[PATCH] c++/reflection: ^^ cannot define types [PR125922]

[Marek Polacek]

Bootstrapped/regtested on x86_64-pc-linux-gnu, ok for trunk?

-- >8 --
The reflect-expression production uses "^^ type-id" which doesn't
allow defining types (it's not defining-type-id), but we aren't
checking this.

        PR c++/125922

gcc/cp/ChangeLog:

        * parser.cc (cp_parser_reflect_expression): Temporarily set
        parser->type_definition_forbidden_message.

gcc/testsuite/ChangeLog:

        * g++.dg/reflect/error14.C: New test.
---
 gcc/cp/parser.cc                       |  9 +++++++--
 gcc/testsuite/g++.dg/reflect/error14.C | 15 +++++++++++++++
 2 files changed, 22 insertions(+), 2 deletions(-)
 create mode 100644 gcc/testsuite/g++.dg/reflect/error14.C

diff --git a/gcc/cp/parser.cc b/gcc/cp/parser.cc
index 8194106c6e9..aeff4535337 100644
--- a/gcc/cp/parser.cc
+++ b/gcc/cp/parser.cc
@@ -10147,8 +10147,13 @@ cp_parser_reflect_expression (cp_parser *parser)
   cp_parser_parse_tentatively (parser);
 
   bool type_alias_p;
-  t = cp_parser_type_id_1 (parser, CP_PARSER_FLAGS_NONE, false, false,
-                          nullptr, &type_alias_p);
+  {
+    auto tdfm =
+      make_temp_override (parser->type_definition_forbidden_message,
+                         G_("types may not be defined in %<^^%> expression"));
+    t = cp_parser_type_id_1 (parser, CP_PARSER_FLAGS_NONE, false, false,
+                            nullptr, &type_alias_p);
+  }
   if (cp_parser_parse_definitely (parser))
     {
       /* With using A = int; ^^A is a type alias but ^^const A or ^^A & or
diff --git a/gcc/testsuite/g++.dg/reflect/error14.C 
b/gcc/testsuite/g++.dg/reflect/error14.C
new file mode 100644
index 00000000000..e525ac92832
--- /dev/null
+++ b/gcc/testsuite/g++.dg/reflect/error14.C
@@ -0,0 +1,15 @@
+// PR c++/125922
+// { dg-do compile { target c++26 } }
+// { dg-additional-options "-freflection" }
+
+void
+f ()
+{
+  consteval {
+    (void) ^^struct { }; // { dg-error "types may not be defined" }
+    (void) ^^struct S { }; // { dg-error "types may not be defined" }
+    (void) ^^struct A { struct B { }; }; // { dg-error "types may not be 
defined" }
+    (void) ^^enum E { }; // { dg-error "types may not be defined" }
+    (void) ^^union U { }; // { dg-error "types may not be defined" }
+  }
+}

base-commit: 33e4cfbd9495a23ffe4639c217442a5459b9e400
-- 
2.54.0