c++/reflection: detect more invalid splices in lambda

The comment for check_splice_expr in
<https://gcc.gnu.org/pipermail/gcc-patches/2025-December/704168.html>
points out that I wasn't giving an error for this testcase.  (clang++
rejects the testcase.)

Fixed by checking if process_outer_var_ref returned a capture.

gcc/cp/ChangeLog:

	* reflect.cc (check_splice_expr): Check if process_outer_var_ref
	returned a capture, and give an error if so.

gcc/testsuite/ChangeLog:

	* g++.dg/reflect/expr15.C: New test.

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

diff --git a/gcc/cp/reflect.cc b/gcc/cp/reflect.cc
index 2f9aa36c787238ce75e9f2e665e819c07252e957..bdeec2f0f38c850e41913d914a5f745d6998fb3e 100644 (file)
--- a/gcc/cp/reflect.cc
+++ b/gcc/cp/reflect.cc
@@ -8395,20 +8395,21 @@ check_splice_expr (location_t loc, location_t start_loc, tree t,
      -- a local entity such that there is a lambda scope that intervenes
      between the expression and the point at which S was introduced"
      This also checks ODR violations (reflect/odr1.C).  */
-  if (outer_automatic_var_p (t)
-      && process_outer_var_ref (t, tf_none) == error_mark_node)
-    {
-      /* Not letting process_outer_var_ref emit the error so that we can
-        say "in a splice expression".  */
-      if (complain_p)
+  if (outer_automatic_var_p (t))
+    if (tree r = process_outer_var_ref (t, tf_none))
+      if (r == error_mark_node || is_capture_proxy (r))
        {
-         auto_diagnostic_group d;
-         error_at (loc, "use of local variable with automatic storage from "
-                   "containing function in a splice expression");
-         inform (DECL_SOURCE_LOCATION (t), "%q#D declared here", t);
+         /* Not letting process_outer_var_ref emit the error so that we can
+            say "in a splice expression".  */
+         if (complain_p)
+           {
+             auto_diagnostic_group d;
+             error_at (loc, "use of local variable with automatic storage "
+                       "from containing function in a splice expression");
+             inform (DECL_SOURCE_LOCATION (t), "%q#D declared here", t);
+           }
+         return false;
        }
-      return false;
-    }
 
   /* If we had a reflect_kind here, we could just check for
      REFLECT_ANNOTATION and be done with it.  But we don't have it yet (TODO),

diff --git a/gcc/testsuite/g++.dg/reflect/expr15.C b/gcc/testsuite/g++.dg/reflect/expr15.C
new file mode 100644 (file)
index 0000000..41da34f
--- /dev/null
+++ b/gcc/testsuite/g++.dg/reflect/expr15.C
@@ -0,0 +1,22 @@
+// { dg-do compile { target c++26 } }
+// { dg-additional-options "-freflection" }
+
+void
+f1 ()
+{
+  int x = 1; // { dg-message ".x. declared here" }
+  constexpr auto r = ^^x;
+  [=] -> decltype(x) {
+    return [:r:]; // { dg-error "use of local variable" }
+  };
+}
+
+void
+f2 ()
+{
+  int x = 1; // { dg-message ".x. declared here" }
+  constexpr auto r = ^^x;
+  [&] -> decltype(x) {
+    return [:r:]; // { dg-error "use of local variable" }
+  };
+}