[PATCH v4] show-index: fix uninitialized hash function

[Abhijeet Sonar <abhijeet.nkt@gmail.com>]

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
thier own default when this is not present.

As stated in the docs, show-index should use SHA1 as the default hash
algorithm when ran outsize of 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 ran outside of a repository). Also add a test that
verifies this behaviour.

Signed-off-by: Abhijeet Sonar <abhijeet.nkt@gmail.com>
---
 builtin/show-index.c   | 6 ++++++
 rm                     | 3 +++
 t/t5300-pack-object.sh | 4 ++++
 3 files changed, 13 insertions(+)
 create mode 100755 rm

diff --git a/builtin/show-index.c b/builtin/show-index.c
index f164c01bbe..645c2548fb 100644
--- a/builtin/show-index.c
+++ b/builtin/show-index.c
@@ -38,6 +38,12 @@ 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/rm b/rm
new file mode 100755
index 0000000000..2237506bf2
--- /dev/null
+++ b/rm
@@ -0,0 +1,3 @@
+#!/bin/sh
+
+echo rm $@
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 &&
-- 
2.47.0.107.g34b6ce9b30