pretty: fix out-of-bounds read when parsing invalid padding format

[git/debian.git] / add-patch.c

#include "cache.h"
#include "add-interactive.h"
#include "strbuf.h"
#include "run-command.h"
#include "strvec.h"
#include "pathspec.h"
#include "color.h"
#include "diff.h"
#include "compat/terminal.h"
#include "prompt.h"

enum prompt_mode_type {
        PROMPT_MODE_CHANGE = 0, PROMPT_DELETION, PROMPT_ADDITION, PROMPT_HUNK,
        PROMPT_MODE_MAX, /* must be last */
};

struct patch_mode {
        /*
         * The magic constant 4 is chosen such that all patch modes
         * provide enough space for three command-line arguments followed by a
         * trailing `NULL`.
         */
        const char *diff_cmd[4], *apply_args[4], *apply_check_args[4];
        unsigned is_reverse:1, index_only:1, apply_for_checkout:1;
        const char *prompt_mode[PROMPT_MODE_MAX];
        const char *edit_hunk_hint, *help_patch_text;
};

static struct patch_mode patch_mode_add = {
        .diff_cmd = { "diff-files", NULL },
        .apply_args = { "--cached", NULL },
        .apply_check_args = { "--cached", NULL },
        .prompt_mode = {
                N_("Stage mode change [y,n,q,a,d%s,?]? "),
                N_("Stage deletion [y,n,q,a,d%s,?]? "),
                N_("Stage addition [y,n,q,a,d%s,?]? "),
                N_("Stage this hunk [y,n,q,a,d%s,?]? ")
        },
        .edit_hunk_hint = N_("If the patch applies cleanly, the edited hunk "
                             "will immediately be marked for staging."),
        .help_patch_text =
                N_("y - stage this hunk\n"
                   "n - do not stage this hunk\n"
                   "q - quit; do not stage this hunk or any of the remaining "
                        "ones\n"
                   "a - stage this hunk and all later hunks in the file\n"
                   "d - do not stage this hunk or any of the later hunks in "
                        "the file\n")
};

static struct patch_mode patch_mode_stash = {
        .diff_cmd = { "diff-index", "HEAD", NULL },
        .apply_args = { "--cached", NULL },
        .apply_check_args = { "--cached", NULL },
        .prompt_mode = {
                N_("Stash mode change [y,n,q,a,d%s,?]? "),
                N_("Stash deletion [y,n,q,a,d%s,?]? "),
                N_("Stash addition [y,n,q,a,d%s,?]? "),
                N_("Stash this hunk [y,n,q,a,d%s,?]? "),
        },
        .edit_hunk_hint = N_("If the patch applies cleanly, the edited hunk "
                             "will immediately be marked for stashing."),
        .help_patch_text =
                N_("y - stash this hunk\n"
                   "n - do not stash this hunk\n"
                   "q - quit; do not stash this hunk or any of the remaining "
                        "ones\n"
                   "a - stash this hunk and all later hunks in the file\n"
                   "d - do not stash this hunk or any of the later hunks in "
                        "the file\n"),
};

static struct patch_mode patch_mode_reset_head = {
        .diff_cmd = { "diff-index", "--cached", NULL },
        .apply_args = { "-R", "--cached", NULL },
        .apply_check_args = { "-R", "--cached", NULL },
        .is_reverse = 1,
        .index_only = 1,
        .prompt_mode = {
                N_("Unstage mode change [y,n,q,a,d%s,?]? "),
                N_("Unstage deletion [y,n,q,a,d%s,?]? "),
                N_("Unstage addition [y,n,q,a,d%s,?]? "),
                N_("Unstage this hunk [y,n,q,a,d%s,?]? "),
        },
        .edit_hunk_hint = N_("If the patch applies cleanly, the edited hunk "
                             "will immediately be marked for unstaging."),
        .help_patch_text =
                N_("y - unstage this hunk\n"
                   "n - do not unstage this hunk\n"
                   "q - quit; do not unstage this hunk or any of the remaining "
                        "ones\n"
                   "a - unstage this hunk and all later hunks in the file\n"
                   "d - do not unstage this hunk or any of the later hunks in "
                        "the file\n"),
};

static struct patch_mode patch_mode_reset_nothead = {
        .diff_cmd = { "diff-index", "-R", "--cached", NULL },
        .apply_args = { "--cached", NULL },
        .apply_check_args = { "--cached", NULL },
        .index_only = 1,
        .prompt_mode = {
                N_("Apply mode change to index [y,n,q,a,d%s,?]? "),
                N_("Apply deletion to index [y,n,q,a,d%s,?]? "),
                N_("Apply addition to index [y,n,q,a,d%s,?]? "),
                N_("Apply this hunk to index [y,n,q,a,d%s,?]? "),
        },
        .edit_hunk_hint = N_("If the patch applies cleanly, the edited hunk "
                             "will immediately be marked for applying."),
        .help_patch_text =
                N_("y - apply this hunk to index\n"
                   "n - do not apply this hunk to index\n"
                   "q - quit; do not apply this hunk or any of the remaining "
                        "ones\n"
                   "a - apply this hunk and all later hunks in the file\n"
                   "d - do not apply this hunk or any of the later hunks in "
                        "the file\n"),
};

static struct patch_mode patch_mode_checkout_index = {
        .diff_cmd = { "diff-files", NULL },
        .apply_args = { "-R", NULL },
        .apply_check_args = { "-R", NULL },
        .is_reverse = 1,
        .prompt_mode = {
                N_("Discard mode change from worktree [y,n,q,a,d%s,?]? "),
                N_("Discard deletion from worktree [y,n,q,a,d%s,?]? "),
                N_("Discard addition from worktree [y,n,q,a,d%s,?]? "),
                N_("Discard this hunk from worktree [y,n,q,a,d%s,?]? "),
        },
        .edit_hunk_hint = N_("If the patch applies cleanly, the edited hunk "
                             "will immediately be marked for discarding."),
        .help_patch_text =
                N_("y - discard this hunk from worktree\n"
                   "n - do not discard this hunk from worktree\n"
                   "q - quit; do not discard this hunk or any of the remaining "
                        "ones\n"
                   "a - discard this hunk and all later hunks in the file\n"
                   "d - do not discard this hunk or any of the later hunks in "
                        "the file\n"),
};

static struct patch_mode patch_mode_checkout_head = {
        .diff_cmd = { "diff-index", NULL },
        .apply_for_checkout = 1,
        .apply_check_args = { "-R", NULL },
        .is_reverse = 1,
        .prompt_mode = {
                N_("Discard mode change from index and worktree [y,n,q,a,d%s,?]? "),
                N_("Discard deletion from index and worktree [y,n,q,a,d%s,?]? "),
                N_("Discard addition from index and worktree [y,n,q,a,d%s,?]? "),
                N_("Discard this hunk from index and worktree [y,n,q,a,d%s,?]? "),
        },
        .edit_hunk_hint = N_("If the patch applies cleanly, the edited hunk "
                             "will immediately be marked for discarding."),
        .help_patch_text =
                N_("y - discard this hunk from index and worktree\n"
                   "n - do not discard this hunk from index and worktree\n"
                   "q - quit; do not discard this hunk or any of the remaining "
                        "ones\n"
                   "a - discard this hunk and all later hunks in the file\n"
                   "d - do not discard this hunk or any of the later hunks in "
                        "the file\n"),
};

static struct patch_mode patch_mode_checkout_nothead = {
        .diff_cmd = { "diff-index", "-R", NULL },
        .apply_for_checkout = 1,
        .apply_check_args = { NULL },
        .prompt_mode = {
                N_("Apply mode change to index and worktree [y,n,q,a,d%s,?]? "),
                N_("Apply deletion to index and worktree [y,n,q,a,d%s,?]? "),
                N_("Apply addition to index and worktree [y,n,q,a,d%s,?]? "),
                N_("Apply this hunk to index and worktree [y,n,q,a,d%s,?]? "),
        },
        .edit_hunk_hint = N_("If the patch applies cleanly, the edited hunk "
                             "will immediately be marked for applying."),
        .help_patch_text =
                N_("y - apply this hunk to index and worktree\n"
                   "n - do not apply this hunk to index and worktree\n"
                   "q - quit; do not apply this hunk or any of the remaining "
                        "ones\n"
                   "a - apply this hunk and all later hunks in the file\n"
                   "d - do not apply this hunk or any of the later hunks in "
                        "the file\n"),
};

static struct patch_mode patch_mode_worktree_head = {
        .diff_cmd = { "diff-index", NULL },
        .apply_args = { "-R", NULL },
        .apply_check_args = { "-R", NULL },
        .is_reverse = 1,
        .prompt_mode = {
                N_("Discard mode change from index and worktree [y,n,q,a,d%s,?]? "),
                N_("Discard deletion from index and worktree [y,n,q,a,d%s,?]? "),
                N_("Discard addition from index and worktree [y,n,q,a,d%s,?]? "),
                N_("Discard this hunk from index and worktree [y,n,q,a,d%s,?]? "),
        },
        .edit_hunk_hint = N_("If the patch applies cleanly, the edited hunk "
                             "will immediately be marked for discarding."),
        .help_patch_text =
                N_("y - discard this hunk from worktree\n"
                   "n - do not discard this hunk from worktree\n"
                   "q - quit; do not discard this hunk or any of the remaining "
                        "ones\n"
                   "a - discard this hunk and all later hunks in the file\n"
                   "d - do not discard this hunk or any of the later hunks in "
                        "the file\n"),
};

static struct patch_mode patch_mode_worktree_nothead = {
        .diff_cmd = { "diff-index", "-R", NULL },
        .apply_args = { NULL },
        .apply_check_args = { NULL },
        .prompt_mode = {
                N_("Apply mode change to index and worktree [y,n,q,a,d%s,?]? "),
                N_("Apply deletion to index and worktree [y,n,q,a,d%s,?]? "),
                N_("Apply addition to index and worktree [y,n,q,a,d%s,?]? "),
                N_("Apply this hunk to index and worktree [y,n,q,a,d%s,?]? "),
        },
        .edit_hunk_hint = N_("If the patch applies cleanly, the edited hunk "
                             "will immediately be marked for applying."),
        .help_patch_text =
                N_("y - apply this hunk to worktree\n"
                   "n - do not apply this hunk to worktree\n"
                   "q - quit; do not apply this hunk or any of the remaining "
                        "ones\n"
                   "a - apply this hunk and all later hunks in the file\n"
                   "d - do not apply this hunk or any of the later hunks in "
                        "the file\n"),
};

struct hunk_header {
        unsigned long old_offset, old_count, new_offset, new_count;
        /*
         * Start/end offsets to the extra text after the second `@@` in the
         * hunk header, e.g. the function signature. This is expected to
         * include the newline.
         */
        size_t extra_start, extra_end, colored_extra_start, colored_extra_end;
};

struct hunk {
        size_t start, end, colored_start, colored_end, splittable_into;
        ssize_t delta;
        enum { UNDECIDED_HUNK = 0, SKIP_HUNK, USE_HUNK } use;
        struct hunk_header header;
};

struct add_p_state {
        struct add_i_state s;
        struct strbuf answer, buf;

        /* parsed diff */
        struct strbuf plain, colored;
        struct file_diff {
                struct hunk head;
                struct hunk *hunk;
                size_t hunk_nr, hunk_alloc;
                unsigned deleted:1, added:1, mode_change:1,binary:1;
        } *file_diff;
        size_t file_diff_nr;

        /* patch mode */
        struct patch_mode *mode;
        const char *revision;
};

static void add_p_state_clear(struct add_p_state *s)
{
        size_t i;

        strbuf_release(&s->answer);
        strbuf_release(&s->buf);
        strbuf_release(&s->plain);
        strbuf_release(&s->colored);
        for (i = 0; i < s->file_diff_nr; i++)
                free(s->file_diff[i].hunk);
        free(s->file_diff);
        clear_add_i_state(&s->s);
}

static void err(struct add_p_state *s, const char *fmt, ...)
{
        va_list args;

        va_start(args, fmt);
        fputs(s->s.error_color, stderr);
        vfprintf(stderr, fmt, args);
        fputs(s->s.reset_color, stderr);
        fputc('\n', stderr);
        va_end(args);
}

static void setup_child_process(struct add_p_state *s,
                                struct child_process *cp, ...)
{
        va_list ap;
        const char *arg;

        va_start(ap, cp);
        while ((arg = va_arg(ap, const char *)))
                strvec_push(&cp->args, arg);
        va_end(ap);

        cp->git_cmd = 1;
        strvec_pushf(&cp->env_array,
                     INDEX_ENVIRONMENT "=%s", s->s.r->index_file);
}

static int parse_range(const char **p,
                       unsigned long *offset, unsigned long *count)
{
        char *pend;

        *offset = strtoul(*p, &pend, 10);
        if (pend == *p)
                return -1;
        if (*pend != ',') {
                *count = 1;
                *p = pend;
                return 0;
        }
        *count = strtoul(pend + 1, (char **)p, 10);
        return *p == pend + 1 ? -1 : 0;
}

static int parse_hunk_header(struct add_p_state *s, struct hunk *hunk)
{
        struct hunk_header *header = &hunk->header;
        const char *line = s->plain.buf + hunk->start, *p = line;
        char *eol = memchr(p, '\n', s->plain.len - hunk->start);

        if (!eol)
                eol = s->plain.buf + s->plain.len;

        if (!skip_prefix(p, "@@ -", &p) ||
            parse_range(&p, &header->old_offset, &header->old_count) < 0 ||
            !skip_prefix(p, " +", &p) ||
            parse_range(&p, &header->new_offset, &header->new_count) < 0 ||
            !skip_prefix(p, " @@", &p))
                return error(_("could not parse hunk header '%.*s'"),
                             (int)(eol - line), line);

        hunk->start = eol - s->plain.buf + (*eol == '\n');
        header->extra_start = p - s->plain.buf;
        header->extra_end = hunk->start;

        if (!s->colored.len) {
                header->colored_extra_start = header->colored_extra_end = 0;
                return 0;
        }

        /* Now find the extra text in the colored diff */
        line = s->colored.buf + hunk->colored_start;
        eol = memchr(line, '\n', s->colored.len - hunk->colored_start);
        if (!eol)
                eol = s->colored.buf + s->colored.len;
        p = memmem(line, eol - line, "@@ -", 4);
        if (!p)
                return error(_("could not parse colored hunk header '%.*s'"),
                             (int)(eol - line), line);
        p = memmem(p + 4, eol - p - 4, " @@", 3);
        if (!p)
                return error(_("could not parse colored hunk header '%.*s'"),
                             (int)(eol - line), line);
        hunk->colored_start = eol - s->colored.buf + (*eol == '\n');
        header->colored_extra_start = p + 3 - s->colored.buf;
        header->colored_extra_end = hunk->colored_start;

        return 0;
}

static int is_octal(const char *p, size_t len)
{
        if (!len)
                return 0;

        while (len--)
                if (*p < '0' || *(p++) > '7')
                        return 0;
        return 1;
}

static int parse_diff(struct add_p_state *s, const struct pathspec *ps)
{
        struct strvec args = STRVEC_INIT;
        const char *diff_algorithm = s->s.interactive_diff_algorithm;
        struct strbuf *plain = &s->plain, *colored = NULL;
        struct child_process cp = CHILD_PROCESS_INIT;
        char *p, *pend, *colored_p = NULL, *colored_pend = NULL, marker = '\0';
        size_t file_diff_alloc = 0, i, color_arg_index;
        struct file_diff *file_diff = NULL;
        struct hunk *hunk = NULL;
        int res;

        strvec_pushv(&args, s->mode->diff_cmd);
        if (diff_algorithm)
                strvec_pushf(&args, "--diff-algorithm=%s", diff_algorithm);
        if (s->revision) {
                struct object_id oid;
                strvec_push(&args,
                            /* could be on an unborn branch */
                            !strcmp("HEAD", s->revision) &&
                            get_oid("HEAD", &oid) ?
                            empty_tree_oid_hex() : s->revision);
        }
        color_arg_index = args.nr;
        /* Use `--no-color` explicitly, just in case `diff.color = always`. */
        strvec_pushl(&args, "--no-color", "-p", "--", NULL);
        for (i = 0; i < ps->nr; i++)
                strvec_push(&args, ps->items[i].original);

        setup_child_process(s, &cp, NULL);
        cp.argv = args.v;
        res = capture_command(&cp, plain, 0);
        if (res) {
                strvec_clear(&args);
                return error(_("could not parse diff"));
        }
        if (!plain->len) {
                strvec_clear(&args);
                return 0;
        }
        strbuf_complete_line(plain);

        if (want_color_fd(1, -1)) {
                struct child_process colored_cp = CHILD_PROCESS_INIT;
                const char *diff_filter = s->s.interactive_diff_filter;

                setup_child_process(s, &colored_cp, NULL);
                xsnprintf((char *)args.v[color_arg_index], 8, "--color");
                colored_cp.argv = args.v;
                colored = &s->colored;
                res = capture_command(&colored_cp, colored, 0);
                strvec_clear(&args);
                if (res)
                        return error(_("could not parse colored diff"));

                if (diff_filter) {
                        struct child_process filter_cp = CHILD_PROCESS_INIT;

                        setup_child_process(s, &filter_cp,
                                            diff_filter, NULL);
                        filter_cp.git_cmd = 0;
                        filter_cp.use_shell = 1;
                        strbuf_reset(&s->buf);
                        if (pipe_command(&filter_cp,
                                         colored->buf, colored->len,
                                         &s->buf, colored->len,
                                         NULL, 0) < 0)
                                return error(_("failed to run '%s'"),
                                             diff_filter);
                        strbuf_swap(colored, &s->buf);
                }

                strbuf_complete_line(colored);
                colored_p = colored->buf;
                colored_pend = colored_p + colored->len;
        }
        strvec_clear(&args);

        /* parse files and hunks */
        p = plain->buf;
        pend = p + plain->len;
        while (p != pend) {
                char *eol = memchr(p, '\n', pend - p);
                const char *deleted = NULL, *mode_change = NULL;

                if (!eol)
                        eol = pend;

                if (starts_with(p, "diff ")) {
                        ALLOC_GROW_BY(s->file_diff, s->file_diff_nr, 1,
                                   file_diff_alloc);
                        file_diff = s->file_diff + s->file_diff_nr - 1;
                        hunk = &file_diff->head;
                        hunk->start = p - plain->buf;
                        if (colored_p)
                                hunk->colored_start = colored_p - colored->buf;
                        marker = '\0';
                } else if (p == plain->buf)
                        BUG("diff starts with unexpected line:\n"
                            "%.*s\n", (int)(eol - p), p);
                else if (file_diff->deleted)
                        ; /* keep the rest of the file in a single "hunk" */
                else if (starts_with(p, "@@ ") ||
                         (hunk == &file_diff->head &&
                          (skip_prefix(p, "deleted file", &deleted)))) {
                        if (marker == '-' || marker == '+')
                                /*
                                 * Should not happen; previous hunk did not end
                                 * in a context line? Handle it anyway.
                                 */
                                hunk->splittable_into++;

                        ALLOC_GROW_BY(file_diff->hunk, file_diff->hunk_nr, 1,
                                   file_diff->hunk_alloc);
                        hunk = file_diff->hunk + file_diff->hunk_nr - 1;

                        hunk->start = p - plain->buf;
                        if (colored)
                                hunk->colored_start = colored_p - colored->buf;

                        if (deleted)
                                file_diff->deleted = 1;
                        else if (parse_hunk_header(s, hunk) < 0)
                                return -1;

                        /*
                         * Start counting into how many hunks this one can be
                         * split
                         */
                        marker = *p;
                } else if (hunk == &file_diff->head &&
                           starts_with(p, "new file")) {
                        file_diff->added = 1;
                } else if (hunk == &file_diff->head &&
                           skip_prefix(p, "old mode ", &mode_change) &&
                           is_octal(mode_change, eol - mode_change)) {
                        if (file_diff->mode_change)
                                BUG("double mode change?\n\n%.*s",
                                    (int)(eol - plain->buf), plain->buf);
                        if (file_diff->hunk_nr)
                                BUG("mode change in the middle?\n\n%.*s",
                                    (int)(eol - plain->buf), plain->buf);

                        /*
                         * Do *not* change `hunk`: the mode change pseudo-hunk
                         * is _part of_ the header "hunk".
                         */
                        file_diff->mode_change = 1;
                        ALLOC_GROW_BY(file_diff->hunk, file_diff->hunk_nr, 1,
                                   file_diff->hunk_alloc);
                        file_diff->hunk->start = p - plain->buf;
                        if (colored_p)
                                file_diff->hunk->colored_start =
                                        colored_p - colored->buf;
                } else if (hunk == &file_diff->head &&
                           skip_prefix(p, "new mode ", &mode_change) &&
                           is_octal(mode_change, eol - mode_change)) {

                        /*
                         * Extend the "mode change" pseudo-hunk to include also
                         * the "new mode" line.
                         */
                        if (!file_diff->mode_change)
                                BUG("'new mode' without 'old mode'?\n\n%.*s",
                                    (int)(eol - plain->buf), plain->buf);
                        if (file_diff->hunk_nr != 1)
                                BUG("mode change in the middle?\n\n%.*s",
                                    (int)(eol - plain->buf), plain->buf);
                        if (p - plain->buf != file_diff->hunk->end)
                                BUG("'new mode' does not immediately follow "
                                    "'old mode'?\n\n%.*s",
                                    (int)(eol - plain->buf), plain->buf);
                } else if (hunk == &file_diff->head &&
                           starts_with(p, "Binary files "))
                        file_diff->binary = 1;

                if (!!file_diff->deleted + !!file_diff->added +
                    !!file_diff->mode_change > 1)
                        BUG("diff can only contain delete *or* add *or* a "
                            "mode change?!?\n%.*s",
                            (int)(eol - (plain->buf + file_diff->head.start)),
                            plain->buf + file_diff->head.start);

                if ((marker == '-' || marker == '+') && *p == ' ')
                        hunk->splittable_into++;
                if (marker && *p != '\\')
                        marker = *p;

                p = eol == pend ? pend : eol + 1;
                hunk->end = p - plain->buf;

                if (colored) {
                        char *colored_eol = memchr(colored_p, '\n',
                                                   colored_pend - colored_p);
                        if (colored_eol)
                                colored_p = colored_eol + 1;
                        else if (p != pend)
                                /* colored shorter than non-colored? */
                                goto mismatched_output;
                        else
                                colored_p = colored_pend;

                        hunk->colored_end = colored_p - colored->buf;
                }

                if (mode_change) {
                        if (file_diff->hunk_nr != 1)
                                BUG("mode change in hunk #%d???",
                                    (int)file_diff->hunk_nr);
                        /* Adjust the end of the "mode change" pseudo-hunk */
                        file_diff->hunk->end = hunk->end;
                        if (colored)
                                file_diff->hunk->colored_end = hunk->colored_end;
                }
        }

        if (marker == '-' || marker == '+')
                /*
                 * Last hunk ended in non-context line (i.e. it appended lines
                 * to the file, so there are no trailing context lines).
                 */
                hunk->splittable_into++;

        /* non-colored shorter than colored? */
        if (colored_p != colored_pend) {
mismatched_output:
                error(_("mismatched output from interactive.diffFilter"));
                advise(_("Your filter must maintain a one-to-one correspondence\n"
                         "between its input and output lines."));
                return -1;
        }

        return 0;
}

static size_t find_next_line(struct strbuf *sb, size_t offset)
{
        char *eol;

        if (offset >= sb->len)
                BUG("looking for next line beyond buffer (%d >= %d)\n%s",
                    (int)offset, (int)sb->len, sb->buf);

        eol = memchr(sb->buf + offset, '\n', sb->len - offset);
        if (!eol)
                return sb->len;
        return eol - sb->buf + 1;
}

static void render_hunk(struct add_p_state *s, struct hunk *hunk,
                        ssize_t delta, int colored, struct strbuf *out)
{
        struct hunk_header *header = &hunk->header;

        if (hunk->header.old_offset != 0 || hunk->header.new_offset != 0) {
                /*
                 * Generate the hunk header dynamically, except for special
                 * hunks (such as the diff header).
                 */
                const char *p;
                size_t len;
                unsigned long old_offset = header->old_offset;
                unsigned long new_offset = header->new_offset;

                if (!colored) {
                        p = s->plain.buf + header->extra_start;
                        len = header->extra_end - header->extra_start;
                } else {
                        strbuf_addstr(out, s->s.fraginfo_color);
                        p = s->colored.buf + header->colored_extra_start;
                        len = header->colored_extra_end
                                - header->colored_extra_start;
                }

                if (s->mode->is_reverse)
                        old_offset -= delta;
                else
                        new_offset += delta;

                strbuf_addf(out, "@@ -%lu", old_offset);
                if (header->old_count != 1)
                        strbuf_addf(out, ",%lu", header->old_count);
                strbuf_addf(out, " +%lu", new_offset);
                if (header->new_count != 1)
                        strbuf_addf(out, ",%lu", header->new_count);
                strbuf_addstr(out, " @@");

                if (len)
                        strbuf_add(out, p, len);
                else if (colored)
                        strbuf_addf(out, "%s\n", s->s.reset_color);
                else
                        strbuf_addch(out, '\n');
        }

        if (colored)
                strbuf_add(out, s->colored.buf + hunk->colored_start,
                           hunk->colored_end - hunk->colored_start);
        else
                strbuf_add(out, s->plain.buf + hunk->start,
                           hunk->end - hunk->start);
}

static void render_diff_header(struct add_p_state *s,
                               struct file_diff *file_diff, int colored,
                               struct strbuf *out)
{
        /*
         * If there was a mode change, the first hunk is a pseudo hunk that
         * corresponds to the mode line in the header. If the user did not want
         * to stage that "hunk", we actually have to cut it out from the header.
         */
        int skip_mode_change =
                file_diff->mode_change && file_diff->hunk->use != USE_HUNK;
        struct hunk *head = &file_diff->head, *first = file_diff->hunk;

        if (!skip_mode_change) {
                render_hunk(s, head, 0, colored, out);
                return;
        }

        if (colored) {
                const char *p = s->colored.buf;

                strbuf_add(out, p + head->colored_start,
                            first->colored_start - head->colored_start);
                strbuf_add(out, p + first->colored_end,
                            head->colored_end - first->colored_end);
        } else {
                const char *p = s->plain.buf;

                strbuf_add(out, p + head->start, first->start - head->start);
                strbuf_add(out, p + first->end, head->end - first->end);
        }
}

/* Coalesce hunks again that were split */
static int merge_hunks(struct add_p_state *s, struct file_diff *file_diff,
                       size_t *hunk_index, int use_all, struct hunk *merged)
{
        size_t i = *hunk_index, delta;
        struct hunk *hunk = file_diff->hunk + i;
        /* `header` corresponds to the merged hunk */
        struct hunk_header *header = &merged->header, *next;

        if (!use_all && hunk->use != USE_HUNK)
                return 0;

        *merged = *hunk;
        /* We simply skip the colored part (if any) when merging hunks */
        merged->colored_start = merged->colored_end = 0;

        for (; i + 1 < file_diff->hunk_nr; i++) {
                hunk++;
                next = &hunk->header;

                /*
                 * Stop merging hunks when:
                 *
                 * - the hunk is not selected for use, or
                 * - the hunk does not overlap with the already-merged hunk(s)
                 */
                if ((!use_all && hunk->use != USE_HUNK) ||
                    header->new_offset >= next->new_offset + merged->delta ||
                    header->new_offset + header->new_count
                    < next->new_offset + merged->delta)
                        break;

                /*
                 * If the hunks were not edited, and overlap, we can simply
                 * extend the line range.
                 */
                if (merged->start < hunk->start && merged->end > hunk->start) {
                        merged->end = hunk->end;
                        merged->colored_end = hunk->colored_end;
                        delta = 0;
                } else {
                        const char *plain = s->plain.buf;
                        size_t  overlapping_line_count = header->new_offset
                                + header->new_count - merged->delta
                                - next->new_offset;
                        size_t overlap_end = hunk->start;
                        size_t overlap_start = overlap_end;
                        size_t overlap_next, len, j;

                        /*
                         * One of the hunks was edited: the modified hunk was
                         * appended to the strbuf `s->plain`.
                         *
                         * Let's ensure that at least the last context line of
                         * the first hunk overlaps with the corresponding line
                         * of the second hunk, and then merge.
                         */
                        for (j = 0; j < overlapping_line_count; j++) {
                                overlap_next = find_next_line(&s->plain,
                                                              overlap_end);

                                if (overlap_next > hunk->end)
                                        BUG("failed to find %d context lines "
                                            "in:\n%.*s",
                                            (int)overlapping_line_count,
                                            (int)(hunk->end - hunk->start),
                                            plain + hunk->start);

                                if (plain[overlap_end] != ' ')
                                        return error(_("expected context line "
                                                       "#%d in\n%.*s"),
                                                     (int)(j + 1),
                                                     (int)(hunk->end
                                                           - hunk->start),
                                                     plain + hunk->start);

                                overlap_start = overlap_end;
                                overlap_end = overlap_next;
                        }
                        len = overlap_end - overlap_start;

                        if (len > merged->end - merged->start ||
                            memcmp(plain + merged->end - len,
                                   plain + overlap_start, len))
                                return error(_("hunks do not overlap:\n%.*s\n"
                                               "\tdoes not end with:\n%.*s"),
                                             (int)(merged->end - merged->start),
                                             plain + merged->start,
                                             (int)len, plain + overlap_start);

                        /*
                         * Since the start-end ranges are not adjacent, we
                         * cannot simply take the union of the ranges. To
                         * address that, we temporarily append the union of the
                         * lines to the `plain` strbuf.
                         */
                        if (merged->end != s->plain.len) {
                                size_t start = s->plain.len;

                                strbuf_add(&s->plain, plain + merged->start,
                                           merged->end - merged->start);
                                plain = s->plain.buf;
                                merged->start = start;
                                merged->end = s->plain.len;
                        }

                        strbuf_add(&s->plain,
                                   plain + overlap_end,
                                   hunk->end - overlap_end);
                        merged->end = s->plain.len;
                        merged->splittable_into += hunk->splittable_into;
                        delta = merged->delta;
                        merged->delta += hunk->delta;
                }

                header->old_count = next->old_offset + next->old_count
                        - header->old_offset;
                header->new_count = next->new_offset + delta
                        + next->new_count - header->new_offset;
        }

        if (i == *hunk_index)
                return 0;

        *hunk_index = i;
        return 1;
}

static void reassemble_patch(struct add_p_state *s,
                             struct file_diff *file_diff, int use_all,
                             struct strbuf *out)
{
        struct hunk *hunk;
        size_t save_len = s->plain.len, i;
        ssize_t delta = 0;

        render_diff_header(s, file_diff, 0, out);

        for (i = file_diff->mode_change; i < file_diff->hunk_nr; i++) {
                struct hunk merged = { 0 };

                hunk = file_diff->hunk + i;
                if (!use_all && hunk->use != USE_HUNK)
                        delta += hunk->header.old_count
                                - hunk->header.new_count;
                else {
                        /* merge overlapping hunks into a temporary hunk */
                        if (merge_hunks(s, file_diff, &i, use_all, &merged))
                                hunk = &merged;

                        render_hunk(s, hunk, delta, 0, out);

                        /*
                         * In case `merge_hunks()` used `plain` as a scratch
                         * pad (this happens when an edited hunk had to be
                         * coalesced with another hunk).
                         */
                        strbuf_setlen(&s->plain, save_len);

                        delta += hunk->delta;
                }
        }
}

static int split_hunk(struct add_p_state *s, struct file_diff *file_diff,
                       size_t hunk_index)
{
        int colored = !!s->colored.len, first = 1;
        struct hunk *hunk = file_diff->hunk + hunk_index;
        size_t splittable_into;
        size_t end, colored_end, current, colored_current = 0, context_line_count;
        struct hunk_header remaining, *header;
        char marker, ch;

        if (hunk_index >= file_diff->hunk_nr)
                BUG("invalid hunk index: %d (must be >= 0 and < %d)",
                    (int)hunk_index, (int)file_diff->hunk_nr);

        if (hunk->splittable_into < 2)
                return 0;
        splittable_into = hunk->splittable_into;

        end = hunk->end;
        colored_end = hunk->colored_end;

        remaining = hunk->header;

        file_diff->hunk_nr += splittable_into - 1;
        ALLOC_GROW(file_diff->hunk, file_diff->hunk_nr, file_diff->hunk_alloc);
        if (hunk_index + splittable_into < file_diff->hunk_nr)
                memmove(file_diff->hunk + hunk_index + splittable_into,
                        file_diff->hunk + hunk_index + 1,
                        (file_diff->hunk_nr - hunk_index - splittable_into)
                        * sizeof(*hunk));
        hunk = file_diff->hunk + hunk_index;
        hunk->splittable_into = 1;
        memset(hunk + 1, 0, (splittable_into - 1) * sizeof(*hunk));

        header = &hunk->header;
        header->old_count = header->new_count = 0;

        current = hunk->start;
        if (colored)
                colored_current = hunk->colored_start;
        marker = '\0';
        context_line_count = 0;

        while (splittable_into > 1) {
                ch = s->plain.buf[current];

                if (!ch)
                        BUG("buffer overrun while splitting hunks");

                /*
                 * Is this the first context line after a chain of +/- lines?
                 * Then record the start of the next split hunk.
                 */
                if ((marker == '-' || marker == '+') && ch == ' ') {
                        first = 0;
                        hunk[1].start = current;
                        if (colored)
                                hunk[1].colored_start = colored_current;
                        context_line_count = 0;
                }

                /*
                 * Was the previous line a +/- one? Alternatively, is this the
                 * first line (and not a +/- one)?
                 *
                 * Then just increment the appropriate counter and continue
                 * with the next line.
                 */
                if (marker != ' ' || (ch != '-' && ch != '+')) {
next_hunk_line:
                        /* Comment lines are attached to the previous line */
                        if (ch == '\\')
                                ch = marker ? marker : ' ';

                        /* current hunk not done yet */
                        if (ch == ' ')
                                context_line_count++;
                        else if (ch == '-')
                                header->old_count++;
                        else if (ch == '+')
                                header->new_count++;
                        else
                                BUG("unhandled diff marker: '%c'", ch);
                        marker = ch;
                        current = find_next_line(&s->plain, current);
                        if (colored)
                                colored_current =
                                        find_next_line(&s->colored,
                                                       colored_current);
                        continue;
                }

                /*
                 * We got us the start of a new hunk!
                 *
                 * This is a context line, so it is shared with the previous
                 * hunk, if any.
                 */

                if (first) {
                        if (header->old_count || header->new_count)
                                BUG("counts are off: %d/%d",
                                    (int)header->old_count,
                                    (int)header->new_count);

                        header->old_count = context_line_count;
                        header->new_count = context_line_count;
                        context_line_count = 0;
                        first = 0;
                        goto next_hunk_line;
                }

                remaining.old_offset += header->old_count;
                remaining.old_count -= header->old_count;
                remaining.new_offset += header->new_count;
                remaining.new_count -= header->new_count;

                /* initialize next hunk header's offsets */
                hunk[1].header.old_offset =
                        header->old_offset + header->old_count;
                hunk[1].header.new_offset =
                        header->new_offset + header->new_count;

                /* add one split hunk */
                header->old_count += context_line_count;
                header->new_count += context_line_count;

                hunk->end = current;
                if (colored)
                        hunk->colored_end = colored_current;

                hunk++;
                hunk->splittable_into = 1;
                hunk->use = hunk[-1].use;
                header = &hunk->header;

                header->old_count = header->new_count = context_line_count;
                context_line_count = 0;

                splittable_into--;
                marker = ch;
        }

        /* last hunk simply gets the rest */
        if (header->old_offset != remaining.old_offset)
                BUG("miscounted old_offset: %lu != %lu",
                    header->old_offset, remaining.old_offset);
        if (header->new_offset != remaining.new_offset)
                BUG("miscounted new_offset: %lu != %lu",
                    header->new_offset, remaining.new_offset);
        header->old_count = remaining.old_count;
        header->new_count = remaining.new_count;
        hunk->end = end;
        if (colored)
                hunk->colored_end = colored_end;

        return 0;
}

static void recolor_hunk(struct add_p_state *s, struct hunk *hunk)
{
        const char *plain = s->plain.buf;
        size_t current, eol, next;

        if (!s->colored.len)
                return;

        hunk->colored_start = s->colored.len;
        for (current = hunk->start; current < hunk->end; ) {
                for (eol = current; eol < hunk->end; eol++)
                        if (plain[eol] == '\n')
                                break;
                next = eol + (eol < hunk->end);
                if (eol > current && plain[eol - 1] == '\r')
                        eol--;

                strbuf_addstr(&s->colored,
                              plain[current] == '-' ?
                              s->s.file_old_color :
                              plain[current] == '+' ?
                              s->s.file_new_color :
                              s->s.context_color);
                strbuf_add(&s->colored, plain + current, eol - current);
                strbuf_addstr(&s->colored, s->s.reset_color);
                if (next > eol)
                        strbuf_add(&s->colored, plain + eol, next - eol);
                current = next;
        }
        hunk->colored_end = s->colored.len;
}

static int edit_hunk_manually(struct add_p_state *s, struct hunk *hunk)
{
        size_t i;

        strbuf_reset(&s->buf);
        strbuf_commented_addf(&s->buf, _("Manual hunk edit mode -- see bottom for "
                                      "a quick guide.\n"));
        render_hunk(s, hunk, 0, 0, &s->buf);
        strbuf_commented_addf(&s->buf,
                              _("---\n"
                                "To remove '%c' lines, make them ' ' lines "
                                "(context).\n"
                                "To remove '%c' lines, delete them.\n"
                                "Lines starting with %c will be removed.\n"),
                              s->mode->is_reverse ? '+' : '-',
                              s->mode->is_reverse ? '-' : '+',
                              comment_line_char);
        strbuf_commented_addf(&s->buf, "%s", _(s->mode->edit_hunk_hint));
        /*
         * TRANSLATORS: 'it' refers to the patch mentioned in the previous
         * messages.
         */
        strbuf_commented_addf(&s->buf,
                              _("If it does not apply cleanly, you will be "
                                "given an opportunity to\n"
                                "edit again.  If all lines of the hunk are "
                                "removed, then the edit is\n"
                                "aborted and the hunk is left unchanged.\n"));

        if (strbuf_edit_interactively(&s->buf, "addp-hunk-edit.diff", NULL) < 0)
                return -1;

        /* strip out commented lines */
        hunk->start = s->plain.len;
        for (i = 0; i < s->buf.len; ) {
                size_t next = find_next_line(&s->buf, i);

                if (s->buf.buf[i] != comment_line_char)
                        strbuf_add(&s->plain, s->buf.buf + i, next - i);
                i = next;
        }

        hunk->end = s->plain.len;
        if (hunk->end == hunk->start)
                /* The user aborted editing by deleting everything */
                return 0;

        recolor_hunk(s, hunk);

        /*
         * If the hunk header is intact, parse it, otherwise simply use the
         * hunk header prior to editing (which will adjust `hunk->start` to
         * skip the hunk header).
         */
        if (s->plain.buf[hunk->start] == '@' &&
            parse_hunk_header(s, hunk) < 0)
                return error(_("could not parse hunk header"));

        return 1;
}

static ssize_t recount_edited_hunk(struct add_p_state *s, struct hunk *hunk,
                                   size_t orig_old_count, size_t orig_new_count)
{
        struct hunk_header *header = &hunk->header;
        size_t i;

        header->old_count = header->new_count = 0;
        for (i = hunk->start; i < hunk->end; ) {
                switch (s->plain.buf[i]) {
                case '-':
                        header->old_count++;
                        break;
                case '+':
                        header->new_count++;
                        break;
                case ' ': case '\r': case '\n':
                        header->old_count++;
                        header->new_count++;
                        break;
                }

                i = find_next_line(&s->plain, i);
        }

        return orig_old_count - orig_new_count
                - header->old_count + header->new_count;
}

static int run_apply_check(struct add_p_state *s,
                           struct file_diff *file_diff)
{
        struct child_process cp = CHILD_PROCESS_INIT;

        strbuf_reset(&s->buf);
        reassemble_patch(s, file_diff, 1, &s->buf);

        setup_child_process(s, &cp,
                            "apply", "--check", NULL);
        strvec_pushv(&cp.args, s->mode->apply_check_args);
        if (pipe_command(&cp, s->buf.buf, s->buf.len, NULL, 0, NULL, 0))
                return error(_("'git apply --cached' failed"));

        return 0;
}

static int read_single_character(struct add_p_state *s)
{
        if (s->s.use_single_key) {
                int res = read_key_without_echo(&s->answer);
                printf("%s\n", res == EOF ? "" : s->answer.buf);
                return res;
        }

        if (git_read_line_interactively(&s->answer) == EOF)
                return EOF;
        return 0;
}

static int prompt_yesno(struct add_p_state *s, const char *prompt)
{
        for (;;) {
                color_fprintf(stdout, s->s.prompt_color, "%s", _(prompt));
                fflush(stdout);
                if (read_single_character(s) == EOF)
                        return -1;
                switch (tolower(s->answer.buf[0])) {
                case 'n': return 0;
                case 'y': return 1;
                }
        }
}

static int edit_hunk_loop(struct add_p_state *s,
                          struct file_diff *file_diff, struct hunk *hunk)
{
        size_t plain_len = s->plain.len, colored_len = s->colored.len;
        struct hunk backup;

        backup = *hunk;

        for (;;) {
                int res = edit_hunk_manually(s, hunk);
                if (res == 0) {
                        /* abandoned */
                        *hunk = backup;
                        return -1;
                }

                if (res > 0) {
                        hunk->delta +=
                                recount_edited_hunk(s, hunk,
                                                    backup.header.old_count,
                                                    backup.header.new_count);
                        if (!run_apply_check(s, file_diff))
                                return 0;
                }

                /* Drop edits (they were appended to s->plain) */
                strbuf_setlen(&s->plain, plain_len);
                strbuf_setlen(&s->colored, colored_len);
                *hunk = backup;

                /*
                 * TRANSLATORS: do not translate [y/n]
                 * The program will only accept that input at this point.
                 * Consider translating (saying "no" discards!) as
                 * (saying "n" for "no" discards!) if the translation
                 * of the word "no" does not start with n.
                 */
                res = prompt_yesno(s, _("Your edited hunk does not apply. "
                                        "Edit again (saying \"no\" discards!) "
                                        "[y/n]? "));
                if (res < 1)
                        return -1;
        }
}

static int apply_for_checkout(struct add_p_state *s, struct strbuf *diff,
                              int is_reverse)
{
        const char *reverse = is_reverse ? "-R" : NULL;
        struct child_process check_index = CHILD_PROCESS_INIT;
        struct child_process check_worktree = CHILD_PROCESS_INIT;
        struct child_process apply_index = CHILD_PROCESS_INIT;
        struct child_process apply_worktree = CHILD_PROCESS_INIT;
        int applies_index, applies_worktree;

        setup_child_process(s, &check_index,
                            "apply", "--cached", "--check", reverse, NULL);
        applies_index = !pipe_command(&check_index, diff->buf, diff->len,
                                      NULL, 0, NULL, 0);

        setup_child_process(s, &check_worktree,
                            "apply", "--check", reverse, NULL);
        applies_worktree = !pipe_command(&check_worktree, diff->buf, diff->len,
                                         NULL, 0, NULL, 0);

        if (applies_worktree && applies_index) {
                setup_child_process(s, &apply_index,
                                    "apply", "--cached", reverse, NULL);
                pipe_command(&apply_index, diff->buf, diff->len,
                             NULL, 0, NULL, 0);

                setup_child_process(s, &apply_worktree,
                                    "apply", reverse, NULL);
                pipe_command(&apply_worktree, diff->buf, diff->len,
                             NULL, 0, NULL, 0);

                return 1;
        }

        if (!applies_index) {
                err(s, _("The selected hunks do not apply to the index!"));
                if (prompt_yesno(s, _("Apply them to the worktree "
                                          "anyway? ")) > 0) {
                        setup_child_process(s, &apply_worktree,
                                            "apply", reverse, NULL);
                        return pipe_command(&apply_worktree, diff->buf,
                                            diff->len, NULL, 0, NULL, 0);
                }
                err(s, _("Nothing was applied.\n"));
        } else
                /* As a last resort, show the diff to the user */
                fwrite(diff->buf, diff->len, 1, stderr);

        return 0;
}

#define SUMMARY_HEADER_WIDTH 20
#define SUMMARY_LINE_WIDTH 80
static void summarize_hunk(struct add_p_state *s, struct hunk *hunk,
                           struct strbuf *out)
{
        struct hunk_header *header = &hunk->header;
        struct strbuf *plain = &s->plain;
        size_t len = out->len, i;

        strbuf_addf(out, " -%lu,%lu +%lu,%lu ",
                    header->old_offset, header->old_count,
                    header->new_offset, header->new_count);
        if (out->len - len < SUMMARY_HEADER_WIDTH)
                strbuf_addchars(out, ' ',
                                SUMMARY_HEADER_WIDTH + len - out->len);
        for (i = hunk->start; i < hunk->end; i = find_next_line(plain, i))
                if (plain->buf[i] != ' ')
                        break;
        if (i < hunk->end)
                strbuf_add(out, plain->buf + i, find_next_line(plain, i) - i);
        if (out->len - len > SUMMARY_LINE_WIDTH)
                strbuf_setlen(out, len + SUMMARY_LINE_WIDTH);
        strbuf_complete_line(out);
}

#define DISPLAY_HUNKS_LINES 20
static size_t display_hunks(struct add_p_state *s,
                            struct file_diff *file_diff, size_t start_index)
{
        size_t end_index = start_index + DISPLAY_HUNKS_LINES;

        if (end_index > file_diff->hunk_nr)
                end_index = file_diff->hunk_nr;

        while (start_index < end_index) {
                struct hunk *hunk = file_diff->hunk + start_index++;

                strbuf_reset(&s->buf);
                strbuf_addf(&s->buf, "%c%2d: ", hunk->use == USE_HUNK ? '+'
                            : hunk->use == SKIP_HUNK ? '-' : ' ',
                            (int)start_index);
                summarize_hunk(s, hunk, &s->buf);
                fputs(s->buf.buf, stdout);
        }

        return end_index;
}

static const char help_patch_remainder[] =
N_("j - leave this hunk undecided, see next undecided hunk\n"
   "J - leave this hunk undecided, see next hunk\n"
   "k - leave this hunk undecided, see previous undecided hunk\n"
   "K - leave this hunk undecided, see previous hunk\n"
   "g - select a hunk to go to\n"
   "/ - search for a hunk matching the given regex\n"
   "s - split the current hunk into smaller hunks\n"
   "e - manually edit the current hunk\n"
   "? - print help\n");

static int patch_update_file(struct add_p_state *s,
                             struct file_diff *file_diff)
{
        size_t hunk_index = 0;
        ssize_t i, undecided_previous, undecided_next;
        struct hunk *hunk;
        char ch;
        struct child_process cp = CHILD_PROCESS_INIT;
        int colored = !!s->colored.len, quit = 0;
        enum prompt_mode_type prompt_mode_type;
        enum {
                ALLOW_GOTO_PREVIOUS_HUNK = 1 << 0,
                ALLOW_GOTO_PREVIOUS_UNDECIDED_HUNK = 1 << 1,
                ALLOW_GOTO_NEXT_HUNK = 1 << 2,
                ALLOW_GOTO_NEXT_UNDECIDED_HUNK = 1 << 3,
                ALLOW_SEARCH_AND_GOTO = 1 << 4,
                ALLOW_SPLIT = 1 << 5,
                ALLOW_EDIT = 1 << 6
        } permitted = 0;

        /* Empty added files have no hunks */
        if (!file_diff->hunk_nr && !file_diff->added)
                return 0;

        strbuf_reset(&s->buf);
        render_diff_header(s, file_diff, colored, &s->buf);
        fputs(s->buf.buf, stdout);
        for (;;) {
                if (hunk_index >= file_diff->hunk_nr)
                        hunk_index = 0;
                hunk = file_diff->hunk_nr
                                ? file_diff->hunk + hunk_index
                                : &file_diff->head;
                undecided_previous = -1;
                undecided_next = -1;

                if (file_diff->hunk_nr) {
                        for (i = hunk_index - 1; i >= 0; i--)
                                if (file_diff->hunk[i].use == UNDECIDED_HUNK) {
                                        undecided_previous = i;
                                        break;
                                }

                        for (i = hunk_index + 1; i < file_diff->hunk_nr; i++)
                                if (file_diff->hunk[i].use == UNDECIDED_HUNK) {
                                        undecided_next = i;
                                        break;
                                }
                }

                /* Everything decided? */
                if (undecided_previous < 0 && undecided_next < 0 &&
                    hunk->use != UNDECIDED_HUNK)
                        break;

                strbuf_reset(&s->buf);
                if (file_diff->hunk_nr) {
                        render_hunk(s, hunk, 0, colored, &s->buf);
                        fputs(s->buf.buf, stdout);

                        strbuf_reset(&s->buf);
                        if (undecided_previous >= 0) {
                                permitted |= ALLOW_GOTO_PREVIOUS_UNDECIDED_HUNK;
                                strbuf_addstr(&s->buf, ",k");
                        }
                        if (hunk_index) {
                                permitted |= ALLOW_GOTO_PREVIOUS_HUNK;
                                strbuf_addstr(&s->buf, ",K");
                        }
                        if (undecided_next >= 0) {
                                permitted |= ALLOW_GOTO_NEXT_UNDECIDED_HUNK;
                                strbuf_addstr(&s->buf, ",j");
                        }
                        if (hunk_index + 1 < file_diff->hunk_nr) {
                                permitted |= ALLOW_GOTO_NEXT_HUNK;
                                strbuf_addstr(&s->buf, ",J");
                        }
                        if (file_diff->hunk_nr > 1) {
                                permitted |= ALLOW_SEARCH_AND_GOTO;
                                strbuf_addstr(&s->buf, ",g,/");
                        }
                        if (hunk->splittable_into > 1) {
                                permitted |= ALLOW_SPLIT;
                                strbuf_addstr(&s->buf, ",s");
                        }
                        if (hunk_index + 1 > file_diff->mode_change &&
                            !file_diff->deleted) {
                                permitted |= ALLOW_EDIT;
                                strbuf_addstr(&s->buf, ",e");
                        }
                }
                if (file_diff->deleted)
                        prompt_mode_type = PROMPT_DELETION;
                else if (file_diff->added)
                        prompt_mode_type = PROMPT_ADDITION;
                else if (file_diff->mode_change && !hunk_index)
                        prompt_mode_type = PROMPT_MODE_CHANGE;
                else
                        prompt_mode_type = PROMPT_HUNK;

                printf("%s(%"PRIuMAX"/%"PRIuMAX") ", s->s.prompt_color,
                              (uintmax_t)hunk_index + 1,
                              (uintmax_t)(file_diff->hunk_nr
                                                ? file_diff->hunk_nr
                                                : 1));
                printf(_(s->mode->prompt_mode[prompt_mode_type]),
                       s->buf.buf);
                if (*s->s.reset_color)
                        fputs(s->s.reset_color, stdout);
                fflush(stdout);
                if (read_single_character(s) == EOF)
                        break;

                if (!s->answer.len)
                        continue;
                ch = tolower(s->answer.buf[0]);
                if (ch == 'y') {
                        hunk->use = USE_HUNK;
soft_increment:
                        hunk_index = undecided_next < 0 ?
                                file_diff->hunk_nr : undecided_next;
                } else if (ch == 'n') {
                        hunk->use = SKIP_HUNK;
                        goto soft_increment;
                } else if (ch == 'a') {
                        if (file_diff->hunk_nr) {
                                for (; hunk_index < file_diff->hunk_nr; hunk_index++) {
                                        hunk = file_diff->hunk + hunk_index;
                                        if (hunk->use == UNDECIDED_HUNK)
                                                hunk->use = USE_HUNK;
                                }
                        } else if (hunk->use == UNDECIDED_HUNK) {
                                hunk->use = USE_HUNK;
                        }
                } else if (ch == 'd' || ch == 'q') {
                        if (file_diff->hunk_nr) {
                                for (; hunk_index < file_diff->hunk_nr; hunk_index++) {
                                        hunk = file_diff->hunk + hunk_index;
                                        if (hunk->use == UNDECIDED_HUNK)
                                                hunk->use = SKIP_HUNK;
                                }
                        } else if (hunk->use == UNDECIDED_HUNK) {
                                hunk->use = SKIP_HUNK;
                        }
                        if (ch == 'q') {
                                quit = 1;
                                break;
                        }
                } else if (s->answer.buf[0] == 'K') {
                        if (permitted & ALLOW_GOTO_PREVIOUS_HUNK)
                                hunk_index--;
                        else
                                err(s, _("No previous hunk"));
                } else if (s->answer.buf[0] == 'J') {
                        if (permitted & ALLOW_GOTO_NEXT_HUNK)
                                hunk_index++;
                        else
                                err(s, _("No next hunk"));
                } else if (s->answer.buf[0] == 'k') {
                        if (permitted & ALLOW_GOTO_PREVIOUS_UNDECIDED_HUNK)
                                hunk_index = undecided_previous;
                        else
                                err(s, _("No previous hunk"));
                } else if (s->answer.buf[0] == 'j') {
                        if (permitted & ALLOW_GOTO_NEXT_UNDECIDED_HUNK)
                                hunk_index = undecided_next;
                        else
                                err(s, _("No next hunk"));
                } else if (s->answer.buf[0] == 'g') {
                        char *pend;
                        unsigned long response;

                        if (!(permitted & ALLOW_SEARCH_AND_GOTO)) {
                                err(s, _("No other hunks to goto"));
                                continue;
                        }
                        strbuf_remove(&s->answer, 0, 1);
                        strbuf_trim(&s->answer);
                        i = hunk_index - DISPLAY_HUNKS_LINES / 2;
                        if (i < file_diff->mode_change)
                                i = file_diff->mode_change;
                        while (s->answer.len == 0) {
                                i = display_hunks(s, file_diff, i);
                                printf("%s", i < file_diff->hunk_nr ?
                                       _("go to which hunk (<ret> to see "
                                         "more)? ") : _("go to which hunk? "));
                                fflush(stdout);
                                if (strbuf_getline(&s->answer,
                                                   stdin) == EOF)
                                        break;
                                strbuf_trim_trailing_newline(&s->answer);
                        }

                        strbuf_trim(&s->answer);
                        response = strtoul(s->answer.buf, &pend, 10);
                        if (*pend || pend == s->answer.buf)
                                err(s, _("Invalid number: '%s'"),
                                    s->answer.buf);
                        else if (0 < response && response <= file_diff->hunk_nr)
                                hunk_index = response - 1;
                        else
                                err(s, Q_("Sorry, only %d hunk available.",
                                          "Sorry, only %d hunks available.",
                                          file_diff->hunk_nr),
                                    (int)file_diff->hunk_nr);
                } else if (s->answer.buf[0] == '/') {
                        regex_t regex;
                        int ret;

                        if (!(permitted & ALLOW_SEARCH_AND_GOTO)) {
                                err(s, _("No other hunks to search"));
                                continue;
                        }
                        strbuf_remove(&s->answer, 0, 1);
                        strbuf_trim_trailing_newline(&s->answer);
                        if (s->answer.len == 0) {
                                printf("%s", _("search for regex? "));
                                fflush(stdout);
                                if (strbuf_getline(&s->answer,
                                                   stdin) == EOF)
                                        break;
                                strbuf_trim_trailing_newline(&s->answer);
                                if (s->answer.len == 0)
                                        continue;
                        }
                        ret = regcomp(&regex, s->answer.buf,
                                      REG_EXTENDED | REG_NOSUB | REG_NEWLINE);
                        if (ret) {
                                char errbuf[1024];

                                regerror(ret, &regex, errbuf, sizeof(errbuf));
                                err(s, _("Malformed search regexp %s: %s"),
                                    s->answer.buf, errbuf);
                                continue;
                        }
                        i = hunk_index;
                        for (;;) {
                                /* render the hunk into a scratch buffer */
                                render_hunk(s, file_diff->hunk + i, 0, 0,
                                            &s->buf);
                                if (regexec(&regex, s->buf.buf, 0, NULL, 0)
                                    != REG_NOMATCH)
                                        break;
                                i++;
                                if (i == file_diff->hunk_nr)
                                        i = 0;
                                if (i != hunk_index)
                                        continue;
                                err(s, _("No hunk matches the given pattern"));
                                break;
                        }
                        hunk_index = i;
                } else if (s->answer.buf[0] == 's') {
                        size_t splittable_into = hunk->splittable_into;
                        if (!(permitted & ALLOW_SPLIT))
                                err(s, _("Sorry, cannot split this hunk"));
                        else if (!split_hunk(s, file_diff,
                                             hunk - file_diff->hunk))
                                color_fprintf_ln(stdout, s->s.header_color,
                                                 _("Split into %d hunks."),
                                                 (int)splittable_into);
                } else if (s->answer.buf[0] == 'e') {
                        if (!(permitted & ALLOW_EDIT))
                                err(s, _("Sorry, cannot edit this hunk"));
                        else if (edit_hunk_loop(s, file_diff, hunk) >= 0) {
                                hunk->use = USE_HUNK;
                                goto soft_increment;
                        }
                } else {
                        const char *p = _(help_patch_remainder), *eol = p;

                        color_fprintf(stdout, s->s.help_color, "%s",
                                      _(s->mode->help_patch_text));

                        /*
                         * Show only those lines of the remainder that are
                         * actually applicable with the current hunk.
                         */
                        for (; *p; p = eol + (*eol == '\n')) {
                                eol = strchrnul(p, '\n');

                                /*
                                 * `s->buf` still contains the part of the
                                 * commands shown in the prompt that are not
                                 * always available.
                                 */
                                if (*p != '?' && !strchr(s->buf.buf, *p))
                                        continue;

                                color_fprintf_ln(stdout, s->s.help_color,
                                                 "%.*s", (int)(eol - p), p);
                        }
                }
        }

        /* Any hunk to be used? */
        for (i = 0; i < file_diff->hunk_nr; i++)
                if (file_diff->hunk[i].use == USE_HUNK)
                        break;

        if (i < file_diff->hunk_nr ||
            (!file_diff->hunk_nr && file_diff->head.use == USE_HUNK)) {
                /* At least one hunk selected: apply */
                strbuf_reset(&s->buf);
                reassemble_patch(s, file_diff, 0, &s->buf);

                discard_index(s->s.r->index);
                if (s->mode->apply_for_checkout)
                        apply_for_checkout(s, &s->buf,
                                           s->mode->is_reverse);
                else {
                        setup_child_process(s, &cp, "apply", NULL);
                        strvec_pushv(&cp.args, s->mode->apply_args);
                        if (pipe_command(&cp, s->buf.buf, s->buf.len,
                                         NULL, 0, NULL, 0))
                                error(_("'git apply' failed"));
                }
                if (repo_read_index(s->s.r) >= 0)
                        repo_refresh_and_write_index(s->s.r, REFRESH_QUIET, 0,
                                                     1, NULL, NULL, NULL);
        }

        putchar('\n');
        return quit;
}

int run_add_p(struct repository *r, enum add_p_mode mode,
              const char *revision, const struct pathspec *ps)
{
        struct add_p_state s = {
                { r }, STRBUF_INIT, STRBUF_INIT, STRBUF_INIT, STRBUF_INIT
        };
        size_t i, binary_count = 0;

        init_add_i_state(&s.s, r);

        if (mode == ADD_P_STASH)
                s.mode = &patch_mode_stash;
        else if (mode == ADD_P_RESET) {
                /*
                 * NEEDSWORK: Instead of comparing to the literal "HEAD",
                 * compare the commit objects instead so that other ways of
                 * saying the same thing (such as "@") are also handled
                 * appropriately.
                 *
                 * This applies to the cases below too.
                 */
                if (!revision || !strcmp(revision, "HEAD"))
                        s.mode = &patch_mode_reset_head;
                else
                        s.mode = &patch_mode_reset_nothead;
        } else if (mode == ADD_P_CHECKOUT) {
                if (!revision)
                        s.mode = &patch_mode_checkout_index;
                else if (!strcmp(revision, "HEAD"))
                        s.mode = &patch_mode_checkout_head;
                else
                        s.mode = &patch_mode_checkout_nothead;
        } else if (mode == ADD_P_WORKTREE) {
                if (!revision)
                        s.mode = &patch_mode_checkout_index;
                else if (!strcmp(revision, "HEAD"))
                        s.mode = &patch_mode_worktree_head;
                else
                        s.mode = &patch_mode_worktree_nothead;
        } else
                s.mode = &patch_mode_add;
        s.revision = revision;

        if (discard_index(r->index) < 0 || repo_read_index(r) < 0 ||
            (!s.mode->index_only &&
             repo_refresh_and_write_index(r, REFRESH_QUIET, 0, 1,
                                          NULL, NULL, NULL) < 0) ||
            parse_diff(&s, ps) < 0) {
                add_p_state_clear(&s);
                return -1;
        }

        for (i = 0; i < s.file_diff_nr; i++)
                if (s.file_diff[i].binary && !s.file_diff[i].hunk_nr)
                        binary_count++;
                else if (patch_update_file(&s, s.file_diff + i))
                        break;

        if (s.file_diff_nr == 0)
                fprintf(stderr, _("No changes.\n"));
        else if (binary_count == s.file_diff_nr)
                fprintf(stderr, _("Only binary files changed.\n"));

        add_p_state_clear(&s);
        return 0;
}