Add modern cmake config targets to s2geometry

CMakeLists.txt

@@ -246,7 +246,9 @@ endif()
 if (S2_USE_SYSTEM_INCLUDES)
     target_include_directories(s2 SYSTEM PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/src)
 else ()
-    target_include_directories(s2 PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/src)
+    target_include_directories(s2 PUBLIC
+      $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/src>
+      $<INSTALL_INTERFACE:include>)
 endif ()
 
 # Add version information to the target
@@ -432,6 +434,17 @@ install(TARGETS ${S2_TARGETS}
         ARCHIVE DESTINATION "${CMAKE_INSTALL_LIBDIR}"
         LIBRARY DESTINATION "${CMAKE_INSTALL_LIBDIR}")
 
+# Create an export type "s2Targets" detailing the targetable artifacts created
+# by this project.
+install(TARGETS s2 EXPORT s2Targets)
+# Install the export targets as a CMake config file in the share/s2 folder so
+# that they can referenced  by downstream projects as `s2::s2` after a
+# successful `find_package` call.
+install(EXPORT s2Targets
+        NAMESPACE s2
+        FILE s2Targets.cmake
+        DESTINATION share/s2/)
+
 if (BUILD_TESTS)
   if (NOT GOOGLETEST_ROOT)
     message(FATAL_ERROR "BUILD_TESTS requires GOOGLETEST_ROOT")
@@ -586,3 +599,13 @@ endif()
 if (${SWIG_FOUND} AND ${Python3_FOUND})
   add_subdirectory("src/python" python)
 endif()
+
+include(CMakePackageConfigHelpers)
+
+# Generate the config file that includes the exports.
+configure_package_config_file(${CMAKE_CURRENT_SOURCE_DIR}/Config.cmake.in
+  "${CMAKE_CURRENT_BINARY_DIR}/s2Config.cmake"
+  INSTALL_DESTINATION "share/s2/"
+  NO_SET_AND_CHECK_MACRO
+  NO_CHECK_REQUIRED_COMPONENTS_MACRO)
+install(FILES ${CMAKE_CURRENT_BINARY_DIR}/s2Config.cmake DESTINATION "share/s2/")

Config.cmake.in

@@ -0,0 +1,3 @@
+@PACKAGE_INIT@
+
+include("${CMAKE_CURRENT_LIST_DIR}/s2Targets.cmake")