cmake: streamline backend detection

We're currently doing unnecessary work to auto-detect backends even if
the functionality is disabled altogether. Let's fix this by removing the
extraneous FOO_BACKEND variables, instead letting auto-detection modify
the variable itself.

cmake/Modules/SelectGSSAPI.cmake

-# Select the backend to use
-
-# We try to find any packages our backends might use
-
 INCLUDE(SanitizeBool)
 
+# We try to find any packages our backends might use
 FIND_PACKAGE(GSSAPI)
 IF (CMAKE_SYSTEM_NAME MATCHES "Darwin")
 	INCLUDE(FindGSSFramework)
 ENDIF()
 
-# Auto-select GSS backend
-SanitizeBool(USE_GSSAPI)
-IF (USE_GSSAPI STREQUAL ON)
-	IF (GSSFRAMEWORK_FOUND)
-		SET(GSS_BACKEND "GSS.framework")
-	ELSEIF(GSSAPI_FOUND)
-		SET(GSS_BACKEND "gssapi")
-	ELSE()
-		MESSAGE(FATAL_ERROR "Unable to autodetect a usable GSS backend."
-			"Please pass the backend name explicitly (-DUSE_GSS=backend)")
+IF(USE_GSSAPI)
+	# Auto-select GSS backend
+	SanitizeBool(USE_GSSAPI)
+	IF (USE_GSSAPI STREQUAL ON)
+		IF (GSSFRAMEWORK_FOUND)
+			SET(USE_GSSAPI "GSS.framework")
+		ELSEIF(GSSAPI_FOUND)
+			SET(USE_GSSAPI "gssapi")
+		ELSE()
+			MESSAGE(FATAL_ERROR "Unable to autodetect a usable GSS backend."
+				"Please pass the backend name explicitly (-DUSE_GSS=backend)")
+		ENDIF()
 	ENDIF()
-ELSEIF(USE_GSSAPI)
-	# Backend was explicitly set
-	SET(GSS_BACKEND ${USE_GSSAPI})
-ELSE()
-	SET(GSS_BACKEND NO)
-ENDIF()
 
-IF(GSS_BACKEND)
 	# Check that we can find what's required for the selected backend
-	IF (GSS_BACKEND STREQUAL "GSS.framework")
+	IF (USE_GSSAPI STREQUAL "GSS.framework")
 		IF (NOT GSSFRAMEWORK_FOUND)
 			MESSAGE(FATAL_ERROR "Asked for GSS.framework backend, but it wasn't found")
 		ENDIF()
@@ -37,8 +29,8 @@ IF(GSS_BACKEND)
 		LIST(APPEND LIBGIT2_LIBS ${GSSFRAMEWORK_LIBRARIES})
 
 		SET(GIT_GSSFRAMEWORK 1)
-		ADD_FEATURE_INFO(SPNEGO GIT_GSSFRAMEWORK "SPNEGO authentication support (${GSS_BACKEND})")
-	ELSEIF (GSS_BACKEND STREQUAL "gssapi")
+		ADD_FEATURE_INFO(SPNEGO GIT_GSSFRAMEWORK "SPNEGO authentication support (${USE_GSSAPI})")
+	ELSEIF (USE_GSSAPI STREQUAL "gssapi")
 		IF (NOT GSSAPI_FOUND)
 			MESSAGE(FATAL_ERROR "Asked for gssapi GSS backend, but it wasn't found")
 		ENDIF()
@@ -46,9 +38,9 @@ IF(GSS_BACKEND)
 		LIST(APPEND LIBGIT2_LIBS ${GSSAPI_LIBRARIES})
 
 		SET(GIT_GSSAPI 1)
-		ADD_FEATURE_INFO(SPNEGO GIT_GSSAPI "SPNEGO authentication support (${GSS_BACKEND})")
+		ADD_FEATURE_INFO(SPNEGO GIT_GSSAPI "SPNEGO authentication support (${USE_GSSAPI})")
 	ELSE()
-		MESSAGE(FATAL_ERROR "Asked for backend ${GSS_BACKEND} but it wasn't found")
+		MESSAGE(FATAL_ERROR "Asked for backend ${USE_GSSAPI} but it wasn't found")
 	ENDIF()
 ELSE()
 	SET(GIT_GSSAPI 0)

cmake/Modules/SelectHTTPSBackend.cmake

-# Select the backend to use
-
 INCLUDE(SanitizeBool)
 
 # We try to find any packages our backends might use
@@ -10,36 +8,31 @@ IF (CMAKE_SYSTEM_NAME MATCHES "Darwin")
 	FIND_PACKAGE(CoreFoundation)
 ENDIF()
 
-# Auto-select TLS backend
-SanitizeBool(USE_HTTPS)
-IF (USE_HTTPS STREQUAL ON)
-	IF (SECURITY_FOUND)
-		IF (SECURITY_HAS_SSLCREATECONTEXT)
-			SET(HTTPS_BACKEND "SecureTransport")
+IF(USE_HTTPS)
+	# Auto-select TLS backend
+	SanitizeBool(USE_HTTPS)
+	IF (USE_HTTPS STREQUAL ON)
+		IF (SECURITY_FOUND)
+			IF (SECURITY_HAS_SSLCREATECONTEXT)
+				SET(USE_HTTPS "SecureTransport")
+			ELSE()
+				MESSAGE(STATUS "Security framework is too old, falling back to OpenSSL")
+				SET(USE_HTTPS "OpenSSL")
+			ENDIF()
+		ELSEIF (WINHTTP)
+			SET(USE_HTTPS "WinHTTP")
+		ELSEIF(OPENSSL_FOUND)
+			SET(USE_HTTPS "OpenSSL")
+		ELSEIF(MBEDTLS_FOUND)
+			SET(USE_HTTPS "mbedTLS")
 		ELSE()
-			MESSAGE(STATUS "Security framework is too old, falling back to OpenSSL")
-			SET(HTTPS_BACKEND "OpenSSL")
+			MESSAGE(FATAL_ERROR "Unable to autodetect a usable HTTPS backend."
+				"Please pass the backend name explicitly (-DUSE_HTTPS=backend)")
 		ENDIF()
-	ELSEIF (WINHTTP)
-		SET(HTTPS_BACKEND "WinHTTP")
-	ELSEIF(OPENSSL_FOUND)
-		SET(HTTPS_BACKEND "OpenSSL")
-	ELSEIF(MBEDTLS_FOUND)
-		SET(HTTPS_BACKEND "mbedTLS")
-	ELSE()
-		MESSAGE(FATAL_ERROR "Unable to autodetect a usable HTTPS backend."
-			"Please pass the backend name explicitly (-DUSE_HTTPS=backend)")
 	ENDIF()
-ELSEIF(USE_HTTPS)
-	# HTTPS backend was explicitly set
-	SET(HTTPS_BACKEND ${USE_HTTPS})
-ELSE()
-	SET(HTTPS_BACKEND NO)
-ENDIF()
 
-IF(HTTPS_BACKEND)
 	# Check that we can find what's required for the selected backend
-	IF (HTTPS_BACKEND STREQUAL "SecureTransport")
+	IF (USE_HTTPS STREQUAL "SecureTransport")
 		IF (NOT COREFOUNDATION_FOUND)
 			MESSAGE(FATAL_ERROR "Cannot use SecureTransport backend, CoreFoundation.framework not found")
 		ENDIF()
@@ -54,7 +47,7 @@ IF(HTTPS_BACKEND)
 		LIST(APPEND LIBGIT2_SYSTEM_INCLUDES ${SECURITY_INCLUDE_DIR})
 		LIST(APPEND LIBGIT2_LIBS ${COREFOUNDATION_LDFLAGS} ${SECURITY_LDFLAGS})
 		LIST(APPEND LIBGIT2_PC_LIBS ${COREFOUNDATION_LDFLAGS} ${SECURITY_LDFLAGS})
-	ELSEIF (HTTPS_BACKEND STREQUAL "OpenSSL")
+	ELSEIF (USE_HTTPS STREQUAL "OpenSSL")
 		IF (NOT OPENSSL_FOUND)
 			MESSAGE(FATAL_ERROR "Asked for OpenSSL TLS backend, but it wasn't found")
 		ENDIF()
@@ -64,7 +57,7 @@ IF(HTTPS_BACKEND)
 		LIST(APPEND LIBGIT2_LIBS ${OPENSSL_LIBRARIES})
 		LIST(APPEND LIBGIT2_PC_LIBS ${OPENSSL_LDFLAGS})
 		LIST(APPEND LIBGIT2_PC_REQUIRES "openssl")
-	ELSEIF(HTTPS_BACKEND STREQUAL "mbedTLS")
+	ELSEIF(USE_HTTPS STREQUAL "mbedTLS")
 		IF (NOT MBEDTLS_FOUND)
 			MESSAGE(FATAL_ERROR "Asked for mbedTLS backend, but it wasn't found")
 		ENDIF()
@@ -113,14 +106,14 @@ IF(HTTPS_BACKEND)
 		# https://github.com/ARMmbed/mbedtls/issues/228
 		# For now, pass its link flags as our own
 		LIST(APPEND LIBGIT2_PC_LIBS ${MBEDTLS_LIBRARIES})
-	ELSEIF (HTTPS_BACKEND STREQUAL "WinHTTP")
+	ELSEIF (USE_HTTPS STREQUAL "WinHTTP")
 		# WinHTTP setup was handled in the WinHTTP-specific block above
 	ELSE()
-		MESSAGE(FATAL_ERROR "Asked for backend ${HTTPS_BACKEND} but it wasn't found")
+		MESSAGE(FATAL_ERROR "Asked for backend ${USE_HTTPS} but it wasn't found")
 	ENDIF()
 
 	SET(GIT_HTTPS 1)
-	ADD_FEATURE_INFO(HTTPS GIT_HTTPS "using ${HTTPS_BACKEND}")
+	ADD_FEATURE_INFO(HTTPS GIT_HTTPS "using ${USE_HTTPS}")
 ELSE()
 	SET(GIT_HTTPS 0)
 	ADD_FEATURE_INFO(HTTPS NO "")

cmake/Modules/SelectHashes.cmake

@@ -5,37 +5,28 @@ INCLUDE(SanitizeBool)
 # USE_SHA1=CollisionDetection(ON)/HTTPS/Generic/OFF
 
 SanitizeBool(USE_SHA1)
-IF(USE_SHA1 STREQUAL ON OR USE_SHA1 STREQUAL "CollisionDetection")
-	SET(SHA1_BACKEND "CollisionDetection")
+IF(USE_SHA1 STREQUAL ON)
+	SET(USE_SHA1 "CollisionDetection")
 ELSEIF(USE_SHA1 STREQUAL "HTTPS")
-	message(STATUS "Checking HTTPS backend… ${HTTPS_BACKEND}")
-	IF(HTTPS_BACKEND STREQUAL "SecureTransport")
-		SET(SHA1_BACKEND "CommonCrypto")
-	ELSEIF(HTTPS_BACKEND STREQUAL "WinHTTP")
-		SET(SHA1_BACKEND "Win32")
-	ELSEIF(HTTPS_BACKEND)
-		SET(SHA1_BACKEND ${HTTPS_BACKEND})
+	IF(USE_HTTPS STREQUAL "SecureTransport")
+		SET(USE_SHA1 "CommonCrypto")
+	ELSEIF(USE_HTTPS STREQUAL "WinHTTP")
+		SET(USE_SHA1 "Win32")
+	ELSEIF(USE_HTTPS)
+		SET(USE_SHA1 ${USE_HTTPS})
 	ELSE()
+		SET(USE_SHA1 "CollisionDetection")
 	ENDIF()
-	IF(NOT HTTPS_BACKEND)
-		SET(SHA1_BACKEND "CollisionDetection")
-	ENDIF()
-	message(STATUS "Using SHA1 backend ${SHA1_BACKEND}")
-ELSEIF(USE_SHA1 STREQUAL "Generic")
-	SET(SHA1_BACKEND "Generic")
-# ELSEIF(NOT USE_SHA1)
-ELSE()
-	MESSAGE(FATAL_ERROR "Invalid value for USE_SHA1: ${USE_SHA1}")
 ENDIF()
 
-IF(SHA1_BACKEND STREQUAL "CollisionDetection")
+IF(USE_SHA1 STREQUAL "CollisionDetection")
 	SET(GIT_SHA1_COLLISIONDETECT 1)
 	ADD_DEFINITIONS(-DSHA1DC_NO_STANDARD_INCLUDES=1)
 	ADD_DEFINITIONS(-DSHA1DC_CUSTOM_INCLUDE_SHA1_C=\"common.h\")
 	ADD_DEFINITIONS(-DSHA1DC_CUSTOM_INCLUDE_UBC_CHECK_C=\"common.h\")
 	FILE(GLOB SRC_SHA1 hash/sha1/collisiondetect.* hash/sha1/sha1dc/*)
-ELSEIF(SHA1_BACKEND STREQUAL "OpenSSL")
-	# OPENSSL_FOUND should already be set, we're checking HTTPS_BACKEND
+ELSEIF(USE_SHA1 STREQUAL "OpenSSL")
+	# OPENSSL_FOUND should already be set, we're checking USE_HTTPS
 
 	SET(GIT_SHA1_OPENSSL 1)
 	IF(CMAKE_SYSTEM_NAME MATCHES "FreeBSD")
@@ -44,10 +35,10 @@ ELSEIF(SHA1_BACKEND STREQUAL "OpenSSL")
 		LIST(APPEND LIBGIT2_PC_REQUIRES "openssl")
 	ENDIF()
 	FILE(GLOB SRC_SHA1 hash/sha1/openssl.*)
-ELSEIF(SHA1_BACKEND STREQUAL "CommonCrypto")
+ELSEIF(USE_SHA1 STREQUAL "CommonCrypto")
 	SET(GIT_SHA1_COMMON_CRYPTO 1)
 	FILE(GLOB SRC_SHA1 hash/sha1/common_crypto.*)
-ELSEIF(SHA1_BACKEND STREQUAL "mbedTLS")
+ELSEIF(USE_SHA1 STREQUAL "mbedTLS")
 	SET(GIT_SHA1_MBEDTLS 1)
 	FILE(GLOB SRC_SHA1 hash/sha1/mbedtls.*)
 	LIST(APPEND LIBGIT2_SYSTEM_INCLUDES ${MBEDTLS_INCLUDE_DIR})
@@ -56,14 +47,13 @@ ELSEIF(SHA1_BACKEND STREQUAL "mbedTLS")
 	# https://github.com/ARMmbed/mbedtls/issues/228
 	# For now, pass its link flags as our own
 	LIST(APPEND LIBGIT2_PC_LIBS ${MBEDTLS_LIBRARIES})
-ELSEIF(SHA1_BACKEND STREQUAL "Win32")
+ELSEIF(USE_SHA1 STREQUAL "Win32")
 	SET(GIT_SHA1_WIN32 1)
 	FILE(GLOB SRC_SHA1 hash/sha1/win32.*)
-ELSEIF(SHA1_BACKEND STREQUAL "Generic")
+ELSEIF(USE_SHA1 STREQUAL "Generic")
 	FILE(GLOB SRC_SHA1 hash/sha1/generic.*)
-# ELSEIF(NOT USE_SHA1)
 ELSE()
-	MESSAGE(FATAL_ERROR "Asked for unknown SHA1 backend: ${SHA1_BACKEND}")
+	MESSAGE(FATAL_ERROR "Asked for unknown SHA1 backend: ${USE_SHA1}")
 ENDIF()
 
-ADD_FEATURE_INFO(SHA ON "using ${SHA1_BACKEND}")
+ADD_FEATURE_INFO(SHA ON "using ${USE_SHA1}")

deps/ntlmclient/CMakeLists.txt

@@ -4,20 +4,20 @@ ADD_DEFINITIONS(-DNTLM_STATIC=1)
 
 DISABLE_WARNINGS(implicit-fallthrough)
 
-IF (HTTPS_BACKEND STREQUAL "SecureTransport")
+IF(USE_HTTPS STREQUAL "SecureTransport")
 	ADD_DEFINITIONS(-DCRYPT_COMMONCRYPTO)
 	SET(SRC_NTLMCLIENT_CRYPTO "crypt_commoncrypto.c")
 	# CC_MD4 has been deprecated in macOS 10.15.
 	SET_SOURCE_FILES_PROPERTIES("crypt_commoncrypto.c" COMPILE_FLAGS "-Wno-deprecated")
-ELSEIF (HTTPS_BACKEND STREQUAL "OpenSSL")
+ELSEIF(USE_HTTPS STREQUAL "OpenSSL")
 	ADD_DEFINITIONS(-DCRYPT_OPENSSL)
 	INCLUDE_DIRECTORIES(${OPENSSL_INCLUDE_DIR})
 	SET(SRC_NTLMCLIENT_CRYPTO "crypt_openssl.c")
-ELSEIF (HTTPS_BACKEND STREQUAL "mbedTLS")
+ELSEIF(USE_HTTPS STREQUAL "mbedTLS")
 	ADD_DEFINITIONS(-DCRYPT_MBEDTLS)
 	SET(SRC_NTLMCLIENT_CRYPTO "crypt_mbedtls.c")
-ELSE ()
-	MESSAGE(FATAL_ERROR "Unable to use libgit2's HTTPS backend (${HTTPS_BACKEND}) for NTLM crypto")
+ELSE()
+	MESSAGE(FATAL_ERROR "Unable to use libgit2's HTTPS backend (${USE_HTTPS}) for NTLM crypto")
 ENDIF()
 
 ADD_LIBRARY(ntlmclient OBJECT ${SRC_NTLMCLIENT} ${SRC_NTLMCLIENT_CRYPTO})