[cxx-interop] Avoid swiftifying private and protected methods

The generated overloads do not get seralized and later on the compiler
crashes due to the missing body of the SILFunction. This PR works this
problem around by not generating these overloads. We plan to address the
serialization issue later.

rdar://152181531

Author: Gabor Horvath

lib/ClangImporter/ImportDecl.cpp

@@ -9188,6 +9188,12 @@ void ClangImporter::Implementation::swiftify(AbstractFunctionDecl *MappedDecl) {
   if (!ClangDecl)
     return;
 
+  // FIXME: for private macro generated functions we do not serialize the
+  // SILFunction's body anywhere triggering assertions.
+  if (ClangDecl->getAccess() == clang::AS_protected ||
+      ClangDecl->getAccess() == clang::AS_private)
+    return;
+
   if (ClangDecl->getNumParams() != MappedDecl->getParameters()->size())
     return;
 

test/Interop/Cxx/class/access/swiftify-private-fileid.swift

@@ -0,0 +1,38 @@
+// RUN: rm -rf %t
+// RUN: split-file %s %t
+
+// RUN: %target-swift-frontend -emit-ir -I %swift_src_root/lib/ClangImporter/SwiftBridging -plugin-path %swift-plugin-dir %t/blessed.swift -module-name main -I %t/Inputs -o %t/out -Xcc -std=c++20  -cxx-interoperability-mode=default -enable-experimental-feature SafeInteropWrappers -verify
+
+// REQUIRES: swift_feature_SafeInteropWrappers
+
+// FIXME swift-ci linux tests do not support std::span
+// UNSUPPORTED: OS=linux-gnu, OS=linux-android, OS=linux-androideabi
+
+//--- Inputs/swiftify-non-public.h
+#pragma once
+
+#include "swift/bridging"
+#include <span>
+
+using IntSpan = std::span<const int>;
+
+class SWIFT_PRIVATE_FILEID("main/blessed.swift") MyClass {
+private:
+    void takesSpan(IntSpan s [[clang::noescape]]) {}
+};
+
+//--- Inputs/module.modulemap
+module SwiftifyNonPublic {
+    requires cplusplus
+    header "swiftify-non-public.h"
+}
+
+//--- blessed.swift
+import CxxStdlib
+import SwiftifyNonPublic
+
+extension MyClass {
+  mutating func passesSpan(_ s: Span<CInt>) {
+    takesSpan(s) // expected-error {{cannot convert value of type}}
+  }
+}