AST: Introduce ModuleDecl::isClangHeaderImportModule() convenience.

Author: tshortli

include/swift/AST/ClangModuleLoader.h

@@ -147,7 +147,7 @@ class ClangModuleLoader : public ModuleLoader {
   virtual void dumpSwiftLookupTables() const = 0;
 
   /// Returns the module that contains imports and declarations from all loaded
-  /// Objective-C header files.
+  /// header files.
   virtual ModuleDecl *getImportedHeaderModule() const = 0;
 
   /// Retrieves the Swift wrapper for the given Clang module, creating

include/swift/AST/Module.h

@@ -614,6 +614,9 @@ class ModuleDecl
   void findDeclaredCrossImportOverlaysTransitive(
       SmallVectorImpl<ModuleDecl *> &overlays);
 
+  /// Returns true if this module is the Clang header import module.
+  bool isClangHeaderImportModule() const;
+
   /// Convenience accessor for clients that know what kind of file they're
   /// dealing with.
   SourceFile &getMainSourceFile() const;

lib/AST/Module.cpp

@@ -2471,6 +2471,14 @@ bool ModuleDecl::getRequiredBystandersIfCrossImportOverlay(
   return false;
 }
 
+bool ModuleDecl::isClangHeaderImportModule() const {
+  auto importer = getASTContext().getClangModuleLoader();
+  if (!importer)
+    return false;
+
+  return this == importer->getImportedHeaderModule();
+}
+
 namespace {
 struct OverlayFileContents {
   struct Module {

lib/PrintAsClang/PrintAsClang.cpp

@@ -404,9 +404,7 @@ writeImports(raw_ostream &out, llvm::SmallPtrSetImpl<ImportModuleTy> &imports,
     if (bridgingHeader.empty())
       return import != &M && import->getName() == M.getName();
 
-    auto importer = static_cast<ClangImporter *>(
-        import->getASTContext().getClangModuleLoader());
-    return import == importer->getImportedHeaderModule();
+    return import->isClangHeaderImportModule();
   };
 
   clang::FileSystemOptions fileSystemOptions;

lib/Serialization/Serialization.cpp

@@ -744,11 +744,7 @@ IdentifierID Serializer::addContainingModuleRef(const DeclContext *DC,
     return CURRENT_MODULE_ID;
   if (M == this->M->getASTContext().TheBuiltinModule)
     return BUILTIN_MODULE_ID;
-
-  auto clangImporter =
-    static_cast<ClangImporter *>(
-      this->M->getASTContext().getClangModuleLoader());
-  if (M == clangImporter->getImportedHeaderModule())
+  if (M->isClangHeaderImportModule())
     return OBJC_HEADER_MODULE_ID;
 
   auto exportedModuleName = file->getExportedModuleName();

tools/SourceKit/lib/SwiftLang/SwiftASTManager.cpp

@@ -1043,8 +1043,6 @@ static void collectModuleDependencies(ModuleDecl *TopMod,
   if (!TopMod)
     return;
 
-  auto ClangModuleLoader = TopMod->getASTContext().getClangModuleLoader();
-
   ModuleDecl::ImportFilter ImportFilter = {
       ModuleDecl::ImportFilterKind::Exported,
       ModuleDecl::ImportFilterKind::Default};
@@ -1061,8 +1059,7 @@ static void collectModuleDependencies(ModuleDecl *TopMod,
     if (Mod->isSystemModule())
       continue;
     // FIXME: Setup dependencies on the included headers.
-    if (ClangModuleLoader &&
-        Mod == ClangModuleLoader->getImportedHeaderModule())
+    if (Mod->isClangHeaderImportModule())
       continue;
     bool NewVisit = Visited.insert(Mod).second;
     if (!NewVisit)