From ef9d09c4699a2a61d6f28b59b7583b2b28c0a531 Mon Sep 17 00:00:00 2001
From: Chandler Carruth <chandlerc@gmail.com>
Date: Mon, 3 Jan 2011 19:27:19 +0000
Subject: [PATCH] Fix PR8841 by checking for  both semantic and lecical
 dependent contexts. This prevents -Wunused-function from firing on friend
 function definitions inside of class templates for example.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@122763 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Sema/SemaDecl.cpp                   |  3 ++-
 test/SemaCXX/warn-unused-filescoped.cpp | 16 ++++++++++++++++
 2 files changed, 18 insertions(+), 1 deletion(-)

diff --git a/lib/Sema/SemaDecl.cpp b/lib/Sema/SemaDecl.cpp
index 32791f9f98..dc851a3e83 100644
--- a/lib/Sema/SemaDecl.cpp
+++ b/lib/Sema/SemaDecl.cpp
@@ -557,7 +557,8 @@ bool Sema::ShouldWarnIfUnusedFileScopedDecl(const DeclaratorDecl *D) const {
     return false;
 
   // Ignore class templates.
-  if (D->getDeclContext()->isDependentContext())
+  if (D->getDeclContext()->isDependentContext() ||
+      D->getLexicalDeclContext()->isDependentContext())
     return false;
 
   if (const FunctionDecl *FD = dyn_cast<FunctionDecl>(D)) {
diff --git a/test/SemaCXX/warn-unused-filescoped.cpp b/test/SemaCXX/warn-unused-filescoped.cpp
index 75fc6a4da0..628075ac04 100644
--- a/test/SemaCXX/warn-unused-filescoped.cpp
+++ b/test/SemaCXX/warn-unused-filescoped.cpp
@@ -54,3 +54,19 @@ namespace {
   };
   template <> int TS2<int>::x;  // expected-warning{{unused}}
 }
+
+namespace PR8841 {
+  // Ensure that friends of class templates are considered to have a dependent
+  // context and not marked unused.
+  namespace {
+    template <typename T> struct X {
+      friend bool operator==(const X&, const X&) { return false; }
+    };
+  }
+  template <typename T> void template_test(X<T> x) {
+    (void)(x == x);
+  }
+  void test(X<int> x) {
+    template_test(x);
+  }
+}
-- 
2.40.0