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Sun, 08 Nov 2026 15:43:10 -0800 (PST) Received: from HP ([102.0.122.224]) by smtp.gmail.com with ESMTPSA id ffacd0b85a97d-4959011c995sm6448619f8f.0.2026.11.08.15.43.07 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Sun, 08 Nov 2026 15:43:09 -0800 (PST) From: Tanga Joris To: git@vger.kernel.org Cc: andy.koppe@gmail.com, gitster@pobox.com, stolee@gmail.com, github@paulisageek.com, christian.couder@gmail.com, siddharthasthana31@gmail.com, kaartic.sivaraam@gmail.com, usmanakinyemi202@gmail.com, Tanga Joris Subject: [Outreachy PATCH] read-cache: do not skip the hash of the shared index Date: Mon, 9 Nov 2026 02:42:35 +0300 Message-ID: <20261108234235.1594316-1-tangajoris@gmail.com> X-Mailer: git-send-email 2.56.0.388.g09a996e1ff In-Reply-To: <20261107121119.2995843-1-andy.koppe@gmail.com> References: <20261107121119.2995843-1-andy.koppe@gmail.com> X-Mailing-List: git@vger.kernel.org List-Id: List-Post: List-Help: List-Subscribe: List-Unsubscribe: List-Owner: Precedence: list MIME-Version: 1.0 Content-Transfer-Encoding: 8bit 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 Signed-off-by: Tanga Joris --- 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