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