transport: deep-copy object-filter struct for fetch-pack

[git/debian.git] / tree-walk.c

#include "cache.h"
#include "tree-walk.h"
#include "dir.h"
#include "object-store.h"
#include "tree.h"
#include "pathspec.h"
#include "json-writer.h"

static const char *get_mode(const char *str, unsigned int *modep)
{
        unsigned char c;
        unsigned int mode = 0;

        if (*str == ' ')
                return NULL;

        while ((c = *str++) != ' ') {
                if (c < '0' || c > '7')
                        return NULL;
                mode = (mode << 3) + (c - '0');
        }
        *modep = mode;
        return str;
}

static int decode_tree_entry(struct tree_desc *desc, const char *buf, unsigned long size, struct strbuf *err)
{
        const char *path;
        unsigned int mode, len;
        const unsigned hashsz = the_hash_algo->rawsz;

        if (size < hashsz + 3 || buf[size - (hashsz + 1)]) {
                strbuf_addstr(err, _("too-short tree object"));
                return -1;
        }

        path = get_mode(buf, &mode);
        if (!path) {
                strbuf_addstr(err, _("malformed mode in tree entry"));
                return -1;
        }
        if (!*path) {
                strbuf_addstr(err, _("empty filename in tree entry"));
                return -1;
        }
        len = strlen(path) + 1;

        /* Initialize the descriptor entry */
        desc->entry.path = path;
        desc->entry.mode = (desc->flags & TREE_DESC_RAW_MODES) ? mode : canon_mode(mode);
        desc->entry.pathlen = len - 1;
        oidread(&desc->entry.oid, (const unsigned char *)path + len);

        return 0;
}

static int init_tree_desc_internal(struct tree_desc *desc, const void *buffer,
                                   unsigned long size, struct strbuf *err,
                                   enum tree_desc_flags flags)
{
        desc->buffer = buffer;
        desc->size = size;
        desc->flags = flags;
        if (size)
                return decode_tree_entry(desc, buffer, size, err);
        return 0;
}

void init_tree_desc(struct tree_desc *desc, const void *buffer, unsigned long size)
{
        struct strbuf err = STRBUF_INIT;
        if (init_tree_desc_internal(desc, buffer, size, &err, 0))
                die("%s", err.buf);
        strbuf_release(&err);
}

int init_tree_desc_gently(struct tree_desc *desc, const void *buffer, unsigned long size,
                          enum tree_desc_flags flags)
{
        struct strbuf err = STRBUF_INIT;
        int result = init_tree_desc_internal(desc, buffer, size, &err, flags);
        if (result)
                error("%s", err.buf);
        strbuf_release(&err);
        return result;
}

void *fill_tree_descriptor(struct repository *r,
                           struct tree_desc *desc,
                           const struct object_id *oid)
{
        unsigned long size = 0;
        void *buf = NULL;

        if (oid) {
                buf = read_object_with_reference(r, oid, OBJ_TREE, &size, NULL);
                if (!buf)
                        die("unable to read tree %s", oid_to_hex(oid));
        }
        init_tree_desc(desc, buf, size);
        return buf;
}

static void entry_clear(struct name_entry *a)
{
        memset(a, 0, sizeof(*a));
}

static void entry_extract(struct tree_desc *t, struct name_entry *a)
{
        *a = t->entry;
}

static int update_tree_entry_internal(struct tree_desc *desc, struct strbuf *err)
{
        const void *buf = desc->buffer;
        const unsigned char *end = (const unsigned char *)desc->entry.path + desc->entry.pathlen + 1 + the_hash_algo->rawsz;
        unsigned long size = desc->size;
        unsigned long len = end - (const unsigned char *)buf;

        if (size < len)
                die(_("too-short tree file"));
        buf = end;
        size -= len;
        desc->buffer = buf;
        desc->size = size;
        if (size)
                return decode_tree_entry(desc, buf, size, err);
        return 0;
}

void update_tree_entry(struct tree_desc *desc)
{
        struct strbuf err = STRBUF_INIT;
        if (update_tree_entry_internal(desc, &err))
                die("%s", err.buf);
        strbuf_release(&err);
}

int update_tree_entry_gently(struct tree_desc *desc)
{
        struct strbuf err = STRBUF_INIT;
        if (update_tree_entry_internal(desc, &err)) {
                error("%s", err.buf);
                strbuf_release(&err);
                /* Stop processing this tree after error */
                desc->size = 0;
                return -1;
        }
        strbuf_release(&err);
        return 0;
}

int tree_entry(struct tree_desc *desc, struct name_entry *entry)
{
        if (!desc->size)
                return 0;

        *entry = desc->entry;
        update_tree_entry(desc);
        return 1;
}

int tree_entry_gently(struct tree_desc *desc, struct name_entry *entry)
{
        if (!desc->size)
                return 0;

        *entry = desc->entry;
        if (update_tree_entry_gently(desc))
                return 0;
        return 1;
}

static int traverse_trees_atexit_registered;
static int traverse_trees_count;
static int traverse_trees_cur_depth;
static int traverse_trees_max_depth;

static void trace2_traverse_trees_statistics_atexit(void)
{
        struct json_writer jw = JSON_WRITER_INIT;

        jw_object_begin(&jw, 0);
        jw_object_intmax(&jw, "traverse_trees_count", traverse_trees_count);
        jw_object_intmax(&jw, "traverse_trees_max_depth", traverse_trees_max_depth);
        jw_end(&jw);

        trace2_data_json("traverse_trees", the_repository, "statistics", &jw);

        jw_release(&jw);
}

void setup_traverse_info(struct traverse_info *info, const char *base)
{
        size_t pathlen = strlen(base);
        static struct traverse_info dummy;

        memset(info, 0, sizeof(*info));
        if (pathlen && base[pathlen-1] == '/')
                pathlen--;
        info->pathlen = pathlen ? pathlen + 1 : 0;
        info->name = base;
        info->namelen = pathlen;
        if (pathlen)
                info->prev = &dummy;

        if (trace2_is_enabled() && !traverse_trees_atexit_registered) {
                atexit(trace2_traverse_trees_statistics_atexit);
                traverse_trees_atexit_registered = 1;
        }
}

char *make_traverse_path(char *path, size_t pathlen,
                         const struct traverse_info *info,
                         const char *name, size_t namelen)
{
        /* Always points to the end of the name we're about to add */
        size_t pos = st_add(info->pathlen, namelen);

        if (pos >= pathlen)
                BUG("too small buffer passed to make_traverse_path");

        path[pos] = 0;
        for (;;) {
                if (pos < namelen)
                        BUG("traverse_info pathlen does not match strings");
                pos -= namelen;
                memcpy(path + pos, name, namelen);

                if (!pos)
                        break;
                path[--pos] = '/';

                if (!info)
                        BUG("traverse_info ran out of list items");
                name = info->name;
                namelen = info->namelen;
                info = info->prev;
        }
        return path;
}

void strbuf_make_traverse_path(struct strbuf *out,
                               const struct traverse_info *info,
                               const char *name, size_t namelen)
{
        size_t len = traverse_path_len(info, namelen);

        strbuf_grow(out, len);
        make_traverse_path(out->buf + out->len, out->alloc - out->len,
                           info, name, namelen);
        strbuf_setlen(out, out->len + len);
}

struct tree_desc_skip {
        struct tree_desc_skip *prev;
        const void *ptr;
};

struct tree_desc_x {
        struct tree_desc d;
        struct tree_desc_skip *skip;
};

static int check_entry_match(const char *a, int a_len, const char *b, int b_len)
{
        /*
         * The caller wants to pick *a* from a tree or nothing.
         * We are looking at *b* in a tree.
         *
         * (0) If a and b are the same name, we are trivially happy.
         *
         * There are three possibilities where *a* could be hiding
         * behind *b*.
         *
         * (1) *a* == "t",   *b* == "ab"  i.e. *b* sorts earlier than *a* no
         *                                matter what.
         * (2) *a* == "t",   *b* == "t-2" and "t" is a subtree in the tree;
         * (3) *a* == "t-2", *b* == "t"   and "t-2" is a blob in the tree.
         *
         * Otherwise we know *a* won't appear in the tree without
         * scanning further.
         */

        int cmp = name_compare(a, a_len, b, b_len);

        /* Most common case first -- reading sync'd trees */
        if (!cmp)
                return cmp;

        if (0 < cmp) {
                /* a comes after b; it does not matter if it is case (3)
                if (b_len < a_len && !memcmp(a, b, b_len) && a[b_len] < '/')
                        return 1;
                */
                return 1; /* keep looking */
        }

        /* b comes after a; are we looking at case (2)? */
        if (a_len < b_len && !memcmp(a, b, a_len) && b[a_len] < '/')
                return 1; /* keep looking */

        return -1; /* a cannot appear in the tree */
}

/*
 * From the extended tree_desc, extract the first name entry, while
 * paying attention to the candidate "first" name.  Most importantly,
 * when looking for an entry, if there are entries that sorts earlier
 * in the tree object representation than that name, skip them and
 * process the named entry first.  We will remember that we haven't
 * processed the first entry yet, and in the later call skip the
 * entry we processed early when update_extended_entry() is called.
 *
 * E.g. if the underlying tree object has these entries:
 *
 *    blob    "t-1"
 *    blob    "t-2"
 *    tree    "t"
 *    blob    "t=1"
 *
 * and the "first" asks for "t", remember that we still need to
 * process "t-1" and "t-2" but extract "t".  After processing the
 * entry "t" from this call, the caller will let us know by calling
 * update_extended_entry() that we can remember "t" has been processed
 * already.
 */

static void extended_entry_extract(struct tree_desc_x *t,
                                   struct name_entry *a,
                                   const char *first,
                                   int first_len)
{
        const char *path;
        int len;
        struct tree_desc probe;
        struct tree_desc_skip *skip;

        /*
         * Extract the first entry from the tree_desc, but skip the
         * ones that we already returned in earlier rounds.
         */
        while (1) {
                if (!t->d.size) {
                        entry_clear(a);
                        break; /* not found */
                }
                entry_extract(&t->d, a);
                for (skip = t->skip; skip; skip = skip->prev)
                        if (a->path == skip->ptr)
                                break; /* found */
                if (!skip)
                        break;
                /* We have processed this entry already. */
                update_tree_entry(&t->d);
        }

        if (!first || !a->path)
                return;

        /*
         * The caller wants "first" from this tree, or nothing.
         */
        path = a->path;
        len = tree_entry_len(a);
        switch (check_entry_match(first, first_len, path, len)) {
        case -1:
                entry_clear(a);
        case 0:
                return;
        default:
                break;
        }

        /*
         * We need to look-ahead -- we suspect that a subtree whose
         * name is "first" may be hiding behind the current entry "path".
         */
        probe = t->d;
        while (probe.size) {
                entry_extract(&probe, a);
                path = a->path;
                len = tree_entry_len(a);
                switch (check_entry_match(first, first_len, path, len)) {
                case -1:
                        entry_clear(a);
                case 0:
                        return;
                default:
                        update_tree_entry(&probe);
                        break;
                }
                /* keep looking */
        }
        entry_clear(a);
}

static void update_extended_entry(struct tree_desc_x *t, struct name_entry *a)
{
        if (t->d.entry.path == a->path) {
                update_tree_entry(&t->d);
        } else {
                /* we have returned this entry early */
                struct tree_desc_skip *skip = xmalloc(sizeof(*skip));
                skip->ptr = a->path;
                skip->prev = t->skip;
                t->skip = skip;
        }
}

static void free_extended_entry(struct tree_desc_x *t)
{
        struct tree_desc_skip *p, *s;

        for (s = t->skip; s; s = p) {
                p = s->prev;
                free(s);
        }
}

static inline int prune_traversal(struct index_state *istate,
                                  struct name_entry *e,
                                  struct traverse_info *info,
                                  struct strbuf *base,
                                  int still_interesting)
{
        if (!info->pathspec || still_interesting == 2)
                return 2;
        if (still_interesting < 0)
                return still_interesting;
        return tree_entry_interesting(istate, e, base,
                                      0, info->pathspec);
}

int traverse_trees(struct index_state *istate,
                   int n, struct tree_desc *t,
                   struct traverse_info *info)
{
        int error = 0;
        struct name_entry entry[MAX_TRAVERSE_TREES];
        int i;
        struct tree_desc_x tx[ARRAY_SIZE(entry)];
        struct strbuf base = STRBUF_INIT;
        int interesting = 1;
        char *traverse_path;

        traverse_trees_count++;
        traverse_trees_cur_depth++;

        if (traverse_trees_cur_depth > traverse_trees_max_depth)
                traverse_trees_max_depth = traverse_trees_cur_depth;

        if (n >= ARRAY_SIZE(entry))
                BUG("traverse_trees() called with too many trees (%d)", n);

        for (i = 0; i < n; i++) {
                tx[i].d = t[i];
                tx[i].skip = NULL;
        }

        if (info->prev) {
                strbuf_make_traverse_path(&base, info->prev,
                                          info->name, info->namelen);
                strbuf_addch(&base, '/');
                traverse_path = xstrndup(base.buf, base.len);
        } else {
                traverse_path = xstrndup(info->name, info->pathlen);
        }
        info->traverse_path = traverse_path;
        for (;;) {
                int trees_used;
                unsigned long mask, dirmask;
                const char *first = NULL;
                int first_len = 0;
                struct name_entry *e = NULL;
                int len;

                for (i = 0; i < n; i++) {
                        e = entry + i;
                        extended_entry_extract(tx + i, e, NULL, 0);
                }

                /*
                 * A tree may have "t-2" at the current location even
                 * though it may have "t" that is a subtree behind it,
                 * and another tree may return "t".  We want to grab
                 * all "t" from all trees to match in such a case.
                 */
                for (i = 0; i < n; i++) {
                        e = entry + i;
                        if (!e->path)
                                continue;
                        len = tree_entry_len(e);
                        if (!first) {
                                first = e->path;
                                first_len = len;
                                continue;
                        }
                        if (name_compare(e->path, len, first, first_len) < 0) {
                                first = e->path;
                                first_len = len;
                        }
                }

                if (first) {
                        for (i = 0; i < n; i++) {
                                e = entry + i;
                                extended_entry_extract(tx + i, e, first, first_len);
                                /* Cull the ones that are not the earliest */
                                if (!e->path)
                                        continue;
                                len = tree_entry_len(e);
                                if (name_compare(e->path, len, first, first_len))
                                        entry_clear(e);
                        }
                }

                /* Now we have in entry[i] the earliest name from the trees */
                mask = 0;
                dirmask = 0;
                for (i = 0; i < n; i++) {
                        if (!entry[i].path)
                                continue;
                        mask |= 1ul << i;
                        if (S_ISDIR(entry[i].mode))
                                dirmask |= 1ul << i;
                        e = &entry[i];
                }
                if (!mask)
                        break;
                interesting = prune_traversal(istate, e, info, &base, interesting);
                if (interesting < 0)
                        break;
                if (interesting) {
                        trees_used = info->fn(n, mask, dirmask, entry, info);
                        if (trees_used < 0) {
                                error = trees_used;
                                if (!info->show_all_errors)
                                        break;
                        }
                        mask &= trees_used;
                }
                for (i = 0; i < n; i++)
                        if (mask & (1ul << i))
                                update_extended_entry(tx + i, entry + i);
        }
        for (i = 0; i < n; i++)
                free_extended_entry(tx + i);
        free(traverse_path);
        info->traverse_path = NULL;
        strbuf_release(&base);

        traverse_trees_cur_depth--;
        return error;
}

struct dir_state {
        void *tree;
        unsigned long size;
        struct object_id oid;
};

static int find_tree_entry(struct repository *r, struct tree_desc *t,
                           const char *name, struct object_id *result,
                           unsigned short *mode)
{
        int namelen = strlen(name);
        while (t->size) {
                const char *entry;
                struct object_id oid;
                int entrylen, cmp;

                oidcpy(&oid, tree_entry_extract(t, &entry, mode));
                entrylen = tree_entry_len(&t->entry);
                update_tree_entry(t);
                if (entrylen > namelen)
                        continue;
                cmp = memcmp(name, entry, entrylen);
                if (cmp > 0)
                        continue;
                if (cmp < 0)
                        break;
                if (entrylen == namelen) {
                        oidcpy(result, &oid);
                        return 0;
                }
                if (name[entrylen] != '/')
                        continue;
                if (!S_ISDIR(*mode))
                        break;
                if (++entrylen == namelen) {
                        oidcpy(result, &oid);
                        return 0;
                }
                return get_tree_entry(r, &oid, name + entrylen, result, mode);
        }
        return -1;
}

int get_tree_entry(struct repository *r,
                   const struct object_id *tree_oid,
                   const char *name,
                   struct object_id *oid,
                   unsigned short *mode)
{
        int retval;
        void *tree;
        unsigned long size;
        struct object_id root;

        tree = read_object_with_reference(r, tree_oid, OBJ_TREE, &size, &root);
        if (!tree)
                return -1;

        if (name[0] == '\0') {
                oidcpy(oid, &root);
                free(tree);
                return 0;
        }

        if (!size) {
                retval = -1;
        } else {
                struct tree_desc t;
                init_tree_desc(&t, tree, size);
                retval = find_tree_entry(r, &t, name, oid, mode);
        }
        free(tree);
        return retval;
}

/*
 * This is Linux's built-in max for the number of symlinks to follow.
 * That limit, of course, does not affect git, but it's a reasonable
 * choice.
 */
#define GET_TREE_ENTRY_FOLLOW_SYMLINKS_MAX_LINKS 40

/**
 * Find a tree entry by following symlinks in tree_sha (which is
 * assumed to be the root of the repository).  In the event that a
 * symlink points outside the repository (e.g. a link to /foo or a
 * root-level link to ../foo), the portion of the link which is
 * outside the repository will be returned in result_path, and *mode
 * will be set to 0.  It is assumed that result_path is uninitialized.
 * If there are no symlinks, or the end result of the symlink chain
 * points to an object inside the repository, result will be filled in
 * with the sha1 of the found object, and *mode will hold the mode of
 * the object.
 *
 * See the code for enum get_oid_result for a description of
 * the return values.
 */
enum get_oid_result get_tree_entry_follow_symlinks(struct repository *r,
                struct object_id *tree_oid, const char *name,
                struct object_id *result, struct strbuf *result_path,
                unsigned short *mode)
{
        int retval = MISSING_OBJECT;
        struct dir_state *parents = NULL;
        size_t parents_alloc = 0;
        size_t i, parents_nr = 0;
        struct object_id current_tree_oid;
        struct strbuf namebuf = STRBUF_INIT;
        struct tree_desc t;
        int follows_remaining = GET_TREE_ENTRY_FOLLOW_SYMLINKS_MAX_LINKS;

        init_tree_desc(&t, NULL, 0UL);
        strbuf_addstr(&namebuf, name);
        oidcpy(&current_tree_oid, tree_oid);

        while (1) {
                int find_result;
                char *first_slash;
                char *remainder = NULL;

                if (!t.buffer) {
                        void *tree;
                        struct object_id root;
                        unsigned long size;
                        tree = read_object_with_reference(r,
                                                          &current_tree_oid,
                                                          OBJ_TREE, &size,
                                                          &root);
                        if (!tree)
                                goto done;

                        ALLOC_GROW(parents, parents_nr + 1, parents_alloc);
                        parents[parents_nr].tree = tree;
                        parents[parents_nr].size = size;
                        oidcpy(&parents[parents_nr].oid, &root);
                        parents_nr++;

                        if (namebuf.buf[0] == '\0') {
                                oidcpy(result, &root);
                                retval = FOUND;
                                goto done;
                        }

                        if (!size)
                                goto done;

                        /* descend */
                        init_tree_desc(&t, tree, size);
                }

                /* Handle symlinks to e.g. a//b by removing leading slashes */
                while (namebuf.buf[0] == '/') {
                        strbuf_remove(&namebuf, 0, 1);
                }

                /* Split namebuf into a first component and a remainder */
                if ((first_slash = strchr(namebuf.buf, '/'))) {
                        *first_slash = 0;
                        remainder = first_slash + 1;
                }

                if (!strcmp(namebuf.buf, "..")) {
                        struct dir_state *parent;
                        /*
                         * We could end up with .. in the namebuf if it
                         * appears in a symlink.
                         */

                        if (parents_nr == 1) {
                                if (remainder)
                                        *first_slash = '/';
                                strbuf_add(result_path, namebuf.buf,
                                           namebuf.len);
                                *mode = 0;
                                retval = FOUND;
                                goto done;
                        }
                        parent = &parents[parents_nr - 1];
                        free(parent->tree);
                        parents_nr--;
                        parent = &parents[parents_nr - 1];
                        init_tree_desc(&t, parent->tree, parent->size);
                        strbuf_remove(&namebuf, 0, remainder ? 3 : 2);
                        continue;
                }

                /* We could end up here via a symlink to dir/.. */
                if (namebuf.buf[0] == '\0') {
                        oidcpy(result, &parents[parents_nr - 1].oid);
                        retval = FOUND;
                        goto done;
                }

                /* Look up the first (or only) path component in the tree. */
                find_result = find_tree_entry(r, &t, namebuf.buf,
                                              &current_tree_oid, mode);
                if (find_result) {
                        goto done;
                }

                if (S_ISDIR(*mode)) {
                        if (!remainder) {
                                oidcpy(result, &current_tree_oid);
                                retval = FOUND;
                                goto done;
                        }
                        /* Descend the tree */
                        t.buffer = NULL;
                        strbuf_remove(&namebuf, 0,
                                      1 + first_slash - namebuf.buf);
                } else if (S_ISREG(*mode)) {
                        if (!remainder) {
                                oidcpy(result, &current_tree_oid);
                                retval = FOUND;
                        } else {
                                retval = NOT_DIR;
                        }
                        goto done;
                } else if (S_ISLNK(*mode)) {
                        /* Follow a symlink */
                        unsigned long link_len;
                        size_t len;
                        char *contents, *contents_start;
                        struct dir_state *parent;
                        enum object_type type;

                        if (follows_remaining-- == 0) {
                                /* Too many symlinks followed */
                                retval = SYMLINK_LOOP;
                                goto done;
                        }

                        /*
                         * At this point, we have followed at a least
                         * one symlink, so on error we need to report this.
                         */
                        retval = DANGLING_SYMLINK;

                        contents = repo_read_object_file(r,
                                                    &current_tree_oid, &type,
                                                    &link_len);

                        if (!contents)
                                goto done;

                        if (contents[0] == '/') {
                                strbuf_addstr(result_path, contents);
                                free(contents);
                                *mode = 0;
                                retval = FOUND;
                                goto done;
                        }

                        if (remainder)
                                len = first_slash - namebuf.buf;
                        else
                                len = namebuf.len;

                        contents_start = contents;

                        parent = &parents[parents_nr - 1];
                        init_tree_desc(&t, parent->tree, parent->size);
                        strbuf_splice(&namebuf, 0, len,
                                      contents_start, link_len);
                        if (remainder)
                                namebuf.buf[link_len] = '/';
                        free(contents);
                }
        }
done:
        for (i = 0; i < parents_nr; i++)
                free(parents[i].tree);
        free(parents);

        strbuf_release(&namebuf);
        return retval;
}

static int match_entry(const struct pathspec_item *item,
                       const struct name_entry *entry, int pathlen,
                       const char *match, int matchlen,
                       enum interesting *never_interesting)
{
        int m = -1; /* signals that we haven't called strncmp() */

        if (item->magic & PATHSPEC_ICASE)
                /*
                 * "Never interesting" trick requires exact
                 * matching. We could do something clever with inexact
                 * matching, but it's trickier (and not to forget that
                 * strcasecmp is locale-dependent, at least in
                 * glibc). Just disable it for now. It can't be worse
                 * than the wildcard's codepath of '[Tt][Hi][Is][Ss]'
                 * pattern.
                 */
                *never_interesting = entry_not_interesting;
        else if (*never_interesting != entry_not_interesting) {
                /*
                 * We have not seen any match that sorts later
                 * than the current path.
                 */

                /*
                 * Does match sort strictly earlier than path
                 * with their common parts?
                 */
                m = strncmp(match, entry->path,
                            (matchlen < pathlen) ? matchlen : pathlen);
                if (m < 0)
                        return 0;

                /*
                 * If we come here even once, that means there is at
                 * least one pathspec that would sort equal to or
                 * later than the path we are currently looking at.
                 * In other words, if we have never reached this point
                 * after iterating all pathspecs, it means all
                 * pathspecs are either outside of base, or inside the
                 * base but sorts strictly earlier than the current
                 * one.  In either case, they will never match the
                 * subsequent entries.  In such a case, we initialized
                 * the variable to -1 and that is what will be
                 * returned, allowing the caller to terminate early.
                 */
                *never_interesting = entry_not_interesting;
        }

        if (pathlen > matchlen)
                return 0;

        if (matchlen > pathlen) {
                if (match[pathlen] != '/')
                        return 0;
                /*
                 * Reject non-directories as partial pathnames, except
                 * when match is a submodule with a trailing slash and
                 * nothing else (to handle 'submod/' and 'submod'
                 * uniformly).
                 */
                if (!S_ISDIR(entry->mode) &&
                    (!S_ISGITLINK(entry->mode) || matchlen > pathlen + 1))
                        return 0;
        }

        if (m == -1)
                /*
                 * we cheated and did not do strncmp(), so we do
                 * that here.
                 */
                m = ps_strncmp(item, match, entry->path, pathlen);

        /*
         * If common part matched earlier then it is a hit,
         * because we rejected the case where path is not a
         * leading directory and is shorter than match.
         */
        if (!m)
                /*
                 * match_entry does not check if the prefix part is
                 * matched case-sensitively. If the entry is a
                 * directory and part of prefix, it'll be rematched
                 * eventually by basecmp with special treatment for
                 * the prefix.
                 */
                return 1;

        return 0;
}

/* :(icase)-aware string compare */
static int basecmp(const struct pathspec_item *item,
                   const char *base, const char *match, int len)
{
        if (item->magic & PATHSPEC_ICASE) {
                int ret, n = len > item->prefix ? item->prefix : len;
                ret = strncmp(base, match, n);
                if (ret)
                        return ret;
                base += n;
                match += n;
                len -= n;
        }
        return ps_strncmp(item, base, match, len);
}

static int match_dir_prefix(const struct pathspec_item *item,
                            const char *base,
                            const char *match, int matchlen)
{
        if (basecmp(item, base, match, matchlen))
                return 0;

        /*
         * If the base is a subdirectory of a path which
         * was specified, all of them are interesting.
         */
        if (!matchlen ||
            base[matchlen] == '/' ||
            match[matchlen - 1] == '/')
                return 1;

        /* Just a random prefix match */
        return 0;
}

/*
 * Perform matching on the leading non-wildcard part of
 * pathspec. item->nowildcard_len must be greater than zero. Return
 * non-zero if base is matched.
 */
static int match_wildcard_base(const struct pathspec_item *item,
                               const char *base, int baselen,
                               int *matched)
{
        const char *match = item->match;
        /* the wildcard part is not considered in this function */
        int matchlen = item->nowildcard_len;

        if (baselen) {
                int dirlen;
                /*
                 * Return early if base is longer than the
                 * non-wildcard part but it does not match.
                 */
                if (baselen >= matchlen) {
                        *matched = matchlen;
                        return !basecmp(item, base, match, matchlen);
                }

                dirlen = matchlen;
                while (dirlen && match[dirlen - 1] != '/')
                        dirlen--;

                /*
                 * Return early if base is shorter than the
                 * non-wildcard part but it does not match. Note that
                 * base ends with '/' so we are sure it really matches
                 * directory
                 */
                if (basecmp(item, base, match, baselen))
                        return 0;
                *matched = baselen;
        } else
                *matched = 0;
        /*
         * we could have checked entry against the non-wildcard part
         * that is not in base and does similar never_interesting
         * optimization as in match_entry. For now just be happy with
         * base comparison.
         */
        return entry_interesting;
}

/*
 * Is a tree entry interesting given the pathspec we have?
 *
 * Pre-condition: either baselen == base_offset (i.e. empty path)
 * or base[baselen-1] == '/' (i.e. with trailing slash).
 */
static enum interesting do_match(struct index_state *istate,
                                 const struct name_entry *entry,
                                 struct strbuf *base, int base_offset,
                                 const struct pathspec *ps,
                                 int exclude)
{
        int i;
        int pathlen, baselen = base->len - base_offset;
        enum interesting never_interesting = ps->has_wildcard ?
                entry_not_interesting : all_entries_not_interesting;

        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 all_entries_interesting;
                return within_depth(base->buf + base_offset, baselen,
                                    !!S_ISDIR(entry->mode),
                                    ps->max_depth) ?
                        entry_interesting : entry_not_interesting;
        }

        pathlen = tree_entry_len(entry);

        for (i = ps->nr - 1; i >= 0; i--) {
                const struct pathspec_item *item = ps->items+i;
                const char *match = item->match;
                const char *base_str = base->buf + base_offset;
                int matchlen = item->len, matched = 0;

                if ((!exclude &&   item->magic & PATHSPEC_EXCLUDE) ||
                    ( exclude && !(item->magic & PATHSPEC_EXCLUDE)))
                        continue;

                if (baselen >= matchlen) {
                        /* If it doesn't match, move along... */
                        if (!match_dir_prefix(item, base_str, match, matchlen))
                                goto match_wildcards;

                        if (!ps->recursive ||
                            !(ps->magic & PATHSPEC_MAXDEPTH) ||
                            ps->max_depth == -1) {
                                if (!item->attr_match_nr)
                                        return all_entries_interesting;
                                else
                                        goto interesting;
                        }

                        if (within_depth(base_str + matchlen + 1,
                                         baselen - matchlen - 1,
                                         !!S_ISDIR(entry->mode),
                                         ps->max_depth))
                                goto interesting;
                        else
                                return entry_not_interesting;
                }

                /* Either there must be no base, or the base must match. */
                if (baselen == 0 || !basecmp(item, base_str, match, baselen)) {
                        if (match_entry(item, entry, pathlen,
                                        match + baselen, matchlen - baselen,
                                        &never_interesting))
                                goto interesting;

                        if (item->nowildcard_len < item->len) {
                                if (!git_fnmatch(item, match + baselen, entry->path,
                                                 item->nowildcard_len - baselen))
                                        goto interesting;

                                /*
                                 * Match all directories. We'll try to
                                 * match files later on.
                                 */
                                if (ps->recursive && S_ISDIR(entry->mode))
                                        return entry_interesting;

                                /*
                                 * When matching against submodules with
                                 * wildcard characters, ensure that the entry
                                 * at least matches up to the first wild
                                 * character.  More accurate matching can then
                                 * be performed in the submodule itself.
                                 */
                                if (ps->recurse_submodules &&
                                    S_ISGITLINK(entry->mode) &&
                                    !ps_strncmp(item, match + baselen,
                                                entry->path,
                                                item->nowildcard_len - baselen))
                                        goto interesting;
                        }

                        continue;
                }

match_wildcards:
                if (item->nowildcard_len == item->len)
                        continue;

                if (item->nowildcard_len &&
                    !match_wildcard_base(item, base_str, baselen, &matched))
                        continue;

                /*
                 * Concatenate base and entry->path into one and do
                 * fnmatch() on it.
                 *
                 * While we could avoid concatenation in certain cases
                 * [1], which saves a memcpy and potentially a
                 * realloc, it turns out not worth it. Measurement on
                 * linux-2.6 does not show any clear improvements,
                 * partly because of the nowildcard_len optimization
                 * in git_fnmatch(). Avoid micro-optimizations here.
                 *
                 * [1] if match_wildcard_base() says the base
                 * directory is already matched, we only need to match
                 * the rest, which is shorter so _in theory_ faster.
                 */

                strbuf_add(base, entry->path, pathlen);

                if (!git_fnmatch(item, match, base->buf + base_offset,
                                 item->nowildcard_len)) {
                        strbuf_setlen(base, base_offset + baselen);
                        goto interesting;
                }

                /*
                 * When matching against submodules with
                 * wildcard characters, ensure that the entry
                 * at least matches up to the first wild
                 * character.  More accurate matching can then
                 * be performed in the submodule itself.
                 */
                if (ps->recurse_submodules && S_ISGITLINK(entry->mode) &&
                    !ps_strncmp(item, match, base->buf + base_offset,
                                item->nowildcard_len)) {
                        strbuf_setlen(base, base_offset + baselen);
                        goto interesting;
                }

                strbuf_setlen(base, base_offset + baselen);

                /*
                 * Match all directories. We'll try to match files
                 * later on.
                 * max_depth is ignored but we may consider support it
                 * in future, see
                 * https://lore.kernel.org/git/7vmxo5l2g4.fsf@alter.siamese.dyndns.org/
                 */
                if (ps->recursive && S_ISDIR(entry->mode))
                        return entry_interesting;
                continue;
interesting:
                if (item->attr_match_nr) {
                        int ret;

                        /*
                         * Must not return all_entries_not_interesting
                         * prematurely. We do not know if all entries do not
                         * match some attributes with current attr API.
                         */
                        never_interesting = entry_not_interesting;

                        /*
                         * Consider all directories interesting (because some
                         * of those files inside may match some attributes
                         * even though the parent dir does not)
                         *
                         * FIXME: attributes _can_ match directories and we
                         * can probably return all_entries_interesting or
                         * all_entries_not_interesting here if matched.
                         */
                        if (S_ISDIR(entry->mode))
                                return entry_interesting;

                        strbuf_add(base, entry->path, pathlen);
                        ret = match_pathspec_attrs(istate, base->buf + base_offset,
                                                   base->len - base_offset, item);
                        strbuf_setlen(base, base_offset + baselen);
                        if (!ret)
                                continue;
                }
                return entry_interesting;
        }
        return never_interesting; /* No matches */
}

/*
 * Is a tree entry interesting given the pathspec we have?
 *
 * Pre-condition: either baselen == base_offset (i.e. empty path)
 * or base[baselen-1] == '/' (i.e. with trailing slash).
 */
enum interesting tree_entry_interesting(struct index_state *istate,
                                        const struct name_entry *entry,
                                        struct strbuf *base, int base_offset,
                                        const struct pathspec *ps)
{
        enum interesting positive, negative;
        positive = do_match(istate, entry, base, base_offset, ps, 0);

        /*
         * case | entry | positive | negative | result
         * -----+-------+----------+----------+-------
         *   1  |  file |   -1     |  -1..2   |  -1
         *   2  |  file |    0     |  -1..2   |   0
         *   3  |  file |    1     |   -1     |   1
         *   4  |  file |    1     |    0     |   1
         *   5  |  file |    1     |    1     |   0
         *   6  |  file |    1     |    2     |   0
         *   7  |  file |    2     |   -1     |   2
         *   8  |  file |    2     |    0     |   1
         *   9  |  file |    2     |    1     |   0
         *  10  |  file |    2     |    2     |  -1
         * -----+-------+----------+----------+-------
         *  11  |  dir  |   -1     |  -1..2   |  -1
         *  12  |  dir  |    0     |  -1..2   |   0
         *  13  |  dir  |    1     |   -1     |   1
         *  14  |  dir  |    1     |    0     |   1
         *  15  |  dir  |    1     |    1     |   1 (*)
         *  16  |  dir  |    1     |    2     |   0
         *  17  |  dir  |    2     |   -1     |   2
         *  18  |  dir  |    2     |    0     |   1
         *  19  |  dir  |    2     |    1     |   1 (*)
         *  20  |  dir  |    2     |    2     |  -1
         *
         * (*) An exclude pattern interested in a directory does not
         * necessarily mean it will exclude all of the directory. In
         * wildcard case, it can't decide until looking at individual
         * files inside. So don't write such directories off yet.
         */

        if (!(ps->magic & PATHSPEC_EXCLUDE) ||
            positive <= entry_not_interesting) /* #1, #2, #11, #12 */
                return positive;

        negative = do_match(istate, entry, base, base_offset, ps, 1);

        /* #8, #18 */
        if (positive == all_entries_interesting &&
            negative == entry_not_interesting)
                return entry_interesting;

        /* #3, #4, #7, #13, #14, #17 */
        if (negative <= entry_not_interesting)
                return positive;

        /* #15, #19 */
        if (S_ISDIR(entry->mode) &&
            positive >= entry_interesting &&
            negative == entry_interesting)
                return entry_interesting;

        if ((positive == entry_interesting &&
             negative >= entry_interesting) || /* #5, #6, #16 */
            (positive == all_entries_interesting &&
             negative == entry_interesting)) /* #9 */
                return entry_not_interesting;

        return all_entries_not_interesting; /* #10, #20 */
}