From fb9e5477faacb94cd5665ab3f2e334451308b0d8 Mon Sep 17 00:00:00 2001
From: Richard Smith <richard-llvm@metafoo.co.uk>
Date: Mon, 3 Feb 2014 20:09:56 +0000
Subject: [PATCH] PR17846, PR17848: don't build a VarTemplateSpecializationDecl
 for a use of a variable template until we know what the template arguments
 actually are.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@200714 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Sema/SemaTemplate.cpp                     | 11 +++---
 .../SemaTemplate/instantiate-var-template.cpp | 36 +++++++++++++++++++
 2 files changed, 43 insertions(+), 4 deletions(-)
 create mode 100644 test/SemaTemplate/instantiate-var-template.cpp

diff --git a/lib/Sema/SemaTemplate.cpp b/lib/Sema/SemaTemplate.cpp
index bc66fdedb6..a6a3535d68 100644
--- a/lib/Sema/SemaTemplate.cpp
+++ b/lib/Sema/SemaTemplate.cpp
@@ -2777,10 +2777,13 @@ ExprResult Sema::BuildTemplateIdExpr(const CXXScopeSpec &SS,
   assert(!R.isAmbiguous() && "ambiguous lookup when building templateid");
 
   // In C++1y, check variable template ids.
-  if (R.getAsSingle<VarTemplateDecl>()) {
-    return Owned(CheckVarTemplateId(SS, R.getLookupNameInfo(),
-                                    R.getAsSingle<VarTemplateDecl>(),
-                                    TemplateKWLoc, TemplateArgs));
+  bool InstantiationDependent;
+  if (R.getAsSingle<VarTemplateDecl>() &&
+      !TemplateSpecializationType::anyDependentTemplateArguments(
+           *TemplateArgs, InstantiationDependent)) {
+    return CheckVarTemplateId(SS, R.getLookupNameInfo(),
+                              R.getAsSingle<VarTemplateDecl>(),
+                              TemplateKWLoc, TemplateArgs);
   }
 
   // We don't want lookup warnings at this point.
diff --git a/test/SemaTemplate/instantiate-var-template.cpp b/test/SemaTemplate/instantiate-var-template.cpp
new file mode 100644
index 0000000000..bd7c43334f
--- /dev/null
+++ b/test/SemaTemplate/instantiate-var-template.cpp
@@ -0,0 +1,36 @@
+// RUN: %clang_cc1 -verify -std=c++1y %s
+
+namespace PR17846 {
+  template <typename T> constexpr T pi = T(3.14);
+  template <typename T> constexpr T tau = 2 * pi<T>;
+  constexpr double tau_double = tau<double>;
+  static_assert(tau_double == 6.28, "");
+}
+
+namespace PR17848 {
+  template<typename T> constexpr T var = 12345;
+  template<typename T> constexpr T f() { return var<T>; }
+  constexpr int k = f<int>();
+  static_assert(k == 12345, "");
+}
+
+namespace NonDependent {
+  template<typename T> constexpr T a = 0;
+  template<typename T> constexpr T b = a<int>;
+  static_assert(b<int> == 0, "");
+}
+
+namespace InstantiationDependent {
+  int f(int);
+  void f(char);
+
+  template<int> constexpr int a = 1;
+  template<typename T> constexpr T b = a<sizeof(sizeof(f(T())))>; // expected-error {{invalid application of 'sizeof' to an incomplete type 'void'}}
+
+  static_assert(b<int> == 1, "");
+  static_assert(b<char> == 1, ""); // expected-note {{in instantiation of}} expected-error {{not an integral constant}}
+
+  template<typename T> void f() {
+    static_assert(a<sizeof(sizeof(f(T())))> == 0, ""); // expected-error {{static_assert failed}}
+  }
+}
-- 
2.40.0