Improve the quality of the CMake build scripts

This commit does a couple changes:

* Actually adheres to the declared CMake 3.8 requirement
  * HOMEPAGE_URL in project() was added in 3.12
  * install(TARGETS) requires the DESTINATION argument
  * Tests' CML uses CONFIGURE_DEPENDS from CMake 3.12
* Removes unnecessary things
  * Looking for RPM and DEB packagers is pointless
  * Misc arguments to CMake commands
* Improves correctness
  * Includes CPack and CTest modules only if top level
  * Assigns install rules to a project specific component to not clobber
    the global, `Unspecified` one
  * Adds a warning guard for projects that vendor ctre
  * CMAKE_INSTALL_PREFIX may change at install time, so .pc file is
    generated at that time to ensure the prefix is always right
  * Enables the install rules to be opt-out using the CMake built-in
    variable
  * Emulates ARCH_INDEPENDENT for the version config
  * Installs headers to their own directory (fixes #207)
* Small optimization
  * LANGUAGES can be set to NONE, because this is a header only library

CMakeLists.txt

@@ -1,105 +1,123 @@
-cmake_minimum_required(VERSION 3.8.0)
-# When updating to a newer version of CMake, see if we can use the following
-project(ctre
-  HOMEPAGE_URL "https://compile-time.re"
-  VERSION 3.0
-  LANGUAGES CXX)
+cmake_minimum_required(VERSION 3.8)
+
+project(ctre VERSION 3.0 LANGUAGES NONE)
+
+# ---- project() variable shims ----
+
+# Added in CMake 3.9
 set(PROJECT_DESCRIPTION "Fast compile-time regular expressions with support for matching/searching/capturing during compile-time or runtime.")
 
-include(CMakePackageConfigHelpers)
-include(CMakeDependentOption)
-include(GNUInstallDirs)
-include(CTest)
-
-find_program(CTRE_DPKG_BUILDPACKAGE_FOUND dpkg-buildpackage)
-find_program(CTRE_RPMBUILD_FOUND rpmbuild)
-
-cmake_dependent_option(CTRE_BUILD_TESTS "Build ctre Tests" ON
-  "BUILD_TESTING;CMAKE_SOURCE_DIR STREQUAL PROJECT_SOURCE_DIR" OFF)
-cmake_dependent_option(CTRE_BUILD_PACKAGE "Build ctre Packages" ON
-  "CMAKE_SOURCE_DIR STREQUAL PROJECT_SOURCE_DIR" OFF)
-cmake_dependent_option(CTRE_BUILD_PACKAGE_DEB
-  "Create DEB Package (${PROJECT_NAME})" ON
-  "CTRE_BUILD_PACKAGE;CTRE_DPKG_BUILDPACKAGE_FOUND" OFF)
-cmake_dependent_option(CTRE_BUILD_PACKAGE_RPM
-  "Create RPM Package (${PROJECT_NAME})" ON
-  "CTRE_BUILD_PACKAGE;CTRE_RPMBUILD_FOUND" OFF)
-
-add_library(${PROJECT_NAME} INTERFACE)
-add_library(${PROJECT_NAME}::${PROJECT_NAME} ALIAS ${PROJECT_NAME})
-
-target_include_directories(${PROJECT_NAME} INTERFACE
-  $<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>
-  $<INSTALL_INTERFACE:include>)
-target_compile_features(ctre INTERFACE cxx_std_17)
-
-install(TARGETS ${PROJECT_NAME} EXPORT ${PROJECT_NAME}-targets)
-
-if (NOT EXISTS "${PROJECT_BINARY_DIR}/${PROJECT_NAME}-config.cmake.in")
-  file(WRITE ${PROJECT_BINARY_DIR}/${PROJECT_NAME}-config.cmake.in [[
-    @PACKAGE_INIT@
-    include("${CMAKE_CURRENT_LIST_DIR}/@[email protected]")
-  ]])
+# Added in CMake 3.12
+set(PROJECT_HOMEPAGE_URL "https://compile-time.re")
+
+# Added in CMake 3.21
+set(PROJECT_IS_TOP_LEVEL NO)
+if(CMAKE_SOURCE_DIR STREQUAL CMAKE_CURRENT_SOURCE_DIR)
+  set(PROJECT_IS_TOP_LEVEL YES)
 endif()
 
-configure_package_config_file(
-  "${PROJECT_BINARY_DIR}/${PROJECT_NAME}-config.cmake.in"
-  "${PROJECT_BINARY_DIR}/${PROJECT_NAME}-config.cmake"
-  INSTALL_DESTINATION "${CMAKE_INSTALL_DATADIR}/cmake/${PROJECT_NAME}"
-  NO_SET_AND_CHECK_MACRO
-  NO_CHECK_REQUIRED_COMPONENTS_MACRO)
-
-write_basic_package_version_file(ctre-config-version.cmake
-  VERSION ${PROJECT_VERSION}
-  COMPATIBILITY SameMajorVersion)
-
-install(EXPORT ${PROJECT_NAME}-targets 
-  DESTINATION "${CMAKE_INSTALL_DATADIR}/cmake/${PROJECT_NAME}"
-  NAMESPACE ${PROJECT_NAME}::)
-install(
-  FILES
-    "${PROJECT_BINARY_DIR}/${PROJECT_NAME}-config-version.cmake"
-    "${PROJECT_BINARY_DIR}/${PROJECT_NAME}-config.cmake"
-  DESTINATION ${CMAKE_INSTALL_DATADIR}/cmake/${PROJECT_NAME})
-install(DIRECTORY include/ DESTINATION include
-    FILES_MATCHING PATTERN *.hpp)
+# ---- Warning guard for vendoring projects ----
 
-if(CTRE_BUILD_TESTS)
-  add_subdirectory(tests)
+set(warning_guard "")
+if(NOT PROJECT_IS_TOP_LEVEL)
+  option(ctre_INCLUDES_WITH_SYSTEM
+    "Use SYSTEM modifier for ctre's includes, disabling warnings" ON)
+  mark_as_advanced(ctre_INCLUDES_WITH_SYSTEM)
+  if(ctre_INCLUDES_WITH_SYSTEM)
+    set(warning_guard SYSTEM)
+  endif()
 endif()
 
-if (NOT CTRE_BUILD_PACKAGE)
-  return()
-endif()
+# ---- Declare library ----
 
-list(APPEND source-generators TBZ2 TGZ TXZ ZIP)
+add_library(ctre_ctre INTERFACE)
+add_library(ctre::ctre ALIAS ctre_ctre)
 
-if (CTRE_BUILD_PACKAGE_DEB)
-  list(APPEND binary-generators "DEB")
-endif()
+set_property(TARGET ctre_ctre PROPERTY EXPORT_NAME ctre)
 
-if (CTRE_BUILD_PACKAGE_RPM)
-  list(APPEND binary-generators "RPM")
-endif()
+target_include_directories(ctre_ctre ${warning_guard} INTERFACE
+  "$<BUILD_INTERFACE:${PROJECT_SOURCE_DIR}/include>")
+target_compile_features(ctre_ctre INTERFACE cxx_std_17)
+
+# ---- Install rules ----
+
+if(NOT CMAKE_SKIP_INSTALL_RULES)
+  # For hygienic reasons, install headers to their own directory (issue #207)
+  if(PROJECT_IS_TOP_LEVEL)
+    set(CMAKE_INSTALL_INCLUDEDIR include/ctre CACHE PATH "")
+  endif()
 
-set(CPACK_SOURCE_GENERATOR ${source-generators})
-set(CPACK_GENERATOR ${binary-generators})
+  # The project is configured without a language, so this needs to be set
+  set(CMAKE_INSTALL_LIBDIR lib CACHE PATH "")
 
-set(CPACK_PACKAGE_FILE_NAME "${PROJECT_NAME}-${PROJECT_VERSION}")
-set(CPACK_SOURCE_PACKAGE_FILE_NAME "${CPACK_PACKAGE_FILE_NAME}")
+  include(CMakePackageConfigHelpers)
+  include(GNUInstallDirs)
 
-set(CPACK_DEBIAN_PACKAGE_MAINTAINER "Hanicka Dusíková")
-set(CPACK_DEBIAN_PACKAGE_DESCRIPTION "${PROJECT_DESCRIPTION}")
-set(CPACK_DEBIAN_PACKAGE_NAME "lib${PROJECT_NAME}-dev")
+  set(CMAKE_INSTALL_DEFAULT_COMPONENT_NAME ctre_Development)
 
-set(CPACK_RPM_PACKAGE_NAME "lib${PROJECT_NAME}-devel")
+  install(DIRECTORY include/
+    DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}"
+    FILES_MATCHING PATTERN *.hpp)
 
-set(PKG_CONFIG_FILE_NAME "${CMAKE_CURRENT_BINARY_DIR}/${PROJECT_NAME}.pc")
-configure_file("${CMAKE_CURRENT_SOURCE_DIR}/packaging/pkgconfig.pc.in" "${PKG_CONFIG_FILE_NAME}" @ONLY)
-install(FILES "${PKG_CONFIG_FILE_NAME}"
-	DESTINATION "${CMAKE_INSTALL_DATADIR}/pkgconfig"
-)
+  install(TARGETS ctre_ctre
+    EXPORT ctre-targets
+    DESTINATION dummy # required until 3.14
+    INCLUDES DESTINATION "${CMAKE_INSTALL_INCLUDEDIR}")
+
+  # Replace with ARCH_INDEPENDENT once updated to CMake 3.14
+  set(tmp_CMAKE_SIZEOF_VOID_P "${CMAKE_SIZEOF_VOID_P}")
+  set(CMAKE_SIZEOF_VOID_P "")
+
+  write_basic_package_version_file(ctre-config-version.cmake
+    COMPATIBILITY SameMajorVersion)
+
+  set(CMAKE_SIZEOF_VOID_P "${tmp_CMAKE_SIZEOF_VOID_P}")
+
+  # Allow package maintainers to freely override the path for the configs
+  set(ctre_INSTALL_CMAKEDIR "${CMAKE_INSTALL_DATADIR}/cmake/ctre"
+    CACHE PATH "CMake package config location relative to the install prefix")
+  mark_as_advanced(ctre_INSTALL_CMAKEDIR)
+
+  install(FILES "${PROJECT_BINARY_DIR}/ctre-config-version.cmake"
+    DESTINATION "${ctre_INSTALL_CMAKEDIR}")
+
+  install(EXPORT ctre-targets
+    FILE ctre-config.cmake
+    DESTINATION "${ctre_INSTALL_CMAKEDIR}"
+    NAMESPACE ctre::)
+
+  option(ctre_ENABLE_PKGCONFIG "Install a .pc file for the project" ON)
+  if(ctre_ENABLE_PKGCONFIG)
+    set(ctre_INSTALL_PKGCONFIG "${CMAKE_INSTALL_DATADIR}/pkgconfig/ctre.pc"
+      CACHE FILEPATH "pkgconfig file location relative to the install prefix")
+    mark_as_advanced(ctre_INSTALL_PKGCONFIG)
+
+    # Export variables for pkgconfig.cmake to use in the install script
+    install(CODE "set(pc_path [==[${ctre_INSTALL_PKGCONFIG}]==])")
+    install(CODE "set(include_dir [==[${CMAKE_INSTALL_INCLUDEDIR}]==])")
+    foreach(var IN ITEMS NAME DESCRIPTION VERSION)
+      install(CODE "set(PROJECT_${var} [==[${PROJECT_${var}}]==])")
+    endforeach()
+    install(SCRIPT packaging/pkgconfig.cmake)
+  endif()
+
+  if(PROJECT_IS_TOP_LEVEL)
+    # This variable is normally used by set_property(INSTALL), but there aren't
+    # any in this project, so it makes this a convenient place to provide some
+    # defaults
+    set(CPACK_PROPERTIES_FILE
+      "${PROJECT_SOURCE_DIR}/packaging/CPackDefaults.cmake")
+    set(CPACK_PACKAGE_DESCRIPTION_SUMMARY "${PROJECT_DESCRIPTION}")
+    set(CPACK_PACKAGE_HOMEPAGE_URL "${PROJECT_HOMEPAGE_URL}")
+    include(CPack)
+  endif()
+endif()
 
-list(APPEND CPACK_SOURCE_IGNORE_FILES /.git/ /build/ .gitignore .DS_Store)
+# ---- Testing ----
 
-include(CPack)
+if(PROJECT_IS_TOP_LEVEL)
+  include(CTest)
+  if(BUILD_TESTING)
+    add_subdirectory(tests)
+  endif()
+endif()

packaging/CPackDefaults.cmake

@@ -0,0 +1,13 @@
+# This file is loaded at the end of the generated CPackConfig.cmake
+
+set(CPACK_PACKAGE_FILE_NAME "ctre-${CPACK_PACKAGE_VERSION}")
+set(CPACK_SOURCE_PACKAGE_FILE_NAME "${CPACK_PACKAGE_FILE_NAME}")
+
+set(CPACK_DEBIAN_PACKAGE_MAINTAINER "Hanicka Dusíková")
+set(CPACK_DEBIAN_PACKAGE_DESCRIPTION "${CPACK_PACKAGE_DESCRIPTION_SUMMARY}")
+set(CPACK_DEBIAN_PACKAGE_NAME libctre-dev)
+
+set(CPACK_RPM_PACKAGE_NAME libctre-devel)
+
+list(APPEND CPACK_SOURCE_IGNORE_FILES
+  "/\\.git/" /build/ "\\.gitignore" "\\.DS_Store")

packaging/pkgconfig.cmake

@@ -0,0 +1,12 @@
+# This script is run at CMake install time
+
+get_filename_component(prefix "${CMAKE_INSTALL_PREFIX}" ABSOLUTE)
+file(WRITE "${CMAKE_INSTALL_PREFIX}/${pc_path}" "\
+prefix=${prefix}
+includedir=\${prefix}/${include_dir}
+
+Name: ${PROJECT_NAME}
+Description: ${PROJECT_DESCRIPTION}
+Version: ${PROJECT_VERSION}
+Cflags: -I\${includedir}
+")

tests/CMakeLists.txt

@@ -1,10 +1,15 @@
+cmake_minimum_required(VERSION 3.12)
+
+enable_language(CXX)
+
+# CONFIGURE_DEPENDS was added in 3.12, so tests require at least that version
 file(GLOB test-sources CONFIGURE_DEPENDS *.cpp)
 
 add_custom_target(ctre-test)
 
-foreach (source IN LISTS test-sources)
+foreach(source IN LISTS test-sources)
   get_filename_component(test "${source}" NAME_WE)
   add_library(ctre-test-${test} STATIC EXCLUDE_FROM_ALL ${source})
-  target_link_libraries(ctre-test-${test} PRIVATE ctre)
+  target_link_libraries(ctre-test-${test} PRIVATE ctre::ctre)
   add_dependencies(ctre-test ctre-test-${test})
 endforeach()