Merge branch 'bc/hash-transition-part-15'
[git] / builtin / checkout.c
1 #include "builtin.h"
2 #include "config.h"
3 #include "checkout.h"
4 #include "lockfile.h"
5 #include "parse-options.h"
6 #include "refs.h"
7 #include "object-store.h"
8 #include "commit.h"
9 #include "tree.h"
10 #include "tree-walk.h"
11 #include "cache-tree.h"
12 #include "unpack-trees.h"
13 #include "dir.h"
14 #include "run-command.h"
15 #include "merge-recursive.h"
16 #include "branch.h"
17 #include "diff.h"
18 #include "revision.h"
19 #include "remote.h"
20 #include "blob.h"
21 #include "xdiff-interface.h"
22 #include "ll-merge.h"
23 #include "resolve-undo.h"
24 #include "submodule-config.h"
25 #include "submodule.h"
26 #include "advice.h"
27
28 static int checkout_optimize_new_branch;
29
30 static const char * const checkout_usage[] = {
31         N_("git checkout [<options>] <branch>"),
32         N_("git checkout [<options>] [<branch>] -- <file>..."),
33         NULL,
34 };
35
36 struct checkout_opts {
37         int patch_mode;
38         int quiet;
39         int merge;
40         int force;
41         int force_detach;
42         int writeout_stage;
43         int overwrite_ignore;
44         int ignore_skipworktree;
45         int ignore_other_worktrees;
46         int show_progress;
47         /*
48          * If new checkout options are added, skip_merge_working_tree
49          * should be updated accordingly.
50          */
51
52         const char *new_branch;
53         const char *new_branch_force;
54         const char *new_orphan_branch;
55         int new_branch_log;
56         enum branch_track track;
57         struct diff_options diff_options;
58
59         int branch_exists;
60         const char *prefix;
61         struct pathspec pathspec;
62         struct tree *source_tree;
63 };
64
65 static int post_checkout_hook(struct commit *old_commit, struct commit *new_commit,
66                               int changed)
67 {
68         return run_hook_le(NULL, "post-checkout",
69                            oid_to_hex(old_commit ? &old_commit->object.oid : &null_oid),
70                            oid_to_hex(new_commit ? &new_commit->object.oid : &null_oid),
71                            changed ? "1" : "0", NULL);
72         /* "new_commit" can be NULL when checking out from the index before
73            a commit exists. */
74
75 }
76
77 static int update_some(const struct object_id *oid, struct strbuf *base,
78                 const char *pathname, unsigned mode, int stage, void *context)
79 {
80         int len;
81         struct cache_entry *ce;
82         int pos;
83
84         if (S_ISDIR(mode))
85                 return READ_TREE_RECURSIVE;
86
87         len = base->len + strlen(pathname);
88         ce = make_empty_cache_entry(&the_index, len);
89         oidcpy(&ce->oid, oid);
90         memcpy(ce->name, base->buf, base->len);
91         memcpy(ce->name + base->len, pathname, len - base->len);
92         ce->ce_flags = create_ce_flags(0) | CE_UPDATE;
93         ce->ce_namelen = len;
94         ce->ce_mode = create_ce_mode(mode);
95
96         /*
97          * If the entry is the same as the current index, we can leave the old
98          * entry in place. Whether it is UPTODATE or not, checkout_entry will
99          * do the right thing.
100          */
101         pos = cache_name_pos(ce->name, ce->ce_namelen);
102         if (pos >= 0) {
103                 struct cache_entry *old = active_cache[pos];
104                 if (ce->ce_mode == old->ce_mode &&
105                     oideq(&ce->oid, &old->oid)) {
106                         old->ce_flags |= CE_UPDATE;
107                         discard_cache_entry(ce);
108                         return 0;
109                 }
110         }
111
112         add_cache_entry(ce, ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
113         return 0;
114 }
115
116 static int read_tree_some(struct tree *tree, const struct pathspec *pathspec)
117 {
118         read_tree_recursive(tree, "", 0, 0, pathspec, update_some, NULL);
119
120         /* update the index with the given tree's info
121          * for all args, expanding wildcards, and exit
122          * with any non-zero return code.
123          */
124         return 0;
125 }
126
127 static int skip_same_name(const struct cache_entry *ce, int pos)
128 {
129         while (++pos < active_nr &&
130                !strcmp(active_cache[pos]->name, ce->name))
131                 ; /* skip */
132         return pos;
133 }
134
135 static int check_stage(int stage, const struct cache_entry *ce, int pos)
136 {
137         while (pos < active_nr &&
138                !strcmp(active_cache[pos]->name, ce->name)) {
139                 if (ce_stage(active_cache[pos]) == stage)
140                         return 0;
141                 pos++;
142         }
143         if (stage == 2)
144                 return error(_("path '%s' does not have our version"), ce->name);
145         else
146                 return error(_("path '%s' does not have their version"), ce->name);
147 }
148
149 static int check_stages(unsigned stages, const struct cache_entry *ce, int pos)
150 {
151         unsigned seen = 0;
152         const char *name = ce->name;
153
154         while (pos < active_nr) {
155                 ce = active_cache[pos];
156                 if (strcmp(name, ce->name))
157                         break;
158                 seen |= (1 << ce_stage(ce));
159                 pos++;
160         }
161         if ((stages & seen) != stages)
162                 return error(_("path '%s' does not have all necessary versions"),
163                              name);
164         return 0;
165 }
166
167 static int checkout_stage(int stage, const struct cache_entry *ce, int pos,
168                           const struct checkout *state)
169 {
170         while (pos < active_nr &&
171                !strcmp(active_cache[pos]->name, ce->name)) {
172                 if (ce_stage(active_cache[pos]) == stage)
173                         return checkout_entry(active_cache[pos], state, NULL);
174                 pos++;
175         }
176         if (stage == 2)
177                 return error(_("path '%s' does not have our version"), ce->name);
178         else
179                 return error(_("path '%s' does not have their version"), ce->name);
180 }
181
182 static int checkout_merged(int pos, const struct checkout *state)
183 {
184         struct cache_entry *ce = active_cache[pos];
185         const char *path = ce->name;
186         mmfile_t ancestor, ours, theirs;
187         int status;
188         struct object_id oid;
189         mmbuffer_t result_buf;
190         struct object_id threeway[3];
191         unsigned mode = 0;
192
193         memset(threeway, 0, sizeof(threeway));
194         while (pos < active_nr) {
195                 int stage;
196                 stage = ce_stage(ce);
197                 if (!stage || strcmp(path, ce->name))
198                         break;
199                 oidcpy(&threeway[stage - 1], &ce->oid);
200                 if (stage == 2)
201                         mode = create_ce_mode(ce->ce_mode);
202                 pos++;
203                 ce = active_cache[pos];
204         }
205         if (is_null_oid(&threeway[1]) || is_null_oid(&threeway[2]))
206                 return error(_("path '%s' does not have necessary versions"), path);
207
208         read_mmblob(&ancestor, &threeway[0]);
209         read_mmblob(&ours, &threeway[1]);
210         read_mmblob(&theirs, &threeway[2]);
211
212         /*
213          * NEEDSWORK: re-create conflicts from merges with
214          * merge.renormalize set, too
215          */
216         status = ll_merge(&result_buf, path, &ancestor, "base",
217                           &ours, "ours", &theirs, "theirs",
218                           state->istate, NULL);
219         free(ancestor.ptr);
220         free(ours.ptr);
221         free(theirs.ptr);
222         if (status < 0 || !result_buf.ptr) {
223                 free(result_buf.ptr);
224                 return error(_("path '%s': cannot merge"), path);
225         }
226
227         /*
228          * NEEDSWORK:
229          * There is absolutely no reason to write this as a blob object
230          * and create a phony cache entry.  This hack is primarily to get
231          * to the write_entry() machinery that massages the contents to
232          * work-tree format and writes out which only allows it for a
233          * cache entry.  The code in write_entry() needs to be refactored
234          * to allow us to feed a <buffer, size, mode> instead of a cache
235          * entry.  Such a refactoring would help merge_recursive as well
236          * (it also writes the merge result to the object database even
237          * when it may contain conflicts).
238          */
239         if (write_object_file(result_buf.ptr, result_buf.size, blob_type, &oid))
240                 die(_("Unable to add merge result for '%s'"), path);
241         free(result_buf.ptr);
242         ce = make_transient_cache_entry(mode, &oid, path, 2);
243         if (!ce)
244                 die(_("make_cache_entry failed for path '%s'"), path);
245         status = checkout_entry(ce, state, NULL);
246         discard_cache_entry(ce);
247         return status;
248 }
249
250 static int checkout_paths(const struct checkout_opts *opts,
251                           const char *revision)
252 {
253         int pos;
254         struct checkout state = CHECKOUT_INIT;
255         static char *ps_matched;
256         struct object_id rev;
257         struct commit *head;
258         int errs = 0;
259         struct lock_file lock_file = LOCK_INIT;
260
261         if (opts->track != BRANCH_TRACK_UNSPECIFIED)
262                 die(_("'%s' cannot be used with updating paths"), "--track");
263
264         if (opts->new_branch_log)
265                 die(_("'%s' cannot be used with updating paths"), "-l");
266
267         if (opts->force && opts->patch_mode)
268                 die(_("'%s' cannot be used with updating paths"), "-f");
269
270         if (opts->force_detach)
271                 die(_("'%s' cannot be used with updating paths"), "--detach");
272
273         if (opts->merge && opts->patch_mode)
274                 die(_("'%s' cannot be used with %s"), "--merge", "--patch");
275
276         if (opts->force && opts->merge)
277                 die(_("'%s' cannot be used with %s"), "-f", "-m");
278
279         if (opts->new_branch)
280                 die(_("Cannot update paths and switch to branch '%s' at the same time."),
281                     opts->new_branch);
282
283         if (opts->patch_mode)
284                 return run_add_interactive(revision, "--patch=checkout",
285                                            &opts->pathspec);
286
287         hold_locked_index(&lock_file, LOCK_DIE_ON_ERROR);
288         if (read_cache_preload(&opts->pathspec) < 0)
289                 return error(_("index file corrupt"));
290
291         if (opts->source_tree)
292                 read_tree_some(opts->source_tree, &opts->pathspec);
293
294         ps_matched = xcalloc(opts->pathspec.nr, 1);
295
296         /*
297          * Make sure all pathspecs participated in locating the paths
298          * to be checked out.
299          */
300         for (pos = 0; pos < active_nr; pos++) {
301                 struct cache_entry *ce = active_cache[pos];
302                 ce->ce_flags &= ~CE_MATCHED;
303                 if (!opts->ignore_skipworktree && ce_skip_worktree(ce))
304                         continue;
305                 if (opts->source_tree && !(ce->ce_flags & CE_UPDATE))
306                         /*
307                          * "git checkout tree-ish -- path", but this entry
308                          * is in the original index; it will not be checked
309                          * out to the working tree and it does not matter
310                          * if pathspec matched this entry.  We will not do
311                          * anything to this entry at all.
312                          */
313                         continue;
314                 /*
315                  * Either this entry came from the tree-ish we are
316                  * checking the paths out of, or we are checking out
317                  * of the index.
318                  *
319                  * If it comes from the tree-ish, we already know it
320                  * matches the pathspec and could just stamp
321                  * CE_MATCHED to it from update_some(). But we still
322                  * need ps_matched and read_tree_recursive (and
323                  * eventually tree_entry_interesting) cannot fill
324                  * ps_matched yet. Once it can, we can avoid calling
325                  * match_pathspec() for _all_ entries when
326                  * opts->source_tree != NULL.
327                  */
328                 if (ce_path_match(&the_index, ce, &opts->pathspec, ps_matched))
329                         ce->ce_flags |= CE_MATCHED;
330         }
331
332         if (report_path_error(ps_matched, &opts->pathspec, opts->prefix)) {
333                 free(ps_matched);
334                 return 1;
335         }
336         free(ps_matched);
337
338         /* "checkout -m path" to recreate conflicted state */
339         if (opts->merge)
340                 unmerge_marked_index(&the_index);
341
342         /* Any unmerged paths? */
343         for (pos = 0; pos < active_nr; pos++) {
344                 const struct cache_entry *ce = active_cache[pos];
345                 if (ce->ce_flags & CE_MATCHED) {
346                         if (!ce_stage(ce))
347                                 continue;
348                         if (opts->force) {
349                                 warning(_("path '%s' is unmerged"), ce->name);
350                         } else if (opts->writeout_stage) {
351                                 errs |= check_stage(opts->writeout_stage, ce, pos);
352                         } else if (opts->merge) {
353                                 errs |= check_stages((1<<2) | (1<<3), ce, pos);
354                         } else {
355                                 errs = 1;
356                                 error(_("path '%s' is unmerged"), ce->name);
357                         }
358                         pos = skip_same_name(ce, pos) - 1;
359                 }
360         }
361         if (errs)
362                 return 1;
363
364         /* Now we are committed to check them out */
365         state.force = 1;
366         state.refresh_cache = 1;
367         state.istate = &the_index;
368
369         enable_delayed_checkout(&state);
370         for (pos = 0; pos < active_nr; pos++) {
371                 struct cache_entry *ce = active_cache[pos];
372                 if (ce->ce_flags & CE_MATCHED) {
373                         if (!ce_stage(ce)) {
374                                 errs |= checkout_entry(ce, &state, NULL);
375                                 continue;
376                         }
377                         if (opts->writeout_stage)
378                                 errs |= checkout_stage(opts->writeout_stage, ce, pos, &state);
379                         else if (opts->merge)
380                                 errs |= checkout_merged(pos, &state);
381                         pos = skip_same_name(ce, pos) - 1;
382                 }
383         }
384         errs |= finish_delayed_checkout(&state);
385
386         if (write_locked_index(&the_index, &lock_file, COMMIT_LOCK))
387                 die(_("unable to write new index file"));
388
389         read_ref_full("HEAD", 0, &rev, NULL);
390         head = lookup_commit_reference_gently(the_repository, &rev, 1);
391
392         errs |= post_checkout_hook(head, head, 0);
393         return errs;
394 }
395
396 static void show_local_changes(struct object *head,
397                                const struct diff_options *opts)
398 {
399         struct rev_info rev;
400         /* I think we want full paths, even if we're in a subdirectory. */
401         repo_init_revisions(the_repository, &rev, NULL);
402         rev.diffopt.flags = opts->flags;
403         rev.diffopt.output_format |= DIFF_FORMAT_NAME_STATUS;
404         diff_setup_done(&rev.diffopt);
405         add_pending_object(&rev, head, NULL);
406         run_diff_index(&rev, 0);
407 }
408
409 static void describe_detached_head(const char *msg, struct commit *commit)
410 {
411         struct strbuf sb = STRBUF_INIT;
412
413         if (!parse_commit(commit))
414                 pp_commit_easy(CMIT_FMT_ONELINE, commit, &sb);
415         if (print_sha1_ellipsis()) {
416                 fprintf(stderr, "%s %s... %s\n", msg,
417                         find_unique_abbrev(&commit->object.oid, DEFAULT_ABBREV), sb.buf);
418         } else {
419                 fprintf(stderr, "%s %s %s\n", msg,
420                         find_unique_abbrev(&commit->object.oid, DEFAULT_ABBREV), sb.buf);
421         }
422         strbuf_release(&sb);
423 }
424
425 static int reset_tree(struct tree *tree, const struct checkout_opts *o,
426                       int worktree, int *writeout_error)
427 {
428         struct unpack_trees_options opts;
429         struct tree_desc tree_desc;
430
431         memset(&opts, 0, sizeof(opts));
432         opts.head_idx = -1;
433         opts.update = worktree;
434         opts.skip_unmerged = !worktree;
435         opts.reset = 1;
436         opts.merge = 1;
437         opts.fn = oneway_merge;
438         opts.verbose_update = o->show_progress;
439         opts.src_index = &the_index;
440         opts.dst_index = &the_index;
441         parse_tree(tree);
442         init_tree_desc(&tree_desc, tree->buffer, tree->size);
443         switch (unpack_trees(1, &tree_desc, &opts)) {
444         case -2:
445                 *writeout_error = 1;
446                 /*
447                  * We return 0 nevertheless, as the index is all right
448                  * and more importantly we have made best efforts to
449                  * update paths in the work tree, and we cannot revert
450                  * them.
451                  */
452                 /* fallthrough */
453         case 0:
454                 return 0;
455         default:
456                 return 128;
457         }
458 }
459
460 struct branch_info {
461         const char *name; /* The short name used */
462         const char *path; /* The full name of a real branch */
463         struct commit *commit; /* The named commit */
464         /*
465          * if not null the branch is detached because it's already
466          * checked out in this checkout
467          */
468         char *checkout;
469 };
470
471 static void setup_branch_path(struct branch_info *branch)
472 {
473         struct strbuf buf = STRBUF_INIT;
474
475         strbuf_branchname(&buf, branch->name, INTERPRET_BRANCH_LOCAL);
476         if (strcmp(buf.buf, branch->name))
477                 branch->name = xstrdup(buf.buf);
478         strbuf_splice(&buf, 0, 0, "refs/heads/", 11);
479         branch->path = strbuf_detach(&buf, NULL);
480 }
481
482 /*
483  * Skip merging the trees, updating the index and working directory if and
484  * only if we are creating a new branch via "git checkout -b <new_branch>."
485  */
486 static int skip_merge_working_tree(const struct checkout_opts *opts,
487         const struct branch_info *old_branch_info,
488         const struct branch_info *new_branch_info)
489 {
490         /*
491          * Do the merge if sparse checkout is on and the user has not opted in
492          * to the optimized behavior
493          */
494         if (core_apply_sparse_checkout && !checkout_optimize_new_branch)
495                 return 0;
496
497         /*
498          * We must do the merge if we are actually moving to a new commit.
499          */
500         if (!old_branch_info->commit || !new_branch_info->commit ||
501                 !oideq(&old_branch_info->commit->object.oid,
502                        &new_branch_info->commit->object.oid))
503                 return 0;
504
505         /*
506          * opts->patch_mode cannot be used with switching branches so is
507          * not tested here
508          */
509
510         /*
511          * opts->quiet only impacts output so doesn't require a merge
512          */
513
514         /*
515          * Honor the explicit request for a three-way merge or to throw away
516          * local changes
517          */
518         if (opts->merge || opts->force)
519                 return 0;
520
521         /*
522          * --detach is documented as "updating the index and the files in the
523          * working tree" but this optimization skips those steps so fall through
524          * to the regular code path.
525          */
526         if (opts->force_detach)
527                 return 0;
528
529         /*
530          * opts->writeout_stage cannot be used with switching branches so is
531          * not tested here
532          */
533
534         /*
535          * Honor the explicit ignore requests
536          */
537         if (!opts->overwrite_ignore || opts->ignore_skipworktree ||
538                 opts->ignore_other_worktrees)
539                 return 0;
540
541         /*
542          * opts->show_progress only impacts output so doesn't require a merge
543          */
544
545         /*
546          * If we aren't creating a new branch any changes or updates will
547          * happen in the existing branch.  Since that could only be updating
548          * the index and working directory, we don't want to skip those steps
549          * or we've defeated any purpose in running the command.
550          */
551         if (!opts->new_branch)
552                 return 0;
553
554         /*
555          * new_branch_force is defined to "create/reset and checkout a branch"
556          * so needs to go through the merge to do the reset
557          */
558         if (opts->new_branch_force)
559                 return 0;
560
561         /*
562          * A new orphaned branch requrires the index and the working tree to be
563          * adjusted to <start_point>
564          */
565         if (opts->new_orphan_branch)
566                 return 0;
567
568         /*
569          * Remaining variables are not checkout options but used to track state
570          */
571
572         return 1;
573 }
574
575 static int merge_working_tree(const struct checkout_opts *opts,
576                               struct branch_info *old_branch_info,
577                               struct branch_info *new_branch_info,
578                               int *writeout_error)
579 {
580         int ret;
581         struct lock_file lock_file = LOCK_INIT;
582
583         hold_locked_index(&lock_file, LOCK_DIE_ON_ERROR);
584         if (read_cache_preload(NULL) < 0)
585                 return error(_("index file corrupt"));
586
587         resolve_undo_clear();
588         if (opts->force) {
589                 ret = reset_tree(get_commit_tree(new_branch_info->commit),
590                                  opts, 1, writeout_error);
591                 if (ret)
592                         return ret;
593         } else {
594                 struct tree_desc trees[2];
595                 struct tree *tree;
596                 struct unpack_trees_options topts;
597
598                 memset(&topts, 0, sizeof(topts));
599                 topts.head_idx = -1;
600                 topts.src_index = &the_index;
601                 topts.dst_index = &the_index;
602
603                 setup_unpack_trees_porcelain(&topts, "checkout");
604
605                 refresh_cache(REFRESH_QUIET);
606
607                 if (unmerged_cache()) {
608                         error(_("you need to resolve your current index first"));
609                         return 1;
610                 }
611
612                 /* 2-way merge to the new branch */
613                 topts.initial_checkout = is_cache_unborn();
614                 topts.update = 1;
615                 topts.merge = 1;
616                 topts.gently = opts->merge && old_branch_info->commit;
617                 topts.verbose_update = opts->show_progress;
618                 topts.fn = twoway_merge;
619                 if (opts->overwrite_ignore) {
620                         topts.dir = xcalloc(1, sizeof(*topts.dir));
621                         topts.dir->flags |= DIR_SHOW_IGNORED;
622                         setup_standard_excludes(topts.dir);
623                 }
624                 tree = parse_tree_indirect(old_branch_info->commit ?
625                                            &old_branch_info->commit->object.oid :
626                                            the_hash_algo->empty_tree);
627                 init_tree_desc(&trees[0], tree->buffer, tree->size);
628                 tree = parse_tree_indirect(&new_branch_info->commit->object.oid);
629                 init_tree_desc(&trees[1], tree->buffer, tree->size);
630
631                 ret = unpack_trees(2, trees, &topts);
632                 clear_unpack_trees_porcelain(&topts);
633                 if (ret == -1) {
634                         /*
635                          * Unpack couldn't do a trivial merge; either
636                          * give up or do a real merge, depending on
637                          * whether the merge flag was used.
638                          */
639                         struct tree *result;
640                         struct tree *work;
641                         struct merge_options o;
642                         if (!opts->merge)
643                                 return 1;
644
645                         /*
646                          * Without old_branch_info->commit, the below is the same as
647                          * the two-tree unpack we already tried and failed.
648                          */
649                         if (!old_branch_info->commit)
650                                 return 1;
651
652                         /* Do more real merge */
653
654                         /*
655                          * We update the index fully, then write the
656                          * tree from the index, then merge the new
657                          * branch with the current tree, with the old
658                          * branch as the base. Then we reset the index
659                          * (but not the working tree) to the new
660                          * branch, leaving the working tree as the
661                          * merged version, but skipping unmerged
662                          * entries in the index.
663                          */
664
665                         add_files_to_cache(NULL, NULL, 0);
666                         /*
667                          * NEEDSWORK: carrying over local changes
668                          * when branches have different end-of-line
669                          * normalization (or clean+smudge rules) is
670                          * a pain; plumb in an option to set
671                          * o.renormalize?
672                          */
673                         init_merge_options(&o);
674                         o.verbosity = 0;
675                         work = write_tree_from_memory(&o);
676
677                         ret = reset_tree(get_commit_tree(new_branch_info->commit),
678                                          opts, 1,
679                                          writeout_error);
680                         if (ret)
681                                 return ret;
682                         o.ancestor = old_branch_info->name;
683                         o.branch1 = new_branch_info->name;
684                         o.branch2 = "local";
685                         ret = merge_trees(&o,
686                                           get_commit_tree(new_branch_info->commit),
687                                           work,
688                                           get_commit_tree(old_branch_info->commit),
689                                           &result);
690                         if (ret < 0)
691                                 exit(128);
692                         ret = reset_tree(get_commit_tree(new_branch_info->commit),
693                                          opts, 0,
694                                          writeout_error);
695                         strbuf_release(&o.obuf);
696                         if (ret)
697                                 return ret;
698                 }
699         }
700
701         if (!active_cache_tree)
702                 active_cache_tree = cache_tree();
703
704         if (!cache_tree_fully_valid(active_cache_tree))
705                 cache_tree_update(&the_index, WRITE_TREE_SILENT | WRITE_TREE_REPAIR);
706
707         if (write_locked_index(&the_index, &lock_file, COMMIT_LOCK))
708                 die(_("unable to write new index file"));
709
710         if (!opts->force && !opts->quiet)
711                 show_local_changes(&new_branch_info->commit->object, &opts->diff_options);
712
713         return 0;
714 }
715
716 static void report_tracking(struct branch_info *new_branch_info)
717 {
718         struct strbuf sb = STRBUF_INIT;
719         struct branch *branch = branch_get(new_branch_info->name);
720
721         if (!format_tracking_info(branch, &sb, AHEAD_BEHIND_FULL))
722                 return;
723         fputs(sb.buf, stdout);
724         strbuf_release(&sb);
725 }
726
727 static void update_refs_for_switch(const struct checkout_opts *opts,
728                                    struct branch_info *old_branch_info,
729                                    struct branch_info *new_branch_info)
730 {
731         struct strbuf msg = STRBUF_INIT;
732         const char *old_desc, *reflog_msg;
733         if (opts->new_branch) {
734                 if (opts->new_orphan_branch) {
735                         char *refname;
736
737                         refname = mkpathdup("refs/heads/%s", opts->new_orphan_branch);
738                         if (opts->new_branch_log &&
739                             !should_autocreate_reflog(refname)) {
740                                 int ret;
741                                 struct strbuf err = STRBUF_INIT;
742
743                                 ret = safe_create_reflog(refname, 1, &err);
744                                 if (ret) {
745                                         fprintf(stderr, _("Can not do reflog for '%s': %s\n"),
746                                                 opts->new_orphan_branch, err.buf);
747                                         strbuf_release(&err);
748                                         free(refname);
749                                         return;
750                                 }
751                                 strbuf_release(&err);
752                         }
753                         free(refname);
754                 }
755                 else
756                         create_branch(opts->new_branch, new_branch_info->name,
757                                       opts->new_branch_force ? 1 : 0,
758                                       opts->new_branch_force ? 1 : 0,
759                                       opts->new_branch_log,
760                                       opts->quiet,
761                                       opts->track);
762                 new_branch_info->name = opts->new_branch;
763                 setup_branch_path(new_branch_info);
764         }
765
766         old_desc = old_branch_info->name;
767         if (!old_desc && old_branch_info->commit)
768                 old_desc = oid_to_hex(&old_branch_info->commit->object.oid);
769
770         reflog_msg = getenv("GIT_REFLOG_ACTION");
771         if (!reflog_msg)
772                 strbuf_addf(&msg, "checkout: moving from %s to %s",
773                         old_desc ? old_desc : "(invalid)", new_branch_info->name);
774         else
775                 strbuf_insert(&msg, 0, reflog_msg, strlen(reflog_msg));
776
777         if (!strcmp(new_branch_info->name, "HEAD") && !new_branch_info->path && !opts->force_detach) {
778                 /* Nothing to do. */
779         } else if (opts->force_detach || !new_branch_info->path) {      /* No longer on any branch. */
780                 update_ref(msg.buf, "HEAD", &new_branch_info->commit->object.oid, NULL,
781                            REF_NO_DEREF, UPDATE_REFS_DIE_ON_ERR);
782                 if (!opts->quiet) {
783                         if (old_branch_info->path &&
784                             advice_detached_head && !opts->force_detach)
785                                 detach_advice(new_branch_info->name);
786                         describe_detached_head(_("HEAD is now at"), new_branch_info->commit);
787                 }
788         } else if (new_branch_info->path) {     /* Switch branches. */
789                 if (create_symref("HEAD", new_branch_info->path, msg.buf) < 0)
790                         die(_("unable to update HEAD"));
791                 if (!opts->quiet) {
792                         if (old_branch_info->path && !strcmp(new_branch_info->path, old_branch_info->path)) {
793                                 if (opts->new_branch_force)
794                                         fprintf(stderr, _("Reset branch '%s'\n"),
795                                                 new_branch_info->name);
796                                 else
797                                         fprintf(stderr, _("Already on '%s'\n"),
798                                                 new_branch_info->name);
799                         } else if (opts->new_branch) {
800                                 if (opts->branch_exists)
801                                         fprintf(stderr, _("Switched to and reset branch '%s'\n"), new_branch_info->name);
802                                 else
803                                         fprintf(stderr, _("Switched to a new branch '%s'\n"), new_branch_info->name);
804                         } else {
805                                 fprintf(stderr, _("Switched to branch '%s'\n"),
806                                         new_branch_info->name);
807                         }
808                 }
809                 if (old_branch_info->path && old_branch_info->name) {
810                         if (!ref_exists(old_branch_info->path) && reflog_exists(old_branch_info->path))
811                                 delete_reflog(old_branch_info->path);
812                 }
813         }
814         remove_branch_state();
815         strbuf_release(&msg);
816         if (!opts->quiet &&
817             (new_branch_info->path || (!opts->force_detach && !strcmp(new_branch_info->name, "HEAD"))))
818                 report_tracking(new_branch_info);
819 }
820
821 static int add_pending_uninteresting_ref(const char *refname,
822                                          const struct object_id *oid,
823                                          int flags, void *cb_data)
824 {
825         add_pending_oid(cb_data, refname, oid, UNINTERESTING);
826         return 0;
827 }
828
829 static void describe_one_orphan(struct strbuf *sb, struct commit *commit)
830 {
831         strbuf_addstr(sb, "  ");
832         strbuf_add_unique_abbrev(sb, &commit->object.oid, DEFAULT_ABBREV);
833         strbuf_addch(sb, ' ');
834         if (!parse_commit(commit))
835                 pp_commit_easy(CMIT_FMT_ONELINE, commit, sb);
836         strbuf_addch(sb, '\n');
837 }
838
839 #define ORPHAN_CUTOFF 4
840 static void suggest_reattach(struct commit *commit, struct rev_info *revs)
841 {
842         struct commit *c, *last = NULL;
843         struct strbuf sb = STRBUF_INIT;
844         int lost = 0;
845         while ((c = get_revision(revs)) != NULL) {
846                 if (lost < ORPHAN_CUTOFF)
847                         describe_one_orphan(&sb, c);
848                 last = c;
849                 lost++;
850         }
851         if (ORPHAN_CUTOFF < lost) {
852                 int more = lost - ORPHAN_CUTOFF;
853                 if (more == 1)
854                         describe_one_orphan(&sb, last);
855                 else
856                         strbuf_addf(&sb, _(" ... and %d more.\n"), more);
857         }
858
859         fprintf(stderr,
860                 Q_(
861                 /* The singular version */
862                 "Warning: you are leaving %d commit behind, "
863                 "not connected to\n"
864                 "any of your branches:\n\n"
865                 "%s\n",
866                 /* The plural version */
867                 "Warning: you are leaving %d commits behind, "
868                 "not connected to\n"
869                 "any of your branches:\n\n"
870                 "%s\n",
871                 /* Give ngettext() the count */
872                 lost),
873                 lost,
874                 sb.buf);
875         strbuf_release(&sb);
876
877         if (advice_detached_head)
878                 fprintf(stderr,
879                         Q_(
880                         /* The singular version */
881                         "If you want to keep it by creating a new branch, "
882                         "this may be a good time\nto do so with:\n\n"
883                         " git branch <new-branch-name> %s\n\n",
884                         /* The plural version */
885                         "If you want to keep them by creating a new branch, "
886                         "this may be a good time\nto do so with:\n\n"
887                         " git branch <new-branch-name> %s\n\n",
888                         /* Give ngettext() the count */
889                         lost),
890                         find_unique_abbrev(&commit->object.oid, DEFAULT_ABBREV));
891 }
892
893 /*
894  * We are about to leave commit that was at the tip of a detached
895  * HEAD.  If it is not reachable from any ref, this is the last chance
896  * for the user to do so without resorting to reflog.
897  */
898 static void orphaned_commit_warning(struct commit *old_commit, struct commit *new_commit)
899 {
900         struct rev_info revs;
901         struct object *object = &old_commit->object;
902
903         repo_init_revisions(the_repository, &revs, NULL);
904         setup_revisions(0, NULL, &revs, NULL);
905
906         object->flags &= ~UNINTERESTING;
907         add_pending_object(&revs, object, oid_to_hex(&object->oid));
908
909         for_each_ref(add_pending_uninteresting_ref, &revs);
910         add_pending_oid(&revs, "HEAD", &new_commit->object.oid, UNINTERESTING);
911
912         if (prepare_revision_walk(&revs))
913                 die(_("internal error in revision walk"));
914         if (!(old_commit->object.flags & UNINTERESTING))
915                 suggest_reattach(old_commit, &revs);
916         else
917                 describe_detached_head(_("Previous HEAD position was"), old_commit);
918
919         /* Clean up objects used, as they will be reused. */
920         clear_commit_marks_all(ALL_REV_FLAGS);
921 }
922
923 static int switch_branches(const struct checkout_opts *opts,
924                            struct branch_info *new_branch_info)
925 {
926         int ret = 0;
927         struct branch_info old_branch_info;
928         void *path_to_free;
929         struct object_id rev;
930         int flag, writeout_error = 0;
931         memset(&old_branch_info, 0, sizeof(old_branch_info));
932         old_branch_info.path = path_to_free = resolve_refdup("HEAD", 0, &rev, &flag);
933         if (old_branch_info.path)
934                 old_branch_info.commit = lookup_commit_reference_gently(the_repository, &rev, 1);
935         if (!(flag & REF_ISSYMREF))
936                 old_branch_info.path = NULL;
937
938         if (old_branch_info.path)
939                 skip_prefix(old_branch_info.path, "refs/heads/", &old_branch_info.name);
940
941         if (!new_branch_info->name) {
942                 new_branch_info->name = "HEAD";
943                 new_branch_info->commit = old_branch_info.commit;
944                 if (!new_branch_info->commit)
945                         die(_("You are on a branch yet to be born"));
946                 parse_commit_or_die(new_branch_info->commit);
947         }
948
949         /* optimize the "checkout -b <new_branch> path */
950         if (skip_merge_working_tree(opts, &old_branch_info, new_branch_info)) {
951                 if (!checkout_optimize_new_branch && !opts->quiet) {
952                         if (read_cache_preload(NULL) < 0)
953                                 return error(_("index file corrupt"));
954                         show_local_changes(&new_branch_info->commit->object, &opts->diff_options);
955                 }
956         } else {
957                 ret = merge_working_tree(opts, &old_branch_info, new_branch_info, &writeout_error);
958                 if (ret) {
959                         free(path_to_free);
960                         return ret;
961                 }
962         }
963
964         if (!opts->quiet && !old_branch_info.path && old_branch_info.commit && new_branch_info->commit != old_branch_info.commit)
965                 orphaned_commit_warning(old_branch_info.commit, new_branch_info->commit);
966
967         update_refs_for_switch(opts, &old_branch_info, new_branch_info);
968
969         ret = post_checkout_hook(old_branch_info.commit, new_branch_info->commit, 1);
970         free(path_to_free);
971         return ret || writeout_error;
972 }
973
974 static int git_checkout_config(const char *var, const char *value, void *cb)
975 {
976         if (!strcmp(var, "checkout.optimizenewbranch")) {
977                 checkout_optimize_new_branch = git_config_bool(var, value);
978                 return 0;
979         }
980
981         if (!strcmp(var, "diff.ignoresubmodules")) {
982                 struct checkout_opts *opts = cb;
983                 handle_ignore_submodules_arg(&opts->diff_options, value);
984                 return 0;
985         }
986
987         if (starts_with(var, "submodule."))
988                 return git_default_submodule_config(var, value, NULL);
989
990         return git_xmerge_config(var, value, NULL);
991 }
992
993 static int parse_branchname_arg(int argc, const char **argv,
994                                 int dwim_new_local_branch_ok,
995                                 struct branch_info *new_branch_info,
996                                 struct checkout_opts *opts,
997                                 struct object_id *rev,
998                                 int *dwim_remotes_matched)
999 {
1000         struct tree **source_tree = &opts->source_tree;
1001         const char **new_branch = &opts->new_branch;
1002         int argcount = 0;
1003         struct object_id branch_rev;
1004         const char *arg;
1005         int dash_dash_pos;
1006         int has_dash_dash = 0;
1007         int i;
1008
1009         /*
1010          * case 1: git checkout <ref> -- [<paths>]
1011          *
1012          *   <ref> must be a valid tree, everything after the '--' must be
1013          *   a path.
1014          *
1015          * case 2: git checkout -- [<paths>]
1016          *
1017          *   everything after the '--' must be paths.
1018          *
1019          * case 3: git checkout <something> [--]
1020          *
1021          *   (a) If <something> is a commit, that is to
1022          *       switch to the branch or detach HEAD at it.  As a special case,
1023          *       if <something> is A...B (missing A or B means HEAD but you can
1024          *       omit at most one side), and if there is a unique merge base
1025          *       between A and B, A...B names that merge base.
1026          *
1027          *   (b) If <something> is _not_ a commit, either "--" is present
1028          *       or <something> is not a path, no -t or -b was given, and
1029          *       and there is a tracking branch whose name is <something>
1030          *       in one and only one remote (or if the branch exists on the
1031          *       remote named in checkout.defaultRemote), then this is a
1032          *       short-hand to fork local <something> from that
1033          *       remote-tracking branch.
1034          *
1035          *   (c) Otherwise, if "--" is present, treat it like case (1).
1036          *
1037          *   (d) Otherwise :
1038          *       - if it's a reference, treat it like case (1)
1039          *       - else if it's a path, treat it like case (2)
1040          *       - else: fail.
1041          *
1042          * case 4: git checkout <something> <paths>
1043          *
1044          *   The first argument must not be ambiguous.
1045          *   - If it's *only* a reference, treat it like case (1).
1046          *   - If it's only a path, treat it like case (2).
1047          *   - else: fail.
1048          *
1049          */
1050         if (!argc)
1051                 return 0;
1052
1053         arg = argv[0];
1054         dash_dash_pos = -1;
1055         for (i = 0; i < argc; i++) {
1056                 if (!strcmp(argv[i], "--")) {
1057                         dash_dash_pos = i;
1058                         break;
1059                 }
1060         }
1061         if (dash_dash_pos == 0)
1062                 return 1; /* case (2) */
1063         else if (dash_dash_pos == 1)
1064                 has_dash_dash = 1; /* case (3) or (1) */
1065         else if (dash_dash_pos >= 2)
1066                 die(_("only one reference expected, %d given."), dash_dash_pos);
1067
1068         if (!strcmp(arg, "-"))
1069                 arg = "@{-1}";
1070
1071         if (get_oid_mb(arg, rev)) {
1072                 /*
1073                  * Either case (3) or (4), with <something> not being
1074                  * a commit, or an attempt to use case (1) with an
1075                  * invalid ref.
1076                  *
1077                  * It's likely an error, but we need to find out if
1078                  * we should auto-create the branch, case (3).(b).
1079                  */
1080                 int recover_with_dwim = dwim_new_local_branch_ok;
1081
1082                 if (!has_dash_dash &&
1083                     (check_filename(opts->prefix, arg) || !no_wildcard(arg)))
1084                         recover_with_dwim = 0;
1085                 /*
1086                  * Accept "git checkout foo" and "git checkout foo --"
1087                  * as candidates for dwim.
1088                  */
1089                 if (!(argc == 1 && !has_dash_dash) &&
1090                     !(argc == 2 && has_dash_dash))
1091                         recover_with_dwim = 0;
1092
1093                 if (recover_with_dwim) {
1094                         const char *remote = unique_tracking_name(arg, rev,
1095                                                                   dwim_remotes_matched);
1096                         if (remote) {
1097                                 *new_branch = arg;
1098                                 arg = remote;
1099                                 /* DWIMmed to create local branch, case (3).(b) */
1100                         } else {
1101                                 recover_with_dwim = 0;
1102                         }
1103                 }
1104
1105                 if (!recover_with_dwim) {
1106                         if (has_dash_dash)
1107                                 die(_("invalid reference: %s"), arg);
1108                         return argcount;
1109                 }
1110         }
1111
1112         /* we can't end up being in (2) anymore, eat the argument */
1113         argcount++;
1114         argv++;
1115         argc--;
1116
1117         new_branch_info->name = arg;
1118         setup_branch_path(new_branch_info);
1119
1120         if (!check_refname_format(new_branch_info->path, 0) &&
1121             !read_ref(new_branch_info->path, &branch_rev))
1122                 oidcpy(rev, &branch_rev);
1123         else
1124                 new_branch_info->path = NULL; /* not an existing branch */
1125
1126         new_branch_info->commit = lookup_commit_reference_gently(the_repository, rev, 1);
1127         if (!new_branch_info->commit) {
1128                 /* not a commit */
1129                 *source_tree = parse_tree_indirect(rev);
1130         } else {
1131                 parse_commit_or_die(new_branch_info->commit);
1132                 *source_tree = get_commit_tree(new_branch_info->commit);
1133         }
1134
1135         if (!*source_tree)                   /* case (1): want a tree */
1136                 die(_("reference is not a tree: %s"), arg);
1137         if (!has_dash_dash) {   /* case (3).(d) -> (1) */
1138                 /*
1139                  * Do not complain the most common case
1140                  *      git checkout branch
1141                  * even if there happen to be a file called 'branch';
1142                  * it would be extremely annoying.
1143                  */
1144                 if (argc)
1145                         verify_non_filename(opts->prefix, arg);
1146         } else {
1147                 argcount++;
1148                 argv++;
1149                 argc--;
1150         }
1151
1152         return argcount;
1153 }
1154
1155 static int switch_unborn_to_new_branch(const struct checkout_opts *opts)
1156 {
1157         int status;
1158         struct strbuf branch_ref = STRBUF_INIT;
1159
1160         if (!opts->new_branch)
1161                 die(_("You are on a branch yet to be born"));
1162         strbuf_addf(&branch_ref, "refs/heads/%s", opts->new_branch);
1163         status = create_symref("HEAD", branch_ref.buf, "checkout -b");
1164         strbuf_release(&branch_ref);
1165         if (!opts->quiet)
1166                 fprintf(stderr, _("Switched to a new branch '%s'\n"),
1167                         opts->new_branch);
1168         return status;
1169 }
1170
1171 static int checkout_branch(struct checkout_opts *opts,
1172                            struct branch_info *new_branch_info)
1173 {
1174         if (opts->pathspec.nr)
1175                 die(_("paths cannot be used with switching branches"));
1176
1177         if (opts->patch_mode)
1178                 die(_("'%s' cannot be used with switching branches"),
1179                     "--patch");
1180
1181         if (opts->writeout_stage)
1182                 die(_("'%s' cannot be used with switching branches"),
1183                     "--ours/--theirs");
1184
1185         if (opts->force && opts->merge)
1186                 die(_("'%s' cannot be used with '%s'"), "-f", "-m");
1187
1188         if (opts->force_detach && opts->new_branch)
1189                 die(_("'%s' cannot be used with '%s'"),
1190                     "--detach", "-b/-B/--orphan");
1191
1192         if (opts->new_orphan_branch) {
1193                 if (opts->track != BRANCH_TRACK_UNSPECIFIED)
1194                         die(_("'%s' cannot be used with '%s'"), "--orphan", "-t");
1195         } else if (opts->force_detach) {
1196                 if (opts->track != BRANCH_TRACK_UNSPECIFIED)
1197                         die(_("'%s' cannot be used with '%s'"), "--detach", "-t");
1198         } else if (opts->track == BRANCH_TRACK_UNSPECIFIED)
1199                 opts->track = git_branch_track;
1200
1201         if (new_branch_info->name && !new_branch_info->commit)
1202                 die(_("Cannot switch branch to a non-commit '%s'"),
1203                     new_branch_info->name);
1204
1205         if (new_branch_info->path && !opts->force_detach && !opts->new_branch &&
1206             !opts->ignore_other_worktrees) {
1207                 int flag;
1208                 char *head_ref = resolve_refdup("HEAD", 0, NULL, &flag);
1209                 if (head_ref &&
1210                     (!(flag & REF_ISSYMREF) || strcmp(head_ref, new_branch_info->path)))
1211                         die_if_checked_out(new_branch_info->path, 1);
1212                 free(head_ref);
1213         }
1214
1215         if (!new_branch_info->commit && opts->new_branch) {
1216                 struct object_id rev;
1217                 int flag;
1218
1219                 if (!read_ref_full("HEAD", 0, &rev, &flag) &&
1220                     (flag & REF_ISSYMREF) && is_null_oid(&rev))
1221                         return switch_unborn_to_new_branch(opts);
1222         }
1223         return switch_branches(opts, new_branch_info);
1224 }
1225
1226 int cmd_checkout(int argc, const char **argv, const char *prefix)
1227 {
1228         struct checkout_opts opts;
1229         struct branch_info new_branch_info;
1230         char *conflict_style = NULL;
1231         int dwim_new_local_branch = 1;
1232         int dwim_remotes_matched = 0;
1233         struct option options[] = {
1234                 OPT__QUIET(&opts.quiet, N_("suppress progress reporting")),
1235                 OPT_STRING('b', NULL, &opts.new_branch, N_("branch"),
1236                            N_("create and checkout a new branch")),
1237                 OPT_STRING('B', NULL, &opts.new_branch_force, N_("branch"),
1238                            N_("create/reset and checkout a branch")),
1239                 OPT_BOOL('l', NULL, &opts.new_branch_log, N_("create reflog for new branch")),
1240                 OPT_BOOL(0, "detach", &opts.force_detach, N_("detach HEAD at named commit")),
1241                 OPT_SET_INT('t', "track",  &opts.track, N_("set upstream info for new branch"),
1242                         BRANCH_TRACK_EXPLICIT),
1243                 OPT_STRING(0, "orphan", &opts.new_orphan_branch, N_("new-branch"), N_("new unparented branch")),
1244                 OPT_SET_INT_F('2', "ours", &opts.writeout_stage,
1245                               N_("checkout our version for unmerged files"),
1246                               2, PARSE_OPT_NONEG),
1247                 OPT_SET_INT_F('3', "theirs", &opts.writeout_stage,
1248                               N_("checkout their version for unmerged files"),
1249                               3, PARSE_OPT_NONEG),
1250                 OPT__FORCE(&opts.force, N_("force checkout (throw away local modifications)"),
1251                            PARSE_OPT_NOCOMPLETE),
1252                 OPT_BOOL('m', "merge", &opts.merge, N_("perform a 3-way merge with the new branch")),
1253                 OPT_BOOL_F(0, "overwrite-ignore", &opts.overwrite_ignore,
1254                            N_("update ignored files (default)"),
1255                            PARSE_OPT_NOCOMPLETE),
1256                 OPT_STRING(0, "conflict", &conflict_style, N_("style"),
1257                            N_("conflict style (merge or diff3)")),
1258                 OPT_BOOL('p', "patch", &opts.patch_mode, N_("select hunks interactively")),
1259                 OPT_BOOL(0, "ignore-skip-worktree-bits", &opts.ignore_skipworktree,
1260                          N_("do not limit pathspecs to sparse entries only")),
1261                 OPT_HIDDEN_BOOL(0, "guess", &dwim_new_local_branch,
1262                                 N_("second guess 'git checkout <no-such-branch>'")),
1263                 OPT_BOOL(0, "ignore-other-worktrees", &opts.ignore_other_worktrees,
1264                          N_("do not check if another worktree is holding the given ref")),
1265                 { OPTION_CALLBACK, 0, "recurse-submodules", NULL,
1266                             "checkout", "control recursive updating of submodules",
1267                             PARSE_OPT_OPTARG, option_parse_recurse_submodules_worktree_updater },
1268                 OPT_BOOL(0, "progress", &opts.show_progress, N_("force progress reporting")),
1269                 OPT_END(),
1270         };
1271
1272         memset(&opts, 0, sizeof(opts));
1273         memset(&new_branch_info, 0, sizeof(new_branch_info));
1274         opts.overwrite_ignore = 1;
1275         opts.prefix = prefix;
1276         opts.show_progress = -1;
1277
1278         git_config(git_checkout_config, &opts);
1279
1280         opts.track = BRANCH_TRACK_UNSPECIFIED;
1281
1282         argc = parse_options(argc, argv, prefix, options, checkout_usage,
1283                              PARSE_OPT_KEEP_DASHDASH);
1284
1285         if (opts.show_progress < 0) {
1286                 if (opts.quiet)
1287                         opts.show_progress = 0;
1288                 else
1289                         opts.show_progress = isatty(2);
1290         }
1291
1292         if (conflict_style) {
1293                 opts.merge = 1; /* implied */
1294                 git_xmerge_config("merge.conflictstyle", conflict_style, NULL);
1295         }
1296
1297         if ((!!opts.new_branch + !!opts.new_branch_force + !!opts.new_orphan_branch) > 1)
1298                 die(_("-b, -B and --orphan are mutually exclusive"));
1299
1300         /*
1301          * From here on, new_branch will contain the branch to be checked out,
1302          * and new_branch_force and new_orphan_branch will tell us which one of
1303          * -b/-B/--orphan is being used.
1304          */
1305         if (opts.new_branch_force)
1306                 opts.new_branch = opts.new_branch_force;
1307
1308         if (opts.new_orphan_branch)
1309                 opts.new_branch = opts.new_orphan_branch;
1310
1311         /* --track without -b/-B/--orphan should DWIM */
1312         if (opts.track != BRANCH_TRACK_UNSPECIFIED && !opts.new_branch) {
1313                 const char *argv0 = argv[0];
1314                 if (!argc || !strcmp(argv0, "--"))
1315                         die(_("--track needs a branch name"));
1316                 skip_prefix(argv0, "refs/", &argv0);
1317                 skip_prefix(argv0, "remotes/", &argv0);
1318                 argv0 = strchr(argv0, '/');
1319                 if (!argv0 || !argv0[1])
1320                         die(_("missing branch name; try -b"));
1321                 opts.new_branch = argv0 + 1;
1322         }
1323
1324         /*
1325          * Extract branch name from command line arguments, so
1326          * all that is left is pathspecs.
1327          *
1328          * Handle
1329          *
1330          *  1) git checkout <tree> -- [<paths>]
1331          *  2) git checkout -- [<paths>]
1332          *  3) git checkout <something> [<paths>]
1333          *
1334          * including "last branch" syntax and DWIM-ery for names of
1335          * remote branches, erroring out for invalid or ambiguous cases.
1336          */
1337         if (argc) {
1338                 struct object_id rev;
1339                 int dwim_ok =
1340                         !opts.patch_mode &&
1341                         dwim_new_local_branch &&
1342                         opts.track == BRANCH_TRACK_UNSPECIFIED &&
1343                         !opts.new_branch;
1344                 int n = parse_branchname_arg(argc, argv, dwim_ok,
1345                                              &new_branch_info, &opts, &rev,
1346                                              &dwim_remotes_matched);
1347                 argv += n;
1348                 argc -= n;
1349         }
1350
1351         if (argc) {
1352                 parse_pathspec(&opts.pathspec, 0,
1353                                opts.patch_mode ? PATHSPEC_PREFIX_ORIGIN : 0,
1354                                prefix, argv);
1355
1356                 if (!opts.pathspec.nr)
1357                         die(_("invalid path specification"));
1358
1359                 /*
1360                  * Try to give more helpful suggestion.
1361                  * new_branch && argc > 1 will be caught later.
1362                  */
1363                 if (opts.new_branch && argc == 1)
1364                         die(_("'%s' is not a commit and a branch '%s' cannot be created from it"),
1365                                 argv[0], opts.new_branch);
1366
1367                 if (opts.force_detach)
1368                         die(_("git checkout: --detach does not take a path argument '%s'"),
1369                             argv[0]);
1370
1371                 if (1 < !!opts.writeout_stage + !!opts.force + !!opts.merge)
1372                         die(_("git checkout: --ours/--theirs, --force and --merge are incompatible when\n"
1373                               "checking out of the index."));
1374         }
1375
1376         if (opts.new_branch) {
1377                 struct strbuf buf = STRBUF_INIT;
1378
1379                 if (opts.new_branch_force)
1380                         opts.branch_exists = validate_branchname(opts.new_branch, &buf);
1381                 else
1382                         opts.branch_exists =
1383                                 validate_new_branchname(opts.new_branch, &buf, 0);
1384                 strbuf_release(&buf);
1385         }
1386
1387         UNLEAK(opts);
1388         if (opts.patch_mode || opts.pathspec.nr) {
1389                 int ret = checkout_paths(&opts, new_branch_info.name);
1390                 if (ret && dwim_remotes_matched > 1 &&
1391                     advice_checkout_ambiguous_remote_branch_name)
1392                         advise(_("'%s' matched more than one remote tracking branch.\n"
1393                                  "We found %d remotes with a reference that matched. So we fell back\n"
1394                                  "on trying to resolve the argument as a path, but failed there too!\n"
1395                                  "\n"
1396                                  "If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
1397                                  "you can do so by fully qualifying the name with the --track option:\n"
1398                                  "\n"
1399                                  "    git checkout --track origin/<name>\n"
1400                                  "\n"
1401                                  "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
1402                                  "one remote, e.g. the 'origin' remote, consider setting\n"
1403                                  "checkout.defaultRemote=origin in your config."),
1404                                argv[0],
1405                                dwim_remotes_matched);
1406                 return ret;
1407         } else {
1408                 return checkout_branch(&opts, &new_branch_info);
1409         }
1410 }