[Sema] Fix a multiple definition bug with friends and templates

The problem was that MergeFunctionDecl sometimes needs the injected template
arguments of a FunctionTemplateDecl, but is called before adding the new
template to the redecl chain. This leads to multiple common pointers in the same
redecl chain, each with their own identical instantiation. Fix this by merging
the the common state before inserting the new template into the redecl chain.

rdar://44810129

Differential revision: https://reviews.llvm.org/D53046

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@344157 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 20 insertions, 0 deletions

diff --git a/test/SemaCXX/friend-template-redecl.cpp b/test/SemaCXX/friend-template-redecl.cpp
new file mode 100644
index 0000000000..3e05964fb2
--- /dev/null
+++ b/test/SemaCXX/friend-template-redecl.cpp
@@ -0,0 +1,20 @@
+// RUN: %clang_cc1 -std=c++17 -verify -emit-llvm-only %s
+
+// expected-no-diagnostics
+
+template <class T> void bar(const T &t) { foo(t); }
+
+template <class>
+struct HasFriend {
+  template <class T>
+  friend void foo(const HasFriend<T> &m) noexcept(false);
+};
+
+template <class T>
+void foo(const HasFriend<T> &m) noexcept(false) {}
+
+void f() {
+  HasFriend<int> x;
+  foo(x);
+  bar(x);
+}