[interop][SwiftToCxx] do not emit unavaialble stubs for internal/private decls

only emit them for public ones

Author: hyp

lib/PrintAsClang/DeclAndTypePrinter.cpp

@@ -2908,6 +2908,12 @@ bool DeclAndTypePrinter::shouldInclude(const ValueDecl *VD) {
          !excludeForObjCImplementation(VD);
 }
 
+bool DeclAndTypePrinter::isVisible(const ValueDecl *vd) const {
+  return outputLang == OutputLanguageMode::Cxx
+             ? cxx_translation::isVisibleToCxx(vd, minRequiredAccess)
+             : isVisibleToObjC(vd, minRequiredAccess);
+}
+
 void DeclAndTypePrinter::print(const Decl *D) {
   getImpl().print(D);
 }

lib/PrintAsClang/DeclAndTypePrinter.h

@@ -106,6 +106,10 @@ class DeclAndTypePrinter {
   /// the options the printer was constructed with.
   bool shouldInclude(const ValueDecl *VD);
 
+  /// Returns true if \p vd is visible given the current access level and thus
+  /// can be included in the generated header.
+  bool isVisible(const ValueDecl *vd) const;
+
   void print(const Decl *D);
   void print(Type ty);
 

lib/PrintAsClang/ModuleContentsWriter.cpp

@@ -820,18 +820,18 @@ class ModuleWriter {
          emissionScope.additionalUnrepresentableDeclarations)
       removedVDList.push_back(removedVD);
 
+    // Do not report internal/private decls as unavailable.
     // @objc declarations are emitted in the Objective-C section, so do not
     // report them as unavailable. Also skip underscored decls from the standard
     // library. Also skip structs from the standard library, they can cause
     // ambiguities because of the arithmetic types that conflict with types we
     // already have in `swift::` namespace. Also skip `Error` protocol from
     // stdlib, we have experimental support for it.
-    // FIXME: Note unrepresented type aliases too.
     removedVDList.erase(
         llvm::remove_if(
             removedVDList,
-            [](const ValueDecl *vd) {
-              return vd->isObjC() ||
+            [&](const ValueDecl *vd) {
+              return !printer.isVisible(vd) || vd->isObjC() ||
                      (vd->isStdlibDecl() && !vd->getName().isSpecial() &&
                       vd->getBaseIdentifier().str().startswith("_")) ||
                      (vd->isStdlibDecl() && isa<StructDecl>(vd)) ||
@@ -897,6 +897,7 @@ class ModuleWriter {
 
       // FIXME: Emit an unavailable stub for a function / function overload set
       // / variable.
+      // FIXME: Note unrepresented type aliases too.
       emitStubComment();
     }
   }

test/Interop/SwiftToCxx/unsupported/unexposed-non-public-api-in-cxx.swift

@@ -0,0 +1,19 @@
+// RUN: %empty-directory(%t)
+// RUN: %target-swift-frontend %s -typecheck -module-name Functions -clang-header-expose-decls=all-public -emit-clang-header-path %t/apis.h
+// RUN: %FileCheck %s < %t/apis.h
+
+internal func takeFloat(_ x: Float) {}
+
+private struct PrivateStruct { let x: Int }
+
+class InternalClass {
+    let x: Int
+    init() { self.x = 0 }
+}
+
+protocol InternalProto {}
+
+// CHECK: namespace Functions SWIFT_PRIVATE_ATTR SWIFT_SYMBOL_MODULE("Functions") {
+// CHECK-EMPTY:
+// CHECK-EMPTY:
+// CHECK-NEXT: } // namespace Functions