Copy legacy layouts to stdlib build directory

This adds a new copy-legacy-layouts-${platform}-${arch} target for each
platform and architecture that the standard library is built for.

If the platform and architecture has a corresponding layout file in
stdlib/public/legacy_layouts/${platform}/layouts-${arch}.yaml, the
target copies this file to the build directory; otherwise, it does
nothing.

When building Swift code, the subroutines in SwiftSource.cmake add a
dependency on this target from each Swift code target.

Finally, we ensure that the YAML files are copied into the toolchain
package when building a toolchain.

Author: slavapestov

cmake/modules/SwiftSource.cmake

@@ -434,6 +434,16 @@ function(_compile_swift_files
   string(REPLACE ";" "'\n'" source_files_quoted "${source_files}")
   file(WRITE "${file_path}" "'${source_files_quoted}'")
 
+  # If this platform/architecture combo supports backward deployment to old
+  # Objective-C runtimes, we need to copy a YAML file with legacy type layout
+  # information to the build directory so that the compiler can find it.
+  #
+  # See stdlib/CMakeLists.txt and TypeConverter::TypeConverter() in
+  # lib/IRGen/GenType.cpp.
+  set(SWIFTFILE_PLATFORM "${SWIFT_SDK_${SWIFTFILE_SDK}_LIB_SUBDIR}")
+  set(copy_legacy_layouts_dep
+      "copy-legacy-layouts-${SWIFTFILE_PLATFORM}-${SWIFTFILE_ARCHITECTURE}")
+
   add_custom_command_target(
       dependency_target
       COMMAND
@@ -447,6 +457,7 @@ function(_compile_swift_files
         ${file_path} ${source_files} ${SWIFTFILE_DEPENDS}
         ${swift_ide_test_dependency}
         ${obj_dirs_dependency_target}
+        ${copy_legacy_layouts_dep}
       COMMENT "Compiling ${first_output}")
   set("${dependency_target_out_var_name}" "${dependency_target}" PARENT_SCOPE)
 

stdlib/CMakeLists.txt

@@ -107,6 +107,48 @@ swift_create_stdlib_targets("swift-stdlib" "sibopt" TRUE)
 swift_create_stdlib_targets("swift-stdlib" "sibgen" TRUE)
 swift_create_stdlib_targets("swift-test-stdlib" "" FALSE)
 
+foreach(sdk ${SWIFT_SDKS})
+  foreach(arch ${SWIFT_SDK_${sdk}_ARCHITECTURES})
+    set(platform "${SWIFT_SDK_${sdk}_LIB_SUBDIR}")
+    set(input "${SWIFT_SOURCE_DIR}/stdlib/public/legacy_layouts/${platform}/layouts-${arch}.yaml")
+    set(output "${SWIFTLIB_DIR}/${platform}/layouts-${arch}.yaml")
+
+    if(EXISTS "${input}")
+      # Copy the input file to the build directory.
+      add_custom_command(
+        OUTPUT "${output}"
+        DEPENDS "${input}"
+        COMMAND
+          "${CMAKE_COMMAND}" -E copy
+          "${input}"
+          "${output}")
+
+      # Define a target for this so that we can depend on it when
+      # building Swift sources.
+      add_custom_target(
+        "copy-legacy-layouts-${platform}-${arch}"
+        DEPENDS "${output}"
+        SOURCES "${input}")
+
+      # Make sure we ultimately always do this as part of building the
+      # standard library. In practice we'll do this earlier if at least
+      # one Swift source file has changed.
+      add_dependencies(
+        "swift-stdlib-${platform}-${arch}"
+        "copy-legacy-layouts-${platform}-${arch}")
+
+      swift_install_in_component(stdlib
+          FILES ${input}
+          DESTINATION "lib/swift/${platform}/")
+    else()
+      # Add a dummy target that does nothing so we can still depend on it
+      # later without checking if the input files exist.
+      add_custom_target(
+        "copy-legacy-layouts-${platform}-${arch}")
+    endif()
+  endforeach()
+endforeach()
+
 add_subdirectory(public)
 add_subdirectory(private)
 add_subdirectory(tools)