Allow sizeof(UnrelatedClass::field) in C++11 class template methods

This feature works outside of templates by forming a DeclRefExpr to a
FieldDecl instead of a MemberExpr, which requires a base object in
addition to the FieldDecl.

Previously, while building up the template AST before instantiation, we
formed a CXXDependentScopeMemberExpr, which always instantiates to a
MemberExpr. Now, in unevaluated contexts we form a
DependentScopeDeclRefExpr, which is a more flexible node that can
instantiate to either a MemberExpr or a DeclRefExpr depending on lookup
results.

Fixes PR26893.

llvm-svn: 263279

1 files changed, 16 insertions, 3 deletions

diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 3b85b98abdd..0b4b083ffbd 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -414,9 +414,22 @@ Sema::ActOnDependentIdExpression(const CXXScopeSpec &SS,
                            const TemplateArgumentListInfo *TemplateArgs) {
   DeclContext *DC = getFunctionLevelDeclContext();
 
-  if (!isAddressOfOperand &&
-      isa<CXXMethodDecl>(DC) &&
-      cast<CXXMethodDecl>(DC)->isInstance()) {
+  // C++11 [expr.prim.general]p12:
+  //   An id-expression that denotes a non-static data member or non-static
+  //   member function of a class can only be used:
+  //   (...)
+  //   - if that id-expression denotes a non-static data member and it
+  //     appears in an unevaluated operand.
+  //
+  // If this might be the case, form a DependentScopeDeclRefExpr instead of a
+  // CXXDependentScopeMemberExpr. The former can instantiate to either
+  // DeclRefExpr or MemberExpr depending on lookup results, while the latter is
+  // always a MemberExpr.
+  bool MightBeCxx11UnevalField =
+      getLangOpts().CPlusPlus11 && isUnevaluatedContext();
+
+  if (!MightBeCxx11UnevalField && !isAddressOfOperand &&
+      isa<CXXMethodDecl>(DC) && cast<CXXMethodDecl>(DC)->isInstance()) {
     QualType ThisType = cast<CXXMethodDecl>(DC)->getThisType(Context);
 
     // Since the 'this' expression is synthesized, we don't need to