builtin-checkout.c

   1 #include "cache.h"
   2 #include "builtin.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 "unpack-trees.h"
   9 #include "dir.h"
  10 #include "run-command.h"
  11 #include "merge-recursive.h"
  12 #include "branch.h"
  13 #include "diff.h"
  14 #include "revision.h"
  15 #include "remote.h"
  16 #include "blob.h"
  17 #include "xdiff-interface.h"
  18 #include "ll-merge.h"
  19
  20 static const char * const checkout_usage[] = {
  21         "git checkout [options] <branch>",
  22         "git checkout [options] [<branch>] -- <file>...",
  23         NULL,
  24 };
  25
  26 struct checkout_opts {
  27         int quiet;
  28         int merge;
  29         int force;
  30         int writeout_stage;
  31         int writeout_error;
  32
  33         const char *new_branch;
  34         int new_branch_log;
  35         enum branch_track track;
  36 };
  37
  38 static int post_checkout_hook(struct commit *old, struct commit *new,
  39                               int changed)
  40 {
  41         return run_hook(NULL, "post-checkout",
  42                         sha1_to_hex(old ? old->object.sha1 : null_sha1),
  43                         sha1_to_hex(new ? new->object.sha1 : null_sha1),
  44                         changed ? "1" : "0", NULL);
  45         /* "new" can be NULL when checking out from the index before
  46            a commit exists. */
  47
  48 }
  49
  50 static int update_some(const unsigned char *sha1, const char *base, int baselen,
  51                 const char *pathname, unsigned mode, int stage, void *context)
  52 {
  53         int len;
  54         struct cache_entry *ce;
  55
  56         if (S_ISDIR(mode))
  57                 return READ_TREE_RECURSIVE;
  58
  59         len = baselen + strlen(pathname);
  60         ce = xcalloc(1, cache_entry_size(len));
  61         hashcpy(ce->sha1, sha1);
  62         memcpy(ce->name, base, baselen);
  63         memcpy(ce->name + baselen, pathname, len - baselen);
  64         ce->ce_flags = create_ce_flags(len, 0);
  65         ce->ce_mode = create_ce_mode(mode);
  66         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
  67         return 0;
  68 }
  69
  70 static int read_tree_some(struct tree *tree, const char **pathspec)
  71 {
  72         read_tree_recursive(tree, "", 0, 0, pathspec, update_some, NULL);
  73
  74         /* update the index with the given tree's info
  75          * for all args, expanding wildcards, and exit
  76          * with any non-zero return code.
  77          */
  78         return 0;
  79 }
  80
  81 static int skip_same_name(struct cache_entry *ce, int pos)
  82 {
  83         while (++pos < active_nr &&
  84                !strcmp(active_cache[pos]->name, ce->name))
  85                 ; /* skip */
  86         return pos;
  87 }
  88
  89 static int check_stage(int stage, struct cache_entry *ce, int pos)
  90 {
  91         while (pos < active_nr &&
  92                !strcmp(active_cache[pos]->name, ce->name)) {
  93                 if (ce_stage(active_cache[pos]) == stage)
  94                         return 0;
  95                 pos++;
  96         }
  97         return error("path '%s' does not have %s version",
  98                      ce->name,
  99                      (stage == 2) ? "our" : "their");
 100 }
 101
 102 static int check_all_stages(struct cache_entry *ce, int pos)
 103 {
 104         if (ce_stage(ce) != 1 ||
 105             active_nr <= pos + 2 ||
 106             strcmp(active_cache[pos+1]->name, ce->name) ||
 107             ce_stage(active_cache[pos+1]) != 2 ||
 108             strcmp(active_cache[pos+2]->name, ce->name) ||
 109             ce_stage(active_cache[pos+2]) != 3)
 110                 return error("path '%s' does not have all three versions",
 111                              ce->name);
 112         return 0;
 113 }
 114
 115 static int checkout_stage(int stage, struct cache_entry *ce, int pos,
 116                           struct checkout *state)
 117 {
 118         while (pos < active_nr &&
 119                !strcmp(active_cache[pos]->name, ce->name)) {
 120                 if (ce_stage(active_cache[pos]) == stage)
 121                         return checkout_entry(active_cache[pos], state, NULL);
 122                 pos++;
 123         }
 124         return error("path '%s' does not have %s version",
 125                      ce->name,
 126                      (stage == 2) ? "our" : "their");
 127 }
 128
 129 /* NEEDSWORK: share with merge-recursive */
 130 static void fill_mm(const unsigned char *sha1, mmfile_t *mm)
 131 {
 132         unsigned long size;
 133         enum object_type type;
 134
 135         if (!hashcmp(sha1, null_sha1)) {
 136                 mm->ptr = xstrdup("");
 137                 mm->size = 0;
 138                 return;
 139         }
 140
 141         mm->ptr = read_sha1_file(sha1, &type, &size);
 142         if (!mm->ptr || type != OBJ_BLOB)
 143                 die("unable to read blob object %s", sha1_to_hex(sha1));
 144         mm->size = size;
 145 }
 146
 147 static int checkout_merged(int pos, struct checkout *state)
 148 {
 149         struct cache_entry *ce = active_cache[pos];
 150         const char *path = ce->name;
 151         mmfile_t ancestor, ours, theirs;
 152         int status;
 153         unsigned char sha1[20];
 154         mmbuffer_t result_buf;
 155
 156         if (ce_stage(ce) != 1 ||
 157             active_nr <= pos + 2 ||
 158             strcmp(active_cache[pos+1]->name, path) ||
 159             ce_stage(active_cache[pos+1]) != 2 ||
 160             strcmp(active_cache[pos+2]->name, path) ||
 161             ce_stage(active_cache[pos+2]) != 3)
 162                 return error("path '%s' does not have all 3 versions", path);
 163
 164         fill_mm(active_cache[pos]->sha1, &ancestor);
 165         fill_mm(active_cache[pos+1]->sha1, &ours);
 166         fill_mm(active_cache[pos+2]->sha1, &theirs);
 167
 168         status = ll_merge(&result_buf, path, &ancestor,
 169                           &ours, "ours", &theirs, "theirs", 1);
 170         free(ancestor.ptr);
 171         free(ours.ptr);
 172         free(theirs.ptr);
 173         if (status < 0 || !result_buf.ptr) {
 174                 free(result_buf.ptr);
 175                 return error("path '%s': cannot merge", path);
 176         }
 177
 178         /*
 179          * NEEDSWORK:
 180          * There is absolutely no reason to write this as a blob object
 181          * and create a phoney cache entry just to leak.  This hack is
 182          * primarily to get to the write_entry() machinery that massages
 183          * the contents to work-tree format and writes out which only
 184          * allows it for a cache entry.  The code in write_entry() needs
 185          * to be refactored to allow us to feed a <buffer, size, mode>
 186          * instead of a cache entry.  Such a refactoring would help
 187          * merge_recursive as well (it also writes the merge result to the
 188          * object database even when it may contain conflicts).
 189          */
 190         if (write_sha1_file(result_buf.ptr, result_buf.size,
 191                             blob_type, sha1))
 192                 die("Unable to add merge result for '%s'", path);
 193         ce = make_cache_entry(create_ce_mode(active_cache[pos+1]->ce_mode),
 194                               sha1,
 195                               path, 2, 0);
 196         if (!ce)
 197                 die("make_cache_entry failed for path '%s'", path);
 198         status = checkout_entry(ce, state, NULL);
 199         return status;
 200 }
 201
 202 static int checkout_paths(struct tree *source_tree, const char **pathspec,
 203                           struct checkout_opts *opts)
 204 {
 205         int pos;
 206         struct checkout state;
 207         static char *ps_matched;
 208         unsigned char rev[20];
 209         int flag;
 210         struct commit *head;
 211         int errs = 0;
 212         int stage = opts->writeout_stage;
 213         int merge = opts->merge;
 214         int newfd;
 215         struct lock_file *lock_file = xcalloc(1, sizeof(struct lock_file));
 216
 217         newfd = hold_locked_index(lock_file, 1);
 218         if (read_cache() < 0)
 219                 return error("corrupt index file");
 220
 221         if (source_tree)
 222                 read_tree_some(source_tree, pathspec);
 223
 224         for (pos = 0; pathspec[pos]; pos++)
 225                 ;
 226         ps_matched = xcalloc(1, pos);
 227
 228         for (pos = 0; pos < active_nr; pos++) {
 229                 struct cache_entry *ce = active_cache[pos];
 230                 match_pathspec(pathspec, ce->name, ce_namelen(ce), 0, ps_matched);
 231         }
 232
 233         if (report_path_error(ps_matched, pathspec, 0))
 234                 return 1;
 235
 236         /* Any unmerged paths? */
 237         for (pos = 0; pos < active_nr; pos++) {
 238                 struct cache_entry *ce = active_cache[pos];
 239                 if (match_pathspec(pathspec, ce->name, ce_namelen(ce), 0, NULL)) {
 240                         if (!ce_stage(ce))
 241                                 continue;
 242                         if (opts->force) {
 243                                 warning("path '%s' is unmerged", ce->name);
 244                         } else if (stage) {
 245                                 errs |= check_stage(stage, ce, pos);
 246                         } else if (opts->merge) {
 247                                 errs |= check_all_stages(ce, pos);
 248                         } else {
 249                                 errs = 1;
 250                                 error("path '%s' is unmerged", ce->name);
 251                         }
 252                         pos = skip_same_name(ce, pos) - 1;
 253                 }
 254         }
 255         if (errs)
 256                 return 1;
 257
 258         /* Now we are committed to check them out */
 259         memset(&state, 0, sizeof(state));
 260         state.force = 1;
 261         state.refresh_cache = 1;
 262         for (pos = 0; pos < active_nr; pos++) {
 263                 struct cache_entry *ce = active_cache[pos];
 264                 if (match_pathspec(pathspec, ce->name, ce_namelen(ce), 0, NULL)) {
 265                         if (!ce_stage(ce)) {
 266                                 errs |= checkout_entry(ce, &state, NULL);
 267                                 continue;
 268                         }
 269                         if (stage)
 270                                 errs |= checkout_stage(stage, ce, pos, &state);
 271                         else if (merge)
 272                                 errs |= checkout_merged(pos, &state);
 273                         pos = skip_same_name(ce, pos) - 1;
 274                 }
 275         }
 276
 277         if (write_cache(newfd, active_cache, active_nr) ||
 278             commit_locked_index(lock_file))
 279                 die("unable to write new index file");
 280
 281         resolve_ref("HEAD", rev, 0, &flag);
 282         head = lookup_commit_reference_gently(rev, 1);
 283
 284         errs |= post_checkout_hook(head, head, 0);
 285         return errs;
 286 }
 287
 288 static void show_local_changes(struct object *head)
 289 {
 290         struct rev_info rev;
 291         /* I think we want full paths, even if we're in a subdirectory. */
 292         init_revisions(&rev, NULL);
 293         rev.abbrev = 0;
 294         rev.diffopt.output_format |= DIFF_FORMAT_NAME_STATUS;
 295         if (diff_setup_done(&rev.diffopt) < 0)
 296                 die("diff_setup_done failed");
 297         add_pending_object(&rev, head, NULL);
 298         run_diff_index(&rev, 0);
 299 }
 300
 301 static void describe_detached_head(char *msg, struct commit *commit)
 302 {
 303         struct strbuf sb = STRBUF_INIT;
 304         parse_commit(commit);
 305         pretty_print_commit(CMIT_FMT_ONELINE, commit, &sb, 0, NULL, NULL, 0, 0);
 306         fprintf(stderr, "%s %s... %s\n", msg,
 307                 find_unique_abbrev(commit->object.sha1, DEFAULT_ABBREV), sb.buf);
 308         strbuf_release(&sb);
 309 }
 310
 311 static int reset_tree(struct tree *tree, struct checkout_opts *o, int worktree)
 312 {
 313         struct unpack_trees_options opts;
 314         struct tree_desc tree_desc;
 315
 316         memset(&opts, 0, sizeof(opts));
 317         opts.head_idx = -1;
 318         opts.update = worktree;
 319         opts.skip_unmerged = !worktree;
 320         opts.reset = 1;
 321         opts.merge = 1;
 322         opts.fn = oneway_merge;
 323         opts.verbose_update = !o->quiet;
 324         opts.src_index = &the_index;
 325         opts.dst_index = &the_index;
 326         parse_tree(tree);
 327         init_tree_desc(&tree_desc, tree->buffer, tree->size);
 328         switch (unpack_trees(1, &tree_desc, &opts)) {
 329         case -2:
 330                 o->writeout_error = 1;
 331                 /*
 332                  * We return 0 nevertheless, as the index is all right
 333                  * and more importantly we have made best efforts to
 334                  * update paths in the work tree, and we cannot revert
 335                  * them.
 336                  */
 337         case 0:
 338                 return 0;
 339         default:
 340                 return 128;
 341         }
 342 }
 343
 344 struct branch_info {
 345         const char *name; /* The short name used */
 346         const char *path; /* The full name of a real branch */
 347         struct commit *commit; /* The named commit */
 348 };
 349
 350 static void setup_branch_path(struct branch_info *branch)
 351 {
 352         struct strbuf buf = STRBUF_INIT;
 353
 354         strbuf_branchname(&buf, branch->name);
 355         if (strcmp(buf.buf, branch->name))
 356                 branch->name = xstrdup(buf.buf);
 357         strbuf_splice(&buf, 0, 0, "refs/heads/", 11);
 358         branch->path = strbuf_detach(&buf, NULL);
 359 }
 360
 361 static int merge_working_tree(struct checkout_opts *opts,
 362                               struct branch_info *old, struct branch_info *new)
 363 {
 364         int ret;
 365         struct lock_file *lock_file = xcalloc(1, sizeof(struct lock_file));
 366         int newfd = hold_locked_index(lock_file, 1);
 367
 368         if (read_cache() < 0)
 369                 return error("corrupt index file");
 370
 371         if (opts->force) {
 372                 ret = reset_tree(new->commit->tree, opts, 1);
 373                 if (ret)
 374                         return ret;
 375         } else {
 376                 struct tree_desc trees[2];
 377                 struct tree *tree;
 378                 struct unpack_trees_options topts;
 379
 380                 memset(&topts, 0, sizeof(topts));
 381                 topts.head_idx = -1;
 382                 topts.src_index = &the_index;
 383                 topts.dst_index = &the_index;
 384
 385                 topts.msgs.not_uptodate_file = "You have local changes to '%s'; cannot switch branches.";
 386
 387                 refresh_cache(REFRESH_QUIET);
 388
 389                 if (unmerged_cache()) {
 390                         error("you need to resolve your current index first");
 391                         return 1;
 392                 }
 393
 394                 /* 2-way merge to the new branch */
 395                 topts.initial_checkout = is_cache_unborn();
 396                 topts.update = 1;
 397                 topts.merge = 1;
 398                 topts.gently = opts->merge;
 399                 topts.verbose_update = !opts->quiet;
 400                 topts.fn = twoway_merge;
 401                 topts.dir = xcalloc(1, sizeof(*topts.dir));
 402                 topts.dir->flags |= DIR_SHOW_IGNORED;
 403                 topts.dir->exclude_per_dir = ".gitignore";
 404                 tree = parse_tree_indirect(old->commit->object.sha1);
 405                 init_tree_desc(&trees[0], tree->buffer, tree->size);
 406                 tree = parse_tree_indirect(new->commit->object.sha1);
 407                 init_tree_desc(&trees[1], tree->buffer, tree->size);
 408
 409                 ret = unpack_trees(2, trees, &topts);
 410                 if (ret == -1) {
 411                         /*
 412                          * Unpack couldn't do a trivial merge; either
 413                          * give up or do a real merge, depending on
 414                          * whether the merge flag was used.
 415                          */
 416                         struct tree *result;
 417                         struct tree *work;
 418                         struct merge_options o;
 419                         if (!opts->merge)
 420                                 return 1;
 421                         parse_commit(old->commit);
 422
 423                         /* Do more real merge */
 424
 425                         /*
 426                          * We update the index fully, then write the
 427                          * tree from the index, then merge the new
 428                          * branch with the current tree, with the old
 429                          * branch as the base. Then we reset the index
 430                          * (but not the working tree) to the new
 431                          * branch, leaving the working tree as the
 432                          * merged version, but skipping unmerged
 433                          * entries in the index.
 434                          */
 435
 436                         add_files_to_cache(NULL, NULL, 0);
 437                         init_merge_options(&o);
 438                         o.verbosity = 0;
 439                         work = write_tree_from_memory(&o);
 440
 441                         ret = reset_tree(new->commit->tree, opts, 1);
 442                         if (ret)
 443                                 return ret;
 444                         o.branch1 = new->name;
 445                         o.branch2 = "local";
 446                         merge_trees(&o, new->commit->tree, work,
 447                                 old->commit->tree, &result);
 448                         ret = reset_tree(new->commit->tree, opts, 0);
 449                         if (ret)
 450                                 return ret;
 451                 }
 452         }
 453
 454         if (write_cache(newfd, active_cache, active_nr) ||
 455             commit_locked_index(lock_file))
 456                 die("unable to write new index file");
 457
 458         if (!opts->force && !opts->quiet)
 459                 show_local_changes(&new->commit->object);
 460
 461         return 0;
 462 }
 463
 464 static void report_tracking(struct branch_info *new)
 465 {
 466         struct strbuf sb = STRBUF_INIT;
 467         struct branch *branch = branch_get(new->name);
 468
 469         if (!format_tracking_info(branch, &sb))
 470                 return;
 471         fputs(sb.buf, stdout);
 472         strbuf_release(&sb);
 473 }
 474
 475 static void update_refs_for_switch(struct checkout_opts *opts,
 476                                    struct branch_info *old,
 477                                    struct branch_info *new)
 478 {
 479         struct strbuf msg = STRBUF_INIT;
 480         const char *old_desc;
 481         if (opts->new_branch) {
 482                 create_branch(old->name, opts->new_branch, new->name, 0,
 483                               opts->new_branch_log, opts->track);
 484                 new->name = opts->new_branch;
 485                 setup_branch_path(new);
 486         }
 487
 488         old_desc = old->name;
 489         if (!old_desc && old->commit)
 490                 old_desc = sha1_to_hex(old->commit->object.sha1);
 491         strbuf_addf(&msg, "checkout: moving from %s to %s",
 492                     old_desc ? old_desc : "(invalid)", new->name);
 493
 494         if (new->path) {
 495                 create_symref("HEAD", new->path, msg.buf);
 496                 if (!opts->quiet) {
 497                         if (old->path && !strcmp(new->path, old->path))
 498                                 fprintf(stderr, "Already on '%s'\n",
 499                                         new->name);
 500                         else
 501                                 fprintf(stderr, "Switched to%s branch '%s'\n",
 502                                         opts->new_branch ? " a new" : "",
 503                                         new->name);
 504                 }
 505         } else if (strcmp(new->name, "HEAD")) {
 506                 update_ref(msg.buf, "HEAD", new->commit->object.sha1, NULL,
 507                            REF_NODEREF, DIE_ON_ERR);
 508                 if (!opts->quiet) {
 509                         if (old->path)
 510                                 fprintf(stderr, "Note: moving to '%s' which isn't a local branch\nIf you want to create a new branch from this checkout, you may do so\n(now or later) by using -b with the checkout command again. Example:\n  git checkout -b <new_branch_name>\n", new->name);
 511                         describe_detached_head("HEAD is now at", new->commit);
 512                 }
 513         }
 514         remove_branch_state();
 515         strbuf_release(&msg);
 516         if (!opts->quiet && (new->path || !strcmp(new->name, "HEAD")))
 517                 report_tracking(new);
 518 }
 519
 520 static int switch_branches(struct checkout_opts *opts, struct branch_info *new)
 521 {
 522         int ret = 0;
 523         struct branch_info old;
 524         unsigned char rev[20];
 525         int flag;
 526         memset(&old, 0, sizeof(old));
 527         old.path = resolve_ref("HEAD", rev, 0, &flag);
 528         old.commit = lookup_commit_reference_gently(rev, 1);
 529         if (!(flag & REF_ISSYMREF))
 530                 old.path = NULL;
 531
 532         if (old.path && !prefixcmp(old.path, "refs/heads/"))
 533                 old.name = old.path + strlen("refs/heads/");
 534
 535         if (!new->name) {
 536                 new->name = "HEAD";
 537                 new->commit = old.commit;
 538                 if (!new->commit)
 539                         die("You are on a branch yet to be born");
 540                 parse_commit(new->commit);
 541         }
 542
 543         /*
 544          * If we were on a detached HEAD, but we are now moving to
 545          * a new commit, we want to mention the old commit once more
 546          * to remind the user that it might be lost.
 547          */
 548         if (!opts->quiet && !old.path && old.commit && new->commit != old.commit)
 549                 describe_detached_head("Previous HEAD position was", old.commit);
 550
 551         if (!old.commit && !opts->force) {
 552                 if (!opts->quiet) {
 553                         warning("You appear to be on a branch yet to be born.");
 554                         warning("Forcing checkout of %s.", new->name);
 555                 }
 556                 opts->force = 1;
 557         }
 558
 559         ret = merge_working_tree(opts, &old, new);
 560         if (ret)
 561                 return ret;
 562
 563         update_refs_for_switch(opts, &old, new);
 564
 565         ret = post_checkout_hook(old.commit, new->commit, 1);
 566         return ret || opts->writeout_error;
 567 }
 568
 569 static int git_checkout_config(const char *var, const char *value, void *cb)
 570 {
 571         return git_xmerge_config(var, value, cb);
 572 }
 573
 574 int cmd_checkout(int argc, const char **argv, const char *prefix)
 575 {
 576         struct checkout_opts opts;
 577         unsigned char rev[20];
 578         const char *arg;
 579         struct branch_info new;
 580         struct tree *source_tree = NULL;
 581         char *conflict_style = NULL;
 582         struct option options[] = {
 583                 OPT__QUIET(&opts.quiet),
 584                 OPT_STRING('b', NULL, &opts.new_branch, "new branch", "branch"),
 585                 OPT_BOOLEAN('l', NULL, &opts.new_branch_log, "log for new branch"),
 586                 OPT_SET_INT('t', "track",  &opts.track, "track",
 587                         BRANCH_TRACK_EXPLICIT),
 588                 OPT_SET_INT('2', "ours", &opts.writeout_stage, "stage",
 589                             2),
 590                 OPT_SET_INT('3', "theirs", &opts.writeout_stage, "stage",
 591                             3),
 592                 OPT_BOOLEAN('f', NULL, &opts.force, "force"),
 593                 OPT_BOOLEAN('m', "merge", &opts.merge, "merge"),
 594                 OPT_STRING(0, "conflict", &conflict_style, "style",
 595                            "conflict style (merge or diff3)"),
 596                 OPT_END(),
 597         };
 598         int has_dash_dash;
 599
 600         memset(&opts, 0, sizeof(opts));
 601         memset(&new, 0, sizeof(new));
 602
 603         git_config(git_checkout_config, NULL);
 604
 605         opts.track = BRANCH_TRACK_UNSPECIFIED;
 606
 607         argc = parse_options(argc, argv, options, checkout_usage,
 608                              PARSE_OPT_KEEP_DASHDASH);
 609
 610         /* --track without -b should DWIM */
 611         if (0 < opts.track && !opts.new_branch) {
 612                 const char *argv0 = argv[0];
 613                 if (!argc || !strcmp(argv0, "--"))
 614                         die ("--track needs a branch name");
 615                 if (!prefixcmp(argv0, "refs/"))
 616                         argv0 += 5;
 617                 if (!prefixcmp(argv0, "remotes/"))
 618                         argv0 += 8;
 619                 argv0 = strchr(argv0, '/');
 620                 if (!argv0 || !argv0[1])
 621                         die ("Missing branch name; try -b");
 622                 opts.new_branch = argv0 + 1;
 623         }
 624
 625         if (opts.track == BRANCH_TRACK_UNSPECIFIED)
 626                 opts.track = git_branch_track;
 627         if (conflict_style) {
 628                 opts.merge = 1; /* implied */
 629                 git_xmerge_config("merge.conflictstyle", conflict_style, NULL);
 630         }
 631
 632         if (opts.force && opts.merge)
 633                 die("git checkout: -f and -m are incompatible");
 634
 635         /*
 636          * case 1: git checkout <ref> -- [<paths>]
 637          *
 638          *   <ref> must be a valid tree, everything after the '--' must be
 639          *   a path.
 640          *
 641          * case 2: git checkout -- [<paths>]
 642          *
 643          *   everything after the '--' must be paths.
 644          *
 645          * case 3: git checkout <something> [<paths>]
 646          *
 647          *   With no paths, if <something> is a commit, that is to
 648          *   switch to the branch or detach HEAD at it.
 649          *
 650          *   Otherwise <something> shall not be ambiguous.
 651          *   - If it's *only* a reference, treat it like case (1).
 652          *   - If it's only a path, treat it like case (2).
 653          *   - else: fail.
 654          *
 655          */
 656         if (argc) {
 657                 if (!strcmp(argv[0], "--")) {       /* case (2) */
 658                         argv++;
 659                         argc--;
 660                         goto no_reference;
 661                 }
 662
 663                 arg = argv[0];
 664                 has_dash_dash = (argc > 1) && !strcmp(argv[1], "--");
 665
 666                 if (!strcmp(arg, "-"))
 667                         arg = "@{-1}";
 668
 669                 if (get_sha1(arg, rev)) {
 670                         if (has_dash_dash)          /* case (1) */
 671                                 die("invalid reference: %s", arg);
 672                         goto no_reference;          /* case (3 -> 2) */
 673                 }
 674
 675                 /* we can't end up being in (2) anymore, eat the argument */
 676                 argv++;
 677                 argc--;
 678
 679                 new.name = arg;
 680                 if ((new.commit = lookup_commit_reference_gently(rev, 1))) {
 681                         setup_branch_path(&new);
 682                         if (resolve_ref(new.path, rev, 1, NULL))
 683                                 new.commit = lookup_commit_reference(rev);
 684                         else
 685                                 new.path = NULL;
 686                         parse_commit(new.commit);
 687                         source_tree = new.commit->tree;
 688                 } else
 689                         source_tree = parse_tree_indirect(rev);
 690
 691                 if (!source_tree)                   /* case (1): want a tree */
 692                         die("reference is not a tree: %s", arg);
 693                 if (!has_dash_dash) {/* case (3 -> 1) */
 694                         /*
 695                          * Do not complain the most common case
 696                          *      git checkout branch
 697                          * even if there happen to be a file called 'branch';
 698                          * it would be extremely annoying.
 699                          */
 700                         if (argc)
 701                                 verify_non_filename(NULL, arg);
 702                 }
 703                 else {
 704                         argv++;
 705                         argc--;
 706                 }
 707         }
 708
 709 no_reference:
 710         if (argc) {
 711                 const char **pathspec = get_pathspec(prefix, argv);
 712
 713                 if (!pathspec)
 714                         die("invalid path specification");
 715
 716                 /* Checkout paths */
 717                 if (opts.new_branch) {
 718                         if (argc == 1) {
 719                                 die("git checkout: updating paths is incompatible with switching branches.\nDid you intend to checkout '%s' which can not be resolved as commit?", argv[0]);
 720                         } else {
 721                                 die("git checkout: updating paths is incompatible with switching branches.");
 722                         }
 723                 }
 724
 725                 if (1 < !!opts.writeout_stage + !!opts.force + !!opts.merge)
 726                         die("git checkout: --ours/--theirs, --force and --merge are incompatible when\nchecking out of the index.");
 727
 728                 return checkout_paths(source_tree, pathspec, &opts);
 729         }
 730
 731         if (opts.new_branch) {
 732                 struct strbuf buf = STRBUF_INIT;
 733                 if (strbuf_check_branch_ref(&buf, opts.new_branch))
 734                         die("git checkout: we do not like '%s' as a branch name.",
 735                             opts.new_branch);
 736                 if (!get_sha1(buf.buf, rev))
 737                         die("git checkout: branch %s already exists", opts.new_branch);
 738                 strbuf_release(&buf);
 739         }
 740
 741         if (new.name && !new.commit) {
 742                 die("Cannot switch branch to a non-commit.");
 743         }
 744         if (opts.writeout_stage)
 745                 die("--ours/--theirs is incompatible with switching branches.");
 746
 747         return switch_branches(&opts, &new);
 748 }