[Serialization] Handle re-export of error enums mapped via import-as-member.

Thanks to Jordan for coming up with the right combination of features to
trigger this code path.

lib/Serialization/Deserialization.cpp

@@ -24,6 +24,7 @@
 #include "swift/AST/PrettyStackTrace.h"
 #include "swift/AST/ProtocolConformance.h"
 #include "swift/ClangImporter/ClangImporter.h"
+#include "swift/ClangImporter/ClangModule.h"
 #include "swift/Serialization/BCReadingExtras.h"
 #include "swift/Serialization/SerializedModuleLoader.h"
 #include "swift/Basic/Defer.h"
@@ -1098,6 +1099,23 @@ getActualCtorInitializerKind(uint8_t raw) {
   return None;
 }
 
+/// Determine whether the two modules are re-exported to the same module.
+static bool reExportedToSameModule(const ModuleDecl *fromModule,
+                                   const ModuleDecl *toModule) {
+  auto fromClangModule
+    = dyn_cast<ClangModuleUnit>(fromModule->getFiles().front());
+  if (!fromClangModule)
+    return false;
+
+  auto toClangModule
+  = dyn_cast<ClangModuleUnit>(toModule->getFiles().front());
+  if (!toClangModule)
+    return false;
+
+  return fromClangModule->getExportedModuleName() ==
+    toClangModule->getExportedModuleName();
+}
+
 /// Remove values from \p values that don't match the expected type or module.
 ///
 /// Any of \p expectedTy, \p expectedModule, or \p expectedGenericSig can be
@@ -1130,7 +1148,8 @@ static void filterValues(Type expectedTy, ModuleDecl *expectedModule,
     // FIXME: Should be able to move a value from an extension in a derived
     // module to the original definition in a base module.
     if (expectedModule && !value->hasClangNode() &&
-        value->getModuleContext() != expectedModule)
+        value->getModuleContext() != expectedModule &&
+        !reExportedToSameModule(value->getModuleContext(), expectedModule))
       return true;
 
     // If we're expecting a member within a constrained extension with a

lib/Serialization/Serialization.cpp

@@ -37,7 +37,6 @@
 #include "swift/ClangImporter/ClangModule.h"
 #include "swift/Serialization/SerializationOptions.h"
 
-#include "clang/Basic/Module.h"
 // FIXME: We're just using CompilerInstance::createOutputFile.
 // This API should be sunk down to LLVM.
 #include "clang/Frontend/CompilerInstance.h"
@@ -533,13 +532,14 @@ IdentifierID Serializer::addModuleRef(const ModuleDecl *M) {
 
   // If we're referring to a member of a private module that will be
   // re-exported via a public module, record the public module's name.
-  if (auto clangModule = M->findUnderlyingClangModule()) {
-    if (!clangModule->ExportAsModule.empty()) {
-      auto publicModuleName =
-        M->getASTContext().getIdentifier(clangModule->ExportAsModule);
-      return addDeclBaseNameRef(publicModuleName);
-    }
+  if (auto clangModuleUnit =
+        dyn_cast<ClangModuleUnit>(M->getFiles().front())) {
+    auto exportedModuleName =
+        M->getASTContext().getIdentifier(
+                                 clangModuleUnit->getExportedModuleName());
+    return addDeclBaseNameRef(exportedModuleName);
   }
+
   assert(!M->getName().empty());
   return addDeclBaseNameRef(M->getName());
 }

test/ClangImporter/Inputs/privateframeworks/overlay/SomeKit.swift

@@ -15,13 +15,13 @@ extension NSObject {
   public func doSomethingElse(_: SKWidget) { }
 }
 
-extension SKWidgetError {
-  public func getCode(from widget: SKWidget) -> SKWidgetError.Code {
+extension SKWidget.Error {
+  public func getCode(from widget: SKWidget) -> SKWidget.Error.Code {
     return widget.getCurrentError()
   }
 }
 
-extension SKWidgetError.Code {
+extension SKWidget.Error.Code {
   public var isBoom: Bool {
     return self == .boom
   }
@@ -42,7 +42,7 @@ public func inlineWidgetOperations(_ widget: SKWidget) {
   widget.doSomethingElse(widget)
   let obj = widget.anObject
   widget.anObject = obj
-  _ = SKWidgetError(.boom).getCode(from: widget).isBoom
+  _ = SKWidget.Error(.boom).getCode(from: widget).isBoom
   var hao: HasAnObject = widget
   someKitGlobalFunc()
   hao.anObject = widget

test/ClangImporter/Inputs/privateframeworks/withoutprivate/SomeKit.framework/Headers/SKWidget.h

@@ -14,7 +14,7 @@
 @end
 
 extern NSString * _Nonnull const SKWidgetErrorDomain;
-typedef enum __attribute__((ns_error_domain(SKWidgetErrorDomain))) SKWidgetErrorCode : NSInteger {
+typedef enum __attribute__((ns_error_domain(SKWidgetErrorDomain))) __attribute__((swift_name("SKWidget.Error"))) SKWidgetErrorCode : NSInteger {
   SKWidgetErrorNone = 0,
   SKWidgetErrorBoom = 1
 } SKWidgetErrorCode;

test/ClangImporter/Inputs/privateframeworks/withprivate/SomeKitCore.framework/Headers/SKWidget.h

@@ -15,7 +15,7 @@
 @end
 
 extern NSString * _Nonnull const SKWidgetErrorDomain;
-typedef enum __attribute__((ns_error_domain(SKWidgetErrorDomain))) SKWidgetErrorCode : NSInteger {
+typedef enum __attribute__((ns_error_domain(SKWidgetErrorDomain))) __attribute__((swift_name("SKWidget.Error"))) SKWidgetErrorCode : NSInteger {
   SKWidgetErrorNone = 0,
   SKWidgetErrorBoom = 1
 } SKWidgetErrorCode;

test/ClangImporter/private_frameworks.swift

@@ -40,7 +40,7 @@ func testWidget(widget: SKWidget) {
 }
 
 func testError(widget: SKWidget) {
-  let c: SKWidgetError.Code = SKWidgetError(.boom).getCode(from: widget)
+  let c: SKWidget.Error.Code = SKWidget.Error(.boom).getCode(from: widget)
   if c.isBoom { }
 }