From: Patrick Palka <ppalka@redhat.com>
Date: Wed, 23 Jul 2025 12:31:46 +0000 (-0400)
Subject: c++: fix __is_invocable for std::reference_wrapper [PR121055]
X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=80a51dae8b9af3f6b318f8ed71c67aab96a3fc91;p=thirdparty%2Fgcc.git

c++: fix __is_invocable for std::reference_wrapper [PR121055]

Our implementation of the INVOKE spec ([func.require]) was incorrectly
treating reference_wrapper<T>::get() as returning T instead of T&, which
notably makes a difference when invoking a ref-qualified memfn pointer.

	PR c++/121055

gcc/cp/ChangeLog:

	* method.cc (build_invoke): Correct reference_wrapper handling.

gcc/testsuite/ChangeLog:

	* g++.dg/ext/is_invocable5.C: New test.

Reviewed-by: Jason Merrill <jason@redhat.com>
(cherry picked from commit 04a176a1d84a84c630cfd4d232736c12b105957a)
---

diff --git a/gcc/cp/method.cc b/gcc/cp/method.cc
index 05c19cf0661..cf16fc9fc25 100644
--- a/gcc/cp/method.cc
+++ b/gcc/cp/method.cc
@@ -2036,10 +2036,11 @@ build_invoke (tree fn_type, const_tree arg_types, tsubst_flags_t complain)
 	      const_tree name = DECL_NAME (datum_decl);
 	      if (name && (id_equal (name, "reference_wrapper")))
 		{
-		  /* 1.2 & 1.5: Retrieve T from std::reference_wrapper<T>,
+		  /* 1.2 & 1.5: Retrieve T& from std::reference_wrapper<T>,
 		     i.e., decltype(datum.get()).  */
 		  datum_type =
 		    TREE_VEC_ELT (TYPE_TI_ARGS (non_ref_datum_type), 0);
+		  datum_type = cp_build_reference_type (datum_type, false);
 		  datum_is_refwrap = true;
 		}
 	    }
diff --git a/gcc/testsuite/g++.dg/ext/is_invocable5.C b/gcc/testsuite/g++.dg/ext/is_invocable5.C
new file mode 100644
index 00000000000..460eed595a9
--- /dev/null
+++ b/gcc/testsuite/g++.dg/ext/is_invocable5.C
@@ -0,0 +1,15 @@
+// PR c++/121055
+// { dg-do compile { target c++11 } }
+// { dg-skip-if "requires hosted libstdc++ for functional function" { ! hostedlib } }
+
+#include <functional>
+
+#define SA(X) static_assert((X),#X)
+
+struct F;
+
+SA( __is_invocable(void (F::*)() &, std::reference_wrapper<F>) );
+SA( ! __is_invocable(void (F::*)() &&, std::reference_wrapper<F>) );
+
+SA( __is_invocable(void (F::*)(int) &, std::reference_wrapper<F>, int) );
+SA( ! __is_invocable(void (F::*)(int) &&, std::reference_wrapper<F>, int) );