dir.c: move prep_exclude

[thirdparty/git.git] / dir.c

/*
 * This handles recursive filename detection with exclude
 * files, index knowledge etc..
 *
 * See Documentation/technical/api-directory-listing.txt
 *
 * Copyright (C) Linus Torvalds, 2005-2006
 *               Junio Hamano, 2005-2006
 */
#include "cache.h"
#include "dir.h"
#include "refs.h"
#include "wildmatch.h"

struct path_simplify {
        int len;
        const char *path;
};

static int read_directory_recursive(struct dir_struct *dir, const char *path, int len,
        int check_only, const struct path_simplify *simplify);
static int get_dtype(struct dirent *de, const char *path, int len);

/* helper string functions with support for the ignore_case flag */
int strcmp_icase(const char *a, const char *b)
{
        return ignore_case ? strcasecmp(a, b) : strcmp(a, b);
}

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

int fnmatch_icase(const char *pattern, const char *string, int flags)
{
        return fnmatch(pattern, string, flags | (ignore_case ? FNM_CASEFOLD : 0));
}

inline int git_fnmatch(const char *pattern, const char *string,
                       int flags, int prefix)
{
        int fnm_flags = 0;
        if (flags & GFNM_PATHNAME)
                fnm_flags |= FNM_PATHNAME;
        if (prefix > 0) {
                if (strncmp(pattern, string, prefix))
                        return FNM_NOMATCH;
                pattern += prefix;
                string += prefix;
        }
        if (flags & GFNM_ONESTAR) {
                int pattern_len = strlen(++pattern);
                int string_len = strlen(string);
                return string_len < pattern_len ||
                       strcmp(pattern,
                              string + string_len - pattern_len);
        }
        return fnmatch(pattern, string, fnm_flags);
}

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, NULL);

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

        return match_status;
}

static size_t common_prefix_len(const char **pathspec)
{
        const char *n, *first;
        size_t max = 0;
        int literal = limit_pathspec_to_literal();

        if (!pathspec)
                return max;

        first = *pathspec;
        while ((n = *pathspec++)) {
                size_t i, len = 0;
                for (i = 0; first == n || i < max; i++) {
                        char c = n[i];
                        if (!c || c != first[i] || (!literal && is_glob_special(c)))
                                break;
                        if (c == '/')
                                len = i + 1;
                }
                if (first == n || 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 char **pathspec)
{
        unsigned long len = common_prefix_len(pathspec);

        return len ? xmemdupz(*pathspec, len) : NULL;
}

int fill_directory(struct dir_struct *dir, const char **pathspec)
{
        size_t len;

        /*
         * Calculate common prefix for the pathspec, and
         * use that to optimize the directory walk
         */
        len = common_prefix_len(pathspec);

        /* Read the directory and prune it */
        read_directory(dir, pathspec ? *pathspec : "", len, pathspec);
        return 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;
}

/*
 * Does 'match' match the given name?
 * A match is found if
 *
 * (1) the 'match' string is leading directory of 'name', or
 * (2) the 'match' string is a wildcard and matches 'name', or
 * (3) the 'match' string is exactly the same as 'name'.
 *
 * and the return value tells which case it was.
 *
 * It returns 0 when there is no match.
 */
static int match_one(const char *match, const char *name, int namelen)
{
        int matchlen;
        int literal = limit_pathspec_to_literal();

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

        if (ignore_case) {
                for (;;) {
                        unsigned char c1 = tolower(*match);
                        unsigned char c2 = tolower(*name);
                        if (c1 == '\0' || (!literal && is_glob_special(c1)))
                                break;
                        if (c1 != c2)
                                return 0;
                        match++;
                        name++;
                        namelen--;
                }
        } else {
                for (;;) {
                        unsigned char c1 = *match;
                        unsigned char c2 = *name;
                        if (c1 == '\0' || (!literal && is_glob_special(c1)))
                                break;
                        if (c1 != c2)
                                return 0;
                        match++;
                        name++;
                        namelen--;
                }
        }

        /*
         * If we don't match the matchstring exactly,
         * we need to match by fnmatch
         */
        matchlen = strlen(match);
        if (strncmp_icase(match, name, matchlen)) {
                if (literal)
                        return 0;
                return !fnmatch_icase(match, name, 0) ? MATCHED_FNMATCH : 0;
        }

        if (namelen == matchlen)
                return MATCHED_EXACTLY;
        if (match[matchlen-1] == '/' || name[matchlen] == '/')
                return MATCHED_RECURSIVELY;
        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.
 */
int match_pathspec(const char **pathspec, const char *name, int namelen,
                int prefix, char *seen)
{
        int i, retval = 0;

        if (!pathspec)
                return 1;

        name += prefix;
        namelen -= prefix;

        for (i = 0; pathspec[i] != NULL; i++) {
                int how;
                const char *match = pathspec[i] + prefix;
                if (seen && seen[i] == MATCHED_EXACTLY)
                        continue;
                how = match_one(match, name, namelen);
                if (how) {
                        if (retval < how)
                                retval = how;
                        if (seen && seen[i] < how)
                                seen[i] = how;
                }
        }
        return retval;
}

/*
 * Does 'match' match the given name?
 * A match is found if
 *
 * (1) the 'match' string is leading directory of 'name', or
 * (2) the 'match' string is a wildcard and matches 'name', or
 * (3) the 'match' string is exactly the same as 'name'.
 *
 * and the return value tells which case it was.
 *
 * It returns 0 when there is no match.
 */
static int match_pathspec_item(const struct pathspec_item *item, int prefix,
                               const char *name, int namelen)
{
        /* name/namelen has prefix cut off by caller */
        const char *match = item->match + prefix;
        int matchlen = item->len - prefix;

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

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

                if (match[matchlen-1] == '/' || name[matchlen] == '/')
                        return MATCHED_RECURSIVELY;
        }

        if (item->nowildcard_len < item->len &&
            !git_fnmatch(match, name,
                         item->flags & PATHSPEC_ONESTAR ? GFNM_ONESTAR : 0,
                         item->nowildcard_len - prefix))
                return MATCHED_FNMATCH;

        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.
 */
int match_pathspec_depth(const struct pathspec *ps,
                         const char *name, int namelen,
                         int prefix, char *seen)
{
        int i, retval = 0;

        if (!ps->nr) {
                if (!ps->recursive || 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 (seen && seen[i] == MATCHED_EXACTLY)
                        continue;
                how = match_pathspec_item(ps->items+i, prefix, name, namelen);
                if (ps->recursive && 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;
}

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

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

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

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

        *flags = 0;
        if (*p == '!') {
                *flags |= EXC_FLAG_NEGATIVE;
                p++;
        }
        len = strlen(p);
        if (len && p[len - 1] == '/') {
                len--;
                *flags |= EXC_FLAG_MUSTBEDIR;
        }
        for (i = 0; i < len; i++) {
                if (p[i] == '/')
                        break;
        }
        if (i == len)
                *flags |= EXC_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 |= EXC_FLAG_ENDSWITH;
        *pattern = p;
        *patternlen = len;
}

void add_exclude(const char *string, const char *base,
                 int baselen, struct exclude_list *el, int srcpos)
{
        struct exclude *x;
        int patternlen;
        int flags;
        int nowildcardlen;

        parse_exclude_pattern(&string, &patternlen, &flags, &nowildcardlen);
        if (flags & EXC_FLAG_MUSTBEDIR) {
                char *s;
                x = xmalloc(sizeof(*x) + patternlen + 1);
                s = (char *)(x+1);
                memcpy(s, string, patternlen);
                s[patternlen] = '\0';
                x->pattern = s;
        } else {
                x = xmalloc(sizeof(*x));
                x->pattern = string;
        }
        x->patternlen = patternlen;
        x->nowildcardlen = nowildcardlen;
        x->base = base;
        x->baselen = baselen;
        x->flags = flags;
        x->srcpos = srcpos;
        ALLOC_GROW(el->excludes, el->nr + 1, el->alloc);
        el->excludes[el->nr++] = x;
        x->el = el;
}

static void *read_skip_worktree_file_from_index(const char *path, size_t *size)
{
        int pos, len;
        unsigned long sz;
        enum object_type type;
        void *data;
        struct index_state *istate = &the_index;

        len = strlen(path);
        pos = index_name_pos(istate, path, len);
        if (pos < 0)
                return NULL;
        if (!ce_skip_worktree(istate->cache[pos]))
                return NULL;
        data = read_sha1_file(istate->cache[pos]->sha1, &type, &sz);
        if (!data || type != OBJ_BLOB) {
                free(data);
                return NULL;
        }
        *size = xsize_t(sz);
        return data;
}

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

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

        el->nr = 0;
        el->excludes = NULL;
        el->filebuf = NULL;
}

int add_excludes_from_file_to_list(const char *fname,
                                   const char *base,
                                   int baselen,
                                   struct exclude_list *el,
                                   int check_index)
{
        struct stat st;
        int fd, i, lineno = 1;
        size_t size = 0;
        char *buf, *entry;

        fd = open(fname, O_RDONLY);
        if (fd < 0 || fstat(fd, &st) < 0) {
                if (errno != ENOENT)
                        warn_on_inaccessible(fname);
                if (0 <= fd)
                        close(fd);
                if (!check_index ||
                    (buf = read_skip_worktree_file_from_index(fname, &size)) == NULL)
                        return -1;
                if (size == 0) {
                        free(buf);
                        return 0;
                }
                if (buf[size-1] != '\n') {
                        buf = xrealloc(buf, size+1);
                        buf[size++] = '\n';
                }
        }
        else {
                size = xsize_t(st.st_size);
                if (size == 0) {
                        close(fd);
                        return 0;
                }
                buf = xmalloc(size+1);
                if (read_in_full(fd, buf, size) != size) {
                        free(buf);
                        close(fd);
                        return -1;
                }
                buf[size++] = '\n';
                close(fd);
        }

        el->filebuf = buf;
        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;
                                add_exclude(entry, base, baselen, el, lineno);
                        }
                        lineno++;
                        entry = buf + i + 1;
                }
        }
        return 0;
}

struct exclude_list *add_exclude_list(struct dir_struct *dir,
                                      int group_type, const char *src)
{
        struct exclude_list *el;
        struct exclude_list_group *group;

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

/*
 * Used to set up core.excludesfile and .git/info/exclude lists.
 */
void add_excludes_from_file(struct dir_struct *dir, const char *fname)
{
        struct exclude_list *el;
        el = add_exclude_list(dir, EXC_FILE, fname);
        if (add_excludes_from_file_to_list(fname, "", 0, el, 0) < 0)
                die("cannot use %s as an exclude file", fname);
}

int match_basename(const char *basename, int basenamelen,
                   const char *pattern, int prefix, int patternlen,
                   int flags)
{
        if (prefix == patternlen) {
                if (patternlen == basenamelen &&
                    !strncmp_icase(pattern, basename, basenamelen))
                        return 1;
        } else if (flags & EXC_FLAG_ENDSWITH) {
                /* "*literal" matching against "fooliteral" */
                if (patternlen - 1 <= basenamelen &&
                    !strncmp_icase(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,
                   int 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] != '/') ||
            strncmp_icase(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 (strncmp_icase(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 exclude *last_exclude_matching_from_list(const char *pathname,
                                                       int pathlen,
                                                       const char *basename,
                                                       int *dtype,
                                                       struct exclude_list *el)
{
        int i;

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

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

                if (x->flags & EXC_FLAG_MUSTBEDIR) {
                        if (*dtype == DT_UNKNOWN)
                                *dtype = get_dtype(NULL, pathname, pathlen);
                        if (*dtype != DT_DIR)
                                continue;
                }

                if (x->flags & EXC_FLAG_NODIR) {
                        if (match_basename(basename,
                                           pathlen - (basename - pathname),
                                           exclude, prefix, x->patternlen,
                                           x->flags))
                                return x;
                        continue;
                }

                assert(x->baselen == 0 || x->base[x->baselen - 1] == '/');
                if (match_pathname(pathname, pathlen,
                                   x->base, x->baselen ? x->baselen - 1 : 0,
                                   exclude, prefix, x->patternlen, x->flags))
                        return x;
        }
        return NULL; /* undecided */
}

/*
 * Scan the list and let the last match determine the fate.
 * Return 1 for exclude, 0 for include and -1 for undecided.
 */
int is_excluded_from_list(const char *pathname,
                          int pathlen, const char *basename, int *dtype,
                          struct exclude_list *el)
{
        struct exclude *exclude;
        exclude = last_exclude_matching_from_list(pathname, pathlen, basename, dtype, el);
        if (exclude)
                return exclude->flags & EXC_FLAG_NEGATIVE ? 0 : 1;
        return -1; /* undecided */
}

static struct exclude *last_exclude_matching_from_lists(struct dir_struct *dir,
                const char *pathname, int pathlen, const char *basename,
                int *dtype_p)
{
        int i, j;
        struct exclude_list_group *group;
        struct exclude *exclude;
        for (i = EXC_CMDL; i <= EXC_FILE; i++) {
                group = &dir->exclude_list_group[i];
                for (j = group->nr - 1; j >= 0; j--) {
                        exclude = last_exclude_matching_from_list(
                                pathname, pathlen, basename, dtype_p,
                                &group->el[j]);
                        if (exclude)
                                return exclude;
                }
        }
        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, const char *base, int baselen)
{
        struct exclude_list_group *group;
        struct exclude_list *el;
        struct exclude_stack *stk = NULL;
        int current;

        if ((!dir->exclude_per_dir) ||
            (baselen + strlen(dir->exclude_per_dir) >= PATH_MAX))
                return; /* too long a path -- ignore */

        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, base, stk->baselen))
                        break;
                el = &group->el[dir->exclude_stack->exclude_ix];
                dir->exclude_stack = stk->prev;
                free((char *)el->src); /* see strdup() below */
                clear_exclude_list(el);
                free(stk);
                group->nr--;
        }

        /* Read from the parent directories and push them down. */
        current = stk ? stk->baselen : -1;
        while (current < baselen) {
                struct exclude_stack *stk = xcalloc(1, sizeof(*stk));
                const char *cp;

                if (current < 0) {
                        cp = base;
                        current = 0;
                }
                else {
                        cp = strchr(base + current + 1, '/');
                        if (!cp)
                                die("oops in prep_exclude");
                        cp++;
                }
                stk->prev = dir->exclude_stack;
                stk->baselen = cp - base;
                memcpy(dir->basebuf + current, base + current,
                       stk->baselen - current);
                strcpy(dir->basebuf + stk->baselen, dir->exclude_per_dir);
                /*
                 * dir->basebuf gets reused by the traversal, but we
                 * need fname to remain unchanged to ensure the src
                 * member of each struct exclude correctly
                 * back-references its source file.  Other invocations
                 * of add_exclude_list provide stable strings, so we
                 * strdup() and free() here in the caller.
                 */
                el = add_exclude_list(dir, EXC_DIRS, strdup(dir->basebuf));
                stk->exclude_ix = group->nr - 1;
                add_excludes_from_file_to_list(dir->basebuf,
                                               dir->basebuf, stk->baselen,
                                               el, 1);
                dir->exclude_stack = stk;
                current = stk->baselen;
        }
        dir->basebuf[baselen] = '\0';
}

/*
 * 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.
 */
static struct exclude *last_exclude_matching(struct dir_struct *dir,
                                             const char *pathname,
                                             int *dtype_p)
{
        int pathlen = strlen(pathname);
        const char *basename = strrchr(pathname, '/');
        basename = (basename) ? basename+1 : pathname;

        prep_exclude(dir, pathname, basename-pathname);

        return last_exclude_matching_from_lists(dir, 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.
 */
static int is_excluded(struct dir_struct *dir, const char *pathname, int *dtype_p)
{
        struct exclude *exclude =
                last_exclude_matching(dir, pathname, dtype_p);
        if (exclude)
                return exclude->flags & EXC_FLAG_NEGATIVE ? 0 : 1;
        return 0;
}

void path_exclude_check_init(struct path_exclude_check *check,
                             struct dir_struct *dir)
{
        check->dir = dir;
        check->exclude = NULL;
        strbuf_init(&check->path, 256);
}

void path_exclude_check_clear(struct path_exclude_check *check)
{
        strbuf_release(&check->path);
}

/*
 * For each subdirectory in name, starting with the top-most, checks
 * to see if that subdirectory is excluded, and if so, returns the
 * corresponding exclude structure.  Otherwise, checks whether name
 * itself (which is presumably a file) is excluded.
 *
 * A path to a directory known to be excluded is left in check->path to
 * optimize for repeated checks for files in the same excluded directory.
 */
struct exclude *last_exclude_matching_path(struct path_exclude_check *check,
                                           const char *name, int namelen,
                                           int *dtype)
{
        int i;
        struct strbuf *path = &check->path;
        struct exclude *exclude;

        /*
         * we allow the caller to pass namelen as an optimization; it
         * must match the length of the name, as we eventually call
         * is_excluded() on the whole name string.
         */
        if (namelen < 0)
                namelen = strlen(name);

        /*
         * If path is non-empty, and name is equal to path or a
         * subdirectory of path, name should be excluded, because
         * it's inside a directory which is already known to be
         * excluded and was previously left in check->path.
         */
        if (path->len &&
            path->len <= namelen &&
            !memcmp(name, path->buf, path->len) &&
            (!name[path->len] || name[path->len] == '/'))
                return check->exclude;

        strbuf_setlen(path, 0);
        for (i = 0; name[i]; i++) {
                int ch = name[i];

                if (ch == '/') {
                        int dt = DT_DIR;
                        exclude = last_exclude_matching(check->dir,
                                                        path->buf, &dt);
                        if (exclude) {
                                check->exclude = exclude;
                                return exclude;
                        }
                }
                strbuf_addch(path, ch);
        }

        /* An entry in the index; cannot be a directory with subentries */
        strbuf_setlen(path, 0);

        return last_exclude_matching(check->dir, name, dtype);
}

/*
 * Is this name excluded?  This is for a caller like show_files() that
 * do not honor directory hierarchy and iterate through paths that are
 * possibly in an ignored directory.
 */
int is_path_excluded(struct path_exclude_check *check,
                  const char *name, int namelen, int *dtype)
{
        struct exclude *exclude =
                last_exclude_matching_path(check, name, namelen, dtype);
        if (exclude)
                return exclude->flags & EXC_FLAG_NEGATIVE ? 0 : 1;
        return 0;
}

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

        ent = xmalloc(sizeof(*ent) + len + 1);
        ent->len = len;
        memcpy(ent->name, pathname, len);
        ent->name[len] = 0;
        return ent;
}

static struct dir_entry *dir_add_name(struct dir_struct *dir, const char *pathname, int len)
{
        if (cache_name_exists(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, const char *pathname, int len)
{
        if (!cache_name_is_other(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 stored index to look up
 * the directory name; instead, use the case insensitive
 * name hash.
 */
static enum exist_status directory_exists_in_index_icase(const char *dirname, int len)
{
        struct cache_entry *ce = index_name_exists(&the_index, dirname, len + 1, ignore_case);
        unsigned char endchar;

        if (!ce)
                return index_nonexistent;
        endchar = ce->name[len];

        /*
         * The cache_entry structure returned will contain this dirname
         * and possibly additional path components.
         */
        if (endchar == '/')
                return index_directory;

        /*
         * If there are no additional path components, then this cache_entry
         * represents a submodule.  Submodules, despite being directories,
         * are stored in the cache without a closing slash.
         */
        if (!endchar && S_ISGITLINK(ce->ce_mode))
                return index_gitdir;

        /* This should never be hit, but it exists just in case. */
        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(const char *dirname, int len)
{
        int pos;

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

        pos = cache_name_pos(dirname, len);
        if (pos < 0)
                pos = -pos-1;
        while (pos < active_nr) {
                struct cache_entry *ce = active_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 and the directory is empty, in which case
 *      we just ignore it entirely.
 *      if we are looking for ignored directories, look if it
 *      contains only ignored files to decide if it must be shown as
 *      ignored or not.
 *  (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.
 */
enum directory_treatment {
        show_directory,
        ignore_directory,
        recurse_into_directory
};

static enum directory_treatment treat_directory(struct dir_struct *dir,
        const char *dirname, int len, int exclude,
        const struct path_simplify *simplify)
{
        /* The "len-1" is to strip the final '/' */
        switch (directory_exists_in_index(dirname, len-1)) {
        case index_directory:
                return recurse_into_directory;

        case index_gitdir:
                if (dir->flags & DIR_SHOW_OTHER_DIRECTORIES)
                        return ignore_directory;
                return show_directory;

        case index_nonexistent:
                if (dir->flags & DIR_SHOW_OTHER_DIRECTORIES)
                        break;
                if (!(dir->flags & DIR_NO_GITLINKS)) {
                        unsigned char sha1[20];
                        if (resolve_gitlink_ref(dirname, "HEAD", sha1) == 0)
                                return show_directory;
                }
                return recurse_into_directory;
        }

        /* This is the "show_other_directories" case */

        /* might be a sub directory in an excluded directory */
        if (!exclude) {
                struct path_exclude_check check;
                int dt = DT_DIR;
                path_exclude_check_init(&check, dir);
                exclude = is_path_excluded(&check, dirname, len, &dt);
                path_exclude_check_clear(&check);
        }

        /*
         * We are looking for ignored files and our directory is not ignored,
         * check if it contains untracked files (i.e. is listed as untracked)
         */
        if ((dir->flags & DIR_SHOW_IGNORED) && !exclude) {
                int ignored;
                dir->flags &= ~DIR_SHOW_IGNORED;
                ignored = read_directory_recursive(dir, dirname, len, 1, simplify);
                dir->flags |= DIR_SHOW_IGNORED;

                if (ignored)
                        return ignore_directory;
        }

        if (!(dir->flags & DIR_HIDE_EMPTY_DIRECTORIES))
                return show_directory;
        if (!read_directory_recursive(dir, dirname, len, 1, simplify))
                return ignore_directory;
        return show_directory;
}

/*
 * Decide what to do when we find a file while traversing the
 * filesystem. Mostly two cases:
 *
 *  1. We are looking for ignored files
 *   (a) File is ignored, include it
 *   (b) File is in ignored path, include it
 *   (c) File is not ignored, exclude it
 *
 *  2. Other scenarios, include the file if not excluded
 *
 * Return 1 for exclude, 0 for include.
 */
static int treat_file(struct dir_struct *dir, struct strbuf *path, int exclude, int *dtype)
{
        struct path_exclude_check check;
        int exclude_file = 0;

        /* Always exclude indexed files */
        if (index_name_exists(&the_index, path->buf, path->len, ignore_case))
                return 1;

        if (exclude)
                exclude_file = !(dir->flags & DIR_SHOW_IGNORED);
        else if (dir->flags & DIR_SHOW_IGNORED) {
                path_exclude_check_init(&check, dir);

                if (!is_path_excluded(&check, path->buf, path->len, dtype))
                        exclude_file = 1;

                path_exclude_check_clear(&check);
        }

        return exclude_file;
}

/*
 * 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 path_simplify *simplify)
{
        if (simplify) {
                for (;;) {
                        const char *match = simplify->path;
                        int len = simplify->len;

                        if (!match)
                                break;
                        if (len > pathlen)
                                len = pathlen;
                        if (!memcmp(path, match, len))
                                return 0;
                        simplify++;
                }
                return 1;
        }
        return 0;
}

/*
 * 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 len,
                const struct path_simplify *simplify)
{
        if (simplify) {
                for (; simplify->path; simplify++) {
                        if (len == simplify->len
                            && !memcmp(path, simplify->path, len))
                                return 1;
                        if (len < simplify->len
                            && simplify->path[len] == '/'
                            && !memcmp(path, simplify->path, len))
                                return 1;
                }
        }
        return 0;
}

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

        ce = cache_name_exists(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 = cache_name_pos(path, len);
        if (pos >= 0)
                return DT_UNKNOWN;
        pos = -pos-1;
        while (pos < active_nr) {
                ce = active_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 get_dtype(struct dirent *de, const char *path, int len)
{
        int dtype = de ? DTYPE(de) : DT_UNKNOWN;
        struct stat st;

        if (dtype != DT_UNKNOWN)
                return dtype;
        dtype = get_index_dtype(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;
}

enum path_treatment {
        path_ignored,
        path_handled,
        path_recurse
};

static enum path_treatment treat_one_path(struct dir_struct *dir,
                                          struct strbuf *path,
                                          const struct path_simplify *simplify,
                                          int dtype, struct dirent *de)
{
        int exclude = is_excluded(dir, path->buf, &dtype);
        if (exclude && (dir->flags & DIR_COLLECT_IGNORED)
            && exclude_matches_pathspec(path->buf, path->len, simplify))
                dir_add_ignored(dir, path->buf, path->len);

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

        if (dtype == DT_UNKNOWN)
                dtype = get_dtype(de, path->buf, path->len);

        switch (dtype) {
        default:
                return path_ignored;
        case DT_DIR:
                strbuf_addch(path, '/');
                switch (treat_directory(dir, path->buf, path->len, exclude, simplify)) {
                case show_directory:
                        break;
                case recurse_into_directory:
                        return path_recurse;
                case ignore_directory:
                        return path_ignored;
                }
                break;
        case DT_REG:
        case DT_LNK:
                switch (treat_file(dir, path, exclude, &dtype)) {
                case 1:
                        return path_ignored;
                default:
                        break;
                }
        }
        return path_handled;
}

static enum path_treatment treat_path(struct dir_struct *dir,
                                      struct dirent *de,
                                      struct strbuf *path,
                                      int baselen,
                                      const struct path_simplify *simplify)
{
        int dtype;

        if (is_dot_or_dotdot(de->d_name) || !strcmp(de->d_name, ".git"))
                return path_ignored;
        strbuf_setlen(path, baselen);
        strbuf_addstr(path, de->d_name);
        if (simplify_away(path->buf, path->len, simplify))
                return path_ignored;

        dtype = DTYPE(de);
        return treat_one_path(dir, path, simplify, dtype, de);
}

/*
 * 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.
 */
static int read_directory_recursive(struct dir_struct *dir,
                                    const char *base, int baselen,
                                    int check_only,
                                    const struct path_simplify *simplify)
{
        DIR *fdir;
        int contents = 0;
        struct dirent *de;
        struct strbuf path = STRBUF_INIT;

        strbuf_add(&path, base, baselen);

        fdir = opendir(path.len ? path.buf : ".");
        if (!fdir)
                goto out;

        while ((de = readdir(fdir)) != NULL) {
                switch (treat_path(dir, de, &path, baselen, simplify)) {
                case path_recurse:
                        contents += read_directory_recursive(dir, path.buf,
                                path.len, check_only, simplify);
                        continue;
                case path_ignored:
                        continue;
                case path_handled:
                        break;
                }
                contents++;
                if (check_only)
                        break;
                dir_add_name(dir, path.buf, path.len);
        }
        closedir(fdir);
 out:
        strbuf_release(&path);

        return contents;
}

static int cmp_name(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 cache_name_compare(e1->name, e1->len,
                                  e2->name, e2->len);
}

static struct path_simplify *create_simplify(const char **pathspec)
{
        int nr, alloc = 0;
        struct path_simplify *simplify = NULL;

        if (!pathspec)
                return NULL;

        for (nr = 0 ; ; nr++) {
                const char *match;
                if (nr >= alloc) {
                        alloc = alloc_nr(alloc);
                        simplify = xrealloc(simplify, alloc * sizeof(*simplify));
                }
                match = *pathspec++;
                if (!match)
                        break;
                simplify[nr].path = match;
                simplify[nr].len = simple_length(match);
        }
        simplify[nr].path = NULL;
        simplify[nr].len = 0;
        return simplify;
}

static void free_simplify(struct path_simplify *simplify)
{
        free(simplify);
}

static int treat_leading_path(struct dir_struct *dir,
                              const char *path, int len,
                              const struct path_simplify *simplify)
{
        struct strbuf sb = STRBUF_INIT;
        int baselen, rc = 0;
        const char *cp;
        int old_flags = dir->flags;

        while (len && path[len - 1] == '/')
                len--;
        if (!len)
                return 1;
        baselen = 0;
        dir->flags &= ~DIR_SHOW_OTHER_DIRECTORIES;
        while (1) {
                cp = path + baselen + !!baselen;
                cp = memchr(cp, '/', path + len - cp);
                if (!cp)
                        baselen = len;
                else
                        baselen = cp - path;
                strbuf_setlen(&sb, 0);
                strbuf_add(&sb, path, baselen);
                if (!is_directory(sb.buf))
                        break;
                if (simplify_away(sb.buf, sb.len, simplify))
                        break;
                if (treat_one_path(dir, &sb, simplify,
                                   DT_DIR, NULL) == path_ignored)
                        break; /* do not recurse into it */
                if (len <= baselen) {
                        rc = 1;
                        break; /* finished checking */
                }
        }
        strbuf_release(&sb);
        dir->flags = old_flags;
        return rc;
}

int read_directory(struct dir_struct *dir, const char *path, int len, const char **pathspec)
{
        struct path_simplify *simplify;

        if (has_symlink_leading_path(path, len))
                return dir->nr;

        simplify = create_simplify(pathspec);
        if (!len || treat_leading_path(dir, path, len, simplify))
                read_directory_recursive(dir, path, len, 0, simplify);
        free_simplify(simplify);
        qsort(dir->entries, dir->nr, sizeof(struct dir_entry *), cmp_name);
        qsort(dir->ignored, dir->ignored_nr, sizeof(struct dir_entry *), cmp_name);
        return dir->nr;
}

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

/*
 * 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 && *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[PATH_MAX];
        if (!dir)
                return 0;
        if (!getcwd(cwd, sizeof(cwd)))
                die_errno("can't find the current directory");
        return dir_inside_of(cwd, dir) >= 0;
}

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);
        unsigned char submodule_head[20];

        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) {
                /* an empty dir could be removed even if it is unreadble */
                if (!keep_toplevel)
                        return rmdir(path->buf);
                else
                        return -1;
        }
        if (path->buf[original_len - 1] != '/')
                strbuf_addch(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))
                        ; /* fall thru */
                else if (S_ISDIR(st.st_mode)) {
                        if (!remove_dir_recurse(path, flag, &kept_down))
                                continue; /* happy */
                } else if (!only_empty && !unlink(path->buf))
                        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);
        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);
}

void setup_standard_excludes(struct dir_struct *dir)
{
        const char *path;
        char *xdg_path;

        dir->exclude_per_dir = ".gitignore";
        path = git_path("info/exclude");
        if (!excludes_file) {
                home_config_paths(NULL, &xdg_path, "ignore");
                excludes_file = xdg_path;
        }
        if (!access_or_warn(path, R_OK))
                add_excludes_from_file(dir, path);
        if (excludes_file && !access_or_warn(excludes_file, R_OK))
                add_excludes_from_file(dir, excludes_file);
}

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

        if (unlink(name) && errno != ENOENT && errno != ENOTDIR)
                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;
}

static int pathspec_item_cmp(const void *a_, const void *b_)
{
        struct pathspec_item *a, *b;

        a = (struct pathspec_item *)a_;
        b = (struct pathspec_item *)b_;
        return strcmp(a->match, b->match);
}

int init_pathspec(struct pathspec *pathspec, const char **paths)
{
        const char **p = paths;
        int i;

        memset(pathspec, 0, sizeof(*pathspec));
        if (!p)
                return 0;
        while (*p)
                p++;
        pathspec->raw = paths;
        pathspec->nr = p - paths;
        if (!pathspec->nr)
                return 0;

        pathspec->items = xmalloc(sizeof(struct pathspec_item)*pathspec->nr);
        for (i = 0; i < pathspec->nr; i++) {
                struct pathspec_item *item = pathspec->items+i;
                const char *path = paths[i];

                item->match = path;
                item->len = strlen(path);
                item->flags = 0;
                if (limit_pathspec_to_literal()) {
                        item->nowildcard_len = item->len;
                } else {
                        item->nowildcard_len = simple_length(path);
                        if (item->nowildcard_len < item->len) {
                                pathspec->has_wildcard = 1;
                                if (path[item->nowildcard_len] == '*' &&
                                    no_wildcard(path + item->nowildcard_len + 1))
                                        item->flags |= PATHSPEC_ONESTAR;
                        }
                }
        }

        qsort(pathspec->items, pathspec->nr,
              sizeof(struct pathspec_item), pathspec_item_cmp);

        return 0;
}

void free_pathspec(struct pathspec *pathspec)
{
        free(pathspec->items);
        pathspec->items = NULL;
}

int limit_pathspec_to_literal(void)
{
        static int flag = -1;
        if (flag < 0)
                flag = git_env_bool(GIT_LITERAL_PATHSPECS_ENVIRONMENT, 0);
        return flag;
}

/*
 * 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 exclude_list *el;
        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++) {
                        el = &group->el[j];
                        if (i == EXC_DIRS)
                                free((char *)el->src);
                        clear_exclude_list(el);
                }
                free(group->el);
        }

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