From ab403367cd1c348ace744b0e9f1eac8e1758fc10 Mon Sep 17 00:00:00 2001
From: Alex Lorenz <arphaman@gmail.com>
Date: Mon, 3 Oct 2022 12:32:16 -0700
Subject: [PATCH] [interop] handle new Swift toolchains correctly, and start
 checking for minimum interop version

---
 cmake/SwiftToCXXInterop.cmake | 37 +++++++++++++++++++++++++++--------
 1 file changed, 29 insertions(+), 8 deletions(-)

diff --git a/cmake/SwiftToCXXInterop.cmake b/cmake/SwiftToCXXInterop.cmake
index d24581698a3..d42c6227398 100644
--- a/cmake/SwiftToCXXInterop.cmake
+++ b/cmake/SwiftToCXXInterop.cmake
@@ -4,9 +4,23 @@ include(FindSwiftLibs)
 # Generates a C++ compatibility header for the given target.
 # FIXME: Can we remove the headerName and match the Swift module name?
 function(generate_cxx_compat_header target headerName)
-  check_swift_source_compiles("@_expose(Cxx) public func test() {}" REVERSE_INTEROP_SUPPORTED)
-  if (NOT ${REVERSE_INTEROP_SUPPORTED})
-    message(FATAL_ERROR "Swift: reverse interop is required, but not supported.  Update your toolcain.")
+  # Verify toolchain support.
+  get_filename_component(SwiftBinPath ${CMAKE_Swift_COMPILER} DIRECTORY)
+  set (SwiftInteropVersionFile ${SwiftBinPath}/../lib/swift/swiftToCxx/experimental-interoperability-version.json)
+  if (EXISTS ${SwiftInteropVersionFile})
+    file(READ ${SwiftInteropVersionFile} SwiftInteropVersion)
+    message(STATUS "Swift: Experimental C++ interop version is ${SwiftInteropVersion}")
+    if (${SwiftInteropVersion} VERSION_LESS 2)
+      message(FATAL_ERROR "Swift: reverse interop support is too old.")
+    endif()
+    set(LegacySwiftToolchain NO) # FIXME: remove
+  else()
+    # FIXME: Once toolchain upgrades to Sept 30th, Always fail here.
+    check_swift_source_compiles("@_expose(Cxx) public func test() {}" REVERSE_INTEROP_SUPPORTED)
+     if (NOT ${REVERSE_INTEROP_SUPPORTED})
+       message(FATAL_ERROR "Swift: reverse interop is required, but not supported.  Update your toolcain.")
+     endif()
+    set(LegacySwiftToolchain YES)
   endif()
 
   set(destpath ${CMAKE_CURRENT_BINARY_DIR}/include/SwiftModules)
@@ -15,13 +29,20 @@ function(generate_cxx_compat_header target headerName)
   # Generate a directory into which the C++ headers will go.
   file(MAKE_DIRECTORY ${destpath})
  
-  # Copy the shim file for C++ to find it.
-  file(MAKE_DIRECTORY ${destpath}/../shims)
-  swift_get_resource_path(SWIFT_RESOURCE_PATH)
-  add_custom_command(TARGET ${target} PRE_BUILD
-                     COMMAND ${CMAKE_COMMAND} -E
+  if (LegacySwiftToolchain)
+    # FIXME: Remove.
+    # Copy the shim file for C++ to find it.
+    file(MAKE_DIRECTORY ${destpath}/../shims)
+    swift_get_resource_path(SWIFT_RESOURCE_PATH)
+    add_custom_command(TARGET ${target} PRE_BUILD
+                       COMMAND ${CMAKE_COMMAND} -E
                          copy ${SWIFT_RESOURCE_PATH}/shims/_SwiftCxxInteroperability.h ${destpath}/../shims/_SwiftCxxInteroperability.h)
+  endif()
 
   # Generate the C++ compatibility header for the Swift module.
   target_compile_options(${target} PRIVATE "$<$<COMPILE_LANGUAGE:Swift>:SHELL: -Xfrontend -emit-clang-header-path -Xfrontend ${destpath}/${headerName}>")
+  if (NOT LegacySwiftToolchain)
+    # Note: do not generate Stdlib bindings yet (C++20 only).
+    target_compile_options(${target} PRIVATE "$<$<COMPILE_LANGUAGE:Swift>:SHELL: -Xfrontend -clang-header-expose-decls=has-expose-attr>")
+  endif()
 endfunction()