From 2843bfa21073dd1ac222540e189e8bcf40afc2c0 Mon Sep 17 00:00:00 2001
From: Jason Merrill <jason@redhat.com>
Date: Fri, 3 Jun 2022 12:35:12 -0400
Subject: [PATCH] c++: redeclared hidden friend [PR105761]

Here, when we see the second declaration of f we match it with the first
one, copy over DECL_TEMPLATE_INFO, and then try to use it when parsing the
definition, leading to confusion.

	PR c++/105761

gcc/cp/ChangeLog:

	* decl.cc (duplicate_decls): Don't copy DECL_TEMPLATE_INFO
	from a hidden friend.

gcc/testsuite/ChangeLog:

	* g++.dg/cpp1y/auto-fn64.C: New test.
---
 gcc/cp/decl.cc                         | 12 ++++++++++--
 gcc/testsuite/g++.dg/cpp1y/auto-fn64.C | 12 ++++++++++++
 2 files changed, 22 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/cpp1y/auto-fn64.C

diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 269c667..f53136c 100644
--- a/gcc/cp/decl.cc
+++ b/gcc/cp/decl.cc
@@ -2655,7 +2655,13 @@ duplicate_decls (tree newdecl, tree olddecl, bool hiding, bool was_hidden)
       if (LANG_DECL_HAS_MIN (newdecl))
 	{
 	  DECL_ACCESS (newdecl) = DECL_ACCESS (olddecl);
-	  if (DECL_TEMPLATE_INFO (newdecl))
+	  if (new_defines_function
+	      && DECL_TEMPLATE_INFO (olddecl)
+	      && DECL_UNIQUE_FRIEND_P (DECL_TEMPLATE_RESULT
+				       (DECL_TI_TEMPLATE (olddecl))))
+	    /* Don't copy template info from a non-template friend declaration
+	       in a class template (PR105761).  */;
+	  else if (DECL_TEMPLATE_INFO (newdecl))
 	    {
 	      new_template_info = DECL_TEMPLATE_INFO (newdecl);
 	      if (DECL_TEMPLATE_INSTANTIATION (olddecl)
@@ -2663,8 +2669,10 @@ duplicate_decls (tree newdecl, tree olddecl, bool hiding, bool was_hidden)
 		/* Remember the presence of explicit specialization args.  */
 		TINFO_USED_TEMPLATE_ID (DECL_TEMPLATE_INFO (olddecl))
 		  = TINFO_USED_TEMPLATE_ID (new_template_info);
+	      DECL_TEMPLATE_INFO (newdecl) = DECL_TEMPLATE_INFO (olddecl);
 	    }
-	  DECL_TEMPLATE_INFO (newdecl) = DECL_TEMPLATE_INFO (olddecl);
+	  else
+	    DECL_TEMPLATE_INFO (newdecl) = DECL_TEMPLATE_INFO (olddecl);
 	}
 
       if (DECL_DECLARES_FUNCTION_P (newdecl))
diff --git a/gcc/testsuite/g++.dg/cpp1y/auto-fn64.C b/gcc/testsuite/g++.dg/cpp1y/auto-fn64.C
new file mode 100644
index 0000000..13f3175
--- /dev/null
+++ b/gcc/testsuite/g++.dg/cpp1y/auto-fn64.C
@@ -0,0 +1,12 @@
+// PR c++/105761
+// { dg-do compile { target c++14 } }
+// { dg-additional-options -Wno-non-template-friend }
+
+template <class T>
+class X {
+  friend auto f(X);
+};
+
+struct Y : X<long> {
+  friend auto f(X) { return 0L; }
+};
-- 
2.7.4