cmake: use imported targets for OpenSSL and zlib

Imported targets are highly preferred over the individual variables
for includes and libs because they will be used in a coherent way
and any spelling mistakes or unavailability won't go unnoticed.

Also it will prevent bugs like conan-io/conan-center-index#16900
or using mismatching header/libs combinations.

Signed-off-by: Gregor Jasny <gjasny@googlemail.com>
Reviewed-by: Andreas Schneider <asn@cryptomilk.org>

CMakeLists.txt

@@ -1,5 +1,4 @@
 cmake_minimum_required(VERSION 3.12.0)
-cmake_policy(SET CMP0048 NEW)
 
 # Specify search path for CMake modules to be loaded by include()
 # and find_package()
@@ -53,11 +52,6 @@ elseif(WITH_MBEDTLS)
     find_package(MbedTLS REQUIRED)
 else()
   find_package(OpenSSL 1.1.1 REQUIRED)
-  # On CMake < 3.16, OPENSSL_CRYPTO_LIBRARIES is usually a synonym for OPENSSL_CRYPTO_LIBRARY, but is not defined
-  # when building on Windows outside of Cygwin. We provide the synonym here, if FindOpenSSL didn't define it already.
-  if (NOT DEFINED OPENSSL_CRYPTO_LIBRARIES)
-    set(OPENSSL_CRYPTO_LIBRARIES ${OPENSSL_CRYPTO_LIBRARY})
-  endif (NOT DEFINED OPENSSL_CRYPTO_LIBRARIES)
 endif()
 
 if (UNIT_TESTING)

ConfigureChecks.cmake

@@ -76,53 +76,32 @@ if (WIN32)
 endif (WIN32)
 
 if (OPENSSL_FOUND)
-    set(CMAKE_REQUIRED_INCLUDES ${OPENSSL_INCLUDE_DIR})
+    set(CMAKE_REQUIRED_LIBRARIES OpenSSL::Crypto)
+
     check_include_file(openssl/des.h HAVE_OPENSSL_DES_H)
     if (NOT HAVE_OPENSSL_DES_H)
         message(FATAL_ERROR "Could not detect openssl/des.h")
     endif()
 
-    set(CMAKE_REQUIRED_INCLUDES ${OPENSSL_INCLUDE_DIR})
     check_include_file(openssl/aes.h HAVE_OPENSSL_AES_H)
     if (NOT HAVE_OPENSSL_AES_H)
         message(FATAL_ERROR "Could not detect openssl/aes.h")
     endif()
 
     if (WITH_BLOWFISH_CIPHER)
-        set(CMAKE_REQUIRED_INCLUDES ${OPENSSL_INCLUDE_DIR})
         check_include_file(openssl/blowfish.h HAVE_OPENSSL_BLOWFISH_H)
     endif()
 
-    set(CMAKE_REQUIRED_INCLUDES ${OPENSSL_INCLUDE_DIR})
     check_include_file(openssl/ecdh.h HAVE_OPENSSL_ECDH_H)
-
-    set(CMAKE_REQUIRED_INCLUDES ${OPENSSL_INCLUDE_DIR})
     check_include_file(openssl/ec.h HAVE_OPENSSL_EC_H)
-
-    set(CMAKE_REQUIRED_INCLUDES ${OPENSSL_INCLUDE_DIR})
     check_include_file(openssl/ecdsa.h HAVE_OPENSSL_ECDSA_H)
 
-    set(CMAKE_REQUIRED_INCLUDES ${OPENSSL_INCLUDE_DIR})
-    set(CMAKE_REQUIRED_LIBRARIES ${OPENSSL_CRYPTO_LIBRARIES})
     check_function_exists(EVP_KDF_CTX_new_id HAVE_OPENSSL_EVP_KDF_CTX_NEW_ID)
-
-    set(CMAKE_REQUIRED_INCLUDES ${OPENSSL_INCLUDE_DIR})
-    set(CMAKE_REQUIRED_LIBRARIES ${OPENSSL_CRYPTO_LIBRARIES})
     check_function_exists(EVP_KDF_CTX_new HAVE_OPENSSL_EVP_KDF_CTX_NEW)
-
-    set(CMAKE_REQUIRED_INCLUDES ${OPENSSL_INCLUDE_DIR})
-    set(CMAKE_REQUIRED_LIBRARIES ${OPENSSL_CRYPTO_LIBRARIES})
     check_function_exists(FIPS_mode HAVE_OPENSSL_FIPS_MODE)
-
-    set(CMAKE_REQUIRED_INCLUDES ${OPENSSL_INCLUDE_DIR})
-    set(CMAKE_REQUIRED_LIBRARIES ${OPENSSL_CRYPTO_LIBRARIES})
     check_function_exists(RAND_priv_bytes HAVE_OPENSSL_RAND_PRIV_BYTES)
-
-    set(CMAKE_REQUIRED_INCLUDES ${OPENSSL_INCLUDE_DIR})
-    set(CMAKE_REQUIRED_LIBRARIES ${OPENSSL_CRYPTO_LIBRARIES})
     check_function_exists(EVP_chacha20 HAVE_OPENSSL_EVP_CHACHA20)
 
-    unset(CMAKE_REQUIRED_INCLUDES)
     unset(CMAKE_REQUIRED_LIBRARIES)
 endif()
 

src/CMakeLists.txt

@@ -8,17 +8,9 @@ set(LIBSSH_LINK_LIBRARIES
   ${LIBSSH_REQUIRED_LIBRARIES}
 )
 
-if (OPENSSL_CRYPTO_LIBRARIES)
-  set(LIBSSH_PRIVATE_INCLUDE_DIRS
-    ${LIBSSH_PRIVATE_INCLUDE_DIRS}
-    ${OPENSSL_INCLUDE_DIR}
-  )
-
-  set(LIBSSH_LINK_LIBRARIES
-    ${LIBSSH_LINK_LIBRARIES}
-    ${OPENSSL_CRYPTO_LIBRARIES}
-  )
-endif (OPENSSL_CRYPTO_LIBRARIES)
+if (TARGET OpenSSL::Crypto)
+  list(APPEND LIBSSH_LINK_LIBRARIES OpenSSL::Crypto)
+endif ()
 
 if (MBEDTLS_CRYPTO_LIBRARY)
     set(LIBSSH_PRIVATE_INCLUDE_DIRS
@@ -43,15 +35,7 @@ if (GCRYPT_LIBRARIES)
 endif()
 
 if (WITH_ZLIB)
-  set(LIBSSH_PRIVATE_INCLUDE_DIRS
-    ${LIBSSH_PRIVATE_INCLUDE_DIRS}
-    ${ZLIB_INCLUDE_DIR}
-  )
-
-  set(LIBSSH_LINK_LIBRARIES
-    ${LIBSSH_LINK_LIBRARIES}
-    ${ZLIB_LIBRARY}
-  )
+  list(APPEND LIBSSH_LINK_LIBRARIES ZLIB::ZLIB)
 endif (WITH_ZLIB)
 
 if (WITH_GSSAPI AND GSSAPI_FOUND)

tests/CMakeLists.txt

@@ -6,9 +6,7 @@ endif (BSD OR SOLARIS OR OSX)
 
 set(TORTURE_LIBRARY torture)
 
-include_directories(${OPENSSL_INCLUDE_DIR}
-                    ${CMOCKA_INCLUDE_DIR}
-                    ${ZLIB_INCLUDE_DIR}
+include_directories(${CMOCKA_INCLUDE_DIR}
                     ${libssh_BINARY_DIR}/include
                     ${libssh_BINARY_DIR}
                     ${libssh_SOURCE_DIR}/src

tests/external_override/CMakeLists.txt

@@ -44,7 +44,7 @@ else ()
         ${libssh_SOURCE_DIR}/src/md_crypto.c
     )
     set(override_libs
-        ${OPENSSL_CRYPTO_LIBRARIES}
+        OpenSSL::Crypto
     )
 endif (WITH_GCRYPT)
 

tests/pkd/CMakeLists.txt

@@ -5,7 +5,6 @@ if (WITH_SERVER AND UNIX AND NOT WIN32)
     include_directories(${libssh_SOURCE_DIR}/include
                         ${libssh_BINARY_DIR}/include
                         ${CMOCKA_INCLUDE_DIR}
-                        ${ZLIB_INCLUDE_DIR}
                         ${CMAKE_BINARY_DIR}
                         ${libssh_SOURCE_DIR}/src
                         ${CMAKE_CURRENT_SOURCE_DIR})

tests/unittests/CMakeLists.txt

@@ -1,7 +1,5 @@
 project(unittests C)
 
-include_directories(${OPENSSL_INCLUDE_DIR})
-
 set(LIBSSH_UNIT_TESTS
     torture_bignum
     torture_buffer