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
  26 #define DEFAULT_TWOHEAD (1<<0)
  27 #define DEFAULT_OCTOPUS (1<<1)
  28 #define NO_FAST_FORWARD (1<<2)
  29 #define NO_TRIVIAL      (1<<3)
  30
  31 struct strategy {
  32         const char *name;
  33         unsigned attr;
  34 };
  35
  36 static const char * const builtin_merge_usage[] = {
  37         "git-merge [options] <remote>...",
  38         "git-merge [options] <msg> HEAD <remote>",
  39         NULL
  40 };
  41
  42 static int show_diffstat = 1, option_log, squash;
  43 static int option_commit = 1, allow_fast_forward = 1;
  44 static int allow_trivial = 1, have_message;
  45 static struct strbuf merge_msg;
  46 static struct commit_list *remoteheads;
  47 static unsigned char head[20], stash[20];
  48 static struct strategy **use_strategies;
  49 static size_t use_strategies_nr, use_strategies_alloc;
  50 static const char *branch;
  51
  52 static struct strategy all_strategy[] = {
  53         { "recursive",  DEFAULT_TWOHEAD | NO_TRIVIAL },
  54         { "octopus",    DEFAULT_OCTOPUS },
  55         { "resolve",    0 },
  56         { "ours",       NO_FAST_FORWARD | NO_TRIVIAL },
  57         { "subtree",    NO_FAST_FORWARD | NO_TRIVIAL },
  58 };
  59
  60 static const char *pull_twohead, *pull_octopus;
  61
  62 static int option_parse_message(const struct option *opt,
  63                                 const char *arg, int unset)
  64 {
  65         struct strbuf *buf = opt->value;
  66
  67         if (unset)
  68                 strbuf_setlen(buf, 0);
  69         else if (arg) {
  70                 strbuf_addf(buf, "%s\n\n", arg);
  71                 have_message = 1;
  72         } else
  73                 return error("switch `m' requires a value");
  74         return 0;
  75 }
  76
  77 static struct strategy *get_strategy(const char *name)
  78 {
  79         int i;
  80         struct strbuf err;
  81
  82         if (!name)
  83                 return NULL;
  84
  85         for (i = 0; i < ARRAY_SIZE(all_strategy); i++)
  86                 if (!strcmp(name, all_strategy[i].name))
  87                         return &all_strategy[i];
  88
  89         strbuf_init(&err, 0);
  90         for (i = 0; i < ARRAY_SIZE(all_strategy); i++)
  91                 strbuf_addf(&err, " %s", all_strategy[i].name);
  92         fprintf(stderr, "Could not find merge strategy '%s'.\n", name);
  93         fprintf(stderr, "Available strategies are:%s.\n", err.buf);
  94         exit(1);
  95 }
  96
  97 static void append_strategy(struct strategy *s)
  98 {
  99         ALLOC_GROW(use_strategies, use_strategies_nr + 1, use_strategies_alloc);
 100         use_strategies[use_strategies_nr++] = s;
 101 }
 102
 103 static int option_parse_strategy(const struct option *opt,
 104                                  const char *name, int unset)
 105 {
 106         if (unset)
 107                 return 0;
 108
 109         append_strategy(get_strategy(name));
 110         return 0;
 111 }
 112
 113 static int option_parse_n(const struct option *opt,
 114                           const char *arg, int unset)
 115 {
 116         show_diffstat = unset;
 117         return 0;
 118 }
 119
 120 static struct option builtin_merge_options[] = {
 121         { OPTION_CALLBACK, 'n', NULL, NULL, NULL,
 122                 "do not show a diffstat at the end of the merge",
 123                 PARSE_OPT_NOARG, option_parse_n },
 124         OPT_BOOLEAN(0, "stat", &show_diffstat,
 125                 "show a diffstat at the end of the merge"),
 126         OPT_BOOLEAN(0, "summary", &show_diffstat, "(synonym to --stat)"),
 127         OPT_BOOLEAN(0, "log", &option_log,
 128                 "add list of one-line log to merge commit message"),
 129         OPT_BOOLEAN(0, "squash", &squash,
 130                 "create a single commit instead of doing a merge"),
 131         OPT_BOOLEAN(0, "commit", &option_commit,
 132                 "perform a commit if the merge succeeds (default)"),
 133         OPT_BOOLEAN(0, "ff", &allow_fast_forward,
 134                 "allow fast forward (default)"),
 135         OPT_CALLBACK('s', "strategy", &use_strategies, "strategy",
 136                 "merge strategy to use", option_parse_strategy),
 137         OPT_CALLBACK('m', "message", &merge_msg, "message",
 138                 "message to be used for the merge commit (if any)",
 139                 option_parse_message),
 140         OPT_END()
 141 };
 142
 143 /* Cleans up metadata that is uninteresting after a succeeded merge. */
 144 static void drop_save(void)
 145 {
 146         unlink(git_path("MERGE_HEAD"));
 147         unlink(git_path("MERGE_MSG"));
 148 }
 149
 150 static void save_state(void)
 151 {
 152         int len;
 153         struct child_process cp;
 154         struct strbuf buffer = STRBUF_INIT;
 155         const char *argv[] = {"stash", "create", NULL};
 156
 157         memset(&cp, 0, sizeof(cp));
 158         cp.argv = argv;
 159         cp.out = -1;
 160         cp.git_cmd = 1;
 161
 162         if (start_command(&cp))
 163                 die("could not run stash.");
 164         len = strbuf_read(&buffer, cp.out, 1024);
 165         close(cp.out);
 166
 167         if (finish_command(&cp) || len < 0)
 168                 die("stash failed");
 169         else if (!len)
 170                 return;
 171         strbuf_setlen(&buffer, buffer.len-1);
 172         if (get_sha1(buffer.buf, stash))
 173                 die("not a valid object: %s", buffer.buf);
 174 }
 175
 176 static void reset_hard(unsigned const char *sha1, int verbose)
 177 {
 178         int i = 0;
 179         const char *args[6];
 180
 181         args[i++] = "read-tree";
 182         if (verbose)
 183                 args[i++] = "-v";
 184         args[i++] = "--reset";
 185         args[i++] = "-u";
 186         args[i++] = sha1_to_hex(sha1);
 187         args[i] = NULL;
 188
 189         if (run_command_v_opt(args, RUN_GIT_CMD))
 190                 die("read-tree failed");
 191 }
 192
 193 static void restore_state(void)
 194 {
 195         struct strbuf sb;
 196         const char *args[] = { "stash", "apply", NULL, NULL };
 197
 198         if (is_null_sha1(stash))
 199                 return;
 200
 201         reset_hard(head, 1);
 202
 203         strbuf_init(&sb, 0);
 204         args[2] = sha1_to_hex(stash);
 205
 206         /*
 207          * It is OK to ignore error here, for example when there was
 208          * nothing to restore.
 209          */
 210         run_command_v_opt(args, RUN_GIT_CMD);
 211
 212         strbuf_release(&sb);
 213         refresh_cache(REFRESH_QUIET);
 214 }
 215
 216 /* This is called when no merge was necessary. */
 217 static void finish_up_to_date(const char *msg)
 218 {
 219         printf("%s%s\n", squash ? " (nothing to squash)" : "", msg);
 220         drop_save();
 221 }
 222
 223 static void squash_message(void)
 224 {
 225         struct rev_info rev;
 226         struct commit *commit;
 227         struct strbuf out;
 228         struct commit_list *j;
 229         int fd;
 230
 231         printf("Squash commit -- not updating HEAD\n");
 232         fd = open(git_path("SQUASH_MSG"), O_WRONLY | O_CREAT, 0666);
 233         if (fd < 0)
 234                 die("Could not write to %s", git_path("SQUASH_MSG"));
 235
 236         init_revisions(&rev, NULL);
 237         rev.ignore_merges = 1;
 238         rev.commit_format = CMIT_FMT_MEDIUM;
 239
 240         commit = lookup_commit(head);
 241         commit->object.flags |= UNINTERESTING;
 242         add_pending_object(&rev, &commit->object, NULL);
 243
 244         for (j = remoteheads; j; j = j->next)
 245                 add_pending_object(&rev, &j->item->object, NULL);
 246
 247         setup_revisions(0, NULL, &rev, NULL);
 248         if (prepare_revision_walk(&rev))
 249                 die("revision walk setup failed");
 250
 251         strbuf_init(&out, 0);
 252         strbuf_addstr(&out, "Squashed commit of the following:\n");
 253         while ((commit = get_revision(&rev)) != NULL) {
 254                 strbuf_addch(&out, '\n');
 255                 strbuf_addf(&out, "commit %s\n",
 256                         sha1_to_hex(commit->object.sha1));
 257                 pretty_print_commit(rev.commit_format, commit, &out, rev.abbrev,
 258                         NULL, NULL, rev.date_mode, 0);
 259         }
 260         write(fd, out.buf, out.len);
 261         close(fd);
 262         strbuf_release(&out);
 263 }
 264
 265 static int run_hook(const char *name)
 266 {
 267         struct child_process hook;
 268         const char *argv[3], *env[2];
 269         char index[PATH_MAX];
 270
 271         argv[0] = git_path("hooks/%s", name);
 272         if (access(argv[0], X_OK) < 0)
 273                 return 0;
 274
 275         snprintf(index, sizeof(index), "GIT_INDEX_FILE=%s", get_index_file());
 276         env[0] = index;
 277         env[1] = NULL;
 278
 279         if (squash)
 280                 argv[1] = "1";
 281         else
 282                 argv[1] = "0";
 283         argv[2] = NULL;
 284
 285         memset(&hook, 0, sizeof(hook));
 286         hook.argv = argv;
 287         hook.no_stdin = 1;
 288         hook.stdout_to_stderr = 1;
 289         hook.env = env;
 290
 291         return run_command(&hook);
 292 }
 293
 294 static void finish(const unsigned char *new_head, const char *msg)
 295 {
 296         struct strbuf reflog_message;
 297
 298         strbuf_init(&reflog_message, 0);
 299         if (!msg)
 300                 strbuf_addstr(&reflog_message, getenv("GIT_REFLOG_ACTION"));
 301         else {
 302                 printf("%s\n", msg);
 303                 strbuf_addf(&reflog_message, "%s: %s",
 304                         getenv("GIT_REFLOG_ACTION"), msg);
 305         }
 306         if (squash) {
 307                 squash_message();
 308         } else {
 309                 if (!merge_msg.len)
 310                         printf("No merge message -- not updating HEAD\n");
 311                 else {
 312                         const char *argv_gc_auto[] = { "gc", "--auto", NULL };
 313                         update_ref(reflog_message.buf, "HEAD",
 314                                 new_head, head, 0,
 315                                 DIE_ON_ERR);
 316                         /*
 317                          * We ignore errors in 'gc --auto', since the
 318                          * user should see them.
 319                          */
 320                         run_command_v_opt(argv_gc_auto, RUN_GIT_CMD);
 321                 }
 322         }
 323         if (new_head && show_diffstat) {
 324                 struct diff_options opts;
 325                 diff_setup(&opts);
 326                 opts.output_format |=
 327                         DIFF_FORMAT_SUMMARY | DIFF_FORMAT_DIFFSTAT;
 328                 opts.detect_rename = DIFF_DETECT_RENAME;
 329                 if (diff_use_color_default > 0)
 330                         DIFF_OPT_SET(&opts, COLOR_DIFF);
 331                 if (diff_setup_done(&opts) < 0)
 332                         die("diff_setup_done failed");
 333                 diff_tree_sha1(head, new_head, "", &opts);
 334                 diffcore_std(&opts);
 335                 diff_flush(&opts);
 336         }
 337
 338         /* Run a post-merge hook */
 339         run_hook("post-merge");
 340
 341         strbuf_release(&reflog_message);
 342 }
 343
 344 /* Get the name for the merge commit's message. */
 345 static void merge_name(const char *remote, struct strbuf *msg)
 346 {
 347         struct object *remote_head;
 348         unsigned char branch_head[20], buf_sha[20];
 349         struct strbuf buf;
 350         const char *ptr;
 351         int len, early;
 352
 353         memset(branch_head, 0, sizeof(branch_head));
 354         remote_head = peel_to_type(remote, 0, NULL, OBJ_COMMIT);
 355         if (!remote_head)
 356                 die("'%s' does not point to a commit", remote);
 357
 358         strbuf_init(&buf, 0);
 359         strbuf_addstr(&buf, "refs/heads/");
 360         strbuf_addstr(&buf, remote);
 361         resolve_ref(buf.buf, branch_head, 0, 0);
 362
 363         if (!hashcmp(remote_head->sha1, branch_head)) {
 364                 strbuf_addf(msg, "%s\t\tbranch '%s' of .\n",
 365                         sha1_to_hex(branch_head), remote);
 366                 return;
 367         }
 368
 369         /* See if remote matches <name>^^^.. or <name>~<number> */
 370         for (len = 0, ptr = remote + strlen(remote);
 371              remote < ptr && ptr[-1] == '^';
 372              ptr--)
 373                 len++;
 374         if (len)
 375                 early = 1;
 376         else {
 377                 early = 0;
 378                 ptr = strrchr(remote, '~');
 379                 if (ptr) {
 380                         int seen_nonzero = 0;
 381
 382                         len++; /* count ~ */
 383                         while (*++ptr && isdigit(*ptr)) {
 384                                 seen_nonzero |= (*ptr != '0');
 385                                 len++;
 386                         }
 387                         if (*ptr)
 388                                 len = 0; /* not ...~<number> */
 389                         else if (seen_nonzero)
 390                                 early = 1;
 391                         else if (len == 1)
 392                                 early = 1; /* "name~" is "name~1"! */
 393                 }
 394         }
 395         if (len) {
 396                 struct strbuf truname = STRBUF_INIT;
 397                 strbuf_addstr(&truname, "refs/heads/");
 398                 strbuf_addstr(&truname, remote);
 399                 strbuf_setlen(&truname, truname.len - len);
 400                 if (resolve_ref(truname.buf, buf_sha, 0, 0)) {
 401                         strbuf_addf(msg,
 402                                     "%s\t\tbranch '%s'%s of .\n",
 403                                     sha1_to_hex(remote_head->sha1),
 404                                     truname.buf + 11,
 405                                     (early ? " (early part)" : ""));
 406                         return;
 407                 }
 408         }
 409
 410         if (!strcmp(remote, "FETCH_HEAD") &&
 411                         !access(git_path("FETCH_HEAD"), R_OK)) {
 412                 FILE *fp;
 413                 struct strbuf line;
 414                 char *ptr;
 415
 416                 strbuf_init(&line, 0);
 417                 fp = fopen(git_path("FETCH_HEAD"), "r");
 418                 if (!fp)
 419                         die("could not open %s for reading: %s",
 420                                 git_path("FETCH_HEAD"), strerror(errno));
 421                 strbuf_getline(&line, fp, '\n');
 422                 fclose(fp);
 423                 ptr = strstr(line.buf, "\tnot-for-merge\t");
 424                 if (ptr)
 425                         strbuf_remove(&line, ptr-line.buf+1, 13);
 426                 strbuf_addbuf(msg, &line);
 427                 strbuf_release(&line);
 428                 return;
 429         }
 430         strbuf_addf(msg, "%s\t\tcommit '%s'\n",
 431                 sha1_to_hex(remote_head->sha1), remote);
 432 }
 433
 434 static int git_merge_config(const char *k, const char *v, void *cb)
 435 {
 436         if (branch && !prefixcmp(k, "branch.") &&
 437                 !prefixcmp(k + 7, branch) &&
 438                 !strcmp(k + 7 + strlen(branch), ".mergeoptions")) {
 439                 const char **argv;
 440                 int argc;
 441                 char *buf;
 442
 443                 buf = xstrdup(v);
 444                 argc = split_cmdline(buf, &argv);
 445                 argv = xrealloc(argv, sizeof(*argv) * (argc + 2));
 446                 memmove(argv + 1, argv, sizeof(*argv) * (argc + 1));
 447                 argc++;
 448                 parse_options(argc, argv, builtin_merge_options,
 449                               builtin_merge_usage, 0);
 450                 free(buf);
 451         }
 452
 453         if (!strcmp(k, "merge.diffstat") || !strcmp(k, "merge.stat"))
 454                 show_diffstat = git_config_bool(k, v);
 455         else if (!strcmp(k, "pull.twohead"))
 456                 return git_config_string(&pull_twohead, k, v);
 457         else if (!strcmp(k, "pull.octopus"))
 458                 return git_config_string(&pull_octopus, k, v);
 459         else if (!strcmp(k, "merge.log") || !strcmp(k, "merge.summary"))
 460                 option_log = git_config_bool(k, v);
 461         return git_diff_ui_config(k, v, cb);
 462 }
 463
 464 static int read_tree_trivial(unsigned char *common, unsigned char *head,
 465                              unsigned char *one)
 466 {
 467         int i, nr_trees = 0;
 468         struct tree *trees[MAX_UNPACK_TREES];
 469         struct tree_desc t[MAX_UNPACK_TREES];
 470         struct unpack_trees_options opts;
 471
 472         memset(&opts, 0, sizeof(opts));
 473         opts.head_idx = 2;
 474         opts.src_index = &the_index;
 475         opts.dst_index = &the_index;
 476         opts.update = 1;
 477         opts.verbose_update = 1;
 478         opts.trivial_merges_only = 1;
 479         opts.merge = 1;
 480         trees[nr_trees] = parse_tree_indirect(common);
 481         if (!trees[nr_trees++])
 482                 return -1;
 483         trees[nr_trees] = parse_tree_indirect(head);
 484         if (!trees[nr_trees++])
 485                 return -1;
 486         trees[nr_trees] = parse_tree_indirect(one);
 487         if (!trees[nr_trees++])
 488                 return -1;
 489         opts.fn = threeway_merge;
 490         cache_tree_free(&active_cache_tree);
 491         for (i = 0; i < nr_trees; i++) {
 492                 parse_tree(trees[i]);
 493                 init_tree_desc(t+i, trees[i]->buffer, trees[i]->size);
 494         }
 495         if (unpack_trees(nr_trees, t, &opts))
 496                 return -1;
 497         return 0;
 498 }
 499
 500 static void write_tree_trivial(unsigned char *sha1)
 501 {
 502         if (write_cache_as_tree(sha1, 0, NULL))
 503                 die("git write-tree failed to write a tree");
 504 }
 505
 506 static int try_merge_strategy(const char *strategy, struct commit_list *common,
 507                               const char *head_arg)
 508 {
 509         const char **args;
 510         int i = 0, ret;
 511         struct commit_list *j;
 512         struct strbuf buf;
 513
 514         args = xmalloc((4 + commit_list_count(common) +
 515                         commit_list_count(remoteheads)) * sizeof(char *));
 516         strbuf_init(&buf, 0);
 517         strbuf_addf(&buf, "merge-%s", strategy);
 518         args[i++] = buf.buf;
 519         for (j = common; j; j = j->next)
 520                 args[i++] = xstrdup(sha1_to_hex(j->item->object.sha1));
 521         args[i++] = "--";
 522         args[i++] = head_arg;
 523         for (j = remoteheads; j; j = j->next)
 524                 args[i++] = xstrdup(sha1_to_hex(j->item->object.sha1));
 525         args[i] = NULL;
 526         ret = run_command_v_opt(args, RUN_GIT_CMD);
 527         strbuf_release(&buf);
 528         i = 1;
 529         for (j = common; j; j = j->next)
 530                 free((void *)args[i++]);
 531         i += 2;
 532         for (j = remoteheads; j; j = j->next)
 533                 free((void *)args[i++]);
 534         free(args);
 535         return -ret;
 536 }
 537
 538 static void count_diff_files(struct diff_queue_struct *q,
 539                              struct diff_options *opt, void *data)
 540 {
 541         int *count = data;
 542
 543         (*count) += q->nr;
 544 }
 545
 546 static int count_unmerged_entries(void)
 547 {
 548         const struct index_state *state = &the_index;
 549         int i, ret = 0;
 550
 551         for (i = 0; i < state->cache_nr; i++)
 552                 if (ce_stage(state->cache[i]))
 553                         ret++;
 554
 555         return ret;
 556 }
 557
 558 static int checkout_fast_forward(unsigned char *head, unsigned char *remote)
 559 {
 560         struct tree *trees[MAX_UNPACK_TREES];
 561         struct unpack_trees_options opts;
 562         struct tree_desc t[MAX_UNPACK_TREES];
 563         int i, fd, nr_trees = 0;
 564         struct dir_struct dir;
 565         struct lock_file *lock_file = xcalloc(1, sizeof(struct lock_file));
 566
 567         refresh_cache(REFRESH_QUIET);
 568
 569         fd = hold_locked_index(lock_file, 1);
 570
 571         memset(&trees, 0, sizeof(trees));
 572         memset(&opts, 0, sizeof(opts));
 573         memset(&t, 0, sizeof(t));
 574         memset(&dir, 0, sizeof(dir));
 575         dir.show_ignored = 1;
 576         dir.exclude_per_dir = ".gitignore";
 577         opts.dir = &dir;
 578
 579         opts.head_idx = 1;
 580         opts.src_index = &the_index;
 581         opts.dst_index = &the_index;
 582         opts.update = 1;
 583         opts.verbose_update = 1;
 584         opts.merge = 1;
 585         opts.fn = twoway_merge;
 586
 587         trees[nr_trees] = parse_tree_indirect(head);
 588         if (!trees[nr_trees++])
 589                 return -1;
 590         trees[nr_trees] = parse_tree_indirect(remote);
 591         if (!trees[nr_trees++])
 592                 return -1;
 593         for (i = 0; i < nr_trees; i++) {
 594                 parse_tree(trees[i]);
 595                 init_tree_desc(t+i, trees[i]->buffer, trees[i]->size);
 596         }
 597         if (unpack_trees(nr_trees, t, &opts))
 598                 return -1;
 599         if (write_cache(fd, active_cache, active_nr) ||
 600                 commit_locked_index(lock_file))
 601                 die("unable to write new index file");
 602         return 0;
 603 }
 604
 605 static void split_merge_strategies(const char *string, struct strategy **list,
 606                                    int *nr, int *alloc)
 607 {
 608         char *p, *q, *buf;
 609
 610         if (!string)
 611                 return;
 612
 613         buf = xstrdup(string);
 614         q = buf;
 615         for (;;) {
 616                 p = strchr(q, ' ');
 617                 if (!p) {
 618                         ALLOC_GROW(*list, *nr + 1, *alloc);
 619                         (*list)[(*nr)++].name = xstrdup(q);
 620                         free(buf);
 621                         return;
 622                 } else {
 623                         *p = '\0';
 624                         ALLOC_GROW(*list, *nr + 1, *alloc);
 625                         (*list)[(*nr)++].name = xstrdup(q);
 626                         q = ++p;
 627                 }
 628         }
 629 }
 630
 631 static void add_strategies(const char *string, unsigned attr)
 632 {
 633         struct strategy *list = NULL;
 634         int list_alloc = 0, list_nr = 0, i;
 635
 636         memset(&list, 0, sizeof(list));
 637         split_merge_strategies(string, &list, &list_nr, &list_alloc);
 638         if (list) {
 639                 for (i = 0; i < list_nr; i++)
 640                         append_strategy(get_strategy(list[i].name));
 641                 return;
 642         }
 643         for (i = 0; i < ARRAY_SIZE(all_strategy); i++)
 644                 if (all_strategy[i].attr & attr)
 645                         append_strategy(&all_strategy[i]);
 646
 647 }
 648
 649 static int merge_trivial(void)
 650 {
 651         unsigned char result_tree[20], result_commit[20];
 652         struct commit_list *parent = xmalloc(sizeof(struct commit_list *));
 653
 654         write_tree_trivial(result_tree);
 655         printf("Wonderful.\n");
 656         parent->item = lookup_commit(head);
 657         parent->next = xmalloc(sizeof(struct commit_list *));
 658         parent->next->item = remoteheads->item;
 659         parent->next->next = NULL;
 660         commit_tree(merge_msg.buf, result_tree, parent, result_commit);
 661         finish(result_commit, "In-index merge");
 662         drop_save();
 663         return 0;
 664 }
 665
 666 static int finish_automerge(struct commit_list *common,
 667                             unsigned char *result_tree,
 668                             const char *wt_strategy)
 669 {
 670         struct commit_list *parents = NULL, *j;
 671         struct strbuf buf = STRBUF_INIT;
 672         unsigned char result_commit[20];
 673
 674         free_commit_list(common);
 675         if (allow_fast_forward) {
 676                 parents = remoteheads;
 677                 commit_list_insert(lookup_commit(head), &parents);
 678                 parents = reduce_heads(parents);
 679         } else {
 680                 struct commit_list **pptr = &parents;
 681
 682                 pptr = &commit_list_insert(lookup_commit(head),
 683                                 pptr)->next;
 684                 for (j = remoteheads; j; j = j->next)
 685                         pptr = &commit_list_insert(j->item, pptr)->next;
 686         }
 687         free_commit_list(remoteheads);
 688         strbuf_addch(&merge_msg, '\n');
 689         commit_tree(merge_msg.buf, result_tree, parents, result_commit);
 690         strbuf_addf(&buf, "Merge made by %s.", wt_strategy);
 691         finish(result_commit, buf.buf);
 692         strbuf_release(&buf);
 693         drop_save();
 694         return 0;
 695 }
 696
 697 static int suggest_conflicts(void)
 698 {
 699         FILE *fp;
 700         int pos;
 701
 702         fp = fopen(git_path("MERGE_MSG"), "a");
 703         if (!fp)
 704                 die("Could open %s for writing", git_path("MERGE_MSG"));
 705         fprintf(fp, "\nConflicts:\n");
 706         for (pos = 0; pos < active_nr; pos++) {
 707                 struct cache_entry *ce = active_cache[pos];
 708
 709                 if (ce_stage(ce)) {
 710                         fprintf(fp, "\t%s\n", ce->name);
 711                         while (pos + 1 < active_nr &&
 712                                         !strcmp(ce->name,
 713                                                 active_cache[pos + 1]->name))
 714                                 pos++;
 715                 }
 716         }
 717         fclose(fp);
 718         rerere();
 719         printf("Automatic merge failed; "
 720                         "fix conflicts and then commit the result.\n");
 721         return 1;
 722 }
 723
 724 static struct commit *is_old_style_invocation(int argc, const char **argv)
 725 {
 726         struct commit *second_token = NULL;
 727         if (argc > 1) {
 728                 unsigned char second_sha1[20];
 729
 730                 if (get_sha1(argv[1], second_sha1))
 731                         return NULL;
 732                 second_token = lookup_commit_reference_gently(second_sha1, 0);
 733                 if (!second_token)
 734                         die("'%s' is not a commit", argv[1]);
 735                 if (hashcmp(second_token->object.sha1, head))
 736                         return NULL;
 737         }
 738         return second_token;
 739 }
 740
 741 static int evaluate_result(void)
 742 {
 743         int cnt = 0;
 744         struct rev_info rev;
 745
 746         discard_cache();
 747         if (read_cache() < 0)
 748                 die("failed to read the cache");
 749
 750         /* Check how many files differ. */
 751         init_revisions(&rev, "");
 752         setup_revisions(0, NULL, &rev, NULL);
 753         rev.diffopt.output_format |=
 754                 DIFF_FORMAT_CALLBACK;
 755         rev.diffopt.format_callback = count_diff_files;
 756         rev.diffopt.format_callback_data = &cnt;
 757         run_diff_files(&rev, 0);
 758
 759         /*
 760          * Check how many unmerged entries are
 761          * there.
 762          */
 763         cnt += count_unmerged_entries();
 764
 765         return cnt;
 766 }
 767
 768 int cmd_merge(int argc, const char **argv, const char *prefix)
 769 {
 770         unsigned char result_tree[20];
 771         struct strbuf buf;
 772         const char *head_arg;
 773         int flag, head_invalid = 0, i;
 774         int best_cnt = -1, merge_was_ok = 0, automerge_was_ok = 0;
 775         struct commit_list *common = NULL;
 776         const char *best_strategy = NULL, *wt_strategy = NULL;
 777         struct commit_list **remotes = &remoteheads;
 778
 779         setup_work_tree();
 780         if (read_cache_unmerged())
 781                 die("You are in the middle of a conflicted merge.");
 782
 783         /*
 784          * Check if we are _not_ on a detached HEAD, i.e. if there is a
 785          * current branch.
 786          */
 787         branch = resolve_ref("HEAD", head, 0, &flag);
 788         if (branch && !prefixcmp(branch, "refs/heads/"))
 789                 branch += 11;
 790         if (is_null_sha1(head))
 791                 head_invalid = 1;
 792
 793         git_config(git_merge_config, NULL);
 794
 795         /* for color.ui */
 796         if (diff_use_color_default == -1)
 797                 diff_use_color_default = git_use_color_default;
 798
 799         argc = parse_options(argc, argv, builtin_merge_options,
 800                         builtin_merge_usage, 0);
 801
 802         if (squash) {
 803                 if (!allow_fast_forward)
 804                         die("You cannot combine --squash with --no-ff.");
 805                 option_commit = 0;
 806         }
 807
 808         if (!argc)
 809                 usage_with_options(builtin_merge_usage,
 810                         builtin_merge_options);
 811
 812         /*
 813          * This could be traditional "merge <msg> HEAD <commit>..."  and
 814          * the way we can tell it is to see if the second token is HEAD,
 815          * but some people might have misused the interface and used a
 816          * committish that is the same as HEAD there instead.
 817          * Traditional format never would have "-m" so it is an
 818          * additional safety measure to check for it.
 819          */
 820         strbuf_init(&buf, 0);
 821
 822         if (!have_message && is_old_style_invocation(argc, argv)) {
 823                 strbuf_addstr(&merge_msg, argv[0]);
 824                 head_arg = argv[1];
 825                 argv += 2;
 826                 argc -= 2;
 827         } else if (head_invalid) {
 828                 struct object *remote_head;
 829                 /*
 830                  * If the merged head is a valid one there is no reason
 831                  * to forbid "git merge" into a branch yet to be born.
 832                  * We do the same for "git pull".
 833                  */
 834                 if (argc != 1)
 835                         die("Can merge only exactly one commit into "
 836                                 "empty head");
 837                 remote_head = peel_to_type(argv[0], 0, NULL, OBJ_COMMIT);
 838                 if (!remote_head)
 839                         die("%s - not something we can merge", argv[0]);
 840                 update_ref("initial pull", "HEAD", remote_head->sha1, NULL, 0,
 841                                 DIE_ON_ERR);
 842                 reset_hard(remote_head->sha1, 0);
 843                 return 0;
 844         } else {
 845                 struct strbuf msg;
 846
 847                 /* We are invoked directly as the first-class UI. */
 848                 head_arg = "HEAD";
 849
 850                 /*
 851                  * All the rest are the commits being merged;
 852                  * prepare the standard merge summary message to
 853                  * be appended to the given message.  If remote
 854                  * is invalid we will die later in the common
 855                  * codepath so we discard the error in this
 856                  * loop.
 857                  */
 858                 strbuf_init(&msg, 0);
 859                 for (i = 0; i < argc; i++)
 860                         merge_name(argv[i], &msg);
 861                 fmt_merge_msg(option_log, &msg, &merge_msg);
 862                 if (merge_msg.len)
 863                         strbuf_setlen(&merge_msg, merge_msg.len-1);
 864         }
 865
 866         if (head_invalid || !argc)
 867                 usage_with_options(builtin_merge_usage,
 868                         builtin_merge_options);
 869
 870         strbuf_addstr(&buf, "merge");
 871         for (i = 0; i < argc; i++)
 872                 strbuf_addf(&buf, " %s", argv[i]);
 873         setenv("GIT_REFLOG_ACTION", buf.buf, 0);
 874         strbuf_reset(&buf);
 875
 876         for (i = 0; i < argc; i++) {
 877                 struct object *o;
 878
 879                 o = peel_to_type(argv[i], 0, NULL, OBJ_COMMIT);
 880                 if (!o)
 881                         die("%s - not something we can merge", argv[i]);
 882                 remotes = &commit_list_insert(lookup_commit(o->sha1),
 883                         remotes)->next;
 884
 885                 strbuf_addf(&buf, "GITHEAD_%s", sha1_to_hex(o->sha1));
 886                 setenv(buf.buf, argv[i], 1);
 887                 strbuf_reset(&buf);
 888         }
 889
 890         if (!use_strategies) {
 891                 if (!remoteheads->next)
 892                         add_strategies(pull_twohead, DEFAULT_TWOHEAD);
 893                 else
 894                         add_strategies(pull_octopus, DEFAULT_OCTOPUS);
 895         }
 896
 897         for (i = 0; i < use_strategies_nr; i++) {
 898                 if (use_strategies[i]->attr & NO_FAST_FORWARD)
 899                         allow_fast_forward = 0;
 900                 if (use_strategies[i]->attr & NO_TRIVIAL)
 901                         allow_trivial = 0;
 902         }
 903
 904         if (!remoteheads->next)
 905                 common = get_merge_bases(lookup_commit(head),
 906                                 remoteheads->item, 1);
 907         else {
 908                 struct commit_list *list = remoteheads;
 909                 commit_list_insert(lookup_commit(head), &list);
 910                 common = get_octopus_merge_bases(list);
 911                 free(list);
 912         }
 913
 914         update_ref("updating ORIG_HEAD", "ORIG_HEAD", head, NULL, 0,
 915                 DIE_ON_ERR);
 916
 917         if (!common)
 918                 ; /* No common ancestors found. We need a real merge. */
 919         else if (!remoteheads->next && !common->next &&
 920                         common->item == remoteheads->item) {
 921                 /*
 922                  * If head can reach all the merge then we are up to date.
 923                  * but first the most common case of merging one remote.
 924                  */
 925                 finish_up_to_date("Already up-to-date.");
 926                 return 0;
 927         } else if (allow_fast_forward && !remoteheads->next &&
 928                         !common->next &&
 929                         !hashcmp(common->item->object.sha1, head)) {
 930                 /* Again the most common case of merging one remote. */
 931                 struct strbuf msg;
 932                 struct object *o;
 933                 char hex[41];
 934
 935                 strcpy(hex, find_unique_abbrev(head, DEFAULT_ABBREV));
 936
 937                 printf("Updating %s..%s\n",
 938                         hex,
 939                         find_unique_abbrev(remoteheads->item->object.sha1,
 940                         DEFAULT_ABBREV));
 941                 strbuf_init(&msg, 0);
 942                 strbuf_addstr(&msg, "Fast forward");
 943                 if (have_message)
 944                         strbuf_addstr(&msg,
 945                                 " (no commit created; -m option ignored)");
 946                 o = peel_to_type(sha1_to_hex(remoteheads->item->object.sha1),
 947                         0, NULL, OBJ_COMMIT);
 948                 if (!o)
 949                         return 1;
 950
 951                 if (checkout_fast_forward(head, remoteheads->item->object.sha1))
 952                         return 1;
 953
 954                 finish(o->sha1, msg.buf);
 955                 drop_save();
 956                 return 0;
 957         } else if (!remoteheads->next && common->next)
 958                 ;
 959                 /*
 960                  * We are not doing octopus and not fast forward.  Need
 961                  * a real merge.
 962                  */
 963         else if (!remoteheads->next && !common->next && option_commit) {
 964                 /*
 965                  * We are not doing octopus, not fast forward, and have
 966                  * only one common.
 967                  */
 968                 refresh_cache(REFRESH_QUIET);
 969                 if (allow_trivial) {
 970                         /* See if it is really trivial. */
 971                         git_committer_info(IDENT_ERROR_ON_NO_NAME);
 972                         printf("Trying really trivial in-index merge...\n");
 973                         if (!read_tree_trivial(common->item->object.sha1,
 974                                         head, remoteheads->item->object.sha1))
 975                                 return merge_trivial();
 976                         printf("Nope.\n");
 977                 }
 978         } else {
 979                 /*
 980                  * An octopus.  If we can reach all the remote we are up
 981                  * to date.
 982                  */
 983                 int up_to_date = 1;
 984                 struct commit_list *j;
 985
 986                 for (j = remoteheads; j; j = j->next) {
 987                         struct commit_list *common_one;
 988
 989                         /*
 990                          * Here we *have* to calculate the individual
 991                          * merge_bases again, otherwise "git merge HEAD^
 992                          * HEAD^^" would be missed.
 993                          */
 994                         common_one = get_merge_bases(lookup_commit(head),
 995                                 j->item, 1);
 996                         if (hashcmp(common_one->item->object.sha1,
 997                                 j->item->object.sha1)) {
 998                                 up_to_date = 0;
 999                                 break;
1000                         }
1001                 }
1002                 if (up_to_date) {
1003                         finish_up_to_date("Already up-to-date. Yeeah!");
1004                         return 0;
1005                 }
1006         }
1007
1008         /* We are going to make a new commit. */
1009         git_committer_info(IDENT_ERROR_ON_NO_NAME);
1010
1011         /*
1012          * At this point, we need a real merge.  No matter what strategy
1013          * we use, it would operate on the index, possibly affecting the
1014          * working tree, and when resolved cleanly, have the desired
1015          * tree in the index -- this means that the index must be in
1016          * sync with the head commit.  The strategies are responsible
1017          * to ensure this.
1018          */
1019         if (use_strategies_nr != 1) {
1020                 /*
1021                  * Stash away the local changes so that we can try more
1022                  * than one.
1023                  */
1024                 save_state();
1025         } else {
1026                 memcpy(stash, null_sha1, 20);
1027         }
1028
1029         for (i = 0; i < use_strategies_nr; i++) {
1030                 int ret;
1031                 if (i) {
1032                         printf("Rewinding the tree to pristine...\n");
1033                         restore_state();
1034                 }
1035                 if (use_strategies_nr != 1)
1036                         printf("Trying merge strategy %s...\n",
1037                                 use_strategies[i]->name);
1038                 /*
1039                  * Remember which strategy left the state in the working
1040                  * tree.
1041                  */
1042                 wt_strategy = use_strategies[i]->name;
1043
1044                 ret = try_merge_strategy(use_strategies[i]->name,
1045                         common, head_arg);
1046                 if (!option_commit && !ret) {
1047                         merge_was_ok = 1;
1048                         /*
1049                          * This is necessary here just to avoid writing
1050                          * the tree, but later we will *not* exit with
1051                          * status code 1 because merge_was_ok is set.
1052                          */
1053                         ret = 1;
1054                 }
1055
1056                 if (ret) {
1057                         /*
1058                          * The backend exits with 1 when conflicts are
1059                          * left to be resolved, with 2 when it does not
1060                          * handle the given merge at all.
1061                          */
1062                         if (ret == 1) {
1063                                 int cnt = evaluate_result();
1064
1065                                 if (best_cnt <= 0 || cnt <= best_cnt) {
1066                                         best_strategy = use_strategies[i]->name;
1067                                         best_cnt = cnt;
1068                                 }
1069                         }
1070                         if (merge_was_ok)
1071                                 break;
1072                         else
1073                                 continue;
1074                 }
1075
1076                 /* Automerge succeeded. */
1077                 discard_cache();
1078                 write_tree_trivial(result_tree);
1079                 automerge_was_ok = 1;
1080                 break;
1081         }
1082
1083         /*
1084          * If we have a resulting tree, that means the strategy module
1085          * auto resolved the merge cleanly.
1086          */
1087         if (automerge_was_ok)
1088                 return finish_automerge(common, result_tree, wt_strategy);
1089
1090         /*
1091          * Pick the result from the best strategy and have the user fix
1092          * it up.
1093          */
1094         if (!best_strategy) {
1095                 restore_state();
1096                 if (use_strategies_nr > 1)
1097                         fprintf(stderr,
1098                                 "No merge strategy handled the merge.\n");
1099                 else
1100                         fprintf(stderr, "Merge with strategy %s failed.\n",
1101                                 use_strategies[0]->name);
1102                 return 2;
1103         } else if (best_strategy == wt_strategy)
1104                 ; /* We already have its result in the working tree. */
1105         else {
1106                 printf("Rewinding the tree to pristine...\n");
1107                 restore_state();
1108                 printf("Using the %s to prepare resolving by hand.\n",
1109                         best_strategy);
1110                 try_merge_strategy(best_strategy, common, head_arg);
1111         }
1112
1113         if (squash)
1114                 finish(NULL, NULL);
1115         else {
1116                 int fd;
1117                 struct commit_list *j;
1118
1119                 for (j = remoteheads; j; j = j->next)
1120                         strbuf_addf(&buf, "%s\n",
1121                                 sha1_to_hex(j->item->object.sha1));
1122                 fd = open(git_path("MERGE_HEAD"), O_WRONLY | O_CREAT, 0666);
1123                 if (fd < 0)
1124                         die("Could open %s for writing",
1125                                 git_path("MERGE_HEAD"));
1126                 if (write_in_full(fd, buf.buf, buf.len) != buf.len)
1127                         die("Could not write to %s", git_path("MERGE_HEAD"));
1128                 close(fd);
1129                 strbuf_addch(&merge_msg, '\n');
1130                 fd = open(git_path("MERGE_MSG"), O_WRONLY | O_CREAT, 0666);
1131                 if (fd < 0)
1132                         die("Could open %s for writing", git_path("MERGE_MSG"));
1133                 if (write_in_full(fd, merge_msg.buf, merge_msg.len) !=
1134                         merge_msg.len)
1135                         die("Could not write to %s", git_path("MERGE_MSG"));
1136                 close(fd);
1137         }
1138
1139         if (merge_was_ok) {
1140                 fprintf(stderr, "Automatic merge went well; "
1141                         "stopped before committing as requested\n");
1142                 return 0;
1143         } else
1144                 return suggest_conflicts();
1145 }