From d7711adcd5226995063342631e1ce5c2ff055981 Mon Sep 17 00:00:00 2001
From: Alexandre Oliva <aoliva@redhat.com>
Date: Thu, 6 Dec 2018 23:18:40 +0000
Subject: [PATCH] [PR86747] tsubst friend tpl ctxt before looking it up for
 dupes

When a member template is redeclared as a friend, we enter the context
of the member before looking it up, and then we check that the decls
are compatible.  However, when the member template references template
types of the enclosing context, say an enclosing template class, the
compare fails because the friend decl is already tsubsted, whereas the
looked up name isn't.

The problem is that the enclosing context is taken from the friend
declaration before tsubsting it, so we look up in the context of the
generic template instead of that of the tsubsted one we're
specializing.  The solution is to tsubst the enclosing context when
it's a non-namespace scope.

for  gcc/cp/ChangeLog

	PR c++/86747
	* pt.c (tsubst_friend_class): Enter tsubsted class context.

for  gcc/testsuite/ChangeLog

	PR c++/86747
	* g++.dg/pr86747.C: New.

From-SVN: r266875
---
 gcc/cp/ChangeLog               | 3 +++
 gcc/cp/pt.c                    | 5 ++++-
 gcc/testsuite/ChangeLog        | 3 +++
 gcc/testsuite/g++.dg/pr86747.C | 8 ++++++++
 4 files changed, 18 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/pr86747.C

diff --git a/gcc/cp/ChangeLog b/gcc/cp/ChangeLog
index 727f2d4f909..e092c4490f5 100644
--- a/gcc/cp/ChangeLog
+++ b/gcc/cp/ChangeLog
@@ -1,5 +1,8 @@
 2018-12-06  Alexandre Oliva <aoliva@redhat.com>
 
+	PR c++/86747
+	* pt.c (tsubst_friend_class): Enter tsubsted class context.
+
 	PR c++/86397
 	* except.c (build_noexcept_spec): Resolve nondependent
 	expressions.
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 90fb3aee82d..8560e588593 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -10558,7 +10558,10 @@ tsubst_friend_class (tree friend_tmpl, tree args)
   if (TREE_CODE (context) == NAMESPACE_DECL)
     push_nested_namespace (context);
   else
-    push_nested_class (context);
+    {
+      context = tsubst (context, args, tf_error, NULL_TREE);
+      push_nested_class (context);
+    }
 
   tmpl = lookup_name_real (DECL_NAME (friend_tmpl), /*prefer_type=*/false,
 			   /*non_class=*/false, /*block_p=*/false,
diff --git a/gcc/testsuite/ChangeLog b/gcc/testsuite/ChangeLog
index eddb4576e0f..1871663415e 100644
--- a/gcc/testsuite/ChangeLog
+++ b/gcc/testsuite/ChangeLog
@@ -1,5 +1,8 @@
 2018-12-06  Alexandre Oliva <aoliva@redhat.com>
 
+	PR c++/86747
+	* g++.dg/pr86747.C: New.
+
 	PR c++/86397
 	* g++.dg/cpp0x/pr86397-1.C: New.
 	* g++.dg/cpp0x/pr86397-2.C: New.
diff --git a/gcc/testsuite/g++.dg/pr86747.C b/gcc/testsuite/g++.dg/pr86747.C
new file mode 100644
index 00000000000..5b0a0bb9514
--- /dev/null
+++ b/gcc/testsuite/g++.dg/pr86747.C
@@ -0,0 +1,8 @@
+// { dg-do compile }
+
+template <typename T> class A {
+  template <void (A::*p)()> class C; // #1
+  template <void (A::*q)()> friend class C; // #2
+};
+
+A<double> a;
-- 
2.30.2