feat: support FetchContent use in CMake

CMakeLists.txt

@@ -1,4 +1,4 @@
-cmake_minimum_required(VERSION 3.15)
+cmake_minimum_required(VERSION 3.21)
 project(yaLanTingLibs
         VERSION 0.2.7
         DESCRIPTION "yaLanTingLibs"
@@ -9,21 +9,24 @@ project(yaLanTingLibs
 # load pack finder
 list(APPEND CMAKE_MODULE_PATH ${PROJECT_SOURCE_DIR}/cmake/Find/)
 
-# add include path
-include_directories(include)
-include_directories(include/ylt/thirdparty)
-include_directories(src/include)
-
 find_package(Threads REQUIRED)
 link_libraries(Threads::Threads)
 
-include(cmake/utils.cmake)
-include(cmake/struct_pb.cmake)
-include(cmake/build.cmake)
-include(cmake/develop.cmake)
 include(cmake/install.cmake)
-# add project config, such as enable_ssl.
-include(cmake/config.cmake)
-# add project's source such as unit test, example & benchmark
-include(cmake/subdir.cmake)
+
+if(PROJECT_IS_TOP_LEVEL) # ref:https://cmake.org/cmake/help/latest/variable/PROJECT_IS_TOP_LEVEL.html
+        # add include path
+        include_directories(include)
+        include_directories(include/ylt/thirdparty)
+        include_directories(src/include)
+
+        include(cmake/utils.cmake)
+        include(cmake/struct_pb.cmake)
+        include(cmake/build.cmake)
+        include(cmake/develop.cmake)
+        # add project config, such as enable_ssl.
+        include(cmake/config.cmake)
+        # add project's source such as unit test, example & benchmark
+        include(cmake/subdir.cmake)
+endif()
 

cmake/install.cmake

@@ -11,8 +11,14 @@ write_basic_package_version_file(
 )
 set(ConfigPackageLocation lib/cmake/yalantinglibs)
 
-
 add_library(yalantinglibs INTERFACE)
+add_library(yalantinglibs::yalantinglibs ALIAS yalantinglibs)
+
+target_include_directories(yalantinglibs INTERFACE 
+        $<INSTALL_INTERFACE:include>
+        $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/../include>
+        $<BUILD_INTERFACE:${CMAKE_CURRENT_LIST_DIR}/../include/ylt/thirdparty>
+)
 install(TARGETS yalantinglibs
        EXPORT yalantinglibsTargets
        LIBRARY DESTINATION lib