Use interface libraries for vendor libraries

vendor/cryptopp/CMakeLists.txt

@@ -1,11 +1,11 @@
 project(mycryptopp)
 
-add_library(cryptopp dummy.cpp)
+add_library(cryptopp INTERFACE)
 # note: include directory is called vendor_cryptopp instead of cryptopp to avoid include clashes with system headers
 target_include_directories(cryptopp SYSTEM INTERFACE ${CMAKE_CURRENT_SOURCE_DIR})
 
 # Forward debug build info (i.e. set CRYPTOPP_DEBUG variable if building in debug mode)
-target_compile_definitions(cryptopp PUBLIC $<$<CONFIG:Debug>:CRYPTOPP_DEBUG>) # add to all targets depending on this
+target_compile_definitions(cryptopp INTERFACE $<$<CONFIG:Debug>:CRYPTOPP_DEBUG>) # add to all targets depending on this
 add_compile_options($<$<CONFIG:Debug>:-DCRYPTOPP_DEBUG>) # add to stuff built in subdirectories (like the actual library)
 
 if(NOT DISABLE_OPENMP)
@@ -68,8 +68,8 @@ if(NOT DISABLE_OPENMP)
         target_link_libraries(OpenMP_TARGET INTERFACE ${OpenMP_CXX_FLAGS} ${Additional_OpenMP_Libraries_Workaround})
     endif()
 
-    target_link_libraries(cryptopp PUBLIC ${OpenMP_CXX_FLAGS}) # Workaround for Ubuntu 18.04 that otherwise doesn't set -fopenmp for linking
-    target_link_libraries(cryptopp PUBLIC OpenMP::OpenMP_CXX)
+    target_link_libraries(cryptopp INTERFACE ${OpenMP_CXX_FLAGS}) # Workaround for Ubuntu 18.04 that otherwise doesn't set -fopenmp for linking
+    target_link_libraries(cryptopp INTERFACE OpenMP::OpenMP_CXX)
 
     # also add these flags to the third party Crypto++ build setup that is built in a subdirectory
     message(STATUS "OpenMP flags: ${OpenMP_CXX_FLAGS}")
@@ -87,4 +87,4 @@ set(BUILD_STATIC ON CACHE BOOL "")
 set(cryptocpp_DISPLAY_CMAKE_SUPPORT_WARNING OFF CACHE BOOL "")
 add_subdirectory(vendor_cryptopp EXCLUDE_FROM_ALL)
 
-target_link_libraries(cryptopp PRIVATE cryptopp-static)
+target_link_libraries(cryptopp INTERFACE cryptopp-static)

vendor/googletest/CMakeLists.txt

@@ -7,13 +7,12 @@ if (BUILD_TESTING)
   set(INSTALL_GMOCK off CACHE BOOL "" FORCE)
   add_subdirectory(gtest EXCLUDE_FROM_ALL)
 
-  project (googletest)
-  add_library(${PROJECT_NAME} dummy.cpp)
-  target_link_libraries(${PROJECT_NAME} PUBLIC gtest gmock)
-  target_include_directories(${PROJECT_NAME} SYSTEM INTERFACE ${gtest_INCLUDE_DIRS}/include SYSTEM ${gmock_INCLUDE_DIRS}/include)
+  add_library(googletest INTERFACE)
+  target_link_libraries(googletest INTERFACE gtest gmock)
+  target_include_directories(googletest SYSTEM INTERFACE ${gtest_INCLUDE_DIRS}/include SYSTEM INTERFACE ${gmock_INCLUDE_DIRS}/include)
 
   # Disable "missing override" warning because gmock MOCK_METHOD() don't use override :(
   if (NOT WIN32)
-    target_compile_options(${PROJECT_NAME} PUBLIC "-Wno-inconsistent-missing-override")
+    target_compile_options(googletest INTERFACE "-Wno-inconsistent-missing-override")
   endif()
 endif()

vendor/range-v3/CMakeLists.txt

@@ -1,8 +1,2 @@
-project (range-v3)
-
-set(SOURCES
-    dummy.cpp
-)
-
-add_library(${PROJECT_NAME} STATIC EXCLUDE_FROM_ALL ${SOURCES})
-target_include_directories(${PROJECT_NAME} SYSTEM PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/range-v3/include)
+add_library(range-v3 INTERFACE)
+target_include_directories(range-v3 SYSTEM INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}/range-v3/include)

vendor/spdlog/CMakeLists.txt

@@ -1,8 +1,2 @@
-project (spdlog)
-
-set(SOURCES
-  dummy.cpp
-)
-
-add_library(${PROJECT_NAME} STATIC ${SOURCES})
-target_include_directories(${PROJECT_NAME} SYSTEM PUBLIC ${CMAKE_CURRENT_SOURCE_DIR})
+add_library(spdlog INTERFACE)
+target_include_directories(spdlog SYSTEM INTERFACE ${CMAKE_CURRENT_SOURCE_DIR})