[gcc r16-7095] c++/modules: Handle reflection SPLICE_SCOPE tree node

[Jason Merrill]

https://gcc.gnu.org/g:fd7635c7d81d8183300934f91b885ecca52dda9b

commit r16-7095-gfd7635c7d81d8183300934f91b885ecca52dda9b
Author: vspefs <vspefs@protonmail.com>
Date:   Mon Jan 26 20:56:52 2026 +0000

    c++/modules: Handle reflection SPLICE_SCOPE tree node
    
    This patch adds support for serializing and deserializing SPLICE_SCOPE trees
    in C++20 modules implementation. SPLICE_SCOPE is introduced by C++26
    reflection, notably used for dependent splice types, thus needing to be
    exported/imported as part of the module interface. Not handling SPLICE_SCOPE
    leads to ICE.
    
    This patch also includes 2 simple test cases: one for exporting splice scope
    types and another for importing them.
    
    gcc/cp/
    
            * module.cc (trees_out::type_node): Add case for SPLICE_SCOPE.
            (trees_in::tree_node): Add case for SPLICE_SCOPE.
    
    gcc/testsuite/
    
            * g++.dg/modules/splice-scope-tree_a.C: New test.
            * g++.dg/modules/splice-scope-tree_b.C: New test.
    
    Reviewed-by: Patrick Palka  <ppalka@redhat.com>
    Reviewed-by: Jason Merrill <jason@redhat.com>

Diff:
---
 gcc/cp/module.cc                                   | 16 ++++++++++++++++
 gcc/testsuite/g++.dg/modules/splice-scope-tree_a.C | 12 ++++++++++++
 gcc/testsuite/g++.dg/modules/splice-scope-tree_b.C | 16 ++++++++++++++++
 3 files changed, 44 insertions(+)

diff --git a/gcc/cp/module.cc b/gcc/cp/module.cc
index e2097027dbd9..2d9b727d2b3d 100644
--- a/gcc/cp/module.cc
+++ b/gcc/cp/module.cc
@@ -9847,6 +9847,12 @@ trees_out::type_node (tree type)
     case META_TYPE:
       /* No additional data.  */
       break;
+
+    case SPLICE_SCOPE:
+      if (streaming_p ())
+	u (SPLICE_SCOPE_TYPE_P (type));
+      tree_node (SPLICE_SCOPE_EXPR (type));
+      break;
     }
 
   tree_node (TYPE_ATTRIBUTES (type));
@@ -10697,6 +10703,16 @@ trees_in::tree_node (bool is_use)
 	    if (!get_overrun ())
 	      res = meta_info_type_node;
 	    break;
+
+	  case SPLICE_SCOPE:
+	    {
+	      bool type = u ();
+	      tree expr = tree_node ();
+
+	      if (!get_overrun ())
+		res = make_splice_scope (expr, type);
+	    }
+	    break;
 	  }
 
 	/* In the exporting TU, a derived type with attributes was built by
diff --git a/gcc/testsuite/g++.dg/modules/splice-scope-tree_a.C b/gcc/testsuite/g++.dg/modules/splice-scope-tree_a.C
new file mode 100644
index 000000000000..3cf638aadb59
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/splice-scope-tree_a.C
@@ -0,0 +1,12 @@
+// { dg-do compile { target c++26 } }
+// { dg-additional-options "-fmodules -freflection" }
+
+export module exporting_splice_scope;
+// { dg-module-cmi exporting_splice_scope }
+
+export template <typename T>
+using dependent_splice_type = typename [: ^^T :];
+
+export template <bool Cond, typename T, typename U>
+using somehow_more_complicated_dependent_splice_type =
+    typename [: Cond ? ^^T : ^^U :];
diff --git a/gcc/testsuite/g++.dg/modules/splice-scope-tree_b.C b/gcc/testsuite/g++.dg/modules/splice-scope-tree_b.C
new file mode 100644
index 000000000000..55132f2d8b1d
--- /dev/null
+++ b/gcc/testsuite/g++.dg/modules/splice-scope-tree_b.C
@@ -0,0 +1,16 @@
+// { dg-do compile { target c++26 } }
+// { dg-additional-options "-fmodules -freflection" }
+
+import exporting_splice_scope;
+
+#include <meta>
+
+int
+main ()
+{
+  static_assert (std::meta::dealias (^^dependent_splice_type<int>) == ^^int);
+  static_assert (std::meta::dealias (
+      ^^somehow_more_complicated_dependent_splice_type<true, int, double>) == ^^int);
+  static_assert (std::meta::dealias (
+      ^^somehow_more_complicated_dependent_splice_type<false, int, double>) == ^^double);
+}