Re: [RFC PATCH] Move SHA-1 implementation selection into a header file

From: Junio C Hamano <gitster@pobox.com>
Date: Mar 14, 2017, 20:44 UTC
Message-ID: <xmqq1stzio5b.fsf@gitster.mtv.corp.google.com>
In-Reply-To: <20170314201424.vccij5z2ortq4a4o@sigill.intra.peff.net>

OK, then I'll queue this. The selection still goes to BASIC_CFLAGS so the dependencies for re-compilation should be right, I'd think.

-- >8 --
From: "brian m. carlson" <sandals@crustytoothpaste.net>
Date: Sat, 11 Mar 2017 22:28:18 +0000
Subject: [PATCH] hash.h: move SHA-1 implementation selection into a header file

Many developers use functionality in their editors that allows for quick syntax checks, including warning about questionable constructs. This functionality allows rapid development with fewer errors. However, such functionality generally does not allow the specification of project-specific defines or command-line options.

Since the SHA1_HEADER include is not defined in such a case, developers see spurious errors when using these tools. Furthermore, while using a macro as the argument to #include is permitted by C11, it isn't permitted by C89 and C99, and there are known implementations which reject it.

Instead of using SHA1_HEADER, create a hash.h header and use #if and #elif to select the desired header. Have the Makefile pass an appropriate option to help the header select the right implementation to use.

[jc: make BLK_SHA1 the fallback default as discussed on list, e.g. <20170314201424.vccij5z2ortq4a4o@sigill.intra.peff.net>; also remove SHA1_HEADER and SHA1_HEADER_SQ that are no longer used].

Signed-off-by: brian m. carlson <sandals@crustytoothpaste.net>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---
 Makefile | 12 +++++-------
 cache.h  |  2 +-
 hash.h   | 14 ++++++++++++++
 3 files changed, 20 insertions(+), 8 deletions(-)

diff --git a/Makefile b/Makefile
index 8e4081e061..25c21f08b1 100644
--- a/Makefile
+++ b/Makefile
@@ -1387,19 +1387,19 @@ ifdef APPLE_COMMON_CRYPTO
 endif
 
 ifdef BLK_SHA1
-	SHA1_HEADER = "block-sha1/sha1.h"
 	LIB_OBJS += block-sha1/sha1.o
+	BASIC_CFLAGS += -DSHA1_BLK
 else
 ifdef PPC_SHA1
-	SHA1_HEADER = "ppc/sha1.h"
 	LIB_OBJS += ppc/sha1.o ppc/sha1ppc.o
+	BASIC_CFLAGS += -DSHA1_PPC
 else
 ifdef APPLE_COMMON_CRYPTO
 	COMPAT_CFLAGS += -DCOMMON_DIGEST_FOR_OPENSSL
-	SHA1_HEADER = <CommonCrypto/CommonDigest.h>
+	BASIC_CFLAGS += -DSHA1_APPLE
 else
-	SHA1_HEADER = <openssl/sha.h>
 	EXTLIBS += $(LIB_4_CRYPTO)
+	BASIC_CFLAGS += -DSHA1_OPENSSL
 endif
 endif
 endif
@@ -1591,7 +1591,6 @@ endif
 
 # Shell quote (do not use $(call) to accommodate ancient setups);
 
-SHA1_HEADER_SQ = $(subst ','\'',$(SHA1_HEADER))
 ETC_GITCONFIG_SQ = $(subst ','\'',$(ETC_GITCONFIG))
 ETC_GITATTRIBUTES_SQ = $(subst ','\'',$(ETC_GITATTRIBUTES))
 
@@ -1624,8 +1623,7 @@ PERLLIB_EXTRA_SQ = $(subst ','\'',$(PERLLIB_EXTRA))
 # from the dependency list, that would make each entry appear twice.
 LIBS = $(filter-out %.o, $(GITLIBS)) $(EXTLIBS)
 
-BASIC_CFLAGS += -DSHA1_HEADER='$(SHA1_HEADER_SQ)' \
-	$(COMPAT_CFLAGS)
+BASIC_CFLAGS += $(COMPAT_CFLAGS)
 LIB_OBJS += $(COMPAT_OBJS)
 
 # Quote for C
diff --git a/cache.h b/cache.h
index 61fc86e6d7..f98c95bf2a 100644
--- a/cache.h
+++ b/cache.h
@@ -10,8 +10,8 @@
 #include "trace.h"
 #include "string-list.h"
 #include "pack-revindex.h"
+#include "hash.h"
 
-#include SHA1_HEADER
 #ifndef platform_SHA_CTX
 /*
  * platform's underlying implementation of SHA-1; could be OpenSSL,
diff --git a/hash.h b/hash.h
new file mode 100644
index 0000000000..f0d9ddd0c2
--- /dev/null
+++ b/hash.h
@@ -0,0 +1,14 @@
+#ifndef HASH_H
+#define HASH_H
+
+#if defined(SHA1_PPC)
+#include "ppc/sha1.h"
+#elif defined(SHA1_APPLE)
+#include <CommonCrypto/CommonDigest.h>
+#elif defined(SHA1_OPENSSL)
+#include <openssl/sha.h>
+#else /* SHA1_BLK */
+#include "block-sha1/sha1.h"
+#endif
+
+#endif