From: Marek Polacek <polacek@redhat.com>
Date: Sun, 1 Feb 2026 20:20:55 +0000 (-0500)
Subject: c++/reflection: wrong error with const meta::info parm [PR123614]
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=9de2f8da0c37f04d67bc3d5dcee6a36034df2f9a;p=thirdparty%2Fgcc.git

c++/reflection: wrong error with const meta::info parm [PR123614]

Here we issue a bogus "not a constant expression" error ultimately
because get_info returns NULL_TREE for the const parameter in Name.
The cxx_eval_constant_expression in get_info produces a NOP_EXPR:

  (info) reflect_expr <int>

which is not REFLECT_EXPR_P.  This isn't caught by the
REFLECTION_TYPE_P && REFLECT_EXPR_P check in _eval_constant_expression
because OP is a NOP_EXPR.  The NOP_EXPR comes from adjust_temp_type.

I suppose I could just add STRIP_NOPS to get_info.  Or I could follow
c++/65695 / r6-41-gfb899e32c16088 and adjust cp_fold_convert to fold
away the conversion.

	PR c++/123614

gcc/cp/ChangeLog:

	* cvt.cc (cp_fold_convert): Avoid wrapping a REFLECT_EXPR in NOP_EXPR.

gcc/testsuite/ChangeLog:

	* g++.dg/reflect/parm5.C: New test.

Reviewed-by: Jason Merrill <jason@redhat.com>
---

diff --git a/gcc/cp/cvt.cc b/gcc/cp/cvt.cc
index a984611ea8e..fe9b9dc6dd1 100644
--- a/gcc/cp/cvt.cc
+++ b/gcc/cp/cvt.cc
@@ -622,11 +622,12 @@ cp_fold_convert (tree type, tree expr)
   tree conv;
   if (TREE_TYPE (expr) == type)
     conv = expr;
-  else if (TREE_CODE (expr) == PTRMEM_CST
-	   && same_type_p (TYPE_PTRMEM_CLASS_TYPE (type),
-			   PTRMEM_CST_CLASS (expr)))
+  else if ((TREE_CODE (expr) == PTRMEM_CST
+	    && same_type_p (TYPE_PTRMEM_CLASS_TYPE (type),
+			    PTRMEM_CST_CLASS (expr)))
+	    || (REFLECT_EXPR_P (expr) && REFLECTION_TYPE_P (type)))
     {
-      /* Avoid wrapping a PTRMEM_CST in NOP_EXPR.  */
+      /* Avoid wrapping a PTRMEM_CST/REFLECT_EXPR in NOP_EXPR.  */
       conv = copy_node (expr);
       TREE_TYPE (conv) = type;
     }
diff --git a/gcc/testsuite/g++.dg/reflect/parm5.C b/gcc/testsuite/g++.dg/reflect/parm5.C
new file mode 100644
index 00000000000..0034b842cc6
--- /dev/null
+++ b/gcc/testsuite/g++.dg/reflect/parm5.C
@@ -0,0 +1,17 @@
+// PR c++/123614
+// { dg-do compile { target c++26 } }
+// { dg-additional-options "-freflection" }
+
+#include <meta>
+
+template<class, class> struct same_type;
+template<class T> struct same_type<T, T> {};
+
+consteval auto Name(const std::meta::info meta){
+    same_type<decltype(meta), const std::meta::info>();
+    return std::meta::display_string_of(meta);
+}
+
+int main() {
+  auto sv = std::define_static_string(Name(^^int));
+}