Modernized CMake and added Boost::headers dependency

.gitignore

@@ -1,2 +1,3 @@
 build*/
 site/
+.cache/

CMakeLists.txt

@@ -4,57 +4,71 @@
 # Distributed under the Boost Software License, Version 1.0.
 # (See accompanying file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
 #
-cmake_minimum_required(VERSION 2.8)
-project(Boost.DI CXX)
-set(CXX_STANDARD 14 CACHE STRING "C++ Standard Version. [14|17|20]")
+cmake_minimum_required(VERSION 3.13)
+project(Boost.DI LANGUAGES CXX)
 
-add_library(${PROJECT_NAME} INTERFACE)
-target_include_directories(
-        ${PROJECT_NAME} INTERFACE
-        ${CMAKE_CURRENT_SOURCE_DIR}/include
-        ${CMAKE_CURRENT_SOURCE_DIR}/extension/include
-)
-
-if(${CMAKE_CXX_COMPILER_ID} STREQUAL GNU)
-    set(COMPILER_SPECIFIC_CXX_STANDARD "-std=c++${CXX_STANDARD}")
-    string(REPLACE "14" "1y" COMPILER_SPECIFIC_CXX_STANDARD ${COMPILER_SPECIFIC_CXX_STANDARD})
-    string(REPLACE "17" "1z" COMPILER_SPECIFIC_CXX_STANDARD ${COMPILER_SPECIFIC_CXX_STANDARD})
-    string(REPLACE "20" "2a" COMPILER_SPECIFIC_CXX_STANDARD ${COMPILER_SPECIFIC_CXX_STANDARD})    
-
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${COMPILER_SPECIFIC_CXX_STANDARD} -fno-exceptions -pedantic -pedantic-errors -Wall -Wextra -Werror")
+if(CMAKE_VERSION VERSION_LESS 3.21)
+    # Emulates CMake 3.21+ behavior.
+    if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
+        set(PROJECT_IS_TOP_LEVEL ON)
+        set(${PROJECT_NAME}_IS_TOP_LEVEL ON)
+    else()
+        set(PROJECT_IS_TOP_LEVEL OFF)
+        set(${PROJECT_NAME}_IS_TOP_LEVEL OFF)
+    endif()
+endif()
 
-elseif (${CMAKE_CXX_COMPILER_ID} STREQUAL Clang OR ${CMAKE_CXX_COMPILER_ID} STREQUAL AppleClang)
-    set(COMPILER_SPECIFIC_CXX_STANDARD "-std=c++${CXX_STANDARD}")
-    string(REPLACE "14" "1y" COMPILER_SPECIFIC_CXX_STANDARD ${COMPILER_SPECIFIC_CXX_STANDARD})
-    string(REPLACE "17" "1z" COMPILER_SPECIFIC_CXX_STANDARD ${COMPILER_SPECIFIC_CXX_STANDARD})
-    string(REPLACE "20" "2a" COMPILER_SPECIFIC_CXX_STANDARD ${COMPILER_SPECIFIC_CXX_STANDARD})    
+include(GNUInstallDirs)
 
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${COMPILER_SPECIFIC_CXX_STANDARD} -fno-exceptions -pedantic -pedantic-errors -Wall -Wextra -Werror")
-
-elseif (${CMAKE_CXX_COMPILER_ID} STREQUAL MSVC)
-    set(COMPILER_SPECIFIC_CXX_STANDARD "/std:c++${CXX_STANDARD}")
-    string(REPLACE "20" "latest" COMPILER_SPECIFIC_CXX_STANDARD ${COMPILER_SPECIFIC_CXX_STANDARD})
+find_package(Boost REQUIRED COMPONENTS headers)
 
-    set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${COMPILER_SPECIFIC_CXX_STANDARD} /W3 /EHsc /Zc:__cplusplus")
+set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
-else()
-    message(WARNING "Unsupported compiler!")
+if(NOT DEFINED CMAKE_CXX_STANDARD)
+    set(CMAKE_CXX_STANDARD 14)
+elseif(CMAKE_CXX_STANDARD LESS 14)
+    message(FATAL_ERROR "Boost.DI requires at least C++14")
 endif()
 
-if (CMAKE_PROJECT_NAME STREQUAL PROJECT_NAME)
-    set(IS_TOPLEVEL_PROJECT TRUE)
-else ()
-    set(IS_TOPLEVEL_PROJECT FALSE)
-endif ()
+add_library(${PROJECT_NAME} INTERFACE)
+target_include_directories(
+    ${PROJECT_NAME} INTERFACE
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
+    $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/extension/include>
+)
+target_link_libraries(${PROJECT_NAME} INTERFACE Boost::headers)
+
+option(BOOST_DI_OPT_BUILD_TESTS "Build and perform Boost.DI tests" ${PROJECT_IS_TOP_LEVEL})
 
-option(BOOST_DI_OPT_BUILD_TESTS "Build and perform Boost.DI tests" ${IS_TOPLEVEL_PROJECT})
-if (BOOST_DI_OPT_BUILD_TESTS)
+if(BOOST_DI_OPT_BUILD_TESTS)
     enable_testing()
     add_subdirectory(extension/test)
     add_subdirectory(test)
-endif ()
+endif()
+
+option(BOOST_DI_OPT_BUILD_EXAMPLES "Build perform Boost.DI examples" ${PROJECT_IS_TOP_LEVEL})
 
-option(BOOST_DI_OPT_BUILD_EXAMPLES "Build perform Boost.DI examples" ${IS_TOPLEVEL_PROJECT})
-if (BOOST_DI_OPT_BUILD_EXAMPLES)
+if(BOOST_DI_OPT_BUILD_EXAMPLES)
     add_subdirectory(example)
-endif ()
+endif()
+
+option(BOOST_DI_OPT_INSTALL "Install Boost.DI" "NOT ${PROJECT_IS_TOP_LEVEL}")
+
+if(BOOST_DI_OPT_INSTALL)
+    install(
+        TARGETS ${PROJECT_NAME}
+        EXPORT ${PROJECT_NAME}Config
+        INCLUDES DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
+    )
+
+    install(
+        EXPORT ${PROJECT_NAME}Config
+        DESTINATION "${CMAKE_INSTALL_LIBDIR}/cmake/${PROJECT_NAME}"
+        NAMESPACE Boost::
+    )
+
+    install(
+        DIRECTORY ${CMAKE_SOURCE_DIR}/include/
+        DESTINATION ${CMAKE_INSTALL_INCLUDEDIR}
+    )
+endif()