From 63644fae3970d4146200e4cb25dd9aace34a3398 Mon Sep 17 00:00:00 2001
From: Douglas Gregor <dgregor@apple.com>
Date: Sun, 7 Feb 2010 10:31:35 +0000
Subject: [PATCH] Workaround for friend template instantiation crash in PR5848,
 from Keir Mierle!

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@95517 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Sema/SemaTemplateInstantiateDecl.cpp | 14 +++++++++++---
 test/SemaCXX/templated-friend-decl.cpp   | 15 +++++++++++++++
 2 files changed, 26 insertions(+), 3 deletions(-)
 create mode 100644 test/SemaCXX/templated-friend-decl.cpp

diff --git a/lib/Sema/SemaTemplateInstantiateDecl.cpp b/lib/Sema/SemaTemplateInstantiateDecl.cpp
index 244b5f511b..d7820bbc2e 100644
--- a/lib/Sema/SemaTemplateInstantiateDecl.cpp
+++ b/lib/Sema/SemaTemplateInstantiateDecl.cpp
@@ -411,9 +411,17 @@ Decl *TemplateDeclInstantiator::VisitFriendDecl(FriendDecl *D) {
     Decl *NewND;
 
     // Hack to make this work almost well pending a rewrite.
-    if (ND->getDeclContext()->isRecord())
-      NewND = SemaRef.FindInstantiatedDecl(ND, TemplateArgs);
-    else if (D->wasSpecialization()) {
+    if (ND->getDeclContext()->isRecord()) {
+      if (!ND->getDeclContext()->isDependentContext()) {
+        NewND = SemaRef.FindInstantiatedDecl(ND, TemplateArgs);
+      } else {
+        // FIXME: Hack to avoid crashing when incorrectly trying to instantiate
+        // templated friend declarations. This doesn't produce a correct AST;
+        // however this is sufficient for some AST analysis. The real solution
+        // must be put in place during the pending rewrite. See PR5848.
+        return 0;
+      }
+    } else if (D->wasSpecialization()) {
       // Totally egregious hack to work around PR5866
       return 0;
     } else
diff --git a/test/SemaCXX/templated-friend-decl.cpp b/test/SemaCXX/templated-friend-decl.cpp
new file mode 100644
index 0000000000..c0034cd72f
--- /dev/null
+++ b/test/SemaCXX/templated-friend-decl.cpp
@@ -0,0 +1,15 @@
+// RUN: %clang_cc1 %s
+
+template <typename T>
+struct Foo {
+  template <typename U>
+  struct Bar {};
+
+  // The templated declaration for class Bar should not be instantiated when
+  // Foo<int> is. This is to protect against PR5848; for now, this "parses" but
+  // requires a rewrite of the templated friend code to be properly fixed.
+  template <typename U>
+  friend struct Bar;
+};
+
+Foo<int> x;
-- 
2.40.0