git.oblomov.eu Git - git/blob - builtin/checkout.c

   1 #include "builtin.h"
   2 #include "lockfile.h"
   3 #include "parse-options.h"
   4 #include "refs.h"
   5 #include "commit.h"
   6 #include "tree.h"
   7 #include "tree-walk.h"
   8 #include "cache-tree.h"
   9 #include "unpack-trees.h"
  10 #include "dir.h"
  11 #include "run-command.h"
  12 #include "merge-recursive.h"
  13 #include "branch.h"
  14 #include "diff.h"
  15 #include "revision.h"
  16 #include "remote.h"
  17 #include "blob.h"
  18 #include "xdiff-interface.h"
  19 #include "ll-merge.h"
  20 #include "resolve-undo.h"
  21 #include "submodule.h"
  22
  23 static const char * const checkout_usage[] = {
  24         N_("git checkout [<options>] <branch>"),
  25         N_("git checkout [<options>] [<branch>] -- <file>..."),
  26         NULL,
  27 };
  28
  29 struct checkout_opts {
  30         int patch_mode;
  31         int quiet;
  32         int merge;
  33         int force;
  34         int force_detach;
  35         int writeout_stage;
  36         int overwrite_ignore;
  37         int ignore_skipworktree;
  38         int ignore_other_worktrees;
  39
  40         const char *new_branch;
  41         const char *new_branch_force;
  42         const char *new_orphan_branch;
  43         int new_branch_log;
  44         enum branch_track track;
  45         struct diff_options diff_options;
  46
  47         int branch_exists;
  48         const char *prefix;
  49         struct pathspec pathspec;
  50         struct tree *source_tree;
  51
  52         int new_worktree_mode;
  53 };
  54
  55 static int post_checkout_hook(struct commit *old, struct commit *new,
  56                               int changed)
  57 {
  58         return run_hook_le(NULL, "post-checkout",
  59                            sha1_to_hex(old ? old->object.sha1 : null_sha1),
  60                            sha1_to_hex(new ? new->object.sha1 : null_sha1),
  61                            changed ? "1" : "0", NULL);
  62         /* "new" can be NULL when checking out from the index before
  63            a commit exists. */
  64
  65 }
  66
  67 static int update_some(const unsigned char *sha1, struct strbuf *base,
  68                 const char *pathname, unsigned mode, int stage, void *context)
  69 {
  70         int len;
  71         struct cache_entry *ce;
  72         int pos;
  73
  74         if (S_ISDIR(mode))
  75                 return READ_TREE_RECURSIVE;
  76
  77         len = base->len + strlen(pathname);
  78         ce = xcalloc(1, cache_entry_size(len));
  79         hashcpy(ce->sha1, sha1);
  80         memcpy(ce->name, base->buf, base->len);
  81         memcpy(ce->name + base->len, pathname, len - base->len);
  82         ce->ce_flags = create_ce_flags(0) | CE_UPDATE;
  83         ce->ce_namelen = len;
  84         ce->ce_mode = create_ce_mode(mode);
  85
  86         /*
  87          * If the entry is the same as the current index, we can leave the old
  88          * entry in place. Whether it is UPTODATE or not, checkout_entry will
  89          * do the right thing.
  90          */
  91         pos = cache_name_pos(ce->name, ce->ce_namelen);
  92         if (pos >= 0) {
  93                 struct cache_entry *old = active_cache[pos];
  94                 if (ce->ce_mode == old->ce_mode &&
  95                     !hashcmp(ce->sha1, old->sha1)) {
  96                         old->ce_flags |= CE_UPDATE;
  97                         free(ce);
  98                         return 0;
  99                 }
 100         }
 101
 102         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
 103         return 0;
 104 }
 105
 106 static int read_tree_some(struct tree *tree, const struct pathspec *pathspec)
 107 {
 108         read_tree_recursive(tree, "", 0, 0, pathspec, update_some, NULL);
 109
 110         /* update the index with the given tree's info
 111          * for all args, expanding wildcards, and exit
 112          * with any non-zero return code.
 113          */
 114         return 0;
 115 }
 116
 117 static int skip_same_name(const struct cache_entry *ce, int pos)
 118 {
 119         while (++pos < active_nr &&
 120                !strcmp(active_cache[pos]->name, ce->name))
 121                 ; /* skip */
 122         return pos;
 123 }
 124
 125 static int check_stage(int stage, const struct cache_entry *ce, int pos)
 126 {
 127         while (pos < active_nr &&
 128                !strcmp(active_cache[pos]->name, ce->name)) {
 129                 if (ce_stage(active_cache[pos]) == stage)
 130                         return 0;
 131                 pos++;
 132         }
 133         if (stage == 2)
 134                 return error(_("path '%s' does not have our version"), ce->name);
 135         else
 136                 return error(_("path '%s' does not have their version"), ce->name);
 137 }
 138
 139 static int check_stages(unsigned stages, const struct cache_entry *ce, int pos)
 140 {
 141         unsigned seen = 0;
 142         const char *name = ce->name;
 143
 144         while (pos < active_nr) {
 145                 ce = active_cache[pos];
 146                 if (strcmp(name, ce->name))
 147                         break;
 148                 seen |= (1 << ce_stage(ce));
 149                 pos++;
 150         }
 151         if ((stages & seen) != stages)
 152                 return error(_("path '%s' does not have all necessary versions"),
 153                              name);
 154         return 0;
 155 }
 156
 157 static int checkout_stage(int stage, struct cache_entry *ce, int pos,
 158                           struct checkout *state)
 159 {
 160         while (pos < active_nr &&
 161                !strcmp(active_cache[pos]->name, ce->name)) {
 162                 if (ce_stage(active_cache[pos]) == stage)
 163                         return checkout_entry(active_cache[pos], state, NULL);
 164                 pos++;
 165         }
 166         if (stage == 2)
 167                 return error(_("path '%s' does not have our version"), ce->name);
 168         else
 169                 return error(_("path '%s' does not have their version"), ce->name);
 170 }
 171
 172 static int checkout_merged(int pos, struct checkout *state)
 173 {
 174         struct cache_entry *ce = active_cache[pos];
 175         const char *path = ce->name;
 176         mmfile_t ancestor, ours, theirs;
 177         int status;
 178         unsigned char sha1[20];
 179         mmbuffer_t result_buf;
 180         unsigned char threeway[3][20];
 181         unsigned mode = 0;
 182
 183         memset(threeway, 0, sizeof(threeway));
 184         while (pos < active_nr) {
 185                 int stage;
 186                 stage = ce_stage(ce);
 187                 if (!stage || strcmp(path, ce->name))
 188                         break;
 189                 hashcpy(threeway[stage - 1], ce->sha1);
 190                 if (stage == 2)
 191                         mode = create_ce_mode(ce->ce_mode);
 192                 pos++;
 193                 ce = active_cache[pos];
 194         }
 195         if (is_null_sha1(threeway[1]) || is_null_sha1(threeway[2]))
 196                 return error(_("path '%s' does not have necessary versions"), path);
 197
 198         read_mmblob(&ancestor, threeway[0]);
 199         read_mmblob(&ours, threeway[1]);
 200         read_mmblob(&theirs, threeway[2]);
 201
 202         /*
 203          * NEEDSWORK: re-create conflicts from merges with
 204          * merge.renormalize set, too
 205          */
 206         status = ll_merge(&result_buf, path, &ancestor, "base",
 207                           &ours, "ours", &theirs, "theirs", NULL);
 208         free(ancestor.ptr);
 209         free(ours.ptr);
 210         free(theirs.ptr);
 211         if (status < 0 || !result_buf.ptr) {
 212                 free(result_buf.ptr);
 213                 return error(_("path '%s': cannot merge"), path);
 214         }
 215
 216         /*
 217          * NEEDSWORK:
 218          * There is absolutely no reason to write this as a blob object
 219          * and create a phony cache entry just to leak.  This hack is
 220          * primarily to get to the write_entry() machinery that massages
 221          * the contents to work-tree format and writes out which only
 222          * allows it for a cache entry.  The code in write_entry() needs
 223          * to be refactored to allow us to feed a <buffer, size, mode>
 224          * instead of a cache entry.  Such a refactoring would help
 225          * merge_recursive as well (it also writes the merge result to the
 226          * object database even when it may contain conflicts).
 227          */
 228         if (write_sha1_file(result_buf.ptr, result_buf.size,
 229                             blob_type, sha1))
 230                 die(_("Unable to add merge result for '%s'"), path);
 231         ce = make_cache_entry(mode, sha1, path, 2, 0);
 232         if (!ce)
 233                 die(_("make_cache_entry failed for path '%s'"), path);
 234         status = checkout_entry(ce, state, NULL);
 235         return status;
 236 }
 237
 238 static int checkout_paths(const struct checkout_opts *opts,
 239                           const char *revision)
 240 {
 241         int pos;
 242         struct checkout state;
 243         static char *ps_matched;
 244         unsigned char rev[20];
 245         int flag;
 246         struct commit *head;
 247         int errs = 0;
 248         struct lock_file *lock_file;
 249
 250         if (opts->track != BRANCH_TRACK_UNSPECIFIED)
 251                 die(_("'%s' cannot be used with updating paths"), "--track");
 252
 253         if (opts->new_branch_log)
 254                 die(_("'%s' cannot be used with updating paths"), "-l");
 255
 256         if (opts->force && opts->patch_mode)
 257                 die(_("'%s' cannot be used with updating paths"), "-f");
 258
 259         if (opts->force_detach)
 260                 die(_("'%s' cannot be used with updating paths"), "--detach");
 261
 262         if (opts->merge && opts->patch_mode)
 263                 die(_("'%s' cannot be used with %s"), "--merge", "--patch");
 264
 265         if (opts->force && opts->merge)
 266                 die(_("'%s' cannot be used with %s"), "-f", "-m");
 267
 268         if (opts->new_branch)
 269                 die(_("Cannot update paths and switch to branch '%s' at the same time."),
 270                     opts->new_branch);
 271
 272         if (opts->patch_mode)
 273                 return run_add_interactive(revision, "--patch=checkout",
 274                                            &opts->pathspec);
 275
 276         lock_file = xcalloc(1, sizeof(struct lock_file));
 277
 278         hold_locked_index(lock_file, 1);
 279         if (read_cache_preload(&opts->pathspec) < 0)
 280                 return error(_("corrupt index file"));
 281
 282         if (opts->source_tree)
 283                 read_tree_some(opts->source_tree, &opts->pathspec);
 284
 285         ps_matched = xcalloc(opts->pathspec.nr, 1);
 286
 287         /*
 288          * Make sure all pathspecs participated in locating the paths
 289          * to be checked out.
 290          */
 291         for (pos = 0; pos < active_nr; pos++) {
 292                 struct cache_entry *ce = active_cache[pos];
 293                 ce->ce_flags &= ~CE_MATCHED;
 294                 if (!opts->ignore_skipworktree && ce_skip_worktree(ce))
 295                         continue;
 296                 if (opts->source_tree && !(ce->ce_flags & CE_UPDATE))
 297                         /*
 298                          * "git checkout tree-ish -- path", but this entry
 299                          * is in the original index; it will not be checked
 300                          * out to the working tree and it does not matter
 301                          * if pathspec matched this entry.  We will not do
 302                          * anything to this entry at all.
 303                          */
 304                         continue;
 305                 /*
 306                  * Either this entry came from the tree-ish we are
 307                  * checking the paths out of, or we are checking out
 308                  * of the index.
 309                  *
 310                  * If it comes from the tree-ish, we already know it
 311                  * matches the pathspec and could just stamp
 312                  * CE_MATCHED to it from update_some(). But we still
 313                  * need ps_matched and read_tree_recursive (and
 314                  * eventually tree_entry_interesting) cannot fill
 315                  * ps_matched yet. Once it can, we can avoid calling
 316                  * match_pathspec() for _all_ entries when
 317                  * opts->source_tree != NULL.
 318                  */
 319                 if (ce_path_match(ce, &opts->pathspec, ps_matched))
 320                         ce->ce_flags |= CE_MATCHED;
 321         }
 322
 323         if (report_path_error(ps_matched, &opts->pathspec, opts->prefix)) {
 324                 free(ps_matched);
 325                 return 1;
 326         }
 327         free(ps_matched);
 328
 329         /* "checkout -m path" to recreate conflicted state */
 330         if (opts->merge)
 331                 unmerge_marked_index(&the_index);
 332
 333         /* Any unmerged paths? */
 334         for (pos = 0; pos < active_nr; pos++) {
 335                 const struct cache_entry *ce = active_cache[pos];
 336                 if (ce->ce_flags & CE_MATCHED) {
 337                         if (!ce_stage(ce))
 338                                 continue;
 339                         if (opts->force) {
 340                                 warning(_("path '%s' is unmerged"), ce->name);
 341                         } else if (opts->writeout_stage) {
 342                                 errs |= check_stage(opts->writeout_stage, ce, pos);
 343                         } else if (opts->merge) {
 344                                 errs |= check_stages((1<<2) | (1<<3), ce, pos);
 345                         } else {
 346                                 errs = 1;
 347                                 error(_("path '%s' is unmerged"), ce->name);
 348                         }
 349                         pos = skip_same_name(ce, pos) - 1;
 350                 }
 351         }
 352         if (errs)
 353                 return 1;
 354
 355         /* Now we are committed to check them out */
 356         memset(&state, 0, sizeof(state));
 357         state.force = 1;
 358         state.refresh_cache = 1;
 359         state.istate = &the_index;
 360         for (pos = 0; pos < active_nr; pos++) {
 361                 struct cache_entry *ce = active_cache[pos];
 362                 if (ce->ce_flags & CE_MATCHED) {
 363                         if (!ce_stage(ce)) {
 364                                 errs |= checkout_entry(ce, &state, NULL);
 365                                 continue;
 366                         }
 367                         if (opts->writeout_stage)
 368                                 errs |= checkout_stage(opts->writeout_stage, ce, pos, &state);
 369                         else if (opts->merge)
 370                                 errs |= checkout_merged(pos, &state);
 371                         pos = skip_same_name(ce, pos) - 1;
 372                 }
 373         }
 374
 375         if (write_locked_index(&the_index, lock_file, COMMIT_LOCK))
 376                 die(_("unable to write new index file"));
 377
 378         read_ref_full("HEAD", 0, rev, &flag);
 379         head = lookup_commit_reference_gently(rev, 1);
 380
 381         errs |= post_checkout_hook(head, head, 0);
 382         return errs;
 383 }
 384
 385 static void show_local_changes(struct object *head,
 386                                const struct diff_options *opts)
 387 {
 388         struct rev_info rev;
 389         /* I think we want full paths, even if we're in a subdirectory. */
 390         init_revisions(&rev, NULL);
 391         rev.diffopt.flags = opts->flags;
 392         rev.diffopt.output_format |= DIFF_FORMAT_NAME_STATUS;
 393         diff_setup_done(&rev.diffopt);
 394         add_pending_object(&rev, head, NULL);
 395         run_diff_index(&rev, 0);
 396 }
 397
 398 static void describe_detached_head(const char *msg, struct commit *commit)
 399 {
 400         struct strbuf sb = STRBUF_INIT;
 401         if (!parse_commit(commit))
 402                 pp_commit_easy(CMIT_FMT_ONELINE, commit, &sb);
 403         fprintf(stderr, "%s %s... %s\n", msg,
 404                 find_unique_abbrev(commit->object.sha1, DEFAULT_ABBREV), sb.buf);
 405         strbuf_release(&sb);
 406 }
 407
 408 static int reset_tree(struct tree *tree, const struct checkout_opts *o,
 409                       int worktree, int *writeout_error)
 410 {
 411         struct unpack_trees_options opts;
 412         struct tree_desc tree_desc;
 413
 414         memset(&opts, 0, sizeof(opts));
 415         opts.head_idx = -1;
 416         opts.update = worktree;
 417         opts.skip_unmerged = !worktree;
 418         opts.reset = 1;
 419         opts.merge = 1;
 420         opts.fn = oneway_merge;
 421         opts.verbose_update = !o->quiet && isatty(2);
 422         opts.src_index = &the_index;
 423         opts.dst_index = &the_index;
 424         parse_tree(tree);
 425         init_tree_desc(&tree_desc, tree->buffer, tree->size);
 426         switch (unpack_trees(1, &tree_desc, &opts)) {
 427         case -2:
 428                 *writeout_error = 1;
 429                 /*
 430                  * We return 0 nevertheless, as the index is all right
 431                  * and more importantly we have made best efforts to
 432                  * update paths in the work tree, and we cannot revert
 433                  * them.
 434                  */
 435         case 0:
 436                 return 0;
 437         default:
 438                 return 128;
 439         }
 440 }
 441
 442 struct branch_info {
 443         const char *name; /* The short name used */
 444         const char *path; /* The full name of a real branch */
 445         struct commit *commit; /* The named commit */
 446         /*
 447          * if not null the branch is detached because it's already
 448          * checked out in this checkout
 449          */
 450         char *checkout;
 451 };
 452
 453 static void setup_branch_path(struct branch_info *branch)
 454 {
 455         struct strbuf buf = STRBUF_INIT;
 456
 457         strbuf_branchname(&buf, branch->name);
 458         if (strcmp(buf.buf, branch->name))
 459                 branch->name = xstrdup(buf.buf);
 460         strbuf_splice(&buf, 0, 0, "refs/heads/", 11);
 461         branch->path = strbuf_detach(&buf, NULL);
 462 }
 463
 464 static int merge_working_tree(const struct checkout_opts *opts,
 465                               struct branch_info *old,
 466                               struct branch_info *new,
 467                               int *writeout_error)
 468 {
 469         int ret;
 470         struct lock_file *lock_file = xcalloc(1, sizeof(struct lock_file));
 471
 472         hold_locked_index(lock_file, 1);
 473         if (read_cache_preload(NULL) < 0)
 474                 return error(_("corrupt index file"));
 475
 476         resolve_undo_clear();
 477         if (opts->force) {
 478                 ret = reset_tree(new->commit->tree, opts, 1, writeout_error);
 479                 if (ret)
 480                         return ret;
 481         } else {
 482                 struct tree_desc trees[2];
 483                 struct tree *tree;
 484                 struct unpack_trees_options topts;
 485
 486                 memset(&topts, 0, sizeof(topts));
 487                 topts.head_idx = -1;
 488                 topts.src_index = &the_index;
 489                 topts.dst_index = &the_index;
 490
 491                 setup_unpack_trees_porcelain(&topts, "checkout");
 492
 493                 refresh_cache(REFRESH_QUIET);
 494
 495                 if (unmerged_cache()) {
 496                         error(_("you need to resolve your current index first"));
 497                         return 1;
 498                 }
 499
 500                 /* 2-way merge to the new branch */
 501                 topts.initial_checkout = is_cache_unborn();
 502                 topts.update = 1;
 503                 topts.merge = 1;
 504                 topts.gently = opts->merge && old->commit;
 505                 topts.verbose_update = !opts->quiet && isatty(2);
 506                 topts.fn = twoway_merge;
 507                 if (opts->overwrite_ignore) {
 508                         topts.dir = xcalloc(1, sizeof(*topts.dir));
 509                         topts.dir->flags |= DIR_SHOW_IGNORED;
 510                         setup_standard_excludes(topts.dir);
 511                 }
 512                 tree = parse_tree_indirect(old->commit && !opts->new_worktree_mode ?
 513                                            old->commit->object.sha1 :
 514                                            EMPTY_TREE_SHA1_BIN);
 515                 init_tree_desc(&trees[0], tree->buffer, tree->size);
 516                 tree = parse_tree_indirect(new->commit->object.sha1);
 517                 init_tree_desc(&trees[1], tree->buffer, tree->size);
 518
 519                 ret = unpack_trees(2, trees, &topts);
 520                 if (ret == -1) {
 521                         /*
 522                          * Unpack couldn't do a trivial merge; either
 523                          * give up or do a real merge, depending on
 524                          * whether the merge flag was used.
 525                          */
 526                         struct tree *result;
 527                         struct tree *work;
 528                         struct merge_options o;
 529                         if (!opts->merge)
 530                                 return 1;
 531
 532                         /*
 533                          * Without old->commit, the below is the same as
 534                          * the two-tree unpack we already tried and failed.
 535                          */
 536                         if (!old->commit)
 537                                 return 1;
 538
 539                         /* Do more real merge */
 540
 541                         /*
 542                          * We update the index fully, then write the
 543                          * tree from the index, then merge the new
 544                          * branch with the current tree, with the old
 545                          * branch as the base. Then we reset the index
 546                          * (but not the working tree) to the new
 547                          * branch, leaving the working tree as the
 548                          * merged version, but skipping unmerged
 549                          * entries in the index.
 550                          */
 551
 552                         add_files_to_cache(NULL, NULL, 0);
 553                         /*
 554                          * NEEDSWORK: carrying over local changes
 555                          * when branches have different end-of-line
 556                          * normalization (or clean+smudge rules) is
 557                          * a pain; plumb in an option to set
 558                          * o.renormalize?
 559                          */
 560                         init_merge_options(&o);
 561                         o.verbosity = 0;
 562                         work = write_tree_from_memory(&o);
 563
 564                         ret = reset_tree(new->commit->tree, opts, 1,
 565                                          writeout_error);
 566                         if (ret)
 567                                 return ret;
 568                         o.ancestor = old->name;
 569                         o.branch1 = new->name;
 570                         o.branch2 = "local";
 571                         merge_trees(&o, new->commit->tree, work,
 572                                 old->commit->tree, &result);
 573                         ret = reset_tree(new->commit->tree, opts, 0,
 574                                          writeout_error);
 575                         if (ret)
 576                                 return ret;
 577                 }
 578         }
 579
 580         if (!active_cache_tree)
 581                 active_cache_tree = cache_tree();
 582
 583         if (!cache_tree_fully_valid(active_cache_tree))
 584                 cache_tree_update(&the_index, WRITE_TREE_SILENT | WRITE_TREE_REPAIR);
 585
 586         if (write_locked_index(&the_index, lock_file, COMMIT_LOCK))
 587                 die(_("unable to write new index file"));
 588
 589         if (!opts->force && !opts->quiet)
 590                 show_local_changes(&new->commit->object, &opts->diff_options);
 591
 592         return 0;
 593 }
 594
 595 static void report_tracking(struct branch_info *new)
 596 {
 597         struct strbuf sb = STRBUF_INIT;
 598         struct branch *branch = branch_get(new->name);
 599
 600         if (!format_tracking_info(branch, &sb))
 601                 return;
 602         fputs(sb.buf, stdout);
 603         strbuf_release(&sb);
 604 }
 605
 606 static void update_refs_for_switch(const struct checkout_opts *opts,
 607                                    struct branch_info *old,
 608                                    struct branch_info *new)
 609 {
 610         struct strbuf msg = STRBUF_INIT;
 611         const char *old_desc, *reflog_msg;
 612         if (opts->new_branch) {
 613                 if (opts->new_orphan_branch) {
 614                         if (opts->new_branch_log && !log_all_ref_updates) {
 615                                 int temp;
 616                                 struct strbuf log_file = STRBUF_INIT;
 617                                 int ret;
 618                                 const char *ref_name;
 619
 620                                 ref_name = mkpath("refs/heads/%s", opts->new_orphan_branch);
 621                                 temp = log_all_ref_updates;
 622                                 log_all_ref_updates = 1;
 623                                 ret = log_ref_setup(ref_name, &log_file);
 624                                 log_all_ref_updates = temp;
 625                                 strbuf_release(&log_file);
 626                                 if (ret) {
 627                                         fprintf(stderr, _("Can not do reflog for '%s'\n"),
 628                                             opts->new_orphan_branch);
 629                                         return;
 630                                 }
 631                         }
 632                 }
 633                 else
 634                         create_branch(old->name, opts->new_branch, new->name,
 635                                       opts->new_branch_force ? 1 : 0,
 636                                       opts->new_branch_log,
 637                                       opts->new_branch_force ? 1 : 0,
 638                                       opts->quiet,
 639                                       opts->track);
 640                 new->name = opts->new_branch;
 641                 setup_branch_path(new);
 642         }
 643
 644         old_desc = old->name;
 645         if (!old_desc && old->commit)
 646                 old_desc = sha1_to_hex(old->commit->object.sha1);
 647
 648         reflog_msg = getenv("GIT_REFLOG_ACTION");
 649         if (!reflog_msg)
 650                 strbuf_addf(&msg, "checkout: moving from %s to %s",
 651                         old_desc ? old_desc : "(invalid)", new->name);
 652         else
 653                 strbuf_insert(&msg, 0, reflog_msg, strlen(reflog_msg));
 654
 655         if (!strcmp(new->name, "HEAD") && !new->path && !opts->force_detach) {
 656                 /* Nothing to do. */
 657         } else if (opts->force_detach || !new->path) {  /* No longer on any branch. */
 658                 update_ref(msg.buf, "HEAD", new->commit->object.sha1, NULL,
 659                            REF_NODEREF, UPDATE_REFS_DIE_ON_ERR);
 660                 if (!opts->quiet) {
 661                         if (old->path && advice_detached_head)
 662                                 detach_advice(new->name);
 663                         describe_detached_head(_("HEAD is now at"), new->commit);
 664                 }
 665         } else if (new->path) { /* Switch branches. */
 666                 create_symref("HEAD", new->path, msg.buf);
 667                 if (!opts->quiet) {
 668                         if (old->path && !strcmp(new->path, old->path)) {
 669                                 if (opts->new_branch_force)
 670                                         fprintf(stderr, _("Reset branch '%s'\n"),
 671                                                 new->name);
 672                                 else
 673                                         fprintf(stderr, _("Already on '%s'\n"),
 674                                                 new->name);
 675                         } else if (opts->new_branch) {
 676                                 if (opts->branch_exists)
 677                                         fprintf(stderr, _("Switched to and reset branch '%s'\n"), new->name);
 678                                 else
 679                                         fprintf(stderr, _("Switched to a new branch '%s'\n"), new->name);
 680                         } else {
 681                                 fprintf(stderr, _("Switched to branch '%s'\n"),
 682                                         new->name);
 683                         }
 684                 }
 685                 if (old->path && old->name) {
 686                         if (!ref_exists(old->path) && reflog_exists(old->path))
 687                                 delete_reflog(old->path);
 688                 }
 689         }
 690         remove_branch_state();
 691         strbuf_release(&msg);
 692         if (!opts->quiet &&
 693             (new->path || (!opts->force_detach && !strcmp(new->name, "HEAD"))))
 694                 report_tracking(new);
 695 }
 696
 697 static int add_pending_uninteresting_ref(const char *refname,
 698                                          const struct object_id *oid,
 699                                          int flags, void *cb_data)
 700 {
 701         add_pending_sha1(cb_data, refname, oid->hash, UNINTERESTING);
 702         return 0;
 703 }
 704
 705 static void describe_one_orphan(struct strbuf *sb, struct commit *commit)
 706 {
 707         strbuf_addstr(sb, "  ");
 708         strbuf_addstr(sb,
 709                 find_unique_abbrev(commit->object.sha1, DEFAULT_ABBREV));
 710         strbuf_addch(sb, ' ');
 711         if (!parse_commit(commit))
 712                 pp_commit_easy(CMIT_FMT_ONELINE, commit, sb);
 713         strbuf_addch(sb, '\n');
 714 }
 715
 716 #define ORPHAN_CUTOFF 4
 717 static void suggest_reattach(struct commit *commit, struct rev_info *revs)
 718 {
 719         struct commit *c, *last = NULL;
 720         struct strbuf sb = STRBUF_INIT;
 721         int lost = 0;
 722         while ((c = get_revision(revs)) != NULL) {
 723                 if (lost < ORPHAN_CUTOFF)
 724                         describe_one_orphan(&sb, c);
 725                 last = c;
 726                 lost++;
 727         }
 728         if (ORPHAN_CUTOFF < lost) {
 729                 int more = lost - ORPHAN_CUTOFF;
 730                 if (more == 1)
 731                         describe_one_orphan(&sb, last);
 732                 else
 733                         strbuf_addf(&sb, _(" ... and %d more.\n"), more);
 734         }
 735
 736         fprintf(stderr,
 737                 Q_(
 738                 /* The singular version */
 739                 "Warning: you are leaving %d commit behind, "
 740                 "not connected to\n"
 741                 "any of your branches:\n\n"
 742                 "%s\n",
 743                 /* The plural version */
 744                 "Warning: you are leaving %d commits behind, "
 745                 "not connected to\n"
 746                 "any of your branches:\n\n"
 747                 "%s\n",
 748                 /* Give ngettext() the count */
 749                 lost),
 750                 lost,
 751                 sb.buf);
 752         strbuf_release(&sb);
 753
 754         if (advice_detached_head)
 755                 fprintf(stderr,
 756                         Q_(
 757                         /* The singular version */
 758                         "If you want to keep it by creating a new branch, "
 759                         "this may be a good time\nto do so with:\n\n"
 760                         " git branch <new-branch-name> %s\n\n",
 761                         /* The plural version */
 762                         "If you want to keep them by creating a new branch, "
 763                         "this may be a good time\nto do so with:\n\n"
 764                         " git branch <new-branch-name> %s\n\n",
 765                         /* Give ngettext() the count */
 766                         lost),
 767                         find_unique_abbrev(commit->object.sha1, DEFAULT_ABBREV));
 768 }
 769
 770 /*
 771  * We are about to leave commit that was at the tip of a detached
 772  * HEAD.  If it is not reachable from any ref, this is the last chance
 773  * for the user to do so without resorting to reflog.
 774  */
 775 static void orphaned_commit_warning(struct commit *old, struct commit *new)
 776 {
 777         struct rev_info revs;
 778         struct object *object = &old->object;
 779         struct object_array refs;
 780
 781         init_revisions(&revs, NULL);
 782         setup_revisions(0, NULL, &revs, NULL);
 783
 784         object->flags &= ~UNINTERESTING;
 785         add_pending_object(&revs, object, sha1_to_hex(object->sha1));
 786
 787         for_each_ref(add_pending_uninteresting_ref, &revs);
 788         add_pending_sha1(&revs, "HEAD", new->object.sha1, UNINTERESTING);
 789
 790         refs = revs.pending;
 791         revs.leak_pending = 1;
 792
 793         if (prepare_revision_walk(&revs))
 794                 die(_("internal error in revision walk"));
 795         if (!(old->object.flags & UNINTERESTING))
 796                 suggest_reattach(old, &revs);
 797         else
 798                 describe_detached_head(_("Previous HEAD position was"), old);
 799
 800         clear_commit_marks_for_object_array(&refs, ALL_REV_FLAGS);
 801         free(refs.objects);
 802 }
 803
 804 static int switch_branches(const struct checkout_opts *opts,
 805                            struct branch_info *new)
 806 {
 807         int ret = 0;
 808         struct branch_info old;
 809         void *path_to_free;
 810         unsigned char rev[20];
 811         int flag, writeout_error = 0;
 812         memset(&old, 0, sizeof(old));
 813         old.path = path_to_free = resolve_refdup("HEAD", 0, rev, &flag);
 814         old.commit = lookup_commit_reference_gently(rev, 1);
 815         if (!(flag & REF_ISSYMREF))
 816                 old.path = NULL;
 817
 818         if (old.path)
 819                 skip_prefix(old.path, "refs/heads/", &old.name);
 820
 821         if (!new->name) {
 822                 new->name = "HEAD";
 823                 new->commit = old.commit;
 824                 if (!new->commit)
 825                         die(_("You are on a branch yet to be born"));
 826                 parse_commit_or_die(new->commit);
 827         }
 828
 829         ret = merge_working_tree(opts, &old, new, &writeout_error);
 830         if (ret) {
 831                 free(path_to_free);
 832                 return ret;
 833         }
 834
 835         if (!opts->quiet && !old.path && old.commit &&
 836             new->commit != old.commit && !opts->new_worktree_mode)
 837                 orphaned_commit_warning(old.commit, new->commit);
 838
 839         update_refs_for_switch(opts, &old, new);
 840
 841         ret = post_checkout_hook(old.commit, new->commit, 1);
 842         free(path_to_free);
 843         return ret || writeout_error;
 844 }
 845
 846 static int git_checkout_config(const char *var, const char *value, void *cb)
 847 {
 848         if (!strcmp(var, "diff.ignoresubmodules")) {
 849                 struct checkout_opts *opts = cb;
 850                 handle_ignore_submodules_arg(&opts->diff_options, value);
 851                 return 0;
 852         }
 853
 854         if (starts_with(var, "submodule."))
 855                 return parse_submodule_config_option(var, value);
 856
 857         return git_xmerge_config(var, value, NULL);
 858 }
 859
 860 struct tracking_name_data {
 861         /* const */ char *src_ref;
 862         char *dst_ref;
 863         unsigned char *dst_sha1;
 864         int unique;
 865 };
 866
 867 static int check_tracking_name(struct remote *remote, void *cb_data)
 868 {
 869         struct tracking_name_data *cb = cb_data;
 870         struct refspec query;
 871         memset(&query, 0, sizeof(struct refspec));
 872         query.src = cb->src_ref;
 873         if (remote_find_tracking(remote, &query) ||
 874             get_sha1(query.dst, cb->dst_sha1)) {
 875                 free(query.dst);
 876                 return 0;
 877         }
 878         if (cb->dst_ref) {
 879                 free(query.dst);
 880                 cb->unique = 0;
 881                 return 0;
 882         }
 883         cb->dst_ref = query.dst;
 884         return 0;
 885 }
 886
 887 static const char *unique_tracking_name(const char *name, unsigned char *sha1)
 888 {
 889         struct tracking_name_data cb_data = { NULL, NULL, NULL, 1 };
 890         char src_ref[PATH_MAX];
 891         snprintf(src_ref, PATH_MAX, "refs/heads/%s", name);
 892         cb_data.src_ref = src_ref;
 893         cb_data.dst_sha1 = sha1;
 894         for_each_remote(check_tracking_name, &cb_data);
 895         if (cb_data.unique)
 896                 return cb_data.dst_ref;
 897         free(cb_data.dst_ref);
 898         return NULL;
 899 }
 900
 901 static void check_linked_checkout(struct branch_info *new, const char *id)
 902 {
 903         struct strbuf sb = STRBUF_INIT;
 904         struct strbuf path = STRBUF_INIT;
 905         struct strbuf gitdir = STRBUF_INIT;
 906         const char *start, *end;
 907
 908         if (id)
 909                 strbuf_addf(&path, "%s/worktrees/%s/HEAD", get_git_common_dir(), id);
 910         else
 911                 strbuf_addf(&path, "%s/HEAD", get_git_common_dir());
 912
 913         if (strbuf_read_file(&sb, path.buf, 0) < 0 ||
 914             !skip_prefix(sb.buf, "ref:", &start))
 915                 goto done;
 916         while (isspace(*start))
 917                 start++;
 918         end = start;
 919         while (*end && !isspace(*end))
 920                 end++;
 921         if (strncmp(start, new->path, end - start) || new->path[end - start] != '\0')
 922                 goto done;
 923         if (id) {
 924                 strbuf_reset(&path);
 925                 strbuf_addf(&path, "%s/worktrees/%s/gitdir", get_git_common_dir(), id);
 926                 if (strbuf_read_file(&gitdir, path.buf, 0) <= 0)
 927                         goto done;
 928                 strbuf_rtrim(&gitdir);
 929         } else
 930                 strbuf_addstr(&gitdir, get_git_common_dir());
 931         die(_("'%s' is already checked out at '%s'"), new->name, gitdir.buf);
 932 done:
 933         strbuf_release(&path);
 934         strbuf_release(&sb);
 935         strbuf_release(&gitdir);
 936 }
 937
 938 static void check_linked_checkouts(struct branch_info *new)
 939 {
 940         struct strbuf path = STRBUF_INIT;
 941         DIR *dir;
 942         struct dirent *d;
 943
 944         strbuf_addf(&path, "%s/worktrees", get_git_common_dir());
 945         if ((dir = opendir(path.buf)) == NULL) {
 946                 strbuf_release(&path);
 947                 return;
 948         }
 949
 950         /*
 951          * $GIT_COMMON_DIR/HEAD is practically outside
 952          * $GIT_DIR so resolve_ref_unsafe() won't work (it
 953          * uses git_path). Parse the ref ourselves.
 954          */
 955         check_linked_checkout(new, NULL);
 956
 957         while ((d = readdir(dir)) != NULL) {
 958                 if (!strcmp(d->d_name, ".") || !strcmp(d->d_name, ".."))
 959                         continue;
 960                 check_linked_checkout(new, d->d_name);
 961         }
 962         strbuf_release(&path);
 963         closedir(dir);
 964 }
 965
 966 static int parse_branchname_arg(int argc, const char **argv,
 967                                 int dwim_new_local_branch_ok,
 968                                 struct branch_info *new,
 969                                 struct checkout_opts *opts,
 970                                 unsigned char rev[20])
 971 {
 972         struct tree **source_tree = &opts->source_tree;
 973         const char **new_branch = &opts->new_branch;
 974         int argcount = 0;
 975         unsigned char branch_rev[20];
 976         const char *arg;
 977         int dash_dash_pos;
 978         int has_dash_dash = 0;
 979         int i;
 980
 981         /*
 982          * case 1: git checkout <ref> -- [<paths>]
 983          *
 984          *   <ref> must be a valid tree, everything after the '--' must be
 985          *   a path.
 986          *
 987          * case 2: git checkout -- [<paths>]
 988          *
 989          *   everything after the '--' must be paths.
 990          *
 991          * case 3: git checkout <something> [--]
 992          *
 993          *   (a) If <something> is a commit, that is to
 994          *       switch to the branch or detach HEAD at it.  As a special case,
 995          *       if <something> is A...B (missing A or B means HEAD but you can
 996          *       omit at most one side), and if there is a unique merge base
 997          *       between A and B, A...B names that merge base.
 998          *
 999          *   (b) If <something> is _not_ a commit, either "--" is present
1000          *       or <something> is not a path, no -t or -b was given, and
1001          *       and there is a tracking branch whose name is <something>
1002          *       in one and only one remote, then this is a short-hand to
1003          *       fork local <something> from that remote-tracking branch.
1004          *
1005          *   (c) Otherwise, if "--" is present, treat it like case (1).
1006          *
1007          *   (d) Otherwise :
1008          *       - if it's a reference, treat it like case (1)
1009          *       - else if it's a path, treat it like case (2)
1010          *       - else: fail.
1011          *
1012          * case 4: git checkout <something> <paths>
1013          *
1014          *   The first argument must not be ambiguous.
1015          *   - If it's *only* a reference, treat it like case (1).
1016          *   - If it's only a path, treat it like case (2).
1017          *   - else: fail.
1018          *
1019          */
1020         if (!argc)
1021                 return 0;
1022
1023         arg = argv[0];
1024         dash_dash_pos = -1;
1025         for (i = 0; i < argc; i++) {
1026                 if (!strcmp(argv[i], "--")) {
1027                         dash_dash_pos = i;
1028                         break;
1029                 }
1030         }
1031         if (dash_dash_pos == 0)
1032                 return 1; /* case (2) */
1033         else if (dash_dash_pos == 1)
1034                 has_dash_dash = 1; /* case (3) or (1) */
1035         else if (dash_dash_pos >= 2)
1036                 die(_("only one reference expected, %d given."), dash_dash_pos);
1037
1038         if (!strcmp(arg, "-"))
1039                 arg = "@{-1}";
1040
1041         if (get_sha1_mb(arg, rev)) {
1042                 /*
1043                  * Either case (3) or (4), with <something> not being
1044                  * a commit, or an attempt to use case (1) with an
1045                  * invalid ref.
1046                  *
1047                  * It's likely an error, but we need to find out if
1048                  * we should auto-create the branch, case (3).(b).
1049                  */
1050                 int recover_with_dwim = dwim_new_local_branch_ok;
1051
1052                 if (check_filename(NULL, arg) && !has_dash_dash)
1053                         recover_with_dwim = 0;
1054                 /*
1055                  * Accept "git checkout foo" and "git checkout foo --"
1056                  * as candidates for dwim.
1057                  */
1058                 if (!(argc == 1 && !has_dash_dash) &&
1059                     !(argc == 2 && has_dash_dash))
1060                         recover_with_dwim = 0;
1061
1062                 if (recover_with_dwim) {
1063                         const char *remote = unique_tracking_name(arg, rev);
1064                         if (remote) {
1065                                 *new_branch = arg;
1066                                 arg = remote;
1067                                 /* DWIMmed to create local branch, case (3).(b) */
1068                         } else {
1069                                 recover_with_dwim = 0;
1070                         }
1071                 }
1072
1073                 if (!recover_with_dwim) {
1074                         if (has_dash_dash)
1075                                 die(_("invalid reference: %s"), arg);
1076                         return argcount;
1077                 }
1078         }
1079
1080         /* we can't end up being in (2) anymore, eat the argument */
1081         argcount++;
1082         argv++;
1083         argc--;
1084
1085         new->name = arg;
1086         setup_branch_path(new);
1087
1088         if (!check_refname_format(new->path, 0) &&
1089             !read_ref(new->path, branch_rev))
1090                 hashcpy(rev, branch_rev);
1091         else
1092                 new->path = NULL; /* not an existing branch */
1093
1094         new->commit = lookup_commit_reference_gently(rev, 1);
1095         if (!new->commit) {
1096                 /* not a commit */
1097                 *source_tree = parse_tree_indirect(rev);
1098         } else {
1099                 parse_commit_or_die(new->commit);
1100                 *source_tree = new->commit->tree;
1101         }
1102
1103         if (!*source_tree)                   /* case (1): want a tree */
1104                 die(_("reference is not a tree: %s"), arg);
1105         if (!has_dash_dash) {/* case (3).(d) -> (1) */
1106                 /*
1107                  * Do not complain the most common case
1108                  *      git checkout branch
1109                  * even if there happen to be a file called 'branch';
1110                  * it would be extremely annoying.
1111                  */
1112                 if (argc)
1113                         verify_non_filename(NULL, arg);
1114         } else {
1115                 argcount++;
1116                 argv++;
1117                 argc--;
1118         }
1119
1120         return argcount;
1121 }
1122
1123 static int switch_unborn_to_new_branch(const struct checkout_opts *opts)
1124 {
1125         int status;
1126         struct strbuf branch_ref = STRBUF_INIT;
1127
1128         if (!opts->new_branch)
1129                 die(_("You are on a branch yet to be born"));
1130         strbuf_addf(&branch_ref, "refs/heads/%s", opts->new_branch);
1131         status = create_symref("HEAD", branch_ref.buf, "checkout -b");
1132         strbuf_release(&branch_ref);
1133         if (!opts->quiet)
1134                 fprintf(stderr, _("Switched to a new branch '%s'\n"),
1135                         opts->new_branch);
1136         return status;
1137 }
1138
1139 static int checkout_branch(struct checkout_opts *opts,
1140                            struct branch_info *new)
1141 {
1142         if (opts->pathspec.nr)
1143                 die(_("paths cannot be used with switching branches"));
1144
1145         if (opts->patch_mode)
1146                 die(_("'%s' cannot be used with switching branches"),
1147                     "--patch");
1148
1149         if (opts->writeout_stage)
1150                 die(_("'%s' cannot be used with switching branches"),
1151                     "--ours/--theirs");
1152
1153         if (opts->force && opts->merge)
1154                 die(_("'%s' cannot be used with '%s'"), "-f", "-m");
1155
1156         if (opts->force_detach && opts->new_branch)
1157                 die(_("'%s' cannot be used with '%s'"),
1158                     "--detach", "-b/-B/--orphan");
1159
1160         if (opts->new_orphan_branch) {
1161                 if (opts->track != BRANCH_TRACK_UNSPECIFIED)
1162                         die(_("'%s' cannot be used with '%s'"), "--orphan", "-t");
1163         } else if (opts->force_detach) {
1164                 if (opts->track != BRANCH_TRACK_UNSPECIFIED)
1165                         die(_("'%s' cannot be used with '%s'"), "--detach", "-t");
1166         } else if (opts->track == BRANCH_TRACK_UNSPECIFIED)
1167                 opts->track = git_branch_track;
1168
1169         if (new->name && !new->commit)
1170                 die(_("Cannot switch branch to a non-commit '%s'"),
1171                     new->name);
1172
1173         if (new->path && !opts->force_detach && !opts->new_branch) {
1174                 unsigned char sha1[20];
1175                 int flag;
1176                 char *head_ref = resolve_refdup("HEAD", 0, sha1, &flag);
1177                 if (head_ref &&
1178                     (!(flag & REF_ISSYMREF) || strcmp(head_ref, new->path)) &&
1179                     !opts->ignore_other_worktrees)
1180                         check_linked_checkouts(new);
1181                 free(head_ref);
1182         }
1183
1184         if (!new->commit && opts->new_branch) {
1185                 unsigned char rev[20];
1186                 int flag;
1187
1188                 if (!read_ref_full("HEAD", 0, rev, &flag) &&
1189                     (flag & REF_ISSYMREF) && is_null_sha1(rev))
1190                         return switch_unborn_to_new_branch(opts);
1191         }
1192         return switch_branches(opts, new);
1193 }
1194
1195 int cmd_checkout(int argc, const char **argv, const char *prefix)
1196 {
1197         struct checkout_opts opts;
1198         struct branch_info new;
1199         char *conflict_style = NULL;
1200         int dwim_new_local_branch = 1;
1201         struct option options[] = {
1202                 OPT__QUIET(&opts.quiet, N_("suppress progress reporting")),
1203                 OPT_STRING('b', NULL, &opts.new_branch, N_("branch"),
1204                            N_("create and checkout a new branch")),
1205                 OPT_STRING('B', NULL, &opts.new_branch_force, N_("branch"),
1206                            N_("create/reset and checkout a branch")),
1207                 OPT_BOOL('l', NULL, &opts.new_branch_log, N_("create reflog for new branch")),
1208                 OPT_BOOL(0, "detach", &opts.force_detach, N_("detach the HEAD at named commit")),
1209                 OPT_SET_INT('t', "track",  &opts.track, N_("set upstream info for new branch"),
1210                         BRANCH_TRACK_EXPLICIT),
1211                 OPT_STRING(0, "orphan", &opts.new_orphan_branch, N_("new-branch"), N_("new unparented branch")),
1212                 OPT_SET_INT('2', "ours", &opts.writeout_stage, N_("checkout our version for unmerged files"),
1213                             2),
1214                 OPT_SET_INT('3', "theirs", &opts.writeout_stage, N_("checkout their version for unmerged files"),
1215                             3),
1216                 OPT__FORCE(&opts.force, N_("force checkout (throw away local modifications)")),
1217                 OPT_BOOL('m', "merge", &opts.merge, N_("perform a 3-way merge with the new branch")),
1218                 OPT_BOOL(0, "overwrite-ignore", &opts.overwrite_ignore, N_("update ignored files (default)")),
1219                 OPT_STRING(0, "conflict", &conflict_style, N_("style"),
1220                            N_("conflict style (merge or diff3)")),
1221                 OPT_BOOL('p', "patch", &opts.patch_mode, N_("select hunks interactively")),
1222                 OPT_BOOL(0, "ignore-skip-worktree-bits", &opts.ignore_skipworktree,
1223                          N_("do not limit pathspecs to sparse entries only")),
1224                 OPT_HIDDEN_BOOL(0, "guess", &dwim_new_local_branch,
1225                                 N_("second guess 'git checkout <no-such-branch>'")),
1226                 OPT_BOOL(0, "ignore-other-worktrees", &opts.ignore_other_worktrees,
1227                          N_("do not check if another worktree is holding the given ref")),
1228                 OPT_END(),
1229         };
1230
1231         memset(&opts, 0, sizeof(opts));
1232         memset(&new, 0, sizeof(new));
1233         opts.overwrite_ignore = 1;
1234         opts.prefix = prefix;
1235
1236         gitmodules_config();
1237         git_config(git_checkout_config, &opts);
1238
1239         opts.track = BRANCH_TRACK_UNSPECIFIED;
1240
1241         argc = parse_options(argc, argv, prefix, options, checkout_usage,
1242                              PARSE_OPT_KEEP_DASHDASH);
1243
1244         opts.new_worktree_mode = getenv("GIT_CHECKOUT_NEW_WORKTREE") != NULL;
1245
1246         if (conflict_style) {
1247                 opts.merge = 1; /* implied */
1248                 git_xmerge_config("merge.conflictstyle", conflict_style, NULL);
1249         }
1250
1251         if ((!!opts.new_branch + !!opts.new_branch_force + !!opts.new_orphan_branch) > 1)
1252                 die(_("-b, -B and --orphan are mutually exclusive"));
1253
1254         /*
1255          * From here on, new_branch will contain the branch to be checked out,
1256          * and new_branch_force and new_orphan_branch will tell us which one of
1257          * -b/-B/--orphan is being used.
1258          */
1259         if (opts.new_branch_force)
1260                 opts.new_branch = opts.new_branch_force;
1261
1262         if (opts.new_orphan_branch)
1263                 opts.new_branch = opts.new_orphan_branch;
1264
1265         /* --track without -b/-B/--orphan should DWIM */
1266         if (opts.track != BRANCH_TRACK_UNSPECIFIED && !opts.new_branch) {
1267                 const char *argv0 = argv[0];
1268                 if (!argc || !strcmp(argv0, "--"))
1269                         die (_("--track needs a branch name"));
1270                 skip_prefix(argv0, "refs/", &argv0);
1271                 skip_prefix(argv0, "remotes/", &argv0);
1272                 argv0 = strchr(argv0, '/');
1273                 if (!argv0 || !argv0[1])
1274                         die (_("Missing branch name; try -b"));
1275                 opts.new_branch = argv0 + 1;
1276         }
1277
1278         /*
1279          * Extract branch name from command line arguments, so
1280          * all that is left is pathspecs.
1281          *
1282          * Handle
1283          *
1284          *  1) git checkout <tree> -- [<paths>]
1285          *  2) git checkout -- [<paths>]
1286          *  3) git checkout <something> [<paths>]
1287          *
1288          * including "last branch" syntax and DWIM-ery for names of
1289          * remote branches, erroring out for invalid or ambiguous cases.
1290          */
1291         if (argc) {
1292                 unsigned char rev[20];
1293                 int dwim_ok =
1294                         !opts.patch_mode &&
1295                         dwim_new_local_branch &&
1296                         opts.track == BRANCH_TRACK_UNSPECIFIED &&
1297                         !opts.new_branch;
1298                 int n = parse_branchname_arg(argc, argv, dwim_ok,
1299                                              &new, &opts, rev);
1300                 argv += n;
1301                 argc -= n;
1302         }
1303
1304         if (argc) {
1305                 parse_pathspec(&opts.pathspec, 0,
1306                                opts.patch_mode ? PATHSPEC_PREFIX_ORIGIN : 0,
1307                                prefix, argv);
1308
1309                 if (!opts.pathspec.nr)
1310                         die(_("invalid path specification"));
1311
1312                 /*
1313                  * Try to give more helpful suggestion.
1314                  * new_branch && argc > 1 will be caught later.
1315                  */
1316                 if (opts.new_branch && argc == 1)
1317                         die(_("Cannot update paths and switch to branch '%s' at the same time.\n"
1318                               "Did you intend to checkout '%s' which can not be resolved as commit?"),
1319                             opts.new_branch, argv[0]);
1320
1321                 if (opts.force_detach)
1322                         die(_("git checkout: --detach does not take a path argument '%s'"),
1323                             argv[0]);
1324
1325                 if (1 < !!opts.writeout_stage + !!opts.force + !!opts.merge)
1326                         die(_("git checkout: --ours/--theirs, --force and --merge are incompatible when\n"
1327                               "checking out of the index."));
1328         }
1329
1330         if (opts.new_branch) {
1331                 struct strbuf buf = STRBUF_INIT;
1332
1333                 opts.branch_exists =
1334                         validate_new_branchname(opts.new_branch, &buf,
1335                                                 !!opts.new_branch_force,
1336                                                 !!opts.new_branch_force);
1337
1338                 strbuf_release(&buf);
1339         }
1340
1341         if (opts.patch_mode || opts.pathspec.nr)
1342                 return checkout_paths(&opts, new.name);
1343         else
1344                 return checkout_branch(&opts, &new);
1345 }