Allow usage as submodule

CMakeLists.txt

@@ -1,14 +1,59 @@
+cmake_minimum_required(VERSION 3.13...3.15)
 
-cmake_minimum_required(VERSION 3.8)
-project(span LANGUAGES CXX)
+project(span LANGUAGES CXX VERSION 0.9.0)
+
+if(PROJECT_SOURCE_DIR STREQUAL CMAKE_SOURCE_DIR)
+    set(SPAN_MASTER_PROJECT ON)
+endif()
+
+include(GNUInstallDirs)
 
-enable_testing()
 
 add_library(span INTERFACE)
-target_sources(span INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}/include/tcb/span.hpp)
-target_include_directories(span INTERFACE ${CMAKE_CURRENT_SOURCE_DIR}/include)
+add_library(tcb::span ALIAS span)
+#XXX target_sources(span INTERFACE include/tcb/span.hpp)
+target_include_directories(span INTERFACE
+        "$<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>"
+        "$<INSTALL_INTERFACE:${CMAKE_INSTALL_INCLUDEDIR}>"
+)
 target_compile_features(span INTERFACE cxx_std_11)
 
 set(TCB_SPAN_TEST_CXX_STD 11 CACHE STRING "C++ standard version for testing")
 
-add_subdirectory(test)
+option(BUILD_TESTS "Build tests" ${SPAN_MASTER_PROJECT})
+option(SPAN_INSTALL "Generate the install target" ${SPAN_MASTER_PROJECT})
+
+
+if(BUILD_TESTS)
+    enable_testing()
+    add_subdirectory(test)
+endif()
+
+
+if(SPAN_INSTALL)
+    include(CMakePackageConfigHelpers)
+
+    install(TARGETS span EXPORT ${PROJECT_NAME}Targets)
+    install(DIRECTORY include/tcb DESTINATION ${CMAKE_INSTALL_INCLUDEDIR})
+    set(configFile ${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}Config.cmake)
+    set(versionFile ${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}ConfigVersion.cmake)
+    set(configInstallDestination lib/cmake/${PROJECT_NAME})
+
+    configure_package_config_file(
+        ${CMAKE_CURRENT_SOURCE_DIR}/Config.cmake.in
+        ${configFile}
+        INSTALL_DESTINATION ${configInstallDestination}
+    )
+    write_basic_package_version_file(
+        ${versionFile}
+        COMPATIBILITY SameMajorVersion
+    )
+
+    install(FILES ${configFile} ${versionFile} DESTINATION ${configInstallDestination})
+    install(
+        EXPORT ${PROJECT_NAME}Targets
+        NAMESPACE "tcb::"
+        DESTINATION ${configInstallDestination}
+    )
+endif()
+

Config.cmake.in

@@ -0,0 +1,3 @@
+@PACKAGE_INIT@
+
+include("${CMAKE_CURRENT_LIST_DIR}/@[email protected]")