Fix typos / spelling in comments
[git] / 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 phony 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 }