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.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@263279 91177308-0d34-0410-b5e6-96231b3b80d8

2 files changed, 42 insertions, 4 deletions

diff --git a/lib/Sema/SemaTemplate.cpp b/lib/Sema/SemaTemplate.cpp
index 3b85b98abd..0b4b083ffb 100644
--- a/lib/Sema/SemaTemplate.cpp
+++ b/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
diff --git a/test/SemaTemplate/instantiate-sizeof.cpp b/test/SemaTemplate/instantiate-sizeof.cpp
index bf66fdc17c..04793f785e 100644
--- a/test/SemaTemplate/instantiate-sizeof.cpp
+++ b/test/SemaTemplate/instantiate-sizeof.cpp
@@ -1,5 +1,4 @@
 // RUN: %clang_cc1 -fsyntax-only -verify -std=c++11 %s
-// expected-no-diagnostics
 
 // Make sure we handle contexts correctly with sizeof
 template<typename T> void f(T n) {
@@ -9,3 +8,29 @@ template<typename T> void f(T n) {
 int main() {
   f<int>(1);
 }
+
+// Make sure we handle references to non-static data members in unevaluated
+// contexts in class template methods correctly. Previously we assumed these
+// would be valid MemberRefExprs, but they have no 'this' so we need to form a
+// DeclRefExpr to the FieldDecl instead.
+// PR26893
+template <class T>
+struct M {
+  M() {}; // expected-note {{in instantiation of default member initializer 'M<S>::m' requested here}}
+  int m = *T::x; // expected-error {{invalid use of non-static data member 'x'}}
+  void f() {
+    // These are valid.
+    static_assert(sizeof(T::x) == 8, "ptr");
+    static_assert(sizeof(*T::x) == 4, "int");
+  }
+};
+struct S { int *x; };
+template struct M<S>; // expected-note {{in instantiation of member function 'M<S>::M' requested here}}
+
+// Similar test case for PR26893.
+template <typename T=void>
+struct bar {
+  struct foo { int array[10]; };
+  int baz() { return sizeof(foo::array); }
+};
+template struct bar<>;