
 967 }
 968
 969 static int suggest_conflicts(int renormalizing)
 970 {
 971         const char *filename;
 972         FILE *fp;
 973         int pos;
 974
 975         filename = git_path("MERGE_MSG");
 976         fp = fopen(filename, "a");
 977         if (!fp)
 978                 die_errno(_("Could not open '%s' for writing"), filename);
 979         fprintf(fp, "\nConflicts:\n");
 980         for (pos = 0; pos < active_nr; pos++) {
 981                 struct cache_entry *ce = active_cache[pos];
 982
 983                 if (ce_stage(ce)) {
 984                         fprintf(fp, "\t%s\n", ce->name);
 985                         while (pos + 1 < active_nr &&
 986                                         !strcmp(ce->name,
 987                                                 active_cache[pos + 1]->name))
 988                                 pos++;
 989                 }
 990         }
 991         fclose(fp);
 992         rerere(allow_rerere_auto);
 993         printf(_("Automatic merge failed; "
 994                         "fix conflicts and then commit the result.\n"));
 995         return 1;
 996 }
 997
 998 static struct commit *is_old_style_invocation(int argc, const char **argv,
 999                                               const unsigned char *head)
1000 {
1001         struct commit *second_token = NULL;
1002         if (argc > 2) {
1003                 unsigned char second_sha1[20];
1004
1005                 if (get_sha1(argv[1], second_sha1))
1006                         return NULL;
1007                 second_token = lookup_commit_reference_gently(second_sha1, 0);
1008                 if (!second_token)
1009                         die(_("'%s' is not a commit"), argv[1]);
1010                 if (hashcmp(second_token->object.sha1, head))
1011                         return NULL;
1012         }
1013         return second_token;
1014 }
1015
1016 static int evaluate_result(void)
1017 {
1018         int cnt = 0;
1019         struct rev_info rev;
1020
1021         /* Check how many files differ. */
1022         init_revisions(&rev, "");
1023         setup_revisions(0, NULL, &rev, NULL);
1024         rev.diffopt.output_format |=
1025                 DIFF_FORMAT_CALLBACK;
1026         rev.diffopt.format_callback = count_diff_files;
1027         rev.diffopt.format_callback_data = &cnt;
1028         run_diff_files(&rev, 0);
1029
1030         /*
1031          * Check how many unmerged entries are
1032          * there.
1033          */
1034         cnt += count_unmerged_entries();
1035
1036         return cnt;
1037 }
1038
1039 /*
1040  * Pretend as if the user told us to merge with the tracking
1041  * branch we have for the upstream of the current branch
1042  */
1043 static int setup_with_upstream(const char ***argv)
1044 {
1045         struct branch *branch = branch_get(NULL);
1046         int i;
1047         const char **args;
1048
1049         if (!branch)
1050                 die(_("No current branch."));
1051         if (!branch->remote)
1052                 die(_("No remote for the current branch."));
1053         if (!branch->merge_nr)
1054                 die(_("No default upstream defined for the current branch."));
1055
1056         args = xcalloc(branch->merge_nr + 1, sizeof(char *));
1057         for (i = 0; i < branch->merge_nr; i++) {
1058                 if (!branch->merge[i]->dst)
1059                         die(_("No remote tracking branch for %s from %s"),
1060                             branch->merge[i]->src, branch->remote_name);
1061                 args[i] = branch->merge[i]->dst;
1062         }
1063         args[i] = NULL;
1064         *argv = args;
1065         return i;
1066 }
1067
1068 static void write_merge_state(struct commit_list *remoteheads)
1069 {
1070         const char *filename;
1071         int fd;
1072         struct commit_list *j;
1073         struct strbuf buf = STRBUF_INIT;
1074
1075         for (j = remoteheads; j; j = j->next) {
1076                 unsigned const char *sha1;
1077                 struct commit *c = j->item;
1078                 if (c->util && merge_remote_util(c)->obj) {
1079                         sha1 = merge_remote_util(c)->obj->sha1;
1080                 } else {
1081                         sha1 = c->object.sha1;
1082                 }
1083                 strbuf_addf(&buf, "%s\n", sha1_to_hex(sha1));
1084         }
1085         filename = git_path("MERGE_HEAD");
1086         fd = open(filename, O_WRONLY | O_CREAT, 0666);
1087         if (fd < 0)
1088                 die_errno(_("Could not open '%s' for writing"), filename);
1089         if (write_in_full(fd, buf.buf, buf.len) != buf.len)
1090                 die_errno(_("Could not write to '%s'"), filename);
1091         close(fd);
1092         strbuf_addch(&merge_msg, '\n');
1093         write_merge_msg(&merge_msg);
1094
1095         filename = git_path("MERGE_MODE");
1096         fd = open(filename, O_WRONLY | O_CREAT | O_TRUNC, 0666);
1097         if (fd < 0)
1098                 die_errno(_("Could not open '%s' for writing"), filename);
1099         strbuf_reset(&buf);
1100         if (!allow_fast_forward)
1101                 strbuf_addf(&buf, "no-ff");
1102         if (write_in_full(fd, buf.buf, buf.len) != buf.len)
1103                 die_errno(_("Could not write to '%s'"), filename);
1104         close(fd);
1105 }
1106
1107 static int default_edit_option(void)
1108 {
1109         static const char name[] = "GIT_MERGE_AUTOEDIT";
1110         const char *e = getenv(name);
1111         struct stat st_stdin, st_stdout;
1112
1113         if (have_message)
1114                 /* an explicit -m msg without --[no-]edit */
1115                 return 0;
1116
1117         if (e) {
1118                 int v = git_config_maybe_bool(name, e);
1119                 if (v < 0)
1120                         die("Bad value '%s' in environment '%s'", e, name);
1121                 return v;
1122         }
1123
1124         /* Use editor if stdin and stdout are the same and is a tty */
1125         return (!fstat(0, &st_stdin) &&
1126                 !fstat(1, &st_stdout) &&
1127                 isatty(0) && isatty(1) &&
1128                 st_stdin.st_dev == st_stdout.st_dev &&
1129                 st_stdin.st_ino == st_stdout.st_ino &&
1130                 st_stdin.st_mode == st_stdout.st_mode);
1131 }
1132
1133 static struct commit_list *collect_parents(struct commit *head_commit,
1134                                            int *head_subsumed,
1135                                            int argc, const char **argv)
1136 {
1137         int i;
1138         struct commit_list *remoteheads = NULL, *parents, *next;
1139         struct commit_list **remotes = &remoteheads;
1140
1141         if (head_commit)
1142                 remotes = &commit_list_insert(head_commit, remotes)->next;
1143         for (i = 0; i < argc; i++) {
1144                 struct commit *commit = get_merge_parent(argv[i]);
1145                 if (!commit)
1146                         die(_("%s - not something we can merge"), argv[i]);
1147                 remotes = &commit_list_insert(commit, remotes)->next;
1148         }
1149         *remotes = NULL;
1150
1151         parents = reduce_heads(remoteheads);
1152
1153         *head_subsumed = 1; /* we will flip this to 0 when we find it */
1154         for (remoteheads = NULL, remotes = &remoteheads;
1155              parents;
1156              parents = next) {
1157                 struct commit *commit = parents->item;
1158                 next = parents->next;
1159                 if (commit == head_commit)
1160                         *head_subsumed = 0;
1161                 else
1162                         remotes = &commit_list_insert(commit, remotes)->next;
1163         }
1164         return remoteheads;
1165 }
1166
1167 int cmd_merge(int argc, const char **argv, const char *prefix)
1168 {
1169         unsigned char result_tree[20];
1170         unsigned char stash[20];
1171         unsigned char head_sha1[20];
1172         struct commit *head_commit;
1173         struct strbuf buf = STRBUF_INIT;
1174         const char *head_arg;
1175         int flag, i, ret = 0, head_subsumed;
1176         int best_cnt = -1, merge_was_ok = 0, automerge_was_ok = 0;
1177         struct commit_list *common = NULL;
1178         const char *best_strategy = NULL, *wt_strategy = NULL;
1179         struct commit_list *remoteheads, *p;
1180         void *branch_to_free;
1181
1182         if (argc == 2 && !strcmp(argv[1], "-h"))
1183                 usage_with_options(builtin_merge_usage, builtin_merge_options);
1184
1185         /*
1186          * Check if we are _not_ on a detached HEAD, i.e. if there is a
1187          * current branch.
1188          */
1189         branch = branch_to_free = resolve_refdup("HEAD", head_sha1, 0, &flag);
1190         if (branch && !prefixcmp(branch, "refs/heads/"))
1191                 branch += 11;
1192         if (!branch || is_null_sha1(head_sha1))
1193                 head_commit = NULL;
1194         else
1195                 head_commit = lookup_commit_or_die(head_sha1, "HEAD");
1196
1197         git_config(git_merge_config, NULL);
1198
1199         if (branch_mergeoptions)
1200                 parse_branch_merge_options(branch_mergeoptions);
1201         argc = parse_options(argc, argv, prefix, builtin_merge_options,
1202                         builtin_merge_usage, 0);
1203         if (shortlog_len < 0)
1204                 shortlog_len = (merge_log_config > 0) ? merge_log_config : 0;
1205
1206         if (verbosity < 0 && show_progress == -1)
1207                 show_progress = 0;
1208
1209         if (abort_current_merge) {
1210                 int nargc = 2;
1211                 const char *nargv[] = {"reset", "--merge", NULL};
1212
1213                 if (!file_exists(git_path("MERGE_HEAD")))
1214                         die(_("There is no merge to abort (MERGE_HEAD missing)."));
1215
1216                 /* Invoke 'git reset --merge' */
1217                 ret = cmd_reset(nargc, nargv, prefix);
1218                 goto done;
1219         }
1220
1221         if (read_cache_unmerged())
1222                 die_resolve_conflict("merge");
1223
1224         if (file_exists(git_path("MERGE_HEAD"))) {
1225                 /*
1226                  * There is no unmerged entry, don't advise 'git
1227                  * add/rm <file>', just 'git commit'.
1228                  */
1229                 if (advice_resolve_conflict)
1230                         die(_("You have not concluded your merge (MERGE_HEAD exists).\n"
1231                                   "Please, commit your changes before you can merge."));
1232                 else
1233                         die(_("You have not concluded your merge (MERGE_HEAD exists)."));
1234         }
1235         if (file_exists(git_path("CHERRY_PICK_HEAD"))) {
1236                 if (advice_resolve_conflict)
1237                         die(_("You have not concluded your cherry-pick (CHERRY_PICK_HEAD exists).\n"
1238                             "Please, commit your changes before you can merge."));
1239                 else
1240                         die(_("You have not concluded your cherry-pick (CHERRY_PICK_HEAD exists)."));
1241         }
1242         resolve_undo_clear();
1243
1244         if (verbosity < 0)
1245                 show_diffstat = 0;
1246
1247         if (squash) {
1248                 if (!allow_fast_forward)
1249                         die(_("You cannot combine --squash with --no-ff."));
1250                 option_commit = 0;
1251         }
1252
1253         if (!allow_fast_forward && fast_forward_only)
1254                 die(_("You cannot combine --no-ff with --ff-only."));
1255
1256         if (!abort_current_merge) {
1257                 if (!argc) {
1258                         if (default_to_upstream)
1259                                 argc = setup_with_upstream(&argv);
1260                         else
1261                                 die(_("No commit specified and merge.defaultToUpstream not set."));
1262                 } else if (argc == 1 && !strcmp(argv[0], "-"))
1263                         argv[0] = "@{-1}";
1264         }
1265         if (!argc)
1266                 usage_with_options(builtin_merge_usage,
1267                         builtin_merge_options);
1268
1269         /*
1270          * This could be traditional "merge <msg> HEAD <commit>..."  and
1271          * the way we can tell it is to see if the second token is HEAD,
1272          * but some people might have misused the interface and used a
1273          * committish that is the same as HEAD there instead.
1274          * Traditional format never would have "-m" so it is an
1275          * additional safety measure to check for it.
1276          */
1277
1278         if (!have_message && head_commit &&
1279             is_old_style_invocation(argc, argv, head_commit->object.sha1)) {
1280                 strbuf_addstr(&merge_msg, argv[0]);
1281                 head_arg = argv[1];
1282                 argv += 2;
1283                 argc -= 2;
1284                 remoteheads = collect_parents(head_commit, &head_subsumed, argc, argv);
1285         } else if (!head_commit) {
1286                 struct commit *remote_head;
1287                 /*
1288                  * If the merged head is a valid one there is no reason
1289                  * to forbid "git merge" into a branch yet to be born.
1290                  * We do the same for "git pull".
1291                  */
1292                 if (argc != 1)
1293                         die(_("Can merge only exactly one commit into "
1294                                 "empty head"));
1295                 if (squash)
1296                         die(_("Squash commit into empty head not supported yet"));
1297                 if (!allow_fast_forward)
1298                         die(_("Non-fast-forward commit does not make sense into "
1299                             "an empty head"));
1300                 remoteheads = collect_parents(head_commit, &head_subsumed, argc, argv);
1301                 remote_head = remoteheads->item;
1302                 if (!remote_head)
1303                         die(_("%s - not something we can merge"), argv[0]);
1304                 read_empty(remote_head->object.sha1, 0);
1305                 update_ref("initial pull", "HEAD", remote_head->object.sha1,
1306                            NULL, 0, DIE_ON_ERR);
1307                 goto done;
1308         } else {
1309                 struct strbuf merge_names = STRBUF_INIT;
1310
1311                 /* We are invoked directly as the first-class UI. */
1312                 head_arg = "HEAD";
1313
1314                 /*
1315                  * All the rest are the commits being merged; prepare
1316                  * the standard merge summary message to be appended
1317                  * to the given message.
1318                  */
1319                 remoteheads = collect_parents(head_commit, &head_subsumed, argc, argv);
1320                 for (p = remoteheads; p; p = p->next)
1321                         merge_name(merge_remote_util(p->item)->name, &merge_names);
1322
1323                 if (!have_message || shortlog_len) {
1324                         struct fmt_merge_msg_opts opts;
1325                         memset(&opts, 0, sizeof(opts));
1326                         opts.add_title = !have_message;
1327                         opts.shortlog_len = shortlog_len;
1328
1329                         fmt_merge_msg(&merge_names, &merge_msg, &opts);
1330                         if (merge_msg.len)
1331                                 strbuf_setlen(&merge_msg, merge_msg.len - 1);
1332                 }
1333         }
1334
1335         if (!head_commit || !argc)
1336                 usage_with_options(builtin_merge_usage,
1337                         builtin_merge_options);
1338
1339         strbuf_addstr(&buf, "merge");
1340         for (p = remoteheads; p; p = p->next)
1341                 strbuf_addf(&buf, " %s", merge_remote_util(p->item)->name);
1342         setenv("GIT_REFLOG_ACTION", buf.buf, 0);
1343         strbuf_reset(&buf);
1344
1345         for (p = remoteheads; p; p = p->next) {
1346                 struct commit *commit = p->item;
1347                 strbuf_addf(&buf, "GITHEAD_%s",
1348                             sha1_to_hex(commit->object.sha1));
1349                 setenv(buf.buf, merge_remote_util(commit)->name, 1);
1350                 strbuf_reset(&buf);
1351                 if (!fast_forward_only &&
1352                     merge_remote_util(commit) &&
1353                     merge_remote_util(commit)->obj &&
1354                     merge_remote_util(commit)->obj->type == OBJ_TAG)
1355                         allow_fast_forward = 0;
1356         }
1357
1358         if (option_edit < 0)
1359                 option_edit = default_edit_option();
1360
1361         if (!use_strategies) {
1362                 if (!remoteheads)
1363                         ; /* already up-to-date */
1364                 else if (!remoteheads->next)
1365                         add_strategies(pull_twohead, DEFAULT_TWOHEAD);
1366                 else
1367                         add_strategies(pull_octopus, DEFAULT_OCTOPUS);
1368         }
1369
1370         for (i = 0; i < use_strategies_nr; i++) {
1371                 if (use_strategies[i]->attr & NO_FAST_FORWARD)
1372                         allow_fast_forward = 0;
1373                 if (use_strategies[i]->attr & NO_TRIVIAL)
1374                         allow_trivial = 0;
1375         }
1376
1377         if (!remoteheads)
1378                 ; /* already up-to-date */
1379         else if (!remoteheads->next)
1380                 common = get_merge_bases(head_commit, remoteheads->item, 1);
1381         else {
1382                 struct commit_list *list = remoteheads;
1383                 commit_list_insert(head_commit, &list);
1384                 common = get_octopus_merge_bases(list);
1385                 free(list);
1386         }
1387
1388         update_ref("updating ORIG_HEAD", "ORIG_HEAD", head_commit->object.sha1,
1389                    NULL, 0, DIE_ON_ERR);
1390
1391         if (remoteheads && !common)
1392                 ; /* No common ancestors found. We need a real merge. */
1393         else if (!remoteheads ||
1394                  (!remoteheads->next && !common->next &&
1395                   common->item == remoteheads->item)) {
1396                 /*
1397                  * If head can reach all the merge then we are up to date.
1398                  * but first the most common case of merging one remote.
1399                  */
1400                 finish_up_to_date("Already up-to-date.");
1401                 goto done;
1402         } else if (allow_fast_forward && !remoteheads->next &&
1403                         !common->next &&
1404                         !hashcmp(common->item->object.sha1, head_commit->object.sha1)) {
1405                 /* Again the most common case of merging one remote. */
1406                 struct strbuf msg = STRBUF_INIT;
1407                 struct commit *commit;
1408                 char hex[41];
1409
1410                 strcpy(hex, find_unique_abbrev(head_commit->object.sha1, DEFAULT_ABBREV));
1411
1412                 if (verbosity >= 0)
1413                         printf(_("Updating %s..%s\n"),
1414                                 hex,
1415                                 find_unique_abbrev(remoteheads->item->object.sha1,
1416                                 DEFAULT_ABBREV));
1417                 strbuf_addstr(&msg, "Fast-forward");
1418                 if (have_message)
1419                         strbuf_addstr(&msg,
1420                                 " (no commit created; -m option ignored)");
1421                 commit = remoteheads->item;
1422                 if (!commit) {
1423                         ret = 1;
1424                         goto done;
1425                 }
1426
1427                 if (checkout_fast_forward(head_commit->object.sha1,
1428                                           commit->object.sha1)) {
1429                         ret = 1;
1430                         goto done;
1431                 }
1432
1433                 finish(head_commit, remoteheads, commit->object.sha1, msg.buf);
1434                 drop_save();
1435                 goto done;
1436         } else if (!remoteheads->next && common->next)
1437                 ;
1438                 /*
1439                  * We are not doing octopus and not fast-forward.  Need
1440                  * a real merge.
1441                  */
1442         else if (!remoteheads->next && !common->next && option_commit) {
1443                 /*
1444                  * We are not doing octopus, not fast-forward, and have
1445                  * only one common.
1446                  */
1447                 refresh_cache(REFRESH_QUIET);
1448                 if (allow_trivial && !fast_forward_only) {
1449                         /* See if it is really trivial. */
1450                         git_committer_info(IDENT_STRICT);
1451                         printf(_("Trying really trivial in-index merge...\n"));
1452                         if (!read_tree_trivial(common->item->object.sha1,
1453                                                head_commit->object.sha1,
1454                                                remoteheads->item->object.sha1)) {
1455                                 ret = merge_trivial(head_commit, remoteheads);
1456                                 goto done;
1457                         }
1458                         printf(_("Nope.\n"));
1459                 }
1460         } else {
1461                 /*
1462                  * An octopus.  If we can reach all the remote we are up
1463                  * to date.
1464                  */
1465                 int up_to_date = 1;
1466                 struct commit_list *j;
1467
1468                 for (j = remoteheads; j; j = j->next) {
1469                         struct commit_list *common_one;
1470
1471                         /*
1472                          * Here we *have* to calculate the individual
1473                          * merge_bases again, otherwise "git merge HEAD^
1474                          * HEAD^^" would be missed.
1475                          */
1476                         common_one = get_merge_bases(head_commit, j->item, 1);
1477                         if (hashcmp(common_one->item->object.sha1,
1478                                 j->item->object.sha1)) {
1479                                 up_to_date = 0;
1480                                 break;
1481                         }
1482                 }
1483                 if (up_to_date) {
1484                         finish_up_to_date("Already up-to-date. Yeeah!");
1485                         goto done;
1486                 }
1487         }
1488
1489         if (fast_forward_only)
1490                 die(_("Not possible to fast-forward, aborting."));
1491
1492         /* We are going to make a new commit. */
1493         git_committer_info(IDENT_STRICT);
1494
1495         /*
1496          * At this point, we need a real merge.  No matter what strategy
1497          * we use, it would operate on the index, possibly affecting the
1498          * working tree, and when resolved cleanly, have the desired
1499          * tree in the index -- this means that the index must be in
1500          * sync with the head commit.  The strategies are responsible
1501          * to ensure this.
1502          */
1503         if (use_strategies_nr == 1 ||
1504             /*
1505              * Stash away the local changes so that we can try more than one.
1506              */
1507             save_state(stash))
1508                 hashcpy(stash, null_sha1);
1509
1510         for (i = 0; i < use_strategies_nr; i++) {
1511                 int ret;
1512                 if (i) {
1513                         printf(_("Rewinding the tree to pristine...\n"));
1514                         restore_state(head_commit->object.sha1, stash);
1515                 }
1516                 if (use_strategies_nr != 1)
1517                         printf(_("Trying merge strategy %s...\n"),
1518                                 use_strategies[i]->name);
1519                 /*
1520                  * Remember which strategy left the state in the working
1521                  * tree.
1522                  */
1523                 wt_strategy = use_strategies[i]->name;
1524
1525                 ret = try_merge_strategy(use_strategies[i]->name,
1526                                          common, remoteheads,
1527                                          head_commit, head_arg);
1528                 if (!option_commit && !ret) {
1529                         merge_was_ok = 1;
1530                         /*
1531                          * This is necessary here just to avoid writing
1532                          * the tree, but later we will *not* exit with
1533                          * status code 1 because merge_was_ok is set.
1534                          */
1535                         ret = 1;
1536                 }
1537
1538                 if (ret) {
1539                         /*
1540                          * The backend exits with 1 when conflicts are
1541                          * left to be resolved, with 2 when it does not
1542                          * handle the given merge at all.
1543                          */
1544                         if (ret == 1) {
1545                                 int cnt = evaluate_result();
1546
1547                                 if (best_cnt <= 0 || cnt <= best_cnt) {
1548                                         best_strategy = use_strategies[i]->name;
1549                                         best_cnt = cnt;
1550                                 }
1551                         }
1552                         if (merge_was_ok)
1553                                 break;
1554                         else
1555                                 continue;
1556                 }
1557
1558                 /* Automerge succeeded. */
1559                 write_tree_trivial(result_tree);
1560                 automerge_was_ok = 1;
1561                 break;
1562         }
1563
1564         /*
1565          * If we have a resulting tree, that means the strategy module
1566          * auto resolved the merge cleanly.
1567          */
1568         if (automerge_was_ok) {
1569                 ret = finish_automerge(head_commit, head_subsumed,
1570                                        common, remoteheads,
1571                                        result_tree, wt_strategy);
1572                 goto done;
1573         }
1574
1575         /*
1576          * Pick the result from the best strategy and have the user fix
1577          * it up.
1578          */
1579         if (!best_strategy) {
1580                 restore_state(head_commit->object.sha1, stash);
1581                 if (use_strategies_nr > 1)
1582                         fprintf(stderr,
1583                                 _("No merge strategy handled the merge.\n"));
1584                 else
1585                         fprintf(stderr, _("Merge with strategy %s failed.\n"),
1586                                 use_strategies[0]->name);
1587                 ret = 2;
1588                 goto done;
1589         } else if (best_strategy == wt_strategy)
1590                 ; /* We already have its result in the working tree. */
1591         else {
1592                 printf(_("Rewinding the tree to pristine...\n"));
1593                 restore_state(head_commit->object.sha1, stash);
1594                 printf(_("Using the %s to prepare resolving by hand.\n"),
1595                         best_strategy);
1596                 try_merge_strategy(best_strategy, common, remoteheads,
1597                                    head_commit, head_arg);
1598         }
1599
1600         if (squash)
1601                 finish(head_commit, remoteheads, NULL, NULL);
1602         else
1603                 write_merge_state(remoteheads);
1604
1605         if (merge_was_ok)
1606                 fprintf(stderr, _("Automatic merge went well; "
1607                         "stopped before committing as requested\n"));
1608         else
1609                 ret = suggest_conflicts(option_renormalize);
1610
1611 done:
1612         free(branch_to_free);
1613         return ret;
1614 }