1 files changed, 1032 insertions, 536 deletions

diff --git a/builtin/rebase.c b/builtin/rebase.c
index 00de70365e..37ba76ac3d 100644
--- a/builtin/rebase.c
+++ b/builtin/rebase.c
@@ -4,6 +4,7 @@
  * Copyright (c) 2018 Pratik Karki
  */
 
+#define USE_THE_INDEX_COMPATIBILITY_MACROS
 #include "builtin.h"
 #include "run-command.h"
 #include "exec-cmd.h"
@@ -24,52 +25,44 @@
 #include "commit-reach.h"
 #include "rerere.h"
 #include "branch.h"
+#include "sequencer.h"
+#include "rebase-interactive.h"
+#include "reset.h"
+
+#define DEFAULT_REFLOG_ACTION "rebase"
 
 static char const * const builtin_rebase_usage[] = {
-	N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
-		"[<upstream>] [<branch>]"),
+	N_("git rebase [-i] [options] [--exec <cmd>] "
+		"[--onto <newbase> | --keep-base] [<upstream> [<branch>]]"),
 	N_("git rebase [-i] [options] [--exec <cmd>] [--onto <newbase>] "
 		"--root [<branch>]"),
 	N_("git rebase --continue | --abort | --skip | --edit-todo"),
 	NULL
 };
 
+static GIT_PATH_FUNC(path_squash_onto, "rebase-merge/squash-onto")
+static GIT_PATH_FUNC(path_interactive, "rebase-merge/interactive")
 static GIT_PATH_FUNC(apply_dir, "rebase-apply")
 static GIT_PATH_FUNC(merge_dir, "rebase-merge")
 
 enum rebase_type {
 	REBASE_UNSPECIFIED = -1,
-	REBASE_AM,
+	REBASE_APPLY,
 	REBASE_MERGE,
-	REBASE_INTERACTIVE,
 	REBASE_PRESERVE_MERGES
 };
 
-static int use_builtin_rebase(void)
-{
-	struct child_process cp = CHILD_PROCESS_INIT;
-	struct strbuf out = STRBUF_INIT;
-	int ret, env = git_env_bool("GIT_TEST_REBASE_USE_BUILTIN", -1);
-
-	if (env != -1)
-		return env;
-
-	argv_array_pushl(&cp.args,
-			 "config", "--bool", "rebase.usebuiltin", NULL);
-	cp.git_cmd = 1;
-	if (capture_command(&cp, &out, 6)) {
-		strbuf_release(&out);
-		return 1;
-	}
-
-	strbuf_trim(&out);
-	ret = !strcmp("true", out.buf);
-	strbuf_release(&out);
-	return ret;
-}
+enum empty_type {
+	EMPTY_UNSPECIFIED = -1,
+	EMPTY_DROP,
+	EMPTY_KEEP,
+	EMPTY_ASK
+};
 
 struct rebase_options {
 	enum rebase_type type;
+	enum empty_type empty;
+	const char *default_backend;
 	const char *state_dir;
 	struct commit *upstream;
 	const char *upstream_name;
@@ -80,7 +73,7 @@ struct rebase_options {
 	const char *onto_name;
 	const char *revisions;
 	const char *switch_to;
-	int root;
+	int root, root_with_onto;
 	struct object_id *squash_onto;
 	struct commit *restrict_revision;
 	int dont_finish_rebase;
@@ -104,27 +97,482 @@ struct rebase_options {
 	int rebase_merges, rebase_cousins;
 	char *strategy, *strategy_opts;
 	struct strbuf git_format_patch_opt;
+	int reschedule_failed_exec;
+	int use_legacy_rebase;
+	int reapply_cherry_picks;
 };
 
-static int is_interactive(struct rebase_options *opts)
+#define REBASE_OPTIONS_INIT {			  	\
+		.type = REBASE_UNSPECIFIED,	  	\
+		.empty = EMPTY_UNSPECIFIED,	  	\
+		.keep_empty = 1,			\
+		.default_backend = "merge",	  	\
+		.flags = REBASE_NO_QUIET, 		\
+		.git_am_opts = ARGV_ARRAY_INIT,		\
+		.git_format_patch_opt = STRBUF_INIT	\
+	}
+
+static struct replay_opts get_replay_opts(const struct rebase_options *opts)
+{
+	struct replay_opts replay = REPLAY_OPTS_INIT;
+
+	replay.action = REPLAY_INTERACTIVE_REBASE;
+	sequencer_init_config(&replay);
+
+	replay.signoff = opts->signoff;
+	replay.allow_ff = !(opts->flags & REBASE_FORCE);
+	if (opts->allow_rerere_autoupdate)
+		replay.allow_rerere_auto = opts->allow_rerere_autoupdate;
+	replay.allow_empty = 1;
+	replay.allow_empty_message = opts->allow_empty_message;
+	replay.drop_redundant_commits = (opts->empty == EMPTY_DROP);
+	replay.keep_redundant_commits = (opts->empty == EMPTY_KEEP);
+	replay.quiet = !(opts->flags & REBASE_NO_QUIET);
+	replay.verbose = opts->flags & REBASE_VERBOSE;
+	replay.reschedule_failed_exec = opts->reschedule_failed_exec;
+	replay.gpg_sign = xstrdup_or_null(opts->gpg_sign_opt);
+	replay.strategy = opts->strategy;
+	if (opts->strategy_opts)
+		parse_strategy_opts(&replay, opts->strategy_opts);
+
+	if (opts->squash_onto) {
+		oidcpy(&replay.squash_onto, opts->squash_onto);
+		replay.have_squash_onto = 1;
+	}
+
+	return replay;
+}
+
+enum action {
+	ACTION_NONE = 0,
+	ACTION_CONTINUE,
+	ACTION_SKIP,
+	ACTION_ABORT,
+	ACTION_QUIT,
+	ACTION_EDIT_TODO,
+	ACTION_SHOW_CURRENT_PATCH,
+	ACTION_SHORTEN_OIDS,
+	ACTION_EXPAND_OIDS,
+	ACTION_CHECK_TODO_LIST,
+	ACTION_REARRANGE_SQUASH,
+	ACTION_ADD_EXEC
+};
+
+static const char *action_names[] = { "undefined",
+				      "continue",
+				      "skip",
+				      "abort",
+				      "quit",
+				      "edit_todo",
+				      "show_current_patch" };
+
+static int add_exec_commands(struct string_list *commands)
+{
+	const char *todo_file = rebase_path_todo();
+	struct todo_list todo_list = TODO_LIST_INIT;
+	int res;
+
+	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
+		return error_errno(_("could not read '%s'."), todo_file);
+
+	if (todo_list_parse_insn_buffer(the_repository, todo_list.buf.buf,
+					&todo_list)) {
+		todo_list_release(&todo_list);
+		return error(_("unusable todo list: '%s'"), todo_file);
+	}
+
+	todo_list_add_exec_commands(&todo_list, commands);
+	res = todo_list_write_to_file(the_repository, &todo_list,
+				      todo_file, NULL, NULL, -1, 0);
+	todo_list_release(&todo_list);
+
+	if (res)
+		return error_errno(_("could not write '%s'."), todo_file);
+	return 0;
+}
+
+static int rearrange_squash_in_todo_file(void)
+{
+	const char *todo_file = rebase_path_todo();
+	struct todo_list todo_list = TODO_LIST_INIT;
+	int res = 0;
+
+	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
+		return error_errno(_("could not read '%s'."), todo_file);
+	if (todo_list_parse_insn_buffer(the_repository, todo_list.buf.buf,
+					&todo_list)) {
+		todo_list_release(&todo_list);
+		return error(_("unusable todo list: '%s'"), todo_file);
+	}
+
+	res = todo_list_rearrange_squash(&todo_list);
+	if (!res)
+		res = todo_list_write_to_file(the_repository, &todo_list,
+					      todo_file, NULL, NULL, -1, 0);
+
+	todo_list_release(&todo_list);
+
+	if (res)
+		return error_errno(_("could not write '%s'."), todo_file);
+	return 0;
+}
+
+static int transform_todo_file(unsigned flags)
+{
+	const char *todo_file = rebase_path_todo();
+	struct todo_list todo_list = TODO_LIST_INIT;
+	int res;
+
+	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
+		return error_errno(_("could not read '%s'."), todo_file);
+
+	if (todo_list_parse_insn_buffer(the_repository, todo_list.buf.buf,
+					&todo_list)) {
+		todo_list_release(&todo_list);
+		return error(_("unusable todo list: '%s'"), todo_file);
+	}
+
+	res = todo_list_write_to_file(the_repository, &todo_list, todo_file,
+				      NULL, NULL, -1, flags);
+	todo_list_release(&todo_list);
+
+	if (res)
+		return error_errno(_("could not write '%s'."), todo_file);
+	return 0;
+}
+
+static int edit_todo_file(unsigned flags)
+{
+	const char *todo_file = rebase_path_todo();
+	struct todo_list todo_list = TODO_LIST_INIT,
+		new_todo = TODO_LIST_INIT;
+	int res = 0;
+
+	if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
+		return error_errno(_("could not read '%s'."), todo_file);
+
+	strbuf_stripspace(&todo_list.buf, 1);
+	res = edit_todo_list(the_repository, &todo_list, &new_todo, NULL, NULL, flags);
+	if (!res && todo_list_write_to_file(the_repository, &new_todo, todo_file,
+					    NULL, NULL, -1, flags & ~(TODO_LIST_SHORTEN_IDS)))
+		res = error_errno(_("could not write '%s'"), todo_file);
+
+	todo_list_release(&todo_list);
+	todo_list_release(&new_todo);
+
+	return res;
+}
+
+static int get_revision_ranges(struct commit *upstream, struct commit *onto,
+			       struct object_id *orig_head, const char **head_hash,
+			       char **revisions, char **shortrevisions)
+{
+	struct commit *base_rev = upstream ? upstream : onto;
+	const char *shorthead;
+
+	*head_hash = find_unique_abbrev(orig_head, GIT_MAX_HEXSZ);
+	*revisions = xstrfmt("%s...%s", oid_to_hex(&base_rev->object.oid),
+						   *head_hash);
+
+	shorthead = find_unique_abbrev(orig_head, DEFAULT_ABBREV);
+
+	if (upstream) {
+		const char *shortrev;
+
+		shortrev = find_unique_abbrev(&base_rev->object.oid,
+					      DEFAULT_ABBREV);
+
+		*shortrevisions = xstrfmt("%s..%s", shortrev, shorthead);
+	} else
+		*shortrevisions = xstrdup(shorthead);
+
+	return 0;
+}
+
+static int init_basic_state(struct replay_opts *opts, const char *head_name,
+			    struct commit *onto, const char *orig_head)
+{
+	FILE *interactive;
+
+	if (!is_directory(merge_dir()) && mkdir_in_gitdir(merge_dir()))
+		return error_errno(_("could not create temporary %s"), merge_dir());
+
+	delete_reflog("REBASE_HEAD");
+
+	interactive = fopen(path_interactive(), "w");
+	if (!interactive)
+		return error_errno(_("could not mark as interactive"));
+	fclose(interactive);
+
+	return write_basic_state(opts, head_name, onto, orig_head);
+}
+
+static void split_exec_commands(const char *cmd, struct string_list *commands)
+{
+	if (cmd && *cmd) {
+		string_list_split(commands, cmd, '\n', -1);
+
+		/* rebase.c adds a new line to cmd after every command,
+		 * so here the last command is always empty */
+		string_list_remove_empty_items(commands, 0);
+	}
+}
+
+static int do_interactive_rebase(struct rebase_options *opts, unsigned flags)
 {
-	return opts->type == REBASE_INTERACTIVE ||
+	int ret;
+	const char *head_hash = NULL;
+	char *revisions = NULL, *shortrevisions = NULL;
+	struct argv_array make_script_args = ARGV_ARRAY_INIT;
+	struct todo_list todo_list = TODO_LIST_INIT;
+	struct replay_opts replay = get_replay_opts(opts);
+	struct string_list commands = STRING_LIST_INIT_DUP;
+
+	if (get_revision_ranges(opts->upstream, opts->onto, &opts->orig_head,
+				&head_hash, &revisions, &shortrevisions))
+		return -1;
+
+	if (init_basic_state(&replay,
+			     opts->head_name ? opts->head_name : "detached HEAD",
+			     opts->onto, head_hash)) {
+		free(revisions);
+		free(shortrevisions);
+
+		return -1;
+	}
+
+	if (!opts->upstream && opts->squash_onto)
+		write_file(path_squash_onto(), "%s\n",
+			   oid_to_hex(opts->squash_onto));
+
+	argv_array_pushl(&make_script_args, "", revisions, NULL);
+	if (opts->restrict_revision)
+		argv_array_pushf(&make_script_args, "^%s",
+				 oid_to_hex(&opts->restrict_revision->object.oid));
+
+	ret = sequencer_make_script(the_repository, &todo_list.buf,
+				    make_script_args.argc, make_script_args.argv,
+				    flags);
+
+	if (ret)
+		error(_("could not generate todo list"));
+	else {
+		discard_cache();
+		if (todo_list_parse_insn_buffer(the_repository, todo_list.buf.buf,
+						&todo_list))
+			BUG("unusable todo list");
+
+		split_exec_commands(opts->cmd, &commands);
+		ret = complete_action(the_repository, &replay, flags,
+			shortrevisions, opts->onto_name, opts->onto, head_hash,
+			&commands, opts->autosquash, &todo_list);
+	}
+
+	string_list_clear(&commands, 0);
+	free(revisions);
+	free(shortrevisions);
+	todo_list_release(&todo_list);
+	argv_array_clear(&make_script_args);
+
+	return ret;
+}
+
+static int run_sequencer_rebase(struct rebase_options *opts,
+				  enum action command)
+{
+	unsigned flags = 0;
+	int abbreviate_commands = 0, ret = 0;
+
+	git_config_get_bool("rebase.abbreviatecommands", &abbreviate_commands);
+
+	flags |= opts->keep_empty ? TODO_LIST_KEEP_EMPTY : 0;
+	flags |= abbreviate_commands ? TODO_LIST_ABBREVIATE_CMDS : 0;
+	flags |= opts->rebase_merges ? TODO_LIST_REBASE_MERGES : 0;
+	flags |= opts->rebase_cousins > 0 ? TODO_LIST_REBASE_COUSINS : 0;
+	flags |= opts->root_with_onto ? TODO_LIST_ROOT_WITH_ONTO : 0;
+	flags |= command == ACTION_SHORTEN_OIDS ? TODO_LIST_SHORTEN_IDS : 0;
+	flags |= opts->reapply_cherry_picks ? TODO_LIST_REAPPLY_CHERRY_PICKS : 0;
+
+	switch (command) {
+	case ACTION_NONE: {
+		if (!opts->onto && !opts->upstream)
+			die(_("a base commit must be provided with --upstream or --onto"));
+
+		ret = do_interactive_rebase(opts, flags);
+		break;
+	}
+	case ACTION_SKIP: {
+		struct string_list merge_rr = STRING_LIST_INIT_DUP;
+
+		rerere_clear(the_repository, &merge_rr);
+	}
+		/* fallthrough */
+	case ACTION_CONTINUE: {
+		struct replay_opts replay_opts = get_replay_opts(opts);
+
+		ret = sequencer_continue(the_repository, &replay_opts);
+		break;
+	}
+	case ACTION_EDIT_TODO:
+		ret = edit_todo_file(flags);
+		break;
+	case ACTION_SHOW_CURRENT_PATCH: {
+		struct child_process cmd = CHILD_PROCESS_INIT;
+
+		cmd.git_cmd = 1;
+		argv_array_pushl(&cmd.args, "show", "REBASE_HEAD", "--", NULL);
+		ret = run_command(&cmd);
+
+		break;
+	}
+	case ACTION_SHORTEN_OIDS:
+	case ACTION_EXPAND_OIDS:
+		ret = transform_todo_file(flags);
+		break;
+	case ACTION_CHECK_TODO_LIST:
+		ret = check_todo_list_from_file(the_repository);
+		break;
+	case ACTION_REARRANGE_SQUASH:
+		ret = rearrange_squash_in_todo_file();
+		break;
+	case ACTION_ADD_EXEC: {
+		struct string_list commands = STRING_LIST_INIT_DUP;
+
+		split_exec_commands(opts->cmd, &commands);
+		ret = add_exec_commands(&commands);
+		string_list_clear(&commands, 0);
+		break;
+	}
+	default:
+		BUG("invalid command '%d'", command);
+	}
+
+	return ret;
+}
+
+static void imply_merge(struct rebase_options *opts, const char *option);
+static int parse_opt_keep_empty(const struct option *opt, const char *arg,
+				int unset)
+{
+	struct rebase_options *opts = opt->value;
+
+	BUG_ON_OPT_ARG(arg);
+
+	imply_merge(opts, unset ? "--no-keep-empty" : "--keep-empty");
+	opts->keep_empty = !unset;
+	opts->type = REBASE_MERGE;
+	return 0;
+}
+
+static const char * const builtin_rebase_interactive_usage[] = {
+	N_("git rebase--interactive [<options>]"),
+	NULL
+};
+
+int cmd_rebase__interactive(int argc, const char **argv, const char *prefix)
+{
+	struct rebase_options opts = REBASE_OPTIONS_INIT;
+	struct object_id squash_onto = null_oid;
+	enum action command = ACTION_NONE;
+	struct option options[] = {
+		OPT_NEGBIT(0, "ff", &opts.flags, N_("allow fast-forward"),
+			   REBASE_FORCE),
+		OPT_CALLBACK_F('k', "keep-empty", &options, NULL,
+			N_("keep commits which start empty"),
+			PARSE_OPT_NOARG | PARSE_OPT_HIDDEN,
+			parse_opt_keep_empty),
+		OPT_BOOL_F(0, "allow-empty-message", &opts.allow_empty_message,
+			   N_("allow commits with empty messages"),
+			   PARSE_OPT_HIDDEN),
+		OPT_BOOL(0, "rebase-merges", &opts.rebase_merges, N_("rebase merge commits")),
+		OPT_BOOL(0, "rebase-cousins", &opts.rebase_cousins,
+			 N_("keep original branch points of cousins")),
+		OPT_BOOL(0, "autosquash", &opts.autosquash,
+			 N_("move commits that begin with squash!/fixup!")),
+		OPT_BOOL(0, "signoff", &opts.signoff, N_("sign commits")),
+		OPT_BIT('v', "verbose", &opts.flags,
+			N_("display a diffstat of what changed upstream"),
+			REBASE_NO_QUIET | REBASE_VERBOSE | REBASE_DIFFSTAT),
+		OPT_CMDMODE(0, "continue", &command, N_("continue rebase"),
+			    ACTION_CONTINUE),
+		OPT_CMDMODE(0, "skip", &command, N_("skip commit"), ACTION_SKIP),
+		OPT_CMDMODE(0, "edit-todo", &command, N_("edit the todo list"),
+			    ACTION_EDIT_TODO),
+		OPT_CMDMODE(0, "show-current-patch", &command, N_("show the current patch"),
+			    ACTION_SHOW_CURRENT_PATCH),
+		OPT_CMDMODE(0, "shorten-ids", &command,
+			N_("shorten commit ids in the todo list"), ACTION_SHORTEN_OIDS),
+		OPT_CMDMODE(0, "expand-ids", &command,
+			N_("expand commit ids in the todo list"), ACTION_EXPAND_OIDS),
+		OPT_CMDMODE(0, "check-todo-list", &command,
+			N_("check the todo list"), ACTION_CHECK_TODO_LIST),
+		OPT_CMDMODE(0, "rearrange-squash", &command,
+			N_("rearrange fixup/squash lines"), ACTION_REARRANGE_SQUASH),
+		OPT_CMDMODE(0, "add-exec-commands", &command,
+			N_("insert exec commands in todo list"), ACTION_ADD_EXEC),
+		{ OPTION_CALLBACK, 0, "onto", &opts.onto, N_("onto"), N_("onto"),
+		  PARSE_OPT_NONEG, parse_opt_commit, 0 },
+		{ OPTION_CALLBACK, 0, "restrict-revision", &opts.restrict_revision,
+		  N_("restrict-revision"), N_("restrict revision"),
+		  PARSE_OPT_NONEG, parse_opt_commit, 0 },
+		{ OPTION_CALLBACK, 0, "squash-onto", &squash_onto, N_("squash-onto"),
+		  N_("squash onto"), PARSE_OPT_NONEG, parse_opt_object_id, 0 },
+		{ OPTION_CALLBACK, 0, "upstream", &opts.upstream, N_("upstream"),
+		  N_("the upstream commit"), PARSE_OPT_NONEG, parse_opt_commit,
+		  0 },
+		OPT_STRING(0, "head-name", &opts.head_name, N_("head-name"), N_("head name")),
+		{ OPTION_STRING, 'S', "gpg-sign", &opts.gpg_sign_opt, N_("key-id"),
+			N_("GPG-sign commits"),
+			PARSE_OPT_OPTARG, NULL, (intptr_t) "" },
+		OPT_STRING(0, "strategy", &opts.strategy, N_("strategy"),
+			   N_("rebase strategy")),
+		OPT_STRING(0, "strategy-opts", &opts.strategy_opts, N_("strategy-opts"),
+			   N_("strategy options")),
+		OPT_STRING(0, "switch-to", &opts.switch_to, N_("switch-to"),
+			   N_("the branch or commit to checkout")),
+		OPT_STRING(0, "onto-name", &opts.onto_name, N_("onto-name"), N_("onto name")),
+		OPT_STRING(0, "cmd", &opts.cmd, N_("cmd"), N_("the command to run")),
+		OPT_RERERE_AUTOUPDATE(&opts.allow_rerere_autoupdate),
+		OPT_BOOL(0, "reschedule-failed-exec", &opts.reschedule_failed_exec,
+			 N_("automatically re-schedule any `exec` that fails")),
+		OPT_END()
+	};
+
+	opts.rebase_cousins = -1;
+
+	if (argc == 1)
+		usage_with_options(builtin_rebase_interactive_usage, options);
+
+	argc = parse_options(argc, argv, prefix, options,
+			builtin_rebase_interactive_usage, PARSE_OPT_KEEP_ARGV0);
+
+	if (!is_null_oid(&squash_onto))
+		opts.squash_onto = &squash_onto;
+
+	if (opts.rebase_cousins >= 0 && !opts.rebase_merges)
+		warning(_("--[no-]rebase-cousins has no effect without "
+			  "--rebase-merges"));
+
+	return !!run_sequencer_rebase(&opts, command);
+}
+
+static int is_merge(struct rebase_options *opts)
+{
+	return opts->type == REBASE_MERGE ||
 		opts->type == REBASE_PRESERVE_MERGES;
 }
 
-static void imply_interactive(struct rebase_options *opts, const char *option)
+static void imply_merge(struct rebase_options *opts, const char *option)
 {
 	switch (opts->type) {
-	case REBASE_AM:
-		die(_("%s requires an interactive rebase"), option);
+	case REBASE_APPLY:
+		die(_("%s requires the merge backend"), option);
 		break;
-	case REBASE_INTERACTIVE:
+	case REBASE_MERGE:
 	case REBASE_PRESERVE_MERGES:
 		break;
-	case REBASE_MERGE:
-		/* we silently *upgrade* --merge to --interactive if needed */
 	default:
-		opts->type = REBASE_INTERACTIVE; /* implied */
+		opts->type = REBASE_MERGE; /* implied */
 		break;
 	}
 }
@@ -145,15 +593,6 @@ static const char *state_dir_path(const char *filename, struct rebase_options *o
 	return path.buf;
 }
 
-/* Read one file, then strip line endings */
-static int read_one(const char *path, struct strbuf *buf)
-{
-	if (strbuf_read_file(buf, path, 0) < 0)
-		return error_errno(_("could not read '%s'"), path);
-	strbuf_trim_trailing_newline(buf);
-	return 0;
-}
-
 /* Initialize the rebase options from the state directory. */
 static int read_basic_state(struct rebase_options *opts)
 {
@@ -161,8 +600,10 @@ static int read_basic_state(struct rebase_options *opts)
 	struct strbuf buf = STRBUF_INIT;
 	struct object_id oid;
 
-	if (read_one(state_dir_path("head-name", opts), &head_name) ||
-	    read_one(state_dir_path("onto", opts), &buf))
+	if (!read_oneliner(&head_name, state_dir_path("head-name", opts),
+			   READ_ONELINER_WARN_MISSING) ||
+	    !read_oneliner(&buf, state_dir_path("onto", opts),
+			   READ_ONELINER_WARN_MISSING))
 		return -1;
 	opts->head_name = starts_with(head_name.buf, "refs/") ?
 		xstrdup(head_name.buf) : NULL;
@@ -178,17 +619,16 @@ static int read_basic_state(struct rebase_options *opts)
 	 */
 	strbuf_reset(&buf);
 	if (file_exists(state_dir_path("orig-head", opts))) {
-		if (read_one(state_dir_path("orig-head", opts), &buf))
+		if (!read_oneliner(&buf, state_dir_path("orig-head", opts),
+				   READ_ONELINER_WARN_MISSING))
 			return -1;
-	} else if (read_one(state_dir_path("head", opts), &buf))
+	} else if (!read_oneliner(&buf, state_dir_path("head", opts),
+				  READ_ONELINER_WARN_MISSING))
 		return -1;
 	if (get_oid(buf.buf, &opts->orig_head))
 		return error(_("invalid orig-head: '%s'"), buf.buf);
 
-	strbuf_reset(&buf);
-	if (read_one(state_dir_path("quiet", opts), &buf))
-		return -1;
-	if (buf.len)
+	if (file_exists(state_dir_path("quiet", opts)))
 		opts->flags &= ~REBASE_NO_QUIET;
 	else
 		opts->flags |= REBASE_NO_QUIET;
@@ -203,23 +643,22 @@ static int read_basic_state(struct rebase_options *opts)
 
 	if (file_exists(state_dir_path("allow_rerere_autoupdate", opts))) {
 		strbuf_reset(&buf);
-		if (read_one(state_dir_path("allow_rerere_autoupdate", opts),
-			    &buf))
+		if (!read_oneliner(&buf, state_dir_path("allow_rerere_autoupdate", opts),
+				   READ_ONELINER_WARN_MISSING))
 			return -1;
 		if (!strcmp(buf.buf, "--rerere-autoupdate"))
-			opts->allow_rerere_autoupdate = 1;
+			opts->allow_rerere_autoupdate = RERERE_AUTOUPDATE;
 		else if (!strcmp(buf.buf, "--no-rerere-autoupdate"))
-			opts->allow_rerere_autoupdate = 0;
+			opts->allow_rerere_autoupdate = RERERE_NOAUTOUPDATE;
 		else
 			warning(_("ignoring invalid allow_rerere_autoupdate: "
 				  "'%s'"), buf.buf);
-	} else
-		opts->allow_rerere_autoupdate = -1;
+	}
 
 	if (file_exists(state_dir_path("gpg_sign_opt", opts))) {
 		strbuf_reset(&buf);
-		if (read_one(state_dir_path("gpg_sign_opt", opts),
-			    &buf))
+		if (!read_oneliner(&buf, state_dir_path("gpg_sign_opt", opts),
+				   READ_ONELINER_WARN_MISSING))
 			return -1;
 		free(opts->gpg_sign_opt);
 		opts->gpg_sign_opt = xstrdup(buf.buf);
@@ -227,7 +666,8 @@ static int read_basic_state(struct rebase_options *opts)
 
 	if (file_exists(state_dir_path("strategy", opts))) {
 		strbuf_reset(&buf);
-		if (read_one(state_dir_path("strategy", opts), &buf))
+		if (!read_oneliner(&buf, state_dir_path("strategy", opts),
+				   READ_ONELINER_WARN_MISSING))
 			return -1;
 		free(opts->strategy);
 		opts->strategy = xstrdup(buf.buf);
@@ -235,7 +675,8 @@ static int read_basic_state(struct rebase_options *opts)
 
 	if (file_exists(state_dir_path("strategy_opts", opts))) {
 		strbuf_reset(&buf);
-		if (read_one(state_dir_path("strategy_opts", opts), &buf))
+		if (!read_oneliner(&buf, state_dir_path("strategy_opts", opts),
+				   READ_ONELINER_WARN_MISSING))
 			return -1;
 		free(opts->strategy_opts);
 		opts->strategy_opts = xstrdup(buf.buf);
@@ -246,69 +687,65 @@ static int read_basic_state(struct rebase_options *opts)
 	return 0;
 }
 
-static int apply_autostash(struct rebase_options *opts)
+static int rebase_write_basic_state(struct rebase_options *opts)
 {
-	const char *path = state_dir_path("autostash", opts);
-	struct strbuf autostash = STRBUF_INIT;
-	struct child_process stash_apply = CHILD_PROCESS_INIT;
+	write_file(state_dir_path("head-name", opts), "%s",
+		   opts->head_name ? opts->head_name : "detached HEAD");
+	write_file(state_dir_path("onto", opts), "%s",
+		   opts->onto ? oid_to_hex(&opts->onto->object.oid) : "");
+	write_file(state_dir_path("orig-head", opts), "%s",
+		   oid_to_hex(&opts->orig_head));
+	if (!(opts->flags & REBASE_NO_QUIET))
+		write_file(state_dir_path("quiet", opts), "%s", "");
+	if (opts->flags & REBASE_VERBOSE)
+		write_file(state_dir_path("verbose", opts), "%s", "");
+	if (opts->strategy)
+		write_file(state_dir_path("strategy", opts), "%s",
+			   opts->strategy);
+	if (opts->strategy_opts)
+		write_file(state_dir_path("strategy_opts", opts), "%s",
+			   opts->strategy_opts);
+	if (opts->allow_rerere_autoupdate > 0)
+		write_file(state_dir_path("allow_rerere_autoupdate", opts),
+			   "-%s-rerere-autoupdate",
+			   opts->allow_rerere_autoupdate == RERERE_AUTOUPDATE ?
+				"" : "-no");
+	if (opts->gpg_sign_opt)
+		write_file(state_dir_path("gpg_sign_opt", opts), "%s",
+			   opts->gpg_sign_opt);
+	if (opts->signoff)
+		write_file(state_dir_path("signoff", opts), "--signoff");
 
-	if (!file_exists(path))
-		return 0;
-
-	if (read_one(path, &autostash))
-		return error(_("Could not read '%s'"), path);
-	/* Ensure that the hash is not mistaken for a number */
-	strbuf_addstr(&autostash, "^0");
-	argv_array_pushl(&stash_apply.args,
-			 "stash", "apply", autostash.buf, NULL);
-	stash_apply.git_cmd = 1;
-	stash_apply.no_stderr = stash_apply.no_stdout =
-		stash_apply.no_stdin = 1;
-	if (!run_command(&stash_apply))
-		printf(_("Applied autostash.\n"));
-	else {
-		struct argv_array args = ARGV_ARRAY_INIT;
-		int res = 0;
-
-		argv_array_pushl(&args,
-				 "stash", "store", "-m", "autostash", "-q",
-				 autostash.buf, NULL);
-		if (run_command_v_opt(args.argv, RUN_GIT_CMD))
-			res = error(_("Cannot store %s"), autostash.buf);
-		argv_array_clear(&args);
-		strbuf_release(&autostash);
-		if (res)
-			return res;
-
-		fprintf(stderr,
-			_("Applying autostash resulted in conflicts.\n"
-			  "Your changes are safe in the stash.\n"
-			  "You can run \"git stash pop\" or \"git stash drop\" "
-			  "at any time.\n"));
-	}
-
-	strbuf_release(&autostash);
 	return 0;
 }
 
 static int finish_rebase(struct rebase_options *opts)
 {
 	struct strbuf dir = STRBUF_INIT;
-	const char *argv_gc_auto[] = { "gc", "--auto", NULL };
+	int ret = 0;
 
 	delete_ref(NULL, "REBASE_HEAD", NULL, REF_NO_DEREF);
-	apply_autostash(opts);
-	close_all_packs(the_repository->objects);
+	apply_autostash(state_dir_path("autostash", opts));
+	close_object_store(the_repository->objects);
 	/*
 	 * We ignore errors in 'gc --auto', since the
 	 * user should see them.
 	 */
-	run_command_v_opt(argv_gc_auto, RUN_GIT_CMD);
-	strbuf_addstr(&dir, opts->state_dir);
-	remove_dir_recursively(&dir, 0);
-	strbuf_release(&dir);
+	run_auto_gc(!(opts->flags & (REBASE_NO_QUIET|REBASE_VERBOSE)));
+	if (opts->type == REBASE_MERGE) {
+		struct replay_opts replay = REPLAY_OPTS_INIT;
 
-	return 0;
+		replay.action = REPLAY_INTERACTIVE_REBASE;
+		ret = sequencer_remove_state(&replay);
+	} else {
+		strbuf_addstr(&dir, opts->state_dir);
+		if (remove_dir_recursively(&dir, 0))
+			ret = error(_("could not remove '%s'"),
+				    opts->state_dir);
+		strbuf_release(&dir);
+	}
+
+	return ret;
 }
 
 static struct commit *peel_committish(const char *name)
@@ -333,6 +770,31 @@ static void add_var(struct strbuf *buf, const char *name, const char *value)
 	}
 }
 
+static int move_to_original_branch(struct rebase_options *opts)
+{
+	struct strbuf orig_head_reflog = STRBUF_INIT, head_reflog = STRBUF_INIT;
+	int ret;
+
+	if (!opts->head_name)
+		return 0; /* nothing to move back to */
+
+	if (!opts->onto)
+		BUG("move_to_original_branch without onto");
+
+	strbuf_addf(&orig_head_reflog, "rebase finished: %s onto %s",
+		    opts->head_name, oid_to_hex(&opts->onto->object.oid));
+	strbuf_addf(&head_reflog, "rebase finished: returning to %s",
+		    opts->head_name);
+	ret = reset_head(the_repository, NULL, "", opts->head_name,
+			 RESET_HEAD_REFS_ONLY,
+			 orig_head_reflog.buf, head_reflog.buf,
+			 DEFAULT_REFLOG_ACTION);
+
+	strbuf_release(&orig_head_reflog);
+	strbuf_release(&head_reflog);
+	return ret;
+}
+
 static const char *resolvemsg =
 N_("Resolve all conflicts manually, mark them as resolved with\n"
 "\"git add/rm <conflicted_files>\", then run \"git rebase --continue\".\n"
@@ -340,83 +802,155 @@ N_("Resolve all conflicts manually, mark them as resolved with\n"
 "To abort and get back to the state before \"git rebase\", run "
 "\"git rebase --abort\".");
 
-static int run_specific_rebase(struct rebase_options *opts)
+static int run_am(struct rebase_options *opts)
+{
+	struct child_process am = CHILD_PROCESS_INIT;
+	struct child_process format_patch = CHILD_PROCESS_INIT;
+	struct strbuf revisions = STRBUF_INIT;
+	int status;
+	char *rebased_patches;
+
+	am.git_cmd = 1;
+	argv_array_push(&am.args, "am");
+
+	if (opts->action && !strcmp("continue", opts->action)) {
+		argv_array_push(&am.args, "--resolved");
+		argv_array_pushf(&am.args, "--resolvemsg=%s", resolvemsg);
+		if (opts->gpg_sign_opt)
+			argv_array_push(&am.args, opts->gpg_sign_opt);
+		status = run_command(&am);
+		if (status)
+			return status;
+
+		return move_to_original_branch(opts);
+	}
+	if (opts->action && !strcmp("skip", opts->action)) {
+		argv_array_push(&am.args, "--skip");
+		argv_array_pushf(&am.args, "--resolvemsg=%s", resolvemsg);
+		status = run_command(&am);
+		if (status)
+			return status;
+
+		return move_to_original_branch(opts);
+	}
+	if (opts->action && !strcmp("show-current-patch", opts->action)) {
+		argv_array_push(&am.args, "--show-current-patch");
+		return run_command(&am);
+	}
+
+	strbuf_addf(&revisions, "%s...%s",
+		    oid_to_hex(opts->root ?
+			       /* this is now equivalent to !opts->upstream */
+			       &opts->onto->object.oid :
+			       &opts->upstream->object.oid),
+		    oid_to_hex(&opts->orig_head));
+
+	rebased_patches = xstrdup(git_path("rebased-patches"));
+	format_patch.out = open(rebased_patches,
+				O_WRONLY | O_CREAT | O_TRUNC, 0666);
+	if (format_patch.out < 0) {
+		status = error_errno(_("could not open '%s' for writing"),
+				     rebased_patches);
+		free(rebased_patches);
+		argv_array_clear(&am.args);
+		return status;
+	}
+
+	format_patch.git_cmd = 1;
+	argv_array_pushl(&format_patch.args, "format-patch", "-k", "--stdout",
+			 "--full-index", "--cherry-pick", "--right-only",
+			 "--src-prefix=a/", "--dst-prefix=b/", "--no-renames",
+			 "--no-cover-letter", "--pretty=mboxrd", "--topo-order",
+			 "--no-base", NULL);
+	if (opts->git_format_patch_opt.len)
+		argv_array_split(&format_patch.args,
+				 opts->git_format_patch_opt.buf);
+	argv_array_push(&format_patch.args, revisions.buf);
+	if (opts->restrict_revision)
+		argv_array_pushf(&format_patch.args, "^%s",
+				 oid_to_hex(&opts->restrict_revision->object.oid));
+
+	status = run_command(&format_patch);
+	if (status) {
+		unlink(rebased_patches);
+		free(rebased_patches);
+		argv_array_clear(&am.args);
+
+		reset_head(the_repository, &opts->orig_head, "checkout",
+			   opts->head_name, 0,
+			   "HEAD", NULL, DEFAULT_REFLOG_ACTION);
+		error(_("\ngit encountered an error while preparing the "
+			"patches to replay\n"
+			"these revisions:\n"
+			"\n    %s\n\n"
+			"As a result, git cannot rebase them."),
+		      opts->revisions);
+
+		strbuf_release(&revisions);
+		return status;
+	}
+	strbuf_release(&revisions);
+
+	am.in = open(rebased_patches, O_RDONLY);
+	if (am.in < 0) {
+		status = error_errno(_("could not open '%s' for reading"),
+				     rebased_patches);
+		free(rebased_patches);
+		argv_array_clear(&am.args);
+		return status;
+	}
+
+	argv_array_pushv(&am.args, opts->git_am_opts.argv);
+	argv_array_push(&am.args, "--rebasing");
+	argv_array_pushf(&am.args, "--resolvemsg=%s", resolvemsg);
+	argv_array_push(&am.args, "--patch-format=mboxrd");
+	if (opts->allow_rerere_autoupdate == RERERE_AUTOUPDATE)
+		argv_array_push(&am.args, "--rerere-autoupdate");
+	else if (opts->allow_rerere_autoupdate == RERERE_NOAUTOUPDATE)
+		argv_array_push(&am.args, "--no-rerere-autoupdate");
+	if (opts->gpg_sign_opt)
+		argv_array_push(&am.args, opts->gpg_sign_opt);
+	status = run_command(&am);
+	unlink(rebased_patches);
+	free(rebased_patches);
+
+	if (!status) {
+		return move_to_original_branch(opts);
+	}
+
+	if (is_directory(opts->state_dir))
+		rebase_write_basic_state(opts);
+
+	return status;
+}
+
+static int run_specific_rebase(struct rebase_options *opts, enum action action)
 {
 	const char *argv[] = { NULL, NULL };
 	struct strbuf script_snippet = STRBUF_INIT, buf = STRBUF_INIT;
 	int status;
 	const char *backend, *backend_func;
 
-	if (opts->type == REBASE_INTERACTIVE) {
-		/* Run builtin interactive rebase */
-		struct child_process child = CHILD_PROCESS_INIT;
-
-		argv_array_pushf(&child.env_array, "GIT_CHERRY_PICK_HELP=%s",
-				 resolvemsg);
+	if (opts->type == REBASE_MERGE) {
+		/* Run sequencer-based rebase */
+		setenv("GIT_CHERRY_PICK_HELP", resolvemsg, 1);
 		if (!(opts->flags & REBASE_INTERACTIVE_EXPLICIT)) {
-			argv_array_push(&child.env_array, "GIT_EDITOR=:");
+			setenv("GIT_SEQUENCE_EDITOR", ":", 1);
 			opts->autosquash = 0;
 		}
+		if (opts->gpg_sign_opt) {
+			/* remove the leading "-S" */
+			char *tmp = xstrdup(opts->gpg_sign_opt + 2);
+			free(opts->gpg_sign_opt);
+			opts->gpg_sign_opt = tmp;
+		}
 
-		child.git_cmd = 1;
-		argv_array_push(&child.args, "rebase--interactive");
-
-		if (opts->action)
-			argv_array_pushf(&child.args, "--%s", opts->action);
-		if (opts->keep_empty)
-			argv_array_push(&child.args, "--keep-empty");
-		if (opts->rebase_merges)
-			argv_array_push(&child.args, "--rebase-merges");
-		if (opts->rebase_cousins)
-			argv_array_push(&child.args, "--rebase-cousins");
-		if (opts->autosquash)
-			argv_array_push(&child.args, "--autosquash");
-		if (opts->flags & REBASE_VERBOSE)
-			argv_array_push(&child.args, "--verbose");
-		if (opts->flags & REBASE_FORCE)
-			argv_array_push(&child.args, "--no-ff");
-		if (opts->restrict_revision)
-			argv_array_pushf(&child.args,
-					 "--restrict-revision=^%s",
-					 oid_to_hex(&opts->restrict_revision->object.oid));
-		if (opts->upstream)
-			argv_array_pushf(&child.args, "--upstream=%s",
-					 oid_to_hex(&opts->upstream->object.oid));
-		if (opts->onto)
-			argv_array_pushf(&child.args, "--onto=%s",
-					 oid_to_hex(&opts->onto->object.oid));
-		if (opts->squash_onto)
-			argv_array_pushf(&child.args, "--squash-onto=%s",
-					 oid_to_hex(opts->squash_onto));
-		if (opts->onto_name)
-			argv_array_pushf(&child.args, "--onto-name=%s",
-					 opts->onto_name);
-		argv_array_pushf(&child.args, "--head-name=%s",
-				 opts->head_name ?
-				 opts->head_name : "detached HEAD");
-		if (opts->strategy)
-			argv_array_pushf(&child.args, "--strategy=%s",
-					 opts->strategy);
-		if (opts->strategy_opts)
-			argv_array_pushf(&child.args, "--strategy-opts=%s",
-					 opts->strategy_opts);
-		if (opts->switch_to)
-			argv_array_pushf(&child.args, "--switch-to=%s",
-					 opts->switch_to);
-		if (opts->cmd)
-			argv_array_pushf(&child.args, "--cmd=%s", opts->cmd);
-		if (opts->allow_empty_message)
-			argv_array_push(&child.args, "--allow-empty-message");
-		if (opts->allow_rerere_autoupdate > 0)
-			argv_array_push(&child.args, "--rerere-autoupdate");
-		else if (opts->allow_rerere_autoupdate == 0)
-			argv_array_push(&child.args, "--no-rerere-autoupdate");
-		if (opts->gpg_sign_opt)
-			argv_array_push(&child.args, opts->gpg_sign_opt);
-		if (opts->signoff)
-			argv_array_push(&child.args, "--signoff");
+		status = run_sequencer_rebase(opts, action);
+		goto finished_rebase;
+	}
 
-		status = run_command(&child);
+	if (opts->type == REBASE_APPLY) {
+		status = run_am(opts);
 		goto finished_rebase;
 	}
 
@@ -435,8 +969,6 @@ static int run_specific_rebase(struct rebase_options *opts)
 	add_var(&script_snippet, "revisions", opts->revisions);
 	add_var(&script_snippet, "restrict_revision", opts->restrict_revision ?
 		oid_to_hex(&opts->restrict_revision->object.oid) : NULL);
-	add_var(&script_snippet, "GIT_QUIET",
-		opts->flags & REBASE_NO_QUIET ? "" : "t");
 	sq_quote_argv_pretty(&buf, opts->git_am_opts.argv);
 	add_var(&script_snippet, "git_am_opt", buf.buf);
 	strbuf_release(&buf);
@@ -451,9 +983,9 @@ static int run_specific_rebase(struct rebase_options *opts)
 	add_var(&script_snippet, "action", opts->action ? opts->action : "");
 	add_var(&script_snippet, "signoff", opts->signoff ? "--signoff" : "");
 	add_var(&script_snippet, "allow_rerere_autoupdate",
-		opts->allow_rerere_autoupdate < 0 ? "" :
 		opts->allow_rerere_autoupdate ?
-		"--rerere-autoupdate" : "--no-rerere-autoupdate");
+			opts->allow_rerere_autoupdate == RERERE_AUTOUPDATE ?
+			"--rerere-autoupdate" : "--no-rerere-autoupdate" : "");
 	add_var(&script_snippet, "keep_empty", opts->keep_empty ? "yes" : "");
 	add_var(&script_snippet, "autosquash", opts->autosquash ? "t" : "");
 	add_var(&script_snippet, "gpg_sign_opt", opts->gpg_sign_opt);
@@ -472,22 +1004,14 @@ static int run_specific_rebase(struct rebase_options *opts)
 	add_var(&script_snippet, "git_format_patch_opt",
 		opts->git_format_patch_opt.buf);
 
-	if (is_interactive(opts) &&
+	if (is_merge(opts) &&
 	    !(opts->flags & REBASE_INTERACTIVE_EXPLICIT)) {
 		strbuf_addstr(&script_snippet,
-			      "GIT_EDITOR=:; export GIT_EDITOR; ");
+			      "GIT_SEQUENCE_EDITOR=:; export GIT_SEQUENCE_EDITOR; ");
 		opts->autosquash = 0;
 	}
 
 	switch (opts->type) {
-	case REBASE_AM:
-		backend = "git-rebase--am";
-		backend_func = "git_rebase__am";
-		break;
-	case REBASE_MERGE:
-		backend = "git-rebase--merge";
-		backend_func = "git_rebase__merge";
-		break;
 	case REBASE_PRESERVE_MERGES:
 		backend = "git-rebase--preserve-merges";
 		backend_func = "git_rebase__preserve_merges";
@@ -498,23 +1022,22 @@ static int run_specific_rebase(struct rebase_options *opts)
 	}
 
 	strbuf_addf(&script_snippet,
-		    ". git-sh-setup && . git-rebase--common &&"
-		    " . %s && %s", backend, backend_func);
+		    ". git-sh-setup && . %s && %s", backend, backend_func);
 	argv[0] = script_snippet.buf;
 
 	status = run_command_v_opt(argv, RUN_USING_SHELL);
 finished_rebase:
 	if (opts->dont_finish_rebase)
 		; /* do nothing */
-	else if (opts->type == REBASE_INTERACTIVE)
-		; /* interactive rebase cleans up after itself */
+	else if (opts->type == REBASE_MERGE)
+		; /* merge backend cleans up after itself */
 	else if (status == 0) {
 		if (!file_exists(state_dir_path("stopped-sha", opts)))
 			finish_rebase(opts);
 	} else if (status == 2) {
 		struct strbuf dir = STRBUF_INIT;
 
-		apply_autostash(opts);
+		apply_autostash(state_dir_path("autostash", opts));
 		strbuf_addstr(&dir, opts->state_dir);
 		remove_dir_recursively(&dir, 0);
 		strbuf_release(&dir);
@@ -526,125 +1049,6 @@ finished_rebase:
 	return status ? -1 : 0;
 }
 
-#define GIT_REFLOG_ACTION_ENVIRONMENT "GIT_REFLOG_ACTION"
-
-#define RESET_HEAD_DETACH (1<<0)
-#define RESET_HEAD_HARD (1<<1)
-
-static int reset_head(struct object_id *oid, const char *action,
-		      const char *switch_to_branch, unsigned flags,
-		      const char *reflog_orig_head, const char *reflog_head)
-{
-	unsigned detach_head = flags & RESET_HEAD_DETACH;
-	unsigned reset_hard = flags & RESET_HEAD_HARD;
-	struct object_id head_oid;
-	struct tree_desc desc[2] = { { NULL }, { NULL } };
-	struct lock_file lock = LOCK_INIT;
-	struct unpack_trees_options unpack_tree_opts;
-	struct tree *tree;
-	const char *reflog_action;
-	struct strbuf msg = STRBUF_INIT;
-	size_t prefix_len;
-	struct object_id *orig = NULL, oid_orig,
-		*old_orig = NULL, oid_old_orig;
-	int ret = 0, nr = 0;
-
-	if (switch_to_branch && !starts_with(switch_to_branch, "refs/"))
-		BUG("Not a fully qualified branch: '%s'", switch_to_branch);
-
-	if (hold_locked_index(&lock, LOCK_REPORT_ON_ERROR) < 0) {
-		ret = -1;
-		goto leave_reset_head;
-	}
-
-	if ((!oid || !reset_hard) && get_oid("HEAD", &head_oid)) {
-		ret = error(_("could not determine HEAD revision"));
-		goto leave_reset_head;
-	}
-
-	if (!oid)
-		oid = &head_oid;
-
-	memset(&unpack_tree_opts, 0, sizeof(unpack_tree_opts));
-	setup_unpack_trees_porcelain(&unpack_tree_opts, action);
-	unpack_tree_opts.head_idx = 1;
-	unpack_tree_opts.src_index = the_repository->index;
-	unpack_tree_opts.dst_index = the_repository->index;
-	unpack_tree_opts.fn = reset_hard ? oneway_merge : twoway_merge;
-	unpack_tree_opts.update = 1;
-	unpack_tree_opts.merge = 1;
-	if (!detach_head)
-		unpack_tree_opts.reset = 1;
-
-	if (read_index_unmerged(the_repository->index) < 0) {
-		ret = error(_("could not read index"));
-		goto leave_reset_head;
-	}
-
-	if (!reset_hard && !fill_tree_descriptor(&desc[nr++], &head_oid)) {
-		ret = error(_("failed to find tree of %s"),
-			    oid_to_hex(&head_oid));
-		goto leave_reset_head;
-	}
-
-	if (!fill_tree_descriptor(&desc[nr++], oid)) {
-		ret = error(_("failed to find tree of %s"), oid_to_hex(oid));
-		goto leave_reset_head;
-	}
-
-	if (unpack_trees(nr, desc, &unpack_tree_opts)) {
-		ret = -1;
-		goto leave_reset_head;
-	}
-
-	tree = parse_tree_indirect(oid);
-	prime_cache_tree(the_repository, the_repository->index, tree);
-
-	if (write_locked_index(the_repository->index, &lock, COMMIT_LOCK) < 0) {
-		ret = error(_("could not write index"));
-		goto leave_reset_head;
-	}
-
-	reflog_action = getenv(GIT_REFLOG_ACTION_ENVIRONMENT);
-	strbuf_addf(&msg, "%s: ", reflog_action ? reflog_action : "rebase");
-	prefix_len = msg.len;
-
-	if (!get_oid("ORIG_HEAD", &oid_old_orig))
-		old_orig = &oid_old_orig;
-	if (!get_oid("HEAD", &oid_orig)) {
-		orig = &oid_orig;
-		if (!reflog_orig_head) {
-			strbuf_addstr(&msg, "updating ORIG_HEAD");
-			reflog_orig_head = msg.buf;
-		}
-		update_ref(reflog_orig_head, "ORIG_HEAD", orig, old_orig, 0,
-			   UPDATE_REFS_MSG_ON_ERR);
-	} else if (old_orig)
-		delete_ref(NULL, "ORIG_HEAD", old_orig, 0);
-	if (!reflog_head) {
-		strbuf_setlen(&msg, prefix_len);
-		strbuf_addstr(&msg, "updating HEAD");
-		reflog_head = msg.buf;
-	}
-	if (!switch_to_branch)
-		ret = update_ref(reflog_head, "HEAD", oid, orig,
-				 detach_head ? REF_NO_DEREF : 0,
-				 UPDATE_REFS_MSG_ON_ERR);
-	else {
-		ret = create_symref("HEAD", switch_to_branch, msg.buf);
-		if (!ret)
-			ret = update_ref(reflog_head, "HEAD", oid, NULL, 0,
-					 UPDATE_REFS_MSG_ON_ERR);
-	}
-
-leave_reset_head:
-	strbuf_release(&msg);
-	rollback_lock_file(&lock);
-	while (nr)
-		free((void *)desc[--nr].buffer);
-	return ret;
-}
-
 static int rebase_config(const char *var, const char *value, void *data)
 {
 	struct rebase_options *opts = data;
@@ -653,7 +1057,7 @@ static int rebase_config(const char *var, const char *value, void *data)
 		if (git_config_bool(var, value))
 			opts->flags |= REBASE_DIFFSTAT;
 		else
-			opts->flags &= !REBASE_DIFFSTAT;
+			opts->flags &= ~REBASE_DIFFSTAT;
 		return 0;
 	}
 
@@ -674,6 +1078,20 @@ static int rebase_config(const char *var, const char *value, void *data)
 		return 0;
 	}
 
+	if (!strcmp(var, "rebase.reschedulefailedexec")) {
+		opts->reschedule_failed_exec = git_config_bool(var, value);
+		return 0;
+	}
+
+	if (!strcmp(var, "rebase.usebuiltin")) {
+		opts->use_legacy_rebase = !git_config_bool(var, value);
+		return 0;
+	}
+
+	if (!strcmp(var, "rebase.backend")) {
+		return git_config_string(&opts->default_backend, var, value);
+	}
+
 	return git_default_config(var, value, data);
 }
 
@@ -695,28 +1113,60 @@ static int is_linear_history(struct commit *from, struct commit *to)
 	return 1;
 }
 
-static int can_fast_forward(struct commit *onto, struct object_id *head_oid,
-			    struct object_id *merge_base)
+static int can_fast_forward(struct commit *onto, struct commit *upstream,
+			    struct commit *restrict_revision,
+			    struct object_id *head_oid, struct object_id *merge_base)
 {
 	struct commit *head = lookup_commit(the_repository, head_oid);
-	struct commit_list *merge_bases;
-	int res;
+	struct commit_list *merge_bases = NULL;
+	int res = 0;
 
 	if (!head)
-		return 0;
+		goto done;
 
 	merge_bases = get_merge_bases(onto, head);
-	if (merge_bases && !merge_bases->next) {
-		oidcpy(merge_base, &merge_bases->item->object.oid);
-		res = oideq(merge_base, &onto->object.oid);
-	} else {
+	if (!merge_bases || merge_bases->next) {
 		oidcpy(merge_base, &null_oid);
-		res = 0;
+		goto done;
 	}
+
+	oidcpy(merge_base, &merge_bases->item->object.oid);
+	if (!oideq(merge_base, &onto->object.oid))
+		goto done;
+
+	if (restrict_revision && !oideq(&restrict_revision->object.oid, merge_base))
+		goto done;
+
+	if (!upstream)
+		goto done;
+
+	free_commit_list(merge_bases);
+	merge_bases = get_merge_bases(upstream, head);
+	if (!merge_bases || merge_bases->next)
+		goto done;
+
+	if (!oideq(&onto->object.oid, &merge_bases->item->object.oid))
+		goto done;
+
+	res = 1;
+
+done:
 	free_commit_list(merge_bases);
 	return res && is_linear_history(onto, head);
 }
 
+static int parse_opt_am(const struct option *opt, const char *arg, int unset)
+{
+	struct rebase_options *opts = opt->value;
+
+	BUG_ON_OPT_NEG(unset);
+	BUG_ON_OPT_ARG(arg);
+
+	opts->type = REBASE_APPLY;
+
+	return 0;
+}
+
 /* -i followed by -m is still -i */
 static int parse_opt_merge(const struct option *opt, const char *arg, int unset)
 {
@@ -725,7 +1175,7 @@ static int parse_opt_merge(const struct option *opt, const char *arg, int unset)
 	BUG_ON_OPT_NEG(unset);
 	BUG_ON_OPT_ARG(arg);
 
-	if (!is_interactive(opts))
+	if (!is_merge(opts))
 		opts->type = REBASE_MERGE;
 
 	return 0;
@@ -740,12 +1190,35 @@ static int parse_opt_interactive(const struct option *opt, const char *arg,
 	BUG_ON_OPT_NEG(unset);
 	BUG_ON_OPT_ARG(arg);
 
-	opts->type = REBASE_INTERACTIVE;
+	opts->type = REBASE_MERGE;
 	opts->flags |= REBASE_INTERACTIVE_EXPLICIT;
 
 	return 0;
 }
 
+static enum empty_type parse_empty_value(const char *value)
+{
+	if (!strcasecmp(value, "drop"))
+		return EMPTY_DROP;
+	else if (!strcasecmp(value, "keep"))
+		return EMPTY_KEEP;
+	else if (!strcasecmp(value, "ask"))
+		return EMPTY_ASK;
+
+	die(_("unrecognized empty type '%s'; valid values are \"drop\", \"keep\", and \"ask\"."), value);
+}
+
+static int parse_opt_empty(const struct option *opt, const char *arg, int unset)
+{
+	struct rebase_options *options = opt->value;
+	enum empty_type value = parse_empty_value(arg);
+
+	BUG_ON_OPT_NEG(unset);
+
+	options->empty = value;
+	return 0;
+}
+
 static void NORETURN error_on_missing_default_upstream(void)
 {
 	struct branch *current_branch = branch_get(NULL);
@@ -781,44 +1254,42 @@ static void set_reflog_action(struct rebase_options *options)
 	const char *env;
 	struct strbuf buf = STRBUF_INIT;
 
-	if (!is_interactive(options))
+	if (!is_merge(options))
 		return;
 
 	env = getenv(GIT_REFLOG_ACTION_ENVIRONMENT);
 	if (env && strcmp("rebase", env))
 		return; /* only override it if it is "rebase" */
 
-	strbuf_addf(&buf, "rebase -i (%s)", options->action);
+	strbuf_addf(&buf, "rebase (%s)", options->action);
 	setenv(GIT_REFLOG_ACTION_ENVIRONMENT, buf.buf, 1);
 	strbuf_release(&buf);
 }
 
+static int check_exec_cmd(const char *cmd)
+{
+	if (strchr(cmd, '\n'))
+		return error(_("exec commands cannot contain newlines"));
+
+	/* Does the command consist purely of whitespace? */
+	if (!cmd[strspn(cmd, " \t\r\f\v")])
+		return error(_("empty exec command"));
+
+	return 0;
+}
+
 int cmd_rebase(int argc, const char **argv, const char *prefix)
 {
-	struct rebase_options options = {
-		.type = REBASE_UNSPECIFIED,
-		.flags = REBASE_NO_QUIET,
-		.git_am_opts = ARGV_ARRAY_INIT,
-		.allow_rerere_autoupdate  = -1,
-		.allow_empty_message = 1,
-		.git_format_patch_opt = STRBUF_INIT,
-	};
+	struct rebase_options options = REBASE_OPTIONS_INIT;
 	const char *branch_name;
 	int ret, flags, total_argc, in_progress = 0;
+	int keep_base = 0;
 	int ok_to_skip_pre_rebase = 0;
 	struct strbuf msg = STRBUF_INIT;
 	struct strbuf revisions = STRBUF_INIT;
 	struct strbuf buf = STRBUF_INIT;
 	struct object_id merge_base;
-	enum {
-		NO_ACTION,
-		ACTION_CONTINUE,
-		ACTION_SKIP,
-		ACTION_ABORT,
-		ACTION_QUIT,
-		ACTION_EDIT_TODO,
-		ACTION_SHOW_CURRENT_PATCH,
-	} action = NO_ACTION;
+	enum action action = ACTION_NONE;
 	const char *gpg_sign = NULL;
 	struct string_list exec = STRING_LIST_INIT_NODUP;
 	const char *rebase_merges = NULL;
@@ -826,15 +1297,19 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	struct string_list strategy_options = STRING_LIST_INIT_NODUP;
 	struct object_id squash_onto;
 	char *squash_onto_name = NULL;
+	int reschedule_failed_exec = -1;
+	int allow_preemptive_ff = 1;
 	struct option builtin_rebase_options[] = {
 		OPT_STRING(0, "onto", &options.onto_name,
 			   N_("revision"),
 			   N_("rebase onto given branch instead of upstream")),
+		OPT_BOOL(0, "keep-base", &keep_base,
+			 N_("use the merge-base of upstream and branch as the current base")),
 		OPT_BOOL(0, "no-verify", &ok_to_skip_pre_rebase,
 			 N_("allow pre-rebase hook to run")),
 		OPT_NEGBIT('q', "quiet", &options.flags,
 			   N_("be quiet. implies --no-stat"),
-			   REBASE_NO_QUIET| REBASE_VERBOSE | REBASE_DIFFSTAT),
+			   REBASE_NO_QUIET | REBASE_VERBOSE | REBASE_DIFFSTAT),
 		OPT_BIT('v', "verbose", &options.flags,
 			N_("display a diffstat of what changed upstream"),
 			REBASE_NO_QUIET | REBASE_VERBOSE | REBASE_DIFFSTAT),
@@ -875,37 +1350,44 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		OPT_CMDMODE(0, "show-current-patch", &action,
 			    N_("show the patch file being applied or merged"),
 			    ACTION_SHOW_CURRENT_PATCH),
-		{ OPTION_CALLBACK, 'm', "merge", &options, NULL,
+		OPT_CALLBACK_F(0, "apply", &options, NULL,
+			N_("use apply strategies to rebase"),
+			PARSE_OPT_NOARG | PARSE_OPT_NONEG,
+			parse_opt_am),
+		OPT_CALLBACK_F('m', "merge", &options, NULL,
 			N_("use merging strategies to rebase"),
 			PARSE_OPT_NOARG | PARSE_OPT_NONEG,
-			parse_opt_merge },
-		{ OPTION_CALLBACK, 'i', "interactive", &options, NULL,
+			parse_opt_merge),
+		OPT_CALLBACK_F('i', "interactive", &options, NULL,
 			N_("let the user edit the list of commits to rebase"),
 			PARSE_OPT_NOARG | PARSE_OPT_NONEG,
-			parse_opt_interactive },
-		OPT_SET_INT('p', "preserve-merges", &options.type,
-			    N_("try to recreate merges instead of ignoring "
-			       "them"), REBASE_PRESERVE_MERGES),
-		OPT_BOOL(0, "rerere-autoupdate",
-			 &options.allow_rerere_autoupdate,
-			 N_("allow rerere to update index with resolved "
-			    "conflict")),
-		OPT_BOOL('k', "keep-empty", &options.keep_empty,
-			 N_("preserve empty commits during rebase")),
+			parse_opt_interactive),
+		OPT_SET_INT_F('p', "preserve-merges", &options.type,
+			      N_("(DEPRECATED) try to recreate merges instead of "
+				 "ignoring them"),
+			      REBASE_PRESERVE_MERGES, PARSE_OPT_HIDDEN),
+		OPT_RERERE_AUTOUPDATE(&options.allow_rerere_autoupdate),
+		OPT_CALLBACK_F(0, "empty", &options, "{drop,keep,ask}",
+			       N_("how to handle commits that become empty"),
+			       PARSE_OPT_NONEG, parse_opt_empty),
+		OPT_CALLBACK_F('k', "keep-empty", &options, NULL,
+			N_("keep commits which start empty"),
+			PARSE_OPT_NOARG | PARSE_OPT_HIDDEN,
+			parse_opt_keep_empty),
 		OPT_BOOL(0, "autosquash", &options.autosquash,
 			 N_("move commits that begin with "
 			    "squash!/fixup! under -i")),
 		{ OPTION_STRING, 'S', "gpg-sign", &gpg_sign, N_("key-id"),
 			N_("GPG-sign commits"),
 			PARSE_OPT_OPTARG, NULL, (intptr_t) "" },
-		OPT_BOOL(0, "autostash", &options.autostash,
-			 N_("automatically stash/stash pop before and after")),
+		OPT_AUTOSTASH(&options.autostash),
 		OPT_STRING_LIST('x', "exec", &exec, N_("exec"),
 				N_("add exec lines after each commit of the "
 				   "editable list")),
-		OPT_BOOL(0, "allow-empty-message",
-			 &options.allow_empty_message,
-			 N_("allow rebasing commits with empty messages")),
+		OPT_BOOL_F(0, "allow-empty-message",
+			   &options.allow_empty_message,
+			   N_("allow rebasing commits with empty messages"),
+			   PARSE_OPT_HIDDEN),
 		{OPTION_STRING, 'r', "rebase-merges", &rebase_merges,
 			N_("mode"),
 			N_("try to rebase merges instead of skipping them"),
@@ -920,35 +1402,29 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 				   "strategy")),
 		OPT_BOOL(0, "root", &options.root,
 			 N_("rebase all reachable commits up to the root(s)")),
+		OPT_BOOL(0, "reschedule-failed-exec",
+			 &reschedule_failed_exec,
+			 N_("automatically re-schedule any `exec` that fails")),
+		OPT_BOOL(0, "reapply-cherry-picks", &options.reapply_cherry_picks,
+			 N_("apply all changes, even those already present upstream")),
 		OPT_END(),
 	};
 	int i;
 
-	/*
-	 * NEEDSWORK: Once the builtin rebase has been tested enough
-	 * and git-legacy-rebase.sh is retired to contrib/, this preamble
-	 * can be removed.
-	 */
-
-	if (!use_builtin_rebase()) {
-		const char *path = mkpath("%s/git-legacy-rebase",
-					  git_exec_path());
-
-		if (sane_execvp(path, (char **)argv) < 0)
-			die_errno(_("could not exec %s"), path);
-		else
-			BUG("sane_execvp() returned???");
-	}
-
 	if (argc == 2 && !strcmp(argv[1], "-h"))
 		usage_with_options(builtin_rebase_usage,
 				   builtin_rebase_options);
 
-	prefix = setup_git_directory();
-	trace_repo_setup(prefix);
-	setup_work_tree();
-
+	options.allow_empty_message = 1;
 	git_config(rebase_config, &options);
+	/* options.gpg_sign_opt will be either "-S" or NULL */
+	gpg_sign = options.gpg_sign_opt ? "" : NULL;
+	FREE_AND_NULL(options.gpg_sign_opt);
+
+	if (options.use_legacy_rebase ||
+	    !git_env_bool("GIT_TEST_REBASE_USE_BUILTIN", -1))
+		warning(_("the rebase.useBuiltin support has been removed!\n"
+			  "See its entry in 'git help config' for details."));
 
 	strbuf_reset(&buf);
 	strbuf_addf(&buf, "%s/applying", apply_dir());
@@ -956,7 +1432,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		die(_("It looks like 'git am' is in progress. Cannot rebase."));
 
 	if (is_directory(apply_dir())) {
-		options.type = REBASE_AM;
+		options.type = REBASE_APPLY;
 		options.state_dir = apply_dir();
 	} else if (is_directory(merge_dir())) {
 		strbuf_reset(&buf);
@@ -968,7 +1444,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 			strbuf_reset(&buf);
 			strbuf_addf(&buf, "%s/interactive", merge_dir());
 			if(file_exists(buf.buf)) {
-				options.type = REBASE_INTERACTIVE;
+				options.type = REBASE_MERGE;
 				options.flags |= REBASE_INTERACTIVE_EXPLICIT;
 			} else
 				options.type = REBASE_MERGE;
@@ -984,7 +1460,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 			     builtin_rebase_options,
 			     builtin_rebase_usage, 0);
 
-	if (action != NO_ACTION && total_argc != 2) {
+	if (action != ACTION_NONE && total_argc != 2) {
 		usage_with_options(builtin_rebase_usage,
 				   builtin_rebase_options);
 	}
@@ -993,14 +1469,37 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		usage_with_options(builtin_rebase_usage,
 				   builtin_rebase_options);
 
-	if (action != NO_ACTION && !in_progress)
+	if (options.type == REBASE_PRESERVE_MERGES)
+		warning(_("git rebase --preserve-merges is deprecated. "
+			  "Use --rebase-merges instead."));
+
+	if (keep_base) {
+		if (options.onto_name)
+			die(_("cannot combine '--keep-base' with '--onto'"));
+		if (options.root)
+			die(_("cannot combine '--keep-base' with '--root'"));
+	}
+
+	if (options.root && fork_point > 0)
+		die(_("cannot combine '--root' with '--fork-point'"));
+
+	if (action != ACTION_NONE && !in_progress)
 		die(_("No rebase in progress?"));
 	setenv(GIT_REFLOG_ACTION_ENVIRONMENT, "rebase", 0);
 
-	if (action == ACTION_EDIT_TODO && !is_interactive(&options))
+	if (action == ACTION_EDIT_TODO && !is_merge(&options))
 		die(_("The --edit-todo action can only be used during "
 		      "interactive rebase."));
 
+	if (trace2_is_enabled()) {
+		if (is_merge(&options))
+			trace2_cmd_mode("interactive");
+		else if (exec.nr)
+			trace2_cmd_mode("interactive-exec");
+		else
+			trace2_cmd_mode(action_names[action]);
+	}
+
 	switch (action) {
 	case ACTION_CONTINUE: {
 		struct object_id head;
@@ -1015,13 +1514,12 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 			die(_("Cannot read HEAD"));
 
 		fd = hold_locked_index(&lock_file, 0);
-		if (read_index(the_repository->index) < 0)
+		if (repo_read_index(the_repository) < 0)
 			die(_("could not read index"));
 		refresh_index(the_repository->index, REFRESH_QUIET, NULL, NULL,
 			      NULL);
 		if (0 <= fd)
-			update_index_if_able(the_repository->index,
-					     &lock_file);
+			repo_update_index_if_able(the_repository, &lock_file);
 		rollback_lock_file(&lock_file);
 
 		if (has_unstaged_changes(the_repository, 1)) {
@@ -1042,10 +1540,10 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		rerere_clear(the_repository, &merge_rr);
 		string_list_clear(&merge_rr, 1);
 
-		if (reset_head(NULL, "reset", NULL, RESET_HEAD_HARD,
-			       NULL, NULL) < 0)
+		if (reset_head(the_repository, NULL, "reset", NULL, RESET_HEAD_HARD,
+			       NULL, NULL, DEFAULT_REFLOG_ACTION) < 0)
 			die(_("could not discard worktree changes"));
-		remove_branch_state(the_repository);
+		remove_branch_state(the_repository, 0);
 		if (read_basic_state(&options))
 			exit(1);
 		goto run_rebase;
@@ -1060,21 +1558,30 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 
 		if (read_basic_state(&options))
 			exit(1);
-		if (reset_head(&options.orig_head, "reset",
+		if (reset_head(the_repository, &options.orig_head, "reset",
 			       options.head_name, RESET_HEAD_HARD,
-			       NULL, NULL) < 0)
+			       NULL, NULL, DEFAULT_REFLOG_ACTION) < 0)
 			die(_("could not move back to %s"),
 			    oid_to_hex(&options.orig_head));
-		remove_branch_state(the_repository);
-		ret = finish_rebase(&options);
+		remove_branch_state(the_repository, 0);
+		ret = !!finish_rebase(&options);
 		goto cleanup;
 	}
 	case ACTION_QUIT: {
-		strbuf_reset(&buf);
-		strbuf_addstr(&buf, options.state_dir);
-		ret = !!remove_dir_recursively(&buf, 0);
-		if (ret)
-			die(_("could not remove '%s'"), options.state_dir);
+		save_autostash(state_dir_path("autostash", &options));
+		if (options.type == REBASE_MERGE) {
+			struct replay_opts replay = REPLAY_OPTS_INIT;
+
+			replay.action = REPLAY_INTERACTIVE_REBASE;
+			ret = !!sequencer_remove_state(&replay);
+		} else {
+			strbuf_reset(&buf);
+			strbuf_addstr(&buf, options.state_dir);
+			ret = !!remove_dir_recursively(&buf, 0);
+			if (ret)
+				error(_("could not remove '%s'"),
+				       options.state_dir);
+		}
 		goto cleanup;
 	}
 	case ACTION_EDIT_TODO:
@@ -1085,7 +1592,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		options.action = "show-current-patch";
 		options.dont_finish_rebase = 1;
 		goto run_rebase;
-	case NO_ACTION:
+	case ACTION_NONE:
 		break;
 	default:
 		BUG("action: %d", action);
@@ -1111,13 +1618,20 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		    state_dir_base, cmd_live_rebase, buf.buf);
 	}
 
+	if ((options.flags & REBASE_INTERACTIVE_EXPLICIT) ||
+	    (action != ACTION_NONE) ||
+	    (exec.nr > 0) ||
+	    options.autosquash) {
+		allow_preemptive_ff = 0;
+	}
+
 	for (i = 0; i < options.git_am_opts.argc; i++) {
 		const char *option = options.git_am_opts.argv[i], *p;
 		if (!strcmp(option, "--committer-date-is-author-date") ||
 		    !strcmp(option, "--ignore-date") ||
 		    !strcmp(option, "--whitespace=fix") ||
 		    !strcmp(option, "--whitespace=strip"))
-			options.flags |= REBASE_FORCE;
+			allow_preemptive_ff = 0;
 		else if (skip_prefix(option, "-C", &p)) {
 			while (*p)
 				if (!isdigit(*(p++)))
@@ -1130,21 +1644,26 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		}
 	}
 
+	for (i = 0; i < exec.nr; i++)
+		if (check_exec_cmd(exec.items[i].string))
+			exit(1);
+
 	if (!(options.flags & REBASE_NO_QUIET))
 		argv_array_push(&options.git_am_opts, "-q");
 
-	if (options.keep_empty)
-		imply_interactive(&options, "--keep-empty");
+	if (options.empty != EMPTY_UNSPECIFIED)
+		imply_merge(&options, "--empty");
 
-	if (gpg_sign) {
-		free(options.gpg_sign_opt);
+	if (options.reapply_cherry_picks)
+		imply_merge(&options, "--reapply-cherry-picks");
+
+	if (gpg_sign)
 		options.gpg_sign_opt = xstrfmt("-S%s", gpg_sign);
-	}
 
 	if (exec.nr) {
 		int i;
 
-		imply_interactive(&options, "--exec");
+		imply_merge(&options, "--exec");
 
 		strbuf_reset(&buf);
 		for (i = 0; i < exec.nr; i++)
@@ -1160,7 +1679,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		else if (strcmp("no-rebase-cousins", rebase_merges))
 			die(_("Unknown mode: %s"), rebase_merges);
 		options.rebase_merges = 1;
-		imply_interactive(&options, "--rebase-merges");
+		imply_merge(&options, "--rebase-merges");
 	}
 
 	if (strategy_options.nr) {
@@ -1179,10 +1698,9 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	if (options.strategy) {
 		options.strategy = xstrdup(options.strategy);
 		switch (options.type) {
-		case REBASE_AM:
+		case REBASE_APPLY:
 			die(_("--strategy requires --merge or --interactive"));
 		case REBASE_MERGE:
-		case REBASE_INTERACTIVE:
 		case REBASE_PRESERVE_MERGES:
 			/* compatible */
 			break;
@@ -1194,44 +1712,65 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		}
 	}
 
+	if (options.type == REBASE_MERGE)
+		imply_merge(&options, "--merge");
+
 	if (options.root && !options.onto_name)
-		imply_interactive(&options, "--root without --onto");
+		imply_merge(&options, "--root without --onto");
 
 	if (isatty(2) && options.flags & REBASE_NO_QUIET)
 		strbuf_addstr(&options.git_format_patch_opt, " --progress");
 
+	if (options.git_am_opts.argc || options.type == REBASE_APPLY) {
+		/* all am options except -q are compatible only with --apply */
+		for (i = options.git_am_opts.argc - 1; i >= 0; i--)
+			if (strcmp(options.git_am_opts.argv[i], "-q"))
+				break;
+
+		if (i >= 0) {
+			if (is_merge(&options))
+				die(_("cannot combine apply options with "
+				      "merge options"));
+			else
+				options.type = REBASE_APPLY;
+		}
+	}
+
+	if (options.type == REBASE_UNSPECIFIED) {
+		if (!strcmp(options.default_backend, "merge"))
+			imply_merge(&options, "--merge");
+		else if (!strcmp(options.default_backend, "apply"))
+			options.type = REBASE_APPLY;
+		else
+			die(_("Unknown rebase backend: %s"),
+			    options.default_backend);
+	}
+
 	switch (options.type) {
 	case REBASE_MERGE:
-	case REBASE_INTERACTIVE:
 	case REBASE_PRESERVE_MERGES:
 		options.state_dir = merge_dir();
 		break;
-	case REBASE_AM:
+	case REBASE_APPLY:
 		options.state_dir = apply_dir();
 		break;
 	default:
-		/* the default rebase backend is `--am` */
-		options.type = REBASE_AM;
-		options.state_dir = apply_dir();
-		break;
+		BUG("options.type was just set above; should be unreachable.");
 	}
 
-	if (options.git_am_opts.argc) {
-		/* all am options except -q are compatible only with --am */
-		for (i = options.git_am_opts.argc - 1; i >= 0; i--)
-			if (strcmp(options.git_am_opts.argv[i], "-q"))
-				break;
-
-		if (is_interactive(&options) && i >= 0)
-			die(_("error: cannot combine interactive options "
-			      "(--interactive, --exec, --rebase-merges, "
-			      "--preserve-merges, --keep-empty, --root + "
-			      "--onto) with am options (%s)"), buf.buf);
-		if (options.type == REBASE_MERGE && i >= 0)
-			die(_("error: cannot combine merge options (--merge, "
-			      "--strategy, --strategy-option) with am options "
-			      "(%s)"), buf.buf);
+	if (options.empty == EMPTY_UNSPECIFIED) {
+		if (options.flags & REBASE_INTERACTIVE_EXPLICIT)
+			options.empty = EMPTY_ASK;
+		else if (exec.nr > 0)
+			options.empty = EMPTY_KEEP;
+		else
+			options.empty = EMPTY_DROP;
 	}
+	if (reschedule_failed_exec > 0 && !is_merge(&options))
+		die(_("--reschedule-failed-exec requires "
+		      "--exec or --interactive"));
+	if (reschedule_failed_exec >= 0)
+		options.reschedule_failed_exec = reschedule_failed_exec;
 
 	if (options.signoff) {
 		if (options.type == REBASE_PRESERVE_MERGES)
@@ -1241,23 +1780,19 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		options.flags |= REBASE_FORCE;
 	}
 
-	if (options.type == REBASE_PRESERVE_MERGES)
+	if (options.type == REBASE_PRESERVE_MERGES) {
 		/*
 		 * Note: incompatibility with --signoff handled in signoff block above
 		 * Note: incompatibility with --interactive is just a strong warning;
 		 *       git-rebase.txt caveats with "unless you know what you are doing"
 		 */
 		if (options.rebase_merges)
-			die(_("error: cannot combine '--preserve-merges' with "
+			die(_("cannot combine '--preserve-merges' with "
 			      "'--rebase-merges'"));
 
-	if (options.rebase_merges) {
-		if (strategy_options.nr)
-			die(_("error: cannot combine '--rebase-merges' with "
-			      "'--strategy-option'"));
-		if (options.strategy)
-			die(_("error: cannot combine '--rebase-merges' with "
-			      "'--strategy'"));
+		if (options.reschedule_failed_exec)
+			die(_("error: cannot combine '--preserve-merges' with "
+			      "'--reschedule-failed-exec'"));
 	}
 
 	if (!options.root) {
@@ -1290,7 +1825,9 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 			options.squash_onto = &squash_onto;
 			options.onto_name = squash_onto_name =
 				xstrdup(oid_to_hex(&squash_onto));
-		}
+		} else
+			options.root_with_onto = 1;
+
 		options.upstream_name = NULL;
 		options.upstream = NULL;
 		if (argc > 1)
@@ -1300,12 +1837,22 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	}
 
 	/* Make sure the branch to rebase onto is valid. */
-	if (!options.onto_name)
+	if (keep_base) {
+		strbuf_reset(&buf);
+		strbuf_addstr(&buf, options.upstream_name);
+		strbuf_addstr(&buf, "...");
+		options.onto_name = xstrdup(buf.buf);
+	} else if (!options.onto_name)
 		options.onto_name = options.upstream_name;
 	if (strstr(options.onto_name, "...")) {
-		if (get_oid_mb(options.onto_name, &merge_base) < 0)
-			die(_("'%s': need exactly one merge base"),
-			    options.onto_name);
+		if (get_oid_mb(options.onto_name, &merge_base) < 0) {
+			if (keep_base)
+				die(_("'%s': need exactly one merge base with branch"),
+				    options.upstream_name);
+			else
+				die(_("'%s': need exactly one merge base"),
+				    options.onto_name);
+		}
 		options.onto = lookup_commit_or_die(&merge_base,
 						    options.onto_name);
 	} else {
@@ -1330,10 +1877,11 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		/* Is it a local branch? */
 		strbuf_reset(&buf);
 		strbuf_addf(&buf, "refs/heads/%s", branch_name);
-		if (!read_ref(buf.buf, &options.orig_head))
+		if (!read_ref(buf.buf, &options.orig_head)) {
+			die_if_checked_out(buf.buf, 1);
 			options.head_name = xstrdup(buf.buf);
 		/* If not is it a valid ref (branch or commit)? */
-		else if (!get_oid(branch_name, &options.orig_head))
+		} else if (!get_oid(branch_name, &options.orig_head))
 			options.head_name = NULL;
 		else
 			die(_("fatal: no such branch/commit '%s'"),
@@ -1351,8 +1899,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 				branch_name = options.head_name;
 
 		} else {
-			free(options.head_name);
-			options.head_name = NULL;
+			FREE_AND_NULL(options.head_name);
 			branch_name = "HEAD";
 		}
 		if (get_oid("HEAD", &options.orig_head))
@@ -1368,64 +1915,12 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 			get_fork_point(options.upstream_name, head);
 	}
 
-	if (read_index(the_repository->index) < 0)
+	if (repo_read_index(the_repository) < 0)
 		die(_("could not read index"));
 
 	if (options.autostash) {
-		struct lock_file lock_file = LOCK_INIT;
-		int fd;
-
-		fd = hold_locked_index(&lock_file, 0);
-		refresh_cache(REFRESH_QUIET);
-		if (0 <= fd)
-			update_index_if_able(&the_index, &lock_file);
-		rollback_lock_file(&lock_file);
-
-		if (has_unstaged_changes(the_repository, 1) ||
-		    has_uncommitted_changes(the_repository, 1)) {
-			const char *autostash =
-				state_dir_path("autostash", &options);
-			struct child_process stash = CHILD_PROCESS_INIT;
-			struct object_id oid;
-			struct commit *head =
-				lookup_commit_reference(the_repository,
-							&options.orig_head);
-
-			argv_array_pushl(&stash.args,
-					 "stash", "create", "autostash", NULL);
-			stash.git_cmd = 1;
-			stash.no_stdin = 1;
-			strbuf_reset(&buf);
-			if (capture_command(&stash, &buf, GIT_MAX_HEXSZ))
-				die(_("Cannot autostash"));
-			strbuf_trim_trailing_newline(&buf);
-			if (get_oid(buf.buf, &oid))
-				die(_("Unexpected stash response: '%s'"),
-				    buf.buf);
-			strbuf_reset(&buf);
-			strbuf_add_unique_abbrev(&buf, &oid, DEFAULT_ABBREV);
-
-			if (safe_create_leading_directories_const(autostash))
-				die(_("Could not create directory for '%s'"),
-				    options.state_dir);
-			write_file(autostash, "%s", oid_to_hex(&oid));
-			printf(_("Created autostash: %s\n"), buf.buf);
-			if (reset_head(&head->object.oid, "reset --hard",
-				       NULL, RESET_HEAD_HARD, NULL, NULL) < 0)
-				die(_("could not reset --hard"));
-			printf(_("HEAD is now at %s"),
-			       find_unique_abbrev(&head->object.oid,
-						  DEFAULT_ABBREV));
-			strbuf_reset(&buf);
-			pp_commit_easy(CMIT_FMT_ONELINE, head, &buf);
-			if (buf.len > 0)
-				printf(" %s", buf.buf);
-			putchar('\n');
-
-			if (discard_index(the_repository->index) < 0 ||
-				read_index(the_repository->index) < 0)
-				die(_("could not read index"));
-		}
+		create_autostash(the_repository, state_dir_path("autostash", &options),
+				 DEFAULT_REFLOG_ACTION);
 	}
 
 	if (require_clean_work_tree(the_repository, "rebase",
@@ -1441,33 +1936,30 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 
 	/*
 	 * Check if we are already based on onto with linear history,
-	 * but this should be done only when upstream and onto are the same
-	 * and if this is not an interactive rebase.
+	 * in which case we could fast-forward without replacing the commits
+	 * with new commits recreated by replaying their changes.
+	 *
+	 * Note that can_fast_forward() initializes merge_base, so we have to
+	 * call it before checking allow_preemptive_ff.
 	 */
-	if (can_fast_forward(options.onto, &options.orig_head, &merge_base) &&
-	    !is_interactive(&options) && !options.restrict_revision &&
-	    options.upstream &&
-	    !oidcmp(&options.upstream->object.oid, &options.onto->object.oid)) {
+	if (can_fast_forward(options.onto, options.upstream, options.restrict_revision,
+		    &options.orig_head, &merge_base) &&
+	    allow_preemptive_ff) {
 		int flag;
 
 		if (!(options.flags & REBASE_FORCE)) {
 			/* Lazily switch to the target branch if needed... */
 			if (options.switch_to) {
-				struct object_id oid;
-
-				if (get_oid(options.switch_to, &oid) < 0) {
-					ret = !!error(_("could not parse '%s'"),
-						      options.switch_to);
-					goto cleanup;
-				}
-
 				strbuf_reset(&buf);
 				strbuf_addf(&buf, "%s: checkout %s",
 					    getenv(GIT_REFLOG_ACTION_ENVIRONMENT),
 					    options.switch_to);
-				if (reset_head(&oid, "checkout",
-					       options.head_name, 0,
-					       NULL, buf.buf) < 0) {
+				if (reset_head(the_repository,
+					       &options.orig_head, "checkout",
+					       options.head_name,
+					       RESET_HEAD_RUN_POST_CHECKOUT_HOOK,
+					       NULL, buf.buf,
+					       DEFAULT_REFLOG_ACTION) < 0) {
 					ret = !!error(_("could not switch to "
 							"%s"),
 						      options.switch_to);
@@ -1529,7 +2021,7 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 		diff_flush(&opts);
 	}
 
-	if (is_interactive(&options))
+	if (is_merge(&options))
 		goto run_rebase;
 
 	/* Detach HEAD and reset the tree */
@@ -1539,8 +2031,10 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 
 	strbuf_addf(&msg, "%s: checkout %s",
 		    getenv(GIT_REFLOG_ACTION_ENVIRONMENT), options.onto_name);
-	if (reset_head(&options.onto->object.oid, "checkout", NULL,
-		       RESET_HEAD_DETACH, NULL, msg.buf))
+	if (reset_head(the_repository, &options.onto->object.oid, "checkout", NULL,
+		       RESET_HEAD_DETACH | RESET_ORIG_HEAD |
+		       RESET_HEAD_RUN_POST_CHECKOUT_HOOK,
+		       NULL, msg.buf, DEFAULT_REFLOG_ACTION))
 		die(_("Could not detach HEAD"));
 	strbuf_release(&msg);
 
@@ -1549,14 +2043,15 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	 * we just fast-forwarded.
 	 */
 	strbuf_reset(&msg);
-	if (!oidcmp(&merge_base, &options.orig_head)) {
+	if (oideq(&merge_base, &options.orig_head)) {
 		printf(_("Fast-forwarded %s to %s.\n"),
 			branch_name, options.onto_name);
 		strbuf_addf(&msg, "rebase finished: %s onto %s",
 			options.head_name ? options.head_name : "detached HEAD",
 			oid_to_hex(&options.onto->object.oid));
-		reset_head(NULL, "Fast-forwarded", options.head_name, 0,
-			   "HEAD", msg.buf);
+		reset_head(the_repository, NULL, "Fast-forwarded", options.head_name,
+			   RESET_HEAD_REFS_ONLY, "HEAD", msg.buf,
+			   DEFAULT_REFLOG_ACTION);
 		strbuf_release(&msg);
 		ret = !!finish_rebase(&options);
 		goto cleanup;
@@ -1572,9 +2067,10 @@ int cmd_rebase(int argc, const char **argv, const char *prefix)
 	options.revisions = revisions.buf;
 
 run_rebase:
-	ret = !!run_specific_rebase(&options);
+	ret = !!run_specific_rebase(&options, action);
 
 cleanup:
+	strbuf_release(&buf);
 	strbuf_release(&revisions);
 	free(options.head_name);
 	free(options.gpg_sign_opt);