[PATCH 01/10] hash: add a constant for the default hash algorithm

From: brian m. carlson <sandals@crustytoothpaste.net>
Date: Jun 20, 2025, 01:19 UTC
Message-ID: <20250620011943.586596-2-sandals@crustytoothpaste.net>
In-Reply-To: <20250620011943.586596-1-sandals@crustytoothpaste.net>

Right now, SHA-1 is the default hash algorithm in Git. However, this may change in the future.

We have many places in our code that use the SHA-1 constant to indicate the default hash if none is specified, but it will end up being more practical to specify this explicitly and clearly using a constant for whatever the default hash algorithm is. Then, if we decide to change it in the future, we can simply replace the constant representing the default with a new value.

For these reasons, introduce GIT_HASH_DEFAULT to represent the default hash algorithm.

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
---
 hash.h | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/hash.h b/hash.h
index d6422ddf45..0d3d85e04c 100644
--- a/hash.h
+++ b/hash.h
@@ -174,6 +174,8 @@ static inline void git_SHA256_Clone(git_SHA256_CTX *dst, const git_SHA256_CTX *s
 #define GIT_HASH_SHA256 2
 /* Number of algorithms supported (including unknown). */
 #define GIT_HASH_NALGOS (GIT_HASH_SHA256 + 1)
+/* Default hash algorithm if unspecified. */
+#define GIT_HASH_DEFAULT GIT_HASH_SHA1
 
 /* "sha1", big-endian */
 #define GIT_SHA1_FORMAT_ID 0x73686131