Merge branch 'jk/alt-odb-cleanup'

Codepaths involved in interacting alternate object store have
been cleaned up.

* jk/alt-odb-cleanup:
  alternates: use fspathcmp to detect duplicates
  sha1_file: always allow relative paths to alternates
  count-objects: report alternates via verbose mode
  fill_sha1_file: write into a strbuf
  alternates: store scratch buffer as strbuf
  fill_sha1_file: write "boring" characters
  alternates: use a separate scratch space
  alternates: encapsulate alt->base munging
  alternates: provide helper for allocating alternate
  alternates: provide helper for adding to alternates list
  link_alt_odb_entry: refactor string handling
  link_alt_odb_entry: handle normalize_path errors
  t5613: clarify "too deep" recursion tests
  t5613: do not chdir in main process
  t5613: whitespace/style cleanups
  t5613: use test_must_fail
  t5613: drop test_valid_repo function
  t5613: drop reachable_via function

12 files changed, 308 insertions, 222 deletions

diff --git a/Documentation/git-count-objects.txt b/Documentation/git-count-objects.txt
index 2ff35683e..cb9b4d2e4 100644
--- a/Documentation/git-count-objects.txt
+++ b/Documentation/git-count-objects.txt
@@ -38,6 +38,11 @@ objects nor valid packs
 +
 size-garbage: disk space consumed by garbage files, in KiB (unless -H is
 specified)
++
+alternate: absolute path of alternate object databases; may appear
+multiple times, one line per path. Note that if the path contains
+non-printable characters, it may be surrounded by double-quotes and
+contain C-style backslashed escape sequences.
 
 -H::
 --human-readable::
diff --git a/builtin/count-objects.c b/builtin/count-objects.c
index ba9291944..a04b4f2ef 100644
--- a/builtin/count-objects.c
+++ b/builtin/count-objects.c
@@ -8,6 +8,7 @@
 #include "dir.h"
 #include "builtin.h"
 #include "parse-options.h"
+#include "quote.h"
 
 static unsigned long garbage;
 static off_t size_garbage;
@@ -73,6 +74,14 @@ static int count_cruft(const char *basename, const char *path, void *data)
 	return 0;
 }
 
+static int print_alternate(struct alternate_object_database *alt, void *data)
+{
+	printf("alternate: ");
+	quote_c_style(alt->path, NULL, stdout, 0);
+	putchar('\n');
+	return 0;
+}
+
 static char const * const count_objects_usage[] = {
 	N_("git count-objects [-v] [-H | --human-readable]"),
 	NULL
@@ -88,6 +97,8 @@ int cmd_count_objects(int argc, const char **argv, const char *prefix)
 		OPT_END(),
 	};
 
+	git_config(git_default_config, NULL);
+
 	argc = parse_options(argc, argv, prefix, opts, count_objects_usage, 0);
 	/* we do not take arguments other than flags for now */
 	if (argc)
@@ -140,6 +151,7 @@ int cmd_count_objects(int argc, const char **argv, const char *prefix)
 		printf("prune-packable: %lu\n", packed_loose);
 		printf("garbage: %lu\n", garbage);
 		printf("size-garbage: %s\n", garbage_buf.buf);
+		foreach_alt_odb(print_alternate, NULL);
 		strbuf_release(&loose_buf);
 		strbuf_release(&pack_buf);
 		strbuf_release(&garbage_buf);
diff --git a/builtin/fsck.c b/builtin/fsck.c
index 055dfdcf9..f01b81eeb 100644
--- a/builtin/fsck.c
+++ b/builtin/fsck.c
@@ -644,14 +644,8 @@ int cmd_fsck(int argc, const char **argv, const char *prefix)
 		fsck_object_dir(get_object_directory());
 
 		prepare_alt_odb();
-		for (alt = alt_odb_list; alt; alt = alt->next) {
-			/* directory name, minus trailing slash */
-			size_t namelen = alt->name - alt->base - 1;
-			struct strbuf name = STRBUF_INIT;
-			strbuf_add(&name, alt->base, namelen);
-			fsck_object_dir(name.buf);
-			strbuf_release(&name);
-		}
+		for (alt = alt_odb_list; alt; alt = alt->next)
+			fsck_object_dir(alt->path);
 	}
 
 	if (check_full) {
diff --git a/builtin/submodule--helper.c b/builtin/submodule--helper.c
index 444ec06c2..6182eb319 100644
--- a/builtin/submodule--helper.c
+++ b/builtin/submodule--helper.c
@@ -492,20 +492,16 @@ static int add_possible_reference_from_superproject(
 {
 	struct submodule_alternate_setup *sas = sas_cb;
 
-	/* directory name, minus trailing slash */
-	size_t namelen = alt->name - alt->base - 1;
-	struct strbuf name = STRBUF_INIT;
-	strbuf_add(&name, alt->base, namelen);
-
 	/*
 	 * If the alternate object store is another repository, try the
 	 * standard layout with .git/modules/<name>/objects
 	 */
-	if (ends_with(name.buf, ".git/objects")) {
+	if (ends_with(alt->path, ".git/objects")) {
 		char *sm_alternate;
 		struct strbuf sb = STRBUF_INIT;
 		struct strbuf err = STRBUF_INIT;
-		strbuf_add(&sb, name.buf, name.len - strlen("objects"));
+		strbuf_add(&sb, alt->path, strlen(alt->path) - strlen("objects"));
+
 		/*
 		 * We need to end the new path with '/' to mark it as a dir,
 		 * otherwise a submodule name containing '/' will be broken
@@ -533,7 +529,6 @@ static int add_possible_reference_from_superproject(
 		strbuf_release(&sb);
 	}
 
-	strbuf_release(&name);
 	return 0;
 }
 
diff --git a/cache.h b/cache.h
index 2cfb1cab6..0dc39a998 100644
--- a/cache.h
+++ b/cache.h
@@ -1390,16 +1390,46 @@ extern void remove_scheduled_dirs(void);
 
 extern struct alternate_object_database {
 	struct alternate_object_database *next;
-	char *name;
-	char base[FLEX_ARRAY]; /* more */
+
+	/* see alt_scratch_buf() */
+	struct strbuf scratch;
+	size_t base_len;
+
+	char path[FLEX_ARRAY];
 } *alt_odb_list;
 extern void prepare_alt_odb(void);
 extern void read_info_alternates(const char * relative_base, int depth);
 extern char *compute_alternate_path(const char *path, struct strbuf *err);
-extern void add_to_alternates_file(const char *reference);
 typedef int alt_odb_fn(struct alternate_object_database *, void *);
 extern int foreach_alt_odb(alt_odb_fn, void*);
 
+/*
+ * Allocate a "struct alternate_object_database" but do _not_ actually
+ * add it to the list of alternates.
+ */
+struct alternate_object_database *alloc_alt_odb(const char *dir);
+
+/*
+ * Add the directory to the on-disk alternates file; the new entry will also
+ * take effect in the current process.
+ */
+extern void add_to_alternates_file(const char *dir);
+
+/*
+ * Add the directory to the in-memory list of alternates (along with any
+ * recursive alternates it points to), but do not modify the on-disk alternates
+ * file.
+ */
+extern void add_to_alternates_memory(const char *dir);
+
+/*
+ * Returns a scratch strbuf pre-filled with the alternate object directory,
+ * including a trailing slash, which can be used to access paths in the
+ * alternate. Always use this over direct access to alt->scratch, as it
+ * cleans up any previous use of the scratch buffer.
+ */
+extern struct strbuf *alt_scratch_buf(struct alternate_object_database *alt);
+
 struct pack_window {
 	struct pack_window *next;
 	unsigned char *base;
diff --git a/sha1_file.c b/sha1_file.c
index 309e87d98..266152de3 100644
--- a/sha1_file.c
+++ b/sha1_file.c
@@ -172,36 +172,42 @@ enum scld_error safe_create_leading_directories_const(const char *path)
 	return result;
 }
 
-static void fill_sha1_path(char *pathbuf, const unsigned char *sha1)
+static void fill_sha1_path(struct strbuf *buf, const unsigned char *sha1)
 {
 	int i;
 	for (i = 0; i < 20; i++) {
 		static char hex[] = "0123456789abcdef";
 		unsigned int val = sha1[i];
-		char *pos = pathbuf + i*2 + (i > 0);
-		*pos++ = hex[val >> 4];
-		*pos = hex[val & 0xf];
+		strbuf_addch(buf, hex[val >> 4]);
+		strbuf_addch(buf, hex[val & 0xf]);
+		if (!i)
+			strbuf_addch(buf, '/');
 	}
 }
 
 const char *sha1_file_name(const unsigned char *sha1)
 {
-	static char buf[PATH_MAX];
-	const char *objdir;
-	int len;
+	static struct strbuf buf = STRBUF_INIT;
 
-	objdir = get_object_directory();
-	len = strlen(objdir);
+	strbuf_reset(&buf);
+	strbuf_addf(&buf, "%s/", get_object_directory());
 
-	/* '/' + sha1(2) + '/' + sha1(38) + '\0' */
-	if (len + 43 > PATH_MAX)
-		die("insanely long object directory %s", objdir);
-	memcpy(buf, objdir, len);
-	buf[len] = '/';
-	buf[len+3] = '/';
-	buf[len+42] = '\0';
-	fill_sha1_path(buf + len + 1, sha1);
-	return buf;
+	fill_sha1_path(&buf, sha1);
+	return buf.buf;
+}
+
+struct strbuf *alt_scratch_buf(struct alternate_object_database *alt)
+{
+	strbuf_setlen(&alt->scratch, alt->base_len);
+	return &alt->scratch;
+}
+
+static const char *alt_sha1_path(struct alternate_object_database *alt,
+				 const unsigned char *sha1)
+{
+	struct strbuf *buf = alt_scratch_buf(alt);
+	fill_sha1_path(buf, sha1);
+	return buf->buf;
 }
 
 /*
@@ -235,6 +241,35 @@ struct alternate_object_database *alt_odb_list;
 static struct alternate_object_database **alt_odb_tail;
 
 /*
+ * Return non-zero iff the path is usable as an alternate object database.
+ */
+static int alt_odb_usable(struct strbuf *path, const char *normalized_objdir)
+{
+	struct alternate_object_database *alt;
+
+	/* Detect cases where alternate disappeared */
+	if (!is_directory(path->buf)) {
+		error("object directory %s does not exist; "
+		      "check .git/objects/info/alternates.",
+		      path->buf);
+		return 0;
+	}
+
+	/*
+	 * Prevent the common mistake of listing the same
+	 * thing twice, or object directory itself.
+	 */
+	for (alt = alt_odb_list; alt; alt = alt->next) {
+		if (!fspathcmp(path->buf, alt->path))
+			return 0;
+	}
+	if (!fspathcmp(path->buf, normalized_objdir))
+		return 0;
+
+	return 1;
+}
+
+/*
  * Prepare alternate object database registry.
  *
  * The variable alt_odb_list points at the list of struct
@@ -253,8 +288,6 @@ static int link_alt_odb_entry(const char *entry, const char *relative_base,
 	int depth, const char *normalized_objdir)
 {
 	struct alternate_object_database *ent;
-	struct alternate_object_database *alt;
-	size_t pfxlen, entlen;
 	struct strbuf pathbuf = STRBUF_INIT;
 
 	if (!is_absolute_path(entry) && relative_base) {
@@ -263,49 +296,26 @@ static int link_alt_odb_entry(const char *entry, const char *relative_base,
 	}
 	strbuf_addstr(&pathbuf, entry);
 
-	normalize_path_copy(pathbuf.buf, pathbuf.buf);
-
-	pfxlen = strlen(pathbuf.buf);
+	if (strbuf_normalize_path(&pathbuf) < 0) {
+		error("unable to normalize alternate object path: %s",
+		      pathbuf.buf);
+		strbuf_release(&pathbuf);
+		return -1;
+	}
 
 	/*
 	 * The trailing slash after the directory name is given by
 	 * this function at the end. Remove duplicates.
 	 */
-	while (pfxlen && pathbuf.buf[pfxlen-1] == '/')
-		pfxlen -= 1;
+	while (pathbuf.len && pathbuf.buf[pathbuf.len - 1] == '/')
+		strbuf_setlen(&pathbuf, pathbuf.len - 1);
 
-	entlen = st_add(pfxlen, 43); /* '/' + 2 hex + '/' + 38 hex + NUL */
-	ent = xmalloc(st_add(sizeof(*ent), entlen));
-	memcpy(ent->base, pathbuf.buf, pfxlen);
-	strbuf_release(&pathbuf);
-
-	ent->name = ent->base + pfxlen + 1;
-	ent->base[pfxlen + 3] = '/';
-	ent->base[pfxlen] = ent->base[entlen-1] = 0;
-
-	/* Detect cases where alternate disappeared */
-	if (!is_directory(ent->base)) {
-		error("object directory %s does not exist; "
-		      "check .git/objects/info/alternates.",
-		      ent->base);
-		free(ent);
+	if (!alt_odb_usable(&pathbuf, normalized_objdir)) {
+		strbuf_release(&pathbuf);
 		return -1;
 	}
 
-	/* Prevent the common mistake of listing the same
-	 * thing twice, or object directory itself.
-	 */
-	for (alt = alt_odb_list; alt; alt = alt->next) {
-		if (pfxlen == alt->name - alt->base - 1 &&
-		    !memcmp(ent->base, alt->base, pfxlen)) {
-			free(ent);
-			return -1;
-		}
-	}
-	if (!fspathcmp(ent->base, normalized_objdir)) {
-		free(ent);
-		return -1;
-	}
+	ent = alloc_alt_odb(pathbuf.buf);
 
 	/* add the alternate entry */
 	*alt_odb_tail = ent;
@@ -313,10 +323,9 @@ static int link_alt_odb_entry(const char *entry, const char *relative_base,
 	ent->next = NULL;
 
 	/* recursively add alternates */
-	read_info_alternates(ent->base, depth + 1);
-
-	ent->base[pfxlen] = '/';
+	read_info_alternates(pathbuf.buf, depth + 1);
 
+	strbuf_release(&pathbuf);
 	return 0;
 }
 
@@ -335,7 +344,9 @@ static void link_alt_odb_entries(const char *alt, int len, int sep,
 	}
 
 	strbuf_add_absolute_path(&objdirbuf, get_object_directory());
-	normalize_path_copy(objdirbuf.buf, objdirbuf.buf);
+	if (strbuf_normalize_path(&objdirbuf) < 0)
+		die("unable to normalize object directory: %s",
+		    objdirbuf.buf);
 
 	alt_copy = xmemdupz(alt, len);
 	string_list_split_in_place(&entries, alt_copy, sep, -1);
@@ -343,12 +354,7 @@ static void link_alt_odb_entries(const char *alt, int len, int sep,
 		const char *entry = entries.items[i].string;
 		if (entry[0] == '\0' || entry[0] == '#')
 			continue;
-		if (!is_absolute_path(entry) && depth) {
-			error("%s: ignoring relative alternate object store %s",
-					relative_base, entry);
-		} else {
-			link_alt_odb_entry(entry, relative_base, depth, objdirbuf.buf);
-		}
+		link_alt_odb_entry(entry, relative_base, depth, objdirbuf.buf);
 	}
 	string_list_clear(&entries, 0);
 	free(alt_copy);
@@ -381,6 +387,18 @@ void read_info_alternates(const char * relative_base, int depth)
 	munmap(map, mapsz);
 }
 
+struct alternate_object_database *alloc_alt_odb(const char *dir)
+{
+	struct alternate_object_database *ent;
+
+	FLEX_ALLOC_STR(ent, path, dir);
+	strbuf_init(&ent->scratch, 0);
+	strbuf_addf(&ent->scratch, "%s/", dir);
+	ent->base_len = ent->scratch.len;
+
+	return ent;
+}
+
 void add_to_alternates_file(const char *reference)
 {
 	struct lock_file *lock = xcalloc(1, sizeof(struct lock_file));
@@ -426,6 +444,17 @@ void add_to_alternates_file(const char *reference)
 	free(alts);
 }
 
+void add_to_alternates_memory(const char *reference)
+{
+	/*
+	 * Make sure alternates are initialized, or else our entry may be
+	 * overwritten when they are.
+	 */
+	prepare_alt_odb();
+
+	link_alt_odb_entries(reference, strlen(reference), '\n', NULL, 0);
+}
+
 /*
  * Compute the exact path an alternate is at and returns it. In case of
  * error NULL is returned and the human readable error is added to `err`
@@ -566,8 +595,8 @@ static int check_and_freshen_nonlocal(const unsigned char *sha1, int freshen)
 	struct alternate_object_database *alt;
 	prepare_alt_odb();
 	for (alt = alt_odb_list; alt; alt = alt->next) {
-		fill_sha1_path(alt->name, sha1);
-		if (check_and_freshen_file(alt->base, freshen))
+		const char *path = alt_sha1_path(alt, sha1);
+		if (check_and_freshen_file(path, freshen))
 			return 1;
 	}
 	return 0;
@@ -1443,11 +1472,8 @@ void prepare_packed_git(void)
 		return;
 	prepare_packed_git_one(get_object_directory(), 1);
 	prepare_alt_odb();
-	for (alt = alt_odb_list; alt; alt = alt->next) {
-		alt->name[-1] = 0;
-		prepare_packed_git_one(alt->base, 0);
-		alt->name[-1] = '/';
-	}
+	for (alt = alt_odb_list; alt; alt = alt->next)
+		prepare_packed_git_one(alt->path, 0);
 	rearrange_packed_git();
 	prepare_packed_git_mru();
 	prepare_packed_git_run_once = 1;
@@ -1565,8 +1591,8 @@ static int stat_sha1_file(const unsigned char *sha1, struct stat *st)
 	prepare_alt_odb();
 	errno = ENOENT;
 	for (alt = alt_odb_list; alt; alt = alt->next) {
-		fill_sha1_path(alt->name, sha1);
-		if (!lstat(alt->base, st))
+		const char *path = alt_sha1_path(alt, sha1);
+		if (!lstat(path, st))
 			return 0;
 	}
 
@@ -1586,8 +1612,8 @@ static int open_sha1_file(const unsigned char *sha1)
 
 	prepare_alt_odb();
 	for (alt = alt_odb_list; alt; alt = alt->next) {
-		fill_sha1_path(alt->name, sha1);
-		fd = git_open_noatime(alt->base);
+		const char *path = alt_sha1_path(alt, sha1);
+		fd = git_open_noatime(path);
 		if (fd >= 0)
 			return fd;
 		if (most_interesting_errno == ENOENT)
@@ -3648,8 +3674,7 @@ static int loose_from_alt_odb(struct alternate_object_database *alt,
 	struct strbuf buf = STRBUF_INIT;
 	int r;
 
-	/* copy base not including trailing '/' */
-	strbuf_add(&buf, alt->base, alt->name - alt->base - 1);
+	strbuf_addstr(&buf, alt->path);
 	r = for_each_loose_file_in_objdir_buf(&buf,
 					      data->cb, NULL, NULL,
 					      data->data);
diff --git a/sha1_name.c b/sha1_name.c
index 3b647fd7c..409283614 100644
--- a/sha1_name.c
+++ b/sha1_name.c
@@ -91,25 +91,18 @@ static void find_short_object_filename(struct disambiguate_state *ds)
 		 * alt->name/alt->base while iterating over the
 		 * object databases including our own.
 		 */
-		const char *objdir = get_object_directory();
-		size_t objdir_len = strlen(objdir);
-		fakeent = xmalloc(st_add3(sizeof(*fakeent), objdir_len, 43));
-		memcpy(fakeent->base, objdir, objdir_len);
-		fakeent->name = fakeent->base + objdir_len + 1;
-		fakeent->name[-1] = '/';
+		fakeent = alloc_alt_odb(get_object_directory());
 	}
 	fakeent->next = alt_odb_list;
 
 	xsnprintf(hex, sizeof(hex), "%.2s", ds->hex_pfx);
 	for (alt = fakeent; alt && !ds->ambiguous; alt = alt->next) {
+		struct strbuf *buf = alt_scratch_buf(alt);
 		struct dirent *de;
 		DIR *dir;
-		/*
-		 * every alt_odb struct has 42 extra bytes after the base
-		 * for exactly this purpose
-		 */
-		xsnprintf(alt->name, 42, "%.2s/", ds->hex_pfx);
-		dir = opendir(alt->base);
+
+		strbuf_addf(buf, "%.2s/", ds->hex_pfx);
+		dir = opendir(buf->buf);
 		if (!dir)
 			continue;
 
diff --git a/strbuf.c b/strbuf.c
index b839be491..8fec6579f 100644
--- a/strbuf.c
+++ b/strbuf.c
@@ -870,3 +870,23 @@ void strbuf_stripspace(struct strbuf *sb, int skip_comments)
 
 	strbuf_setlen(sb, j);
 }
+
+int strbuf_normalize_path(struct strbuf *src)
+{
+	struct strbuf dst = STRBUF_INIT;
+
+	strbuf_grow(&dst, src->len);
+	if (normalize_path_copy(dst.buf, src->buf) < 0) {
+		strbuf_release(&dst);
+		return -1;
+	}
+
+	/*
+	 * normalize_path does not tell us the new length, so we have to
+	 * compute it by looking for the new NUL it placed
+	 */
+	strbuf_setlen(&dst, strlen(dst.buf));
+	strbuf_swap(src, &dst);
+	strbuf_release(&dst);
+	return 0;
+}
diff --git a/strbuf.h b/strbuf.h
index ba8d5f1d4..2262b1268 100644
--- a/strbuf.h
+++ b/strbuf.h
@@ -443,6 +443,14 @@ extern int strbuf_getcwd(struct strbuf *sb);
  */
 extern void strbuf_add_absolute_path(struct strbuf *sb, const char *path);
 
+
+/**
+ * Normalize in-place the path contained in the strbuf. See
+ * normalize_path_copy() for details. If an error occurs, the contents of "sb"
+ * are left untouched, and -1 is returned.
+ */
+extern int strbuf_normalize_path(struct strbuf *sb);
+
 /**
  * Strip whitespace from a buffer. The second parameter controls if
  * comments are considered contents to be removed or not.
diff --git a/submodule.c b/submodule.c
index 2de06a335..733332035 100644
--- a/submodule.c
+++ b/submodule.c
@@ -123,9 +123,7 @@ void stage_updated_gitmodules(void)
 static int add_submodule_odb(const char *path)
 {
 	struct strbuf objects_directory = STRBUF_INIT;
-	struct alternate_object_database *alt_odb;
 	int ret = 0;
-	size_t alloc;
 
 	ret = strbuf_git_path_submodule(&objects_directory, path, "objects/");
 	if (ret)
@@ -134,26 +132,7 @@ static int add_submodule_odb(const char *path)
 		ret = -1;
 		goto done;
 	}
-	/* avoid adding it twice */
-	prepare_alt_odb();
-	for (alt_odb = alt_odb_list; alt_odb; alt_odb = alt_odb->next)
-		if (alt_odb->name - alt_odb->base == objects_directory.len &&
-				!strncmp(alt_odb->base, objects_directory.buf,
-					objects_directory.len))
-			goto done;
-
-	alloc = st_add(objects_directory.len, 42); /* for "12/345..." sha1 */
-	alt_odb = xmalloc(st_add(sizeof(*alt_odb), alloc));
-	alt_odb->next = alt_odb_list;
-	xsnprintf(alt_odb->base, alloc, "%s", objects_directory.buf);
-	alt_odb->name = alt_odb->base + objects_directory.len;
-	alt_odb->name[2] = '/';
-	alt_odb->name[40] = '\0';
-	alt_odb->name[41] = '\0';
-	alt_odb_list = alt_odb;
-
-	/* add possible alternates from the submodule */
-	read_info_alternates(objects_directory.buf, 0);
+	add_to_alternates_memory(objects_directory.buf);
 done:
 	strbuf_release(&objects_directory);
 	return ret;
diff --git a/t/t5613-info-alternate.sh b/t/t5613-info-alternate.sh
index 9cd2626db..895f46bb9 100755
--- a/t/t5613-info-alternate.sh
+++ b/t/t5613-info-alternate.sh
@@ -6,107 +6,134 @@
 test_description='test transitive info/alternate entries'
 . ./test-lib.sh
 
-# test that a file is not reachable in the current repository
-# but that it is after creating a info/alternate entry
-reachable_via() {
-	alternate="$1"
-	file="$2"
-	if git cat-file -e "HEAD:$file"; then return 1; fi
-	echo "$alternate" >> .git/objects/info/alternate
-	git cat-file -e "HEAD:$file"
-}
-
-test_valid_repo() {
-	git fsck --full > fsck.log &&
-	test_line_count = 0 fsck.log
-}
-
-base_dir=$(pwd)
-
-test_expect_success 'preparing first repository' \
-'test_create_repo A && cd A &&
-echo "Hello World" > file1 &&
-git add file1 &&
-git commit -m "Initial commit" file1 &&
-git repack -a -d &&
-git prune'
-
-cd "$base_dir"
-
-test_expect_success 'preparing second repository' \
-'git clone -l -s A B && cd B &&
-echo "foo bar" > file2 &&
-git add file2 &&
-git commit -m "next commit" file2 &&
-git repack -a -d -l &&
-git prune'
-
-cd "$base_dir"
-
-test_expect_success 'preparing third repository' \
-'git clone -l -s B C && cd C &&
-echo "Goodbye, cruel world" > file3 &&
-git add file3 &&
-git commit -m "one more" file3 &&
-git repack -a -d -l &&
-git prune'
-
-cd "$base_dir"
-
-test_expect_success 'creating too deep nesting' \
-'git clone -l -s C D &&
-git clone -l -s D E &&
-git clone -l -s E F &&
-git clone -l -s F G &&
-git clone --bare -l -s G H'
-
-test_expect_success 'invalidity of deepest repository' \
-'cd H && {
-	test_valid_repo
-	test $? -ne 0
-}'
-
-cd "$base_dir"
+test_expect_success 'preparing first repository' '
+	test_create_repo A && (
+		cd A &&
+		echo "Hello World" > file1 &&
+		git add file1 &&
+		git commit -m "Initial commit" file1 &&
+		git repack -a -d &&
+		git prune
+	)
+'
 
-test_expect_success 'validity of third repository' \
-'cd C &&
-test_valid_repo'
+test_expect_success 'preparing second repository' '
+	git clone -l -s A B && (
+		cd B &&
+		echo "foo bar" > file2 &&
+		git add file2 &&
+		git commit -m "next commit" file2 &&
+		git repack -a -d -l &&
+		git prune
+	)
+'
 
-cd "$base_dir"
+test_expect_success 'preparing third repository' '
+	git clone -l -s B C && (
+		cd C &&
+		echo "Goodbye, cruel world" > file3 &&
+		git add file3 &&
+		git commit -m "one more" file3 &&
+		git repack -a -d -l &&
+		git prune
+	)
+'
 
-test_expect_success 'validity of fourth repository' \
-'cd D &&
-test_valid_repo'
+test_expect_success 'count-objects shows the alternates' '
+	cat >expect <<-EOF &&
+	alternate: $(pwd)/B/.git/objects
+	alternate: $(pwd)/A/.git/objects
+	EOF
+	git -C C count-objects -v >actual &&
+	grep ^alternate: actual >actual.alternates &&
+	test_cmp expect actual.alternates
+'
 
-cd "$base_dir"
+# Note: These tests depend on the hard-coded value of 5 as the maximum depth
+# we will follow recursion. We start the depth at 0 and count links, not
+# repositories. This means that in a chain like:
+#
+#   A --> B --> C --> D --> E --> F --> G --> H
+#      0     1     2     3     4     5     6
+#
+# we are OK at "G", but break at "H", even though "H" is actually the 8th
+# repository, not the 6th, which you might expect. Counting the links allows
+# N+1 repositories, and counting from 0 to 5 inclusive allows 6 links.
+#
+# Note also that we must use "--bare -l" to make the link to H. The "-l"
+# ensures we do not do a connectivity check, and the "--bare" makes sure
+# we do not try to checkout the result (which needs objects), either of
+# which would cause the clone to fail.
+test_expect_success 'creating too deep nesting' '
+	git clone -l -s C D &&
+	git clone -l -s D E &&
+	git clone -l -s E F &&
+	git clone -l -s F G &&
+	git clone --bare -l -s G H
+'
 
-test_expect_success 'breaking of loops' \
-'echo "$base_dir"/B/.git/objects >> "$base_dir"/A/.git/objects/info/alternates&&
-cd C &&
-test_valid_repo'
+test_expect_success 'validity of seventh repository' '
+	git -C G fsck
+'
 
-cd "$base_dir"
+test_expect_success 'invalidity of eighth repository' '
+	test_must_fail git -C H fsck
+'
 
-test_expect_success 'that info/alternates is necessary' \
-'cd C &&
-rm -f .git/objects/info/alternates &&
-! (test_valid_repo)'
+test_expect_success 'breaking of loops' '
+	echo "$(pwd)"/B/.git/objects >>A/.git/objects/info/alternates &&
+	git -C C fsck
+'
 
-cd "$base_dir"
+test_expect_success 'that info/alternates is necessary' '
+	rm -f C/.git/objects/info/alternates &&
+	test_must_fail git -C C fsck
+'
 
-test_expect_success 'that relative alternate is possible for current dir' \
-'cd C &&
-echo "../../../B/.git/objects" > .git/objects/info/alternates &&
-test_valid_repo'
+test_expect_success 'that relative alternate is possible for current dir' '
+	echo "../../../B/.git/objects" >C/.git/objects/info/alternates &&
+	git fsck
+'
 
-cd "$base_dir"
+test_expect_success 'that relative alternate is recursive' '
+	git -C D fsck
+'
 
-test_expect_success \
-    'that relative alternate is only possible for current dir' '
-    cd D &&
-    ! (test_valid_repo)
+# we can reach "A" from our new repo both directly, and via "C".
+# The deep/subdir is there to make sure we are not doing a stupid
+# pure-text comparison of the alternate names.
+test_expect_success 'relative duplicates are eliminated' '
+	mkdir -p deep/subdir &&
+	git init --bare deep/subdir/duplicate.git &&
+	cat >deep/subdir/duplicate.git/objects/info/alternates <<-\EOF &&
+	../../../../C/.git/objects
+	../../../../A/.git/objects
+	EOF
+	cat >expect <<-EOF &&
+	alternate: $(pwd)/C/.git/objects
+	alternate: $(pwd)/B/.git/objects
+	alternate: $(pwd)/A/.git/objects
+	EOF
+	git -C deep/subdir/duplicate.git count-objects -v >actual &&
+	grep ^alternate: actual >actual.alternates &&
+	test_cmp expect actual.alternates
 '
 
-cd "$base_dir"
+test_expect_success CASE_INSENSITIVE_FS 'dup finding can be case-insensitive' '
+	git init --bare insensitive.git &&
+	# the previous entry for "A" will have used uppercase
+	cat >insensitive.git/objects/info/alternates <<-\EOF &&
+	../../C/.git/objects
+	../../a/.git/objects
+	EOF
+	cat >expect <<-EOF &&
+	alternate: $(pwd)/C/.git/objects
+	alternate: $(pwd)/B/.git/objects
+	alternate: $(pwd)/A/.git/objects
+	EOF
+	git -C insensitive.git count-objects -v >actual &&
+	grep ^alternate: actual >actual.alternates &&
+	test_cmp expect actual.alternates
+'
 
 test_done
diff --git a/transport.c b/transport.c
index a85801042..079499dba 100644
--- a/transport.c
+++ b/transport.c
@@ -1096,9 +1096,7 @@ static int refs_from_alternate_cb(struct alternate_object_database *e,
 	const struct ref *extra;
 	struct alternate_refs_data *cb = data;
 
-	e->name[-1] = '\0';
-	other = xstrdup(real_path(e->base));
-	e->name[-1] = '/';
+	other = xstrdup(real_path(e->path));
 	len = strlen(other);
 
 	while (other[len-1] == '/')