doc: clarify practices for submitting updated patch versions

[git/gitster.git] / trailer.c

#include "git-compat-util.h"
#include "config.h"
#include "environment.h"
#include "gettext.h"
#include "string-list.h"
#include "run-command.h"
#include "commit.h"
#include "trailer.h"
#include "list.h"
/*
 * Copyright (c) 2013, 2014 Christian Couder <chriscool@tuxfamily.org>
 */

struct conf_info {
        char *name;
        char *key;
        char *command;
        char *cmd;
        enum trailer_where where;
        enum trailer_if_exists if_exists;
        enum trailer_if_missing if_missing;
};

static struct conf_info default_conf_info;

struct trailer_item {
        struct list_head list;
        /*
         * If this is not a trailer line, the line is stored in value
         * (excluding the terminating newline) and token is NULL.
         */
        char *token;
        char *value;
};

struct arg_item {
        struct list_head list;
        char *token;
        char *value;
        struct conf_info conf;
};

static LIST_HEAD(conf_head);

static char *separators = ":";

static int configured;

#define TRAILER_ARG_STRING "$ARG"

static const char *git_generated_prefixes[] = {
        "Signed-off-by: ",
        "(cherry picked from commit ",
        NULL
};

/* Iterate over the elements of the list. */
#define list_for_each_dir(pos, head, is_reverse) \
        for (pos = is_reverse ? (head)->prev : (head)->next; \
                pos != (head); \
                pos = is_reverse ? pos->prev : pos->next)

static int after_or_end(enum trailer_where where)
{
        return (where == WHERE_AFTER) || (where == WHERE_END);
}

/*
 * Return the length of the string not including any final
 * punctuation. E.g., the input "Signed-off-by:" would return
 * 13, stripping the trailing punctuation but retaining
 * internal punctuation.
 */
static size_t token_len_without_separator(const char *token, size_t len)
{
        while (len > 0 && !isalnum(token[len - 1]))
                len--;
        return len;
}

static int same_token(struct trailer_item *a, struct arg_item *b)
{
        size_t a_len, b_len, min_len;

        if (!a->token)
                return 0;

        a_len = token_len_without_separator(a->token, strlen(a->token));
        b_len = token_len_without_separator(b->token, strlen(b->token));
        min_len = (a_len > b_len) ? b_len : a_len;

        return !strncasecmp(a->token, b->token, min_len);
}

static int same_value(struct trailer_item *a, struct arg_item *b)
{
        return !strcasecmp(a->value, b->value);
}

static int same_trailer(struct trailer_item *a, struct arg_item *b)
{
        return same_token(a, b) && same_value(a, b);
}

static inline int is_blank_line(const char *str)
{
        const char *s = str;
        while (*s && *s != '\n' && isspace(*s))
                s++;
        return !*s || *s == '\n';
}

static inline void strbuf_replace(struct strbuf *sb, const char *a, const char *b)
{
        const char *ptr = strstr(sb->buf, a);
        if (ptr)
                strbuf_splice(sb, ptr - sb->buf, strlen(a), b, strlen(b));
}

static void free_trailer_item(struct trailer_item *item)
{
        free(item->token);
        free(item->value);
        free(item);
}

static void free_arg_item(struct arg_item *item)
{
        free(item->conf.name);
        free(item->conf.key);
        free(item->conf.command);
        free(item->conf.cmd);
        free(item->token);
        free(item->value);
        free(item);
}

static char last_non_space_char(const char *s)
{
        int i;
        for (i = strlen(s) - 1; i >= 0; i--)
                if (!isspace(s[i]))
                        return s[i];
        return '\0';
}

static struct trailer_item *trailer_from_arg(struct arg_item *arg_tok)
{
        struct trailer_item *new_item = xcalloc(1, sizeof(*new_item));
        new_item->token = arg_tok->token;
        new_item->value = arg_tok->value;
        arg_tok->token = arg_tok->value = NULL;
        free_arg_item(arg_tok);
        return new_item;
}

static void add_arg_to_input_list(struct trailer_item *on_tok,
                                  struct arg_item *arg_tok)
{
        int aoe = after_or_end(arg_tok->conf.where);
        struct trailer_item *to_add = trailer_from_arg(arg_tok);
        if (aoe)
                list_add(&to_add->list, &on_tok->list);
        else
                list_add_tail(&to_add->list, &on_tok->list);
}

static int check_if_different(struct trailer_item *in_tok,
                              struct arg_item *arg_tok,
                              int check_all,
                              struct list_head *head)
{
        enum trailer_where where = arg_tok->conf.where;
        struct list_head *next_head;
        do {
                if (same_trailer(in_tok, arg_tok))
                        return 0;
                /*
                 * if we want to add a trailer after another one,
                 * we have to check those before this one
                 */
                next_head = after_or_end(where) ? in_tok->list.prev
                                                : in_tok->list.next;
                if (next_head == head)
                        break;
                in_tok = list_entry(next_head, struct trailer_item, list);
        } while (check_all);
        return 1;
}

static char *apply_command(struct conf_info *conf, const char *arg)
{
        struct strbuf cmd = STRBUF_INIT;
        struct strbuf buf = STRBUF_INIT;
        struct child_process cp = CHILD_PROCESS_INIT;
        char *result;

        if (conf->cmd) {
                strbuf_addstr(&cmd, conf->cmd);
                strvec_push(&cp.args, cmd.buf);
                if (arg)
                        strvec_push(&cp.args, arg);
        } else if (conf->command) {
                strbuf_addstr(&cmd, conf->command);
                if (arg)
                        strbuf_replace(&cmd, TRAILER_ARG_STRING, arg);
                strvec_push(&cp.args, cmd.buf);
        }
        strvec_pushv(&cp.env, (const char **)local_repo_env);
        cp.no_stdin = 1;
        cp.use_shell = 1;

        if (capture_command(&cp, &buf, 1024)) {
                error(_("running trailer command '%s' failed"), cmd.buf);
                strbuf_release(&buf);
                result = xstrdup("");
        } else {
                strbuf_trim(&buf);
                result = strbuf_detach(&buf, NULL);
        }

        strbuf_release(&cmd);
        return result;
}

static void apply_item_command(struct trailer_item *in_tok, struct arg_item *arg_tok)
{
        if (arg_tok->conf.command || arg_tok->conf.cmd) {
                const char *arg;
                if (arg_tok->value && arg_tok->value[0]) {
                        arg = arg_tok->value;
                } else {
                        if (in_tok && in_tok->value)
                                arg = xstrdup(in_tok->value);
                        else
                                arg = xstrdup("");
                }
                arg_tok->value = apply_command(&arg_tok->conf, arg);
                free((char *)arg);
        }
}

static void apply_arg_if_exists(struct trailer_item *in_tok,
                                struct arg_item *arg_tok,
                                struct trailer_item *on_tok,
                                struct list_head *head)
{
        switch (arg_tok->conf.if_exists) {
        case EXISTS_DO_NOTHING:
                free_arg_item(arg_tok);
                break;
        case EXISTS_REPLACE:
                apply_item_command(in_tok, arg_tok);
                add_arg_to_input_list(on_tok, arg_tok);
                list_del(&in_tok->list);
                free_trailer_item(in_tok);
                break;
        case EXISTS_ADD:
                apply_item_command(in_tok, arg_tok);
                add_arg_to_input_list(on_tok, arg_tok);
                break;
        case EXISTS_ADD_IF_DIFFERENT:
                apply_item_command(in_tok, arg_tok);
                if (check_if_different(in_tok, arg_tok, 1, head))
                        add_arg_to_input_list(on_tok, arg_tok);
                else
                        free_arg_item(arg_tok);
                break;
        case EXISTS_ADD_IF_DIFFERENT_NEIGHBOR:
                apply_item_command(in_tok, arg_tok);
                if (check_if_different(on_tok, arg_tok, 0, head))
                        add_arg_to_input_list(on_tok, arg_tok);
                else
                        free_arg_item(arg_tok);
                break;
        default:
                BUG("trailer.c: unhandled value %d",
                    arg_tok->conf.if_exists);
        }
}

static void apply_arg_if_missing(struct list_head *head,
                                 struct arg_item *arg_tok)
{
        enum trailer_where where;
        struct trailer_item *to_add;

        switch (arg_tok->conf.if_missing) {
        case MISSING_DO_NOTHING:
                free_arg_item(arg_tok);
                break;
        case MISSING_ADD:
                where = arg_tok->conf.where;
                apply_item_command(NULL, arg_tok);
                to_add = trailer_from_arg(arg_tok);
                if (after_or_end(where))
                        list_add_tail(&to_add->list, head);
                else
                        list_add(&to_add->list, head);
                break;
        default:
                BUG("trailer.c: unhandled value %d",
                    arg_tok->conf.if_missing);
        }
}

static int find_same_and_apply_arg(struct list_head *head,
                                   struct arg_item *arg_tok)
{
        struct list_head *pos;
        struct trailer_item *in_tok;
        struct trailer_item *on_tok;

        enum trailer_where where = arg_tok->conf.where;
        int middle = (where == WHERE_AFTER) || (where == WHERE_BEFORE);
        int backwards = after_or_end(where);
        struct trailer_item *start_tok;

        if (list_empty(head))
                return 0;

        start_tok = list_entry(backwards ? head->prev : head->next,
                               struct trailer_item,
                               list);

        list_for_each_dir(pos, head, backwards) {
                in_tok = list_entry(pos, struct trailer_item, list);
                if (!same_token(in_tok, arg_tok))
                        continue;
                on_tok = middle ? in_tok : start_tok;
                apply_arg_if_exists(in_tok, arg_tok, on_tok, head);
                return 1;
        }
        return 0;
}

void process_trailers_lists(struct list_head *head,
                            struct list_head *arg_head)
{
        struct list_head *pos, *p;
        struct arg_item *arg_tok;

        list_for_each_safe(pos, p, arg_head) {
                int applied = 0;
                arg_tok = list_entry(pos, struct arg_item, list);

                list_del(pos);

                applied = find_same_and_apply_arg(head, arg_tok);

                if (!applied)
                        apply_arg_if_missing(head, arg_tok);
        }
}

int trailer_set_where(enum trailer_where *item, const char *value)
{
        if (!value)
                *item = WHERE_DEFAULT;
        else if (!strcasecmp("after", value))
                *item = WHERE_AFTER;
        else if (!strcasecmp("before", value))
                *item = WHERE_BEFORE;
        else if (!strcasecmp("end", value))
                *item = WHERE_END;
        else if (!strcasecmp("start", value))
                *item = WHERE_START;
        else
                return -1;
        return 0;
}

int trailer_set_if_exists(enum trailer_if_exists *item, const char *value)
{
        if (!value)
                *item = EXISTS_DEFAULT;
        else if (!strcasecmp("addIfDifferent", value))
                *item = EXISTS_ADD_IF_DIFFERENT;
        else if (!strcasecmp("addIfDifferentNeighbor", value))
                *item = EXISTS_ADD_IF_DIFFERENT_NEIGHBOR;
        else if (!strcasecmp("add", value))
                *item = EXISTS_ADD;
        else if (!strcasecmp("replace", value))
                *item = EXISTS_REPLACE;
        else if (!strcasecmp("doNothing", value))
                *item = EXISTS_DO_NOTHING;
        else
                return -1;
        return 0;
}

int trailer_set_if_missing(enum trailer_if_missing *item, const char *value)
{
        if (!value)
                *item = MISSING_DEFAULT;
        else if (!strcasecmp("doNothing", value))
                *item = MISSING_DO_NOTHING;
        else if (!strcasecmp("add", value))
                *item = MISSING_ADD;
        else
                return -1;
        return 0;
}

static void duplicate_conf(struct conf_info *dst, const struct conf_info *src)
{
        *dst = *src;
        dst->name = xstrdup_or_null(src->name);
        dst->key = xstrdup_or_null(src->key);
        dst->command = xstrdup_or_null(src->command);
        dst->cmd = xstrdup_or_null(src->cmd);
}

static struct arg_item *get_conf_item(const char *name)
{
        struct list_head *pos;
        struct arg_item *item;

        /* Look up item with same name */
        list_for_each(pos, &conf_head) {
                item = list_entry(pos, struct arg_item, list);
                if (!strcasecmp(item->conf.name, name))
                        return item;
        }

        /* Item does not already exists, create it */
        CALLOC_ARRAY(item, 1);
        duplicate_conf(&item->conf, &default_conf_info);
        item->conf.name = xstrdup(name);

        list_add_tail(&item->list, &conf_head);

        return item;
}

enum trailer_info_type { TRAILER_KEY, TRAILER_COMMAND, TRAILER_CMD,
                        TRAILER_WHERE, TRAILER_IF_EXISTS, TRAILER_IF_MISSING };

static struct {
        const char *name;
        enum trailer_info_type type;
} trailer_config_items[] = {
        { "key", TRAILER_KEY },
        { "command", TRAILER_COMMAND },
        { "cmd", TRAILER_CMD },
        { "where", TRAILER_WHERE },
        { "ifexists", TRAILER_IF_EXISTS },
        { "ifmissing", TRAILER_IF_MISSING }
};

static int git_trailer_default_config(const char *conf_key, const char *value,
                                      const struct config_context *ctx UNUSED,
                                      void *cb UNUSED)
{
        const char *trailer_item, *variable_name;

        if (!skip_prefix(conf_key, "trailer.", &trailer_item))
                return 0;

        variable_name = strrchr(trailer_item, '.');
        if (!variable_name) {
                if (!strcmp(trailer_item, "where")) {
                        if (trailer_set_where(&default_conf_info.where,
                                              value) < 0)
                                warning(_("unknown value '%s' for key '%s'"),
                                        value, conf_key);
                } else if (!strcmp(trailer_item, "ifexists")) {
                        if (trailer_set_if_exists(&default_conf_info.if_exists,
                                                  value) < 0)
                                warning(_("unknown value '%s' for key '%s'"),
                                        value, conf_key);
                } else if (!strcmp(trailer_item, "ifmissing")) {
                        if (trailer_set_if_missing(&default_conf_info.if_missing,
                                                   value) < 0)
                                warning(_("unknown value '%s' for key '%s'"),
                                        value, conf_key);
                } else if (!strcmp(trailer_item, "separators")) {
                        if (!value)
                                return config_error_nonbool(conf_key);
                        separators = xstrdup(value);
                }
        }
        return 0;
}

static int git_trailer_config(const char *conf_key, const char *value,
                              const struct config_context *ctx UNUSED,
                              void *cb UNUSED)
{
        const char *trailer_item, *variable_name;
        struct arg_item *item;
        struct conf_info *conf;
        char *name = NULL;
        enum trailer_info_type type;
        int i;

        if (!skip_prefix(conf_key, "trailer.", &trailer_item))
                return 0;

        variable_name = strrchr(trailer_item, '.');
        if (!variable_name)
                return 0;

        variable_name++;
        for (i = 0; i < ARRAY_SIZE(trailer_config_items); i++) {
                if (strcmp(trailer_config_items[i].name, variable_name))
                        continue;
                name = xstrndup(trailer_item,  variable_name - trailer_item - 1);
                type = trailer_config_items[i].type;
                break;
        }

        if (!name)
                return 0;

        item = get_conf_item(name);
        conf = &item->conf;
        free(name);

        switch (type) {
        case TRAILER_KEY:
                if (conf->key)
                        warning(_("more than one %s"), conf_key);
                if (!value)
                        return config_error_nonbool(conf_key);
                conf->key = xstrdup(value);
                break;
        case TRAILER_COMMAND:
                if (conf->command)
                        warning(_("more than one %s"), conf_key);
                if (!value)
                        return config_error_nonbool(conf_key);
                conf->command = xstrdup(value);
                break;
        case TRAILER_CMD:
                if (conf->cmd)
                        warning(_("more than one %s"), conf_key);
                if (!value)
                        return config_error_nonbool(conf_key);
                conf->cmd = xstrdup(value);
                break;
        case TRAILER_WHERE:
                if (trailer_set_where(&conf->where, value))
                        warning(_("unknown value '%s' for key '%s'"), value, conf_key);
                break;
        case TRAILER_IF_EXISTS:
                if (trailer_set_if_exists(&conf->if_exists, value))
                        warning(_("unknown value '%s' for key '%s'"), value, conf_key);
                break;
        case TRAILER_IF_MISSING:
                if (trailer_set_if_missing(&conf->if_missing, value))
                        warning(_("unknown value '%s' for key '%s'"), value, conf_key);
                break;
        default:
                BUG("trailer.c: unhandled type %d", type);
        }
        return 0;
}

void trailer_config_init(void)
{
        if (configured)
                return;

        /* Default config must be setup first */
        default_conf_info.where = WHERE_END;
        default_conf_info.if_exists = EXISTS_ADD_IF_DIFFERENT_NEIGHBOR;
        default_conf_info.if_missing = MISSING_ADD;
        git_config(git_trailer_default_config, NULL);
        git_config(git_trailer_config, NULL);
        configured = 1;
}

static const char *token_from_item(struct arg_item *item, char *tok)
{
        if (item->conf.key)
                return item->conf.key;
        if (tok)
                return tok;
        return item->conf.name;
}

static int token_matches_item(const char *tok, struct arg_item *item, size_t tok_len)
{
        if (!strncasecmp(tok, item->conf.name, tok_len))
                return 1;
        return item->conf.key ? !strncasecmp(tok, item->conf.key, tok_len) : 0;
}

/*
 * If the given line is of the form
 * "<token><optional whitespace><separator>..." or "<separator>...", return the
 * location of the separator. Otherwise, return -1.  The optional whitespace
 * is allowed there primarily to allow things like "Bug #43" where <token> is
 * "Bug" and <separator> is "#".
 *
 * The separator-starts-line case (in which this function returns 0) is
 * distinguished from the non-well-formed-line case (in which this function
 * returns -1) because some callers of this function need such a distinction.
 */
static ssize_t find_separator(const char *line, const char *separators)
{
        int whitespace_found = 0;
        const char *c;
        for (c = line; *c; c++) {
                if (strchr(separators, *c))
                        return c - line;
                if (!whitespace_found && (isalnum(*c) || *c == '-'))
                        continue;
                if (c != line && (*c == ' ' || *c == '\t')) {
                        whitespace_found = 1;
                        continue;
                }
                break;
        }
        return -1;
}

/*
 * Obtain the token, value, and conf from the given trailer.
 *
 * separator_pos must not be 0, since the token cannot be an empty string.
 *
 * If separator_pos is -1, interpret the whole trailer as a token.
 */
static void parse_trailer(struct strbuf *tok, struct strbuf *val,
                         const struct conf_info **conf, const char *trailer,
                         ssize_t separator_pos)
{
        struct arg_item *item;
        size_t tok_len;
        struct list_head *pos;

        if (separator_pos != -1) {
                strbuf_add(tok, trailer, separator_pos);
                strbuf_trim(tok);
                strbuf_addstr(val, trailer + separator_pos + 1);
                strbuf_trim(val);
        } else {
                strbuf_addstr(tok, trailer);
                strbuf_trim(tok);
        }

        /* Lookup if the token matches something in the config */
        tok_len = token_len_without_separator(tok->buf, tok->len);
        if (conf)
                *conf = &default_conf_info;
        list_for_each(pos, &conf_head) {
                item = list_entry(pos, struct arg_item, list);
                if (token_matches_item(tok->buf, item, tok_len)) {
                        char *tok_buf = strbuf_detach(tok, NULL);
                        if (conf)
                                *conf = &item->conf;
                        strbuf_addstr(tok, token_from_item(item, tok_buf));
                        free(tok_buf);
                        break;
                }
        }
}

static struct trailer_item *add_trailer_item(struct list_head *head, char *tok,
                                             char *val)
{
        struct trailer_item *new_item = xcalloc(1, sizeof(*new_item));
        new_item->token = tok;
        new_item->value = val;
        list_add_tail(&new_item->list, head);
        return new_item;
}

static void add_arg_item(struct list_head *arg_head, char *tok, char *val,
                         const struct conf_info *conf,
                         const struct new_trailer_item *new_trailer_item)
{
        struct arg_item *new_item = xcalloc(1, sizeof(*new_item));
        new_item->token = tok;
        new_item->value = val;
        duplicate_conf(&new_item->conf, conf);
        if (new_trailer_item) {
                if (new_trailer_item->where != WHERE_DEFAULT)
                        new_item->conf.where = new_trailer_item->where;
                if (new_trailer_item->if_exists != EXISTS_DEFAULT)
                        new_item->conf.if_exists = new_trailer_item->if_exists;
                if (new_trailer_item->if_missing != MISSING_DEFAULT)
                        new_item->conf.if_missing = new_trailer_item->if_missing;
        }
        list_add_tail(&new_item->list, arg_head);
}

void parse_trailers_from_config(struct list_head *config_head)
{
        struct arg_item *item;
        struct list_head *pos;

        /* Add an arg item for each configured trailer with a command */
        list_for_each(pos, &conf_head) {
                item = list_entry(pos, struct arg_item, list);
                if (item->conf.command)
                        add_arg_item(config_head,
                                     xstrdup(token_from_item(item, NULL)),
                                     xstrdup(""),
                                     &item->conf, NULL);
        }
}

void parse_trailers_from_command_line_args(struct list_head *arg_head,
                                           struct list_head *new_trailer_head)
{
        struct strbuf tok = STRBUF_INIT;
        struct strbuf val = STRBUF_INIT;
        const struct conf_info *conf;
        struct list_head *pos;

        /*
         * In command-line arguments, '=' is accepted (in addition to the
         * separators that are defined).
         */
        char *cl_separators = xstrfmt("=%s", separators);

        /* Add an arg item for each trailer on the command line */
        list_for_each(pos, new_trailer_head) {
                struct new_trailer_item *tr =
                        list_entry(pos, struct new_trailer_item, list);
                ssize_t separator_pos = find_separator(tr->text, cl_separators);

                if (separator_pos == 0) {
                        struct strbuf sb = STRBUF_INIT;
                        strbuf_addstr(&sb, tr->text);
                        strbuf_trim(&sb);
                        error(_("empty trailer token in trailer '%.*s'"),
                              (int) sb.len, sb.buf);
                        strbuf_release(&sb);
                } else {
                        parse_trailer(&tok, &val, &conf, tr->text,
                                      separator_pos);
                        add_arg_item(arg_head,
                                     strbuf_detach(&tok, NULL),
                                     strbuf_detach(&val, NULL),
                                     conf, tr);
                }
        }

        free(cl_separators);
}

static const char *next_line(const char *str)
{
        const char *nl = strchrnul(str, '\n');
        return nl + !!*nl;
}

/*
 * Return the position of the start of the last line. If len is 0, return -1.
 */
static ssize_t last_line(const char *buf, size_t len)
{
        ssize_t i;
        if (len == 0)
                return -1;
        if (len == 1)
                return 0;
        /*
         * Skip the last character (in addition to the null terminator),
         * because if the last character is a newline, it is considered as part
         * of the last line anyway.
         */
        i = len - 2;

        for (; i >= 0; i--) {
                if (buf[i] == '\n')
                        return i + 1;
        }
        return 0;
}

/*
 * Find the end of the log message as an offset from the start of the input
 * (where callers of this function are interested in looking for a trailers
 * block in the same input). We have to consider two categories of content that
 * can come at the end of the input which we want to ignore (because they don't
 * belong in the log message):
 *
 * (1) the "patch part" which begins with a "---" divider and has patch
 * information (like the output of git-format-patch), and
 *
 * (2) any trailing comment lines, blank lines like in the output of "git
 * commit -v", or stuff below the "cut" (scissor) line.
 *
 * As a formula, the situation looks like this:
 *
 *     INPUT = LOG MESSAGE + IGNORED
 *
 * where IGNORED can be either of the two categories described above. It may be
 * that there is nothing to ignore. Now it may be the case that the LOG MESSAGE
 * contains a trailer block, but that's not the concern of this function.
 */
static size_t find_end_of_log_message(const char *input, int no_divider)
{
        size_t end;
        const char *s;

        /* Assume the naive end of the input is already what we want. */
        end = strlen(input);

        /* Optionally skip over any patch part ("---" line and below). */
        if (!no_divider) {
                for (s = input; *s; s = next_line(s)) {
                        const char *v;

                        if (skip_prefix(s, "---", &v) && isspace(*v)) {
                                end = s - input;
                                break;
                        }
                }
        }

        /* Skip over other ignorable bits. */
        return end - ignored_log_message_bytes(input, end);
}

/*
 * Return the position of the first trailer line or len if there are no
 * trailers.
 */
static size_t find_trailer_block_start(const char *buf, size_t len)
{
        const char *s;
        ssize_t end_of_title, l;
        int only_spaces = 1;
        int recognized_prefix = 0, trailer_lines = 0, non_trailer_lines = 0;
        /*
         * Number of possible continuation lines encountered. This will be
         * reset to 0 if we encounter a trailer (since those lines are to be
         * considered continuations of that trailer), and added to
         * non_trailer_lines if we encounter a non-trailer (since those lines
         * are to be considered non-trailers).
         */
        int possible_continuation_lines = 0;

        /* The first paragraph is the title and cannot be trailers */
        for (s = buf; s < buf + len; s = next_line(s)) {
                if (starts_with_mem(s, buf + len - s, comment_line_str))
                        continue;
                if (is_blank_line(s))
                        break;
        }
        end_of_title = s - buf;

        /*
         * Get the start of the trailers by looking starting from the end for a
         * blank line before a set of non-blank lines that (i) are all
         * trailers, or (ii) contains at least one Git-generated trailer and
         * consists of at least 25% trailers.
         */
        for (l = last_line(buf, len);
             l >= end_of_title;
             l = last_line(buf, l)) {
                const char *bol = buf + l;
                const char **p;
                ssize_t separator_pos;

                if (starts_with_mem(bol, buf + len - bol, comment_line_str)) {
                        non_trailer_lines += possible_continuation_lines;
                        possible_continuation_lines = 0;
                        continue;
                }
                if (is_blank_line(bol)) {
                        if (only_spaces)
                                continue;
                        non_trailer_lines += possible_continuation_lines;
                        if (recognized_prefix &&
                            trailer_lines * 3 >= non_trailer_lines)
                                return next_line(bol) - buf;
                        else if (trailer_lines && !non_trailer_lines)
                                return next_line(bol) - buf;
                        return len;
                }
                only_spaces = 0;

                for (p = git_generated_prefixes; *p; p++) {
                        if (starts_with(bol, *p)) {
                                trailer_lines++;
                                possible_continuation_lines = 0;
                                recognized_prefix = 1;
                                goto continue_outer_loop;
                        }
                }

                separator_pos = find_separator(bol, separators);
                if (separator_pos >= 1 && !isspace(bol[0])) {
                        struct list_head *pos;

                        trailer_lines++;
                        possible_continuation_lines = 0;
                        if (recognized_prefix)
                                continue;
                        list_for_each(pos, &conf_head) {
                                struct arg_item *item;
                                item = list_entry(pos, struct arg_item, list);
                                if (token_matches_item(bol, item,
                                                       separator_pos)) {
                                        recognized_prefix = 1;
                                        break;
                                }
                        }
                } else if (isspace(bol[0]))
                        possible_continuation_lines++;
                else {
                        non_trailer_lines++;
                        non_trailer_lines += possible_continuation_lines;
                        possible_continuation_lines = 0;
                }
continue_outer_loop:
                ;
        }

        return len;
}

static int ends_with_blank_line(const char *buf, size_t len)
{
        ssize_t ll = last_line(buf, len);
        if (ll < 0)
                return 0;
        return is_blank_line(buf + ll);
}

static void unfold_value(struct strbuf *val)
{
        struct strbuf out = STRBUF_INIT;
        size_t i;

        strbuf_grow(&out, val->len);
        i = 0;
        while (i < val->len) {
                char c = val->buf[i++];
                if (c == '\n') {
                        /* Collapse continuation down to a single space. */
                        while (i < val->len && isspace(val->buf[i]))
                                i++;
                        strbuf_addch(&out, ' ');
                } else {
                        strbuf_addch(&out, c);
                }
        }

        /* Empty lines may have left us with whitespace cruft at the edges */
        strbuf_trim(&out);

        /* output goes back to val as if we modified it in-place */
        strbuf_swap(&out, val);
        strbuf_release(&out);
}

/*
 * Parse trailers in "str", populating the trailer info and "head"
 * linked list structure.
 */
void parse_trailers(const struct process_trailer_options *opts,
                    struct trailer_info *info,
                    const char *str,
                    struct list_head *head)
{
        struct strbuf tok = STRBUF_INIT;
        struct strbuf val = STRBUF_INIT;
        size_t i;

        trailer_info_get(opts, str, info);

        for (i = 0; i < info->trailer_nr; i++) {
                int separator_pos;
                char *trailer = info->trailers[i];
                if (starts_with(trailer, comment_line_str))
                        continue;
                separator_pos = find_separator(trailer, separators);
                if (separator_pos >= 1) {
                        parse_trailer(&tok, &val, NULL, trailer,
                                      separator_pos);
                        if (opts->unfold)
                                unfold_value(&val);
                        add_trailer_item(head,
                                         strbuf_detach(&tok, NULL),
                                         strbuf_detach(&val, NULL));
                } else if (!opts->only_trailers) {
                        strbuf_addstr(&val, trailer);
                        strbuf_strip_suffix(&val, "\n");
                        add_trailer_item(head,
                                         NULL,
                                         strbuf_detach(&val, NULL));
                }
        }
}

void free_trailers(struct list_head *trailers)
{
        struct list_head *pos, *p;
        list_for_each_safe(pos, p, trailers) {
                list_del(pos);
                free_trailer_item(list_entry(pos, struct trailer_item, list));
        }
}

void trailer_info_get(const struct process_trailer_options *opts,
                      const char *str,
                      struct trailer_info *info)
{
        size_t end_of_log_message = 0, trailer_block_start = 0;
        struct strbuf **trailer_lines, **ptr;
        char **trailer_strings = NULL;
        size_t nr = 0, alloc = 0;
        char **last = NULL;

        trailer_config_init();

        end_of_log_message = find_end_of_log_message(str, opts->no_divider);
        trailer_block_start = find_trailer_block_start(str, end_of_log_message);

        trailer_lines = strbuf_split_buf(str + trailer_block_start,
                                         end_of_log_message - trailer_block_start,
                                         '\n',
                                         0);
        for (ptr = trailer_lines; *ptr; ptr++) {
                if (last && isspace((*ptr)->buf[0])) {
                        struct strbuf sb = STRBUF_INIT;
                        strbuf_attach(&sb, *last, strlen(*last), strlen(*last));
                        strbuf_addbuf(&sb, *ptr);
                        *last = strbuf_detach(&sb, NULL);
                        continue;
                }
                ALLOC_GROW(trailer_strings, nr + 1, alloc);
                trailer_strings[nr] = strbuf_detach(*ptr, NULL);
                last = find_separator(trailer_strings[nr], separators) >= 1
                        ? &trailer_strings[nr]
                        : NULL;
                nr++;
        }
        strbuf_list_free(trailer_lines);

        info->blank_line_before_trailer = ends_with_blank_line(str,
                                                               trailer_block_start);
        info->trailer_block_start = trailer_block_start;
        info->trailer_block_end = end_of_log_message;
        info->trailers = trailer_strings;
        info->trailer_nr = nr;
}

void trailer_info_release(struct trailer_info *info)
{
        size_t i;
        for (i = 0; i < info->trailer_nr; i++)
                free(info->trailers[i]);
        free(info->trailers);
}

void format_trailers(const struct process_trailer_options *opts,
                     struct list_head *trailers,
                     struct strbuf *out)
{
        size_t origlen = out->len;
        struct list_head *pos;
        struct trailer_item *item;

        list_for_each(pos, trailers) {
                item = list_entry(pos, struct trailer_item, list);
                if (item->token) {
                        struct strbuf tok = STRBUF_INIT;
                        struct strbuf val = STRBUF_INIT;
                        strbuf_addstr(&tok, item->token);
                        strbuf_addstr(&val, item->value);

                        /*
                         * Skip key/value pairs where the value was empty. This
                         * can happen from trailers specified without a
                         * separator, like `--trailer "Reviewed-by"` (no
                         * corresponding value).
                         */
                        if (opts->trim_empty && !strlen(item->value))
                                continue;

                        if (!opts->filter || opts->filter(&tok, opts->filter_data)) {
                                if (opts->separator && out->len != origlen)
                                        strbuf_addbuf(out, opts->separator);
                                if (!opts->value_only)
                                        strbuf_addbuf(out, &tok);
                                if (!opts->key_only && !opts->value_only) {
                                        if (opts->key_value_separator)
                                                strbuf_addbuf(out, opts->key_value_separator);
                                        else {
                                                char c = last_non_space_char(tok.buf);
                                                if (c && !strchr(separators, c))
                                                        strbuf_addf(out, "%c ", separators[0]);
                                        }
                                }
                                if (!opts->key_only)
                                        strbuf_addbuf(out, &val);
                                if (!opts->separator)
                                        strbuf_addch(out, '\n');
                        }
                        strbuf_release(&tok);
                        strbuf_release(&val);

                } else if (!opts->only_trailers) {
                        if (opts->separator && out->len != origlen) {
                                strbuf_addbuf(out, opts->separator);
                        }
                        strbuf_addstr(out, item->value);
                        if (opts->separator)
                                strbuf_rtrim(out);
                        else
                                strbuf_addch(out, '\n');
                }
        }
}

void format_trailers_from_commit(const struct process_trailer_options *opts,
                                 const char *msg,
                                 struct strbuf *out)
{
        LIST_HEAD(trailer_objects);
        struct trailer_info info;

        parse_trailers(opts, &info, msg, &trailer_objects);

        /* If we want the whole block untouched, we can take the fast path. */
        if (!opts->only_trailers && !opts->unfold && !opts->filter &&
            !opts->separator && !opts->key_only && !opts->value_only &&
            !opts->key_value_separator) {
                strbuf_add(out, msg + info.trailer_block_start,
                           info.trailer_block_end - info.trailer_block_start);
        } else
                format_trailers(opts, &trailer_objects, out);

        free_trailers(&trailer_objects);
        trailer_info_release(&info);
}

void trailer_iterator_init(struct trailer_iterator *iter, const char *msg)
{
        struct process_trailer_options opts = PROCESS_TRAILER_OPTIONS_INIT;
        strbuf_init(&iter->key, 0);
        strbuf_init(&iter->val, 0);
        opts.no_divider = 1;
        trailer_info_get(&opts, msg, &iter->internal.info);
        iter->internal.cur = 0;
}

int trailer_iterator_advance(struct trailer_iterator *iter)
{
        while (iter->internal.cur < iter->internal.info.trailer_nr) {
                char *trailer = iter->internal.info.trailers[iter->internal.cur++];
                int separator_pos = find_separator(trailer, separators);

                if (separator_pos < 1)
                        continue; /* not a real trailer */

                strbuf_reset(&iter->key);
                strbuf_reset(&iter->val);
                parse_trailer(&iter->key, &iter->val, NULL,
                              trailer, separator_pos);
                /* Always unfold values during iteration. */
                unfold_value(&iter->val);
                return 1;
        }
        return 0;
}

void trailer_iterator_release(struct trailer_iterator *iter)
{
        trailer_info_release(&iter->internal.info);
        strbuf_release(&iter->val);
        strbuf_release(&iter->key);
}