merge(third_party/git): Merge squashed git subtree at v2.23.0 r/373

Merge commit '1b593e1ea4d2af0f6444d9a7788d5d99abd6fde5' as 'third_party/git'

1 files changed, 1801 insertions, 0 deletions

diff --git a/third_party/git/builtin/checkout.c b/third_party/git/builtin/checkout.c
new file mode 100644
index 000000000000..6123f732a2c8
--- /dev/null
+++ b/third_party/git/builtin/checkout.c
@@ -0,0 +1,1801 @@
+#define USE_THE_INDEX_COMPATIBILITY_MACROS
+#include "builtin.h"
+#include "advice.h"
+#include "blob.h"
+#include "branch.h"
+#include "cache-tree.h"
+#include "checkout.h"
+#include "commit.h"
+#include "config.h"
+#include "diff.h"
+#include "dir.h"
+#include "ll-merge.h"
+#include "lockfile.h"
+#include "merge-recursive.h"
+#include "object-store.h"
+#include "parse-options.h"
+#include "refs.h"
+#include "remote.h"
+#include "resolve-undo.h"
+#include "revision.h"
+#include "run-command.h"
+#include "submodule.h"
+#include "submodule-config.h"
+#include "tree.h"
+#include "tree-walk.h"
+#include "unpack-trees.h"
+#include "wt-status.h"
+#include "xdiff-interface.h"
+
+static const char * const checkout_usage[] = {
+	N_("git checkout [<options>] <branch>"),
+	N_("git checkout [<options>] [<branch>] -- <file>..."),
+	NULL,
+};
+
+static const char * const switch_branch_usage[] = {
+	N_("git switch [<options>] [<branch>]"),
+	NULL,
+};
+
+static const char * const restore_usage[] = {
+	N_("git restore [<options>] [--source=<branch>] <file>..."),
+	NULL,
+};
+
+struct checkout_opts {
+	int patch_mode;
+	int quiet;
+	int merge;
+	int force;
+	int force_detach;
+	int implicit_detach;
+	int writeout_stage;
+	int overwrite_ignore;
+	int ignore_skipworktree;
+	int ignore_other_worktrees;
+	int show_progress;
+	int count_checkout_paths;
+	int overlay_mode;
+	int dwim_new_local_branch;
+	int discard_changes;
+	int accept_ref;
+	int accept_pathspec;
+	int switch_branch_doing_nothing_is_ok;
+	int only_merge_on_switching_branches;
+	int can_switch_when_in_progress;
+	int orphan_from_empty_tree;
+	int empty_pathspec_ok;
+	int checkout_index;
+	int checkout_worktree;
+	const char *ignore_unmerged_opt;
+	int ignore_unmerged;
+
+	const char *new_branch;
+	const char *new_branch_force;
+	const char *new_orphan_branch;
+	int new_branch_log;
+	enum branch_track track;
+	struct diff_options diff_options;
+	char *conflict_style;
+
+	int branch_exists;
+	const char *prefix;
+	struct pathspec pathspec;
+	const char *from_treeish;
+	struct tree *source_tree;
+};
+
+static int post_checkout_hook(struct commit *old_commit, struct commit *new_commit,
+			      int changed)
+{
+	return run_hook_le(NULL, "post-checkout",
+			   oid_to_hex(old_commit ? &old_commit->object.oid : &null_oid),
+			   oid_to_hex(new_commit ? &new_commit->object.oid : &null_oid),
+			   changed ? "1" : "0", NULL);
+	/* "new_commit" can be NULL when checking out from the index before
+	   a commit exists. */
+
+}
+
+static int update_some(const struct object_id *oid, struct strbuf *base,
+		const char *pathname, unsigned mode, int stage, void *context)
+{
+	int len;
+	struct cache_entry *ce;
+	int pos;
+
+	if (S_ISDIR(mode))
+		return READ_TREE_RECURSIVE;
+
+	len = base->len + strlen(pathname);
+	ce = make_empty_cache_entry(&the_index, len);
+	oidcpy(&ce->oid, oid);
+	memcpy(ce->name, base->buf, base->len);
+	memcpy(ce->name + base->len, pathname, len - base->len);
+	ce->ce_flags = create_ce_flags(0) | CE_UPDATE;
+	ce->ce_namelen = len;
+	ce->ce_mode = create_ce_mode(mode);
+
+	/*
+	 * If the entry is the same as the current index, we can leave the old
+	 * entry in place. Whether it is UPTODATE or not, checkout_entry will
+	 * do the right thing.
+	 */
+	pos = cache_name_pos(ce->name, ce->ce_namelen);
+	if (pos >= 0) {
+		struct cache_entry *old = active_cache[pos];
+		if (ce->ce_mode == old->ce_mode &&
+		    oideq(&ce->oid, &old->oid)) {
+			old->ce_flags |= CE_UPDATE;
+			discard_cache_entry(ce);
+			return 0;
+		}
+	}
+
+	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 struct pathspec *pathspec)
+{
+	read_tree_recursive(the_repository, 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(const 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, const struct cache_entry *ce, int pos,
+		       int overlay_mode)
+{
+	while (pos < active_nr &&
+	       !strcmp(active_cache[pos]->name, ce->name)) {
+		if (ce_stage(active_cache[pos]) == stage)
+			return 0;
+		pos++;
+	}
+	if (!overlay_mode)
+		return 0;
+	if (stage == 2)
+		return error(_("path '%s' does not have our version"), ce->name);
+	else
+		return error(_("path '%s' does not have their version"), ce->name);
+}
+
+static int check_stages(unsigned stages, const struct cache_entry *ce, int pos)
+{
+	unsigned seen = 0;
+	const char *name = ce->name;
+
+	while (pos < active_nr) {
+		ce = active_cache[pos];
+		if (strcmp(name, ce->name))
+			break;
+		seen |= (1 << ce_stage(ce));
+		pos++;
+	}
+	if ((stages & seen) != stages)
+		return error(_("path '%s' does not have all necessary versions"),
+			     name);
+	return 0;
+}
+
+static int checkout_stage(int stage, const struct cache_entry *ce, int pos,
+			  const struct checkout *state, int *nr_checkouts,
+			  int overlay_mode)
+{
+	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, nr_checkouts);
+		pos++;
+	}
+	if (!overlay_mode) {
+		unlink_entry(ce);
+		return 0;
+	}
+	if (stage == 2)
+		return error(_("path '%s' does not have our version"), ce->name);
+	else
+		return error(_("path '%s' does not have their version"), ce->name);
+}
+
+static int checkout_merged(int pos, const struct checkout *state, int *nr_checkouts)
+{
+	struct cache_entry *ce = active_cache[pos];
+	const char *path = ce->name;
+	mmfile_t ancestor, ours, theirs;
+	int status;
+	struct object_id oid;
+	mmbuffer_t result_buf;
+	struct object_id threeway[3];
+	unsigned mode = 0;
+
+	memset(threeway, 0, sizeof(threeway));
+	while (pos < active_nr) {
+		int stage;
+		stage = ce_stage(ce);
+		if (!stage || strcmp(path, ce->name))
+			break;
+		oidcpy(&threeway[stage - 1], &ce->oid);
+		if (stage == 2)
+			mode = create_ce_mode(ce->ce_mode);
+		pos++;
+		ce = active_cache[pos];
+	}
+	if (is_null_oid(&threeway[1]) || is_null_oid(&threeway[2]))
+		return error(_("path '%s' does not have necessary versions"), path);
+
+	read_mmblob(&ancestor, &threeway[0]);
+	read_mmblob(&ours, &threeway[1]);
+	read_mmblob(&theirs, &threeway[2]);
+
+	/*
+	 * NEEDSWORK: re-create conflicts from merges with
+	 * merge.renormalize set, too
+	 */
+	status = ll_merge(&result_buf, path, &ancestor, "base",
+			  &ours, "ours", &theirs, "theirs",
+			  state->istate, NULL);
+	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.  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_object_file(result_buf.ptr, result_buf.size, blob_type, &oid))
+		die(_("Unable to add merge result for '%s'"), path);
+	free(result_buf.ptr);
+	ce = make_transient_cache_entry(mode, &oid, path, 2);
+	if (!ce)
+		die(_("make_cache_entry failed for path '%s'"), path);
+	status = checkout_entry(ce, state, NULL, nr_checkouts);
+	discard_cache_entry(ce);
+	return status;
+}
+
+static void mark_ce_for_checkout_overlay(struct cache_entry *ce,
+					 char *ps_matched,
+					 const struct checkout_opts *opts)
+{
+	ce->ce_flags &= ~CE_MATCHED;
+	if (!opts->ignore_skipworktree && ce_skip_worktree(ce))
+		return;
+	if (opts->source_tree && !(ce->ce_flags & CE_UPDATE))
+		/*
+		 * "git checkout tree-ish -- path", but this entry
+		 * is in the original index but is not in tree-ish
+		 * or does not match the pathspec; it will not be
+		 * checked out to the working tree.  We will not do
+		 * anything to this entry at all.
+		 */
+		return;
+	/*
+	 * Either this entry came from the tree-ish we are
+	 * checking the paths out of, or we are checking out
+	 * of the index.
+	 *
+	 * If it comes from the tree-ish, we already know it
+	 * matches the pathspec and could just stamp
+	 * CE_MATCHED to it from update_some(). But we still
+	 * need ps_matched and read_tree_recursive (and
+	 * eventually tree_entry_interesting) cannot fill
+	 * ps_matched yet. Once it can, we can avoid calling
+	 * match_pathspec() for _all_ entries when
+	 * opts->source_tree != NULL.
+	 */
+	if (ce_path_match(&the_index, ce, &opts->pathspec, ps_matched))
+		ce->ce_flags |= CE_MATCHED;
+}
+
+static void mark_ce_for_checkout_no_overlay(struct cache_entry *ce,
+					    char *ps_matched,
+					    const struct checkout_opts *opts)
+{
+	ce->ce_flags &= ~CE_MATCHED;
+	if (!opts->ignore_skipworktree && ce_skip_worktree(ce))
+		return;
+	if (ce_path_match(&the_index, ce, &opts->pathspec, ps_matched)) {
+		ce->ce_flags |= CE_MATCHED;
+		if (opts->source_tree && !(ce->ce_flags & CE_UPDATE))
+			/*
+			 * In overlay mode, but the path is not in
+			 * tree-ish, which means we should remove it
+			 * from the index and the working tree.
+			 */
+			ce->ce_flags |= CE_REMOVE | CE_WT_REMOVE;
+	}
+}
+
+static int checkout_worktree(const struct checkout_opts *opts)
+{
+	struct checkout state = CHECKOUT_INIT;
+	int nr_checkouts = 0, nr_unmerged = 0;
+	int errs = 0;
+	int pos;
+
+	state.force = 1;
+	state.refresh_cache = 1;
+	state.istate = &the_index;
+
+	enable_delayed_checkout(&state);
+	for (pos = 0; pos < active_nr; pos++) {
+		struct cache_entry *ce = active_cache[pos];
+		if (ce->ce_flags & CE_MATCHED) {
+			if (!ce_stage(ce)) {
+				errs |= checkout_entry(ce, &state,
+						       NULL, &nr_checkouts);
+				continue;
+			}
+			if (opts->writeout_stage)
+				errs |= checkout_stage(opts->writeout_stage,
+						       ce, pos,
+						       &state,
+						       &nr_checkouts, opts->overlay_mode);
+			else if (opts->merge)
+				errs |= checkout_merged(pos, &state,
+							&nr_unmerged);
+			pos = skip_same_name(ce, pos) - 1;
+		}
+	}
+	remove_marked_cache_entries(&the_index, 1);
+	remove_scheduled_dirs();
+	errs |= finish_delayed_checkout(&state, &nr_checkouts);
+
+	if (opts->count_checkout_paths) {
+		if (nr_unmerged)
+			fprintf_ln(stderr, Q_("Recreated %d merge conflict",
+					      "Recreated %d merge conflicts",
+					      nr_unmerged),
+				   nr_unmerged);
+		if (opts->source_tree)
+			fprintf_ln(stderr, Q_("Updated %d path from %s",
+					      "Updated %d paths from %s",
+					      nr_checkouts),
+				   nr_checkouts,
+				   find_unique_abbrev(&opts->source_tree->object.oid,
+						      DEFAULT_ABBREV));
+		else if (!nr_unmerged || nr_checkouts)
+			fprintf_ln(stderr, Q_("Updated %d path from the index",
+					      "Updated %d paths from the index",
+					      nr_checkouts),
+				   nr_checkouts);
+	}
+
+	return errs;
+}
+
+static int checkout_paths(const struct checkout_opts *opts,
+			  const char *revision)
+{
+	int pos;
+	static char *ps_matched;
+	struct object_id rev;
+	struct commit *head;
+	int errs = 0;
+	struct lock_file lock_file = LOCK_INIT;
+	int checkout_index;
+
+	trace2_cmd_mode(opts->patch_mode ? "patch" : "path");
+
+	if (opts->track != BRANCH_TRACK_UNSPECIFIED)
+		die(_("'%s' cannot be used with updating paths"), "--track");
+
+	if (opts->new_branch_log)
+		die(_("'%s' cannot be used with updating paths"), "-l");
+
+	if (opts->ignore_unmerged && opts->patch_mode)
+		die(_("'%s' cannot be used with updating paths"),
+		    opts->ignore_unmerged_opt);
+
+	if (opts->force_detach)
+		die(_("'%s' cannot be used with updating paths"), "--detach");
+
+	if (opts->merge && opts->patch_mode)
+		die(_("'%s' cannot be used with %s"), "--merge", "--patch");
+
+	if (opts->ignore_unmerged && opts->merge)
+		die(_("'%s' cannot be used with %s"),
+		    opts->ignore_unmerged_opt, "-m");
+
+	if (opts->new_branch)
+		die(_("Cannot update paths and switch to branch '%s' at the same time."),
+		    opts->new_branch);
+
+	if (!opts->checkout_worktree && !opts->checkout_index)
+		die(_("neither '%s' or '%s' is specified"),
+		    "--staged", "--worktree");
+
+	if (!opts->checkout_worktree && !opts->from_treeish)
+		die(_("'%s' must be used when '%s' is not specified"),
+		    "--worktree", "--source");
+
+	if (opts->checkout_index && !opts->checkout_worktree &&
+	    opts->writeout_stage)
+		die(_("'%s' or '%s' cannot be used with %s"),
+		    "--ours", "--theirs", "--staged");
+
+	if (opts->checkout_index && !opts->checkout_worktree &&
+	    opts->merge)
+		die(_("'%s' or '%s' cannot be used with %s"),
+		    "--merge", "--conflict", "--staged");
+
+	if (opts->patch_mode) {
+		const char *patch_mode;
+
+		if (opts->checkout_index && opts->checkout_worktree)
+			patch_mode = "--patch=checkout";
+		else if (opts->checkout_index && !opts->checkout_worktree)
+			patch_mode = "--patch=reset";
+		else if (!opts->checkout_index && opts->checkout_worktree)
+			patch_mode = "--patch=worktree";
+		else
+			BUG("either flag must have been set, worktree=%d, index=%d",
+			    opts->checkout_worktree, opts->checkout_index);
+		return run_add_interactive(revision, patch_mode, &opts->pathspec);
+	}
+
+	repo_hold_locked_index(the_repository, &lock_file, LOCK_DIE_ON_ERROR);
+	if (read_cache_preload(&opts->pathspec) < 0)
+		return error(_("index file corrupt"));
+
+	if (opts->source_tree)
+		read_tree_some(opts->source_tree, &opts->pathspec);
+
+	ps_matched = xcalloc(opts->pathspec.nr, 1);
+
+	/*
+	 * Make sure all pathspecs participated in locating the paths
+	 * to be checked out.
+	 */
+	for (pos = 0; pos < active_nr; pos++)
+		if (opts->overlay_mode)
+			mark_ce_for_checkout_overlay(active_cache[pos],
+						     ps_matched,
+						     opts);
+		else
+			mark_ce_for_checkout_no_overlay(active_cache[pos],
+							ps_matched,
+							opts);
+
+	if (report_path_error(ps_matched, &opts->pathspec)) {
+		free(ps_matched);
+		return 1;
+	}
+	free(ps_matched);
+
+	/* "checkout -m path" to recreate conflicted state */
+	if (opts->merge)
+		unmerge_marked_index(&the_index);
+
+	/* Any unmerged paths? */
+	for (pos = 0; pos < active_nr; pos++) {
+		const struct cache_entry *ce = active_cache[pos];
+		if (ce->ce_flags & CE_MATCHED) {
+			if (!ce_stage(ce))
+				continue;
+			if (opts->ignore_unmerged) {
+				if (!opts->quiet)
+					warning(_("path '%s' is unmerged"), ce->name);
+			} else if (opts->writeout_stage) {
+				errs |= check_stage(opts->writeout_stage, ce, pos, opts->overlay_mode);
+			} else if (opts->merge) {
+				errs |= check_stages((1<<2) | (1<<3), 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 */
+	if (opts->checkout_worktree)
+		errs |= checkout_worktree(opts);
+
+	/*
+	 * Allow updating the index when checking out from the index.
+	 * This is to save new stat info.
+	 */
+	if (opts->checkout_worktree && !opts->checkout_index && !opts->source_tree)
+		checkout_index = 1;
+	else
+		checkout_index = opts->checkout_index;
+
+	if (checkout_index) {
+		if (write_locked_index(&the_index, &lock_file, COMMIT_LOCK))
+			die(_("unable to write new index file"));
+	} else {
+		/*
+		 * NEEDSWORK: if --worktree is not specified, we
+		 * should save stat info of checked out files in the
+		 * index to avoid the next (potentially costly)
+		 * refresh. But it's a bit tricker to do...
+		 */
+		rollback_lock_file(&lock_file);
+	}
+
+	read_ref_full("HEAD", 0, &rev, NULL);
+	head = lookup_commit_reference_gently(the_repository, &rev, 1);
+
+	errs |= post_checkout_hook(head, head, 0);
+	return errs;
+}
+
+static void show_local_changes(struct object *head,
+			       const struct diff_options *opts)
+{
+	struct rev_info rev;
+	/* I think we want full paths, even if we're in a subdirectory. */
+	repo_init_revisions(the_repository, &rev, NULL);
+	rev.diffopt.flags = opts->flags;
+	rev.diffopt.output_format |= DIFF_FORMAT_NAME_STATUS;
+	diff_setup_done(&rev.diffopt);
+	add_pending_object(&rev, head, NULL);
+	run_diff_index(&rev, 0);
+}
+
+static void describe_detached_head(const char *msg, struct commit *commit)
+{
+	struct strbuf sb = STRBUF_INIT;
+
+	if (!parse_commit(commit))
+		pp_commit_easy(CMIT_FMT_ONELINE, commit, &sb);
+	if (print_sha1_ellipsis()) {
+		fprintf(stderr, "%s %s... %s\n", msg,
+			find_unique_abbrev(&commit->object.oid, DEFAULT_ABBREV), sb.buf);
+	} else {
+		fprintf(stderr, "%s %s %s\n", msg,
+			find_unique_abbrev(&commit->object.oid, DEFAULT_ABBREV), sb.buf);
+	}
+	strbuf_release(&sb);
+}
+
+static int reset_tree(struct tree *tree, const struct checkout_opts *o,
+		      int worktree, int *writeout_error)
+{
+	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->show_progress;
+	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:
+		*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.
+		 */
+		/* fallthrough */
+	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 */
+	/*
+	 * if not null the branch is detached because it's already
+	 * checked out in this checkout
+	 */
+	char *checkout;
+};
+
+static void setup_branch_path(struct branch_info *branch)
+{
+	struct strbuf buf = STRBUF_INIT;
+
+	strbuf_branchname(&buf, branch->name, INTERPRET_BRANCH_LOCAL);
+	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(const struct checkout_opts *opts,
+			      struct branch_info *old_branch_info,
+			      struct branch_info *new_branch_info,
+			      int *writeout_error)
+{
+	int ret;
+	struct lock_file lock_file = LOCK_INIT;
+	struct tree *new_tree;
+
+	hold_locked_index(&lock_file, LOCK_DIE_ON_ERROR);
+	if (read_cache_preload(NULL) < 0)
+		return error(_("index file corrupt"));
+
+	resolve_undo_clear();
+	if (opts->new_orphan_branch && opts->orphan_from_empty_tree) {
+		if (new_branch_info->commit)
+			BUG("'switch --orphan' should never accept a commit as starting point");
+		new_tree = parse_tree_indirect(the_hash_algo->empty_tree);
+	} else
+		new_tree = get_commit_tree(new_branch_info->commit);
+	if (opts->discard_changes) {
+		ret = reset_tree(new_tree, opts, 1, writeout_error);
+		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;
+
+		setup_unpack_trees_porcelain(&topts, "checkout");
+
+		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.quiet = opts->merge && old_branch_info->commit;
+		topts.verbose_update = opts->show_progress;
+		topts.fn = twoway_merge;
+		if (opts->overwrite_ignore) {
+			topts.dir = xcalloc(1, sizeof(*topts.dir));
+			topts.dir->flags |= DIR_SHOW_IGNORED;
+			setup_standard_excludes(topts.dir);
+		}
+		tree = parse_tree_indirect(old_branch_info->commit ?
+					   &old_branch_info->commit->object.oid :
+					   the_hash_algo->empty_tree);
+		init_tree_desc(&trees[0], tree->buffer, tree->size);
+		parse_tree(new_tree);
+		tree = new_tree;
+		init_tree_desc(&trees[1], tree->buffer, tree->size);
+
+		ret = unpack_trees(2, trees, &topts);
+		clear_unpack_trees_porcelain(&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 tree *old_tree;
+			struct merge_options o;
+			struct strbuf sb = STRBUF_INIT;
+
+			if (!opts->merge)
+				return 1;
+
+			/*
+			 * Without old_branch_info->commit, the below is the same as
+			 * the two-tree unpack we already tried and failed.
+			 */
+			if (!old_branch_info->commit)
+				return 1;
+			old_tree = get_commit_tree(old_branch_info->commit);
+
+			if (repo_index_has_changes(the_repository, old_tree, &sb))
+				die(_("cannot continue with staged changes in "
+				      "the following files:\n%s"), sb.buf);
+			strbuf_release(&sb);
+
+			if (repo_index_has_changes(the_repository,
+						   get_commit_tree(old_branch_info->commit),
+						   &sb))
+				warning(_("staged changes in the following files may be lost: %s"),
+					sb.buf);
+			strbuf_release(&sb);
+
+			/* 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);
+			/*
+			 * NEEDSWORK: carrying over local changes
+			 * when branches have different end-of-line
+			 * normalization (or clean+smudge rules) is
+			 * a pain; plumb in an option to set
+			 * o.renormalize?
+			 */
+			init_merge_options(&o, the_repository);
+			o.verbosity = 0;
+			work = write_tree_from_memory(&o);
+
+			ret = reset_tree(new_tree,
+					 opts, 1,
+					 writeout_error);
+			if (ret)
+				return ret;
+			o.ancestor = old_branch_info->name;
+			o.branch1 = new_branch_info->name;
+			o.branch2 = "local";
+			ret = merge_trees(&o,
+					  new_tree,
+					  work,
+					  old_tree,
+					  &result);
+			if (ret < 0)
+				exit(128);
+			ret = reset_tree(new_tree,
+					 opts, 0,
+					 writeout_error);
+			strbuf_release(&o.obuf);
+			if (ret)
+				return ret;
+		}
+	}
+
+	if (!active_cache_tree)
+		active_cache_tree = cache_tree();
+
+	if (!cache_tree_fully_valid(active_cache_tree))
+		cache_tree_update(&the_index, WRITE_TREE_SILENT | WRITE_TREE_REPAIR);
+
+	if (write_locked_index(&the_index, &lock_file, COMMIT_LOCK))
+		die(_("unable to write new index file"));
+
+	if (!opts->discard_changes && !opts->quiet && new_branch_info->commit)
+		show_local_changes(&new_branch_info->commit->object, &opts->diff_options);
+
+	return 0;
+}
+
+static void report_tracking(struct branch_info *new_branch_info)
+{
+	struct strbuf sb = STRBUF_INIT;
+	struct branch *branch = branch_get(new_branch_info->name);
+
+	if (!format_tracking_info(branch, &sb, AHEAD_BEHIND_FULL))
+		return;
+	fputs(sb.buf, stdout);
+	strbuf_release(&sb);
+}
+
+static void update_refs_for_switch(const struct checkout_opts *opts,
+				   struct branch_info *old_branch_info,
+				   struct branch_info *new_branch_info)
+{
+	struct strbuf msg = STRBUF_INIT;
+	const char *old_desc, *reflog_msg;
+	if (opts->new_branch) {
+		if (opts->new_orphan_branch) {
+			char *refname;
+
+			refname = mkpathdup("refs/heads/%s", opts->new_orphan_branch);
+			if (opts->new_branch_log &&
+			    !should_autocreate_reflog(refname)) {
+				int ret;
+				struct strbuf err = STRBUF_INIT;
+
+				ret = safe_create_reflog(refname, 1, &err);
+				if (ret) {
+					fprintf(stderr, _("Can not do reflog for '%s': %s\n"),
+						opts->new_orphan_branch, err.buf);
+					strbuf_release(&err);
+					free(refname);
+					return;
+				}
+				strbuf_release(&err);
+			}
+			free(refname);
+		}
+		else
+			create_branch(the_repository,
+				      opts->new_branch, new_branch_info->name,
+				      opts->new_branch_force ? 1 : 0,
+				      opts->new_branch_force ? 1 : 0,
+				      opts->new_branch_log,
+				      opts->quiet,
+				      opts->track);
+		new_branch_info->name = opts->new_branch;
+		setup_branch_path(new_branch_info);
+	}
+
+	old_desc = old_branch_info->name;
+	if (!old_desc && old_branch_info->commit)
+		old_desc = oid_to_hex(&old_branch_info->commit->object.oid);
+
+	reflog_msg = getenv("GIT_REFLOG_ACTION");
+	if (!reflog_msg)
+		strbuf_addf(&msg, "checkout: moving from %s to %s",
+			old_desc ? old_desc : "(invalid)", new_branch_info->name);
+	else
+		strbuf_insert(&msg, 0, reflog_msg, strlen(reflog_msg));
+
+	if (!strcmp(new_branch_info->name, "HEAD") && !new_branch_info->path && !opts->force_detach) {
+		/* Nothing to do. */
+	} else if (opts->force_detach || !new_branch_info->path) {	/* No longer on any branch. */
+		update_ref(msg.buf, "HEAD", &new_branch_info->commit->object.oid, NULL,
+			   REF_NO_DEREF, UPDATE_REFS_DIE_ON_ERR);
+		if (!opts->quiet) {
+			if (old_branch_info->path &&
+			    advice_detached_head && !opts->force_detach)
+				detach_advice(new_branch_info->name);
+			describe_detached_head(_("HEAD is now at"), new_branch_info->commit);
+		}
+	} else if (new_branch_info->path) {	/* Switch branches. */
+		if (create_symref("HEAD", new_branch_info->path, msg.buf) < 0)
+			die(_("unable to update HEAD"));
+		if (!opts->quiet) {
+			if (old_branch_info->path && !strcmp(new_branch_info->path, old_branch_info->path)) {
+				if (opts->new_branch_force)
+					fprintf(stderr, _("Reset branch '%s'\n"),
+						new_branch_info->name);
+				else
+					fprintf(stderr, _("Already on '%s'\n"),
+						new_branch_info->name);
+			} else if (opts->new_branch) {
+				if (opts->branch_exists)
+					fprintf(stderr, _("Switched to and reset branch '%s'\n"), new_branch_info->name);
+				else
+					fprintf(stderr, _("Switched to a new branch '%s'\n"), new_branch_info->name);
+			} else {
+				fprintf(stderr, _("Switched to branch '%s'\n"),
+					new_branch_info->name);
+			}
+		}
+		if (old_branch_info->path && old_branch_info->name) {
+			if (!ref_exists(old_branch_info->path) && reflog_exists(old_branch_info->path))
+				delete_reflog(old_branch_info->path);
+		}
+	}
+	remove_branch_state(the_repository, !opts->quiet);
+	strbuf_release(&msg);
+	if (!opts->quiet &&
+	    (new_branch_info->path || (!opts->force_detach && !strcmp(new_branch_info->name, "HEAD"))))
+		report_tracking(new_branch_info);
+}
+
+static int add_pending_uninteresting_ref(const char *refname,
+					 const struct object_id *oid,
+					 int flags, void *cb_data)
+{
+	add_pending_oid(cb_data, refname, oid, UNINTERESTING);
+	return 0;
+}
+
+static void describe_one_orphan(struct strbuf *sb, struct commit *commit)
+{
+	strbuf_addstr(sb, "  ");
+	strbuf_add_unique_abbrev(sb, &commit->object.oid, DEFAULT_ABBREV);
+	strbuf_addch(sb, ' ');
+	if (!parse_commit(commit))
+		pp_commit_easy(CMIT_FMT_ONELINE, commit, sb);
+	strbuf_addch(sb, '\n');
+}
+
+#define ORPHAN_CUTOFF 4
+static void suggest_reattach(struct commit *commit, struct rev_info *revs)
+{
+	struct commit *c, *last = NULL;
+	struct strbuf sb = STRBUF_INIT;
+	int lost = 0;
+	while ((c = get_revision(revs)) != NULL) {
+		if (lost < ORPHAN_CUTOFF)
+			describe_one_orphan(&sb, c);
+		last = c;
+		lost++;
+	}
+	if (ORPHAN_CUTOFF < lost) {
+		int more = lost - ORPHAN_CUTOFF;
+		if (more == 1)
+			describe_one_orphan(&sb, last);
+		else
+			strbuf_addf(&sb, _(" ... and %d more.\n"), more);
+	}
+
+	fprintf(stderr,
+		Q_(
+		/* The singular version */
+		"Warning: you are leaving %d commit behind, "
+		"not connected to\n"
+		"any of your branches:\n\n"
+		"%s\n",
+		/* The plural version */
+		"Warning: you are leaving %d commits behind, "
+		"not connected to\n"
+		"any of your branches:\n\n"
+		"%s\n",
+		/* Give ngettext() the count */
+		lost),
+		lost,
+		sb.buf);
+	strbuf_release(&sb);
+
+	if (advice_detached_head)
+		fprintf(stderr,
+			Q_(
+			/* The singular version */
+			"If you want to keep it by creating a new branch, "
+			"this may be a good time\nto do so with:\n\n"
+			" git branch <new-branch-name> %s\n\n",
+			/* The plural version */
+			"If you want to keep them by creating a new branch, "
+			"this may be a good time\nto do so with:\n\n"
+			" git branch <new-branch-name> %s\n\n",
+			/* Give ngettext() the count */
+			lost),
+			find_unique_abbrev(&commit->object.oid, DEFAULT_ABBREV));
+}
+
+/*
+ * We are about to leave commit that was at the tip of a detached
+ * HEAD.  If it is not reachable from any ref, this is the last chance
+ * for the user to do so without resorting to reflog.
+ */
+static void orphaned_commit_warning(struct commit *old_commit, struct commit *new_commit)
+{
+	struct rev_info revs;
+	struct object *object = &old_commit->object;
+
+	repo_init_revisions(the_repository, &revs, NULL);
+	setup_revisions(0, NULL, &revs, NULL);
+
+	object->flags &= ~UNINTERESTING;
+	add_pending_object(&revs, object, oid_to_hex(&object->oid));
+
+	for_each_ref(add_pending_uninteresting_ref, &revs);
+	if (new_commit)
+		add_pending_oid(&revs, "HEAD",
+				&new_commit->object.oid,
+				UNINTERESTING);
+
+	if (prepare_revision_walk(&revs))
+		die(_("internal error in revision walk"));
+	if (!(old_commit->object.flags & UNINTERESTING))
+		suggest_reattach(old_commit, &revs);
+	else
+		describe_detached_head(_("Previous HEAD position was"), old_commit);
+
+	/* Clean up objects used, as they will be reused. */
+	clear_commit_marks_all(ALL_REV_FLAGS);
+}
+
+static int switch_branches(const struct checkout_opts *opts,
+			   struct branch_info *new_branch_info)
+{
+	int ret = 0;
+	struct branch_info old_branch_info;
+	void *path_to_free;
+	struct object_id rev;
+	int flag, writeout_error = 0;
+	int do_merge = 1;
+
+	trace2_cmd_mode("branch");
+
+	memset(&old_branch_info, 0, sizeof(old_branch_info));
+	old_branch_info.path = path_to_free = resolve_refdup("HEAD", 0, &rev, &flag);
+	if (old_branch_info.path)
+		old_branch_info.commit = lookup_commit_reference_gently(the_repository, &rev, 1);
+	if (!(flag & REF_ISSYMREF))
+		old_branch_info.path = NULL;
+
+	if (old_branch_info.path)
+		skip_prefix(old_branch_info.path, "refs/heads/", &old_branch_info.name);
+
+	if (opts->new_orphan_branch && opts->orphan_from_empty_tree) {
+		if (new_branch_info->name)
+			BUG("'switch --orphan' should never accept a commit as starting point");
+		new_branch_info->commit = NULL;
+		new_branch_info->name = "(empty)";
+		do_merge = 1;
+	}
+
+	if (!new_branch_info->name) {
+		new_branch_info->name = "HEAD";
+		new_branch_info->commit = old_branch_info.commit;
+		if (!new_branch_info->commit)
+			die(_("You are on a branch yet to be born"));
+		parse_commit_or_die(new_branch_info->commit);
+
+		if (opts->only_merge_on_switching_branches)
+			do_merge = 0;
+	}
+
+	if (do_merge) {
+		ret = merge_working_tree(opts, &old_branch_info, new_branch_info, &writeout_error);
+		if (ret) {
+			free(path_to_free);
+			return ret;
+		}
+	}
+
+	if (!opts->quiet && !old_branch_info.path && old_branch_info.commit && new_branch_info->commit != old_branch_info.commit)
+		orphaned_commit_warning(old_branch_info.commit, new_branch_info->commit);
+
+	update_refs_for_switch(opts, &old_branch_info, new_branch_info);
+
+	ret = post_checkout_hook(old_branch_info.commit, new_branch_info->commit, 1);
+	free(path_to_free);
+	return ret || writeout_error;
+}
+
+static int git_checkout_config(const char *var, const char *value, void *cb)
+{
+	if (!strcmp(var, "diff.ignoresubmodules")) {
+		struct checkout_opts *opts = cb;
+		handle_ignore_submodules_arg(&opts->diff_options, value);
+		return 0;
+	}
+
+	if (starts_with(var, "submodule."))
+		return git_default_submodule_config(var, value, NULL);
+
+	return git_xmerge_config(var, value, NULL);
+}
+
+static void setup_new_branch_info_and_source_tree(
+	struct branch_info *new_branch_info,
+	struct checkout_opts *opts,
+	struct object_id *rev,
+	const char *arg)
+{
+	struct tree **source_tree = &opts->source_tree;
+	struct object_id branch_rev;
+
+	new_branch_info->name = arg;
+	setup_branch_path(new_branch_info);
+
+	if (!check_refname_format(new_branch_info->path, 0) &&
+	    !read_ref(new_branch_info->path, &branch_rev))
+		oidcpy(rev, &branch_rev);
+	else
+		new_branch_info->path = NULL; /* not an existing branch */
+
+	new_branch_info->commit = lookup_commit_reference_gently(the_repository, rev, 1);
+	if (!new_branch_info->commit) {
+		/* not a commit */
+		*source_tree = parse_tree_indirect(rev);
+	} else {
+		parse_commit_or_die(new_branch_info->commit);
+		*source_tree = get_commit_tree(new_branch_info->commit);
+	}
+}
+
+static int parse_branchname_arg(int argc, const char **argv,
+				int dwim_new_local_branch_ok,
+				struct branch_info *new_branch_info,
+				struct checkout_opts *opts,
+				struct object_id *rev,
+				int *dwim_remotes_matched)
+{
+	const char **new_branch = &opts->new_branch;
+	int argcount = 0;
+	const char *arg;
+	int dash_dash_pos;
+	int has_dash_dash = 0;
+	int i;
+
+	/*
+	 * 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> [--]
+	 *
+	 *   (a) 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.
+	 *
+	 *   (b) If <something> is _not_ a commit, either "--" is present
+	 *       or <something> is not a path, no -t or -b was given, and
+	 *       and there is a tracking branch whose name is <something>
+	 *       in one and only one remote (or if the branch exists on the
+	 *       remote named in checkout.defaultRemote), then this is a
+	 *       short-hand to fork local <something> from that
+	 *       remote-tracking branch.
+	 *
+	 *   (c) Otherwise, if "--" is present, treat it like case (1).
+	 *
+	 *   (d) Otherwise :
+	 *       - if it's a reference, treat it like case (1)
+	 *       - else if it's a path, treat it like case (2)
+	 *       - else: fail.
+	 *
+	 * case 4: git checkout <something> <paths>
+	 *
+	 *   The first argument must 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)
+		return 0;
+
+	if (!opts->accept_pathspec) {
+		if (argc > 1)
+			die(_("only one reference expected"));
+		has_dash_dash = 1; /* helps disambiguate */
+	}
+
+	arg = argv[0];
+	dash_dash_pos = -1;
+	for (i = 0; i < argc; i++) {
+		if (opts->accept_pathspec && !strcmp(argv[i], "--")) {
+			dash_dash_pos = i;
+			break;
+		}
+	}
+	if (dash_dash_pos == 0)
+		return 1; /* case (2) */
+	else if (dash_dash_pos == 1)
+		has_dash_dash = 1; /* case (3) or (1) */
+	else if (dash_dash_pos >= 2)
+		die(_("only one reference expected, %d given."), dash_dash_pos);
+	opts->count_checkout_paths = !opts->quiet && !has_dash_dash;
+
+	if (!strcmp(arg, "-"))
+		arg = "@{-1}";
+
+	if (get_oid_mb(arg, rev)) {
+		/*
+		 * Either case (3) or (4), with <something> not being
+		 * a commit, or an attempt to use case (1) with an
+		 * invalid ref.
+		 *
+		 * It's likely an error, but we need to find out if
+		 * we should auto-create the branch, case (3).(b).
+		 */
+		int recover_with_dwim = dwim_new_local_branch_ok;
+
+		int could_be_checkout_paths = !has_dash_dash &&
+			check_filename(opts->prefix, arg);
+
+		if (!has_dash_dash && !no_wildcard(arg))
+			recover_with_dwim = 0;
+
+		/*
+		 * Accept "git checkout foo", "git checkout foo --"
+		 * and "git switch foo" as candidates for dwim.
+		 */
+		if (!(argc == 1 && !has_dash_dash) &&
+		    !(argc == 2 && has_dash_dash) &&
+		    opts->accept_pathspec)
+			recover_with_dwim = 0;
+
+		if (recover_with_dwim) {
+			const char *remote = unique_tracking_name(arg, rev,
+								  dwim_remotes_matched);
+			if (remote) {
+				if (could_be_checkout_paths)
+					die(_("'%s' could be both a local file and a tracking branch.\n"
+					      "Please use -- (and optionally --no-guess) to disambiguate"),
+					    arg);
+				*new_branch = arg;
+				arg = remote;
+				/* DWIMmed to create local branch, case (3).(b) */
+			} else {
+				recover_with_dwim = 0;
+			}
+		}
+
+		if (!recover_with_dwim) {
+			if (has_dash_dash)
+				die(_("invalid reference: %s"), arg);
+			return argcount;
+		}
+	}
+
+	/* we can't end up being in (2) anymore, eat the argument */
+	argcount++;
+	argv++;
+	argc--;
+
+	setup_new_branch_info_and_source_tree(new_branch_info, opts, rev, arg);
+
+	if (!opts->source_tree)                   /* case (1): want a tree */
+		die(_("reference is not a tree: %s"), arg);
+
+	if (!has_dash_dash) {	/* case (3).(d) -> (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(opts->prefix, arg);
+	} else if (opts->accept_pathspec) {
+		argcount++;
+		argv++;
+		argc--;
+	}
+
+	return argcount;
+}
+
+static int switch_unborn_to_new_branch(const struct checkout_opts *opts)
+{
+	int status;
+	struct strbuf branch_ref = STRBUF_INIT;
+
+	trace2_cmd_mode("unborn");
+
+	if (!opts->new_branch)
+		die(_("You are on a branch yet to be born"));
+	strbuf_addf(&branch_ref, "refs/heads/%s", opts->new_branch);
+	status = create_symref("HEAD", branch_ref.buf, "checkout -b");
+	strbuf_release(&branch_ref);
+	if (!opts->quiet)
+		fprintf(stderr, _("Switched to a new branch '%s'\n"),
+			opts->new_branch);
+	return status;
+}
+
+static void die_expecting_a_branch(const struct branch_info *branch_info)
+{
+	struct object_id oid;
+	char *to_free;
+
+	if (dwim_ref(branch_info->name, strlen(branch_info->name), &oid, &to_free) == 1) {
+		const char *ref = to_free;
+
+		if (skip_prefix(ref, "refs/tags/", &ref))
+			die(_("a branch is expected, got tag '%s'"), ref);
+		if (skip_prefix(ref, "refs/remotes/", &ref))
+			die(_("a branch is expected, got remote branch '%s'"), ref);
+		die(_("a branch is expected, got '%s'"), ref);
+	}
+	if (branch_info->commit)
+		die(_("a branch is expected, got commit '%s'"), branch_info->name);
+	/*
+	 * This case should never happen because we already die() on
+	 * non-commit, but just in case.
+	 */
+	die(_("a branch is expected, got '%s'"), branch_info->name);
+}
+
+static void die_if_some_operation_in_progress(void)
+{
+	struct wt_status_state state;
+
+	memset(&state, 0, sizeof(state));
+	wt_status_get_state(the_repository, &state, 0);
+
+	if (state.merge_in_progress)
+		die(_("cannot switch branch while merging\n"
+		      "Consider \"git merge --quit\" "
+		      "or \"git worktree add\"."));
+	if (state.am_in_progress)
+		die(_("cannot switch branch in the middle of an am session\n"
+		      "Consider \"git am --quit\" "
+		      "or \"git worktree add\"."));
+	if (state.rebase_interactive_in_progress || state.rebase_in_progress)
+		die(_("cannot switch branch while rebasing\n"
+		      "Consider \"git rebase --quit\" "
+		      "or \"git worktree add\"."));
+	if (state.cherry_pick_in_progress)
+		die(_("cannot switch branch while cherry-picking\n"
+		      "Consider \"git cherry-pick --quit\" "
+		      "or \"git worktree add\"."));
+	if (state.revert_in_progress)
+		die(_("cannot switch branch while reverting\n"
+		      "Consider \"git revert --quit\" "
+		      "or \"git worktree add\"."));
+	if (state.bisect_in_progress)
+		warning(_("you are switching branch while bisecting"));
+}
+
+static int checkout_branch(struct checkout_opts *opts,
+			   struct branch_info *new_branch_info)
+{
+	if (opts->pathspec.nr)
+		die(_("paths cannot be used with switching branches"));
+
+	if (opts->patch_mode)
+		die(_("'%s' cannot be used with switching branches"),
+		    "--patch");
+
+	if (opts->overlay_mode != -1)
+		die(_("'%s' cannot be used with switching branches"),
+		    "--[no]-overlay");
+
+	if (opts->writeout_stage)
+		die(_("'%s' cannot be used with switching branches"),
+		    "--ours/--theirs");
+
+	if (opts->force && opts->merge)
+		die(_("'%s' cannot be used with '%s'"), "-f", "-m");
+
+	if (opts->discard_changes && opts->merge)
+		die(_("'%s' cannot be used with '%s'"), "--discard-changes", "--merge");
+
+	if (opts->force_detach && opts->new_branch)
+		die(_("'%s' cannot be used with '%s'"),
+		    "--detach", "-b/-B/--orphan");
+
+	if (opts->new_orphan_branch) {
+		if (opts->track != BRANCH_TRACK_UNSPECIFIED)
+			die(_("'%s' cannot be used with '%s'"), "--orphan", "-t");
+		if (opts->orphan_from_empty_tree && new_branch_info->name)
+			die(_("'%s' cannot take <start-point>"), "--orphan");
+	} else if (opts->force_detach) {
+		if (opts->track != BRANCH_TRACK_UNSPECIFIED)
+			die(_("'%s' cannot be used with '%s'"), "--detach", "-t");
+	} else if (opts->track == BRANCH_TRACK_UNSPECIFIED)
+		opts->track = git_branch_track;
+
+	if (new_branch_info->name && !new_branch_info->commit)
+		die(_("Cannot switch branch to a non-commit '%s'"),
+		    new_branch_info->name);
+
+	if (!opts->switch_branch_doing_nothing_is_ok &&
+	    !new_branch_info->name &&
+	    !opts->new_branch &&
+	    !opts->force_detach)
+		die(_("missing branch or commit argument"));
+
+	if (!opts->implicit_detach &&
+	    !opts->force_detach &&
+	    !opts->new_branch &&
+	    !opts->new_branch_force &&
+	    new_branch_info->name &&
+	    !new_branch_info->path)
+		die_expecting_a_branch(new_branch_info);
+
+	if (!opts->can_switch_when_in_progress)
+		die_if_some_operation_in_progress();
+
+	if (new_branch_info->path && !opts->force_detach && !opts->new_branch &&
+	    !opts->ignore_other_worktrees) {
+		int flag;
+		char *head_ref = resolve_refdup("HEAD", 0, NULL, &flag);
+		if (head_ref &&
+		    (!(flag & REF_ISSYMREF) || strcmp(head_ref, new_branch_info->path)))
+			die_if_checked_out(new_branch_info->path, 1);
+		free(head_ref);
+	}
+
+	if (!new_branch_info->commit && opts->new_branch) {
+		struct object_id rev;
+		int flag;
+
+		if (!read_ref_full("HEAD", 0, &rev, &flag) &&
+		    (flag & REF_ISSYMREF) && is_null_oid(&rev))
+			return switch_unborn_to_new_branch(opts);
+	}
+	return switch_branches(opts, new_branch_info);
+}
+
+static struct option *add_common_options(struct checkout_opts *opts,
+					 struct option *prevopts)
+{
+	struct option options[] = {
+		OPT__QUIET(&opts->quiet, N_("suppress progress reporting")),
+		{ OPTION_CALLBACK, 0, "recurse-submodules", NULL,
+			    "checkout", "control recursive updating of submodules",
+			    PARSE_OPT_OPTARG, option_parse_recurse_submodules_worktree_updater },
+		OPT_BOOL(0, "progress", &opts->show_progress, N_("force progress reporting")),
+		OPT_BOOL('m', "merge", &opts->merge, N_("perform a 3-way merge with the new branch")),
+		OPT_STRING(0, "conflict", &opts->conflict_style, N_("style"),
+			   N_("conflict style (merge or diff3)")),
+		OPT_END()
+	};
+	struct option *newopts = parse_options_concat(prevopts, options);
+	free(prevopts);
+	return newopts;
+}
+
+static struct option *add_common_switch_branch_options(
+	struct checkout_opts *opts, struct option *prevopts)
+{
+	struct option options[] = {
+		OPT_BOOL('d', "detach", &opts->force_detach, N_("detach HEAD at named commit")),
+		OPT_SET_INT('t', "track",  &opts->track, N_("set upstream info for new branch"),
+			BRANCH_TRACK_EXPLICIT),
+		OPT__FORCE(&opts->force, N_("force checkout (throw away local modifications)"),
+			   PARSE_OPT_NOCOMPLETE),
+		OPT_STRING(0, "orphan", &opts->new_orphan_branch, N_("new-branch"), N_("new unparented branch")),
+		OPT_BOOL_F(0, "overwrite-ignore", &opts->overwrite_ignore,
+			   N_("update ignored files (default)"),
+			   PARSE_OPT_NOCOMPLETE),
+		OPT_BOOL(0, "ignore-other-worktrees", &opts->ignore_other_worktrees,
+			 N_("do not check if another worktree is holding the given ref")),
+		OPT_END()
+	};
+	struct option *newopts = parse_options_concat(prevopts, options);
+	free(prevopts);
+	return newopts;
+}
+
+static struct option *add_checkout_path_options(struct checkout_opts *opts,
+						struct option *prevopts)
+{
+	struct option options[] = {
+		OPT_SET_INT_F('2', "ours", &opts->writeout_stage,
+			      N_("checkout our version for unmerged files"),
+			      2, PARSE_OPT_NONEG),
+		OPT_SET_INT_F('3', "theirs", &opts->writeout_stage,
+			      N_("checkout their version for unmerged files"),
+			      3, PARSE_OPT_NONEG),
+		OPT_BOOL('p', "patch", &opts->patch_mode, N_("select hunks interactively")),
+		OPT_BOOL(0, "ignore-skip-worktree-bits", &opts->ignore_skipworktree,
+			 N_("do not limit pathspecs to sparse entries only")),
+		OPT_END()
+	};
+	struct option *newopts = parse_options_concat(prevopts, options);
+	free(prevopts);
+	return newopts;
+}
+
+static int checkout_main(int argc, const char **argv, const char *prefix,
+			 struct checkout_opts *opts, struct option *options,
+			 const char * const usagestr[])
+{
+	struct branch_info new_branch_info;
+	int dwim_remotes_matched = 0;
+	int parseopt_flags = 0;
+
+	memset(&new_branch_info, 0, sizeof(new_branch_info));
+	opts->overwrite_ignore = 1;
+	opts->prefix = prefix;
+	opts->show_progress = -1;
+
+	git_config(git_checkout_config, opts);
+
+	opts->track = BRANCH_TRACK_UNSPECIFIED;
+
+	if (!opts->accept_pathspec && !opts->accept_ref)
+		BUG("make up your mind, you need to take _something_");
+	if (opts->accept_pathspec && opts->accept_ref)
+		parseopt_flags = PARSE_OPT_KEEP_DASHDASH;
+
+	argc = parse_options(argc, argv, prefix, options,
+			     usagestr, parseopt_flags);
+
+	if (opts->show_progress < 0) {
+		if (opts->quiet)
+			opts->show_progress = 0;
+		else
+			opts->show_progress = isatty(2);
+	}
+
+	if (opts->conflict_style) {
+		opts->merge = 1; /* implied */
+		git_xmerge_config("merge.conflictstyle", opts->conflict_style, NULL);
+	}
+	if (opts->force) {
+		opts->discard_changes = 1;
+		opts->ignore_unmerged_opt = "--force";
+		opts->ignore_unmerged = 1;
+	}
+
+	if ((!!opts->new_branch + !!opts->new_branch_force + !!opts->new_orphan_branch) > 1)
+		die(_("-b, -B and --orphan are mutually exclusive"));
+
+	if (opts->overlay_mode == 1 && opts->patch_mode)
+		die(_("-p and --overlay are mutually exclusive"));
+
+	if (opts->checkout_index >= 0 || opts->checkout_worktree >= 0) {
+		if (opts->checkout_index < 0)
+			opts->checkout_index = 0;
+		if (opts->checkout_worktree < 0)
+			opts->checkout_worktree = 0;
+	} else {
+		if (opts->checkout_index < 0)
+			opts->checkout_index = -opts->checkout_index - 1;
+		if (opts->checkout_worktree < 0)
+			opts->checkout_worktree = -opts->checkout_worktree - 1;
+	}
+	if (opts->checkout_index < 0 || opts->checkout_worktree < 0)
+		BUG("these flags should be non-negative by now");
+	/*
+	 * convenient shortcut: "git restore --staged" equals
+	 * "git restore --staged --source HEAD"
+	 */
+	if (!opts->from_treeish && opts->checkout_index && !opts->checkout_worktree)
+		opts->from_treeish = "HEAD";
+
+	/*
+	 * From here on, new_branch will contain the branch to be checked out,
+	 * and new_branch_force and new_orphan_branch will tell us which one of
+	 * -b/-B/--orphan is being used.
+	 */
+	if (opts->new_branch_force)
+		opts->new_branch = opts->new_branch_force;
+
+	if (opts->new_orphan_branch)
+		opts->new_branch = opts->new_orphan_branch;
+
+	/* --track without -b/-B/--orphan should DWIM */
+	if (opts->track != BRANCH_TRACK_UNSPECIFIED && !opts->new_branch) {
+		const char *argv0 = argv[0];
+		if (!argc || !strcmp(argv0, "--"))
+			die(_("--track needs a branch name"));
+		skip_prefix(argv0, "refs/", &argv0);
+		skip_prefix(argv0, "remotes/", &argv0);
+		argv0 = strchr(argv0, '/');
+		if (!argv0 || !argv0[1])
+			die(_("missing branch name; try -b"));
+		opts->new_branch = argv0 + 1;
+	}
+
+	/*
+	 * Extract branch name from command line arguments, so
+	 * all that is left is pathspecs.
+	 *
+	 * Handle
+	 *
+	 *  1) git checkout <tree> -- [<paths>]
+	 *  2) git checkout -- [<paths>]
+	 *  3) git checkout <something> [<paths>]
+	 *
+	 * including "last branch" syntax and DWIM-ery for names of
+	 * remote branches, erroring out for invalid or ambiguous cases.
+	 */
+	if (argc && opts->accept_ref) {
+		struct object_id rev;
+		int dwim_ok =
+			!opts->patch_mode &&
+			opts->dwim_new_local_branch &&
+			opts->track == BRANCH_TRACK_UNSPECIFIED &&
+			!opts->new_branch;
+		int n = parse_branchname_arg(argc, argv, dwim_ok,
+					     &new_branch_info, opts, &rev,
+					     &dwim_remotes_matched);
+		argv += n;
+		argc -= n;
+	} else if (!opts->accept_ref && opts->from_treeish) {
+		struct object_id rev;
+
+		if (get_oid_mb(opts->from_treeish, &rev))
+			die(_("could not resolve %s"), opts->from_treeish);
+
+		setup_new_branch_info_and_source_tree(&new_branch_info,
+						      opts, &rev,
+						      opts->from_treeish);
+
+		if (!opts->source_tree)
+			die(_("reference is not a tree: %s"), opts->from_treeish);
+	}
+
+	if (opts->accept_pathspec && !opts->empty_pathspec_ok && !argc &&
+	    !opts->patch_mode)	/* patch mode is special */
+		die(_("you must specify path(s) to restore"));
+
+	if (argc) {
+		parse_pathspec(&opts->pathspec, 0,
+			       opts->patch_mode ? PATHSPEC_PREFIX_ORIGIN : 0,
+			       prefix, argv);
+
+		if (!opts->pathspec.nr)
+			die(_("invalid path specification"));
+
+		/*
+		 * Try to give more helpful suggestion.
+		 * new_branch && argc > 1 will be caught later.
+		 */
+		if (opts->new_branch && argc == 1)
+			die(_("'%s' is not a commit and a branch '%s' cannot be created from it"),
+				argv[0], opts->new_branch);
+
+		if (opts->force_detach)
+			die(_("git checkout: --detach does not take a path argument '%s'"),
+			    argv[0]);
+
+		if (1 < !!opts->writeout_stage + !!opts->force + !!opts->merge)
+			die(_("git checkout: --ours/--theirs, --force and --merge are incompatible when\n"
+			      "checking out of the index."));
+	}
+
+	if (opts->new_branch) {
+		struct strbuf buf = STRBUF_INIT;
+
+		if (opts->new_branch_force)
+			opts->branch_exists = validate_branchname(opts->new_branch, &buf);
+		else
+			opts->branch_exists =
+				validate_new_branchname(opts->new_branch, &buf, 0);
+		strbuf_release(&buf);
+	}
+
+	UNLEAK(opts);
+	if (opts->patch_mode || opts->pathspec.nr) {
+		int ret = checkout_paths(opts, new_branch_info.name);
+		if (ret && dwim_remotes_matched > 1 &&
+		    advice_checkout_ambiguous_remote_branch_name)
+			advise(_("'%s' matched more than one remote tracking branch.\n"
+				 "We found %d remotes with a reference that matched. So we fell back\n"
+				 "on trying to resolve the argument as a path, but failed there too!\n"
+				 "\n"
+				 "If you meant to check out a remote tracking branch on, e.g. 'origin',\n"
+				 "you can do so by fully qualifying the name with the --track option:\n"
+				 "\n"
+				 "    git checkout --track origin/<name>\n"
+				 "\n"
+				 "If you'd like to always have checkouts of an ambiguous <name> prefer\n"
+				 "one remote, e.g. the 'origin' remote, consider setting\n"
+				 "checkout.defaultRemote=origin in your config."),
+			       argv[0],
+			       dwim_remotes_matched);
+		return ret;
+	} else {
+		return checkout_branch(opts, &new_branch_info);
+	}
+}
+
+int cmd_checkout(int argc, const char **argv, const char *prefix)
+{
+	struct checkout_opts opts;
+	struct option *options;
+	struct option checkout_options[] = {
+		OPT_STRING('b', NULL, &opts.new_branch, N_("branch"),
+			   N_("create and checkout a new branch")),
+		OPT_STRING('B', NULL, &opts.new_branch_force, N_("branch"),
+			   N_("create/reset and checkout a branch")),
+		OPT_BOOL('l', NULL, &opts.new_branch_log, N_("create reflog for new branch")),
+		OPT_BOOL(0, "guess", &opts.dwim_new_local_branch,
+			 N_("second guess 'git checkout <no-such-branch>' (default)")),
+		OPT_BOOL(0, "overlay", &opts.overlay_mode, N_("use overlay mode (default)")),
+		OPT_END()
+	};
+	int ret;
+
+	memset(&opts, 0, sizeof(opts));
+	opts.dwim_new_local_branch = 1;
+	opts.switch_branch_doing_nothing_is_ok = 1;
+	opts.only_merge_on_switching_branches = 0;
+	opts.accept_ref = 1;
+	opts.accept_pathspec = 1;
+	opts.implicit_detach = 1;
+	opts.can_switch_when_in_progress = 1;
+	opts.orphan_from_empty_tree = 0;
+	opts.empty_pathspec_ok = 1;
+	opts.overlay_mode = -1;
+	opts.checkout_index = -2;    /* default on */
+	opts.checkout_worktree = -2; /* default on */
+
+	options = parse_options_dup(checkout_options);
+	options = add_common_options(&opts, options);
+	options = add_common_switch_branch_options(&opts, options);
+	options = add_checkout_path_options(&opts, options);
+
+	ret = checkout_main(argc, argv, prefix, &opts,
+			    options, checkout_usage);
+	FREE_AND_NULL(options);
+	return ret;
+}
+
+int cmd_switch(int argc, const char **argv, const char *prefix)
+{
+	struct checkout_opts opts;
+	struct option *options = NULL;
+	struct option switch_options[] = {
+		OPT_STRING('c', "create", &opts.new_branch, N_("branch"),
+			   N_("create and switch to a new branch")),
+		OPT_STRING('C', "force-create", &opts.new_branch_force, N_("branch"),
+			   N_("create/reset and switch to a branch")),
+		OPT_BOOL(0, "guess", &opts.dwim_new_local_branch,
+			 N_("second guess 'git switch <no-such-branch>'")),
+		OPT_BOOL(0, "discard-changes", &opts.discard_changes,
+			 N_("throw away local modifications")),
+		OPT_END()
+	};
+	int ret;
+
+	memset(&opts, 0, sizeof(opts));
+	opts.dwim_new_local_branch = 1;
+	opts.accept_ref = 1;
+	opts.accept_pathspec = 0;
+	opts.switch_branch_doing_nothing_is_ok = 0;
+	opts.only_merge_on_switching_branches = 1;
+	opts.implicit_detach = 0;
+	opts.can_switch_when_in_progress = 0;
+	opts.orphan_from_empty_tree = 1;
+	opts.overlay_mode = -1;
+
+	options = parse_options_dup(switch_options);
+	options = add_common_options(&opts, options);
+	options = add_common_switch_branch_options(&opts, options);
+
+	ret = checkout_main(argc, argv, prefix, &opts,
+			    options, switch_branch_usage);
+	FREE_AND_NULL(options);
+	return ret;
+}
+
+int cmd_restore(int argc, const char **argv, const char *prefix)
+{
+	struct checkout_opts opts;
+	struct option *options;
+	struct option restore_options[] = {
+		OPT_STRING('s', "source", &opts.from_treeish, "<tree-ish>",
+			   N_("which tree-ish to checkout from")),
+		OPT_BOOL('S', "staged", &opts.checkout_index,
+			   N_("restore the index")),
+		OPT_BOOL('W', "worktree", &opts.checkout_worktree,
+			   N_("restore the working tree (default)")),
+		OPT_BOOL(0, "ignore-unmerged", &opts.ignore_unmerged,
+			 N_("ignore unmerged entries")),
+		OPT_BOOL(0, "overlay", &opts.overlay_mode, N_("use overlay mode")),
+		OPT_END()
+	};
+	int ret;
+
+	memset(&opts, 0, sizeof(opts));
+	opts.accept_ref = 0;
+	opts.accept_pathspec = 1;
+	opts.empty_pathspec_ok = 0;
+	opts.overlay_mode = 0;
+	opts.checkout_index = -1;    /* default off */
+	opts.checkout_worktree = -2; /* default on */
+	opts.ignore_unmerged_opt = "--ignore-unmerged";
+
+	options = parse_options_dup(restore_options);
+	options = add_common_options(&opts, options);
+	options = add_checkout_path_options(&opts, options);
+
+	ret = checkout_main(argc, argv, prefix, &opts,
+			    options, restore_usage);
+	FREE_AND_NULL(options);
+	return ret;
+}