sequencer: fast-forward `merge` commands, if possible

[git] / sequencer.c

#include "cache.h"
#include "config.h"
#include "lockfile.h"
#include "dir.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"

#define GIT_REFLOG_ACTION "GIT_REFLOG_ACTION"

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'.
 */
static GIT_PATH_FUNC(rebase_path_todo, "rebase-merge/git-rebase-todo")
/*
 * 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.
 *
 * The first line of the file is of the form
 *     # This is a combination of $count commits.
 * where $count is the number of commits whose messages have been
 * written to the file so far (including the initial "pick" commit).
 * Each time that a commit message is processed, this line is read and
 * updated. It is deleted just before the combined commit is made.
 */
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")
/*
 * 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 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 (and are only consumed, not modified, by the sequencer).
 */
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_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 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;
                else if (!strcmp(s, "whitespace"))
                        opts->default_msg_cleanup = COMMIT_MSG_CLEANUP_SPACE;
                else if (!strcmp(s, "strip"))
                        opts->default_msg_cleanup = COMMIT_MSG_CLEANUP_ALL;
                else if (!strcmp(s, "scissors"))
                        opts->default_msg_cleanup = COMMIT_MSG_CLEANUP_SPACE;
                else
                        warning(_("invalid commit message cleanup mode '%s'"),
                                  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,
        int ignore_footer)
{
        struct trailer_info info;
        int i;
        int found_sob = 0, found_sob_last = 0;

        trailer_info_get(&info, sb->buf);

        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;

        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);
                        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_reset(&buf);
        strbuf_addstr(&buf, get_dir(opts));
        remove_dir_recursively(&buf, 0);
        strbuf_release(&buf);

        return 0;
}

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(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());
                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(void)
{
        return lookup_tree(the_hash_algo->empty_tree);
}

static int error_dirty_index(struct replay_opts *opts)
{
        if (read_cache_unmerged())
                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(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;

        read_cache();
        if (checkout_fast_forward(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 ? &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;
}

void append_conflicts_hint(struct strbuf *msgbuf)
{
        int i;

        strbuf_addch(msgbuf, '\n');
        strbuf_commented_addf(msgbuf, "Conflicts:\n");
        for (i = 0; i < active_nr;) {
                const struct cache_entry *ce = active_cache[i++];
                if (ce_stage(ce)) {
                        strbuf_commented_addf(msgbuf, "\t%s\n", ce->name);
                        while (i < active_nr && !strcmp(ce->name,
                                                        active_cache[i]->name))
                                i++;
                }
        }
}

static int do_recursive_merge(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 (hold_locked_index(&index_lock, LOCK_REPORT_ON_ERROR) < 0)
                return -1;

        read_cache();

        init_merge_options(&o);
        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 ? next->tree : empty_tree();
        base_tree = base ? base->tree : empty_tree();

        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(&the_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(msgbuf);

        return !clean;
}

static int is_index_unchanged(void)
{
        struct object_id head_oid;
        struct commit *head_commit;

        if (!resolve_ref_unsafe("HEAD", RESOLVE_REF_READING, &head_oid, NULL))
                return error(_("could not resolve HEAD commit"));

        head_commit = lookup_commit(&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 (!active_cache_tree)
                active_cache_tree = cache_tree();

        if (!cache_tree_fully_valid(active_cache_tree))
                if (cache_tree_update(&the_index, 0))
                        return error(_("unable to update cache tree"));

        return !oidcmp(&active_cache_tree->oid,
                       &head_commit->tree->object.oid);
}

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++));
        res = write_message(buf.buf, buf.len, rebase_path_author_script(), 1);
        strbuf_release(&buf);
        return res;
}

/*
 * Read a list of environment variable assignments (such as the author-script
 * file) into an environment block. Returns -1 on error, 0 otherwise.
 */
static int read_env_script(struct argv_array *env)
{
        struct strbuf script = STRBUF_INIT;
        int i, count = 0;
        char *p, *p2;

        if (strbuf_read_file(&script, rebase_path_author_script(), 256) <= 0)
                return -1;

        for (p = script.buf; *p; p++)
                if (skip_prefix(p, "'\\\\''", (const char **)&p2))
                        strbuf_splice(&script, p - script.buf, p2 - p, "'", 1);
                else if (*p == '\'')
                        strbuf_splice(&script, p-- - script.buf, 1, "", 0);
                else if (*p == '\n') {
                        *p = '\0';
                        count++;
                }

        for (i = 0, p = script.buf; i < count; i++) {
                argv_array_push(env, p);
                p += strlen(p) + 1;
        }

        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;
}

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)

/*
 * 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(const char *defmsg, struct replay_opts *opts,
                          unsigned int flags)
{
        struct child_process cmd = CHILD_PROCESS_INIT;
        const char *value;

        cmd.git_cmd = 1;

        if (is_rebase_i(opts)) {
                if (!(flags & EDIT_MSG)) {
                        cmd.stdout_to_stderr = 1;
                        cmd.err = -1;
                }

                if (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);
        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 &&
                 git_config_get_value("commit.cleanup", &value))
                argv_array_push(&cmd.args, "--cleanup=verbatim");

        if ((flags & ALLOW_EMPTY))
                argv_array_push(&cmd.args, "--allow-empty");

        if (opts->allow_empty_message)
                argv_array_push(&cmd.args, "--allow-empty-message");

        if (cmd.err == -1) {
                /* hide stderr on success */
                struct strbuf buf = STRBUF_INIT;
                int rc = pipe_command(&cmd,
                                      NULL, 0,
                                      /* stdout is already redirected */
                                      NULL, 0,
                                      &buf, 0);
                if (rc)
                        fputs(buf.buf, stderr);
                strbuf_release(&buf);
                return rc;
        }

        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;
}

/*
 * 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;

        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(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(cfg, "Notes added by 'git commit --amend'");
        }
        run_rewrite_hook(&old_head->object.oid, new_head);
}

static int run_prepare_commit_msg_hook(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", get_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(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(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);

        init_revisions(&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 commit **head)
{
        struct commit *current_head;
        struct object_id oid;

        if (get_oid("HEAD", &oid)) {
                current_head = NULL;
        } else {
                current_head = lookup_commit_reference(&oid);
                if (!current_head)
                        return error(_("could not parse HEAD"));
                if (oidcmp(&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 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(&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_cache_as_tree(&tree, 0, NULL)) {
                res = error(_("git write-tree failed to write a tree"));
                goto out;
        }

        if (!(flags & ALLOW_EMPTY) && !oidcmp(current_head ?
                                              &current_head->tree->object.oid :
                                              &empty_tree_oid, &tree)) {
                res = 1; /* run 'git commit' to display error message */
                goto out;
        }

        if (find_hook("prepare-commit-msg")) {
                res = run_prepare_commit_msg_hook(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;
        }

        cleanup = (flags & CLEANUP_MSG) ? COMMIT_MSG_CLEANUP_ALL :
                                          opts->default_msg_cleanup;

        if (cleanup != COMMIT_MSG_CLEANUP_NONE)
                strbuf_stripspace(msg, cleanup == COMMIT_MSG_CLEANUP_ALL);
        if (!opts->allow_empty_message && message_is_empty(msg, cleanup)) {
                res = 1; /* run 'git commit' to display error message */
                goto out;
        }

        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(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(const char *msg_file, const char *author,
                     struct replay_opts *opts, unsigned int flags)
{
        int res = 1;

        if (!(flags & EDIT_MSG) && !(flags & VERIFY_MSG)) {
                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(msg_file ? &sb : NULL, author, opts, flags,
                                    &oid);
                strbuf_release(&sb);
                if (!res) {
                        unlink(git_path_cherry_pick_head());
                        unlink(git_path_merge_msg());
                        if (!is_rebase_i(opts))
                                print_commit_summary(NULL, &oid,
                                                SUMMARY_SHOW_AUTHOR_DATE);
                        return res;
                }
        }
        if (res == 1)
                return run_git_commit(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 = &parent->tree->object.oid;
        } else {
                ptree_oid = the_hash_algo->empty_tree; /* commit is root */
        }

        return !oidcmp(ptree_oid, &commit->tree->object.oid);
}

/*
 * Do we run "git commit" with "--allow-empty"?
 */
static int allow_empty(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();
        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;
}

/*
 * Note that ordering matters in this enum. Not only must it match the mapping
 * below, it is also divided into several sections that matter.  When adding
 * new commands, make sure you add it in the right section.
 */
enum todo_command {
        /* commands that handle commits */
        TODO_PICK = 0,
        TODO_REVERT,
        TODO_EDIT,
        TODO_REWORD,
        TODO_FIXUP,
        TODO_SQUASH,
        /* commands that do something else than handling a single commit */
        TODO_EXEC,
        TODO_LABEL,
        TODO_RESET,
        TODO_MERGE,
        /* commands that do nothing but are counted for reporting progress */
        TODO_NOOP,
        TODO_DROP,
        /* comments (not counted for reporting progress) */
        TODO_COMMENT
};

static struct {
        char c;
        const char *str;
} todo_command_info[] = {
        { 'p', "pick" },
        { 0,   "revert" },
        { 'e', "edit" },
        { 'r', "reword" },
        { 'f', "fixup" },
        { 's', "squash" },
        { 'x', "exec" },
        { '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;
}

static int update_squash_messages(enum todo_command command,
                struct commit *commit, struct replay_opts *opts)
{
        struct strbuf buf = STRBUF_INIT;
        int count, res;
        const char *message, *body;

        if (file_exists(rebase_path_squash_msg())) {
                struct strbuf header = STRBUF_INIT;
                char *eol, *p;

                if (strbuf_read_file(&buf, rebase_path_squash_msg(), 2048) <= 0)
                        return error(_("could not read '%s'"),
                                rebase_path_squash_msg());

                p = buf.buf + 1;
                eol = strchrnul(buf.buf, '\n');
                if (buf.buf[0] != comment_line_char ||
                    (p += strcspn(p, "0123456789\n")) == eol)
                        return error(_("unexpected 1st line of squash message:"
                                       "\n\n\t%.*s"),
                                     (int)(eol - buf.buf), buf.buf);
                count = strtol(p, NULL, 10);

                if (count < 1)
                        return error(_("invalid 1st line of squash message:\n"
                                       "\n\t%.*s"),
                                     (int)(eol - buf.buf), buf.buf);

                strbuf_addf(&header, "%c ", comment_line_char);
                strbuf_addf(&header,
                            _("This is a combination of %d commits."), ++count);
                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(&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());
                }

                count = 2;
                strbuf_addf(&buf, "%c ", comment_line_char);
                strbuf_addf(&buf, _("This is a combination of %d commits."),
                            count);
                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:"), count);
                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:"),
                            count);
                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);
        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(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();
        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_cache_as_tree(&head, 0, NULL))
                        return error(_("your index file is unmerged."));
        } else {
                unborn = get_oid("HEAD", &head);
                if (unborn)
                        oidcpy(&head, the_hash_algo->empty_tree);
                if (index_differs_from(unborn ? EMPTY_TREE_SHA1_HEX : "HEAD",
                                       NULL, 0))
                        return error_dirty_index(opts);
        }
        discard_cache();

        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 (0 < opts->mainline)
                return error(_("mainline was specified but commit %s is not a merge."),
                        oid_to_hex(&commit->object.oid));
        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 && !oidcmp(&parent->object.oid, &head)) ||
             (!parent && unborn))) {
                if (is_rebase_i(opts))
                        write_author_script(msg.message);
                res = fast_forward_to(&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(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();
                        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());
                        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(base, next, base_label, next_label,
                                         &head, &msgbuf, opts);
                if (res < 0)
                        return res;
                res |= write_message(msgbuf.buf, msgbuf.len,
                                     git_path_merge_msg(), 0);
        } else {
                struct commit_list *common = NULL;
                struct commit_list *remotes = NULL;

                res = write_message(msgbuf.buf, msgbuf.len,
                                    git_path_merge_msg(), 0);

                commit_list_insert(base, &common);
                commit_list_insert(next, &remotes);
                res |= try_merge_command(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(res == 1, opts);
                rerere(opts->allow_rerere_auto);
                goto leave;
        }

        allow = allow_empty(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(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());
        }

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"));

        if (!opts->revs->commits)
                return error(_("empty commit set passed"));
        return 0;
}

static int read_and_refresh_cache(struct replay_opts *opts)
{
        struct lock_file index_lock = LOCK_INIT;
        int index_fd = hold_locked_index(&index_lock, 0);
        if (read_index_preload(&the_index, NULL) < 0) {
                rollback_lock_file(&index_lock);
                return error(_("git %s: failed to read the index"),
                        _(action_name(opts)));
        }
        refresh_index(&the_index, REFRESH_QUIET|REFRESH_UNMERGED, NULL, NULL, NULL);
        if (index_fd >= 0) {
                if (write_locked_index(&the_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
};

struct todo_item {
        enum todo_command command;
        struct commit *commit;
        unsigned int flags;
        const char *arg;
        int arg_len;
        size_t offset_in_buf;
};

struct todo_list {
        struct strbuf buf;
        struct todo_item *items;
        int nr, alloc, current;
        int done_nr, total_nr;
        struct stat_data stat;
};

#define TODO_LIST_INIT { STRBUF_INIT }

static 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++;
}

static int parse_insn_line(struct todo_item *item, 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 = bol;
                item->arg_len = eol - bol;
                return 0;
        }

        for (i = 0; i < TODO_COMMENT; i++)
                if (skip_prefix(bol, todo_command_info[i].str, &bol)) {
                        item->command = i;
                        break;
                } else if (bol[1] == ' ' && *bol == todo_command_info[i].c) {
                        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) {
                if (bol != eol)
                        return error(_("%s does not accept arguments: '%s'"),
                                     command_to_string(item->command), bol);
                item->commit = NULL;
                item->arg = bol;
                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 = bol;
                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 = bol;
                        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;

        item->arg = end_of_object_name + strspn(end_of_object_name, " \t");
        item->arg_len = (int)(eol - item->arg);

        if (status < 0)
                return -1;

        item->commit = lookup_commit_reference(&commit_oid);
        return !item->commit;
}

static int parse_insn_buffer(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());

        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(item, p, eol)) {
                        res = error(_("invalid line %d: %.*s"),
                                i, (int)(eol - p), p);
                        item->command = TODO_NOOP;
                }

                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 read_populate_todo(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 = parse_insn_buffer(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 &&
                                !parse_insn_buffer(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.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
                return error(_("invalid key: %s"), key);

        if (!error_flag)
                return error(_("invalid value for %s: %s"), key, value);

        return 0;
}

static void read_strategy_opts(struct replay_opts *opts, struct strbuf *buf)
{
        int i;

        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;

        opts->xopts_nr = split_cmdline(buf->buf, (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 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_signoff())) {
                        opts->allow_ff = 0;
                        opts->signoff = 1;
                }

                read_strategy_opts(opts, &buf);
                strbuf_release(&buf);

                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 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 = NULL;
                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);
        }
        return 0;
}

static int create_seq_dir(void)
{
        if (file_exists(git_path_seq_dir())) {
                error(_("a cherry-pick or revert is already in progress"));
                advise(_("try \"git cherry-pick (--continue | --quit | --abort)\""));
                return -1;
        } else 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 !oidcmp(&actual_head, &expected_head);
}

static int reset_for_rollback(const struct object_id *oid)
{
        const char *argv[4];    /* reset --merge <arg> + NULL */

        argv[0] = "reset";
        argv[1] = "--merge";
        argv[2] = oid_to_hex(oid);
        argv[3] = NULL;
        return run_command_v_opt(argv, RUN_GIT_CMD);
}

static int rollback_single_pick(void)
{
        struct object_id head_oid;

        if (!file_exists(git_path_cherry_pick_head()) &&
            !file_exists(git_path_revert_head()))
                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_for_rollback(&head_oid);
}

int sequencer_rollback(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();
        }
        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_for_rollback(&oid))
                goto fail;
        strbuf_release(&buf);
        return sequencer_remove_state(opts);
fail:
        strbuf_release(&buf);
        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->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");
        return res;
}

static int make_patch(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));
        init_revisions(&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 commit *commit,
        const char *subject, int subject_len,
        struct replay_opts *opts, int exit_code, int to_amend)
{
        if (make_patch(commit, opts))
                return -1;

        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)
                fprintf(stderr, "Could not apply %s... %.*s\n",
                        short_commit_name(commit), subject_len, subject);

        return exit_code;
}

static int error_failed_squash(struct commit *commit,
        struct replay_opts *opts, int subject_len, const char *subject)
{
        if (rename(rebase_path_squash_msg(), rebase_path_message()))
                return error(_("could not rename '%s' to '%s'"),
                        rebase_path_squash_msg(), rebase_path_message());
        unlink(rebase_path_fixup_msg());
        unlink(git_path_merge_msg());
        if (copy_file(git_path_merge_msg(), rebase_path_message(), 0666))
                return error(_("could not copy '%s' to '%s'"),
                             rebase_path_message(), git_path_merge_msg());
        return error_with_patch(commit, subject, subject_len, opts, 1, 0);
}

static int do_exec(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()));
        status = run_command_v_opt_cd_env(child_argv, RUN_USING_SHELL, NULL,
                                          child_env.argv);

        /* force re-reading of the cache */
        if (discard_cache() < 0 || read_cache() < 0)
                return error(_("could not read index"));

        dirty = require_clean_work_tree("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(const char *name, int len)
{
        struct ref_store *refs = get_main_ref_store();
        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(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, i;

        if (hold_locked_index(&lock, LOCK_REPORT_ON_ERROR) < 0)
                return -1;

        /* Determine the length of the label */
        for (i = 0; i < len; i++)
                if (isspace(name[i]))
                        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 = &the_index;
        unpack_tree_opts.dst_index = &the_index;
        unpack_tree_opts.fn = oneway_merge;
        unpack_tree_opts.merge = 1;
        unpack_tree_opts.update = 1;

        if (read_cache_unmerged()) {
                rollback_lock_file(&lock);
                strbuf_release(&ref_name);
                return error_resolve_conflict(_(action_name(opts)));
        }

        if (!fill_tree_descriptor(&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(&the_index, tree);

        if (write_locked_index(&the_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 int do_merge(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 merge_options o;
        int merge_arg_len, oneline_offset, can_fast_forward, ret;
        static struct lock_file lock;
        const char *p;

        if (hold_locked_index(&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;
        }

        oneline_offset = arg_len;
        merge_arg_len = strcspn(arg, " \t\n");
        p = arg + merge_arg_len;
        p += strspn(p, " \t\n");
        if (*p == '#' && (!p[1] || isspace(p[1]))) {
                p += 1 + strspn(p + 1, " \t\n");
                oneline_offset = p - arg;
        } else if (p - arg < arg_len)
                BUG("octopus merges are not supported yet: '%s'", p);

        strbuf_addf(&ref_name, "refs/rewritten/%.*s", merge_arg_len, arg);
        merge_commit = lookup_commit_reference_by_name(ref_name.buf);
        if (!merge_commit) {
                /* fall back to non-rewritten ref or commit */
                strbuf_splice(&ref_name, 0, strlen("refs/rewritten/"), "", 0);
                merge_commit = lookup_commit_reference_by_name(ref_name.buf);
        }

        if (!merge_commit) {
                ret = error(_("could not resolve '%s'"), ref_name.buf);
                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(), 0);
                unuse_commit_buffer(commit, message);
                if (ret) {
                        error_errno(_("could not write '%s'"),
                                    git_path_merge_msg());
                        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 branch '%.*s'",
                                    merge_arg_len, arg);
                        p = buf.buf;
                        len = buf.len;
                }

                ret = write_message(p, len, git_path_merge_msg(), 0);
                strbuf_release(&buf);
                if (ret) {
                        error_errno(_("could not write '%s'"),
                                    git_path_merge_msg());
                        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 &&
                !oidcmp(&commit->parents->item->object.oid,
                        &head_commit->object.oid);

        /*
         * If the merge head is different from the original one, we cannot
         * fast-forward.
         */
        if (can_fast_forward) {
                struct commit_list *second_parent = commit->parents->next;

                if (second_parent && !second_parent->next &&
                    oidcmp(&merge_commit->object.oid,
                           &second_parent->item->object.oid))
                        can_fast_forward = 0;
        }

        if (can_fast_forward && commit->parents->next &&
            !commit->parents->next->next &&
            !oidcmp(&commit->parents->next->item->object.oid,
                    &merge_commit->object.oid)) {
                rollback_lock_file(&lock);
                ret = fast_forward_to(&commit->object.oid,
                                      &head_commit->object.oid, 0, opts);
                goto leave_merge;
        }

        write_message(oid_to_hex(&merge_commit->object.oid), GIT_SHA1_HEXSZ,
                      git_path_merge_head(), 0);
        write_message("no-ff", 5, git_path_merge_mode(), 0);

        bases = get_merge_bases(head_commit, merge_commit);
        for (j = bases; j; j = j->next)
                commit_list_insert(j->item, &reversed);
        free_commit_list(bases);

        read_cache();
        init_merge_options(&o);
        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 (active_cache_changed &&
            write_locked_index(&the_index, &lock, COMMIT_LOCK)) {
                ret = error(_("merge: Unable to write new index file"));
                goto leave_merge;
        }

        rollback_lock_file(&lock);
        if (ret)
                rerere(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).
                 */
                ret = !!run_git_commit(git_path_merge_msg(), opts,
                                     run_commit_flags);

leave_merge:
        strbuf_release(&ref_name);
        rollback_lock_file(&lock);
        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 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 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(opts))
                return -1;

        while (todo_list->current < todo_list->nr) {
                struct todo_item *item = todo_list->items + todo_list->current;
                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);
                                }
                                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());
                        delete_ref(NULL, "REBASE_HEAD", NULL, REF_NO_DEREF);
                }
                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(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)
                                        fprintf(stderr,
                                                _("Stopped at %s...  %.*s\n"),
                                                short_commit_name(commit),
                                                item->arg_len, item->arg);
                                return error_with_patch(commit,
                                        item->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(item->commit, opts,
                                        item->arg_len, item->arg);
                        } else if (res && is_rebase_i(opts) && item->commit)
                                return res | error_with_patch(item->commit,
                                        item->arg, item->arg_len, opts, res,
                                        item->command == TODO_REWORD);
                } else if (item->command == TODO_EXEC) {
                        char *end_of_arg = (char *)(item->arg + item->arg_len);
                        int saved = *end_of_arg;
                        struct stat st;

                        *end_of_arg = '\0';
                        res = do_exec(item->arg);
                        *end_of_arg = saved;

                        /* Reread the todo file if it has changed. */
                        if (res)
                                ; /* fall through */
                        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)) {
                                todo_list_release(todo_list);
                                if (read_populate_todo(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(item->arg, item->arg_len)))
                                reschedule = 1;
                } else if (item->command == TODO_RESET) {
                        if ((res = do_reset(item->arg, item->arg_len, opts)))
                                reschedule = 1;
                } else if (item->command == TODO_MERGE) {
                        if ((res = do_merge(item->commit,
                                            item->arg, item->arg_len,
                                            item->flags, opts)) < 0)
                                reschedule = 1;
                        else if (res > 0)
                                /* failed with merge conflicts */
                                return error_with_patch(item->commit,
                                                        item->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(item->commit,
                                                        item->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));
                        init_revisions(&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;
                                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);

                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(void)
{
        const char *argv[] = { "commit", NULL };

        if (!file_exists(git_path_cherry_pick_head()) &&
            !file_exists(git_path_revert_head()))
                return error(_("no cherry-pick or revert in progress"));
        return run_command_v_opt(argv, RUN_GIT_CMD);
}

static int commit_staged_changes(struct replay_opts *opts)
{
        unsigned int flags = ALLOW_EMPTY | EDIT_MSG;

        if (has_unstaged_changes(1))
                return error(_("cannot rebase: You have unstaged changes."));
        if (!has_uncommitted_changes(0)) {
                const char *cherry_pick_head = git_path_cherry_pick_head();

                if (file_exists(cherry_pick_head) && unlink(cherry_pick_head))
                        return error(_("could not remove CHERRY_PICK_HEAD"));
                return 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 (oidcmp(&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."));

                strbuf_release(&rev);
                flags |= AMEND_MSG;
        }

        if (run_git_commit(rebase_path_message(), opts, flags))
                return error(_("could not commit staged changes."));
        unlink(rebase_path_amend());
        return 0;
}

int sequencer_continue(struct replay_opts *opts)
{
        struct todo_list todo_list = TODO_LIST_INIT;
        int res;

        if (read_and_refresh_cache(opts))
                return -1;

        if (is_rebase_i(opts)) {
                if (commit_staged_changes(opts))
                        return -1;
        } else if (!file_exists(get_todo_path(opts)))
                return continue_single_pick();
        if (read_populate_opts(opts))
                return -1;
        if ((res = read_populate_todo(&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()) ||
                    file_exists(git_path_revert_head())) {
                        res = continue_single_pick();
                        if (res)
                                goto release_todo_list;
                }
                if (index_differs_from("HEAD", NULL, 0)) {
                        res = error_dirty_index(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(&todo_list, opts);
release_todo_list:
        todo_list_release(&todo_list);
        return res;
}

static int single_pick(struct commit *cmit, struct replay_opts *opts)
{
        setenv(GIT_REFLOG_ACTION, action_name(opts), 0);
        return do_pick_commit(opts->action == REPLAY_PICK ?
                TODO_PICK : TODO_REVERT, cmit, opts, 0);
}

int sequencer_pick_revisions(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(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(&oid, 1)) {
                                enum object_type type = oid_object_info(&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 || get_revision(opts->revs))
                        return error("BUG: expected exactly one commit from walk");
                return single_pick(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() < 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(&todo_list, opts);
        todo_list_release(&todo_list);
        return res;
}

void append_signoff(struct strbuf *msgbuf, int 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(getenv("GIT_COMMITTER_NAME"),
                                getenv("GIT_COMMITTER_EMAIL")));
        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);
}

int sequencer_make_script(FILE *out, int argc, const char **argv,
                          unsigned flags)
{
        char *format = NULL;
        struct pretty_print_context pp = {0};
        struct strbuf buf = STRBUF_INIT;
        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";

        init_revisions(&revs, NULL);
        revs.verbose_header = 1;
        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"));

        while ((commit = get_revision(&revs))) {
                int is_empty  = is_original_commit_empty(commit);

                if (!is_empty && (commit->object.flags & PATCHSAME))
                        continue;
                strbuf_reset(&buf);
                if (!keep_empty && is_empty)
                        strbuf_addf(&buf, "%c ", comment_line_char);
                strbuf_addf(&buf, "%s %s ", insn,
                            oid_to_hex(&commit->object.oid));
                pretty_print_commit(&pp, commit, &buf);
                strbuf_addch(&buf, '\n');
                fputs(buf.buf, out);
        }
        strbuf_release(&buf);
        return 0;
}

/*
 * Add commands after pick and (series of) squash/fixup commands
 * in the todo list.
 */
int sequencer_add_exec_commands(const char *commands)
{
        const char *todo_file = rebase_path_todo();
        struct todo_list todo_list = TODO_LIST_INIT;
        struct todo_item *item;
        struct strbuf *buf = &todo_list.buf;
        size_t offset = 0, commands_len = strlen(commands);
        int i, first;

        if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
                return error(_("could not read '%s'."), todo_file);

        if (parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
                todo_list_release(&todo_list);
                return error(_("unusable todo list: '%s'"), todo_file);
        }

        first = 1;
        /* insert <commands> before every pick except the first one */
        for (item = todo_list.items, i = 0; i < todo_list.nr; i++, item++) {
                if (item->command == TODO_PICK && !first) {
                        strbuf_insert(buf, item->offset_in_buf + offset,
                                      commands, commands_len);
                        offset += commands_len;
                }
                first = 0;
        }

        /* append final <commands> */
        strbuf_add(buf, commands, commands_len);

        i = write_message(buf->buf, buf->len, todo_file, 0);
        todo_list_release(&todo_list);
        return i;
}

int transform_todos(unsigned flags)
{
        const char *todo_file = rebase_path_todo();
        struct todo_list todo_list = TODO_LIST_INIT;
        struct strbuf buf = STRBUF_INIT;
        struct todo_item *item;
        int i;

        if (strbuf_read_file(&todo_list.buf, todo_file, 0) < 0)
                return error(_("could not read '%s'."), todo_file);

        if (parse_insn_buffer(todo_list.buf.buf, &todo_list)) {
                todo_list_release(&todo_list);
                return error(_("unusable todo list: '%s'"), todo_file);
        }

        for (item = todo_list.items, i = 0; i < todo_list.nr; 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, item->arg);
                        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, item->arg);
        }

        i = write_message(buf.buf, buf.len, todo_file, 0);
        todo_list_release(&todo_list);
        return i;
}

enum check_level {
        CHECK_IGNORE = 0, CHECK_WARN, CHECK_ERROR
};

static enum check_level get_missing_commit_check_level(void)
{
        const char *value;

        if (git_config_get_value("rebase.missingcommitscheck", &value) ||
                        !strcasecmp("ignore", value))
                return CHECK_IGNORE;
        if (!strcasecmp("warn", value))
                return CHECK_WARN;
        if (!strcasecmp("error", value))
                return CHECK_ERROR;
        warning(_("unrecognized setting %s for option "
                  "rebase.missingCommitsCheck. Ignoring."), value);
        return CHECK_IGNORE;
}

/*
 * Check if the user dropped some commits by mistake
 * Behaviour determined by rebase.missingCommitsCheck.
 * Check if there is an unrecognized command or a
 * bad SHA-1 in a command.
 */
int check_todo_list(void)
{
        enum check_level check_level = get_missing_commit_check_level();
        struct strbuf todo_file = STRBUF_INIT;
        struct todo_list todo_list = TODO_LIST_INIT;
        struct strbuf missing = STRBUF_INIT;
        int advise_to_edit_todo = 0, res = 0, i;

        strbuf_addstr(&todo_file, rebase_path_todo());
        if (strbuf_read_file_or_whine(&todo_list.buf, todo_file.buf) < 0) {
                res = -1;
                goto leave_check;
        }
        advise_to_edit_todo = res =
                parse_insn_buffer(todo_list.buf.buf, &todo_list);

        if (res || check_level == CHECK_IGNORE)
                goto leave_check;

        /* Mark the commits in git-rebase-todo as seen */
        for (i = 0; i < todo_list.nr; i++) {
                struct commit *commit = todo_list.items[i].commit;
                if (commit)
                        commit->util = (void *)1;
        }

        todo_list_release(&todo_list);
        strbuf_addstr(&todo_file, ".backup");
        if (strbuf_read_file_or_whine(&todo_list.buf, todo_file.buf) < 0) {
                res = -1;
                goto leave_check;
        }
        strbuf_release(&todo_file);
        res = !!parse_insn_buffer(todo_list.buf.buf, &todo_list);

        /* Find commits in git-rebase-todo.backup yet unseen */
        for (i = todo_list.nr - 1; i >= 0; i--) {
                struct todo_item *item = todo_list.items + i;
                struct commit *commit = item->commit;
                if (commit && !commit->util) {
                        strbuf_addf(&missing, " - %s %.*s\n",
                                    short_commit_name(commit),
                                    item->arg_len, item->arg);
                        commit->util = (void *)1;
                }
        }

        /* Warn about missing commits */
        if (!missing.len)
                goto leave_check;

        if (check_level == CHECK_ERROR)
                advise_to_edit_todo = res = 1;

        fprintf(stderr,
                _("Warning: some commits may have been dropped accidentally.\n"
                "Dropped commits (newer to older):\n"));

        /* Make the list user-friendly and display */
        fputs(missing.buf, stderr);
        strbuf_release(&missing);

        fprintf(stderr, _("To avoid this message, use \"drop\" to "
                "explicitly remove a commit.\n\n"
                "Use 'git config rebase.missingCommitsCheck' to change "
                "the level of warnings.\n"
                "The possible behaviours are: ignore, warn, error.\n\n"));

leave_check:
        strbuf_release(&todo_file);
        todo_list_release(&todo_list);

        if (advise_to_edit_todo)
                fprintf(stderr,
                        _("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"));

        return res;
}

static int rewrite_file(const char *path, const char *buf, size_t len)
{
        int rc = 0;
        int fd = open(path, O_WRONLY | O_TRUNC);
        if (fd < 0)
                return error_errno(_("could not open '%s' for writing"), path);
        if (write_in_full(fd, buf, len) < 0)
                rc = error_errno(_("could not write to '%s'"), path);
        if (close(fd) && !rc)
                rc = error_errno(_("could not close '%s'"), path);
        return rc;
}

/* skip picking commits whose parents are unchanged */
int skip_unnecessary_picks(void)
{
        const char *todo_file = rebase_path_todo();
        struct strbuf buf = STRBUF_INIT;
        struct todo_list todo_list = TODO_LIST_INIT;
        struct object_id onto_oid, *oid = &onto_oid, *parent_oid;
        int fd, i;

        if (!read_oneliner(&buf, rebase_path_onto(), 0))
                return error(_("could not read 'onto'"));
        if (get_oid(buf.buf, &onto_oid)) {
                strbuf_release(&buf);
                return error(_("need a HEAD to fixup"));
        }
        strbuf_release(&buf);

        if (strbuf_read_file_or_whine(&todo_list.buf, todo_file) < 0)
                return -1;
        if (parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
                todo_list_release(&todo_list);
                return -1;
        }

        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)) {
                        todo_list_release(&todo_list);
                        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 (hashcmp(parent_oid->hash, oid->hash))
                        break;
                oid = &item->commit->object.oid;
        }
        if (i > 0) {
                int offset = get_item_line_offset(&todo_list, i);
                const char *done_path = rebase_path_done();

                fd = open(done_path, O_CREAT | O_WRONLY | O_APPEND, 0666);
                if (fd < 0) {
                        error_errno(_("could not open '%s' for writing"),
                                    done_path);
                        todo_list_release(&todo_list);
                        return -1;
                }
                if (write_in_full(fd, todo_list.buf.buf, offset) < 0) {
                        error_errno(_("could not write to '%s'"), done_path);
                        todo_list_release(&todo_list);
                        close(fd);
                        return -1;
                }
                close(fd);

                if (rewrite_file(rebase_path_todo(), todo_list.buf.buf + offset,
                                 todo_list.buf.len - offset) < 0) {
                        todo_list_release(&todo_list);
                        return -1;
                }

                todo_list.current = i;
                if (is_fixup(peek_command(&todo_list, 0)))
                        record_in_rewritten(oid, peek_command(&todo_list, 0));
        }

        todo_list_release(&todo_list);
        printf("%s\n", oid_to_hex(oid));

        return 0;
}

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);
}

/*
 * 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 rearrange_squash(void)
{
        const char *todo_file = rebase_path_todo();
        struct todo_list todo_list = TODO_LIST_INIT;
        struct hashmap subject2item;
        int res = 0, rearranged = 0, *next, *tail, i;
        char **subjects;

        if (strbuf_read_file_or_whine(&todo_list.buf, todo_file) < 0)
                return -1;
        if (parse_insn_buffer(todo_list.buf.buf, &todo_list) < 0) {
                todo_list_release(&todo_list);
                return -1;
        }

        /*
         * 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)) {
                        todo_list_release(&todo_list);
                        return error(_("the script was already rearranged."));
                }

                item->commit->util = 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)) &&
                                 commit2->util)
                                /* found by commit name */
                                i2 = (struct todo_item *)commit2->util
                                        - 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) {
                struct strbuf buf = STRBUF_INIT;

                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) {
                                const char *bol =
                                        get_item_line(&todo_list, cur);
                                const char *eol =
                                        get_item_line(&todo_list, cur + 1);

                                /* replace 'pick', by 'fixup' or 'squash' */
                                command = todo_list.items[cur].command;
                                if (is_fixup(command)) {
                                        strbuf_addstr(&buf,
                                                todo_command_info[command].str);
                                        bol += strcspn(bol, " \t");
                                }

                                strbuf_add(&buf, bol, eol - bol);

                                cur = next[cur];
                        }
                }

                res = rewrite_file(todo_file, buf.buf, buf.len);
                strbuf_release(&buf);
        }

        free(next);
        free(tail);
        for (i = 0; i < todo_list.nr; i++)
                free(subjects[i]);
        free(subjects);
        hashmap_free(&subject2item, 1);
        todo_list_release(&todo_list);

        return res;
}