Move 'builtin-*' into a 'builtin/' subdirectory

This shrinks the top-level directory a bit, and makes it much more
pleasant to use auto-completion on the thing. Instead of

	[torvalds@nehalem git]$ em buil<tab>
	Display all 180 possibilities? (y or n)
	[torvalds@nehalem git]$ em builtin-sh
	builtin-shortlog.c     builtin-show-branch.c  builtin-show-ref.c
	builtin-shortlog.o     builtin-show-branch.o  builtin-show-ref.o
	[torvalds@nehalem git]$ em builtin-shor<tab>
	builtin-shortlog.c  builtin-shortlog.o
	[torvalds@nehalem git]$ em builtin-shortlog.c

you get

	[torvalds@nehalem git]$ em buil<tab>		[type]
	builtin/   builtin.h
	[torvalds@nehalem git]$ em builtin		[auto-completes to]
	[torvalds@nehalem git]$ em builtin/sh<tab>	[type]
	shortlog.c     shortlog.o     show-branch.c  show-branch.o  show-ref.c     show-ref.o
	[torvalds@nehalem git]$ em builtin/sho		[auto-completes to]
	[torvalds@nehalem git]$ em builtin/shor<tab>	[type]
	shortlog.c  shortlog.o
	[torvalds@nehalem git]$ em builtin/shortlog.c

which doesn't seem all that different, but not having that annoying
break in "Display all 180 possibilities?" is quite a relief.

NOTE! If you do this in a clean tree (no object files etc), or using an
editor that has auto-completion rules that ignores '*.o' files, you
won't see that annoying 'Display all 180 possibilities?' message - it
will just show the choices instead.  I think bash has some cut-off
around 100 choices or something.

So the reason I see this is that I'm using an odd editory, and thus
don't have the rules to cut down on auto-completion.  But you can
simulate that by using 'ls' instead, or something similar.

Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

1 files changed, 853 insertions, 0 deletions

diff --git a/builtin/checkout.c b/builtin/checkout.c
new file mode 100644
index 0000000..c5ab783
--- /dev/null
+++ b/builtin/checkout.c
@@ -0,0 +1,853 @@
+#include "cache.h"
+#include "builtin.h"
+#include "parse-options.h"
+#include "refs.h"
+#include "commit.h"
+#include "tree.h"
+#include "tree-walk.h"
+#include "cache-tree.h"
+#include "unpack-trees.h"
+#include "dir.h"
+#include "run-command.h"
+#include "merge-recursive.h"
+#include "branch.h"
+#include "diff.h"
+#include "revision.h"
+#include "remote.h"
+#include "blob.h"
+#include "xdiff-interface.h"
+#include "ll-merge.h"
+#include "resolve-undo.h"
+
+static const char * const checkout_usage[] = {
+	"git checkout [options] <branch>",
+	"git checkout [options] [<branch>] -- <file>...",
+	NULL,
+};
+
+struct checkout_opts {
+	int quiet;
+	int merge;
+	int force;
+	int writeout_stage;
+	int writeout_error;
+
+	const char *new_branch;
+	int new_branch_log;
+	enum branch_track track;
+};
+
+static int post_checkout_hook(struct commit *old, struct commit *new,
+			      int changed)
+{
+	return run_hook(NULL, "post-checkout",
+			sha1_to_hex(old ? old->object.sha1 : null_sha1),
+			sha1_to_hex(new ? new->object.sha1 : null_sha1),
+			changed ? "1" : "0", NULL);
+	/* "new" can be NULL when checking out from the index before
+	   a commit exists. */
+
+}
+
+static int update_some(const unsigned char *sha1, const char *base, int baselen,
+		const char *pathname, unsigned mode, int stage, void *context)
+{
+	int len;
+	struct cache_entry *ce;
+
+	if (S_ISDIR(mode))
+		return READ_TREE_RECURSIVE;
+
+	len = baselen + strlen(pathname);
+	ce = xcalloc(1, cache_entry_size(len));
+	hashcpy(ce->sha1, sha1);
+	memcpy(ce->name, base, baselen);
+	memcpy(ce->name + baselen, pathname, len - baselen);
+	ce->ce_flags = create_ce_flags(len, 0);
+	ce->ce_mode = create_ce_mode(mode);
+	add_cache_entry(ce, ADD_CACHE_OK_TO_ADD | ADD_CACHE_OK_TO_REPLACE);
+	return 0;
+}
+
+static int read_tree_some(struct tree *tree, const char **pathspec)
+{
+	read_tree_recursive(tree, "", 0, 0, pathspec, update_some, NULL);
+
+	/* update the index with the given tree's info
+	 * for all args, expanding wildcards, and exit
+	 * with any non-zero return code.
+	 */
+	return 0;
+}
+
+static int skip_same_name(struct cache_entry *ce, int pos)
+{
+	while (++pos < active_nr &&
+	       !strcmp(active_cache[pos]->name, ce->name))
+		; /* skip */
+	return pos;
+}
+
+static int check_stage(int stage, struct cache_entry *ce, int pos)
+{
+	while (pos < active_nr &&
+	       !strcmp(active_cache[pos]->name, ce->name)) {
+		if (ce_stage(active_cache[pos]) == stage)
+			return 0;
+		pos++;
+	}
+	return error("path '%s' does not have %s version",
+		     ce->name,
+		     (stage == 2) ? "our" : "their");
+}
+
+static int check_all_stages(struct cache_entry *ce, int pos)
+{
+	if (ce_stage(ce) != 1 ||
+	    active_nr <= pos + 2 ||
+	    strcmp(active_cache[pos+1]->name, ce->name) ||
+	    ce_stage(active_cache[pos+1]) != 2 ||
+	    strcmp(active_cache[pos+2]->name, ce->name) ||
+	    ce_stage(active_cache[pos+2]) != 3)
+		return error("path '%s' does not have all three versions",
+			     ce->name);
+	return 0;
+}
+
+static int checkout_stage(int stage, struct cache_entry *ce, int pos,
+			  struct checkout *state)
+{
+	while (pos < active_nr &&
+	       !strcmp(active_cache[pos]->name, ce->name)) {
+		if (ce_stage(active_cache[pos]) == stage)
+			return checkout_entry(active_cache[pos], state, NULL);
+		pos++;
+	}
+	return error("path '%s' does not have %s version",
+		     ce->name,
+		     (stage == 2) ? "our" : "their");
+}
+
+/* NEEDSWORK: share with merge-recursive */
+static void fill_mm(const unsigned char *sha1, mmfile_t *mm)
+{
+	unsigned long size;
+	enum object_type type;
+
+	if (!hashcmp(sha1, null_sha1)) {
+		mm->ptr = xstrdup("");
+		mm->size = 0;
+		return;
+	}
+
+	mm->ptr = read_sha1_file(sha1, &type, &size);
+	if (!mm->ptr || type != OBJ_BLOB)
+		die("unable to read blob object %s", sha1_to_hex(sha1));
+	mm->size = size;
+}
+
+static int checkout_merged(int pos, struct checkout *state)
+{
+	struct cache_entry *ce = active_cache[pos];
+	const char *path = ce->name;
+	mmfile_t ancestor, ours, theirs;
+	int status;
+	unsigned char sha1[20];
+	mmbuffer_t result_buf;
+
+	if (ce_stage(ce) != 1 ||
+	    active_nr <= pos + 2 ||
+	    strcmp(active_cache[pos+1]->name, path) ||
+	    ce_stage(active_cache[pos+1]) != 2 ||
+	    strcmp(active_cache[pos+2]->name, path) ||
+	    ce_stage(active_cache[pos+2]) != 3)
+		return error("path '%s' does not have all 3 versions", path);
+
+	fill_mm(active_cache[pos]->sha1, &ancestor);
+	fill_mm(active_cache[pos+1]->sha1, &ours);
+	fill_mm(active_cache[pos+2]->sha1, &theirs);
+
+	status = ll_merge(&result_buf, path, &ancestor,
+			  &ours, "ours", &theirs, "theirs", 0);
+	free(ancestor.ptr);
+	free(ours.ptr);
+	free(theirs.ptr);
+	if (status < 0 || !result_buf.ptr) {
+		free(result_buf.ptr);
+		return error("path '%s': cannot merge", path);
+	}
+
+	/*
+	 * NEEDSWORK:
+	 * There is absolutely no reason to write this as a blob object
+	 * and create a phony cache entry just to leak.  This hack is
+	 * primarily to get to the write_entry() machinery that massages
+	 * the contents to work-tree format and writes out which only
+	 * allows it for a cache entry.  The code in write_entry() needs
+	 * to be refactored to allow us to feed a <buffer, size, mode>
+	 * instead of a cache entry.  Such a refactoring would help
+	 * merge_recursive as well (it also writes the merge result to the
+	 * object database even when it may contain conflicts).
+	 */
+	if (write_sha1_file(result_buf.ptr, result_buf.size,
+			    blob_type, sha1))
+		die("Unable to add merge result for '%s'", path);
+	ce = make_cache_entry(create_ce_mode(active_cache[pos+1]->ce_mode),
+			      sha1,
+			      path, 2, 0);
+	if (!ce)
+		die("make_cache_entry failed for path '%s'", path);
+	status = checkout_entry(ce, state, NULL);
+	return status;
+}
+
+static int checkout_paths(struct tree *source_tree, const char **pathspec,
+			  struct checkout_opts *opts)
+{
+	int pos;
+	struct checkout state;
+	static char *ps_matched;
+	unsigned char rev[20];
+	int flag;
+	struct commit *head;
+	int errs = 0;
+	int stage = opts->writeout_stage;
+	int merge = opts->merge;
+	int newfd;
+	struct lock_file *lock_file = xcalloc(1, sizeof(struct lock_file));
+
+	newfd = hold_locked_index(lock_file, 1);
+	if (read_cache_preload(pathspec) < 0)
+		return error("corrupt index file");
+
+	if (source_tree)
+		read_tree_some(source_tree, pathspec);
+
+	for (pos = 0; pathspec[pos]; pos++)
+		;
+	ps_matched = xcalloc(1, pos);
+
+	for (pos = 0; pos < active_nr; pos++) {
+		struct cache_entry *ce = active_cache[pos];
+		match_pathspec(pathspec, ce->name, ce_namelen(ce), 0, ps_matched);
+	}
+
+	if (report_path_error(ps_matched, pathspec, 0))
+		return 1;
+
+	/* "checkout -m path" to recreate conflicted state */
+	if (opts->merge)
+		unmerge_cache(pathspec);
+
+	/* Any unmerged paths? */
+	for (pos = 0; pos < active_nr; pos++) {
+		struct cache_entry *ce = active_cache[pos];
+		if (match_pathspec(pathspec, ce->name, ce_namelen(ce), 0, NULL)) {
+			if (!ce_stage(ce))
+				continue;
+			if (opts->force) {
+				warning("path '%s' is unmerged", ce->name);
+			} else if (stage) {
+				errs |= check_stage(stage, ce, pos);
+			} else if (opts->merge) {
+				errs |= check_all_stages(ce, pos);
+			} else {
+				errs = 1;
+				error("path '%s' is unmerged", ce->name);
+			}
+			pos = skip_same_name(ce, pos) - 1;
+		}
+	}
+	if (errs)
+		return 1;
+
+	/* Now we are committed to check them out */
+	memset(&state, 0, sizeof(state));
+	state.force = 1;
+	state.refresh_cache = 1;
+	for (pos = 0; pos < active_nr; pos++) {
+		struct cache_entry *ce = active_cache[pos];
+		if (match_pathspec(pathspec, ce->name, ce_namelen(ce), 0, NULL)) {
+			if (!ce_stage(ce)) {
+				errs |= checkout_entry(ce, &state, NULL);
+				continue;
+			}
+			if (stage)
+				errs |= checkout_stage(stage, ce, pos, &state);
+			else if (merge)
+				errs |= checkout_merged(pos, &state);
+			pos = skip_same_name(ce, pos) - 1;
+		}
+	}
+
+	if (write_cache(newfd, active_cache, active_nr) ||
+	    commit_locked_index(lock_file))
+		die("unable to write new index file");
+
+	resolve_ref("HEAD", rev, 0, &flag);
+	head = lookup_commit_reference_gently(rev, 1);
+
+	errs |= post_checkout_hook(head, head, 0);
+	return errs;
+}
+
+static void show_local_changes(struct object *head)
+{
+	struct rev_info rev;
+	/* I think we want full paths, even if we're in a subdirectory. */
+	init_revisions(&rev, NULL);
+	rev.abbrev = 0;
+	rev.diffopt.output_format |= DIFF_FORMAT_NAME_STATUS;
+	if (diff_setup_done(&rev.diffopt) < 0)
+		die("diff_setup_done failed");
+	add_pending_object(&rev, head, NULL);
+	run_diff_index(&rev, 0);
+}
+
+static void describe_detached_head(char *msg, struct commit *commit)
+{
+	struct strbuf sb = STRBUF_INIT;
+	struct pretty_print_context ctx = {0};
+	parse_commit(commit);
+	pretty_print_commit(CMIT_FMT_ONELINE, commit, &sb, &ctx);
+	fprintf(stderr, "%s %s... %s\n", msg,
+		find_unique_abbrev(commit->object.sha1, DEFAULT_ABBREV), sb.buf);
+	strbuf_release(&sb);
+}
+
+static int reset_tree(struct tree *tree, struct checkout_opts *o, int worktree)
+{
+	struct unpack_trees_options opts;
+	struct tree_desc tree_desc;
+
+	memset(&opts, 0, sizeof(opts));
+	opts.head_idx = -1;
+	opts.update = worktree;
+	opts.skip_unmerged = !worktree;
+	opts.reset = 1;
+	opts.merge = 1;
+	opts.fn = oneway_merge;
+	opts.verbose_update = !o->quiet;
+	opts.src_index = &the_index;
+	opts.dst_index = &the_index;
+	parse_tree(tree);
+	init_tree_desc(&tree_desc, tree->buffer, tree->size);
+	switch (unpack_trees(1, &tree_desc, &opts)) {
+	case -2:
+		o->writeout_error = 1;
+		/*
+		 * We return 0 nevertheless, as the index is all right
+		 * and more importantly we have made best efforts to
+		 * update paths in the work tree, and we cannot revert
+		 * them.
+		 */
+	case 0:
+		return 0;
+	default:
+		return 128;
+	}
+}
+
+struct branch_info {
+	const char *name; /* The short name used */
+	const char *path; /* The full name of a real branch */
+	struct commit *commit; /* The named commit */
+};
+
+static void setup_branch_path(struct branch_info *branch)
+{
+	struct strbuf buf = STRBUF_INIT;
+
+	strbuf_branchname(&buf, branch->name);
+	if (strcmp(buf.buf, branch->name))
+		branch->name = xstrdup(buf.buf);
+	strbuf_splice(&buf, 0, 0, "refs/heads/", 11);
+	branch->path = strbuf_detach(&buf, NULL);
+}
+
+static int merge_working_tree(struct checkout_opts *opts,
+			      struct branch_info *old, struct branch_info *new)
+{
+	int ret;
+	struct lock_file *lock_file = xcalloc(1, sizeof(struct lock_file));
+	int newfd = hold_locked_index(lock_file, 1);
+
+	if (read_cache_preload(NULL) < 0)
+		return error("corrupt index file");
+
+	resolve_undo_clear();
+	if (opts->force) {
+		ret = reset_tree(new->commit->tree, opts, 1);
+		if (ret)
+			return ret;
+	} else {
+		struct tree_desc trees[2];
+		struct tree *tree;
+		struct unpack_trees_options topts;
+
+		memset(&topts, 0, sizeof(topts));
+		topts.head_idx = -1;
+		topts.src_index = &the_index;
+		topts.dst_index = &the_index;
+
+		topts.msgs.not_uptodate_file = "You have local changes to '%s'; cannot switch branches.";
+
+		refresh_cache(REFRESH_QUIET);
+
+		if (unmerged_cache()) {
+			error("you need to resolve your current index first");
+			return 1;
+		}
+
+		/* 2-way merge to the new branch */
+		topts.initial_checkout = is_cache_unborn();
+		topts.update = 1;
+		topts.merge = 1;
+		topts.gently = opts->merge && old->commit;
+		topts.verbose_update = !opts->quiet;
+		topts.fn = twoway_merge;
+		topts.dir = xcalloc(1, sizeof(*topts.dir));
+		topts.dir->flags |= DIR_SHOW_IGNORED;
+		topts.dir->exclude_per_dir = ".gitignore";
+		tree = parse_tree_indirect(old->commit ?
+					   old->commit->object.sha1 :
+					   (unsigned char *)EMPTY_TREE_SHA1_BIN);
+		init_tree_desc(&trees[0], tree->buffer, tree->size);
+		tree = parse_tree_indirect(new->commit->object.sha1);
+		init_tree_desc(&trees[1], tree->buffer, tree->size);
+
+		ret = unpack_trees(2, trees, &topts);
+		if (ret == -1) {
+			/*
+			 * Unpack couldn't do a trivial merge; either
+			 * give up or do a real merge, depending on
+			 * whether the merge flag was used.
+			 */
+			struct tree *result;
+			struct tree *work;
+			struct merge_options o;
+			if (!opts->merge)
+				return 1;
+
+			/*
+			 * Without old->commit, the below is the same as
+			 * the two-tree unpack we already tried and failed.
+			 */
+			if (!old->commit)
+				return 1;
+
+			/* Do more real merge */
+
+			/*
+			 * We update the index fully, then write the
+			 * tree from the index, then merge the new
+			 * branch with the current tree, with the old
+			 * branch as the base. Then we reset the index
+			 * (but not the working tree) to the new
+			 * branch, leaving the working tree as the
+			 * merged version, but skipping unmerged
+			 * entries in the index.
+			 */
+
+			add_files_to_cache(NULL, NULL, 0);
+			init_merge_options(&o);
+			o.verbosity = 0;
+			work = write_tree_from_memory(&o);
+
+			ret = reset_tree(new->commit->tree, opts, 1);
+			if (ret)
+				return ret;
+			o.branch1 = new->name;
+			o.branch2 = "local";
+			merge_trees(&o, new->commit->tree, work,
+				old->commit->tree, &result);
+			ret = reset_tree(new->commit->tree, opts, 0);
+			if (ret)
+				return ret;
+		}
+	}
+
+	if (write_cache(newfd, active_cache, active_nr) ||
+	    commit_locked_index(lock_file))
+		die("unable to write new index file");
+
+	if (!opts->force && !opts->quiet)
+		show_local_changes(&new->commit->object);
+
+	return 0;
+}
+
+static void report_tracking(struct branch_info *new)
+{
+	struct strbuf sb = STRBUF_INIT;
+	struct branch *branch = branch_get(new->name);
+
+	if (!format_tracking_info(branch, &sb))
+		return;
+	fputs(sb.buf, stdout);
+	strbuf_release(&sb);
+}
+
+static void detach_advice(const char *old_path, const char *new_name)
+{
+	const char fmt[] =
+	"Note: checking out '%s'.\n\n"
+	"You are in 'detached HEAD' state. You can look around, make experimental\n"
+	"changes and commit them, and you can discard any commits you make in this\n"
+	"state without impacting any branches by performing another checkout.\n\n"
+	"If you want to create a new branch to retain commits you create, you may\n"
+	"do so (now or later) by using -b with the checkout command again. Example:\n\n"
+	"  git checkout -b new_branch_name\n\n";
+
+	fprintf(stderr, fmt, new_name);
+}
+
+static void update_refs_for_switch(struct checkout_opts *opts,
+				   struct branch_info *old,
+				   struct branch_info *new)
+{
+	struct strbuf msg = STRBUF_INIT;
+	const char *old_desc;
+	if (opts->new_branch) {
+		create_branch(old->name, opts->new_branch, new->name, 0,
+			      opts->new_branch_log, opts->track);
+		new->name = opts->new_branch;
+		setup_branch_path(new);
+	}
+
+	old_desc = old->name;
+	if (!old_desc && old->commit)
+		old_desc = sha1_to_hex(old->commit->object.sha1);
+	strbuf_addf(&msg, "checkout: moving from %s to %s",
+		    old_desc ? old_desc : "(invalid)", new->name);
+
+	if (new->path) {
+		create_symref("HEAD", new->path, msg.buf);
+		if (!opts->quiet) {
+			if (old->path && !strcmp(new->path, old->path))
+				fprintf(stderr, "Already on '%s'\n",
+					new->name);
+			else
+				fprintf(stderr, "Switched to%s branch '%s'\n",
+					opts->new_branch ? " a new" : "",
+					new->name);
+		}
+	} else if (strcmp(new->name, "HEAD")) {
+		update_ref(msg.buf, "HEAD", new->commit->object.sha1, NULL,
+			   REF_NODEREF, DIE_ON_ERR);
+		if (!opts->quiet) {
+			if (old->path && advice_detached_head)
+				detach_advice(old->path, new->name);
+			describe_detached_head("HEAD is now at", new->commit);
+		}
+	}
+	remove_branch_state();
+	strbuf_release(&msg);
+	if (!opts->quiet && (new->path || !strcmp(new->name, "HEAD")))
+		report_tracking(new);
+}
+
+static int switch_branches(struct checkout_opts *opts, struct branch_info *new)
+{
+	int ret = 0;
+	struct branch_info old;
+	unsigned char rev[20];
+	int flag;
+	memset(&old, 0, sizeof(old));
+	old.path = resolve_ref("HEAD", rev, 0, &flag);
+	old.commit = lookup_commit_reference_gently(rev, 1);
+	if (!(flag & REF_ISSYMREF))
+		old.path = NULL;
+
+	if (old.path && !prefixcmp(old.path, "refs/heads/"))
+		old.name = old.path + strlen("refs/heads/");
+
+	if (!new->name) {
+		new->name = "HEAD";
+		new->commit = old.commit;
+		if (!new->commit)
+			die("You are on a branch yet to be born");
+		parse_commit(new->commit);
+	}
+
+	ret = merge_working_tree(opts, &old, new);
+	if (ret)
+		return ret;
+
+	/*
+	 * If we were on a detached HEAD, but have now moved to
+	 * a new commit, we want to mention the old commit once more
+	 * to remind the user that it might be lost.
+	 */
+	if (!opts->quiet && !old.path && old.commit && new->commit != old.commit)
+		describe_detached_head("Previous HEAD position was", old.commit);
+
+	update_refs_for_switch(opts, &old, new);
+
+	ret = post_checkout_hook(old.commit, new->commit, 1);
+	return ret || opts->writeout_error;
+}
+
+static int git_checkout_config(const char *var, const char *value, void *cb)
+{
+	return git_xmerge_config(var, value, cb);
+}
+
+static int interactive_checkout(const char *revision, const char **pathspec,
+				struct checkout_opts *opts)
+{
+	return run_add_interactive(revision, "--patch=checkout", pathspec);
+}
+
+struct tracking_name_data {
+	const char *name;
+	char *remote;
+	int unique;
+};
+
+static int check_tracking_name(const char *refname, const unsigned char *sha1,
+			       int flags, void *cb_data)
+{
+	struct tracking_name_data *cb = cb_data;
+	const char *slash;
+
+	if (prefixcmp(refname, "refs/remotes/"))
+		return 0;
+	slash = strchr(refname + 13, '/');
+	if (!slash || strcmp(slash + 1, cb->name))
+		return 0;
+	if (cb->remote) {
+		cb->unique = 0;
+		return 0;
+	}
+	cb->remote = xstrdup(refname);
+	return 0;
+}
+
+static const char *unique_tracking_name(const char *name)
+{
+	struct tracking_name_data cb_data = { name, NULL, 1 };
+	for_each_ref(check_tracking_name, &cb_data);
+	if (cb_data.unique)
+		return cb_data.remote;
+	free(cb_data.remote);
+	return NULL;
+}
+
+int cmd_checkout(int argc, const char **argv, const char *prefix)
+{
+	struct checkout_opts opts;
+	unsigned char rev[20];
+	const char *arg;
+	struct branch_info new;
+	struct tree *source_tree = NULL;
+	char *conflict_style = NULL;
+	int patch_mode = 0;
+	int dwim_new_local_branch = 1;
+	struct option options[] = {
+		OPT__QUIET(&opts.quiet),
+		OPT_STRING('b', NULL, &opts.new_branch, "new branch", "branch"),
+		OPT_BOOLEAN('l', NULL, &opts.new_branch_log, "log for new branch"),
+		OPT_SET_INT('t', "track",  &opts.track, "track",
+			BRANCH_TRACK_EXPLICIT),
+		OPT_SET_INT('2', "ours", &opts.writeout_stage, "stage",
+			    2),
+		OPT_SET_INT('3', "theirs", &opts.writeout_stage, "stage",
+			    3),
+		OPT_BOOLEAN('f', "force", &opts.force, "force"),
+		OPT_BOOLEAN('m', "merge", &opts.merge, "merge"),
+		OPT_STRING(0, "conflict", &conflict_style, "style",
+			   "conflict style (merge or diff3)"),
+		OPT_BOOLEAN('p', "patch", &patch_mode, "select hunks interactively"),
+		{ OPTION_BOOLEAN, 0, "guess", &dwim_new_local_branch, NULL,
+		  "second guess 'git checkout no-such-branch'",
+		  PARSE_OPT_NOARG | PARSE_OPT_HIDDEN },
+		OPT_END(),
+	};
+	int has_dash_dash;
+
+	memset(&opts, 0, sizeof(opts));
+	memset(&new, 0, sizeof(new));
+
+	git_config(git_checkout_config, NULL);
+
+	opts.track = BRANCH_TRACK_UNSPECIFIED;
+
+	argc = parse_options(argc, argv, prefix, options, checkout_usage,
+			     PARSE_OPT_KEEP_DASHDASH);
+
+	if (patch_mode && (opts.track > 0 || opts.new_branch
+			   || opts.new_branch_log || opts.merge || opts.force))
+		die ("--patch is incompatible with all other options");
+
+	/* --track without -b should DWIM */
+	if (0 < opts.track && !opts.new_branch) {
+		const char *argv0 = argv[0];
+		if (!argc || !strcmp(argv0, "--"))
+			die ("--track needs a branch name");
+		if (!prefixcmp(argv0, "refs/"))
+			argv0 += 5;
+		if (!prefixcmp(argv0, "remotes/"))
+			argv0 += 8;
+		argv0 = strchr(argv0, '/');
+		if (!argv0 || !argv0[1])
+			die ("Missing branch name; try -b");
+		opts.new_branch = argv0 + 1;
+	}
+
+	if (conflict_style) {
+		opts.merge = 1; /* implied */
+		git_xmerge_config("merge.conflictstyle", conflict_style, NULL);
+	}
+
+	if (opts.force && opts.merge)
+		die("git checkout: -f and -m are incompatible");
+
+	/*
+	 * case 1: git checkout <ref> -- [<paths>]
+	 *
+	 *   <ref> must be a valid tree, everything after the '--' must be
+	 *   a path.
+	 *
+	 * case 2: git checkout -- [<paths>]
+	 *
+	 *   everything after the '--' must be paths.
+	 *
+	 * case 3: git checkout <something> [<paths>]
+	 *
+	 *   With no paths, if <something> is a commit, that is to
+	 *   switch to the branch or detach HEAD at it.  As a special case,
+	 *   if <something> is A...B (missing A or B means HEAD but you can
+	 *   omit at most one side), and if there is a unique merge base
+	 *   between A and B, A...B names that merge base.
+	 *
+	 *   With no paths, if <something> is _not_ a commit, no -t nor -b
+	 *   was given, and there is a tracking branch whose name is
+	 *   <something> in one and only one remote, then this is a short-hand
+	 *   to fork local <something> from that remote tracking branch.
+	 *
+	 *   Otherwise <something> shall not be ambiguous.
+	 *   - If it's *only* a reference, treat it like case (1).
+	 *   - If it's only a path, treat it like case (2).
+	 *   - else: fail.
+	 *
+	 */
+	if (argc) {
+		if (!strcmp(argv[0], "--")) {       /* case (2) */
+			argv++;
+			argc--;
+			goto no_reference;
+		}
+
+		arg = argv[0];
+		has_dash_dash = (argc > 1) && !strcmp(argv[1], "--");
+
+		if (!strcmp(arg, "-"))
+			arg = "@{-1}";
+
+		if (get_sha1_mb(arg, rev)) {
+			if (has_dash_dash)          /* case (1) */
+				die("invalid reference: %s", arg);
+			if (!patch_mode &&
+			    dwim_new_local_branch &&
+			    opts.track == BRANCH_TRACK_UNSPECIFIED &&
+			    !opts.new_branch &&
+			    !check_filename(NULL, arg) &&
+			    argc == 1) {
+				const char *remote = unique_tracking_name(arg);
+				if (!remote || get_sha1(remote, rev))
+					goto no_reference;
+				opts.new_branch = arg;
+				arg = remote;
+				/* DWIMmed to create local branch */
+			}
+			else
+				goto no_reference;
+		}
+
+		/* we can't end up being in (2) anymore, eat the argument */
+		argv++;
+		argc--;
+
+		new.name = arg;
+		if ((new.commit = lookup_commit_reference_gently(rev, 1))) {
+			setup_branch_path(&new);
+
+			if ((check_ref_format(new.path) == CHECK_REF_FORMAT_OK) &&
+			    resolve_ref(new.path, rev, 1, NULL))
+				;
+			else
+				new.path = NULL;
+			parse_commit(new.commit);
+			source_tree = new.commit->tree;
+		} else
+			source_tree = parse_tree_indirect(rev);
+
+		if (!source_tree)                   /* case (1): want a tree */
+			die("reference is not a tree: %s", arg);
+		if (!has_dash_dash) {/* case (3 -> 1) */
+			/*
+			 * Do not complain the most common case
+			 *	git checkout branch
+			 * even if there happen to be a file called 'branch';
+			 * it would be extremely annoying.
+			 */
+			if (argc)
+				verify_non_filename(NULL, arg);
+		}
+		else {
+			argv++;
+			argc--;
+		}
+	}
+
+no_reference:
+
+	if (opts.track == BRANCH_TRACK_UNSPECIFIED)
+		opts.track = git_branch_track;
+
+	if (argc) {
+		const char **pathspec = get_pathspec(prefix, argv);
+
+		if (!pathspec)
+			die("invalid path specification");
+
+		if (patch_mode)
+			return interactive_checkout(new.name, pathspec, &opts);
+
+		/* Checkout paths */
+		if (opts.new_branch) {
+			if (argc == 1) {
+				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]);
+			} else {
+				die("git checkout: updating paths is incompatible with switching branches.");
+			}
+		}
+
+		if (1 < !!opts.writeout_stage + !!opts.force + !!opts.merge)
+			die("git checkout: --ours/--theirs, --force and --merge are incompatible when\nchecking out of the index.");
+
+		return checkout_paths(source_tree, pathspec, &opts);
+	}
+
+	if (patch_mode)
+		return interactive_checkout(new.name, NULL, &opts);
+
+	if (opts.new_branch) {
+		struct strbuf buf = STRBUF_INIT;
+		if (strbuf_check_branch_ref(&buf, opts.new_branch))
+			die("git checkout: we do not like '%s' as a branch name.",
+			    opts.new_branch);
+		if (!get_sha1(buf.buf, rev))
+			die("git checkout: branch %s already exists", opts.new_branch);
+		strbuf_release(&buf);
+	}
+
+	if (new.name && !new.commit) {
+		die("Cannot switch branch to a non-commit.");
+	}
+	if (opts.writeout_stage)
+		die("--ours/--theirs is incompatible with switching branches.");
+
+	return switch_branches(&opts, &new);
+}