[PATCH v2 4/4] pack-write: rename *.idx file into place last (really!)

["Ævar Arnfjörð Bjarmason" <avarab@gmail.com>]

Follow-up a preceding commit (pack-write.c: rename `.idx` file into
place last, 2021-08-16)[1] and rename the *.idx file in-place after we
write the *.bitmap. The preceding commit fixed the issue of *.idx
being written before *.rev files, but did not do so for *.idx files.

See 7cc8f971085 (pack-objects: implement bitmap writing, 2013-12-21)
for commentary at the time when *.bitmap was implemented about how
those files are written out, nothing in that commit contradicts what's
being done here.

Note that the referenced earlier commit[1] is overly optimistic about
"clos[ing the] race", i.e. yes we'll now write the files in the right
order, but we might still race due to our sloppy use of fsync(). See
the thread at [2] for a rabbit hole of various discussions about
filesystem races in the face of doing and not doing fsync() (and if
doing fsync(), not doing it properly).

1. https://lore.kernel.org/git/a6a4d2154e83d41c10986c5f455279ab249a910c.1630461918.git.me@ttaylorr.com/
2. https://lore.kernel.org/git/8735qgkvv1.fsf@evledraar.gmail.com/

Signed-off-by: Ævar Arnfjörð Bjarmason <avarab@gmail.com>
---
 builtin/pack-objects.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/builtin/pack-objects.c b/builtin/pack-objects.c
index 33567aaa74..396240c25a 100644
--- a/builtin/pack-objects.c
+++ b/builtin/pack-objects.c
@@ -1249,7 +1249,6 @@ static void write_pack_file(void)
 			stage_tmp_packfiles(&tmpname, pack_tmp_name,
 					    written_list, nr_written,
 					    &pack_idx_opts, hash, &idx_tmp_name);
-			rename_tmp_packfile_idx(&tmpname, hash, &idx_tmp_name);
 
 			if (write_bitmap_index) {
 				struct strbuf sb = STRBUF_INIT;
@@ -1268,6 +1267,8 @@ static void write_pack_file(void)
 				strbuf_release(&sb);
 			}
 
+			rename_tmp_packfile_idx(&tmpname, hash, &idx_tmp_name);
+
 			free(idx_tmp_name);
 			strbuf_release(&tmpname);
 			free(pack_tmp_name);
-- 
2.33.0.819.gea1b153a43c