Add -emit-public-type-metadata-accessors to work around metadata linkage bug.

include/swift/Basic/LangOptions.h

@@ -223,6 +223,9 @@ namespace swift {
     /// Enables key path resilience.
     bool EnableKeyPathResilience = false;
 
+    /// Enables public emission of private metadata accessors.
+    bool EmitPublicTypeMetadataAccessors = false;
+
     /// If set to true, the diagnosis engine can assume the emitted diagnostics
     /// will be used in editor. This usually leads to more aggressive fixit.
     bool DiagnosticsEditorMode = false;

include/swift/Option/Options.td

@@ -355,6 +355,11 @@ def warn_swift3_objc_inference : Flag<["-"], "warn-swift3-objc-inference">,
   Alias<warn_swift3_objc_inference_complete>,
   Flags<[FrontendOption, DoesNotAffectIncrementalBuild, HelpHidden]>;
 
+def emit_public_type_metadata_accessors :
+  Flag<["-"], "emit-public-type-metadata-accessors">,
+  Flags<[FrontendOption]>,
+  HelpText<"Emit all type metadata accessors as public">;
+
 def Rpass_EQ : Joined<["-"], "Rpass=">,
   Flags<[FrontendOption]>,
   HelpText<"Report performed transformations by optimization passes whose "

lib/Driver/ToolChains.cpp

@@ -183,6 +183,8 @@ static void addCommonFrontendArgs(const ToolChain &TC, const OutputInfo &OI,
                        options::OPT_warn_swift3_objc_inference_minimal,
                        options::OPT_warn_swift3_objc_inference_complete);
   inputArgs.AddLastArg(arguments, options::OPT_typo_correction_limit);
+  inputArgs.AddLastArg(arguments,
+                       options::OPT_emit_public_type_metadata_accessors);
   inputArgs.AddLastArg(arguments, options::OPT_enable_app_extension);
   inputArgs.AddLastArg(arguments, options::OPT_enable_testing);
   inputArgs.AddLastArg(arguments, options::OPT_g_Group);

lib/Frontend/CompilerInvocation.cpp

@@ -309,6 +309,9 @@ static bool ParseLangArgs(LangOptions &Opts, ArgList &Args,
     }
   }
 
+  Opts.EmitPublicTypeMetadataAccessors =
+    Args.hasArg(OPT_emit_public_type_metadata_accessors);
+
   Opts.EnableNSKeyedArchiverDiagnostics =
       Args.hasFlag(OPT_enable_nskeyedarchiver_diagnostics,
                    OPT_disable_nskeyedarchiver_diagnostics,

lib/IRGen/MetadataRequest.cpp

@@ -589,6 +589,17 @@ bool irgen::isTypeMetadataAccessTrivial(IRGenModule &IGM, CanType type) {
   return false;
 }
 
+/// Determine whether we should promote the type metadata access function
+/// for the given nominal type to "public".
+static bool promoteMetadataAccessFunctionToPublic(
+                                              const NominalTypeDecl *nominal) {
+  ASTContext &ctx = nominal->getASTContext();
+
+  // When -emit-public-type-metadata-accessors is provided, promote all
+  // of the metadata access functions to public.
+  return ctx.LangOpts.EmitPublicTypeMetadataAccessors;
+}
+
 /// Return the standard access strategy for getting a non-dependent
 /// type metadata object.
 MetadataAccessStrategy irgen::getTypeMetadataAccessStrategy(CanType type) {
@@ -621,8 +632,12 @@ MetadataAccessStrategy irgen::getTypeMetadataAccessStrategy(CanType type) {
     case FormalLinkage::PublicUnique:
       return MetadataAccessStrategy::PublicUniqueAccessor;
     case FormalLinkage::HiddenUnique:
+      if (promoteMetadataAccessFunctionToPublic(nominal))
+        return MetadataAccessStrategy::PublicUniqueAccessor;
       return MetadataAccessStrategy::HiddenUniqueAccessor;
     case FormalLinkage::Private:
+      if (promoteMetadataAccessFunctionToPublic(nominal))
+        return MetadataAccessStrategy::PublicUniqueAccessor;
       return MetadataAccessStrategy::PrivateAccessor;
 
     case FormalLinkage::PublicNonUnique:

test/IRGen/Inputs/emit_public_type_metadata_accessors_other.swift

@@ -0,0 +1,3 @@
+func foo() -> Any {
+  return Wrapper()
+}

test/IRGen/emit_public_type_metadata_accessors.swift

@@ -0,0 +1,17 @@
+// RUN: %swift -module-name test -target x86_64-apple-macosx10.9  -emit-ir -parse-stdlib -emit-public-type-metadata-accessors -primary-file %s %S/Inputs/emit_public_type_metadata_accessors_other.swift | %FileCheck --check-prefix=CHECK-PUBLIC %s
+
+// RUN: %swift -module-name test -target x86_64-apple-macosx10.9  -emit-ir -parse-stdlib -primary-file %s %S/Inputs/emit_public_type_metadata_accessors_other.swift | %FileCheck --check-prefix=CHECK-NONPUBLIC %s
+
+private class C { }
+
+// CHECK-PUBLIC: define swiftcc %swift.metadata_response @"$S4test3Foo33_DEC9477CC6E8E6E7A9CE422B1DBE7EA4LLVMa"
+// CHECK-NONPUBLIC: define internal swiftcc %swift.metadata_response @"$S4test3Foo33_DEC9477CC6E8E6E7A9CE422B1DBE7EA4LLVMa"
+private struct Foo {
+  private let c: C = C()
+}
+
+public struct Wrapper {
+  private let foo: Foo = Foo()
+}
+
+