[AST/ClangImporter] Eliminate layering violation with isInOverlayModuleForImportedModule.

#16951 introduced a layering violation between the
AST and ClangImporter libraries; break the layering violation by moving the function
isInOverlayModuleForImportedModule() to ClangModuleLoader.

Author: DougGregor

include/swift/AST/ClangModuleLoader.h

@@ -24,6 +24,8 @@ class Sema;
 
 namespace swift {
 
+class DeclContext;
+
 class ClangModuleLoader : public ModuleLoader {
 private:
   virtual void anchor();
@@ -46,6 +48,16 @@ class ClangModuleLoader : public ModuleLoader {
   /// \returns true if there was an error adding the search path.
   virtual bool addSearchPath(StringRef newSearchPath, bool isFramework,
                              bool isSystem) = 0;
+
+  /// Determine whether \c overlayDC is within an overlay module for the
+  /// imported context enclosing \c importedDC.
+  ///
+  /// This routine is used for various hacks that are only permitted within
+  /// overlays of imported modules, e.g., Objective-C bridging conformances.
+  virtual bool isInOverlayModuleForImportedModule(
+                                            const DeclContext *overlayDC,
+                                            const DeclContext *importedDC) = 0;
+
 };
 
 } // namespace swift

include/swift/ClangImporter/ClangImporter.h

@@ -143,6 +143,15 @@ class ClangImporter final : public ClangModuleLoader {
                         ArrayRef<std::pair<Identifier, SourceLoc>> path)
                       override;
 
+  /// Determine whether \c overlayDC is within an overlay module for the
+  /// imported context enclosing \c importedDC.
+  ///
+  /// This routine is used for various hacks that are only permitted within
+  /// overlays of imported modules, e.g., Objective-C bridging conformances.
+  bool isInOverlayModuleForImportedModule(
+                                      const DeclContext *overlayDC,
+                                      const DeclContext *importedDC) override;
+
   /// \brief Look for declarations associated with the given name.
   ///
   /// \param name The name we're searching for.
@@ -350,14 +359,6 @@ class ClangImporter final : public ClangModuleLoader {
 ImportDecl *createImportDecl(ASTContext &Ctx, DeclContext *DC, ClangNode ClangN,
                              ArrayRef<clang::Module *> Exported);
 
-/// Determine whether \c overlayDC is within an overlay module for the
-/// imported context enclosing \c importedDC.
-///
-/// This routine is used for various hacks that are only permitted within
-/// overlays of imported modules, e.g., Objective-C bridging conformances.
-bool isInOverlayModuleForImportedModule(const DeclContext *overlayDC,
-                                        const DeclContext *importedDC);
-
 } // end namespace swift
 
 #endif

lib/AST/NameLookup.cpp

@@ -15,11 +15,11 @@
 //===----------------------------------------------------------------------===//
 
 #include "NameLookupImpl.h"
-#include "swift/ClangImporter/ClangImporter.h"
 #include "swift/AST/NameLookup.h"
 #include "swift/AST/ASTContext.h"
 #include "swift/AST/ASTScope.h"
 #include "swift/AST/ASTVisitor.h"
+#include "swift/AST/ClangModuleLoader.h"
 #include "swift/AST/DebuggerClient.h"
 #include "swift/AST/ExistentialLayout.h"
 #include "swift/AST/LazyResolver.h"
@@ -299,13 +299,18 @@ bool swift::removeShadowedDecls(SmallVectorImpl<ValueDecl*> &decls,
         // Prefer declarations in an overlay to similar declarations in
         // the Clang module it customizes.
         if (firstDecl->hasClangNode() != secondDecl->hasClangNode()) {
-          if (isInOverlayModuleForImportedModule(firstDecl->getDeclContext(),
-                                                 secondDecl->getDeclContext())){
+          auto clangLoader = ctx.getClangModuleLoader();
+          if (!clangLoader) continue;
+
+          if (clangLoader->isInOverlayModuleForImportedModule(
+                                                firstDecl->getDeclContext(),
+                                                secondDecl->getDeclContext())) {
             shadowed.insert(secondDecl);
             continue;
           }
 
-          if (isInOverlayModuleForImportedModule(secondDecl->getDeclContext(),
+          if (clangLoader->isInOverlayModuleForImportedModule(
+                                                 secondDecl->getDeclContext(),
                                                  firstDecl->getDeclContext())) {
             shadowed.insert(firstDecl);
             break;

lib/ClangImporter/ClangImporter.cpp

@@ -3598,7 +3598,8 @@ importName(const clang::NamedDecl *D,
     getDeclName();
 }
 
-bool swift::isInOverlayModuleForImportedModule(const DeclContext *overlayDC,
+bool ClangImporter::isInOverlayModuleForImportedModule(
+                                               const DeclContext *overlayDC,
                                                const DeclContext *importedDC) {
   overlayDC = overlayDC->getModuleScopeContext();
   importedDC = importedDC->getModuleScopeContext();
@@ -3613,7 +3614,7 @@ bool swift::isInOverlayModuleForImportedModule(const DeclContext *overlayDC,
 
   // Is this a private module that's re-exported to the public (overlay) name?
   auto clangModule =
-    importedClangModuleUnit->getClangModule()->getTopLevelModule();
+  importedClangModuleUnit->getClangModule()->getTopLevelModule();
   return !clangModule->ExportAsModule.empty() &&
-    clangModule->ExportAsModule == overlayModule->getName().str();
+  clangModule->ExportAsModule == overlayModule->getName().str();
 }

lib/Sema/TypeCheckAttr.cpp

@@ -18,11 +18,11 @@
 #include "MiscDiagnostics.h"
 #include "swift/AST/GenericSignatureBuilder.h"
 #include "swift/AST/ASTVisitor.h"
+#include "swift/AST/ClangModuleLoader.h"
 #include "swift/AST/GenericEnvironment.h"
 #include "swift/AST/NameLookup.h"
 #include "swift/AST/ParameterList.h"
 #include "swift/AST/Types.h"
-#include "swift/ClangImporter/ClangImporter.h"
 #include "swift/Parse/Lexer.h"
 #include "llvm/Support/Debug.h"
 
@@ -1413,7 +1413,9 @@ static bool isObjCClassExtensionInOverlay(DeclContext *dc) {
   if (!classDecl)
     return false;
 
-  return isInOverlayModuleForImportedModule(ext, classDecl);
+  auto clangLoader = dc->getASTContext().getClangModuleLoader();
+  if (!clangLoader) return false;
+  return clangLoader->isInOverlayModuleForImportedModule(ext, classDecl);
 }
 
 void AttributeChecker::visitRequiredAttr(RequiredAttr *attr) {

lib/Sema/TypeCheckProtocol.cpp

@@ -27,6 +27,7 @@
 #include "swift/AST/ASTContext.h"
 #include "swift/AST/ASTMangler.h"
 #include "swift/AST/ASTPrinter.h"
+#include "swift/AST/ClangModuleLoader.h"
 #include "swift/AST/Decl.h"
 #include "swift/AST/ExistentialLayout.h"
 #include "swift/AST/GenericEnvironment.h"
@@ -3628,8 +3629,10 @@ void ConformanceChecker::checkConformance(MissingWitnessDiagnosisKind Kind) {
   if (Proto->isSpecificProtocol(KnownProtocolKind::ObjectiveCBridgeable)) {
     auto nominal = Adoptee->getAnyNominal();
     if (!TC.Context.isTypeBridgedInExternalModule(nominal)) {
+      auto clangLoader = TC.Context.getClangModuleLoader();
       if (nominal->getParentModule() != DC->getParentModule() &&
-          !isInOverlayModuleForImportedModule(DC, nominal)) {
+          !(clangLoader &&
+            clangLoader->isInOverlayModuleForImportedModule(DC, nominal))) {
         auto nominalModule = nominal->getParentModule();
         TC.diagnose(Loc, diag::nonlocal_bridged_to_objc, nominal->getName(),
                     Proto->getName(), nominalModule->getName());