Fix problems with determening whether project is build as subproject

Author: Anton Pantyukhin

CMakeLists.txt

@@ -8,22 +8,19 @@ include(cmake/utils.cmake)
 add_library(mylib) # initialized below
 add_library(mylib::mylib ALIAS mylib)
 
+string(COMPARE EQUAL "${CMAKE_SOURCE_DIR}" "${CMAKE_CURRENT_SOURCE_DIR}" is_top_level)
+
 #----------------------------------------------------------------------------------------------------------------------
 # general settings and options
 #----------------------------------------------------------------------------------------------------------------------
 
 include(GNUInstallDirs)
 
-if(NOT DEFINED PROJECT_IS_TOP_LEVEL AND "${CMAKE_SOURCE_DIR}" STREQUAL "${CMAKE_CURRENT_SOURCE_DIR}")
-    # support older CMake versions (prior 3.21) which do not define this variable
-    set(PROJECT_IS_TOP_LEVEL YES)
-endif()
-
 # MYLIB_SHARED_LIBS option (undefined by default) can be used to force shared/static build
 option(MYLIB_BUILD_TESTS "Build mylib tests" OFF)
 option(MYLIB_BUILD_EXAMPLES "Build mylib examples" OFF)
 option(MYLIB_BUILD_DOCS "Build mylib documentation" OFF)
-option(MYLIB_INSTALL "Generate target for installing mylib" ${PROJECT_IS_TOP_LEVEL})
+option(MYLIB_INSTALL "Generate target for installing mylib" ${is_top_level})
 set_if_undefined(MYLIB_INSTALL_CMAKEDIR "${CMAKE_INSTALL_LIBDIR}/cmake/mylib-${PROJECT_VERSION}" CACHE
     STRING "Install path for mylib package-related CMake files")
 
@@ -148,7 +145,7 @@ endif()
 #----------------------------------------------------------------------------------------------------------------------
 
 if(MYLIB_BUILD_TESTS)
-    if(PROJECT_IS_TOP_LEVEL)
+    if(is_top_level)
         enable_testing()
     endif()
 

examples/add/CMakeLists.txt

@@ -2,12 +2,9 @@ cmake_minimum_required(VERSION 3.14)
 project(mylib-add LANGUAGES CXX)
 include("../../cmake/utils.cmake")
 
-if(NOT DEFINED PROJECT_IS_TOP_LEVEL AND "${CMAKE_SOURCE_DIR}" STREQUAL "${CMAKE_CURRENT_SOURCE_DIR}")
-    # support older CMake versions (prior 3.21) which do not define this variable
-    set(PROJECT_IS_TOP_LEVEL YES)
-endif()
+string(COMPARE EQUAL "${CMAKE_SOURCE_DIR}" "${CMAKE_CURRENT_SOURCE_DIR}" is_top_level)
 
-if(PROJECT_IS_TOP_LEVEL)
+if(is_top_level)
     find_package(mylib REQUIRED)
 endif()
 
@@ -18,6 +15,6 @@ add_executable(mylib-add)
 target_sources(mylib-add PRIVATE ${sources})
 target_link_libraries(mylib-add PRIVATE mylib::mylib)
 
-if(NOT PROJECT_IS_TOP_LEVEL)
+if(NOT is_top_level)
     win_copy_deps_to_target_dir(mylib-add mylib::mylib)
 endif()

tests/CMakeLists.txt

@@ -2,16 +2,13 @@ cmake_minimum_required(VERSION 3.14)
 project(mylib-tests)
 include("../cmake/utils.cmake")
 
+string(COMPARE EQUAL "${CMAKE_SOURCE_DIR}" "${CMAKE_CURRENT_SOURCE_DIR}" is_top_level)
+
 #----------------------------------------------------------------------------------------------------------------------
 # general settings and options
 #----------------------------------------------------------------------------------------------------------------------
 
-if(NOT DEFINED PROJECT_IS_TOP_LEVEL AND "${CMAKE_SOURCE_DIR}" STREQUAL "${CMAKE_CURRENT_SOURCE_DIR}")
-    # support older CMake versions (prior 3.21) which do not define this variable
-    set(PROJECT_IS_TOP_LEVEL YES)
-endif()
-
-if(PROJECT_IS_TOP_LEVEL)
+if(is_top_level)
     enable_testing()
 endif()
 
@@ -35,7 +32,7 @@ FetchContent_MakeAvailable(googletest)
 # tests dependencies
 #----------------------------------------------------------------------------------------------------------------------
 
-if(PROJECT_IS_TOP_LEVEL)
+if(is_top_level)
     find_package(mylib REQUIRED)
 endif()
 
@@ -59,7 +56,7 @@ target_link_libraries(mylib-tests
         mylib::mylib
         gtest_main)
 
-if(NOT PROJECT_IS_TOP_LEVEL)
+if(NOT is_top_level)
     win_copy_deps_to_target_dir(mylib-tests mylib::mylib)
 endif()