c++: uninstantiated template friends

template friends need to be recognized by module streaming and
associated with the befriending class.  but their context is that of
the friend (a namespace or other class).  This adds a flag to mark
such templates, and uses their DECL_CHAIN to point at the befriender.

	gcc/cp
	* cp-tree.h (DECL_UNINSTANTIATED_TEMPLATE_FRIEND): New.
	* pt.c (push_template_decl): Set it.
	(tsubst_friend_function): Clear it.

2 files changed, 20 insertions, 1 deletions

diff --git a/gcc/cp/cp-tree.h b/gcc/cp/cp-tree.h
index 69f8ed5..4db5012 100644
--- a/gcc/cp/cp-tree.h
+++ b/gcc/cp/cp-tree.h
@@ -545,6 +545,7 @@ extern GTY(()) tree cp_global_trees[CPTI_MAX];
       DECL_ANON_UNION_VAR_P (in a VAR_DECL)
       DECL_SELF_REFERENCE_P (in a TYPE_DECL)
       DECL_INVALID_OVERRIDER_P (in a FUNCTION_DECL)
+      DECL_UNINSTANIATED_TEMPLATE_FRIEND_P (in TEMPLATE_DECL)
    5: DECL_INTERFACE_KNOWN.
    6: DECL_THIS_STATIC (in VAR_DECL, FUNCTION_DECL or PARM_DECL)
       DECL_FIELD_IS_BASE (in FIELD_DECL)
@@ -3161,6 +3162,13 @@ struct GTY(()) lang_decl {
   (DECL_LANG_SPECIFIC (FUNCTION_DECL_CHECK (NODE)) \
    ->u.base.friend_or_tls)
 
+/* True of a TEMPLATE_DECL that is a template class friend.  Such
+   decls are not pushed until instantiated (as they may depend on
+   parameters of the befriending class).  DECL_CHAIN is the
+   befriending class.  */
+#define DECL_UNINSTANTIATED_TEMPLATE_FRIEND_P(NODE) \
+  (DECL_LANG_FLAG_4 (TEMPLATE_DECL_CHECK (NODE)))
+
 /* Nonzero if the thread-local variable was declared with __thread as
    opposed to thread_local.  */
 #define DECL_GNU_TLS_P(NODE)				\
diff --git a/gcc/cp/pt.c b/gcc/cp/pt.c
index 3ca2813..0893182 100644
--- a/gcc/cp/pt.c
+++ b/gcc/cp/pt.c
@@ -22,7 +22,9 @@ along with GCC; see the file COPYING3.  If not see
 /* Known bugs or deficiencies include:
 
      all methods must be provided in header files; can't use a source
-     file that contains only the method templates and "just win".  */
+     file that contains only the method templates and "just win".
+
+     Fixed by: C++20 modules.  */
 
 #include "config.h"
 #include "system.h"
@@ -6044,6 +6046,14 @@ push_template_decl (tree decl, bool is_friend)
 	      tmpl = NULL_TREE;
 	    }
 	}
+      else if (is_friend)
+	{
+	  /* Record this decl as belonging to the current class.  It's
+	     not chained onto anything else.  */
+	  DECL_UNINSTANTIATED_TEMPLATE_FRIEND_P (tmpl) = true;
+	  gcc_checking_assert (!DECL_CHAIN (tmpl));
+	  DECL_CHAIN (tmpl) = current_scope ();
+	}
     }
   else if (tmpl)
     /* The type may have been completed, or (erroneously) changed.  */
@@ -11053,6 +11063,7 @@ tsubst_friend_function (tree decl, tree args)
   DECL_USE_TEMPLATE (new_friend) = 0;
   if (TREE_CODE (new_friend) == TEMPLATE_DECL)
     {
+      DECL_UNINSTANTIATED_TEMPLATE_FRIEND_P (new_friend) = false;
       DECL_USE_TEMPLATE (DECL_TEMPLATE_RESULT (new_friend)) = 0;
       DECL_SAVED_TREE (DECL_TEMPLATE_RESULT (new_friend))
 	= DECL_SAVED_TREE (DECL_TEMPLATE_RESULT (decl));