From 4da8d90fdda420e981b49452719fc4aea322e815 Mon Sep 17 00:00:00 2001
From: Abhijeet Sonar <abhijeet.nkt@gmail.com>
Date: Sat, 9 Nov 2024 14:57:38 +0530
Subject: [PATCH 1/2] show-index: fix uninitialized hash function

In c8aed5e8da (repository: stop setting SHA1 as the default object
hash), we got rid of the default hash algorithm for the_repository.
Due to this change, it is now the responsibility of the callers to set
their own default when this is not present.

As stated in the docs, show-index should use SHA1 as the default hash
algorithm when run outside a repository. Make sure this promise is
met by falling back to SHA1 when the_hash_algo is not present (i.e.
when the command is run outside a repository). Also add a test that
verifies this behavior.

Signed-off-by: Abhijeet Sonar <abhijeet.nkt@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 builtin/show-index.c   | 9 +++++++++
 t/t5300-pack-object.sh | 4 ++++
 2 files changed, 13 insertions(+)

diff --git a/builtin/show-index.c b/builtin/show-index.c
index f164c01bbe..b5e337869d 100644
--- a/builtin/show-index.c
+++ b/builtin/show-index.c
@@ -38,6 +38,15 @@ int cmd_show_index(int argc,
 		repo_set_hash_algo(the_repository, hash_algo);
 	}
 
+	/*
+	 * Fallback to SHA1 if we are running outside of a repository.
+	 *
+	 * TODO: Figure out and implement a way to detect the hash algorithm in use by the
+	 *       the index file passed in and use that instead.
+	 */
+	if (!the_hash_algo)
+		repo_set_hash_algo(the_repository, GIT_HASH_SHA1);
+
 	hashsz = the_hash_algo->rawsz;
 
 	if (fread(top_index, 2 * 4, 1, stdin) != 1)
diff --git a/t/t5300-pack-object.sh b/t/t5300-pack-object.sh
index 3b9dae331a..51fed26cc4 100755
--- a/t/t5300-pack-object.sh
+++ b/t/t5300-pack-object.sh
@@ -523,6 +523,10 @@ test_expect_success 'index-pack --strict <pack> works in non-repo' '
 	test_path_is_file foo.idx
 '
 
+test_expect_success SHA1 'show-index works OK outside a repository' '
+	nongit git show-index <foo.idx
+'
+
 test_expect_success !PTHREADS,!FAIL_PREREQS \
 	'index-pack --threads=N or pack.threads=N warns when no pthreads' '
 	test_must_fail git index-pack --threads=2 2>err &&

From 34d3f2a984eed5c31384e384f391293d38478036 Mon Sep 17 00:00:00 2001
From: Abhijeet Sonar <abhijeet.nkt@gmail.com>
Date: Sat, 9 Nov 2024 14:57:39 +0530
Subject: [PATCH 2/2] t5300: add test for 'show-index --object-format'

In 88a09a557c (builtin/show-index: provide options to determine hash
algo), the flag --object-format was added to show-index builtin as a way
to provide a hash algorithm explicitly. However, we do not have tests in
place for that functionality. Add them.

Signed-off-by: Abhijeet Sonar <abhijeet.nkt@gmail.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 t/t5300-pack-object.sh | 14 ++++++++++++++
 1 file changed, 14 insertions(+)

diff --git a/t/t5300-pack-object.sh b/t/t5300-pack-object.sh
index 51fed26cc4..bb6a22b438 100755
--- a/t/t5300-pack-object.sh
+++ b/t/t5300-pack-object.sh
@@ -527,6 +527,20 @@ test_expect_success SHA1 'show-index works OK outside a repository' '
 	nongit git show-index <foo.idx
 '
 
+for hash in sha1 sha256
+do
+	test_expect_success 'show-index works OK outside a repository with hash algo passed in via --object-format' '
+		test_when_finished "rm -rf explicit-hash-$hash" &&
+		git init --object-format=$hash explicit-hash-$hash &&
+		test_commit -C explicit-hash-$hash one &&
+		git -C explicit-hash-$hash rev-parse one >in &&
+		git -C explicit-hash-$hash pack-objects explicit-hash-$hash <in &&
+		idx=$(echo explicit-hash-$hash/explicit-hash-$hash*.idx) &&
+		nongit git show-index --object-format=$hash <"$idx" >actual &&
+		test_line_count = 1 actual
+	'
+done
+
 test_expect_success !PTHREADS,!FAIL_PREREQS \
 	'index-pack --threads=N or pack.threads=N warns when no pthreads' '
 	test_must_fail git index-pack --threads=2 2>err &&