diff --git a/include/clang/AST/ASTImporter.h b/include/clang/AST/ASTImporter.h
index 69d825e238..9c6619aa32 100644
--- a/include/clang/AST/ASTImporter.h
+++ b/include/clang/AST/ASTImporter.h
@@ -46,6 +46,9 @@ namespace clang {
     /// \brief The file managers we're importing to and from.
     FileManager &ToFileManager, &FromFileManager;
 
+    /// \brief Whether to perform a minimal import.
+    bool Minimal;
+    
     /// \brief Mapping from the already-imported types in the "from" context
     /// to the corresponding types in the "to" context.
     llvm::DenseMap<Type *, Type *> ImportedTypes;
@@ -71,11 +74,29 @@ namespace clang {
     NonEquivalentDeclSet NonEquivalentDecls;
     
   public:
+    /// \brief Create a new AST importer.
+    ///
+    /// \param ToContext The context we'll be importing into.
+    ///
+    /// \param ToFileManager The file manager we'll be importing into.
+    ///
+    /// \param FromContext The context we'll be importing from.
+    ///
+    /// \param FromFileManager The file manager we'll be importing into.
+    ///
+    /// \param MinimalImport If true, the importer will attempt to import
+    /// as little as it can, e.g., by importing declarations as forward
+    /// declarations that can be completed at a later point.
     ASTImporter(ASTContext &ToContext, FileManager &ToFileManager,
-                ASTContext &FromContext, FileManager &FromFileManager);
+                ASTContext &FromContext, FileManager &FromFileManager,
+                bool MinimalImport);
     
     virtual ~ASTImporter();
     
+    /// \brief Whether the importer will perform a minimal import, creating
+    /// to-be-completed forward declarations when possible.
+    bool isMinimalImport() const { return Minimal; }
+    
     /// \brief Import the given type from the "from" context into the "to"
     /// context.
     ///
@@ -169,6 +190,12 @@ namespace clang {
     /// context.
     FileID Import(FileID);
     
+    /// \brief Import the definition of the given declaration, including all of
+    /// the declarations it contains.
+    ///
+    /// This routine is intended to be used 
+    void ImportDefinition(Decl *From);
+
     /// \brief Cope with a name conflict when importing a declaration into the
     /// given context.
     ///
@@ -225,12 +252,13 @@ namespace clang {
     /// \brief Note that we have imported the "from" declaration by mapping it
     /// to the (potentially-newly-created) "to" declaration.
     ///
-    /// \returns \p To
-    Decl *Imported(Decl *From, Decl *To);
+    /// Subclasses can override this function to observe all of the \c From ->
+    /// \c To declaration mappings as they are imported.
+    virtual Decl *Imported(Decl *From, Decl *To);
     
     /// \brief Determine whether the given types are structurally
     /// equivalent.
-    bool IsStructurallyEquivalent(QualType From, QualType To);
+    bool IsStructurallyEquivalent(QualType From, QualType To);    
   };
 }
 
diff --git a/lib/AST/ASTImporter.cpp b/lib/AST/ASTImporter.cpp
index eaab3d3e6c..315f4feca6 100644
--- a/lib/AST/ASTImporter.cpp
+++ b/lib/AST/ASTImporter.cpp
@@ -83,7 +83,7 @@ namespace {
                          SourceLocation &Loc);
     void ImportDeclarationNameLoc(const DeclarationNameInfo &From,
                                   DeclarationNameInfo& To);
-    void ImportDeclContext(DeclContext *FromDC);
+    void ImportDeclContext(DeclContext *FromDC, bool ForceImport = false);
     bool ImportDefinition(RecordDecl *From, RecordDecl *To);
     TemplateParameterList *ImportTemplateParameterList(
                                                  TemplateParameterList *Params);
@@ -1713,7 +1713,15 @@ ASTNodeImporter::ImportDeclarationNameLoc(const DeclarationNameInfo &From,
   }
 }
 
-void ASTNodeImporter::ImportDeclContext(DeclContext *FromDC) {
+void ASTNodeImporter::ImportDeclContext(DeclContext *FromDC, bool ForceImport) {
+  if (Importer.isMinimalImport() && !ForceImport) {
+    if (DeclContext *ToDC = Importer.ImportContext(FromDC)) {
+      ToDC->setHasExternalLexicalStorage();
+      ToDC->setHasExternalVisibleStorage();
+    }
+    return;
+  }
+  
   for (DeclContext::decl_iterator From = FromDC->decls_begin(),
                                FromEnd = FromDC->decls_end();
        From != FromEnd;
@@ -3897,9 +3905,12 @@ Expr *ASTNodeImporter::VisitCStyleCastExpr(CStyleCastExpr *E) {
 }
 
 ASTImporter::ASTImporter(ASTContext &ToContext, FileManager &ToFileManager,
-                         ASTContext &FromContext, FileManager &FromFileManager)
+                         ASTContext &FromContext, FileManager &FromFileManager,
+                         bool MinimalImport)
   : ToContext(ToContext), FromContext(FromContext),
-    ToFileManager(ToFileManager), FromFileManager(FromFileManager) {
+    ToFileManager(ToFileManager), FromFileManager(FromFileManager),
+    Minimal(MinimalImport) 
+{
   ImportedDecls[FromContext.getTranslationUnitDecl()]
     = ToContext.getTranslationUnitDecl();
 }
@@ -4163,6 +4174,17 @@ FileID ASTImporter::Import(FileID FromID) {
   return ToID;
 }
 
+void ASTImporter::ImportDefinition(Decl *From) {
+  Decl *To = Import(From);
+  if (!To)
+    return;
+  
+  if (DeclContext *FromDC = cast<DeclContext>(From)) {
+    ASTNodeImporter Importer(*this);
+    Importer.ImportDeclContext(FromDC, true);
+  }
+}
+
 DeclarationName ASTImporter::Import(DeclarationName FromName) {
   if (!FromName)
     return DeclarationName();
diff --git a/lib/Frontend/ASTMerge.cpp b/lib/Frontend/ASTMerge.cpp
index ec074415c1..3905b99b02 100644
--- a/lib/Frontend/ASTMerge.cpp
+++ b/lib/Frontend/ASTMerge.cpp
@@ -52,7 +52,8 @@ void ASTMergeAction::ExecuteAction() {
     ASTImporter Importer(CI.getASTContext(), 
                          CI.getFileManager(),
                          Unit->getASTContext(), 
-                         Unit->getFileManager());
+                         Unit->getFileManager(),
+                         /*MinimalImport=*/false);
 
     TranslationUnitDecl *TU = Unit->getASTContext().getTranslationUnitDecl();
     for (DeclContext::decl_iterator D = TU->decls_begin(),