1 files changed, 664 insertions, 359 deletions

diff --git a/builtin/checkout.c b/builtin/checkout.c
index ffa776c..d677381 100644
--- a/builtin/checkout.c
+++ b/builtin/checkout.c
@@ -1,32 +1,31 @@
 #define USE_THE_INDEX_COMPATIBILITY_MACROS
 #include "builtin.h"
-#include "config.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 "object-store.h"
-#include "commit.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 "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 "wt-status.h"
 #include "xdiff-interface.h"
-#include "ll-merge.h"
-#include "resolve-undo.h"
-#include "submodule-config.h"
-#include "submodule.h"
-#include "advice.h"
-
-static int checkout_optimize_new_branch;
 
 static const char * const checkout_usage[] = {
 	N_("git checkout [<options>] <branch>"),
@@ -34,12 +33,23 @@ static const char * const checkout_usage[] = {
 	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;
@@ -47,10 +57,21 @@ struct checkout_opts {
 	int show_progress;
 	int count_checkout_paths;
 	int overlay_mode;
-	/*
-	 * If new checkout options are added, skip_merge_working_tree
-	 * should be updated accordingly.
-	 */
+	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;
+	int pathspec_file_nul;
+	const char *pathspec_from_file;
 
 	const char *new_branch;
 	const char *new_branch_force;
@@ -58,10 +79,12 @@ struct checkout_opts {
 	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;
 };
 
@@ -105,6 +128,7 @@ static int update_some(const struct object_id *oid, struct strbuf *base,
 	if (pos >= 0) {
 		struct cache_entry *old = active_cache[pos];
 		if (ce->ce_mode == old->ce_mode &&
+		    !ce_intent_to_add(old) &&
 		    oideq(&ce->oid, &old->oid)) {
 			old->ce_flags |= CE_UPDATE;
 			discard_cache_entry(ce);
@@ -313,17 +337,74 @@ static void mark_ce_for_checkout_no_overlay(struct cache_entry *ce,
 	}
 }
 
+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;
-	struct checkout state = CHECKOUT_INIT;
 	static char *ps_matched;
 	struct object_id rev;
 	struct commit *head;
 	int errs = 0;
 	struct lock_file lock_file = LOCK_INIT;
-	int nr_checkouts = 0, nr_unmerged = 0;
+	int checkout_index;
 
 	trace2_cmd_mode(opts->patch_mode ? "patch" : "path");
 
@@ -333,8 +414,9 @@ static int checkout_paths(const struct checkout_opts *opts,
 	if (opts->new_branch_log)
 		die(_("'%s' cannot be used with updating paths"), "-l");
 
-	if (opts->force && opts->patch_mode)
-		die(_("'%s' cannot be used with updating paths"), "-f");
+	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");
@@ -342,16 +424,46 @@ static int checkout_paths(const struct checkout_opts *opts,
 	if (opts->merge && opts->patch_mode)
 		die(_("'%s' cannot be used with %s"), "--merge", "--patch");
 
-	if (opts->force && opts->merge)
-		die(_("'%s' cannot be used with %s"), "-f", "-m");
+	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->patch_mode)
-		return run_add_interactive(revision, "--patch=checkout",
-					   &opts->pathspec);
+	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)
@@ -392,8 +504,9 @@ static int checkout_paths(const struct checkout_opts *opts,
 		if (ce->ce_flags & CE_MATCHED) {
 			if (!ce_stage(ce))
 				continue;
-			if (opts->force) {
-				warning(_("path '%s' is unmerged"), ce->name);
+			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) {
@@ -409,57 +522,33 @@ static int checkout_paths(const struct checkout_opts *opts,
 		return 1;
 
 	/* Now we are committed to check them out */
-	state.force = 1;
-	state.refresh_cache = 1;
-	state.istate = &the_index;
+	if (opts->checkout_worktree)
+		errs |= checkout_worktree(opts);
+	else
+		remove_marked_cache_entries(&the_index, 1);
 
-	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);
+	/*
+	 * 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 (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);
+	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);
 	}
 
-	if (write_locked_index(&the_index, &lock_file, COMMIT_LOCK))
-		die(_("unable to write new index file"));
-
 	read_ref_full("HEAD", 0, &rev, NULL);
 	head = lookup_commit_reference_gently(the_repository, &rev, 1);
 
@@ -553,112 +642,6 @@ static void setup_branch_path(struct branch_info *branch)
 	branch->path = strbuf_detach(&buf, NULL);
 }
 
-/*
- * Skip merging the trees, updating the index and working directory if and
- * only if we are creating a new branch via "git checkout -b <new_branch>."
- */
-static int skip_merge_working_tree(const struct checkout_opts *opts,
-	const struct branch_info *old_branch_info,
-	const struct branch_info *new_branch_info)
-{
-	/*
-	 * Do the merge if sparse checkout is on and the user has not opted in
-	 * to the optimized behavior
-	 */
-	if (core_apply_sparse_checkout && !checkout_optimize_new_branch)
-		return 0;
-
-	/*
-	 * We must do the merge if we are actually moving to a new commit.
-	 */
-	if (!old_branch_info->commit || !new_branch_info->commit ||
-		!oideq(&old_branch_info->commit->object.oid,
-		       &new_branch_info->commit->object.oid))
-		return 0;
-
-	/*
-	 * opts->patch_mode cannot be used with switching branches so is
-	 * not tested here
-	 */
-
-	/*
-	 * opts->quiet only impacts output so doesn't require a merge
-	 */
-
-	/*
-	 * Honor the explicit request for a three-way merge or to throw away
-	 * local changes
-	 */
-	if (opts->merge || opts->force)
-		return 0;
-
-	/*
-	 * --detach is documented as "updating the index and the files in the
-	 * working tree" but this optimization skips those steps so fall through
-	 * to the regular code path.
-	 */
-	if (opts->force_detach)
-		return 0;
-
-	/*
-	 * opts->writeout_stage cannot be used with switching branches so is
-	 * not tested here
-	 */
-
-	/*
-	 * Honor the explicit ignore requests
-	 */
-	if (!opts->overwrite_ignore || opts->ignore_skipworktree ||
-		opts->ignore_other_worktrees)
-		return 0;
-
-	/*
-	 * opts->show_progress only impacts output so doesn't require a merge
-	 */
-
-	/*
-	 * opts->overlay_mode cannot be used with switching branches so is
-	 * not tested here
-	 */
-
-	/*
-	 * If we aren't creating a new branch any changes or updates will
-	 * happen in the existing branch.  Since that could only be updating
-	 * the index and working directory, we don't want to skip those steps
-	 * or we've defeated any purpose in running the command.
-	 */
-	if (!opts->new_branch)
-		return 0;
-
-	/*
-	 * new_branch_force is defined to "create/reset and checkout a branch"
-	 * so needs to go through the merge to do the reset
-	 */
-	if (opts->new_branch_force)
-		return 0;
-
-	/*
-	 * A new orphaned branch requrires the index and the working tree to be
-	 * adjusted to <start_point>
-	 */
-	if (opts->new_orphan_branch)
-		return 0;
-
-	/*
-	 * Remaining variables are not checkout options but used to track state
-	 */
-
-	 /*
-	  * Do the merge if this is the initial checkout. We cannot use
-	  * is_cache_unborn() here because the index hasn't been loaded yet
-	  * so cache_nr and timestamp.sec are always zero.
-	  */
-	if (!file_exists(get_index_file()))
-		return 0;
-
-	return 1;
-}
-
 static int merge_working_tree(const struct checkout_opts *opts,
 			      struct branch_info *old_branch_info,
 			      struct branch_info *new_branch_info,
@@ -666,15 +649,21 @@ static int merge_working_tree(const struct checkout_opts *opts,
 {
 	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->force) {
-		ret = reset_tree(get_commit_tree(new_branch_info->commit),
-				 opts, 1, writeout_error);
+	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 {
@@ -712,7 +701,8 @@ static int merge_working_tree(const struct checkout_opts *opts,
 					   &old_branch_info->commit->object.oid :
 					   the_hash_algo->empty_tree);
 		init_tree_desc(&trees[0], tree->buffer, tree->size);
-		tree = parse_tree_indirect(&new_branch_info->commit->object.oid);
+		parse_tree(new_tree);
+		tree = new_tree;
 		init_tree_desc(&trees[1], tree->buffer, tree->size);
 
 		ret = unpack_trees(2, trees, &topts);
@@ -723,11 +713,11 @@ static int merge_working_tree(const struct checkout_opts *opts,
 			 * 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;
+			struct strbuf old_commit_shortname = STRBUF_INIT;
 
 			if (!opts->merge)
 				return 1;
@@ -745,13 +735,6 @@ static int merge_working_tree(const struct checkout_opts *opts,
 				      "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 */
 
 			/*
@@ -775,27 +758,33 @@ static int merge_working_tree(const struct checkout_opts *opts,
 			 */
 			init_merge_options(&o, the_repository);
 			o.verbosity = 0;
-			work = write_tree_from_memory(&o);
+			work = write_in_core_index_as_tree(the_repository);
 
-			ret = reset_tree(get_commit_tree(new_branch_info->commit),
+			ret = reset_tree(new_tree,
 					 opts, 1,
 					 writeout_error);
 			if (ret)
 				return ret;
 			o.ancestor = old_branch_info->name;
+			if (old_branch_info->name == NULL) {
+				strbuf_add_unique_abbrev(&old_commit_shortname,
+							 &old_branch_info->commit->object.oid,
+							 DEFAULT_ABBREV);
+				o.ancestor = old_commit_shortname.buf;
+			}
 			o.branch1 = new_branch_info->name;
 			o.branch2 = "local";
 			ret = merge_trees(&o,
-					  get_commit_tree(new_branch_info->commit),
+					  new_tree,
 					  work,
-					  old_tree,
-					  &result);
+					  old_tree);
 			if (ret < 0)
 				exit(128);
-			ret = reset_tree(get_commit_tree(new_branch_info->commit),
+			ret = reset_tree(new_tree,
 					 opts, 0,
 					 writeout_error);
 			strbuf_release(&o.obuf);
+			strbuf_release(&old_commit_shortname);
 			if (ret)
 				return ret;
 		}
@@ -810,7 +799,7 @@ static int merge_working_tree(const struct checkout_opts *opts,
 	if (write_locked_index(&the_index, &lock_file, COMMIT_LOCK))
 		die(_("unable to write new index file"));
 
-	if (!opts->force && !opts->quiet)
+	if (!opts->discard_changes && !opts->quiet && new_branch_info->commit)
 		show_local_changes(&new_branch_info->commit->object, &opts->diff_options);
 
 	return 0;
@@ -876,7 +865,7 @@ static void update_refs_for_switch(const struct checkout_opts *opts,
 		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));
+		strbuf_insertstr(&msg, 0, reflog_msg);
 
 	if (!strcmp(new_branch_info->name, "HEAD") && !new_branch_info->path && !opts->force_detach) {
 		/* Nothing to do. */
@@ -915,7 +904,7 @@ static void update_refs_for_switch(const struct checkout_opts *opts,
 				delete_reflog(old_branch_info->path);
 		}
 	}
-	remove_branch_state(the_repository);
+	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"))))
@@ -1011,7 +1000,10 @@ static void orphaned_commit_warning(struct commit *old_commit, struct commit *ne
 	add_pending_object(&revs, object, oid_to_hex(&object->oid));
 
 	for_each_ref(add_pending_uninteresting_ref, &revs);
-	add_pending_oid(&revs, "HEAD", &new_commit->object.oid, UNINTERESTING);
+	if (new_commit)
+		add_pending_oid(&revs, "HEAD",
+				&new_commit->object.oid,
+				UNINTERESTING);
 
 	if (prepare_revision_walk(&revs))
 		die(_("internal error in revision walk"));
@@ -1032,6 +1024,7 @@ static int switch_branches(const struct checkout_opts *opts,
 	void *path_to_free;
 	struct object_id rev;
 	int flag, writeout_error = 0;
+	int do_merge = 1;
 
 	trace2_cmd_mode("branch");
 
@@ -1045,22 +1038,26 @@ static int switch_branches(const struct checkout_opts *opts,
 	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;
 	}
 
-	/* optimize the "checkout -b <new_branch> path */
-	if (skip_merge_working_tree(opts, &old_branch_info, new_branch_info)) {
-		if (!checkout_optimize_new_branch && !opts->quiet) {
-			if (read_cache_preload(NULL) < 0)
-				return error(_("index file corrupt"));
-			show_local_changes(&new_branch_info->commit->object, &opts->diff_options);
-		}
-	} else {
+	if (do_merge) {
 		ret = merge_working_tree(opts, &old_branch_info, new_branch_info, &writeout_error);
 		if (ret) {
 			free(path_to_free);
@@ -1080,11 +1077,6 @@ static int switch_branches(const struct checkout_opts *opts,
 
 static int git_checkout_config(const char *var, const char *value, void *cb)
 {
-	if (!strcmp(var, "checkout.optimizenewbranch")) {
-		checkout_optimize_new_branch = git_config_bool(var, value);
-		return 0;
-	}
-
 	if (!strcmp(var, "diff.ignoresubmodules")) {
 		struct checkout_opts *opts = cb;
 		handle_ignore_submodules_arg(&opts->diff_options, value);
@@ -1097,17 +1089,74 @@ static int git_checkout_config(const char *var, const char *value, void *cb)
 	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 const char *parse_remote_branch(const char *arg,
+				       struct object_id *rev,
+				       int could_be_checkout_paths)
+{
+	int num_matches = 0;
+	const char *remote = unique_tracking_name(arg, rev, &num_matches);
+
+	if (remote && 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);
+	}
+
+	if (!remote && num_matches > 1) {
+	    if (advice_checkout_ambiguous_remote_branch_name) {
+		    advise(_("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."));
+	    }
+
+	    die(_("'%s' matched multiple (%d) remote tracking branches"),
+		arg, num_matches);
+	}
+
+	return remote;
+}
+
 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)
+				struct object_id *rev)
 {
-	struct tree **source_tree = &opts->source_tree;
 	const char **new_branch = &opts->new_branch;
 	int argcount = 0;
-	struct object_id branch_rev;
 	const char *arg;
 	int dash_dash_pos;
 	int has_dash_dash = 0;
@@ -1157,10 +1206,16 @@ static int parse_branchname_arg(int argc, const char **argv,
 	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 (!strcmp(argv[i], "--")) {
+		if (opts->accept_pathspec && !strcmp(argv[i], "--")) {
 			dash_dash_pos = i;
 			break;
 		}
@@ -1194,21 +1249,18 @@ static int parse_branchname_arg(int argc, const char **argv,
 			recover_with_dwim = 0;
 
 		/*
-		 * Accept "git checkout foo" and "git checkout foo --"
-		 * as candidates for dwim.
+		 * 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))
+		    !(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);
+			const char *remote = parse_remote_branch(arg, rev,
+								 could_be_checkout_paths);
 			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) */
@@ -1229,26 +1281,11 @@ static int parse_branchname_arg(int argc, const char **argv,
 	argv++;
 	argc--;
 
-	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 */
+	setup_new_branch_info_and_source_tree(new_branch_info, opts, rev, arg);
 
-	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);
-	}
-
-	if (!*source_tree)                   /* case (1): want a tree */
+	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
@@ -1258,7 +1295,7 @@ static int parse_branchname_arg(int argc, const char **argv,
 		 */
 		if (argc)
 			verify_non_filename(opts->prefix, arg);
-	} else {
+	} else if (opts->accept_pathspec) {
 		argcount++;
 		argv++;
 		argc--;
@@ -1285,6 +1322,60 @@ static int switch_unborn_to_new_branch(const struct checkout_opts *opts)
 	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)
 {
@@ -1295,9 +1386,9 @@ static int checkout_branch(struct checkout_opts *opts,
 		die(_("'%s' cannot be used with switching branches"),
 		    "--patch");
 
-	if (!opts->overlay_mode)
+	if (opts->overlay_mode != -1)
 		die(_("'%s' cannot be used with switching branches"),
-		    "--no-overlay");
+		    "--[no]-overlay");
 
 	if (opts->writeout_stage)
 		die(_("'%s' cannot be used with switching branches"),
@@ -1306,6 +1397,9 @@ static int checkout_branch(struct checkout_opts *opts,
 	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");
@@ -1313,6 +1407,8 @@ static int checkout_branch(struct checkout_opts *opts,
 	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");
@@ -1323,6 +1419,23 @@ static int checkout_branch(struct checkout_opts *opts,
 		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;
@@ -1344,99 +1457,149 @@ static int checkout_branch(struct checkout_opts *opts,
 	return switch_branches(opts, new_branch_info);
 }
 
-int cmd_checkout(int argc, const char **argv, const char *prefix)
+static struct option *add_common_options(struct checkout_opts *opts,
+					 struct option *prevopts)
 {
-	struct checkout_opts opts;
-	struct branch_info new_branch_info;
-	char *conflict_style = NULL;
-	int dwim_new_local_branch, no_dwim_new_local_branch = 0;
-	int dwim_remotes_matched = 0;
 	struct option options[] = {
-		OPT__QUIET(&opts.quiet, N_("suppress progress reporting")),
-		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, "detach", &opts.force_detach, N_("detach HEAD at named commit")),
-		OPT_SET_INT('t', "track",  &opts.track, N_("set upstream info for new branch"),
+		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_STRING(0, "orphan", &opts.new_orphan_branch, N_("new-branch"), N_("new unparented branch")),
-		OPT_SET_INT_F('2', "ours", &opts.writeout_stage,
+		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,
+		OPT_SET_INT_F('3', "theirs", &opts->writeout_stage,
 			      N_("checkout their version for unmerged files"),
 			      3, PARSE_OPT_NONEG),
-		OPT__FORCE(&opts.force, N_("force checkout (throw away local modifications)"),
-			   PARSE_OPT_NOCOMPLETE),
-		OPT_BOOL('m', "merge", &opts.merge, N_("perform a 3-way merge with the new branch")),
-		OPT_BOOL_F(0, "overwrite-ignore", &opts.overwrite_ignore,
-			   N_("update ignored files (default)"),
-			   PARSE_OPT_NOCOMPLETE),
-		OPT_STRING(0, "conflict", &conflict_style, N_("style"),
-			   N_("conflict style (merge or diff3)")),
-		OPT_BOOL('p', "patch", &opts.patch_mode, N_("select hunks interactively")),
-		OPT_BOOL(0, "ignore-skip-worktree-bits", &opts.ignore_skipworktree,
+		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_BOOL(0, "no-guess", &no_dwim_new_local_branch,
-			 N_("do not second guess 'git checkout <no-such-branch>'")),
-		OPT_BOOL(0, "ignore-other-worktrees", &opts.ignore_other_worktrees,
-			 N_("do not check if another worktree is holding the given ref")),
-		{ 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(0, "overlay", &opts.overlay_mode, N_("use overlay mode (default)")),
-		OPT_END(),
+		OPT_PATHSPEC_FROM_FILE(&opts->pathspec_from_file),
+		OPT_PATHSPEC_FILE_NUL(&opts->pathspec_file_nul),
+		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 parseopt_flags = 0;
 
-	memset(&opts, 0, sizeof(opts));
 	memset(&new_branch_info, 0, sizeof(new_branch_info));
-	opts.overwrite_ignore = 1;
-	opts.prefix = prefix;
-	opts.show_progress = -1;
-	opts.overlay_mode = -1;
+	opts->overwrite_ignore = 1;
+	opts->prefix = prefix;
+	opts->show_progress = -1;
+
+	git_config(git_checkout_config, opts);
 
-	git_config(git_checkout_config, &opts);
+	opts->track = BRANCH_TRACK_UNSPECIFIED;
 
-	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, checkout_usage,
-			     PARSE_OPT_KEEP_DASHDASH);
+	argc = parse_options(argc, argv, prefix, options,
+			     usagestr, parseopt_flags);
 
-	dwim_new_local_branch = !no_dwim_new_local_branch;
-	if (opts.show_progress < 0) {
-		if (opts.quiet)
-			opts.show_progress = 0;
+	if (opts->show_progress < 0) {
+		if (opts->quiet)
+			opts->show_progress = 0;
 		else
-			opts.show_progress = isatty(2);
+			opts->show_progress = isatty(2);
 	}
 
-	if (conflict_style) {
-		opts.merge = 1; /* implied */
-		git_xmerge_config("merge.conflictstyle", conflict_style, NULL);
+	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)
+	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)
+	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_branch_force)
+		opts->new_branch = opts->new_branch_force;
 
-	if (opts.new_orphan_branch)
-		opts.new_branch = opts.new_orphan_branch;
+	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) {
+	if (opts->track != BRANCH_TRACK_UNSPECIFIED && !opts->new_branch) {
 		const char *argv0 = argv[0];
 		if (!argc || !strcmp(argv0, "--"))
 			die(_("--track needs a branch name"));
@@ -1445,7 +1608,7 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 		argv0 = strchr(argv0, '/');
 		if (!argv0 || !argv0[1])
 			die(_("missing branch name; try -b"));
-		opts.new_branch = argv0 + 1;
+		opts->new_branch = argv0 + 1;
 	}
 
 	/*
@@ -1461,77 +1624,219 @@ int cmd_checkout(int argc, const char **argv, const char *prefix)
 	 * including "last branch" syntax and DWIM-ery for names of
 	 * remote branches, erroring out for invalid or ambiguous cases.
 	 */
-	if (argc) {
+	if (argc && opts->accept_ref) {
 		struct object_id rev;
 		int dwim_ok =
-			!opts.patch_mode &&
-			dwim_new_local_branch &&
-			opts.track == BRANCH_TRACK_UNSPECIFIED &&
-			!opts.new_branch;
+			!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);
+					     &new_branch_info, opts, &rev);
 		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 (argc) {
-		parse_pathspec(&opts.pathspec, 0,
-			       opts.patch_mode ? PATHSPEC_PREFIX_ORIGIN : 0,
+		parse_pathspec(&opts->pathspec, 0,
+			       opts->patch_mode ? PATHSPEC_PREFIX_ORIGIN : 0,
 			       prefix, argv);
 
-		if (!opts.pathspec.nr)
+		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)
+		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);
+				argv[0], opts->new_branch);
 
-		if (opts.force_detach)
+		if (opts->force_detach)
 			die(_("git checkout: --detach does not take a path argument '%s'"),
 			    argv[0]);
+	}
+
+	if (opts->pathspec_from_file) {
+		if (opts->pathspec.nr)
+			die(_("--pathspec-from-file is incompatible with pathspec arguments"));
+
+		if (opts->force_detach)
+			die(_("--pathspec-from-file is incompatible with --detach"));
+
+		if (opts->patch_mode)
+			die(_("--pathspec-from-file is incompatible with --patch"));
+
+		parse_pathspec_file(&opts->pathspec, 0,
+				    0,
+				    prefix, opts->pathspec_from_file, opts->pathspec_file_nul);
+	} else if (opts->pathspec_file_nul) {
+		die(_("--pathspec-file-nul requires --pathspec-from-file"));
+	}
 
-		if (1 < !!opts.writeout_stage + !!opts.force + !!opts.merge)
+	if (opts->pathspec.nr) {
+		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."));
+	} else {
+		if (opts->accept_pathspec && !opts->empty_pathspec_ok &&
+		    !opts->patch_mode)	/* patch mode is special */
+			die(_("you must specify path(s) to restore"));
 	}
 
-	if (opts.new_branch) {
+	if (opts->new_branch) {
 		struct strbuf buf = STRBUF_INIT;
 
-		if (opts.new_branch_force)
-			opts.branch_exists = validate_branchname(opts.new_branch, &buf);
+		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);
+			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);
+	if (opts->patch_mode || opts->pathspec.nr)
+		return checkout_paths(opts, new_branch_info.name);
+	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 */
+
+	if (argc == 3 && !strcmp(argv[1], "-b")) {
+		/*
+		 * User ran 'git checkout -b <branch>' and expects
+		 * the same behavior as 'git switch -c <branch>'.
+		 */
+		opts.switch_branch_doing_nothing_is_ok = 0;
+		opts.only_merge_on_switching_branches = 1;
 	}
+
+	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;
 }