[interop][SwiftToCxx] only emit metadata references for record types

Author: hyp

lib/PrintAsClang/ModuleContentsWriter.cpp

@@ -280,9 +280,14 @@ class ModuleWriter {
     if (!isa<clang::TypeDecl>(typeDecl->getClangDecl()))
       return;
     // Get the underlying clang type from a type alias decl or record decl.
-    clang::QualType clangType(
-        cast<clang::TypeDecl>(typeDecl->getClangDecl())->getTypeForDecl(), 0);
-    auto it = seenClangTypes.insert(clangType.getCanonicalType().getTypePtr());
+    auto clangType =
+        clang::QualType(
+            cast<clang::TypeDecl>(typeDecl->getClangDecl())->getTypeForDecl(),
+            0)
+            .getCanonicalType();
+    if (!isa<clang::RecordType>(clangType.getTypePtr()))
+      return;
+    auto it = seenClangTypes.insert(clangType.getTypePtr());
     if (it.second)
       ClangValueTypePrinter::printClangTypeSwiftGenericTraits(os, typeDecl, &M);
   }

test/Interop/CxxToSwiftToCxx/bridge-cxx-struct-back-to-cxx.swift

@@ -73,6 +73,8 @@ namespace ns {
     using NonTrivialTemplateTrivial = NonTrivialTemplate<TrivialinNS>;
 }
 
+using SimpleTypedef = int;
+
 //--- module.modulemap
 module CxxTest {
     header "header.h"
@@ -112,6 +114,11 @@ public func retNonTrivialTypeAlias() -> ns.TypeAlias {
     return ns.TypeAlias()
 }
 
+@_expose(Cxx)
+public func retSimpleTypedef() -> SimpleTypedef {
+    return SimpleTypedef()
+}
+
 @_expose(Cxx)
 public func retTrivial() -> Trivial {
     return Trivial()