From: Nathaniel Shead <nathanieloshead@gmail.com>
Date: Mon, 1 Dec 2025 13:43:18 +0000 (+1100)
Subject: c++/modules: Stream DECL_CHAIN for decl_specialization_friend_p functions
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=4247fc98bd910ff8af8bae2aec0dfc256fdde585;p=thirdparty%2Fgcc.git

c++/modules: Stream DECL_CHAIN for decl_specialization_friend_p functions

r16-5298 attached the owning class for a friend template specialisation
on its DECL_CHAIN.  However we don't stream DECL_CHAIN in general to
avoid walking into unrelated entities on the scope chain; this patch
adds a special case for these functions to ensure we don't lose this
information.

Ideally this would occur in trees_{out,in}::core_vals, but we can't
check decl_specialization_friend_p until after DECL_TEMPLATE_INFO has
been streamed, hence the slightly unusual placement.

gcc/cp/ChangeLog:

	* module.cc (trees_out::lang_decl_vals): Stream DECL_CHAIN for
	decl_specialization_friend_p functions.
	(trees_in::lang_decl_vals): Likewise.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/friend-12_a.C: New test.
	* g++.dg/modules/friend-12_b.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
Reviewed-by: Jason Merrill <jason@redhat.com>
---

diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index 91e305c280b..042b029a036 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -7524,6 +7524,12 @@ trees_out::lang_decl_vals (tree t)
 
 	WT (access);
       }
+      /* A friend template specialisation stashes its owning class on its
+	 DECL_CHAIN; we need to reconstruct this, but it needs to happen
+	 after we stream the template_info so readers can know this is such
+	 an entity.  */
+      if (decl_specialization_friend_p (t))
+	WT (t->common.chain);
       break;
 
     case lds_ns:  /* lang_decl_ns.  */
@@ -7593,6 +7599,8 @@ trees_in::lang_decl_vals (tree t)
     lds_min:
       RT (lang->u.min.template_info);
       RT (lang->u.min.access);
+      if (decl_specialization_friend_p (t))
+	RT (t->common.chain);
       break;
 
     case lds_ns:  /* lang_decl_ns.  */
diff --git a/gcc/testsuite/g++.dg/modules/friend-12_a.C b/gcc/testsuite/g++.dg/modules/friend-12_a.C
new file mode 100644
index 00000000000..827c74b8f58
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/friend-12_a.C
@@ -0,0 +1,11 @@
+// { dg-additional-options "-fmodules -Wno-global-module" }
+// { dg-module-cmi M:part }
+
+module;
+template <typename T> struct basic_streambuf;
+template <typename T> void __copy_streambufs_eof(basic_streambuf<T>*);
+template <typename T> struct basic_streambuf {
+  friend void __copy_streambufs_eof<>(basic_streambuf*);
+};
+export module M:part;
+void foo(basic_streambuf<char>&) {}
diff --git a/gcc/testsuite/g++.dg/modules/friend-12_b.C b/gcc/testsuite/g++.dg/modules/friend-12_b.C
new file mode 100644
index 00000000000..7eb7014660f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/friend-12_b.C
@@ -0,0 +1,5 @@
+// { dg-additional-options "-fmodules -Wno-global-module" }
+// { dg-module-cmi M }
+
+export module M;
+export import :part;