cache-tree.c

#include "cache.h"
#include "lockfile.h"
#include "tree.h"
#include "tree-walk.h"
#include "cache-tree.h"
#include "bulk-checkin.h"
#include "object-store.h"
#include "replace-object.h"
#include "promisor-remote.h"
#include "sparse-index.h"

#ifndef DEBUG_CACHE_TREE
#define DEBUG_CACHE_TREE 0
#endif

struct cache_tree *cache_tree(void)
{
	struct cache_tree *it = xcalloc(1, sizeof(struct cache_tree));
	it->entry_count = -1;
	return it;
}

void cache_tree_free(struct cache_tree **it_p)
{
	int i;
	struct cache_tree *it = *it_p;

	if (!it)
		return;
	for (i = 0; i < it->subtree_nr; i++)
		if (it->down[i]) {
			cache_tree_free(&it->down[i]->cache_tree);
			free(it->down[i]);
		}
	free(it->down);
	free(it);
	*it_p = NULL;
}

static int subtree_name_cmp(const char *one, int onelen,
			    const char *two, int twolen)
{
	if (onelen < twolen)
		return -1;
	if (twolen < onelen)
		return 1;
	return memcmp(one, two, onelen);
}

int cache_tree_subtree_pos(struct cache_tree *it, const char *path, int pathlen)
{
	struct cache_tree_sub **down = it->down;
	int lo, hi;
	lo = 0;
	hi = it->subtree_nr;
	while (lo < hi) {
		int mi = lo + (hi - lo) / 2;
		struct cache_tree_sub *mdl = down[mi];
		int cmp = subtree_name_cmp(path, pathlen,
					   mdl->name, mdl->namelen);
		if (!cmp)
			return mi;
		if (cmp < 0)
			hi = mi;
		else
			lo = mi + 1;
	}
	return -lo-1;
}

static struct cache_tree_sub *find_subtree(struct cache_tree *it,
					   const char *path,
					   int pathlen,
					   int create)
{
	struct cache_tree_sub *down;
	int pos = cache_tree_subtree_pos(it, path, pathlen);
	if (0 <= pos)
		return it->down[pos];
	if (!create)
		return NULL;

	pos = -pos-1;
	ALLOC_GROW(it->down, it->subtree_nr + 1, it->subtree_alloc);
	it->subtree_nr++;

	FLEX_ALLOC_MEM(down, name, path, pathlen);
	down->cache_tree = NULL;
	down->namelen = pathlen;

	if (pos < it->subtree_nr)
		MOVE_ARRAY(it->down + pos + 1, it->down + pos,
			   it->subtree_nr - pos - 1);
	it->down[pos] = down;
	return down;
}

struct cache_tree_sub *cache_tree_sub(struct cache_tree *it, const char *path)
{
	int pathlen = strlen(path);
	return find_subtree(it, path, pathlen, 1);
}

static int do_invalidate_path(struct cache_tree *it, const char *path)
{
	/* a/b/c
	 * ==> invalidate self
	 * ==> find "a", have it invalidate "b/c"
	 * a
	 * ==> invalidate self
	 * ==> if "a" exists as a subtree, remove it.
	 */
	const char *slash;
	int namelen;
	struct cache_tree_sub *down;

#if DEBUG_CACHE_TREE
	fprintf(stderr, "cache-tree invalidate <%s>\n", path);
#endif

	if (!it)
		return 0;
	slash = strchrnul(path, '/');
	namelen = slash - path;
	it->entry_count = -1;
	if (!*slash) {
		int pos;
		pos = cache_tree_subtree_pos(it, path, namelen);
		if (0 <= pos) {
			cache_tree_free(&it->down[pos]->cache_tree);
			free(it->down[pos]);
			/* 0 1 2 3 4 5
			 *       ^     ^subtree_nr = 6
			 *       pos
			 * move 4 and 5 up one place (2 entries)
			 * 2 = 6 - 3 - 1 = subtree_nr - pos - 1
			 */
			MOVE_ARRAY(it->down + pos, it->down + pos + 1,
				   it->subtree_nr - pos - 1);
			it->subtree_nr--;
		}
		return 1;
	}
	down = find_subtree(it, path, namelen, 0);
	if (down)
		do_invalidate_path(down->cache_tree, slash + 1);
	return 1;
}

void cache_tree_invalidate_path(struct index_state *istate, const char *path)
{
	if (do_invalidate_path(istate->cache_tree, path))
		istate->cache_changed |= CACHE_TREE_CHANGED;
}

static int verify_cache(struct index_state *istate, int flags)
{
	unsigned i, funny;
	int silent = flags & WRITE_TREE_SILENT;

	/* Verify that the tree is merged */
	funny = 0;
	for (i = 0; i < istate->cache_nr; i++) {
		const struct cache_entry *ce = istate->cache[i];
		if (ce_stage(ce)) {
			if (silent)
				return -1;
			if (10 < ++funny) {
				fprintf(stderr, "...\n");
				break;
			}
			fprintf(stderr, "%s: unmerged (%s)\n",
				ce->name, oid_to_hex(&ce->oid));
		}
	}
	if (funny)
		return -1;

	/* Also verify that the cache does not have path and path/file
	 * at the same time.  At this point we know the cache has only
	 * stage 0 entries.
	 */
	funny = 0;
	for (i = 0; i + 1 < istate->cache_nr; i++) {
		/* path/file always comes after path because of the way
		 * the cache is sorted.  Also path can appear only once,
		 * which means conflicting one would immediately follow.
		 */
		const struct cache_entry *this_ce = istate->cache[i];
		const struct cache_entry *next_ce = istate->cache[i + 1];
		const char *this_name = this_ce->name;
		const char *next_name = next_ce->name;
		int this_len = ce_namelen(this_ce);
		if (this_len < ce_namelen(next_ce) &&
		    next_name[this_len] == '/' &&
		    strncmp(this_name, next_name, this_len) == 0) {
			if (10 < ++funny) {
				fprintf(stderr, "...\n");
				break;
			}
			fprintf(stderr, "You have both %s and %s\n",
				this_name, next_name);
		}
	}
	if (funny)
		return -1;
	return 0;
}

static void discard_unused_subtrees(struct cache_tree *it)
{
	struct cache_tree_sub **down = it->down;
	int nr = it->subtree_nr;
	int dst, src;
	for (dst = src = 0; src < nr; src++) {
		struct cache_tree_sub *s = down[src];
		if (s->used)
			down[dst++] = s;
		else {
			cache_tree_free(&s->cache_tree);
			free(s);
			it->subtree_nr--;
		}
	}
}

int cache_tree_fully_valid(struct cache_tree *it)
{
	int i;
	if (!it)
		return 0;
	if (it->entry_count < 0 || !has_object_file(&it->oid))
		return 0;
	for (i = 0; i < it->subtree_nr; i++) {
		if (!cache_tree_fully_valid(it->down[i]->cache_tree))
			return 0;
	}
	return 1;
}

static int must_check_existence(const struct cache_entry *ce)
{
	return !(has_promisor_remote() && ce_skip_worktree(ce));
}

static int update_one(struct cache_tree *it,
		      struct cache_entry **cache,
		      int entries,
		      const char *base,
		      int baselen,
		      int *skip_count,
		      int flags)
{
	struct strbuf buffer;
	int missing_ok = flags & WRITE_TREE_MISSING_OK;
	int dryrun = flags & WRITE_TREE_DRY_RUN;
	int repair = flags & WRITE_TREE_REPAIR;
	int to_invalidate = 0;
	int i;

	assert(!(dryrun && repair));

	*skip_count = 0;

	/*
	 * If the first entry of this region is a sparse directory
	 * entry corresponding exactly to 'base', then this cache_tree
	 * struct is a "leaf" in the data structure, pointing to the
	 * tree OID specified in the entry.
	 */
	if (entries > 0) {
		const struct cache_entry *ce = cache[0];

		if (S_ISSPARSEDIR(ce->ce_mode) &&
		    ce->ce_namelen == baselen &&
		    !strncmp(ce->name, base, baselen)) {
			it->entry_count = 1;
			oidcpy(&it->oid, &ce->oid);
			return 1;
		}
	}

	if (0 <= it->entry_count && has_object_file(&it->oid))
		return it->entry_count;

	/*
	 * We first scan for subtrees and update them; we start by
	 * marking existing subtrees -- the ones that are unmarked
	 * should not be in the result.
	 */
	for (i = 0; i < it->subtree_nr; i++)
		it->down[i]->used = 0;

	/*
	 * Find the subtrees and update them.
	 */
	i = 0;
	while (i < entries) {
		const struct cache_entry *ce = cache[i];
		struct cache_tree_sub *sub;
		const char *path, *slash;
		int pathlen, sublen, subcnt, subskip;

		path = ce->name;
		pathlen = ce_namelen(ce);
		if (pathlen <= baselen || memcmp(base, path, baselen))
			break; /* at the end of this level */

		slash = strchr(path + baselen, '/');
		if (!slash) {
			i++;
			continue;
		}
		/*
		 * a/bbb/c (base = a/, slash = /c)
		 * ==>
		 * path+baselen = bbb/c, sublen = 3
		 */
		sublen = slash - (path + baselen);
		sub = find_subtree(it, path + baselen, sublen, 1);
		if (!sub->cache_tree)
			sub->cache_tree = cache_tree();
		subcnt = update_one(sub->cache_tree,
				    cache + i, entries - i,
				    path,
				    baselen + sublen + 1,
				    &subskip,
				    flags);
		if (subcnt < 0)
			return subcnt;
		if (!subcnt)
			die("index cache-tree records empty sub-tree");
		i += subcnt;
		sub->count = subcnt; /* to be used in the next loop */
		*skip_count += subskip;
		sub->used = 1;
	}

	discard_unused_subtrees(it);

	/*
	 * Then write out the tree object for this level.
	 */
	strbuf_init(&buffer, 8192);

	i = 0;
	while (i < entries) {
		const struct cache_entry *ce = cache[i];
		struct cache_tree_sub *sub = NULL;
		const char *path, *slash;
		int pathlen, entlen;
		const struct object_id *oid;
		unsigned mode;
		int expected_missing = 0;
		int contains_ita = 0;
		int ce_missing_ok;

		path = ce->name;
		pathlen = ce_namelen(ce);
		if (pathlen <= baselen || memcmp(base, path, baselen))
			break; /* at the end of this level */

		slash = strchr(path + baselen, '/');
		if (slash) {
			entlen = slash - (path + baselen);
			sub = find_subtree(it, path + baselen, entlen, 0);
			if (!sub)
				die("cache-tree.c: '%.*s' in '%s' not found",
				    entlen, path + baselen, path);
			i += sub->count;
			oid = &sub->cache_tree->oid;
			mode = S_IFDIR;
			contains_ita = sub->cache_tree->entry_count < 0;
			if (contains_ita) {
				to_invalidate = 1;
				expected_missing = 1;
			}
		}
		else {
			oid = &ce->oid;
			mode = ce->ce_mode;
			entlen = pathlen - baselen;
			i++;
		}

		ce_missing_ok = mode == S_IFGITLINK || missing_ok ||
			!must_check_existence(ce);
		if (is_null_oid(oid) ||
		    (!ce_missing_ok && !has_object_file(oid))) {
			strbuf_release(&buffer);
			if (expected_missing)
				return -1;
			return error("invalid object %06o %s for '%.*s'",
				mode, oid_to_hex(oid), entlen+baselen, path);
		}

		/*
		 * CE_REMOVE entries are removed before the index is
		 * written to disk. Skip them to remain consistent
		 * with the future on-disk index.
		 */
		if (ce->ce_flags & CE_REMOVE) {
			*skip_count = *skip_count + 1;
			continue;
		}

		/*
		 * CE_INTENT_TO_ADD entries exist in on-disk index but
		 * they are not part of generated trees. Invalidate up
		 * to root to force cache-tree users to read elsewhere.
		 */
		if (!sub && ce_intent_to_add(ce)) {
			to_invalidate = 1;
			continue;
		}

		/*
		 * "sub" can be an empty tree if all subentries are i-t-a.
		 */
		if (contains_ita && is_empty_tree_oid(oid))
			continue;

		strbuf_grow(&buffer, entlen + 100);
		strbuf_addf(&buffer, "%o %.*s%c", mode, entlen, path + baselen, '\0');
		strbuf_add(&buffer, oid->hash, the_hash_algo->rawsz);

#if DEBUG_CACHE_TREE
		fprintf(stderr, "cache-tree update-one %o %.*s\n",
			mode, entlen, path + baselen);
#endif
	}

	if (repair) {
		struct object_id oid;
		hash_object_file(the_hash_algo, buffer.buf, buffer.len,
				 OBJ_TREE, &oid);
		if (has_object_file_with_flags(&oid, OBJECT_INFO_SKIP_FETCH_OBJECT))
			oidcpy(&it->oid, &oid);
		else
			to_invalidate = 1;
	} else if (dryrun) {
		hash_object_file(the_hash_algo, buffer.buf, buffer.len,
				 OBJ_TREE, &it->oid);
	} else if (write_object_file_flags(buffer.buf, buffer.len, OBJ_TREE,
					   &it->oid, flags & WRITE_TREE_SILENT
					   ? HASH_SILENT : 0)) {
		strbuf_release(&buffer);
		return -1;
	}

	strbuf_release(&buffer);
	it->entry_count = to_invalidate ? -1 : i - *skip_count;
#if DEBUG_CACHE_TREE
	fprintf(stderr, "cache-tree update-one (%d ent, %d subtree) %s\n",
		it->entry_count, it->subtree_nr,
		oid_to_hex(&it->oid));
#endif
	return i;
}

int cache_tree_update(struct index_state *istate, int flags)
{
	int skip, i;

	i = verify_cache(istate, flags);

	if (i)
		return i;

	if (!istate->cache_tree)
		istate->cache_tree = cache_tree();

	if (!(flags & WRITE_TREE_MISSING_OK) && has_promisor_remote())
		prefetch_cache_entries(istate, must_check_existence);

	trace_performance_enter();
	trace2_region_enter("cache_tree", "update", the_repository);
	begin_odb_transaction();
	i = update_one(istate->cache_tree, istate->cache, istate->cache_nr,
		       "", 0, &skip, flags);
	end_odb_transaction();
	trace2_region_leave("cache_tree", "update", the_repository);
	trace_performance_leave("cache_tree_update");
	if (i < 0)
		return i;
	istate->cache_changed |= CACHE_TREE_CHANGED;
	return 0;
}

static void write_one(struct strbuf *buffer, struct cache_tree *it,
		      const char *path, int pathlen)
{
	int i;

	/* One "cache-tree" entry consists of the following:
	 * path (NUL terminated)
	 * entry_count, subtree_nr ("%d %d\n")
	 * tree-sha1 (missing if invalid)
	 * subtree_nr "cache-tree" entries for subtrees.
	 */
	strbuf_grow(buffer, pathlen + 100);
	strbuf_add(buffer, path, pathlen);
	strbuf_addf(buffer, "%c%d %d\n", 0, it->entry_count, it->subtree_nr);

#if DEBUG_CACHE_TREE
	if (0 <= it->entry_count)
		fprintf(stderr, "cache-tree <%.*s> (%d ent, %d subtree) %s\n",
			pathlen, path, it->entry_count, it->subtree_nr,
			oid_to_hex(&it->oid));
	else
		fprintf(stderr, "cache-tree <%.*s> (%d subtree) invalid\n",
			pathlen, path, it->subtree_nr);
#endif

	if (0 <= it->entry_count) {
		strbuf_add(buffer, it->oid.hash, the_hash_algo->rawsz);
	}
	for (i = 0; i < it->subtree_nr; i++) {
		struct cache_tree_sub *down = it->down[i];
		if (i) {
			struct cache_tree_sub *prev = it->down[i-1];
			if (subtree_name_cmp(down->name, down->namelen,
					     prev->name, prev->namelen) <= 0)
				die("fatal - unsorted cache subtree");
		}
		write_one(buffer, down->cache_tree, down->name, down->namelen);
	}
}

void cache_tree_write(struct strbuf *sb, struct cache_tree *root)
{
	trace2_region_enter("cache_tree", "write", the_repository);
	write_one(sb, root, "", 0);
	trace2_region_leave("cache_tree", "write", the_repository);
}

static struct cache_tree *read_one(const char **buffer, unsigned long *size_p)
{
	const char *buf = *buffer;
	unsigned long size = *size_p;
	const char *cp;
	char *ep;
	struct cache_tree *it;
	int i, subtree_nr;
	const unsigned rawsz = the_hash_algo->rawsz;

	it = NULL;
	/* skip name, but make sure name exists */
	while (size && *buf) {
		size--;
		buf++;
	}
	if (!size)
		goto free_return;
	buf++; size--;
	it = cache_tree();

	cp = buf;
	it->entry_count = strtol(cp, &ep, 10);
	if (cp == ep)
		goto free_return;
	cp = ep;
	subtree_nr = strtol(cp, &ep, 10);
	if (cp == ep)
		goto free_return;
	while (size && *buf && *buf != '\n') {
		size--;
		buf++;
	}
	if (!size)
		goto free_return;
	buf++; size--;
	if (0 <= it->entry_count) {
		if (size < rawsz)
			goto free_return;
		oidread(&it->oid, (const unsigned char *)buf);
		buf += rawsz;
		size -= rawsz;
	}

#if DEBUG_CACHE_TREE
	if (0 <= it->entry_count)
		fprintf(stderr, "cache-tree <%s> (%d ent, %d subtree) %s\n",
			*buffer, it->entry_count, subtree_nr,
			oid_to_hex(&it->oid));
	else
		fprintf(stderr, "cache-tree <%s> (%d subtrees) invalid\n",
			*buffer, subtree_nr);
#endif

	/*
	 * Just a heuristic -- we do not add directories that often but
	 * we do not want to have to extend it immediately when we do,
	 * hence +2.
	 */
	it->subtree_alloc = subtree_nr + 2;
	CALLOC_ARRAY(it->down, it->subtree_alloc);
	for (i = 0; i < subtree_nr; i++) {
		/* read each subtree */
		struct cache_tree *sub;
		struct cache_tree_sub *subtree;
		const char *name = buf;

		sub = read_one(&buf, &size);
		if (!sub)
			goto free_return;
		subtree = cache_tree_sub(it, name);
		subtree->cache_tree = sub;
	}
	if (subtree_nr != it->subtree_nr)
		die("cache-tree: internal error");
	*buffer = buf;
	*size_p = size;
	return it;

 free_return:
	cache_tree_free(&it);
	return NULL;
}

struct cache_tree *cache_tree_read(const char *buffer, unsigned long size)
{
	struct cache_tree *result;

	if (buffer[0])
		return NULL; /* not the whole tree */

	trace2_region_enter("cache_tree", "read", the_repository);
	result = read_one(&buffer, &size);
	trace2_region_leave("cache_tree", "read", the_repository);

	return result;
}

static struct cache_tree *cache_tree_find(struct cache_tree *it, const char *path)
{
	if (!it)
		return NULL;
	while (*path) {
		const char *slash;
		struct cache_tree_sub *sub;

		slash = strchrnul(path, '/');
		/*
		 * Between path and slash is the name of the subtree
		 * to look for.
		 */
		sub = find_subtree(it, path, slash - path, 0);
		if (!sub)
			return NULL;
		it = sub->cache_tree;

		path = slash;
		while (*path == '/')
			path++;
	}
	return it;
}

static int write_index_as_tree_internal(struct object_id *oid,
					struct index_state *index_state,
					int cache_tree_valid,
					int flags,
					const char *prefix)
{
	if (flags & WRITE_TREE_IGNORE_CACHE_TREE) {
		cache_tree_free(&index_state->cache_tree);
		cache_tree_valid = 0;
	}

	if (!cache_tree_valid && cache_tree_update(index_state, flags) < 0)
		return WRITE_TREE_UNMERGED_INDEX;

	if (prefix) {
		struct cache_tree *subtree;
		subtree = cache_tree_find(index_state->cache_tree, prefix);
		if (!subtree)
			return WRITE_TREE_PREFIX_ERROR;
		oidcpy(oid, &subtree->oid);
	}
	else
		oidcpy(oid, &index_state->cache_tree->oid);

	return 0;
}

struct tree* write_in_core_index_as_tree(struct repository *repo) {
	struct object_id o;
	int was_valid, ret;

	struct index_state *index_state	= repo->index;
	was_valid = index_state->cache_tree &&
		    cache_tree_fully_valid(index_state->cache_tree);

	ret = write_index_as_tree_internal(&o, index_state, was_valid, 0, NULL);
	if (ret == WRITE_TREE_UNMERGED_INDEX) {
		int i;
		bug("there are unmerged index entries:");
		for (i = 0; i < index_state->cache_nr; i++) {
			const struct cache_entry *ce = index_state->cache[i];
			if (ce_stage(ce))
				bug("%d %.*s", ce_stage(ce),
				    (int)ce_namelen(ce), ce->name);
		}
		BUG("unmerged index entries when writing in-core index");
	}

	return lookup_tree(repo, &index_state->cache_tree->oid);
}


int write_index_as_tree(struct object_id *oid, struct index_state *index_state, const char *index_path, int flags, const char *prefix)
{
	int entries, was_valid;
	struct lock_file lock_file = LOCK_INIT;
	int ret;

	hold_lock_file_for_update(&lock_file, index_path, LOCK_DIE_ON_ERROR);

	entries = read_index_from(index_state, index_path, get_git_dir());
	if (entries < 0) {
		ret = WRITE_TREE_UNREADABLE_INDEX;
		goto out;
	}

	was_valid = !(flags & WRITE_TREE_IGNORE_CACHE_TREE) &&
		    index_state->cache_tree &&
		    cache_tree_fully_valid(index_state->cache_tree);

	ret = write_index_as_tree_internal(oid, index_state, was_valid, flags,
					   prefix);
	if (!ret && !was_valid) {
		write_locked_index(index_state, &lock_file, COMMIT_LOCK);
		/* Not being able to write is fine -- we are only interested
		 * in updating the cache-tree part, and if the next caller
		 * ends up using the old index with unupdated cache-tree part
		 * it misses the work we did here, but that is just a
		 * performance penalty and not a big deal.
		 */
	}

out:
	rollback_lock_file(&lock_file);
	return ret;
}

static void prime_cache_tree_sparse_dir(struct cache_tree *it,
					struct tree *tree)
{

	oidcpy(&it->oid, &tree->object.oid);
	it->entry_count = 1;
}

static void prime_cache_tree_rec(struct repository *r,
				 struct cache_tree *it,
				 struct tree *tree,
				 struct strbuf *tree_path)
{
	struct tree_desc desc;
	struct name_entry entry;
	int cnt;
	size_t base_path_len = tree_path->len;

	oidcpy(&it->oid, &tree->object.oid);

	init_tree_desc(&desc, tree->buffer, tree->size);
	cnt = 0;
	while (tree_entry(&desc, &entry)) {
		if (!S_ISDIR(entry.mode))
			cnt++;
		else {
			struct cache_tree_sub *sub;
			struct tree *subtree = lookup_tree(r, &entry.oid);

			if (!subtree->object.parsed)
				parse_tree(subtree);
			sub = cache_tree_sub(it, entry.path);
			sub->cache_tree = cache_tree();

			/*
			 * Recursively-constructed subtree path is only needed when working
			 * in a sparse index (where it's used to determine whether the
			 * subtree is a sparse directory in the index).
			 */
			if (r->index->sparse_index) {
				strbuf_setlen(tree_path, base_path_len);
				strbuf_add(tree_path, entry.path, entry.pathlen);
				strbuf_addch(tree_path, '/');
			}

			/*
			 * If a sparse index is in use, the directory being processed may be
			 * sparse. To confirm that, we can check whether an entry with that
			 * exact name exists in the index. If it does, the created subtree
			 * should be sparse. Otherwise, cache tree expansion should continue
			 * as normal.
			 */
			if (r->index->sparse_index &&
			    index_entry_exists(r->index, tree_path->buf, tree_path->len))
				prime_cache_tree_sparse_dir(sub->cache_tree, subtree);
			else
				prime_cache_tree_rec(r, sub->cache_tree, subtree, tree_path);
			cnt += sub->cache_tree->entry_count;
		}
	}

	it->entry_count = cnt;
}

void prime_cache_tree(struct repository *r,
		      struct index_state *istate,
		      struct tree *tree)
{
	struct strbuf tree_path = STRBUF_INIT;

	trace2_region_enter("cache-tree", "prime_cache_tree", the_repository);
	cache_tree_free(&istate->cache_tree);
	istate->cache_tree = cache_tree();

	prime_cache_tree_rec(r, istate->cache_tree, tree, &tree_path);
	strbuf_release(&tree_path);
	istate->cache_changed |= CACHE_TREE_CHANGED;
	trace2_region_leave("cache-tree", "prime_cache_tree", the_repository);
}

/*
 * find the cache_tree that corresponds to the current level without
 * exploding the full path into textual form.  The root of the
 * cache tree is given as "root", and our current level is "info".
 * (1) When at root level, info->prev is NULL, so it is "root" itself.
 * (2) Otherwise, find the cache_tree that corresponds to one level
 *     above us, and find ourselves in there.
 */
static struct cache_tree *find_cache_tree_from_traversal(struct cache_tree *root,
							 struct traverse_info *info)
{
	struct cache_tree *our_parent;

	if (!info->prev)
		return root;
	our_parent = find_cache_tree_from_traversal(root, info->prev);
	return cache_tree_find(our_parent, info->name);
}

int cache_tree_matches_traversal(struct cache_tree *root,
				 struct name_entry *ent,
				 struct traverse_info *info)
{
	struct cache_tree *it;

	it = find_cache_tree_from_traversal(root, info);
	it = cache_tree_find(it, ent->path);
	if (it && it->entry_count > 0 && oideq(&ent->oid, &it->oid))
		return it->entry_count;
	return 0;
}

static void verify_one_sparse(struct index_state *istate,
			      struct strbuf *path,
			      int pos)
{
	struct cache_entry *ce = istate->cache[pos];

	if (!S_ISSPARSEDIR(ce->ce_mode))
		BUG("directory '%s' is present in index, but not sparse",
		    path->buf);
}

/*
 * Returns:
 *  0 - Verification completed.
 *  1 - Restart verification - a call to ensure_full_index() freed the cache
 *      tree that is being verified and verification needs to be restarted from
 *      the new toplevel cache tree.
 */
static int verify_one(struct repository *r,
		      struct index_state *istate,
		      struct cache_tree *it,
		      struct strbuf *path)
{
	int i, pos, len = path->len;
	struct strbuf tree_buf = STRBUF_INIT;
	struct object_id new_oid;

	for (i = 0; i < it->subtree_nr; i++) {
		strbuf_addf(path, "%s/", it->down[i]->name);
		if (verify_one(r, istate, it->down[i]->cache_tree, path))
			return 1;
		strbuf_setlen(path, len);
	}

	if (it->entry_count < 0 ||
	    /* no verification on tests (t7003) that replace trees */
	    lookup_replace_object(r, &it->oid) != &it->oid)
		return 0;

	if (path->len) {
		/*
		 * If the index is sparse and the cache tree is not
		 * index_name_pos() may trigger ensure_full_index() which will
		 * free the tree that is being verified.
		 */
		int is_sparse = istate->sparse_index;
		pos = index_name_pos(istate, path->buf, path->len);
		if (is_sparse && !istate->sparse_index)
			return 1;

		if (pos >= 0) {
			verify_one_sparse(istate, path, pos);
			return 0;
		}

		pos = -pos - 1;
	} else {
		pos = 0;
	}

	i = 0;
	while (i < it->entry_count) {
		struct cache_entry *ce = istate->cache[pos + i];
		const char *slash;
		struct cache_tree_sub *sub = NULL;
		const struct object_id *oid;
		const char *name;
		unsigned mode;
		int entlen;

		if (ce->ce_flags & (CE_STAGEMASK | CE_INTENT_TO_ADD | CE_REMOVE))
			BUG("%s with flags 0x%x should not be in cache-tree",
			    ce->name, ce->ce_flags);
		name = ce->name + path->len;
		slash = strchr(name, '/');
		if (slash) {
			entlen = slash - name;
			sub = find_subtree(it, ce->name + path->len, entlen, 0);
			if (!sub || sub->cache_tree->entry_count < 0)
				BUG("bad subtree '%.*s'", entlen, name);
			oid = &sub->cache_tree->oid;
			mode = S_IFDIR;
			i += sub->cache_tree->entry_count;
		} else {
			oid = &ce->oid;
			mode = ce->ce_mode;
			entlen = ce_namelen(ce) - path->len;
			i++;
		}
		strbuf_addf(&tree_buf, "%o %.*s%c", mode, entlen, name, '\0');
		strbuf_add(&tree_buf, oid->hash, r->hash_algo->rawsz);
	}
	hash_object_file(r->hash_algo, tree_buf.buf, tree_buf.len, OBJ_TREE,
			 &new_oid);
	if (!oideq(&new_oid, &it->oid))
		BUG("cache-tree for path %.*s does not match. "
		    "Expected %s got %s", len, path->buf,
		    oid_to_hex(&new_oid), oid_to_hex(&it->oid));
	strbuf_setlen(path, len);
	strbuf_release(&tree_buf);
	return 0;
}

void cache_tree_verify(struct repository *r, struct index_state *istate)
{
	struct strbuf path = STRBUF_INIT;

	if (!istate->cache_tree)
		return;
	if (verify_one(r, istate, istate->cache_tree, &path)) {
		strbuf_reset(&path);
		if (verify_one(r, istate, istate->cache_tree, &path))
			BUG("ensure_full_index() called twice while verifying cache tree");
	}
	strbuf_release(&path);
}