From 0488f189a43b4957f8307447c1f8bbdc10399ad4 Mon Sep 17 00:00:00 2001
From: James Morris <jamesmorris2@gmail.com>
Date: Tue, 26 Nov 2024 20:31:03 -0500
Subject: [PATCH] fix: Avoid -Wgnu-zero-variadic-macro-arguments in C++20 on
 clang

---
 include/pybind11/cast.h | 11 +++++++++--
 1 file changed, 9 insertions(+), 2 deletions(-)

diff --git a/include/pybind11/cast.h b/include/pybind11/cast.h
index 2ae25c2ebf..baccbcca46 100644
--- a/include/pybind11/cast.h
+++ b/include/pybind11/cast.h
@@ -868,13 +868,20 @@ struct always_construct_holder {
     static constexpr bool value = Value;
 };
 
+// Avoid -Wgnu-zero-variadic-macro-arguments in C++20 on clang
+#ifdef PYBIND11_CPP20
+#    define PYBIND11_DECLARE_HOLDER_TYPE_ARGS(...) void __VA_OPT__(, ) __VA_ARGS__
+#else
+#    define PYBIND11_DECLARE_HOLDER_TYPE_ARGS(...) void, ##__VA_ARGS__
+#endif
+
 /// Create a specialization for custom holder types (silently ignores std::shared_ptr)
 #define PYBIND11_DECLARE_HOLDER_TYPE(type, holder_type, ...)                                      \
     PYBIND11_NAMESPACE_BEGIN(PYBIND11_NAMESPACE)                                                  \
     namespace detail {                                                                            \
     template <typename type>                                                                      \
-    struct always_construct_holder<holder_type> : always_construct_holder<void, ##__VA_ARGS__> {  \
-    };                                                                                            \
+    struct always_construct_holder<holder_type>                                                   \
+        : always_construct_holder<PYBIND11_DECLARE_HOLDER_TYPE_ARGS(__VA_ARGS__)> {};             \
     template <typename type>                                                                      \
     class type_caster<holder_type, enable_if_t<!is_shared_ptr<holder_type>::value>>               \
         : public type_caster_holder<type, holder_type> {};                                        \