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.

2 files changed, 22 insertions, 2 deletions

diff --git a/gcc/cp/decl.cc b/gcc/cp/decl.cc
index 269c6679ca26..f53136cc04d6 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 000000000000..13f3175da45b
--- /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; }
+};