Merge branch 'jt/help-sha-backend-info-in-build-options'

"git help --build-options" reports SHA-1 and SHA-256 backends used
in the build.

* jt/help-sha-backend-info-in-build-options:
  help: include unsafe SHA-1 build info in version
  help: include SHA implementation in version info

Author: gitster

Documentation/git-version.adoc

@@ -22,6 +22,14 @@ OPTIONS
 --build-options::
 	Include additional information about how git was built for diagnostic
 	purposes.
++
+The libraries used to implement the SHA-1 and SHA-256 algorithms are displayed
+in the form `SHA-1: <option>` and `SHA-256: <option>`. Note that the SHA-1
+options `SHA1_APPLE`, `SHA1_OPENSSL`, and `SHA1_BLK` do not use a collision
+detection algorithm and thus may be vulnerable to known SHA-1 collision
+attacks. When a faster SHA-1 implementation without collision detection is used
+for only non-cryptographic purposes, the algorithm is displayed in the form
+`non-collision-detecting-SHA-1: <option>`.
 
 GIT
 ---

hash.h

@@ -2,26 +2,32 @@
 #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
 
 #if defined(SHA1_APPLE_UNSAFE)
+#  define SHA1_UNSAFE_BACKEND "SHA1_APPLE_UNSAFE"
 #  include <CommonCrypto/CommonDigest.h>
 #  define platform_SHA_CTX_unsafe CC_SHA1_CTX
 #  define platform_SHA1_Init_unsafe CC_SHA1_Init
 #  define platform_SHA1_Update_unsafe CC_SHA1_Update
 #  define platform_SHA1_Final_unsafe CC_SHA1_Final
 #elif defined(SHA1_OPENSSL_UNSAFE)
+#  define SHA1_UNSAFE_BACKEND "SHA1_OPENSSL_UNSAFE"
 #  include <openssl/sha.h>
 #  if defined(OPENSSL_API_LEVEL) && OPENSSL_API_LEVEL >= 3
 #    define SHA1_NEEDS_CLONE_HELPER_UNSAFE
@@ -38,6 +44,7 @@
 #    define platform_SHA1_Final_unsafe SHA1_Final
 #  endif
 #elif defined(SHA1_BLK_UNSAFE)
+#  define SHA1_UNSAFE_BACKEND "SHA1_BLK_UNSAFE"
 #  include "block-sha1/sha1.h"
 #  define platform_SHA_CTX_unsafe blk_SHA_CTX
 #  define platform_SHA1_Init_unsafe blk_SHA1_Init
@@ -46,17 +53,21 @@
 #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
 

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"
@@ -803,6 +804,12 @@ void get_version_info(struct strbuf *buf, int show_build_options)
 #elif defined ZLIB_VERSION
 		strbuf_addf(buf, "zlib: %s\n", ZLIB_VERSION);
 #endif
+		strbuf_addf(buf, "SHA-1: %s\n", SHA1_BACKEND);
+#if defined SHA1_UNSAFE_BACKEND
+		strbuf_addf(buf, "non-collision-detecting-SHA-1: %s\n",
+			    SHA1_UNSAFE_BACKEND);
+#endif
+		strbuf_addf(buf, "SHA-256: %s\n", SHA256_BACKEND);
 	}
 }