cmake: Modulize our TLS & hash detection

The interactions between `USE_HTTPS` and `SHA1_BACKEND` have been
streamlined. Previously we would have accepted not quite working
configurations (like, `-DUSE_HTTPS=OFF -DSHA1_BACKEND=OpenSSL`) and, as
the OpenSSL detection only ran with `USE_HTTPS`, the link would fail.

The detection was moved to a new `USE_SHA1`, modeled after `USE_HTTPS`,
which takes the values "CollisionDetection/Backend/Generic", to better
match how the "hashing backend" is selected, the default (ON) being
"CollisionDetection".

Note that, as `SHA1_BACKEND` is still used internally, you might need to
check what customization you're using it for.

1 files changed, 2 insertions, 166 deletions

diff --git a/src/CMakeLists.txt b/src/CMakeLists.txt
index 5a0cf347c..7ab183210 100644
--- a/src/CMakeLists.txt
+++ b/src/CMakeLists.txt
@@ -122,172 +122,8 @@ IF (WIN32 AND WINHTTP)
 	LIST(APPEND LIBGIT2_PC_LIBS "-lrpcrt4" "-lcrypt32" "-lole32")
 ENDIF()
 
-IF (USE_HTTPS)
-	# We try to find any packages our backends might use
-	FIND_PACKAGE(OpenSSL)
-	FIND_PACKAGE(mbedTLS)
-	IF (CMAKE_SYSTEM_NAME MATCHES "Darwin")
-		FIND_PACKAGE(Security)
-		FIND_PACKAGE(CoreFoundation)
-	ENDIF()
-
-	# Auto-select TLS backend
-	IF (USE_HTTPS STREQUAL ON)
-		IF (SECURITY_FOUND)
-			IF (SECURITY_HAS_SSLCREATECONTEXT)
-				SET(HTTPS_BACKEND "SecureTransport")
-			ELSE()
-				MESSAGE("-- Security framework is too old, falling back to OpenSSL")
-				SET(HTTPS_BACKEND "OpenSSL")
-			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()
-	ELSE()
-		# Backend was explicitly set
-		SET(HTTPS_BACKEND ${USE_HTTPS})
-	ENDIF()
-
-	# Check that we can find what's required for the selected backend
-	IF (HTTPS_BACKEND STREQUAL "SecureTransport")
-		IF (NOT COREFOUNDATION_FOUND)
-			MESSAGE(FATAL_ERROR "Cannot use SecureTransport backend, CoreFoundation.framework not found")
-		ENDIF()
-		IF (NOT SECURITY_FOUND)
-			MESSAGE(FATAL_ERROR "Cannot use SecureTransport backend, Security.framework not found")
-		ENDIF()
-		IF (NOT SECURITY_HAS_SSLCREATECONTEXT)
-			MESSAGE(FATAL_ERROR "Cannot use SecureTransport backend, SSLCreateContext not supported")
-		ENDIF()
-
-		SET(GIT_SECURE_TRANSPORT 1)
-		LIST(APPEND LIBGIT2_SYSTEM_INCLUDES ${SECURITY_INCLUDE_DIR})
-		LIST(APPEND LIBGIT2_LIBS ${COREFOUNDATION_LIBRARIES} ${SECURITY_LIBRARIES})
-		LIST(APPEND LIBGIT2_PC_LIBS ${COREFOUNDATION_LDFLAGS} ${SECURITY_LDFLAGS})
-	ELSEIF (HTTPS_BACKEND STREQUAL "OpenSSL")
-		IF (NOT OPENSSL_FOUND)
-			MESSAGE(FATAL_ERROR "Asked for OpenSSL TLS backend, but it wasn't found")
-		ENDIF()
-
-		SET(GIT_OPENSSL 1)
-		LIST(APPEND LIBGIT2_SYSTEM_INCLUDES ${OPENSSL_INCLUDE_DIR})
-		LIST(APPEND LIBGIT2_LIBS ${OPENSSL_LIBRARIES})
-		LIST(APPEND LIBGIT2_PC_LIBS ${OPENSSL_LDFLAGS})
-		LIST(APPEND LIBGIT2_PC_REQUIRES "openssl")
-	ELSEIF(HTTPS_BACKEND STREQUAL "mbedTLS")
-		IF (NOT MBEDTLS_FOUND)
-			MESSAGE(FATAL_ERROR "Asked for mbedTLS backend, but it wasn't found")
-		ENDIF()
-
-		IF(NOT CERT_LOCATION)
-			MESSAGE("Auto-detecting default certificates location")
-			IF(CMAKE_SYSTEM_NAME MATCHES Darwin)
-				# Check for an Homebrew installation
-				SET(OPENSSL_CMD "/usr/local/opt/openssl/bin/openssl")
-			ELSE()
-				SET(OPENSSL_CMD "openssl")
-			ENDIF()
-			EXECUTE_PROCESS(COMMAND ${OPENSSL_CMD} version -d OUTPUT_VARIABLE OPENSSL_DIR OUTPUT_STRIP_TRAILING_WHITESPACE)
-			IF(OPENSSL_DIR)
-				STRING(REGEX REPLACE "^OPENSSLDIR: \"(.*)\"$" "\\1/" OPENSSL_DIR ${OPENSSL_DIR})
-
-				SET(OPENSSL_CA_LOCATIONS
-					"ca-bundle.pem"             # OpenSUSE Leap 42.1
-					"cert.pem"                  # Ubuntu 14.04, FreeBSD
-					"certs/ca-certificates.crt" # Ubuntu 16.04
-					"certs/ca.pem"              # Debian 7
-				)
-				FOREACH(SUFFIX IN LISTS OPENSSL_CA_LOCATIONS)
-					SET(LOC "${OPENSSL_DIR}${SUFFIX}")
-					IF(NOT CERT_LOCATION AND EXISTS "${OPENSSL_DIR}${SUFFIX}")
-						SET(CERT_LOCATION ${LOC})
-					ENDIF()
-				ENDFOREACH()
-			ELSE()
-				MESSAGE("Unable to find OpenSSL executable. Please provide default certificate location via CERT_LOCATION")
-			ENDIF()
-		ENDIF()
-
-		IF(CERT_LOCATION)
-			IF(NOT EXISTS ${CERT_LOCATION})
-				MESSAGE(FATAL_ERROR "Cannot use CERT_LOCATION=${CERT_LOCATION} as it doesn't exist")
-			ENDIF()
-			ADD_FEATURE_INFO(CERT_LOCATION ON "using certificates from ${CERT_LOCATION}")
-			ADD_DEFINITIONS(-DGIT_DEFAULT_CERT_LOCATION="${CERT_LOCATION}")
-		ENDIF()
-
-		SET(GIT_MBEDTLS 1)
-		LIST(APPEND LIBGIT2_SYSTEM_INCLUDES ${MBEDTLS_INCLUDE_DIR})
-		LIST(APPEND LIBGIT2_LIBS ${MBEDTLS_LIBRARIES})
-		# mbedTLS has no pkgconfig file, hence we can't require it
-		# 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")
-		# WinHTTP setup was handled in the WinHTTP-specific block above
-	ELSE()
-		MESSAGE(FATAL_ERROR "Asked for backend ${HTTPS_BACKEND} but it wasn't found")
-	ENDIF()
-
-	ADD_FEATURE_INFO(HTTPS ON "using ${HTTPS_BACKEND}")
-	SET(GIT_HTTPS 1)
-ELSE()
-	ADD_FEATURE_INFO(HTTPS OFF "no support")
-ENDIF()
-
-# Specify sha1 implementation
-IF(SHA1_BACKEND STREQUAL "OpenSSL")
-	IF(NOT OPENSSL_FOUND)
-		FIND_PACKAGE(OpenSSL)
-		IF(NOT OPENSSL_FOUND)
-		    MESSAGE(FATAL_ERROR "Requested OpenSSL SHA1 backend, but OpenSSL could not be found")
-		ENDIF()
-	ENDIF()
-
-	ADD_FEATURE_INFO(SHA ON "using OpenSSL")
-	SET(GIT_SHA1_OPENSSL 1)
-	IF(CMAKE_SYSTEM_NAME MATCHES "FreeBSD")
-		LIST(APPEND LIBGIT2_PC_LIBS "-lssl")
-	ELSE()
-		LIST(APPEND LIBGIT2_PC_REQUIRES "openssl")
-	ENDIF()
-ELSEIF(SHA1_BACKEND STREQUAL "CollisionDetection")
-	ADD_FEATURE_INFO(SHA ON "using 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/hash_collisiondetect.c hash/sha1dc/*)
-ELSEIF(SHA1_BACKEND STREQUAL "Generic")
-	ADD_FEATURE_INFO(SHA ON "using Generic")
-	FILE(GLOB SRC_SHA1 hash/hash_generic.c)
-ELSEIF(SHA1_BACKEND STREQUAL "Win32")
-	ADD_FEATURE_INFO(SHA ON "using Win32")
-	SET(GIT_SHA1_WIN32 1)
-	FILE(GLOB SRC_SHA1 hash/hash_win32.c)
-ELSEIF(SHA1_BACKEND STREQUAL "CommonCrypto")
-	ADD_FEATURE_INFO(SHA ON "using CommonCrypto")
-	SET(GIT_SHA1_COMMON_CRYPTO 1)
-ELSEIF (SHA1_BACKEND STREQUAL "mbedTLS")
-	ADD_FEATURE_INFO(SHA ON "using mbedTLS")
-	SET(GIT_SHA1_MBEDTLS 1)
-	FILE(GLOB SRC_SHA1 hash/hash_mbedtls.c)
-	LIST(APPEND LIBGIT2_SYSTEM_INCLUDES ${MBEDTLS_INCLUDE_DIR})
-	LIST(APPEND LIBGIT2_LIBS ${MBEDTLS_LIBRARIES})
-	# mbedTLS has no pkgconfig file, hence we can't require it
-	# https://github.com/ARMmbed/mbedtls/issues/228
-	# For now, pass its link flags as our own
-	LIST(APPEND LIBGIT2_PC_LIBS ${MBEDTLS_LIBRARIES})
-ELSE()
-	MESSAGE(FATAL_ERROR "Asked for unknown SHA1 backend ${SHA1_BACKEND}")
-ENDIF()
+Include(SelectHTTPSBackend)
+Include(SelectHashes)
 
 # Specify regular expression implementation
 FIND_PACKAGE(PCRE)