builtin/pull.c

   1 /*
   2  * Builtin "git pull"
   3  *
   4  * Based on git-pull.sh by Junio C Hamano
   5  *
   6  * Fetch one or more remote refs and merge it/them into the current HEAD.
   7  */
   8 #include "cache.h"
   9 #include "builtin.h"
  10 #include "parse-options.h"
  11 #include "exec_cmd.h"
  12 #include "run-command.h"
  13 #include "sha1-array.h"
  14 #include "remote.h"
  15 #include "dir.h"
  16 #include "refs.h"
  17 #include "revision.h"
  18 #include "lockfile.h"
  19
  20 enum rebase_type {
  21         REBASE_INVALID = -1,
  22         REBASE_FALSE = 0,
  23         REBASE_TRUE,
  24         REBASE_PRESERVE
  25 };
  26
  27 /**
  28  * Parses the value of --rebase. If value is a false value, returns
  29  * REBASE_FALSE. If value is a true value, returns REBASE_TRUE. If value is
  30  * "preserve", returns REBASE_PRESERVE. If value is a invalid value, dies with
  31  * a fatal error if fatal is true, otherwise returns REBASE_INVALID.
  32  */
  33 static enum rebase_type parse_config_rebase(const char *key, const char *value,
  34                 int fatal)
  35 {
  36         int v = git_config_maybe_bool("pull.rebase", value);
  37
  38         if (!v)
  39                 return REBASE_FALSE;
  40         else if (v > 0)
  41                 return REBASE_TRUE;
  42         else if (!strcmp(value, "preserve"))
  43                 return REBASE_PRESERVE;
  44
  45         if (fatal)
  46                 die(_("Invalid value for %s: %s"), key, value);
  47         else
  48                 error(_("Invalid value for %s: %s"), key, value);
  49
  50         return REBASE_INVALID;
  51 }
  52
  53 /**
  54  * Callback for --rebase, which parses arg with parse_config_rebase().
  55  */
  56 static int parse_opt_rebase(const struct option *opt, const char *arg, int unset)
  57 {
  58         enum rebase_type *value = opt->value;
  59
  60         if (arg)
  61                 *value = parse_config_rebase("--rebase", arg, 0);
  62         else
  63                 *value = unset ? REBASE_FALSE : REBASE_TRUE;
  64         return *value == REBASE_INVALID ? -1 : 0;
  65 }
  66
  67 static const char * const pull_usage[] = {
  68         N_("git pull [options] [<repository> [<refspec>...]]"),
  69         NULL
  70 };
  71
  72 /* Shared options */
  73 static int opt_verbosity;
  74 static char *opt_progress;
  75
  76 /* Options passed to git-merge or git-rebase */
  77 static enum rebase_type opt_rebase = -1;
  78 static char *opt_diffstat;
  79 static char *opt_log;
  80 static char *opt_squash;
  81 static char *opt_commit;
  82 static char *opt_edit;
  83 static char *opt_ff;
  84 static char *opt_verify_signatures;
  85 static struct argv_array opt_strategies = ARGV_ARRAY_INIT;
  86 static struct argv_array opt_strategy_opts = ARGV_ARRAY_INIT;
  87 static char *opt_gpg_sign;
  88
  89 /* Options passed to git-fetch */
  90 static char *opt_all;
  91 static char *opt_append;
  92 static char *opt_upload_pack;
  93 static int opt_force;
  94 static char *opt_tags;
  95 static char *opt_prune;
  96 static char *opt_recurse_submodules;
  97 static int opt_dry_run;
  98 static char *opt_keep;
  99 static char *opt_depth;
 100 static char *opt_unshallow;
 101 static char *opt_update_shallow;
 102 static char *opt_refmap;
 103
 104 static struct option pull_options[] = {
 105         /* Shared options */
 106         OPT__VERBOSITY(&opt_verbosity),
 107         OPT_PASSTHRU(0, "progress", &opt_progress, NULL,
 108                 N_("force progress reporting"),
 109                 PARSE_OPT_NOARG),
 110
 111         /* Options passed to git-merge or git-rebase */
 112         OPT_GROUP(N_("Options related to merging")),
 113         { OPTION_CALLBACK, 'r', "rebase", &opt_rebase,
 114           N_("false|true|preserve"),
 115           N_("incorporate changes by rebasing rather than merging"),
 116           PARSE_OPT_OPTARG, parse_opt_rebase },
 117         OPT_PASSTHRU('n', NULL, &opt_diffstat, NULL,
 118                 N_("do not show a diffstat at the end of the merge"),
 119                 PARSE_OPT_NOARG | PARSE_OPT_NONEG),
 120         OPT_PASSTHRU(0, "stat", &opt_diffstat, NULL,
 121                 N_("show a diffstat at the end of the merge"),
 122                 PARSE_OPT_NOARG),
 123         OPT_PASSTHRU(0, "summary", &opt_diffstat, NULL,
 124                 N_("(synonym to --stat)"),
 125                 PARSE_OPT_NOARG | PARSE_OPT_HIDDEN),
 126         OPT_PASSTHRU(0, "log", &opt_log, N_("n"),
 127                 N_("add (at most <n>) entries from shortlog to merge commit message"),
 128                 PARSE_OPT_OPTARG),
 129         OPT_PASSTHRU(0, "squash", &opt_squash, NULL,
 130                 N_("create a single commit instead of doing a merge"),
 131                 PARSE_OPT_NOARG),
 132         OPT_PASSTHRU(0, "commit", &opt_commit, NULL,
 133                 N_("perform a commit if the merge succeeds (default)"),
 134                 PARSE_OPT_NOARG),
 135         OPT_PASSTHRU(0, "edit", &opt_edit, NULL,
 136                 N_("edit message before committing"),
 137                 PARSE_OPT_NOARG),
 138         OPT_PASSTHRU(0, "ff", &opt_ff, NULL,
 139                 N_("allow fast-forward"),
 140                 PARSE_OPT_NOARG),
 141         OPT_PASSTHRU(0, "ff-only", &opt_ff, NULL,
 142                 N_("abort if fast-forward is not possible"),
 143                 PARSE_OPT_NOARG | PARSE_OPT_NONEG),
 144         OPT_PASSTHRU(0, "verify-signatures", &opt_verify_signatures, NULL,
 145                 N_("verify that the named commit has a valid GPG signature"),
 146                 PARSE_OPT_NOARG),
 147         OPT_PASSTHRU_ARGV('s', "strategy", &opt_strategies, N_("strategy"),
 148                 N_("merge strategy to use"),
 149                 0),
 150         OPT_PASSTHRU_ARGV('X', "strategy-option", &opt_strategy_opts,
 151                 N_("option=value"),
 152                 N_("option for selected merge strategy"),
 153                 0),
 154         OPT_PASSTHRU('S', "gpg-sign", &opt_gpg_sign, N_("key-id"),
 155                 N_("GPG sign commit"),
 156                 PARSE_OPT_OPTARG),
 157
 158         /* Options passed to git-fetch */
 159         OPT_GROUP(N_("Options related to fetching")),
 160         OPT_PASSTHRU(0, "all", &opt_all, NULL,
 161                 N_("fetch from all remotes"),
 162                 PARSE_OPT_NOARG),
 163         OPT_PASSTHRU('a', "append", &opt_append, NULL,
 164                 N_("append to .git/FETCH_HEAD instead of overwriting"),
 165                 PARSE_OPT_NOARG),
 166         OPT_PASSTHRU(0, "upload-pack", &opt_upload_pack, N_("path"),
 167                 N_("path to upload pack on remote end"),
 168                 0),
 169         OPT__FORCE(&opt_force, N_("force overwrite of local branch")),
 170         OPT_PASSTHRU('t', "tags", &opt_tags, NULL,
 171                 N_("fetch all tags and associated objects"),
 172                 PARSE_OPT_NOARG),
 173         OPT_PASSTHRU('p', "prune", &opt_prune, NULL,
 174                 N_("prune remote-tracking branches no longer on remote"),
 175                 PARSE_OPT_NOARG),
 176         OPT_PASSTHRU(0, "recurse-submodules", &opt_recurse_submodules,
 177                 N_("on-demand"),
 178                 N_("control recursive fetching of submodules"),
 179                 PARSE_OPT_OPTARG),
 180         OPT_BOOL(0, "dry-run", &opt_dry_run,
 181                 N_("dry run")),
 182         OPT_PASSTHRU('k', "keep", &opt_keep, NULL,
 183                 N_("keep downloaded pack"),
 184                 PARSE_OPT_NOARG),
 185         OPT_PASSTHRU(0, "depth", &opt_depth, N_("depth"),
 186                 N_("deepen history of shallow clone"),
 187                 0),
 188         OPT_PASSTHRU(0, "unshallow", &opt_unshallow, NULL,
 189                 N_("convert to a complete repository"),
 190                 PARSE_OPT_NONEG | PARSE_OPT_NOARG),
 191         OPT_PASSTHRU(0, "update-shallow", &opt_update_shallow, NULL,
 192                 N_("accept refs that update .git/shallow"),
 193                 PARSE_OPT_NOARG),
 194         OPT_PASSTHRU(0, "refmap", &opt_refmap, N_("refmap"),
 195                 N_("specify fetch refmap"),
 196                 PARSE_OPT_NONEG),
 197
 198         OPT_END()
 199 };
 200
 201 /**
 202  * Pushes "-q" or "-v" switches into arr to match the opt_verbosity level.
 203  */
 204 static void argv_push_verbosity(struct argv_array *arr)
 205 {
 206         int verbosity;
 207
 208         for (verbosity = opt_verbosity; verbosity > 0; verbosity--)
 209                 argv_array_push(arr, "-v");
 210
 211         for (verbosity = opt_verbosity; verbosity < 0; verbosity++)
 212                 argv_array_push(arr, "-q");
 213 }
 214
 215 /**
 216  * Pushes "-f" switches into arr to match the opt_force level.
 217  */
 218 static void argv_push_force(struct argv_array *arr)
 219 {
 220         int force = opt_force;
 221         while (force-- > 0)
 222                 argv_array_push(arr, "-f");
 223 }
 224
 225 /**
 226  * Sets the GIT_REFLOG_ACTION environment variable to the concatenation of argv
 227  */
 228 static void set_reflog_message(int argc, const char **argv)
 229 {
 230         int i;
 231         struct strbuf msg = STRBUF_INIT;
 232
 233         for (i = 0; i < argc; i++) {
 234                 if (i)
 235                         strbuf_addch(&msg, ' ');
 236                 strbuf_addstr(&msg, argv[i]);
 237         }
 238
 239         setenv("GIT_REFLOG_ACTION", msg.buf, 0);
 240
 241         strbuf_release(&msg);
 242 }
 243
 244 /**
 245  * If pull.ff is unset, returns NULL. If pull.ff is "true", returns "--ff". If
 246  * pull.ff is "false", returns "--no-ff". If pull.ff is "only", returns
 247  * "--ff-only". Otherwise, if pull.ff is set to an invalid value, die with an
 248  * error.
 249  */
 250 static const char *config_get_ff(void)
 251 {
 252         const char *value;
 253
 254         if (git_config_get_value("pull.ff", &value))
 255                 return NULL;
 256
 257         switch (git_config_maybe_bool("pull.ff", value)) {
 258         case 0:
 259                 return "--no-ff";
 260         case 1:
 261                 return "--ff";
 262         }
 263
 264         if (!strcmp(value, "only"))
 265                 return "--ff-only";
 266
 267         die(_("Invalid value for pull.ff: %s"), value);
 268 }
 269
 270 /**
 271  * Returns the default configured value for --rebase. It first looks for the
 272  * value of "branch.$curr_branch.rebase", where $curr_branch is the current
 273  * branch, and if HEAD is detached or the configuration key does not exist,
 274  * looks for the value of "pull.rebase". If both configuration keys do not
 275  * exist, returns REBASE_FALSE.
 276  */
 277 static enum rebase_type config_get_rebase(void)
 278 {
 279         struct branch *curr_branch = branch_get("HEAD");
 280         const char *value;
 281
 282         if (curr_branch) {
 283                 char *key = xstrfmt("branch.%s.rebase", curr_branch->name);
 284
 285                 if (!git_config_get_value(key, &value)) {
 286                         enum rebase_type ret = parse_config_rebase(key, value, 1);
 287                         free(key);
 288                         return ret;
 289                 }
 290
 291                 free(key);
 292         }
 293
 294         if (!git_config_get_value("pull.rebase", &value))
 295                 return parse_config_rebase("pull.rebase", value, 1);
 296
 297         return REBASE_FALSE;
 298 }
 299
 300 /**
 301  * Returns 1 if there are unstaged changes, 0 otherwise.
 302  */
 303 static int has_unstaged_changes(const char *prefix)
 304 {
 305         struct rev_info rev_info;
 306         int result;
 307
 308         init_revisions(&rev_info, prefix);
 309         DIFF_OPT_SET(&rev_info.diffopt, IGNORE_SUBMODULES);
 310         DIFF_OPT_SET(&rev_info.diffopt, QUICK);
 311         diff_setup_done(&rev_info.diffopt);
 312         result = run_diff_files(&rev_info, 0);
 313         return diff_result_code(&rev_info.diffopt, result);
 314 }
 315
 316 /**
 317  * Returns 1 if there are uncommitted changes, 0 otherwise.
 318  */
 319 static int has_uncommitted_changes(const char *prefix)
 320 {
 321         struct rev_info rev_info;
 322         int result;
 323
 324         if (is_cache_unborn())
 325                 return 0;
 326
 327         init_revisions(&rev_info, prefix);
 328         DIFF_OPT_SET(&rev_info.diffopt, IGNORE_SUBMODULES);
 329         DIFF_OPT_SET(&rev_info.diffopt, QUICK);
 330         add_head_to_pending(&rev_info);
 331         diff_setup_done(&rev_info.diffopt);
 332         result = run_diff_index(&rev_info, 1);
 333         return diff_result_code(&rev_info.diffopt, result);
 334 }
 335
 336 /**
 337  * If the work tree has unstaged or uncommitted changes, dies with the
 338  * appropriate message.
 339  */
 340 static void die_on_unclean_work_tree(const char *prefix)
 341 {
 342         struct lock_file *lock_file = xcalloc(1, sizeof(*lock_file));
 343         int do_die = 0;
 344
 345         hold_locked_index(lock_file, 0);
 346         refresh_cache(REFRESH_QUIET);
 347         update_index_if_able(&the_index, lock_file);
 348         rollback_lock_file(lock_file);
 349
 350         if (has_unstaged_changes(prefix)) {
 351                 error(_("Cannot pull with rebase: You have unstaged changes."));
 352                 do_die = 1;
 353         }
 354
 355         if (has_uncommitted_changes(prefix)) {
 356                 if (do_die)
 357                         error(_("Additionally, your index contains uncommitted changes."));
 358                 else
 359                         error(_("Cannot pull with rebase: Your index contains uncommitted changes."));
 360                 do_die = 1;
 361         }
 362
 363         if (do_die)
 364                 exit(1);
 365 }
 366
 367 /**
 368  * Appends merge candidates from FETCH_HEAD that are not marked not-for-merge
 369  * into merge_heads.
 370  */
 371 static void get_merge_heads(struct sha1_array *merge_heads)
 372 {
 373         const char *filename = git_path("FETCH_HEAD");
 374         FILE *fp;
 375         struct strbuf sb = STRBUF_INIT;
 376         unsigned char sha1[GIT_SHA1_RAWSZ];
 377
 378         if (!(fp = fopen(filename, "r")))
 379                 die_errno(_("could not open '%s' for reading"), filename);
 380         while (strbuf_getline(&sb, fp, '\n') != EOF) {
 381                 if (get_sha1_hex(sb.buf, sha1))
 382                         continue;  /* invalid line: does not start with SHA1 */
 383                 if (starts_with(sb.buf + GIT_SHA1_HEXSZ, "\tnot-for-merge\t"))
 384                         continue;  /* ref is not-for-merge */
 385                 sha1_array_append(merge_heads, sha1);
 386         }
 387         fclose(fp);
 388         strbuf_release(&sb);
 389 }
 390
 391 /**
 392  * Used by die_no_merge_candidates() as a for_each_remote() callback to
 393  * retrieve the name of the remote if the repository only has one remote.
 394  */
 395 static int get_only_remote(struct remote *remote, void *cb_data)
 396 {
 397         const char **remote_name = cb_data;
 398
 399         if (*remote_name)
 400                 return -1;
 401
 402         *remote_name = remote->name;
 403         return 0;
 404 }
 405
 406 /**
 407  * Dies with the appropriate reason for why there are no merge candidates:
 408  *
 409  * 1. We fetched from a specific remote, and a refspec was given, but it ended
 410  *    up not fetching anything. This is usually because the user provided a
 411  *    wildcard refspec which had no matches on the remote end.
 412  *
 413  * 2. We fetched from a non-default remote, but didn't specify a branch to
 414  *    merge. We can't use the configured one because it applies to the default
 415  *    remote, thus the user must specify the branches to merge.
 416  *
 417  * 3. We fetched from the branch's or repo's default remote, but:
 418  *
 419  *    a. We are not on a branch, so there will never be a configured branch to
 420  *       merge with.
 421  *
 422  *    b. We are on a branch, but there is no configured branch to merge with.
 423  *
 424  * 4. We fetched from the branch's or repo's default remote, but the configured
 425  *    branch to merge didn't get fetched. (Either it doesn't exist, or wasn't
 426  *    part of the configured fetch refspec.)
 427  */
 428 static void NORETURN die_no_merge_candidates(const char *repo, const char **refspecs)
 429 {
 430         struct branch *curr_branch = branch_get("HEAD");
 431         const char *remote = curr_branch ? curr_branch->remote_name : NULL;
 432
 433         if (*refspecs) {
 434                 if (opt_rebase)
 435                         fprintf_ln(stderr, _("There is no candidate for rebasing against among the refs that you just fetched."));
 436                 else
 437                         fprintf_ln(stderr, _("There are no candidates for merging among the refs that you just fetched."));
 438                 fprintf_ln(stderr, _("Generally this means that you provided a wildcard refspec which had no\n"
 439                                         "matches on the remote end."));
 440         } else if (repo && curr_branch && (!remote || strcmp(repo, remote))) {
 441                 fprintf_ln(stderr, _("You asked to pull from the remote '%s', but did not specify\n"
 442                         "a branch. Because this is not the default configured remote\n"
 443                         "for your current branch, you must specify a branch on the command line."),
 444                         repo);
 445         } else if (!curr_branch) {
 446                 fprintf_ln(stderr, _("You are not currently on a branch."));
 447                 if (opt_rebase)
 448                         fprintf_ln(stderr, _("Please specify which branch you want to rebase against."));
 449                 else
 450                         fprintf_ln(stderr, _("Please specify which branch you want to merge with."));
 451                 fprintf_ln(stderr, _("See git-pull(1) for details."));
 452                 fprintf(stderr, "\n");
 453                 fprintf_ln(stderr, "    git pull <remote> <branch>");
 454                 fprintf(stderr, "\n");
 455         } else if (!curr_branch->merge_nr) {
 456                 const char *remote_name = NULL;
 457
 458                 if (for_each_remote(get_only_remote, &remote_name) || !remote_name)
 459                         remote_name = "<remote>";
 460
 461                 fprintf_ln(stderr, _("There is no tracking information for the current branch."));
 462                 if (opt_rebase)
 463                         fprintf_ln(stderr, _("Please specify which branch you want to rebase against."));
 464                 else
 465                         fprintf_ln(stderr, _("Please specify which branch you want to merge with."));
 466                 fprintf_ln(stderr, _("See git-pull(1) for details."));
 467                 fprintf(stderr, "\n");
 468                 fprintf_ln(stderr, "    git pull <remote> <branch>");
 469                 fprintf(stderr, "\n");
 470                 fprintf_ln(stderr, _("If you wish to set tracking information for this branch you can do so with:\n"
 471                                 "\n"
 472                                 "    git branch --set-upstream-to=%s/<branch> %s\n"),
 473                                 remote_name, curr_branch->name);
 474         } else
 475                 fprintf_ln(stderr, _("Your configuration specifies to merge with the ref '%s'\n"
 476                         "from the remote, but no such ref was fetched."),
 477                         *curr_branch->merge_name);
 478         exit(1);
 479 }
 480
 481 /**
 482  * Parses argv into [<repo> [<refspecs>...]], returning their values in `repo`
 483  * as a string and `refspecs` as a null-terminated array of strings. If `repo`
 484  * is not provided in argv, it is set to NULL.
 485  */
 486 static void parse_repo_refspecs(int argc, const char **argv, const char **repo,
 487                 const char ***refspecs)
 488 {
 489         if (argc > 0) {
 490                 *repo = *argv++;
 491                 argc--;
 492         } else
 493                 *repo = NULL;
 494         *refspecs = argv;
 495 }
 496
 497 /**
 498  * Runs git-fetch, returning its exit status. `repo` and `refspecs` are the
 499  * repository and refspecs to fetch, or NULL if they are not provided.
 500  */
 501 static int run_fetch(const char *repo, const char **refspecs)
 502 {
 503         struct argv_array args = ARGV_ARRAY_INIT;
 504         int ret;
 505
 506         argv_array_pushl(&args, "fetch", "--update-head-ok", NULL);
 507
 508         /* Shared options */
 509         argv_push_verbosity(&args);
 510         if (opt_progress)
 511                 argv_array_push(&args, opt_progress);
 512
 513         /* Options passed to git-fetch */
 514         if (opt_all)
 515                 argv_array_push(&args, opt_all);
 516         if (opt_append)
 517                 argv_array_push(&args, opt_append);
 518         if (opt_upload_pack)
 519                 argv_array_push(&args, opt_upload_pack);
 520         argv_push_force(&args);
 521         if (opt_tags)
 522                 argv_array_push(&args, opt_tags);
 523         if (opt_prune)
 524                 argv_array_push(&args, opt_prune);
 525         if (opt_recurse_submodules)
 526                 argv_array_push(&args, opt_recurse_submodules);
 527         if (opt_dry_run)
 528                 argv_array_push(&args, "--dry-run");
 529         if (opt_keep)
 530                 argv_array_push(&args, opt_keep);
 531         if (opt_depth)
 532                 argv_array_push(&args, opt_depth);
 533         if (opt_unshallow)
 534                 argv_array_push(&args, opt_unshallow);
 535         if (opt_update_shallow)
 536                 argv_array_push(&args, opt_update_shallow);
 537         if (opt_refmap)
 538                 argv_array_push(&args, opt_refmap);
 539
 540         if (repo) {
 541                 argv_array_push(&args, repo);
 542                 argv_array_pushv(&args, refspecs);
 543         } else if (*refspecs)
 544                 die("BUG: refspecs without repo?");
 545         ret = run_command_v_opt(args.argv, RUN_GIT_CMD);
 546         argv_array_clear(&args);
 547         return ret;
 548 }
 549
 550 /**
 551  * "Pulls into void" by branching off merge_head.
 552  */
 553 static int pull_into_void(const unsigned char *merge_head,
 554                 const unsigned char *curr_head)
 555 {
 556         /*
 557          * Two-way merge: we treat the index as based on an empty tree,
 558          * and try to fast-forward to HEAD. This ensures we will not lose
 559          * index/worktree changes that the user already made on the unborn
 560          * branch.
 561          */
 562         if (checkout_fast_forward(EMPTY_TREE_SHA1_BIN, merge_head, 0))
 563                 return 1;
 564
 565         if (update_ref("initial pull", "HEAD", merge_head, curr_head, 0, UPDATE_REFS_DIE_ON_ERR))
 566                 return 1;
 567
 568         return 0;
 569 }
 570
 571 /**
 572  * Runs git-merge, returning its exit status.
 573  */
 574 static int run_merge(void)
 575 {
 576         int ret;
 577         struct argv_array args = ARGV_ARRAY_INIT;
 578
 579         argv_array_pushl(&args, "merge", NULL);
 580
 581         /* Shared options */
 582         argv_push_verbosity(&args);
 583         if (opt_progress)
 584                 argv_array_push(&args, opt_progress);
 585
 586         /* Options passed to git-merge */
 587         if (opt_diffstat)
 588                 argv_array_push(&args, opt_diffstat);
 589         if (opt_log)
 590                 argv_array_push(&args, opt_log);
 591         if (opt_squash)
 592                 argv_array_push(&args, opt_squash);
 593         if (opt_commit)
 594                 argv_array_push(&args, opt_commit);
 595         if (opt_edit)
 596                 argv_array_push(&args, opt_edit);
 597         if (opt_ff)
 598                 argv_array_push(&args, opt_ff);
 599         if (opt_verify_signatures)
 600                 argv_array_push(&args, opt_verify_signatures);
 601         argv_array_pushv(&args, opt_strategies.argv);
 602         argv_array_pushv(&args, opt_strategy_opts.argv);
 603         if (opt_gpg_sign)
 604                 argv_array_push(&args, opt_gpg_sign);
 605
 606         argv_array_push(&args, "FETCH_HEAD");
 607         ret = run_command_v_opt(args.argv, RUN_GIT_CMD);
 608         argv_array_clear(&args);
 609         return ret;
 610 }
 611
 612 /**
 613  * Returns remote's upstream branch for the current branch. If remote is NULL,
 614  * the current branch's configured default remote is used. Returns NULL if
 615  * `remote` does not name a valid remote, HEAD does not point to a branch,
 616  * remote is not the branch's configured remote or the branch does not have any
 617  * configured upstream branch.
 618  */
 619 static const char *get_upstream_branch(const char *remote)
 620 {
 621         struct remote *rm;
 622         struct branch *curr_branch;
 623         const char *curr_branch_remote;
 624
 625         rm = remote_get(remote);
 626         if (!rm)
 627                 return NULL;
 628
 629         curr_branch = branch_get("HEAD");
 630         if (!curr_branch)
 631                 return NULL;
 632
 633         curr_branch_remote = remote_for_branch(curr_branch, NULL);
 634         assert(curr_branch_remote);
 635
 636         if (strcmp(curr_branch_remote, rm->name))
 637                 return NULL;
 638
 639         return branch_get_upstream(curr_branch, NULL);
 640 }
 641
 642 /**
 643  * Derives the remote tracking branch from the remote and refspec.
 644  *
 645  * FIXME: The current implementation assumes the default mapping of
 646  * refs/heads/<branch_name> to refs/remotes/<remote_name>/<branch_name>.
 647  */
 648 static const char *get_tracking_branch(const char *remote, const char *refspec)
 649 {
 650         struct refspec *spec;
 651         const char *spec_src;
 652         const char *merge_branch;
 653
 654         spec = parse_fetch_refspec(1, &refspec);
 655         spec_src = spec->src;
 656         if (!*spec_src || !strcmp(spec_src, "HEAD"))
 657                 spec_src = "HEAD";
 658         else if (skip_prefix(spec_src, "heads/", &spec_src))
 659                 ;
 660         else if (skip_prefix(spec_src, "refs/heads/", &spec_src))
 661                 ;
 662         else if (starts_with(spec_src, "refs/") ||
 663                 starts_with(spec_src, "tags/") ||
 664                 starts_with(spec_src, "remotes/"))
 665                 spec_src = "";
 666
 667         if (*spec_src) {
 668                 if (!strcmp(remote, "."))
 669                         merge_branch = mkpath("refs/heads/%s", spec_src);
 670                 else
 671                         merge_branch = mkpath("refs/remotes/%s/%s", remote, spec_src);
 672         } else
 673                 merge_branch = NULL;
 674
 675         free_refspec(1, spec);
 676         return merge_branch;
 677 }
 678
 679 /**
 680  * Given the repo and refspecs, sets fork_point to the point at which the
 681  * current branch forked from its remote tracking branch. Returns 0 on success,
 682  * -1 on failure.
 683  */
 684 static int get_rebase_fork_point(unsigned char *fork_point, const char *repo,
 685                 const char *refspec)
 686 {
 687         int ret;
 688         struct branch *curr_branch;
 689         const char *remote_branch;
 690         struct child_process cp = CHILD_PROCESS_INIT;
 691         struct strbuf sb = STRBUF_INIT;
 692
 693         curr_branch = branch_get("HEAD");
 694         if (!curr_branch)
 695                 return -1;
 696
 697         if (refspec)
 698                 remote_branch = get_tracking_branch(repo, refspec);
 699         else
 700                 remote_branch = get_upstream_branch(repo);
 701
 702         if (!remote_branch)
 703                 return -1;
 704
 705         argv_array_pushl(&cp.args, "merge-base", "--fork-point",
 706                         remote_branch, curr_branch->name, NULL);
 707         cp.no_stdin = 1;
 708         cp.no_stderr = 1;
 709         cp.git_cmd = 1;
 710
 711         ret = capture_command(&cp, &sb, GIT_SHA1_HEXSZ);
 712         if (ret)
 713                 goto cleanup;
 714
 715         ret = get_sha1_hex(sb.buf, fork_point);
 716         if (ret)
 717                 goto cleanup;
 718
 719 cleanup:
 720         strbuf_release(&sb);
 721         return ret ? -1 : 0;
 722 }
 723
 724 /**
 725  * Sets merge_base to the octopus merge base of curr_head, merge_head and
 726  * fork_point. Returns 0 if a merge base is found, 1 otherwise.
 727  */
 728 static int get_octopus_merge_base(unsigned char *merge_base,
 729                 const unsigned char *curr_head,
 730                 const unsigned char *merge_head,
 731                 const unsigned char *fork_point)
 732 {
 733         struct commit_list *revs = NULL, *result;
 734
 735         commit_list_insert(lookup_commit_reference(curr_head), &revs);
 736         commit_list_insert(lookup_commit_reference(merge_head), &revs);
 737         if (!is_null_sha1(fork_point))
 738                 commit_list_insert(lookup_commit_reference(fork_point), &revs);
 739
 740         result = reduce_heads(get_octopus_merge_bases(revs));
 741         free_commit_list(revs);
 742         if (!result)
 743                 return 1;
 744
 745         hashcpy(merge_base, result->item->object.sha1);
 746         return 0;
 747 }
 748
 749 /**
 750  * Given the current HEAD SHA1, the merge head returned from git-fetch and the
 751  * fork point calculated by get_rebase_fork_point(), runs git-rebase with the
 752  * appropriate arguments and returns its exit status.
 753  */
 754 static int run_rebase(const unsigned char *curr_head,
 755                 const unsigned char *merge_head,
 756                 const unsigned char *fork_point)
 757 {
 758         int ret;
 759         unsigned char oct_merge_base[GIT_SHA1_RAWSZ];
 760         struct argv_array args = ARGV_ARRAY_INIT;
 761
 762         if (!get_octopus_merge_base(oct_merge_base, curr_head, merge_head, fork_point))
 763                 if (!is_null_sha1(fork_point) && !hashcmp(oct_merge_base, fork_point))
 764                         fork_point = NULL;
 765
 766         argv_array_push(&args, "rebase");
 767
 768         /* Shared options */
 769         argv_push_verbosity(&args);
 770
 771         /* Options passed to git-rebase */
 772         if (opt_rebase == REBASE_PRESERVE)
 773                 argv_array_push(&args, "--preserve-merges");
 774         if (opt_diffstat)
 775                 argv_array_push(&args, opt_diffstat);
 776         argv_array_pushv(&args, opt_strategies.argv);
 777         argv_array_pushv(&args, opt_strategy_opts.argv);
 778         if (opt_gpg_sign)
 779                 argv_array_push(&args, opt_gpg_sign);
 780
 781         argv_array_push(&args, "--onto");
 782         argv_array_push(&args, sha1_to_hex(merge_head));
 783
 784         if (fork_point && !is_null_sha1(fork_point))
 785                 argv_array_push(&args, sha1_to_hex(fork_point));
 786         else
 787                 argv_array_push(&args, sha1_to_hex(merge_head));
 788
 789         ret = run_command_v_opt(args.argv, RUN_GIT_CMD);
 790         argv_array_clear(&args);
 791         return ret;
 792 }
 793
 794 int cmd_pull(int argc, const char **argv, const char *prefix)
 795 {
 796         const char *repo, **refspecs;
 797         struct sha1_array merge_heads = SHA1_ARRAY_INIT;
 798         unsigned char orig_head[GIT_SHA1_RAWSZ], curr_head[GIT_SHA1_RAWSZ];
 799         unsigned char rebase_fork_point[GIT_SHA1_RAWSZ];
 800
 801         if (!getenv("GIT_REFLOG_ACTION"))
 802                 set_reflog_message(argc, argv);
 803
 804         argc = parse_options(argc, argv, prefix, pull_options, pull_usage, 0);
 805
 806         parse_repo_refspecs(argc, argv, &repo, &refspecs);
 807
 808         if (!opt_ff)
 809                 opt_ff = xstrdup_or_null(config_get_ff());
 810
 811         if (opt_rebase < 0)
 812                 opt_rebase = config_get_rebase();
 813
 814         git_config(git_default_config, NULL);
 815
 816         if (read_cache_unmerged())
 817                 die_resolve_conflict("Pull");
 818
 819         if (file_exists(git_path("MERGE_HEAD")))
 820                 die_conclude_merge();
 821
 822         if (get_sha1("HEAD", orig_head))
 823                 hashclr(orig_head);
 824
 825         if (opt_rebase) {
 826                 if (is_null_sha1(orig_head) && !is_cache_unborn())
 827                         die(_("Updating an unborn branch with changes added to the index."));
 828
 829                 die_on_unclean_work_tree(prefix);
 830
 831                 if (get_rebase_fork_point(rebase_fork_point, repo, *refspecs))
 832                         hashclr(rebase_fork_point);
 833         }
 834
 835         if (run_fetch(repo, refspecs))
 836                 return 1;
 837
 838         if (opt_dry_run)
 839                 return 0;
 840
 841         if (get_sha1("HEAD", curr_head))
 842                 hashclr(curr_head);
 843
 844         if (!is_null_sha1(orig_head) && !is_null_sha1(curr_head) &&
 845                         hashcmp(orig_head, curr_head)) {
 846                 /*
 847                  * The fetch involved updating the current branch.
 848                  *
 849                  * The working tree and the index file are still based on
 850                  * orig_head commit, but we are merging into curr_head.
 851                  * Update the working tree to match curr_head.
 852                  */
 853
 854                 warning(_("fetch updated the current branch head.\n"
 855                         "fast-forwarding your working tree from\n"
 856                         "commit %s."), sha1_to_hex(orig_head));
 857
 858                 if (checkout_fast_forward(orig_head, curr_head, 0))
 859                         die(_("Cannot fast-forward your working tree.\n"
 860                                 "After making sure that you saved anything precious from\n"
 861                                 "$ git diff %s\n"
 862                                 "output, run\n"
 863                                 "$ git reset --hard\n"
 864                                 "to recover."), sha1_to_hex(orig_head));
 865         }
 866
 867         get_merge_heads(&merge_heads);
 868
 869         if (!merge_heads.nr)
 870                 die_no_merge_candidates(repo, refspecs);
 871
 872         if (is_null_sha1(orig_head)) {
 873                 if (merge_heads.nr > 1)
 874                         die(_("Cannot merge multiple branches into empty head."));
 875                 return pull_into_void(*merge_heads.sha1, curr_head);
 876         } else if (opt_rebase) {
 877                 if (merge_heads.nr > 1)
 878                         die(_("Cannot rebase onto multiple branches."));
 879                 return run_rebase(curr_head, *merge_heads.sha1, rebase_fork_point);
 880         } else
 881                 return run_merge();
 882 }