From fdfc07e571eb7f046013052a9fa57db51c6a2cb9 Mon Sep 17 00:00:00 2001
From: Matt Van Horn <mvanhorn@users.noreply.github.com>
Date: Thu, 20 Aug 2026 16:39:01 +0100
Subject: [PATCH] fix: work around clang 20/21 + libc++ compile failure in
 TEMPLATE_PRODUCT_TEST_CASE with differing arities (#3173)

* fix: work around clang 20/21 + libc++ compile failure in TEMPLATE_PRODUCT_TEST_CASE with differing arities

Fixes #3115

* docs: reference llvm/llvm-project#130778 in the clang 20/21 workaround comment

---------

Co-authored-by: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>
---
 src/catch2/internal/catch_preprocessor.hpp           | 11 +++++++----
 src/catch2/internal/catch_template_test_registry.hpp |  4 ++--
 2 files changed, 9 insertions(+), 6 deletions(-)

diff --git a/src/catch2/internal/catch_preprocessor.hpp b/src/catch2/internal/catch_preprocessor.hpp
index 1fc8fb8c..fae95e9d 100644
--- a/src/catch2/internal/catch_preprocessor.hpp
+++ b/src/catch2/internal/catch_preprocessor.hpp
@@ -113,8 +113,11 @@ namespace Catch {
     template<typename... Ts>\
     constexpr auto get_wrapper(Catch::Detail::priority_tag<1>) noexcept -> TypeList<Ts...> { return {}; }\
     template<template<typename...> class...> struct TemplateTypeList{};\
-    template<template<typename...> class...Cs>\
-    constexpr auto get_wrapper(Catch::Detail::priority_tag<1>) noexcept -> TemplateTypeList<Cs...> { return {}; }\
+    /* Clang 20 and 21 cannot handle an explicitly specified all-pack template-template parameter here\
+       ("conflicting deduction" regression, llvm/llvm-project#130778; fixed for Clang 22).\
+       Remove get_template_wrapper once Clang 21 is no longer supported. */\
+    template<template<typename...> class C, template<typename...> class...Cs>\
+    constexpr auto get_template_wrapper(Catch::Detail::priority_tag<1>) noexcept -> TemplateTypeList<C, Cs...> { return {}; }\
     template<typename...>\
     struct append;\
     template<typename...>\
@@ -146,8 +149,8 @@ namespace Catch {
     template<INTERNAL_CATCH_REMOVE_PARENS(signature)>\
     constexpr auto get_wrapper(Catch::Detail::priority_tag<0>) noexcept -> Nttp<__VA_ARGS__> { return {}; } \
     template<template<INTERNAL_CATCH_REMOVE_PARENS(signature)> class...> struct NttpTemplateTypeList{};\
-    template<template<INTERNAL_CATCH_REMOVE_PARENS(signature)> class...Cs>\
-    constexpr auto get_wrapper(Catch::Detail::priority_tag<0>) noexcept -> NttpTemplateTypeList<Cs...> { return {}; } \
+    template<template<INTERNAL_CATCH_REMOVE_PARENS(signature)> class C, template<INTERNAL_CATCH_REMOVE_PARENS(signature)> class...Cs>\
+    constexpr auto get_template_wrapper(Catch::Detail::priority_tag<0>) noexcept -> NttpTemplateTypeList<C, Cs...> { return {}; } \
     \
     template< template<INTERNAL_CATCH_REMOVE_PARENS(signature)> class Container, template<INTERNAL_CATCH_REMOVE_PARENS(signature)> class List, INTERNAL_CATCH_REMOVE_PARENS(signature)>\
     struct rewrap<NttpTemplateTypeList<Container>, List<__VA_ARGS__>> { using type = TypeList<Container<__VA_ARGS__>>; };\
diff --git a/src/catch2/internal/catch_template_test_registry.hpp b/src/catch2/internal/catch_template_test_registry.hpp
index 400c308c..96b76aaf 100644
--- a/src/catch2/internal/catch_template_test_registry.hpp
+++ b/src/catch2/internal/catch_template_test_registry.hpp
@@ -139,7 +139,7 @@
                 }                                                     \
             };                                                        \
             static const int INTERNAL_CATCH_UNIQUE_NAME( globalRegistrar ) = [](){ \
-                using TestInit = typename create<TestName, decltype(get_wrapper<INTERNAL_CATCH_REMOVE_PARENS(TmplTypes)>(Catch::Detail::priority_tag<1>{})), TypeList<INTERNAL_CATCH_MAKE_TYPE_LISTS_FROM_TYPES(INTERNAL_CATCH_REMOVE_PARENS(TypesList))>>::type; \
+                using TestInit = typename create<TestName, decltype(get_template_wrapper<INTERNAL_CATCH_REMOVE_PARENS(TmplTypes)>(Catch::Detail::priority_tag<1>{})), TypeList<INTERNAL_CATCH_MAKE_TYPE_LISTS_FROM_TYPES(INTERNAL_CATCH_REMOVE_PARENS(TypesList))>>::type; \
                 TestInit t;                                           \
                 t.reg_tests();                                        \
                 return 0;                                             \
@@ -271,7 +271,7 @@
             }\
         };\
         static const int INTERNAL_CATCH_UNIQUE_NAME( globalRegistrar ) = [](){\
-            using TestInit = typename create<TestNameClass, decltype(get_wrapper<INTERNAL_CATCH_REMOVE_PARENS(TmplTypes)>(Catch::Detail::priority_tag<1>{})), TypeList<INTERNAL_CATCH_MAKE_TYPE_LISTS_FROM_TYPES(INTERNAL_CATCH_REMOVE_PARENS(TypesList))>>::type;\
+            using TestInit = typename create<TestNameClass, decltype(get_template_wrapper<INTERNAL_CATCH_REMOVE_PARENS(TmplTypes)>(Catch::Detail::priority_tag<1>{})), TypeList<INTERNAL_CATCH_MAKE_TYPE_LISTS_FROM_TYPES(INTERNAL_CATCH_REMOVE_PARENS(TypesList))>>::type;\
             TestInit t;\
             t.reg_tests();\
             return 0;\