Merge branch 'ds/partial-clone-fixes' into maint

[git] / dir.c

/*
 * This handles recursive filename detection with exclude
 * files, index knowledge etc..
 *
 * Copyright (C) Linus Torvalds, 2005-2006
 *               Junio Hamano, 2005-2006
 */
#include "cache.h"
#include "config.h"
#include "dir.h"
#include "object-store.h"
#include "attr.h"
#include "refs.h"
#include "wildmatch.h"
#include "pathspec.h"
#include "utf8.h"
#include "varint.h"
#include "ewah/ewok.h"
#include "fsmonitor.h"
#include "submodule-config.h"

/*
 * Tells read_directory_recursive how a file or directory should be treated.
 * Values are ordered by significance, e.g. if a directory contains both
 * excluded and untracked files, it is listed as untracked because
 * path_untracked > path_excluded.
 */
enum path_treatment {
        path_none = 0,
        path_recurse,
        path_excluded,
        path_untracked
};

/*
 * Support data structure for our opendir/readdir/closedir wrappers
 */
struct cached_dir {
        DIR *fdir;
        struct untracked_cache_dir *untracked;
        int nr_files;
        int nr_dirs;

        const char *d_name;
        int d_type;
        const char *file;
        struct untracked_cache_dir *ucd;
};

static enum path_treatment read_directory_recursive(struct dir_struct *dir,
        struct index_state *istate, const char *path, int len,
        struct untracked_cache_dir *untracked,
        int check_only, int stop_at_first_file, const struct pathspec *pathspec);
static int resolve_dtype(int dtype, struct index_state *istate,
                         const char *path, int len);

int count_slashes(const char *s)
{
        int cnt = 0;
        while (*s)
                if (*s++ == '/')
                        cnt++;
        return cnt;
}

int fspathcmp(const char *a, const char *b)
{
        return ignore_case ? strcasecmp(a, b) : strcmp(a, b);
}

int fspathncmp(const char *a, const char *b, size_t count)
{
        return ignore_case ? strncasecmp(a, b, count) : strncmp(a, b, count);
}

int git_fnmatch(const struct pathspec_item *item,
                const char *pattern, const char *string,
                int prefix)
{
        if (prefix > 0) {
                if (ps_strncmp(item, pattern, string, prefix))
                        return WM_NOMATCH;
                pattern += prefix;
                string += prefix;
        }
        if (item->flags & PATHSPEC_ONESTAR) {
                int pattern_len = strlen(++pattern);
                int string_len = strlen(string);
                return string_len < pattern_len ||
                        ps_strcmp(item, pattern,
                                  string + string_len - pattern_len);
        }
        if (item->magic & PATHSPEC_GLOB)
                return wildmatch(pattern, string,
                                 WM_PATHNAME |
                                 (item->magic & PATHSPEC_ICASE ? WM_CASEFOLD : 0));
        else
                /* wildmatch has not learned no FNM_PATHNAME mode yet */
                return wildmatch(pattern, string,
                                 item->magic & PATHSPEC_ICASE ? WM_CASEFOLD : 0);
}

static int fnmatch_icase_mem(const char *pattern, int patternlen,
                             const char *string, int stringlen,
                             int flags)
{
        int match_status;
        struct strbuf pat_buf = STRBUF_INIT;
        struct strbuf str_buf = STRBUF_INIT;
        const char *use_pat = pattern;
        const char *use_str = string;

        if (pattern[patternlen]) {
                strbuf_add(&pat_buf, pattern, patternlen);
                use_pat = pat_buf.buf;
        }
        if (string[stringlen]) {
                strbuf_add(&str_buf, string, stringlen);
                use_str = str_buf.buf;
        }

        if (ignore_case)
                flags |= WM_CASEFOLD;
        match_status = wildmatch(use_pat, use_str, flags);

        strbuf_release(&pat_buf);
        strbuf_release(&str_buf);

        return match_status;
}

static size_t common_prefix_len(const struct pathspec *pathspec)
{
        int n;
        size_t max = 0;

        /*
         * ":(icase)path" is treated as a pathspec full of
         * wildcard. In other words, only prefix is considered common
         * prefix. If the pathspec is abc/foo abc/bar, running in
         * subdir xyz, the common prefix is still xyz, not xyz/abc as
         * in non-:(icase).
         */
        GUARD_PATHSPEC(pathspec,
                       PATHSPEC_FROMTOP |
                       PATHSPEC_MAXDEPTH |
                       PATHSPEC_LITERAL |
                       PATHSPEC_GLOB |
                       PATHSPEC_ICASE |
                       PATHSPEC_EXCLUDE |
                       PATHSPEC_ATTR);

        for (n = 0; n < pathspec->nr; n++) {
                size_t i = 0, len = 0, item_len;
                if (pathspec->items[n].magic & PATHSPEC_EXCLUDE)
                        continue;
                if (pathspec->items[n].magic & PATHSPEC_ICASE)
                        item_len = pathspec->items[n].prefix;
                else
                        item_len = pathspec->items[n].nowildcard_len;
                while (i < item_len && (n == 0 || i < max)) {
                        char c = pathspec->items[n].match[i];
                        if (c != pathspec->items[0].match[i])
                                break;
                        if (c == '/')
                                len = i + 1;
                        i++;
                }
                if (n == 0 || len < max) {
                        max = len;
                        if (!max)
                                break;
                }
        }
        return max;
}

/*
 * Returns a copy of the longest leading path common among all
 * pathspecs.
 */
char *common_prefix(const struct pathspec *pathspec)
{
        unsigned long len = common_prefix_len(pathspec);

        return len ? xmemdupz(pathspec->items[0].match, len) : NULL;
}

int fill_directory(struct dir_struct *dir,
                   struct index_state *istate,
                   const struct pathspec *pathspec)
{
        const char *prefix;
        size_t prefix_len;

        /*
         * Calculate common prefix for the pathspec, and
         * use that to optimize the directory walk
         */
        prefix_len = common_prefix_len(pathspec);
        prefix = prefix_len ? pathspec->items[0].match : "";

        /* Read the directory and prune it */
        read_directory(dir, istate, prefix, prefix_len, pathspec);

        return prefix_len;
}

int within_depth(const char *name, int namelen,
                        int depth, int max_depth)
{
        const char *cp = name, *cpe = name + namelen;

        while (cp < cpe) {
                if (*cp++ != '/')
                        continue;
                depth++;
                if (depth > max_depth)
                        return 0;
        }
        return 1;
}

/*
 * Read the contents of the blob with the given OID into a buffer.
 * Append a trailing LF to the end if the last line doesn't have one.
 *
 * Returns:
 *    -1 when the OID is invalid or unknown or does not refer to a blob.
 *     0 when the blob is empty.
 *     1 along with { data, size } of the (possibly augmented) buffer
 *       when successful.
 *
 * Optionally updates the given oid_stat with the given OID (when valid).
 */
static int do_read_blob(const struct object_id *oid, struct oid_stat *oid_stat,
                        size_t *size_out, char **data_out)
{
        enum object_type type;
        unsigned long sz;
        char *data;

        *size_out = 0;
        *data_out = NULL;

        data = read_object_file(oid, &type, &sz);
        if (!data || type != OBJ_BLOB) {
                free(data);
                return -1;
        }

        if (oid_stat) {
                memset(&oid_stat->stat, 0, sizeof(oid_stat->stat));
                oidcpy(&oid_stat->oid, oid);
        }

        if (sz == 0) {
                free(data);
                return 0;
        }

        if (data[sz - 1] != '\n') {
                data = xrealloc(data, st_add(sz, 1));
                data[sz++] = '\n';
        }

        *size_out = xsize_t(sz);
        *data_out = data;

        return 1;
}

#define DO_MATCH_EXCLUDE   (1<<0)
#define DO_MATCH_DIRECTORY (1<<1)
#define DO_MATCH_LEADING_PATHSPEC (1<<2)

/*
 * Does the given pathspec match the given name?  A match is found if
 *
 * (1) the pathspec string is leading directory of 'name' ("RECURSIVELY"), or
 * (2) the pathspec string has a leading part matching 'name' ("LEADING"), or
 * (3) the pathspec string is a wildcard and matches 'name' ("WILDCARD"), or
 * (4) the pathspec string is exactly the same as 'name' ("EXACT").
 *
 * Return value tells which case it was (1-4), or 0 when there is no match.
 *
 * It may be instructive to look at a small table of concrete examples
 * to understand the differences between 1, 2, and 4:
 *
 *                              Pathspecs
 *                |    a/b    |   a/b/    |   a/b/c
 *          ------+-----------+-----------+------------
 *          a/b   |  EXACT    |  EXACT[1] | LEADING[2]
 *  Names   a/b/  | RECURSIVE |   EXACT   | LEADING[2]
 *          a/b/c | RECURSIVE | RECURSIVE |   EXACT
 *
 * [1] Only if DO_MATCH_DIRECTORY is passed; otherwise, this is NOT a match.
 * [2] Only if DO_MATCH_LEADING_PATHSPEC is passed; otherwise, not a match.
 */
static int match_pathspec_item(const struct index_state *istate,
                               const struct pathspec_item *item, int prefix,
                               const char *name, int namelen, unsigned flags)
{
        /* name/namelen has prefix cut off by caller */
        const char *match = item->match + prefix;
        int matchlen = item->len - prefix;

        /*
         * The normal call pattern is:
         * 1. prefix = common_prefix_len(ps);
         * 2. prune something, or fill_directory
         * 3. match_pathspec()
         *
         * 'prefix' at #1 may be shorter than the command's prefix and
         * it's ok for #2 to match extra files. Those extras will be
         * trimmed at #3.
         *
         * Suppose the pathspec is 'foo' and '../bar' running from
         * subdir 'xyz'. The common prefix at #1 will be empty, thanks
         * to "../". We may have xyz/foo _and_ XYZ/foo after #2. The
         * user does not want XYZ/foo, only the "foo" part should be
         * case-insensitive. We need to filter out XYZ/foo here. In
         * other words, we do not trust the caller on comparing the
         * prefix part when :(icase) is involved. We do exact
         * comparison ourselves.
         *
         * Normally the caller (common_prefix_len() in fact) does
         * _exact_ matching on name[-prefix+1..-1] and we do not need
         * to check that part. Be defensive and check it anyway, in
         * case common_prefix_len is changed, or a new caller is
         * introduced that does not use common_prefix_len.
         *
         * If the penalty turns out too high when prefix is really
         * long, maybe change it to
         * strncmp(match, name, item->prefix - prefix)
         */
        if (item->prefix && (item->magic & PATHSPEC_ICASE) &&
            strncmp(item->match, name - prefix, item->prefix))
                return 0;

        if (item->attr_match_nr &&
            !match_pathspec_attrs(istate, name, namelen, item))
                return 0;

        /* If the match was just the prefix, we matched */
        if (!*match)
                return MATCHED_RECURSIVELY;

        if (matchlen <= namelen && !ps_strncmp(item, match, name, matchlen)) {
                if (matchlen == namelen)
                        return MATCHED_EXACTLY;

                if (match[matchlen-1] == '/' || name[matchlen] == '/')
                        return MATCHED_RECURSIVELY;
        } else if ((flags & DO_MATCH_DIRECTORY) &&
                   match[matchlen - 1] == '/' &&
                   namelen == matchlen - 1 &&
                   !ps_strncmp(item, match, name, namelen))
                return MATCHED_EXACTLY;

        if (item->nowildcard_len < item->len &&
            !git_fnmatch(item, match, name,
                         item->nowildcard_len - prefix))
                return MATCHED_FNMATCH;

        /* Perform checks to see if "name" is a leading string of the pathspec */
        if (flags & DO_MATCH_LEADING_PATHSPEC) {
                /* name is a literal prefix of the pathspec */
                int offset = name[namelen-1] == '/' ? 1 : 0;
                if ((namelen < matchlen) &&
                    (match[namelen-offset] == '/') &&
                    !ps_strncmp(item, match, name, namelen))
                        return MATCHED_RECURSIVELY_LEADING_PATHSPEC;

                /* name doesn't match up to the first wild character */
                if (item->nowildcard_len < item->len &&
                    ps_strncmp(item, match, name,
                               item->nowildcard_len - prefix))
                        return 0;

                /*
                 * name has no wildcard, and it didn't match as a leading
                 * pathspec so return.
                 */
                if (item->nowildcard_len == item->len)
                        return 0;

                /*
                 * Here is where we would perform a wildmatch to check if
                 * "name" can be matched as a directory (or a prefix) against
                 * the pathspec.  Since wildmatch doesn't have this capability
                 * at the present we have to punt and say that it is a match,
                 * potentially returning a false positive
                 * The submodules themselves will be able to perform more
                 * accurate matching to determine if the pathspec matches.
                 */
                return MATCHED_RECURSIVELY_LEADING_PATHSPEC;
        }

        return 0;
}

/*
 * Given a name and a list of pathspecs, returns the nature of the
 * closest (i.e. most specific) match of the name to any of the
 * pathspecs.
 *
 * The caller typically calls this multiple times with the same
 * pathspec and seen[] array but with different name/namelen
 * (e.g. entries from the index) and is interested in seeing if and
 * how each pathspec matches all the names it calls this function
 * with.  A mark is left in the seen[] array for each pathspec element
 * indicating the closest type of match that element achieved, so if
 * seen[n] remains zero after multiple invocations, that means the nth
 * pathspec did not match any names, which could indicate that the
 * user mistyped the nth pathspec.
 */
static int do_match_pathspec(const struct index_state *istate,
                             const struct pathspec *ps,
                             const char *name, int namelen,
                             int prefix, char *seen,
                             unsigned flags)
{
        int i, retval = 0, exclude = flags & DO_MATCH_EXCLUDE;

        GUARD_PATHSPEC(ps,
                       PATHSPEC_FROMTOP |
                       PATHSPEC_MAXDEPTH |
                       PATHSPEC_LITERAL |
                       PATHSPEC_GLOB |
                       PATHSPEC_ICASE |
                       PATHSPEC_EXCLUDE |
                       PATHSPEC_ATTR);

        if (!ps->nr) {
                if (!ps->recursive ||
                    !(ps->magic & PATHSPEC_MAXDEPTH) ||
                    ps->max_depth == -1)
                        return MATCHED_RECURSIVELY;

                if (within_depth(name, namelen, 0, ps->max_depth))
                        return MATCHED_EXACTLY;
                else
                        return 0;
        }

        name += prefix;
        namelen -= prefix;

        for (i = ps->nr - 1; i >= 0; i--) {
                int how;

                if ((!exclude &&   ps->items[i].magic & PATHSPEC_EXCLUDE) ||
                    ( exclude && !(ps->items[i].magic & PATHSPEC_EXCLUDE)))
                        continue;

                if (seen && seen[i] == MATCHED_EXACTLY)
                        continue;
                /*
                 * Make exclude patterns optional and never report
                 * "pathspec ':(exclude)foo' matches no files"
                 */
                if (seen && ps->items[i].magic & PATHSPEC_EXCLUDE)
                        seen[i] = MATCHED_FNMATCH;
                how = match_pathspec_item(istate, ps->items+i, prefix, name,
                                          namelen, flags);
                if (ps->recursive &&
                    (ps->magic & PATHSPEC_MAXDEPTH) &&
                    ps->max_depth != -1 &&
                    how && how != MATCHED_FNMATCH) {
                        int len = ps->items[i].len;
                        if (name[len] == '/')
                                len++;
                        if (within_depth(name+len, namelen-len, 0, ps->max_depth))
                                how = MATCHED_EXACTLY;
                        else
                                how = 0;
                }
                if (how) {
                        if (retval < how)
                                retval = how;
                        if (seen && seen[i] < how)
                                seen[i] = how;
                }
        }
        return retval;
}

int match_pathspec(const struct index_state *istate,
                   const struct pathspec *ps,
                   const char *name, int namelen,
                   int prefix, char *seen, int is_dir)
{
        int positive, negative;
        unsigned flags = is_dir ? DO_MATCH_DIRECTORY : 0;
        positive = do_match_pathspec(istate, ps, name, namelen,
                                     prefix, seen, flags);
        if (!(ps->magic & PATHSPEC_EXCLUDE) || !positive)
                return positive;
        negative = do_match_pathspec(istate, ps, name, namelen,
                                     prefix, seen,
                                     flags | DO_MATCH_EXCLUDE);
        return negative ? 0 : positive;
}

/**
 * Check if a submodule is a superset of the pathspec
 */
int submodule_path_match(const struct index_state *istate,
                         const struct pathspec *ps,
                         const char *submodule_name,
                         char *seen)
{
        int matched = do_match_pathspec(istate, ps, submodule_name,
                                        strlen(submodule_name),
                                        0, seen,
                                        DO_MATCH_DIRECTORY |
                                        DO_MATCH_LEADING_PATHSPEC);
        return matched;
}

int report_path_error(const char *ps_matched,
                      const struct pathspec *pathspec)
{
        /*
         * Make sure all pathspec matched; otherwise it is an error.
         */
        int num, errors = 0;
        for (num = 0; num < pathspec->nr; num++) {
                int other, found_dup;

                if (ps_matched[num])
                        continue;
                /*
                 * The caller might have fed identical pathspec
                 * twice.  Do not barf on such a mistake.
                 * FIXME: parse_pathspec should have eliminated
                 * duplicate pathspec.
                 */
                for (found_dup = other = 0;
                     !found_dup && other < pathspec->nr;
                     other++) {
                        if (other == num || !ps_matched[other])
                                continue;
                        if (!strcmp(pathspec->items[other].original,
                                    pathspec->items[num].original))
                                /*
                                 * Ok, we have a match already.
                                 */
                                found_dup = 1;
                }
                if (found_dup)
                        continue;

                error(_("pathspec '%s' did not match any file(s) known to git"),
                      pathspec->items[num].original);
                errors++;
        }
        return errors;
}

/*
 * Return the length of the "simple" part of a path match limiter.
 */
int simple_length(const char *match)
{
        int len = -1;

        for (;;) {
                unsigned char c = *match++;
                len++;
                if (c == '\0' || is_glob_special(c))
                        return len;
        }
}

int no_wildcard(const char *string)
{
        return string[simple_length(string)] == '\0';
}

void parse_path_pattern(const char **pattern,
                           int *patternlen,
                           unsigned *flags,
                           int *nowildcardlen)
{
        const char *p = *pattern;
        size_t i, len;

        *flags = 0;
        if (*p == '!') {
                *flags |= PATTERN_FLAG_NEGATIVE;
                p++;
        }
        len = strlen(p);
        if (len && p[len - 1] == '/') {
                len--;
                *flags |= PATTERN_FLAG_MUSTBEDIR;
        }
        for (i = 0; i < len; i++) {
                if (p[i] == '/')
                        break;
        }
        if (i == len)
                *flags |= PATTERN_FLAG_NODIR;
        *nowildcardlen = simple_length(p);
        /*
         * we should have excluded the trailing slash from 'p' too,
         * but that's one more allocation. Instead just make sure
         * nowildcardlen does not exceed real patternlen
         */
        if (*nowildcardlen > len)
                *nowildcardlen = len;
        if (*p == '*' && no_wildcard(p + 1))
                *flags |= PATTERN_FLAG_ENDSWITH;
        *pattern = p;
        *patternlen = len;
}

int pl_hashmap_cmp(const void *unused_cmp_data,
                   const struct hashmap_entry *a,
                   const struct hashmap_entry *b,
                   const void *key)
{
        const struct pattern_entry *ee1 =
                        container_of(a, struct pattern_entry, ent);
        const struct pattern_entry *ee2 =
                        container_of(b, struct pattern_entry, ent);

        size_t min_len = ee1->patternlen <= ee2->patternlen
                         ? ee1->patternlen
                         : ee2->patternlen;

        if (ignore_case)
                return strncasecmp(ee1->pattern, ee2->pattern, min_len);
        return strncmp(ee1->pattern, ee2->pattern, min_len);
}

static void add_pattern_to_hashsets(struct pattern_list *pl, struct path_pattern *given)
{
        struct pattern_entry *translated;
        char *truncated;
        char *data = NULL;

        if (!pl->use_cone_patterns)
                return;

        if (given->flags & PATTERN_FLAG_NEGATIVE &&
            given->flags & PATTERN_FLAG_MUSTBEDIR &&
            !strcmp(given->pattern, "/*")) {
                pl->full_cone = 0;
                return;
        }

        if (!given->flags && !strcmp(given->pattern, "/*")) {
                pl->full_cone = 1;
                return;
        }

        if (given->patternlen > 2 &&
            !strcmp(given->pattern + given->patternlen - 2, "/*")) {
                if (!(given->flags & PATTERN_FLAG_NEGATIVE)) {
                        /* Not a cone pattern. */
                        pl->use_cone_patterns = 0;
                        warning(_("unrecognized pattern: '%s'"), given->pattern);
                        goto clear_hashmaps;
                }

                truncated = xstrdup(given->pattern);
                truncated[given->patternlen - 2] = 0;

                translated = xmalloc(sizeof(struct pattern_entry));
                translated->pattern = truncated;
                translated->patternlen = given->patternlen - 2;
                hashmap_entry_init(&translated->ent,
                                   ignore_case ?
                                   strihash(translated->pattern) :
                                   strhash(translated->pattern));

                if (!hashmap_get_entry(&pl->recursive_hashmap,
                                       translated, ent, NULL)) {
                        /* We did not see the "parent" included */
                        warning(_("unrecognized negative pattern: '%s'"),
                                given->pattern);
                        free(truncated);
                        free(translated);
                        goto clear_hashmaps;
                }

                hashmap_add(&pl->parent_hashmap, &translated->ent);
                hashmap_remove(&pl->recursive_hashmap, &translated->ent, &data);
                free(data);
                return;
        }

        if (given->flags & PATTERN_FLAG_NEGATIVE) {
                warning(_("unrecognized negative pattern: '%s'"),
                        given->pattern);
                goto clear_hashmaps;
        }

        translated = xmalloc(sizeof(struct pattern_entry));

        translated->pattern = xstrdup(given->pattern);
        translated->patternlen = given->patternlen;
        hashmap_entry_init(&translated->ent,
                           ignore_case ?
                           strihash(translated->pattern) :
                           strhash(translated->pattern));

        hashmap_add(&pl->recursive_hashmap, &translated->ent);

        if (hashmap_get_entry(&pl->parent_hashmap, translated, ent, NULL)) {
                /* we already included this at the parent level */
                warning(_("your sparse-checkout file may have issues: pattern '%s' is repeated"),
                        given->pattern);
                hashmap_remove(&pl->parent_hashmap, &translated->ent, &data);
                free(data);
                free(translated);
        }

        return;

clear_hashmaps:
        warning(_("disabling cone pattern matching"));
        hashmap_free_entries(&pl->parent_hashmap, struct pattern_entry, ent);
        hashmap_free_entries(&pl->recursive_hashmap, struct pattern_entry, ent);
        pl->use_cone_patterns = 0;
}

static int hashmap_contains_path(struct hashmap *map,
                                 struct strbuf *pattern)
{
        struct pattern_entry p;

        /* Check straight mapping */
        p.pattern = pattern->buf;
        p.patternlen = pattern->len;
        hashmap_entry_init(&p.ent,
                           ignore_case ?
                           strihash(p.pattern) :
                           strhash(p.pattern));
        return !!hashmap_get_entry(map, &p, ent, NULL);
}

int hashmap_contains_parent(struct hashmap *map,
                            const char *path,
                            struct strbuf *buffer)
{
        char *slash_pos;

        strbuf_setlen(buffer, 0);

        if (path[0] != '/')
                strbuf_addch(buffer, '/');

        strbuf_addstr(buffer, path);

        slash_pos = strrchr(buffer->buf, '/');

        while (slash_pos > buffer->buf) {
                strbuf_setlen(buffer, slash_pos - buffer->buf);

                if (hashmap_contains_path(map, buffer))
                        return 1;

                slash_pos = strrchr(buffer->buf, '/');
        }

        return 0;
}

void add_pattern(const char *string, const char *base,
                 int baselen, struct pattern_list *pl, int srcpos)
{
        struct path_pattern *pattern;
        int patternlen;
        unsigned flags;
        int nowildcardlen;

        parse_path_pattern(&string, &patternlen, &flags, &nowildcardlen);
        if (flags & PATTERN_FLAG_MUSTBEDIR) {
                FLEXPTR_ALLOC_MEM(pattern, pattern, string, patternlen);
        } else {
                pattern = xmalloc(sizeof(*pattern));
                pattern->pattern = string;
        }
        pattern->patternlen = patternlen;
        pattern->nowildcardlen = nowildcardlen;
        pattern->base = base;
        pattern->baselen = baselen;
        pattern->flags = flags;
        pattern->srcpos = srcpos;
        ALLOC_GROW(pl->patterns, pl->nr + 1, pl->alloc);
        pl->patterns[pl->nr++] = pattern;
        pattern->pl = pl;

        add_pattern_to_hashsets(pl, pattern);
}

static int read_skip_worktree_file_from_index(const struct index_state *istate,
                                              const char *path,
                                              size_t *size_out, char **data_out,
                                              struct oid_stat *oid_stat)
{
        int pos, len;

        len = strlen(path);
        pos = index_name_pos(istate, path, len);
        if (pos < 0)
                return -1;
        if (!ce_skip_worktree(istate->cache[pos]))
                return -1;

        return do_read_blob(&istate->cache[pos]->oid, oid_stat, size_out, data_out);
}

/*
 * Frees memory within pl which was allocated for exclude patterns and
 * the file buffer.  Does not free pl itself.
 */
void clear_pattern_list(struct pattern_list *pl)
{
        int i;

        for (i = 0; i < pl->nr; i++)
                free(pl->patterns[i]);
        free(pl->patterns);
        free(pl->filebuf);

        memset(pl, 0, sizeof(*pl));
}

static void trim_trailing_spaces(char *buf)
{
        char *p, *last_space = NULL;

        for (p = buf; *p; p++)
                switch (*p) {
                case ' ':
                        if (!last_space)
                                last_space = p;
                        break;
                case '\\':
                        p++;
                        if (!*p)
                                return;
                        /* fallthrough */
                default:
                        last_space = NULL;
                }

        if (last_space)
                *last_space = '\0';
}

/*
 * Given a subdirectory name and "dir" of the current directory,
 * search the subdir in "dir" and return it, or create a new one if it
 * does not exist in "dir".
 *
 * If "name" has the trailing slash, it'll be excluded in the search.
 */
static struct untracked_cache_dir *lookup_untracked(struct untracked_cache *uc,
                                                    struct untracked_cache_dir *dir,
                                                    const char *name, int len)
{
        int first, last;
        struct untracked_cache_dir *d;
        if (!dir)
                return NULL;
        if (len && name[len - 1] == '/')
                len--;
        first = 0;
        last = dir->dirs_nr;
        while (last > first) {
                int cmp, next = first + ((last - first) >> 1);
                d = dir->dirs[next];
                cmp = strncmp(name, d->name, len);
                if (!cmp && strlen(d->name) > len)
                        cmp = -1;
                if (!cmp)
                        return d;
                if (cmp < 0) {
                        last = next;
                        continue;
                }
                first = next+1;
        }

        uc->dir_created++;
        FLEX_ALLOC_MEM(d, name, name, len);

        ALLOC_GROW(dir->dirs, dir->dirs_nr + 1, dir->dirs_alloc);
        MOVE_ARRAY(dir->dirs + first + 1, dir->dirs + first,
                   dir->dirs_nr - first);
        dir->dirs_nr++;
        dir->dirs[first] = d;
        return d;
}

static void do_invalidate_gitignore(struct untracked_cache_dir *dir)
{
        int i;
        dir->valid = 0;
        dir->untracked_nr = 0;
        for (i = 0; i < dir->dirs_nr; i++)
                do_invalidate_gitignore(dir->dirs[i]);
}

static void invalidate_gitignore(struct untracked_cache *uc,
                                 struct untracked_cache_dir *dir)
{
        uc->gitignore_invalidated++;
        do_invalidate_gitignore(dir);
}

static void invalidate_directory(struct untracked_cache *uc,
                                 struct untracked_cache_dir *dir)
{
        int i;

        /*
         * Invalidation increment here is just roughly correct. If
         * untracked_nr or any of dirs[].recurse is non-zero, we
         * should increment dir_invalidated too. But that's more
         * expensive to do.
         */
        if (dir->valid)
                uc->dir_invalidated++;

        dir->valid = 0;
        dir->untracked_nr = 0;
        for (i = 0; i < dir->dirs_nr; i++)
                dir->dirs[i]->recurse = 0;
}

static int add_patterns_from_buffer(char *buf, size_t size,
                                    const char *base, int baselen,
                                    struct pattern_list *pl);

/*
 * Given a file with name "fname", read it (either from disk, or from
 * an index if 'istate' is non-null), parse it and store the
 * exclude rules in "pl".
 *
 * If "ss" is not NULL, compute SHA-1 of the exclude file and fill
 * stat data from disk (only valid if add_patterns returns zero). If
 * ss_valid is non-zero, "ss" must contain good value as input.
 */
static int add_patterns(const char *fname, const char *base, int baselen,
                        struct pattern_list *pl, struct index_state *istate,
                        struct oid_stat *oid_stat)
{
        struct stat st;
        int r;
        int fd;
        size_t size = 0;
        char *buf;

        fd = open(fname, O_RDONLY);
        if (fd < 0 || fstat(fd, &st) < 0) {
                if (fd < 0)
                        warn_on_fopen_errors(fname);
                else
                        close(fd);
                if (!istate)
                        return -1;
                r = read_skip_worktree_file_from_index(istate, fname,
                                                       &size, &buf,
                                                       oid_stat);
                if (r != 1)
                        return r;
        } else {
                size = xsize_t(st.st_size);
                if (size == 0) {
                        if (oid_stat) {
                                fill_stat_data(&oid_stat->stat, &st);
                                oidcpy(&oid_stat->oid, the_hash_algo->empty_blob);
                                oid_stat->valid = 1;
                        }
                        close(fd);
                        return 0;
                }
                buf = xmallocz(size);
                if (read_in_full(fd, buf, size) != size) {
                        free(buf);
                        close(fd);
                        return -1;
                }
                buf[size++] = '\n';
                close(fd);
                if (oid_stat) {
                        int pos;
                        if (oid_stat->valid &&
                            !match_stat_data_racy(istate, &oid_stat->stat, &st))
                                ; /* no content change, ss->sha1 still good */
                        else if (istate &&
                                 (pos = index_name_pos(istate, fname, strlen(fname))) >= 0 &&
                                 !ce_stage(istate->cache[pos]) &&
                                 ce_uptodate(istate->cache[pos]) &&
                                 !would_convert_to_git(istate, fname))
                                oidcpy(&oid_stat->oid,
                                       &istate->cache[pos]->oid);
                        else
                                hash_object_file(buf, size, "blob",
                                                 &oid_stat->oid);
                        fill_stat_data(&oid_stat->stat, &st);
                        oid_stat->valid = 1;
                }
        }

        add_patterns_from_buffer(buf, size, base, baselen, pl);
        return 0;
}

static int add_patterns_from_buffer(char *buf, size_t size,
                                    const char *base, int baselen,
                                    struct pattern_list *pl)
{
        int i, lineno = 1;
        char *entry;

        hashmap_init(&pl->recursive_hashmap, pl_hashmap_cmp, NULL, 0);
        hashmap_init(&pl->parent_hashmap, pl_hashmap_cmp, NULL, 0);

        pl->filebuf = buf;

        if (skip_utf8_bom(&buf, size))
                size -= buf - pl->filebuf;

        entry = buf;

        for (i = 0; i < size; i++) {
                if (buf[i] == '\n') {
                        if (entry != buf + i && entry[0] != '#') {
                                buf[i - (i && buf[i-1] == '\r')] = 0;
                                trim_trailing_spaces(entry);
                                add_pattern(entry, base, baselen, pl, lineno);
                        }
                        lineno++;
                        entry = buf + i + 1;
                }
        }
        return 0;
}

int add_patterns_from_file_to_list(const char *fname, const char *base,
                                   int baselen, struct pattern_list *pl,
                                   struct index_state *istate)
{
        return add_patterns(fname, base, baselen, pl, istate, NULL);
}

int add_patterns_from_blob_to_list(
        struct object_id *oid,
        const char *base, int baselen,
        struct pattern_list *pl)
{
        char *buf;
        size_t size;
        int r;

        r = do_read_blob(oid, NULL, &size, &buf);
        if (r != 1)
                return r;

        add_patterns_from_buffer(buf, size, base, baselen, pl);
        return 0;
}

struct pattern_list *add_pattern_list(struct dir_struct *dir,
                                      int group_type, const char *src)
{
        struct pattern_list *pl;
        struct exclude_list_group *group;

        group = &dir->exclude_list_group[group_type];
        ALLOC_GROW(group->pl, group->nr + 1, group->alloc);
        pl = &group->pl[group->nr++];
        memset(pl, 0, sizeof(*pl));
        pl->src = src;
        return pl;
}

/*
 * Used to set up core.excludesfile and .git/info/exclude lists.
 */
static void add_patterns_from_file_1(struct dir_struct *dir, const char *fname,
                                     struct oid_stat *oid_stat)
{
        struct pattern_list *pl;
        /*
         * catch setup_standard_excludes() that's called before
         * dir->untracked is assigned. That function behaves
         * differently when dir->untracked is non-NULL.
         */
        if (!dir->untracked)
                dir->unmanaged_exclude_files++;
        pl = add_pattern_list(dir, EXC_FILE, fname);
        if (add_patterns(fname, "", 0, pl, NULL, oid_stat) < 0)
                die(_("cannot use %s as an exclude file"), fname);
}

void add_patterns_from_file(struct dir_struct *dir, const char *fname)
{
        dir->unmanaged_exclude_files++; /* see validate_untracked_cache() */
        add_patterns_from_file_1(dir, fname, NULL);
}

int match_basename(const char *basename, int basenamelen,
                   const char *pattern, int prefix, int patternlen,
                   unsigned flags)
{
        if (prefix == patternlen) {
                if (patternlen == basenamelen &&
                    !fspathncmp(pattern, basename, basenamelen))
                        return 1;
        } else if (flags & PATTERN_FLAG_ENDSWITH) {
                /* "*literal" matching against "fooliteral" */
                if (patternlen - 1 <= basenamelen &&
                    !fspathncmp(pattern + 1,
                                   basename + basenamelen - (patternlen - 1),
                                   patternlen - 1))
                        return 1;
        } else {
                if (fnmatch_icase_mem(pattern, patternlen,
                                      basename, basenamelen,
                                      0) == 0)
                        return 1;
        }
        return 0;
}

int match_pathname(const char *pathname, int pathlen,
                   const char *base, int baselen,
                   const char *pattern, int prefix, int patternlen,
                   unsigned flags)
{
        const char *name;
        int namelen;

        /*
         * match with FNM_PATHNAME; the pattern has base implicitly
         * in front of it.
         */
        if (*pattern == '/') {
                pattern++;
                patternlen--;
                prefix--;
        }

        /*
         * baselen does not count the trailing slash. base[] may or
         * may not end with a trailing slash though.
         */
        if (pathlen < baselen + 1 ||
            (baselen && pathname[baselen] != '/') ||
            fspathncmp(pathname, base, baselen))
                return 0;

        namelen = baselen ? pathlen - baselen - 1 : pathlen;
        name = pathname + pathlen - namelen;

        if (prefix) {
                /*
                 * if the non-wildcard part is longer than the
                 * remaining pathname, surely it cannot match.
                 */
                if (prefix > namelen)
                        return 0;

                if (fspathncmp(pattern, name, prefix))
                        return 0;
                pattern += prefix;
                patternlen -= prefix;
                name    += prefix;
                namelen -= prefix;

                /*
                 * If the whole pattern did not have a wildcard,
                 * then our prefix match is all we need; we
                 * do not need to call fnmatch at all.
                 */
                if (!patternlen && !namelen)
                        return 1;
        }

        return fnmatch_icase_mem(pattern, patternlen,
                                 name, namelen,
                                 WM_PATHNAME) == 0;
}

/*
 * Scan the given exclude list in reverse to see whether pathname
 * should be ignored.  The first match (i.e. the last on the list), if
 * any, determines the fate.  Returns the exclude_list element which
 * matched, or NULL for undecided.
 */
static struct path_pattern *last_matching_pattern_from_list(const char *pathname,
                                                       int pathlen,
                                                       const char *basename,
                                                       int *dtype,
                                                       struct pattern_list *pl,
                                                       struct index_state *istate)
{
        struct path_pattern *res = NULL; /* undecided */
        int i;

        if (!pl->nr)
                return NULL;    /* undefined */

        for (i = pl->nr - 1; 0 <= i; i--) {
                struct path_pattern *pattern = pl->patterns[i];
                const char *exclude = pattern->pattern;
                int prefix = pattern->nowildcardlen;

                if (pattern->flags & PATTERN_FLAG_MUSTBEDIR) {
                        *dtype = resolve_dtype(*dtype, istate, pathname, pathlen);
                        if (*dtype != DT_DIR)
                                continue;
                }

                if (pattern->flags & PATTERN_FLAG_NODIR) {
                        if (match_basename(basename,
                                           pathlen - (basename - pathname),
                                           exclude, prefix, pattern->patternlen,
                                           pattern->flags)) {
                                res = pattern;
                                break;
                        }
                        continue;
                }

                assert(pattern->baselen == 0 ||
                       pattern->base[pattern->baselen - 1] == '/');
                if (match_pathname(pathname, pathlen,
                                   pattern->base,
                                   pattern->baselen ? pattern->baselen - 1 : 0,
                                   exclude, prefix, pattern->patternlen,
                                   pattern->flags)) {
                        res = pattern;
                        break;
                }
        }
        return res;
}

/*
 * Scan the list of patterns to determine if the ordered list
 * of patterns matches on 'pathname'.
 *
 * Return 1 for a match, 0 for not matched and -1 for undecided.
 */
enum pattern_match_result path_matches_pattern_list(
                                const char *pathname, int pathlen,
                                const char *basename, int *dtype,
                                struct pattern_list *pl,
                                struct index_state *istate)
{
        struct path_pattern *pattern;
        struct strbuf parent_pathname = STRBUF_INIT;
        int result = NOT_MATCHED;
        const char *slash_pos;

        if (!pl->use_cone_patterns) {
                pattern = last_matching_pattern_from_list(pathname, pathlen, basename,
                                                        dtype, pl, istate);
                if (pattern) {
                        if (pattern->flags & PATTERN_FLAG_NEGATIVE)
                                return NOT_MATCHED;
                        else
                                return MATCHED;
                }

                return UNDECIDED;
        }

        if (pl->full_cone)
                return MATCHED;

        strbuf_addch(&parent_pathname, '/');
        strbuf_add(&parent_pathname, pathname, pathlen);

        if (hashmap_contains_path(&pl->recursive_hashmap,
                                  &parent_pathname)) {
                result = MATCHED_RECURSIVE;
                goto done;
        }

        slash_pos = strrchr(parent_pathname.buf, '/');

        if (slash_pos == parent_pathname.buf) {
                /* include every file in root */
                result = MATCHED;
                goto done;
        }

        strbuf_setlen(&parent_pathname, slash_pos - parent_pathname.buf);

        if (hashmap_contains_path(&pl->parent_hashmap, &parent_pathname)) {
                result = MATCHED;
                goto done;
        }

        if (hashmap_contains_parent(&pl->recursive_hashmap,
                                    pathname,
                                    &parent_pathname))
                result = MATCHED_RECURSIVE;

done:
        strbuf_release(&parent_pathname);
        return result;
}

static struct path_pattern *last_matching_pattern_from_lists(
                struct dir_struct *dir, struct index_state *istate,
                const char *pathname, int pathlen,
                const char *basename, int *dtype_p)
{
        int i, j;
        struct exclude_list_group *group;
        struct path_pattern *pattern;
        for (i = EXC_CMDL; i <= EXC_FILE; i++) {
                group = &dir->exclude_list_group[i];
                for (j = group->nr - 1; j >= 0; j--) {
                        pattern = last_matching_pattern_from_list(
                                pathname, pathlen, basename, dtype_p,
                                &group->pl[j], istate);
                        if (pattern)
                                return pattern;
                }
        }
        return NULL;
}

/*
 * Loads the per-directory exclude list for the substring of base
 * which has a char length of baselen.
 */
static void prep_exclude(struct dir_struct *dir,
                         struct index_state *istate,
                         const char *base, int baselen)
{
        struct exclude_list_group *group;
        struct pattern_list *pl;
        struct exclude_stack *stk = NULL;
        struct untracked_cache_dir *untracked;
        int current;

        group = &dir->exclude_list_group[EXC_DIRS];

        /*
         * Pop the exclude lists from the EXCL_DIRS exclude_list_group
         * which originate from directories not in the prefix of the
         * path being checked.
         */
        while ((stk = dir->exclude_stack) != NULL) {
                if (stk->baselen <= baselen &&
                    !strncmp(dir->basebuf.buf, base, stk->baselen))
                        break;
                pl = &group->pl[dir->exclude_stack->exclude_ix];
                dir->exclude_stack = stk->prev;
                dir->pattern = NULL;
                free((char *)pl->src); /* see strbuf_detach() below */
                clear_pattern_list(pl);
                free(stk);
                group->nr--;
        }

        /* Skip traversing into sub directories if the parent is excluded */
        if (dir->pattern)
                return;

        /*
         * Lazy initialization. All call sites currently just
         * memset(dir, 0, sizeof(*dir)) before use. Changing all of
         * them seems lots of work for little benefit.
         */
        if (!dir->basebuf.buf)
                strbuf_init(&dir->basebuf, PATH_MAX);

        /* Read from the parent directories and push them down. */
        current = stk ? stk->baselen : -1;
        strbuf_setlen(&dir->basebuf, current < 0 ? 0 : current);
        if (dir->untracked)
                untracked = stk ? stk->ucd : dir->untracked->root;
        else
                untracked = NULL;

        while (current < baselen) {
                const char *cp;
                struct oid_stat oid_stat;

                stk = xcalloc(1, sizeof(*stk));
                if (current < 0) {
                        cp = base;
                        current = 0;
                } else {
                        cp = strchr(base + current + 1, '/');
                        if (!cp)
                                die("oops in prep_exclude");
                        cp++;
                        untracked =
                                lookup_untracked(dir->untracked, untracked,
                                                 base + current,
                                                 cp - base - current);
                }
                stk->prev = dir->exclude_stack;
                stk->baselen = cp - base;
                stk->exclude_ix = group->nr;
                stk->ucd = untracked;
                pl = add_pattern_list(dir, EXC_DIRS, NULL);
                strbuf_add(&dir->basebuf, base + current, stk->baselen - current);
                assert(stk->baselen == dir->basebuf.len);

                /* Abort if the directory is excluded */
                if (stk->baselen) {
                        int dt = DT_DIR;
                        dir->basebuf.buf[stk->baselen - 1] = 0;
                        dir->pattern = last_matching_pattern_from_lists(dir,
                                                                        istate,
                                dir->basebuf.buf, stk->baselen - 1,
                                dir->basebuf.buf + current, &dt);
                        dir->basebuf.buf[stk->baselen - 1] = '/';
                        if (dir->pattern &&
                            dir->pattern->flags & PATTERN_FLAG_NEGATIVE)
                                dir->pattern = NULL;
                        if (dir->pattern) {
                                dir->exclude_stack = stk;
                                return;
                        }
                }

                /* Try to read per-directory file */
                oidclr(&oid_stat.oid);
                oid_stat.valid = 0;
                if (dir->exclude_per_dir &&
                    /*
                     * If we know that no files have been added in
                     * this directory (i.e. valid_cached_dir() has
                     * been executed and set untracked->valid) ..
                     */
                    (!untracked || !untracked->valid ||
                     /*
                      * .. and .gitignore does not exist before
                      * (i.e. null exclude_oid). Then we can skip
                      * loading .gitignore, which would result in
                      * ENOENT anyway.
                      */
                     !is_null_oid(&untracked->exclude_oid))) {
                        /*
                         * dir->basebuf gets reused by the traversal, but we
                         * need fname to remain unchanged to ensure the src
                         * member of each struct path_pattern correctly
                         * back-references its source file.  Other invocations
                         * of add_pattern_list provide stable strings, so we
                         * strbuf_detach() and free() here in the caller.
                         */
                        struct strbuf sb = STRBUF_INIT;
                        strbuf_addbuf(&sb, &dir->basebuf);
                        strbuf_addstr(&sb, dir->exclude_per_dir);
                        pl->src = strbuf_detach(&sb, NULL);
                        add_patterns(pl->src, pl->src, stk->baselen, pl, istate,
                                     untracked ? &oid_stat : NULL);
                }
                /*
                 * NEEDSWORK: when untracked cache is enabled, prep_exclude()
                 * will first be called in valid_cached_dir() then maybe many
                 * times more in last_matching_pattern(). When the cache is
                 * used, last_matching_pattern() will not be called and
                 * reading .gitignore content will be a waste.
                 *
                 * So when it's called by valid_cached_dir() and we can get
                 * .gitignore SHA-1 from the index (i.e. .gitignore is not
                 * modified on work tree), we could delay reading the
                 * .gitignore content until we absolutely need it in
                 * last_matching_pattern(). Be careful about ignore rule
                 * order, though, if you do that.
                 */
                if (untracked &&
                    !oideq(&oid_stat.oid, &untracked->exclude_oid)) {
                        invalidate_gitignore(dir->untracked, untracked);
                        oidcpy(&untracked->exclude_oid, &oid_stat.oid);
                }
                dir->exclude_stack = stk;
                current = stk->baselen;
        }
        strbuf_setlen(&dir->basebuf, baselen);
}

/*
 * Loads the exclude lists for the directory containing pathname, then
 * scans all exclude lists to determine whether pathname is excluded.
 * Returns the exclude_list element which matched, or NULL for
 * undecided.
 */
struct path_pattern *last_matching_pattern(struct dir_struct *dir,
                                      struct index_state *istate,
                                      const char *pathname,
                                      int *dtype_p)
{
        int pathlen = strlen(pathname);
        const char *basename = strrchr(pathname, '/');
        basename = (basename) ? basename+1 : pathname;

        prep_exclude(dir, istate, pathname, basename-pathname);

        if (dir->pattern)
                return dir->pattern;

        return last_matching_pattern_from_lists(dir, istate, pathname, pathlen,
                        basename, dtype_p);
}

/*
 * Loads the exclude lists for the directory containing pathname, then
 * scans all exclude lists to determine whether pathname is excluded.
 * Returns 1 if true, otherwise 0.
 */
int is_excluded(struct dir_struct *dir, struct index_state *istate,
                const char *pathname, int *dtype_p)
{
        struct path_pattern *pattern =
                last_matching_pattern(dir, istate, pathname, dtype_p);
        if (pattern)
                return pattern->flags & PATTERN_FLAG_NEGATIVE ? 0 : 1;
        return 0;
}

static struct dir_entry *dir_entry_new(const char *pathname, int len)
{
        struct dir_entry *ent;

        FLEX_ALLOC_MEM(ent, name, pathname, len);
        ent->len = len;
        return ent;
}

static struct dir_entry *dir_add_name(struct dir_struct *dir,
                                      struct index_state *istate,
                                      const char *pathname, int len)
{
        if (index_file_exists(istate, pathname, len, ignore_case))
                return NULL;

        ALLOC_GROW(dir->entries, dir->nr+1, dir->alloc);
        return dir->entries[dir->nr++] = dir_entry_new(pathname, len);
}

struct dir_entry *dir_add_ignored(struct dir_struct *dir,
                                  struct index_state *istate,
                                  const char *pathname, int len)
{
        if (!index_name_is_other(istate, pathname, len))
                return NULL;

        ALLOC_GROW(dir->ignored, dir->ignored_nr+1, dir->ignored_alloc);
        return dir->ignored[dir->ignored_nr++] = dir_entry_new(pathname, len);
}

enum exist_status {
        index_nonexistent = 0,
        index_directory,
        index_gitdir
};

/*
 * Do not use the alphabetically sorted index to look up
 * the directory name; instead, use the case insensitive
 * directory hash.
 */
static enum exist_status directory_exists_in_index_icase(struct index_state *istate,
                                                         const char *dirname, int len)
{
        struct cache_entry *ce;

        if (index_dir_exists(istate, dirname, len))
                return index_directory;

        ce = index_file_exists(istate, dirname, len, ignore_case);
        if (ce && S_ISGITLINK(ce->ce_mode))
                return index_gitdir;

        return index_nonexistent;
}

/*
 * The index sorts alphabetically by entry name, which
 * means that a gitlink sorts as '\0' at the end, while
 * a directory (which is defined not as an entry, but as
 * the files it contains) will sort with the '/' at the
 * end.
 */
static enum exist_status directory_exists_in_index(struct index_state *istate,
                                                   const char *dirname, int len)
{
        int pos;

        if (ignore_case)
                return directory_exists_in_index_icase(istate, dirname, len);

        pos = index_name_pos(istate, dirname, len);
        if (pos < 0)
                pos = -pos-1;
        while (pos < istate->cache_nr) {
                const struct cache_entry *ce = istate->cache[pos++];
                unsigned char endchar;

                if (strncmp(ce->name, dirname, len))
                        break;
                endchar = ce->name[len];
                if (endchar > '/')
                        break;
                if (endchar == '/')
                        return index_directory;
                if (!endchar && S_ISGITLINK(ce->ce_mode))
                        return index_gitdir;
        }
        return index_nonexistent;
}

/*
 * When we find a directory when traversing the filesystem, we
 * have three distinct cases:
 *
 *  - ignore it
 *  - see it as a directory
 *  - recurse into it
 *
 * and which one we choose depends on a combination of existing
 * git index contents and the flags passed into the directory
 * traversal routine.
 *
 * Case 1: If we *already* have entries in the index under that
 * directory name, we always recurse into the directory to see
 * all the files.
 *
 * Case 2: If we *already* have that directory name as a gitlink,
 * we always continue to see it as a gitlink, regardless of whether
 * there is an actual git directory there or not (it might not
 * be checked out as a subproject!)
 *
 * Case 3: if we didn't have it in the index previously, we
 * have a few sub-cases:
 *
 *  (a) if "show_other_directories" is true, we show it as
 *      just a directory, unless "hide_empty_directories" is
 *      also true, in which case we need to check if it contains any
 *      untracked and / or ignored files.
 *  (b) if it looks like a git directory, and we don't have
 *      'no_gitlinks' set we treat it as a gitlink, and show it
 *      as a directory.
 *  (c) otherwise, we recurse into it.
 */
static enum path_treatment treat_directory(struct dir_struct *dir,
        struct index_state *istate,
        struct untracked_cache_dir *untracked,
        const char *dirname, int len, int baselen, int exclude,
        const struct pathspec *pathspec)
{
        int nested_repo = 0;

        /* The "len-1" is to strip the final '/' */
        switch (directory_exists_in_index(istate, dirname, len-1)) {
        case index_directory:
                return path_recurse;

        case index_gitdir:
                return path_none;

        case index_nonexistent:
                if ((dir->flags & DIR_SKIP_NESTED_GIT) ||
                    !(dir->flags & DIR_NO_GITLINKS)) {
                        struct strbuf sb = STRBUF_INIT;
                        strbuf_addstr(&sb, dirname);
                        nested_repo = is_nonbare_repository_dir(&sb);
                        strbuf_release(&sb);
                }
                if (nested_repo)
                        return ((dir->flags & DIR_SKIP_NESTED_GIT) ? path_none :
                                (exclude ? path_excluded : path_untracked));

                if (dir->flags & DIR_SHOW_OTHER_DIRECTORIES)
                        break;
                if (exclude &&
                        (dir->flags & DIR_SHOW_IGNORED_TOO) &&
                        (dir->flags & DIR_SHOW_IGNORED_TOO_MODE_MATCHING)) {

                        /*
                         * This is an excluded directory and we are
                         * showing ignored paths that match an exclude
                         * pattern.  (e.g. show directory as ignored
                         * only if it matches an exclude pattern).
                         * This path will either be 'path_excluded`
                         * (if we are showing empty directories or if
                         * the directory is not empty), or will be
                         * 'path_none' (empty directory, and we are
                         * not showing empty directories).
                         */
                        if (!(dir->flags & DIR_HIDE_EMPTY_DIRECTORIES))
                                return path_excluded;

                        if (read_directory_recursive(dir, istate, dirname, len,
                                                     untracked, 1, 1, pathspec) == path_excluded)
                                return path_excluded;

                        return path_none;
                }
                return path_recurse;
        }

        /* This is the "show_other_directories" case */

        if (!(dir->flags & DIR_HIDE_EMPTY_DIRECTORIES))
                return exclude ? path_excluded : path_untracked;

        untracked = lookup_untracked(dir->untracked, untracked,
                                     dirname + baselen, len - baselen);

        /*
         * If this is an excluded directory, then we only need to check if
         * the directory contains any files.
         */
        return read_directory_recursive(dir, istate, dirname, len,
                                        untracked, 1, exclude, pathspec);
}

/*
 * This is an inexact early pruning of any recursive directory
 * reading - if the path cannot possibly be in the pathspec,
 * return true, and we'll skip it early.
 */
static int simplify_away(const char *path, int pathlen,
                         const struct pathspec *pathspec)
{
        int i;

        if (!pathspec || !pathspec->nr)
                return 0;

        GUARD_PATHSPEC(pathspec,
                       PATHSPEC_FROMTOP |
                       PATHSPEC_MAXDEPTH |
                       PATHSPEC_LITERAL |
                       PATHSPEC_GLOB |
                       PATHSPEC_ICASE |
                       PATHSPEC_EXCLUDE |
                       PATHSPEC_ATTR);

        for (i = 0; i < pathspec->nr; i++) {
                const struct pathspec_item *item = &pathspec->items[i];
                int len = item->nowildcard_len;

                if (len > pathlen)
                        len = pathlen;
                if (!ps_strncmp(item, item->match, path, len))
                        return 0;
        }

        return 1;
}

/*
 * This function tells us whether an excluded path matches a
 * list of "interesting" pathspecs. That is, whether a path matched
 * by any of the pathspecs could possibly be ignored by excluding
 * the specified path. This can happen if:
 *
 *   1. the path is mentioned explicitly in the pathspec
 *
 *   2. the path is a directory prefix of some element in the
 *      pathspec
 */
static int exclude_matches_pathspec(const char *path, int pathlen,
                                    const struct pathspec *pathspec)
{
        int i;

        if (!pathspec || !pathspec->nr)
                return 0;

        GUARD_PATHSPEC(pathspec,
                       PATHSPEC_FROMTOP |
                       PATHSPEC_MAXDEPTH |
                       PATHSPEC_LITERAL |
                       PATHSPEC_GLOB |
                       PATHSPEC_ICASE |
                       PATHSPEC_EXCLUDE);

        for (i = 0; i < pathspec->nr; i++) {
                const struct pathspec_item *item = &pathspec->items[i];
                int len = item->nowildcard_len;

                if (len == pathlen &&
                    !ps_strncmp(item, item->match, path, pathlen))
                        return 1;
                if (len > pathlen &&
                    item->match[pathlen] == '/' &&
                    !ps_strncmp(item, item->match, path, pathlen))
                        return 1;
        }
        return 0;
}

static int get_index_dtype(struct index_state *istate,
                           const char *path, int len)
{
        int pos;
        const struct cache_entry *ce;

        ce = index_file_exists(istate, path, len, 0);
        if (ce) {
                if (!ce_uptodate(ce))
                        return DT_UNKNOWN;
                if (S_ISGITLINK(ce->ce_mode))
                        return DT_DIR;
                /*
                 * Nobody actually cares about the
                 * difference between DT_LNK and DT_REG
                 */
                return DT_REG;
        }

        /* Try to look it up as a directory */
        pos = index_name_pos(istate, path, len);
        if (pos >= 0)
                return DT_UNKNOWN;
        pos = -pos-1;
        while (pos < istate->cache_nr) {
                ce = istate->cache[pos++];
                if (strncmp(ce->name, path, len))
                        break;
                if (ce->name[len] > '/')
                        break;
                if (ce->name[len] < '/')
                        continue;
                if (!ce_uptodate(ce))
                        break;  /* continue? */
                return DT_DIR;
        }
        return DT_UNKNOWN;
}

static int resolve_dtype(int dtype, struct index_state *istate,
                         const char *path, int len)
{
        struct stat st;

        if (dtype != DT_UNKNOWN)
                return dtype;
        dtype = get_index_dtype(istate, path, len);
        if (dtype != DT_UNKNOWN)
                return dtype;
        if (lstat(path, &st))
                return dtype;
        if (S_ISREG(st.st_mode))
                return DT_REG;
        if (S_ISDIR(st.st_mode))
                return DT_DIR;
        if (S_ISLNK(st.st_mode))
                return DT_LNK;
        return dtype;
}

static enum path_treatment treat_one_path(struct dir_struct *dir,
                                          struct untracked_cache_dir *untracked,
                                          struct index_state *istate,
                                          struct strbuf *path,
                                          int baselen,
                                          const struct pathspec *pathspec,
                                          int dtype)
{
        int exclude;
        int has_path_in_index = !!index_file_exists(istate, path->buf, path->len, ignore_case);
        enum path_treatment path_treatment;

        dtype = resolve_dtype(dtype, istate, path->buf, path->len);

        /* Always exclude indexed files */
        if (dtype != DT_DIR && has_path_in_index)
                return path_none;

        /*
         * When we are looking at a directory P in the working tree,
         * there are three cases:
         *
         * (1) P exists in the index.  Everything inside the directory P in
         * the working tree needs to go when P is checked out from the
         * index.
         *
         * (2) P does not exist in the index, but there is P/Q in the index.
         * We know P will stay a directory when we check out the contents
         * of the index, but we do not know yet if there is a directory
         * P/Q in the working tree to be killed, so we need to recurse.
         *
         * (3) P does not exist in the index, and there is no P/Q in the index
         * to require P to be a directory, either.  Only in this case, we
         * know that everything inside P will not be killed without
         * recursing.
         */
        if ((dir->flags & DIR_COLLECT_KILLED_ONLY) &&
            (dtype == DT_DIR) &&
            !has_path_in_index &&
            (directory_exists_in_index(istate, path->buf, path->len) == index_nonexistent))
                return path_none;

        exclude = is_excluded(dir, istate, path->buf, &dtype);

        /*
         * Excluded? If we don't explicitly want to show
         * ignored files, ignore it
         */
        if (exclude && !(dir->flags & (DIR_SHOW_IGNORED|DIR_SHOW_IGNORED_TOO)))
                return path_excluded;

        switch (dtype) {
        default:
                return path_none;
        case DT_DIR:
                strbuf_addch(path, '/');
                path_treatment = treat_directory(dir, istate, untracked,
                                                 path->buf, path->len,
                                                 baselen, exclude, pathspec);
                /*
                 * If 1) we only want to return directories that
                 * match an exclude pattern and 2) this directory does
                 * not match an exclude pattern but all of its
                 * contents are excluded, then indicate that we should
                 * recurse into this directory (instead of marking the
                 * directory itself as an ignored path).
                 */
                if (!exclude &&
                    path_treatment == path_excluded &&
                    (dir->flags & DIR_SHOW_IGNORED_TOO) &&
                    (dir->flags & DIR_SHOW_IGNORED_TOO_MODE_MATCHING))
                        return path_recurse;
                return path_treatment;
        case DT_REG:
        case DT_LNK:
                return exclude ? path_excluded : path_untracked;
        }
}

static enum path_treatment treat_path_fast(struct dir_struct *dir,
                                           struct untracked_cache_dir *untracked,
                                           struct cached_dir *cdir,
                                           struct index_state *istate,
                                           struct strbuf *path,
                                           int baselen,
                                           const struct pathspec *pathspec)
{
        strbuf_setlen(path, baselen);
        if (!cdir->ucd) {
                strbuf_addstr(path, cdir->file);
                return path_untracked;
        }
        strbuf_addstr(path, cdir->ucd->name);
        /* treat_one_path() does this before it calls treat_directory() */
        strbuf_complete(path, '/');
        if (cdir->ucd->check_only)
                /*
                 * check_only is set as a result of treat_directory() getting
                 * to its bottom. Verify again the same set of directories
                 * with check_only set.
                 */
                return read_directory_recursive(dir, istate, path->buf, path->len,
                                                cdir->ucd, 1, 0, pathspec);
        /*
         * We get path_recurse in the first run when
         * directory_exists_in_index() returns index_nonexistent. We
         * are sure that new changes in the index does not impact the
         * outcome. Return now.
         */
        return path_recurse;
}

static enum path_treatment treat_path(struct dir_struct *dir,
                                      struct untracked_cache_dir *untracked,
                                      struct cached_dir *cdir,
                                      struct index_state *istate,
                                      struct strbuf *path,
                                      int baselen,
                                      const struct pathspec *pathspec)
{
        if (!cdir->d_name)
                return treat_path_fast(dir, untracked, cdir, istate, path,
                                       baselen, pathspec);
        if (is_dot_or_dotdot(cdir->d_name) || !fspathcmp(cdir->d_name, ".git"))
                return path_none;
        strbuf_setlen(path, baselen);
        strbuf_addstr(path, cdir->d_name);
        if (simplify_away(path->buf, path->len, pathspec))
                return path_none;

        return treat_one_path(dir, untracked, istate, path, baselen, pathspec,
                              cdir->d_type);
}

static void add_untracked(struct untracked_cache_dir *dir, const char *name)
{
        if (!dir)
                return;
        ALLOC_GROW(dir->untracked, dir->untracked_nr + 1,
                   dir->untracked_alloc);
        dir->untracked[dir->untracked_nr++] = xstrdup(name);
}

static int valid_cached_dir(struct dir_struct *dir,
                            struct untracked_cache_dir *untracked,
                            struct index_state *istate,
                            struct strbuf *path,
                            int check_only)
{
        struct stat st;

        if (!untracked)
                return 0;

        /*
         * With fsmonitor, we can trust the untracked cache's valid field.
         */
        refresh_fsmonitor(istate);
        if (!(dir->untracked->use_fsmonitor && untracked->valid)) {
                if (lstat(path->len ? path->buf : ".", &st)) {
                        memset(&untracked->stat_data, 0, sizeof(untracked->stat_data));
                        return 0;
                }
                if (!untracked->valid ||
                        match_stat_data_racy(istate, &untracked->stat_data, &st)) {
                        fill_stat_data(&untracked->stat_data, &st);
                        return 0;
                }
        }

        if (untracked->check_only != !!check_only)
                return 0;

        /*
         * prep_exclude will be called eventually on this directory,
         * but it's called much later in last_matching_pattern(). We
         * need it now to determine the validity of the cache for this
         * path. The next calls will be nearly no-op, the way
         * prep_exclude() is designed.
         */
        if (path->len && path->buf[path->len - 1] != '/') {
                strbuf_addch(path, '/');
                prep_exclude(dir, istate, path->buf, path->len);
                strbuf_setlen(path, path->len - 1);
        } else
                prep_exclude(dir, istate, path->buf, path->len);

        /* hopefully prep_exclude() haven't invalidated this entry... */
        return untracked->valid;
}

static int open_cached_dir(struct cached_dir *cdir,
                           struct dir_struct *dir,
                           struct untracked_cache_dir *untracked,
                           struct index_state *istate,
                           struct strbuf *path,
                           int check_only)
{
        const char *c_path;

        memset(cdir, 0, sizeof(*cdir));
        cdir->untracked = untracked;
        if (valid_cached_dir(dir, untracked, istate, path, check_only))
                return 0;
        c_path = path->len ? path->buf : ".";
        cdir->fdir = opendir(c_path);
        if (!cdir->fdir)
                warning_errno(_("could not open directory '%s'"), c_path);
        if (dir->untracked) {
                invalidate_directory(dir->untracked, untracked);
                dir->untracked->dir_opened++;
        }
        if (!cdir->fdir)
                return -1;
        return 0;
}

static int read_cached_dir(struct cached_dir *cdir)
{
        struct dirent *de;

        if (cdir->fdir) {
                de = readdir(cdir->fdir);
                if (!de) {
                        cdir->d_name = NULL;
                        cdir->d_type = DT_UNKNOWN;
                        return -1;
                }
                cdir->d_name = de->d_name;
                cdir->d_type = DTYPE(de);
                return 0;
        }
        while (cdir->nr_dirs < cdir->untracked->dirs_nr) {
                struct untracked_cache_dir *d = cdir->untracked->dirs[cdir->nr_dirs];
                if (!d->recurse) {
                        cdir->nr_dirs++;
                        continue;
                }
                cdir->ucd = d;
                cdir->nr_dirs++;
                return 0;
        }
        cdir->ucd = NULL;
        if (cdir->nr_files < cdir->untracked->untracked_nr) {
                struct untracked_cache_dir *d = cdir->untracked;
                cdir->file = d->untracked[cdir->nr_files++];
                return 0;
        }
        return -1;
}

static void close_cached_dir(struct cached_dir *cdir)
{
        if (cdir->fdir)
                closedir(cdir->fdir);
        /*
         * We have gone through this directory and found no untracked
         * entries. Mark it valid.
         */
        if (cdir->untracked) {
                cdir->untracked->valid = 1;
                cdir->untracked->recurse = 1;
        }
}

static void add_path_to_appropriate_result_list(struct dir_struct *dir,
        struct untracked_cache_dir *untracked,
        struct cached_dir *cdir,
        struct index_state *istate,
        struct strbuf *path,
        int baselen,
        const struct pathspec *pathspec,
        enum path_treatment state)
{
        /* add the path to the appropriate result list */
        switch (state) {
        case path_excluded:
                if (dir->flags & DIR_SHOW_IGNORED)
                        dir_add_name(dir, istate, path->buf, path->len);
                else if ((dir->flags & DIR_SHOW_IGNORED_TOO) ||
                        ((dir->flags & DIR_COLLECT_IGNORED) &&
                        exclude_matches_pathspec(path->buf, path->len,
                                                 pathspec)))
                        dir_add_ignored(dir, istate, path->buf, path->len);
                break;

        case path_untracked:
                if (dir->flags & DIR_SHOW_IGNORED)
                        break;
                dir_add_name(dir, istate, path->buf, path->len);
                if (cdir->fdir)
                        add_untracked(untracked, path->buf + baselen);
                break;

        default:
                break;
        }
}

/*
 * Read a directory tree. We currently ignore anything but
 * directories, regular files and symlinks. That's because git
 * doesn't handle them at all yet. Maybe that will change some
 * day.
 *
 * Also, we ignore the name ".git" (even if it is not a directory).
 * That likely will not change.
 *
 * If 'stop_at_first_file' is specified, 'path_excluded' is returned
 * to signal that a file was found. This is the least significant value that
 * indicates that a file was encountered that does not depend on the order of
 * whether an untracked or exluded path was encountered first.
 *
 * Returns the most significant path_treatment value encountered in the scan.
 * If 'stop_at_first_file' is specified, `path_excluded` is the most
 * significant path_treatment value that will be returned.
 */

static enum path_treatment read_directory_recursive(struct dir_struct *dir,
        struct index_state *istate, const char *base, int baselen,
        struct untracked_cache_dir *untracked, int check_only,
        int stop_at_first_file, const struct pathspec *pathspec)
{
        /*
         * WARNING WARNING WARNING:
         *
         * Any updates to the traversal logic here may need corresponding
         * updates in treat_leading_path().  See the commit message for the
         * commit adding this warning as well as the commit preceding it
         * for details.
         */

        struct cached_dir cdir;
        enum path_treatment state, subdir_state, dir_state = path_none;
        struct strbuf path = STRBUF_INIT;

        strbuf_add(&path, base, baselen);

        if (open_cached_dir(&cdir, dir, untracked, istate, &path, check_only))
                goto out;

        if (untracked)
                untracked->check_only = !!check_only;

        while (!read_cached_dir(&cdir)) {
                /* check how the file or directory should be treated */
                state = treat_path(dir, untracked, &cdir, istate, &path,
                                   baselen, pathspec);

                if (state > dir_state)
                        dir_state = state;

                /* recurse into subdir if instructed by treat_path */
                if ((state == path_recurse) ||
                        ((state == path_untracked) &&
                         (resolve_dtype(cdir.d_type, istate, path.buf, path.len) == DT_DIR) &&
                         ((dir->flags & DIR_SHOW_IGNORED_TOO) ||
                          (pathspec &&
                           do_match_pathspec(istate, pathspec, path.buf, path.len,
                                             baselen, NULL, DO_MATCH_LEADING_PATHSPEC) == MATCHED_RECURSIVELY_LEADING_PATHSPEC)))) {
                        struct untracked_cache_dir *ud;
                        ud = lookup_untracked(dir->untracked, untracked,
                                              path.buf + baselen,
                                              path.len - baselen);
                        subdir_state =
                                read_directory_recursive(dir, istate, path.buf,
                                                         path.len, ud,
                                                         check_only, stop_at_first_file, pathspec);
                        if (subdir_state > dir_state)
                                dir_state = subdir_state;

                        if (pathspec &&
                            !match_pathspec(istate, pathspec, path.buf, path.len,
                                            0 /* prefix */, NULL,
                                            0 /* do NOT special case dirs */))
                                state = path_none;
                }

                if (check_only) {
                        if (stop_at_first_file) {
                                /*
                                 * If stopping at first file, then
                                 * signal that a file was found by
                                 * returning `path_excluded`. This is
                                 * to return a consistent value
                                 * regardless of whether an ignored or
                                 * excluded file happened to be
                                 * encountered 1st.
                                 *
                                 * In current usage, the
                                 * `stop_at_first_file` is passed when
                                 * an ancestor directory has matched
                                 * an exclude pattern, so any found
                                 * files will be excluded.
                                 */
                                if (dir_state >= path_excluded) {
                                        dir_state = path_excluded;
                                        break;
                                }
                        }

                        /* abort early if maximum state has been reached */
                        if (dir_state == path_untracked) {
                                if (cdir.fdir)
                                        add_untracked(untracked, path.buf + baselen);
                                break;
                        }
                        /* skip the dir_add_* part */
                        continue;
                }

                add_path_to_appropriate_result_list(dir, untracked, &cdir,
                                                    istate, &path, baselen,
                                                    pathspec, state);
        }
        close_cached_dir(&cdir);
 out:
        strbuf_release(&path);

        return dir_state;
}

int cmp_dir_entry(const void *p1, const void *p2)
{
        const struct dir_entry *e1 = *(const struct dir_entry **)p1;
        const struct dir_entry *e2 = *(const struct dir_entry **)p2;

        return name_compare(e1->name, e1->len, e2->name, e2->len);
}

/* check if *out lexically strictly contains *in */
int check_dir_entry_contains(const struct dir_entry *out, const struct dir_entry *in)
{
        return (out->len < in->len) &&
                (out->name[out->len - 1] == '/') &&
                !memcmp(out->name, in->name, out->len);
}

static int treat_leading_path(struct dir_struct *dir,
                              struct index_state *istate,
                              const char *path, int len,
                              const struct pathspec *pathspec)
{
        /*
         * WARNING WARNING WARNING:
         *
         * Any updates to the traversal logic here may need corresponding
         * updates in read_directory_recursive().  See 777b420347 (dir:
         * synchronize treat_leading_path() and read_directory_recursive(),
         * 2019-12-19) and its parent commit for details.
         */

        struct strbuf sb = STRBUF_INIT;
        struct strbuf subdir = STRBUF_INIT;
        int prevlen, baselen;
        const char *cp;
        struct cached_dir cdir;
        enum path_treatment state = path_none;

        /*
         * For each directory component of path, we are going to check whether
         * that path is relevant given the pathspec.  For example, if path is
         *    foo/bar/baz/
         * then we will ask treat_path() whether we should go into foo, then
         * whether we should go into bar, then whether baz is relevant.
         * Checking each is important because e.g. if path is
         *    .git/info/
         * then we need to check .git to know we shouldn't traverse it.
         * If the return from treat_path() is:
         *    * path_none, for any path, we return false.
         *    * path_recurse, for all path components, we return true
         *    * <anything else> for some intermediate component, we make sure
         *        to add that path to the relevant list but return false
         *        signifying that we shouldn't recurse into it.
         */

        while (len && path[len - 1] == '/')
                len--;
        if (!len)
                return 1;

        memset(&cdir, 0, sizeof(cdir));
        cdir.d_type = DT_DIR;
        baselen = 0;
        prevlen = 0;
        while (1) {
                prevlen = baselen + !!baselen;
                cp = path + prevlen;
                cp = memchr(cp, '/', path + len - cp);
                if (!cp)
                        baselen = len;
                else
                        baselen = cp - path;
                strbuf_reset(&sb);
                strbuf_add(&sb, path, baselen);
                if (!is_directory(sb.buf))
                        break;
                strbuf_reset(&sb);
                strbuf_add(&sb, path, prevlen);
                strbuf_reset(&subdir);
                strbuf_add(&subdir, path+prevlen, baselen-prevlen);
                cdir.d_name = subdir.buf;
                state = treat_path(dir, NULL, &cdir, istate, &sb, prevlen,
                                    pathspec);
                if (state == path_untracked &&
                    resolve_dtype(cdir.d_type, istate, sb.buf, sb.len) == DT_DIR &&
                    (dir->flags & DIR_SHOW_IGNORED_TOO ||
                     do_match_pathspec(istate, pathspec, sb.buf, sb.len,
                                       baselen, NULL, DO_MATCH_LEADING_PATHSPEC) == MATCHED_RECURSIVELY_LEADING_PATHSPEC)) {
                        if (!match_pathspec(istate, pathspec, sb.buf, sb.len,
                                            0 /* prefix */, NULL,
                                            0 /* do NOT special case dirs */))
                                state = path_none;
                        add_path_to_appropriate_result_list(dir, NULL, &cdir,
                                                            istate,
                                                            &sb, baselen,
                                                            pathspec, state);
                        state = path_recurse;
                }

                if (state != path_recurse)
                        break; /* do not recurse into it */
                if (len <= baselen)
                        break; /* finished checking */
        }
        add_path_to_appropriate_result_list(dir, NULL, &cdir, istate,
                                            &sb, baselen, pathspec,
                                            state);

        strbuf_release(&subdir);
        strbuf_release(&sb);
        return state == path_recurse;
}

static const char *get_ident_string(void)
{
        static struct strbuf sb = STRBUF_INIT;
        struct utsname uts;

        if (sb.len)
                return sb.buf;
        if (uname(&uts) < 0)
                die_errno(_("failed to get kernel name and information"));
        strbuf_addf(&sb, "Location %s, system %s", get_git_work_tree(),
                    uts.sysname);
        return sb.buf;
}

static int ident_in_untracked(const struct untracked_cache *uc)
{
        /*
         * Previous git versions may have saved many NUL separated
         * strings in the "ident" field, but it is insane to manage
         * many locations, so just take care of the first one.
         */

        return !strcmp(uc->ident.buf, get_ident_string());
}

static void set_untracked_ident(struct untracked_cache *uc)
{
        strbuf_reset(&uc->ident);
        strbuf_addstr(&uc->ident, get_ident_string());

        /*
         * This strbuf used to contain a list of NUL separated
         * strings, so save NUL too for backward compatibility.
         */
        strbuf_addch(&uc->ident, 0);
}

static void new_untracked_cache(struct index_state *istate)
{
        struct untracked_cache *uc = xcalloc(1, sizeof(*uc));
        strbuf_init(&uc->ident, 100);
        uc->exclude_per_dir = ".gitignore";
        /* should be the same flags used by git-status */
        uc->dir_flags = DIR_SHOW_OTHER_DIRECTORIES | DIR_HIDE_EMPTY_DIRECTORIES;
        set_untracked_ident(uc);
        istate->untracked = uc;
        istate->cache_changed |= UNTRACKED_CHANGED;
}

void add_untracked_cache(struct index_state *istate)
{
        if (!istate->untracked) {
                new_untracked_cache(istate);
        } else {
                if (!ident_in_untracked(istate->untracked)) {
                        free_untracked_cache(istate->untracked);
                        new_untracked_cache(istate);
                }
        }
}

void remove_untracked_cache(struct index_state *istate)
{
        if (istate->untracked) {
                free_untracked_cache(istate->untracked);
                istate->untracked = NULL;
                istate->cache_changed |= UNTRACKED_CHANGED;
        }
}

static struct untracked_cache_dir *validate_untracked_cache(struct dir_struct *dir,
                                                      int base_len,
                                                      const struct pathspec *pathspec)
{
        struct untracked_cache_dir *root;
        static int untracked_cache_disabled = -1;

        if (!dir->untracked)
                return NULL;
        if (untracked_cache_disabled < 0)
                untracked_cache_disabled = git_env_bool("GIT_DISABLE_UNTRACKED_CACHE", 0);
        if (untracked_cache_disabled)
                return NULL;

        /*
         * We only support $GIT_DIR/info/exclude and core.excludesfile
         * as the global ignore rule files. Any other additions
         * (e.g. from command line) invalidate the cache. This
         * condition also catches running setup_standard_excludes()
         * before setting dir->untracked!
         */
        if (dir->unmanaged_exclude_files)
                return NULL;

        /*
         * Optimize for the main use case only: whole-tree git
         * status. More work involved in treat_leading_path() if we
         * use cache on just a subset of the worktree. pathspec
         * support could make the matter even worse.
         */
        if (base_len || (pathspec && pathspec->nr))
                return NULL;

        /* Different set of flags may produce different results */
        if (dir->flags != dir->untracked->dir_flags ||
            /*
             * See treat_directory(), case index_nonexistent. Without
             * this flag, we may need to also cache .git file content
             * for the resolve_gitlink_ref() call, which we don't.
             */
            !(dir->flags & DIR_SHOW_OTHER_DIRECTORIES) ||
            /* We don't support collecting ignore files */
            (dir->flags & (DIR_SHOW_IGNORED | DIR_SHOW_IGNORED_TOO |
                           DIR_COLLECT_IGNORED)))
                return NULL;

        /*
         * If we use .gitignore in the cache and now you change it to
         * .gitexclude, everything will go wrong.
         */
        if (dir->exclude_per_dir != dir->untracked->exclude_per_dir &&
            strcmp(dir->exclude_per_dir, dir->untracked->exclude_per_dir))
                return NULL;

        /*
         * EXC_CMDL is not considered in the cache. If people set it,
         * skip the cache.
         */
        if (dir->exclude_list_group[EXC_CMDL].nr)
                return NULL;

        if (!ident_in_untracked(dir->untracked)) {
                warning(_("untracked cache is disabled on this system or location"));
                return NULL;
        }

        if (!dir->untracked->root) {
                const int len = sizeof(*dir->untracked->root);
                dir->untracked->root = xmalloc(len);
                memset(dir->untracked->root, 0, len);
        }

        /* Validate $GIT_DIR/info/exclude and core.excludesfile */
        root = dir->untracked->root;
        if (!oideq(&dir->ss_info_exclude.oid,
                   &dir->untracked->ss_info_exclude.oid)) {
                invalidate_gitignore(dir->untracked, root);
                dir->untracked->ss_info_exclude = dir->ss_info_exclude;
        }
        if (!oideq(&dir->ss_excludes_file.oid,
                   &dir->untracked->ss_excludes_file.oid)) {
                invalidate_gitignore(dir->untracked, root);
                dir->untracked->ss_excludes_file = dir->ss_excludes_file;
        }

        /* Make sure this directory is not dropped out at saving phase */
        root->recurse = 1;
        return root;
}

int read_directory(struct dir_struct *dir, struct index_state *istate,
                   const char *path, int len, const struct pathspec *pathspec)
{
        struct untracked_cache_dir *untracked;

        trace_performance_enter();

        if (has_symlink_leading_path(path, len)) {
                trace_performance_leave("read directory %.*s", len, path);
                return dir->nr;
        }

        untracked = validate_untracked_cache(dir, len, pathspec);
        if (!untracked)
                /*
                 * make sure untracked cache code path is disabled,
                 * e.g. prep_exclude()
                 */
                dir->untracked = NULL;
        if (!len || treat_leading_path(dir, istate, path, len, pathspec))
                read_directory_recursive(dir, istate, path, len, untracked, 0, 0, pathspec);
        QSORT(dir->entries, dir->nr, cmp_dir_entry);
        QSORT(dir->ignored, dir->ignored_nr, cmp_dir_entry);

        /*
         * If DIR_SHOW_IGNORED_TOO is set, read_directory_recursive() will
         * also pick up untracked contents of untracked dirs; by default
         * we discard these, but given DIR_KEEP_UNTRACKED_CONTENTS we do not.
         */
        if ((dir->flags & DIR_SHOW_IGNORED_TOO) &&
                     !(dir->flags & DIR_KEEP_UNTRACKED_CONTENTS)) {
                int i, j;

                /* remove from dir->entries untracked contents of untracked dirs */
                for (i = j = 0; j < dir->nr; j++) {
                        if (i &&
                            check_dir_entry_contains(dir->entries[i - 1], dir->entries[j])) {
                                FREE_AND_NULL(dir->entries[j]);
                        } else {
                                dir->entries[i++] = dir->entries[j];
                        }
                }

                dir->nr = i;
        }

        trace_performance_leave("read directory %.*s", len, path);
        if (dir->untracked) {
                static int force_untracked_cache = -1;
                static struct trace_key trace_untracked_stats = TRACE_KEY_INIT(UNTRACKED_STATS);

                if (force_untracked_cache < 0)
                        force_untracked_cache =
                                git_env_bool("GIT_FORCE_UNTRACKED_CACHE", 0);
                trace_printf_key(&trace_untracked_stats,
                                 "node creation: %u\n"
                                 "gitignore invalidation: %u\n"
                                 "directory invalidation: %u\n"
                                 "opendir: %u\n",
                                 dir->untracked->dir_created,
                                 dir->untracked->gitignore_invalidated,
                                 dir->untracked->dir_invalidated,
                                 dir->untracked->dir_opened);
                if (force_untracked_cache &&
                        dir->untracked == istate->untracked &&
                    (dir->untracked->dir_opened ||
                     dir->untracked->gitignore_invalidated ||
                     dir->untracked->dir_invalidated))
                        istate->cache_changed |= UNTRACKED_CHANGED;
                if (dir->untracked != istate->untracked) {
                        FREE_AND_NULL(dir->untracked);
                }
        }
        return dir->nr;
}

int file_exists(const char *f)
{
        struct stat sb;
        return lstat(f, &sb) == 0;
}

int repo_file_exists(struct repository *repo, const char *path)
{
        if (repo != the_repository)
                BUG("do not know how to check file existence in arbitrary repo");

        return file_exists(path);
}

static int cmp_icase(char a, char b)
{
        if (a == b)
                return 0;
        if (ignore_case)
                return toupper(a) - toupper(b);
        return a - b;
}

/*
 * Given two normalized paths (a trailing slash is ok), if subdir is
 * outside dir, return -1.  Otherwise return the offset in subdir that
 * can be used as relative path to dir.
 */
int dir_inside_of(const char *subdir, const char *dir)
{
        int offset = 0;

        assert(dir && subdir && *dir && *subdir);

        while (*dir && *subdir && !cmp_icase(*dir, *subdir)) {
                dir++;
                subdir++;
                offset++;
        }

        /* hel[p]/me vs hel[l]/yeah */
        if (*dir && *subdir)
                return -1;

        if (!*subdir)
                return !*dir ? offset : -1; /* same dir */

        /* foo/[b]ar vs foo/[] */
        if (is_dir_sep(dir[-1]))
                return is_dir_sep(subdir[-1]) ? offset : -1;

        /* foo[/]bar vs foo[] */
        return is_dir_sep(*subdir) ? offset + 1 : -1;
}

int is_inside_dir(const char *dir)
{
        char *cwd;
        int rc;

        if (!dir)
                return 0;

        cwd = xgetcwd();
        rc = (dir_inside_of(cwd, dir) >= 0);
        free(cwd);
        return rc;
}

int is_empty_dir(const char *path)
{
        DIR *dir = opendir(path);
        struct dirent *e;
        int ret = 1;

        if (!dir)
                return 0;

        while ((e = readdir(dir)) != NULL)
                if (!is_dot_or_dotdot(e->d_name)) {
                        ret = 0;
                        break;
                }

        closedir(dir);
        return ret;
}

static int remove_dir_recurse(struct strbuf *path, int flag, int *kept_up)
{
        DIR *dir;
        struct dirent *e;
        int ret = 0, original_len = path->len, len, kept_down = 0;
        int only_empty = (flag & REMOVE_DIR_EMPTY_ONLY);
        int keep_toplevel = (flag & REMOVE_DIR_KEEP_TOPLEVEL);
        struct object_id submodule_head;

        if ((flag & REMOVE_DIR_KEEP_NESTED_GIT) &&
            !resolve_gitlink_ref(path->buf, "HEAD", &submodule_head)) {
                /* Do not descend and nuke a nested git work tree. */
                if (kept_up)
                        *kept_up = 1;
                return 0;
        }

        flag &= ~REMOVE_DIR_KEEP_TOPLEVEL;
        dir = opendir(path->buf);
        if (!dir) {
                if (errno == ENOENT)
                        return keep_toplevel ? -1 : 0;
                else if (errno == EACCES && !keep_toplevel)
                        /*
                         * An empty dir could be removable even if it
                         * is unreadable:
                         */
                        return rmdir(path->buf);
                else
                        return -1;
        }
        strbuf_complete(path, '/');

        len = path->len;
        while ((e = readdir(dir)) != NULL) {
                struct stat st;
                if (is_dot_or_dotdot(e->d_name))
                        continue;

                strbuf_setlen(path, len);
                strbuf_addstr(path, e->d_name);
                if (lstat(path->buf, &st)) {
                        if (errno == ENOENT)
                                /*
                                 * file disappeared, which is what we
                                 * wanted anyway
                                 */
                                continue;
                        /* fall through */
                } else if (S_ISDIR(st.st_mode)) {
                        if (!remove_dir_recurse(path, flag, &kept_down))
                                continue; /* happy */
                } else if (!only_empty &&
                           (!unlink(path->buf) || errno == ENOENT)) {
                        continue; /* happy, too */
                }

                /* path too long, stat fails, or non-directory still exists */
                ret = -1;
                break;
        }
        closedir(dir);

        strbuf_setlen(path, original_len);
        if (!ret && !keep_toplevel && !kept_down)
                ret = (!rmdir(path->buf) || errno == ENOENT) ? 0 : -1;
        else if (kept_up)
                /*
                 * report the uplevel that it is not an error that we
                 * did not rmdir() our directory.
                 */
                *kept_up = !ret;
        return ret;
}

int remove_dir_recursively(struct strbuf *path, int flag)
{
        return remove_dir_recurse(path, flag, NULL);
}

static GIT_PATH_FUNC(git_path_info_exclude, "info/exclude")

void setup_standard_excludes(struct dir_struct *dir)
{
        dir->exclude_per_dir = ".gitignore";

        /* core.excludesfile defaulting to $XDG_CONFIG_HOME/git/ignore */
        if (!excludes_file)
                excludes_file = xdg_config_home("ignore");
        if (excludes_file && !access_or_warn(excludes_file, R_OK, 0))
                add_patterns_from_file_1(dir, excludes_file,
                                         dir->untracked ? &dir->ss_excludes_file : NULL);

        /* per repository user preference */
        if (startup_info->have_repository) {
                const char *path = git_path_info_exclude();
                if (!access_or_warn(path, R_OK, 0))
                        add_patterns_from_file_1(dir, path,
                                                 dir->untracked ? &dir->ss_info_exclude : NULL);
        }
}

int remove_path(const char *name)
{
        char *slash;

        if (unlink(name) && !is_missing_file_error(errno))
                return -1;

        slash = strrchr(name, '/');
        if (slash) {
                char *dirs = xstrdup(name);
                slash = dirs + (slash - name);
                do {
                        *slash = '\0';
                } while (rmdir(dirs) == 0 && (slash = strrchr(dirs, '/')));
                free(dirs);
        }
        return 0;
}

/*
 * Frees memory within dir which was allocated for exclude lists and
 * the exclude_stack.  Does not free dir itself.
 */
void clear_directory(struct dir_struct *dir)
{
        int i, j;
        struct exclude_list_group *group;
        struct pattern_list *pl;
        struct exclude_stack *stk;

        for (i = EXC_CMDL; i <= EXC_FILE; i++) {
                group = &dir->exclude_list_group[i];
                for (j = 0; j < group->nr; j++) {
                        pl = &group->pl[j];
                        if (i == EXC_DIRS)
                                free((char *)pl->src);
                        clear_pattern_list(pl);
                }
                free(group->pl);
        }

        stk = dir->exclude_stack;
        while (stk) {
                struct exclude_stack *prev = stk->prev;
                free(stk);
                stk = prev;
        }
        strbuf_release(&dir->basebuf);
}

struct ondisk_untracked_cache {
        struct stat_data info_exclude_stat;
        struct stat_data excludes_file_stat;
        uint32_t dir_flags;
};

#define ouc_offset(x) offsetof(struct ondisk_untracked_cache, x)

struct write_data {
        int index;         /* number of written untracked_cache_dir */
        struct ewah_bitmap *check_only; /* from untracked_cache_dir */
        struct ewah_bitmap *valid;      /* from untracked_cache_dir */
        struct ewah_bitmap *sha1_valid; /* set if exclude_sha1 is not null */
        struct strbuf out;
        struct strbuf sb_stat;
        struct strbuf sb_sha1;
};

static void stat_data_to_disk(struct stat_data *to, const struct stat_data *from)
{
        to->sd_ctime.sec  = htonl(from->sd_ctime.sec);
        to->sd_ctime.nsec = htonl(from->sd_ctime.nsec);
        to->sd_mtime.sec  = htonl(from->sd_mtime.sec);
        to->sd_mtime.nsec = htonl(from->sd_mtime.nsec);
        to->sd_dev        = htonl(from->sd_dev);
        to->sd_ino        = htonl(from->sd_ino);
        to->sd_uid        = htonl(from->sd_uid);
        to->sd_gid        = htonl(from->sd_gid);
        to->sd_size       = htonl(from->sd_size);
}

static void write_one_dir(struct untracked_cache_dir *untracked,
                          struct write_data *wd)
{
        struct stat_data stat_data;
        struct strbuf *out = &wd->out;
        unsigned char intbuf[16];
        unsigned int intlen, value;
        int i = wd->index++;

        /*
         * untracked_nr should be reset whenever valid is clear, but
         * for safety..
         */
        if (!untracked->valid) {
                untracked->untracked_nr = 0;
                untracked->check_only = 0;
        }

        if (untracked->check_only)
                ewah_set(wd->check_only, i);
        if (untracked->valid) {
                ewah_set(wd->valid, i);
                stat_data_to_disk(&stat_data, &untracked->stat_data);
                strbuf_add(&wd->sb_stat, &stat_data, sizeof(stat_data));
        }
        if (!is_null_oid(&untracked->exclude_oid)) {
                ewah_set(wd->sha1_valid, i);
                strbuf_add(&wd->sb_sha1, untracked->exclude_oid.hash,
                           the_hash_algo->rawsz);
        }

        intlen = encode_varint(untracked->untracked_nr, intbuf);
        strbuf_add(out, intbuf, intlen);

        /* skip non-recurse directories */
        for (i = 0, value = 0; i < untracked->dirs_nr; i++)
                if (untracked->dirs[i]->recurse)
                        value++;
        intlen = encode_varint(value, intbuf);
        strbuf_add(out, intbuf, intlen);

        strbuf_add(out, untracked->name, strlen(untracked->name) + 1);

        for (i = 0; i < untracked->untracked_nr; i++)
                strbuf_add(out, untracked->untracked[i],
                           strlen(untracked->untracked[i]) + 1);

        for (i = 0; i < untracked->dirs_nr; i++)
                if (untracked->dirs[i]->recurse)
                        write_one_dir(untracked->dirs[i], wd);
}

void write_untracked_extension(struct strbuf *out, struct untracked_cache *untracked)
{
        struct ondisk_untracked_cache *ouc;
        struct write_data wd;
        unsigned char varbuf[16];
        int varint_len;
        const unsigned hashsz = the_hash_algo->rawsz;

        ouc = xcalloc(1, sizeof(*ouc));
        stat_data_to_disk(&ouc->info_exclude_stat, &untracked->ss_info_exclude.stat);
        stat_data_to_disk(&ouc->excludes_file_stat, &untracked->ss_excludes_file.stat);
        ouc->dir_flags = htonl(untracked->dir_flags);

        varint_len = encode_varint(untracked->ident.len, varbuf);
        strbuf_add(out, varbuf, varint_len);
        strbuf_addbuf(out, &untracked->ident);

        strbuf_add(out, ouc, sizeof(*ouc));
        strbuf_add(out, untracked->ss_info_exclude.oid.hash, hashsz);
        strbuf_add(out, untracked->ss_excludes_file.oid.hash, hashsz);
        strbuf_add(out, untracked->exclude_per_dir, strlen(untracked->exclude_per_dir) + 1);
        FREE_AND_NULL(ouc);

        if (!untracked->root) {
                varint_len = encode_varint(0, varbuf);
                strbuf_add(out, varbuf, varint_len);
                return;
        }

        wd.index      = 0;
        wd.check_only = ewah_new();
        wd.valid      = ewah_new();
        wd.sha1_valid = ewah_new();
        strbuf_init(&wd.out, 1024);
        strbuf_init(&wd.sb_stat, 1024);
        strbuf_init(&wd.sb_sha1, 1024);
        write_one_dir(untracked->root, &wd);

        varint_len = encode_varint(wd.index, varbuf);
        strbuf_add(out, varbuf, varint_len);
        strbuf_addbuf(out, &wd.out);
        ewah_serialize_strbuf(wd.valid, out);
        ewah_serialize_strbuf(wd.check_only, out);
        ewah_serialize_strbuf(wd.sha1_valid, out);
        strbuf_addbuf(out, &wd.sb_stat);
        strbuf_addbuf(out, &wd.sb_sha1);
        strbuf_addch(out, '\0'); /* safe guard for string lists */

        ewah_free(wd.valid);
        ewah_free(wd.check_only);
        ewah_free(wd.sha1_valid);
        strbuf_release(&wd.out);
        strbuf_release(&wd.sb_stat);
        strbuf_release(&wd.sb_sha1);
}

static void free_untracked(struct untracked_cache_dir *ucd)
{
        int i;
        if (!ucd)
                return;
        for (i = 0; i < ucd->dirs_nr; i++)
                free_untracked(ucd->dirs[i]);
        for (i = 0; i < ucd->untracked_nr; i++)
                free(ucd->untracked[i]);
        free(ucd->untracked);
        free(ucd->dirs);
        free(ucd);
}

void free_untracked_cache(struct untracked_cache *uc)
{
        if (uc)
                free_untracked(uc->root);
        free(uc);
}

struct read_data {
        int index;
        struct untracked_cache_dir **ucd;
        struct ewah_bitmap *check_only;
        struct ewah_bitmap *valid;
        struct ewah_bitmap *sha1_valid;
        const unsigned char *data;
        const unsigned char *end;
};

static void stat_data_from_disk(struct stat_data *to, const unsigned char *data)
{
        memcpy(to, data, sizeof(*to));
        to->sd_ctime.sec  = ntohl(to->sd_ctime.sec);
        to->sd_ctime.nsec = ntohl(to->sd_ctime.nsec);
        to->sd_mtime.sec  = ntohl(to->sd_mtime.sec);
        to->sd_mtime.nsec = ntohl(to->sd_mtime.nsec);
        to->sd_dev        = ntohl(to->sd_dev);
        to->sd_ino        = ntohl(to->sd_ino);
        to->sd_uid        = ntohl(to->sd_uid);
        to->sd_gid        = ntohl(to->sd_gid);
        to->sd_size       = ntohl(to->sd_size);
}

static int read_one_dir(struct untracked_cache_dir **untracked_,
                        struct read_data *rd)
{
        struct untracked_cache_dir ud, *untracked;
        const unsigned char *data = rd->data, *end = rd->end;
        const unsigned char *eos;
        unsigned int value;
        int i;

        memset(&ud, 0, sizeof(ud));

        value = decode_varint(&data);
        if (data > end)
                return -1;
        ud.recurse         = 1;
        ud.untracked_alloc = value;
        ud.untracked_nr    = value;
        if (ud.untracked_nr)
                ALLOC_ARRAY(ud.untracked, ud.untracked_nr);

        ud.dirs_alloc = ud.dirs_nr = decode_varint(&data);
        if (data > end)
                return -1;
        ALLOC_ARRAY(ud.dirs, ud.dirs_nr);

        eos = memchr(data, '\0', end - data);
        if (!eos || eos == end)
                return -1;

        *untracked_ = untracked = xmalloc(st_add3(sizeof(*untracked), eos - data, 1));
        memcpy(untracked, &ud, sizeof(ud));
        memcpy(untracked->name, data, eos - data + 1);
        data = eos + 1;

        for (i = 0; i < untracked->untracked_nr; i++) {
                eos = memchr(data, '\0', end - data);
                if (!eos || eos == end)
                        return -1;
                untracked->untracked[i] = xmemdupz(data, eos - data);
                data = eos + 1;
        }

        rd->ucd[rd->index++] = untracked;
        rd->data = data;

        for (i = 0; i < untracked->dirs_nr; i++) {
                if (read_one_dir(untracked->dirs + i, rd) < 0)
                        return -1;
        }
        return 0;
}

static void set_check_only(size_t pos, void *cb)
{
        struct read_data *rd = cb;
        struct untracked_cache_dir *ud = rd->ucd[pos];
        ud->check_only = 1;
}

static void read_stat(size_t pos, void *cb)
{
        struct read_data *rd = cb;
        struct untracked_cache_dir *ud = rd->ucd[pos];
        if (rd->data + sizeof(struct stat_data) > rd->end) {
                rd->data = rd->end + 1;
                return;
        }
        stat_data_from_disk(&ud->stat_data, rd->data);
        rd->data += sizeof(struct stat_data);
        ud->valid = 1;
}

static void read_oid(size_t pos, void *cb)
{
        struct read_data *rd = cb;
        struct untracked_cache_dir *ud = rd->ucd[pos];
        if (rd->data + the_hash_algo->rawsz > rd->end) {
                rd->data = rd->end + 1;
                return;
        }
        hashcpy(ud->exclude_oid.hash, rd->data);
        rd->data += the_hash_algo->rawsz;
}

static void load_oid_stat(struct oid_stat *oid_stat, const unsigned char *data,
                          const unsigned char *sha1)
{
        stat_data_from_disk(&oid_stat->stat, data);
        hashcpy(oid_stat->oid.hash, sha1);
        oid_stat->valid = 1;
}

struct untracked_cache *read_untracked_extension(const void *data, unsigned long sz)
{
        struct untracked_cache *uc;
        struct read_data rd;
        const unsigned char *next = data, *end = (const unsigned char *)data + sz;
        const char *ident;
        int ident_len;
        ssize_t len;
        const char *exclude_per_dir;
        const unsigned hashsz = the_hash_algo->rawsz;
        const unsigned offset = sizeof(struct ondisk_untracked_cache);
        const unsigned exclude_per_dir_offset = offset + 2 * hashsz;

        if (sz <= 1 || end[-1] != '\0')
                return NULL;
        end--;

        ident_len = decode_varint(&next);
        if (next + ident_len > end)
                return NULL;
        ident = (const char *)next;
        next += ident_len;

        if (next + exclude_per_dir_offset + 1 > end)
                return NULL;

        uc = xcalloc(1, sizeof(*uc));
        strbuf_init(&uc->ident, ident_len);
        strbuf_add(&uc->ident, ident, ident_len);
        load_oid_stat(&uc->ss_info_exclude,
                      next + ouc_offset(info_exclude_stat),
                      next + offset);
        load_oid_stat(&uc->ss_excludes_file,
                      next + ouc_offset(excludes_file_stat),
                      next + offset + hashsz);
        uc->dir_flags = get_be32(next + ouc_offset(dir_flags));
        exclude_per_dir = (const char *)next + exclude_per_dir_offset;
        uc->exclude_per_dir = xstrdup(exclude_per_dir);
        /* NUL after exclude_per_dir is covered by sizeof(*ouc) */
        next += exclude_per_dir_offset + strlen(exclude_per_dir) + 1;
        if (next >= end)
                goto done2;

        len = decode_varint(&next);
        if (next > end || len == 0)
                goto done2;

        rd.valid      = ewah_new();
        rd.check_only = ewah_new();
        rd.sha1_valid = ewah_new();
        rd.data       = next;
        rd.end        = end;
        rd.index      = 0;
        ALLOC_ARRAY(rd.ucd, len);

        if (read_one_dir(&uc->root, &rd) || rd.index != len)
                goto done;

        next = rd.data;
        len = ewah_read_mmap(rd.valid, next, end - next);
        if (len < 0)
                goto done;

        next += len;
        len = ewah_read_mmap(rd.check_only, next, end - next);
        if (len < 0)
                goto done;

        next += len;
        len = ewah_read_mmap(rd.sha1_valid, next, end - next);
        if (len < 0)
                goto done;

        ewah_each_bit(rd.check_only, set_check_only, &rd);
        rd.data = next + len;
        ewah_each_bit(rd.valid, read_stat, &rd);
        ewah_each_bit(rd.sha1_valid, read_oid, &rd);
        next = rd.data;

done:
        free(rd.ucd);
        ewah_free(rd.valid);
        ewah_free(rd.check_only);
        ewah_free(rd.sha1_valid);
done2:
        if (next != end) {
                free_untracked_cache(uc);
                uc = NULL;
        }
        return uc;
}

static void invalidate_one_directory(struct untracked_cache *uc,
                                     struct untracked_cache_dir *ucd)
{
        uc->dir_invalidated++;
        ucd->valid = 0;
        ucd->untracked_nr = 0;
}

/*
 * Normally when an entry is added or removed from a directory,
 * invalidating that directory is enough. No need to touch its
 * ancestors. When a directory is shown as "foo/bar/" in git-status
 * however, deleting or adding an entry may have cascading effect.
 *
 * Say the "foo/bar/file" has become untracked, we need to tell the
 * untracked_cache_dir of "foo" that "bar/" is not an untracked
 * directory any more (because "bar" is managed by foo as an untracked
 * "file").
 *
 * Similarly, if "foo/bar/file" moves from untracked to tracked and it
 * was the last untracked entry in the entire "foo", we should show
 * "foo/" instead. Which means we have to invalidate past "bar" up to
 * "foo".
 *
 * This function traverses all directories from root to leaf. If there
 * is a chance of one of the above cases happening, we invalidate back
 * to root. Otherwise we just invalidate the leaf. There may be a more
 * sophisticated way than checking for SHOW_OTHER_DIRECTORIES to
 * detect these cases and avoid unnecessary invalidation, for example,
 * checking for the untracked entry named "bar/" in "foo", but for now
 * stick to something safe and simple.
 */
static int invalidate_one_component(struct untracked_cache *uc,
                                    struct untracked_cache_dir *dir,
                                    const char *path, int len)
{
        const char *rest = strchr(path, '/');

        if (rest) {
                int component_len = rest - path;
                struct untracked_cache_dir *d =
                        lookup_untracked(uc, dir, path, component_len);
                int ret =
                        invalidate_one_component(uc, d, rest + 1,
                                                 len - (component_len + 1));
                if (ret)
                        invalidate_one_directory(uc, dir);
                return ret;
        }

        invalidate_one_directory(uc, dir);
        return uc->dir_flags & DIR_SHOW_OTHER_DIRECTORIES;
}

void untracked_cache_invalidate_path(struct index_state *istate,
                                     const char *path, int safe_path)
{
        if (!istate->untracked || !istate->untracked->root)
                return;
        if (!safe_path && !verify_path(path, 0))
                return;
        invalidate_one_component(istate->untracked, istate->untracked->root,
                                 path, strlen(path));
}

void untracked_cache_remove_from_index(struct index_state *istate,
                                       const char *path)
{
        untracked_cache_invalidate_path(istate, path, 1);
}

void untracked_cache_add_to_index(struct index_state *istate,
                                  const char *path)
{
        untracked_cache_invalidate_path(istate, path, 1);
}

static void connect_wt_gitdir_in_nested(const char *sub_worktree,
                                        const char *sub_gitdir)
{
        int i;
        struct repository subrepo;
        struct strbuf sub_wt = STRBUF_INIT;
        struct strbuf sub_gd = STRBUF_INIT;

        const struct submodule *sub;

        /* If the submodule has no working tree, we can ignore it. */
        if (repo_init(&subrepo, sub_gitdir, sub_worktree))
                return;

        if (repo_read_index(&subrepo) < 0)
                die(_("index file corrupt in repo %s"), subrepo.gitdir);

        for (i = 0; i < subrepo.index->cache_nr; i++) {
                const struct cache_entry *ce = subrepo.index->cache[i];

                if (!S_ISGITLINK(ce->ce_mode))
                        continue;

                while (i + 1 < subrepo.index->cache_nr &&
                       !strcmp(ce->name, subrepo.index->cache[i + 1]->name))
                        /*
                         * Skip entries with the same name in different stages
                         * to make sure an entry is returned only once.
                         */
                        i++;

                sub = submodule_from_path(&subrepo, &null_oid, ce->name);
                if (!sub || !is_submodule_active(&subrepo, ce->name))
                        /* .gitmodules broken or inactive sub */
                        continue;

                strbuf_reset(&sub_wt);
                strbuf_reset(&sub_gd);
                strbuf_addf(&sub_wt, "%s/%s", sub_worktree, sub->path);
                strbuf_addf(&sub_gd, "%s/modules/%s", sub_gitdir, sub->name);

                connect_work_tree_and_git_dir(sub_wt.buf, sub_gd.buf, 1);
        }
        strbuf_release(&sub_wt);
        strbuf_release(&sub_gd);
        repo_clear(&subrepo);
}

void connect_work_tree_and_git_dir(const char *work_tree_,
                                   const char *git_dir_,
                                   int recurse_into_nested)
{
        struct strbuf gitfile_sb = STRBUF_INIT;
        struct strbuf cfg_sb = STRBUF_INIT;
        struct strbuf rel_path = STRBUF_INIT;
        char *git_dir, *work_tree;

        /* Prepare .git file */
        strbuf_addf(&gitfile_sb, "%s/.git", work_tree_);
        if (safe_create_leading_directories_const(gitfile_sb.buf))
                die(_("could not create directories for %s"), gitfile_sb.buf);

        /* Prepare config file */
        strbuf_addf(&cfg_sb, "%s/config", git_dir_);
        if (safe_create_leading_directories_const(cfg_sb.buf))
                die(_("could not create directories for %s"), cfg_sb.buf);

        git_dir = real_pathdup(git_dir_, 1);
        work_tree = real_pathdup(work_tree_, 1);

        /* Write .git file */
        write_file(gitfile_sb.buf, "gitdir: %s",
                   relative_path(git_dir, work_tree, &rel_path));
        /* Update core.worktree setting */
        git_config_set_in_file(cfg_sb.buf, "core.worktree",
                               relative_path(work_tree, git_dir, &rel_path));

        strbuf_release(&gitfile_sb);
        strbuf_release(&cfg_sb);
        strbuf_release(&rel_path);

        if (recurse_into_nested)
                connect_wt_gitdir_in_nested(work_tree, git_dir);

        free(work_tree);
        free(git_dir);
}

/*
 * Migrate the git directory of the given path from old_git_dir to new_git_dir.
 */
void relocate_gitdir(const char *path, const char *old_git_dir, const char *new_git_dir)
{
        if (rename(old_git_dir, new_git_dir) < 0)
                die_errno(_("could not migrate git directory from '%s' to '%s'"),
                        old_git_dir, new_git_dir);

        connect_work_tree_and_git_dir(path, new_git_dir, 0);
}