cherry-pick: regression fix for empty commits

[alt-git.git] / sequencer.c

#include "cache.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"

#define GIT_REFLOG_ACTION "GIT_REFLOG_ACTION"

void remove_sequencer_state(void)
{
        struct strbuf seq_dir = STRBUF_INIT;

        strbuf_addf(&seq_dir, "%s", git_path(SEQ_DIR));
        remove_dir_recursively(&seq_dir, 0);
        strbuf_release(&seq_dir);
}

static const char *action_name(const struct replay_opts *opts)
{
        return opts->action == REPLAY_REVERT ? "revert" : "cherry-pick";
}

static char *get_encoding(const char *message);

struct commit_message {
        char *parent_label;
        const char *label;
        const char *subject;
        char *reencoded_message;
        const char *message;
};

static int get_message(struct commit *commit, struct commit_message *out)
{
        const char *encoding;
        const char *abbrev, *subject;
        int abbrev_len, subject_len;
        char *q;

        if (!commit->buffer)
                return -1;
        encoding = get_encoding(commit->buffer);
        if (!encoding)
                encoding = "UTF-8";
        if (!git_commit_encoding)
                git_commit_encoding = "UTF-8";

        out->reencoded_message = NULL;
        out->message = commit->buffer;
        if (strcmp(encoding, git_commit_encoding))
                out->reencoded_message = reencode_string(commit->buffer,
                                        git_commit_encoding, encoding);
        if (out->reencoded_message)
                out->message = out->reencoded_message;

        abbrev = find_unique_abbrev(commit->object.sha1, DEFAULT_ABBREV);
        abbrev_len = strlen(abbrev);

        subject_len = find_commit_subject(out->message, &subject);

        out->parent_label = xmalloc(strlen("parent of ") + abbrev_len +
                              strlen("... ") + subject_len + 1);
        q = out->parent_label;
        q = mempcpy(q, "parent of ", strlen("parent of "));
        out->label = q;
        q = mempcpy(q, abbrev, abbrev_len);
        q = mempcpy(q, "... ", strlen("... "));
        out->subject = q;
        q = mempcpy(q, subject, subject_len);
        *q = '\0';
        return 0;
}

static void free_message(struct commit_message *msg)
{
        free(msg->parent_label);
        free(msg->reencoded_message);
}

static char *get_encoding(const char *message)
{
        const char *p = message, *eol;

        while (*p && *p != '\n') {
                for (eol = p + 1; *eol && *eol != '\n'; eol++)
                        ; /* do nothing */
                if (!prefixcmp(p, "encoding ")) {
                        char *result = xmalloc(eol - 8 - p);
                        strlcpy(result, p + 9, eol - 8 - p);
                        return result;
                }
                p = eol;
                if (*p == '\n')
                        p++;
        }
        return NULL;
}

static void write_cherry_pick_head(struct commit *commit, const char *pseudoref)
{
        const char *filename;
        int fd;
        struct strbuf buf = STRBUF_INIT;

        strbuf_addf(&buf, "%s\n", sha1_to_hex(commit->object.sha1));

        filename = git_path("%s", pseudoref);
        fd = open(filename, O_WRONLY | O_CREAT, 0666);
        if (fd < 0)
                die_errno(_("Could not open '%s' for writing"), filename);
        if (write_in_full(fd, buf.buf, buf.len) != buf.len || close(fd))
                die_errno(_("Could not write to '%s'"), filename);
        strbuf_release(&buf);
}

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 occured 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 void write_message(struct strbuf *msgbuf, const char *filename)
{
        static struct lock_file msg_file;

        int msg_fd = hold_lock_file_for_update(&msg_file, filename,
                                               LOCK_DIE_ON_ERROR);
        if (write_in_full(msg_fd, msgbuf->buf, msgbuf->len) < 0)
                die_errno(_("Could not write to %s"), filename);
        strbuf_release(msgbuf);
        if (commit_lock_file(&msg_file) < 0)
                die(_("Error wrapping up %s"), filename);
}

static struct tree *empty_tree(void)
{
        return lookup_tree((const unsigned char *)EMPTY_TREE_SHA1_BIN);
}

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

        /* Different translation strings for cherry-pick and revert */
        if (opts->action == REPLAY_PICK)
                error(_("Your local changes would be overwritten by cherry-pick."));
        else
                error(_("Your local changes would be overwritten by revert."));

        if (advice_commit_before_merge)
                advise(_("Commit your changes or stash them to proceed."));
        return -1;
}

static int fast_forward_to(const unsigned char *to, const unsigned char *from)
{
        struct ref_lock *ref_lock;

        read_cache();
        if (checkout_fast_forward(from, to))
                exit(1); /* the callee should have complained already */
        ref_lock = lock_any_ref_for_update("HEAD", from, 0);
        return write_ref_sha1(ref_lock, to, "cherry-pick");
}

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, index_fd;
        const char **xopt;
        static struct lock_file index_lock;

        index_fd = hold_locked_index(&index_lock, 1);

        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);

        if (active_cache_changed &&
            (write_cache(index_fd, active_cache, active_nr) ||
             commit_locked_index(&index_lock)))
                /* TRANSLATORS: %s will be "revert" or "cherry-pick" */
                die(_("%s: Unable to write new index file"), action_name(opts));
        rollback_lock_file(&index_lock);

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

        return !clean;
}

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

        if (!resolve_ref_unsafe("HEAD", head_sha1, 1, 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(active_cache_tree, active_cache,
                                  active_nr, 0))
                        return error(_("Unable to update cache tree\n"));

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

/*
 * 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.
 */
static int run_git_commit(const char *defmsg, struct replay_opts *opts,
                          int allow_empty)
{
        struct argv_array array;
        int rc;

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

        if (opts->signoff)
                argv_array_push(&array, "-s");
        if (!opts->edit) {
                argv_array_push(&array, "-F");
                argv_array_push(&array, defmsg);
        }

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

        rc = run_command_v_opt(array.argv, RUN_GIT_CMD);
        argv_array_clear(&array);
        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"),
                             sha1_to_hex(commit->object.sha1));
        if (commit->parents) {
                struct commit *parent = commit->parents->item;
                if (parse_commit(parent))
                        return error(_("Could not parse parent commit %s\n"),
                                sha1_to_hex(parent->object.sha1));
                ptree_sha1 = parent->tree->object.sha1;
        } else {
                ptree_sha1 = EMPTY_TREE_SHA1_BIN; /* commit is root */
        }

        return !hashcmp(ptree_sha1, commit->tree->object.sha1);
}

/*
 * 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;
}

static int do_pick_commit(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, NULL };
        char *defmsg = NULL;
        struct strbuf msgbuf = STRBUF_INIT;
        int res;

        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))
                        die (_("Your index file is unmerged."));
        } else {
                if (get_sha1("HEAD", head))
                        return error(_("You do not have a valid HEAD"));
                if (index_differs_from("HEAD", 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."),
                                sha1_to_hex(commit->object.sha1));

                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"),
                                sha1_to_hex(commit->object.sha1), opts->mainline);
                parent = p->item;
        } else if (0 < opts->mainline)
                return error(_("Mainline was specified but commit %s is not a merge."),
                        sha1_to_hex(commit->object.sha1));
        else
                parent = commit->parents->item;

        if (opts->allow_ff && parent && !hashcmp(parent->object.sha1, head))
                return fast_forward_to(commit->object.sha1, head);

        if (parent && parse_commit(parent) < 0)
                /* TRANSLATORS: The first %s will be "revert" or
                   "cherry-pick", the second %s a SHA1 */
                return error(_("%s: cannot parse parent commit %s"),
                        action_name(opts), sha1_to_hex(parent->object.sha1));

        if (get_message(commit, &msg) != 0)
                return error(_("Cannot get commit message for %s"),
                        sha1_to_hex(commit->object.sha1));

        /*
         * "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.
         */

        defmsg = git_pathdup("MERGE_MSG");

        if (opts->action == REPLAY_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, sha1_to_hex(commit->object.sha1));

                if (commit->parents && commit->parents->next) {
                        strbuf_addstr(&msgbuf, ", reversing\nchanges made to ");
                        strbuf_addstr(&msgbuf, sha1_to_hex(parent->object.sha1));
                }
                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; it starts
                 * after the tree, parent, author, committer
                 * information followed by "\n\n".
                 */
                p = strstr(msg.message, "\n\n");
                if (p) {
                        p += 2;
                        strbuf_addstr(&msgbuf, p);
                }

                if (opts->record_origin) {
                        strbuf_addstr(&msgbuf, "(cherry picked from commit ");
                        strbuf_addstr(&msgbuf, sha1_to_hex(commit->object.sha1));
                        strbuf_addstr(&msgbuf, ")\n");
                }
        }

        if (!opts->strategy || !strcmp(opts->strategy, "recursive") || opts->action == REPLAY_REVERT) {
                res = do_recursive_merge(base, next, base_label, next_label,
                                         head, &msgbuf, opts);
                write_message(&msgbuf, defmsg);
        } else {
                struct commit_list *common = NULL;
                struct commit_list *remotes = NULL;

                write_message(&msgbuf, defmsg);

                commit_list_insert(base, &common);
                commit_list_insert(next, &remotes);
                res = try_merge_command(opts->strategy, opts->xopts_nr, opts->xopts,
                                        common, sha1_to_hex(head), remotes);
                free_commit_list(common);
                free_commit_list(remotes);
        }

        /*
         * 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 (opts->action == REPLAY_PICK && !opts->no_commit && (res == 0 || res == 1))
                write_cherry_pick_head(commit, "CHERRY_PICK_HEAD");
        if (opts->action == REPLAY_REVERT && ((opts->no_commit && res == 0) || res == 1))
                write_cherry_pick_head(commit, "REVERT_HEAD");

        if (res) {
                error(opts->action == REPLAY_REVERT
                      ? _("could not revert %s... %s")
                      : _("could not apply %s... %s"),
                      find_unique_abbrev(commit->object.sha1, DEFAULT_ABBREV),
                      msg.subject);
                print_advice(res == 1, opts);
                rerere(opts->allow_rerere_auto);
        } else {
                int allow = allow_empty(opts, commit);
                if (allow < 0)
                        return allow;
                if (!opts->no_commit)
                        res = run_git_commit(defmsg, opts, allow);
        }

        free_message(&msg);
        free(defmsg);

        return res;
}

static void prepare_revs(struct replay_opts *opts)
{
        if (opts->action != REPLAY_REVERT)
                opts->revs->reverse ^= 1;

        if (prepare_revision_walk(opts->revs))
                die(_("revision walk setup failed"));

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

static void 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)
                die(_("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) {
                if (write_index(&the_index, index_fd) ||
                    commit_locked_index(&index_lock))
                        die(_("git %s: failed to refresh the index"), action_name(opts));
        }
        rollback_lock_file(&index_lock);
}

/*
 * Append a commit to the end of the commit_list.
 *
 * next starts by pointing to the variable that holds the head of an
 * empty commit_list, and is updated to point to the "next" field of
 * the last item on the list as new commits are appended.
 *
 * Usage example:
 *
 *     struct commit_list *list;
 *     struct commit_list **next = &list;
 *
 *     next = commit_list_append(c1, next);
 *     next = commit_list_append(c2, next);
 *     assert(commit_list_count(list) == 2);
 *     return list;
 */
static struct commit_list **commit_list_append(struct commit *commit,
                                               struct commit_list **next)
{
        struct commit_list *new = xmalloc(sizeof(struct commit_list));
        new->item = commit;
        *next = new;
        new->next = NULL;
        return &new->next;
}

static int format_todo(struct strbuf *buf, struct commit_list *todo_list,
                struct replay_opts *opts)
{
        struct commit_list *cur = NULL;
        const char *sha1_abbrev = NULL;
        const char *action_str = opts->action == REPLAY_REVERT ? "revert" : "pick";
        const char *subject;
        int subject_len;

        for (cur = todo_list; cur; cur = cur->next) {
                sha1_abbrev = find_unique_abbrev(cur->item->object.sha1, DEFAULT_ABBREV);
                subject_len = find_commit_subject(cur->item->buffer, &subject);
                strbuf_addf(buf, "%s %s %.*s\n", action_str, sha1_abbrev,
                        subject_len, subject);
        }
        return 0;
}

static struct commit *parse_insn_line(char *bol, char *eol, struct replay_opts *opts)
{
        unsigned char commit_sha1[20];
        enum replay_action action;
        char *end_of_object_name;
        int saved, status, padding;

        if (!prefixcmp(bol, "pick")) {
                action = REPLAY_PICK;
                bol += strlen("pick");
        } else if (!prefixcmp(bol, "revert")) {
                action = REPLAY_REVERT;
                bol += strlen("revert");
        } else
                return NULL;

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

        end_of_object_name = 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;

        /*
         * Verify that the action matches up with the one in
         * opts; we don't support arbitrary instructions
         */
        if (action != opts->action) {
                const char *action_str;
                action_str = action == REPLAY_REVERT ? "revert" : "cherry-pick";
                error(_("Cannot %s during a %s"), action_str, action_name(opts));
                return NULL;
        }

        if (status < 0)
                return NULL;

        return lookup_commit_reference(commit_sha1);
}

static int parse_insn_buffer(char *buf, struct commit_list **todo_list,
                        struct replay_opts *opts)
{
        struct commit_list **next = todo_list;
        struct commit *commit;
        char *p = buf;
        int i;

        for (i = 1; *p; i++) {
                char *eol = strchrnul(p, '\n');
                commit = parse_insn_line(p, eol, opts);
                if (!commit)
                        return error(_("Could not parse line %d."), i);
                next = commit_list_append(commit, next);
                p = *eol ? eol + 1 : eol;
        }
        if (!*todo_list)
                return error(_("No commits parsed."));
        return 0;
}

static void read_populate_todo(struct commit_list **todo_list,
                        struct replay_opts *opts)
{
        const char *todo_file = git_path(SEQ_TODO_FILE);
        struct strbuf buf = STRBUF_INIT;
        int fd, res;

        fd = open(todo_file, O_RDONLY);
        if (fd < 0)
                die_errno(_("Could not open %s"), todo_file);
        if (strbuf_read(&buf, fd, 0) < 0) {
                close(fd);
                strbuf_release(&buf);
                die(_("Could not read %s."), todo_file);
        }
        close(fd);

        res = parse_insn_buffer(buf.buf, todo_list, opts);
        strbuf_release(&buf);
        if (res)
                die(_("Unusable instruction sheet: %s"), todo_file);
}

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(&opts->strategy, 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 void read_populate_opts(struct replay_opts **opts_ptr)
{
        const char *opts_file = git_path(SEQ_OPTS_FILE);

        if (!file_exists(opts_file))
                return;
        if (git_config_from_file(populate_opts_cb, opts_file, *opts_ptr) < 0)
                die(_("Malformed options sheet: %s"), opts_file);
}

static void walk_revs_populate_todo(struct commit_list **todo_list,
                                struct replay_opts *opts)
{
        struct commit *commit;
        struct commit_list **next;

        prepare_revs(opts);

        next = todo_list;
        while ((commit = get_revision(opts->revs)))
                next = commit_list_append(commit, next);
}

static int create_seq_dir(void)
{
        const char *seq_dir = git_path(SEQ_DIR);

        if (file_exists(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(seq_dir, 0777) < 0)
                die_errno(_("Could not create sequencer directory %s"), seq_dir);
        return 0;
}

static void save_head(const char *head)
{
        const char *head_file = git_path(SEQ_HEAD_FILE);
        static struct lock_file head_lock;
        struct strbuf buf = STRBUF_INIT;
        int fd;

        fd = hold_lock_file_for_update(&head_lock, head_file, LOCK_DIE_ON_ERROR);
        strbuf_addf(&buf, "%s\n", head);
        if (write_in_full(fd, buf.buf, buf.len) < 0)
                die_errno(_("Could not write to %s"), head_file);
        if (commit_lock_file(&head_lock) < 0)
                die(_("Error wrapping up %s."), head_file);
}

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", head_sha1, 0, 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);
}

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

        filename = git_path(SEQ_HEAD_FILE);
        f = fopen(filename, "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(_("cannot open %s: %s"), filename,
                                                strerror(errno));
        if (strbuf_getline(&buf, f, '\n')) {
                error(_("cannot read %s: %s"), filename, 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"),
                        filename);
                goto fail;
        }
        if (reset_for_rollback(sha1))
                goto fail;
        remove_sequencer_state();
        strbuf_release(&buf);
        return 0;
fail:
        strbuf_release(&buf);
        return -1;
}

static void save_todo(struct commit_list *todo_list, struct replay_opts *opts)
{
        const char *todo_file = git_path(SEQ_TODO_FILE);
        static struct lock_file todo_lock;
        struct strbuf buf = STRBUF_INIT;
        int fd;

        fd = hold_lock_file_for_update(&todo_lock, todo_file, LOCK_DIE_ON_ERROR);
        if (format_todo(&buf, todo_list, opts) < 0)
                die(_("Could not format %s."), todo_file);
        if (write_in_full(fd, buf.buf, buf.len) < 0) {
                strbuf_release(&buf);
                die_errno(_("Could not write to %s"), todo_file);
        }
        if (commit_lock_file(&todo_lock) < 0) {
                strbuf_release(&buf);
                die(_("Error wrapping up %s."), todo_file);
        }
        strbuf_release(&buf);
}

static void save_opts(struct replay_opts *opts)
{
        const char *opts_file = git_path(SEQ_OPTS_FILE);

        if (opts->no_commit)
                git_config_set_in_file(opts_file, "options.no-commit", "true");
        if (opts->edit)
                git_config_set_in_file(opts_file, "options.edit", "true");
        if (opts->signoff)
                git_config_set_in_file(opts_file, "options.signoff", "true");
        if (opts->record_origin)
                git_config_set_in_file(opts_file, "options.record-origin", "true");
        if (opts->allow_ff)
                git_config_set_in_file(opts_file, "options.allow-ff", "true");
        if (opts->mainline) {
                struct strbuf buf = STRBUF_INIT;
                strbuf_addf(&buf, "%d", opts->mainline);
                git_config_set_in_file(opts_file, "options.mainline", buf.buf);
                strbuf_release(&buf);
        }
        if (opts->strategy)
                git_config_set_in_file(opts_file, "options.strategy", opts->strategy);
        if (opts->xopts) {
                int i;
                for (i = 0; i < opts->xopts_nr; i++)
                        git_config_set_multivar_in_file(opts_file,
                                                        "options.strategy-option",
                                                        opts->xopts[i], "^$", 0);
        }
}

static int pick_commits(struct commit_list *todo_list, struct replay_opts *opts)
{
        struct commit_list *cur;
        int res;

        setenv(GIT_REFLOG_ACTION, action_name(opts), 0);
        if (opts->allow_ff)
                assert(!(opts->signoff || opts->no_commit ||
                                opts->record_origin || opts->edit));
        read_and_refresh_cache(opts);

        for (cur = todo_list; cur; cur = cur->next) {
                save_todo(cur, opts);
                res = do_pick_commit(cur->item, opts);
                if (res)
                        return res;
        }

        /*
         * Sequence of picks finished successfully; cleanup by
         * removing the .git/sequencer directory
         */
        remove_sequencer_state();
        return 0;
}

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 sequencer_continue(struct replay_opts *opts)
{
        struct commit_list *todo_list = NULL;

        if (!file_exists(git_path(SEQ_TODO_FILE)))
                return continue_single_pick();
        read_populate_opts(&opts);
        read_populate_todo(&todo_list, opts);

        /* Verify that the conflict has been resolved */
        if (file_exists(git_path("CHERRY_PICK_HEAD")) ||
            file_exists(git_path("REVERT_HEAD"))) {
                int ret = continue_single_pick();
                if (ret)
                        return ret;
        }
        if (index_differs_from("HEAD", 0))
                return error_dirty_index(opts);
        todo_list = todo_list->next;
        return pick_commits(todo_list, opts);
}

static int single_pick(struct commit *cmit, struct replay_opts *opts)
{
        setenv(GIT_REFLOG_ACTION, action_name(opts), 0);
        return do_pick_commit(cmit, opts);
}

int sequencer_pick_revisions(struct replay_opts *opts)
{
        struct commit_list *todo_list = NULL;
        unsigned char sha1[20];

        if (opts->subcommand == REPLAY_NONE)
                assert(opts->revs);

        read_and_refresh_cache(opts);

        /*
         * Decide what to do depending on the arguments; a fresh
         * cherry-pick should be handled differently from an existing
         * one that is being continued
         */
        if (opts->subcommand == REPLAY_REMOVE_STATE) {
                remove_sequencer_state();
                return 0;
        }
        if (opts->subcommand == REPLAY_ROLLBACK)
                return sequencer_rollback(opts);
        if (opts->subcommand == REPLAY_CONTINUE)
                return sequencer_continue(opts);

        /*
         * 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))
                        die(_("revision walk setup failed"));
                cmit = get_revision(opts->revs);
                if (!cmit || get_revision(opts->revs))
                        die("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
         */

        walk_revs_populate_todo(&todo_list, opts);
        if (create_seq_dir() < 0)
                return -1;
        if (get_sha1("HEAD", sha1)) {
                if (opts->action == REPLAY_REVERT)
                        return error(_("Can't revert as initial commit"));
                return error(_("Can't cherry-pick into empty head"));
        }
        save_head(sha1_to_hex(sha1));
        save_opts(opts);
        return pick_commits(todo_list, opts);
}