[cxx-interop] WA: skip virtual function import when symbolic import enabled

This is a simple work around to avoid importing virtual functions when symbolic
imports are turned on. Test cases that were failing before this WA are in
test/Interop/Cxx/symbolic-imports.

Thanks to Alex Lorenz for providing this WA to me (@hyp).

Author: plotfi

include/swift/ClangImporter/ClangImporter.h

@@ -611,6 +611,9 @@ class ClangImporter final : public ClangModuleLoader {
   /// Enable the symbolic import experimental feature for the given callback.
   void withSymbolicFeatureEnabled(llvm::function_ref<void(void)> callback);
 
+  /// Returns true when the symbolic import experimental feature is enabled.
+  bool isSymbolicImportEnabled() const;
+
   const clang::TypedefType *getTypeDefForCXXCFOptionsDefinition(
       const clang::Decl *candidateDecl) override;
 

lib/ClangImporter/ClangImporter.cpp

@@ -4789,6 +4789,12 @@ static clang::CXXMethodDecl *synthesizeCxxBaseMethod(
     bool isVirtualCall = false) {
   auto &clangCtx = impl.getClangASTContext();
   auto &clangSema = impl.getClangSema();
+  // When emitting symbolic decls, the method might not have a concrete
+  // record type as this type.
+  if (impl.isSymbolicImportEnabled()
+      && !method->getThisType()->getPointeeCXXRecordDecl()) {
+    return nullptr;
+  }
 
   // Create a new method in the derived class that calls the base method.
   clang::DeclarationName name = method->getNameInfo().getName();
@@ -7454,6 +7460,10 @@ void ClangImporter::withSymbolicFeatureEnabled(
       oldImportSymbolicCXXDecls.get());
 }
 
+bool ClangImporter::isSymbolicImportEnabled() const {
+  return Impl.importSymbolicCXXDecls;
+}
+
 const clang::TypedefType *ClangImporter::getTypeDefForCXXCFOptionsDefinition(
     const clang::Decl *candidateDecl) {
 

lib/ClangImporter/ImportDecl.cpp

@@ -3723,7 +3723,8 @@ namespace {
               decl->getParent(), decl->getParent(), decl);
 
           // call the __synthesizedVirtualCall_ C++ thunk from a Swift thunk
-          if (Decl *swiftThunk = VisitCXXMethodDecl(cxxThunk);
+          if (Decl *swiftThunk =
+                  cxxThunk ? VisitCXXMethodDecl(cxxThunk) : nullptr;
               isa_and_nonnull<FuncDecl>(swiftThunk)) {
             // synthesize the body of the Swift method to call the swiftThunk
             synthesizeForwardingThunkBody(cast<FuncDecl>(method),