Put C foreign refernece types behind a flag.

Author: zoecarver

include/swift/Basic/LangOptions.h

@@ -278,6 +278,8 @@ namespace swift {
     /// disabled because it is not complete.
     bool EnableCXXInterop = false;
 
+    bool CForeignReferenceTypes = false;
+
     /// Imports getters and setters as computed properties.
     bool CxxInteropGettersSettersAsProperties = false;
 

include/swift/Option/Options.td

@@ -634,6 +634,11 @@ def enable_experimental_cxx_interop :
   Flags<[FrontendOption, HelpHidden, ModuleInterfaceOption]>,
   HelpText<"Enable experimental C++ interop code generation and config directives">;
 
+def experimental_c_foreign_reference_types :
+  Flag<["-"], "experimental-c-foreign-reference-types">,
+  Flags<[FrontendOption, HelpHidden, ModuleInterfaceOption]>,
+  HelpText<"Enable experimental C foreign references types (with reference coutning).">;
+
 def enable_experimental_cxx_interop_in_clang_header :
   Flag<["-"], "enable-experimental-cxx-interop-in-clang-header">,
   Flags<[FrontendOption, NoDriverOption, HelpHidden]>,

lib/ClangImporter/ImportDecl.cpp

@@ -1945,6 +1945,10 @@ namespace {
     }
 
     bool recordHasReferenceSemantics(const clang::RecordDecl *decl) {
+      if (!isa<clang::CXXRecordDecl>(decl) &&
+          !Impl.SwiftContext.LangOpts.CForeignReferenceTypes)
+        return false;
+
       auto semanticsKind = evaluateOrDefault(
           Impl.SwiftContext.evaluator,
           CxxRecordSemantics({decl, Impl.SwiftContext}), {});

lib/Frontend/CompilerInvocation.cpp

@@ -871,6 +871,9 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
       Args.hasFlag(OPT_enable_objc_interop, OPT_disable_objc_interop,
                    Target.isOSDarwin());
 
+  Opts.CForeignReferenceTypes =
+      Args.hasArg(OPT_experimental_c_foreign_reference_types);
+
   Opts.CxxInteropGettersSettersAsProperties = Args.hasArg(OPT_cxx_interop_getters_setters_as_properties);
 
   Opts.VerifyAllSubstitutionMaps |= Args.hasArg(OPT_verify_all_substitution_maps);

test/Interop/C/struct/foreign-reference.swift

@@ -1,4 +1,4 @@
-// RUN: %target-run-simple-swift(-I %S/Inputs/ -Xfrontend -validate-tbd-against-ir=none)
+// RUN: %target-run-simple-swift(-I %S/Inputs/ -Xfrontend -validate-tbd-against-ir=none -Xfrontend -experimental-c-foreign-reference-types)
 //
 // REQUIRES: executable_test
 // TODO: This should work without ObjC interop in the future rdar://97497120