From 43dddeef7a870ce4db7407f73660504b67a0a919 Mon Sep 17 00:00:00 2001
From: Nathaniel Shead <nathanieloshead@gmail.com>
Date: Sat, 24 May 2025 00:51:49 +1000
Subject: [PATCH] c++/modules: Fix stream-in of member using-decls [PR120414]

When streaming in a reference to a data member, we have an oversight
where we did not consider USING_DECLs, despite otherwise handling them
here the same as fields.  This patch corrects that mistake.

	PR c++/120414

gcc/cp/ChangeLog:

	* module.cc (trees_in::tree_node): Allow reading a USING_DECL
	when streaming tt_data_member.

gcc/testsuite/ChangeLog:

	* g++.dg/modules/using-31_a.C: New test.
	* g++.dg/modules/using-31_b.C: New test.

Signed-off-by: Nathaniel Shead <nathanieloshead@gmail.com>
Reviewed-by: Jason Merrill <jason@redhat.com>
---
 gcc/cp/module.cc                          |  3 ++-
 gcc/testsuite/g++.dg/modules/using-31_a.C | 18 ++++++++++++++++++
 gcc/testsuite/g++.dg/modules/using-31_b.C |  5 +++++
 3 files changed, 25 insertions(+), 1 deletion(-)
 create mode 100644 gcc/testsuite/g++.dg/modules/using-31_a.C
 create mode 100644 gcc/testsuite/g++.dg/modules/using-31_b.C

diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index 13f8770b7bd..17c040d26b0 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -10512,7 +10512,8 @@ trees_in::tree_node (bool is_use)
 	      res = lookup_field_ident (ctx, u ());
 
 	    if (!res
-		|| TREE_CODE (res) != FIELD_DECL
+		|| (TREE_CODE (res) != FIELD_DECL
+		    && TREE_CODE (res) != USING_DECL)
 		|| DECL_CONTEXT (res) != ctx)
 	      res = NULL_TREE;
 	  }
diff --git a/gcc/testsuite/g++.dg/modules/using-31_a.C b/gcc/testsuite/g++.dg/modules/using-31_a.C
new file mode 100644
index 00000000000..75bd87285e1
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/using-31_a.C
@@ -0,0 +1,18 @@
+// PR c++/120414
+// { dg-additional-options "-fmodules" }
+// { dg-module-cmi m }
+
+export module m;
+
+template <int n>
+struct Base {
+  static constexpr int base_static_mbr_n = n;
+};
+
+template <int n>
+struct Derived : Base<n> {
+  using Base<n>::base_static_mbr_n;
+  static constexpr int go(int x = base_static_mbr_n) { return x; }
+};
+
+template struct Derived<1>;
diff --git a/gcc/testsuite/g++.dg/modules/using-31_b.C b/gcc/testsuite/g++.dg/modules/using-31_b.C
new file mode 100644
index 00000000000..e913a77aaf9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/using-31_b.C
@@ -0,0 +1,5 @@
+// PR c++/120414
+// { dg-additional-options "-fmodules" }
+
+module m;
+static_assert(Derived<1>::go() == 1);
-- 
2.47.2