Some CMake improvements

CMakeLists.txt

@@ -18,31 +18,33 @@ set(CMAKE_CXX_STANDARD 11)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 set(CMAKE_CXX_EXTENSIONS OFF)
 
-# --- dependencies  --
-find_package(
-    Boost 1.68
-    COMPONENTS date_time
-               thread
-               chrono
-               random
-    REQUIRED)
-
-# Try to find Boost::system
-find_package(Boost COMPONENTS system)
-if (NOT Boost_SYSTEM_FOUND)
-    message(WARNING "Boost::system not found, some examples may not compile")
+if(NOT PROJECT_IS_TOP_LEVEL OR AZMQ_BUILD_TESTS OR AZMQ_BUILD_DOC)
+    # --- dependencies  --
+    find_package(
+        Boost 1.68
+        COMPONENTS date_time
+                thread
+                chrono
+                random
+        OPTIONAL_COMPONENTS
+                system
+        REQUIRED)
+
+    include(FindAzmqLibzmq.cmake)
+
+    set(THREADS_PREFER_PTHREAD_FLAG TRUE)
+    find_package(Threads REQUIRED)
+else()
+    add_library(Azmq::libzmq INTERFACE IMPORTED)
+    add_library(Boost::headers INTERFACE IMPORTED)
+    add_library(Threads::Threads INTERFACE IMPORTED)
 endif()
 
-include(FindAzmqLibzmq.cmake)
-
-set(CMAKE_THREAD_PREFER_PTHREAD TRUE)
-find_package(Threads REQUIRED)
-
 # --- create library --
 add_library(${PROJECT_NAME} INTERFACE)
 add_library(Azmq::${PROJECT_NAME} ALIAS ${PROJECT_NAME})
 
-target_link_libraries(${PROJECT_NAME} INTERFACE Azmq::libzmq Boost::boost ${Boost_SYSTEM_LIBRARY} ${CMAKE_THREAD_LIBS_INIT})
+target_link_libraries(${PROJECT_NAME} INTERFACE Azmq::libzmq Boost::headers "$<$<TARGET_EXISTS:Boost::system>:Boost::system>" Threads::Threads)
 target_include_directories(${PROJECT_NAME} INTERFACE "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}>"
                                                      "$<INSTALL_INTERFACE:include>")
 

FindAzmqLibzmq.cmake

@@ -9,12 +9,17 @@
 if (TARGET Azmq::libzmq)
     # allow overriding from the calling script
     message(STATUS "using provided Azmq::libzmq target")
-elseif (TARGET libzmq AND BUILD_SHARED_LIBS)
+    return()
+else()
+    add_library(Azmq::libzmq INTERFACE IMPORTED)
+endif()
+
+if (TARGET libzmq AND BUILD_SHARED_LIBS)
     message(STATUS "using existing shared library target")
-    add_library(Azmq::libzmq ALIAS libzmq)
+    target_link_libraries(Azmq::libzmq INTERFACE libzmq)
 elseif (TARGET libzmq-static AND NOT BUILD_SHARED_LIBS)
     message(STATUS "using existing static library target")
-    add_library(Azmq::libzmq ALIAS libzmq-static)
+    target_link_libraries(Azmq::libzmq INTERFACE libzmq-static)
 else ()
     # try finding the package
     find_package(ZeroMQ QUIET)
@@ -24,14 +29,14 @@ else ()
         if (BUILD_SHARED_LIBS)
             if (TARGET libzmq)
                 message(STATUS "using cmake config libzmq")
-                add_library(Azmq::libzmq ALIAS libzmq)
+                target_link_libraries(Azmq::libzmq INTERFACE libzmq)
             else ()
                 message(FATAL_ERROR "libzmq not exported in the cmake configuration")
             endif ()
         else ()
             if (TARGET libzmq-static)
                 message(STATUS "using cmake config static libzmq")
-                add_library(Azmq::libzmq ALIAS libzmq-static)
+                target_link_libraries(Azmq::libzmq INTERFACE libzmq-static)
             else ()
                 message(FATAL_ERROR "libzmq-static not exported in the cmake configuration")
             endif ()
@@ -42,7 +47,7 @@ else ()
         find_package(PkgConfig REQUIRED)
         pkg_check_modules(LIBZMQ REQUIRED IMPORTED_TARGET GLOBAL libzmq)
         if (LIBZMQ_FOUND)
-            add_library(Azmq::libzmq ALIAS PkgConfig::LIBZMQ)
+            target_link_libraries(Azmq::libzmq INTERFACE PkgConfig::LIBZMQ)
         else ()
             message(FAIL_ERROR "Can't find the required libzmq library")
         endif ()

azmqConfig.cmake

@@ -1,11 +1,6 @@
 include(CMakeFindDependencyMacro)
-find_package(Boost 1.68 COMPONENTS date_time thread chrono random REQUIRED)
-find_package(Boost 1.68 COMPONENTS system)
-if (NOT Boost_SYSTEM_FOUND)
-    message(WARNING "Boost::system not found")
-endif()
+find_dependency(Boost 1.68 OPTIONAL_COMPONENTS system)
 
 include(${CMAKE_CURRENT_LIST_DIR}/FindAzmqLibzmq.cmake)
-set(CMAKE_THREAD_PREFER_PTHREAD TRUE)
-find_package(Threads REQUIRED)
+find_dependency(Threads)
 include("${CMAKE_CURRENT_LIST_DIR}/azmqTargets.cmake")