midx: fix *.rev cleanups with --object-dir

If using --object-dir to point into an object directory which belongs to
a different repository than the one in the current working directory,
such as:

  git init repo
  git -C repo ... # add some objects
  cd alternate
  git multi-pack-index --object-dir ../repo/.git/objects write

the binary will segfault trying to access the object-dir via the repo it
found, but that's not fully initialized. Worse, if we later call
clear_midx_files_ext(), we will use `the_repository` and remove files
out of the wrong object directory.

Fix this by using the given object_dir (or the object directory of
`the_repository` if `--object-dir` wasn't given) to properly to clean up
the *.rev files, avoiding the crash.

Original-patch-by: Johannes Berg <[email protected]>
Signed-off-by: Taylor Blau <[email protected]>
Signed-off-by: Junio C Hamano <[email protected]>

Author: ttaylorr

midx.c

@@ -882,7 +882,7 @@ static void write_midx_reverse_index(char *midx_name, unsigned char *midx_hash,
 	strbuf_release(&buf);
 }
 
-static void clear_midx_files_ext(struct repository *r, const char *ext,
+static void clear_midx_files_ext(const char *object_dir, const char *ext,
 				 unsigned char *keep_hash);
 
 static int midx_checksum_valid(struct multi_pack_index *m)
@@ -1086,7 +1086,7 @@ static int write_midx_internal(const char *object_dir, struct multi_pack_index *
 
 	if (flags & MIDX_WRITE_REV_INDEX)
 		write_midx_reverse_index(midx_name, midx_hash, &ctx);
-	clear_midx_files_ext(the_repository, ".rev", midx_hash);
+	clear_midx_files_ext(object_dir, ".rev", midx_hash);
 
 	commit_lock_file(&lk);
 
@@ -1135,7 +1135,7 @@ static void clear_midx_file_ext(const char *full_path, size_t full_path_len,
 		die_errno(_("failed to remove %s"), full_path);
 }
 
-static void clear_midx_files_ext(struct repository *r, const char *ext,
+static void clear_midx_files_ext(const char *object_dir, const char *ext,
 				 unsigned char *keep_hash)
 {
 	struct clear_midx_data data;
@@ -1146,7 +1146,7 @@ static void clear_midx_files_ext(struct repository *r, const char *ext,
 				    hash_to_hex(keep_hash), ext);
 	data.ext = ext;
 
-	for_each_file_in_pack_dir(r->objects->odb->path,
+	for_each_file_in_pack_dir(object_dir,
 				  clear_midx_file_ext,
 				  &data);
 
@@ -1165,7 +1165,7 @@ void clear_midx_file(struct repository *r)
 	if (remove_path(midx))
 		die(_("failed to clear multi-pack-index at %s"), midx);
 
-	clear_midx_files_ext(r, ".rev", NULL);
+	clear_midx_files_ext(r->objects->odb->path, ".rev", NULL);
 
 	free(midx);
 }

t/t5319-multi-pack-index.sh

@@ -201,6 +201,34 @@ test_expect_success 'write midx with twelve packs' '
 
 compare_results_with_midx "twelve packs"
 
+test_expect_success 'multi-pack-index *.rev cleanup with --object-dir' '
+	git init repo &&
+	git clone -s repo alternate &&
+
+	test_when_finished "rm -rf repo alternate" &&
+
+	(
+		cd repo &&
+		test_commit base &&
+		git repack -d
+	) &&
+
+	ours="alternate/.git/objects/pack/multi-pack-index-123.rev" &&
+	theirs="repo/.git/objects/pack/multi-pack-index-abc.rev" &&
+	touch "$ours" "$theirs" &&
+
+	(
+		cd alternate &&
+		git multi-pack-index --object-dir ../repo/.git/objects write
+	) &&
+
+	# writing a midx in "repo" should not remove the .rev file in the
+	# alternate
+	test_path_is_file repo/.git/objects/pack/multi-pack-index &&
+	test_path_is_file $ours &&
+	test_path_is_missing $theirs
+'
+
 test_expect_success 'warn on improper hash version' '
 	git init --object-format=sha1 sha1 &&
 	(