2 files changed, 20 insertions, 9 deletions
diff --git a/clang/lib/Parse/ParseExpr.cpp b/clang/lib/Parse/ParseExpr.cpp
index bcdc72df305..c739a50f0b3 100644
--- a/clang/lib/Parse/ParseExpr.cpp
+++ b/clang/lib/Parse/ParseExpr.cpp
@@ -192,6 +192,16 @@ Parser::ParseAssignmentExprWithObjCMessageExprStart(SourceLocation LBracLoc,
   return ParseRHSOfBinaryExpression(R, prec::Assignment);
 }
 
+ExprResult
+Parser::ParseConstantExpressionInExprEvalContext(TypeCastState isTypeCast) {
+  assert(Actions.ExprEvalContexts.back().Context ==
+             Sema::ExpressionEvaluationContext::ConstantEvaluated &&
+         "Call this function only if your ExpressionEvaluationContext is "
+         "already ConstantEvaluated");
+  ExprResult LHS(ParseCastExpression(false, false, isTypeCast));
+  ExprResult Res(ParseRHSOfBinaryExpression(LHS, prec::Conditional));
+  return Actions.ActOnConstantExpression(Res);
+}
 
 ExprResult Parser::ParseConstantExpression(TypeCastState isTypeCast) {
   // C++03 [basic.def.odr]p2:
@@ -200,10 +210,7 @@ ExprResult Parser::ParseConstantExpression(TypeCastState isTypeCast) {
   // C++98 and C++11 have no such rule, but this is only a defect in C++98.
   EnterExpressionEvaluationContext ConstantEvaluated(
       Actions, Sema::ExpressionEvaluationContext::ConstantEvaluated);
-
-  ExprResult LHS(ParseCastExpression(false, false, isTypeCast));
-  ExprResult Res(ParseRHSOfBinaryExpression(LHS, prec::Conditional));
-  return Actions.ActOnConstantExpression(Res);
+  return ParseConstantExpressionInExprEvalContext(isTypeCast);
 }
 
 /// \brief Parse a constraint-expression.
diff --git a/clang/lib/Parse/ParseTemplate.cpp b/clang/lib/Parse/ParseTemplate.cpp
index 28ae113a511..a919d870810 100644
--- a/clang/lib/Parse/ParseTemplate.cpp
+++ b/clang/lib/Parse/ParseTemplate.cpp
@@ -1186,7 +1186,13 @@ ParsedTemplateArgument Parser::ParseTemplateArgument() {
   //   expression is resolved to a type-id, regardless of the form of
   //   the corresponding template-parameter.
   //
-  // Therefore, we initially try to parse a type-id.  
+  // Therefore, we initially try to parse a type-id - and isCXXTypeId might look
+  // up and annotate an identifier as an id-expression during disambiguation,
+  // so enter the appropriate context for a constant expression template
+  // argument before trying to disambiguate.
+
+  EnterExpressionEvaluationContext EnterConstantEvaluated(
+      Actions, Sema::ExpressionEvaluationContext::ConstantEvaluated);
   if (isCXXTypeId(TypeIdAsTemplateArgument)) {
     SourceLocation Loc = Tok.getLocation();
     TypeResult TypeArg = ParseTypeName(/*Range=*/nullptr,
@@ -1216,7 +1222,7 @@ ParsedTemplateArgument Parser::ParseTemplateArgument() {
   
   // Parse a non-type template argument. 
   SourceLocation Loc = Tok.getLocation();
-  ExprResult ExprArg = ParseConstantExpression(MaybeTypeCast);
+  ExprResult ExprArg = ParseConstantExpressionInExprEvalContext(MaybeTypeCast);
   if (ExprArg.isInvalid() || !ExprArg.get())
     return ParsedTemplateArgument();
 
@@ -1262,9 +1268,7 @@ bool Parser::IsTemplateArgumentList(unsigned Skip) {
 ///         template-argument-list ',' template-argument
 bool
 Parser::ParseTemplateArgumentList(TemplateArgList &TemplateArgs) {
-  // Template argument lists are constant-evaluation contexts.
-  EnterExpressionEvaluationContext EvalContext(
-      Actions, Sema::ExpressionEvaluationContext::ConstantEvaluated);
+  
   ColonProtectionRAIIObject ColonProtection(*this, false);
 
   do {