Subject: [PATCH v2 1/2] help: include SHA implementation in version info

From: Justin Tobler <[email-masked]>
Date: Tue, 1 Apr 2025 15:36:29 -0500

When the `--build-options` flag is used with git-version(1), additional
information about the built version of Git is printed. During build
time, different SHA implementations may be configured, but this
information is not included in the version info.

Add the SHA implementations Git is built with to the version info by
requiring each backend to define a SHA1_BACKEND or SHA256_BACKEND symbol
as appropriate and use the value in the printed build options.

Signed-off-by: Justin Tobler <[email-masked]>
---
 Documentation/git-version.adoc | 3 +++
 hash.h                         | 8 ++++++++
 help.c                         | 8 ++++++++
 3 files changed, 19 insertions(+)

diff --git a/Documentation/git-version.adoc b/Documentation/git-version.adoc
index 80fa7754a6..f06758a7cf 100644
--- a/Documentation/git-version.adoc
+++ b/Documentation/git-version.adoc
@@ -22,6 +22,9 @@ OPTIONS
 --build-options::
 	Include additional information about how git was built for diagnostic
 	purposes.
++
+Note that the SHA1 options `SHA1_APPLE`, `SHA1_OPENSSL`, and `SHA1_BLK` do not
+have collision detection.
 
 GIT
 ---
diff --git a/hash.h b/hash.h
index 4367acfec5..51cd0ec7b6 100644
--- a/hash.h
+++ b/hash.h
@@ -2,16 +2,20 @@
 #define HASH_H
 
 #if defined(SHA1_APPLE)
+#define SHA1_BACKEND "SHA1_APPLE (No collision detection)"
 #include <CommonCrypto/CommonDigest.h>
 #elif defined(SHA1_OPENSSL)
+#  define SHA1_BACKEND "SHA1_OPENSSL (No collision detection)"
 #  include <openssl/sha.h>
 #  if defined(OPENSSL_API_LEVEL) && OPENSSL_API_LEVEL >= 3
 #    define SHA1_NEEDS_CLONE_HELPER
 #    include "sha1/openssl.h"
 #  endif
 #elif defined(SHA1_DC)
+#define SHA1_BACKEND "SHA1_DC"
 #include "sha1dc_git.h"
 #else /* SHA1_BLK */
+#define SHA1_BACKEND "SHA1_BLK (No collision detection)"
 #include "block-sha1/sha1.h"
 #endif
 
@@ -46,17 +50,21 @@
 #endif
 
 #if defined(SHA256_NETTLE)
+#define SHA256_BACKEND "SHA256_NETTLE"
 #include "sha256/nettle.h"
 #elif defined(SHA256_GCRYPT)
+#define SHA256_BACKEND "SHA256_GCRYPT"
 #define SHA256_NEEDS_CLONE_HELPER
 #include "sha256/gcrypt.h"
 #elif defined(SHA256_OPENSSL)
+#  define SHA256_BACKEND "SHA256_OPENSSL"
 #  include <openssl/sha.h>
 #  if defined(OPENSSL_API_LEVEL) && OPENSSL_API_LEVEL >= 3
 #    define SHA256_NEEDS_CLONE_HELPER
 #    include "sha256/openssl.h"
 #  endif
 #else
+#define SHA256_BACKEND "SHA256_BLK"
 #include "sha256/block/sha256.h"
 #endif
 
diff --git a/help.c b/help.c
index c54bd9918a..3aebfb3681 100644
--- a/help.c
+++ b/help.c
@@ -9,6 +9,7 @@
 #include "run-command.h"
 #include "levenshtein.h"
 #include "gettext.h"
+#include "hash.h"
 #include "help.h"
 #include "command-list.h"
 #include "string-list.h"
@@ -768,6 +769,12 @@ char *help_unknown_cmd(const char *cmd)
 	exit(1);
 }
 
+static void get_sha_impl(struct strbuf *buf)
+{
+	strbuf_addf(buf, "SHA-1: %s\n", SHA1_BACKEND);
+	strbuf_addf(buf, "SHA-256: %s\n", SHA256_BACKEND);
+}
+
 void get_version_info(struct strbuf *buf, int show_build_options)
 {
 	/*
@@ -803,6 +810,7 @@ void get_version_info(struct strbuf *buf, int show_build_options)
 #elif defined ZLIB_VERSION
 		strbuf_addf(buf, "zlib: %s\n", ZLIB_VERSION);
 #endif
+		get_sha_impl(buf);
 	}
 }
 
-- 
2.49.0