From 743461090a2027058cd438ed643ed5ed939cf1ca Mon Sep 17 00:00:00 2001
From: Mark de Wever <koraq@xs4all.nl>
Date: Tue, 5 Nov 2019 20:39:55 +0100
Subject: [PATCH] [Sema] Fixes templated friend member assertion

Fixes PR41792: Clang assertion failure on templated friend member function

Differential Revision: https://reviews.llvm.org/D69481
---
 clang/lib/Sema/SemaTemplate.cpp                      |  3 +++
 clang/test/CXX/temp/temp.spec/temp.expl.spec/p20.cpp | 11 ++++++++++-
 2 files changed, 13 insertions(+), 1 deletion(-)

diff --git a/clang/lib/Sema/SemaTemplate.cpp b/clang/lib/Sema/SemaTemplate.cpp
index 3f2d386..a85fb6c 100644
--- a/clang/lib/Sema/SemaTemplate.cpp
+++ b/clang/lib/Sema/SemaTemplate.cpp
@@ -2549,6 +2549,9 @@ struct DependencyChecker : RecursiveASTVisitor<DependencyChecker> {
 /// list.
 static bool
 DependsOnTemplateParameters(QualType T, TemplateParameterList *Params) {
+  if (!Params->size())
+    return false;
+
   DependencyChecker Checker(Params, /*IgnoreNonTypeDependent*/false);
   Checker.TraverseType(T);
   return Checker.Match;
diff --git a/clang/test/CXX/temp/temp.spec/temp.expl.spec/p20.cpp b/clang/test/CXX/temp/temp.spec/temp.expl.spec/p20.cpp
index 86cdcf8..0283dba 100644
--- a/clang/test/CXX/temp/temp.spec/temp.expl.spec/p20.cpp
+++ b/clang/test/CXX/temp/temp.spec/temp.expl.spec/p20.cpp
@@ -3,7 +3,7 @@ template<typename T>
 void f(T);
 
 template<typename T>
-struct A { };
+struct A { }; // expected-note{{template is declared here}}
 
 struct X {
   template<> friend void f<int>(int); // expected-error{{in a friend}}
@@ -12,3 +12,12 @@ struct X {
   friend void f<float>(float); // okay
   friend class A<float>; // okay
 };
+
+struct PR41792 {
+  // expected-error@+1{{cannot declare an explicit specialization in a friend}}
+  template <> friend void f<>(int);
+
+  // expected-error@+2{{template specialization declaration cannot be a friend}}
+  // expected-error@+1{{too few template arguments for class template 'A'}}
+  template <> friend class A<>;
+};
-- 
2.7.4