add support for cmake's find_package() (refs #52)

This rewrite of the main CMakeLists.txt cleans up the way ICU flags
are attached to the library target and adds the cmake helper files
(cxxopts-config.cmake, cxxopts-config-version.cmake,
cxxopts-targets.cmake) which are needed for exporting the cxxopts
target. Cmake's find_package command uses these files when the
library is consumed by another project.

Additionally, two new tests have been added which build the example
application via add_subdirectory and find_package.

CMakeLists.txt

@@ -36,34 +36,57 @@ elseif(CMAKE_CXX_COMPILER_ID MATCHES "[Cc]lang" OR CMAKE_CXX_COMPILER_ID MATCHES
     set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Wall -Werror -Wextra -Wshadow")
 endif()
 
-set(CXXOPTS_LINKER_LIBRARIES "")
+add_library(cxxopts INTERFACE)
+
+# optionally, enable unicode support using the ICU library
 set(CXXOPTS_USE_UNICODE_HELP FALSE CACHE BOOL "Use ICU Unicode library")
 if(CXXOPTS_USE_UNICODE_HELP)
+    find_package(PkgConfig)
+    pkg_check_modules(ICU REQUIRED icu-uc)
 
-  find_package(PkgConfig)
-
-  pkg_check_modules(ICU REQUIRED icu-uc)
-
-  set(CXXOPTS_LINKER_LIBRARIES "${ICU_LDFLAGS}")
-  set(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} ${ICU_CFLAGS} -DCXXOPTS_USE_UNICODE")
+    target_link_libraries(cxxopts INTERFACE ${ICU_LIBRARIES})
+    target_compile_options(cxxopts INTERFACE ${ICU_CFLAGS})
+    target_compile_definitions(cxxopts INTERFACE CXXOPTS_USE_UNICODE)
 endif()
 
+target_sources(cxxopts INTERFACE
+    $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include/cxxopts.hpp>
+    $<INSTALL_INTERFACE:include/cxxopts.hpp>
+    )
+target_include_directories(cxxopts INTERFACE
+    $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>
+    $<INSTALL_INTERFACE:include>
+    )
 
-add_library(cxxopts INTERFACE)
-target_sources(
-  cxxopts INTERFACE
-  ${CMAKE_CURRENT_SOURCE_DIR}/include/cxxopts.hpp
-  )
-target_include_directories(
-  cxxopts INTERFACE
-  include/
-  )
-target_link_libraries(
-  cxxopts
-  INTERFACE ${CXXOPTS_LINKER_LIBRARIES}
-  )
+include(CMakePackageConfigHelpers)
+set(CXXOPTS_CMAKE_DIR "lib/cmake/cxxopts" CACHE STRING
+  "Installation directory for cmake files, relative to ${CMAKE_INSTALL_PREFIX}.")
+set(version_config "${PROJECT_BINARY_DIR}/cxxopts-config-version.cmake")
+set(project_config "${PROJECT_BINARY_DIR}/cxxopts-config.cmake")
+set(targets_export_name cxxopts-targets)
 
-install(FILES ${CMAKE_CURRENT_SOURCE_DIR}/include/cxxopts.hpp DESTINATION include)
+# Generate the version, config and target files into the build directory.
+write_basic_package_version_file(
+    ${version_config}
+    VERSION ${VERSION}
+    COMPATIBILITY AnyNewerVersion)
+configure_package_config_file(
+    ${PROJECT_SOURCE_DIR}/cxxopts-config.cmake.in
+    ${project_config}
+    INSTALL_DESTINATION ${CXXOPTS_CMAKE_DIR})
+export(TARGETS cxxopts NAMESPACE cxxopts::
+    FILE ${PROJECT_BINARY_DIR}/${targets_export_name}.cmake)
+
+# Install version, config and target files.
+install(
+    FILES ${project_config} ${version_config}
+    DESTINATION ${CXXOPTS_CMAKE_DIR})
+install(EXPORT ${targets_export_name} DESTINATION ${CXXOPTS_CMAKE_DIR}
+    NAMESPACE cxxopts::)
+
+# Install the header file and export the target
+install(TARGETS cxxopts EXPORT ${targets_export_name} DESTINATION lib)
+install(FILES ${PROJECT_SOURCE_DIR}/include/cxxopts.hpp DESTINATION include)
 
 add_subdirectory(src)
 add_subdirectory(test)

cxxopts-config.cmake.in

@@ -0,0 +1,4 @@
+@PACKAGE_INIT@
+
+include(${CMAKE_CURRENT_LIST_DIR}/@targets_export_name@.cmake)
+check_required_components(cxxopts)

test/CMakeLists.txt

@@ -1,8 +1,32 @@
 if (CXXOPTS_BUILD_TESTS)
     add_executable(options_test main.cpp options.cpp)
     target_link_libraries(options_test cxxopts)
-
-
     add_test(options options_test)
-endif()
 
+    # test if the targets are findable from the build directory
+    add_test(find-package-test ${CMAKE_CTEST_COMMAND}
+        -C ${CMAKE_BUILD_TYPE}
+        --build-and-test
+        "${CMAKE_CURRENT_SOURCE_DIR}/find-package-test"
+        "${CMAKE_CURRENT_BINARY_DIR}/find-package-test"
+        --build-generator ${CMAKE_GENERATOR}
+        --build-makeprogram ${CMAKE_MAKE_PROGRAM}
+        --build-options
+        "-DCMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER}"
+        "-DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}"
+        "-Dcxxopts_DIR=${PROJECT_BINARY_DIR}"
+    )
+
+    # test if the targets are findable when add_subdirectory is used
+    add_test(add-subdirectory-test ${CMAKE_CTEST_COMMAND}
+        -C ${CMAKE_BUILD_TYPE}
+        --build-and-test
+        "${CMAKE_CURRENT_SOURCE_DIR}/add-subdirectory-test"
+        "${CMAKE_CURRENT_BINARY_DIR}/add-subdirectory-test"
+        --build-generator ${CMAKE_GENERATOR}
+        --build-makeprogram ${CMAKE_MAKE_PROGRAM}
+        --build-options
+        "-DCMAKE_CXX_COMPILER=${CMAKE_CXX_COMPILER}"
+        "-DCMAKE_BUILD_TYPE=${CMAKE_BUILD_TYPE}"
+    )
+endif()

test/add-subdirectory-test/CMakeLists.txt

@@ -0,0 +1,11 @@
+cmake_minimum_required(VERSION 3.1)
+
+project(cxxopts-test)
+
+set(CMAKE_CXX_STANDARD   11)
+set(CMAKE_CXX_EXTENSIONS OFF)
+
+add_subdirectory(../.. cxxopts EXCLUDE_FROM_ALL)
+
+add_executable(library-test "../../src/example.cpp")
+target_link_libraries(library-test cxxopts)

test/find-package-test/CMakeLists.txt

@@ -0,0 +1,11 @@
+cmake_minimum_required(VERSION 3.1)
+
+project(cxxopts-test)
+
+set(CMAKE_CXX_STANDARD   11)
+set(CMAKE_CXX_EXTENSIONS OFF)
+
+find_package(cxxopts REQUIRED)
+
+add_executable(library-test "../../src/example.cpp")
+target_link_libraries(library-test cxxopts::cxxopts)