[CMake] Add initial build system support for macCatalyst

This commit adds initial build system support for macCatalyst,
an Apple technology that enables code targeting iOS
to be recompiled so that it can be executed on macOS while still using
iOS APIs. This is the first in a series of commits building out support for
macCatalyst in the compiler, runtime, standard library, and overlays. Swift
for macCatalyst represents the work of multiple people, including
Devin Coughlin, Ross Bayer, and Brent Royal-Gordon.

Under macCatalyst, compiler-provided shared libraries (including overlays)
are built as one of four kinds (or "flavors") of libraries,
each with different install names and Mach-O load commands. This commit
adds the build system infrastructure to produce these different
library flavors.

**macOS-like Libraries**

A "macOS-like" library (such as the GLKit overlay) is a plain-old macOS library
that can only be loaded into regular macOS processes. It has a macOS slice with
a single load command allowing it to be loaded into normal macOS processes.

**iOS-like Libraries**

An "iOS-like" library, such as the UIKit overlay, is a library with a
macOS slice but with a load command that only allows it be loaded into
macCatalyst processes. iOS-like libraries are produced by passing a new
target tuple to the compiler:

  swiftc ... -target x86_64-apple-ios13.0-macabi ...

Here 'ios' (and an iOS version number) is used for OS portion
of the triple, but the 'macabi' environment tells the compiler
that the library is intended for macCatalyst.

**Zippered Libraries**

A "zippered" library can be loaded into either a macCatalyst process or
a standard macOS process. Since macCatalyst does not introduce a new Mach-O
slice, the same code is shared between both processes. Zippered libraries
are usually relatively low level and with an API surface that is similar
between macOS and iOS (for example, both the Foundation overlay and the Swift
Standard Library/Runtime itself are zippered).

Zippered libraries are created by passing both the usual `-target`
flag to the compiler and an additional `-target-variant` flag:

   swiftc ... -target x86_64-apple-macos10.15 \
              -target-variant x86_64-apple-ios13.0-macabi

Just like the -target flag, -target-variant takes a target tuple.
This tells the compiler to compile the library for the -target tuple but
to add an extra load command, allowing the library to be loaded into processes
of the -target-variant flavor as well.

While a single zippered library and slice is shared between macOS and
macCatalyst, zippered libraries require two separate .swiftinterface/.swiftmodule
files, one for macOS and one for macCatalyst. When a macOS or macCatalyst client
imports the library, it will use module file for its flavor to determine what
symbols are present. This enables a zippered library to expose a subset of its
target APIs to its target-variant.

**Unzippered-Twin Libraries**

"Unzippered Twins" are pairs of libraries with the same name but different
contents and install locations, one for use from macOS processes and one for
use from macCatalyst processes. Unzippered twins are usually libraries that
depend on AppKit on macOS and UIKit on iOS (for example, the MapKit overlay)
and so do not share a common implementation between macOS and macCatalyst.

The macCatalyst version of an unzippered twin is installed in a parallel
directory hierarchy rooted at /System/iOSSupport/. So, for example, while macOS
and zippered Swift overlays are installed in /usr/lib/swift/, iOS-like and
the macCatalyst side of unzippered twins are installed in
/System/iOSSupport/usr/lib/swift. When building for macCatalyst, the build system
passes additional search paths so that the macCatalyst version of libraries is
found before macOS versions.

The add_swift_target_library() funciton now take an
optional  MACCATALYST_BUILD_FLAVOR, which enables swift libraries to indicate
which flavor of library they are.

Author: devincoughlin

cmake/modules/AddSwift.cmake

@@ -93,6 +93,12 @@ set(SWIFT_BUILD_STANDALONE_OVERLAY TRUE)
 set(SWIFT_STDLIB_LIBRARY_BUILD_TYPES "SHARED")
 set(SWIFT_SDK_OVERLAY_LIBRARY_BUILD_TYPES "SHARED")
 
+option(SWIFT_ENABLE_MACCATALYST
+  "Build the overlays with macCatalyst support"
+  FALSE)
+
+set(SWIFT_DARWIN_DEPLOYMENT_VERSION_MACCATALYST "13.0" CACHE STRING
+  "Minimum deployment target version for macCatalyst")
 
 # -----------------------------------------------------------------------------
 

cmake/modules/StandaloneOverlay.cmake

@@ -133,7 +133,7 @@ macro(configure_sdk_darwin
   endif()
 
   if(NOT EXISTS "${SWIFT_SDK_${prefix}_PATH}/System/Library/Frameworks/module.map")
-    message(FATAL_ERROR "${name} SDK not found at ${SWIFT_SDK_${prefix}_PATH}.")
+    message(FATAL_ERROR "${name} SDK not found at SWIFT_SDK_${prefix}_PATH.")
   endif()
 
   # Determine the SDK version we found.
@@ -183,6 +183,20 @@ macro(configure_sdk_darwin
 
     set(SWIFT_SDK_${prefix}_ARCH_${arch}_TRIPLE
         "${arch}-apple-${SWIFT_SDK_${prefix}_TRIPLE_NAME}")
+
+    if(SWIFT_ENABLE_MACCATALYST AND "${prefix}" STREQUAL "OSX")
+      # For macCatalyst append the '-macabi' environment to the target triple.
+      set(SWIFT_SDK_MACCATALYST_ARCH_${arch}_TRIPLE
+        "${SWIFT_SDK_${prefix}_ARCH_${arch}_TRIPLE}-macabi")
+
+      # macCatalyst triple
+      set(SWIFT_MACCATALYST_TRIPLE
+        "x86_64-apple-ios${SWIFT_DARWIN_DEPLOYMENT_VERSION_MACCATALYST}-macabi")
+
+      # For macCatalyst, the xcrun_name is "macosx" since it uses that sdk.
+      # Hard code the library subdirectory to "maccatalyst" in that case.
+      set(SWIFT_SDK_MACCATALYST_LIB_SUBDIR "maccatalyst")
+    endif()
   endforeach()
 
   # Add this to the list of known SDKs.

cmake/modules/SwiftConfigureSDK.cmake

@@ -1,3 +1,4 @@
+include(macCatalystUtils)
 include(SwiftUtils)
 
 # Process the sources within the given variable, pulling out any Swift
@@ -7,6 +8,9 @@ include(SwiftUtils)
 #
 # Usage:
 #   handle_swift_sources(sourcesvar externalvar)
+#
+# MACCATALYST_BUILD_FLAVOR
+#   Possible values are 'ios-like', 'macos-like', 'zippered', 'unzippered-twin'
 function(handle_swift_sources
     dependency_target_out_var_name
     dependency_module_target_out_var_name
@@ -16,7 +20,7 @@ function(handle_swift_sources
     sourcesvar externalvar name)
   cmake_parse_arguments(SWIFTSOURCES
       "IS_MAIN;IS_STDLIB;IS_STDLIB_CORE;IS_SDK_OVERLAY;EMBED_BITCODE"
-      "SDK;ARCHITECTURE;INSTALL_IN_COMPONENT"
+      "SDK;ARCHITECTURE;INSTALL_IN_COMPONENT;MACCATALYST_BUILD_FLAVOR"
       "DEPENDS;COMPILE_FLAGS;MODULE_NAME"
       ${ARGN})
   translate_flag(${SWIFTSOURCES_IS_MAIN} "IS_MAIN" IS_MAIN_arg)
@@ -63,6 +67,12 @@ function(handle_swift_sources
   if(swift_sources)
     set(objsubdir "/${SWIFTSOURCES_SDK}/${SWIFTSOURCES_ARCHITECTURE}")
 
+    get_maccatalyst_build_flavor(maccatalyst_build_flavor
+      "${SWIFTSOURCES_SDK}" "${SWIFTSOURCES_MACCATALYST_BUILD_FLAVOR}")
+    if(maccatalyst_build_flavor STREQUAL "ios-like")
+      set(objsubdir "/MACCATALYST/${SWIFTSOURCES_ARCHITECTURE}")
+    endif()
+
     file(MAKE_DIRECTORY "${CMAKE_CURRENT_BINARY_DIR}${objsubdir}")
 
     set(swift_obj
@@ -91,7 +101,8 @@ function(handle_swift_sources
         ${IS_SDK_OVERLAY_arg}
         ${EMBED_BITCODE_arg}
         ${STATIC_arg}
-        INSTALL_IN_COMPONENT "${SWIFTSOURCES_INSTALL_IN_COMPONENT}")
+        INSTALL_IN_COMPONENT "${SWIFTSOURCES_INSTALL_IN_COMPONENT}"
+        MACCATALYST_BUILD_FLAVOR "${SWIFTSOURCES_MACCATALYST_BUILD_FLAVOR}")
     set("${dependency_target_out_var_name}" "${dependency_target}" PARENT_SCOPE)
     set("${dependency_module_target_out_var_name}" "${module_dependency_target}" PARENT_SCOPE)
     set("${dependency_sib_target_out_var_name}" "${sib_dependency_target}" PARENT_SCOPE)
@@ -131,6 +142,7 @@ endfunction()
 #     OUTPUT objfile                    # Name of the resulting object file
 #     SOURCES swift_src [swift_src...]  # Swift source files to compile
 #     FLAGS -module-name foo            # Flags to add to the compilation
+#     MACCATALYST_BUILD_FLAVOR flavor        # macCatalyst flavor
 #     [SDK sdk]                         # SDK to build for
 #     [ARCHITECTURE architecture]       # Architecture to build for
 #     [DEPENDS cmake_target...]         # CMake targets on which the object
@@ -151,7 +163,7 @@ function(_compile_swift_files
     dependency_sibgen_target_out_var_name)
   cmake_parse_arguments(SWIFTFILE
     "IS_MAIN;IS_STDLIB;IS_STDLIB_CORE;IS_SDK_OVERLAY;EMBED_BITCODE"
-    "OUTPUT;MODULE_NAME;INSTALL_IN_COMPONENT"
+    "OUTPUT;MODULE_NAME;INSTALL_IN_COMPONENT;MACCATALYST_BUILD_FLAVOR"
     "SOURCES;FLAGS;DEPENDS;SDK;ARCHITECTURE;OPT_FLAGS;MODULE_DIR"
     ${ARGN})
 
@@ -175,6 +187,27 @@ function(_compile_swift_files
   precondition(SWIFTFILE_ARCHITECTURE MESSAGE "Should specify an architecture")
   precondition(SWIFTFILE_INSTALL_IN_COMPONENT MESSAGE "INSTALL_IN_COMPONENT is required")
 
+  # Determine if/what macCatalyst build variant we are
+  get_maccatalyst_build_flavor(maccatalyst_build_flavor
+    "${SWIFTFILE_SDK}" "${SWIFTFILE_MACCATALYST_BUILD_FLAVOR}")
+
+  # Determine target triples
+  get_target_triple(target_triple ignored_target_variant_triple
+    "${SWIFTFILE_SDK}"
+    "${SWIFTFILE_ARCHITECTURE}"
+    DEPLOYMENT_VERSION "${SWIFT_SDK_${SWIFTFILE_SDK}_DEPLOYMENT_VERSION}")
+
+  get_target_triple(maccatalyst_target_triple ignored_target_variant_triple
+    "${SWIFTFILE_SDK}"
+    "${SWIFTFILE_ARCHITECTURE}"
+    DEPLOYMENT_VERSION "${SWIFT_SDK_${SWIFTFILE_SDK}_DEPLOYMENT_VERSION}"
+    MACCATALYST_BUILD_FLAVOR "${maccatalyst_build_flavor}")
+
+  # macCatalyst ios-like target triple
+  if(maccatalyst_build_flavor STREQUAL "ios-like")
+    set(target_triple "${maccatalyst_target_triple}")
+  endif()
+
   if ("${SWIFTFILE_MODULE_NAME}" STREQUAL "")
     get_filename_component(SWIFTFILE_MODULE_NAME "${first_output}" NAME_WE)
     message(SEND_ERROR
@@ -202,17 +235,18 @@ function(_compile_swift_files
       "${SWIFTFILE_ARCHITECTURE}"
       "${SWIFT_STDLIB_BUILD_TYPE}"
       "${SWIFT_STDLIB_ASSERTIONS}"
-      swift_flags)
+      swift_flags
+      MACCATALYST_BUILD_FLAVOR "${maccatalyst_build_flavor}"
+      )
 
   # Determine the subdirectory where the binary should be placed.
   compute_library_subdir(library_subdir
       "${SWIFTFILE_SDK}" "${SWIFTFILE_ARCHITECTURE}")
 
-  # Allow import of other Swift modules we just built.
-  list(APPEND swift_flags
-      "-I" "${SWIFTLIB_DIR}/${library_subdir}")
-  # FIXME: should we use '-resource-dir' here?  Seems like it has no advantage
-  # over '-I' in this case.
+  if(maccatalyst_build_flavor STREQUAL "ios-like")
+  	compute_library_subdir(library_subdir
+      "MACCATALYST" "${SWIFTFILE_ARCHITECTURE}")
+  endif()
 
   # If we have a custom module cache path, use it.
   if (SWIFT_MODULE_CACHE_PATH)
@@ -308,7 +342,8 @@ function(_compile_swift_files
     list(APPEND swift_flags "-parse-as-library")
 
     set(module_base "${module_dir}/${SWIFTFILE_MODULE_NAME}")
-    if(SWIFTFILE_SDK IN_LIST SWIFT_APPLE_PLATFORMS)
+    if(SWIFTFILE_SDK IN_LIST SWIFT_APPLE_PLATFORMS OR
+       SWIFTFILE_SDK STREQUAL "MACCATALYST")
       set(specific_module_dir "${module_base}.swiftmodule")
       set(specific_module_project_dir "${specific_module_dir}/Project")
       set(source_info_file "${specific_module_project_dir}/${SWIFTFILE_ARCHITECTURE}.swiftsourceinfo")
@@ -338,6 +373,57 @@ function(_compile_swift_files
            "-Xfrontend" "-experimental-skip-non-inlinable-function-bodies")
     endif()
 
+    set(module_outputs "${module_file}" "${module_doc_file}")
+
+    if(interface_file)
+      list(APPEND module_outputs "${interface_file}")
+    endif()
+
+    set(optional_arg)
+    if(SWIFTFILE_SDK IN_LIST SWIFT_APPLE_PLATFORMS OR
+       SWIFTFILE_SDK STREQUAL "MACCATALYST")
+      # Allow installation of stdlib without building all variants on Darwin.
+      set(optional_arg "OPTIONAL")
+    endif()
+
+    if(SWIFTFILE_SDK IN_LIST SWIFT_APPLE_PLATFORMS OR
+       SWIFTFILE_SDK STREQUAL "MACCATALYST")
+      swift_install_in_component(DIRECTORY "${specific_module_dir}"
+                                 DESTINATION "lib${LLVM_LIBDIR_SUFFIX}/swift/${library_subdir}"
+                                 COMPONENT "${SWIFTFILE_INSTALL_IN_COMPONENT}")
+    else()
+      swift_install_in_component(FILES ${module_outputs}
+                                 DESTINATION "lib${LLVM_LIBDIR_SUFFIX}/swift/${library_subdir}"
+                                 COMPONENT "${SWIFTFILE_INSTALL_IN_COMPONENT}")
+    endif()
+
+    # macCatalyst zippered module setup
+    if(maccatalyst_build_flavor STREQUAL "zippered")
+      compute_library_subdir(maccatalyst_library_subdir
+        "MACCATALYST" "${SWIFTFILE_ARCHITECTURE}")
+
+      if(SWIFTFILE_MODULE_DIR)
+        set(maccatalyst_module_dir "${SWIFTFILE_MODULE_DIR}")
+      elseif(SWIFTFILE_IS_STDLIB)
+        set(maccatalyst_module_dir "${SWIFTLIB_DIR}/${maccatalyst_library_subdir}")
+      else()
+        message(FATAL_ERROR "Don't know where to put the module files")
+      endif()
+
+      set(maccatalyst_specific_module_dir
+          "${maccatalyst_module_dir}/${SWIFTFILE_MODULE_NAME}.swiftmodule")
+      set(maccatalyst_module_base "${maccatalyst_specific_module_dir}/${SWIFTFILE_ARCHITECTURE}")
+      set(maccatalyst_module_file "${maccatalyst_module_base}.swiftmodule")
+      set(maccatalyst_module_doc_file "${maccatalyst_module_base}.swiftdoc")
+
+      set(maccatalyst_module_outputs "${maccatalyst_module_file}" "${maccatalyst_module_doc_file}")
+
+      swift_install_in_component(DIRECTORY ${maccatalyst_specific_module_dir}
+                                 DESTINATION "lib${LLVM_LIBDIR_SUFFIX}/swift/${maccatalyst_library_subdir}"
+                                 COMPONENT "${SWIFTFILE_INSTALL_IN_COMPONENT}"
+                                 "${optional_arg}")
+    endif()
+
     # If we have extra regexp flags, check if we match any of the regexps. If so
     # add the relevant flags to our swift_flags.
     if (SWIFT_EXPERIMENTAL_EXTRA_REGEXP_FLAGS OR SWIFT_EXPERIMENTAL_EXTRA_NEGATIVE_REGEXP_FLAGS)
@@ -401,6 +487,26 @@ function(_compile_swift_files
   set(sibopt_outputs "${sibopt_file}")
   set(sibgen_outputs "${sibgen_file}")
 
+  # macCatalyst zippered swiftmodule
+  if(maccatalyst_build_flavor STREQUAL "zippered")
+    set(maccatalyst_swift_flags "${swift_flags}")
+    list(APPEND maccatalyst_swift_flags
+      "-I" "${SWIFTLIB_DIR}/${maccatalyst_library_subdir}")
+    set(maccatalyst_swift_module_flags ${swift_module_flags})
+  elseif(maccatalyst_build_flavor STREQUAL "ios-like")
+    compute_library_subdir(maccatalyst_library_subdir
+      "MACCATALYST" "${SWIFTFILE_ARCHITECTURE}")
+    list(APPEND swift_flags
+      "-I" "${SWIFTLIB_DIR}/${maccatalyst_library_subdir}")
+  else()
+    # Allow import of other Swift modules we just built.
+    list(APPEND swift_flags
+      "-I" "${SWIFTLIB_DIR}/${library_subdir}")
+
+    # FIXME: should we use '-resource-dir' here?  Seems like it has no advantage
+    # over '-I' in this case.
+  endif()
+
   if(XCODE)
     # HACK: work around an issue with CMake Xcode generator and the Swift
     # driver.
@@ -424,6 +530,12 @@ function(_compile_swift_files
       COMMAND "${CMAKE_COMMAND}" -E touch ${sibopt_outputs})
     set(command_touch_sibgen_outputs
       COMMAND "${CMAKE_COMMAND}" -E touch ${sibgen_outputs})
+
+    # macCatalyst zippered outputs
+    if(maccatalyst_build_flavor STREQUAL "zippered")
+      set(command_touch_maccatalyst_module_outputs
+        COMMAND "${CMAKE_COMMAND}" -E touch ${maccatalyst_module_outputs})
+    endif()
   endif()
 
   # First generate the obj dirs
@@ -516,6 +628,49 @@ function(_compile_swift_files
         COMMENT "Generating ${module_file}")
     set("${dependency_module_target_out_var_name}" "${module_dependency_target}" PARENT_SCOPE)
 
+    # macCatalyst zippered swiftmodule
+    if(maccatalyst_build_flavor STREQUAL "zippered")
+      get_target_triple(ios_like_target_triple ignored_target_variant
+        "${SWIFTFILE_SDK}"
+        "${SWIFTFILE_ARCHITECTURE}"
+        MACCATALYST_BUILD_FLAVOR "ios-like")
+
+      # Remove previous -target <triple> and -target-variant flags from
+      # the zippered Swift flags and add an ios-like target.
+      remove_given_flag(maccatalyst_swift_flags "target")
+      remove_given_flag(maccatalyst_swift_flags "target-variant")
+      list(APPEND maccatalyst_swift_flags
+        "-target" "${ios_like_target_triple}")
+
+      add_custom_command_target(
+        maccatalyst_module_dependency_target
+        COMMAND
+          "${CMAKE_COMMAND}" "-E" "remove" "-f" ${maccatalyst_module_outputs}
+        COMMAND
+          "${CMAKE_COMMAND}" "-E" "make_directory" ${maccatalyst_specific_module_dir}
+        COMMAND
+          "${PYTHON_EXECUTABLE}" "${line_directive_tool}" "@${file_path}" --
+          "${swift_compiler_tool}" "-emit-module" "-o" "${maccatalyst_module_file}"
+          ${maccatalyst_swift_flags} ${maccatalyst_swift_module_flags} "@${file_path}"
+        ${command_touch_maccatalyst_module_outputs}
+        OUTPUT
+          ${maccatalyst_module_outputs}
+        DEPENDS
+          ${swift_compiler_tool_dep}
+          ${source_files}
+          ${SWIFTFILE_DEPENDS}
+          ${swift_ide_test_dependency}
+          ${obj_dirs_dependency_target}
+        COMMENT
+          "Generating ${maccatalyst_module_file}")
+
+      # Piggy-back on the same out-var as the regular swiftmodule
+      set("${dependency_module_target_out_var_name}"
+        "${module_dependency_target}"
+        "${maccatalyst_module_dependency_target}"
+        PARENT_SCOPE)
+    endif()
+
     # This is the target to generate the .sib files. It is not built by default.
     add_custom_command_target(
         sib_dependency_target