[cmake] Install libraries in standard directories (#685)

* [cmake] Install libraries in standard directories

Previously, libraries were installed under `lib/swift/${os}/`. They
should be installed in the default library directory for the relevant
target system.
In addition, swiftmodules were installed in the older layout format on
non-Darwin platforms. This changes to use the standard modern layout
format for swiftmodules.

* Use full triple for swiftmodule filenames

* Extract Swift_MODULE_TRIPLE from the function

* Fail early in case the triple cannot be found

* Enable C language before using GNUInstallDirs

* Add C language in project definition

Enabling the C language after Swift was causing issues with using the C
compiler.

Author: Steelskin

CMakeLists.txt

@@ -1,7 +1,9 @@
 cmake_minimum_required(VERSION 3.19)
 
+# Due to a bug in CMake, we need to enable the C language before we can use
+# GNUInstallDirs.
 project(swift-argument-parser
-  LANGUAGES Swift)
+  LANGUAGES C Swift)
 
 option(BUILD_EXAMPLES "Build Example Programs" TRUE)
 option(BUILD_SHARED_LIBS "Build shared libraries by default" YES)
@@ -15,6 +17,8 @@ set(CMAKE_RUNTIME_OUTPUT_DIRECTORY ${CMAKE_BINARY_DIR}/bin)
 set(CMAKE_Swift_MODULE_DIRECTORY ${CMAKE_BINARY_DIR}/swift)
 
 include(CTest)
+
+include(GNUInstallDirs)
 include(SwiftSupport)
 
 find_package(dispatch CONFIG)

cmake/modules/SwiftSupport.cmake

@@ -61,6 +61,28 @@ function(get_swift_host_os result_var_name)
   endif()
 endfunction()
 
+if(NOT Swift_MODULE_TRIPLE)
+  # Attempt to get the module triple from the Swift compiler.
+  set(module_triple_command "${CMAKE_Swift_COMPILER}" -print-target-info)
+  if(CMAKE_Swift_COMPILER_TARGET)
+    list(APPEND module_triple_command -target ${CMAKE_Swift_COMPILER_TARGET})
+  endif()
+  execute_process(COMMAND ${module_triple_command}
+    OUTPUT_VARIABLE target_info_json)
+  string(JSON module_triple GET "${target_info_json}" "target" "moduleTriple")
+
+  # Exit now if we failed to infer the triple.
+  if(NOT module_triple)
+    message(FATAL_ERROR
+      "Failed to get module triple from Swift compiler. "
+      "Compiler output: ${target_info_json}")
+  endif()
+
+  # Cache the module triple for future use.
+  set(Swift_MODULE_TRIPLE "${module_triple}" CACHE STRING "swift module triple used for installed swiftmodule and swiftinterface files")
+  mark_as_advanced(Swift_MODULE_TRIPLE)
+endif()
+
 function(_install_target module)
   get_swift_host_os(swift_os)
   get_target_property(type ${module} TYPE)
@@ -71,31 +93,20 @@ function(_install_target module)
     set(swift swift)
   endif()
 
-  install(TARGETS ${module}
-    ARCHIVE DESTINATION lib/${swift}/${swift_os}
-    LIBRARY DESTINATION lib/${swift}/${swift_os}
-    RUNTIME DESTINATION bin)
+  install(TARGETS ${module})
   if(type STREQUAL EXECUTABLE)
     return()
   endif()
 
-  get_swift_host_arch(swift_arch)
   get_target_property(module_name ${module} Swift_MODULE_NAME)
   if(NOT module_name)
     set(module_name ${module})
   endif()
 
-  if(CMAKE_SYSTEM_NAME STREQUAL Darwin)
-    install(FILES $<TARGET_PROPERTY:${module},Swift_MODULE_DIRECTORY>/${module_name}.swiftdoc
-      DESTINATION lib/${swift}/${swift_os}/${module_name}.swiftmodule
-      RENAME ${swift_arch}.swiftdoc)
-    install(FILES $<TARGET_PROPERTY:${module},Swift_MODULE_DIRECTORY>/${module_name}.swiftmodule
-      DESTINATION lib/${swift}/${swift_os}/${module_name}.swiftmodule
-      RENAME ${swift_arch}.swiftmodule)
-  else()
-    install(FILES
-      $<TARGET_PROPERTY:${module},Swift_MODULE_DIRECTORY>/${module_name}.swiftdoc
-      $<TARGET_PROPERTY:${module},Swift_MODULE_DIRECTORY>/${module_name}.swiftmodule
-      DESTINATION lib/${swift}/${swift_os}/${swift_arch})
-  endif()
+  install(FILES $<TARGET_PROPERTY:${module},Swift_MODULE_DIRECTORY>/${module_name}.swiftdoc
+    DESTINATION ${CMAKE_INSTALL_LIBDIR}/${swift}/${swift_os}/${module_name}.swiftmodule
+    RENAME ${Swift_MODULE_TRIPLE}.swiftdoc)
+  install(FILES $<TARGET_PROPERTY:${module},Swift_MODULE_DIRECTORY>/${module_name}.swiftmodule
+    DESTINATION ${CMAKE_INSTALL_LIBDIR}/${swift}/${swift_os}/${module_name}.swiftmodule
+    RENAME ${Swift_MODULE_TRIPLE}.swiftmodule)
 endfunction()