[libcxx-commits] [libcxx] [libc++] Define behaviour for calling target() and target_type() on -fno-rtti std::functions (PR #209471)

[Nikolas Klauser via libcxx-commits]

https://github.com/philnik777 created https://github.com/llvm/llvm-project/pull/209471

None

>From 1fc6b517b7647c0a85c36b301720bb1955289875 Mon Sep 17 00:00:00 2001
From: Nikolas Klauser <nikolasklauser at berlin.de>
Date: Tue, 14 Jul 2026 15:05:59 +0200
Subject: [PATCH] [libc++] Define behaviour for calling target() and
 target_type() on -fno-rtti std::functions

---
 libcxx/include/__functional/function.h        | 12 +++----
 .../func.wrap.func/rtti_mixing.sh.cpp         | 33 +++++++++++++++++++
 2 files changed, 39 insertions(+), 6 deletions(-)
 create mode 100644 libcxx/test/extensions/libcxx/utilities/function.objects/func.wrap/func.wrap.func/rtti_mixing.sh.cpp

diff --git a/libcxx/include/__functional/function.h b/libcxx/include/__functional/function.h
index 90072e9528484..8160759724d96 100644
--- a/libcxx/include/__functional/function.h
+++ b/libcxx/include/__functional/function.h
@@ -145,10 +145,8 @@ class __base<_Rp(_ArgTypes...)> {
   virtual void destroy() _NOEXCEPT            = 0;
   virtual void destroy_deallocate() _NOEXCEPT = 0;
   virtual _Rp operator()(_ArgTypes&&...)      = 0;
-#  if _LIBCPP_HAS_RTTI
-  virtual const void* target(const type_info&) const _NOEXCEPT = 0;
-  virtual const std::type_info& target_type() const _NOEXCEPT  = 0;
-#  endif // _LIBCPP_HAS_RTTI
+  virtual const void* target(const type_info&) const _NOEXCEPT { return nullptr; }
+  virtual const std::type_info* target_type() const _NOEXCEPT { return nullptr; }
 };
 _LIBCPP_END_EXPLICIT_ABI_ANNOTATIONS
 
@@ -182,7 +180,7 @@ class __func<_Fp, _Rp(_ArgTypes...)> : public __base<_Rp(_ArgTypes...)> {
       return std::addressof(__func_);
     return nullptr;
   }
-  _LIBCPP_HIDE_FROM_ABI_VIRTUAL const std::type_info& target_type() const _NOEXCEPT override { return typeid(_Fp); }
+  _LIBCPP_HIDE_FROM_ABI_VIRTUAL const std::type_info* target_type() const _NOEXCEPT override { return &typeid(_Fp); }
 #  endif // _LIBCPP_HAS_RTTI
 };
 
@@ -316,7 +314,9 @@ class __value_func<_Rp(_ArgTypes...)> {
   _LIBCPP_HIDE_FROM_ABI const std::type_info& target_type() const _NOEXCEPT {
     if (__f_ == nullptr)
       return typeid(void);
-    return __f_->target_type();
+    if (auto __ptr = __f_->target_type())
+      return *__ptr;
+    return typeid(void);
   }
 
   template <typename _Tp>
diff --git a/libcxx/test/extensions/libcxx/utilities/function.objects/func.wrap/func.wrap.func/rtti_mixing.sh.cpp b/libcxx/test/extensions/libcxx/utilities/function.objects/func.wrap/func.wrap.func/rtti_mixing.sh.cpp
new file mode 100644
index 0000000000000..9a6eda694eee8
--- /dev/null
+++ b/libcxx/test/extensions/libcxx/utilities/function.objects/func.wrap/func.wrap.func/rtti_mixing.sh.cpp
@@ -0,0 +1,33 @@
+//===----------------------------------------------------------------------===//
+//
+// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
+// See https://llvm.org/LICENSE.txt for license information.
+// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
+//
+//===----------------------------------------------------------------------===//
+
+// Ensure that passing std::functions across -fno-rtti/-frtti boundaries works.
+
+#include <cassert>
+#include <functional>
+#include <typeinfo>
+
+// RUN: %{cxx} %s %{flags} %{compile_flags} -c -frtti -o %t.tu1.o
+// RUN: %{cxx} %s %{flags} %{compile_flags} -c -DNO_RTTI -fno-rtti -o %t.tu2.o
+// RUN: %{cxx} %t.tu1.o %t.tu2.o %{flags} %{link_flags} -o %t.exe
+// RUN: %{exec} %t.exe
+
+std::function<void()> get_func();
+
+#ifdef NO_RTTI
+std::function<void()> get_func() {
+  return get_func;
+}
+#else
+int main(int, char**) {
+  assert(!get_func().target<int>());
+  assert(get_func().target_type() == typeid(void));
+
+  return 0;
+}
+#endif