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         struct child_process proc;
  42         const char *name = git_path("hooks/post-checkout");
  43         const char *argv[5];
  44
  45         if (access(name, X_OK) < 0)
  46                 return 0;
  47
  48         memset(&proc, 0, sizeof(proc));
  49         argv[0] = name;
  50         argv[1] = sha1_to_hex(old ? old->object.sha1 : null_sha1);
  51         argv[2] = sha1_to_hex(new ? new->object.sha1 : null_sha1);
  52         /* "new" can be NULL when checking out from the index before
  53            a commit exists. */
  54         argv[3] = changed ? "1" : "0";
  55         argv[4] = NULL;
  56         proc.argv = argv;
  57         proc.no_stdin = 1;
  58         proc.stdout_to_stderr = 1;
  59         return run_command(&proc);
  60 }
  61
  62 static int update_some(const unsigned char *sha1, const char *base, int baselen,
  63                 const char *pathname, unsigned mode, int stage, void *context)
  64 {
  65         int len;
  66         struct cache_entry *ce;
  67
  68         if (S_ISGITLINK(mode))
  69                 return 0;
  70
  71         if (S_ISDIR(mode))
  72                 return READ_TREE_RECURSIVE;
  73
  74         len = baselen + strlen(pathname);
  75         ce = xcalloc(1, cache_entry_size(len));
  76         hashcpy(ce->sha1, sha1);
  77         memcpy(ce->name, base, baselen);
  78         memcpy(ce->name + baselen, pathname, len - baselen);
  79         ce->ce_flags = create_ce_flags(len, 0);
  80         ce->ce_mode = create_ce_mode(mode);
  81         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
  82         return 0;
  83 }
  84
  85 static int read_tree_some(struct tree *tree, const char **pathspec)
  86 {
  87         read_tree_recursive(tree, "", 0, 0, pathspec, update_some, NULL);
  88
  89         /* update the index with the given tree's info
  90          * for all args, expanding wildcards, and exit
  91          * with any non-zero return code.
  92          */
  93         return 0;
  94 }
  95
  96 static int skip_same_name(struct cache_entry *ce, int pos)
  97 {
  98         while (++pos < active_nr &&
  99                !strcmp(active_cache[pos]->name, ce->name))
 100                 ; /* skip */
 101         return pos;
 102 }
 103
 104 static int check_stage(int stage, struct cache_entry *ce, int pos)
 105 {
 106         while (pos < active_nr &&
 107                !strcmp(active_cache[pos]->name, ce->name)) {
 108                 if (ce_stage(active_cache[pos]) == stage)
 109                         return 0;
 110                 pos++;
 111         }
 112         return error("path '%s' does not have %s version",
 113                      ce->name,
 114                      (stage == 2) ? "our" : "their");
 115 }
 116
 117 static int check_all_stages(struct cache_entry *ce, int pos)
 118 {
 119         if (ce_stage(ce) != 1 ||
 120             active_nr <= pos + 2 ||
 121             strcmp(active_cache[pos+1]->name, ce->name) ||
 122             ce_stage(active_cache[pos+1]) != 2 ||
 123             strcmp(active_cache[pos+2]->name, ce->name) ||
 124             ce_stage(active_cache[pos+2]) != 3)
 125                 return error("path '%s' does not have all three versions",
 126                              ce->name);
 127         return 0;
 128 }
 129
 130 static int checkout_stage(int stage, struct cache_entry *ce, int pos,
 131                           struct checkout *state)
 132 {
 133         while (pos < active_nr &&
 134                !strcmp(active_cache[pos]->name, ce->name)) {
 135                 if (ce_stage(active_cache[pos]) == stage)
 136                         return checkout_entry(active_cache[pos], state, NULL);
 137                 pos++;
 138         }
 139         return error("path '%s' does not have %s version",
 140                      ce->name,
 141                      (stage == 2) ? "our" : "their");
 142 }
 143
 144 /* NEEDSWORK: share with merge-recursive */
 145 static void fill_mm(const unsigned char *sha1, mmfile_t *mm)
 146 {
 147         unsigned long size;
 148         enum object_type type;
 149
 150         if (!hashcmp(sha1, null_sha1)) {
 151                 mm->ptr = xstrdup("");
 152                 mm->size = 0;
 153                 return;
 154         }
 155
 156         mm->ptr = read_sha1_file(sha1, &type, &size);
 157         if (!mm->ptr || type != OBJ_BLOB)
 158                 die("unable to read blob object %s", sha1_to_hex(sha1));
 159         mm->size = size;
 160 }
 161
 162 static int checkout_merged(int pos, struct checkout *state)
 163 {
 164         struct cache_entry *ce = active_cache[pos];
 165         const char *path = ce->name;
 166         mmfile_t ancestor, ours, theirs;
 167         int status;
 168         unsigned char sha1[20];
 169         mmbuffer_t result_buf;
 170
 171         if (ce_stage(ce) != 1 ||
 172             active_nr <= pos + 2 ||
 173             strcmp(active_cache[pos+1]->name, path) ||
 174             ce_stage(active_cache[pos+1]) != 2 ||
 175             strcmp(active_cache[pos+2]->name, path) ||
 176             ce_stage(active_cache[pos+2]) != 3)
 177                 return error("path '%s' does not have all 3 versions", path);
 178
 179         fill_mm(active_cache[pos]->sha1, &ancestor);
 180         fill_mm(active_cache[pos+1]->sha1, &ours);
 181         fill_mm(active_cache[pos+2]->sha1, &theirs);
 182
 183         status = ll_merge(&result_buf, path, &ancestor,
 184                           &ours, "ours", &theirs, "theirs", 1);
 185         free(ancestor.ptr);
 186         free(ours.ptr);
 187         free(theirs.ptr);
 188         if (status < 0 || !result_buf.ptr) {
 189                 free(result_buf.ptr);
 190                 return error("path '%s': cannot merge", path);
 191         }
 192
 193         /*
 194          * NEEDSWORK:
 195          * There is absolutely no reason to write this as a blob object
 196          * and create a phoney cache entry just to leak.  This hack is
 197          * primarily to get to the write_entry() machinery that massages
 198          * the contents to work-tree format and writes out which only
 199          * allows it for a cache entry.  The code in write_entry() needs
 200          * to be refactored to allow us to feed a <buffer, size, mode>
 201          * instead of a cache entry.  Such a refactoring would help
 202          * merge_recursive as well (it also writes the merge result to the
 203          * object database even when it may contain conflicts).
 204          */
 205         if (write_sha1_file(result_buf.ptr, result_buf.size,
 206                             blob_type, sha1))
 207                 die("Unable to add merge result for '%s'", path);
 208         ce = make_cache_entry(create_ce_mode(active_cache[pos+1]->ce_mode),
 209                               sha1,
 210                               path, 2, 0);
 211         if (!ce)
 212                 die("make_cache_entry failed for path '%s'", path);
 213         status = checkout_entry(ce, state, NULL);
 214         return status;
 215 }
 216
 217 static int checkout_paths(struct tree *source_tree, const char **pathspec,
 218                           struct checkout_opts *opts)
 219 {
 220         int pos;
 221         struct checkout state;
 222         static char *ps_matched;
 223         unsigned char rev[20];
 224         int flag;
 225         struct commit *head;
 226         int errs = 0;
 227         int stage = opts->writeout_stage;
 228         int merge = opts->merge;
 229         int newfd;
 230         struct lock_file *lock_file = xcalloc(1, sizeof(struct lock_file));
 231
 232         newfd = hold_locked_index(lock_file, 1);
 233         if (read_cache() < 0)
 234                 return error("corrupt index file");
 235
 236         if (source_tree)
 237                 read_tree_some(source_tree, pathspec);
 238
 239         for (pos = 0; pathspec[pos]; pos++)
 240                 ;
 241         ps_matched = xcalloc(1, pos);
 242
 243         for (pos = 0; pos < active_nr; pos++) {
 244                 struct cache_entry *ce = active_cache[pos];
 245                 pathspec_match(pathspec, ps_matched, ce->name, 0);
 246         }
 247
 248         if (report_path_error(ps_matched, pathspec, 0))
 249                 return 1;
 250
 251         /* Any unmerged paths? */
 252         for (pos = 0; pos < active_nr; pos++) {
 253                 struct cache_entry *ce = active_cache[pos];
 254                 if (pathspec_match(pathspec, NULL, ce->name, 0)) {
 255                         if (!ce_stage(ce))
 256                                 continue;
 257                         if (opts->force) {
 258                                 warning("path '%s' is unmerged", ce->name);
 259                         } else if (stage) {
 260                                 errs |= check_stage(stage, ce, pos);
 261                         } else if (opts->merge) {
 262                                 errs |= check_all_stages(ce, pos);
 263                         } else {
 264                                 errs = 1;
 265                                 error("path '%s' is unmerged", ce->name);
 266                         }
 267                         pos = skip_same_name(ce, pos) - 1;
 268                 }
 269         }
 270         if (errs)
 271                 return 1;
 272
 273         /* Now we are committed to check them out */
 274         memset(&state, 0, sizeof(state));
 275         state.force = 1;
 276         state.refresh_cache = 1;
 277         for (pos = 0; pos < active_nr; pos++) {
 278                 struct cache_entry *ce = active_cache[pos];
 279                 if (pathspec_match(pathspec, NULL, ce->name, 0)) {
 280                         if (!ce_stage(ce)) {
 281                                 errs |= checkout_entry(ce, &state, NULL);
 282                                 continue;
 283                         }
 284                         if (stage)
 285                                 errs |= checkout_stage(stage, ce, pos, &state);
 286                         else if (merge)
 287                                 errs |= checkout_merged(pos, &state);
 288                         pos = skip_same_name(ce, pos) - 1;
 289                 }
 290         }
 291
 292         if (write_cache(newfd, active_cache, active_nr) ||
 293             commit_locked_index(lock_file))
 294                 die("unable to write new index file");
 295
 296         resolve_ref("HEAD", rev, 0, &flag);
 297         head = lookup_commit_reference_gently(rev, 1);
 298
 299         errs |= post_checkout_hook(head, head, 0);
 300         return errs;
 301 }
 302
 303 static void show_local_changes(struct object *head)
 304 {
 305         struct rev_info rev;
 306         /* I think we want full paths, even if we're in a subdirectory. */
 307         init_revisions(&rev, NULL);
 308         rev.abbrev = 0;
 309         rev.diffopt.output_format |= DIFF_FORMAT_NAME_STATUS;
 310         add_pending_object(&rev, head, NULL);
 311         run_diff_index(&rev, 0);
 312 }
 313
 314 static void describe_detached_head(char *msg, struct commit *commit)
 315 {
 316         struct strbuf sb = STRBUF_INIT;
 317         parse_commit(commit);
 318         pretty_print_commit(CMIT_FMT_ONELINE, commit, &sb, 0, NULL, NULL, 0, 0);
 319         fprintf(stderr, "%s %s... %s\n", msg,
 320                 find_unique_abbrev(commit->object.sha1, DEFAULT_ABBREV), sb.buf);
 321         strbuf_release(&sb);
 322 }
 323
 324 static int reset_tree(struct tree *tree, struct checkout_opts *o, int worktree)
 325 {
 326         struct unpack_trees_options opts;
 327         struct tree_desc tree_desc;
 328
 329         memset(&opts, 0, sizeof(opts));
 330         opts.head_idx = -1;
 331         opts.update = worktree;
 332         opts.skip_unmerged = !worktree;
 333         opts.reset = 1;
 334         opts.merge = 1;
 335         opts.fn = oneway_merge;
 336         opts.verbose_update = !o->quiet;
 337         opts.src_index = &the_index;
 338         opts.dst_index = &the_index;
 339         parse_tree(tree);
 340         init_tree_desc(&tree_desc, tree->buffer, tree->size);
 341         switch (unpack_trees(1, &tree_desc, &opts)) {
 342         case -2:
 343                 o->writeout_error = 1;
 344                 /*
 345                  * We return 0 nevertheless, as the index is all right
 346                  * and more importantly we have made best efforts to
 347                  * update paths in the work tree, and we cannot revert
 348                  * them.
 349                  */
 350         case 0:
 351                 return 0;
 352         default:
 353                 return 128;
 354         }
 355 }
 356
 357 struct branch_info {
 358         const char *name; /* The short name used */
 359         const char *path; /* The full name of a real branch */
 360         struct commit *commit; /* The named commit */
 361 };
 362
 363 static void setup_branch_path(struct branch_info *branch)
 364 {
 365         struct strbuf buf = STRBUF_INIT;
 366         strbuf_addstr(&buf, "refs/heads/");
 367         strbuf_addstr(&buf, branch->name);
 368         branch->path = strbuf_detach(&buf, NULL);
 369 }
 370
 371 static int merge_working_tree(struct checkout_opts *opts,
 372                               struct branch_info *old, struct branch_info *new)
 373 {
 374         int ret;
 375         struct lock_file *lock_file = xcalloc(1, sizeof(struct lock_file));
 376         int newfd = hold_locked_index(lock_file, 1);
 377
 378         if (read_cache() < 0)
 379                 return error("corrupt index file");
 380
 381         if (opts->force) {
 382                 ret = reset_tree(new->commit->tree, opts, 1);
 383                 if (ret)
 384                         return ret;
 385         } else {
 386                 struct tree_desc trees[2];
 387                 struct tree *tree;
 388                 struct unpack_trees_options topts;
 389
 390                 memset(&topts, 0, sizeof(topts));
 391                 topts.head_idx = -1;
 392                 topts.src_index = &the_index;
 393                 topts.dst_index = &the_index;
 394
 395                 topts.msgs.not_uptodate_file = "You have local changes to '%s'; cannot switch branches.";
 396
 397                 refresh_cache(REFRESH_QUIET);
 398
 399                 if (unmerged_cache()) {
 400                         error("you need to resolve your current index first");
 401                         return 1;
 402                 }
 403
 404                 /* 2-way merge to the new branch */
 405                 topts.initial_checkout = is_cache_unborn();
 406                 topts.update = 1;
 407                 topts.merge = 1;
 408                 topts.gently = opts->merge;
 409                 topts.verbose_update = !opts->quiet;
 410                 topts.fn = twoway_merge;
 411                 topts.dir = xcalloc(1, sizeof(*topts.dir));
 412                 topts.dir->show_ignored = 1;
 413                 topts.dir->exclude_per_dir = ".gitignore";
 414                 tree = parse_tree_indirect(old->commit->object.sha1);
 415                 init_tree_desc(&trees[0], tree->buffer, tree->size);
 416                 tree = parse_tree_indirect(new->commit->object.sha1);
 417                 init_tree_desc(&trees[1], tree->buffer, tree->size);
 418
 419                 ret = unpack_trees(2, trees, &topts);
 420                 if (ret == -1) {
 421                         /*
 422                          * Unpack couldn't do a trivial merge; either
 423                          * give up or do a real merge, depending on
 424                          * whether the merge flag was used.
 425                          */
 426                         struct tree *result;
 427                         struct tree *work;
 428                         struct merge_options o;
 429                         if (!opts->merge)
 430                                 return 1;
 431                         parse_commit(old->commit);
 432
 433                         /* Do more real merge */
 434
 435                         /*
 436                          * We update the index fully, then write the
 437                          * tree from the index, then merge the new
 438                          * branch with the current tree, with the old
 439                          * branch as the base. Then we reset the index
 440                          * (but not the working tree) to the new
 441                          * branch, leaving the working tree as the
 442                          * merged version, but skipping unmerged
 443                          * entries in the index.
 444                          */
 445
 446                         add_files_to_cache(NULL, NULL, 0);
 447                         init_merge_options(&o);
 448                         o.verbosity = 0;
 449                         work = write_tree_from_memory(&o);
 450
 451                         ret = reset_tree(new->commit->tree, opts, 1);
 452                         if (ret)
 453                                 return ret;
 454                         o.branch1 = new->name;
 455                         o.branch2 = "local";
 456                         merge_trees(&o, new->commit->tree, work,
 457                                 old->commit->tree, &result);
 458                         ret = reset_tree(new->commit->tree, opts, 0);
 459                         if (ret)
 460                                 return ret;
 461                 }
 462         }
 463
 464         if (write_cache(newfd, active_cache, active_nr) ||
 465             commit_locked_index(lock_file))
 466                 die("unable to write new index file");
 467
 468         if (!opts->force && !opts->quiet)
 469                 show_local_changes(&new->commit->object);
 470
 471         return 0;
 472 }
 473
 474 static void report_tracking(struct branch_info *new)
 475 {
 476         struct strbuf sb = STRBUF_INIT;
 477         struct branch *branch = branch_get(new->name);
 478
 479         if (!format_tracking_info(branch, &sb))
 480                 return;
 481         fputs(sb.buf, stdout);
 482         strbuf_release(&sb);
 483 }
 484
 485 static void update_refs_for_switch(struct checkout_opts *opts,
 486                                    struct branch_info *old,
 487                                    struct branch_info *new)
 488 {
 489         struct strbuf msg = STRBUF_INIT;
 490         const char *old_desc;
 491         if (opts->new_branch) {
 492                 create_branch(old->name, opts->new_branch, new->name, 0,
 493                               opts->new_branch_log, opts->track);
 494                 new->name = opts->new_branch;
 495                 setup_branch_path(new);
 496         }
 497
 498         old_desc = old->name;
 499         if (!old_desc && old->commit)
 500                 old_desc = sha1_to_hex(old->commit->object.sha1);
 501         strbuf_addf(&msg, "checkout: moving from %s to %s",
 502                     old_desc ? old_desc : "(invalid)", new->name);
 503
 504         if (new->path) {
 505                 create_symref("HEAD", new->path, msg.buf);
 506                 if (!opts->quiet) {
 507                         if (old->path && !strcmp(new->path, old->path))
 508                                 fprintf(stderr, "Already on \"%s\"\n",
 509                                         new->name);
 510                         else
 511                                 fprintf(stderr, "Switched to%s branch \"%s\"\n",
 512                                         opts->new_branch ? " a new" : "",
 513                                         new->name);
 514                 }
 515         } else if (strcmp(new->name, "HEAD")) {
 516                 update_ref(msg.buf, "HEAD", new->commit->object.sha1, NULL,
 517                            REF_NODEREF, DIE_ON_ERR);
 518                 if (!opts->quiet) {
 519                         if (old->path)
 520                                 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);
 521                         describe_detached_head("HEAD is now at", new->commit);
 522                 }
 523         }
 524         remove_branch_state();
 525         strbuf_release(&msg);
 526         if (!opts->quiet && (new->path || !strcmp(new->name, "HEAD")))
 527                 report_tracking(new);
 528 }
 529
 530 static int switch_branches(struct checkout_opts *opts, struct branch_info *new)
 531 {
 532         int ret = 0;
 533         struct branch_info old;
 534         unsigned char rev[20];
 535         int flag;
 536         memset(&old, 0, sizeof(old));
 537         old.path = resolve_ref("HEAD", rev, 0, &flag);
 538         old.commit = lookup_commit_reference_gently(rev, 1);
 539         if (!(flag & REF_ISSYMREF))
 540                 old.path = NULL;
 541
 542         if (old.path && !prefixcmp(old.path, "refs/heads/"))
 543                 old.name = old.path + strlen("refs/heads/");
 544
 545         if (!new->name) {
 546                 new->name = "HEAD";
 547                 new->commit = old.commit;
 548                 if (!new->commit)
 549                         die("You are on a branch yet to be born");
 550                 parse_commit(new->commit);
 551         }
 552
 553         /*
 554          * If we were on a detached HEAD, but we are now moving to
 555          * a new commit, we want to mention the old commit once more
 556          * to remind the user that it might be lost.
 557          */
 558         if (!opts->quiet && !old.path && old.commit && new->commit != old.commit)
 559                 describe_detached_head("Previous HEAD position was", old.commit);
 560
 561         if (!old.commit && !opts->force) {
 562                 if (!opts->quiet) {
 563                         fprintf(stderr, "warning: You appear to be on a branch yet to be born.\n");
 564                         fprintf(stderr, "warning: Forcing checkout of %s.\n", new->name);
 565                 }
 566                 opts->force = 1;
 567         }
 568
 569         ret = merge_working_tree(opts, &old, new);
 570         if (ret)
 571                 return ret;
 572
 573         update_refs_for_switch(opts, &old, new);
 574
 575         ret = post_checkout_hook(old.commit, new->commit, 1);
 576         return ret || opts->writeout_error;
 577 }
 578
 579 static int git_checkout_config(const char *var, const char *value, void *cb)
 580 {
 581         return git_xmerge_config(var, value, cb);
 582 }
 583
 584 int cmd_checkout(int argc, const char **argv, const char *prefix)
 585 {
 586         struct checkout_opts opts;
 587         unsigned char rev[20];
 588         const char *arg;
 589         struct branch_info new;
 590         struct tree *source_tree = NULL;
 591         char *conflict_style = NULL;
 592         struct option options[] = {
 593                 OPT__QUIET(&opts.quiet),
 594                 OPT_STRING('b', NULL, &opts.new_branch, "new branch", "branch"),
 595                 OPT_BOOLEAN('l', NULL, &opts.new_branch_log, "log for new branch"),
 596                 OPT_SET_INT('t', "track",  &opts.track, "track",
 597                         BRANCH_TRACK_EXPLICIT),
 598                 OPT_SET_INT('2', "ours", &opts.writeout_stage, "stage",
 599                             2),
 600                 OPT_SET_INT('3', "theirs", &opts.writeout_stage, "stage",
 601                             3),
 602                 OPT_BOOLEAN('f', NULL, &opts.force, "force"),
 603                 OPT_BOOLEAN('m', "merge", &opts.merge, "merge"),
 604                 OPT_STRING(0, "conflict", &conflict_style, "style",
 605                            "conflict style (merge or diff3)"),
 606                 OPT_END(),
 607         };
 608         int has_dash_dash;
 609
 610         memset(&opts, 0, sizeof(opts));
 611         memset(&new, 0, sizeof(new));
 612
 613         git_config(git_checkout_config, NULL);
 614
 615         opts.track = BRANCH_TRACK_UNSPECIFIED;
 616
 617         argc = parse_options(argc, argv, options, checkout_usage,
 618                              PARSE_OPT_KEEP_DASHDASH);
 619
 620         /* --track without -b should DWIM */
 621         if (0 < opts.track && !opts.new_branch) {
 622                 const char *argv0 = argv[0];
 623                 if (!argc || !strcmp(argv0, "--"))
 624                         die ("--track needs a branch name");
 625                 if (!prefixcmp(argv0, "refs/"))
 626                         argv0 += 5;
 627                 if (!prefixcmp(argv0, "remotes/"))
 628                         argv0 += 8;
 629                 argv0 = strchr(argv0, '/');
 630                 if (!argv0 || !argv0[1])
 631                         die ("Missing branch name; try -b");
 632                 opts.new_branch = argv0 + 1;
 633         }
 634
 635         if (opts.track == BRANCH_TRACK_UNSPECIFIED)
 636                 opts.track = git_branch_track;
 637         if (conflict_style) {
 638                 opts.merge = 1; /* implied */
 639                 git_xmerge_config("merge.conflictstyle", conflict_style, NULL);
 640         }
 641
 642         if (opts.force && opts.merge)
 643                 die("git checkout: -f and -m are incompatible");
 644
 645         /*
 646          * case 1: git checkout <ref> -- [<paths>]
 647          *
 648          *   <ref> must be a valid tree, everything after the '--' must be
 649          *   a path.
 650          *
 651          * case 2: git checkout -- [<paths>]
 652          *
 653          *   everything after the '--' must be paths.
 654          *
 655          * case 3: git checkout <something> [<paths>]
 656          *
 657          *   With no paths, if <something> is a commit, that is to
 658          *   switch to the branch or detach HEAD at it.
 659          *
 660          *   Otherwise <something> shall not be ambiguous.
 661          *   - If it's *only* a reference, treat it like case (1).
 662          *   - If it's only a path, treat it like case (2).
 663          *   - else: fail.
 664          *
 665          */
 666         if (argc) {
 667                 if (!strcmp(argv[0], "--")) {       /* case (2) */
 668                         argv++;
 669                         argc--;
 670                         goto no_reference;
 671                 }
 672
 673                 arg = argv[0];
 674                 has_dash_dash = (argc > 1) && !strcmp(argv[1], "--");
 675
 676                 if (get_sha1(arg, rev)) {
 677                         if (has_dash_dash)          /* case (1) */
 678                                 die("invalid reference: %s", arg);
 679                         goto no_reference;          /* case (3 -> 2) */
 680                 }
 681
 682                 /* we can't end up being in (2) anymore, eat the argument */
 683                 argv++;
 684                 argc--;
 685
 686                 new.name = arg;
 687                 if ((new.commit = lookup_commit_reference_gently(rev, 1))) {
 688                         setup_branch_path(&new);
 689                         if (resolve_ref(new.path, rev, 1, NULL))
 690                                 new.commit = lookup_commit_reference(rev);
 691                         else
 692                                 new.path = NULL;
 693                         parse_commit(new.commit);
 694                         source_tree = new.commit->tree;
 695                 } else
 696                         source_tree = parse_tree_indirect(rev);
 697
 698                 if (!source_tree)                   /* case (1): want a tree */
 699                         die("reference is not a tree: %s", arg);
 700                 if (!has_dash_dash) {/* case (3 -> 1) */
 701                         /*
 702                          * Do not complain the most common case
 703                          *      git checkout branch
 704                          * even if there happen to be a file called 'branch';
 705                          * it would be extremely annoying.
 706                          */
 707                         if (argc)
 708                                 verify_non_filename(NULL, arg);
 709                 }
 710                 else {
 711                         argv++;
 712                         argc--;
 713                 }
 714         }
 715
 716 no_reference:
 717         if (argc) {
 718                 const char **pathspec = get_pathspec(prefix, argv);
 719
 720                 if (!pathspec)
 721                         die("invalid path specification");
 722
 723                 /* Checkout paths */
 724                 if (opts.new_branch) {
 725                         if (argc == 1) {
 726                                 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]);
 727                         } else {
 728                                 die("git checkout: updating paths is incompatible with switching branches.");
 729                         }
 730                 }
 731
 732                 if (1 < !!opts.writeout_stage + !!opts.force + !!opts.merge)
 733                         die("git checkout: --ours/--theirs, --force and --merge are incompatible when\nchecking out of the index.");
 734
 735                 return checkout_paths(source_tree, pathspec, &opts);
 736         }
 737
 738         if (opts.new_branch) {
 739                 struct strbuf buf = STRBUF_INIT;
 740                 strbuf_addstr(&buf, "refs/heads/");
 741                 strbuf_addstr(&buf, opts.new_branch);
 742                 if (!get_sha1(buf.buf, rev))
 743                         die("git checkout: branch %s already exists", opts.new_branch);
 744                 if (check_ref_format(buf.buf))
 745                         die("git checkout: we do not like '%s' as a branch name.", opts.new_branch);
 746                 strbuf_release(&buf);
 747         }
 748
 749         if (new.name && !new.commit) {
 750                 die("Cannot switch branch to a non-commit.");
 751         }
 752         if (opts.writeout_stage)
 753                 die("--ours/--theirs is incompatible with switching branches.");
 754
 755         return switch_branches(&opts, &new);
 756 }