ms-compat: Fix taking the address of a member of a dependent base

If unqualified id lookup fails while parsing a class template with a
dependent base, clang with -fms-compatibility will pretend the user
prefixed the name with 'this->' in order to delay the lookup.  However,
if there was a unary ampersand, Sema::ActOnDependentIdExpression() will
create a DependentDeclRefExpr, which is not what we wanted at all.  Fix
this by building the CXXDependentScopeMemberExpr directly instead.

In order to be fully MSVC compatible, we would have to defer all
attempts at name lookup to instantiation time.  However, until we have
real problems with system headers that can't be parsed, we'll put off
implementing that.

Fixes PR16014.

Reviewers: rsmith

Differential Revision: http://llvm-reviews.chandlerc.com/D1892

llvm-svn: 192727

3 files changed, 20 insertions, 6 deletions

diff --git a/clang/lib/AST/ExprCXX.cpp b/clang/lib/AST/ExprCXX.cpp
index 069404aa7cb..3738c0e4f2c 100644
--- a/clang/lib/AST/ExprCXX.cpp
+++ b/clang/lib/AST/ExprCXX.cpp
@@ -456,6 +456,7 @@ DependentScopeDeclRefExpr::Create(const ASTContext &C,
                                   SourceLocation TemplateKWLoc,
                                   const DeclarationNameInfo &NameInfo,
                                   const TemplateArgumentListInfo *Args) {
+  assert(QualifierLoc && "should be created for dependent qualifiers");
   std::size_t size = sizeof(DependentScopeDeclRefExpr);
   if (Args)
     size += ASTTemplateKWAndArgsInfo::sizeFor(Args->size());
diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index 04e01f6ccb7..14059035e70 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -2020,14 +2020,26 @@ ExprResult Sema::ActOnIdExpression(Scope *S,
     if (R.empty()) {
       // In Microsoft mode, if we are inside a template class member function
       // whose parent class has dependent base classes, and we can't resolve
-      // an identifier, then assume the identifier is type dependent.  The
-      // goal is to postpone name lookup to instantiation time to be able to
-      // search into the type dependent base classes.
+      // an identifier, then assume the identifier is a member of a dependent
+      // base class.  The goal is to postpone name lookup to instantiation time
+      // to be able to search into the type dependent base classes.
+      // FIXME: If we want 100% compatibility with MSVC, we will have delay all
+      // unqualified name lookup.  Any name lookup during template parsing means
+      // clang might find something that MSVC doesn't.  For now, we only handle
+      // the common case of members of a dependent base class.
       if (getLangOpts().MicrosoftMode) {
         CXXMethodDecl *MD = dyn_cast<CXXMethodDecl>(CurContext);
-        if (MD && MD->getParent()->hasAnyDependentBases())
-          return ActOnDependentIdExpression(SS, TemplateKWLoc, NameInfo,
-                                            IsAddressOfOperand, TemplateArgs);
+        if (MD && MD->isInstance() && MD->getParent()->hasAnyDependentBases()) {
+          assert(SS.isEmpty() && "qualifiers should be already handled");
+          QualType ThisType = MD->getThisType(Context);
+          // Since the 'this' expression is synthesized, we don't need to
+          // perform the double-lookup check.
+          NamedDecl *FirstQualifierInScope = 0;
+          return Owned(CXXDependentScopeMemberExpr::Create(
+              Context, /*This=*/0, ThisType, /*IsArrow=*/true,
+              /*Op=*/SourceLocation(), SS.getWithLocInContext(Context),
+              TemplateKWLoc, FirstQualifierInScope, NameInfo, TemplateArgs));
+        }
       }
 
       // Don't diagnose an empty lookup for inline assmebly.
diff --git a/clang/lib/Sema/TreeTransform.h b/clang/lib/Sema/TreeTransform.h
index 6f5f72ecf61..97e12d77a19 100644
--- a/clang/lib/Sema/TreeTransform.h
+++ b/clang/lib/Sema/TreeTransform.h
@@ -8109,6 +8109,7 @@ ExprResult
 TreeTransform<Derived>::TransformDependentScopeDeclRefExpr(
                                                DependentScopeDeclRefExpr *E,
                                                bool IsAddressOfOperand) {
+  assert(E->getQualifierLoc());
   NestedNameSpecifierLoc QualifierLoc
   = getDerived().TransformNestedNameSpecifierLoc(E->getQualifierLoc());
   if (!QualifierLoc)