sequencer (rebase -i): implement the 'edit' command

[alt-git.git] / sequencer.c

#include "cache.h"
#include "lockfile.h"
#include "sequencer.h"
#include "dir.h"
#include "object.h"
#include "commit.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"

#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_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")
/*
 * 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")
/*
 * 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 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 dir = STRBUF_INIT;
        int i;

        free(opts->gpg_sign);
        free(opts->strategy);
        for (i = 0; i < opts->xopts_nr; i++)
                free(opts->xopts[i]);
        free(opts->xopts);

        strbuf_addf(&dir, "%s", get_dir(opts));
        remove_dir_recursively(&dir, 0);
        strbuf_release(&dir);

        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.hash, 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)
{
        static struct lock_file msg_file;

        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) {
                rollback_lock_file(&msg_file);
                return error_errno(_("could not write to '%s'"), filename);
        }
        if (append_eol && write(msg_fd, "\n", 1) < 0) {
                rollback_lock_file(&msg_file);
                return error_errno(_("could not write eol to '%s'"), filename);
        }
        if (commit_lock_file(&msg_file) < 0) {
                rollback_lock_file(&msg_file);
                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(EMPTY_TREE_SHA1_BIN);
}

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 unsigned char *to, const unsigned char *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_sha1 : 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,
                              unsigned char *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;
        static struct lock_file index_lock;

        hold_locked_index(&index_lock, LOCK_DIE_ON_ERROR);

        read_cache();

        init_merge_options(&o);
        o.ancestor = base ? base_label : "(empty tree)";
        o.branch1 = "HEAD";
        o.branch2 = next ? next_label : "(empty tree)";

        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);
        strbuf_release(&o.obuf);
        if (clean < 0)
                return clean;

        if (active_cache_changed &&
            write_locked_index(&the_index, &index_lock, COMMIT_LOCK))
                /* TRANSLATORS: %s will be "revert", "cherry-pick" or
                 * "rebase -i".
                 */
                return error(_("%s: Unable to write new index file"),
                        _(action_name(opts)));
        rollback_lock_file(&index_lock);

        if (opts->signoff)
                append_signoff(msgbuf, 0, 0);

        if (!clean)
                append_conflicts_hint(msgbuf);

        return !clean;
}

static int is_index_unchanged(void)
{
        unsigned char head_sha1[20];
        struct commit *head_commit;

        if (!resolve_ref_unsafe("HEAD", RESOLVE_REF_READING, head_sha1, NULL))
                return error(_("could not resolve HEAD commit\n"));

        head_commit = lookup_commit(head_sha1);

        /*
         * 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\n"));

        return !hashcmp(active_cache_tree->sha1, head_commit->tree->object.oid.hash);
}

/*
 * Read the author-script file into an environment block, ready for use in
 * run_command(), that can be free()d afterwards.
 */
static char **read_author_script(void)
{
        struct strbuf script = STRBUF_INIT;
        int i, count = 0;
        char *p, *p2, **env;
        size_t env_size;

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

        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++;
                }

        env_size = (count + 1) * sizeof(*env);
        strbuf_grow(&script, env_size);
        memmove(script.buf + env_size, script.buf, script.len);
        p = script.buf + env_size;
        env = (char **)strbuf_detach(&script, NULL);

        for (i = 0; i < count; i++) {
                env[i] = p;
                p += strlen(p) + 1;
        }
        env[count] = NULL;

        return env;
}

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");

/*
 * 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,
                          int allow_empty, int edit, int amend,
                          int cleanup_commit_message)
{
        char **env = NULL;
        struct argv_array array;
        int rc;
        const char *value;

        if (is_rebase_i(opts)) {
                env = read_author_script();
                if (!env) {
                        const char *gpg_opt = gpg_sign_opt_quoted(opts);

                        return error(_(staged_changes_advice),
                                     gpg_opt, gpg_opt);
                }
        }

        argv_array_init(&array);
        argv_array_push(&array, "commit");
        argv_array_push(&array, "-n");

        if (amend)
                argv_array_push(&array, "--amend");
        if (opts->gpg_sign)
                argv_array_pushf(&array, "-S%s", opts->gpg_sign);
        if (opts->signoff)
                argv_array_push(&array, "-s");
        if (defmsg)
                argv_array_pushl(&array, "-F", defmsg, NULL);
        if (cleanup_commit_message)
                argv_array_push(&array, "--cleanup=strip");
        if (edit)
                argv_array_push(&array, "-e");
        else if (!cleanup_commit_message &&
                 !opts->signoff && !opts->record_origin &&
                 git_config_get_value("commit.cleanup", &value))
                argv_array_push(&array, "--cleanup=verbatim");

        if (allow_empty)
                argv_array_push(&array, "--allow-empty");

        if (opts->allow_empty_message)
                argv_array_push(&array, "--allow-empty-message");

        rc = run_command_v_opt_cd_env(array.argv, RUN_GIT_CMD, NULL,
                        (const char *const *)env);
        argv_array_clear(&array);
        free(env);

        return rc;
}

static int is_original_commit_empty(struct commit *commit)
{
        const unsigned char *ptree_sha1;

        if (parse_commit(commit))
                return error(_("could not parse commit %s\n"),
                             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\n"),
                                oid_to_hex(&parent->object.oid));
                ptree_sha1 = parent->tree->object.oid.hash;
        } else {
                ptree_sha1 = EMPTY_TREE_SHA1_BIN; /* commit is root */
        }

        return !hashcmp(ptree_sha1, commit->tree->object.oid.hash);
}

/*
 * 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,
        /* commands that do nothing but are counted for reporting progress */
        TODO_NOOP
};

static const char *todo_command_strings[] = {
        "pick",
        "revert",
        "edit",
        "noop"
};

static const char *command_to_string(const enum todo_command command)
{
        if ((size_t)command < ARRAY_SIZE(todo_command_strings))
                return todo_command_strings[command];
        die("Unknown command: %d", command);
}

static int is_noop(const enum todo_command command)
{
        return TODO_NOOP <= (size_t)command;
}

static int do_pick_commit(enum todo_command command, struct commit *commit,
                struct replay_opts *opts)
{
        unsigned char head[20];
        struct commit *base, *next, *parent;
        const char *base_label, *next_label;
        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_sha1("HEAD", head);
                if (unborn)
                        hashcpy(head, EMPTY_TREE_SHA1_BIN);
                if (index_differs_from(unborn ? EMPTY_TREE_SHA1_HEX : "HEAD", 0, 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 (opts->allow_ff &&
            ((parent && !hashcmp(parent->object.oid.hash, head)) ||
             (!parent && unborn)))
                return fast_forward_to(commit->object.oid.hash, head, unborn, opts);

        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));

        if (get_message(commit, &msg) != 0)
                return error(_("cannot get commit message for %s"),
                        oid_to_hex(&commit->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) {
                        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 (!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, sha1_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.hash, NULL,
                       REF_NODEREF, 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.hash, NULL,
                       REF_NODEREF, 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;
        }
        if (!opts->no_commit)
                res = run_git_commit(opts->edit ? NULL : git_path_merge_msg(),
                                     opts, allow, opts->edit, 0, 0);

leave:
        free_message(commit, &msg);
        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)
{
        static struct lock_file index_lock;
        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 (the_index.cache_changed && index_fd >= 0) {
                if (write_locked_index(&the_index, &index_lock, COMMIT_LOCK)) {
                        rollback_lock_file(&index_lock);
                        return error(_("git %s: failed to refresh the index"),
                                _(action_name(opts)));
                }
        }
        rollback_lock_file(&index_lock);
        return 0;
}

struct todo_item {
        enum todo_command command;
        struct commit *commit;
        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;
};

#define TODO_LIST_INIT { STRBUF_INIT }

static void todo_list_release(struct todo_list *todo_list)
{
        strbuf_release(&todo_list->buf);
        free(todo_list->items);
        todo_list->items = NULL;
        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)
{
        unsigned char commit_sha1[20];
        char *end_of_object_name;
        int i, saved, status, padding;

        /* left-trim */
        bol += strspn(bol, " \t");

        if (bol == eol || *bol == '\r' || *bol == comment_line_char) {
                item->command = TODO_NOOP;
                item->commit = NULL;
                item->arg = bol;
                item->arg_len = eol - bol;
                return 0;
        }

        for (i = 0; i < ARRAY_SIZE(todo_command_strings); i++)
                if (skip_prefix(bol, todo_command_strings[i], &bol)) {
                        item->command = i;
                        break;
                }
        if (i >= ARRAY_SIZE(todo_command_strings))
                return -1;

        if (item->command == TODO_NOOP) {
                item->commit = NULL;
                item->arg = bol;
                item->arg_len = eol - bol;
                return 0;
        }

        /* Eat up extra spaces/ tabs before object name */
        padding = strspn(bol, " \t");
        if (!padding)
                return -1;
        bol += padding;

        end_of_object_name = (char *) bol + strcspn(bol, " \t\n");
        saved = *end_of_object_name;
        *end_of_object_name = '\0';
        status = get_sha1(bol, commit_sha1);
        *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_sha1);
        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;

        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 = -1;
                }
        }
        if (!todo_list->nr)
                return error(_("no commits parsed."));
        return res;
}

static int read_populate_todo(struct todo_list *todo_list,
                        struct replay_opts *opts)
{
        const char *todo_file = get_todo_path(opts);
        int fd, res;

        strbuf_reset(&todo_list->buf);
        fd = open(todo_file, O_RDONLY);
        if (fd < 0)
                return error_errno(_("could not open '%s'"), todo_file);
        if (strbuf_read(&todo_list->buf, fd, 0) < 0) {
                close(fd);
                return error(_("could not read '%s'."), todo_file);
        }
        close(fd);

        res = parse_insn_buffer(todo_list->buf.buf, todo_list);
        if (res)
                return error(_("unusable instruction sheet: '%s'"), todo_file);

        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."));
        }

        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
                return error(_("invalid key: %s"), key);

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

        return 0;
}

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_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_strings[command];
        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)
{
        static struct lock_file head_lock;
        struct strbuf buf = STRBUF_INIT;
        int fd;

        fd = hold_lock_file_for_update(&head_lock, git_path_head_file(), 0);
        if (fd < 0) {
                rollback_lock_file(&head_lock);
                return error_errno(_("could not lock HEAD"));
        }
        strbuf_addf(&buf, "%s\n", head);
        if (write_in_full(fd, buf.buf, buf.len) < 0) {
                rollback_lock_file(&head_lock);
                return error_errno(_("could not write to '%s'"),
                                   git_path_head_file());
        }
        if (commit_lock_file(&head_lock) < 0) {
                rollback_lock_file(&head_lock);
                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 unsigned char *sha1)
{
        const char *argv[4];    /* reset --merge <arg> + NULL */

        argv[0] = "reset";
        argv[1] = "--merge";
        argv[2] = sha1_to_hex(sha1);
        argv[3] = NULL;
        return run_command_v_opt(argv, RUN_GIT_CMD);
}

static int rollback_single_pick(void)
{
        unsigned char head_sha1[20];

        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_sha1, NULL))
                return error(_("cannot resolve HEAD"));
        if (is_null_sha1(head_sha1))
                return error(_("cannot abort from a branch yet to be born"));
        return reset_for_rollback(head_sha1);
}

int sequencer_rollback(struct replay_opts *opts)
{
        FILE *f;
        unsigned char sha1[20];
        struct strbuf buf = STRBUF_INIT;

        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 (get_sha1_hex(buf.buf, sha1) || buf.buf[40] != '\0') {
                error(_("stored pre-cherry-pick HEAD file '%s' is corrupt"),
                        git_path_head_file());
                goto fail;
        }
        if (is_null_sha1(sha1)) {
                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(sha1))
                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)
{
        static struct lock_file todo_lock;
        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 = next < todo_list->nr ?
                todo_list->items[next].offset_in_buf : todo_list->buf.len;
        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);
        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);
        }
        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;

        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)
{
        unsigned char head[20];
        char *p;

        if (get_sha1("HEAD", head))
                return error(_("cannot read HEAD"));

        p = sha1_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 pick_commits(struct todo_list *todo_list, struct replay_opts *opts)
{
        int res = 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 (item->command <= TODO_EDIT) {
                        res = do_pick_commit(item->command, item->commit,
                                        opts);
                        if (item->command == TODO_EDIT) {
                                struct commit *commit = item->commit;
                                if (!res)
                                        warning(_("stopped at %s... %.*s"),
                                                short_commit_name(commit),
                                                item->arg_len, item->arg);
                                return error_with_patch(commit,
                                        item->arg, item->arg_len, opts, res,
                                        !res);
                        }
                } else if (!is_noop(item->command))
                        return error(_("unknown command %d"), item->command);

                todo_list->current++;
                if (res)
                        return res;
        }

        if (is_rebase_i(opts)) {
                /* Stopped in the middle, as planned? */
                if (todo_list->current < todo_list->nr)
                        return 0;
        }

        /*
         * 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);
}

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 (!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;

        /* 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", 0, 0)) {
                res = error_dirty_index(opts);
                goto release_todo_list;
        }
        todo_list.current++;
        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);
}

int sequencer_pick_revisions(struct replay_opts *opts)
{
        struct todo_list todo_list = TODO_LIST_INIT;
        unsigned char sha1[20];
        int i, res;

        assert(opts->revs);
        if (read_and_refresh_cache(opts))
                return -1;

        for (i = 0; i < opts->revs->pending.nr; i++) {
                unsigned char sha1[20];
                const char *name = opts->revs->pending.objects[i].name;

                /* This happens when using --stdin. */
                if (!strlen(name))
                        continue;

                if (!get_sha1(name, sha1)) {
                        if (!lookup_commit_reference_gently(sha1, 1)) {
                                enum object_type type = sha1_object_info(sha1, NULL);
                                return error(_("%s: can't cherry-pick a %s"),
                                        name, typename(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_sha1("HEAD", sha1) && (opts->action == REPLAY_REVERT))
                return error(_("can't revert as initial commit"));
        if (save_head(sha1_to_hex(sha1)))
                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 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 (msgbuf->buf[len - 1] != '\n') {
                        /*
                         * Incomplete line.  Complete the line and add a
                         * blank one so that there is an empty line between
                         * the message body and the sob.
                         */
                        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);
}