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

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

1 files changed, 5295 insertions, 0 deletions

diff --git a/third_party/git/sequencer.c b/third_party/git/sequencer.c
new file mode 100644
index 0000000000..34ebf8ed94
--- /dev/null
+++ b/third_party/git/sequencer.c
@@ -0,0 +1,5295 @@
+#include "cache.h"
+#include "config.h"
+#include "lockfile.h"
+#include "dir.h"
+#include "object-store.h"
+#include "object.h"
+#include "commit.h"
+#include "sequencer.h"
+#include "tag.h"
+#include "run-command.h"
+#include "exec-cmd.h"
+#include "utf8.h"
+#include "cache-tree.h"
+#include "diff.h"
+#include "revision.h"
+#include "rerere.h"
+#include "merge-recursive.h"
+#include "refs.h"
+#include "argv-array.h"
+#include "quote.h"
+#include "trailer.h"
+#include "log-tree.h"
+#include "wt-status.h"
+#include "hashmap.h"
+#include "notes-utils.h"
+#include "sigchain.h"
+#include "unpack-trees.h"
+#include "worktree.h"
+#include "oidmap.h"
+#include "oidset.h"
+#include "commit-slab.h"
+#include "alias.h"
+#include "commit-reach.h"
+#include "rebase-interactive.h"
+
+#define GIT_REFLOG_ACTION "GIT_REFLOG_ACTION"
+
+static const char sign_off_header[] = "Signed-off-by: ";
+static const char cherry_picked_prefix[] = "(cherry picked from commit ";
+
+GIT_PATH_FUNC(git_path_commit_editmsg, "COMMIT_EDITMSG")
+
+GIT_PATH_FUNC(git_path_seq_dir, "sequencer")
+
+static GIT_PATH_FUNC(git_path_todo_file, "sequencer/todo")
+static GIT_PATH_FUNC(git_path_opts_file, "sequencer/opts")
+static GIT_PATH_FUNC(git_path_head_file, "sequencer/head")
+static GIT_PATH_FUNC(git_path_abort_safety_file, "sequencer/abort-safety")
+
+static GIT_PATH_FUNC(rebase_path, "rebase-merge")
+/*
+ * The file containing rebase commands, comments, and empty lines.
+ * This file is created by "git rebase -i" then edited by the user. As
+ * the lines are processed, they are removed from the front of this
+ * file and written to the tail of 'done'.
+ */
+GIT_PATH_FUNC(rebase_path_todo, "rebase-merge/git-rebase-todo")
+GIT_PATH_FUNC(rebase_path_todo_backup, "rebase-merge/git-rebase-todo.backup")
+
+/*
+ * The rebase command lines that have already been processed. A line
+ * is moved here when it is first handled, before any associated user
+ * actions.
+ */
+static GIT_PATH_FUNC(rebase_path_done, "rebase-merge/done")
+/*
+ * The file to keep track of how many commands were already processed (e.g.
+ * for the prompt).
+ */
+static GIT_PATH_FUNC(rebase_path_msgnum, "rebase-merge/msgnum")
+/*
+ * The file to keep track of how many commands are to be processed in total
+ * (e.g. for the prompt).
+ */
+static GIT_PATH_FUNC(rebase_path_msgtotal, "rebase-merge/end")
+/*
+ * The commit message that is planned to be used for any changes that
+ * need to be committed following a user interaction.
+ */
+static GIT_PATH_FUNC(rebase_path_message, "rebase-merge/message")
+/*
+ * The file into which is accumulated the suggested commit message for
+ * squash/fixup commands. When the first of a series of squash/fixups
+ * is seen, the file is created and the commit message from the
+ * previous commit and from the first squash/fixup commit are written
+ * to it. The commit message for each subsequent squash/fixup commit
+ * is appended to the file as it is processed.
+ */
+static GIT_PATH_FUNC(rebase_path_squash_msg, "rebase-merge/message-squash")
+/*
+ * If the current series of squash/fixups has not yet included a squash
+ * command, then this file exists and holds the commit message of the
+ * original "pick" commit.  (If the series ends without a "squash"
+ * command, then this can be used as the commit message of the combined
+ * commit without opening the editor.)
+ */
+static GIT_PATH_FUNC(rebase_path_fixup_msg, "rebase-merge/message-fixup")
+/*
+ * This file contains the list fixup/squash commands that have been
+ * accumulated into message-fixup or message-squash so far.
+ */
+static GIT_PATH_FUNC(rebase_path_current_fixups, "rebase-merge/current-fixups")
+/*
+ * A script to set the GIT_AUTHOR_NAME, GIT_AUTHOR_EMAIL, and
+ * GIT_AUTHOR_DATE that will be used for the commit that is currently
+ * being rebased.
+ */
+static GIT_PATH_FUNC(rebase_path_author_script, "rebase-merge/author-script")
+/*
+ * When an "edit" rebase command is being processed, the SHA1 of the
+ * commit to be edited is recorded in this file.  When "git rebase
+ * --continue" is executed, if there are any staged changes then they
+ * will be amended to the HEAD commit, but only provided the HEAD
+ * commit is still the commit to be edited.  When any other rebase
+ * command is processed, this file is deleted.
+ */
+static GIT_PATH_FUNC(rebase_path_amend, "rebase-merge/amend")
+/*
+ * When we stop at a given patch via the "edit" command, this file contains
+ * the abbreviated commit name of the corresponding patch.
+ */
+static GIT_PATH_FUNC(rebase_path_stopped_sha, "rebase-merge/stopped-sha")
+/*
+ * For the post-rewrite hook, we make a list of rewritten commits and
+ * their new sha1s.  The rewritten-pending list keeps the sha1s of
+ * commits that have been processed, but not committed yet,
+ * e.g. because they are waiting for a 'squash' command.
+ */
+static GIT_PATH_FUNC(rebase_path_rewritten_list, "rebase-merge/rewritten-list")
+static GIT_PATH_FUNC(rebase_path_rewritten_pending,
+	"rebase-merge/rewritten-pending")
+
+/*
+ * The path of the file containig the OID of the "squash onto" commit, i.e.
+ * the dummy commit used for `reset [new root]`.
+ */
+static GIT_PATH_FUNC(rebase_path_squash_onto, "rebase-merge/squash-onto")
+
+/*
+ * The path of the file listing refs that need to be deleted after the rebase
+ * finishes. This is used by the `label` command to record the need for cleanup.
+ */
+static GIT_PATH_FUNC(rebase_path_refs_to_delete, "rebase-merge/refs-to-delete")
+
+/*
+ * The following files are written by git-rebase just after parsing the
+ * command-line.
+ */
+static GIT_PATH_FUNC(rebase_path_gpg_sign_opt, "rebase-merge/gpg_sign_opt")
+static GIT_PATH_FUNC(rebase_path_orig_head, "rebase-merge/orig-head")
+static GIT_PATH_FUNC(rebase_path_verbose, "rebase-merge/verbose")
+static GIT_PATH_FUNC(rebase_path_quiet, "rebase-merge/quiet")
+static GIT_PATH_FUNC(rebase_path_signoff, "rebase-merge/signoff")
+static GIT_PATH_FUNC(rebase_path_head_name, "rebase-merge/head-name")
+static GIT_PATH_FUNC(rebase_path_onto, "rebase-merge/onto")
+static GIT_PATH_FUNC(rebase_path_autostash, "rebase-merge/autostash")
+static GIT_PATH_FUNC(rebase_path_strategy, "rebase-merge/strategy")
+static GIT_PATH_FUNC(rebase_path_strategy_opts, "rebase-merge/strategy_opts")
+static GIT_PATH_FUNC(rebase_path_allow_rerere_autoupdate, "rebase-merge/allow_rerere_autoupdate")
+static GIT_PATH_FUNC(rebase_path_reschedule_failed_exec, "rebase-merge/reschedule-failed-exec")
+
+static int git_sequencer_config(const char *k, const char *v, void *cb)
+{
+	struct replay_opts *opts = cb;
+	int status;
+
+	if (!strcmp(k, "commit.cleanup")) {
+		const char *s;
+
+		status = git_config_string(&s, k, v);
+		if (status)
+			return status;
+
+		if (!strcmp(s, "verbatim")) {
+			opts->default_msg_cleanup = COMMIT_MSG_CLEANUP_NONE;
+			opts->explicit_cleanup = 1;
+		} else if (!strcmp(s, "whitespace")) {
+			opts->default_msg_cleanup = COMMIT_MSG_CLEANUP_SPACE;
+			opts->explicit_cleanup = 1;
+		} else if (!strcmp(s, "strip")) {
+			opts->default_msg_cleanup = COMMIT_MSG_CLEANUP_ALL;
+			opts->explicit_cleanup = 1;
+		} else if (!strcmp(s, "scissors")) {
+			opts->default_msg_cleanup = COMMIT_MSG_CLEANUP_SCISSORS;
+			opts->explicit_cleanup = 1;
+		} else {
+			warning(_("invalid commit message cleanup mode '%s'"),
+				  s);
+		}
+
+		free((char *)s);
+		return status;
+	}
+
+	if (!strcmp(k, "commit.gpgsign")) {
+		opts->gpg_sign = git_config_bool(k, v) ? xstrdup("") : NULL;
+		return 0;
+	}
+
+	status = git_gpg_config(k, v, NULL);
+	if (status)
+		return status;
+
+	return git_diff_basic_config(k, v, NULL);
+}
+
+void sequencer_init_config(struct replay_opts *opts)
+{
+	opts->default_msg_cleanup = COMMIT_MSG_CLEANUP_NONE;
+	git_config(git_sequencer_config, opts);
+}
+
+static inline int is_rebase_i(const struct replay_opts *opts)
+{
+	return opts->action == REPLAY_INTERACTIVE_REBASE;
+}
+
+static const char *get_dir(const struct replay_opts *opts)
+{
+	if (is_rebase_i(opts))
+		return rebase_path();
+	return git_path_seq_dir();
+}
+
+static const char *get_todo_path(const struct replay_opts *opts)
+{
+	if (is_rebase_i(opts))
+		return rebase_path_todo();
+	return git_path_todo_file();
+}
+
+/*
+ * Returns 0 for non-conforming footer
+ * Returns 1 for conforming footer
+ * Returns 2 when sob exists within conforming footer
+ * Returns 3 when sob exists within conforming footer as last entry
+ */
+static int has_conforming_footer(struct strbuf *sb, struct strbuf *sob,
+	size_t ignore_footer)
+{
+	struct process_trailer_options opts = PROCESS_TRAILER_OPTIONS_INIT;
+	struct trailer_info info;
+	size_t i;
+	int found_sob = 0, found_sob_last = 0;
+
+	opts.no_divider = 1;
+
+	trailer_info_get(&info, sb->buf, &opts);
+
+	if (info.trailer_start == info.trailer_end)
+		return 0;
+
+	for (i = 0; i < info.trailer_nr; i++)
+		if (sob && !strncmp(info.trailers[i], sob->buf, sob->len)) {
+			found_sob = 1;
+			if (i == info.trailer_nr - 1)
+				found_sob_last = 1;
+		}
+
+	trailer_info_release(&info);
+
+	if (found_sob_last)
+		return 3;
+	if (found_sob)
+		return 2;
+	return 1;
+}
+
+static const char *gpg_sign_opt_quoted(struct replay_opts *opts)
+{
+	static struct strbuf buf = STRBUF_INIT;
+
+	strbuf_reset(&buf);
+	if (opts->gpg_sign)
+		sq_quotef(&buf, "-S%s", opts->gpg_sign);
+	return buf.buf;
+}
+
+int sequencer_remove_state(struct replay_opts *opts)
+{
+	struct strbuf buf = STRBUF_INIT;
+	int i, ret = 0;
+
+	if (is_rebase_i(opts) &&
+	    strbuf_read_file(&buf, rebase_path_refs_to_delete(), 0) > 0) {
+		char *p = buf.buf;
+		while (*p) {
+			char *eol = strchr(p, '\n');
+			if (eol)
+				*eol = '\0';
+			if (delete_ref("(rebase -i) cleanup", p, NULL, 0) < 0) {
+				warning(_("could not delete '%s'"), p);
+				ret = -1;
+			}
+			if (!eol)
+				break;
+			p = eol + 1;
+		}
+	}
+
+	free(opts->gpg_sign);
+	free(opts->strategy);
+	for (i = 0; i < opts->xopts_nr; i++)
+		free(opts->xopts[i]);
+	free(opts->xopts);
+	strbuf_release(&opts->current_fixups);
+
+	strbuf_reset(&buf);
+	strbuf_addstr(&buf, get_dir(opts));
+	if (remove_dir_recursively(&buf, 0))
+		ret = error(_("could not remove '%s'"), buf.buf);
+	strbuf_release(&buf);
+
+	return ret;
+}
+
+static const char *action_name(const struct replay_opts *opts)
+{
+	switch (opts->action) {
+	case REPLAY_REVERT:
+		return N_("revert");
+	case REPLAY_PICK:
+		return N_("cherry-pick");
+	case REPLAY_INTERACTIVE_REBASE:
+		return N_("rebase -i");
+	}
+	die(_("unknown action: %d"), opts->action);
+}
+
+struct commit_message {
+	char *parent_label;
+	char *label;
+	char *subject;
+	const char *message;
+};
+
+static const char *short_commit_name(struct commit *commit)
+{
+	return find_unique_abbrev(&commit->object.oid, DEFAULT_ABBREV);
+}
+
+static int get_message(struct commit *commit, struct commit_message *out)
+{
+	const char *abbrev, *subject;
+	int subject_len;
+
+	out->message = logmsg_reencode(commit, NULL, get_commit_output_encoding());
+	abbrev = short_commit_name(commit);
+
+	subject_len = find_commit_subject(out->message, &subject);
+
+	out->subject = xmemdupz(subject, subject_len);
+	out->label = xstrfmt("%s... %s", abbrev, out->subject);
+	out->parent_label = xstrfmt("parent of %s", out->label);
+
+	return 0;
+}
+
+static void free_message(struct commit *commit, struct commit_message *msg)
+{
+	free(msg->parent_label);
+	free(msg->label);
+	free(msg->subject);
+	unuse_commit_buffer(commit, msg->message);
+}
+
+static void print_advice(struct repository *r, int show_hint,
+			 struct replay_opts *opts)
+{
+	char *msg = getenv("GIT_CHERRY_PICK_HELP");
+
+	if (msg) {
+		fprintf(stderr, "%s\n", msg);
+		/*
+		 * A conflict has occurred but the porcelain
+		 * (typically rebase --interactive) wants to take care
+		 * of the commit itself so remove CHERRY_PICK_HEAD
+		 */
+		unlink(git_path_cherry_pick_head(r));
+		return;
+	}
+
+	if (show_hint) {
+		if (opts->no_commit)
+			advise(_("after resolving the conflicts, mark the corrected paths\n"
+				 "with 'git add <paths>' or 'git rm <paths>'"));
+		else
+			advise(_("after resolving the conflicts, mark the corrected paths\n"
+				 "with 'git add <paths>' or 'git rm <paths>'\n"
+				 "and commit the result with 'git commit'"));
+	}
+}
+
+static int write_message(const void *buf, size_t len, const char *filename,
+			 int append_eol)
+{
+	struct lock_file msg_file = LOCK_INIT;
+
+	int msg_fd = hold_lock_file_for_update(&msg_file, filename, 0);
+	if (msg_fd < 0)
+		return error_errno(_("could not lock '%s'"), filename);
+	if (write_in_full(msg_fd, buf, len) < 0) {
+		error_errno(_("could not write to '%s'"), filename);
+		rollback_lock_file(&msg_file);
+		return -1;
+	}
+	if (append_eol && write(msg_fd, "\n", 1) < 0) {
+		error_errno(_("could not write eol to '%s'"), filename);
+		rollback_lock_file(&msg_file);
+		return -1;
+	}
+	if (commit_lock_file(&msg_file) < 0)
+		return error(_("failed to finalize '%s'"), filename);
+
+	return 0;
+}
+
+/*
+ * Reads a file that was presumably written by a shell script, i.e. with an
+ * end-of-line marker that needs to be stripped.
+ *
+ * Note that only the last end-of-line marker is stripped, consistent with the
+ * behavior of "$(cat path)" in a shell script.
+ *
+ * Returns 1 if the file was read, 0 if it could not be read or does not exist.
+ */
+static int read_oneliner(struct strbuf *buf,
+	const char *path, int skip_if_empty)
+{
+	int orig_len = buf->len;
+
+	if (!file_exists(path))
+		return 0;
+
+	if (strbuf_read_file(buf, path, 0) < 0) {
+		warning_errno(_("could not read '%s'"), path);
+		return 0;
+	}
+
+	if (buf->len > orig_len && buf->buf[buf->len - 1] == '\n') {
+		if (--buf->len > orig_len && buf->buf[buf->len - 1] == '\r')
+			--buf->len;
+		buf->buf[buf->len] = '\0';
+	}
+
+	if (skip_if_empty && buf->len == orig_len)
+		return 0;
+
+	return 1;
+}
+
+static struct tree *empty_tree(struct repository *r)
+{
+	return lookup_tree(r, the_hash_algo->empty_tree);
+}
+
+static int error_dirty_index(struct repository *repo, struct replay_opts *opts)
+{
+	if (repo_read_index_unmerged(repo))
+		return error_resolve_conflict(_(action_name(opts)));
+
+	error(_("your local changes would be overwritten by %s."),
+		_(action_name(opts)));
+
+	if (advice_commit_before_merge)
+		advise(_("commit your changes or stash them to proceed."));
+	return -1;
+}
+
+static void update_abort_safety_file(void)
+{
+	struct object_id head;
+
+	/* Do nothing on a single-pick */
+	if (!file_exists(git_path_seq_dir()))
+		return;
+
+	if (!get_oid("HEAD", &head))
+		write_file(git_path_abort_safety_file(), "%s", oid_to_hex(&head));
+	else
+		write_file(git_path_abort_safety_file(), "%s", "");
+}
+
+static int fast_forward_to(struct repository *r,
+			   const struct object_id *to,
+			   const struct object_id *from,
+			   int unborn,
+			   struct replay_opts *opts)
+{
+	struct ref_transaction *transaction;
+	struct strbuf sb = STRBUF_INIT;
+	struct strbuf err = STRBUF_INIT;
+
+	repo_read_index(r);
+	if (checkout_fast_forward(r, from, to, 1))
+		return -1; /* the callee should have complained already */
+
+	strbuf_addf(&sb, _("%s: fast-forward"), _(action_name(opts)));
+
+	transaction = ref_transaction_begin(&err);
+	if (!transaction ||
+	    ref_transaction_update(transaction, "HEAD",
+				   to, unborn && !is_rebase_i(opts) ?
+				   &null_oid : from,
+				   0, sb.buf, &err) ||
+	    ref_transaction_commit(transaction, &err)) {
+		ref_transaction_free(transaction);
+		error("%s", err.buf);
+		strbuf_release(&sb);
+		strbuf_release(&err);
+		return -1;
+	}
+
+	strbuf_release(&sb);
+	strbuf_release(&err);
+	ref_transaction_free(transaction);
+	update_abort_safety_file();
+	return 0;
+}
+
+enum commit_msg_cleanup_mode get_cleanup_mode(const char *cleanup_arg,
+	int use_editor)
+{
+	if (!cleanup_arg || !strcmp(cleanup_arg, "default"))
+		return use_editor ? COMMIT_MSG_CLEANUP_ALL :
+				    COMMIT_MSG_CLEANUP_SPACE;
+	else if (!strcmp(cleanup_arg, "verbatim"))
+		return COMMIT_MSG_CLEANUP_NONE;
+	else if (!strcmp(cleanup_arg, "whitespace"))
+		return COMMIT_MSG_CLEANUP_SPACE;
+	else if (!strcmp(cleanup_arg, "strip"))
+		return COMMIT_MSG_CLEANUP_ALL;
+	else if (!strcmp(cleanup_arg, "scissors"))
+		return use_editor ? COMMIT_MSG_CLEANUP_SCISSORS :
+				    COMMIT_MSG_CLEANUP_SPACE;
+	else
+		die(_("Invalid cleanup mode %s"), cleanup_arg);
+}
+
+/*
+ * NB using int rather than enum cleanup_mode to stop clang's
+ * -Wtautological-constant-out-of-range-compare complaining that the comparison
+ * is always true.
+ */
+static const char *describe_cleanup_mode(int cleanup_mode)
+{
+	static const char *modes[] = { "whitespace",
+				       "verbatim",
+				       "scissors",
+				       "strip" };
+
+	if (cleanup_mode < ARRAY_SIZE(modes))
+		return modes[cleanup_mode];
+
+	BUG("invalid cleanup_mode provided (%d)", cleanup_mode);
+}
+
+void append_conflicts_hint(struct index_state *istate,
+	struct strbuf *msgbuf, enum commit_msg_cleanup_mode cleanup_mode)
+{
+	int i;
+
+	if (cleanup_mode == COMMIT_MSG_CLEANUP_SCISSORS) {
+		strbuf_addch(msgbuf, '\n');
+		wt_status_append_cut_line(msgbuf);
+		strbuf_addch(msgbuf, comment_line_char);
+	}
+
+	strbuf_addch(msgbuf, '\n');
+	strbuf_commented_addf(msgbuf, "Conflicts:\n");
+	for (i = 0; i < istate->cache_nr;) {
+		const struct cache_entry *ce = istate->cache[i++];
+		if (ce_stage(ce)) {
+			strbuf_commented_addf(msgbuf, "\t%s\n", ce->name);
+			while (i < istate->cache_nr &&
+			       !strcmp(ce->name, istate->cache[i]->name))
+				i++;
+		}
+	}
+}
+
+static int do_recursive_merge(struct repository *r,
+			      struct commit *base, struct commit *next,
+			      const char *base_label, const char *next_label,
+			      struct object_id *head, struct strbuf *msgbuf,
+			      struct replay_opts *opts)
+{
+	struct merge_options o;
+	struct tree *result, *next_tree, *base_tree, *head_tree;
+	int clean;
+	char **xopt;
+	struct lock_file index_lock = LOCK_INIT;
+
+	if (repo_hold_locked_index(r, &index_lock, LOCK_REPORT_ON_ERROR) < 0)
+		return -1;
+
+	repo_read_index(r);
+
+	init_merge_options(&o, r);
+	o.ancestor = base ? base_label : "(empty tree)";
+	o.branch1 = "HEAD";
+	o.branch2 = next ? next_label : "(empty tree)";
+	if (is_rebase_i(opts))
+		o.buffer_output = 2;
+	o.show_rename_progress = 1;
+
+	head_tree = parse_tree_indirect(head);
+	next_tree = next ? get_commit_tree(next) : empty_tree(r);
+	base_tree = base ? get_commit_tree(base) : empty_tree(r);
+
+	for (xopt = opts->xopts; xopt != opts->xopts + opts->xopts_nr; xopt++)
+		parse_merge_opt(&o, *xopt);
+
+	clean = merge_trees(&o,
+			    head_tree,
+			    next_tree, base_tree, &result);
+	if (is_rebase_i(opts) && clean <= 0)
+		fputs(o.obuf.buf, stdout);
+	strbuf_release(&o.obuf);
+	diff_warn_rename_limit("merge.renamelimit", o.needed_rename_limit, 0);
+	if (clean < 0) {
+		rollback_lock_file(&index_lock);
+		return clean;
+	}
+
+	if (write_locked_index(r->index, &index_lock,
+			       COMMIT_LOCK | SKIP_IF_UNCHANGED))
+		/*
+		 * TRANSLATORS: %s will be "revert", "cherry-pick" or
+		 * "rebase -i".
+		 */
+		return error(_("%s: Unable to write new index file"),
+			_(action_name(opts)));
+
+	if (!clean)
+		append_conflicts_hint(r->index, msgbuf,
+				      opts->default_msg_cleanup);
+
+	return !clean;
+}
+
+static struct object_id *get_cache_tree_oid(struct index_state *istate)
+{
+	if (!istate->cache_tree)
+		istate->cache_tree = cache_tree();
+
+	if (!cache_tree_fully_valid(istate->cache_tree))
+		if (cache_tree_update(istate, 0)) {
+			error(_("unable to update cache tree"));
+			return NULL;
+		}
+
+	return &istate->cache_tree->oid;
+}
+
+static int is_index_unchanged(struct repository *r)
+{
+	struct object_id head_oid, *cache_tree_oid;
+	struct commit *head_commit;
+	struct index_state *istate = r->index;
+
+	if (!resolve_ref_unsafe("HEAD", RESOLVE_REF_READING, &head_oid, NULL))
+		return error(_("could not resolve HEAD commit"));
+
+	head_commit = lookup_commit(r, &head_oid);
+
+	/*
+	 * If head_commit is NULL, check_commit, called from
+	 * lookup_commit, would have indicated that head_commit is not
+	 * a commit object already.  parse_commit() will return failure
+	 * without further complaints in such a case.  Otherwise, if
+	 * the commit is invalid, parse_commit() will complain.  So
+	 * there is nothing for us to say here.  Just return failure.
+	 */
+	if (parse_commit(head_commit))
+		return -1;
+
+	if (!(cache_tree_oid = get_cache_tree_oid(istate)))
+		return -1;
+
+	return oideq(cache_tree_oid, get_commit_tree_oid(head_commit));
+}
+
+static int write_author_script(const char *message)
+{
+	struct strbuf buf = STRBUF_INIT;
+	const char *eol;
+	int res;
+
+	for (;;)
+		if (!*message || starts_with(message, "\n")) {
+missing_author:
+			/* Missing 'author' line? */
+			unlink(rebase_path_author_script());
+			return 0;
+		} else if (skip_prefix(message, "author ", &message))
+			break;
+		else if ((eol = strchr(message, '\n')))
+			message = eol + 1;
+		else
+			goto missing_author;
+
+	strbuf_addstr(&buf, "GIT_AUTHOR_NAME='");
+	while (*message && *message != '\n' && *message != '\r')
+		if (skip_prefix(message, " <", &message))
+			break;
+		else if (*message != '\'')
+			strbuf_addch(&buf, *(message++));
+		else
+			strbuf_addf(&buf, "'\\%c'", *(message++));
+	strbuf_addstr(&buf, "'\nGIT_AUTHOR_EMAIL='");
+	while (*message && *message != '\n' && *message != '\r')
+		if (skip_prefix(message, "> ", &message))
+			break;
+		else if (*message != '\'')
+			strbuf_addch(&buf, *(message++));
+		else
+			strbuf_addf(&buf, "'\\%c'", *(message++));
+	strbuf_addstr(&buf, "'\nGIT_AUTHOR_DATE='@");
+	while (*message && *message != '\n' && *message != '\r')
+		if (*message != '\'')
+			strbuf_addch(&buf, *(message++));
+		else
+			strbuf_addf(&buf, "'\\%c'", *(message++));
+	strbuf_addch(&buf, '\'');
+	res = write_message(buf.buf, buf.len, rebase_path_author_script(), 1);
+	strbuf_release(&buf);
+	return res;
+}
+
+/**
+ * Take a series of KEY='VALUE' lines where VALUE part is
+ * sq-quoted, and append <KEY, VALUE> at the end of the string list
+ */
+static int parse_key_value_squoted(char *buf, struct string_list *list)
+{
+	while (*buf) {
+		struct string_list_item *item;
+		char *np;
+		char *cp = strchr(buf, '=');
+		if (!cp) {
+			np = strchrnul(buf, '\n');
+			return error(_("no key present in '%.*s'"),
+				     (int) (np - buf), buf);
+		}
+		np = strchrnul(cp, '\n');
+		*cp++ = '\0';
+		item = string_list_append(list, buf);
+
+		buf = np + (*np == '\n');
+		*np = '\0';
+		cp = sq_dequote(cp);
+		if (!cp)
+			return error(_("unable to dequote value of '%s'"),
+				     item->string);
+		item->util = xstrdup(cp);
+	}
+	return 0;
+}
+
+/**
+ * Reads and parses the state directory's "author-script" file, and sets name,
+ * email and date accordingly.
+ * Returns 0 on success, -1 if the file could not be parsed.
+ *
+ * The author script is of the format:
+ *
+ *	GIT_AUTHOR_NAME='$author_name'
+ *	GIT_AUTHOR_EMAIL='$author_email'
+ *	GIT_AUTHOR_DATE='$author_date'
+ *
+ * where $author_name, $author_email and $author_date are quoted. We are strict
+ * with our parsing, as the file was meant to be eval'd in the now-removed
+ * git-am.sh/git-rebase--interactive.sh scripts, and thus if the file differs
+ * from what this function expects, it is better to bail out than to do
+ * something that the user does not expect.
+ */
+int read_author_script(const char *path, char **name, char **email, char **date,
+		       int allow_missing)
+{
+	struct strbuf buf = STRBUF_INIT;
+	struct string_list kv = STRING_LIST_INIT_DUP;
+	int retval = -1; /* assume failure */
+	int i, name_i = -2, email_i = -2, date_i = -2, err = 0;
+
+	if (strbuf_read_file(&buf, path, 256) <= 0) {
+		strbuf_release(&buf);
+		if (errno == ENOENT && allow_missing)
+			return 0;
+		else
+			return error_errno(_("could not open '%s' for reading"),
+					   path);
+	}
+
+	if (parse_key_value_squoted(buf.buf, &kv))
+		goto finish;
+
+	for (i = 0; i < kv.nr; i++) {
+		if (!strcmp(kv.items[i].string, "GIT_AUTHOR_NAME")) {
+			if (name_i != -2)
+				name_i = error(_("'GIT_AUTHOR_NAME' already given"));
+			else
+				name_i = i;
+		} else if (!strcmp(kv.items[i].string, "GIT_AUTHOR_EMAIL")) {
+			if (email_i != -2)
+				email_i = error(_("'GIT_AUTHOR_EMAIL' already given"));
+			else
+				email_i = i;
+		} else if (!strcmp(kv.items[i].string, "GIT_AUTHOR_DATE")) {
+			if (date_i != -2)
+				date_i = error(_("'GIT_AUTHOR_DATE' already given"));
+			else
+				date_i = i;
+		} else {
+			err = error(_("unknown variable '%s'"),
+				    kv.items[i].string);
+		}
+	}
+	if (name_i == -2)
+		error(_("missing 'GIT_AUTHOR_NAME'"));
+	if (email_i == -2)
+		error(_("missing 'GIT_AUTHOR_EMAIL'"));
+	if (date_i == -2)
+		error(_("missing 'GIT_AUTHOR_DATE'"));
+	if (date_i < 0 || email_i < 0 || date_i < 0 || err)
+		goto finish;
+	*name = kv.items[name_i].util;
+	*email = kv.items[email_i].util;
+	*date = kv.items[date_i].util;
+	retval = 0;
+finish:
+	string_list_clear(&kv, !!retval);
+	strbuf_release(&buf);
+	return retval;
+}
+
+/*
+ * Read a GIT_AUTHOR_NAME, GIT_AUTHOR_EMAIL AND GIT_AUTHOR_DATE from a
+ * file with shell quoting into struct argv_array. Returns -1 on
+ * error, 0 otherwise.
+ */
+static int read_env_script(struct argv_array *env)
+{
+	char *name, *email, *date;
+
+	if (read_author_script(rebase_path_author_script(),
+			       &name, &email, &date, 0))
+		return -1;
+
+	argv_array_pushf(env, "GIT_AUTHOR_NAME=%s", name);
+	argv_array_pushf(env, "GIT_AUTHOR_EMAIL=%s", email);
+	argv_array_pushf(env, "GIT_AUTHOR_DATE=%s", date);
+	free(name);
+	free(email);
+	free(date);
+
+	return 0;
+}
+
+static char *get_author(const char *message)
+{
+	size_t len;
+	const char *a;
+
+	a = find_commit_header(message, "author", &len);
+	if (a)
+		return xmemdupz(a, len);
+
+	return NULL;
+}
+
+/* Read author-script and return an ident line (author <email> timestamp) */
+static const char *read_author_ident(struct strbuf *buf)
+{
+	struct strbuf out = STRBUF_INIT;
+	char *name, *email, *date;
+
+	if (read_author_script(rebase_path_author_script(),
+			       &name, &email, &date, 0))
+		return NULL;
+
+	/* validate date since fmt_ident() will die() on bad value */
+	if (parse_date(date, &out)){
+		warning(_("invalid date format '%s' in '%s'"),
+			date, rebase_path_author_script());
+		strbuf_release(&out);
+		return NULL;
+	}
+
+	strbuf_reset(&out);
+	strbuf_addstr(&out, fmt_ident(name, email, WANT_AUTHOR_IDENT, date, 0));
+	strbuf_swap(buf, &out);
+	strbuf_release(&out);
+	free(name);
+	free(email);
+	free(date);
+	return buf->buf;
+}
+
+static const char staged_changes_advice[] =
+N_("you have staged changes in your working tree\n"
+"If these changes are meant to be squashed into the previous commit, run:\n"
+"\n"
+"  git commit --amend %s\n"
+"\n"
+"If they are meant to go into a new commit, run:\n"
+"\n"
+"  git commit %s\n"
+"\n"
+"In both cases, once you're done, continue with:\n"
+"\n"
+"  git rebase --continue\n");
+
+#define ALLOW_EMPTY (1<<0)
+#define EDIT_MSG    (1<<1)
+#define AMEND_MSG   (1<<2)
+#define CLEANUP_MSG (1<<3)
+#define VERIFY_MSG  (1<<4)
+#define CREATE_ROOT_COMMIT (1<<5)
+
+static int run_command_silent_on_success(struct child_process *cmd)
+{
+	struct strbuf buf = STRBUF_INIT;
+	int rc;
+
+	cmd->stdout_to_stderr = 1;
+	rc = pipe_command(cmd,
+			  NULL, 0,
+			  NULL, 0,
+			  &buf, 0);
+
+	if (rc)
+		fputs(buf.buf, stderr);
+	strbuf_release(&buf);
+	return rc;
+}
+
+/*
+ * If we are cherry-pick, and if the merge did not result in
+ * hand-editing, we will hit this commit and inherit the original
+ * author date and name.
+ *
+ * If we are revert, or if our cherry-pick results in a hand merge,
+ * we had better say that the current user is responsible for that.
+ *
+ * An exception is when run_git_commit() is called during an
+ * interactive rebase: in that case, we will want to retain the
+ * author metadata.
+ */
+static int run_git_commit(struct repository *r,
+			  const char *defmsg,
+			  struct replay_opts *opts,
+			  unsigned int flags)
+{
+	struct child_process cmd = CHILD_PROCESS_INIT;
+
+	if ((flags & CREATE_ROOT_COMMIT) && !(flags & AMEND_MSG)) {
+		struct strbuf msg = STRBUF_INIT, script = STRBUF_INIT;
+		const char *author = NULL;
+		struct object_id root_commit, *cache_tree_oid;
+		int res = 0;
+
+		if (is_rebase_i(opts)) {
+			author = read_author_ident(&script);
+			if (!author) {
+				strbuf_release(&script);
+				return -1;
+			}
+		}
+
+		if (!defmsg)
+			BUG("root commit without message");
+
+		if (!(cache_tree_oid = get_cache_tree_oid(r->index)))
+			res = -1;
+
+		if (!res)
+			res = strbuf_read_file(&msg, defmsg, 0);
+
+		if (res <= 0)
+			res = error_errno(_("could not read '%s'"), defmsg);
+		else
+			res = commit_tree(msg.buf, msg.len, cache_tree_oid,
+					  NULL, &root_commit, author,
+					  opts->gpg_sign);
+
+		strbuf_release(&msg);
+		strbuf_release(&script);
+		if (!res) {
+			update_ref(NULL, "CHERRY_PICK_HEAD", &root_commit, NULL,
+				   REF_NO_DEREF, UPDATE_REFS_MSG_ON_ERR);
+			res = update_ref(NULL, "HEAD", &root_commit, NULL, 0,
+					 UPDATE_REFS_MSG_ON_ERR);
+		}
+		return res < 0 ? error(_("writing root commit")) : 0;
+	}
+
+	cmd.git_cmd = 1;
+
+	if (is_rebase_i(opts) && read_env_script(&cmd.env_array)) {
+		const char *gpg_opt = gpg_sign_opt_quoted(opts);
+
+		return error(_(staged_changes_advice),
+			     gpg_opt, gpg_opt);
+	}
+
+	argv_array_push(&cmd.args, "commit");
+
+	if (!(flags & VERIFY_MSG))
+		argv_array_push(&cmd.args, "-n");
+	if ((flags & AMEND_MSG))
+		argv_array_push(&cmd.args, "--amend");
+	if (opts->gpg_sign)
+		argv_array_pushf(&cmd.args, "-S%s", opts->gpg_sign);
+	if (defmsg)
+		argv_array_pushl(&cmd.args, "-F", defmsg, NULL);
+	else if (!(flags & EDIT_MSG))
+		argv_array_pushl(&cmd.args, "-C", "HEAD", NULL);
+	if ((flags & CLEANUP_MSG))
+		argv_array_push(&cmd.args, "--cleanup=strip");
+	if ((flags & EDIT_MSG))
+		argv_array_push(&cmd.args, "-e");
+	else if (!(flags & CLEANUP_MSG) &&
+		 !opts->signoff && !opts->record_origin &&
+		 !opts->explicit_cleanup)
+		argv_array_push(&cmd.args, "--cleanup=verbatim");
+
+	if ((flags & ALLOW_EMPTY))
+		argv_array_push(&cmd.args, "--allow-empty");
+
+	if (!(flags & EDIT_MSG))
+		argv_array_push(&cmd.args, "--allow-empty-message");
+
+	if (is_rebase_i(opts) && !(flags & EDIT_MSG))
+		return run_command_silent_on_success(&cmd);
+	else
+		return run_command(&cmd);
+}
+
+static int rest_is_empty(const struct strbuf *sb, int start)
+{
+	int i, eol;
+	const char *nl;
+
+	/* Check if the rest is just whitespace and Signed-off-by's. */
+	for (i = start; i < sb->len; i++) {
+		nl = memchr(sb->buf + i, '\n', sb->len - i);
+		if (nl)
+			eol = nl - sb->buf;
+		else
+			eol = sb->len;
+
+		if (strlen(sign_off_header) <= eol - i &&
+		    starts_with(sb->buf + i, sign_off_header)) {
+			i = eol;
+			continue;
+		}
+		while (i < eol)
+			if (!isspace(sb->buf[i++]))
+				return 0;
+	}
+
+	return 1;
+}
+
+void cleanup_message(struct strbuf *msgbuf,
+	enum commit_msg_cleanup_mode cleanup_mode, int verbose)
+{
+	if (verbose || /* Truncate the message just before the diff, if any. */
+	    cleanup_mode == COMMIT_MSG_CLEANUP_SCISSORS)
+		strbuf_setlen(msgbuf, wt_status_locate_end(msgbuf->buf, msgbuf->len));
+	if (cleanup_mode != COMMIT_MSG_CLEANUP_NONE)
+		strbuf_stripspace(msgbuf, cleanup_mode == COMMIT_MSG_CLEANUP_ALL);
+}
+
+/*
+ * Find out if the message in the strbuf contains only whitespace and
+ * Signed-off-by lines.
+ */
+int message_is_empty(const struct strbuf *sb,
+		     enum commit_msg_cleanup_mode cleanup_mode)
+{
+	if (cleanup_mode == COMMIT_MSG_CLEANUP_NONE && sb->len)
+		return 0;
+	return rest_is_empty(sb, 0);
+}
+
+/*
+ * See if the user edited the message in the editor or left what
+ * was in the template intact
+ */
+int template_untouched(const struct strbuf *sb, const char *template_file,
+		       enum commit_msg_cleanup_mode cleanup_mode)
+{
+	struct strbuf tmpl = STRBUF_INIT;
+	const char *start;
+
+	if (cleanup_mode == COMMIT_MSG_CLEANUP_NONE && sb->len)
+		return 0;
+
+	if (!template_file || strbuf_read_file(&tmpl, template_file, 0) <= 0)
+		return 0;
+
+	strbuf_stripspace(&tmpl, cleanup_mode == COMMIT_MSG_CLEANUP_ALL);
+	if (!skip_prefix(sb->buf, tmpl.buf, &start))
+		start = sb->buf;
+	strbuf_release(&tmpl);
+	return rest_is_empty(sb, start - sb->buf);
+}
+
+int update_head_with_reflog(const struct commit *old_head,
+			    const struct object_id *new_head,
+			    const char *action, const struct strbuf *msg,
+			    struct strbuf *err)
+{
+	struct ref_transaction *transaction;
+	struct strbuf sb = STRBUF_INIT;
+	const char *nl;
+	int ret = 0;
+
+	if (action) {
+		strbuf_addstr(&sb, action);
+		strbuf_addstr(&sb, ": ");
+	}
+
+	nl = strchr(msg->buf, '\n');
+	if (nl) {
+		strbuf_add(&sb, msg->buf, nl + 1 - msg->buf);
+	} else {
+		strbuf_addbuf(&sb, msg);
+		strbuf_addch(&sb, '\n');
+	}
+
+	transaction = ref_transaction_begin(err);
+	if (!transaction ||
+	    ref_transaction_update(transaction, "HEAD", new_head,
+				   old_head ? &old_head->object.oid : &null_oid,
+				   0, sb.buf, err) ||
+	    ref_transaction_commit(transaction, err)) {
+		ret = -1;
+	}
+	ref_transaction_free(transaction);
+	strbuf_release(&sb);
+
+	return ret;
+}
+
+static int run_rewrite_hook(const struct object_id *oldoid,
+			    const struct object_id *newoid)
+{
+	struct child_process proc = CHILD_PROCESS_INIT;
+	const char *argv[3];
+	int code;
+	struct strbuf sb = STRBUF_INIT;
+
+	argv[0] = find_hook("post-rewrite");
+	if (!argv[0])
+		return 0;
+
+	argv[1] = "amend";
+	argv[2] = NULL;
+
+	proc.argv = argv;
+	proc.in = -1;
+	proc.stdout_to_stderr = 1;
+	proc.trace2_hook_name = "post-rewrite";
+
+	code = start_command(&proc);
+	if (code)
+		return code;
+	strbuf_addf(&sb, "%s %s\n", oid_to_hex(oldoid), oid_to_hex(newoid));
+	sigchain_push(SIGPIPE, SIG_IGN);
+	write_in_full(proc.in, sb.buf, sb.len);
+	close(proc.in);
+	strbuf_release(&sb);
+	sigchain_pop(SIGPIPE);
+	return finish_command(&proc);
+}
+
+void commit_post_rewrite(struct repository *r,
+			 const struct commit *old_head,
+			 const struct object_id *new_head)
+{
+	struct notes_rewrite_cfg *cfg;
+
+	cfg = init_copy_notes_for_rewrite("amend");
+	if (cfg) {
+		/* we are amending, so old_head is not NULL */
+		copy_note_for_rewrite(cfg, &old_head->object.oid, new_head);
+		finish_copy_notes_for_rewrite(r, cfg, "Notes added by 'git commit --amend'");
+	}
+	run_rewrite_hook(&old_head->object.oid, new_head);
+}
+
+static int run_prepare_commit_msg_hook(struct repository *r,
+				       struct strbuf *msg,
+				       const char *commit)
+{
+	struct argv_array hook_env = ARGV_ARRAY_INIT;
+	int ret;
+	const char *name;
+
+	name = git_path_commit_editmsg();
+	if (write_message(msg->buf, msg->len, name, 0))
+		return -1;
+
+	argv_array_pushf(&hook_env, "GIT_INDEX_FILE=%s", r->index_file);
+	argv_array_push(&hook_env, "GIT_EDITOR=:");
+	if (commit)
+		ret = run_hook_le(hook_env.argv, "prepare-commit-msg", name,
+				  "commit", commit, NULL);
+	else
+		ret = run_hook_le(hook_env.argv, "prepare-commit-msg", name,
+				  "message", NULL);
+	if (ret)
+		ret = error(_("'prepare-commit-msg' hook failed"));
+	argv_array_clear(&hook_env);
+
+	return ret;
+}
+
+static const char implicit_ident_advice_noconfig[] =
+N_("Your name and email address were configured automatically based\n"
+"on your username and hostname. Please check that they are accurate.\n"
+"You can suppress this message by setting them explicitly. Run the\n"
+"following command and follow the instructions in your editor to edit\n"
+"your configuration file:\n"
+"\n"
+"    git config --global --edit\n"
+"\n"
+"After doing this, you may fix the identity used for this commit with:\n"
+"\n"
+"    git commit --amend --reset-author\n");
+
+static const char implicit_ident_advice_config[] =
+N_("Your name and email address were configured automatically based\n"
+"on your username and hostname. Please check that they are accurate.\n"
+"You can suppress this message by setting them explicitly:\n"
+"\n"
+"    git config --global user.name \"Your Name\"\n"
+"    git config --global user.email you@example.com\n"
+"\n"
+"After doing this, you may fix the identity used for this commit with:\n"
+"\n"
+"    git commit --amend --reset-author\n");
+
+static const char *implicit_ident_advice(void)
+{
+	char *user_config = expand_user_path("~/.gitconfig", 0);
+	char *xdg_config = xdg_config_home("config");
+	int config_exists = file_exists(user_config) || file_exists(xdg_config);
+
+	free(user_config);
+	free(xdg_config);
+
+	if (config_exists)
+		return _(implicit_ident_advice_config);
+	else
+		return _(implicit_ident_advice_noconfig);
+
+}
+
+void print_commit_summary(struct repository *r,
+			  const char *prefix,
+			  const struct object_id *oid,
+			  unsigned int flags)
+{
+	struct rev_info rev;
+	struct commit *commit;
+	struct strbuf format = STRBUF_INIT;
+	const char *head;
+	struct pretty_print_context pctx = {0};
+	struct strbuf author_ident = STRBUF_INIT;
+	struct strbuf committer_ident = STRBUF_INIT;
+
+	commit = lookup_commit(r, oid);
+	if (!commit)
+		die(_("couldn't look up newly created commit"));
+	if (parse_commit(commit))
+		die(_("could not parse newly created commit"));
+
+	strbuf_addstr(&format, "format:%h] %s");
+
+	format_commit_message(commit, "%an <%ae>", &author_ident, &pctx);
+	format_commit_message(commit, "%cn <%ce>", &committer_ident, &pctx);
+	if (strbuf_cmp(&author_ident, &committer_ident)) {
+		strbuf_addstr(&format, "\n Author: ");
+		strbuf_addbuf_percentquote(&format, &author_ident);
+	}
+	if (flags & SUMMARY_SHOW_AUTHOR_DATE) {
+		struct strbuf date = STRBUF_INIT;
+
+		format_commit_message(commit, "%ad", &date, &pctx);
+		strbuf_addstr(&format, "\n Date: ");
+		strbuf_addbuf_percentquote(&format, &date);
+		strbuf_release(&date);
+	}
+	if (!committer_ident_sufficiently_given()) {
+		strbuf_addstr(&format, "\n Committer: ");
+		strbuf_addbuf_percentquote(&format, &committer_ident);
+		if (advice_implicit_identity) {
+			strbuf_addch(&format, '\n');
+			strbuf_addstr(&format, implicit_ident_advice());
+		}
+	}
+	strbuf_release(&author_ident);
+	strbuf_release(&committer_ident);
+
+	repo_init_revisions(r, &rev, prefix);
+	setup_revisions(0, NULL, &rev, NULL);
+
+	rev.diff = 1;
+	rev.diffopt.output_format =
+		DIFF_FORMAT_SHORTSTAT | DIFF_FORMAT_SUMMARY;
+
+	rev.verbose_header = 1;
+	rev.show_root_diff = 1;
+	get_commit_format(format.buf, &rev);
+	rev.always_show_header = 0;
+	rev.diffopt.detect_rename = DIFF_DETECT_RENAME;
+	rev.diffopt.break_opt = 0;
+	diff_setup_done(&rev.diffopt);
+
+	head = resolve_ref_unsafe("HEAD", 0, NULL, NULL);
+	if (!head)
+		die_errno(_("unable to resolve HEAD after creating commit"));
+	if (!strcmp(head, "HEAD"))
+		head = _("detached HEAD");
+	else
+		skip_prefix(head, "refs/heads/", &head);
+	printf("[%s%s ", head, (flags & SUMMARY_INITIAL_COMMIT) ?
+						_(" (root-commit)") : "");
+
+	if (!log_tree_commit(&rev, commit)) {
+		rev.always_show_header = 1;
+		rev.use_terminator = 1;
+		log_tree_commit(&rev, commit);
+	}
+
+	strbuf_release(&format);
+}
+
+static int parse_head(struct repository *r, struct commit **head)
+{
+	struct commit *current_head;
+	struct object_id oid;
+
+	if (get_oid("HEAD", &oid)) {
+		current_head = NULL;
+	} else {
+		current_head = lookup_commit_reference(r, &oid);
+		if (!current_head)
+			return error(_("could not parse HEAD"));
+		if (!oideq(&oid, &current_head->object.oid)) {
+			warning(_("HEAD %s is not a commit!"),
+				oid_to_hex(&oid));
+		}
+		if (parse_commit(current_head))
+			return error(_("could not parse HEAD commit"));
+	}
+	*head = current_head;
+
+	return 0;
+}
+
+/*
+ * Try to commit without forking 'git commit'. In some cases we need
+ * to run 'git commit' to display an error message
+ *
+ * Returns:
+ *  -1 - error unable to commit
+ *   0 - success
+ *   1 - run 'git commit'
+ */
+static int try_to_commit(struct repository *r,
+			 struct strbuf *msg, const char *author,
+			 struct replay_opts *opts, unsigned int flags,
+			 struct object_id *oid)
+{
+	struct object_id tree;
+	struct commit *current_head;
+	struct commit_list *parents = NULL;
+	struct commit_extra_header *extra = NULL;
+	struct strbuf err = STRBUF_INIT;
+	struct strbuf commit_msg = STRBUF_INIT;
+	char *amend_author = NULL;
+	const char *hook_commit = NULL;
+	enum commit_msg_cleanup_mode cleanup;
+	int res = 0;
+
+	if (parse_head(r, &current_head))
+		return -1;
+
+	if (flags & AMEND_MSG) {
+		const char *exclude_gpgsig[] = { "gpgsig", NULL };
+		const char *out_enc = get_commit_output_encoding();
+		const char *message = logmsg_reencode(current_head, NULL,
+						      out_enc);
+
+		if (!msg) {
+			const char *orig_message = NULL;
+
+			find_commit_subject(message, &orig_message);
+			msg = &commit_msg;
+			strbuf_addstr(msg, orig_message);
+			hook_commit = "HEAD";
+		}
+		author = amend_author = get_author(message);
+		unuse_commit_buffer(current_head, message);
+		if (!author) {
+			res = error(_("unable to parse commit author"));
+			goto out;
+		}
+		parents = copy_commit_list(current_head->parents);
+		extra = read_commit_extra_headers(current_head, exclude_gpgsig);
+	} else if (current_head) {
+		commit_list_insert(current_head, &parents);
+	}
+
+	if (write_index_as_tree(&tree, r->index, r->index_file, 0, NULL)) {
+		res = error(_("git write-tree failed to write a tree"));
+		goto out;
+	}
+
+	if (!(flags & ALLOW_EMPTY) && oideq(current_head ?
+					    get_commit_tree_oid(current_head) :
+					    the_hash_algo->empty_tree, &tree)) {
+		res = 1; /* run 'git commit' to display error message */
+		goto out;
+	}
+
+	if (find_hook("prepare-commit-msg")) {
+		res = run_prepare_commit_msg_hook(r, msg, hook_commit);
+		if (res)
+			goto out;
+		if (strbuf_read_file(&commit_msg, git_path_commit_editmsg(),
+				     2048) < 0) {
+			res = error_errno(_("unable to read commit message "
+					      "from '%s'"),
+					    git_path_commit_editmsg());
+			goto out;
+		}
+		msg = &commit_msg;
+	}
+
+	if (flags & CLEANUP_MSG)
+		cleanup = COMMIT_MSG_CLEANUP_ALL;
+	else if ((opts->signoff || opts->record_origin) &&
+		 !opts->explicit_cleanup)
+		cleanup = COMMIT_MSG_CLEANUP_SPACE;
+	else
+		cleanup = opts->default_msg_cleanup;
+
+	if (cleanup != COMMIT_MSG_CLEANUP_NONE)
+		strbuf_stripspace(msg, cleanup == COMMIT_MSG_CLEANUP_ALL);
+	if ((flags & EDIT_MSG) && message_is_empty(msg, cleanup)) {
+		res = 1; /* run 'git commit' to display error message */
+		goto out;
+	}
+
+	reset_ident_date();
+
+	if (commit_tree_extended(msg->buf, msg->len, &tree, parents,
+				 oid, author, opts->gpg_sign, extra)) {
+		res = error(_("failed to write commit object"));
+		goto out;
+	}
+
+	if (update_head_with_reflog(current_head, oid,
+				    getenv("GIT_REFLOG_ACTION"), msg, &err)) {
+		res = error("%s", err.buf);
+		goto out;
+	}
+
+	if (flags & AMEND_MSG)
+		commit_post_rewrite(r, current_head, oid);
+
+out:
+	free_commit_extra_headers(extra);
+	strbuf_release(&err);
+	strbuf_release(&commit_msg);
+	free(amend_author);
+
+	return res;
+}
+
+static int do_commit(struct repository *r,
+		     const char *msg_file, const char *author,
+		     struct replay_opts *opts, unsigned int flags)
+{
+	int res = 1;
+
+	if (!(flags & EDIT_MSG) && !(flags & VERIFY_MSG) &&
+	    !(flags & CREATE_ROOT_COMMIT)) {
+		struct object_id oid;
+		struct strbuf sb = STRBUF_INIT;
+
+		if (msg_file && strbuf_read_file(&sb, msg_file, 2048) < 0)
+			return error_errno(_("unable to read commit message "
+					     "from '%s'"),
+					   msg_file);
+
+		res = try_to_commit(r, msg_file ? &sb : NULL,
+				    author, opts, flags, &oid);
+		strbuf_release(&sb);
+		if (!res) {
+			unlink(git_path_cherry_pick_head(r));
+			unlink(git_path_merge_msg(r));
+			if (!is_rebase_i(opts))
+				print_commit_summary(r, NULL, &oid,
+						SUMMARY_SHOW_AUTHOR_DATE);
+			return res;
+		}
+	}
+	if (res == 1)
+		return run_git_commit(r, msg_file, opts, flags);
+
+	return res;
+}
+
+static int is_original_commit_empty(struct commit *commit)
+{
+	const struct object_id *ptree_oid;
+
+	if (parse_commit(commit))
+		return error(_("could not parse commit %s"),
+			     oid_to_hex(&commit->object.oid));
+	if (commit->parents) {
+		struct commit *parent = commit->parents->item;
+		if (parse_commit(parent))
+			return error(_("could not parse parent commit %s"),
+				oid_to_hex(&parent->object.oid));
+		ptree_oid = get_commit_tree_oid(parent);
+	} else {
+		ptree_oid = the_hash_algo->empty_tree; /* commit is root */
+	}
+
+	return oideq(ptree_oid, get_commit_tree_oid(commit));
+}
+
+/*
+ * Do we run "git commit" with "--allow-empty"?
+ */
+static int allow_empty(struct repository *r,
+		       struct replay_opts *opts,
+		       struct commit *commit)
+{
+	int index_unchanged, empty_commit;
+
+	/*
+	 * Three cases:
+	 *
+	 * (1) we do not allow empty at all and error out.
+	 *
+	 * (2) we allow ones that were initially empty, but
+	 * forbid the ones that become empty;
+	 *
+	 * (3) we allow both.
+	 */
+	if (!opts->allow_empty)
+		return 0; /* let "git commit" barf as necessary */
+
+	index_unchanged = is_index_unchanged(r);
+	if (index_unchanged < 0)
+		return index_unchanged;
+	if (!index_unchanged)
+		return 0; /* we do not have to say --allow-empty */
+
+	if (opts->keep_redundant_commits)
+		return 1;
+
+	empty_commit = is_original_commit_empty(commit);
+	if (empty_commit < 0)
+		return empty_commit;
+	if (!empty_commit)
+		return 0;
+	else
+		return 1;
+}
+
+static struct {
+	char c;
+	const char *str;
+} todo_command_info[] = {
+	{ 'p', "pick" },
+	{ 0,   "revert" },
+	{ 'e', "edit" },
+	{ 'r', "reword" },
+	{ 'f', "fixup" },
+	{ 's', "squash" },
+	{ 'x', "exec" },
+	{ 'b', "break" },
+	{ 'l', "label" },
+	{ 't', "reset" },
+	{ 'm', "merge" },
+	{ 0,   "noop" },
+	{ 'd', "drop" },
+	{ 0,   NULL }
+};
+
+static const char *command_to_string(const enum todo_command command)
+{
+	if (command < TODO_COMMENT)
+		return todo_command_info[command].str;
+	die(_("unknown command: %d"), command);
+}
+
+static char command_to_char(const enum todo_command command)
+{
+	if (command < TODO_COMMENT && todo_command_info[command].c)
+		return todo_command_info[command].c;
+	return comment_line_char;
+}
+
+static int is_noop(const enum todo_command command)
+{
+	return TODO_NOOP <= command;
+}
+
+static int is_fixup(enum todo_command command)
+{
+	return command == TODO_FIXUP || command == TODO_SQUASH;
+}
+
+/* Does this command create a (non-merge) commit? */
+static int is_pick_or_similar(enum todo_command command)
+{
+	switch (command) {
+	case TODO_PICK:
+	case TODO_REVERT:
+	case TODO_EDIT:
+	case TODO_REWORD:
+	case TODO_FIXUP:
+	case TODO_SQUASH:
+		return 1;
+	default:
+		return 0;
+	}
+}
+
+static int update_squash_messages(struct repository *r,
+				  enum todo_command command,
+				  struct commit *commit,
+				  struct replay_opts *opts)
+{
+	struct strbuf buf = STRBUF_INIT;
+	int res;
+	const char *message, *body;
+
+	if (opts->current_fixup_count > 0) {
+		struct strbuf header = STRBUF_INIT;
+		char *eol;
+
+		if (strbuf_read_file(&buf, rebase_path_squash_msg(), 9) <= 0)
+			return error(_("could not read '%s'"),
+				rebase_path_squash_msg());
+
+		eol = buf.buf[0] != comment_line_char ?
+			buf.buf : strchrnul(buf.buf, '\n');
+
+		strbuf_addf(&header, "%c ", comment_line_char);
+		strbuf_addf(&header, _("This is a combination of %d commits."),
+			    opts->current_fixup_count + 2);
+		strbuf_splice(&buf, 0, eol - buf.buf, header.buf, header.len);
+		strbuf_release(&header);
+	} else {
+		struct object_id head;
+		struct commit *head_commit;
+		const char *head_message, *body;
+
+		if (get_oid("HEAD", &head))
+			return error(_("need a HEAD to fixup"));
+		if (!(head_commit = lookup_commit_reference(r, &head)))
+			return error(_("could not read HEAD"));
+		if (!(head_message = get_commit_buffer(head_commit, NULL)))
+			return error(_("could not read HEAD's commit message"));
+
+		find_commit_subject(head_message, &body);
+		if (write_message(body, strlen(body),
+				  rebase_path_fixup_msg(), 0)) {
+			unuse_commit_buffer(head_commit, head_message);
+			return error(_("cannot write '%s'"),
+				     rebase_path_fixup_msg());
+		}
+
+		strbuf_addf(&buf, "%c ", comment_line_char);
+		strbuf_addf(&buf, _("This is a combination of %d commits."), 2);
+		strbuf_addf(&buf, "\n%c ", comment_line_char);
+		strbuf_addstr(&buf, _("This is the 1st commit message:"));
+		strbuf_addstr(&buf, "\n\n");
+		strbuf_addstr(&buf, body);
+
+		unuse_commit_buffer(head_commit, head_message);
+	}
+
+	if (!(message = get_commit_buffer(commit, NULL)))
+		return error(_("could not read commit message of %s"),
+			     oid_to_hex(&commit->object.oid));
+	find_commit_subject(message, &body);
+
+	if (command == TODO_SQUASH) {
+		unlink(rebase_path_fixup_msg());
+		strbuf_addf(&buf, "\n%c ", comment_line_char);
+		strbuf_addf(&buf, _("This is the commit message #%d:"),
+			    ++opts->current_fixup_count + 1);
+		strbuf_addstr(&buf, "\n\n");
+		strbuf_addstr(&buf, body);
+	} else if (command == TODO_FIXUP) {
+		strbuf_addf(&buf, "\n%c ", comment_line_char);
+		strbuf_addf(&buf, _("The commit message #%d will be skipped:"),
+			    ++opts->current_fixup_count + 1);
+		strbuf_addstr(&buf, "\n\n");
+		strbuf_add_commented_lines(&buf, body, strlen(body));
+	} else
+		return error(_("unknown command: %d"), command);
+	unuse_commit_buffer(commit, message);
+
+	res = write_message(buf.buf, buf.len, rebase_path_squash_msg(), 0);
+	strbuf_release(&buf);
+
+	if (!res) {
+		strbuf_addf(&opts->current_fixups, "%s%s %s",
+			    opts->current_fixups.len ? "\n" : "",
+			    command_to_string(command),
+			    oid_to_hex(&commit->object.oid));
+		res = write_message(opts->current_fixups.buf,
+				    opts->current_fixups.len,
+				    rebase_path_current_fixups(), 0);
+	}
+
+	return res;
+}
+
+static void flush_rewritten_pending(void)
+{
+	struct strbuf buf = STRBUF_INIT;
+	struct object_id newoid;
+	FILE *out;
+
+	if (strbuf_read_file(&buf, rebase_path_rewritten_pending(), (GIT_MAX_HEXSZ + 1) * 2) > 0 &&
+	    !get_oid("HEAD", &newoid) &&
+	    (out = fopen_or_warn(rebase_path_rewritten_list(), "a"))) {
+		char *bol = buf.buf, *eol;
+
+		while (*bol) {
+			eol = strchrnul(bol, '\n');
+			fprintf(out, "%.*s %s\n", (int)(eol - bol),
+					bol, oid_to_hex(&newoid));
+			if (!*eol)
+				break;
+			bol = eol + 1;
+		}
+		fclose(out);
+		unlink(rebase_path_rewritten_pending());
+	}
+	strbuf_release(&buf);
+}
+
+static void record_in_rewritten(struct object_id *oid,
+		enum todo_command next_command)
+{
+	FILE *out = fopen_or_warn(rebase_path_rewritten_pending(), "a");
+
+	if (!out)
+		return;
+
+	fprintf(out, "%s\n", oid_to_hex(oid));
+	fclose(out);
+
+	if (!is_fixup(next_command))
+		flush_rewritten_pending();
+}
+
+static int do_pick_commit(struct repository *r,
+			  enum todo_command command,
+			  struct commit *commit,
+			  struct replay_opts *opts,
+			  int final_fixup)
+{
+	unsigned int flags = opts->edit ? EDIT_MSG : 0;
+	const char *msg_file = opts->edit ? NULL : git_path_merge_msg(r);
+	struct object_id head;
+	struct commit *base, *next, *parent;
+	const char *base_label, *next_label;
+	char *author = NULL;
+	struct commit_message msg = { NULL, NULL, NULL, NULL };
+	struct strbuf msgbuf = STRBUF_INIT;
+	int res, unborn = 0, allow;
+
+	if (opts->no_commit) {
+		/*
+		 * We do not intend to commit immediately.  We just want to
+		 * merge the differences in, so let's compute the tree
+		 * that represents the "current" state for merge-recursive
+		 * to work on.
+		 */
+		if (write_index_as_tree(&head, r->index, r->index_file, 0, NULL))
+			return error(_("your index file is unmerged."));
+	} else {
+		unborn = get_oid("HEAD", &head);
+		/* Do we want to generate a root commit? */
+		if (is_pick_or_similar(command) && opts->have_squash_onto &&
+		    oideq(&head, &opts->squash_onto)) {
+			if (is_fixup(command))
+				return error(_("cannot fixup root commit"));
+			flags |= CREATE_ROOT_COMMIT;
+			unborn = 1;
+		} else if (unborn)
+			oidcpy(&head, the_hash_algo->empty_tree);
+		if (index_differs_from(r, unborn ? empty_tree_oid_hex() : "HEAD",
+				       NULL, 0))
+			return error_dirty_index(r, opts);
+	}
+	discard_index(r->index);
+
+	if (!commit->parents)
+		parent = NULL;
+	else if (commit->parents->next) {
+		/* Reverting or cherry-picking a merge commit */
+		int cnt;
+		struct commit_list *p;
+
+		if (!opts->mainline)
+			return error(_("commit %s is a merge but no -m option was given."),
+				oid_to_hex(&commit->object.oid));
+
+		for (cnt = 1, p = commit->parents;
+		     cnt != opts->mainline && p;
+		     cnt++)
+			p = p->next;
+		if (cnt != opts->mainline || !p)
+			return error(_("commit %s does not have parent %d"),
+				oid_to_hex(&commit->object.oid), opts->mainline);
+		parent = p->item;
+	} else if (1 < opts->mainline)
+		/*
+		 *  Non-first parent explicitly specified as mainline for
+		 *  non-merge commit
+		 */
+		return error(_("commit %s does not have parent %d"),
+			     oid_to_hex(&commit->object.oid), opts->mainline);
+	else
+		parent = commit->parents->item;
+
+	if (get_message(commit, &msg) != 0)
+		return error(_("cannot get commit message for %s"),
+			oid_to_hex(&commit->object.oid));
+
+	if (opts->allow_ff && !is_fixup(command) &&
+	    ((parent && oideq(&parent->object.oid, &head)) ||
+	     (!parent && unborn))) {
+		if (is_rebase_i(opts))
+			write_author_script(msg.message);
+		res = fast_forward_to(r, &commit->object.oid, &head, unborn,
+			opts);
+		if (res || command != TODO_REWORD)
+			goto leave;
+		flags |= EDIT_MSG | AMEND_MSG | VERIFY_MSG;
+		msg_file = NULL;
+		goto fast_forward_edit;
+	}
+	if (parent && parse_commit(parent) < 0)
+		/* TRANSLATORS: The first %s will be a "todo" command like
+		   "revert" or "pick", the second %s a SHA1. */
+		return error(_("%s: cannot parse parent commit %s"),
+			command_to_string(command),
+			oid_to_hex(&parent->object.oid));
+
+	/*
+	 * "commit" is an existing commit.  We would want to apply
+	 * the difference it introduces since its first parent "prev"
+	 * on top of the current HEAD if we are cherry-pick.  Or the
+	 * reverse of it if we are revert.
+	 */
+
+	if (command == TODO_REVERT) {
+		base = commit;
+		base_label = msg.label;
+		next = parent;
+		next_label = msg.parent_label;
+		strbuf_addstr(&msgbuf, "Revert \"");
+		strbuf_addstr(&msgbuf, msg.subject);
+		strbuf_addstr(&msgbuf, "\"\n\nThis reverts commit ");
+		strbuf_addstr(&msgbuf, oid_to_hex(&commit->object.oid));
+
+		if (commit->parents && commit->parents->next) {
+			strbuf_addstr(&msgbuf, ", reversing\nchanges made to ");
+			strbuf_addstr(&msgbuf, oid_to_hex(&parent->object.oid));
+		}
+		strbuf_addstr(&msgbuf, ".\n");
+	} else {
+		const char *p;
+
+		base = parent;
+		base_label = msg.parent_label;
+		next = commit;
+		next_label = msg.label;
+
+		/* Append the commit log message to msgbuf. */
+		if (find_commit_subject(msg.message, &p))
+			strbuf_addstr(&msgbuf, p);
+
+		if (opts->record_origin) {
+			strbuf_complete_line(&msgbuf);
+			if (!has_conforming_footer(&msgbuf, NULL, 0))
+				strbuf_addch(&msgbuf, '\n');
+			strbuf_addstr(&msgbuf, cherry_picked_prefix);
+			strbuf_addstr(&msgbuf, oid_to_hex(&commit->object.oid));
+			strbuf_addstr(&msgbuf, ")\n");
+		}
+		if (!is_fixup(command))
+			author = get_author(msg.message);
+	}
+
+	if (command == TODO_REWORD)
+		flags |= EDIT_MSG | VERIFY_MSG;
+	else if (is_fixup(command)) {
+		if (update_squash_messages(r, command, commit, opts))
+			return -1;
+		flags |= AMEND_MSG;
+		if (!final_fixup)
+			msg_file = rebase_path_squash_msg();
+		else if (file_exists(rebase_path_fixup_msg())) {
+			flags |= CLEANUP_MSG;
+			msg_file = rebase_path_fixup_msg();
+		} else {
+			const char *dest = git_path_squash_msg(r);
+			unlink(dest);
+			if (copy_file(dest, rebase_path_squash_msg(), 0666))
+				return error(_("could not rename '%s' to '%s'"),
+					     rebase_path_squash_msg(), dest);
+			unlink(git_path_merge_msg(r));
+			msg_file = dest;
+			flags |= EDIT_MSG;
+		}
+	}
+
+	if (opts->signoff && !is_fixup(command))
+		append_signoff(&msgbuf, 0, 0);
+
+	if (is_rebase_i(opts) && write_author_script(msg.message) < 0)
+		res = -1;
+	else if (!opts->strategy || !strcmp(opts->strategy, "recursive") || command == TODO_REVERT) {
+		res = do_recursive_merge(r, base, next, base_label, next_label,
+					 &head, &msgbuf, opts);
+		if (res < 0)
+			goto leave;
+
+		res |= write_message(msgbuf.buf, msgbuf.len,
+				     git_path_merge_msg(r), 0);
+	} else {
+		struct commit_list *common = NULL;
+		struct commit_list *remotes = NULL;
+
+		res = write_message(msgbuf.buf, msgbuf.len,
+				    git_path_merge_msg(r), 0);
+
+		commit_list_insert(base, &common);
+		commit_list_insert(next, &remotes);
+		res |= try_merge_command(r, opts->strategy,
+					 opts->xopts_nr, (const char **)opts->xopts,
+					common, oid_to_hex(&head), remotes);
+		free_commit_list(common);
+		free_commit_list(remotes);
+	}
+	strbuf_release(&msgbuf);
+
+	/*
+	 * If the merge was clean or if it failed due to conflict, we write
+	 * CHERRY_PICK_HEAD for the subsequent invocation of commit to use.
+	 * However, if the merge did not even start, then we don't want to
+	 * write it at all.
+	 */
+	if (command == TODO_PICK && !opts->no_commit && (res == 0 || res == 1) &&
+	    update_ref(NULL, "CHERRY_PICK_HEAD", &commit->object.oid, NULL,
+		       REF_NO_DEREF, UPDATE_REFS_MSG_ON_ERR))
+		res = -1;
+	if (command == TODO_REVERT && ((opts->no_commit && res == 0) || res == 1) &&
+	    update_ref(NULL, "REVERT_HEAD", &commit->object.oid, NULL,
+		       REF_NO_DEREF, UPDATE_REFS_MSG_ON_ERR))
+		res = -1;
+
+	if (res) {
+		error(command == TODO_REVERT
+		      ? _("could not revert %s... %s")
+		      : _("could not apply %s... %s"),
+		      short_commit_name(commit), msg.subject);
+		print_advice(r, res == 1, opts);
+		repo_rerere(r, opts->allow_rerere_auto);
+		goto leave;
+	}
+
+	allow = allow_empty(r, opts, commit);
+	if (allow < 0) {
+		res = allow;
+		goto leave;
+	} else if (allow)
+		flags |= ALLOW_EMPTY;
+	if (!opts->no_commit) {
+fast_forward_edit:
+		if (author || command == TODO_REVERT || (flags & AMEND_MSG))
+			res = do_commit(r, msg_file, author, opts, flags);
+		else
+			res = error(_("unable to parse commit author"));
+	}
+
+	if (!res && final_fixup) {
+		unlink(rebase_path_fixup_msg());
+		unlink(rebase_path_squash_msg());
+		unlink(rebase_path_current_fixups());
+		strbuf_reset(&opts->current_fixups);
+		opts->current_fixup_count = 0;
+	}
+
+leave:
+	free_message(commit, &msg);
+	free(author);
+	update_abort_safety_file();
+
+	return res;
+}
+
+static int prepare_revs(struct replay_opts *opts)
+{
+	/*
+	 * picking (but not reverting) ranges (but not individual revisions)
+	 * should be done in reverse
+	 */
+	if (opts->action == REPLAY_PICK && !opts->revs->no_walk)
+		opts->revs->reverse ^= 1;
+
+	if (prepare_revision_walk(opts->revs))
+		return error(_("revision walk setup failed"));
+
+	return 0;
+}
+
+static int read_and_refresh_cache(struct repository *r,
+				  struct replay_opts *opts)
+{
+	struct lock_file index_lock = LOCK_INIT;
+	int index_fd = repo_hold_locked_index(r, &index_lock, 0);
+	if (repo_read_index(r) < 0) {
+		rollback_lock_file(&index_lock);
+		return error(_("git %s: failed to read the index"),
+			_(action_name(opts)));
+	}
+	refresh_index(r->index, REFRESH_QUIET|REFRESH_UNMERGED, NULL, NULL, NULL);
+	if (index_fd >= 0) {
+		if (write_locked_index(r->index, &index_lock,
+				       COMMIT_LOCK | SKIP_IF_UNCHANGED)) {
+			return error(_("git %s: failed to refresh the index"),
+				_(action_name(opts)));
+		}
+	}
+	return 0;
+}
+
+enum todo_item_flags {
+	TODO_EDIT_MERGE_MSG = 1
+};
+
+void todo_list_release(struct todo_list *todo_list)
+{
+	strbuf_release(&todo_list->buf);
+	FREE_AND_NULL(todo_list->items);
+	todo_list->nr = todo_list->alloc = 0;
+}
+
+static struct todo_item *append_new_todo(struct todo_list *todo_list)
+{
+	ALLOC_GROW(todo_list->items, todo_list->nr + 1, todo_list->alloc);
+	return todo_list->items + todo_list->nr++;
+}
+
+const char *todo_item_get_arg(struct todo_list *todo_list,
+			      struct todo_item *item)
+{
+	return todo_list->buf.buf + item->arg_offset;
+}
+
+static int is_command(enum todo_command command, const char **bol)
+{
+	const char *str = todo_command_info[command].str;
+	const char nick = todo_command_info[command].c;
+	const char *p = *bol + 1;
+
+	return skip_prefix(*bol, str, bol) ||
+		((nick && **bol == nick) &&
+		 (*p == ' ' || *p == '\t' || *p == '\n' || *p == '\r' || !*p) &&
+		 (*bol = p));
+}
+
+static int parse_insn_line(struct repository *r, struct todo_item *item,
+			   const char *buf, const char *bol, char *eol)
+{
+	struct object_id commit_oid;
+	char *end_of_object_name;
+	int i, saved, status, padding;
+
+	item->flags = 0;
+
+	/* left-trim */
+	bol += strspn(bol, " \t");
+
+	if (bol == eol || *bol == '\r' || *bol == comment_line_char) {
+		item->command = TODO_COMMENT;
+		item->commit = NULL;
+		item->arg_offset = bol - buf;
+		item->arg_len = eol - bol;
+		return 0;
+	}
+
+	for (i = 0; i < TODO_COMMENT; i++)
+		if (is_command(i, &bol)) {
+			item->command = i;
+			break;
+		}
+	if (i >= TODO_COMMENT)
+		return -1;
+
+	/* Eat up extra spaces/ tabs before object name */
+	padding = strspn(bol, " \t");
+	bol += padding;
+
+	if (item->command == TODO_NOOP || item->command == TODO_BREAK) {
+		if (bol != eol)
+			return error(_("%s does not accept arguments: '%s'"),
+				     command_to_string(item->command), bol);
+		item->commit = NULL;
+		item->arg_offset = bol - buf;
+		item->arg_len = eol - bol;
+		return 0;
+	}
+
+	if (!padding)
+		return error(_("missing arguments for %s"),
+			     command_to_string(item->command));
+
+	if (item->command == TODO_EXEC || item->command == TODO_LABEL ||
+	    item->command == TODO_RESET) {
+		item->commit = NULL;
+		item->arg_offset = bol - buf;
+		item->arg_len = (int)(eol - bol);
+		return 0;
+	}
+
+	if (item->command == TODO_MERGE) {
+		if (skip_prefix(bol, "-C", &bol))
+			bol += strspn(bol, " \t");
+		else if (skip_prefix(bol, "-c", &bol)) {
+			bol += strspn(bol, " \t");
+			item->flags |= TODO_EDIT_MERGE_MSG;
+		} else {
+			item->flags |= TODO_EDIT_MERGE_MSG;
+			item->commit = NULL;
+			item->arg_offset = bol - buf;
+			item->arg_len = (int)(eol - bol);
+			return 0;
+		}
+	}
+
+	end_of_object_name = (char *) bol + strcspn(bol, " \t\n");
+	saved = *end_of_object_name;
+	*end_of_object_name = '\0';
+	status = get_oid(bol, &commit_oid);
+	*end_of_object_name = saved;
+
+	bol = end_of_object_name + strspn(end_of_object_name, " \t");
+	item->arg_offset = bol - buf;
+	item->arg_len = (int)(eol - bol);
+
+	if (status < 0)
+		return error(_("could not parse '%.*s'"),
+			     (int)(end_of_object_name - bol), bol);
+
+	item->commit = lookup_commit_reference(r, &commit_oid);
+	return !item->commit;
+}
+
+int sequencer_get_last_command(struct repository *r, enum replay_action *action)
+{
+	const char *todo_file, *bol;
+	struct strbuf buf = STRBUF_INIT;
+	int ret = 0;
+
+	todo_file = git_path_todo_file();
+	if (strbuf_read_file(&buf, todo_file, 0) < 0) {
+		if (errno == ENOENT || errno == ENOTDIR)
+			return -1;
+		else
+			return error_errno("unable to open '%s'", todo_file);
+	}
+	bol = buf.buf + strspn(buf.buf, " \t\r\n");
+	if (is_command(TODO_PICK, &bol) && (*bol == ' ' || *bol == '\t'))
+		*action = REPLAY_PICK;
+	else if (is_command(TODO_REVERT, &bol) &&
+		 (*bol == ' ' || *bol == '\t'))
+		*action = REPLAY_REVERT;
+	else
+		ret = -1;
+
+	strbuf_release(&buf);
+
+	return ret;
+}
+
+int todo_list_parse_insn_buffer(struct repository *r, char *buf,
+				struct todo_list *todo_list)
+{
+	struct todo_item *item;
+	char *p = buf, *next_p;
+	int i, res = 0, fixup_okay = file_exists(rebase_path_done());
+
+	todo_list->current = todo_list->nr = 0;
+
+	for (i = 1; *p; i++, p = next_p) {
+		char *eol = strchrnul(p, '\n');
+
+		next_p = *eol ? eol + 1 /* skip LF */ : eol;
+
+		if (p != eol && eol[-1] == '\r')
+			eol--; /* strip Carriage Return */
+
+		item = append_new_todo(todo_list);
+		item->offset_in_buf = p - todo_list->buf.buf;
+		if (parse_insn_line(r, item, buf, p, eol)) {
+			res = error(_("invalid line %d: %.*s"),
+				i, (int)(eol - p), p);
+			item->command = TODO_COMMENT + 1;
+			item->arg_offset = p - buf;
+			item->arg_len = (int)(eol - p);
+			item->commit = NULL;
+		}
+
+		if (fixup_okay)
+			; /* do nothing */
+		else if (is_fixup(item->command))
+			return error(_("cannot '%s' without a previous commit"),
+				command_to_string(item->command));
+		else if (!is_noop(item->command))
+			fixup_okay = 1;
+	}
+
+	return res;
+}
+
+static int count_commands(struct todo_list *todo_list)
+{
+	int count = 0, i;
+
+	for (i = 0; i < todo_list->nr; i++)
+		if (todo_list->items[i].command != TODO_COMMENT)
+			count++;
+
+	return count;
+}
+
+static int get_item_line_offset(struct todo_list *todo_list, int index)
+{
+	return index < todo_list->nr ?
+		todo_list->items[index].offset_in_buf : todo_list->buf.len;
+}
+
+static const char *get_item_line(struct todo_list *todo_list, int index)
+{
+	return todo_list->buf.buf + get_item_line_offset(todo_list, index);
+}
+
+static int get_item_line_length(struct todo_list *todo_list, int index)
+{
+	return get_item_line_offset(todo_list, index + 1)
+		-  get_item_line_offset(todo_list, index);
+}
+
+static ssize_t strbuf_read_file_or_whine(struct strbuf *sb, const char *path)
+{
+	int fd;
+	ssize_t len;
+
+	fd = open(path, O_RDONLY);
+	if (fd < 0)
+		return error_errno(_("could not open '%s'"), path);
+	len = strbuf_read(sb, fd, 0);
+	close(fd);
+	if (len < 0)
+		return error(_("could not read '%s'."), path);
+	return len;
+}
+
+static int have_finished_the_last_pick(void)
+{
+	struct strbuf buf = STRBUF_INIT;
+	const char *eol;
+	const char *todo_path = git_path_todo_file();
+	int ret = 0;
+
+	if (strbuf_read_file(&buf, todo_path, 0) < 0) {
+		if (errno == ENOENT) {
+			return 0;
+		} else {
+			error_errno("unable to open '%s'", todo_path);
+			return 0;
+		}
+	}
+	/* If there is only one line then we are done */
+	eol = strchr(buf.buf, '\n');
+	if (!eol || !eol[1])
+		ret = 1;
+
+	strbuf_release(&buf);
+
+	return ret;
+}
+
+void sequencer_post_commit_cleanup(struct repository *r, int verbose)
+{
+	struct replay_opts opts = REPLAY_OPTS_INIT;
+	int need_cleanup = 0;
+
+	if (file_exists(git_path_cherry_pick_head(r))) {
+		if (!unlink(git_path_cherry_pick_head(r)) && verbose)
+			warning(_("cancelling a cherry picking in progress"));
+		opts.action = REPLAY_PICK;
+		need_cleanup = 1;
+	}
+
+	if (file_exists(git_path_revert_head(r))) {
+		if (!unlink(git_path_revert_head(r)) && verbose)
+			warning(_("cancelling a revert in progress"));
+		opts.action = REPLAY_REVERT;
+		need_cleanup = 1;
+	}
+
+	if (!need_cleanup)
+		return;
+
+	if (!have_finished_the_last_pick())
+		return;
+
+	sequencer_remove_state(&opts);
+}
+
+static int read_populate_todo(struct repository *r,
+			      struct todo_list *todo_list,
+			      struct replay_opts *opts)
+{
+	struct stat st;
+	const char *todo_file = get_todo_path(opts);
+	int res;
+
+	strbuf_reset(&todo_list->buf);
+	if (strbuf_read_file_or_whine(&todo_list->buf, todo_file) < 0)
+		return -1;
+
+	res = stat(todo_file, &st);
+	if (res)
+		return error(_("could not stat '%s'"), todo_file);
+	fill_stat_data(&todo_list->stat, &st);
+
+	res = todo_list_parse_insn_buffer(r, todo_list->buf.buf, todo_list);
+	if (res) {
+		if (is_rebase_i(opts))
+			return error(_("please fix this using "
+				       "'git rebase --edit-todo'."));
+		return error(_("unusable instruction sheet: '%s'"), todo_file);
+	}
+
+	if (!todo_list->nr &&
+	    (!is_rebase_i(opts) || !file_exists(rebase_path_done())))
+		return error(_("no commits parsed."));
+
+	if (!is_rebase_i(opts)) {
+		enum todo_command valid =
+			opts->action == REPLAY_PICK ? TODO_PICK : TODO_REVERT;
+		int i;
+
+		for (i = 0; i < todo_list->nr; i++)
+			if (valid == todo_list->items[i].command)
+				continue;
+			else if (valid == TODO_PICK)
+				return error(_("cannot cherry-pick during a revert."));
+			else
+				return error(_("cannot revert during a cherry-pick."));
+	}
+
+	if (is_rebase_i(opts)) {
+		struct todo_list done = TODO_LIST_INIT;
+		FILE *f = fopen_or_warn(rebase_path_msgtotal(), "w");
+
+		if (strbuf_read_file(&done.buf, rebase_path_done(), 0) > 0 &&
+		    !todo_list_parse_insn_buffer(r, done.buf.buf, &done))
+			todo_list->done_nr = count_commands(&done);
+		else
+			todo_list->done_nr = 0;
+
+		todo_list->total_nr = todo_list->done_nr
+			+ count_commands(todo_list);
+		todo_list_release(&done);
+
+		if (f) {
+			fprintf(f, "%d\n", todo_list->total_nr);
+			fclose(f);
+		}
+	}
+
+	return 0;
+}
+
+static int git_config_string_dup(char **dest,
+				 const char *var, const char *value)
+{
+	if (!value)
+		return config_error_nonbool(var);
+	free(*dest);
+	*dest = xstrdup(value);
+	return 0;
+}
+
+static int populate_opts_cb(const char *key, const char *value, void *data)
+{
+	struct replay_opts *opts = data;
+	int error_flag = 1;
+
+	if (!value)
+		error_flag = 0;
+	else if (!strcmp(key, "options.no-commit"))
+		opts->no_commit = git_config_bool_or_int(key, value, &error_flag);
+	else if (!strcmp(key, "options.edit"))
+		opts->edit = git_config_bool_or_int(key, value, &error_flag);
+	else if (!strcmp(key, "options.allow-empty"))
+		opts->allow_empty =
+			git_config_bool_or_int(key, value, &error_flag);
+	else if (!strcmp(key, "options.allow-empty-message"))
+		opts->allow_empty_message =
+			git_config_bool_or_int(key, value, &error_flag);
+	else if (!strcmp(key, "options.keep-redundant-commits"))
+		opts->keep_redundant_commits =
+			git_config_bool_or_int(key, value, &error_flag);
+	else if (!strcmp(key, "options.signoff"))
+		opts->signoff = git_config_bool_or_int(key, value, &error_flag);
+	else if (!strcmp(key, "options.record-origin"))
+		opts->record_origin = git_config_bool_or_int(key, value, &error_flag);
+	else if (!strcmp(key, "options.allow-ff"))
+		opts->allow_ff = git_config_bool_or_int(key, value, &error_flag);
+	else if (!strcmp(key, "options.mainline"))
+		opts->mainline = git_config_int(key, value);
+	else if (!strcmp(key, "options.strategy"))
+		git_config_string_dup(&opts->strategy, key, value);
+	else if (!strcmp(key, "options.gpg-sign"))
+		git_config_string_dup(&opts->gpg_sign, key, value);
+	else if (!strcmp(key, "options.strategy-option")) {
+		ALLOC_GROW(opts->xopts, opts->xopts_nr + 1, opts->xopts_alloc);
+		opts->xopts[opts->xopts_nr++] = xstrdup(value);
+	} else if (!strcmp(key, "options.allow-rerere-auto"))
+		opts->allow_rerere_auto =
+			git_config_bool_or_int(key, value, &error_flag) ?
+				RERERE_AUTOUPDATE : RERERE_NOAUTOUPDATE;
+	else if (!strcmp(key, "options.default-msg-cleanup")) {
+		opts->explicit_cleanup = 1;
+		opts->default_msg_cleanup = get_cleanup_mode(value, 1);
+	} else
+		return error(_("invalid key: %s"), key);
+
+	if (!error_flag)
+		return error(_("invalid value for %s: %s"), key, value);
+
+	return 0;
+}
+
+void parse_strategy_opts(struct replay_opts *opts, char *raw_opts)
+{
+	int i;
+	char *strategy_opts_string = raw_opts;
+
+	if (*strategy_opts_string == ' ')
+		strategy_opts_string++;
+
+	opts->xopts_nr = split_cmdline(strategy_opts_string,
+				       (const char ***)&opts->xopts);
+	for (i = 0; i < opts->xopts_nr; i++) {
+		const char *arg = opts->xopts[i];
+
+		skip_prefix(arg, "--", &arg);
+		opts->xopts[i] = xstrdup(arg);
+	}
+}
+
+static void read_strategy_opts(struct replay_opts *opts, struct strbuf *buf)
+{
+	strbuf_reset(buf);
+	if (!read_oneliner(buf, rebase_path_strategy(), 0))
+		return;
+	opts->strategy = strbuf_detach(buf, NULL);
+	if (!read_oneliner(buf, rebase_path_strategy_opts(), 0))
+		return;
+
+	parse_strategy_opts(opts, buf->buf);
+}
+
+static int read_populate_opts(struct replay_opts *opts)
+{
+	if (is_rebase_i(opts)) {
+		struct strbuf buf = STRBUF_INIT;
+
+		if (read_oneliner(&buf, rebase_path_gpg_sign_opt(), 1)) {
+			if (!starts_with(buf.buf, "-S"))
+				strbuf_reset(&buf);
+			else {
+				free(opts->gpg_sign);
+				opts->gpg_sign = xstrdup(buf.buf + 2);
+			}
+			strbuf_reset(&buf);
+		}
+
+		if (read_oneliner(&buf, rebase_path_allow_rerere_autoupdate(), 1)) {
+			if (!strcmp(buf.buf, "--rerere-autoupdate"))
+				opts->allow_rerere_auto = RERERE_AUTOUPDATE;
+			else if (!strcmp(buf.buf, "--no-rerere-autoupdate"))
+				opts->allow_rerere_auto = RERERE_NOAUTOUPDATE;
+			strbuf_reset(&buf);
+		}
+
+		if (file_exists(rebase_path_verbose()))
+			opts->verbose = 1;
+
+		if (file_exists(rebase_path_quiet()))
+			opts->quiet = 1;
+
+		if (file_exists(rebase_path_signoff())) {
+			opts->allow_ff = 0;
+			opts->signoff = 1;
+		}
+
+		if (file_exists(rebase_path_reschedule_failed_exec()))
+			opts->reschedule_failed_exec = 1;
+
+		read_strategy_opts(opts, &buf);
+		strbuf_release(&buf);
+
+		if (read_oneliner(&opts->current_fixups,
+				  rebase_path_current_fixups(), 1)) {
+			const char *p = opts->current_fixups.buf;
+			opts->current_fixup_count = 1;
+			while ((p = strchr(p, '\n'))) {
+				opts->current_fixup_count++;
+				p++;
+			}
+		}
+
+		if (read_oneliner(&buf, rebase_path_squash_onto(), 0)) {
+			if (get_oid_hex(buf.buf, &opts->squash_onto) < 0)
+				return error(_("unusable squash-onto"));
+			opts->have_squash_onto = 1;
+		}
+
+		return 0;
+	}
+
+	if (!file_exists(git_path_opts_file()))
+		return 0;
+	/*
+	 * The function git_parse_source(), called from git_config_from_file(),
+	 * may die() in case of a syntactically incorrect file. We do not care
+	 * about this case, though, because we wrote that file ourselves, so we
+	 * are pretty certain that it is syntactically correct.
+	 */
+	if (git_config_from_file(populate_opts_cb, git_path_opts_file(), opts) < 0)
+		return error(_("malformed options sheet: '%s'"),
+			git_path_opts_file());
+	return 0;
+}
+
+static void write_strategy_opts(struct replay_opts *opts)
+{
+	int i;
+	struct strbuf buf = STRBUF_INIT;
+
+	for (i = 0; i < opts->xopts_nr; ++i)
+		strbuf_addf(&buf, " --%s", opts->xopts[i]);
+
+	write_file(rebase_path_strategy_opts(), "%s\n", buf.buf);
+	strbuf_release(&buf);
+}
+
+int write_basic_state(struct replay_opts *opts, const char *head_name,
+		      struct commit *onto, const char *orig_head)
+{
+	const char *quiet = getenv("GIT_QUIET");
+
+	if (head_name)
+		write_file(rebase_path_head_name(), "%s\n", head_name);
+	if (onto)
+		write_file(rebase_path_onto(), "%s\n",
+			   oid_to_hex(&onto->object.oid));
+	if (orig_head)
+		write_file(rebase_path_orig_head(), "%s\n", orig_head);
+
+	if (quiet)
+		write_file(rebase_path_quiet(), "%s\n", quiet);
+	if (opts->verbose)
+		write_file(rebase_path_verbose(), "%s", "");
+	if (opts->strategy)
+		write_file(rebase_path_strategy(), "%s\n", opts->strategy);
+	if (opts->xopts_nr > 0)
+		write_strategy_opts(opts);
+
+	if (opts->allow_rerere_auto == RERERE_AUTOUPDATE)
+		write_file(rebase_path_allow_rerere_autoupdate(), "--rerere-autoupdate\n");
+	else if (opts->allow_rerere_auto == RERERE_NOAUTOUPDATE)
+		write_file(rebase_path_allow_rerere_autoupdate(), "--no-rerere-autoupdate\n");
+
+	if (opts->gpg_sign)
+		write_file(rebase_path_gpg_sign_opt(), "-S%s\n", opts->gpg_sign);
+	if (opts->signoff)
+		write_file(rebase_path_signoff(), "--signoff\n");
+	if (opts->reschedule_failed_exec)
+		write_file(rebase_path_reschedule_failed_exec(), "%s", "");
+
+	return 0;
+}
+
+static int walk_revs_populate_todo(struct todo_list *todo_list,
+				struct replay_opts *opts)
+{
+	enum todo_command command = opts->action == REPLAY_PICK ?
+		TODO_PICK : TODO_REVERT;
+	const char *command_string = todo_command_info[command].str;
+	struct commit *commit;
+
+	if (prepare_revs(opts))
+		return -1;
+
+	while ((commit = get_revision(opts->revs))) {
+		struct todo_item *item = append_new_todo(todo_list);
+		const char *commit_buffer = get_commit_buffer(commit, NULL);
+		const char *subject;
+		int subject_len;
+
+		item->command = command;
+		item->commit = commit;
+		item->arg_offset = 0;
+		item->arg_len = 0;
+		item->offset_in_buf = todo_list->buf.len;
+		subject_len = find_commit_subject(commit_buffer, &subject);
+		strbuf_addf(&todo_list->buf, "%s %s %.*s\n", command_string,
+			short_commit_name(commit), subject_len, subject);
+		unuse_commit_buffer(commit, commit_buffer);
+	}
+
+	if (!todo_list->nr)
+		return error(_("empty commit set passed"));
+
+	return 0;
+}
+
+static int create_seq_dir(struct repository *r)
+{
+	enum replay_action action;
+	const char *in_progress_error = NULL;
+	const char *in_progress_advice = NULL;
+	unsigned int advise_skip = file_exists(git_path_revert_head(r)) ||
+				file_exists(git_path_cherry_pick_head(r));
+
+	if (!sequencer_get_last_command(r, &action)) {
+		switch (action) {
+		case REPLAY_REVERT:
+			in_progress_error = _("revert is already in progress");
+			in_progress_advice =
+			_("try \"git revert (--continue | %s--abort | --quit)\"");
+			break;
+		case REPLAY_PICK:
+			in_progress_error = _("cherry-pick is already in progress");
+			in_progress_advice =
+			_("try \"git cherry-pick (--continue | %s--abort | --quit)\"");
+			break;
+		default:
+			BUG("unexpected action in create_seq_dir");
+		}
+	}
+	if (in_progress_error) {
+		error("%s", in_progress_error);
+		if (advice_sequencer_in_use)
+			advise(in_progress_advice,
+				advise_skip ? "--skip | " : "");
+		return -1;
+	}
+	if (mkdir(git_path_seq_dir(), 0777) < 0)
+		return error_errno(_("could not create sequencer directory '%s'"),
+				   git_path_seq_dir());
+
+	return 0;
+}
+
+static int save_head(const char *head)
+{
+	struct lock_file head_lock = LOCK_INIT;
+	struct strbuf buf = STRBUF_INIT;
+	int fd;
+	ssize_t written;
+
+	fd = hold_lock_file_for_update(&head_lock, git_path_head_file(), 0);
+	if (fd < 0)
+		return error_errno(_("could not lock HEAD"));
+	strbuf_addf(&buf, "%s\n", head);
+	written = write_in_full(fd, buf.buf, buf.len);
+	strbuf_release(&buf);
+	if (written < 0) {
+		error_errno(_("could not write to '%s'"), git_path_head_file());
+		rollback_lock_file(&head_lock);
+		return -1;
+	}
+	if (commit_lock_file(&head_lock) < 0)
+		return error(_("failed to finalize '%s'"), git_path_head_file());
+	return 0;
+}
+
+static int rollback_is_safe(void)
+{
+	struct strbuf sb = STRBUF_INIT;
+	struct object_id expected_head, actual_head;
+
+	if (strbuf_read_file(&sb, git_path_abort_safety_file(), 0) >= 0) {
+		strbuf_trim(&sb);
+		if (get_oid_hex(sb.buf, &expected_head)) {
+			strbuf_release(&sb);
+			die(_("could not parse %s"), git_path_abort_safety_file());
+		}
+		strbuf_release(&sb);
+	}
+	else if (errno == ENOENT)
+		oidclr(&expected_head);
+	else
+		die_errno(_("could not read '%s'"), git_path_abort_safety_file());
+
+	if (get_oid("HEAD", &actual_head))
+		oidclr(&actual_head);
+
+	return oideq(&actual_head, &expected_head);
+}
+
+static int reset_merge(const struct object_id *oid)
+{
+	int ret;
+	struct argv_array argv = ARGV_ARRAY_INIT;
+
+	argv_array_pushl(&argv, "reset", "--merge", NULL);
+
+	if (!is_null_oid(oid))
+		argv_array_push(&argv, oid_to_hex(oid));
+
+	ret = run_command_v_opt(argv.argv, RUN_GIT_CMD);
+	argv_array_clear(&argv);
+
+	return ret;
+}
+
+static int rollback_single_pick(struct repository *r)
+{
+	struct object_id head_oid;
+
+	if (!file_exists(git_path_cherry_pick_head(r)) &&
+	    !file_exists(git_path_revert_head(r)))
+		return error(_("no cherry-pick or revert in progress"));
+	if (read_ref_full("HEAD", 0, &head_oid, NULL))
+		return error(_("cannot resolve HEAD"));
+	if (is_null_oid(&head_oid))
+		return error(_("cannot abort from a branch yet to be born"));
+	return reset_merge(&head_oid);
+}
+
+static int skip_single_pick(void)
+{
+	struct object_id head;
+
+	if (read_ref_full("HEAD", 0, &head, NULL))
+		return error(_("cannot resolve HEAD"));
+	return reset_merge(&head);
+}
+
+int sequencer_rollback(struct repository *r, struct replay_opts *opts)
+{
+	FILE *f;
+	struct object_id oid;
+	struct strbuf buf = STRBUF_INIT;
+	const char *p;
+
+	f = fopen(git_path_head_file(), "r");
+	if (!f && errno == ENOENT) {
+		/*
+		 * There is no multiple-cherry-pick in progress.
+		 * If CHERRY_PICK_HEAD or REVERT_HEAD indicates
+		 * a single-cherry-pick in progress, abort that.
+		 */
+		return rollback_single_pick(r);
+	}
+	if (!f)
+		return error_errno(_("cannot open '%s'"), git_path_head_file());
+	if (strbuf_getline_lf(&buf, f)) {
+		error(_("cannot read '%s': %s"), git_path_head_file(),
+		      ferror(f) ?  strerror(errno) : _("unexpected end of file"));
+		fclose(f);
+		goto fail;
+	}
+	fclose(f);
+	if (parse_oid_hex(buf.buf, &oid, &p) || *p != '\0') {
+		error(_("stored pre-cherry-pick HEAD file '%s' is corrupt"),
+			git_path_head_file());
+		goto fail;
+	}
+	if (is_null_oid(&oid)) {
+		error(_("cannot abort from a branch yet to be born"));
+		goto fail;
+	}
+
+	if (!rollback_is_safe()) {
+		/* Do not error, just do not rollback */
+		warning(_("You seem to have moved HEAD. "
+			  "Not rewinding, check your HEAD!"));
+	} else
+	if (reset_merge(&oid))
+		goto fail;
+	strbuf_release(&buf);
+	return sequencer_remove_state(opts);
+fail:
+	strbuf_release(&buf);
+	return -1;
+}
+
+int sequencer_skip(struct repository *r, struct replay_opts *opts)
+{
+	enum replay_action action = -1;
+	sequencer_get_last_command(r, &action);
+
+	/*
+	 * Check whether the subcommand requested to skip the commit is actually
+	 * in progress and that it's safe to skip the commit.
+	 *
+	 * opts->action tells us which subcommand requested to skip the commit.
+	 * If the corresponding .git/<ACTION>_HEAD exists, we know that the
+	 * action is in progress and we can skip the commit.
+	 *
+	 * Otherwise we check that the last instruction was related to the
+	 * particular subcommand we're trying to execute and barf if that's not
+	 * the case.
+	 *
+	 * Finally we check that the rollback is "safe", i.e., has the HEAD
+	 * moved? In this case, it doesn't make sense to "reset the merge" and
+	 * "skip the commit" as the user already handled this by committing. But
+	 * we'd not want to barf here, instead give advice on how to proceed. We
+	 * only need to check that when .git/<ACTION>_HEAD doesn't exist because
+	 * it gets removed when the user commits, so if it still exists we're
+	 * sure the user can't have committed before.
+	 */
+	switch (opts->action) {
+	case REPLAY_REVERT:
+		if (!file_exists(git_path_revert_head(r))) {
+			if (action != REPLAY_REVERT)
+				return error(_("no revert in progress"));
+			if (!rollback_is_safe())
+				goto give_advice;
+		}
+		break;
+	case REPLAY_PICK:
+		if (!file_exists(git_path_cherry_pick_head(r))) {
+			if (action != REPLAY_PICK)
+				return error(_("no cherry-pick in progress"));
+			if (!rollback_is_safe())
+				goto give_advice;
+		}
+		break;
+	default:
+		BUG("unexpected action in sequencer_skip");
+	}
+
+	if (skip_single_pick())
+		return error(_("failed to skip the commit"));
+	if (!is_directory(git_path_seq_dir()))
+		return 0;
+
+	return sequencer_continue(r, opts);
+
+give_advice:
+	error(_("there is nothing to skip"));
+
+	if (advice_resolve_conflict) {
+		advise(_("have you committed already?\n"
+			 "try \"git %s --continue\""),
+			 action == REPLAY_REVERT ? "revert" : "cherry-pick");
+	}
+	return -1;
+}
+
+static int save_todo(struct todo_list *todo_list, struct replay_opts *opts)
+{
+	struct lock_file todo_lock = LOCK_INIT;
+	const char *todo_path = get_todo_path(opts);
+	int next = todo_list->current, offset, fd;
+
+	/*
+	 * rebase -i writes "git-rebase-todo" without the currently executing
+	 * command, appending it to "done" instead.
+	 */
+	if (is_rebase_i(opts))
+		next++;
+
+	fd = hold_lock_file_for_update(&todo_lock, todo_path, 0);
+	if (fd < 0)
+		return error_errno(_("could not lock '%s'"), todo_path);
+	offset = get_item_line_offset(todo_list, next);
+	if (write_in_full(fd, todo_list->buf.buf + offset,
+			todo_list->buf.len - offset) < 0)
+		return error_errno(_("could not write to '%s'"), todo_path);
+	if (commit_lock_file(&todo_lock) < 0)
+		return error(_("failed to finalize '%s'"), todo_path);
+
+	if (is_rebase_i(opts) && next > 0) {
+		const char *done = rebase_path_done();
+		int fd = open(done, O_CREAT | O_WRONLY | O_APPEND, 0666);
+		int ret = 0;
+
+		if (fd < 0)
+			return 0;
+		if (write_in_full(fd, get_item_line(todo_list, next - 1),
+				  get_item_line_length(todo_list, next - 1))
+		    < 0)
+			ret = error_errno(_("could not write to '%s'"), done);
+		if (close(fd) < 0)
+			ret = error_errno(_("failed to finalize '%s'"), done);
+		return ret;
+	}
+	return 0;
+}
+
+static int save_opts(struct replay_opts *opts)
+{
+	const char *opts_file = git_path_opts_file();
+	int res = 0;
+
+	if (opts->no_commit)
+		res |= git_config_set_in_file_gently(opts_file,
+					"options.no-commit", "true");
+	if (opts->edit)
+		res |= git_config_set_in_file_gently(opts_file,
+					"options.edit", "true");
+	if (opts->allow_empty)
+		res |= git_config_set_in_file_gently(opts_file,
+					"options.allow-empty", "true");
+	if (opts->allow_empty_message)
+		res |= git_config_set_in_file_gently(opts_file,
+				"options.allow-empty-message", "true");
+	if (opts->keep_redundant_commits)
+		res |= git_config_set_in_file_gently(opts_file,
+				"options.keep-redundant-commits", "true");
+	if (opts->signoff)
+		res |= git_config_set_in_file_gently(opts_file,
+					"options.signoff", "true");
+	if (opts->record_origin)
+		res |= git_config_set_in_file_gently(opts_file,
+					"options.record-origin", "true");
+	if (opts->allow_ff)
+		res |= git_config_set_in_file_gently(opts_file,
+					"options.allow-ff", "true");
+	if (opts->mainline) {
+		struct strbuf buf = STRBUF_INIT;
+		strbuf_addf(&buf, "%d", opts->mainline);
+		res |= git_config_set_in_file_gently(opts_file,
+					"options.mainline", buf.buf);
+		strbuf_release(&buf);
+	}
+	if (opts->strategy)
+		res |= git_config_set_in_file_gently(opts_file,
+					"options.strategy", opts->strategy);
+	if (opts->gpg_sign)
+		res |= git_config_set_in_file_gently(opts_file,
+					"options.gpg-sign", opts->gpg_sign);
+	if (opts->xopts) {
+		int i;
+		for (i = 0; i < opts->xopts_nr; i++)
+			res |= git_config_set_multivar_in_file_gently(opts_file,
+					"options.strategy-option",
+					opts->xopts[i], "^$", 0);
+	}
+	if (opts->allow_rerere_auto)
+		res |= git_config_set_in_file_gently(opts_file,
+				"options.allow-rerere-auto",
+				opts->allow_rerere_auto == RERERE_AUTOUPDATE ?
+				"true" : "false");
+
+	if (opts->explicit_cleanup)
+		res |= git_config_set_in_file_gently(opts_file,
+				"options.default-msg-cleanup",
+				describe_cleanup_mode(opts->default_msg_cleanup));
+	return res;
+}
+
+static int make_patch(struct repository *r,
+		      struct commit *commit,
+		      struct replay_opts *opts)
+{
+	struct strbuf buf = STRBUF_INIT;
+	struct rev_info log_tree_opt;
+	const char *subject, *p;
+	int res = 0;
+
+	p = short_commit_name(commit);
+	if (write_message(p, strlen(p), rebase_path_stopped_sha(), 1) < 0)
+		return -1;
+	if (update_ref("rebase", "REBASE_HEAD", &commit->object.oid,
+		       NULL, REF_NO_DEREF, UPDATE_REFS_MSG_ON_ERR))
+		res |= error(_("could not update %s"), "REBASE_HEAD");
+
+	strbuf_addf(&buf, "%s/patch", get_dir(opts));
+	memset(&log_tree_opt, 0, sizeof(log_tree_opt));
+	repo_init_revisions(r, &log_tree_opt, NULL);
+	log_tree_opt.abbrev = 0;
+	log_tree_opt.diff = 1;
+	log_tree_opt.diffopt.output_format = DIFF_FORMAT_PATCH;
+	log_tree_opt.disable_stdin = 1;
+	log_tree_opt.no_commit_id = 1;
+	log_tree_opt.diffopt.file = fopen(buf.buf, "w");
+	log_tree_opt.diffopt.use_color = GIT_COLOR_NEVER;
+	if (!log_tree_opt.diffopt.file)
+		res |= error_errno(_("could not open '%s'"), buf.buf);
+	else {
+		res |= log_tree_commit(&log_tree_opt, commit);
+		fclose(log_tree_opt.diffopt.file);
+	}
+	strbuf_reset(&buf);
+
+	strbuf_addf(&buf, "%s/message", get_dir(opts));
+	if (!file_exists(buf.buf)) {
+		const char *commit_buffer = get_commit_buffer(commit, NULL);
+		find_commit_subject(commit_buffer, &subject);
+		res |= write_message(subject, strlen(subject), buf.buf, 1);
+		unuse_commit_buffer(commit, commit_buffer);
+	}
+	strbuf_release(&buf);
+
+	return res;
+}
+
+static int intend_to_amend(void)
+{
+	struct object_id head;
+	char *p;
+
+	if (get_oid("HEAD", &head))
+		return error(_("cannot read HEAD"));
+
+	p = oid_to_hex(&head);
+	return write_message(p, strlen(p), rebase_path_amend(), 1);
+}
+
+static int error_with_patch(struct repository *r,
+			    struct commit *commit,
+			    const char *subject, int subject_len,
+			    struct replay_opts *opts,
+			    int exit_code, int to_amend)
+{
+	if (commit) {
+		if (make_patch(r, commit, opts))
+			return -1;
+	} else if (copy_file(rebase_path_message(),
+			     git_path_merge_msg(r), 0666))
+		return error(_("unable to copy '%s' to '%s'"),
+			     git_path_merge_msg(r), rebase_path_message());
+
+	if (to_amend) {
+		if (intend_to_amend())
+			return -1;
+
+		fprintf(stderr,
+			_("You can amend the commit now, with\n"
+			  "\n"
+			  "  git commit --amend %s\n"
+			  "\n"
+			  "Once you are satisfied with your changes, run\n"
+			  "\n"
+			  "  git rebase --continue\n"),
+			gpg_sign_opt_quoted(opts));
+	} else if (exit_code) {
+		if (commit)
+			fprintf_ln(stderr, _("Could not apply %s... %.*s"),
+				   short_commit_name(commit), subject_len, subject);
+		else
+			/*
+			 * We don't have the hash of the parent so
+			 * just print the line from the todo file.
+			 */
+			fprintf_ln(stderr, _("Could not merge %.*s"),
+				   subject_len, subject);
+	}
+
+	return exit_code;
+}
+
+static int error_failed_squash(struct repository *r,
+			       struct commit *commit,
+			       struct replay_opts *opts,
+			       int subject_len,
+			       const char *subject)
+{
+	if (copy_file(rebase_path_message(), rebase_path_squash_msg(), 0666))
+		return error(_("could not copy '%s' to '%s'"),
+			rebase_path_squash_msg(), rebase_path_message());
+	unlink(git_path_merge_msg(r));
+	if (copy_file(git_path_merge_msg(r), rebase_path_message(), 0666))
+		return error(_("could not copy '%s' to '%s'"),
+			     rebase_path_message(),
+			     git_path_merge_msg(r));
+	return error_with_patch(r, commit, subject, subject_len, opts, 1, 0);
+}
+
+static int do_exec(struct repository *r, const char *command_line)
+{
+	struct argv_array child_env = ARGV_ARRAY_INIT;
+	const char *child_argv[] = { NULL, NULL };
+	int dirty, status;
+
+	fprintf(stderr, "Executing: %s\n", command_line);
+	child_argv[0] = command_line;
+	argv_array_pushf(&child_env, "GIT_DIR=%s", absolute_path(get_git_dir()));
+	argv_array_pushf(&child_env, "GIT_WORK_TREE=%s",
+			 absolute_path(get_git_work_tree()));
+	status = run_command_v_opt_cd_env(child_argv, RUN_USING_SHELL, NULL,
+					  child_env.argv);
+
+	/* force re-reading of the cache */
+	if (discard_index(r->index) < 0 || repo_read_index(r) < 0)
+		return error(_("could not read index"));
+
+	dirty = require_clean_work_tree(r, "rebase", NULL, 1, 1);
+
+	if (status) {
+		warning(_("execution failed: %s\n%s"
+			  "You can fix the problem, and then run\n"
+			  "\n"
+			  "  git rebase --continue\n"
+			  "\n"),
+			command_line,
+			dirty ? N_("and made changes to the index and/or the "
+				"working tree\n") : "");
+		if (status == 127)
+			/* command not found */
+			status = 1;
+	} else if (dirty) {
+		warning(_("execution succeeded: %s\nbut "
+			  "left changes to the index and/or the working tree\n"
+			  "Commit or stash your changes, and then run\n"
+			  "\n"
+			  "  git rebase --continue\n"
+			  "\n"), command_line);
+		status = 1;
+	}
+
+	argv_array_clear(&child_env);
+
+	return status;
+}
+
+static int safe_append(const char *filename, const char *fmt, ...)
+{
+	va_list ap;
+	struct lock_file lock = LOCK_INIT;
+	int fd = hold_lock_file_for_update(&lock, filename,
+					   LOCK_REPORT_ON_ERROR);
+	struct strbuf buf = STRBUF_INIT;
+
+	if (fd < 0)
+		return -1;
+
+	if (strbuf_read_file(&buf, filename, 0) < 0 && errno != ENOENT) {
+		error_errno(_("could not read '%s'"), filename);
+		rollback_lock_file(&lock);
+		return -1;
+	}
+	strbuf_complete(&buf, '\n');
+	va_start(ap, fmt);
+	strbuf_vaddf(&buf, fmt, ap);
+	va_end(ap);
+
+	if (write_in_full(fd, buf.buf, buf.len) < 0) {
+		error_errno(_("could not write to '%s'"), filename);
+		strbuf_release(&buf);
+		rollback_lock_file(&lock);
+		return -1;
+	}
+	if (commit_lock_file(&lock) < 0) {
+		strbuf_release(&buf);
+		rollback_lock_file(&lock);
+		return error(_("failed to finalize '%s'"), filename);
+	}
+
+	strbuf_release(&buf);
+	return 0;
+}
+
+static int do_label(struct repository *r, const char *name, int len)
+{
+	struct ref_store *refs = get_main_ref_store(r);
+	struct ref_transaction *transaction;
+	struct strbuf ref_name = STRBUF_INIT, err = STRBUF_INIT;
+	struct strbuf msg = STRBUF_INIT;
+	int ret = 0;
+	struct object_id head_oid;
+
+	if (len == 1 && *name == '#')
+		return error(_("illegal label name: '%.*s'"), len, name);
+
+	strbuf_addf(&ref_name, "refs/rewritten/%.*s", len, name);
+	strbuf_addf(&msg, "rebase -i (label) '%.*s'", len, name);
+
+	transaction = ref_store_transaction_begin(refs, &err);
+	if (!transaction) {
+		error("%s", err.buf);
+		ret = -1;
+	} else if (get_oid("HEAD", &head_oid)) {
+		error(_("could not read HEAD"));
+		ret = -1;
+	} else if (ref_transaction_update(transaction, ref_name.buf, &head_oid,
+					  NULL, 0, msg.buf, &err) < 0 ||
+		   ref_transaction_commit(transaction, &err)) {
+		error("%s", err.buf);
+		ret = -1;
+	}
+	ref_transaction_free(transaction);
+	strbuf_release(&err);
+	strbuf_release(&msg);
+
+	if (!ret)
+		ret = safe_append(rebase_path_refs_to_delete(),
+				  "%s\n", ref_name.buf);
+	strbuf_release(&ref_name);
+
+	return ret;
+}
+
+static const char *reflog_message(struct replay_opts *opts,
+	const char *sub_action, const char *fmt, ...);
+
+static int do_reset(struct repository *r,
+		    const char *name, int len,
+		    struct replay_opts *opts)
+{
+	struct strbuf ref_name = STRBUF_INIT;
+	struct object_id oid;
+	struct lock_file lock = LOCK_INIT;
+	struct tree_desc desc;
+	struct tree *tree;
+	struct unpack_trees_options unpack_tree_opts;
+	int ret = 0;
+
+	if (repo_hold_locked_index(r, &lock, LOCK_REPORT_ON_ERROR) < 0)
+		return -1;
+
+	if (len == 10 && !strncmp("[new root]", name, len)) {
+		if (!opts->have_squash_onto) {
+			const char *hex;
+			if (commit_tree("", 0, the_hash_algo->empty_tree,
+					NULL, &opts->squash_onto,
+					NULL, NULL))
+				return error(_("writing fake root commit"));
+			opts->have_squash_onto = 1;
+			hex = oid_to_hex(&opts->squash_onto);
+			if (write_message(hex, strlen(hex),
+					  rebase_path_squash_onto(), 0))
+				return error(_("writing squash-onto"));
+		}
+		oidcpy(&oid, &opts->squash_onto);
+	} else {
+		int i;
+
+		/* Determine the length of the label */
+		for (i = 0; i < len; i++)
+			if (isspace(name[i]))
+				break;
+		len = i;
+
+		strbuf_addf(&ref_name, "refs/rewritten/%.*s", len, name);
+		if (get_oid(ref_name.buf, &oid) &&
+		    get_oid(ref_name.buf + strlen("refs/rewritten/"), &oid)) {
+			error(_("could not read '%s'"), ref_name.buf);
+			rollback_lock_file(&lock);
+			strbuf_release(&ref_name);
+			return -1;
+		}
+	}
+
+	memset(&unpack_tree_opts, 0, sizeof(unpack_tree_opts));
+	setup_unpack_trees_porcelain(&unpack_tree_opts, "reset");
+	unpack_tree_opts.head_idx = 1;
+	unpack_tree_opts.src_index = r->index;
+	unpack_tree_opts.dst_index = r->index;
+	unpack_tree_opts.fn = oneway_merge;
+	unpack_tree_opts.merge = 1;
+	unpack_tree_opts.update = 1;
+
+	if (repo_read_index_unmerged(r)) {
+		rollback_lock_file(&lock);
+		strbuf_release(&ref_name);
+		return error_resolve_conflict(_(action_name(opts)));
+	}
+
+	if (!fill_tree_descriptor(r, &desc, &oid)) {
+		error(_("failed to find tree of %s"), oid_to_hex(&oid));
+		rollback_lock_file(&lock);
+		free((void *)desc.buffer);
+		strbuf_release(&ref_name);
+		return -1;
+	}
+
+	if (unpack_trees(1, &desc, &unpack_tree_opts)) {
+		rollback_lock_file(&lock);
+		free((void *)desc.buffer);
+		strbuf_release(&ref_name);
+		return -1;
+	}
+
+	tree = parse_tree_indirect(&oid);
+	prime_cache_tree(r, r->index, tree);
+
+	if (write_locked_index(r->index, &lock, COMMIT_LOCK) < 0)
+		ret = error(_("could not write index"));
+	free((void *)desc.buffer);
+
+	if (!ret)
+		ret = update_ref(reflog_message(opts, "reset", "'%.*s'",
+						len, name), "HEAD", &oid,
+				 NULL, 0, UPDATE_REFS_MSG_ON_ERR);
+
+	strbuf_release(&ref_name);
+	return ret;
+}
+
+static struct commit *lookup_label(const char *label, int len,
+				   struct strbuf *buf)
+{
+	struct commit *commit;
+
+	strbuf_reset(buf);
+	strbuf_addf(buf, "refs/rewritten/%.*s", len, label);
+	commit = lookup_commit_reference_by_name(buf->buf);
+	if (!commit) {
+		/* fall back to non-rewritten ref or commit */
+		strbuf_splice(buf, 0, strlen("refs/rewritten/"), "", 0);
+		commit = lookup_commit_reference_by_name(buf->buf);
+	}
+
+	if (!commit)
+		error(_("could not resolve '%s'"), buf->buf);
+
+	return commit;
+}
+
+static int do_merge(struct repository *r,
+		    struct commit *commit,
+		    const char *arg, int arg_len,
+		    int flags, struct replay_opts *opts)
+{
+	int run_commit_flags = (flags & TODO_EDIT_MERGE_MSG) ?
+		EDIT_MSG | VERIFY_MSG : 0;
+	struct strbuf ref_name = STRBUF_INIT;
+	struct commit *head_commit, *merge_commit, *i;
+	struct commit_list *bases, *j, *reversed = NULL;
+	struct commit_list *to_merge = NULL, **tail = &to_merge;
+	struct merge_options o;
+	int merge_arg_len, oneline_offset, can_fast_forward, ret, k;
+	static struct lock_file lock;
+	const char *p;
+
+	if (repo_hold_locked_index(r, &lock, LOCK_REPORT_ON_ERROR) < 0) {
+		ret = -1;
+		goto leave_merge;
+	}
+
+	head_commit = lookup_commit_reference_by_name("HEAD");
+	if (!head_commit) {
+		ret = error(_("cannot merge without a current revision"));
+		goto leave_merge;
+	}
+
+	/*
+	 * For octopus merges, the arg starts with the list of revisions to be
+	 * merged. The list is optionally followed by '#' and the oneline.
+	 */
+	merge_arg_len = oneline_offset = arg_len;
+	for (p = arg; p - arg < arg_len; p += strspn(p, " \t\n")) {
+		if (!*p)
+			break;
+		if (*p == '#' && (!p[1] || isspace(p[1]))) {
+			p += 1 + strspn(p + 1, " \t\n");
+			oneline_offset = p - arg;
+			break;
+		}
+		k = strcspn(p, " \t\n");
+		if (!k)
+			continue;
+		merge_commit = lookup_label(p, k, &ref_name);
+		if (!merge_commit) {
+			ret = error(_("unable to parse '%.*s'"), k, p);
+			goto leave_merge;
+		}
+		tail = &commit_list_insert(merge_commit, tail)->next;
+		p += k;
+		merge_arg_len = p - arg;
+	}
+
+	if (!to_merge) {
+		ret = error(_("nothing to merge: '%.*s'"), arg_len, arg);
+		goto leave_merge;
+	}
+
+	if (opts->have_squash_onto &&
+	    oideq(&head_commit->object.oid, &opts->squash_onto)) {
+		/*
+		 * When the user tells us to "merge" something into a
+		 * "[new root]", let's simply fast-forward to the merge head.
+		 */
+		rollback_lock_file(&lock);
+		if (to_merge->next)
+			ret = error(_("octopus merge cannot be executed on "
+				      "top of a [new root]"));
+		else
+			ret = fast_forward_to(r, &to_merge->item->object.oid,
+					      &head_commit->object.oid, 0,
+					      opts);
+		goto leave_merge;
+	}
+
+	if (commit) {
+		const char *message = get_commit_buffer(commit, NULL);
+		const char *body;
+		int len;
+
+		if (!message) {
+			ret = error(_("could not get commit message of '%s'"),
+				    oid_to_hex(&commit->object.oid));
+			goto leave_merge;
+		}
+		write_author_script(message);
+		find_commit_subject(message, &body);
+		len = strlen(body);
+		ret = write_message(body, len, git_path_merge_msg(r), 0);
+		unuse_commit_buffer(commit, message);
+		if (ret) {
+			error_errno(_("could not write '%s'"),
+				    git_path_merge_msg(r));
+			goto leave_merge;
+		}
+	} else {
+		struct strbuf buf = STRBUF_INIT;
+		int len;
+
+		strbuf_addf(&buf, "author %s", git_author_info(0));
+		write_author_script(buf.buf);
+		strbuf_reset(&buf);
+
+		if (oneline_offset < arg_len) {
+			p = arg + oneline_offset;
+			len = arg_len - oneline_offset;
+		} else {
+			strbuf_addf(&buf, "Merge %s '%.*s'",
+				    to_merge->next ? "branches" : "branch",
+				    merge_arg_len, arg);
+			p = buf.buf;
+			len = buf.len;
+		}
+
+		ret = write_message(p, len, git_path_merge_msg(r), 0);
+		strbuf_release(&buf);
+		if (ret) {
+			error_errno(_("could not write '%s'"),
+				    git_path_merge_msg(r));
+			goto leave_merge;
+		}
+	}
+
+	/*
+	 * If HEAD is not identical to the first parent of the original merge
+	 * commit, we cannot fast-forward.
+	 */
+	can_fast_forward = opts->allow_ff && commit && commit->parents &&
+		oideq(&commit->parents->item->object.oid,
+		      &head_commit->object.oid);
+
+	/*
+	 * If any merge head is different from the original one, we cannot
+	 * fast-forward.
+	 */
+	if (can_fast_forward) {
+		struct commit_list *p = commit->parents->next;
+
+		for (j = to_merge; j && p; j = j->next, p = p->next)
+			if (!oideq(&j->item->object.oid,
+				   &p->item->object.oid)) {
+				can_fast_forward = 0;
+				break;
+			}
+		/*
+		 * If the number of merge heads differs from the original merge
+		 * commit, we cannot fast-forward.
+		 */
+		if (j || p)
+			can_fast_forward = 0;
+	}
+
+	if (can_fast_forward) {
+		rollback_lock_file(&lock);
+		ret = fast_forward_to(r, &commit->object.oid,
+				      &head_commit->object.oid, 0, opts);
+		if (flags & TODO_EDIT_MERGE_MSG) {
+			run_commit_flags |= AMEND_MSG;
+			goto fast_forward_edit;
+		}
+		goto leave_merge;
+	}
+
+	if (to_merge->next) {
+		/* Octopus merge */
+		struct child_process cmd = CHILD_PROCESS_INIT;
+
+		if (read_env_script(&cmd.env_array)) {
+			const char *gpg_opt = gpg_sign_opt_quoted(opts);
+
+			ret = error(_(staged_changes_advice), gpg_opt, gpg_opt);
+			goto leave_merge;
+		}
+
+		cmd.git_cmd = 1;
+		argv_array_push(&cmd.args, "merge");
+		argv_array_push(&cmd.args, "-s");
+		argv_array_push(&cmd.args, "octopus");
+		argv_array_push(&cmd.args, "--no-edit");
+		argv_array_push(&cmd.args, "--no-ff");
+		argv_array_push(&cmd.args, "--no-log");
+		argv_array_push(&cmd.args, "--no-stat");
+		argv_array_push(&cmd.args, "-F");
+		argv_array_push(&cmd.args, git_path_merge_msg(r));
+		if (opts->gpg_sign)
+			argv_array_push(&cmd.args, opts->gpg_sign);
+
+		/* Add the tips to be merged */
+		for (j = to_merge; j; j = j->next)
+			argv_array_push(&cmd.args,
+					oid_to_hex(&j->item->object.oid));
+
+		strbuf_release(&ref_name);
+		unlink(git_path_cherry_pick_head(r));
+		rollback_lock_file(&lock);
+
+		rollback_lock_file(&lock);
+		ret = run_command(&cmd);
+
+		/* force re-reading of the cache */
+		if (!ret && (discard_index(r->index) < 0 ||
+			     repo_read_index(r) < 0))
+			ret = error(_("could not read index"));
+		goto leave_merge;
+	}
+
+	merge_commit = to_merge->item;
+	bases = get_merge_bases(head_commit, merge_commit);
+	if (bases && oideq(&merge_commit->object.oid,
+			   &bases->item->object.oid)) {
+		ret = 0;
+		/* skip merging an ancestor of HEAD */
+		goto leave_merge;
+	}
+
+	write_message(oid_to_hex(&merge_commit->object.oid), GIT_SHA1_HEXSZ,
+		      git_path_merge_head(r), 0);
+	write_message("no-ff", 5, git_path_merge_mode(r), 0);
+
+	for (j = bases; j; j = j->next)
+		commit_list_insert(j->item, &reversed);
+	free_commit_list(bases);
+
+	repo_read_index(r);
+	init_merge_options(&o, r);
+	o.branch1 = "HEAD";
+	o.branch2 = ref_name.buf;
+	o.buffer_output = 2;
+
+	ret = merge_recursive(&o, head_commit, merge_commit, reversed, &i);
+	if (ret <= 0)
+		fputs(o.obuf.buf, stdout);
+	strbuf_release(&o.obuf);
+	if (ret < 0) {
+		error(_("could not even attempt to merge '%.*s'"),
+		      merge_arg_len, arg);
+		goto leave_merge;
+	}
+	/*
+	 * The return value of merge_recursive() is 1 on clean, and 0 on
+	 * unclean merge.
+	 *
+	 * Let's reverse that, so that do_merge() returns 0 upon success and
+	 * 1 upon failed merge (keeping the return value -1 for the cases where
+	 * we will want to reschedule the `merge` command).
+	 */
+	ret = !ret;
+
+	if (r->index->cache_changed &&
+	    write_locked_index(r->index, &lock, COMMIT_LOCK)) {
+		ret = error(_("merge: Unable to write new index file"));
+		goto leave_merge;
+	}
+
+	rollback_lock_file(&lock);
+	if (ret)
+		repo_rerere(r, opts->allow_rerere_auto);
+	else
+		/*
+		 * In case of problems, we now want to return a positive
+		 * value (a negative one would indicate that the `merge`
+		 * command needs to be rescheduled).
+		 */
+	fast_forward_edit:
+		ret = !!run_git_commit(r, git_path_merge_msg(r), opts,
+				       run_commit_flags);
+
+leave_merge:
+	strbuf_release(&ref_name);
+	rollback_lock_file(&lock);
+	free_commit_list(to_merge);
+	return ret;
+}
+
+static int is_final_fixup(struct todo_list *todo_list)
+{
+	int i = todo_list->current;
+
+	if (!is_fixup(todo_list->items[i].command))
+		return 0;
+
+	while (++i < todo_list->nr)
+		if (is_fixup(todo_list->items[i].command))
+			return 0;
+		else if (!is_noop(todo_list->items[i].command))
+			break;
+	return 1;
+}
+
+static enum todo_command peek_command(struct todo_list *todo_list, int offset)
+{
+	int i;
+
+	for (i = todo_list->current + offset; i < todo_list->nr; i++)
+		if (!is_noop(todo_list->items[i].command))
+			return todo_list->items[i].command;
+
+	return -1;
+}
+
+static int apply_autostash(struct replay_opts *opts)
+{
+	struct strbuf stash_sha1 = STRBUF_INIT;
+	struct child_process child = CHILD_PROCESS_INIT;
+	int ret = 0;
+
+	if (!read_oneliner(&stash_sha1, rebase_path_autostash(), 1)) {
+		strbuf_release(&stash_sha1);
+		return 0;
+	}
+	strbuf_trim(&stash_sha1);
+
+	child.git_cmd = 1;
+	child.no_stdout = 1;
+	child.no_stderr = 1;
+	argv_array_push(&child.args, "stash");
+	argv_array_push(&child.args, "apply");
+	argv_array_push(&child.args, stash_sha1.buf);
+	if (!run_command(&child))
+		fprintf(stderr, _("Applied autostash.\n"));
+	else {
+		struct child_process store = CHILD_PROCESS_INIT;
+
+		store.git_cmd = 1;
+		argv_array_push(&store.args, "stash");
+		argv_array_push(&store.args, "store");
+		argv_array_push(&store.args, "-m");
+		argv_array_push(&store.args, "autostash");
+		argv_array_push(&store.args, "-q");
+		argv_array_push(&store.args, stash_sha1.buf);
+		if (run_command(&store))
+			ret = error(_("cannot store %s"), stash_sha1.buf);
+		else
+			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(&stash_sha1);
+	return ret;
+}
+
+static const char *reflog_message(struct replay_opts *opts,
+	const char *sub_action, const char *fmt, ...)
+{
+	va_list ap;
+	static struct strbuf buf = STRBUF_INIT;
+
+	va_start(ap, fmt);
+	strbuf_reset(&buf);
+	strbuf_addstr(&buf, action_name(opts));
+	if (sub_action)
+		strbuf_addf(&buf, " (%s)", sub_action);
+	if (fmt) {
+		strbuf_addstr(&buf, ": ");
+		strbuf_vaddf(&buf, fmt, ap);
+	}
+	va_end(ap);
+
+	return buf.buf;
+}
+
+static int run_git_checkout(struct repository *r, struct replay_opts *opts,
+			    const char *commit, const char *action)
+{
+	struct child_process cmd = CHILD_PROCESS_INIT;
+	int ret;
+
+	cmd.git_cmd = 1;
+
+	argv_array_push(&cmd.args, "checkout");
+	argv_array_push(&cmd.args, commit);
+	argv_array_pushf(&cmd.env_array, GIT_REFLOG_ACTION "=%s", action);
+
+	if (opts->verbose)
+		ret = run_command(&cmd);
+	else
+		ret = run_command_silent_on_success(&cmd);
+
+	if (!ret)
+		discard_index(r->index);
+
+	return ret;
+}
+
+int prepare_branch_to_be_rebased(struct repository *r, struct replay_opts *opts,
+				 const char *commit)
+{
+	const char *action;
+
+	if (commit && *commit) {
+		action = reflog_message(opts, "start", "checkout %s", commit);
+		if (run_git_checkout(r, opts, commit, action))
+			return error(_("could not checkout %s"), commit);
+	}
+
+	return 0;
+}
+
+static int checkout_onto(struct repository *r, struct replay_opts *opts,
+			 const char *onto_name, const struct object_id *onto,
+			 const char *orig_head)
+{
+	struct object_id oid;
+	const char *action = reflog_message(opts, "start", "checkout %s", onto_name);
+
+	if (get_oid(orig_head, &oid))
+		return error(_("%s: not a valid OID"), orig_head);
+
+	if (run_git_checkout(r, opts, oid_to_hex(onto), action)) {
+		apply_autostash(opts);
+		sequencer_remove_state(opts);
+		return error(_("could not detach HEAD"));
+	}
+
+	return update_ref(NULL, "ORIG_HEAD", &oid, NULL, 0, UPDATE_REFS_MSG_ON_ERR);
+}
+
+static int stopped_at_head(struct repository *r)
+{
+	struct object_id head;
+	struct commit *commit;
+	struct commit_message message;
+
+	if (get_oid("HEAD", &head) ||
+	    !(commit = lookup_commit(r, &head)) ||
+	    parse_commit(commit) || get_message(commit, &message))
+		fprintf(stderr, _("Stopped at HEAD\n"));
+	else {
+		fprintf(stderr, _("Stopped at %s\n"), message.label);
+		free_message(commit, &message);
+	}
+	return 0;
+
+}
+
+static const char rescheduled_advice[] =
+N_("Could not execute the todo command\n"
+"\n"
+"    %.*s"
+"\n"
+"It has been rescheduled; To edit the command before continuing, please\n"
+"edit the todo list first:\n"
+"\n"
+"    git rebase --edit-todo\n"
+"    git rebase --continue\n");
+
+static int pick_commits(struct repository *r,
+			struct todo_list *todo_list,
+			struct replay_opts *opts)
+{
+	int res = 0, reschedule = 0;
+
+	setenv(GIT_REFLOG_ACTION, action_name(opts), 0);
+	if (opts->allow_ff)
+		assert(!(opts->signoff || opts->no_commit ||
+				opts->record_origin || opts->edit));
+	if (read_and_refresh_cache(r, opts))
+		return -1;
+
+	while (todo_list->current < todo_list->nr) {
+		struct todo_item *item = todo_list->items + todo_list->current;
+		const char *arg = todo_item_get_arg(todo_list, item);
+
+		if (save_todo(todo_list, opts))
+			return -1;
+		if (is_rebase_i(opts)) {
+			if (item->command != TODO_COMMENT) {
+				FILE *f = fopen(rebase_path_msgnum(), "w");
+
+				todo_list->done_nr++;
+
+				if (f) {
+					fprintf(f, "%d\n", todo_list->done_nr);
+					fclose(f);
+				}
+				if (!opts->quiet)
+					fprintf(stderr, "Rebasing (%d/%d)%s",
+						todo_list->done_nr,
+						todo_list->total_nr,
+						opts->verbose ? "\n" : "\r");
+			}
+			unlink(rebase_path_message());
+			unlink(rebase_path_author_script());
+			unlink(rebase_path_stopped_sha());
+			unlink(rebase_path_amend());
+			unlink(git_path_merge_head(r));
+			delete_ref(NULL, "REBASE_HEAD", NULL, REF_NO_DEREF);
+
+			if (item->command == TODO_BREAK) {
+				if (!opts->verbose)
+					term_clear_line();
+				return stopped_at_head(r);
+			}
+		}
+		if (item->command <= TODO_SQUASH) {
+			if (is_rebase_i(opts))
+				setenv("GIT_REFLOG_ACTION", reflog_message(opts,
+					command_to_string(item->command), NULL),
+					1);
+			res = do_pick_commit(r, item->command, item->commit,
+					opts, is_final_fixup(todo_list));
+			if (is_rebase_i(opts) && res < 0) {
+				/* Reschedule */
+				advise(_(rescheduled_advice),
+				       get_item_line_length(todo_list,
+							    todo_list->current),
+				       get_item_line(todo_list,
+						     todo_list->current));
+				todo_list->current--;
+				if (save_todo(todo_list, opts))
+					return -1;
+			}
+			if (item->command == TODO_EDIT) {
+				struct commit *commit = item->commit;
+				if (!res) {
+					if (!opts->verbose)
+						term_clear_line();
+					fprintf(stderr,
+						_("Stopped at %s...  %.*s\n"),
+						short_commit_name(commit),
+						item->arg_len, arg);
+				}
+				return error_with_patch(r, commit,
+					arg, item->arg_len, opts, res, !res);
+			}
+			if (is_rebase_i(opts) && !res)
+				record_in_rewritten(&item->commit->object.oid,
+					peek_command(todo_list, 1));
+			if (res && is_fixup(item->command)) {
+				if (res == 1)
+					intend_to_amend();
+				return error_failed_squash(r, item->commit, opts,
+					item->arg_len, arg);
+			} else if (res && is_rebase_i(opts) && item->commit) {
+				int to_amend = 0;
+				struct object_id oid;
+
+				/*
+				 * If we are rewording and have either
+				 * fast-forwarded already, or are about to
+				 * create a new root commit, we want to amend,
+				 * otherwise we do not.
+				 */
+				if (item->command == TODO_REWORD &&
+				    !get_oid("HEAD", &oid) &&
+				    (oideq(&item->commit->object.oid, &oid) ||
+				     (opts->have_squash_onto &&
+				      oideq(&opts->squash_onto, &oid))))
+					to_amend = 1;
+
+				return res | error_with_patch(r, item->commit,
+						arg, item->arg_len, opts,
+						res, to_amend);
+			}
+		} else if (item->command == TODO_EXEC) {
+			char *end_of_arg = (char *)(arg + item->arg_len);
+			int saved = *end_of_arg;
+			struct stat st;
+
+			if (!opts->verbose)
+				term_clear_line();
+			*end_of_arg = '\0';
+			res = do_exec(r, arg);
+			*end_of_arg = saved;
+
+			if (res) {
+				if (opts->reschedule_failed_exec)
+					reschedule = 1;
+			} else if (stat(get_todo_path(opts), &st))
+				res = error_errno(_("could not stat '%s'"),
+						  get_todo_path(opts));
+			else if (match_stat_data(&todo_list->stat, &st)) {
+				/* Reread the todo file if it has changed. */
+				todo_list_release(todo_list);
+				if (read_populate_todo(r, todo_list, opts))
+					res = -1; /* message was printed */
+				/* `current` will be incremented below */
+				todo_list->current = -1;
+			}
+		} else if (item->command == TODO_LABEL) {
+			if ((res = do_label(r, arg, item->arg_len)))
+				reschedule = 1;
+		} else if (item->command == TODO_RESET) {
+			if ((res = do_reset(r, arg, item->arg_len, opts)))
+				reschedule = 1;
+		} else if (item->command == TODO_MERGE) {
+			if ((res = do_merge(r, item->commit,
+					    arg, item->arg_len,
+					    item->flags, opts)) < 0)
+				reschedule = 1;
+			else if (item->commit)
+				record_in_rewritten(&item->commit->object.oid,
+						    peek_command(todo_list, 1));
+			if (res > 0)
+				/* failed with merge conflicts */
+				return error_with_patch(r, item->commit,
+							arg, item->arg_len,
+							opts, res, 0);
+		} else if (!is_noop(item->command))
+			return error(_("unknown command %d"), item->command);
+
+		if (reschedule) {
+			advise(_(rescheduled_advice),
+			       get_item_line_length(todo_list,
+						    todo_list->current),
+			       get_item_line(todo_list, todo_list->current));
+			todo_list->current--;
+			if (save_todo(todo_list, opts))
+				return -1;
+			if (item->commit)
+				return error_with_patch(r,
+							item->commit,
+							arg, item->arg_len,
+							opts, res, 0);
+		}
+
+		todo_list->current++;
+		if (res)
+			return res;
+	}
+
+	if (is_rebase_i(opts)) {
+		struct strbuf head_ref = STRBUF_INIT, buf = STRBUF_INIT;
+		struct stat st;
+
+		/* Stopped in the middle, as planned? */
+		if (todo_list->current < todo_list->nr)
+			return 0;
+
+		if (read_oneliner(&head_ref, rebase_path_head_name(), 0) &&
+				starts_with(head_ref.buf, "refs/")) {
+			const char *msg;
+			struct object_id head, orig;
+			int res;
+
+			if (get_oid("HEAD", &head)) {
+				res = error(_("cannot read HEAD"));
+cleanup_head_ref:
+				strbuf_release(&head_ref);
+				strbuf_release(&buf);
+				return res;
+			}
+			if (!read_oneliner(&buf, rebase_path_orig_head(), 0) ||
+					get_oid_hex(buf.buf, &orig)) {
+				res = error(_("could not read orig-head"));
+				goto cleanup_head_ref;
+			}
+			strbuf_reset(&buf);
+			if (!read_oneliner(&buf, rebase_path_onto(), 0)) {
+				res = error(_("could not read 'onto'"));
+				goto cleanup_head_ref;
+			}
+			msg = reflog_message(opts, "finish", "%s onto %s",
+				head_ref.buf, buf.buf);
+			if (update_ref(msg, head_ref.buf, &head, &orig,
+				       REF_NO_DEREF, UPDATE_REFS_MSG_ON_ERR)) {
+				res = error(_("could not update %s"),
+					head_ref.buf);
+				goto cleanup_head_ref;
+			}
+			msg = reflog_message(opts, "finish", "returning to %s",
+				head_ref.buf);
+			if (create_symref("HEAD", head_ref.buf, msg)) {
+				res = error(_("could not update HEAD to %s"),
+					head_ref.buf);
+				goto cleanup_head_ref;
+			}
+			strbuf_reset(&buf);
+		}
+
+		if (opts->verbose) {
+			struct rev_info log_tree_opt;
+			struct object_id orig, head;
+
+			memset(&log_tree_opt, 0, sizeof(log_tree_opt));
+			repo_init_revisions(r, &log_tree_opt, NULL);
+			log_tree_opt.diff = 1;
+			log_tree_opt.diffopt.output_format =
+				DIFF_FORMAT_DIFFSTAT;
+			log_tree_opt.disable_stdin = 1;
+
+			if (read_oneliner(&buf, rebase_path_orig_head(), 0) &&
+			    !get_oid(buf.buf, &orig) &&
+			    !get_oid("HEAD", &head)) {
+				diff_tree_oid(&orig, &head, "",
+					      &log_tree_opt.diffopt);
+				log_tree_diff_flush(&log_tree_opt);
+			}
+		}
+		flush_rewritten_pending();
+		if (!stat(rebase_path_rewritten_list(), &st) &&
+				st.st_size > 0) {
+			struct child_process child = CHILD_PROCESS_INIT;
+			const char *post_rewrite_hook =
+				find_hook("post-rewrite");
+
+			child.in = open(rebase_path_rewritten_list(), O_RDONLY);
+			child.git_cmd = 1;
+			argv_array_push(&child.args, "notes");
+			argv_array_push(&child.args, "copy");
+			argv_array_push(&child.args, "--for-rewrite=rebase");
+			/* we don't care if this copying failed */
+			run_command(&child);
+
+			if (post_rewrite_hook) {
+				struct child_process hook = CHILD_PROCESS_INIT;
+
+				hook.in = open(rebase_path_rewritten_list(),
+					O_RDONLY);
+				hook.stdout_to_stderr = 1;
+				hook.trace2_hook_name = "post-rewrite";
+				argv_array_push(&hook.args, post_rewrite_hook);
+				argv_array_push(&hook.args, "rebase");
+				/* we don't care if this hook failed */
+				run_command(&hook);
+			}
+		}
+		apply_autostash(opts);
+
+		if (!opts->quiet) {
+			if (!opts->verbose)
+				term_clear_line();
+			fprintf(stderr,
+				"Successfully rebased and updated %s.\n",
+				head_ref.buf);
+		}
+
+		strbuf_release(&buf);
+		strbuf_release(&head_ref);
+	}
+
+	/*
+	 * Sequence of picks finished successfully; cleanup by
+	 * removing the .git/sequencer directory
+	 */
+	return sequencer_remove_state(opts);
+}
+
+static int continue_single_pick(struct repository *r)
+{
+	const char *argv[] = { "commit", NULL };
+
+	if (!file_exists(git_path_cherry_pick_head(r)) &&
+	    !file_exists(git_path_revert_head(r)))
+		return error(_("no cherry-pick or revert in progress"));
+	return run_command_v_opt(argv, RUN_GIT_CMD);
+}
+
+static int commit_staged_changes(struct repository *r,
+				 struct replay_opts *opts,
+				 struct todo_list *todo_list)
+{
+	unsigned int flags = ALLOW_EMPTY | EDIT_MSG;
+	unsigned int final_fixup = 0, is_clean;
+
+	if (has_unstaged_changes(r, 1))
+		return error(_("cannot rebase: You have unstaged changes."));
+
+	is_clean = !has_uncommitted_changes(r, 0);
+
+	if (file_exists(rebase_path_amend())) {
+		struct strbuf rev = STRBUF_INIT;
+		struct object_id head, to_amend;
+
+		if (get_oid("HEAD", &head))
+			return error(_("cannot amend non-existing commit"));
+		if (!read_oneliner(&rev, rebase_path_amend(), 0))
+			return error(_("invalid file: '%s'"), rebase_path_amend());
+		if (get_oid_hex(rev.buf, &to_amend))
+			return error(_("invalid contents: '%s'"),
+				rebase_path_amend());
+		if (!is_clean && !oideq(&head, &to_amend))
+			return error(_("\nYou have uncommitted changes in your "
+				       "working tree. Please, commit them\n"
+				       "first and then run 'git rebase "
+				       "--continue' again."));
+		/*
+		 * When skipping a failed fixup/squash, we need to edit the
+		 * commit message, the current fixup list and count, and if it
+		 * was the last fixup/squash in the chain, we need to clean up
+		 * the commit message and if there was a squash, let the user
+		 * edit it.
+		 */
+		if (!is_clean || !opts->current_fixup_count)
+			; /* this is not the final fixup */
+		else if (!oideq(&head, &to_amend) ||
+			 !file_exists(rebase_path_stopped_sha())) {
+			/* was a final fixup or squash done manually? */
+			if (!is_fixup(peek_command(todo_list, 0))) {
+				unlink(rebase_path_fixup_msg());
+				unlink(rebase_path_squash_msg());
+				unlink(rebase_path_current_fixups());
+				strbuf_reset(&opts->current_fixups);
+				opts->current_fixup_count = 0;
+			}
+		} else {
+			/* we are in a fixup/squash chain */
+			const char *p = opts->current_fixups.buf;
+			int len = opts->current_fixups.len;
+
+			opts->current_fixup_count--;
+			if (!len)
+				BUG("Incorrect current_fixups:\n%s", p);
+			while (len && p[len - 1] != '\n')
+				len--;
+			strbuf_setlen(&opts->current_fixups, len);
+			if (write_message(p, len, rebase_path_current_fixups(),
+					  0) < 0)
+				return error(_("could not write file: '%s'"),
+					     rebase_path_current_fixups());
+
+			/*
+			 * If a fixup/squash in a fixup/squash chain failed, the
+			 * commit message is already correct, no need to commit
+			 * it again.
+			 *
+			 * Only if it is the final command in the fixup/squash
+			 * chain, and only if the chain is longer than a single
+			 * fixup/squash command (which was just skipped), do we
+			 * actually need to re-commit with a cleaned up commit
+			 * message.
+			 */
+			if (opts->current_fixup_count > 0 &&
+			    !is_fixup(peek_command(todo_list, 0))) {
+				final_fixup = 1;
+				/*
+				 * If there was not a single "squash" in the
+				 * chain, we only need to clean up the commit
+				 * message, no need to bother the user with
+				 * opening the commit message in the editor.
+				 */
+				if (!starts_with(p, "squash ") &&
+				    !strstr(p, "\nsquash "))
+					flags = (flags & ~EDIT_MSG) | CLEANUP_MSG;
+			} else if (is_fixup(peek_command(todo_list, 0))) {
+				/*
+				 * We need to update the squash message to skip
+				 * the latest commit message.
+				 */
+				struct commit *commit;
+				const char *path = rebase_path_squash_msg();
+
+				if (parse_head(r, &commit) ||
+				    !(p = get_commit_buffer(commit, NULL)) ||
+				    write_message(p, strlen(p), path, 0)) {
+					unuse_commit_buffer(commit, p);
+					return error(_("could not write file: "
+						       "'%s'"), path);
+				}
+				unuse_commit_buffer(commit, p);
+			}
+		}
+
+		strbuf_release(&rev);
+		flags |= AMEND_MSG;
+	}
+
+	if (is_clean) {
+		const char *cherry_pick_head = git_path_cherry_pick_head(r);
+
+		if (file_exists(cherry_pick_head) && unlink(cherry_pick_head))
+			return error(_("could not remove CHERRY_PICK_HEAD"));
+		if (!final_fixup)
+			return 0;
+	}
+
+	if (run_git_commit(r, final_fixup ? NULL : rebase_path_message(),
+			   opts, flags))
+		return error(_("could not commit staged changes."));
+	unlink(rebase_path_amend());
+	unlink(git_path_merge_head(r));
+	if (final_fixup) {
+		unlink(rebase_path_fixup_msg());
+		unlink(rebase_path_squash_msg());
+	}
+	if (opts->current_fixup_count > 0) {
+		/*
+		 * Whether final fixup or not, we just cleaned up the commit
+		 * message...
+		 */
+		unlink(rebase_path_current_fixups());
+		strbuf_reset(&opts->current_fixups);
+		opts->current_fixup_count = 0;
+	}
+	return 0;
+}
+
+int sequencer_continue(struct repository *r, struct replay_opts *opts)
+{
+	struct todo_list todo_list = TODO_LIST_INIT;
+	int res;
+
+	if (read_and_refresh_cache(r, opts))
+		return -1;
+
+	if (read_populate_opts(opts))
+		return -1;
+	if (is_rebase_i(opts)) {
+		if ((res = read_populate_todo(r, &todo_list, opts)))
+			goto release_todo_list;
+		if (commit_staged_changes(r, opts, &todo_list))
+			return -1;
+	} else if (!file_exists(get_todo_path(opts)))
+		return continue_single_pick(r);
+	else if ((res = read_populate_todo(r, &todo_list, opts)))
+		goto release_todo_list;
+
+	if (!is_rebase_i(opts)) {
+		/* Verify that the conflict has been resolved */
+		if (file_exists(git_path_cherry_pick_head(r)) ||
+		    file_exists(git_path_revert_head(r))) {
+			res = continue_single_pick(r);
+			if (res)
+				goto release_todo_list;
+		}
+		if (index_differs_from(r, "HEAD", NULL, 0)) {
+			res = error_dirty_index(r, opts);
+			goto release_todo_list;
+		}
+		todo_list.current++;
+	} else if (file_exists(rebase_path_stopped_sha())) {
+		struct strbuf buf = STRBUF_INIT;
+		struct object_id oid;
+
+		if (read_oneliner(&buf, rebase_path_stopped_sha(), 1) &&
+		    !get_oid_committish(buf.buf, &oid))
+			record_in_rewritten(&oid, peek_command(&todo_list, 0));
+		strbuf_release(&buf);
+	}
+
+	res = pick_commits(r, &todo_list, opts);
+release_todo_list:
+	todo_list_release(&todo_list);
+	return res;
+}
+
+static int single_pick(struct repository *r,
+		       struct commit *cmit,
+		       struct replay_opts *opts)
+{
+	setenv(GIT_REFLOG_ACTION, action_name(opts), 0);
+	return do_pick_commit(r, opts->action == REPLAY_PICK ?
+		TODO_PICK : TODO_REVERT, cmit, opts, 0);
+}
+
+int sequencer_pick_revisions(struct repository *r,
+			     struct replay_opts *opts)
+{
+	struct todo_list todo_list = TODO_LIST_INIT;
+	struct object_id oid;
+	int i, res;
+
+	assert(opts->revs);
+	if (read_and_refresh_cache(r, opts))
+		return -1;
+
+	for (i = 0; i < opts->revs->pending.nr; i++) {
+		struct object_id oid;
+		const char *name = opts->revs->pending.objects[i].name;
+
+		/* This happens when using --stdin. */
+		if (!strlen(name))
+			continue;
+
+		if (!get_oid(name, &oid)) {
+			if (!lookup_commit_reference_gently(r, &oid, 1)) {
+				enum object_type type = oid_object_info(r,
+									&oid,
+									NULL);
+				return error(_("%s: can't cherry-pick a %s"),
+					name, type_name(type));
+			}
+		} else
+			return error(_("%s: bad revision"), name);
+	}
+
+	/*
+	 * If we were called as "git cherry-pick <commit>", just
+	 * cherry-pick/revert it, set CHERRY_PICK_HEAD /
+	 * REVERT_HEAD, and don't touch the sequencer state.
+	 * This means it is possible to cherry-pick in the middle
+	 * of a cherry-pick sequence.
+	 */
+	if (opts->revs->cmdline.nr == 1 &&
+	    opts->revs->cmdline.rev->whence == REV_CMD_REV &&
+	    opts->revs->no_walk &&
+	    !opts->revs->cmdline.rev->flags) {
+		struct commit *cmit;
+		if (prepare_revision_walk(opts->revs))
+			return error(_("revision walk setup failed"));
+		cmit = get_revision(opts->revs);
+		if (!cmit)
+			return error(_("empty commit set passed"));
+		if (get_revision(opts->revs))
+			BUG("unexpected extra commit from walk");
+		return single_pick(r, cmit, opts);
+	}
+
+	/*
+	 * Start a new cherry-pick/ revert sequence; but
+	 * first, make sure that an existing one isn't in
+	 * progress
+	 */
+
+	if (walk_revs_populate_todo(&todo_list, opts) ||
+			create_seq_dir(r) < 0)
+		return -1;
+	if (get_oid("HEAD", &oid) && (opts->action == REPLAY_REVERT))
+		return error(_("can't revert as initial commit"));
+	if (save_head(oid_to_hex(&oid)))
+		return -1;
+	if (save_opts(opts))
+		return -1;
+	update_abort_safety_file();
+	res = pick_commits(r, &todo_list, opts);
+	todo_list_release(&todo_list);
+	return res;
+}
+
+void append_signoff(struct strbuf *msgbuf, size_t ignore_footer, unsigned flag)
+{
+	unsigned no_dup_sob = flag & APPEND_SIGNOFF_DEDUP;
+	struct strbuf sob = STRBUF_INIT;
+	int has_footer;
+
+	strbuf_addstr(&sob, sign_off_header);
+	strbuf_addstr(&sob, fmt_name(WANT_COMMITTER_IDENT));
+	strbuf_addch(&sob, '\n');
+
+	if (!ignore_footer)
+		strbuf_complete_line(msgbuf);
+
+	/*
+	 * If the whole message buffer is equal to the sob, pretend that we
+	 * found a conforming footer with a matching sob
+	 */
+	if (msgbuf->len - ignore_footer == sob.len &&
+	    !strncmp(msgbuf->buf, sob.buf, sob.len))
+		has_footer = 3;
+	else
+		has_footer = has_conforming_footer(msgbuf, &sob, ignore_footer);
+
+	if (!has_footer) {
+		const char *append_newlines = NULL;
+		size_t len = msgbuf->len - ignore_footer;
+
+		if (!len) {
+			/*
+			 * The buffer is completely empty.  Leave foom for
+			 * the title and body to be filled in by the user.
+			 */
+			append_newlines = "\n\n";
+		} else if (len == 1) {
+			/*
+			 * Buffer contains a single newline.  Add another
+			 * so that we leave room for the title and body.
+			 */
+			append_newlines = "\n";
+		} else if (msgbuf->buf[len - 2] != '\n') {
+			/*
+			 * Buffer ends with a single newline.  Add another
+			 * so that there is an empty line between the message
+			 * body and the sob.
+			 */
+			append_newlines = "\n";
+		} /* else, the buffer already ends with two newlines. */
+
+		if (append_newlines)
+			strbuf_splice(msgbuf, msgbuf->len - ignore_footer, 0,
+				append_newlines, strlen(append_newlines));
+	}
+
+	if (has_footer != 3 && (!no_dup_sob || has_footer != 2))
+		strbuf_splice(msgbuf, msgbuf->len - ignore_footer, 0,
+				sob.buf, sob.len);
+
+	strbuf_release(&sob);
+}
+
+struct labels_entry {
+	struct hashmap_entry entry;
+	char label[FLEX_ARRAY];
+};
+
+static int labels_cmp(const void *fndata, const struct labels_entry *a,
+		      const struct labels_entry *b, const void *key)
+{
+	return key ? strcmp(a->label, key) : strcmp(a->label, b->label);
+}
+
+struct string_entry {
+	struct oidmap_entry entry;
+	char string[FLEX_ARRAY];
+};
+
+struct label_state {
+	struct oidmap commit2label;
+	struct hashmap labels;
+	struct strbuf buf;
+};
+
+static const char *label_oid(struct object_id *oid, const char *label,
+			     struct label_state *state)
+{
+	struct labels_entry *labels_entry;
+	struct string_entry *string_entry;
+	struct object_id dummy;
+	size_t len;
+	int i;
+
+	string_entry = oidmap_get(&state->commit2label, oid);
+	if (string_entry)
+		return string_entry->string;
+
+	/*
+	 * For "uninteresting" commits, i.e. commits that are not to be
+	 * rebased, and which can therefore not be labeled, we use a unique
+	 * abbreviation of the commit name. This is slightly more complicated
+	 * than calling find_unique_abbrev() because we also need to make
+	 * sure that the abbreviation does not conflict with any other
+	 * label.
+	 *
+	 * We disallow "interesting" commits to be labeled by a string that
+	 * is a valid full-length hash, to ensure that we always can find an
+	 * abbreviation for any uninteresting commit's names that does not
+	 * clash with any other label.
+	 */
+	if (!label) {
+		char *p;
+
+		strbuf_reset(&state->buf);
+		strbuf_grow(&state->buf, GIT_SHA1_HEXSZ);
+		label = p = state->buf.buf;
+
+		find_unique_abbrev_r(p, oid, default_abbrev);
+
+		/*
+		 * We may need to extend the abbreviated hash so that there is
+		 * no conflicting label.
+		 */
+		if (hashmap_get_from_hash(&state->labels, strihash(p), p)) {
+			size_t i = strlen(p) + 1;
+
+			oid_to_hex_r(p, oid);
+			for (; i < GIT_SHA1_HEXSZ; i++) {
+				char save = p[i];
+				p[i] = '\0';
+				if (!hashmap_get_from_hash(&state->labels,
+							   strihash(p), p))
+					break;
+				p[i] = save;
+			}
+		}
+	} else if (((len = strlen(label)) == the_hash_algo->hexsz &&
+		    !get_oid_hex(label, &dummy)) ||
+		   (len == 1 && *label == '#') ||
+		   hashmap_get_from_hash(&state->labels,
+					 strihash(label), label)) {
+		/*
+		 * If the label already exists, or if the label is a valid full
+		 * OID, or the label is a '#' (which we use as a separator
+		 * between merge heads and oneline), we append a dash and a
+		 * number to make it unique.
+		 */
+		struct strbuf *buf = &state->buf;
+
+		strbuf_reset(buf);
+		strbuf_add(buf, label, len);
+
+		for (i = 2; ; i++) {
+			strbuf_setlen(buf, len);
+			strbuf_addf(buf, "-%d", i);
+			if (!hashmap_get_from_hash(&state->labels,
+						   strihash(buf->buf),
+						   buf->buf))
+				break;
+		}
+
+		label = buf->buf;
+	}
+
+	FLEX_ALLOC_STR(labels_entry, label, label);
+	hashmap_entry_init(labels_entry, strihash(label));
+	hashmap_add(&state->labels, labels_entry);
+
+	FLEX_ALLOC_STR(string_entry, string, label);
+	oidcpy(&string_entry->entry.oid, oid);
+	oidmap_put(&state->commit2label, string_entry);
+
+	return string_entry->string;
+}
+
+static int make_script_with_merges(struct pretty_print_context *pp,
+				   struct rev_info *revs, struct strbuf *out,
+				   unsigned flags)
+{
+	int keep_empty = flags & TODO_LIST_KEEP_EMPTY;
+	int rebase_cousins = flags & TODO_LIST_REBASE_COUSINS;
+	struct strbuf buf = STRBUF_INIT, oneline = STRBUF_INIT;
+	struct strbuf label = STRBUF_INIT;
+	struct commit_list *commits = NULL, **tail = &commits, *iter;
+	struct commit_list *tips = NULL, **tips_tail = &tips;
+	struct commit *commit;
+	struct oidmap commit2todo = OIDMAP_INIT;
+	struct string_entry *entry;
+	struct oidset interesting = OIDSET_INIT, child_seen = OIDSET_INIT,
+		shown = OIDSET_INIT;
+	struct label_state state = { OIDMAP_INIT, { NULL }, STRBUF_INIT };
+
+	int abbr = flags & TODO_LIST_ABBREVIATE_CMDS;
+	const char *cmd_pick = abbr ? "p" : "pick",
+		*cmd_label = abbr ? "l" : "label",
+		*cmd_reset = abbr ? "t" : "reset",
+		*cmd_merge = abbr ? "m" : "merge";
+
+	oidmap_init(&commit2todo, 0);
+	oidmap_init(&state.commit2label, 0);
+	hashmap_init(&state.labels, (hashmap_cmp_fn) labels_cmp, NULL, 0);
+	strbuf_init(&state.buf, 32);
+
+	if (revs->cmdline.nr && (revs->cmdline.rev[0].flags & BOTTOM)) {
+		struct object_id *oid = &revs->cmdline.rev[0].item->oid;
+		FLEX_ALLOC_STR(entry, string, "onto");
+		oidcpy(&entry->entry.oid, oid);
+		oidmap_put(&state.commit2label, entry);
+	}
+
+	/*
+	 * First phase:
+	 * - get onelines for all commits
+	 * - gather all branch tips (i.e. 2nd or later parents of merges)
+	 * - label all branch tips
+	 */
+	while ((commit = get_revision(revs))) {
+		struct commit_list *to_merge;
+		const char *p1, *p2;
+		struct object_id *oid;
+		int is_empty;
+
+		tail = &commit_list_insert(commit, tail)->next;
+		oidset_insert(&interesting, &commit->object.oid);
+
+		is_empty = is_original_commit_empty(commit);
+		if (!is_empty && (commit->object.flags & PATCHSAME))
+			continue;
+
+		strbuf_reset(&oneline);
+		pretty_print_commit(pp, commit, &oneline);
+
+		to_merge = commit->parents ? commit->parents->next : NULL;
+		if (!to_merge) {
+			/* non-merge commit: easy case */
+			strbuf_reset(&buf);
+			if (!keep_empty && is_empty)
+				strbuf_addf(&buf, "%c ", comment_line_char);
+			strbuf_addf(&buf, "%s %s %s", cmd_pick,
+				    oid_to_hex(&commit->object.oid),
+				    oneline.buf);
+
+			FLEX_ALLOC_STR(entry, string, buf.buf);
+			oidcpy(&entry->entry.oid, &commit->object.oid);
+			oidmap_put(&commit2todo, entry);
+
+			continue;
+		}
+
+		/* Create a label */
+		strbuf_reset(&label);
+		if (skip_prefix(oneline.buf, "Merge ", &p1) &&
+		    (p1 = strchr(p1, '\'')) &&
+		    (p2 = strchr(++p1, '\'')))
+			strbuf_add(&label, p1, p2 - p1);
+		else if (skip_prefix(oneline.buf, "Merge pull request ",
+				     &p1) &&
+			 (p1 = strstr(p1, " from ")))
+			strbuf_addstr(&label, p1 + strlen(" from "));
+		else
+			strbuf_addbuf(&label, &oneline);
+
+		for (p1 = label.buf; *p1; p1++)
+			if (isspace(*p1))
+				*(char *)p1 = '-';
+
+		strbuf_reset(&buf);
+		strbuf_addf(&buf, "%s -C %s",
+			    cmd_merge, oid_to_hex(&commit->object.oid));
+
+		/* label the tips of merged branches */
+		for (; to_merge; to_merge = to_merge->next) {
+			oid = &to_merge->item->object.oid;
+			strbuf_addch(&buf, ' ');
+
+			if (!oidset_contains(&interesting, oid)) {
+				strbuf_addstr(&buf, label_oid(oid, NULL,
+							      &state));
+				continue;
+			}
+
+			tips_tail = &commit_list_insert(to_merge->item,
+							tips_tail)->next;
+
+			strbuf_addstr(&buf, label_oid(oid, label.buf, &state));
+		}
+		strbuf_addf(&buf, " # %s", oneline.buf);
+
+		FLEX_ALLOC_STR(entry, string, buf.buf);
+		oidcpy(&entry->entry.oid, &commit->object.oid);
+		oidmap_put(&commit2todo, entry);
+	}
+
+	/*
+	 * Second phase:
+	 * - label branch points
+	 * - add HEAD to the branch tips
+	 */
+	for (iter = commits; iter; iter = iter->next) {
+		struct commit_list *parent = iter->item->parents;
+		for (; parent; parent = parent->next) {
+			struct object_id *oid = &parent->item->object.oid;
+			if (!oidset_contains(&interesting, oid))
+				continue;
+			if (oidset_insert(&child_seen, oid))
+				label_oid(oid, "branch-point", &state);
+		}
+
+		/* Add HEAD as implict "tip of branch" */
+		if (!iter->next)
+			tips_tail = &commit_list_insert(iter->item,
+							tips_tail)->next;
+	}
+
+	/*
+	 * Third phase: output the todo list. This is a bit tricky, as we
+	 * want to avoid jumping back and forth between revisions. To
+	 * accomplish that goal, we walk backwards from the branch tips,
+	 * gathering commits not yet shown, reversing the list on the fly,
+	 * then outputting that list (labeling revisions as needed).
+	 */
+	strbuf_addf(out, "%s onto\n", cmd_label);
+	for (iter = tips; iter; iter = iter->next) {
+		struct commit_list *list = NULL, *iter2;
+
+		commit = iter->item;
+		if (oidset_contains(&shown, &commit->object.oid))
+			continue;
+		entry = oidmap_get(&state.commit2label, &commit->object.oid);
+
+		if (entry)
+			strbuf_addf(out, "\n%c Branch %s\n", comment_line_char, entry->string);
+		else
+			strbuf_addch(out, '\n');
+
+		while (oidset_contains(&interesting, &commit->object.oid) &&
+		       !oidset_contains(&shown, &commit->object.oid)) {
+			commit_list_insert(commit, &list);
+			if (!commit->parents) {
+				commit = NULL;
+				break;
+			}
+			commit = commit->parents->item;
+		}
+
+		if (!commit)
+			strbuf_addf(out, "%s %s\n", cmd_reset,
+				    rebase_cousins ? "onto" : "[new root]");
+		else {
+			const char *to = NULL;
+
+			entry = oidmap_get(&state.commit2label,
+					   &commit->object.oid);
+			if (entry)
+				to = entry->string;
+			else if (!rebase_cousins)
+				to = label_oid(&commit->object.oid, NULL,
+					       &state);
+
+			if (!to || !strcmp(to, "onto"))
+				strbuf_addf(out, "%s onto\n", cmd_reset);
+			else {
+				strbuf_reset(&oneline);
+				pretty_print_commit(pp, commit, &oneline);
+				strbuf_addf(out, "%s %s # %s\n",
+					    cmd_reset, to, oneline.buf);
+			}
+		}
+
+		for (iter2 = list; iter2; iter2 = iter2->next) {
+			struct object_id *oid = &iter2->item->object.oid;
+			entry = oidmap_get(&commit2todo, oid);
+			/* only show if not already upstream */
+			if (entry)
+				strbuf_addf(out, "%s\n", entry->string);
+			entry = oidmap_get(&state.commit2label, oid);
+			if (entry)
+				strbuf_addf(out, "%s %s\n",
+					    cmd_label, entry->string);
+			oidset_insert(&shown, oid);
+		}
+
+		free_commit_list(list);
+	}
+
+	free_commit_list(commits);
+	free_commit_list(tips);
+
+	strbuf_release(&label);
+	strbuf_release(&oneline);
+	strbuf_release(&buf);
+
+	oidmap_free(&commit2todo, 1);
+	oidmap_free(&state.commit2label, 1);
+	hashmap_free(&state.labels, 1);
+	strbuf_release(&state.buf);
+
+	return 0;
+}
+
+int sequencer_make_script(struct repository *r, struct strbuf *out, int argc,
+			  const char **argv, unsigned flags)
+{
+	char *format = NULL;
+	struct pretty_print_context pp = {0};
+	struct rev_info revs;
+	struct commit *commit;
+	int keep_empty = flags & TODO_LIST_KEEP_EMPTY;
+	const char *insn = flags & TODO_LIST_ABBREVIATE_CMDS ? "p" : "pick";
+	int rebase_merges = flags & TODO_LIST_REBASE_MERGES;
+
+	repo_init_revisions(r, &revs, NULL);
+	revs.verbose_header = 1;
+	if (!rebase_merges)
+		revs.max_parents = 1;
+	revs.cherry_mark = 1;
+	revs.limited = 1;
+	revs.reverse = 1;
+	revs.right_only = 1;
+	revs.sort_order = REV_SORT_IN_GRAPH_ORDER;
+	revs.topo_order = 1;
+
+	revs.pretty_given = 1;
+	git_config_get_string("rebase.instructionFormat", &format);
+	if (!format || !*format) {
+		free(format);
+		format = xstrdup("%s");
+	}
+	get_commit_format(format, &revs);
+	free(format);
+	pp.fmt = revs.commit_format;
+	pp.output_encoding = get_log_output_encoding();
+
+	if (setup_revisions(argc, argv, &revs, NULL) > 1)
+		return error(_("make_script: unhandled options"));
+
+	if (prepare_revision_walk(&revs) < 0)
+		return error(_("make_script: error preparing revisions"));
+
+	if (rebase_merges)
+		return make_script_with_merges(&pp, &revs, out, flags);
+
+	while ((commit = get_revision(&revs))) {
+		int is_empty  = is_original_commit_empty(commit);
+
+		if (!is_empty && (commit->object.flags & PATCHSAME))
+			continue;
+		if (!keep_empty && is_empty)
+			strbuf_addf(out, "%c ", comment_line_char);
+		strbuf_addf(out, "%s %s ", insn,
+			    oid_to_hex(&commit->object.oid));
+		pretty_print_commit(&pp, commit, out);
+		strbuf_addch(out, '\n');
+	}
+	return 0;
+}
+
+/*
+ * Add commands after pick and (series of) squash/fixup commands
+ * in the todo list.
+ */
+void todo_list_add_exec_commands(struct todo_list *todo_list,
+				 struct string_list *commands)
+{
+	struct strbuf *buf = &todo_list->buf;
+	size_t base_offset = buf->len;
+	int i, insert, nr = 0, alloc = 0;
+	struct todo_item *items = NULL, *base_items = NULL;
+
+	base_items = xcalloc(commands->nr, sizeof(struct todo_item));
+	for (i = 0; i < commands->nr; i++) {
+		size_t command_len = strlen(commands->items[i].string);
+
+		strbuf_addstr(buf, commands->items[i].string);
+		strbuf_addch(buf, '\n');
+
+		base_items[i].command = TODO_EXEC;
+		base_items[i].offset_in_buf = base_offset;
+		base_items[i].arg_offset = base_offset + strlen("exec ");
+		base_items[i].arg_len = command_len - strlen("exec ");
+
+		base_offset += command_len + 1;
+	}
+
+	/*
+	 * Insert <commands> after every pick. Here, fixup/squash chains
+	 * are considered part of the pick, so we insert the commands *after*
+	 * those chains if there are any.
+	 *
+	 * As we insert the exec commands immediatly after rearranging
+	 * any fixups and before the user edits the list, a fixup chain
+	 * can never contain comments (any comments are empty picks that
+	 * have been commented out because the user did not specify
+	 * --keep-empty).  So, it is safe to insert an exec command
+	 * without looking at the command following a comment.
+	 */
+	insert = 0;
+	for (i = 0; i < todo_list->nr; i++) {
+		enum todo_command command = todo_list->items[i].command;
+		if (insert && !is_fixup(command)) {
+			ALLOC_GROW(items, nr + commands->nr, alloc);
+			COPY_ARRAY(items + nr, base_items, commands->nr);
+			nr += commands->nr;
+
+			insert = 0;
+		}
+
+		ALLOC_GROW(items, nr + 1, alloc);
+		items[nr++] = todo_list->items[i];
+
+		if (command == TODO_PICK || command == TODO_MERGE)
+			insert = 1;
+	}
+
+	/* insert or append final <commands> */
+	if (insert || nr == todo_list->nr) {
+		ALLOC_GROW(items, nr + commands->nr, alloc);
+		COPY_ARRAY(items + nr, base_items, commands->nr);
+		nr += commands->nr;
+	}
+
+	free(base_items);
+	FREE_AND_NULL(todo_list->items);
+	todo_list->items = items;
+	todo_list->nr = nr;
+	todo_list->alloc = alloc;
+}
+
+static void todo_list_to_strbuf(struct repository *r, struct todo_list *todo_list,
+				struct strbuf *buf, int num, unsigned flags)
+{
+	struct todo_item *item;
+	int i, max = todo_list->nr;
+
+	if (num > 0 && num < max)
+		max = num;
+
+	for (item = todo_list->items, i = 0; i < max; i++, item++) {
+		/* if the item is not a command write it and continue */
+		if (item->command >= TODO_COMMENT) {
+			strbuf_addf(buf, "%.*s\n", item->arg_len,
+				    todo_item_get_arg(todo_list, item));
+			continue;
+		}
+
+		/* add command to the buffer */
+		if (flags & TODO_LIST_ABBREVIATE_CMDS)
+			strbuf_addch(buf, command_to_char(item->command));
+		else
+			strbuf_addstr(buf, command_to_string(item->command));
+
+		/* add commit id */
+		if (item->commit) {
+			const char *oid = flags & TODO_LIST_SHORTEN_IDS ?
+					  short_commit_name(item->commit) :
+					  oid_to_hex(&item->commit->object.oid);
+
+			if (item->command == TODO_MERGE) {
+				if (item->flags & TODO_EDIT_MERGE_MSG)
+					strbuf_addstr(buf, " -c");
+				else
+					strbuf_addstr(buf, " -C");
+			}
+
+			strbuf_addf(buf, " %s", oid);
+		}
+
+		/* add all the rest */
+		if (!item->arg_len)
+			strbuf_addch(buf, '\n');
+		else
+			strbuf_addf(buf, " %.*s\n", item->arg_len,
+				    todo_item_get_arg(todo_list, item));
+	}
+}
+
+int todo_list_write_to_file(struct repository *r, struct todo_list *todo_list,
+			    const char *file, const char *shortrevisions,
+			    const char *shortonto, int num, unsigned flags)
+{
+	int res;
+	struct strbuf buf = STRBUF_INIT;
+
+	todo_list_to_strbuf(r, todo_list, &buf, num, flags);
+	if (flags & TODO_LIST_APPEND_TODO_HELP)
+		append_todo_help(flags & TODO_LIST_KEEP_EMPTY, count_commands(todo_list),
+				 shortrevisions, shortonto, &buf);
+
+	res = write_message(buf.buf, buf.len, file, 0);
+	strbuf_release(&buf);
+
+	return res;
+}
+
+static const char edit_todo_list_advice[] =
+N_("You can fix this with 'git rebase --edit-todo' "
+"and then run 'git rebase --continue'.\n"
+"Or you can abort the rebase with 'git rebase"
+" --abort'.\n");
+
+int check_todo_list_from_file(struct repository *r)
+{
+	struct todo_list old_todo = TODO_LIST_INIT, new_todo = TODO_LIST_INIT;
+	int res = 0;
+
+	if (strbuf_read_file_or_whine(&new_todo.buf, rebase_path_todo()) < 0) {
+		res = -1;
+		goto out;
+	}
+
+	if (strbuf_read_file_or_whine(&old_todo.buf, rebase_path_todo_backup()) < 0) {
+		res = -1;
+		goto out;
+	}
+
+	res = todo_list_parse_insn_buffer(r, old_todo.buf.buf, &old_todo);
+	if (!res)
+		res = todo_list_parse_insn_buffer(r, new_todo.buf.buf, &new_todo);
+	if (!res)
+		res = todo_list_check(&old_todo, &new_todo);
+	if (res)
+		fprintf(stderr, _(edit_todo_list_advice));
+out:
+	todo_list_release(&old_todo);
+	todo_list_release(&new_todo);
+
+	return res;
+}
+
+/* skip picking commits whose parents are unchanged */
+static int skip_unnecessary_picks(struct repository *r,
+				  struct todo_list *todo_list,
+				  struct object_id *base_oid)
+{
+	struct object_id *parent_oid;
+	int i;
+
+	for (i = 0; i < todo_list->nr; i++) {
+		struct todo_item *item = todo_list->items + i;
+
+		if (item->command >= TODO_NOOP)
+			continue;
+		if (item->command != TODO_PICK)
+			break;
+		if (parse_commit(item->commit)) {
+			return error(_("could not parse commit '%s'"),
+				oid_to_hex(&item->commit->object.oid));
+		}
+		if (!item->commit->parents)
+			break; /* root commit */
+		if (item->commit->parents->next)
+			break; /* merge commit */
+		parent_oid = &item->commit->parents->item->object.oid;
+		if (!oideq(parent_oid, base_oid))
+			break;
+		oidcpy(base_oid, &item->commit->object.oid);
+	}
+	if (i > 0) {
+		const char *done_path = rebase_path_done();
+
+		if (todo_list_write_to_file(r, todo_list, done_path, NULL, NULL, i, 0)) {
+			error_errno(_("could not write to '%s'"), done_path);
+			return -1;
+		}
+
+		MOVE_ARRAY(todo_list->items, todo_list->items + i, todo_list->nr - i);
+		todo_list->nr -= i;
+		todo_list->current = 0;
+
+		if (is_fixup(peek_command(todo_list, 0)))
+			record_in_rewritten(base_oid, peek_command(todo_list, 0));
+	}
+
+	return 0;
+}
+
+int complete_action(struct repository *r, struct replay_opts *opts, unsigned flags,
+		    const char *shortrevisions, const char *onto_name,
+		    struct commit *onto, const char *orig_head,
+		    struct string_list *commands, unsigned autosquash,
+		    struct todo_list *todo_list)
+{
+	const char *shortonto, *todo_file = rebase_path_todo();
+	struct todo_list new_todo = TODO_LIST_INIT;
+	struct strbuf *buf = &todo_list->buf;
+	struct object_id oid = onto->object.oid;
+	int res;
+
+	shortonto = find_unique_abbrev(&oid, DEFAULT_ABBREV);
+
+	if (buf->len == 0) {
+		struct todo_item *item = append_new_todo(todo_list);
+		item->command = TODO_NOOP;
+		item->commit = NULL;
+		item->arg_len = item->arg_offset = item->flags = item->offset_in_buf = 0;
+	}
+
+	if (autosquash && todo_list_rearrange_squash(todo_list))
+		return -1;
+
+	if (commands->nr)
+		todo_list_add_exec_commands(todo_list, commands);
+
+	if (count_commands(todo_list) == 0) {
+		apply_autostash(opts);
+		sequencer_remove_state(opts);
+
+		return error(_("nothing to do"));
+	}
+
+	res = edit_todo_list(r, todo_list, &new_todo, shortrevisions,
+			     shortonto, flags);
+	if (res == -1)
+		return -1;
+	else if (res == -2) {
+		apply_autostash(opts);
+		sequencer_remove_state(opts);
+
+		return -1;
+	} else if (res == -3) {
+		apply_autostash(opts);
+		sequencer_remove_state(opts);
+		todo_list_release(&new_todo);
+
+		return error(_("nothing to do"));
+	}
+
+	if (todo_list_parse_insn_buffer(r, new_todo.buf.buf, &new_todo) ||
+	    todo_list_check(todo_list, &new_todo)) {
+		fprintf(stderr, _(edit_todo_list_advice));
+		checkout_onto(r, opts, onto_name, &onto->object.oid, orig_head);
+		todo_list_release(&new_todo);
+
+		return -1;
+	}
+
+	if (opts->allow_ff && skip_unnecessary_picks(r, &new_todo, &oid)) {
+		todo_list_release(&new_todo);
+		return error(_("could not skip unnecessary pick commands"));
+	}
+
+	if (todo_list_write_to_file(r, &new_todo, todo_file, NULL, NULL, -1,
+				    flags & ~(TODO_LIST_SHORTEN_IDS))) {
+		todo_list_release(&new_todo);
+		return error_errno(_("could not write '%s'"), todo_file);
+	}
+
+	todo_list_release(&new_todo);
+
+	if (checkout_onto(r, opts, onto_name, &oid, orig_head))
+		return -1;
+
+	if (require_clean_work_tree(r, "rebase", "", 1, 1))
+		return -1;
+
+	return sequencer_continue(r, opts);
+}
+
+struct subject2item_entry {
+	struct hashmap_entry entry;
+	int i;
+	char subject[FLEX_ARRAY];
+};
+
+static int subject2item_cmp(const void *fndata,
+			    const struct subject2item_entry *a,
+			    const struct subject2item_entry *b, const void *key)
+{
+	return key ? strcmp(a->subject, key) : strcmp(a->subject, b->subject);
+}
+
+define_commit_slab(commit_todo_item, struct todo_item *);
+
+/*
+ * Rearrange the todo list that has both "pick commit-id msg" and "pick
+ * commit-id fixup!/squash! msg" in it so that the latter is put immediately
+ * after the former, and change "pick" to "fixup"/"squash".
+ *
+ * Note that if the config has specified a custom instruction format, each log
+ * message will have to be retrieved from the commit (as the oneline in the
+ * script cannot be trusted) in order to normalize the autosquash arrangement.
+ */
+int todo_list_rearrange_squash(struct todo_list *todo_list)
+{
+	struct hashmap subject2item;
+	int rearranged = 0, *next, *tail, i, nr = 0, alloc = 0;
+	char **subjects;
+	struct commit_todo_item commit_todo;
+	struct todo_item *items = NULL;
+
+	init_commit_todo_item(&commit_todo);
+	/*
+	 * The hashmap maps onelines to the respective todo list index.
+	 *
+	 * If any items need to be rearranged, the next[i] value will indicate
+	 * which item was moved directly after the i'th.
+	 *
+	 * In that case, last[i] will indicate the index of the latest item to
+	 * be moved to appear after the i'th.
+	 */
+	hashmap_init(&subject2item, (hashmap_cmp_fn) subject2item_cmp,
+		     NULL, todo_list->nr);
+	ALLOC_ARRAY(next, todo_list->nr);
+	ALLOC_ARRAY(tail, todo_list->nr);
+	ALLOC_ARRAY(subjects, todo_list->nr);
+	for (i = 0; i < todo_list->nr; i++) {
+		struct strbuf buf = STRBUF_INIT;
+		struct todo_item *item = todo_list->items + i;
+		const char *commit_buffer, *subject, *p;
+		size_t subject_len;
+		int i2 = -1;
+		struct subject2item_entry *entry;
+
+		next[i] = tail[i] = -1;
+		if (!item->commit || item->command == TODO_DROP) {
+			subjects[i] = NULL;
+			continue;
+		}
+
+		if (is_fixup(item->command)) {
+			clear_commit_todo_item(&commit_todo);
+			return error(_("the script was already rearranged."));
+		}
+
+		*commit_todo_item_at(&commit_todo, item->commit) = item;
+
+		parse_commit(item->commit);
+		commit_buffer = get_commit_buffer(item->commit, NULL);
+		find_commit_subject(commit_buffer, &subject);
+		format_subject(&buf, subject, " ");
+		subject = subjects[i] = strbuf_detach(&buf, &subject_len);
+		unuse_commit_buffer(item->commit, commit_buffer);
+		if ((skip_prefix(subject, "fixup! ", &p) ||
+		     skip_prefix(subject, "squash! ", &p))) {
+			struct commit *commit2;
+
+			for (;;) {
+				while (isspace(*p))
+					p++;
+				if (!skip_prefix(p, "fixup! ", &p) &&
+				    !skip_prefix(p, "squash! ", &p))
+					break;
+			}
+
+			if ((entry = hashmap_get_from_hash(&subject2item,
+							   strhash(p), p)))
+				/* found by title */
+				i2 = entry->i;
+			else if (!strchr(p, ' ') &&
+				 (commit2 =
+				  lookup_commit_reference_by_name(p)) &&
+				 *commit_todo_item_at(&commit_todo, commit2))
+				/* found by commit name */
+				i2 = *commit_todo_item_at(&commit_todo, commit2)
+					- todo_list->items;
+			else {
+				/* copy can be a prefix of the commit subject */
+				for (i2 = 0; i2 < i; i2++)
+					if (subjects[i2] &&
+					    starts_with(subjects[i2], p))
+						break;
+				if (i2 == i)
+					i2 = -1;
+			}
+		}
+		if (i2 >= 0) {
+			rearranged = 1;
+			todo_list->items[i].command =
+				starts_with(subject, "fixup!") ?
+				TODO_FIXUP : TODO_SQUASH;
+			if (next[i2] < 0)
+				next[i2] = i;
+			else
+				next[tail[i2]] = i;
+			tail[i2] = i;
+		} else if (!hashmap_get_from_hash(&subject2item,
+						strhash(subject), subject)) {
+			FLEX_ALLOC_MEM(entry, subject, subject, subject_len);
+			entry->i = i;
+			hashmap_entry_init(entry, strhash(entry->subject));
+			hashmap_put(&subject2item, entry);
+		}
+	}
+
+	if (rearranged) {
+		for (i = 0; i < todo_list->nr; i++) {
+			enum todo_command command = todo_list->items[i].command;
+			int cur = i;
+
+			/*
+			 * Initially, all commands are 'pick's. If it is a
+			 * fixup or a squash now, we have rearranged it.
+			 */
+			if (is_fixup(command))
+				continue;
+
+			while (cur >= 0) {
+				ALLOC_GROW(items, nr + 1, alloc);
+				items[nr++] = todo_list->items[cur];
+				cur = next[cur];
+			}
+		}
+
+		FREE_AND_NULL(todo_list->items);
+		todo_list->items = items;
+		todo_list->nr = nr;
+		todo_list->alloc = alloc;
+	}
+
+	free(next);
+	free(tail);
+	for (i = 0; i < todo_list->nr; i++)
+		free(subjects[i]);
+	free(subjects);
+	hashmap_free(&subject2item, 1);
+
+	clear_commit_todo_item(&commit_todo);
+
+	return 0;
+}