From 8732bd9de16b52bc521f49f416ceeda368f357c7 Mon Sep 17 00:00:00 2001
From: Dana Jansens <danakj@orodu.net>
Date: Thu, 10 Sep 2026 21:26:37 +0000
Subject: [PATCH] Replace C-style variadic with a concept (#7761)

clang-tidy 24 warns on C-style variadics, and we don't need to use one
here anymore. Instead of a function call with an argument list, use a
concept to determine if a type can be list initialized.
---
 common/struct_reflection.h        | 10 ++--------
 common/struct_reflection_test.cpp | 12 ++++++------
 2 files changed, 8 insertions(+), 14 deletions(-)

diff --git a/common/struct_reflection.h b/common/struct_reflection.h
index 8cc01dca05e0..7d19dd796e5c 100644
--- a/common/struct_reflection.h
+++ b/common/struct_reflection.h
@@ -55,13 +55,7 @@ struct AnyField {
 
 // Detector for whether we can list-initialize T from the given list of fields.
 template <typename T, typename... Fields>
-constexpr auto CanListInitialize(decltype(T{Fields()...})* /*unused*/) -> bool {
-  return true;
-}
-template <typename T, typename... Fields>
-constexpr auto CanListInitialize(...) -> bool {
-  return false;
-}
+concept CanListInitialize = requires { T{Fields()...}; };
 
 #pragma clang diagnostic pop
 
@@ -72,7 +66,7 @@ constexpr auto CanListInitialize(...) -> bool {
 // 2) Add more AnyField<T>s until we can't initialize any more.
 template <typename T, bool AnyWorkedSoFar = false, typename... Fields>
 constexpr auto CountFields() -> int {
-  if constexpr (CanListInitialize<T, Fields...>(nullptr)) {
+  if constexpr (CanListInitialize<T, Fields...>) {
     return CountFields<T, true, Fields..., AnyField<T>>();
   } else if constexpr (AnyWorkedSoFar) {
     constexpr int NumFields = sizeof...(Fields) - 1;
diff --git a/common/struct_reflection_test.cpp b/common/struct_reflection_test.cpp
index 39b58d410a75..2104aab1c2fd 100644
--- a/common/struct_reflection_test.cpp
+++ b/common/struct_reflection_test.cpp
@@ -53,17 +53,17 @@ TEST(StructReflectionTest, CanListInitialize) {
   {
     using Type = OneField;
     using Field = Internal::AnyField<Type>;
-    static_assert(Internal::CanListInitialize<Type>(nullptr));
-    static_assert(Internal::CanListInitialize<Type, Field>(nullptr));
-    static_assert(!Internal::CanListInitialize<Type, Field, Field>(0));
+    static_assert(Internal::CanListInitialize<Type>);
+    static_assert(Internal::CanListInitialize<Type, Field>);
+    static_assert(!Internal::CanListInitialize<Type, Field, Field>);
   }
 
   {
     using Type = OneFieldNoDefaultConstructor;
     using Field = Internal::AnyField<Type>;
-    static_assert(!Internal::CanListInitialize<Type>(0));
-    static_assert(Internal::CanListInitialize<Type, Field>(nullptr));
-    static_assert(!Internal::CanListInitialize<Type, Field, Field>(0));
+    static_assert(!Internal::CanListInitialize<Type>);
+    static_assert(Internal::CanListInitialize<Type, Field>);
+    static_assert(!Internal::CanListInitialize<Type, Field, Field>);
   }
 }