* [Outreachy PATCH] read-cache: do not skip the hash of the shared index
2026-11-07 12:11 [BUG] splitIndex with skipHash corrupts index and crashes status Andy Koppe
2026-11-07 21:10 ` Tanga Joris
@ 2026-11-08 23:42 ` Tanga Joris
1 sibling, 0 replies; 5+ messages in thread
From: Tanga Joris @ 2026-11-08 23:42 UTC (permalink / raw)
To: git
Cc: andy.koppe, gitster, stolee, github, christian.couder,
siddharthasthana31, kaartic.sivaraam, usmanakinyemi202,
Tanga Joris
With core.splitIndex and index.skipHash both set, index entries are
lost when a new shared index is written:
$ git init -q r && cd r
$ git config core.splitIndex true
$ git config index.skipHash true
$ touch foo && git add foo
$ git status --short
?? foo
write_shared_index() names the file after the shared index's trailing
checksum. With index.skipHash, that checksum is written as zeros. The
split index then records a null base, and read_index_from() treats a
null base as "no shared index". So the entries stored in the shared
index are lost, and "git status" can die with a BUG().
This has been broken since ee1f0c242e (read-cache: add index.skipHash
config option, 2023-01-06).
Never skip the hash when writing the shared index. $GIT_DIR/index
still honors index.skipHash, because it is written on every index
update. A new shared index is written much less often, so only those
writes pay for the hash.
"git reset" repairs an index that is already broken.
Reported-by: Andy Koppe <andy.koppe@gmail.com>
Signed-off-by: Tanga Joris <tangajoris@gmail.com>
---
A new shared index is only written when more than
splitIndex.maxPercentChange (20% by default) of the entries are not in
it, or by "git update-index --split-index".
Entries that the split index stores as replacements show up with an
empty name, so "git ls-files" prints "./" for them.
read-cache.c | 16 +++++++++++-----
t/t1700-split-index.sh | 41 +++++++++++++++++++++++++++++++++++++++++
2 files changed, 52 insertions(+), 5 deletions(-)
diff --git a/read-cache.c b/read-cache.c
index e40f290bb3..c48ea7b1e0 100644
--- a/read-cache.c
+++ b/read-cache.c
@@ -2818,7 +2818,8 @@ enum write_extensions {
* rely on it.
*/
static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
- enum write_extensions write_extensions, unsigned flags)
+ enum write_extensions write_extensions, unsigned flags,
+ int skip_hash)
{
uint64_t start = getnanotime();
struct hashfile *f;
@@ -2841,8 +2842,7 @@ static int do_write_index(struct index_state *istate, struct tempfile *tempfile,
f = hashfd(the_repository->hash_algo, tempfile->fd, tempfile->filename.buf);
- prepare_repo_settings(r);
- f->skip_hash = r->settings.index_skip_hash;
+ f->skip_hash = skip_hash;
for (i = removed = extended = 0; i < entries; i++) {
if (cache[i]->ce_flags & CE_REMOVE)
@@ -3147,9 +3147,11 @@ static int do_write_locked_index(struct index_state *istate,
return ret;
}
+ prepare_repo_settings(istate->repo);
trace2_region_enter_printf("index", "do_write_index", istate->repo,
"%s", get_lock_file_path(lock));
- ret = do_write_index(istate, lock->tempfile, write_extensions, flags);
+ ret = do_write_index(istate, lock->tempfile, write_extensions, flags,
+ istate->repo->settings.index_skip_hash);
trace2_region_leave_printf("index", "do_write_index", istate->repo,
"%s", get_lock_file_path(lock));
@@ -3262,9 +3264,13 @@ static int write_shared_index(struct index_state *istate,
move_cache_to_base_index(istate);
convert_to_sparse(istate, 0);
+ /*
+ * The shared index is named after its hash, and the split index
+ * refers to it by that hash, so never skip it here.
+ */
trace2_region_enter_printf("index", "shared/do_write_index",
the_repository, "%s", get_tempfile_path(*temp));
- ret = do_write_index(si->base, *temp, WRITE_NO_EXTENSION, flags);
+ ret = do_write_index(si->base, *temp, WRITE_NO_EXTENSION, flags, 0);
trace2_region_leave_printf("index", "shared/do_write_index",
the_repository, "%s", get_tempfile_path(*temp));
diff --git a/t/t1700-split-index.sh b/t/t1700-split-index.sh
index 887e72a5fa..2517ac9eff 100755
--- a/t/t1700-split-index.sh
+++ b/t/t1700-split-index.sh
@@ -544,4 +544,45 @@ test_expect_success 'GIT_TEST_SPLIT_INDEX works' '
)
'
+test_expect_success 'index.skipHash does not apply to the shared index' '
+ git init skip-hash-rewrite &&
+ (
+ cd skip-hash-rewrite &&
+ git config core.splitIndex true &&
+ >foo &&
+ >bar &&
+ git add foo bar &&
+ git commit -m initial &&
+ git config index.skipHash true &&
+ git update-index --split-index &&
+ test_path_is_missing .git/sharedindex.$ZERO_OID &&
+ test_trailing_hash .git/index >hash &&
+ echo $ZERO_OID >expect &&
+ test_cmp expect hash &&
+ cat >expect <<-\EOF &&
+ bar
+ foo
+ EOF
+ git ls-files >actual &&
+ test_cmp expect actual &&
+ git status --short --untracked-files=no >actual &&
+ test_must_be_empty actual
+ )
+'
+
+test_expect_success 'index.skipHash does not lose the first entry in split mode' '
+ git init skip-hash-first-add &&
+ (
+ cd skip-hash-first-add &&
+ git config core.splitIndex true &&
+ git config index.skipHash true &&
+ >foo &&
+ git add foo &&
+ test_path_is_missing .git/sharedindex.$ZERO_OID &&
+ echo foo >expect &&
+ git ls-files >actual &&
+ test_cmp expect actual
+ )
+'
+
test_done
--
2.56.0.388.g09a996e1ff
^ permalink raw reply related [flat|nested] 5+ messages in thread