PR13236 - Microsoft compatibility: support __super specifier to access members of base classes

[nikola]

Summary

This is a re-based version of Martin's patch from the bug report with few minor changes by me.

I don't think that we have to implement this feature identically to msvc, but I'm not opposed to it. I'd like to implement it in such a way that allows us to compile MFC code that depends on it. With that said here are some open questions.

• MSDN says that __super can't be used with using declarations but current patch doesn't emit a diagnostic in this case. I'd say that we don't have to because since msvc doesn't allow this there's no code written that does it.
• MSDN says that all accessible base class methods are considered during overload resolution with best one being selected. This is different from normal C++ rules where ordinary name lookup results in ambiguity. Current patch doesn't implement this logic (second test case fails) but similarly to my previous observation we might not need it as MFC doesn't use multiple inheritance. Client's might run into this issue in their classes, but in that case they can fix the code and move away from this extension.

What are your thoughts on this?

[rnk]

lib/AST/ItaniumMangle.cpp

804–806

This seems bad. IMO we can mangle this as a source name of super. It's in the implementer's namespace, so we should be OK. Please add a test for this. I think if you instantiate a template with a non-type template parameter using super you'll get this mangling.

lib/AST/NestedNameSpecifier.cpp

190–191

That seems wrong. It's dependent if there are dependent bases. Consider:

template <typename T>
struct A : T {
  __super::TypeFromBase x;
};

Maybe a __super specifier should store the RecordType that it will search inside of so that we can ask it this kind of question?

lib/Parse/ParseExprCXX.cpp

230

Please fix.

lib/Sema/SemaCXXScopeSpec.cpp

153

It might make more sense to treat this more like a TypeSpec NNS, and to return a stored tag decl here.

lib/Sema/SemaExpr.cpp

1953–1955 ↗

(On Diff #11305)

I'm not sure what should happen here...

lib/Sema/TreeTransform.h

3067–3068

If we go the route of storing the tag decl of the class that __super was used in, we will end up wanting to transform that decl from a pattern to a specialization.

test/SemaCXX/MicrosoftExtensions.cpp

444

Missing semicolon and closing brace for namespace?

This could also use a lot more tests.

[nikola]

Thanks for the input guys, I have two questions:

1. MSDN states "__super can only appear within the body of a member function." and yet msvc accepts it in a number of places (data member declaration, typedef, etc.). Do we wan't to be bug for bug compatible with msvc as I see that as major pain?

2. I agree with Aaron that we should support the 'name found in multiple bases' scenario. In theory this is simple enough, but I don't know how hard it is to implement in practice. I guess this is a question for Richard, can I get ambiguous declarations from LookupResult (I see that this is possible) and do an overload resolution on them (this looks more difficult as I don't know how to access the call arguments)?

[nikola]

I've gone full circle on this, Richard suggested resolving 'super' right away. I consumed tokens and annotated the trailing identifier as either type or primary expression. It was so simple and worked perfectly, until dependent bases showed up...

I started hacking and soon enough ended up with something that looks very much like the original patch with few minor changes. NNS now stores the CXXRecordDecl of the class 'super' appeared in, this is replaced by appropriate instantiation in case of templates. This makes us handle the 'derive from template parameter' case just fine, unlike msvc, but I'm fine with it. I guess we could produce an error like them if we wanted but I don't see the point.

I played with printfs to check if the right overload was selected but having tests would be nice. Do I emit IR, dump ast, or to something else?

[nikola]

This patch addresses issues raised by Aaron.

I don't think this could break ObjC, __super is treated as keyword unlike super from ObjC.

[nikola]

Modified tests to cover two issues I found when I ran the patch over our code base at work.

Gentle ping.

[rnk]

include/clang/AST/DataRecursiveASTVisitor.h

627

I would drop the "Ms" prefix, and just have a NestedNameSpecifier::Super enumerator. If gcc adds an incompatible super-like NNS we can cross that bridge when we get there.

include/clang/Sema/Sema.h

2611

"LookupInSuper"

4493

"ActOnSuperSpecifier"

lib/AST/ASTContext.cpp

4199

The super specifier isn't unique. I think we can canonicalize them similarly to how namespace specifiers are canonicalized: get the original CXXRecordDecl.

Unfortunately, I'm not sure how to test this.

lib/AST/ItaniumMangle.cpp

1462

This should be an assertion. We can't mangle __super, it is dependent.

lib/Sema/SemaCXXScopeSpec.cpp

256–259

I wonder if there is a better way to find the enclosing class scope. What about this test case:

struct B { typedef int T; };
struct A : B { enum C { X = sizeof(__super::T) }; };

test/SemaCXX/MicrosoftExtensions.cpp

404

"with a using declaration" :)

512

Can you add some tests with more nested DeclContexts? enums form a DeclContext, so those are handy and can go inside records and functions.

You can also use inner classes like:

struct Base { typedef int T; };
struct Outer { struct Inner : Base { static const int x = sizeof(__super::T); }; };

I bet __super also misbehaves inside a lambda. I won't insist on actually handling this case in this patch, but we should at least have test coverage that shows we don't crash.

[nikola]

lib/Sema/SemaCXXScopeSpec.cpp

256–259

You're right, but instead of handling this case I'd like to turn the assert bellow into an error. That will handle the lambdas as well. What do you think? This seems like an abuse to me :)

test/SemaCXX/MicrosoftExtensions.cpp

512

This example works just fine, I'll add it to existing tests.

We're not crashing on lambdas but I'll add the tests. Currently we error out because lambda has no base classes but hopefully we can fix this by doing what I suggested in the previous comment.

msvc is so funny:

void foo() {
  []{ __super::bar(); };
}

will fail with: 'super' : this keyword can only be used within the body of class member

struct A {
  void foo() {
    []{ __super::bar(); };
  }
};

will fail with: illegal use of 'super': 'A' does not have any base classes

Adding a base class will change the error to: illegal use of 'super': 'A::foo::lambda_hash>' does not have any base classes

Have I missed any cases?

[rnk]

lib/Sema/SemaCXXScopeSpec.cpp

256–259

I think your Scope check will actually break on simple things like:

struct B { typedef int T; };
struct A : B { void f() { if (int x = 1) { return sizeof(__super::T); } } };

Scopes have a fairly close mapping to curly braces in the source level.

I think you can use something like:

CXXRecordDecl *RD = nullptr;
for (const Scope *S = getCurScope(); S; S = S->getParent()) {
  if (S->isFnScope()) {
    MD = dyn_cast<CXXMethodDecl>(S->getEntity());
    if (MD) RD = MD->getParent();
    break;
  } else if (S->isClassScope()) {
    RD = cast<CXXRecordDecl>(S->getEntity());
    break;
  }
}
if (!RD) error

test/SemaCXX/MicrosoftExtensions.cpp

512

Nope, sounds good.

[nikola]

Fingers crossed.

I'm not too happy with what I had to do with FileCheck to get the lambda test case working. This whole file expects c++11 to be disabled which prevents me from using -verify. I thought about moving this to MicrosoftCompatibility.cpp but that's misleading as super is controlled by -mfs-extensions. Separate file for super tests would be the way to solve all problems?

[rnk]

lgtm

Please commit, this looks pretty good. If you want to make any more substantial changes I'd rather see a new patch. Thanks for the feature!

In D4468#15, @nikola wrote:

Fingers crossed.

I'm not too happy with what I had to do with FileCheck to get the lambda test case working. This whole file expects c++11 to be disabled which prevents me from using -verify. I thought about moving this to MicrosoftCompatibility.cpp but that's misleading as super is controlled by -mfs-extensions. Separate file for super tests would be the way to solve all problems?

I don't see the FileCheck hacks in this patch. Did you add the file? That said, feel free to split the __super test cases out. MicrosoftExtensions.cpp dates back to a simpler time when there were fewer extensions. :)

lib/Sema/SemaCXXScopeSpec.cpp

259

Why can't we use this in static member functions? It appears to work with MSVC 2013, and MSDN just says "can only appear inside a member function". This prints B::f:

extern "C" void puts(const char *);
struct B {
  static void f() {
    puts("B::f");
  }
};
struct A : B {
  static void f() {
    __super::f();
  }
};
int main() {
  A::f();
}

269

I think we should give a custom diagnostic for lambdas. The diagnostic we issue currently will confuse users, because it will appear that they are using __super from a method, and we will say they aren't.

lib/Sema/TreeTransform.h

3106

Use Q.getBeginLoc() instead of no SLoc?

test/SemaCXX/MicrosoftExtensions.cpp

407–409

Ouch, this is bad error recovery. It'd be nice to figure out why we can recover from 'Undeclared::foo();' with less spew.

[nikola]

Done in r218484. Thanks for the review and all suggestions.

Last patch was not the final version, but something I uploaded by mistake. I've allowed use from static members, added lambda diagnostic and moved test to a separate file. The only thing left would be to improve error recovery, I'll check this when I get the time.

include/clang/AST/DataRecursiveASTVisitor.h

   case NestedNameSpecifier::Namespace:
   case NestedNameSpecifier::NamespaceAlias:
   case NestedNameSpecifier::Global:
+  case NestedNameSpecifier::Super:
     return true;
 
   case NestedNameSpecifier::TypeSpec:

   case NestedNameSpecifier::Namespace:
   case NestedNameSpecifier::NamespaceAlias:
   case NestedNameSpecifier::Global:
+  case NestedNameSpecifier::Super:
     return true;
 
   case NestedNameSpecifier::TypeSpec:

include/clang/AST/NestedNameSpecifier.h

 namespace clang {
 
 class ASTContext;
+class CXXRecordDecl;
 class NamespaceAliasDecl;
 class NamespaceDecl;
 class IdentifierInfo;

   /// \brief Enumeration describing
   enum StoredSpecifierKind {
     StoredIdentifier = 0,
-    StoredNamespaceOrAlias = 1,
+    StoredDecl = 1,
     StoredTypeSpec = 2,
     StoredTypeSpecWithTemplate = 3
   };

     /// stored as a Type*.
     TypeSpecWithTemplate,
     /// \brief The global specifier '::'. There is no stored value.
-    Global
+    Global,
+    /// \brief Microsoft's '__super' specifier, stored as a CXXRecordDecl* of
+    /// the class it appeared in.
+    Super
   };
 
 private:

   /// scope.
   static NestedNameSpecifier *GlobalSpecifier(const ASTContext &Context);
 
+  /// \brief Returns the nested name specifier representing the __super scope
+  /// for the given CXXRecordDecl.
+  static NestedNameSpecifier *SuperSpecifier(const ASTContext &Context,
+                                             CXXRecordDecl *RD);
+
   /// \brief Return the prefix of this nested name specifier.
   ///
   /// The prefix contains all of the parts of the nested name

   /// specifier.
   NamespaceAliasDecl *getAsNamespaceAlias() const;
 
+  /// \brief Retrieve the record declaration stored in this nested name
+  /// specifier.
+  CXXRecordDecl *getAsRecordDecl() const;
+
   /// \brief Retrieve the type stored in this nested name specifier.
   const Type *getAsType() const {
     if (Prefix.getInt() == StoredTypeSpec ||

   /// \brief Turn this (empty) nested-name-specifier into the global
   /// nested-name-specifier '::'.
   void MakeGlobal(ASTContext &Context, SourceLocation ColonColonLoc);
   
+  /// \brief Turns this (empty) nested-name-specifier into '__super'
+  /// nested-name-specifier.
+  ///
+  /// \param Context The AST context in which this nested-name-specifier
+  /// resides.
+  ///
+  /// \param RD The declaration of the class in which nested-name-specifier
+  /// appeared.
+  ///
+  /// \param SuperLoc The location of the '__super' keyword.
+  /// name.
+  ///
+  /// \param ColonColonLoc The location of the trailing '::'.
+  void MakeSuper(ASTContext &Context, CXXRecordDecl *RD, 
+                 SourceLocation SuperLoc, SourceLocation ColonColonLoc);
   /// \brief Make a new nested-name-specifier from incomplete source-location
   /// information.
   ///

include/clang/AST/RecursiveASTVisitor.h

   case NestedNameSpecifier::Namespace:
   case NestedNameSpecifier::NamespaceAlias:
   case NestedNameSpecifier::Global:
+  case NestedNameSpecifier::Super:
     return true;
 
   case NestedNameSpecifier::TypeSpec:

   case NestedNameSpecifier::Namespace:
   case NestedNameSpecifier::NamespaceAlias:
   case NestedNameSpecifier::Global:
+  case NestedNameSpecifier::Super:
     return true;
 
   case NestedNameSpecifier::TypeSpec:

include/clang/Basic/DiagnosticParseKinds.td

   "function definition is not allowed here">;
 def err_expected_end_of_enumerator : Error<
   "expected '= constant-expression' or end of enumerator definition">;
+def err_expected_coloncolon_after_super : Error<
+  "expected '::' after '__super'">;
 
 /// Objective-C parser diagnostics
 def err_expected_minus_or_plus : Error<

   InGroup<DiagGroup<"anonymous-pack-parens">>;
 def err_function_is_not_record : Error<
   "unexpected %0 in function call; perhaps remove the %0?">;
+def err_super_in_using_declaration : Error<
+  "'__super' cannot be used with a using declaration">;
 
 // C++ derived classes
 def err_dup_virtual : Error<"duplicate 'virtual' in base specifier">;

include/clang/Basic/DiagnosticSemaKinds.td

           "with base classes or virtual functions">,
   DefaultError, InGroup<IncompatibleMSStruct>;
 def err_section_conflict : Error<"%0 causes a section type conflict with %1">;
+def err_no_base_classes : Error<"invalid use of '__super', %0 has no base classes">;
+def err_invalid_super_scope : Error<"invalid use of '__super', "
+  "this keyword can only be used inside class or non-static member function scope">;
 
 def warn_pragma_unused_undeclared_var : Warning<
   "undeclared variable %0 used as an argument for '#pragma unused'">,

include/clang/Basic/TokenKinds.def

 KEYWORD(__thiscall                  , KEYALL)
 KEYWORD(__forceinline               , KEYMS)
 KEYWORD(__unaligned                 , KEYMS)
+KEYWORD(__super                     , KEYMS)
 
 // OpenCL address space qualifiers
 KEYWORD(__global                    , KEYOPENCL)

include/clang/Sema/DeclSpec.h

 
 namespace clang {
   class ASTContext;
+  class CXXRecordDecl;
   class TypeLoc;
   class LangOptions;
   class DiagnosticsEngine;

   /// nested-name-specifier '::'.
   void MakeGlobal(ASTContext &Context, SourceLocation ColonColonLoc);
   
+  /// \brief Turns this (empty) nested-name-specifier into '__super'
+  /// nested-name-specifier.
+  ///
+  /// \param Context The AST context in which this nested-name-specifier
+  /// resides.
+  ///
+  /// \param RD The declaration of the class in which nested-name-specifier
+  /// appeared.
+  ///
+  /// \param SuperLoc The location of the '__super' keyword.
+  /// name.
+  ///
+  /// \param ColonColonLoc The location of the trailing '::'.
+  void MakeSuper(ASTContext &Context, CXXRecordDecl *RD,
+                 SourceLocation SuperLoc, SourceLocation ColonColonLoc);
+
   /// \brief Make a new nested-name-specifier from incomplete source-location
   /// information.
   ///

include/clang/Sema/Scope.h

     return ErrorTrap.hasUnrecoverableErrorOccurred();
   }
 
+  /// isFunctionScope() - Return true if this scope is a function scope.
+  bool isFunctionScope() const { return (getFlags() & Scope::FnScope); }
+
   /// isClassScope - Return true if this scope is a class/struct/union scope.
   bool isClassScope() const {
     return (getFlags() & Scope::ClassScope);

include/clang/Sema/Sema.h

   ObjCProtocolDecl *LookupProtocol(IdentifierInfo *II, SourceLocation IdLoc,
                                    RedeclarationKind Redecl
                                      = NotForRedeclaration);
+  void LookupInSuper(LookupResult &R, CXXRecordDecl *Class);
 
   void LookupOverloadedOperatorName(OverloadedOperatorKind Op, Scope *S,
                                     QualType T1, QualType T2,

 
   /// \brief The parser has parsed a global nested-name-specifier '::'.
   ///
-  /// \param S The scope in which this nested-name-specifier occurs.
-  ///
   /// \param CCLoc The location of the '::'.
   ///
   /// \param SS The nested-name-specifier, which will be updated in-place
   /// to reflect the parsed nested-name-specifier.
   ///
   /// \returns true if an error occurred, false otherwise.
-  bool ActOnCXXGlobalScopeSpecifier(Scope *S, SourceLocation CCLoc,
-                                    CXXScopeSpec &SS);
+  bool ActOnCXXGlobalScopeSpecifier(SourceLocation CCLoc, CXXScopeSpec &SS);
+
+  /// \brief The parser has parsed a '__super' nested-name-specifier.
+  ///
+  /// \param SuperLoc The location of the '__super' keyword.
+  ///
+  /// \param ColonColonLoc The location of the '::'.
+  ///
+  /// \param SS The nested-name-specifier, which will be updated in-place
+  /// to reflect the parsed nested-name-specifier.
+  ///
+  /// \returns true if an error occurred, false otherwise.
+  bool ActOnSuperScopeSpecifier(SourceLocation SuperLoc,
+                                SourceLocation ColonColonLoc, CXXScopeSpec &SS);
 
   bool isAcceptableNestedNameSpecifier(const NamedDecl *SD);
   NamedDecl *FindFirstQualifierInScope(Scope *S, NestedNameSpecifier *NNS);

lib/AST/ASTContext.cpp

   }
 
   case NestedNameSpecifier::Global:
-    // The global specifier is canonical and unique.
+  case NestedNameSpecifier::Super:
+    // The global specifier and __super specifer are canonical and unique.
     return NNS;
   }
 

lib/AST/ASTImporter.cpp

   case NestedNameSpecifier::Global:
     return NestedNameSpecifier::GlobalSpecifier(ToContext);
 
+  case NestedNameSpecifier::Super:
+    if (CXXRecordDecl *RD =
+            cast<CXXRecordDecl>(Import(FromNNS->getAsRecordDecl()))) {
+      return NestedNameSpecifier::SuperSpecifier(ToContext, RD);
+    }
+    return nullptr;
+
   case NestedNameSpecifier::TypeSpec:
   case NestedNameSpecifier::TypeSpecWithTemplate: {
       QualType T = Import(QualType(FromNNS->getAsType(), 0u));

lib/AST/ExprCXX.cpp

   // It can't be dependent: after all, we were actually able to do the
   // lookup.
   CXXRecordDecl *Record = nullptr;
-  if (getQualifier()) {
+  auto *NNS = getQualifier();
+  if (NNS && NNS->getKind() != NestedNameSpecifier::Super) {
     const Type *T = getQualifier()->getAsType();
     assert(T && "qualifier in member expression does not name type");
     Record = T->getAsCXXRecordDecl();

lib/AST/ItaniumMangle.cpp

     // We never want an 'E' here.
     return;
 
+  case NestedNameSpecifier::Super:
+    llvm_unreachable("Can't mangle __super specifier");
+
   case NestedNameSpecifier::Namespace:
     if (qualifier->getPrefix())
       mangleUnresolvedPrefix(qualifier->getPrefix(), firstQualifierLookup,

     // nothing
     return;
 
+  case NestedNameSpecifier::Super:
+    llvm_unreachable("Can't mangle __super specifier");
+
   case NestedNameSpecifier::Namespace:
     mangleName(qualifier->getAsNamespace());
     return;

lib/AST/NestedNameSpecifier.cpp

          "Broken nested name specifier");
   NestedNameSpecifier Mockup;
   Mockup.Prefix.setPointer(Prefix);
-  Mockup.Prefix.setInt(StoredNamespaceOrAlias);
+  Mockup.Prefix.setInt(StoredDecl);
   Mockup.Specifier = const_cast<NamespaceDecl *>(NS);
   return FindOrInsert(Context, Mockup);
 }

          "Broken nested name specifier");
   NestedNameSpecifier Mockup;
   Mockup.Prefix.setPointer(Prefix);
-  Mockup.Prefix.setInt(StoredNamespaceOrAlias);
+  Mockup.Prefix.setInt(StoredDecl);
   Mockup.Specifier = Alias;
   return FindOrInsert(Context, Mockup);
 }

   return Context.GlobalNestedNameSpecifier;
 }
 
+NestedNameSpecifier *
+NestedNameSpecifier::SuperSpecifier(const ASTContext &Context,
+                                    CXXRecordDecl *RD) {
+  NestedNameSpecifier Mockup;
+  Mockup.Prefix.setPointer(nullptr);
+  Mockup.Prefix.setInt(StoredDecl);
+  Mockup.Specifier = RD;
+  return FindOrInsert(Context, Mockup);
+}
+
 NestedNameSpecifier::SpecifierKind NestedNameSpecifier::getKind() const {
   if (!Specifier)
     return Global;

   case StoredIdentifier:
     return Identifier;
 
-  case StoredNamespaceOrAlias:
-    return isa<NamespaceDecl>(static_cast<NamedDecl *>(Specifier))? Namespace
-                                                            : NamespaceAlias;
+  case StoredDecl: {
+    NamedDecl *ND = static_cast<NamedDecl *>(Specifier);
+    if (isa<CXXRecordDecl>(ND))
+      return Super;
+    return isa<NamespaceDecl>(ND) ? Namespace : NamespaceAlias;
+  }
 
   case StoredTypeSpec:
     return TypeSpec;

   llvm_unreachable("Invalid NNS Kind!");
 }
 
-/// \brief Retrieve the namespace stored in this nested name
-/// specifier.
+/// \brief Retrieve the namespace stored in this nested name specifier.
 NamespaceDecl *NestedNameSpecifier::getAsNamespace() const {
-  if (Prefix.getInt() == StoredNamespaceOrAlias)
+  if (Prefix.getInt() == StoredDecl)
     return dyn_cast<NamespaceDecl>(static_cast<NamedDecl *>(Specifier));
 
   return nullptr;
 }
 
-/// \brief Retrieve the namespace alias stored in this nested name
-/// specifier.
+/// \brief Retrieve the namespace alias stored in this nested name specifier.
 NamespaceAliasDecl *NestedNameSpecifier::getAsNamespaceAlias() const {
-  if (Prefix.getInt() == StoredNamespaceOrAlias)
+  if (Prefix.getInt() == StoredDecl)
     return dyn_cast<NamespaceAliasDecl>(static_cast<NamedDecl *>(Specifier));
 
   return nullptr;
 }
 
+/// \brief Retrieve the record declaration stored in this nested name specifier.
+CXXRecordDecl *NestedNameSpecifier::getAsRecordDecl() const {
+  if (Prefix.getInt() == StoredDecl)
+    return dyn_cast<CXXRecordDecl>(static_cast<NamedDecl *>(Specifier));
+
+  return nullptr;
+}
 
 /// \brief Whether this nested name specifier refers to a dependent
 /// type or not.

   case Global:
     return false;
 
+  case Super: {
+    CXXRecordDecl *RD = static_cast<CXXRecordDecl *>(Specifier);
+    for (const auto &Base : RD->bases())
+      if (Base.getType()->isDependentType())
+        return true;
+
+    return false;
+  }
+
   case TypeSpec:
   case TypeSpecWithTemplate:
     return getAsType()->isDependentType();

   case Namespace:
   case NamespaceAlias:
   case Global:
+  case Super:
     return false;
-    
   case TypeSpec:
   case TypeSpecWithTemplate:
     return getAsType()->isInstantiationDependentType();

   case Namespace:
   case NamespaceAlias:
   case Global:
+  case Super:
     return false;
 
   case TypeSpec:

   case Global:
     break;
 
+  case Super:
+    OS << "__super";
+    break;
+
   case TypeSpecWithTemplate:
     OS << "template ";
     // Fall through to print the type.

   case NestedNameSpecifier::Identifier:
   case NestedNameSpecifier::Namespace:
   case NestedNameSpecifier::NamespaceAlias:
+  case NestedNameSpecifier::Super:
     // The location of the identifier or namespace name.
     Length += sizeof(unsigned);
     break;

   case NestedNameSpecifier::Identifier:
   case NestedNameSpecifier::Namespace:
   case NestedNameSpecifier::NamespaceAlias:
+  case NestedNameSpecifier::Super:
     return SourceRange(LoadSourceLocation(Data, Offset),
                        LoadSourceLocation(Data, Offset + sizeof(unsigned)));
 

   SaveSourceLocation(ColonColonLoc, Buffer, BufferSize, BufferCapacity);
 }
 
+void NestedNameSpecifierLocBuilder::MakeSuper(ASTContext &Context,
+                                              CXXRecordDecl *RD,
+                                              SourceLocation SuperLoc,
+                                              SourceLocation ColonColonLoc) {
+  Representation = NestedNameSpecifier::SuperSpecifier(Context, RD);
+
+  // Push source-location info into the buffer.
+  SaveSourceLocation(SuperLoc, Buffer, BufferSize, BufferCapacity);
+  SaveSourceLocation(ColonColonLoc, Buffer, BufferSize, BufferCapacity);
+}
+
 void NestedNameSpecifierLocBuilder::MakeTrivial(ASTContext &Context, 
                                                 NestedNameSpecifier *Qualifier, 
                                                 SourceRange R) {

       }
         
       case NestedNameSpecifier::Global:
+      case NestedNameSpecifier::Super:
         break;
     }
     

lib/Parse/ParseDecl.cpp

       goto DoneWithDeclSpec;
 
       // typedef-name
+    case tok::kw___super:
     case tok::kw_decltype:
     case tok::identifier: {
       // This identifier can only be a typedef name if we haven't already seen

lib/Parse/ParseDeclCXX.cpp

   if (TryConsumeToken(tok::kw_typename, TypenameLoc))
     HasTypenameKeyword = true;
 
+  if (Tok.is(tok::kw___super)) {
+    Diag(Tok.getLocation(), diag::err_super_in_using_declaration);
+    SkipUntil(tok::semi);
+    return nullptr;
+  }
+
   // Parse nested-name-specifier.
   IdentifierInfo *LastII = nullptr;
   ParseOptionalCXXScopeSpecifier(SS, ParsedType(), /*EnteringContext=*/false,

   // Access declarations.
   bool MalformedTypeSpec = false;
   if (!TemplateInfo.Kind &&
-      (Tok.is(tok::identifier) || Tok.is(tok::coloncolon))) {
+      (Tok.is(tok::identifier) || Tok.is(tok::coloncolon) ||
+       Tok.is(tok::kw___super))) {
     if (TryAnnotateCXXScopeToken())
       MalformedTypeSpec = true;
 

lib/Parse/ParseExpr.cpp

     ConsumeToken();
     break;
 
+  case tok::kw___super:
   case tok::kw_decltype:
     // Annotate the token and tail recurse.
     if (TryAnnotateTypeOrScopeToken())
       return ExprError();
-    assert(Tok.isNot(tok::kw_decltype));
+    assert(Tok.isNot(tok::kw_decltype) && Tok.isNot(tok::kw___super));
     return ParseCastExpression(isUnaryExpression, isAddressOfOperand);
       
   case tok::identifier: {      // primary-expression: identifier

lib/Parse/ParseExprCXX.cpp

       return false;
 
     // '::' - Global scope qualifier.
-    if (Actions.ActOnCXXGlobalScopeSpecifier(getCurScope(), ConsumeToken(), SS))
+    if (Actions.ActOnCXXGlobalScopeSpecifier(ConsumeToken(), SS))
       return true;
 
     CheckForLParenAfterColonColon();

     HasScopeSpecifier = true;
   }
 
+  if (Tok.is(tok::kw___super)) {
+    SourceLocation SuperLoc = ConsumeToken();
+    if (!Tok.is(tok::coloncolon)) {
+      Diag(Tok.getLocation(), diag::err_expected_coloncolon_after_super);
+      return true;
+    }
+
+    return Actions.ActOnSuperScopeSpecifier(SuperLoc, ConsumeToken(), SS);
+  }
+
   bool CheckForDestructor = false;
   if (MayBePseudoDestructor && *MayBePseudoDestructor) {
     CheckForDestructor = true;

lib/Parse/ParseTentative.cpp

       return TPResult::False;
   }
     // Fall through.
+  case tok::kw___super:
   case tok::kw_decltype:
     // Annotate typenames and C++ scope specifiers.  If we get one, just
     // recurse to handle whatever we get.

lib/Parse/Parser.cpp

 /// Note that this routine emits an error if you call it with ::new or ::delete
 /// as the current tokens, so only call it in contexts where these are invalid.
 bool Parser::TryAnnotateTypeOrScopeToken(bool EnteringContext, bool NeedType) {
-  assert((Tok.is(tok::identifier) || Tok.is(tok::coloncolon)
-          || Tok.is(tok::kw_typename) || Tok.is(tok::annot_cxxscope)
-          || Tok.is(tok::kw_decltype) || Tok.is(tok::annot_template_id))
-          && "Cannot be a type or scope token!");
+  assert((Tok.is(tok::identifier) || Tok.is(tok::coloncolon) ||
+          Tok.is(tok::kw_typename) || Tok.is(tok::annot_cxxscope) ||
+          Tok.is(tok::kw_decltype) || Tok.is(tok::annot_template_id) ||
+          Tok.is(tok::kw___super)) &&
+         "Cannot be a type or scope token!");
 
   if (Tok.is(tok::kw_typename)) {
     // MSVC lets you do stuff like:

          "Call sites of this function should be guarded by checking for C++");
   assert((Tok.is(tok::identifier) || Tok.is(tok::coloncolon) ||
           (Tok.is(tok::annot_template_id) && NextToken().is(tok::coloncolon)) ||
-         Tok.is(tok::kw_decltype)) && "Cannot be a type or scope token!");
+          Tok.is(tok::kw_decltype) || Tok.is(tok::kw___super)) &&
+         "Cannot be a type or scope token!");
 
   CXXScopeSpec SS;
   if (ParseOptionalCXXScopeSpecifier(SS, ParsedType(), EnteringContext))

lib/Sema/DeclSpec.cpp

          "NestedNameSpecifierLoc range computation incorrect");
 }
 
+void CXXScopeSpec::MakeSuper(ASTContext &Context, CXXRecordDecl *RD,
+                             SourceLocation SuperLoc,
+                             SourceLocation ColonColonLoc) {
+  Builder.MakeSuper(Context, RD, SuperLoc, ColonColonLoc);
+
+  Range.setBegin(SuperLoc);
+  Range.setEnd(ColonColonLoc);
+
+  assert(Range == Builder.getSourceRange() &&
+  "NestedNameSpecifierLoc range computation incorrect");
+}
+
 void CXXScopeSpec::MakeTrivial(ASTContext &Context, 
                                NestedNameSpecifier *Qualifier, SourceRange R) {
   Builder.MakeTrivial(Context, Qualifier, R);

lib/Sema/SemaCXXScopeSpec.cpp

 
   case NestedNameSpecifier::Global:
     return Context.getTranslationUnitDecl();
+
+  case NestedNameSpecifier::Super:
+    return NNS->getAsRecordDecl();
   }
 
   llvm_unreachable("Invalid NestedNameSpecifier::Kind!");

   return true;
 }
 
-bool Sema::ActOnCXXGlobalScopeSpecifier(Scope *S, SourceLocation CCLoc,
+bool Sema::ActOnCXXGlobalScopeSpecifier(SourceLocation CCLoc,
                                         CXXScopeSpec &SS) {
   SS.MakeGlobal(Context, CCLoc);
   return false;
 }
 
+bool Sema::ActOnSuperScopeSpecifier(SourceLocation SuperLoc,
+                                    SourceLocation ColonColonLoc,
+                                    CXXScopeSpec &SS) {
+  CXXRecordDecl *RD = nullptr;
+  for (Scope *S = getCurScope(); S; S = S->getParent()) {
+    if (S->isFunctionScope()) {
+      CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(S->getEntity());
+      if (MD && !MD->isStatic())
+        RD = MD->getParent();
+      break;
+    }
+    if (S->isClassScope()) {
+      RD = cast<CXXRecordDecl>(S->getEntity());
+      break;
+    }
+  }
+
+  if (!RD || RD->isLambda()) {
+    Diag(SuperLoc, diag::err_invalid_super_scope);
+    return true;
+  }
+
+  if (RD->getNumBases() == 0) {
+    Diag(SuperLoc, diag::err_no_base_classes) << RD->getName();
+    return true;
+  }
+
+  SS.MakeSuper(Context, RD, SuperLoc, ColonColonLoc);
+  return false;
+}
+
 /// \brief Determines whether the given declaration is an valid acceptable
 /// result for name lookup of a nested-name-specifier.
 bool Sema::isAcceptableNestedNameSpecifier(const NamedDecl *SD) {

   case NestedNameSpecifier::Identifier:
   case NestedNameSpecifier::TypeSpec:
   case NestedNameSpecifier::TypeSpecWithTemplate:
+  case NestedNameSpecifier::Super:
     // These are never namespace scopes.
     return true;
   }

lib/Sema/SemaDecl.cpp

 /// @endcode
 bool Sema::isMicrosoftMissingTypename(const CXXScopeSpec *SS, Scope *S) {
   if (CurContext->isRecord()) {
+    if (SS->getScopeRep()->getKind() == NestedNameSpecifier::Super)
+      return true;
+
     const Type *Ty = SS->getScopeRep()->getAsType();
 
     CXXRecordDecl *RD = cast<CXXRecordDecl>(CurContext);

   }
 
   LookupResult Result(*this, Name, NameLoc, LookupOrdinaryName);
-  LookupParsedName(Result, S, &SS, !CurMethod);
+  NestedNameSpecifier *NNS = SS.getScopeRep();
+  if (NNS && NNS->getKind() == NestedNameSpecifier::Super)
+    LookupInSuper(Result, NNS->getAsRecordDecl());
+  else
+    LookupParsedName(Result, S, &SS, !CurMethod);
 
   // For unqualified lookup in a class template in MSVC mode, look into
   // dependent base classes where the primary class template is known.

lib/Sema/SemaExprCXX.cpp

     break;
 
   case NestedNameSpecifier::Global:
+  case NestedNameSpecifier::Super:
   case NestedNameSpecifier::Namespace:
   case NestedNameSpecifier::NamespaceAlias:
     llvm_unreachable("Nested name specifier is not a type for inheriting ctor");

     return true;
 
   case NestedNameSpecifier::Global:
+  case NestedNameSpecifier::Super:
   case NestedNameSpecifier::Namespace:
   case NestedNameSpecifier::NamespaceAlias:
     return false;

lib/Sema/SemaLookup.cpp

   return LookupName(R, S, AllowBuiltinCreation);
 }
 
+/// \brief Perform qualified name lookup into all base classes of the given
+/// class.
+///
+/// \param R captures both the lookup criteria and any lookup results found.
+///
+/// \param Class The context in which qualified name lookup will
+/// search. Name lookup will search in all base classes merging the results.
+void Sema::LookupInSuper(LookupResult &R, CXXRecordDecl *Class) {
+  for (const auto &BaseSpec : Class->bases()) {
+    CXXRecordDecl *RD = cast<CXXRecordDecl>(
+        BaseSpec.getType()->castAs<RecordType>()->getDecl());
+    LookupResult Result(*this, R.getLookupNameInfo(), R.getLookupKind());
+  Result.setBaseObjectType(Context.getRecordType(Class));
+    LookupQualifiedName(Result, RD);
+    for (auto *Decl : Result)
+      R.addDecl(Decl);
+  }
+
+  R.resolveKind();
+}
 
 /// \brief Produce a diagnostic describing the ambiguity that resulted
 /// from name lookup.

     break;
 
   case NestedNameSpecifier::Global:
+  case NestedNameSpecifier::Super:
     return;
   }
 

lib/Sema/SemaTemplate.cpp

   case NestedNameSpecifier::Namespace:
   case NestedNameSpecifier::NamespaceAlias:
   case NestedNameSpecifier::Global:
+  case NestedNameSpecifier::Super:
     return false;
 
   case NestedNameSpecifier::TypeSpec:

 
   DeclarationName Name(&II);
   LookupResult Result(*this, Name, IILoc, LookupOrdinaryName);
-  LookupQualifiedName(Result, Ctx);
+  NestedNameSpecifier *NNS = SS.getScopeRep();
+  if (NNS->getKind() == NestedNameSpecifier::Super)
+    LookupInSuper(Result, NNS->getAsRecordDecl());
+  else
+    LookupQualifiedName(Result, Ctx);
   unsigned DiagID = 0;
   Decl *Referenced = nullptr;
   switch (Result.getResultKind()) {

lib/Sema/SemaType.cpp

         case NestedNameSpecifier::Namespace:
         case NestedNameSpecifier::NamespaceAlias:
         case NestedNameSpecifier::Global:
+        case NestedNameSpecifier::Super:
           llvm_unreachable("Nested-name-specifier must name a type");
 
         case NestedNameSpecifier::TypeSpec:

       case NestedNameSpecifier::Namespace:
       case NestedNameSpecifier::NamespaceAlias:
       case NestedNameSpecifier::Global:
+      case NestedNameSpecifier::Super:
         llvm_unreachable("Nested-name-specifier must name a type");
       }
 

lib/Sema/TreeTransform.h

       SS.MakeGlobal(SemaRef.Context, Q.getBeginLoc());
       break;
 
+    case NestedNameSpecifier::Super: {
+      CXXRecordDecl *RD =
+          cast_or_null<CXXRecordDecl>(getDerived().TransformDecl(
+              SourceLocation(), QNNS->getAsRecordDecl()));
+      SS.MakeSuper(SemaRef.Context, RD, Q.getBeginLoc(), Q.getEndLoc());
+      break;
+    }
+
     case NestedNameSpecifier::TypeSpecWithTemplate:
     case NestedNameSpecifier::TypeSpec: {
       TypeLoc TL = TransformTypeInObjectScope(Q.getTypeLoc(), ObjectType,

lib/Serialization/ASTReader.cpp

       // No associated value, and there can't be a prefix.
       break;
     }
+
+    case NestedNameSpecifier::Super: {
+      CXXRecordDecl *RD = ReadDeclAs<CXXRecordDecl>(F, Record, Idx);
+      NNS = NestedNameSpecifier::SuperSpecifier(Context, RD);
+      break;
+    }
     }
     Prev = NNS;
   }

       Builder.MakeGlobal(Context, ColonColonLoc);
       break;
     }
+
+    case NestedNameSpecifier::Super: {
+      CXXRecordDecl *RD = ReadDeclAs<CXXRecordDecl>(F, Record, Idx);
+      SourceRange Range = ReadSourceRange(F, Record, Idx);
+      Builder.MakeSuper(Context, RD, Range.getBegin(), Range.getEnd());
+      break;
+    }
     }
   }
-  
   return Builder.getWithLocInContext(Context);
 }
 

lib/Serialization/ASTWriter.cpp

     case NestedNameSpecifier::Global:
       // Don't need to write an associated value.
       break;
+
+    case NestedNameSpecifier::Super:
+      AddDeclRef(NNS->getAsRecordDecl(), Record);
+      break;
     }
   }
 }

     case NestedNameSpecifier::Global:
       AddSourceLocation(NNS.getLocalSourceRange().getEnd(), Record);
       break;
+
+    case NestedNameSpecifier::Super:
+      AddDeclRef(NNS.getNestedNameSpecifier()->getAsRecordDecl(), Record);
+      AddSourceRange(NNS.getLocalSourceRange(), Record);
+      break;
     }
   }
 }

test/SemaCXX/MicrosoftExtensions.cpp

   _Static_assert(__alignof(s1) == 8, "");
   _Static_assert(__alignof(s2) == 4, "");
 }
+
+namespace Super {
+struct Errors {
+  using __super::foo; // expected-error {{'__super' cannot be used with a using declaration}}
+  __super::XXX x; // expected-error {{invalid use of '__super', Errors has no base classes}} expected-error {{expected}}
+
+  // expected-error@+4 {{C++ requires a type specifier for all declarations}}
+  // expected-warning@+3 {{empty parentheses interpreted as a function declaration}}
+  // expected-note@+2 {{replace parentheses with an initializer to declare a variable}}
+  static void foo() {
+    __super::foo(); // expected-error {{invalid use of '__super', this keyword}}
+  }
+
+  // expected-error@+4 {{C++ requires a type specifier for all declarations}}
+  // expected-warning@+3 {{empty parentheses interpreted as a function declaration}}
+  // expected-note@+2 {{replace parentheses with an initializer to declare a variable}}
+  void bar() {
+    auto a = [] { __super::foo(); }; // expected-error {{invalid use of '__super', this keyword}}
+  }
+};
+
+struct Base1 {
+  void foo(int) {}
+
+  typedef int XXX;
+};
+
+struct Derived : Base1 {
+  __super::XXX x;
+  typedef __super::XXX Type;
+
+  enum E {
+    X = sizeof(__super::XXX)
+  };
+
+  void foo(int i) {
+    __super::foo(i);
+  }
+};
+
+struct Outer {
+  struct Inner : Base1 {
+    static const int x = sizeof(__super::XXX);
+  };
+};
+
+struct Base2 {
+  void foo(char) {}
+};
+
+struct MemberFunctionInMultipleBases : Base1, Base2 {
+  void foo() {
+    __super::foo('x');
+  }
+};
+
+struct Base3 {
+  void foo(int) {}
+  void foo(char) {}
+};
+
+struct OverloadedMemberFunction : Base3 {
+  void foo() {
+    __super::foo('x');
+  }
+};
+
+struct PointerToMember : Base1 {
+  template <void (Base1::*MP)(int)>
+  struct Wrapper {
+    static void bar() {}
+  };
+
+  static void baz();
+};
+
+void PointerToMember::baz() {
+  Wrapper<&__super::foo>::bar();
+}
+
+template <typename T>
+struct BaseTemplate {
+  typedef int XXX;
+
+  void foo() {}
+};
+
+struct DerivedFromKnownSpecialization : BaseTemplate<int> {
+  __super::XXX a;
+  typedef __super::XXX b;
+
+  void test() {
+    __super::XXX c;
+    typedef __super::XXX d;
+
+    __super::foo();
+  }
+};
+
+template <typename T>
+struct DerivedFromDependentBase : BaseTemplate<T> {
+  typename __super::XXX a;
+  typedef typename __super::XXX b;
+
+  __super::XXX c;         // expected-error {{missing 'typename'}}
+  typedef __super::XXX d; // expected-error {{missing 'typename'}}
+
+  void test() {
+    typename __super::XXX e;
+    typedef typename __super::XXX f;
+
+    __super::XXX g;         // expected-error {{missing 'typename'}}
+    typedef __super::XXX h; // expected-error {{missing 'typename'}}
+
+    __super::foo();
+  }
+};
+
+template <typename T>
+struct DerivedFromTemplateParameter : T {
+  typename __super::XXX a;
+  typedef typename __super::XXX b;
+
+  __super::XXX c;         // expected-error {{missing 'typename'}}
+  typedef __super::XXX d; // expected-error {{missing 'typename'}}
+
+  void test() {
+    typename __super::XXX e;
+    typedef typename __super::XXX f;
+
+    __super::XXX g;         // expected-error {{missing 'typename'}}
+    typedef __super::XXX h; // expected-error {{missing 'typename'}}
+
+    __super::foo(1);
+  }
+};
+
+void instantiate() {
+  DerivedFromDependentBase<int> d;
+  d.test();
+  DerivedFromTemplateParameter<Base1> t;
+  t.test();
+}
+}

tools/libclang/CIndex.cpp

   case NestedNameSpecifier::TypeSpecWithTemplate:
   case NestedNameSpecifier::Global:
   case NestedNameSpecifier::Identifier:
+  case NestedNameSpecifier::Super:
     break;      
   }
   

         
     case NestedNameSpecifier::Global:
     case NestedNameSpecifier::Identifier:
+    case NestedNameSpecifier::Super:
       break;              
     }
   }

tools/libclang/IndexTypeSourceInfo.cpp

   switch (NNS.getNestedNameSpecifier()->getKind()) {
   case NestedNameSpecifier::Identifier:
   case NestedNameSpecifier::Global:
+  case NestedNameSpecifier::Super:
     break;
 
   case NestedNameSpecifier::Namespace: