From 7f61d441789c7b1f7c96d7672a176eb996ecb73f Mon Sep 17 00:00:00 2001
From: Richard Smith <richard-llvm@metafoo.co.uk>
Date: Tue, 11 Jun 2019 23:51:46 +0000
Subject: [PATCH] Mark declarations as referenced by a default argument in a
 potentially-evaluated context.

This applies even if the use of the default argument is within an
unevaluated context.

llvm-svn: 363113
---
 clang/lib/Sema/SemaExpr.cpp                   | 2 ++
 clang/test/SemaTemplate/default-arguments.cpp | 6 ++++++
 2 files changed, 8 insertions(+)

diff --git a/clang/lib/Sema/SemaExpr.cpp b/clang/lib/Sema/SemaExpr.cpp
index ed39278b1adb..d444a35be863 100644
--- a/clang/lib/Sema/SemaExpr.cpp
+++ b/clang/lib/Sema/SemaExpr.cpp
@@ -4855,6 +4855,8 @@ bool Sema::CheckCXXDefaultArgExpr(SourceLocation CallLoc, FunctionDecl *FD,
   // We already type-checked the argument, so we know it works.
   // Just mark all of the declarations in this potentially-evaluated expression
   // as being "referenced".
+  EnterExpressionEvaluationContext EvalContext(
+      *this, ExpressionEvaluationContext::PotentiallyEvaluated, Param);
   MarkDeclarationsReferencedInExpr(Param->getDefaultArg(),
                                    /*SkipLocalVariables=*/true);
   return false;
diff --git a/clang/test/SemaTemplate/default-arguments.cpp b/clang/test/SemaTemplate/default-arguments.cpp
index b5b042c64a71..882b279de1d0 100644
--- a/clang/test/SemaTemplate/default-arguments.cpp
+++ b/clang/test/SemaTemplate/default-arguments.cpp
@@ -223,3 +223,9 @@ namespace friends {
     X<int> *p;
   }
 }
+
+namespace unevaluated {
+  int a;
+  template<int = 0> int f(int = a); // expected-warning 0-1{{extension}}
+  int k = sizeof(f());
+}