cmake: enforce USE_HTTPS validity

Author: ethomson

CMakeLists.txt

@@ -31,7 +31,7 @@ option(USE_NSEC                "Support nanosecond precision file mtimes and cti
 
 # Backend selection
    set(USE_SSH                 "" CACHE STRING "Enables SSH support. One of libssh2, exec, or OFF. (Defaults to OFF.)")
-option(USE_HTTPS               "Enable HTTPS support. Can be set to a specific backend" ON)
+   set(USE_HTTPS               "" CACHE STRING "Enable HTTPS support. One of ON (to autodetect), OFF, or a specific backend: OpenSSL, OpenSSL-FIPS, OpenSSL-Dynamic, mbedTLS, SecureTransport, Schannel, or WinHTTP. (Defaults to ON.)")
 option(USE_SHA1                "Enable SHA1. Can be set to CollisionDetection(ON)/HTTPS" ON)
 option(USE_SHA256              "Enable SHA256. Can be set to HTTPS/Builtin" ON)
 option(USE_GSSAPI              "Link with libgssapi for SPNEGO auth"       OFF)
@@ -64,7 +64,7 @@ option(ENABLE_WERROR           "Enable compilation with -Werror"
 
 if(UNIX)
 	# NTLM client requires crypto libraries from the system HTTPS stack
-	if(NOT USE_HTTPS)
+	if(USE_HTTPS STREQUAL "OFF")
 		option(USE_NTLMCLIENT  "Enable NTLM support on Unix."                  OFF)
 	else()
 		option(USE_NTLMCLIENT  "Enable NTLM support on Unix."                   ON)

cmake/SelectHTTPSBackend.cmake

@@ -8,9 +8,14 @@ if(CMAKE_SYSTEM_NAME MATCHES "Darwin" OR CMAKE_SYSTEM_NAME MATCHES "iOS")
 	find_package(CoreFoundation)
 endif()
 
+if(USE_HTTPS STREQUAL "")
+	set(USE_HTTPS ON)
+endif()
+
+sanitizebool(USE_HTTPS)
+
 if(USE_HTTPS)
 	# Auto-select TLS backend
-	sanitizebool(USE_HTTPS)
 	if(USE_HTTPS STREQUAL ON)
 		if(SECURITY_FOUND)
 			if(SECURITY_HAS_SSLCREATECONTEXT)
@@ -136,12 +141,12 @@ if(USE_HTTPS)
 		set(GIT_OPENSSL_DYNAMIC 1)
 		list(APPEND LIBGIT2_SYSTEM_LIBS dl)
 	else()
-		message(FATAL_ERROR "Asked for backend ${USE_HTTPS} but it wasn't found")
+		message(FATAL_ERROR "unknown HTTPS backend: ${USE_HTTPS}")
 	endif()
 
 	set(GIT_HTTPS 1)
 	add_feature_info(HTTPS GIT_HTTPS "using ${USE_HTTPS}")
 else()
 	set(GIT_HTTPS 0)
-	add_feature_info(HTTPS NO "")
+	add_feature_info(HTTPS NO "HTTPS support is disabled")
 endif()