[CMake] Build modules into a proper ".swiftmodule" directory

Author: DougGregor

cmake/modules/AddSwiftHostLibrary.cmake

@@ -10,14 +10,48 @@
 function(add_swift_host_library name)
   set(ASHL_SOURCES ${ARGN})
 
+  # Create the library target.
   add_library(${name} ${ASHL_SOURCES})
 
   # Add this to the list of exported targets.
   set_property(GLOBAL APPEND PROPERTY SWIFTSYNTAX_EXPORTS ${name})
 
+  # Determine the module triple based on the target triple.
+  # FIXME: We would prefer to have build-script tell us.
+  string(REGEX REPLACE "macosx[0-9]+([.][0-9]+)?" "macos" module_triple
+    ${CMAKE_Swift_COMPILER_TARGET})
+
+  # Determine where Swift modules will be built and installed.
+  set(module_dir ${CMAKE_LIBRARY_OUTPUT_DIRECTORY})
+  set(module_base "${module_dir}/${name}.swiftmodule")
+  set(module_file "${module_base}/${module_triple}.swiftmodule")
+  set(module_interface_file "${module_base}/${module_triple}.swiftinterface")
+  set(module_sourceinfo_file "${module_base}/${module_triple}.swiftsourceinfo")
+
+  # Add a custom target to create the module directory.
+  add_custom_command(
+      TARGET ${name}
+      PRE_BUILD
+      COMMAND "${CMAKE_COMMAND}" -E make_directory ${module_base}
+      COMMENT "Generating module directory for ${name}")
+
+  # Install the Swift module into the appropriate location.
+  set_target_properties(${name}
+    PROPERTIES Swift_MODULE_DIRECTORY ${module_base}
+  )
+
+  # Configure the emission of the Swift module files.
+  target_compile_options("${name}" PRIVATE
+    $<$<COMPILE_LANGUAGE:Swift>:
+      -module-name;${name};
+      -emit-module-path;${module_file};
+      -emit-module-source-info-path;${module_sourceinfo_file}
+      >)
+
   # NOTE: workaround for CMake not setting up include flags yet
   set_target_properties(${name} PROPERTIES
-    INTERFACE_INCLUDE_DIRECTORIES ${CMAKE_Swift_MODULE_DIRECTORY})
+    INTERFACE_INCLUDE_DIRECTORIES ${module_dir}
+  )
 
   # Install this target
   install(TARGETS ${name}